Claudia I. Vallo

Polymethylmethacrylate-based bone cement modified with hydroxyapatite.

A commercial acrylic bone cement was modified by the incorporation of different weight fractions of polycrystalline hydroxyapatite (HA), and the modified formulation was investigated. The influence of the filler proportion on the flow characteristics and the mechanical behavior of the resultant composite was evaluated. The residual monomer present in the cured materials was measured by gas chromatography. The comparison of the residual monomer present in the cements with and without reinforcement demonstrated that the degree of polymerization was not affected by the addition of HA. Porosity morphology was analyzed by optical and scanning electron microscopy. Image examination revealed that the porosity and the pore size of the hardened cement increased with an increasing amount of particulate filler. Flexural, compressive, and fracture properties of the cement with varying amounts of HA reinforcement were measured. It was found that up to 15 wt% HA could be added for increases in flexural modulus and fracture toughness. HA acts as a rigid filler that enhances fracture resistance and flexural modulus. Our results show that the workability of the modified formulation limited the incorporation of the ceramic filler to a maximum value of 15 wt%.

Polymerization of methacrylate resins photoinitiated by camphorquinone and bulky amine-functionalized silsesquioxanes

Polyhedral oligomeric silsesquioxanes (SSQO) functionalized with bulky amino groups were prepared by a two-stage synthesis procedure. In a first stage, a modified organotrimethoxysilane was synthesized by reacting 1xa0mol of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane with 3xa0mol of 1,2-epoxy-3-phenoxypropane. The second stage consisted of the hydrolytic condensation of the modified silane catalyzed by formic acid. Methacrylate resins were activated for visible light polymerization by the addition of camphorquinone (CQ) in combination with different mass fractions of SSQO. The progress of monomer conversion versus irradiation time showed that the CQ/SSQO pair is an efficient photoinitiator system because a fast reaction and high conversion results from 60xa0s irradiation at 600xa0mW/cm2. The SSQO were incorporated up to 22xa0wt% in the methacrylate resin without compromising the flexural or the compressive properties of the final material.