Cross-linking of amniotic membranes.

Human amniotic membrane was cross-linked with chemical and radiation methods to investigate the effect of cross-linking on its physicochemical and biodegradation properties. Radiation cross-linking was performed with gamma-ray and electron beam while chemical cross-linking was with glutaraldehyde (GA). Both gamma-ray and electron beam irradiation decreased the tensile strength and elongation at break of the amniotic membrane with an increase in the irradiation dose, whereas GA cross-linking had no effect on the tensile properties. This is probably due to the scission of collagen chains through irradiation. No significant change was observed on the water content of cross-linked amniotic membranes for any of the crosslinking methods and in marked contrast with cross-linking of a gelatin membrane. A permeation study revealed that protein permeation through the amniotic membrane was not influenced by the GA concentration at cross-linking. These findings are ascribed to the structure characteristic of the amniotic membrane. The membrane is composed of a fibrous mesh structure from an assemblage of collagen fibers. It is possible that cross-linking takes place in the interior of the fiber assembly without impairing the mesh structure, resulting in no change of the water content and protein permeability. In vitro degradation of cross-linked amniotic membranes revealed that radiation cross-linking appeared to be much less effective than GA cross-linking in retarding the degradation, probably because of low cross-linking densities. GA-cross-linked amniotic membranes were degraded more slowly as the GA concentration at cross-linking increased. When the GA-cross-linked amniotic membrane was subcutaneously implanted in the rat, the tissue response was mild, similar to that of the non-cross-linked native membrane.

[Biocompatibility testing and function of a pancreatic prosthesis consisting of viable pancreatic islets encapsulated in PVA macrocapsules]. / Badanie biokompatybilnosci i funkcjonowania protezy wewnatrzwydzielniczej czesci trzustki, wykonanej z zasiedlonych zywymi wyspami trzustki makrokapsulek PVA.

The application of semipermeable membranes for immunoisolation of living pancreatic islets is an interesting alternative for treatment in diabetes mellitus patients. The aim of this work was in vivo evaluation of biocompatibility of poly(vinyl alcohol) (PVA) macrocapsules and of the polyethylene foil itself as well. To establish the value of the artificial prosthesis made from settled with viable pancreatic islets (PVA) macrocapsules the glucose plasma levels were analyzed versus time after implantation into peritoneal cavity of rats with alloxane-induced diabetes. The results of the experiment revealed the progressive disadvantageous alterations of PVA hydrogel membrane resulting in decrease of permeability of albumin and glucose. The histologic examination of the cellular enzyme activities to estimate the intensity of inflammation in surrounding tissues showed changes typical or chronic proliferative inflammation. The correct function of artificial prosthesis of the pancreas manifested in normalization glucose plasma level has been observed for from 14 to 42 days after implantation.

Long-term in vivo performance and biocompatibility of poly(vinyl alcohol) hydrogel macrocapsules for hybrid-type artificial pancreas.

A bag-shaped macrocapsule suitable for Langerhans islets entrapment and immunoisolation was constructed using a semipermeable hydrogel membrane of poly(vinyl alcohol)(PVA) cross-linked chemically and sterilized by a radiation method. Empty (not seeded with Langerhans islets), sealed, sterile macrocapsules were implanted into the intraperitoneal cavity of adult female Buffalo rats for periods of up to 6.5 months. Long-term in vivo performance of the macrocapsule membrane was evaluated on the basis of the permeability measurements of glucose and albumin. The results of experiments revealed the progressive, disadvantageous alterations of the PVA hydrogel membrane resulting in a decrease in the permeability of solutes. Histochemical examinations of the cellular enzyme activities in the implant-encapsulating tissue, regarding the acid and alkaline phosphatases, were performed to evaluate the activity of cells involved in the inflammatory response to the long-term macrocapsule implantation.

Protein permeation through poly(vinyl alcohol) hydrogel membranes.

