Synthesis, characterization, bioactivity and biocompatibility of nanostructured materials based on the wollastonite-poly(ethylmethacrylate-co-vinylpyrrolidone) system.

Composite materials are very promising biomaterials for hard tissue augmentation. The approach assayed in this work involves the manufacturing of a composite made of a bioactive ceramic, natural wollastonite (W) and a nanostructured copolymer of ethylmethacrylate (EMA) and vinylpyrrolidone (VP) to yield a bioresorbable and biocompatible VP-EMA copolymer. A bulk polymerization was induced thermally at 50 degrees C, using 1 wt % azobis(isobutyronitrile) (AIBN) as free-radical initiator. Structural characterization, compressive strength, flexural strength (FS), degradation, bioactivity, and biocompatibility were evaluated in specimens with a 60/40 VP/EMA ratio and ceramic content in the range 0-60%. A good integration between phases was achieved. Greater compression and FS, in comparison with the pure copolymer specimens was obtained only when the ceramic load got up to 60% of the total weight. The soaking in NaCl solution resulted in the initial swelling of the specimens tested. The maximum swelling was reached after 2-3 h of immersion and it was significantly greater for lower ceramic loads. This result makes the polymer component the main responsible for the interactions with the media. After soaking in SBF, microdomains segregation can be observed in the polymer component that can be related with a dramatic difference in the reactivity of both monomers in free radical polymerization, whereas the formation of an apatite-like layer on the W surfaces can be observed. Biocompatibility in vitro studies showed the absence of cytotoxicity of all formulations. The cells were able to adhere on the polystyrene negative control and on specimens containing 60 wt % wollastonite forming a monolayer and showing a normal morphology. However, a low cellular growth was observed.