Degradation of metal-labeled collagen implants: ultrastructural and X-ray microanalysis

Bioaccumulation and localization of exogenous cadmium in a teleost by electron microscopy (TEM) and its specific quantitation by electron probe X-ray microanalysis (EPMA)

A cadmium bioconcentration study was carried out in a fresh water teleost, Colisa fasciatus, to study the bioaccumulation kinetics and fate of exogenous cadmium (Cd) in biological tissues. Study shows that on exposure of the fish to a sublethal concentration of cadmium in test water, Cd uptake results in its bioconcentration in gills, liver and muscle tissues. To explore whether the accumulated Cd reaches the membranes or inside the cells, transmission electron microscopy (TEM) of the thin sections of tissues was done after histochemical localization of Cd in cells by modified SST method. TEM studies of sections of gills, liver and muscle tissues showed the deposits of exogenous Cd (visualized as dense clouds) in biological cells. This suggests the presence of free or loosely bound Cd on the membranes and inside the cells, which in the presence of Na2S is converted into insoluble metal sulfides. Electron probe X-ray microanalysis (EPMA) studies confirmed the presence of Cd on the membrane surface as well as inside the cells of bioindicator organs suggesting involvement of membrane transport of exogenous Cd inside the cells and its deposition as loosely bound insoluble metal complexes.

Inhibition of calcification in vivo by acyl azide cross-linking of a collagen-glycosaminoglycan sponge

A collagen-glycosaminoglycan sponge composed of collagen (80%), chondroitin-4-sulfate (13.3%) and heparan sulfate (6.6%) was cross-linked using the acyl azide method or glutaraldehyde (0.0075%). Under optimal conditions, the denaturation temperature (Td) was raised to 69 degrees C (+23 degrees C) for the sponge treated by the acyl azide method and to 68 degrees C (+22 degrees C) for that treated with glutaraldehyde. The biocompatibility of the treated and control sponges was studied up to 3 months after subcutaneous implantation in rats by analysing cellular responses and calcification by histological and ultrastructural methods. A control collagen-glycosaminoglycan sponge was rapidly invaded by mononuclear cells (8 days), with the formation of granulation tissue. Calcification was observed at the periphery of the implant after 8 days, and the implant was entirely calcified after 15 days; it was degraded progressively after 30 days. Acyl azide treatment increased the persistence of the sponge in vivo up to 90 days and inhibited its calcification. A glutaraldehyde-treated sponge was completely calcified after 15 days, and calcified nodules persisted after 90 days. Thus, acyl azide method efficiently cross-linked a collagen-glycosaminoglycan sponge and inhibited calcification after subcutaneous implantation in rats (at least up to 90 days after implantation).