A Multi-Layered Membrane And A Method Of Preparing The Same

Abstract

There is provided a multi-layered membrane for separating components in an aqueous sample. There is also provided a method of preparing said multi-layered membrane, a method of separating blood plasma from a whole blood sample and a diagnostic device for separation of blood plasma from a whole blood sample.

Claims

1-27. (canceled)

28. A multi-layered membrane for separating components in an aqueous sample comprising: a porous layer for separating or retaining at least one component from said aqueous sample therein; and an absorbent layer comprising a superabsorbent or absorbent material for removing liquid from said porous layer.

29. The multi-layered membrane of claim 28, wherein said porous layer contains pores having an effective pore diameter in the range of 0.1 μm to more than 30 μm, or wherein said porous layer has a pore density in the range of 40% to 95%.

30. The multi-layered membrane of claim 28, wherein said porous layer is a peelable layer, or wherein said porous layer is further modified to prevent blood clotting and reduce free radicals.

31. The multi-layered membrane of claim 28, wherein said superabsorbent or absorbent material is selected from the group consisting of sodium polyacrylate, polyacrylic acid, alginic acid, starch, hydroxylethyl starch, modified starch, alpha cellulose, modified cellulose, chitosan, carboxylmethyl cellulose, montmorillonite, polyvinyl alcohol, polyethylene oxide, polyacrylamide, hydrolysed polyacrylonitrile, dextran, carboxylmethyl dextran, carbon nanotubes, silica, cotton, rayon, cellulosic pulp, synthetic pulp, bamboo silk, zeolite, glass fibers, polyester fibers, polyethylene fibers, fleece, and mixtures thereof.

32. The multi-layered membrane of claim 28, further comprising a top layer comprising a peelable matrix layer.

33. The multi-layered membrane of claim 32, wherein said top layer comprises a symmetric or an asymmetric membrane matrix.

34. The multi-layered membrane of claim 32, wherein said top layer comprises a material selected from the group consisting of polyarylonitrile (PAN), polyethersulfone (PES), sulfonated polysulfone (SPSf), sulfonated polyethersulfone (SPES), cellulose acetate (CA), cellulose acetate butyrate, ethylcellulose, hydroxylpropyl cellulose, polyurethane, poloxamer polyols, poly(vinyl alcohol), poly(vinyl chlorine), polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF) and combinations thereof.

35. A method of preparing a multi-layered membrane comprising a porous layer and an absorbent layer, the method comprising the steps of: (a) providing a dope solution of a porous layer material in a solvent; (b) casting the dope solution to form the porous layer via a method selected from the group consisting of electrospinning, non-solvent induced phase separation (NIPS), thermally induced phase separation (TIPS), vapor induced phase separation (VIPS), a combination of NIPS and TIPS (N-TIPS), and combinations thereof; and (c) incorporating the absorbent layer adjacent to the porous layer via physical interaction or chemical treatment, wherein the absorbent layer comprises a superabsorbent or absorbent material for removing liquid from said porous layer.

36. The method of claim 35, wherein: the porous layer material has a concentration in the range of 3.0 weight % to 10.0 weight %; and the solvent has a concentration in the range of 90.0 weight % to 97.0 weight %, based on the total weight of the dope solution.

37. The method of claim 35, wherein said porous layer material is selected from the group consisting of polyarylonitrile (PAN), polyethersulfone (PES), sulfonated polysulfone (SPSf), sulfonated polyethersulfone (SPES), cellulose acetate (CA), cellulose acetate butyrate, ethylcellulose, hydroxylpropyl cellulose, polyurethane, poloxamer polyols, poly(vinyl alcohol), poly(vinyl chlorine), polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF) and combinations thereof, or wherein said solvent is selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), hexafluoroisopropanol, and combinations thereof.

38. The method of claim 35, wherein when the method used in casting the dope solution to form the membrane is electrospinning, the time taken to collect the porous layer is in the range of 15 minutes to 120 minutes, or wherein when the method used in casting the dope solution to form the membrane is electrospinning, the porous layer is collected using a drum roller with a roller speed in the range of 70 rpm to 1000 rpm.

