Ultrafilteration device and method of forming same

Abstract

An ultrafiltration device has a filter membrane sealed inside a reservoir body, such as a tube. The tube has one or more ports and a closed portion distal to the port(s), and the filter membrane is sealed to the body along a closed contour widely surrounding the port(s) to provide a large area filtered outflow path. The method is effective to rapidly isolate a predetermined amount of a desired retentate in the distal portion of the tube. The method and device are also useful for quantitative transfer of smaller molecules and for multi-step processing of sample arrays. A frusto-conical peripheral filter provides high ratio of effective filter area, and may be configured for hydrostatic deadstopping and little or no wicking, greatly enhancing recovery time and efficiency. Linear array strips of such chambers may be formed by bonding together mating halves with filter areas over the chamber ports. The vessel may include a rib to guide and orient filter during assembly, and/or a ledge or recess to engage and align the filter, assuring that the filter is precisely positioned and does not wander during manufacture and bonding. In one embodiment a deflectable lip or other integral feature of the vessel geometry seals the vessel in a capped receiving tube, and opens under pressure to pass pressure between the tube and vessel during centrifugation, to permit overfilling of the vessel in a tilted rotor assembly without spillage or leakage, and increasing the concentration ratio. The vessels have a high filter area to volume ratio, maintain open filter surfaces and high rates of filtration throughout the spin, and are fully compatible with robotic loading, multistage operation and in situ multiwell plate filtrate and/or retentate assay or transfer. Attachment of the filter may be effected by heat welding. Preferably the vessel and filter are positioned between a press member and a heat sink and a superheated tool contacts the press member to selectively deliver a defined bolus of heat to the weld areas.

What is claimed is:  
     
         1 . A method of forming an ultrafiltration device, comprising 
 providing a reservoir body having a sloped bounding wall region including a port and a closed portion distal to the port    providing a filter membrane supported by said bounding wall region and entirely covering the port, and    sealing the filter membrane to the sloped bounding wall region such that solvent and lower molecular weight material pass through the filter membrane and out the port, to effectively isolate a predetermined amount of retentate in the closed portion distal to the port.    
     
     
         2 . The method of    claim 1   , wherein the filter membrane has an active filter area greater than about 0.5 cm 2  and is bonded to said bounding wall at plural discrete spots to prevent separation due to gravitational peeling forces arising during centrifuging.  
     
     
         3 . A method of forming an ultrafiltration device, comprising 
 providing a hollow reservoir body formed as a single integral shell wall having a length, a proximal inlet at an inlet end, a closed distal end, and a port located in an intermediate region between said inlet end and said closed distal end, and    sealing a filter membrane to said shell wall around the interior of said intermediate region and over said port,    such that when centrifuged under predetermined conditions, fluid and solutes of a predetermined molecular weight range pass through the filter membrane and exits said port, while a retentate having a greater predetermined molecular weight accumulates in said closed distal end.    
     
     
         4 . The method of    claim 3   , wherein 
 i) said closed distal end has a receiving volume less than two percent of the volume of said reservoir body    ii) ratio of area of said filter membrane to volume of said reservoir body is greater than 0.75/cm, and    iii) volume of said reservoir body is between about one-half and two hundred cubic centimeters.    
     
     
         5 . The method of    claim 3   , wherein said closed distal end forms a deadstop having a volume under about 1.0% of the volume of said body.  
     
     
         6 . The method of    claim 3   , wherein said filter forms a truncated cone-shaped active filter area when sealed.  
     
     
         7 . The method of    claim 6   , wherein said filter is sealed along an axial-release direction along narrow band segments that allow filtration through a preponderance of its surface area to said port while being supported by the wall of the reservoir body.  
     
     
         8 . An ultrafiltration device, comprising 
 a hollow, smooth, continuous convex reservoir body having a length, a proximal inlet end, and a closed distal end with a port located in a sloping wall lying in an intermediate region between said inlet end and said closed distal end, and    a filter membrane sealed around the interior of said intermediate region and over said port,    such that 
 when centrifuged under predetermined conditions, fluid and solutes of a predetermined molecular weight range pass through the filter membrane and exits said port, and  
 a retentate having a greater predetermined molecular weight accumulates in said closed distal end.  
   
     
     
         9 . A method of forming an ultrafiltration device, comprising 
 providing a reservoir body having a port and a distal body portion distal to the    port    providing a filter, and    sealing the filter to the body around an axial-release direction so as to entirely cover said port, such that the device is effective to isolate a predetermined amount of a desired retentate in the distal body portion.    
     
     
         10 . The method of    claim 9   , wherein the filter has an area of about 0.5 to about 120 cm 2 , more than 70% of which is active filter area.  
     
     
         11 . A method of forming an ultrafiltration device, comprising 
 providing a hollow reservoir body having a length, a proximal inlet, and a closed distal end with a port extending through a wall of the body in an intermediate region located between said inlet end and said closed distal end, and    sealing a filter around the interior of said intermediate region and over said port,    such that 
 when centrifuged under predetermined conditions, material below a predetermined molecular weight passes through a broad region of the filter and flows along the wall to exit said port, and  
 solute having a molecular weight greater than the predetermined molecular weight is retained by the filter in said tube and accumulates in said closed end.  
   
     
     
         12 . The method of    claim 11   , wherein said closed distal end forms a deadstop having a volume between about 0.3% and about 1.0% of the volume of said body.  
     
     
         13 . The method of    claim 11   , wherein said filter forms a truncated cone-shaped active filter area when sealed.  
     
     
         14 . The method of    claim 11   , wherein said closed distal end forms a deadstop having a volume between about 0.04% and 0.3% of the volume of said body.  
     
     
         15 . The method of    claim 11   , wherein the step of sealing is performed in stages to first drive moisture from a sealing region of the filter and then fuse the sealing region and vessel.  
     
     
         16 . An ultrafiltration device, comprising 
 at least one hollow reservoir body, each said body having a length, a proximal inlet, a closed distal end, and a port intermediate its inlet and its distal end, and filter sealed about its perimeter to a wall of said intermediate region and over said port to define between said wall and the filter an interstitial space communicating with the port, such that when centrifuged under predetermined conditions, solvent and solutes having a molecular weight substantially smaller than a predetermined molecular weight pass through the filter and exit the port via said interstitial space, and may optionally be collected in a mating receiving well, while solutes having a molecular weight greater than the predetermined molecular weight accumulate in the closed distal end.