Size-selective hemocompatible polymer system

Abstract

A size-selective hemocompatible porous polymeric adsorbent system is provided, the polymer system comprises at least one crosslinking agent and at least one dispersing agent, and the polymer has a plurality of pores with diameters in the range from about 17 to about 40,000 Angstroms.

Claims

1. A hemocompatible size selective polymer system comprising at least one polymer formed with at least one crosslinking agent and in the presence of at one least dispersant, said at least one polymer defining a porous structure wherein said porous structure consists of a plurality of pores with diameters in the range of 17 Angstroms to about 2000 Angstroms, said at least one polymer comprising transport pores with diameters from about 250 Angstroms to about 2000 Angstroms and effective pores with diameters greater than 100 Angstroms to about 250 Angstroms, said at least one polymer having a transport pore volume greater than about 1.8 to about 78% of a capacity pore volume of said at least one polymer and an effective pore volume greater than about 22 to less than about 98.2% of the capacity pore volume.

2. The system of claim 1 wherein said at least one crosslinking agent is selected from a group consisting of divinylbenzene, trivinylbenzene, divinylnaphthalene, trivinylcyclohexane, divinylsulfone, trimethylolpropane trimethacrylate, trimethylolpropane dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane diacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate pentaerythritol tetraacrylate, dipentaerythritol dimethacrylate, dipentaerythritol trimethacrylate, dipentaerythritol tetramethacrylate, dipentaerythritol diacrylate, dipentaerythritol triacrylate, dipentaerythritol tetraacrylate, divinylformamide and mixtures thereof.

3. The system of claim 1 wherein said at least one dispersant is selected from a group consisting of albumin, carrageenan, konjac flour, guar gum, xanthan gum, gum Arabic, gum tragcanth, locust bean gum, karaya gum, salts of carboxymethylcellulose, salts of carboxyethylcellulose, salts of hyaluronic acid, salts of poly(maleic acid), salts of poly(itaconic acid), Type B gelatin, poly(acrylamide), poly(methacrylamide), salts of poly(acrylamide-co-acrylic acid), salts of poly(acrylamide-co-methacrylic acid), salts of poly(methacrylamide-co-acrylic acid), salts of poly(methacrylamide-co-methacrylic acid), hydroxyethyl cellulose, hydroxypropyl cellulose, poly(hydroxyethyl methacrylate), poly(hydroxypropyl acrylate), poly(dimethylaminoethyl methacrylate), poly(dimethylaminoethyl acrylate), poly(dimethylaminoethyl methacrylate), poly(diethylaminoethyl acrylate), poly(vinyl alcohol), poly(N-vinylpyrrolidinone), salts of poly(methacrylic acid), and salts of poly(acrylic acid) and mixtures thereof.

4. The system of claim 1 wherein the presence of said at least one dispersant forms a hemocompatible surface on said at least one polymer.

5. The system of claim 1 wherein said at least one polymer is used in direct contact with whole blood to sorb protein molecules selected from a group consisting essentially of cytokines and 82-microglobulin and exclude the sorption of large blood proteins, said large blood proteins being selected from a group consisting essentially of hemoglobin, albumin, immunoglobulins, fibinogen, serum proteins and other blood proteins larger than 50,000 Daltons.

6. The system of claim 1 wherein said at least one polymer has an internal surface selectivity for absorbing proteins being smaller than 50,000 Daltons, having little to no selectivity for adsorbing vitamins, glucose, electrolytes, fats, and other hydrophilic small molecular nutrients carried by the blood.

7. The system of claim 1 wherein said at least one polymer is made using suspension polymerization.

8. The system of claim 1 wherein said at least one polymer is formed by polymerizing monomers in the presence of at least one free radical inhibitor and at least one buffering agent.

