Patent Publication Number: US-2001000277-A1

Title: Method of making a glass array plate with closure

Description:
FIELD OF INVENTION  
       1. The invention relates to a glass multiple well assay plate for applications in biological or chemical assays.  
       BACKGROUND OF INVENTION  
       2. The relationship between structure and function of molecules is a fundamental issue in the study of biological and other chemical based systems. Structure-function relationships are important in understanding, for example, the function of enzymes, cellular communication, and cellular control and feedback mechanisms. Certain macromolecules are known to interact and bind to other molecules having a specific three-dimensional spacial and electronic distribution. Any macromolecule having such specificity can be considered a receptor, whether the macromolecule is an enzyme, a protein, a glycoprotein, an antibody, an oligonucleotide sequence of DNA, RNA or the like. The various molecules to which receptors bind are known as ligands.  
       3. Pharmaceutical drug discovery is one type of research that relies on the study of structure-function relationships. Much contemporary drug discovery involves discovering novel ligands with desirable patterns of specificity for biologically important receptors. Thus, the time to bring new drugs to market could be greatly reduced through the use of methods and apparatus which allow rapid generation and screening of large numbers of ligands.  
       4. A common way to generate such ligands is to synthesize libraries of ligands on solid phase resins. Since the introduction of solid phase synthesis methods for peptides, oligonucleotides, and other polynucleotides, new methods employing solid phase strategies have been developed that are capable of generating thousands, and in some cases millions of individual peptide or nucleic acid polymers using automated or manual techniques. These synthesis strategies, which generate families or libraries of compounds are generally referred to as “combinatorial chemistry” or “combinatorial synthesis” strategies.  
       5. The current storage format for compound libraries is a 96 well format well plate typically made from polypropylene and having rubber stopper sheets or hot seal covers. Certain processes and chemistries require that chemical reagents (which may be reactants, solvents, or reactants dissolved in solvents) be kept under inert or anhydrous conditions to prevent reactive groups from reacting with molecular oxygen, water vapor, or other agents. Examples of moisture sensitive chemistries include peptide chemistry, nucleic acid chemistry, organometallic, heterocyclic, and chemistries commonly used to construct combinatorial chemistry libraries. The solvent used for storage of synthesized chemicals is typically dimethylsulfoxide (DMSO).  
       6. Storage plates made from polymers have the disadvantage of being incapable of withstanding the extreme temperature variations that are sometimes required in combinatorial chemistry reactions and storage (between −20° and 370° C.).  
       7. Creating a multiwell plate from glass is a solution to this and other problems that are inherent in using polymers, such as sample interaction with the base polymer making up the plate. Glass, however cannot be injection molded and it is extremely difficult to press a gob of glass into a 96 well plate mold. One method currently used in producing a multiwell plate from glass involves a boring process. In this process, slabs of borosilicate glass conforming to the industry standard 96 well plate footprint are machined such that 96 individual wells are bored into the slab. This approach however is extremely costly.  
       8. Another method of making glass well plates involves vacuum thermoforming. By this method, small plates are produced from glass by vacuum thermoforming a thin glass sheet, as described in commonly assigned French Patent application 96-13530. This technique offers well volumes of anywhere from 200 μml to 0.1 μml volume capacity per well. While these volumes may be convenient for high-throughput screening bioassay applications aimed at sample and reagent conservation, they are probably too small for chemical synthesis in organic solvent, the storage of drugs or drug candidates in organic solvent or long term storage where closure is required.  
       9. The potential for using sealable multiwell plates made of glass extend beyond use as a storage device for combinatorial chemistry. Glass multiwell plates may also be used for such tasks as: interfacing with instruments, extraction, derivatization, synthesis, and more.  
       SUMMARY OF INVENTION  
       10. It is therefore an object of the present invention to provide a multiwell plate that can be manufactured from glass in a cost effective way. Further, it is an object to provide a method of making a glass multiwell plate that can produce varied and unique well designs. It is another object to provide a glass multiwell plate having wells that can be sealed from the external environment, for example by means of a septa. It is yet another object of the present invention to provide a multiwell plate that can withstand great variations in temperature.  