39. The method of claim 35, wherein when the method used in casting the dope solution to form the membrane is selected from NIPS, TIPS or N-TIPS, the porous layer is casted using a casting knife with a height in the range of 50 μm to 500 μm.

40. The method of claim 35, wherein said dope solution in step (a) further comprises an additive.

41. The method of claim 40, wherein said additive is selected from the group consisting of methanol, ethanol, isopropanol, acetone, tetrahydrofuran, water, glycerol, ethylene glycol, and combinations thereof, or wherein during electrospinning, the weight percent ratio of the solvent and additive is in the range of 100:1 to 3:1.

42. The method of claim 35, wherein during TIPS, a partial dope phase separation through VIPS process occurs, or wherein during TIPS, the porous layer material is PAN, the solvent is a mixed solvent of DMSO/water at 85/15% by volume, or the porous layer material has a concentration in the range of 40.0 mg/ml to 120.0 mg/ml.

43. The method of claim 35, wherein when using N-TIPS, the casting dope solution is cooled in water at 25° C., or wherein when using N-TIPS, the porous layer material is PAN, or the porous layer material has a concentration in the range of 3.60 weight % to 6.50 weight % of the dope solution.

44. The method of claim 35, further comprising the step of modifying said porous layer by physical or chemical means to contain specific binding sites for desired molecules.

45. A method of separating blood plasma from a whole blood sample, comprising applying said whole blood sample to a multi-layered membrane, wherein said multi-layered membrane comprises a porous layer and an absorbent layer comprising a superabsorbent or absorbent material for removing liquid from said porous layer.

46. The method of claim 45, wherein said whole blood sample is applied to a bottom surface of the porous layer where there are larger pores of greater than 30 μm pore size as compared to a top surface of the porous layer.

47. A diagnostic device for separation of blood plasma from a whole blood sample, comprising a multi-layered membrane comprising a porous layer and an absorbent layer comprising a superabsorbent or absorbent material for removing liquid from said porous layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0119] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0120] FIG. 1 is a schematic illustration of a diagnostic device 100 for plasma separation and dehydration from blood cells. The diagnostic device 100 comprises a multi-layered membrane 3. The diagnostic device may further comprise a blood filter 2. The multi-layered membrane 3 (as expanded from the circular region) comprises a porous layer 5 and an absorbent layer 6. A sample of blood 1 may be separated by the device into retained blood cells 4 and plasma which is absorbed into the absorbent layer 6.

[0121] FIG. 2 is a schematic diagram of a method used to assess the performance of the formed multi-layered membrane 3. Within a sample of blood 1, only plasma 7 may permeate through the porous layer 5 to be absorbed by the absorbent layer 6. The top surface 8 and the bottom surface 9 are marked in FIG. 2.

[0122] FIG. 3A to FIG. 3O are images showing the influence of fiber collection time on morphology, the appearance of blood drops, plasma recovery and red blood cell retention of formed porous layer. FIG. 3A to FIG. 3E are field emission scanning electron microscope (FESEM) images of the membranes; FIG. 3F to FIG. 3J are photographic images of the top surface 8 of the membrane where a sample of blood is applied; FIG. 3K to FIG. 3O are photographic images of the absorbent layer 6. The fiber collection time is 15 minutes for FIGS. 3A, 3f, 3K; 30 minutes for FIGS. 3B, 3G, 3L; 60 minutes for FIGS. 3C, 3H, 3M; 90 minutes for FIGS. 3D, 3I, 3N or 120 minutes for FIGS. 3E, 3J, 3O. The plasma recovery is 11.45±0.47% for FIGS. 3A, 3F, 3K; 10.30±0.53% for FIGS. 3B, 3G, 3L; 10.71±3.05% for FIGS. 3C, 3H, 3M; 2.69±0.51% for FIGS. 3D, 3I, 3N or 0.94±0.23% for FIGS. 3E, 3J, 3O.

