Patent Publication Number: US-6982171-B2

Title: Cell motility and chemotaxis test device and methods of using same

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 10/097,351 filed Mar. 15, 2002; U.S. application Ser. No. 10/097,329 filed Mar. 15,2002; U.S. application Ser. No. 10/097,302 filed Mar. 15, 2002; U.S. application Ser. No. 10/097,304 filed Mar. 15, 2002 now U.S. Pat. No. 6,818,403; U.S. application Ser. No. 10/097,322 filed Mar. 15, 2002 now U.S. Pat. No. 6,811,968; U.S. application Ser. No. 10/097,306 filed Mar. 15, 2002, all of which are herein incorporated by reference in their entirety. This application also claims priority to both Provisional U.S. Application No. 60/363,354, filed on Mar. 12, 2002, and Provisional U.S. Application No. 60/373,783, filed on Apr. 24, 2002, all of which are herein incorporated reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to device for monitoring cell motility and chemotaxis. 
     BACKGROUND ART 
     Test devices, such as those used in chemotaxis, haptotaxis and chemoinvasion are well known. Such devices are disclosed for example in U.S. Pat. Nos. 6,329,164, 6,238,874, and 5,302,515. 
     Three processes involved in cell migration are chemotaxis, haptotaxis, and chemoinvasion. Chemotaxis is defined as the movement of cells induced by a concentration gradient of a soluble chemotactic stimulus. Haptotaxis is defined as the movement of cells in response to a concentration gradient of a substrate-bound stimulus. Chemoinvasion is defined as the movement of cells into and/or through a barrier or gel matrix. The study of chemotaxis/haptotaxis and chemoinvasion and the effects of external stimuli on such behavior are prevalent throughout contemporary biological research. Generally, this research involves exposing a cell to external stimuli and studying the cell&#39;s reaction. By placing a living cell into various environments and exposing it to different external stimuli, both the internal workings of the cell and the effects of the external stimuli on the cell can be measured, recorded, and better understood. 
     A cell&#39;s migration in response to a chemical stimulus is a particularly important consideration for understanding various disease processes and accordingly developing and evaluating therapeutic candidates for these diseases. By documenting the cell migration of a cell or a group of cells in response to a chemical stimulus, such as a therapeutic agent, the effectiveness of the chemical stimulus can be better understood. Typically, studies of disease processes in various medical fields, such as oncology, immunology, angiogenesis, wound healing, and neurobiology involve analyzing the chemotactic and invasive properties of living cells. For example, in the field of oncology, cell migration is an important consideration in understanding the process of metastasis. During metastasis, cancer cells of a typical solid tumor must loosen their adhesion to neighboring cells, escape from the tissue of origin, invade other tissues by degrading the tissues&#39; extracellular matrix until reaching a blood or lymphatic vessel, cross the basal lamina and endothelial lining of the vessel to enter circulation, exit from circulation elsewhere in the body, and survive and proliferate in the new environment in which they ultimately reside. Therefore, studying the cancer cells&#39; migration may aid in understanding the process of metastasis and developing therapeutic agents that potentially inhibit this process. In the inflammatory disease field, cell migration is also an important consideration in understanding the inflammatory response. During the inflammation response, leukocytes migrate to the damaged tissue area and assist in fighting the infection or healing the wound. The leukocytes migrate through the capillary adhering to the endothelial cells lining the capillary. The leukocytes then squeeze between the endothelial cells and use digestive enzymes to crawl across the basal lamina. Therefore, studying the leukocytes migrating across the endothelial cells and invading the basal lamina may aid in understanding the inflammation process and developing therapeutic agents that inhibit this process in inflammatory diseases such as adult respiratory distress sydrome (ARDS), rheumotoid arthritis, and inflammatory skin diseases. Cell migration is also an important consideration in the field of angiogenesis. When a capillary sprouts from an existing small vessel, an endothelial cell initially extends from the wall of the existing small vessel generating a new capillary branch and pseudopodia guide the growth of the capillary sprout into the surrounding connective tissue. New growth of these capillaries enables cancerous growths to enlarge and spread and contributes, for example, to the blindness that can accompany diabetes. Conversely, lack of capillary production can contribute to tissue death in cardiac muscle after, for example, a heart attack. Therefore studying the migration of endothelial cells as new capillaries form from existing capillaries may aid in understanding angiogenesis and optimizing drugs that block vessel growth or improve vessel function. In addition, studying cell migration can also provide insight into the processes of tissue regeneration, organ transplantation, autoimmune diseases, and many other degenerative diseases and conditions. 
     Cell migration assays are often used in conducting these types of research. Commercially available devices for creating such assays are sometimes based on or employ a transwell system (a vessel partitioned by a thin porous membrane to form an upper compartment and a lower compartment). To study cell chemotaxis, cells are placed in the upper compartment and a migratory stimulus is placed in the lower compartment. After a sufficient incubation period, the cells are fixed, stained, and counted to study the effects of the stimulus on cell chemotaxis across the membrane. 
     To study chemoinvasion, a uniform layer of a MATRIGEL™ matrix is placed over the membrane to occlude the pores of the membrane. Cells are seeded onto the MATRIGEL™ matrix in the upper compartment and a chemoattractant is placed in the lower compartment. Invasive cells attach to and invade the matrix passing through the porous membrane. Non-invasive cells do not migrate through the occluded pores. After a sufficient incubation period, the cells may be fixed, stained, and counted to study the effects of the stimulus on cell invasion across the membrane. 
     The use of transwells has several shortcomings. Assays employing transwells require a labor-intensive protocol that is not readily adaptable to high-throughput screening and processing. Because of the configuration of a transwell system, it is difficult to integrate with existing robotic liquid handling systems and automatic image acquisition systems. Therefore, much of the screening and processing, such as counting cells, is done manually which is a time-consuming, tedious, and expensive process. Cell counting is also subjective and often involves statistical approximations. Specifically, due to the time and expense associated with examining an entire filter, only randomly selected representative areas may be counted. Moreover, even when these areas are counted, a technician must exercise his or her judgment when accounting for a cell that has only partially migrated through the filter. 
     Transwell-based assays have intrinsic limitations imposed by the thin membranes utilized in transwell systems. The membrane is only 50-30 microns (μm) thick, and a chemical concentration gradient that forms across the membrane is transient and lasts for a short period. If a cell chemotaxis assay requires the chemotactic gradient to be generated over a long distance (&gt;100-200 μm) and to be stable over at least two hours, currently available transwell assays cannot be satisfactorily performed. 
     Notwithstanding the above, perhaps the most significant disadvantage of transwells is the lack of real-time observation of chemotaxis and chemoinvasion. In particular, the changes in cell morphology during chemotaxis cannot be observed in real-time with the use of transwells. In transwells, when the cells are fixed to a slide, as required for observation, they are killed. Consequently, once a cell is observed it can no longer be reintroduced into the assay or studied at subsequent periods of exposure to a test agent. Therefore, in order to study the progress of a cell and the changes in a cell&#39;s morphology in response to a test agent, it is necessary to run concurrent samples that may be slated for observation at various time periods before and after the introduction of the test agent. In light of the multiple samples required for each test, in addition to the positive and negative controls required to obtain reliable data, a single chemotaxis assay is can require dozens of filters, each of which needs to be individually examined and counted-an onerous and time-consuming task. 
     More recently, devices for measuring chemotaxis and chemoinvasion have become available which employ a configuration in which two wells are horizontally offset with respect to one another. This configuration of a device was introduced by Sally Zigmond in 1977 and, hereafter referred to as the “Zigmond device,” consists of a 25 millimeters (mm)×75 mm glass slide with two grooves 4 mm wide and 1 mm deep, separated by a 1 mm bridge. One of the grooves is filled with an attractant and the other groove is filled with a control solution, thus forming a concentration gradient across the bridge. Cells are then added to the other groove. Two holes are provided at each end of the slide to accept pin clamps. The clamps hold a cover glass in place during incubation and observation of the cells. Because of the size and configuration of the Zigmond chamber, it does not allow integration with existing robotic liquid handling systems and automatic image acquisition systems. Further, as with transwell-based systems, the changes in cell morphology during chemotaxis cannot be observed in real-time with the use of the Zigmond chamber as the cells are fixed to a slide for observation. In addition, the pin clamps must be assembled with an allen wrench and thus the device requires extra handling, positioning, and alignment before performing the assay. Such handling and positioning of the cover glass on the glass slide, as well as the rigidity of the cover glass, can potentially damage or interfere any surface treatment on the bridge. 
     A chemotaxis device attempting to solve the problem of lack of real-time observation is the “Dunn chamber.” The Dunn chamber consists of a specially constructed microslide with a central circular sink and a concentric annular moat. In an assay using a Dunn chamber, cells migrate on a coverslip, which is placed inverted on the Dunn chamber, towards a chemotactic stimulus. The cells are monitored over-night using a phase-contrast microscope fitted with a video camera connected to a computer with an image-grabber board. 
     In addition to the problems of rigidity of the coverslip and the lack of integration into existing robotic liquid handling systems, a major problem with the Dunn chamber assay is that only a very small number of cells are monitored (typically ten). The average behavior of this very small sample may not be typical of the population as a whole. A second major problem is that replication is very restricted. Each control chamber and each treatment chamber must be viewed in separate microscopes, each one similarly equipped with camera and computer. 
     Another chemotaxis device known in the art is disclosed in U.S. Pat. No. 6,238,874 to Jarnigan et. al. (the &#39;874 patent). The &#39;874 patent discloses various embodiments of test devices that may be used to monitor chemotaxis. However, disadvantageously, the devices in Jarnagin et al. can not be easily sealed or assembled or peeled and disassembled. Thus, it is difficult to maintain surfaces that are prepared chemically or biologically during assembly. The test devices of the &#39;874 patent are therefore more suited for one-time use. Also, disassembly and collection of cells is difficult to do without damage to the cells or without disturbing the cell positions. 
     The prior art has failed to provide a test device, such as a device for monitoring chemotaxis, haptotaxis, and/or chemoinvasion, which device is easily assembled and dissembled. In addition, the prior art has failed to provide a test device for monitoring chemotaxis and/or chemoinvasion, which is not limited to measuring the effects on cell migration of chemoattractants, chemorepellants and chemostimulants. 
     SUMMARY OF THE INVENTION 
     The present invention provides a device for monitoring chemotaxis or chemoinvasion including a housing comprising a support member and a top member, the top member mounted to the support member by being placed in substantially fluid-tight conformal contact with the support member, wherein the support member and the top member are configured such that they together define a discrete chamber. The discrete chamber including a first well region including at least one first well, the first well region configured to receive a test agent therein; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device, the second well region configured to receive a cell sample therein; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention further provides a device for monitoring chemotaxis or chemoinvasion including a housing comprising: a support member and a top member. The top member is mounted to the support member by being placed in substantially fluid-tight, conformal contact with the support member, wherein the support member and the top member are configured such that they together define a discrete chamber adapted to allow a monitoring of chemotaxis or chemoinvasion therein. The discrete chamber has an opening facing vertically upward in a test orientation of the device. The discrete chamber includes: a first well region including at least one first well, the at least one first well configured to receive a test agent therein; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device, the at least one second well configured to receive a sample comprising cells therein; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention furthermore provides a device for monitoring chemotaxis or chemoinvasion comprising: a support means and means mounted to the support means for defining a discrete chamber with the support means by being placed in substantially fluid-tight, conformal contact with the support means. The discrete chamber is adapted to allow a monitoring of chemotaxis or chemoinvasion therein. The discrete chamber includes a first well region including at least one first well, the at least one first well configured to receive a test agent therein; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device, the at least one second well configured to receive a sample comprising cells therein; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention also provides a device for monitoring chemotaxis or chemoinvasion comprising: a support member and a top member. The top member is mounted to the support member by forming a substantially instantaneous seal with the support member, wherein the support member and the top member are configured such that they together define a discrete chamber. The discrete chamber is adapted to allow for a monitoring of chemotaxis or chemoinvasion therein. The discrete chamber includes a first well region including at least one first well, the at least one first well configured to receive a test agent therein; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device, the at least one second well configured to receive a sample comprising cells therein; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention moreover provides a device for monitoring chemotaxis or chemoinvasion including a housing defining a chamber adapted to allow for a monitoring of chemotaxis or chemoinvasion therein. The chamber comprises: a first well region including at least one first well, the at least one first well configured to receive a test agent therein; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device, the at least one second well configured to receive a sample comprising cells therein; and a channel region including a plurality of channels connecting the first well region and the second well region with one another. 