       11. The present invention relates to a method of making a glass multiwell plate for use in biological and chemical assays, experimentation and storage. The method comprises the steps of: delivering and depositing a first length of a molten glass ribbon to a surface of a mold having a mold cavity possessing at least one well-forming depression and a peripheral surface, wherein the first length of ribbon overlies the mold cavity and the peripheral surface; causing the first length of ribbon to substantially conform to the contour of the mold cavity thereby forming at least one well in the first length; delivering and depositing a second length of the molten glass ribbon to the exposed surface of the earlier deposited first length of molten glass ribbon; and, puncturing a hole through the second length and over the approximate center of at least one well thereby forming a series of self contained wells that may be accessed through the hole in the second length.  
       12. The glass multiwell plate of the present invention comprises a substantially rectangular plate having a peripheral skirt and formed by a uniform sheet of glass having therein a plurality of wells, each well having sidewalls, a bottom and a top surface, the top surface defining a hole capable of being hermetically sealed by a sealing means such as a multi-plugged rubber mat.  
     
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
     13.FIG. 1 is a perspective view of the glass multiwell plate of the present invention with a section cut out therefrom.  
     14.FIG. 2 is a diagrammatic perspective and cutout view of the beginning stages of the instant method of making glass multiwell plates.  
     15.FIG. 3 is a diagrammatic perspective and cutout view of a later, intermediate stage of the instant method of making glass multiwell plates.  
     16.FIG. 4 is a partial cross sectional view of a later stage of the instant method of making glass multiwell plates.  
     17.FIG. 5 is a partial cross sectional view of the multiwell plates of the present invention.  
     18.FIG. 6 is a partial cross sectional view of the multiwell plates of the present invention having a sealing mat attached and being accessed by a needle.  
     19.FIG. 7 is a diagrammatic perspective and cutout view of a stage of an alternative method for making the glass multiwell plates of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     20.FIG. 1 illustrates one typical embodiment of a glass multiwell plate capable of being produced using the forming method disclosed herein. The glass plate  10  takes the form of a 96 well plate having a plurality of well openings  14  on the top surface. The dimensions of the plate and spacings between wells  12  preferably conform to industry standards for microplates; that is to say, a plate bordered by a peripheral skirt having 96 wells, each having an approximate volume of 500 μl and a depth of 12 mm, arranged in an 8×12 matrix (mutually perpendicular 8 and 12 well rows) with a spacing of approximately 9 mm between the center lines of rows both in the x and y directions. The overall height, width, and length dimensions of the plate are preferably standardized at approximately 14 mm, 85 mm, and 128 mm, respectively.  
     21. Referring now to FIG. 2, illustrated is the apparatus for forming glass plates containing an array of wells. The apparatus is similar to the one disclosed in commonly assigned PCT application PCT/US97/20484, incorporated herein by reference. In general, the instant method comprises the following steps: (a) delivering and depositing a first length of a molten glass ribbon to a surface of a mold having a mold cavity possessing at least one well-forming depression and a peripheral surface, wherein the first length of ribbon overlies the mold cavity and the peripheral surface; (b) causing the first length of ribbon to substantially conform to the contour of the mold cavity thereby forming at least one well in the first length; (c) delivering and depositing a second length of the molten glass ribbon to the exposed surface of the earlier deposited first length of molten glass ribbon; and, (d) puncturing a hole through the second length and over the approximate center of at least one well thereby forming a series of self contained wells that may be individually accessed through the corresponding holes in the second length. The viscosity of the molten glass ribbon at delivery is between about 1000 to 5000 poise so that the following is achieved: (1) the second length of the molten glass ribbon bridges, but does not sag into complete contact with the entire surface of the well of the first length of the molten glass ribbon; and, (2) a hermetic seal is formed between the first and second lengths of the molten glass ribbon wherever they contact.  
     22. The actual delivering of the glass ribbon, assuming a product exhibiting two layers, may be accomplished by either using one glass delivery orifice moving a single ribbon over a mold cavity twice, or two separate glass delivery orifices moving different ribbons over the mold cavity. In making a glass multiwell plate, the ribbon thickness should preferably be approximately between 1-3 mm, and more preferably, approximately 2 mm. In the case of making plates from ribbon of such thickness, a simple round orifice would be sufficient.  