[0123] FIG. 4A to FIG. 4X are images showing the influence of solvent and solvent/additive ratio on plasma recoveries and membrane morphologies of the porous layer formed by the electrospinning method, where FIGS. 4Ato 4L show FESEM images of the porous layer's morphology and FIGS. 4M to 4X show camera images of the absorbent layer. The solvent used is N-methylpyrrolidone (NMP) for FIGS. 4A to 4D and 4M to 4P; Dimethylformamide (DMF) for FIGS. 4E to 4H and 4Q to 4T or (c) Dimethylacetamide (DMAc) for FIGS. 4I to 4L and 4U to 4X. Using acetone as the additive, the solvent/additive ratio is 100/0 for FIGS. 4A, 4E, 4I, 4M, 4Q, 4U; 19/1 for FIGS. 4B, 4F, 4J, 4N, 4R, 4V; 9/1 for FIGS. 4C, 4G, 4K, 4O, 4S, 4W or 8/2 for FIGS. 4D, 4H, 4L, 4P, 4T, 4X. The plasma recovery is 6.67±0.31% for FIGS. 4A and 4M; 9.96±0.84% for FIGS. 4E and 4Q; 6.94±0.31% for FIGS. 4I and 4U; 7.27±0.81% for FIGS. 4B and 4N; 11.64±1.11% for FIGS. 4F and 4R; 5.32±1.11% for FIGS. 4J and 4V; 9.63±1.22% for FIGS. 4C and 4O; 21.54±2.68% for FIGS. 4G and 4S; 13.33±1.21% for FIGS. 4K and 4W 10.30±0.53% for FIGS. 4D and 4P; 21.07±0.31% for FIGS. 4H and 4T or 27.94±1.76% for FIGS. 4L and 4X. Red blood cells are observed on FIGS. 4S, 4T and 4X.

[0124] FIG. 5A to FIG. 5I are FESEM images showing the influence of polymer concentration on morphologies of the top surface (FIGS. 5A, 5D and 5G), the bottom surface (FIGS. 5B, 5E and 5H) and the vertical cross-section (FIGS. 5C, 5F and 5I) of the porous layer made from thermally induced phase separation (TIPS) with 87.0 mg/ml (FIGS. 5A to 5C), 63.8 mg/ml (FIGS. 5D to 5F) or 41.7 mg/ml (FIGS. 5G to 5I) polyacrylonitrile (PAN).

[0125] FIG. 6A to FIG. 6I are camera images showing the influence of polymer concentration on the plasma recovery and the red blood cell retention of the top surface (FIGS. 6A, 6D and 6G) and the bottom surface (FIGS. 6B, 6E and 6H) of the porous layer made from TIPS with 87.0 mg/ml (FIGS. 6A to 6C), 63.8 mg/ml (FIGS. 6D to 6F) or 41.7 mg/ml PAN (FIGS. 6G to 6J). Images of the absorbent layer are provided in FIGS. 6C, 6F and 6I. The membrane formed by the condition of as shown in FIGS. 6A to 6C had a plasma recovery of 1.81% while red blood cells have flowed through the membranes formed by the conditions as shown in FIGS. 6D to 6I.

[0126] FIG. 7A to FIG. 7I are a series of FESEM images of the top surface (FIGS. 7A, 7D and 7G), the bottom surface (FIGS. 7B, 7E and 7H) and the vertical cross-section (FIGS. 7C, 7F and 7I) of the porous layer made from TIPS with 87.0 mg/ml PAN. The membranes were cooled in air for 1 hour on a hot plate that is cooled from 90° C. (FIGS. 7A to 7C), in room temperature (FIGS. 7D to 7F) or in water (FIGS. 7G to 7J). The membrane formation further included a step of additive induced phase separation (NIPS) when cooled in water, being made by N-TIPS.