9. A size selective hemocompatible surface coated polymer system comprising at least one polymer formed by polymerizing monomers in an organic phase, said organic phase comprises polymerizable monomers and at least one initiator and wherein said organic phase is dispersed in an aqueous phase, said aqueous phase comprises at least one dispersing agent, at least one free radical inhibitor and at least one buffering agent, said at least one polymer defining a porous structure wherein said porous structure consists of a plurality of pores with diameters in the range of 17 Angstroms to about 2000 Angstroms, said at least one polymer comprising transport pores with diameters from about 250 Angstroms to about 2000 Angstroms and effective pores with diameters greater than 100 Angstroms to about 250 Angstroms, said at least one polymer having a transport pore volume greater than about 1.8 to about 78% of a capacity pore volume of said at least one polymer and an effective pore volume greater than about 22 to less than about 98.2% of the capacity pore volume.

10. The system of claim 9 wherein said polymerizable monomers are monofunctional monomers, said monofunctional monomers are selected from a group consisting of styrene and ethylvinylbenzene, and said system further comprises at least one crosslinking agent selected from a group consisting essentially of divinylbenzene, trivinylcyclohexane, trivinylbenzene, divinylnaphthalene, divinylsulfone, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate and mixtures thereof.

11. The system of claim 9 further comprising at least one crosslinking agent is selected from a group consisting of divinylbenzene, trivinylbenzene, divinylnaphthalene, trivinylcyclohexane, divinylsulfone, trimethylolpropane trimethacrylate, trimethylolpropane dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane diacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol dimethacrylate, dipentaerythritol trimethacrylate, dipentaerythritol tetramethacrylate, dipentaerythritol diacrylate, dipentaerythritol triacrylate, dipentaerythritol tetraacrylate, divinylformamide and mixtures thereof.

12. The system of claim 9 wherein said at least one initiator is selected from a group consisting of diacylperoxides, ketone peroxides, peroxyesters, dialkyl peroxides, peroxyketals, azoalkylnitriles, peroxydicarbonates and mixtures thereof.

13. The system of claim 9 wherein said at least one dispersant is selected from a group consisting of albumin, carrageenan, konjac flour, guar gum xanthan gum, gum Arabic, gum tragcanth, locust bean gum, karaya gum, salts of carboxymethylcellulose, salts of carboxyethylcellulose, salts of hyaluronic acid, salts of poly(maleic acid), salts of poly(itaconic acid), Type B gelatin, poly(acrylamide), poly(methacrylamide), salts of poly(acrylamide-co-acrylic acid), salts of poly(acrylamide-co-methacrylic acid), salts of poly(methacrylamide-co-acrylic acid), salts of poly(methacrylamide-co-methacrylic acid), hydroxyethyl cellulose, hydroxypropyl cellulose, poly(hydroxyethyl methacrylate), poly(hydroxypropyl acrylate), poly(dimethylaminoethyl methacrylate), poly(dimethylaminoethyl acrylate), poly(dimethylaminoethyl methacrylate), poly(diethylaminoethyl acrylate), poly(vinyl alcohol), poly(N-vinylpyrrolidinone), salts of poly(methacrylic acid), and salts of poly(acrylic acid) and mixtures thereof.

14. The system of claim 9 wherein said at least one free radical inhibitor is selected from a group consisting of p-nitrosophenoxide salts, sodium nitrate, N-hydroxy-N-methylglucamine, N-nitroso-N-methylglucamine and mixtures thereof.

15. The system of claim 9 wherein said at least one buffering agent is selected from a group consisting of carbonate salts, bicarbonate salts, boric acid salts, salts of phosphoric acid and mixtures thereof.

16. The system of claim 9 wherein said organic phase further comprises at least one porogen, said at least one porogen being selected from a group consisting of aliphatic hydrocarbons, dialkyl ketones, aliphatic carbinols and mixtures thereof.

