Chemical screening system using strip arrays

Arrays of distinct chemically reactive materials used for assaying or screening are assembled by arranging premanufactured strips, each having a linear array of chemically reactive materials on its surface, into a frame to be exposed to a substance to be analyzed. The strips provide great flexibility in generating different types of arrays while still permitting efficiencies to be gained by batch processing of each strip type. The arrays further provide for novel read-out and reaction promotion techniques making use of the ability of the strips to direct and received energy to and from particular sites.

BACKGROUND OF THE INVENTION

The present invention relates to devices for screening attributes of chemical compounds, and in particular, to a method and apparatus for flexibly producing arrays of different chemically active substances for large scale chemical screening and assaying.

The analysis of chemical substances (e.g., nucleotide sequences) may be facilitated by the preparation of an array having many different chemical compounds (sampling compounds) placed at known sites. Each sampling compound selectively bonds with a different substance that may be part of the material to be analyzed. The sampling compounds are arranged in a regular pattern of array elements over the plane of the array.

In the field of genetic research, the sampling compounds may be different oligonucleotides at least one of which is expected to hybridize with portions of a genetic material to be tested. Fluorescent or radioactive markers bonded to the genetic material to be tested, or other well-known techniques, may be used to determine the location of the hybridizations, and from these locations (and a map of known locations of the sample oligonucleotides in the planar array), information about the make-up or other attributes of the genetic material may be determined.

A number of different methods have been used to create such arrays of different sampling compounds. In one sequential method, different sampling compounds are synthesized and placed in different wells of a microtiter place. The sampling compounds are then transferred from a microtiter plate to one or more array substrates by a robotically controlled dipping stick immersed first in a sampling compound then touched to different elements of the array where that sampling compound is to be located. In the case where the sampling compounds are oligonucleotides, the components are nucleic acids generated by using PCR and suitable templates.

A variation on this system, particularly useful in the generation of oligonucleotides, employs an ink jet-type process similar to that used in standard commercial printers to build up the sampling compounds, one component at a time, through layers laid down on particular elements of the array in a spatially controlled manner. For oligonucleotides, the process cycles through each of the four nucleic acids so that arbitrary oligonucleotides may be formed at the different array elements.

An alternative approach that processes many elements in parallel creates a series of masks, for example, using photolithographic techniques, where the masks have openings over specified array elements where a component is to be deposited. After each mask is in place, the desired component is washed over the mask and attaches only to those array elements corresponding to an open mask position. The mask is then removed and a new mask laid in place and this process repeated with a different component, for example, a different nucleic acid.

The laborious process of generating, applying and removing masks may be eliminated through the use photo-activation techniques in which the constituent components to be applied to array elements are suffused at the surface of the array and selective array elements irradiated with light to bond the components only at the illuminated elements. Mirror systems using micro-machined mirrors to direct intense light selectively to different portions in the array provide simultaneous processing of many array elements.

While this last technique eliminates the need for mask generation, constraints in maximum light flux that can be controlled, limit the speed at which arrays may be formed. Generally, mask techniques will be used when large numbers of a given type of array must be produced and sequential or mask-less photo activation techniques will be used for limited productions of different types of arrays.

A tradeoff between the speed of manufacturing the arrays and flexibility in manufacturing arrays of different types is provided by forming the different sampling compounds of an array on small beads. Those beads having a given sampling compound may be manufactured using parallel processing techniques. Later, beads with different sampling compounds are mechanically assembled into arrays using robotic manipulation or the like.

It is in this latter stage of manipulating the beads into usable arrays, that the shortcoming of using beads becomes most pronounced, and that causes, as a practical matter, the use of beads in manufacturing planar arrays, to be limited.

BRIEF SUMMARY OF THE INVENTION

Rather than placing sampling compounds on beads or in planar arrays, the present invention places the sampling compounds in linear arrays on slender strips. Multiple strips may be processed in parallel to obtain the benefit of efficient production of large numbers of the strips. Yet, the strips are easily handled and identified and may be assembled into dense, planar arrays with desired, arbitrary row variations. By using strips, an improved tradeoff between mass production and flexibility is obtained.

