METHOD FOR THE MANUFACTURE OF FILTER WELLS

Abstract: A filter well of plastic having a bottom portion (16) with an outlet and supporting a filter (28) provided on top of the outlet (18), which filter (28) is well sealed against leakage of liquid, is produced by first forming a bottom portion (16) having a supporting surface for the filter and an outlet opening (18). Thereafter, a filter (28) is applied on the bottom portion (16) so that it covers at least essentially the whole bottom portion. Then, the cylindrical wall portion (36) of the filter well is formed against the bottom portion (16) with the lower part of the wall portion surrounding the edge of the filter and the upper edge of the bottom portion so that the bottom and wall portions (16, 36) form a fused unit with the outer edge of the filter (28) being fused into the filter well material.

Description: METHOD FOR THE MANUFACTURE OF FILTER WELLS The present invention relates to the production of filter wells useful for separating a solid phase from a liquid. Separating a solid phase from a solution is a common process in a biotechnological laboratory and is carried out mainly either by centrifugation or by collecting the solid phase on a filter. As examples, the preparation of nucleic acids from bacteria, bacteriophages, DNA- synthesis, PCR products, etc., can be mentioned. Normally, such filtering is carried out in so called filter wells, i.e. a small tube or the like containing a filter through which the liquid phase is forced by applying vacuum on the underside of the filter or pressure on the upside of the filter. A device for carrying out biochemical reactions in microtitre plates, where a solution is forced through filter wells by means of gas pressure, is described in our US patent 5,273,718. Relative to the application of vacuum, the use of a positive pressure on the upside of the filter has i.a. the advantages that the solid phase as well as the liquid phase easily can be collected and that a greater pressure difference between the upside and the underside of the filter is possible (greater than 1 bar) but requires on the other hand a very good sealing between the filter and the wall of the filter well in order to avoid a leakage of liquid past the filter. A method of providing the necessary sealing upon filtering by means of vacuum is described in WO 86/07606, where a test plate of microtitre well type is produced in that a filter membrane is placed between an upper part and lower part which are then pressed together so that a number of wells provided with filters, are formed. The sealing between the wells is secured in that the upper and lower parts between the well portions are provided with matching ridges and recesses so that the filter membrane breaks upon pressing the parts together when a ridge is forced into the corresponding recess. The upper and lower secures an extraordinary sealing of the edge of the filter or the membrane so that there is no risk of any leakage past the filter when a positive pressure is applied to the upside of the filter. Moreover, the filter well gives support to the filter at high pressures. Similar to the method according to the above mentioned EP-A-328 038, the invention is based upon the idea of producing the filter well by forming of plastic and at the same time fix the filter in the filter well. However, according to the invention, the filter is fixed in that the filter edge is double-sidedly embedded or fused into the wall of the well during the actual forming process at the same time as the filter is supported by a bottom portion formed in advance and having a supporting surface for the filter. More in detail, the filter well is produced by first forming a bottom portion provided with a supporting surface for the filter and a preferably central outlet opening for freely dripping liquid. Thereafter, a filter (or membrane) is applied on the supporting surface of the bottom portion so that the filter at least essentially covers the whole bottom portion. Finally, the cylindrical wall portion of the filter well is formed against the bottom portion with the lower part of the wall portion surrounding the edge of the filter and the upper edge of the bottom portion so that the bottom and wall portions form a fused unit, the outer edge of the filter being fused into the filter well material. Preferably, the supporting surface extends inside the inner side of the cylinder wall so that it supports at least part of the active filtering surface of the filter. Preferably, the filter is somewhat larger than the bottom portion so that the filter, before the forming of the cylindrical wall portion, extends beyond the periphery of the bottom portion. According to a preferred embodiment, the bottom portion is produced with a fine flow channel pattern in the supporting surface, which results in very small losses upon recovery of the liquid phase. A device for producing the filter well, thus, has means for forming the bottom portion, means for applying a filter on the bottom portion, and means for forming the wall portion of the filter well against the bottom portion. Such a device can advantageously be in the form of a single moulding tool with several stations. Injection moulding is a preferred forming method. Preferably, the wall portion and the bottom portion of the filter well are produced from the same material, particularly a thermoplastic resin. An embodiment of the method according to the invention will be described more in detail below with reference to the appended drawings on which Figs. 1-7 are cross-sectional views of parts of an injection moulding tool at different stages of the manufacturing of a filter well according to the invention, Fig. 8 is a cross-sectional view of the finished filter well, Fig. 9 is a section along the line A-A in Fig. 8 with the filter partly broken away and Fig. 10 is a schematical, exploded view of an injection moulding tool comprising the tool parts of Figs. 1-7. The tool parts illustrated in Figs. 1-7 are included in an integrated tool for carrying out all steps in the production of the filter well. The tool which for reasons of clarity is not shown in its whole, has a stationary part shown uppermost in the Figures and, therefore, henceforth called upper part, and a movable, lower part in the Figures, henceforth called lower part which by rotation in the horizontal direction can be moved to different stations of the upper part. Fig. 1 shows the tool portion for injection moulding of the bottom portion of the filter well. The portion that is included in the above-mentioned upper, stationary tool part is denoted 1 and the portion that is included in the movable lower part is denoted 2. The two parts 1 and 2 are horizontally displaceable relative to each other, e.g. by rotation, in a partition plane 3 when the lower part 2 of the tool has been moved away from the upper part 1. (The same reference numerals for the upper and lower tool part, respectively, are used throughout the other Figures.) The upper tool part 1 has a cylindrical, upper mould element 4 having a central, threaded boring 5 which abrubtly changes into a boring 6 with a smaller diameter. The latter extends in its turn up to the lower end 7 of the mould element. A pin 8 adapted to the borings 5, 6 is screwed into the boring 5 and has a needle portion 9 which extends below the mould element end 7. A pattern of elongated ridges 10 which run radially and, possibly, also in the transverse direction, e.g. annularly, starting a distance inside the edge and up to the bore 6, are formed in the end 7 for forming flow channels in the bottom of the filter well. A method for forming, by etching, a fine pattern of ridges which are to form a corresponding fine pattern of flow channels in the filter well, is described in our PCT-application "Filter well and a method for its manufacture", of even date and based on the Swedish patent application No. 9400437-1 (the contents of which is incorporated herein by reference) . A matching, cylindrical, lower mould element 11 is vertically displaceable in the lower tool part 2 right in front of the mould element 4. Together with the end 7 of the mould element 4 and the uppermost part of the adjacent main portion of the lower tool part 2, the upper part 12 of this mould element 11 is designed to delimit a mould cavity 13 for forming the bottom portion of the filter well . A pointed depression 14 into which the needle portion 9 of the mould element 4 extends, ends in a central boring 15 in the mould element 11. For reasons that will be apparent further below, the boring 15 is connectable to a vacuum source. In Fig. 1, the mould cavity 13 is shown filled with the. desired injection moulding material, e.g. polypropylene, injected via an opening which is not shown