17. A hemocompatible size selective polymer system comprising at least one polymer formed by polymerizing monomers in an organic phase dispersed in an aqueous phase, said organic phase comprises polymerizable monomers and at least one initiator and wherein said organic phase is dispersed in an aqueous phase, said aqueous phase comprises at least one dispersing agent, at least one free radical inhibitor and at least one buffering agent, said at least one polymer defining a porous structure, said porous structure consisting of pores with diameters in the range of 17 Angstroms to about 2000 Angstroms, said at least one polymer comprising transport pores with diameters from about 250 Angstroms to about 2000 Angstroms and effective pores with diameters greater than 100 Angstroms to about 250 Angstroms, said at least one polymer having a transport pore volume greater than about 1.8 to about 78% of a capacity pore volume of said at least one polymer and an effective pore volume greater than about 22 to less than about 98.2% of the capacity pore volume.

18. The system of claim 17 wherein said polymerizable monomers are monofunctional monomers, said monofunctional monomers are selected from a group consisting of styrene and ethylvinylbenzene, and said system further comprises at least one crosslinking agent selected from a group consisting essentially of divinylbenzene trivinylcyclohexane, trivinylbenzene, divinylnaphthalene, divinylsulfone, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate and mixtures thereof.

19. The system of claim 17 wherein said at least one initiator is selected from a group consisting of diacylperoxides, ketone peroxides, peroxyesters, dialkyl peroxides, peroxyketals, azoalkylnitriles, peroxydicarbonates and mixtures thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are included to provide a further understanding of the present invention. These drawings are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the present invention and together with the description, serve to explain the principles of the present invention.

(2) FIG. 1 is a graph of Table 2 showing a plot of pore volume v pore diameter (dV/dD vs. D) for Various Adsorbents Measured by Nitrogen Desorption Isotherm.

(3) Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.

DETAILED DESCRIPTION OF THE INVENTION

(4) As required, detailed embodiments of the present invention are disclosed herein; it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limits, but merely as a basis for teaching one skilled in the art to employ the present invention. The specific examples below will enable the invention to be better understood. However, they are given merely by way of guidance and do not imply any limitation.

(5) Five porous polymeric adsorbents are characterized for their pore structures and are assessed for their competitive adsorption of cytochrome-c (11,685 Daltons in size) over serum albumin (66,462 Daltons in size). The adsorbent syntheses are described in Example 1; the pore structure characterization is given in Example 2; the competitive dynamic adsorption procedure and results are provided in Example 3; and the competitive efficacy for pick up the smaller cyclochrome-c protein over the larger albumin molecule is discussed under Example 4.

EXAMPLE 1

Adsorbent Syntheses

(6) The synthesis process consists of (1) preparing the aqueous phase, (2) preparing the organic phase, (3) carrying out the suspension polymerization, and (4) purifying the resulting porous polymeric adsorbent product. The aqueous phase compositions are the same for all the polymerizations. Table 1A lists the percentage composition of the aqueous phase and Table 1B gives the material charges typical for a five (5) liter-reactor polymerization run.

(7) TABLE-US-00001 TABLE 1A Aqueous Phase Composition Wt. % Ultrapure Water 97.787 Dispersing Agent: Polyvinylalcohol 0.290 Monosodium Phosphate 0.300 Disodium Phosphate 1.000 Trisodium Phosphate 0.620 Sodium Nitrite 0.003

(8) TABLE-US-00002 TABLE 1B Material Charges for a Typical Five (5) Liter-Reactor Polymerization Run Volume of Aqueous Phase 1750.00 ml Density of Aqueous Phase 1.035 g/ml Weight of Aqueous Phase 1811.25 g Volumetric Ratio, Aqueous Phase/Organic Phase 1.05 Volume of Organic Phase 1665.0 ml Density of Organic Phase 0.84093 g/ml Weight of Organic Phase, Excluding Initiator Charge 1400.15 g Total Reaction Volume 3415.0 ml Total Reaction Weight 3211.40 g Initiator, Pure Benzoyl Peroxide (BPO) 8.07606 g Initiator, 97% BPO 8.3258 g Commercial 63% Divinylbenzene (DVB) 794.814 g [98.65 Polymerizable Monomers of DVB and EVB (Ethylvinylbenzene); 1.35% inert compounds; 63.17% DVB; 35.48% EVB] Toluene 269.300 g Isooctane 336.036 g Benzoyl Peroxide, 97% 8.3258 g Total, Organic Charge 1408.4758 g (Note: Initiator charge is calculated on only the quantity of polymerizable monomers introduced into the reactor.)