     23. In the preferred embodiment, referring again to FIGS. 2 and 3, the method will now be explained in greater detail. Molten glass from a common furnace (not shown) and a common “main-line” forehearth  20  is fed to delivery conduit having a glass orifice  22  which thereafter delivers a stream of molten glass to a set of water-cooled rollers  24 A/ 24 B. A forehearth temperature control (not shown) allows control of the temperature of the molten glass, which, in turn, allows the glass stream to be delivered at a predetermined and controlled glass viscosity. Water-cooled rollers  24 A/ 24 B, rotating in opposite directions, thereafter squeeze the molten glass into a continuous ribbon shape.  
     24. Upon exiting the rollers, first length of the molten glass ribbon  26  is deposited upon mold  28  which is moved along a predetermined path, preferably a direction along the mold&#39;s width; although, the molten ribbon could be deposited, in a direction along the mold&#39;s length. Mold  28 , as depicted in FIGS. 2 and 3, is a diagrammatic and perspective cross-section view, cut along a row of wells.  
     25. First length of molten glass ribbon  26  is deposited so as to overlie well-forming depression  30  and the surrounding peripheral surface area  32 . Once delivered, first length of the molten glass ribbon  26  is thereafter caused to substantially conform to the contour of well-forming depressions  30  resulting in the formation of wells  34  in the first length of the molten glass ribbon  26 . First length of the molten glass ribbon  26  is allowed to substantially conform to the contour of well forming depression  22  solely by means of the force of gravity.  
     26. In a preferred embodiment, resulting in enhanced and accelerated conformance of the first length of the molten glass ribbon  26  to well forming depression  30 , the method involves the additional step of applying a vacuum to the under surface of first length  26 . As soon as the complete mold area is covered by first length of the molten glass ribbon  26 , a vacuum is applied between mold  28  and first length  26  via a vacuum line (not shown). Vacuum line, attached to a vacuum source (not shown), communicates with a series of vacuum ports  36  which are routed through the mold body itself and open at several locations on the glass surface of the mold, namely at the bottom of well-forming depressions  30 . A vacuum may be applied immediately after the first length of the molten glass ribbon is deposited, or such vacuum may be applied immediately after the first length  26  has initially sagged partially within the mold cavity well forming depressions. When the vacuum is applied between the glass and mold, the glass is forced to be in immediate and intimate contact with the mold, allowing the glass to be formed to the desired shape, while also initiating the cooling and hardening of first length of the molten glass ribbon  26 .  
     27. Referring now to FIG. 3, following the conformance of the first length  26  to the mold cavity, through either gravity or vacuum forming or a combination of the two, the mold  28  is thereafter moved back along a second predetermined path opposite that of direction A; i.e., direction B. As earlier, the stream of molten glass continues to be delivered from the glass orifice  22  and thereafter to the water-cooled rollers  24 A/ 24 B which are rotating in opposite directions with respect to each other. These rollers thereafter squeeze the molten glass into to a continuous ribbon shape, i.e., second length of the molten glass ribbon  38 , which is deposited upon and overlies the exposed surface of the first length of the molten glass ribbon  26 . Second length of the molten glass ribbon  38  simply lies on the on first length  26 , bridging itself across the formed wells due to the relatively low viscosity of the molten glass ribbon. In other words, second length of the molten glass ribbon  38  is essentially folded over and onto first length of the molten glass ribbon  26 .  
     28. The bulk viscosity, at delivery, of the molten glass of the first and second ribbon lengths should be such that the following is achieved: (1) the second length of the molten glass ribbon  38  bridges, but does not sag into complete contact with, the channel portion of the previously deposited first length of molten glass ribbon  26  and (2) a hermetic seal is formed wherever the first and second lengths of the molten glass ribbon contact; via inherent flow viscosity characteristics of the particular glass. Preferably, the molten glass, at delivery, exhibits a bulk viscosity, of between about 1000-5000 poise.  