[0127] FIG. 8A to FIG. 8L are a series of camera images showing the influence of cooling methods on the plasma recovery and the red blood cell retention of the top surface (FIGS. 8A, 8D, 8G and 8J) and the bottom surface (FIGS. 8B, 8E, 8H and 8K) of the porous layer cooled on a hot plate that is cooled from 90° C. (FIGS. 8A to 8C), in room temperature (FIGS. 8D to 8E), and in water (FIGS. 8F to 8L). Images of the absorbent layer are provided in FIGS. 8C, 8F, 8I and 8L. In FIGS. 8A to 8I, the sample of blood was applied on the top surface 8 of the porous layer, while in FIGS. 8J to 8L, the sample of blood was applied on the bottom surface 9 of the porous layer, which was flipped vertically before use. The plasma recovery is 1.61% for FIGS. 8A to 8C, 1.81% for FIGS. 8D to 8F, 2.83% for FIGS. 8G to 8I or 10.84% for FIGS. 8J to 8L.

[0128] FIG. 9A to FIG. 9I are a series of camera images shows the influence of polymer concentration on the plasma recovery and the red blood cell retention of the top surface (FIGS. 9A, 9D and 9G) and the bottom surface (FIGS. 9B, 9E and 9H) of the porous layer made from N-TIPS with 87.0 mg/ml (FIGS. 9A to 9C), 63.8 mg/ml (FIGS. 9D to 9F) or 41.7 mg/ml PAN (FIGS. 9G to 9I). Images of the absorbent layer are provided in FIGS. 9C, 9F and 9Ii. The plasma recovery is 10.84% (FIGS. 9A to 9C) or 33.76% (FIGS. 9D to 9F). Red blood cells have flowed through the membrane of FIGS. 9G to 9I.

[0129] FIG. 10A to FIG. 10L are a number of FESEM images on morphologies of the top surface (FIGS. 10A, 10E and 10I), the vertical cross-section (FIGS. 10B, 10F and 10J), the bottom surface (FIGS. 10C, 10G and 10K), and the enlarged bottom surface (FIGS. 10D, 10H and 10L) of the porous layer made from N-TIPS with 87.0 mg/ml PAN. The coagulant used was water (FIGS. 10A to 10D), 70 weight % NMP in water (FIGS. 10E to 10H) or 70 weight % isopropanol (IPA) in water (FIGS. 10I to 10L).

[0130] FIG. 11A to FIG. 11F are a series of camera images of the porous layer (FIGS. 11A to 11C) and the absorbent layer (FIGS. 11D to 11F) of the multi-layered membrane after use. The porous layer was prepared with the coagulant of water (FIGS. 11A and 11D), 70 weight % NMP in water (FIGS. 11B and 11E) or 70 weight % IPA in water (FIGS. 11C and 11F).

EXAMPLES

[0131] Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1

Structure of the Diagnostic Device

[0132] The membrane is of great importance in the DPS devices. A good membrane should have a 100% rejection of blood cells but no retentions to useful analytes. Since suitable membranes for the application are still lacking, the main target would be the development and optimization of required membranes for decellularization via gravity. A few membrane materials, for instance, polyacrylonitrile (PAN), polyethersulfone (PES) and cellulose acetate (CA), were investigated; and different additives were added to the dope solutions to tune the pore sizes and properties of formed membranes.

[0133] Furthermore, membranes were formed through a few methods, such as non-solvent induced phase separation (NIPS), electrospinning and thermally induced phase separation (TIPS).

[0134] As shown in FIG. 1, a diagnostic device 100 for plasma separation and dehydration from blood cells is provided. The diagnostic device 100 comprises a multi-layered membrane 3. The diagnostic device may further comprise a blood filter 2. The multi-layered membrane 3 (as expanded from the circular region) comprises a porous layer 5 and an absorbent layer 6. A sample of blood 1 may be separated by the device into retained blood cells 4 and plasma which is absorbed into the absorbent layer 6.