     The present invention provides for the optional inclusion of a gel matrix in the channel(s) of the above-mentioned embodiments. 
     The present invention provides a test device including a housing comprising: a support member, a top member mounted to the support member by being placed in substantially fluid-tight, conformal contact with the support member, wherein the support member and the top member are configured such that they together define a discrete chamber. The discrete chamber includes a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention further provides a kit for forming the housing of a test device. The kit comprises: a support member, a top member adapted to be mounted to the support member by being placed in substantially fluid-tight, conformal contact with the support member, wherein the support member and the top member are configured such that they together define a discrete chamber when the top member is mounted to the support member. The discrete chamber includes: a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention additionally provides a top member adapted to be mounted to a support member for forming the housing of a test device by being placed in substantially fluid-tight, conformal contact with the support member, wherein the top member is configured such that it defines a discrete chamber with the support member when the top member is mounted to the support member. The discrete chamber includes a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention also provides a test device including a housing comprising: a support member; and a top member mounted to the support member by being placed in substantially fluid tight, conformal contact with the support member, wherein the support member and the top member are configured such that they together define a discrete chamber, the discrete chamber having an opening facing upwardly in a test orientation of the device. 
     The present invention additionally provides a test device comprising: a support member and top member wherein the top member is mounted to the support member by forming a substantially instantaneous seal with the support member. The support member and the top member are configured such that they together define a discrete chamber. The discrete chamber includes a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention furthermore provides a test device including a housing defining a chamber. The chamber comprises a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at a plurality of channels connecting the first well region and the second well region with one another. 
     The present invention furthermore provides a test device comprising: support means; means mounted to the support means for defining a discrete chamber with the support means by being placed in substantially fluid-tight, conformal contact with the support means. The discrete chamber includes a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention additionally provides a method of providing a test device comprising: providing a support member; providing a top member; mounting the top member to the support member, wherein providing a top member comprises selecting a predetermined material for the top member such that the top member is mounted to the support member by being placed against the support member for forming a substantially fluid-tight, conformal contact with the support member; and configuring the top member and the support member such that they together define a discrete chamber when the top member is mounted to the support member. The discrete chamber includes: a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention further provides a method of making a top member of a test device comprising the steps of: selecting a predetermined material for the top member such that the top member is adapted to be mounted to a support member by being placed against the support member for forming a substantially fluid-tight, conformal contact with the support member, and configuring the top member such that it defines a discrete chamber with the support member when it is mounted to the support member. The discrete chamber includes: a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another. 
     The present invention moreover provides a method of making a test device comprising: providing a support member; providing a top member; mounting the top member to the support member by placing the top member in substantially fluid tight, conformal contact with the support member, wherein the support member and the top member are configured such that they together define a discrete chamber, the discrete chamber having an opening facing vertically upward in a test orientation of the device. 
     The present invention provides an image processing method for use in analyzing image data of a cellular migration assay. The method includes defining a major axis within the image data that is perpendicular to an orientation of channels in the image data, determining an aggregate light intensity within the image data along the major axis, and identifying locations of channels within the image data from the projection. 
     The present invention provide a method of monitoring haptotaxis. The method includes providing a device for monitoring haptotaxis having a housing defining a chamber. The chamber includes a first well region including at least one first well, the first well region configured to receive a test agent therein and further including biomolecules immobilized therein; a second well region including at least one second well, the second well region configured to receive a sample comprising cells therein and further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region with biomolecules immobilized therein and including at least one channel connecting the first well region and the second well region with one another. The method further includes forming a surface concentration gradient along a longitudinal axis of the chamber by decreasing the concentration of biomolecules from the at least one first well to the at least one second well. The method additionally includes placing a first sample comprising cells in the at least one second well. The method also includes monitoring haptotaxis of the cells. 
     The present invention provides a method of monitoring chemotaxis and chemoinvasion comprising: providing a device for monitoring chemotaxis, the device having a support member; a top member mounted to the support member by being placed in substantially fluid-tight, conformal contact with the support member, wherein the support member and the top member are configured such that they together define a discrete assay chamber. The discrete chamber includes: a first well region including at least one first well, each of the at least one first well being adapted to receive a soluble test substance therein; a second well region including at least one second well horizontally offset with respect to the first well region in a test orientation of the device, the at least one second well being adapted to receive a sample comprising cells therein; and a channel region including a plurality of channels connecting the first well region and the second well region with one another. The method further comprises: placing the soluble test substance in the at least one first well; forming a solution concentration gradient along a longitudinal axis of the chamber; placing a sample comprising cells in the at least one second well; and monitoring chemotaxis of the cells. 
     The present invention provides a device for monitoring haptotaxis including a housing comprising: a support member and a top member, the top member mounted to the support member wherein the support member and the top member are configured such that they together define a discrete chamber. The discrete chamber includes a first well region including at least one first well, the first well configured to receive a test agent therein and further including biomolecules immobilized therein; a second well region including at least one second well, the second well region configured to receive a sample comprising cells therein and further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another, the channel region further including biomolecules immobilized therein. 
     The present invention moreover provides a device for monitoring haptotaxis including a housing defining a discrete chamber. The chamber has an opening facing vertically upward in a test orientation of the device. The chamber further comprises: a first well region including at least one first well, the at least one first well configured to receive a test agent therein and further including biomolecules immobilized therein; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device, the at least one second well configured to receive a sample comprising cells therein; and a channel region including at least one channel connecting the first well region and the second well region with one another, the at least one channel further including biomolecules immobilized therein. 
     The present invention additionally provides a device for monitoring haptotaxis. The device comprises support means; means mounted to the support means for defining a discrete chamber with the support means. The discrete chamber includes a first well region including at least one first well, the at least one first well configured to receive a test agent therein and further including biomolecules immobilized therein; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device, the at least one second well configured to receive a sample comprising cells; and a channel region including at least one channel connecting the first well region and the second well region with one another, the at least one channel further including biomolecules immobilized therein. 
     The present invention also provides a device for monitoring haptotaxis comprising a support member and a top member mounted to the support member by forming a substantially instantaneous seal with the support member. The support member and the top member are configured such that they together define a discrete chamber. The discrete chamber includes: a first well region including at least one first well, the at least one first well configured to receive a test agent therein and further including biomolecules immobilized therein; a second well region including at least one second well, the second well region configured to receive a sample comprising cells therein and further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another, the channel region further including biomolecules immobilized therein. 
     The present invention furthermore provides a device for monitoring haptotaxis including a housing defining a chamber. The chamber comprises: a first well region including at least one first well, the first well configured to receive a test agent therein and further including biomolecules immobilized therein; a second well region including at least one second well, the second well region configured to receive a sample comprising cells therein and further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at a least one channel connecting the first well region and the second well region with one another, the channel region further including biomolecules immobilized therein. 
     The present invention also provides a kit for monitoring haptotaxis comprising: a device including a housing defining a chamber. The chamber comprises: a first well region including at least one first well, the first well configured to receive a test agent therein; a second well region including at least one second well, the second well region configured to receive a sample comprising cells therein and further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at a least one channel connecting the first well region and the second well region with one another. The kit further comprises a sample comprising biomolecules. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features of the invention will best be appreciated by simultaneous reference to the description that follows and the accompanying drawings, in which: 
         FIG. 1A  is a top, perspective view, in partial cross section, of a portion of an embodiment of test device according to the present invention; 
         FIG. 1B  is a top, perspective view of an embodiment of a test device of the present invention; 
         FIG. 1C  is a side-elevational view of a longitudinal cross section of one of the chambers of the test device of  FIG. 1B ; 
         FIG. 2A  is a schematic outline depicting a top plan view of an alternative embodiment of a chamber defined in a test device of the present invention, where the channel region defines a single channel; 
         FIG. 2B  is a schematic outline depicting a top plan view of the embodiment of the chambers defined in the embodiment of the test device according to  FIG. 1B , where the channel region defines a single channel; 
         FIG. 2C  is a figure similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where the channel region defines a single channel; 
         FIG. 3A  is a figure similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where the channel region defines a plurality of channels having identical lengths; 
         FIG. 3B  is a figure similar to  FIG. 3A , showing a channel region defining a plurality of channels having lengths that increase from one side of the chamber to another side of the chamber; 
         FIG. 3C  is a figure similar to  FIG. 3A , showing a channel region defining a plurality of channels having widths that increase from one side of the chamber to another side of the chamber; 
         FIG. 4A  is a figure similar to  FIG. 1B  showing an alternative embodiment of a test device according to the present invention; 
         FIG. 4B  is an enlarged, schematic, top plan view of a channel of  FIG. 4A  showing cells on the sides of the channel; 
         FIGS. 5 and 6  are views similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where the wells are trapezoidal in a top plan view thereof; 
         FIG. 7  is a view similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where the chamber is in the form of a  FIG. 8  in a top plan view thereof; 
         FIG. 8  is a view similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where one well is rectangular and the other well circular in a top plan view of the device; 
         FIG. 9  is a view similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where the first well region and the second well region each define a plurality of wells, and where the channel region defines a plurality of channels joining respective wells of each well region; 
         FIG. 10  is a view similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where the channel region defines a plurality of channels joining respective wells of each well region; 
         FIG. 11  is a view similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where the first well region has a plurality of wells and a respective capillary for each well, the channel region has a single channel, and the second well region has a single well; 
         FIG. 12  is a side, cross-sectional view of an embodiment of a portion of the support member according to the present invention, the portion of the support member being shown along a longitudinal axis of a chamber according to the present invention; 
         FIG. 13  is an isometric view of a collective system according to one embodiment of the present invention; 
         FIG. 14  is a view similar to  FIG. 2A , showing an alternative embodiment of a chamber defined in a test device of the present invention, where the first well region includes a plurality of wells interconnected by a network of capillaries, where the channel region includes a single channel, and where the second well includes a single well; 
         FIG. 15  is a block diagram of an automated analysis system according to an embodiment of the present invention; 
         FIG. 16  is a flow diagram of a method according to an embodiment of the present invention; 
         FIG. 17  illustrates exemplary image data on which the method of  FIG. 16  may operate; 
         FIG. 18  illustrates a histogram that may be obtained from the image data of  FIG. 17 ; 
         FIG. 19  illustrates exemplary image data; 
         FIG. 20  illustrates exemplary dilated image data. 
         FIG. 21  depicts various cell types that have been patterned using soft lithographic techniques. 
         FIG. 22  depicts various biological reactions involving patterned biomolecules. 
         FIG. 23  depicts a device according to one embodiment of our invention versus a transwell system. In a transwell system, the concentration of chemoattractant is transient and the chemotactic gradient is not stable or quantifiable. In a device according to the present invention, the chemotactic gradient is internally calibrated. According to one embodiment of the present invention where the device comprises multiple chambers, one chamber may be used to calibrate the cell migration assay, and the other chambers may be used to monitor cell migration. At any particular point in time, cell migration may be monitored in different chambers at a particular concentration of the chemoattractant. 
         FIG. 24  depicts formation of a monocyte chemoattractant protein-1 (MCP-1) gradient and migration of human monocytoid (THP-1) cells in a channel in the direction of a gradient. 
         FIG. 25  depicts the characterization of a citokine gradient using rhodamine dextran. 
         FIG. 26  depicts THP-1 cells migrating in channels in the direction of an MCP-1 gradient. Hydrogels are filled in the channels of the device. According to one method of placing the gel in channels, the gel stops at a definite point in the channel and does not spill over into the wells. 
       FIG.  27 . In this assay, a known chemokine (CC motif) receptor 2 (CCR2) binding inhibitor is used to test whether the inhibitor has an effect on THP-1 cells migrating towards MCP-1. Results show that the inhibitor does indeed inhibit cell migration. Using the devices of the present invention allows for the correlation of pharmacologically relevant data to cell based systems. 