(9) Upon preparation of the aqueous phase and the organic phase, the aqueous phase is poured into the five-liter reactor and heated to 65 C. with agitation. The pre-mixed organic phase including the initiator is poured into the reactor onto the aqueous phase with the stirring speed set at the rpm for formation of the appropriate droplet size. The dispersion of organic droplets is heated to the temperature selected for the polymerization and is held at this temperature for the desired length of time to complete the conversion of the monomers into the crosslinked polymer and, thereby, set the pore structure. Unreacted initiator is destroyed by heating the bead slurry for two (2) hours at a temperature where the initiator half-life is one hour or less. For the initiator, benzoyl peroxide, the unreacted initiator is destroyed by heating the slurry at 95 C. for two (2) hours.

(10) The slurry is cooled, the mother liquor is siphoned from the beads and the beads are washed five (5) times with ultrapure water. The beads are freed of porogen and other organic compounds by a thermal cleaning technique. This process results in a clean, dry porous adsorbent in the form of spherical, porous polymer beads.

(11) TABLE-US-00003 TABLE 1C Components of Adsorbent Syntheses Adsorbent 1 Adsorbent 3 Adsorbent 4 Adsorbent 5 Porous Polymer Identity Wt. %.sup.a Adsorbent 2 Wt. %.sup.a Wt. %.sup.a Wt. %.sup.a Divinylbenzene, 35.859 Adsorbent 2 26.163 22.4127 22.4127 (DVB), Pure is a comercial Ethylvinylbenzene 20.141 resin, 14.695 12.5883 12.5883 (EVB), Pure Amberlite Inerts 0.766 XAD-16, made 0.559 0.4790 0.4790 Toluene 19.234 by Rohm and 27.263 64.521 54.841 Isooctane 24.00 Haas Company 31.319 0.00 9.680 Polymerizable 56.00 40.8584 35.00 35.00 Monomers Porogen 44.00 59.1416 65.00 65.00 Benzoyl Peroxide 1.03 0.7447 2.00 4.00 (BPO), Pure; Wt. % Based Upon Polymerizable Monomer Content Polymerization, 75/10 hrs 80/16 hrs 70/24 hrs 65/24 hrs C./time, hrs. 95/2 hrs 95/2 hrs .sup.aWt. % value is based upon the total weight of the organic phase excluding the initiator.

EXAMPLE 2

Pore Structure Characterization

(12) The pore structures of the adsorbent polymer beds identified in TABLE 1C were analyzed with a Micromeritics ASAP 2010 instrument. The results are provided in GRAPH 1 where the pore volume is plotted as a function of the pore diameter. This graph displays the pore volume distribution across the range of pore sizes.

(13) The pore volume is divided up into categories within pore size ranges for each of the five adsorbent polymers and these values are provided in TABLE 2. The Capacity Pore Volume is that pore volume that is accessible to protein sorption and consists of the pore volume in pores larger than 100 diameter. The Effective Pore Volume is that pore volume that is selectively accessible to proteins smaller than 35,000 Daltons and consists of pore diameters within the range of 100 to 250 diameter. The Oversized Pore Volume is the pore volume accessible to proteins larger than 35,000 Daltons and consists of the pore volume in pores larger than 250 diameter. The Undersize Pore Volume is the pore volume in pores smaller than 100 diameter and is not accessible to proteins larger than about 10,000 Daltons.