The strips further enable a variety of novel techniques of detecting and promoting the reactions of interest. In these techniques, the strips provide conduits for light or electrical energy.

Specifically then, the present invention provides a chemical screening apparatus having at least two different strips of a non-reactive substrate extending along a longitudinal axis and, supporting spaced along that longitudinal axis, a linear array of different chemically reactive sampling compounds exposed on a surface of the strip. A support frame receives and holds the strips for mutual exposure to a material to be screened.

Thus it is one object of the invention to facilitate the screening of a chemical compound against large numbers of sampling compounds in an efficient and yet flexible way. Each strip may be manufactured in a batch including many other strips and, then separated from the batch and assembled to produce a variety of different arrays.

The support frame may hold the strips transversely spaced in parallel relationship.

Thus it is another object of the invention to provide for a high density planar array of sampling compounds using easily manufactured strips.

The support frame may also hold strips transversely spaced along two 30 perpendicular axes.

Thus it is another object of the invention to enable the creation of three-dimensional arrays of sampling compounds allowing efficient sampling for many thousands of materials.

The strips may include isolating bands of repellant coatings between the sampling compounds or recessed portions receiving the sampling compounds.

Thus it is another object of the invention to facilitate the precise location of the sampling compounds, less cross contamination between the sampling compounds and greater densities of the sampling compounds on the strip.

The strip may include a marker allowing the strip to be uniquely identified, for example, using printing or fluorescent material and allowing a given end of the strip to be identified.

Thus it is another object of the invention to overcome a significant problem with beads being the difficulty of labeling the beads. An ample portion of the strip is available for marking without adversely affecting the density of sampling compounds and such marking may therefore use relatively simple techniques such as bar coding or the like.

The present invention allows for a number of methods of manufacturing the strips. In one method, the strips are fixed in a frame to be transversely spaced in parallel relationship in a plane to expose at a plane surface locations for the sampling compounds. The frame is then immersed in a sequence of component solutions. The solutions may be light activated to bond their components to the strips at a subset of locations for each of a set of different components or may be controlled through the use of masks to similar effect. After the series of component solutions has been applied, the frame may be removed and the strips released from the frame.

Thus it is one object of the invention to apply the same techniques now applied to the manufacture of planar arrays of sampling compounds to the manufacture of strips. Flexibility in the assembly of the arrays is preserved by the later release of the strips from the frame.

In a second method of manufacture, a strip is positioned having different longitudinal portions in adjacent volumes holding different component solutions. Light then activates a bonding of the components of the solutions with the strip at locations for at least one of the sampling compounds. The strip is then repositioned within the volumes of different component solutions and these steps are repeated to create the sampling compounds at the locations.

Thus it is another object of the invention to make use of the linear nature of the strips to allow for rapid fabrication on semi-continuous basis of the chemically reactive compounds. The strips may be easily moved between baths of a component solution in a way that would not be possible with planar arrays.

In yet another method of manufacture, the strips may be positioned to pass through a volume bracketing a segment of the strips. Once positioned, the volume may be filled with the component solution bonding a substance of that solution onto the segment to form a portion of the sampling compounds. The volume may be then flushed of component solution and the strip repositioned. These steps may be repeated with different component solutions to create the sampling compounds at the locations.

Thus it is another object of the invention to provide for rapid manufacture of the strips without the need for light activating techniques. In this case, the volumes serve as atomistic masks that need no changing as arbitrary sequences sampling compounds are deposited.

The present invention may also be used for manufacture of beads. In such manufacture, strips are prepared and then are cut between the locations where the sampling compounds are found.

It is thus another object of the invention to eliminate much of the handling problems of the creation of such beads.