         FIG. 28  depicts the flexibility of the device according to one embodiment of the present invention. The channel width, length, and architecture may be varied. Using the device of the present invention, allows for monitoring of the maximum distances the cells traveled, weighted average of distance the cells traveled and measurement of cell pixels (all the cells that traveled any distance), average distance traveled, and number of cells that traveled. Transmigration mimicks cells moving through endothelium. In one embodiment, the width of the channels is 2-10 microns. In one embodiment of the present invention, the device may use a configuration of channels that mimic human vasculature. For example, the height of the channels may be 80 microns tall. 
         FIG. 29  depicts small molecule inhibition of cell migration. 
       FIG.  30 . Algorithms of the present invention convert digital images into data that is then converted to usable graphic interfaces. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     As shown in  FIG. 1A , according to one embodiment of the present invention, a test device  10 , such as, for example, a cellular chemotaxis/haptotaxis and/or chemoinvasion device, includes a housing  10   a  comprising a support member  16  and a top member  11  mounted to the support member  16  by being placed in substantially fluid-tight, conformal contact with the support member  16 . In the context of the present invention, “conformal contact” means substantially form-fitting, substantially fluid-tight contact. The support member  16  and the top member  11  are configured such that they together define a discrete chamber  12  as shown. Preferably test device  10  comprises a plurality of discrete chambers, as shown by way of example in the embodiment of FIG.  1 B. The discrete chamber  12  includes a first well region  13   a  including at least one first well  13  and second well region  14   a  including at least one second well  14 , the second well region further being horizontally offset with respect to the first well region in a test orientation of the device. The “test orientation” of the device is meant to refer to a spatial orientation of the device during testing. As shown in  FIG. 1C , device  10  further includes a channel region  15   a  including at least one channel  15  connecting the first well region  13   a  and the second well region  14   a  with one another. In the embodiments of  FIGS. 1A-2C , each well region includes a single well, and the channel region includes a single channel. As seen in  FIG. 1C , each well is defined by a through-hole in top member  11 , corresponding to well  13  and well  14  respectively, and by an upper surface U of support member  16 . In particular, the sides of each well  13  and  14  are defined by the walls of the through holes in the top member  11 , and the bottoms of well  13  and  14  are defined by the upper surface U of support member  16 . It is noted that in the context of the present invention, “top,” “bottom,” “upper” and “side” are defined relative to the test orientation of the device. As seen collectively in  FIGS. 1A and 1C , a length L of channel region  15   a  is defined in a direction of the longitudinal axis of channel region  15   a ; a depth D of channel region  15   a  is defined in a direction normal to upper surface U of support member  16 ; a width W is defined in a direction normal to the length L and depth D of channel region  15   a . According to one embodiment of the present invention, the chamber&#39;s first well  13  is adapted to receive a test agent, a soluble test substance and/or a test agent comprising immobilized biomolecules, which potentially affects chemotaxis or haptotaxis. Biomolecules include, but not limited to, DNA, RNA, proteins, peptides, carbohydrates, cells, chemicals, biochemicals, and small molecules. The chamber&#39;s second well  14  is adapted to receive a biological sample of cells. Immobilized biomolecules are biomolecules that are attracted to support member  16  with an attractive force stronger than the attractive forces that are present in the environment surrounding the support member, such as solvating and turbulent forces present in a fluid medium. Non-limiting examples of the test agent include chemorepellants, chemotactic inhibitors, and chemoattractants, such as growth factors, cytokines, chemokines, nutrients, small molecules, and peptides. Alternatively, the chamber&#39;s first well  13  is adapted to receive a biological sample of cells and the chamber&#39;s second well  14  is adapted to receive a test agent. 
     In one embodiment of the present invention, when a soluble test substance is used as the test agent, channel region  15   a  preferably contains a gel matrix. The gel matrix allows the formation of a solution concentration gradient from first well region  13   a  towards second well region  14   a  as the solute diffuses from an area of higher concentration (well region  13   a ) through a semi-permeable matrix (the gel matrix) to an area of lower concentration (well region  14   a ). If the soluble test substance comprises a chemoattractant, in order for the cells to migrate through the matrix in the direction of the solution concentration gradient towards well region  13   a , the cells must degrade this matrix by releasing enzymes such as matrix metalloproteases. This cell chemotaxis and invasion may be subsequently observed, measured, and recorded. 
     In one embodiment of the present invention, utilizing immobilized biomolecules as the test agent, the biomolecules are preferably immobilized or bound on the portion of support member  16  underlying channel region  15   a  and underlying through hole for well region  13   a . The concentration of biomolecules decreases along the longitudinal axis of the device from well region  13   a  towards well region  14   a  forming a surface concentration gradient of immobilized biomolecules and the biological sample of cells potentially responds to this surface gradient. This cell haptotaxis may be subsequently observed, measured, and recorded. 
     With respect to particular specifications of device  10 , top member  11  is made of a material that is adapted to effect conformal contact, preferably reversible conformal contact, with support member  16 . According to embodiments of the present invention, the flexibility of such a material, among other things, allows the top member to form-fittingly adhere to the upper surface U of support member  16  in such a way as to form a substantially fluid-tight seal therewith. The conformal contact should preferably be strong enough to prevent slippage of the top member on the support member surface. Where the conformal contact is reversible, the top member may be made of a material having the structural integrity to allow the top member to be removed by a simple peeling process. This would allow top member  11  to be removed and cells at certain positions collected. Preferably, the peeling process does not disturb any surface treatment or cell positions of support member  16 . Physical striations, pockets, SAMs, gels, peptides, antibodies, or carbohydrates can be placed on support member  16  and the top member  11  subsequently can be placed over support member  16  without any damage to these structures. Additionally, the substantially fluid-tight seal effected between top member  11  and support member  16  by virtue of the conformal contact of top member  11  with support member  16  prevents fluid from leaking from one chamber to an adjacent chamber, and also prevents contaminants from entering the wells. The seal preferably occurs essentially instantaneously without the necessity to maintain external pressure. The conformal contact obviates the need to use a sealing agent to seal top member  11  to support member  16 . Although embodiments of the present invention encompass use of a sealing agent, the fact that such a use is obviated according to a preferred embodiment provides a cost-saving, time-saving alternative, and further eliminates a risk of contamination of each chamber  12  by a sealing agent. Preferably, the top member  11  is made of a material that does not degrade and is not easily damaged by virtue of being used in multiple tests, and that affords considerable variability in the top member&#39;s configuration during manufacture of the same. More preferably, the material may be selected for allowing the top member to be made using photolithography. In a preferred embodiment, the material comprises an elastomer such as silicone, natural or synthetic rubber, or polyurethane. In a more preferred embodiment, the material is polydimethylsiloxane (“PDMS”). 
     In another embodiment of the present invention, device  10  includes a housing defining a chamber, the chamber including a first well region including at least one first well; a second well region including at least one second well; and a channel region including a plurality of channels connecting the first well region and the second well region with one another. The second well region is preferably horizontally offset with respect to the first well region is a test orientation of the device. 
     According to a preferred embodiment of a method of the present invention, standard photolithographic procedures can be used to produce a silicon master that is the negative image of any desired configuration of top member  11 . For example, the dimensions of chambers  12 , such as the size of well regions  13   a  and  14   a , or the length of channel region  15   a , can be altered to fit any advantageous specification. Once a suitable design for the master is chosen and the master is fabricated according to such a design, the material is either spin cast, injected, or poured over the master and cured. Once the mold is created, this process may be repeated as often as necessary. This process not only provides great flexibility in the top member&#39;s design, it also allows the top members to be massively replicated. The present invention also contemplates different methods of fabricating device  10  including, for example, e-beam lithography, laser-assisted etching, and transfer printing. 
     Device  10  preferably fits in the footprint of an industry standard microtiter plate. As such, device  10  preferably has the same outer dimensions and overall size of an industry standard microtiter plate. Additionally, when chamber  12  comprises a plurality of chambers, either the chambers  12  themselves, or the wells of each chamber  12 , may have the same pitch of an industry standard microtiter plate. The term “pitch” used herein refers to the distance between respective vertical centerlines between adjacent chambers or adjacent wells in the test orientation of the device. The embodiment of device  10 , shown in  FIG. 1B , comprises 48 chambers designed in the format of a standard 96-well plate, with each well fitting in the space of each macrowell of the plate. The size and number of the plurality of chambers  12  can correspond to the footprint of standard 24-, 96-, 384-, 768- and 1536-well microtiter plates. For example, for a 96 well microtiter plate, device  10  may comprise 48 chambers  12  and therefore 48 experiments can be conducted, and for a  384  well microtiter plate, the device may comprise 192 chambers  12 , and therefore 192 experiments can be conducted. The present invention also contemplates any other number of chambers and/or wells disposed in any suitable configuration. For example, if pitch or footprint standards change or new applications demand new dimensions, then device  10  may easily be changed to meet these new dimensions. By conforming to the exact dimension and specification of standard microtiter plates, embodiments of device  10  would advantageously fit into existing infrastructure of fluid handling, storage, registration, and detection. Embodiments of device  10 , therefore, may be conducive to high throughput screening as they may allow robotic fluid handling and automated detection and data analysis. Top member  11  may additionally take on several different variations and embodiments. Depending on the test parameters, such as, for example, where chemotaxis, haptotaxis and/or chemoinvasion are to be monitored, the cell type, cell number, or distance over which chemotaxis or haptotaxis is required, chamber  12  of top member  11  may have various embodiments of which a few exemplary embodiments are discussed herein. With respect to a discrete chamber  12 , the shape, dimensions, location, surface treatment, and numbers of channels in channel region  15   a  and the shape and number of wells  13  and  14  may vary. 
     Regarding the shape of channel region  15   a , each channel  15  in the channel region  15   a  is not limited to a particular cross-sectional shape, as taken in a plane perpendicular to its longitudinal axis. For example, the cross section of any given channel  15  can be hexagonal, circular, semicircular, ellipsoidal, rectangular, square, or any other polygonal or curved shape. 
     Regarding the dimensions of a channel  15 , the length L of a given channel  15  can vary based on various test parameters. For instance, the length L of a given channel  15  may vary in relation to the distance over which chemotaxis or haptotaxis is required to occur. For example, the length L of a given channel  15  can range from about 3 μm to about 18 mm in order to allow cells sufficient distance to travel and therefore sufficient opportunity to observe cell chemotaxisahaptotaxis and chemoinvasion. The width W and depth D of a given channel  15  may also vary as a function of various test parameters. For examples, the width W and depth D of a given channel  15  may vary, in a chemotaxis, haptotaxis and/or chemoinvasion device, depending on the size of the cell being studied and whether a gel matrix is added to the given channel  15 . Generally, where the test device is a chemotaxis, haptotaxis and/or chemoinvasion device, a given channel  15 &#39;s width W and depth D may be approximately in the range of the diameter of the cell being assayed. To discount random cellular movement, at least one of the depth D or width W of a given channel  15  should preferably be smaller than the diameter of the cell when no gel matrix is placed in the given channel  15  so that when the cells are activated, they can “squeeze” themselves through the given channel toward the test agent. If a given channel  15  contains a gel matrix, then, the depth D and width W of the given channel  15  may be greater than the diameter of the cell being assayed. Referring by way of example to the embodiments of  FIGS. 1A-2C , if suspension cells such as leukocytes, which are about 3-12 μm in diameter, are in well  14  and channel  15  contains no gel, then the width W of channel  15  should range from about 3 microns to about 20 μm, and the depth D of channel  15  should range from about 3 microns to about 20 μm but at least either the depth D or width W of channel  15  should be smaller than the diameter of the cell. If leukocytes are in well  14  and channel  15  contains a gel matrix, then the width W of channel  15  should range from about 20 to about 100 μm and the depth D should range from about 20 μm to about 100 μm, and both the width W and depth D of channel  15  can be greater than the diameter of the cell assayed. Similarly, if adherent cells, such as endothelial cells which are 3-10 microns in diameter before adherence, are in well  14  and channel  15  contains no gel, then the width W and depth D of channel  15  can range from about 3 to about 20 μm, but at least either the width W or depth D of channel  15  should be smaller than the diameter of the cell assayed. If adherent cells are in well  14  and channel  15  contains a gel matrix then the width W and depth D of channel  15  should range from about 20 μm to about 200 μm and both the width W and depth D of channel  15  can be greater than the diameter of the cell assayed. 