Claims: CLAIMS 1. A method of producing a filter well of plastic having a bottom portion (16) with an outlet and supporting a filter (28) provided on top of the outlet, characterized by (i) forming a bottom portion (16) having a supporting surface (16a) for the filter (28) and an outlet opening (18), (ii) applying a filter (28) on the bottom portion (16) so that the filter at least essentially covers the whole bottom portion, (iii) forming the cylindrical wall portion (36) of the filter well against the bottom portion (16) with the lower part of the wall portion surrounding the edge of the filter and the upper edge of the bottom portion so that the bottom and wall portions (16, 36) form a fused unit, the outer edge of the filter (28) being fused into the filter well material. 2. The method according to claim 1, characterized in that the forming of the bottom and wall portions (16, 36) of the filter well (37) is carried out by injection moulding. 3. The method according to claim 1 or 2, characterized in that the bottom portion (16) and the wall portion (36) are formed from the same material. 4. The method according to any one of claims 1-3 , characterized in that, during forming of the wall portion (36) , the filter (28) inside the edge portion that is to be fused is pressed against a rim portion (21) of the upside of the bottom portion (16) . 5. The method according to any one of claims 1-4, characterized in that the upside of the bottom portion (16) is formed with radial flow channels (20) which run towards the outlet opening (18) , and, possibly, also flow channels (38) which are concentric with the outlet opening and which mutually connects the radial flow channels (20) , ridge portions between the flow channels supporting the filter (28) . 6. The method according to any one of claims 1-5, characterized in that step (ii) comprises punching the filter (28) from a filter blank (26) . 7. The method according to any one ' of claims 1-6, characterized in that the filter (28) in step (ii) extends beyond the periphery of the bottom portion (16) . 8. The method according to any of claims 1-7, characterized in that the supporting surface (16a) of the bottom portion (16) for the filter (28) extends inside the inner side of the cylindrical wall (36) to support at least part of the active filtering surface of the filter (28) . 9. The method according to any of claims 1-8, characterized in that the outlet opening (18) is centrally located in the bottom portion (16) .

Inventors: AKSBERG ARVI, AKSBERG, ARVI
Applicants: AKSBERG ARVI, PHARMACIA BIOTECH AB, AKSBERG, ARVI
Application year: 1995
Main classification: B01D29
IPC codes: B01D29, B29C33, B29C45, G01N33