Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Plural – intermittent pressure applying
Reexamination Certificate
1999-05-04
2001-07-17
Fortuna, Ana (Department: 1723)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Plural, intermittent pressure applying
C264S127000, C264S345000
Reexamination Certificate
active
06261497
ABSTRACT:
TECHNICAL FIELD
This invention relates to porous, synthetic resin membranes having particulate inorganic porous material embedded therein, to methods for the production of such membranes, and to the use of such membranes in various biotechnical procedures.
BACKGROUND OF THE INVENTION
One form of particulate inorganic porous material useful in the invention is controlled pore glass (CPG) described in U.S. Pat. Nos. 3,549,524 and 3,758,284 commercially available from CPG, Inc., 3 Borinski Road, Lincoln Park, N.J. 07035. It is widely used in methods for the synthesis of nucleic acids and for the isolation or purification of nucleic acids and proteins.
U.S. Pat. No. 3,890,417 describes a method for making a porous diaphragm suitable for use in electrolytic cells. The diaphragm is formed as a sheet from aqueous polytetrafluoroethylene (PTFE) and a solid, non-porous particle additive. Porosity is imparted to the product by removal of the particulate additive. U.S. Pat. No. 4,153,661 describes a similar method for making high tensile strength PTFE composite sheet material from aqueous PTFE, and organic or inorganic particles which comprises mixing and calendering at an elevated temperature (50-100° C.) to produce a self-supporting film for use as an electronic insulator.
U.S. Pat. Nos. 4,373,519, 4,460,642, 4,565,663 and 4,971,736 disclose methods for making water-swellable composite sheets having hydrophilic, absorptive particles enmeshed in the PTFE matrix for use as wound dressing and chromatographic supports.
DEFINITIONS
Particulate Inorganic Porous Material—Any particulate porous, inorganic material, preferably controlled pore glass (CPG). Particulate porous inorganic materials, including CPG have a particle size range of 0.1 to 200 microns and a pore diameter up to 4000 Å. Porous inorganic materials other than glass (CPG) include metal oxides such as aluminum oxide and titanium oxide.
Pore—A channel which may be closed or open-ended.
Pore Diameter—Cross section of a pore generally from about 40 Å to about 4000 Å.
Pore Volume—Volume of pores per unit mass of porous inorganic material generally at least 0.05 cc/g.
Synthetic Resin—Any non-naturally occurring, normally solid thermoplastic polymer, preferably polytetrafluoroethylene (PTFE) which is soluble or dispersible, for example as particles, in an aqueous medium.
Flow Rate—ml/min/cm
2
at 10 psi of acetonitrile through a 13 mm diameter membrane disc in a plastic Swinney disc filter holder.
Flow rate is particle size, pore diameter and pore volume dependent. In general, flow rate increases as a function of pore diameter and particle size. These factors are preferably selected to provide a flow rate of 20 to 200 ml/min/cm
2
of membrane.
Aqueous Resin—A solution of a synthetic resin or a suspension or dispersion of particulate synthetic resin in an aqueous medium which may contain a surfactant and in which the same or a different synthetic resin may be in solution. The preferred medium is water.
SUMMARY OF THE INVENTION
This invention provides a porous, synthetic resin, preferably PTFE, membrane having particulate inorganic porous material, preferably CPG embedded therein. The surfaces of the membrane may be modified, for example, by silanization to provide functional groups for the binding of biological moieties such as cells and biomolocules. Such functional groups include, but are not limited to amino, hydroxyl, carboxyl, epoxide, aldehyde, phenyl, and long chain, e.g., 5 to 50 carbon atom alkyl groups. The membranes of the invention, preferably functionalized, are useful inter alia in lieu of CPG as a support for the synthesis, isolation and purification of nucleic acids and for the isolation and purification of proteins.
DETAILED DESCRIPTION OF THE INVENTION
The particle size and pore diameter of the inorganic porous material utilized are selected to provide a membrane having a desired flow rate. In general, inorganic porous material having a particle size of 0.1 to 200 microns and a pore diameter from 40 Å to 4000 Å may be used.
Any synthetic resin may be utilized having due regard to the conditions, including reagents and temperature, to which the membrane will be subjected. Solid polyolefins such as polyethylene, polypropylene and polybutylene; vinyl resins such as polytetrafluoroethylene (PTFE), polyvinylchloride, polyvinylacetate and polymethylmethacrylate; polycarbonates and polysulfones are examples of suitable solid, thermoplastic resins. This disclosure is intended to include any and all solid, thermoplastic resins. PTFE is preferred.
To produce the membranes of the invention, inorganic porous material and the selected synthetic resin are appropriately combined in a dry or solid weight ratio of from 5% to 90%, preferably from 30% to 90% pore material. The resin is preferably provided as a particulate suspension in water. The particle size of resin may be from 0.01 to 1.0 &mgr;m, preferable from 0.05 to 0.5 &mgr;m. DuPont T-30 60% PTFE suspended in water, particle size 0.05 to 0.5 &mgr;m, is preferred.
The membranes of this invention are preferably formed from a paste-like mixture of inorganic porous material, particulate synthetic resin and water. The mixture is then formed into a sheet, as by calendering, which is sintered. The amount of water required to produce a porous sheet of suitable rigidity that contains 50 to 80% porous material by weight appears to be a function of the pore volume of the inorganic porous material used. The following formula may be used to determine an appropriate quantity of water to provide one form of a PTFE-CPG membrane of the invention:
Water (ml)=weight of inorganic porous material (gm)×2.6 ×pore volume (ml/gm).
One method for producing membranes of this invention includes the following steps:
1. Mix inorganic porous material, e.g., CPG, water and aqueous resin, preferably a dispersion of PTFE, with stirring to form a paste-like mass.
2. Gel the mass, with occasional stirring, between a temperature of 50-70° C. (preferably 65° C.) for a mixing time vary from 5 to 15 minutes (e.g., 8 minutes).
3. Calender the gelled mass through a gap of 1.5-2 mm (preferably 1.8 mm) into a sheet under a calender roll pressure of 80 to 500 PLI.
4. Fold the sheet, rotate 90°, and pass through the calender rolls again. Repeat this step as needed to provide generally uniform dispersion of the inorganic porous material in the resin. For example, six repetitions may produce a uniform CPG dispersion in PTFE.
5. Reduce the calender roll gap to produce a membrane of the desired thickness, e.g., 5 to 200 mils.
6. Sinter the sheet at 340-375° C. for 30 to 60 minutes.
Sintered sheets may then be subjected to surface modification, for example, by silanization to provide functional groups for the binding of biological moieties including cells and biomolecules. See, e.g., Grusha, supra and U.S. Pat. Nos. 3,383,299 and 4,554,088.
A general formula for the silicone compounds useful for silanization is: R—Si—X, where R represents an organic moiety with a terminal functional group such as an amino, hydroxyl, epoxy, aldehyde, sulfhydryl, phenyl, long chain alkyl or other group that will chemically react or physically absorb with the biological molecules and X may be a mono-, di- or trialkoxy or halide group which will react with the silanol groups on the surface of the inorganic material. The degree of silanization can be demonstrated through quantitative analysis of the respective functional groups.
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Chen Richard
Wong Yuan N.
Cowan Liebowitz & Latman P.C.
CPG, Inc.
Fortuna Ana
Ward Richard W.
Wolfson Michael I.
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