In vivo degradation of processed dermal sheep collagen evaluated with transmission electron microscopy (original) (raw)

The in viva degradation of hexamethylenediisocyanate-tanned dermal sheep collagen was studied with transmission electron microscopy. Discs of hexamethylenediisocyanate-tanned dermal sheep collagen were subcutaneously implanted in rats. Both an intra-and an extracellular route of degradation could be distinguished. In addition to normal components of a typical foreign body reaction, remarkable phenomena, such as locally deviant neutrophil morphology, infiltration of basophil-like cells, indications of foreign body multinucleate giant cells formed from different cell types, aluminium silicate accumulations and calcium phosphate depositions, were observed. Foreign body multinucleate giant cells intracellularly degraded hexamethylenediisocyanate-tanned dermal sheep collagen after internalization. Both internalized and cellularly enveloped hexamethylenediisocyanate-tanned dermal sheep collagen degraded by the detachment of fibrils. Another extracellular route of degradation was characterized by calcium phosphate depositions in large bundles of hexamethylenediisocyanate-tanned dermal sheep collagen. From 6 wk. the hexamethylenediisocyanate-tanned dermal sheep collagen implant was replaced by rat connective tissue, which was subsequently also degraded. After 15 wk. the presence of basophil-like foreign body multinucleated giant cells containing aluminium/silicon-crystalline accumulations still persisted. These phenomena were related to the specific nature of the material used and suggest cytotoxicity. They emphasize the need for detailed evaluation at the ultrastructural level of newly developed biomaterials before they can be used for medical applications. Various collagen-based biomaterials have found applications in the biomedical fieldlm3. Interactions between such biomaterials and tissue have been extensively described4-6. However, these reports predominantly concern light microscopy evaluations. In our opinion, more detailed knowledge of the cellular events is needed for a better understanding and further improvement of the function of collagen-based biomaterials. In this study, we used hexamethylenediisocyanate-tanned dermal sheep collagen (HDSC), which was subcutaneously implanted in rats. The material is successfully Correspondence to Dr P.B. van Wachem @ 1991 Butterworth-Heinemann Ltd. 0142-9612/91/020215-09 used as a biological wound dressing'. It was tested in rabbits both after intramuscular implantation of small pieces' and after intracutaneous injections of extracts9 in accordance with US Pharmacopeia XXI (1985). The light microscopy evaluation of the intramuscular implantation test showed a very slight toxic reaction. No adverse reactions related to the material were observed in the intracutaneous injection test. Referring to the very slight toxic reaction observed in the intramuscular implantation test, it was the aim of this study to evaluate the degradation of HDSC in detail using transmission electron microscopy (TEM). . The material was processed from sheep skin, which was depilated, immersed in a lime-sodium sulphide solution for removal of the epidermis and purified with proteolytic enzymes7. The skin was then split with an industrial band-knife splitting machine to obtain the dermal layer. This layer was then tanned with HMDIC (Desmodur@ obtained from Bayer, Germany). Discs with a diameter of 8 mm were punched from HDSC. The weight of the discs varied from 15 to 30 mg. Discs were sterilized by gamma irradiation (2.5 Mrad, Gammaster, Ede, The Netherlands). Implantations. A0 rats of approximately 3 month of age Si were used. The rats were ether anaesthesized, their backs I were shaved and their skins disinfected with ethanol. Two midline incisions were made. Subcutaneous pockets were made with surgical scissors at the right and left sides of each incision. Four HDSC discs per rat were implanted in the pockets at a distance of about 1 cm from the incisions.