Structural alterations of p(HEMA)--collagen implants.

Samples of linear (additionally crosslinked) p(HEMA) with different amounts of fibrillar collagen were implanted into the popliteal region of rats. After 3 month, the implanted materials were harvested and examined by SEM. The implants underwent marked structural or morphological changes. While the fibrillar collagen was readily resorbed by invading cells, the synthetic constituent persisted to biodegradation. The p(HEMA) residues were shaped into spherical particles, approx. 1-15 microns in diameter. The possible fate of these microparticles in the host organism is discussed.

Silicone rubber-hydrogel composites as polymeric biomaterials. I. Biological properties of the silicone rubber-p(HEMA) composite.

A composite material was prepared consisting of silicone rubber matrix and particulate lightly cross-linked poly(2-hydroxyethyl methacrylate) (p(HEMA] hydrogel. The material resembling common silicone rubber is hydrophilic and swells in water like hydrogels. The effects of the implanted composite on tissues of the living organism were tested in rats by methods assessing local acute and chronic inflammatory reactions and calcification by means of radioactive indicators and by histological examination. Results of a 6 month implant study indicated no difference in reactions of the animal body on the silicone rubber-p(HEMA) composite and a non-toxic, non-irritant pure solid p(HEMA) control.

Irritation effects of residual products derived from p(HEMA) gels. II. Compounds extracted from hydrogels.

Samples of poly(2-hydroxyethyl methacrylate) p(HEMA) hydrogels were prepared using three different polymerization initiators. The gels were washed in water under standard conditions. The extracts were then examined for intradermal irritation in rats using a radioactive indicator (113mIn). The irritation effects were dependent on the concentrations of the irritating substances and also on the gel type. Solid discs made of the gels, washed to varying degrees of purity, were also implanted into rats. Tissue irritation, as well as some other biological responses, were followed in situ using the radioindicator and common histological techniques. The irritation effects were very mild (even with the unextracted gel material). A possible explanation for the events taking place at the site of implantation is presented.

Irritation effects of residual products derived from poly(2-hydroxyethyl methacrylate) gels. I. Testing of some model compounds.

2-Hydroxyethyl methacrylate (HEMA) monomer and sodium benzoate, diluted with saline in the range 0-20%, were tested for intradermal irritation in rats. Radioactive indicator (113mIn) was used to quantify this biological response. At low concentrations (up to 1%) only a little irritation was recorded, while at higher levels (5% or more) a significant adverse reaction developed. The degree of irritation was dose dependent. In the concentration range 0-10%, the response was exponential. Model decomposition products derived from three different polymerization initiators were also tested. How the results obtained with the model irritants relate to real polymerization systems is discussed.

Calcification of poly(2-hydroxyethyl methacrylate)-collagen composites implanted in rats.

Samples of the polyHEMA-collagen composites with varying collagen content have been implanted into the popliteal region of rats. Three, six and twelve months after the implantation, calcification of the implanted material was determined using a radioactive indicator. At the same time, the implants and surrounding tissue were examined histologically. The degree of calcification of the implants was dependent on the collagen content; it was more pronounced with a higher amount of collagen. The composites with 30% (w/w) or more collagen were biodegraded during the long-term implantation. It is suggested that the composites containing less than 20% (w/w) of fibrillar collagen are used for biomedical applications and that those with a higher collagen content for the in vitro studies.

The removal of residuals and oligomers from poly(2-hydroxyethylmethacrylate).

Poly(2-hydroxyethyl methacrylate) gels obtained by the cross-linking polymerization using four different free-radical initiators were washed with water. Chromatographically, the eluate appeared to be a mixture of low-molecular-weight compounds and of a small amount of the high-molecular-weight component. The UV and IR absorption spectra of compounds present in the eluate were compared with those of model compounds that were assumed to exist in the gel as impurities after the polymerization (monomers and oligomers of hydroxyethyl methacrylate, decomposition products of initiators). Time dependences of the removal of impurities from the gels by washing were measured. Most of the impurities were washed out within a few hours. In addition to the assumed impurities, the eluate was found to contain an unidentified compound that was still washed out after several months. Intracutaneous applications of this compound did not produce local irritation of the tested tissue.

Cisplatin-induced tubular injury studied by water-soluble synthetic polymers.

Accumulation of a synthetic water-soluble polymer, poly-alpha, beta-[N(2-hydroxyethyl)-D,L-aspartamide-co-N(4-hydroxyphenethyl )- D,L-aspartamide] in the cells of kidney proximal tubules was used as an indicator for the functional localization of Cisplatin (CDDP) induced tubular injury in rats. Tubular accumulation of polymer was examined using 131I and fluorescence labelling for quantitative as well as morphological evaluation. It was found that reabsorption of the polymer, in which mainly the epithelium of proximal convolutions is involved, remains unaffected upon CDDP treatment in the course of one to six days after the drug administration. This finding supports on the functional level the morphological localization of CDDP injury into the straight segment of the proximal tubule.

Evaluation of infusion sets by biological and chemical testing.

Some of the biological and chemical tests used in toxicological evaluation of synthetic polymers were correlated. The individual tests (sperm cell motility, tissue culture inhibition, intracutaneous test, optical absorption at 220-360 nm, reducing impurities) did not mutually correspond. The final estimation of the tested device is assessed as a sum of these units. Therefore, it is necessary to evaluate the results of the individual tests in arbitrary units.

The use of 99Tc-pyrophosphate for imaging and measuring of calcification caused by implanted polymers.

Pyrophosphate labeled with 99Tc was evaluated as an indicator of the calcification which occurs after implantation of polymeric materials in rats. Poly(2-hydroxyethyl methacrylate), both porous and homogeneous, had been implanted. 99Tc pyrophosphate was applied intravenously to rats in intervals from 14 days to 15 months. Scintigraphy, x-ray examination, and histology were carried out. The ratio of specific activity in the capsule around the implant to specific activity in the reference tissue was determined. The cumulation of activity was parallel with the development of calcification as revealed by histology. The method can be used not only in the screening test of new polymeric materials, but also in a quantitative determination of the degree of calcification in general.

On the question of biological control methods for plastic materials.

Biological and chemical testing of plastic materials and devices needs the extraction of the analyzed sample. Polyamide was used as the model material and various effects of the extraction conditions on some biological (intracutaneous irritation, rat heart in situ, blood pressure on rats) and chemical (mass of the residue after evaporation) tests were studied. The material was extracted at 120, 55 and 37 degrees C for 0.5, 72 and 504 hr, respectively. Moreover, the polyamide was extracted at 120 degrees C for 5, 10, 15, 20, 25, 30, 60 and 120 min. Extracts were evaporated on the water bath. The increasing extraction period at 120 degrees C resulted in the increase in values of intracutaneous irritation as well as the residue mass after evaporation and in the decrease of rat heart amplitude and frequency. It was found that the extraction conditions at different temperature mentioned above were not equivalent. Various methods of extract concentration were also tested. Extracts evaporated at 35 degrees C in vacuo decreased the blood pressure more than those evaporated in the water bath.