Hydrogel membranes were prepared by radiation and chemical cross-linking of poly(vinyl alcohol) (PVA) in aqueous solutions. Effects of PVA concentration, PVA molecular weight and radiation dose, as well as concentration of cross-linking agent, in the case of the chemical cross-linking procedure, on the permeation of insulin, albumin and immunoglobulin (IgG) through the membranes were investigated. Glucose permeation was also studied. The cross-linking density affected the size of the macromolecular mesh of the hydrogel network and thus the water content of the membrane responsible for the diffusion of the solutes. The diffusion coefficient linearly increased for all the solutes with increasing water content in the PVA hydrogels, indicating that diffusion occurs primarily through the water hydrating the polymer network. The permeability study showed that the water content as well as the mesh size had an influence on the diffusion of low molecular weight glucose and insulin. Although the diffusion of higher molecular weight solutes, such as albumin and IgG, was not so much affected by the mesh size of elaborated PVA hydrogel membranes, the diffusion of these proteins was very low.

[Polymeric materials for biomedical purposes obtained by radiation methods. V. hybrid artificial pancreas]. / Materialy polimerowe do celów biomedycznych otrzymywane metodami radiacyjnymi V. hybrydowa sztuczna trzustka.

The authors present a review of works done on the elaboration of a hybrid-type artificial pancreas. The article discusses construction designs, applied polymeric materials as well as biocompatibility problems of polymeric membranes that encapsulate the Langerhans islets. On example of hydrogel membranes prepared by radiation crosslinking of poly(vinyl alcohol) (PVA) the dependence of the diffusion coefficients of glucose, insulin and immunoglobulin G on the crosslinking degree of hydrogels has been shown.

Insulin release from a bioartificial pancreas using a mesh reinforced polyvinyl alcohol hydrogel tube. An in vitro study.

Islet transplantation with a bioartificial pancreas is a potential alternative to whole pancreas transplantation. The authors constructed a bioartificial pancreas using mesh reinforced polyvinyl alcohol hydrogel tubes (MRPT), in an attempt to clarify the in vitro responsiveness to glucose of islets seeded in the MRPT. When the MRPT were perfused in a small chamber with buffer containing 3.3 mmol or 16.7 mmol glucose, insulin release from the MRPT began to increase at 9 +/- 3 min, reaching a plateau at approximately 40 min after the glucose concentration in the perfusate increased from 3.3 to 16.7 mmol. When MRPT seeded with islets were subjected to static incubation in buffer containing 3.3 mmol or 16.7 mmol glucose, insulin release from the MRPT remained elevated for 3 hr of high glucose stimulation, the amount of secreted insulin depending upon the number of islets seeded. Although pre incubation of semipermeable membranes in culture medium containing fetal bovine serum prior to seeding with islets has recently been reported to improve insulin release, the authors found that such pre treatment of the MRPT did not have a beneficial effect. Their in vitro findings in this study suggest that the bioartificial pancreas using MRPT could be a promising therapeutic approach to human diabetes mellitus.

Experimental hybrid islet transplantation: application of polyvinyl alcohol membrane for entrapment of islets.

In this study, we first examined in vitro a polyvinyl alcohol membrane to be used to contain hybrid islet cells, and second we tested a bioartificial pancreas with entrapment of pancreatic islets in polyvinyl alcohol membrane in rats with experimentally induced diabetes. The permeability of the polyvinyl alcohol membrane to different substances was studied in a two-cell chamber system. Glucose, insulin, and nutrients passed through the membrane easily, whereas the passage of immunoglobulin G was completely prevented, indicating that this membrane could be effective in protecting the bioartificial pancreas from immunorejection. Approximately 2,000 islets collected from three Sprague-Dawley rats were enclosed in a mesh-reinforced polyvinyl alcohol tube and transplanted into the peritoneal cavity of six Wistar rats with streptozotocin-induced diabetes. Their nonfasting serum glucose levels were significantly decreased for at least 12 days. Six diabetic rats receiving intraperitoneal transplantation of free islets without the tube showed a slight but significant decrease in nonfasting serum glucose levels for only 3 days. One diabetic rat with transplantation of the bioartificial pancreas had a significant and sustained decrease in nonfasting glucose levels from pretransplanted levels of 440-500 mg/dl to a mean value of 162 +/- 13 mg/dl for over 3 months without immunosuppression. The bioartificial pancreas was then removed, and glucose levels gradually increased to over 500 mg/dl. The results of the present study suggest that a bioartificial pancreas with entrapment of islets in a polyvinyl alcohol membrane could be a promising therapeutic approach to diabetes mellitus.