[0135] The membranes were then tested with the process shown in FIG. 2. Before testing, the membrane was held together with a filter paper or an absorbent. Blood was then dropped on the top of the membrane. If the plasma could permeate through the membrane and be absorbed by the filter paper, a watermark could be observed on the filter paper. If the watermark turned red, it suggested that red blood cells have passed through the membrane and the membrane was not desired.

[0136] The recovery of plasma could be derived from the following formula:

Plasma Recovery (%)=(weight of filter paper after adsorption−weight of filter paper before adsorption)/(density of plasma×total feed blood volume).

[0137] Membranes were optimized through two methods, which were electrospinning and TIPS. TIPS may be further combined with NIPS into N-TIPS for the formation of membranes.

Example 2

Fabrication Process of the Porous Layer via Electrospinning

[0138] The first kind of membranes was formed through the electrospinning process. In electrospinning, the polymer dope solution is pushed out of the syringes filled with the solution at a certain flow rate. By adding a high voltage at the needle tip, the solution droplets coming out of the needle can be stretched when electrostatic repulsion overcomes the surface tension of the solution, resulting in the formation of nanofibers. The nanofiber membrane can be formed by collecting the nanofibrous structures for a prolonged time. The physical properties of the membrane can be tuned by several factors, such as electric potential, dope flow rate, fiber collection time and dope formulas. By choosing proper electrospinning conditions, membranes with optimized performance can be achieved subsequently.

[0139] Since PAN has moderate hydrophilicity and has already been applied in the kidney dialysis, it was chosen in this disclosure to form the membrane separator. The polymer (obtained from R&D Center for Membrane Technology, Department of Chemical Engineering, Chung Yuan University, Chung-Li 32023, Taiwan) had a concentration of 9 weight %. N-methylpyrrolidone (NMP, 99.5%, purchased from Merck, Germany) and acetone (Ace, ≥99.8%, AR grade, purchased from Fisher Chemical) were used as the solvent and additives, respectively, at a ratio of 8:2 (weight %) to prepare the polymer solution for electrospinning. The two solvents made up of 91 weight % of the total dope weight. The influence of fiber collection time on membrane performance was investigated first as it determined the thickness and thus the permeability of the formed membranes.

[0140] FIGS. 3A to 3O depict the results. At a collection time of 15 minutes, the formed membrane was too thin and porous. Red blood cells could pass through the membrane from defect points and stain the absorbent filter paper. By increasing the collection time, the presence of red blood cells on the filter paper disappeared. However, a decrease in plasma permeation was also observed. The membrane only had a less than 1% plasma recovery when collected for 120 minutes, indicating that a prolonged collection time may generate a membrane too thick to conduct the decellularization application. An optimal collection time could be 30 minutes. A collection time of 30 minutes is choose because (1) the membrane collected by 30 minutes has similar performance as compared to the membrane collected by 60 minutes; (2) the membrane can reject 100% of blood cells; and (3) it saves materials and time during fabrication.

[0141] After determining the suitable collection time, the influence of dope formula was subsequently studied, with the results shown in FIGS. 4A to 4X. Since dope solutions contained both solvent and additive, they were manipulated in two ways: (1) substituting NMP to other commonly used solvents such as dimethylformamide (DMF, ≥99.9%, HPLC grade, purchased from VWR Chemicals) or dimethylacetamide (DMAc, ≥99.5%, HPLC grade, purchased from VWR Chemicals) in electrospinning; and (2) varying additive (acetone) to solvent (NMP) ratio. NMP, DMF, and DMAc are good solvents to dissolve PAN. However, they are different in many physical properties, such as boiling point, viscosity, etc. By using different solvents, the viscosities and surface tensions of the polymer solutions could be altered, which in turn affect the evaporation rate of the solvents.

[0142] As shown in FIGS. 4A to 4X, membranes made from DMF had a higher plasma recovery as compared to the membranes made from NMP and DMAc. It was easy to interpret as the boiling point of DMF is lower than that of DMAc and NMP. By increasing the acetone to solvent ratio, a higher plasma recovery was discovered. It was due to the formation of a more porous layer from a fast evaporation of acetone. Red blood cells could even pass through the membranes when the membranes were made from DMF or DMAc with high acetone contents. Based on membrane morphologies in FIGS. 4A to 4X, the membranes formed were highly porous and the pore distribution is uniform for the electrospinning membranes, such that the pore size of the formed membranes could be in the range of 0.25 to 3.00 μm.

