J. Vacík

Biological tolerance of poly(N-substituted methacrylamides)

The biological tolerance of poly(N-substituted acrylamides) implanted subcutaneously to rats and pigs was investigated. Besides a macro- and microscopical evaluation of the implant and its surroundings, the surface changes of the implants were determined by means of a Stereoscan electron-optical microscope;the results obtained confirmed the very good in vivo stability of the polymers used. The histological analysis showed that all the polymers under investigation are very well tolerated by the organism and do not provoke any unfavorable reaction. The implants become surrounded with a granulation tissue which is gradually replaced by fibrocytes and collagen fibers situated in the basic substance staining positively with the alcian blue and PAS. In contrast with some authors we did not find a thicker capsule surrounding the implant on the sharp edges but on the flat planes. No calcification could be observed within the intervals investigated. The surface changes, which were studied electronoptically, were insignificant and connected with the way in which the implant was treated. No indications of malignant growth were observed.

Silicone rubber-hydrogel composites as polymeric biomaterials. II. Hydrophilicity and permeability to water-soluble low-molecular-weight compounds.

The surface and transport properties of water-swollen silicone rubber-hydrogel composites were investigated. Surface wettability of these materials, composed of a polysiloxane matrix and the hydrogel phase consisting of very fine particles of lightly cross-linked poly(2-hydroxyethylmethacrylate), increased markedly with increasing content of the hydrogel phase. For composite materials containing a lightly cross-linked 2-hydroxyethylmethacrylate (HEMA)-methacrylic acid (MAA) copolymer and polymethacrylic acid (PMAA) as the hydrogel phase, permeability to water-soluble organic compounds and drugs were measured. The permeability varied within a broad range depending on the composition and content of the hydrogel phase. High permeation rates could be obtained while still retaining relatively fair mechanical properties. Relationships between the composition of silicone rubber-hydrogel composites, their structure and the permeation coefficients of the individual permeates are discussed.

The influence of chemical functional groups on implant biocompatibility

Abstract It is known that poorly tolerated implants are colonized by multinucleate foreign-body giant cells. This paper summarizes the influence of chemical functional groups of implanted materials on the fusion of macrophages into these multinucleate cells, stressing the inhibitory effect of anionic groups. This phenomenon was used in constructing a new intraocular lens for patients after cataract surgery.

The preparation of ultrafiltration membranes from a moderately sulfonated poly(Oxy(2,6-Dimethyl-1,4-Phenylene))

Abstract Poly(oxy(2,6-dimethyl-1,4-phenylene)) was sulfonated with concentrated sulfuric acid in the heterogeneous phase. Ultrafiltration membranes were prepared by casting a solution of the sulfonated polymer in the binary solvent chloroform—1-butanol followed by coagulation in methanol. A comparison of the flow rates of pure water through membranes prepared under the same conditions (the same concentration, evaporation time, etc.), but from polymers with varying degree of sulfonation shows that with increasing hydrophilicity of the polymer the flow rate of water through the membrane markedly increases. For polymers containing more than 1.5 wt% of sulfur, methanol is already a poor precipitant, and the membranes thus obtained again have poorer permeation properties. For membranes made from a polymer with the optimal sulfur content of 1.2 wt%, the permeate flux increases and the rejection of dextrans decreases with increasing content of l-butanol in the binary solvent and with decreasing polymer concentration in the casting solution. However, membranes prepared from dilute solutions have a strong tendency towards compaction.

Strong-acid membranes with enhanced hydrophilicity

Abstract A number of membranes have been synthesized on the basis of a cross-linked gel with a hydrophilic neutral matrix, containing polymerized hydrophilic monomers with strongly dissociable groups. p]The membrane is a copolymer of 2-hydroxyethyl methacrylate (matrix) and sulfooxyethyl methacrylate with the crosslinking agent (ethylenedimethacrylate). Presented in this paper are the effects of cross-linking, concentration of the dissociable groups, and pH on the membrane concentration potentials, electrical conductivity, and swelling of the merebranes. The hydrophilic character of the membrane matrix causes departures from the theoretical behavior derived for membranes with a hydrophobic character, and influences its behavior more than would be anticipated from the presence of the strong-acid groups. Cross-linking is more effective in attaining a high permsetectivity than is the density of fixed dissociable groups and/or their dissociation, so that by combining the content of the ionogenic component with cross-linking it was possible to find highly hydrophilic merebrane gels with a virtually theoretical electrochemical behavior and with a small dependence on pH.

Regulation of transport in artificial membranes by environmental hydrogen-ion concentration

Abstract Transport phenomena in biological membranes and in biocatalysis (immobilized enzymes) are influenced by the structure of the matrix. This structure is not invariable but may depend on parameters of adjacent solutions. Weakly acidic ion-exchange membranes are useful tools for modelling ionic influences on such charged matrices. The pH dependence of tracer permeabilities of [ 3 H] water and [ 14 C] non-electrolytes was determined on polymethacrylic acid/polyhydroxyethylmethacrylate membranes as a function of their cross-linking and hydrophobicity. At lower buffer concentrations, the non-electrolyte permeabilities increase between 20 and 500% if the pH is raised from 6.5 to 7.5. The relative increase depends on membrane properties and the molecular weights of the permeants. Water permeabilities were measured between pH 5 and 8, the whole interval of pH controllability of the ion-exchange membranes used. The results are similar to those for the [ 14 C] non-electrolytes. This control of permeability experimentally established by pH-variation is consistent with assumptions about the influence of the kind of counter ions (H + , Me + , Me 2+ ) on the degree of dissociation of carboxyl groups within the membrane. Thus the stage of dissociation is responsible for the structure and transport properties of weak ion exchangers.