     As seen in  FIGS. 2A-2C  channel  15  may connect the first well  13  to the second well  14  at respective sides of the wells, as shown in  FIGS. 2A and 2C  or at a central region of the wells, as shown in FIG.  2 B. 
     The number of channels in channel region  15   a  between well regions  13   a  and  14   a  can also vary. Channel region  15   a  may include a plurality of channels, as shown by way of example in  FIGS. 3A-3C . As seen in  FIG. 3A , in a preferred configuration, the length L of each channel  15   i-n  between well  13  and well  14  is identical. In another embodiment as seen in  FIG. 3B , the length L of each channel  15   i - 15   n  of channel region  15   a  increases in the direction of well  14 , starting from channel  15   i  in the side portion  12   a  of chamber  12  to channel  15   n  in the side portion  12   b  of chamber  12 . In one embodiment, as seen in  FIG. 3B , the length L of each successive channel in the plurality of channels  15  of chamber  12  increases in a direction of a width W of the channels with respect to a preceding one of the plurality of channels such that respective channel inlets at one of the first well region and the second well region, such as well region  13   a  as shown, are aligned along the direction of the width W of the channels. Although, in this configuration, the cells traveling in any particular channel will exit the channels and enter well  14  at points longitudinally offset with respect to one another, the section of channel region  15   a  closest to well region  13   a  is positioned so that cells ultimately entering the different channels will be aligned in a direction of the width W of the channels so that there is no longitudinal offset between them. Therefore, in comparing two adjacent channels, a first group of cells entering channel  15   i  has an entry position that is not longitudinally offset with respect to a second different group of cells entering channel  15   j , but the first group of cells exiting channel  15   i  has an exit point longitudinally offset from the second group of cells exiting channel  15   j . In a different embodiment of the present invention illustrated in  FIG. 3C , the width W of each channel  15   i - 15   n  increases starting from channel  15   i  in the side portion  12   a  of chamber  12  to channel  15   n  in the side portion  12   b  of chamber  12 . Preferably, the width W or depth D of each successive channel of the plurality of channels to increases in a direction of a width W of the channels with respect to a preceding one of the plurality of channels. Alternatively, a depth D of each successive channel could increase (not shown) along a direction of the width W of the channels. It is understood to those skilled in the art, that various embodiments altering the dimensions of the channels in the channel region  15   a  are within the scope of the present invention. For example, the length of the channels  15   i - 15   n  need not increase in a continuous manner from channel  15   i  to  15   n  as illustrated in FIG.  3 B. Instead, channel  15   i - 15   n  may have varying lengths following no particular order or pattern. 
     With respect to surface treatment of a given channel  15 , to simulate in vivo conditions where cells are surrounded by other cells, the lateral walls of a given channel  15  may be coated with cells, such as endothelial cells  40  as seen in FIG.  4 B. Non-limiting examples of endothelial cells include human umbilical vein endothelial cells or high endothelial venule cells. In another embodiment, a given channel  15  is filled with a gel matrix such as gelatin, agarose, collagen, fibrin, any natural or synthetic extracellular proteinous matrix or basal membrane mimic including, but not limited to MATRIGEL™ (Becton Dickenson Labware), or ECM GEL, (Sigma, St. Louis, Mo.), or other hydrogels containing certain factors such as cytokines, growth factors, antibodies, ligands for cell surface receptors, or chemokines. Preferably, the gel has a substantially high water content and is porous enough to allow cell chemotaxis and invasion. As mentioned above, when the test agent comprising a soluble test substance is placed in well  13 , the gel facilitates formation of a solution concentration gradient along the longitudinal axis of chamber  12 . Additionally, adding a gel matrix to a given channel  15  simulates the natural environment in the body, as enzyme degradation through extracellular matrix is a crucial step in the invasive process. 
     According to the present invention, the individual wells of each well region  13   a  or  14   a  may have any shape and size. For example, the top plan contour of a given well may be circular, as shown in  FIGS. 1A-2C , or trapezoidal as shown in  FIGS. 5 and 6 . Alternatively, the top plan contour of a given chamber may be generally in the shape of a “FIG.  8 ” as shown in FIG.  7 . Preferably when using a soluble test substance as the test agent, the shape of well  13  is such that soluble test substance is readily able to access the channel  15  and thereby form the necessary solution concentration gradient along the length L of channel  15 . Preferably, the shape of well  14  is such that cells are not deferred, detained, or hindered from migrating out of the first well  14 , for example, by accumulating in a corner, side or other dead space of well  14 . Although possible accumulation of cells in a dead space of well  14  is not restricted to any particular cell number, there exists a greater likelihood of cells accumulating in a corner of well  14  if a large number of cells are used. Therefore to maximize accessibility to the concentration gradient and to minimize the “wasting” of cells when a large cell sample is utilized, it is important that the shape of well  14  be such that a sufficiently high percentage of cells, particularly the cells in the area of well  14  furthest from channel  15 , are capable of migrating out of well  14 . In a different embodiment that also addresses the problem of the wasting of cells, well  14  may be shaped such that all cells have a higher probability of accessing the concentration gradient. For example as seen in  FIG. 8 , the length L w  of well  14  in a top plan view thereof is minimized to decrease the surface area of the well. As such, the cells are closer to the concentration gradient formed in channel  15 . In a preferred embodiment, the L w  of well  14  in a top plan view thereof is about 1 mm to about 2 mm. 
     In addition to variations of components of a discrete chamber  12 , the present invention also contemplates variations in the overall chamber  12  as well as variations from chamber to chamber. With respect to the overall chamber  12 , in one embodiment, the chambers  12  are sized so that a complete chamber  12  fits into the area normally required for a single well of a 96-well plate. In this configuration, 96 different assays could be performed in a 96-well plate. In another embodiment, the 1:1 ratio of a first well to second well, as present in the aforementioned embodiments, is altered by modifying chamber  12 . For example as seen in  FIG. 9 , device  10  includes a chamber  12  having a first well region  13   a  having a plurality of first wells  102 ,  103 ,  104  and  105  connected to one another, a second well region  14   a  having a plurality of wells  106 ,  107 ,  108  and  109 , and a channel region  15   a  having a plurality of channels  15  connecting respective ones of the first wells to respective ones of the second wells. Each well of the first well region  13   a  may receive the same test agent, and each well of the second well region  14   a  may receive a different cell type. Alternatively, each well of the first well region  13   a  may receive a different test agent, and each well of the second well region  14   a  may receive the same cell type. This configuration allows several different cell types or different test agents to be tested simultaneously. In an alternative embodiment as seen in  FIG. 10 , each channel  15  of channel region  15   a  comprises subchannels as shown. This arrangement not only allows several different cell types or test agents to be tested simultaneously but also generates several tests of each test agent or cell type. 
       FIG. 11  illustrates an alternative chamber configuration of a test device according to an alternative embodiment of the present invention. In this embodiment, chamber  12  comprises a first well region  13   a  connected by a channel region  15   a  including a single channel  15  to a second well region  14   a  including a single well  14 . The first well region contains a plurality of first wells,  17   a ,  18   a , and  19   a  and a plurality of capillaries, a first perimeter capillary  17 , a center capillary  18 , and a second perimeter capillary  19  connected to respective ones of the plurality of first wells. All three of the capillaries converge at a junction into channel  15 , which is connected with the second well region  14   a . Well region  13   a  is not limited to containing only three capillaries and can contain any number of additional capillaries (not shown). First wells  17   a - 19   a  may, for example, be adapted to receive solutions of biomolecules, which are allowed to flow into channel  15  and adsorb nonspecifically to the regions of the surface over which the solution containing the biomolecules flows. First wells  17   a - 19   a  are also adapted to subsequently receive cells. With respect to variations from chamber to chamber, in one embodiment, the length L of each channel  15  increases along one or more dimensions of top member  11  from one chamber to the adjacent chamber. In an alternative embodiment, all chambers  12  have channel  15  of the same length L. The width W of each channel  15  can also vary and can increase along one or more dimensions of top member  11  from one chamber to the adjacent chamber. In an alternative embodiment, all chambers  12  have channel  15  of the same width W.  FIG. 4A  is a top plan view of an embodiment of the present invention where, within top member  11 , different chambers have various channel sizes and shapes, such sizes and shapes being in no particular order, pattern, or arrangement. By employing this varied configuration, the best channel region design for a given test may be obtained. In other words, where the optimal channel region design is determined, a new assay plate configured solely to those specifications may be employed. 
     Support member  16  of device  10  provides a support upon which top member  11  rests and can be made of any material suitable for this function. Suitable materials are known in the art such as glass, polystyrene, polycarbonate, PMMA, polyacrylates, and other plastics. Where device  10  is a chemotaxis, haptotaxis and/or chemoinvasion device, it is preferable that support member  16  comprise a material that is compatible with cells that may be placed on the surface of support member  16 . Suitable materials may include standard materials used in cell biology, such as glass, ceramics, metals, polystyrene, polycarbonate, polypropylene, as well as other plastics including polymeric thin films. A preferred material is glass with a thickness of about 0.1 to about 2 mm, as this may allow the viewing of the cells with optical microscopy techniques. 
     Similar to top member  11 , support member  16  can have several different embodiments. In particular, the configuration and surface treatment of support member  16  may vary. 
     As seen in a side view of support member  16  in  FIG. 12 , the upper surface U of support member  16 , which underlies top member  11 , may be sloped at predetermined regions thereof with respect to a horizontal plane at less than a 90° angle. In the shown embodiment, the predetermined regions correspond to bottom surfaces of respective wells, surface  16   a  corresponding to a bottom surface of a well  13 , and surface  16   b  corresponding to a bottom surface of well  14 . Surface  16   c , in turn, corresponds to a bottom surface of channel  15 . In this embodiment, the given configuration facilitates suspended cells flowing in the direction of the downward slope of top surface  16   b  of support member  16  to become more readily exposed to the concentration gradient. If a soluble test substance is used as the test agent in well  13  of device  10 , then top surface  16   a  of support member  16  may also be downwardly sloped with respect to a horizontal plane at less than a 90° angle to facilitate exposure of the test substance to channel  15  in order to facilitate formation of the solution concentration gradient. 
     Support member  16  may also have a treatment on or embedded into its surface. This treatment may serve numerous functions, including, for example, facilitating the placement, adhesion or movement of cells being studied, and simulating in vivo conditions. Numerous surface configurations and chemicals may be used alone or in conjunction for this treatment. 
     For example, in one embodiment support member  16  includes a patterned self-assembled monolayer (SAM) on a gold surface or other suitable material. SAMs are monolayers typically formed of molecules each having a functional group that selectively attaches to a particular surface, the remainder of each molecule interacting with neighboring molecules in the monolayer to form a relatively ordered array. By using SAMs, various controls of biological interactions may be employed. For example, SAMs may be arrayed or modified with various “head groups” to produce “islands” of biospecific surfaces surrounded by areas of bio-inert head groups. Further, SAMs may be modified to have “switchable surfaces” that may be designed to capture a cell and then be subsequently modified to release the captured cell. Moreover, it may also be desirable to utilize a bioinert support member material to resist non-specific adsorption of cells, proteins, or any other biological material. Consequently, the use of SAMs on support member  16  may be advantageous. 