(14) TABLE-US-00004 TABLE 2 Pore Structures of Adsorbents Polymer Adsorber ID Adsorbent 1 Adsorbent 2 Adsorbent 3 Adsorbent 4 Adsorbent 5 Capacity Pore Volume, cc/g; Dp, 100 0.5850 1.2450 1.5156 0.3148 0.6854 .fwdarw.2000 Effective Pore Volume, cc/g; Dp, 100 0.5678 0.9860 0.3330 0.3060 0.6728 .fwdarw.250 Transport Pore Volume of 0.0172 0.2590 1.1826 0.0088 0.0126 Dp = 250~2000 , cc/g Effective Pore (100~250 )Volume, as 97.06% 79.20% 21.97% 97.20% 98.16% % of capacity pore Transport Pore (250-2000 ) Volume, 2.9% 20.8% 78.0% 2.8% 1.8% as % of capacity pore Undersized Pore Volume, cc/g; Dp < 0.3941 0.5340 0.4068 0.6311 0.4716 100 Total Pore Volume, cc/g; Dp, 17 0.9792 1.7790 1.9225 0.9459 1.1569 .fwdarw.2000 Pore Vol (cc/g) of Dp = 500 to 2,000 0.0066 0.016 0.668 0.0036 0.0053 Volune of Pores in 100~750 , cc/g 0.5816 1.2357 1.4915 0.3133 0.6825 Volume of Pores in 100~750 , as % of 99.4% 99.3% 98.4% 99.5% 99.6% capacity pore Dp = Pore Diameter in (Angstrom)

(15) FIG. 1 depicts a Graph of Table 2 showing a plot of pore volume v pore diameter (dV/dD vs. D) for Various Adsorbents Measured by Nitrogen Desorption Isotherm.

EXAMPLE 3

Protein Adsorption Selectivity

(16) The polymeric adsorbent beads produced in Example 1 are wetted out with an aqueous solution of 20 wt. % isopropyl alcohol and thoroughly washed with ultrapure water. The beads with diameters within 300 to 850 microns are packed into a 200 ml hemoperfusion device which is a cylindrical cartridge 5.4 cm in inside diameter and 8.7 cm in length. The beads are retained within the cartridge by screens at each end with an orifice size of 200 microns. End caps with a center luer port are threaded onto each end to secure the screens and to provide for fluid distribution and attachment for tubing.

(17) Four liters of an aqueous 0.9% saline solution buffered to a pH of 7.4 are prepared with 50 mg/liter of horse heart cytochrome-c and 30 g/liter of serum albumin. These concentrations are chosen to simulate a clinical treatment of a typical renal patient where albumin is abundant and .sub.2-microglobulin is at much lower levels in their blood. Horse heart cytochrome-c with a molecular weight 11,685 daltons has a molecular size very close to .sub.2-microglobulin at 11,845 daltons and, therefore, is chosen as the surrogate for .sub.2-microglobulin. Serum albumin is a much larger molecule than cytochrome-c with a molecular weight of 66,462 daltons and, therefore, allows for the appropriate competitive adsorption studies needed for selecting the porous polymer with the optimum pore structure for size-selective exclusion of albumin.

(18) The protein solution is circulated by a dialysis pump from a reservoir through a flow-through UV spectrophotometer cell, the bead bed, and returned to the reservoir. The pumping rate is 400 ml/minute for a duration of four (4) hours. The concentration of both proteins in the reservoir is measured periodically by their UV absorbance at 408 nm for cytochrome-c and at 279 nm for albumin.

(19) All five adsorbents identified in TABLE 1C were examined by this competitive protein sorption assessment and the measured results are given in TABLE 3.