[0143] The best membrane made from electrospinning had a plasma recovery of 13.33±1.21% with almost zero retentions to large molecules, such as human albumin protein (MW: 66.5 kDa). It also had almost 100% permeations of amino acids, for instance, glutamine acid, histidine, etc.

Example 3

Fabrication Process of the Porous Layer via Phase Separation

[0144] Membranes can also be formed through the thermally induced phase separation (TIPS) process. In this process, polymers are dissolved into a solvent mixture and cast at an elevated temperature. The cast polymer solution will undergo a precipitation process at a lower temperature, resulting in the formation of membranes. Membranes made from TIPS can be tuned in several ways by changing, for instance, dope formula and cooling condition in membrane formation.

[0145] The impact of dope formula on membrane morphologies and plasma recoveries were investigated first by varying the polymer concentration in the dope formula. The polymer was dissolved in 100 ml dimethyl sulfoxide (DMSO, 99.9%, ACS reagent, purchased from Sigma-Aldrich)/deionized water (DI water) (85/15 volume %) mixed solvent.

[0146] FIGS. 5A to 5I and FIGS. 6A to 6I present the influence of polymer concentration on morphologies and performance of the formed membranes, respectively. By decreasing the polymer concentration from 87.0 mg/ml to 63.8 mg/ml, membranes became more porous with large pores being observed on both top and bottom surfaces of the membrane.

[0147] The increased pores of membranes could also be buttressed by the spreading of blood on the membranes in FIGS. 6A to 6I. The blood droplet could spread fast on the membrane made from 63.8 mg/ml PAN, whereas it remained its shape on the membrane made from 87.0 mg/ml PAN. Furthermore, blood could also be observed on the bottom surface of the membrane and the filter paper beneath the membrane for membrane made from 63.8 mg/ml PAN, indicating that the membrane had much larger pore sizes. By further decreasing the polymer concentration of the membranes from 63.8 mg/ml to 41.7 mg/ml, the membrane pore size, however, reduced in the FESEM images. It might be caused by the weak mechanical properties of the membranes made from 41.7 mg/ml PAN, which resulted in shrinkage and loss of morphologies of the membrane during the vacuum drying process. The plasma recovery results reconfirmed that a PAN concentration of 41.7 mg/ml might be too low to form a good membrane in the DPS application because the plasma spot on the filter paper was small and contains red blood cells. Since membranes made from 87.0 mg/ml of PAN had a positive plasma permeation and full retention of red blood cells, the dope formula was used subsequently to investigate the influence of cooling conditions on membrane performance.

[0148] FIGS. 7A to 7I and FIGS. 8A to 8L represent the influence of cooling conditions on the morphologies and the performance of the formed membranes accordingly. Three cooling conditions are chosen; namely: (1) cooling gradually on the hotplate, (2) cooling in room temperature; and (3) cooling in water at room temperature. Compared to the cooling gradually on the hotplate, membranes made from cooling in room temperature might have a slightly more porous structure because they had a small increase in plasma recovery. Even though larger pores were observed on the membrane made from cooling gradually on the hotplate, the membrane could still be relatively dense due to the fast evaporation of the solvents at elevated temperatures. The plasma recovery further increased for the membrane made from cooling in water at room temperature. Comparing to the rest two membranes, the membranes made from cooling in water involved two-phase inversion mechanisms, i.e., TIPS and non-solvent induced phase separation (NIPS). The formed membranes had relatively denser selective layers and more porous bottom surfaces. Their cross-sections also contained finger-like macrovoids, which were caused by the additive (water) intrusion during the NIPS process. The presence of macrovoids might decrease the permeate resistance of plasma, leading to an enhanced plasma recovery. However, a plasma recovery of 2.82% was still low for the membrane to be used in the DPS applications. More effective methods are required to enhance the membrane plasma recoveries.

