PubMed · 2670430
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H Klinkmann, D Falkenhagen, S Stefoni, V Bonomini. 1989. Biocompatibility: a systems approach.. https://doi.org/10.1159/000416926
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Using one parametric variation in solution composition, this paper documents that the surface reactions on bioactive glass (BG) 45S5 are exquisitely dependent upon the modeling conditions. The solutions used were 0.05 M tris hydroxymethyl aminomethane/HCl (tris buffer), tris buffer complemented with plasma electrolyte and/or serum, and serum. The reacted surfaces were analyzed using Fourier transform infrared (FTIR), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDXA), and Rutherford backscattering spectroscopy (RBS). Post-immersion solutions were analyzed for changes in Ca and PO4 concentrations. After a short immersion (3 h), a crystalline, carbonated hydroxyapatite (c-HA) layer formed only in tris. Reaction surfaces of different structure, morphology, and composition were observed after various short and longer term immersions in all other solutions. They comprised two layers with the layer in contact with the bulk consisting mainly of Si; the outer layer, composed of Si, Ca, and P, was amorphous, and had a Ca/P ratio of about 1. Serum proteins adsorbed on the BG surfaces at the early stages of the solution-mediated BG reactions. Formation of a crystalline c-HA layer was delayed up to three or more days in solution with plasma ions. In the presence of serum, only amorphous surfaces composed of Si, Ca, and P were observed for any time up to seven days of immersion. The present data suggest that serum proteins adsorb in tandem with the occurrence of solution-mediated reactions leading to formation of a silica-gel. Amorphous Ca-P phases accumulate in the Si-rich matrix. Furthermore, the present data, in conjunction with the data published before, suggest that physicochemical and cell-mediated reactions occur in parallel to form the glass-tissue interfacial layer.
In order to provide a fixation vehicle between a polymeric composite femoral hip prosthesis and bone tissue, we fabricated bioactive glass fibers. The glass fibers had a tensile strength of 596 MPa, 14 times that of bulk bioactive glass. After immersion in protein-free simulated body fluid for 10 days, we observed the development of a calcium phosphate layer (specifically, partially crystallized, calcium-deficient carbonated hydroxyapatite) on the surface of the glass fibers. The stages of the surface reaction layer formation were similar to those of 45S5 bioactive glass although the kinetics of the reaction layer formation were slower. We combined the bioactive glass fibers with a polymeric matrix to form a fiber-reinforced composite material and observed the formation of a calcium phosphate layer on the surface of the glass fibers within the composite material after immersion in both protein-free and protein-containing simulated body fluids. The rate of reaction layer formation was reduced in the presence of proteins. In both protein-free and protein-containing solutions, a "halo" of bioactivity reactions was observed on the surface of the polymer in regions surrounding the glass fibers. Our results suggest these glass fibers and glass fiber composites will exhibit bioactivity reactions in vivo.
As part of ongoing investigations into the biological degradation of biomaterials, methods have been developed to isolate and chemically analyze polymer biodegradation products. The use of these methods can provide information on the biodegradation product profiles and yield concentration levels for the isolated products. The latter information is required to assess the toxicological nature of biomaterials and their related degradation products. In this study a model biomedical polyurethane was synthesized with toluene diisocyanate, polyester diol and ethylene diamine, and then incubated at 37 degrees C in a biological solution containing enzyme. The biodegradation products were isolated from the in vitro system and prepared for HPLC analysis, by using a combination of ultrafiltration, freeze drying and liquid-solid extraction. The ultrafiltration and the liquid-solid extraction effectively removed protein contamination. The separation of more than 20 degradation products, with gradient HPLC, was optimized using a photodiode array detector. The separated degradation products were identified using a tandem mass spectrometer. The model polyurethane was labeled with 14C in different segments, in order to assist in confirming the efficiency of the sample preparation and isolation methods. A detection limit of 2 ng was found. No toluene diamine - a suspected human carcinogen associated with some medical implants - could be found in the test samples. This represents a significant finding since the amount of this injected sample actually contained a total of 28 microg of degradation products isolated from the incubation medium.