(20) TABLE-US-00005 TABLE 3 Size-Selective Efficacy of Porous Polymeric Adsorbents Polymer Adsorber ID Adsorbent 1 Adsorbent 2 Adsorbent 3 Adsorbent 4 Adsorbent 5 Capacity Pore Volume, 0.5850 1.2450 1.5156 0.3148 0.6854 cc/g; Dp, 100 .fwdarw.2000 Effective Pore Volume, 0.5678 0.9860 0.3330 0.3060 0.6728 cc/g; Dp, 100 .fwdarw.250 Transport Pore Volume of 0.0172 0.2590 1.1826 0.0088 0.0126 Dp = 250~2000 , cc/g Effective Pore 97.06% 79.20% 21.97% 97.20% 98.16% (100~250 )Volume, as % of capacity pore Transport Pore 2.9% 20.8% 78.0% 2.8% 1.8% (250~2000 ) Volume, as % of capacity pore Undersized Pore Volume, 0.3941 0.5340 0.4068 0.6311 0.4716 cc/g; Dp < 100 Total Pore Volume, cc/g; 0.9792 1.7790 1.9225 0.9459 1.1569 Dp, 17 .fwdarw.2000 Pore Vol (cc/g) of 0.0066 0.016 0.668 0.0036 0.0053 Dp = 500 to 2,000 Volune of Pores in 0.5816 1.2357 1.4915 0.3133 0.6825 100~750 , cc/g Volume of Pores in 99.4% 99.3% 98.4% 99.5% 99.6% 100~750 , as % of capacity pore % Cytochrome-C, 89.0% 96.7% 95.3% 57.4% 90.1% Adsorbed % Albumin Adsorbed 3.7% 8.1% 13% 1.0% 1.8% Selectivity 24.05 11.94 7.27 57.1 50.06 Dp = Pore Diameter in (Angstrom)

EXAMPLE 4

Pore Volume and Pore Size Range for Suitable Kinetics and Size-Selectivity for Cytochrome-C Over Albumin

(21) TABLE 3 and GRAPH 1 summarize the pertinent pore structure data and the protein perfusion results carried out on all five (5) adsorbents. The selectivity for adsorbing cytochrome-c over albumin decreased in the following order: Adsorbent 4>Adsorbent 5>Adsorbent 1>Adsorbent 2>Adsorbent 3.

(22) The quantity of cytochrome-c adsorbed during the four hour perfusion decreased in the following order: Adsorbent 2>Adsorbent 3>Adsorbent 5>Adsorbent 1>Adsorbent 4.

(23) Adsorbent 4 with the highest selectivity at 57.1 had the poorest kinetics picking up only 57.4% of the available cytochrome-c over the four hour perfusion. This kinetic result occurs from the Effective Pore Volume being located at the small end of the pore size range, having all its Effective Pore Volume within the pore size range of 130 to 100 . There is insignificant pore volume in pores larger than 130 and this small pore size retards the ingress of cytochrome-c.

(24) Adsorbent 5 with its major pore volume between 100 to 200 had the second highest selectivity for cytochrome-c over albumin at 50.6 and it had good mass transport into the Effective Pore Volume pores picking up 90.1% of the cytochrome-c during the four hour perfusion. This porous polymer has the best balance of properties with excellent size-selectivity for cytochrome-c over albumin and very good capacity for cytochrome-c during a four hour perfusion.

(25) Adsorbent 1 showed reasonably good selectivity at 24.05 for sorbing cytochrome-c over albumin. It also exhibited good capacity for sorbing cytochrome-c during the four hour perfusion, picking up 89.0% of the quantity available.

(26) Adsorbent 2 with the highest capacity for sorbing cytochrome-c during the four hour perfusion picked up 96.7% of the available cytochrome-c. This high capacity arises from having a large pore volume, 0.986 cc/g, and within the Effective Pore Volume range of 100 to 250 . However, this porous polymer allowed more albumin to be adsorbed than Adsorbents 1, 4, and 5, since it has significant pore volume, 0.250 cc/g, in the pore size group from 250 to 300 .

(27) Adsorbent 3 with a very broad pore size distribution (see GRAPH 1) had the poorest selectivity among the group at 7.27. It has a very large pore volume in the pore size range larger than 250 . This porous polymer has a pore volume of 1.15 cc/g within the pore size range of 250 to 740 . In contrast with the other four adsorbents, this porous polymer is not size-selective for proteins smaller than about 150,000 Daltons, although it did sorb 95.3% of the available cytochrome-c during the perfusion.

(28) On balance of properties of selectively for sorbing cytochrome-c over albumin and its capacity for picking up cytochrome-c during a four hour perfusion, porous polymeric Adsorbent 5, gave the best performance. This porous polymer has the proper pore structure to perform well in hemoperfusion in concert with hemodialysis for people with End Stage Renal Disease.

(29) Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the attendant claims attached hereto, this invention may be practiced other than as specifically disclosed herein.