     29. It follows that the bulk viscosity of the first length of the molten glass ribbon at the time of the deposition of the second length of the molten glass ribbon, is higher than that of the second length due to the working time or cooling which has occurred. Furthermore, a surface-to-mold viscosity gradient is likely to have developed in this first length. However, this first length of the molten glass ribbon should not have been allowed to cool or become so viscous at its surface that the two lengths of the molten glass ribbon can not “set-up” wherever they contact and therefore not form the desired hermetic glass-to-glass seal. Ideally, the bulk and surface viscosities should be maintained such that hermetic sealing detailed above is achieved; i.e., glass viscosities when the second ribbon length is delivered and deposited on the first ribbon length such that a glass-to-glass hermetic seal is formed. Furthermore, it is also necessary to minimize the surface to mold viscosity gradient of the first length so that unnecessary stresses do not build up within the so-formed glass plate. By utilizing rollers and molds which are comprised of a low-conductive material, less heat will be extracted from the surface of the either length of the molten glass ribbon and therefore less of viscosity gradient has developed; mold materials which have been utilized include stainless steel  420 , while rollers fabricated of Inconel  718  have been utilized. In addition, the quicker the depositing of the second length of the molten glass ribbon, the less variation in the surface to mold viscosity. In sum, the materials which should be used for the roller and the mold, as well as the cycle time between the ribbon deliveries should be empirically determined by one skilled in the art such that a hermetically sealed glass article exhibiting manageable internal stresses results. Preferably, the mold temperature is approximately 400-600° C. less than the temperature of the glass as it passes the rollers. One final parameter which should be noted: the typical interval between delivery of the first length of the molten glass ribbon and second length of the molten glass ribbon was approximately 1-2 seconds.  
     30. Referring to FIGS. 2 and 3, mold  28  has a predetermined shape possessing the design necessary to result in product which meets desired final product specification, i.e., a matrix of wells and a peripheral skirt.  
     31. The roller apparatus may have patterns machined into the two rollers  24 A/ 24 B for purposes of changing the thickness distribution of the glass ribbon as well for as imparting trade names or numbering, for example, to the surface of the so-formed glass plate.  
     32. The second length of molten glass ribbon  38  preferably is subjected to further forming measures. Preferably, and as shown in FIG. 4, after the second length  38  is deposited onto the first length, an upper vacuum forming head which comprises a plunger having a plurality of indentations aligned in a matrix substantially identical to the matrix of depressions in the mold cavity, is placed in contact with the second length. The plunger assures good glass-to-glass sealing between the respective ribbon lengths in the peripheral area surrounding the wells. A vacuum is applied through vacuum ports that are in fluid communication with the indentations on the plunger. The vacuum serves to pull the second length into contact with the indentations on the plunger. The glass sections that have been pulled into the array of vacuum ports is subsequently sheered off and finished with a corresponding array of gas flame. The sheering may occur while the glass is still in a semi molten state or after the plate has been ejected from the mold. The glass may be sheered off by any of a variety of ways including by flame, water jet, drilling laser, etc. A plurality of wells  12  having an opening  14  of approximately 2 mm is left on the finished plate  10  as shown in FIG. 5, a partial cross section of a glass multiwell plate of the present invention. A peripheral skirt  11  defines the borders of the plate. The finished plate may be inserted into a plastic frame to limit the possibility of breakage.  
     33. Around the outer portion of the mold, a peripheral skirt can be formed by properly manipulating the mold design. The peripheral skirt serves to frame and support the plate. Upon completion of the molding operation it becomes necessary to trim the excess glass from the peripheral skirt of the glass plate and thereafter remove the glass plate from the mold. A suitable trimming operation is one which, not only severs the product, supported by the mold, from the excess hot glass surrounding the periphery of the mold, but which results in a positive seal to the outside edges of both glass layers. Two suitable conventional trimming operations, one “male” and one “female”, are disclosed respectively in U.S. Pat. Nos. 4,605,429 (Rajnik) and 3,528,791 (Giffen); both of which are hereby incorporated by reference. Furthermore, an abrasive water-jet, which removes material by a lapping-type action, or a laser-cutting technique may be utilized in the trimming operation.  