     The present invention also contemplates, as seen in  FIG. 13 , the use of any system known in the art to detect and analyze cell chemotaxis, haptotaxis, and chemoinvasion. In particular, the present invention contemplates the use of any system known in the art to visualize changes in cell morphology as cells move across channel  15 , to measure the distance cells travel in channel  15 , and to quantify the number of cells that travel to particular points in channel  15 . As such the present invention contemplates both “real-time” and “end-point” analysis of chemotaxis, haptotaxis, and chemoinvasion. In one embodiment, the device  122  includes an observation system  120  and a controller  121 . The controller  121  is in communication with the observation system  120  via line  122 . The controller  121  and observation system  120  may be positioned and programmed to observe, record, and analyze chemotaxis and chemoinvasion of the cells in the device. The observation system  120  may be any of numerous systems, including a microscope, a high-speed video camera, and an array of individual sensors. Nonlimiting examples of microscopes include phase-contrast, fluorescence, luminescence, differential-interference-contrast, dark field, confocal laser-scanning, digital deconvolution, and video microscopes. Each of these embodiments may view or sense the movement and behavior of the cells before, during, and after the test agent is introduced. At the same time, the observation system  120  may generate signals for the controller  121  to interpret and analyze. This analysis can include determining the physical movement of the cells over time as well as their change in shape, activity level or any other observable characteristic. In each instance, the conduct of the cells being studied may be observed in real time, at a later time, or both. The observation system  120  and controller  121  may provide for real-time observation via a monitor. They may also provide for subsequent playback via a recording system of some kind either integrated with these components or coupled to them. For example, in one embodiment, cell behavior during the desired period of observation is recorded on VHS format videotape through a standard video camera positioned in the vertical ocular tubes of a triocular compound microscope or in the body of an inverted microscope and attached to a high quality video recorder. The video recorder is then played into a digitization means, e.g., PCI frame grabber, for the conversion of analog data to digital form. The electronic readable (digitized) data is then accessed and processed by an appropriate dynamic image analysis system, such as that disclosed in U.S. Pat. No. 5,655,028 expressly incorporated in its entirety herein by reference. Such a system is commercially available under the trademark DIAS® from Solltech Inc. (Oakland, Iowa). Software capable of assisting in discriminating cells from debris and other detection artifacts that might be present in the sample should be particularly advantageous. In either case, these components may also analyze the cells as they progress through their reaction to the test agent. 
     In one embodiment, the present invention contemplates the use of an automated analysis system, as illustrated in  FIG. 15 , to analyze data measuring the distance cells travel in channel  15 , and to quantify the number of cells that travel to particular points in channel  15 .  FIG. 15  is a block diagram of an automated analysis system  100  including, for example, an image preprocessing stage  110 , an object identification stage  120  and a migration analysis stage  130 . The image preprocessing stage  110  may receive digital image data of chamber  12  from a digital camera or other imaging apparatus as described above. The data typically includes a plurality of image samples at various spatial locations (called, “pixels” for short) and may be provided as color or grayscale data. The image preprocessing stage  110  may alter the captured image data to permit algorithms of the other stages to operate on it. The object identification stage  120  may identify objects from within the image data. Various objects may be identified based on the test to be performed. For example, the object identifier may identify channels  15 , cells or cell groups from within the image data. The migration analysis stage  130  may perform the migration analysis designated for testing. 
       FIG. 15  illustrates a number of blocks that may be included within the image preprocessing stage  110 . Essentially, the image preprocessing stage  110  counteracts image artifacts that may be present in the captured image data as a result of imperfections in the imager or the device. In one embodiment, the image preprocessing stage  110  may include an image equalization block  140 . The equalization  140  may find application in embodiments where sample values of captured image data do not occupy the full quantization range available for the data. For example, an 8-bit grayscale system permits 256 different quantization levels for input data (0-255). Due to imperfections in the imaging process, it is possible that pixel values may be limited to a narrow range, say the first 20 quantization levels (0-20). The equalization  140  may re-scale sample values to ensure that they occupy the full range available in the 8-bit system. 
     In another embodiment, the equalization block  140  may re-scale sample values based on a color or wavelength. Conventional cellular analysis techniques often cause cells to appear in predetermined colors or with predetermined wavelengths, which permits them to be distinguished from other materials captured by the imager. For example, in fluorescent applications, cells emit light at predetermined wavelengths. In nuclear staining applications, cell nuclei are dyed with a material that causes them to appear in the image data with predetermined colors. The equalization block  140  may re-scale sample values having components that coincide with these expected colors or wavelengths. In so doing, the equalization block  140  effectively filters out other colors or wavelengths, a consequence that may be advantageous in later image processing. 
     Image rotation is another image artifact that may occur from imperfect imaging apparatus. Although the channels  15  are likely to be generally aligned with columns and rows of pixels in the image data, further analysis may be facilitated if the alignment is improved. Accordingly, in an embodiment, the image preprocessing stage  110  may include an image alignment block  150  that rotates the captured image data to counteract this artifact. Once the rotation artifact has been removed from the captured image data, then image from individual channels  15  are likely to coincide with a regular row or column array of pixel data. 
       FIG. 16  illustrates a method of operation for the image alignment block  150  according to an embodiment of the present invention and described in connection with exemplary image data illustrated in FIG.  17 . In the example of  FIG. 17 , channels  15  are aligned generally with rows of image data but for the rotation artifact. To counteract the rotation artifact, the image preprocessor may identify a band of image data coinciding with a boundary between second well  14  and the channels  15  themselves (block  1010 ). In the case of  FIG. 17 , the band may constitute column  310 . Generally, the area of second well  14  will be bright relative to the area of channels  15  due the greater number of cells present therein. Thus, a histogram of image data values along a presumed direction of the channels  15  may appear as shown in FIG.  18 . The band  310  may be identified from an abrupt change in image data values along this direction. 
     Having identified a column of image data to be considered, the column  310  may be split into two boundary boxes  320 ,  330  (block  1020 ). By summing the intensity of the image data in each of the two boundary boxes and comparing summed values to each other, an orientation of the rotation artifact may be determined (blocks  1030 ,  1040 ). In the example of  FIG. 17 , the rotation artifact causes more of second well  14  to fall within the area of boundary box  320  than of boundary box  330  (a clockwise artifact). The image data may be rotated counterclockwise until the summed values of each boundary box  320 ,  330  become balanced. 
     Thus, if the image intensity of the first bounding box is greater than that of the second bounding box  330 , the image data may be rotated in a first direction (block  1050 ). If the image intensity of the second bounding box  330  is greater than that if the first bounding box  320 , the image data may be rotated in a second direction (block  1060 ). And when the image intensities are balanced, the method  1000  may conclude; the rotation artifact has been corrected. 
     Returning to  FIG. 15 , the image preprocessing stage  110  also may process the captured image data by cropping the image to the area occupied by channels  15  themselves (block  160 ). As described, each test bed may include a pair of wells interconnected by a plurality of channels. For much of the migration analysis, it is sufficient to measure cellular movement or activity within channels  15  only. Activity in second well  14  or the first well  13  need not be considered. In such an embodiment, the image preprocessing stage  110  may crop the image data to remove pixels that lie outside channels  15 . 
     The image preprocessing stage  110  also may include a thresholding block  170 , performing threshold detection upon the image data. The thresholding block  170  may truncate to zero any sample having a re-scaled value that fails to exceed a predetermined threshold. Such thresholding is useful to remove noise from the captured image data. In an embodiment, the thresholding block  170  may be integrated with the equalization block  140  discussed above. It need not be present as a separate element. In some embodiments, particularly those where the equalization block  140  scales pixel values according to wavelength components, the thresholding block  170  may be omitted altogether. An output of the image preprocessing stage  110  may be input to the object identification stage  120 . 
     The object identification stage  120  identifies objects from within the image data, including the channels themselves and, optionally, individual cells. According to an embodiment, in a fluorescent system, channels  15  may be identified by developing a histogram of the fluorescent light along a major axis in the system (block  180 ).  FIG. 19  illustrates image data that may have been determined from the example of FIG.  17 . The major axis may coincide with the boundary between the well adapted to receive cells and the channel region. Light intensity from within channel region  15   a  area may be summed along this axis, yielding a data set represented in FIG.  19 . In a second stage, the data set is “dilated” (block  190 ). Dilation may be achieved by applying a high pass filter to the data set or any other analogous technique.  FIG. 20  illustrates the data set of  FIG. 19  having been subject to dilation. 
     From the data set of  FIG. 20 , the channels may be identified. Candidate channel  15  positions may be identified to coincide with relative maximums of the data set. Alternatively, candidate positions of boundaries between channels  15  may be determined from relative minimums from within the data set of  FIG. 20. A  final set of channel  15  positions may be determined from a set of parameters known about channel region  15   a  itself For example, if channels  15  are known to have been provided with a regular spacing among channels  15 , any candidate channel  15  position that would violate the spacing can be eliminated from consideration. 
     Returning to  FIG. 15 , in addition to identifying channels  15 , individual cells may be identified within the image data (block  200 ). In an application where cells are marked with nuclear staining, identification of individual cells merely requires an image processor to identify and count the number of marked nuclei. The nuclei appear is a number of dots of a predetermined color. In an application using fluorescing cells, identification of individual cells becomes more complicated. Individual cells can be identified relatively easily; they appear as objects of relatively uniform area in the image data. Identifying a number of cells clustered together becomes more difficult. In this case, the number of cells may be determined from the area or radius of the cluster in the image data. The cluster is likely to appear in the image having some area or cluster radius. By comparing the cluster&#39;s area or radius to the area or radius of an individual cell, the number of cells may be interpolated. Of course, identification of individual cells may be omitted depending upon the requirements of the migration analysis. 
     The final stage in the image processing system is the migration analysis  130  itself. In one embodiment, coordinate data of each cell in the channels  15  may be gathered and recorded. However, some testing need not be so complicated. In a first embodiment, it may be sufficient merely to identify the number of cells present in channel  15 . In this case, identification of individual cells may be avoided by merely summing quantities of fluorescent light detected in each channel  15 . From this measurement, the number of cells may be derived without investing the processing expense of identifying individual cells. The foregoing description presents image analysis that is relevant to a single channel  15  to be tested. Of course, depending upon the requirements of the migration analysis  130 , it may be desired to generate image samples of a number of different channels  15 . Further, it may be desirable to generate image samples of a single channel  15  at different times. The image processing described above may be repeated for different channels  15  and different times to accommodate for such test scenarios. 
     According to an embodiment, the image processing may account for manufacturing defects of individual channels  15 . During image processing, manufacturing defects may prevent cell migrations into a channel  15 . In an embodiment, when the system  100  counts a number of cells in the channel  15  (or derives the number from identified cell locations), it may compare the number to an expectation threshold. If the number is below the expectation threshold, the system  100  may exclude the channel  15  from migration analysis. In practice, this expectation threshold may be established as a minimum number of cells that are likely to enter a properly configured cell given the test conditions being analyzed under the migration analysis. If the actual number of cells falls below this threshold, it may lead to a conclusion that channel  15  blocking conditions may be present. 
     The foregoing operations and processes of the analysis system  100  may be performed by general purpose processing apparatus, such as computers, workstations or servers, executing software. Alternatively, some of the operations or processes may be provided in a digital signal processor or application specific integrated circuit (colloquially, an “ASIC”). Additionally, these operations and processes, particularly those associated with image preprocessing, may be distributed in processors of a digital microscope system. Such variations are fully within the scope of the present invention. 
     The present invention also contemplates the use of the aforementioned embodiments of device  10  to assay various elements of chemotaxis, haptotaxis and chemoinvasion. In general, the present invention provides for a first assay comprising high throughput screening of test agents to determine whether they influence chemotaxis, haptotaxis, and chemoinvasion. Test agents generally comprise either soluble test substances or immobilized test biomolecules and are generally placed in first well region  13   a  of chamber  12  of device  10 . After determining which test agents influence chemotaxis, by acting as chemoattractants and promoting or initiating chemotaxis, by acting as chemorepellants and repelling chemotaxis, or by acting as inhibitors and halting or inhibiting chemotaxis, then a second assay can be performed screening test compounds. The test compounds generally comprise therapeutics or chemotaxis/haptotaxis inhibitors and are generally introduced in second well region  14   a , which contains a biological sample of cells. The test compounds are screened to determine if and how they influence the cells&#39; chemotaxis or haptotaxis in response to the test agents. 
     In particular, a chemotaxis/haptotaxis and/or chemoinvasion assay according to an embodiment of the present invention involves a device  10  including a housing comprising a top member  11  mounted to a support member  16 . The top member and the support member are configured such that they together define a discrete assay chamber  12 . The discrete assay chamber  12  includes a first well region  13   a  connected by a channel  15  to a second well region  14   a . The first well region  13   a  includes at least one first well  13 , each of the at least one first well  13  being adapted to receive a test agent therein. The second well region  14   a  includes at least one second well  14  horizontally offset with respect to the first well region  13   a  in a test orientation of the device, each of the at least one second well  14  being adapted to receive a cell sample therein. Channel  15  includes at least one channel connecting the first well region  13   a  and the second well region  14   a  to one another. The test agent received in first well  13  is a soluble test substance and/or immobilized test biomolecules. When the test agent comprises immobilized test biomolecules, the biomolecules are immobilized on an upper surface U of support member  16  constituting the bottom surface of well region  13   a  as well as on upper surface U of support member  16  constituting the bottom surface of channel region  15   a.    