The present invention also provides a method of automatic read-out of reactions between the sampling compounds and an analyzed material. In this method, two different strips are prepared and arranged to cross at a read-out site. Energy is emitted from an energetic interaction with a sampling compound at the read-out site. Energy from the read-out side is detected as conducted by at least one of the strips.

Thus it is another object of the invention to make use of the energy carrying and isolating capacity of strip substrates to simplify the read-out process.

In a similar way, the strip substrates may be used to promote reactions at particular sites. In this case, at least two strips are arranged to cross at a promotion site. Energy is applied to at least one of the strips to promote an energetic interaction with a sampling compound at the promotion site causing a localized chemical reaction.

Thus it is another object of the invention to provide for more complex assaying and screening techniques requiring intermediary reactions selectively controlled at specific array elements.

These objects will not be realized by all embodiments of the invention. For this reason, the objects should not be considered as limiting the scope of the invention. The scope of the invention should be determined by reference to the claims. A preferred embodiment is also described. The preferred embodiment is not exhaustive of all practical embodiments of the invention nor is it intended to be. For this reason, again, the claims should be consulted to determine the scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIG. 1, a filament10of the present invention extends along a longitudinal axis by a length12to provide, at an exposed outer surface of the filament, a number of different chemically reactive substances henceforth termed sampling compounds14spaced at locations16by a regular spacing distance18.

Generally the filament10may include a substrate strip of material of low chemical reactivity with the material to be tested and may be constructed of a variety of materials including glass, plastic, carbon and metal. As used herein, the term “strip” is intended to encompass any long, thin member providing substantially a single dimension of locations16. More precisely, the strip will have a length12that will exceed the diameter20(or a greatest cross-sectional span for non-round strips) by at least a factor of ten and typically by many thousands of times. The strip may but need not be constructed of a flexible material.

A marker24may be placed at one end22of the filament10, so as to allow the filament10to be identified and oriented. The marker24may be a printed bar code such as may be read automatically by bar code scanners or may be formed by a number of other techniques including characters, fluorescent markings or the like attached directly or indirectly to the end22.

Referring now toFIG. 2, the sampling compounds14distributed along the filament10in one embodiment are oligonucleotides26built up of nucleic acids28deposited sequentially onto the preceding nucleic acid as will be described below. Alternatively, but not shown, the sampling compounds may be other chemically reactive compounds synthesized on site at the locations or presynthesized and applied to the locations. Each sampling compound14may be unique and their order along the length12may be of an arbitrary predetermined sequence. A number of methods of applying the sampling compounds14to the filament10will be described further below.

Referring now toFIG. 3, the filaments10may be used directly for assaying an unknown material. In this regard, a one-meter fiber with ten-micron spacing distance18could hold 100,000 sampling compounds14. Each sampling compound14can be identified by its locations and sequence on the filament10with respect to the marker24. When multiple filaments10are used, a unique identifier of the marker24may distinguish them. Flexibility of the filament10can allow it to be coiled within a small volume of tested solutions.

In an alternative embodiment, providing more convenient handling of filaments10and providing the ability to vary the sampling compounds14while still partaking of possible batch efficiencies in creating the filaments10, a number of short filaments10are attached at their ends on opposite sides of a rectangular frame30to span an open area defined thereby. Preferably, the ends of the filaments10where they are attached are free from sampling compounds14and may be retained by adhesive or mechanical clamps or other well-known techniques. A fifty-micron diameter fiber cut into 200 one-centimeter pieces, could fill a one-by-one centimeter frame30with two meters of fibers or about 200,000 sampling compounds14. In this way an array32may be generated.

The use of such arrays32is not limited to assaying and screening, terms that will henceforth be used interchangeably, but may also be used for the screening of other materials including generally other organic molecules, peptides and other compounds.

