Hydroxyapatite (HA) powder was treated with different silane adhesion promoters, to optimize its performance as a filler in polymer composites. The silane coupling agents investigated possessed vinyl, methacryloxy, primary amine, secondary amine, and diamine functionality. The different coatings were evaluated with respect to their influence on ionic exchange. X-ray photoelectron spectroscopy revealed the presence of a few monolayers thin silane films on HA powder. Silane coupling agents were able to bond chemically on the HA surface because a thin coating remained after washing of the powder with water. The water stability of this bond was evaluated by successive extractions and was judged limited, especially in the case of the hydrophilic aminosilanes. Zeta-potential measurements indicated the "transparency" of the coatings for ionic transport, that was corroborated by two in vitro dissolution studies, in Gomori's Tris-maleate buffer, and in simulated body fluid. However, aminosilane coatings could delay the release of calcium and phosphate ions during the first 2 days of immersion of treated HA powder in Gomori's buffer.
This study reports in vitro biocompatibility screening of different kinds of silane-treated hydroxyapatite (HA) powders, for use as modified filler in resorbable composite. The silane coupling agents investigated were all methoxysilanes, with either vinyl (VS), or methacryloxy (MPS), or primary amine (AMMO), or secondary amine (TRIAMO), or diamine (DAS) functionality. Evaluation of cell adhesion on the different silanized HA surfaces, indirect agar-overlay test and direct contact test on extracts showed the acute toxicity of all five free silane agents, the innocuity of strongly adsorbed silane molecules on HA surfaces and the dose-dependent toxicity of leachable silanol molecules.
Biphasic calcium phosphate particles (BCP), alone or combined with a cellulosic ether vehicle in an injectable composite material (COMP), were implanted in femurs of rabbits. The long-term follow-up (up to 78 weeks) indicated: (1) BCP and COMP induced a foreign-body inflammatory reaction but without fibrous encapsulation. Phagocytosis was mediated by mononucleated macrophages (MC) and giant multinucleated cells (GMNC). Phagocytosis was stronger with COMP and required the recruitment of GMNC while it primarily involved MC in the case of BCP. (2) There appeared to be no significant difference between the bone ingrowth in the defects packed with BCP (dBCP) and in those filled with COMP (dCOMP). Bone reconstruction mostly was achieved after 4 weeks in dBCP but took more time to reach the center of dCOMP. High bone remodeling was observed at the last evaluation times, especially in the case of COMP. (3) Degradation of the materials occurred mainly during the first 4 weeks and was more severe for COMP, which probably was related to the smaller granulometry of its mineral phase. Cell-mediated degradation went on for the 78 weeks and followed two processes: phagocytosis and/or extracellular dissolution of the calcium phosphate particles.
The results of microscopic and spectroscopic analysis of a mixture of biphasic calcium phosphate (BCP) powder and cellulose ether aqueous sol are reported in this study. This new composite is injectable and is aimed to be used as bone substitute for spine surgery. The influence of the polymer on the physico-chemical properties of BCP was investigated by complementary techniques such as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), infrared and Raman spectroscopies and X-ray photoelectron spectroscopy (XPS). When brought into contact with the polymer solution, the ceramic is modified in its granulometry, crystallinity, and surface chemistry. A dissolution/precipitation reaction occurs, leading to a phosphorus-rich and amorphous outer layer of the ceramic surface. Moreover, the bonding state of the composite involves new features that could be assigned to calcium complexes (calcium carbonate or calcium hydroxide).
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