     Nonlimiting examples of biological samples of cells include lymphocytes, monocytes, leukocytes, macrophages, mast cells, T-cells, neutrophils, basophils, eosinophils, fibroblasts, endothelial cells, epithelial cells, neurons, tumor cells, motile gametes, motile forms of bacteria, and fungi, cells involved in metastasis, and any other types of cells involved in response to inflammation, injury, or infection, including human leukemic cell line (HL-60) cells. 
     Nonlimiting examples of immobilized biomolecules include chemoattractants, chemorepellants, and chemotactic inhibitors as described above. Further non-limiting examples of immobilized chemoattactants include chemokines, cytokines, and small molecules. Further non-limiting examples of chemoattractants include IL-8, GCP-2, GRO-α, GRO-β, MGSA-β, MGSA-γ, PF 4 , ENA-78, GCP-2, NAP-2, IL-8, IP10, I-309, I-TAC, stromal cell derived factor (SDF-1) including SDF-1α, BLC, BRAK, bolekine, ELC, LKTN-1, SCM-1β, MIG, MCAF, LD7α, eotaxin, IP-110, HCC-1, HCC-2, Lkn-1, HCC-4, LARC, LEC, DC-CK1, PARC, AMAC-1, MIP-2β, ELC, exodus-3, ARC, exodus-1, 6Ckine, exodus 2, STCP-1, MPIF-1, MPIF-2, Eotaxin-2, TECK, Eotaxin-3, ILC, ITAC, BCA-1, MIP-1α, MIP-1β, MIP-3α, MIP-3β, MCP-1, MCP-2, MCP-3, MCP-4, MCP-5, RANTES, eotaxin-1, eotaxin-2, TARC, MDC, TECK, CTACK, SLC, lymphotactin, and fractalkine; and other cells. Further non-limiting examples of chemorepellants include receptor agonists and other cells. 
     Nonlimiting examples of soluble test substances include chemoattractants, chemorepellants, or chemotactic inhibitors. As explained above, chemoattractants are chemotactic substances that attract cells and once placed in well region  14   a , cause cells to migrate towards well region  14   a . Chemorepellents are chemotactic substances that repel cells and once placed in well region  14   a , cause cells to migrate away from well region  14   a . Chemotactic inhibitors are chemotactic substances that inhibit or stop chemotaxis and once placed in well region  14   a , cause cells to have inhibited migration or no migration from well region  14   a . Non-limiting examples of chemoattractants include hormones such as T 3  and T 4 , epinephrine and vasopressin; immunological agents such as interleukein-2, epidermal growth factor and monoclonal antibodies; growth factors; peptides; small molecules; and cells. Cells may act as chemoattractants by releasing chemotactic factors. For example, in one embodiment, a sample including cancer cells may be added to well  13 . A sample including a different cell type may be added to well  14 . As the cancer cells grow they may release factors that act as chemoattractants attracting the cells in well  14  to migrate towards well  13 . In another embodiment, endothelial cells are added to well  13  and activated by adding a chemoattractant such as TNF-α or IL-1 to well  13 . Leukocytes are added to well  14  and may be attracted to the endothelial cells in well  14 . 
     Non-limiting examples of chemorepellants include irritants such as benzalkonium chloride, propylene glycol, methanol, acetone, sodium dodecyl sulfate, hydrogen peroxide, 1-butanol, ethanol, and dimethylsulfoxide; and toxins such as cyanide, carbonylcyanide chlorophenylhydrazone, endotoxins and bacterial lipopolysaccharides; viruses; pathogens; and pyrogens. 
     In order to perform a test, such as a chemotaxis and/or chemoinvasion assay utilizing a soluble test substance, the test device  10  is first fabricated. A preferred embodiment of the method of making the device according to the present invention will now be described. A master that is the negative of top-plate  11  is fabricated by standard photolithographic procedures. A predetermined material is spin coated or injection molded onto the master. The predetermined material is then cured, peeled off the master to comprise top member  11  and placed onto support member  16 . 
     Where the test device  10  is a chemotaxis, haptotaxis and/or chemoinvasion device, a rigid frame with the standard microtiter footprint is preferably placed around the outer perimeter of top member  11 . In one embodiment, a gel matrix is poured into well region  13   a  and allowed to flow into channel region  15   a . After the gel matrix sets, excess gel is removed from well regions  13   a  and  14   a . In another embodiment, no gel matrix is added to channel region  15   a  Subsequently, a biological sample of cells is placed in well region  14   a  and a test substance is placed in well region  13   a . In one embodiment, a low concentration of a test substance is placed in well region  14   a  in order to activate the cells and expedite the beginning of the assay. Alternatively, depending on the cells being studied and the soluble test substance being used, the soluble test substance may be introduced during or after the cells have been placed in well region  14   a . Once the soluble test substance has been introduced, by the process of diffusion, a solution concentration gradient of the test substance forms along the longitudinal axis of channel region  15   a  from well region  13   a  containing the test agent towards well region  14   a  containing the biological sample of cells. A secondary effect of this solution gradient is the formation of a physisorbed (immnobilized) gradient. When this solution gradient is established, some fraction of the solute of the test substance may adsorb onto support member  16 . This adsorbed layer of test solute may also contribute to chemotaxis and chemoinvasion. The biological sample of cells may respond to this concentration gradient and migrate towards the higher concentration of the test substance, migrate away from the higher concentration of the test substance, or exhibit inhibited movement in response to the higher concentration of the test substance. It is through this chemotaxis in response to the gradient, that the chemotactic influence of the chemotactic substance can be measured. Chemotaxis is assayed by measuring the distance the cells travel and the amount of time the cells take to reach a predetermined point in the channel region  15   a  or the distance the cells travel and the amount of time the cells take to reach a certain point in well region  14   a  (in the case of a chemorepellant that causes cells to move away from the chemotactic substance). 
     Utilizing an alternative embodiment of device  10  containing an alternative design of chamber  12 , a solution concentration gradient is formed using a network of microfluidic channel regions. In this embodiment as seen in  FIG. 14 , first well region well region  13   a  of chamber  12  has first wells,  20 ,  21 , and  22 , connected by a network of microfluidic capillaries  23  to channel  15 . In particular, first well region  13   a  includes a plurality of first wells connected by a plurality of capillaries  24  connected to respective ones of the plurality of first wells and a plurality of subcapillaries  25  branched off such that each of the plurality of subeapillaries is connected to each of the plurality of capillaries at one end thereof and to channel  15  at another end thereof. Each first well,  20 ,  21 , and  22  receives a different concentration of soluble test substance. After the three first wells,  20 ,  21 , and  22  are simultaneously infused with the three different concentrations of soluble test substance, the solution streams travel down the network of channel regions, continuously splitting, mixing and recombining. After several generations of branched subcapillaries, each subcapillary containing different proportions of soluble test substances are merged into a single channel  15 , forming a concentration gradient across channel  15 , perpendicular to the flow direction. 
     According to one embodiment of the present invention, biomolecules are immobilized onto support member  16 , preferably on the portion of upper surface U constituting the bottom surface of channel  15  and of well region  13   a  in any one of the embodiments of the test device of the present invention, such as the embodiments shown in  FIGS. 1A-14 . The concentration of biomolecules increases or decreases along the longitudinal axis of the device from the upper surface of support member  16  constituting the bottom surface of well region  13   a  towards the upper surface U of support member  16  constituting the bottom surface of well region  14   a  thus forming a surface gradient. After the test biomolecules are immobilized on support member  16 , the top member is placed onto support member  16  and a rigid frame with the standard microtiter footprint is placed around the outer perimeter of top member  11  and cells are added to well region  14   a . in an alternative embodiment, after the test biomolecules are immobilized on support member  16  and the top member is placed over support member  16 , a gel matrix is added to channel region  15   a . Cells are subsequently added to well region  14   a . The biological sample of cells potentially respond to the concentration gradient of immobilized biomolecules and migrates towards the higher concentrations of the test biomolecules, away from the higher concentrations of the test biomolecules, or exhibit inhibited migration in response to the higher concentrations of the test biomolecules. The surface gradient can increase linearly or as a squared, cubed, or logarithmic function or in any surface profile that can be approximated in steps up or down. 
     The test biomolecules can be attached to and form surface gradients on the upper surface U of support member  16  by various specific or non-specific approaches known in the art as described in K. Efimenko and J. Genzer, “How to Prepare Tunable Planar Molecular Chemical Gradient,” 13  Applied Materials,  2001, No. 20, October 16; U.S Pat. No. 5,514, incorporated herein by reference. For example, microcontact printing techniques, or any other method known in the art, can be used to immobilize on upper surface U of support member  16  a layer of SAMs presenting hexadecanethiol. Support member  16  is then exposed to high energy light through a photolithographic mask of the desired gradient micropattern or a grayscale mask with continuous gradations from white to black. When the mask is removed, a surface gradient of SAMs presenting hexandecanethiol remains. Support member  16  is then immersed in a solution of ethylene glycol terminated alkanethiol. The regions of support member  16  with SAMs presenting hexadecanethiol will rapidly adsorb biomolecules and the regions of the support member with SAMs presenting oligomers of the ethylene glycol group will resist adsorption of protein. Support member  16  is then immersed in a solution of the desired test biomolecules and the biomolecules rapidly adsorb only to the regions of support member  16  containing SAMs presenting hexadecanethiol creating a surface gradient of immobilized biomolecules. 
     In another embodiment, the test biomolecules are immobilized on the support member  16  and a surface concentration gradient forms after the top member  11  has been placed over support member  16  in any one of the embodiments of the test device of the present invention, such as the embodiments shown in  FIGS. 1A-14 . In this embodiment, discrete concentrations of solution containing test biomolecules are consecutively placed in well region  14   a  and allowed to adsorb non-specifically to support member  16 . For example, first, a 1 milligram/milliliter (mg/ml) of solution can first be placed in well region  14   a ; second, a 1 microgram/milliliter (μg/ml) solution can be placed in well region  14   a ; last, a 1 nanogram/milliliter (ng/ml) solution of test biomolecules can be placed in well region  14   a . The differing concentrations of test biomolecules in solution result in differing amounts of adsorption on support member  16 . 
     Utilizing an alternative embodiment of device  10  containing an alternative design of chamber  12  as seen in  FIG. 11 , an immobilized biomolecular surface gradient is formed based on the concept of laminar flow of multiple parallel liquid streams, a method known in the art. Based on this concept, when two or more streams with low Reynolds numbers are joined into a single stream, also with a low Reynolds number, the combined streams flow parallel to each other without turbulent mixing. According to one embodiment, a solution of chemotactic biomolecules is placed in  17   a  and  19   a  and a protein solution is placed in  18   a . The solutions are allowed to flow into channel region  15   a  under the influence of gentle aspiration at well region  14   a . Biomolecules adsorb nonspecifically to the regions of the surface over which the solution containing the biomolecules flows forming a surface gradient. The wells are then filled with a suspension of cells and potential haptotaxis of the cells towards the increasing concentration gradient of biomolecules is observed and monitored. See generally, S. Takayama et al., “Patterning Cells and their Environment Using Multiple Laminar Fluid Flows in Capillary Networks”  Pro. Natl. Acad. Sci. USA,  Vol. 96, pp. 5545-5548, May 1999. 
     The present invention also contemplates an assay using both a soluble and surface gradient to determine whether the soluble test substance or the immobilized test biomolecules more heavily influence chemotaxis and chemoinvasion. In this embodiment, an assay is performed by forming a surface gradient as described above, an assay is performed by forming a solution gradient as described above, an assay is performed by forming both types of gradients and the results of all three assays are compared. With respect to the combined gradient assay, test biomolecules are immobilized on the upper surface U of support member  16  constituting the bottom surface of well region  13   a  and on the upper surface of support member  16  underlying channel region  15   a  and the concentration of biomolecules decreases along the longitudinal axis of chamber  12  from well region  13   a  to well region  14   a , in any one of the embodiments of the test device of the present invention, such as the embodiments shown in  FIGS. 1A-14 . Additionally, a soluble test substance is added to well region  13   a . Such an embodiment creates surface and soluble chemotactic concentration gradients that decrease in the same direction. If the combined concentration gradients have a synergistic effect on chemotaxis and/or chemoinvasion, then both gradients should be used in screening both the cell receptor binding the chemotactic ligands of the soluble chemotactic substance and the cell receptor binding the immobilized biomolecules. Both types of receptors are identified as important and therapeutic agents that target both these receptors or a combination of therapeutic agents, one targeting one receptor and another targeting the other receptor can be screened. If the combined concentration gradients do not have a synergistic effect, then the individual gradient that more strongly promotes chemotaxis and/or chemoinvasion can be identified and the cell receptor that binds to the chemotactic ligands of the test agent forming the gradient can be targeted. 