Referring now toFIG. 4, it will be understood that the technique of assembling short lengths of the filaments10into an array32allows a wide variety of semi-custom arrays32to be created from a more limited set of standard filaments10. InFIG. 4, the letters indicate different sampling compounds14. The sequence of sampling compounds14of each row formed by a filament10will be defined by the set of standard filaments10. Nevertheless, the number of different arrays32will be equal to the mathematical combination of the number of different filament types, a far larger number. For example, from a library of 400 standard fibers, 10119different 200 fiber arrays32may be created.

In this way, the use of filaments10to create an array32, leverages a limited number of filament types into an extremely flexible variety of arrays32. The arrays32may be assembled efficiently by robotic techniques or the like and may be verified by reading the identification markers24unique to each filament.

Referring now toFIG. 5, higher volumetric sample densities may be obtained by stacking the frames30ofFIG. 2into a column34as held by clips36. In this case, the spaces between the filaments10, allow ready circulation of material to be analyzed through the frames30past the sampling compounds14of each of the filaments10.

Referring now toFIG. 6, guard bands40may be placed on the surface of the filaments10between the locations16of the sampling compounds14. These guard bands40may be, for example, a repellant such as a siliconized coating or hydrophobic material attached to the filaments10prior to placement of the sampling compounds14by resist techniques or the like. The guard bands40increase the densities of sampling compounds14that maybe placed on the filament10(reducing the spacing distance18) while preserving the separation of the sampling compounds14.

Referring toFIG. 7, the filaments10may alternatively or in addition, include notches or pits42for receiving the sampling compounds14at the locations16and thereby providing radially extending walls44between sampling compounds14, offering a function similar to that of the guard bands40but also protecting the sampling compounds14from mechanical abrasion.

Referring now toFIGS. 8 and 9, the ability to offer semi-custom arrays32by mixing and matching different filaments10is consistent with the filaments10being manufactured in batches in which many of the same type of filaments10are produced in parallel thus reducing the total manufacture time of a given array32.

In a first manufacturing technique, strips for use as filaments10prior to placement of the sampling compounds14, may be aligned in a frame30similar to that described with respect toFIG. 3and immersed in a bath46holding one of the constituents50of the sampling compounds14. When the sampling compounds14are oligonucleotides, the constituents50can be individual nucleic acids.

Once the strips of the filaments10are in place, a columnar beam of light48, i.e., a beam of light focused along a column perpendicular to the rows defined by the filaments10, having a width substantially equal to the width of the sampling compounds14as shown inFIG. 1, but substantially less than the spacing distance18, may illuminate corresponding locations16on the strips where it is desired that the constituent50be deposited. The light photo activates the constituent materials50bound to the surface46to further deposit them at the location16where the columnar beam of light48is located thus attaching them directly to the filament10or to another constituent50earlier deposited on filament10. According to techniques similar to those used in the prior art, after the conclusion of the photo activation of a first constituent50, the frame30and filaments10are rinsed and immersed in a second bath with a second constituent50which may be selectively deposited by photo activation at different locations or the same locations16. In this way, an arbitrary oligonucleotide may be produced or other similar polymeric chains.

Referring now toFIG. 10, an apparatus holding strips in a frame30similar to that shown inFIG. 8may be used to deposit a photoresist52onto the filaments10to create a mask covering the filaments10except for pockets54that allow deposition of the constituent50of the bath46onto the filament10or other earlier constituent50deposited at the pocket54. As is understood in the art, the mask may then be removed by a solvent or other technique and a new mask placed over the filament10using a similar photo resist technique. With this new mask in place, a new or the same constituent material50may be placed around the filaments10in the bath46and this process repeated until the necessary polymeric chain is produced.

The mask may be produced photo lithographically through the use of a columnar beam of light48similar to that shown inFIG. 9. The filaments10are bathed in a photoresist and the light hardens selected columns of a photo resist outside of the pockets54. Excess photo resist is washed off to produce the necessary mask structure.

In both these cases, a larger number of filaments10may be simultaneously processed in the same baths46thus significantly improving the efficiency and speed of the manufacturing process on a per array32basis.