pH-dependent electrochemical behaviour of hydrophilic ampholytic membranes

Abstract Ampholytic membranes were synthesized by copolymerizing (2-hydroxyethyl)methacrylate as the hydrophilic component, methacrylic acid and (N,N-diethylaminoethyl)methacrylate as ionogenic components (both ionogenic monomers in amounts 2.5 mol% or 10 mol%), and ethylenedimethacrylate as the crosslinking agent (3,5 or 10 mol%). The effects of pH on the swelling and membrane potentials of the membranes were investigated. The dependence of the membrane potentials on pH is characterized by the position of the isoelectric point and by the slope of the straight part of the dependence. This slope reflects the attained degree of ideality of the membrane. By varying the degree of cross linking and the content of ionogenic components, it is possible to vary the pH-dependent response of the membranes.

Relaxation Behaviour of Poly(2-Hydroxyethyl Acrylate) and of Its Copolymers with 2-Hydroxyethyl Methacrylate

Abstract The molecular mobility of poly(2-hydroxyethyl acrylate) (PHEA) and of its copolymers with 2-hydroxyethyl methacrylate (H EM A) was determined by means of dynamic mechanical measurements with a torsional pendulum. The low-temperature dispersion assigned to the motion of the hydroxyethyl groups of the side chains was observed at -133°C (1 Hz) for all polymers; its intensity increased with the content of HEMA. Another secondary dispersion of PHEA detected at -95°C(1 Hz) was ascribed to the motion of the side chains including oxycarbonyl groups. With the incorporation of HEMA the temperature of the latter dispersion remained virtually unchanged, but its intensity rapidly decreased. The main transition temperature of PHEA, Ta = 9°C (1 Hz) is lower than Ta of PHEMA by approximately 94°C; the effect of the copolymer composition on Ta could be described by means of a one-parameter equation. The sorption of water led to a significant decrease in the Ta of PHEA and to an intensification of the secondary re...

Relaxation Behavior of Poly(N-monosubstituted Methacrylamides)

Abstract A free-oscillating torsional pendulum was used to investigate the effect of substituents R on the dynamic mechanical relaxation behavior of poly(N-monosubstituted methacrylamides) in the temperature interval from –196 to 130°C. A comparison with the corresponding polymethacrylates shows that the relaxation motion of the side groups R, which gives rise to the low temperature dispersion (below – 130°C), is virtually independent of whether R is attached to COO or CONH groups. On the other hand the obtained data give evidence that a strong intermolecular interaction and high steric hindrances suppress the onset of the motion of CONH–R side chains as a whole. For the same reason the glass transition temperature of the poly(N-monosubstituted methacrylamides) is about 100°C higher than that of the corresponding polymethacrylates. The incorporation of low molecular weight substances leads to reduction of the low-temperature dispersion and to formation of a new secondary dispersion at a temperature of abo...

Influence of intraperitoneal injection of three types of hydrogel beads on expression of carbohydrate-binding sites in spleen macrophages

The influence of the chemical structure of polymer implants on selected characteristics of macrophages was studied to improve our understanding of the mechanisms of non-self recognition of synthetic materials. Three types of polymers differing in net charge were prepared to compare in vivo responses. Beads from preparation of poly(2-hydroxyethyl methacrylate), a copolymer of 2-hydroxyethyl methacrylate with sodium methacrylate, and a copolymer of 2-hydroxyethyl methacrylate and dimethylaminoethyl methacrylate were injected intraperitoneally into rats and harvested 48 h later. The effects of these polymers on the presence of inflammatory cells in the peritoneal exudate, on the adhesion of macrophages to individual batches of the different types of beads and on distinct molecular aspects of macrophages in the red pulp of spleen were evaluated. Beads from both types of copolymer caused an elevation in the number of macrophages in the exudate, in contrast to the situation in rats treated with poly(2-hydroxyethyl methacrylate) beads and physiological saline solution as control. The molecular design of the implant had no significant influence on the extent of macrophage adhesion to beads or on the expression of selected carbohydrate-binding sites. Since important cellular functions such as cell adhesion and glycoprotein routing depend on the sugar part of glycoconjugates, labelled neoglycoproteins were employed to analyse this aspect of macrophages in the tested animals. The beads of the copolymer of 2-hydroxyethyl methacrylate with dimethylaminoethyl methacrylate clearly led to an elevation of the expression of specific binding sites for beta-galactoside-terminating structures which are presented by asialofetuin, for mannose, fucose, sialic acid and N-acetylgalactosamine, which had been used as the ligand parts of biotinylated neoglycoproteins, in spleen macrophages whereas the levels of sites which recognize mannose-6-phosphate were unaffected. Expression of sites with specificity to N-acetylglucosamine was lessened. The effect of beads from the copolymer of 2-hydroxyethyl methacrylate with sodium methacrylate on the measured glycobiological features in the splenic macrophages was only negligible. These results suggest the possibility of systemic effects of implanted polymers on the distinct recognitive functions of macrophages.