     34. The glass multiwell plate disclosed hereinabove is preferably comprised of a transparent glass material, preferably a hard glass exhibiting excellent thermal expansion characteristics selected from the group consisting of soda-lime silicate, borosilicate, aluminosilicate, boro-aluminosilicate and the like. For example, glass envelopes have been produced from Corning Code 7251 glass which consists essentially of the following composition, expressed in terms of weight percent on the oxide: 77.4% SiO 2 , 5.3% Na 2 O, 15.4% B 2 O 3 , 1.9% Al 2 O 3 , 0.48 Cl.  
     35. The glass multiwell plate that is a product of the above described method comprises a substantially rectangular plate having a peripheral skirt and formed by a uniform sheet of glass having therein a plurality of wells, each well having sidewalls, a bottom and a top surface, the top surface defining a hole capable of being hermetically sealed by a rubber stopper. The plate need not be limited to a 96 well matrix. A plate having any number of wells may be achieved by using the methods described herein. Further, the plate shape need not be limited to rectangular. Conceivably, any plate shape is possible by variations in the mold design.  
     36.FIG. 6 shows a partial cross sectional view of the multiwell plate  10  of the present invention wherein each well  12  is sealed by a molded polymer sealing mat  13  having an array of plugs  15  that conform to the well spacings of the plate. The sealing mat  13  allows access to the wells  12  by means of a hypodermic needle  17  or syringe, for example. A cone  19  molded into the mat facilitates needle penetration. Liquid sample  21  can remain sealed from the external environment by employing the sealing mat  13  thereby allowing for long term storage with the reduction of evaporation of sample.  
     37. It should be noted that an alternative method for making the multiwell plate of the present invention exists. The alternative method comprises the following steps: (a) delivering and depositing a first or well-forming ribbon of molten glass  21  to a surface of a mold assembly  23  having a mold cavity area  24  possessing at least one well-forming depression  25  formed therewithin and a peripheral surface area  28 , wherein the well-forming ribbon  21  overlies the mold cavity area  24  and the peripheral surface  28  areas of the mold assembly; (b) causing the well-forming ribbon  21  of molten glass to substantially conform to the contour of the mold cavity resulting in the formation of a plurality of wells in the ribbon of the molten glass deposited; (c) delivering and depositing a second or sealing ribbon of molten glass  22  to the outer surface of the well-forming ribbon  21  of molten glass wherein the viscosity of the sealing ribbon  22  is such that the sealing ribbon  22  (i) bridges but does not sag into complete contact with the surface of the well of the well-forming ribbon and (ii) forms a hermetic seal wherever the sealing ribbon  22  contacts the well-forming ribbon  21  thereby resulting in a glass plate possessing at least one enclosed well; (d) removing the glass envelope from the mold; and (e) puncturing a hole through the sealing ribbon and over the approximate center of at least one well thereby forming a series of self contained wells that may be accessed through the hole in the sealing ribbon.  
     38. Referring to FIG. 7, molten glass from a common furnace (not shown) and a common “main-line” forehearth  60  which is split into a “Y” shaped delivery conduit is delivered to separate orifices  61 A and  62 A which thereafter deliver respective streams of glass to two sets of water-cooled rollers  64 A/ 64 B and  66 A/ 66 B. A forehearth temperature control (not shown) could allow each conduit to be controlled separately, thus allowing the molten glass within each conduit to be maintained at different temperatures, therefore allowing two separate molten glass streams to be delivered with different glass viscosities. The first of the two fixed orifices  61 A delivers a stream of molten glass to a first set of two water-cooled rollers  64 A and  64 B, rotating in opposite directions, which thereafter squeeze the hot glass into to a continuous ribbon shape upon exiting the rollers. These rollers may be adjusted for the proper spacing, depending upon the desired ribbon thickness for the desired product dimensions. Patterns may also be machined into the rollers for purposes of changing the thickness distribution of the glass ribbon as well for as imparting trade names or numbering, for example, to the surface of the so-formed glass plate.  
     39. Upon exiting the rollers  64 A and  64 B, the well-forming molten glass ribbon  61  is deposited upon mold assembly  68  which is moved along a predetermined path A corresponding to a direction along the mold&#39;s width. The mold could be positioned such that the mold assembly is moved, and the ribbon is subsequently deposited, in a direction along the mold&#39;s length.  