     Identifying optimal chemotactic ligand and receptor pairs is important in understanding the biological pathways implicated in chemotaxis and/or chemoinvasion and developing therapeutic agents that target these pathways. Accordingly, the present invention generally provides using chemotactic test agents to determine which chemotactic receptors expressed on a cell&#39;s surface most heavily influence chemotaxis and/or chemoinvasion. In one embodiment, the present invention provides for high throughput screening of a class of chemoattractants known to attract a particular cell type having a receptor on the cell&#39;s surface for each chemoattractant within this class in order to identify which receptor is more strongly implicated in the chemotaxis and/or chemoinvasion process. After identifying this receptor, the present invention contemplates high-throughput screening of therapeutic agents that potentially block this receptor or bind to this receptor, depending on whether chemotaxis and/or chemoinvasion is desired to be promoted or prevented. In another embodiment, the present invention provides for high throughput screening of different chemoattractants known to bind to the same receptor on a particular cell type&#39;s surface, in order to determine which chemoattractant ligand/receptor pair more heavily influences chemotaxis and/or chemoinvasion. After identifying this ligand/receptor pair, the present invention contemplates high throughput screening of therapeutic agents that target this receptor and either block or activate this receptor depending one whether chemotaxis and/or chemoinvasion is desired to be promoted or prevented. 
     The present invention also contemplates high-throughput screening of a class of chemotactic inhibitors known to inhibit chemotaxis of a particular cell type having various chemotactic receptors on the cell&#39;s surface in order identify which receptor is more strongly implicated in the chemotaxis and chemoinvasion process. After identifying this receptor, the present invention provides for high throughput screening of therapeutic agents that potentially block this receptor as well (if such action is desired). 
     In one embodiment of the present invention, an assay is performed to determine whether a test compound inhibits cancer cell invasion. In this embodiment, untreated cancer cells are placed in well region  14   a  and a test agent is placed in well region  13   a  of chamber  12  in any one of the embodiments of the test device of the present invention, such as the embodiments shown in  FIGS. 1A-14 . Cell chemotaxis and invasion is measured and recorded. After a suitable test agent is identified (one that chemically attracts the cancer cells) another assay is run in chamber  12 . In this subsequent assay, cancer cells are placed in well region  14   a  and a test compound, for example, a therapeutic, is also placed in well region  14   a . In another embodiment, the test compound is also placed in channel region  15   a . If a gel matrix is to be added to channel region  15   a , the test compound can be mixed with the gel matrix before the gel is contacted with channel region  15   a  during fabrication of device  10 . A subsequent sample of the test agent identified in the first assay is placed in well region  13   a  and the chemotaxis and invasion of the cells treated with the test compound is compared to the chemotaxis and invasion of the cells not treated with the test compound. The test compound&#39;s anti-cancer potential is measured by whether the treated cancer cells have a slower chemotaxis and invasion rate than the untreated cancer cells. 
     With respect to another exemplary use of the chemotaxis and chemoinvasion device of the present invention, the device can be used to assay cells&#39; response to the inflammatory response. A local infection or injury in any tissue of the body attracts leukocytes into the damaged tissue as part of the inflammatory response. The inflammatory response is mediated by a variety of signaling molecules produced within the damaged tissue site by mast cells, platelets, nerve endings and leukocytes. Some of these mediators act on capillary endothelial cells, causing them to loosen their attachments to their neighboring endothelial cells so that the capillary becomes more permeable. The endothelial cells are also stimulated to express cell-surface molecules that recognize specific carbohydrates that are present on the surface of leukocytes in the blood and cause these leukocytes to adhere to the endothelial cells. Other mediators released from the damaged tissue act as chemoattractants, causing the bound leukocytes to migrate between the capillary endothelial cells into the damaged tissue. To study leukocyte chemotaxis, in one embodiment, channel region  15   a  is treated to simulate conditions in a human blood capillary during the inflammatory response. For example, the side walls of channel region  15   a  are coated with endothelial cells expressing cell surface molecules such as selecting, for example as shown in FIG.  4 B. Leukocytes are then added to well region  14   a  and a known chemoattractant is added to well region  13   a  in any one of the embodiments of the test device of the present invention, such as the embodiments shown in  FIGS. 1A-14 . Other suitable cell types that can be added to well region  14   a  are neutrophils, monocytes, T and B lymphocytes, macrophages or other cell types involved in response to injury or inflammation. The leukocytes&#39; chemotaxis across channel region  15   a  towards well region  13   a  is observed. Depending on the type of infection to be studied, different categories of leukocytes can be used. For example, in one embodiment studying cell chemotaxis in response to a bacterial infection, well region  14   a  receives neutrophils. In another embodiment studying cell chemotaxis in response to a viral infection, well region  14   a  receives T-cells. 
     In another embodiment simulating the process of angiogenesis, it is known in the art that growth factors applied to the cornea induce the growth of new blood vessels from the rim of highly vascularized tissue surrounding the cornea towards the sparsely vascularized center of the cornea Therefore in another exemplary assay utilizing the chemotaxis and chemoinvasion device, cells from corneal tissue are placed in well region  13   a  and endothelial cells are placed in well region  14   a  in any one of the embodiments of the test device of the present invention, such as the embodiments shown in  FIGS. 1A-14 . A growth factor is added to well region  13   a  and chemotaxis of the endothelial cells is observed, measured and recorded. Alternatively, since angiogenesis is also important in tumor growth (in order to supply oxygen and nutrients to the tumor mass), instead of adding growth factor to well region  13   a , cancer cells from corneal tissue that produce angiogenic factors such as vascular endothelial growth factor (VEGF) could be added to well region  13   a  and normal endothelial cells added to well region  14   a . In a different embodiment also related to the study of angiogenesis, mast cells, macrophages, and fat cells that release fibroblast growth factor during tissue repair, inflammation, and tissue growth are placed in well region  13   a  and endothelial cells are placed in well region  14   a . Since during angiogenesis, a capillary sprout grows into surrounding connective tissue, to further simulate conditions in vivo, channel region  15   a  can be filled with a gel matrix. 
     There are several variations and embodiments of the aforementioned assays. One embodiment involves the number of channels connecting well region  13   a  and well region  14   a  of chamber  12  of device  10 . In one embodiment, such as the ones shown in  FIGS. 3A-3C , there are multiple channels connecting well region  13   a  to well region  14   a . By using multiple channels, multiple assays can be performed simultaneously using one biological sample of cells. In such an embodiment, all assays are performed under uniform and consistent conditions and therefore provide statistically more accurate results. For example, each assay begins with exactly the same number of potentially migratory cells and exactly the same concentration of test agent. Once a concentration gradient forms, each assay is exposed to the gradient for the same period of time. These multiple channels also provide redundancy in case of failure in the assay. 
     Another embodiment of the cell invasion and chemotaxis assay of the present invention involves the placement of cells in well region  14   a  of chamber  12  in any one of the embodiments of the test device of the present invention, such as the embodiments shown in  FIGS. 1A-14 . The cells may be patterned in a specific array on the upper surface U of support member  16  constituting the bottom surface of well region  14   a  or may simply be deposited in no specific pattern or arrangement in well region  14   a  If the cells are patterned in a specific array on the upper surface of support member  16  constituting the bottom surface of well region  14   a , then preferably, during the fabrication of device  10 , the upper surface of support member  16  constituting the bottom surface of well region  14   a  is first patterned with cells and then top member  11  is placed over support member  16 . It is desirable to monitor cellular movement from a predetermined “starting” position to accurately measure the distance and time periods the cells travel. As such, in one embodiment, the cells are immobilized or patterned upon the support member underlying the first well in such a manner that the cells&#39; viability is maintained and their position is definable so that chemotaxis and invasion may be observed. There are several techniques known in the art to immobilize and pattern the cells into discreet arrays onto the support member. A preferred technique is described in copending application No. 60/330,456. In one embodiment, a cell position patterning member is used to pattern the cells into definable areas onto the upper surface U of support member  16  constituting the bottom surface of well region  14   a  of top member  11 . 
     If, for example, top member  11  is fabricated in the footprint of a standard 96-well microtiter plate such that wells  13  and  14  correspond to the size and shape of the macrowells of the microtiter plate (not shown), then the cell position pattern member has outlined areas which correspond to the size and shape of wells  13  and  14  and therefore correspond to the size and shape of the macrowells of the microtiter plate. Each outlined area has micro through holes through which the cells will be patterned. In order to pattern the cells, the cell position patterning member is contacted with support member  16  and the outlined areas of the cell position patterning member are aligned with portion of upper surface U of support member  16  that constitutes the bottom surface of well region  14   a , and will ultimately correspond to well region  14   a  once top member  11  is contacted with support member  16 . Cells are then deposited over the cell position patterning member and filter through the micro through holes of the patterning member onto the support member underlying the areas corresponding to through-holes corresponding to second well regions  14   a  of chambers  12 . Top member  11  is then placed over support member  16  such that through-holes  14   a  are placed over the area of support member  16  in which the cells are patterned. These patterning steps result in discrete arrays of cells in well region  14   a.    
     Preferably, the cell position patterning member comprises an elastomeric material such as PDMS. Using PDMS for the patterning member provides a substantially fluid-tight seal between the patterning member and the support member. This substantially fluid-tight seal is preferable between these two components because cells placed in the wells are less likely to infiltrate adjoining wells if such a seal exists between the patterning member and the support member. The arrangement of the micro through holes of the patterning member may be rectangular, hexagonal, or another array resulting in the cells being patterned in these respective shapes. The width of each micro-through hole may be varied according to cell types and desired number of cells to be patterned. For example, if the width of both cell and micro through hole is 10 microns, only one cell will deposit through each micro through hole. Thus, in this example, if the width of micro through hole is 100 microns up to approximately 100 cells may be deposited. 
     The present invention also contemplates the patterning of more than one cell type on the upper surface of support member  16  constituting the bottom surface of well region  14   a  in any one of the embodiments of the test device of the present invention, such as the embodiments shown in  FIGS. 1A-14 . Since cells of one type in vivo rarely exist in isolation and are instead in contact and communication with other cell types, it is desirable to have a system in which cells can be assayed in an environment more like that of the body. For example, since cancer cells are never found in isolation, but rather surrounded by normal cells, an assay designed to test the effect of a drug on cancer cells would be more accurate if the cancer cells in the assay were surrounded by normal cells. In testing an anti-cancer drug, cancer cells may be patterned on the upper surface of support member  16  constituting the bottom surface of well region  14   a  in any given one of the embodiments of the test device of the present invention, such as the embodiments of  FIGS. 1A-14 , and then through a separate patterning procedure, the cancer cells may be surrounded by stromal cells. To pattern two different cell types on the upper surface of support member  16  constituting the bottom surface of well region  14   a , a micro cell position patterning member, as described above, is contacted with support member  16  and the outlined areas of the cell position patterning member are aligned with the portion of upper surface U of support member  16  that constitutes the bottom surface of well region  14   a , and will ultimately correspond to well region  14   a  once top member  11  is contacted with support member  16 . Cells of a first type may then be deposited over the cell position patterning member and filter through the micro through holes of the patterning member onto the portion of the upper surface U of support member  16  constituting the bottom surface of well region  14   a  The micro cell position patterning member may then be removed from support member  16 . A macro cell position patterning member with outlined areas that correspond to the size and shape of wells  13  and  14  and may therefore correspond to the size and shape of the macrowells of a 96 well microtiter plate. The macro cell position patterning member has macro through holes. A macro through hole of the macro cell position patterning member encompasses an area larger than the surface area defined by a micro through hole of the micro cell position patterning member, but smaller than the surface area defined by well region  14   a  of chamber  12 . The macro cell position patterning member may then be contacted with support member  16 . Cells of a second type may then be deposited over the macro cell position patterning member and filter through the macro through holes of the macro cell position patterning member onto the portion of upper surface U of support member  16  constituting the bottom surface of well regions  14   a  once top member  11  is contacted with support member  16 . Such patterning arrangement may result in cells of a second type surrounding and “stacking” cells of a first type. If it is desired to only have the cells of the second type stack the cells of the first type, then the same micro cell position patterning member used to deposit the first cell type or a different micro cell position patterning member having the exact same configuration as the patterning member used to deposit cells of a first type, may be used to deposit cells of a second type. After the cells are patterned on support member  16 , top member  11  may be contacted with support member  16  such that through holes in top member  11  corresponding to the well region  14   a  encompass the areas patterned with cells. This essentially results in cells being immobilized in a specific array within well region  14   a.    