[Polymer materials for biomedical use obtained by radiation methods. III. Radiation cross-linking of acrylamide and N-vinylpyrrolidone]. / Materialy polimerowe do celów biomedycznych otrzymywane metodami radiacyjnymi. III. Sieciowanie radiacyjne akryloamidu i N-winylopirolidonu.

The course of the radiation formation of hydrogels in aqueous solutions of acrylamide and N-vinylpyrrolidone was investigated on the base of gel-sol analysis. Using relations from Inokuti's equation as a test of crosslinking mechanism it was pointed out that creation of gels takes place according to classical mechanism e.g. through four-functional joining points. In the systems containing oxygen gel formation results from simultaneous crosslinking and degradation. On the base of swelling measurements of gels (ROCH method) the yields of radiation processes were calculated. Using a method of pulse radiolysis the absorption spectra of macroradicals were recorded, their structures discussed and the rate constants of crosslinking estimated.

[Polymer materials for biomedical purposes obtained by radiological methods. II. Radiation polymerization of acrylamides and N-vinylpyrrolidone]. / Materialy polimerowe do celów biomedycznych otrzymywane metodami radiacyjnymi. II. Polimeryzacja radiacyjna akryloamidu i N-winylopirolidonu.

The radiation polymerization of acrylamide and N-vinylpyrrolidin-2-one in aqueous solutions has been investigated. The effect of the monomer concentration as well as the dose rate of the ionizing radiation on the process has been determined. The radical mechanism of the polymerization process has been confirmed experimentally. The effect of the individual transient species of the water radiolysis on the initiation of the polymerization process as well as the changes of the molecular weights of the arising polymers have been investigated. The dependence of the galation dose of the system on the monomer concentration has been determined.

[Packaging in the process of radiation sterilization. II. Physicochemical studies]. / Opakowania w procesie sterylizacji radiacyjnej. II. Badania fizykochemiczne.

The penetrability of the ionizing radiation through the matter makes possible the sterilization of the medical devices in the packed form by radiation method. The effect of the radiation should not bring any destructive changes in the material used for the package. In this paper have been discussed the results of the investigations of the one--and multilayer packaging materials from the point of view their utility for the radiation sterilization purposes. The changes of the useful parameters of the investigated materials have been determined in the dependence on the absorbed dose immediately after irradiation and the period of the durable keeping after the sterilization. The results of the mechanical investigations in the correlation to the results of the microbiological effects of the sterilized materials enabled to draw practical conclusions concerned the usability of the particular packages.

[Sterilization of packages using radiation. I. Microbiological studies]. / Opakowania w procesie sterylizacji radiacyjnej. I. Badania mikrobiologiczne.

Utilization of ionizing radiation for the sterilization purposes enables the sterilization of dressing materials in packed form together with the protecting packages. This procedure secures advantageous conditions for prolongation of storage time of manufactured articles in the sterile state. In this work the results of six years investigations dealing with the sterility of dressings sterilized by 60Co gamma-irradiation and packed in one--and multilayer packaging materials were shown. After sterilization those materials were storaged in various temperature conditions.

Radiation sterilization of cellulose dressing materials.

The results of investigations in the field of application of 60 Co gamma-irradiation for sterilization of cellulose dressing materials have been presented on the ground of our own experiments. The investigations were carried out for the model objects which are contents of all dressing materials, nowadays used in medical practice: cotton gauze, viscose-cotton gauze, cotton wool and cotton-viscose wool. In the present report there have been discussed the results of the test estimation of sterilized materials immediately after irradiation and during long storage as well (3-5 years after irradiation). The estimation was carried out according to the requirements of Pharmacopoeia. Moreover, the choice of parameters of sterilization process from the view-point of microbiological experiments and estimation of initial contamination degree of irradiated materials have been discussed.