Referring now toFIG. 11, the structure of the filaments10provides for a novel method of manufacturing using a plurality of baths46athrough46darranged in a line to receive a strand56of the filament10passing sequentially through each bath46athrough46din sequence. The strand56may be continuous as shown, held by a number of idler rollers58and advanced by a drive wheel60, or may be discontinuous and clamped at either end for similar motion as will now be described.

In the former embodiment, the drive wheel60moves by an angular increment62in either of two directions64so as to advance or retreat the filament10through the baths46athrough46dby the spacing distance18separating the sampling compounds14. Rinsing baths, not shown, may be placed between these baths46athrough46d. Each bath may be associated with an intense light source66focused at a corresponding location68athrough68don the filament10as immersed in a given bath. The separation of the locations68athrough68dis an integral multiple of the spacing distance18between sampling compounds14.

A computer controller70, such as a programmable logic controller, coordinates the motion of the wheel60and the illumination of selected light sources66so as to photo actively deposit the particular constituents50of any or all of the baths46athrough46don the locations according to a predetermined program. After each illumination step, resulting in the deposition of a constituent material50at least one of the baths46, the computer controller70may advance or retreat the filament10to a new position and the process repeated until the desired sampling compounds14have been built up at the locations16.

The linear nature of the filament10makes this process possible by allowing the filament10to be easily moved between baths46for rapid generation of the necessary sampling compounds14s. Because the light sources66are fixed, and motion is constrained to motion of the filament10, the light sources may be easily focused to provide for high light flux commensurate with rapid generation of the necessary compounds. The filament10produced by this process may then be broken into a number of separate shorter filaments.

Referring now toFIG. 12, the filament10processed as described above with respect toFIG. 11, need not be alone but may be processed in parallel with a number of other filaments10on a carrier strip68. In this case, the light sources66are focused into a columnar form similar to that shown inFIG. 8to cross each of the filaments10for parallel processing of those filaments. The filaments10may then be removed from the carrier strip68.

A bar code or other printer (not shown) may be incorporated into the processing line ofFIG. 11to appropriately label the ends and identities of the filaments10or of segments from which filaments10will be cut. Alternatively, the bar codes or other identifications may be preattached to the filaments prior to the process ofFIG. 11.

Referring now toFIG. 13, using a different manufacturing technique, filaments10may be moved through orifices72formed in the parallel opposing walls of the volume71. The orifices may have flexible seals76so that the volume may retain a bath46of a constituent material to be deposited on the filament10while allowing free movement of the filament through the volume71. The separation of the walls74may be commensurate with the width of the sampling compounds14to be deposited on the filament10.

In this method, a filament10is positioned with a location16centered between the walls74by sliding the filament10through flexible seals76. The desired bath46of constituent material50is then pumped into the volume71to bond at the exposed location16of the filament, either directly to the filament10or to a previously bonded material of the sampling compounds14. The bath46is then withdrawn from the volume71and the filament10repositioned. Then the same or different bath46may be introduced into the volume71. In this case, no photo activation is necessary and the walls74act as an effective mask yet without the normal drawbacks of a masking process of changing the mask between different baths46. A series of volumes71each separately filled with different or the same baths may be used to simultaneously treat a number of locations16long the filament10.

Referring now toFIG. 14, this approach is also adaptable to the parallel processing of many filaments10, the ends of which may be held by filament retention plates80positioned on either side of the walls74outside of the volume71. The filament retention plates80hold the filaments in parallel fashion spaced from each other by an arbitrary distance along two axes perpendicular to the extent of the filaments10. A positioning mechanism82, preferably under computer control (similar to the controller70described with respect toFIG. 11) may reposition the filaments10within the volume71as different baths are introduced and withdrawn (also preferably under computer control) through an attached pipe84.