[0149] The selective layer (top surface) of a membrane is the barrier to separate blood cells from blood, especially for asymmetric membranes made from a combination of TIPS and NIPS (N-TIPS). The presence of the support layer (bottom surface) would be a barrier between the selective layer and the absorbent below the membrane, attenuating the function of the absorbent in taking in the plasma. If the membrane is flipped vertically with the supporting layer facing up, the selective layer would be in contact with the filter paper. The contact helps to provide an additional capillary force in addition to the gravity in transportation and separation of blood, facilitating the adsorption of plasma by the absorbent. By flipping the membrane and dropping blood at the membrane bottom surface, a high plasma recovery of 10.84% could be achieved, which was almost 4 times as compared to the one at the original placement. Furthermore, a good spreading of blood could be observed at the membrane's porous bottom surface. It might increase the contact area between the blood spot and the absorbent, which in turn further enhanced the plasma recovery of the membrane.

[0150] The cooling in water approach was applied to the rest two dope formulas, which were made from 41.7 mg/ml and 63.8 mg/ml PAN, with the results shown in FIGS. 9A to 9I. All fabricated membranes were flipped with blood dropping on the bottom surfaces of the membranes. By decreasing the polymer concentration from 87.0 mg/ml to 63.8 mg/ml, the fabricated membrane had an almost tripled plasma recovery. However, red blood cells started to permeate through the membrane by further decreasing the membrane polymer concentration from 63.8 mg/ml to 41.7 mg/ml. Thus, a polymer concentration of 63.8 mg/ml was the optimal polymer concentration for the membrane formation method of N-TIPS. The membrane made from the method could have a plasma recovery as high as 33.76±4.53%.

[0151] Since the membrane made from N-TIPS can have an impressive plasma recovery as high as 33.76±4.53%, it is hypothesized that a better membrane could be formed by changing the coagulant from water to solvent mixtures. By using a coagulant that could induce a slow demixing of the dope solution, a porous layer with large pores could be achieved. Thus, two solvent mixtures, i.e. NMP/water and isopropanol (IPA, 99.5%, purchased from Fisher Chemical)/water, were used in the study.

[0152] FIGS. 10A to 10L show the morphologies of the membranes made from a combination of TIPS/NIPS by using water, NMP/water or IPA/water as the coagulant. It can be found that the formed membranes had more porous top surfaces with clearly observed pores by using NMP/water and IPA/water as the coagulant.

[0153] FIGS. 11A to 11F depict the influence of different coagulant on the plasma recovery and the red blood cell retention of the membranes. Surprisingly, the plasma recoveries of the membranes made from IPA/water and NMP/water as the coagulants were even lower than the membrane made from water as the coagulant. The plasma recovery of a membrane may not only relate to the pore size of the selective layer but also corresponds to the affinity between the membrane and the absorbent and the spreading of blood on the bottom surface of the membrane. Membranes produced from a coagulant of NMP/water were wrinkled, resulting in an ineffective contact between the membrane and the absorbent. Thus, less plasma could be drawn to the absorbent. Membrane made from a coagulant of IPA/water had a relatively dense bottom surface. As a result, the spreading of blood at the membrane bottom surface might not be as good as the membranes made from NMP/water or water as the coagulants. All membranes fabricated in the sections had almost 100% permeations of amino acids, for instance, glutamine acid, histidine, etc. Based on the membrane morphologies in FIGS. 10A to 10L, the pore size distribution was not uniform for membranes made from a combination of TIPS and NIPS. The pore size of the formed membranes could be in the range of 0.10 to 1.00 μm.

INDUSTRIAL APPLICABILITY

[0154] The multi-layered membrane may be used as a diagnostic device and may be used in a variety of applications such as biosensors and as an extractor of cells or liquids from a sample of body fluid. It may be used as a membrane with tunable permeability in a wide range of applications.

[0155] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.