     40. Preferably, the bulk viscosity of this well-forming glass ribbon, as deposited should be about between 2000-5000 poise. The glass ribbon  61  is deposited thereon so as to overlie the mold cavity area  70  containing the well forming depression  72  and the surrounding peripheral surface area  74 . Once delivered this well-forming glass ribbon  61  is thereafter caused to substantially conform to the contour of the mold cavity resulting in the formation of a plurality of wells in the delivered ribbon of the molten glass. The channel forming ribbon  61  of molten glass may be allowed to substantially conform to the contour of the mold cavity well forming depressions  72  solely by means of the force of gravity.  
     41. As in the previously described method, and in a preferred embodiment, resulting in enhanced and accelerated conformance of the molten glass to the contour of the mold cavity well forming depressions  72  the method may involve the additional step of applying a vacuum through vacuum ports  75  to the under surface of the well forming ribbon of molten glass  61  as described previously. As soon as the complete mold area is covered by the hot glass ribbon, a vacuum is applied between the mold and the channel-forming molten glass ribbon  61  via a vacuum line (not shown) attached to vacuum ports  75  which are routed from the base of each depression in the mold, and attached to the vacuum source (not shown). A vacuum may be applied immediately after the well-forming ribbon of molten glass is deposited, or such vacuum may be applied immediately after the ribbon has initially sagged partially within the mold cavity well forming depressions.  
     42. Following the conformance of the well-forming molten glass ribbon  61  to the mold cavity, through either gravity or vacuum forming or a combination of the two, the mold assembly  68  is thereafter further moved along the direction A and thereafter positioned under the aforementioned second set of water-cooled rollers  66 A and  66 B. As earlier mentioned, a stream of molten glass is directed from the second orifice  62 A and thereafter to the water-cooled rollers  66 A/ 66 B which are rotating in opposite directions. These rollers thereafter squeeze the molten glass into to a continuous ribbon shape, i.e, sealing ribbon  62 , which is deposited upon and overlies the surface of the well-forming molten glass ribbon  61  which has conformed to and is supported by the mold cavity  70  and peripheral surfaces  74 . This sealing ribbon of molten glass  62  simply lies on the channel forming ribbon, bridging itself across the formed channels due to the relatively high viscosity of the sealing ribbon.  
     43. Specifically, the bulk viscosity of the sealing ribbon  62  of molten glass, as deposited on the well-forming ribbon  61 , is such that the sealing ribbon  62  bridges the previously formed well  76  but does not sag into contact with the surface of the well. Furthermore, the temperatures of the respective glass ribbons, well-forming and sealing, are such that the two ribbons hermetically seal together wherever they touch via inherent flow viscosity characteristics of the particular glass used for fabricating the chosen product. Preferably, the bulk viscosity of the sealing ribbon  62  when deposited onto the well-forming ribbon  61  of molten glass is similar to that of the well-forming ribbon as deposited; i.e., a bulk viscosity range between 2000-5000 poise. The well forming ribbon is delivered at a slightly lower initial bulk viscosity in order to compensate for the working time prior to delivery of the sealing ribbon.  
     44. As in the earlier described method, the materials which should be used for the roller and the mold, as well as the cycle time between the ribbon deliveries should be empirically determined by one skilled in the art such that a hermetically sealed glass plate exhibiting manageable internal stresses results.  
     45. Sealing molten glass ribbon  62  could be subjected to forming and finishing measures for the second length in the single ribbon method as previously described.  
     46. It should be further noted that the second length or sealing ribbon (top layer) could be allowed to sag into the respective wells as defined by the first length or the well forming ribbon (bottom layer), respectively, but not so far as to contact the bottom layer. In this embodiment, a series of wells are formed by the top layer and the bottom layer with an envelope of air sealed therebetween. A hole may then be punctured through the top layer such that the envelope of air is in fluid communication with the well as defined by the top layer. Having a design such as this may be useful in certain combinatorial chemistry applications, or for filtering.  
     47. Although the now preferred embodiments of the invention have been set forth, it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as set forth in the following claims.