Referring now toFIG. 15, although the present invention contemplates that the filaments10may be used as filaments, after the deposition of the necessary sampling compounds14, the ability to easily process the filaments10also makes them attractive as a precursor to the production of beads. In this case, after deposition of the sampling compounds14, the filament10may be sheared by cutter blades86into short segments at places between the locations16, thus dividing the sampling compounds14from each other. In this way, the handling of separate beads during the deposition of the sampling compounds is eliminated. Further, because each of the sampling compounds14will be the same along a filament10, the need for masks or tightly focused light beams is reduced or eliminated.

Referring now toFIG. 16, although one function of the filaments is to provide a flexible yet easy to handle substrate for the deposition of sampling compounds14, by their nature, the filaments10also enable a number of novel reaction detection and reaction control techniques.

Referring now toFIG. 16, an array32of filaments assembled on a frame30may be used to test or assay a substance having a fluorescent marker. An excitation light source88may then be scanned across the rows described by the filaments10as held in the frame30causing fluorescence of given sampling compounds14′ where a reaction with the substance to be tested has occurred, and no fluorescence of other sampling compounds14that have not participated in such a reaction. If the filaments10are constructed of optical fibers, this fluorescence may be conducted to the ends of the filaments to be received by a light receptor90affiliated with each of the filaments10. The light receptors may be photodiodes or phototransistors or other light detection devices well known in the art. A controller92coordinating the scanning of the excitation light source88and the detection of light from the given filaments may automatically identify those sampling compounds14′ at which hybridization has occurred by matching the position of the scanning light source88and the particular light receptor90providing a signal output.

Referring toFIG. 17, the scanning excitation light source88may be replaced by an array of separate parallel optical fiber94crossing the given optical fiber filaments10at the locations16to conduct the excitation light98through themselves to the location16to produce fluorescence at the given sampling compound14′ on the filament10as shown inFIG. 16. Light lost through interstices between crossing filaments may serve to distinguish the location16from other locations through which the fluorescence may be conducted along more circuitous paths.

The introduction of yet another array of separate parallel optical fibers100orthogonal to both fibers94and filaments10allows this process to be extended into the three-dimensional array ofFIG. 17where the excitation light98is introduced into ones of fibers94and the florescence detected in pairs of the fibers100and filaments10.

Alternatively, the two-dimensional configuration ofFIG. 17with crossing of only the fibers94and filaments10or the three dimensional crossing of fibers94,10and100may be used to selectively encourage photo sensitive reactions at particular sampling compounds14through the introduction of light through two fibers100and94whose additive combination at the location16of particular sampling compound14within a bath46produce a threshold energy level sufficient for the reaction. In this way, fibers94and100and filaments10may conduct energy to control or initiate given reactions that may be of interest.

Each of the fibers94and100and filaments may have portions of the sampling compounds and their intersection may create the necessary juxtaposition of materials needed for a particular assay. In this way, a fixed library of filaments may be used to create a much greater variety of arrays32than would be dictated by a simple mathematical combination of the filament types.

Referring now toFIG. 18, use of an electrically conducting strip for the substrate of a filament10, allows electrical signals to be passed along orthogonal filaments102,104, and106crossing at location16′ to electrically or thermally activate chemical reactions or to electrically detect the results of those reaction through impedance or voltage measurements. So called, sneak electrical paths taking a more circuitous route through intersections of filaments102,106, and104and their neighbors may be eliminated by the deposition of a rectification material using semiconductor compounds on the outer surface of the fibers such as creates diodes110providing for a unique single conductive path from filament102to filament104through a single location16′.

Example I

As one use of this invention, one may wish to screen expression patterns developed by a particular cell-type, under a given set of environmental stresses. Standard methods can be used for the extraction of RNA molecules from cells, followed by fluorochrome labeling. Many labeling schemes exist in the literature, which utilize direct incorporation during complementary strand synthesis, or covalent attachment with psoaralated compounds (see e.g. Lockhart, D. J. and Winzeler, E. A., “Genomic, gene expression and DNA arrays”,Nature,405, 827 (2000)). The resulting probes can be hybridized against a known array as described above with respect toFIG. 4as one would for a conventional planar array.