     Notwithstanding how many different cell types are patterned on the upper surface of support member  16  constituting the bottom surface of well region  14   a , the cells may be patterned on the support member through several methods known in the art. For example, the cells may be patterned on support member  16  through the use of SAMS. There are several techniques known in the art to pattern cells through the use of SAMs of which a few exemplary techniques disclosed in U.S. Pat. No. 5,512,131 to Kumar et al., U.S. Pat. No. 5,620,850 to Bambad et al., U.S. Pat. No. 5,721,131 to Rudolph et al., U.S. Pat. Nos. 5,776,748 and 5,976,826 to Singhvi et al. are incorporated by reference herein. 
     Several methods are known in the art to tag the cells in order to observe and measure the aforementioned parameters. In one embodiment, an unpurified sample containing a cell type of interest is incubated with a staining agent that is differentially absorbed by the various cell types. The cells are then placed in well region  14   a  of chamber  12  in any given one of the embodiments of the test device of the present invention, such as the embodiments of  FIGS. 1A-14 . Individual, stained cells are then detected based upon color or intensity contrast, using any suitable microscopy technique(s), and such cells are assigned positional coordinates. In another embodiment, an unpurified cell sample is incubated with one or more detectable reporters, each reporter capable of selectively binding to a specific cell type of interest and imparting a characteristic fluorescence to all labeled cells. The sample is then placed in well region  14   a  of chamber  12  in any given one of the embodiments of the test device of the present invention, such as the embodiments of  FIGS. 1A-14 . The sample is then irradiated with the appropriate wavelength light and fluorescing cells are detected and assigned positional coordinates. One skilled in the art will recognize that a variety of methods for discriminating selected cells from other components in an unpurified sample are available. For example, these methods can include dyes, radioisotopes, fluorescers, chemiluminescers, beads, enzymes, and antibodies. Specific labeling of cell types can be accomplished, for example, utilizing fluorescently-labeled antibodies. The process of labeling cells is well known in the art as is the variety of fluorescent dyes that may be used for labeling particular cell types. 
     Cells of a chosen type may be also differentiated in a mixed-cell population, for example, using a detectable reporter or a selected combination of detectable reporters that selectively and/or preferentially bind to such cells. Labeling may be accomplished, for example, using monoclonal antibodies that bind selectively to expressed CDs, antigens, receptors, and the like. Examples of tumor cell antigens include CD13 and CD33 present on myeloid cells; CD10 and CD19 present on B-cells; and CD2, CD5, and CD7 present on T-cells. One of skill in the art will recognize that numerous markers are available that identify various known cell markers. Moreover, additional markers are continually being discovered. Any such markers, whether known now or discovered in the future, that are useful in labeling cells may be exploited in practicing the invention. 
     Since few, if any markers are absolutely specific to only a single type of cell, it may be desirable to label at least two markers, each with a different label, for each chosen cell type. Detection of multiple labels for each chosen cell type should help to ensure that the chemotaxis and chemoinvasion analysis is limited only to the cells of interest. 
     The present invention further provides a test device comprising: support means; means mounted to the support means for defining a discrete chamber with the support means by being placed in fluid-tight, conformal contact with the support means. The discrete chamber includes a first well region including at least one first well; a second well region including at least one second well, the second well region further being horizontally offset with respect to the first well region in a test orientation of the device; and a channel region including at least one channel connecting the first well region and the second well region with one another. An example of the support means comprises the support member  16  shown in  FIGS. 1A ,  1 B,  12  and  13 , while an example of the means mounted to the support means comprises the top member  11  shown in  FIGS. 1A-11 ,  13  and  14 . Other such means would be well known by persons skilled in the art. 
     From the foregoing, it will be observed that numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. For example, different embodiments of a device of the present invention may be combined. Embodiments of the present invention further contemplate different types of assays, for example, an assay wherein the test agent comprises a buffer solution instead of a chemotactic agent. In such an assay, cell migration through channel region  15   a  in observed in the absence of a chemotactic gradient. 
     It will be appreciated that the present disclosure is intended to set forth the exemplifications of the invention, and the exemplifications set forth are not intended to limit the invention to the specific embodiments illustrated. The disclosure is intended to cover by the appended claims all such modifications as fall within the spirit and scope of the claims. 
     EXAMPLES 
     Example 1 
     Procedure for Fabrication of Chemoinvasion Device 
     A silicon wafer (6 inches) is spin coated with photoresist (SU8-50) at 2000 rpm for 45 seconds. After baking the wafer on a hot plate at 115° C. for  10  minutes, the wafer is allowed to cool to room temperature. A mask aligner (EVG620) is used to expose the photoresist film through a photomask. Exposure of 45 seconds is followed by another hard bake at 115° C. for 10 minutes. The silicon wafer is allowed to cool to room temperature for over 30 minutes. The uncrosslinked photoresist is removed using propylene glycol methyl ether acetate (PGMEA). The wafer is dried under a stream of nitrogen, and the patterned photoresist is ready for subsequent processing. 
     In one embodiment, the patterned photoresist is spin-coated with another layer of SU8-100 at 1500 rpm for 45 seconds. A mask aligner is used to selectively expose macrofeatures (i.e. wells) of the top member but not expose channel regions connecting the wells and other areas of the top member. After post exposure processing and photoresist removal, the master contains multiple layered features. This step may be repeated to introduce macro-features on the master, which have the height of approximately 3 mm. 
     When a PDMS prepolymer is cast against the master, it faithfully replicates the features in the master. When casting, PDMS is added in an amount slightly lower than the height of the macrofeatures. After curing the PDMS for four hours at 65 degrees C., the PDMS is peeled off the silicon master and thoroughly cleaned with soap and water and rinsed with 100% ethanol. A glass support member is also cleaned and rinsed with ethanol. The PDMS membrane and glass support member are plasma oxidized for 1 minute with the sides that would be bonded together facing upward. The PDMS membrane is then placed onto the glass support member and pressure is applied to remove any air bubbles that may have formed between the PDMS membrane and the glass support member. The assembled device is then cooled to 4° C. Within 15 minutes of the plasma oxidation of the PDMS membrane and the glass support member, 20 microliters (μl) of Matrigel (any other hydrogel may be used) is poured into the first well and allowed to flow into the capillaries. The device is placed at room temperature for 15 minutes to set the Matrigel. Excess gel is then removed from the wells of the top member using a vacuum and a Pasteur pipette. 
     Example 2 
     Cell Chemoinvasion Assay 
     Placement of Cells and Test Agent in Chamber 
     The first and second wells of a chamber of a top member are filled with phosphate buffered saline solution, PBS. The bottom of the second well may be treated with fibronectin (1 mg/ml) or other extracellular matrix protein for 30 minutes, followed by washing twice with PBS. After aspirating PBS, astrocytoma cells (U87-MG) are plated in 50 μl of freshly warmed medium in the second well (25,000 cells per well of a 24-well plate, in volume of 50 μl of solution per well). The cells deposit through the second well of the chamber, and attach to the bottom of the second well. 
     Cells are left to attach and spread in the second well overnight in a 37° C. incubator. At the start of the experiment, the cell medium is exchanged for fresh serum-free medium. 10 μg of bFGF (basic fibroblast growth factor) per ml of medium is added to the first well of each chamber. 
     Image Acquisition and Data Analysis 
     Digital Images are taken on a Zeiss inverted microscope using AXIOCAM™. Data was analyzed on AXIOVISION™ software. Time-lapsed images are taken every day at the same time for four days. 
     Example 3 
     Cell Chemoinvasion Inhibition Assay Using Solution Gradient 
     Placement of Cells and Test Agent in Chambers 
     With respect to three chambers, the wells of each chamber of a top member are filled with PBS. The bottom of the second wells may be treated with fibronectin (1 mg/ml) or other extracellular matrix protein for 30 minutes, followed by washing twice with PBS. After aspirating PBS, U87-MG cells are plated in 50 μl of freshly warmed medium in the second wells (10,000 cells per well of a 24-well plate, in volume of 50 μl of medium per well). The cells deposit through the second wells of each chamber, and adhere to the bottom of the second wells. 
     Cells are left to attach and spread in the second wells overnight in a 37° C. incubator. At the start of the experiment, the cell medium is exchanged for fresh serum-free medium or 1% serum. 1 μg of bFGF (basic fibroblast growth factor) per ml of medium is added to the first wells of the chamber. A solution gradient is allowed to form for one hour. 
     With respect to the three different chambers, 100 μM of LY294002 are placed in the second well of chamber # 1 , 10 μM LY294002 of are placed in the second well of chamber # 2 , and 1.0 μM of LY294002 are placed in the second well of chamber # 3 . 
     Image Acquisition and Data Analysis 
     Digital Images are taken on a Zeiss inverted microscope using AXIOCAM™. Data was analyzed on AXIOVISION™ software. Time-lapsed images are taken every day at the same time for four days. 
     Example 4 
     Immobilization of Biomolecules on Support Member 
     After assembling the device as described above, the channel regions are filled with ethanolic solution containing (CH 3 CH 2 O) 3 Si (CH 2 ) 3 NH 2 . After 20 minutes at room temperature, the channel regions are washed off using ethanol. The device is incubated at 105° C. for one hour to crosslink the siloxane monolayer formed on the support member. The device is washed with ethanol to remove residues. The channel regions are filled with a solution of diisocyanate, either hexamethylene diisocyanate or tolyl diisocyanate (1% in acetonitrile or N-methyl pyrrolidinone). The diisocyanate is allowed to react for two hours with the terminal amino groups of the siloxane monolayer formed on the support member. The diisocyanate is washed off. The channel regions are filled with 1 mg/ml solution of heparan sulfate or other sulfated carbohydrates (for example, di-acetylated form of heparin, heparin fragments, lectins containing sulfated sugars, etc.) The heparan sulfate is allowed to react with the support member to form immobilized species. The heparan sulfate solution and other reagents are washed off. A chemokine solution (any chemokine from CC, CXC, CX3C, or XC families may be used) is introduced into the channel region. By electrostatic interaction, chemokines that have higher pI (˜9-10) adsorb onto the negatively charged sulfated support member. 
     Example 5 
     Chemotaxis Inhibition Assay Using Surface Gradient 
     Two wells are filled with 50 μl of PBS, and hydrostatic pressure is allowed to equalize. 5 μl of anti-hisx 6  antibody are added to the first well and 5 μl of buffer are added to the second well to equalize hydrostatic pressure. By diffusion, the antibody concentration forms a gradient from the first well to the second well. After 2 hours at room temperature, the two wells are washed off by adding 50 μl of buffer to the second well and removing 50 μl from the first well. By physisorption, the solution gradient is transferred onto a surface thereby forming a surface gradient. A solution of IL-8 (recombinant human IL-8 with a HISx6 fusion tag, R+D systems, catalog No. 968-IL) at concentration of 25 μg/ml is added to the channel regions. The solution is allowed to incubate for 30 minutes at room temperature. Excess IL-8 chemokine is washed off and the surface is decorated with bound IL-8. Neutrophils(freshly isolated from a healthy donor) are added to the second well. Typically 20,000-100,000 cells are added in volume ranging from 10-550 μl. Neutrophils are allowed to adhere to the support member and allowed to migrate towards the higher concentration of IL-8. Inhibition of migration is achieved by adding polyclonal antibody against IL-8.