Example II

Another possible utility of this invention is to screen multiple loci in a genome for rearrangements, insertions, and deletions. One prepares a number of PCR products using primer which will amplify across a known breakpoint. As an example, Prader-Willi syndrome (PWS) is most often caused by interstitial deletion of the chromosome segment 15q11-q13 from the paternally derived copy of chromosome 15. Similarly, Angelman syndrome (AS) involves a comparable maternal deletion. Thus, a series of PCR products could be prepare across the chromosomal segment 15q11-q13, using standard PCR techniques amplification protocols. Oligonucleotides can be synthesized using the present invention to screen or narrow down the breakpoint site. Since the region of this deletion is quite large, many thousands of oligonucleotides would have to be synthesized to cover the many possible breakpoint regions. Hybridization of fluorochrome-labeled PCR products against the synthesized oligonucleotides, would use standard protocols and procedures. These protocols are fully described on the website (microarrays.org/protocols.html), maintained by Prof. J. Derisi's laboratory (University of California, San Francisco). Another site maintained by TeleChem Corp, also list many useful protocols for mutation detection and fluorochrome-labeling: of probes: arrayit.com/DNA-Microarray-Protocols/#Protocol10.

Example III

Using the patterning technology described by the present invention, cells can be attached onto glass fibers. Simple incubation of treated fibers in cell culture will permit efficient attachment. Non-specific attachment of cells to glass surface can be made using standard protocols. For example, following the protocols of Webb, Hlady and Tresco (Webb K, Hlady V, Tresco P A. “Relative importance of surface wettability and charged functional groups on NIH 3T3 fibroblast attachment, spreading, and cytoskeletal organization.”, J Biomed Mater Res. 1998 Sep. 5; 41(3):422-30), clean glass fibers (30% hydrogen peroxide in concentrated sulfuric acid, 30 minutes; followed by extensive washing with high purity water) can be treated with 1% 3-aminopropyltriethoxysilane (1% v/v in dry toluene), followed by further reaction with methyl iodide (5% v/v in redistilled absolute ethanol), to produce a quaternary amine. Prepared fibers can then be preincubated in fetal calf serum (5% in phosphate-buffer saline—PBS), and then incubated in harvested NIH 3T3 cells. Simple rinsing of fibers with PBS will remove unattached cells. Fibers holding attached cells can be stored for hours in PBS—for extended periods in cell culture media, housed in a cell culture incubator. The latter conditions would promote cell proliferation. A series of different cell type can be attached to different fibers and then assembled into mixed-cell arrays using the frame technology described in this invention. Arrays incubated under a broad range of conditions, followed by assays would permit simultaneous screening of a broad range of cell-type. Fluorogenic assays could be accomplished by incubating cells with labeled substrates, followed by imaging by fluorescence microscopy.

Cellular function is influenced by neighboring cells. Different cell-types, once arrayed as described above can be brought into designated proximity with each other by simple rearrangement cell-laden fibers. Crisscrossing of different cell-fiber arrays arranged in overlapping frames will allow a large number of different cell-cell interaction to be made—if a frame containing 100 different cell-types attached to 100 different fibers, then this would produce 10,000 combinations (this produces a matrix). The diagonal elements of this arrangement (thought of as a matrix) are the same cell-type arranged in proximity with itself, on two different fibers. This arrangement would serve as an excellent control. Intersections of cell types, on either side would also be redundant, with the cell-type pair existing on different fibers (matrix analogy: row and column). Again such redundancy would serve as excellent controls, or they could be eliminated by using a series of shortened fibers. Likewise a three-dimensional array of cell-types could be constructed by inter-crossing of cell-laden fibers in the x-, y- and z-dimensions.

It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as comes within the scope of the following claims.