Stiff and bioactive composites based on starch, polyethylene and SiO_2-CaOP_2O_5-MgO glasses and glass-ceramics

摘要

This study evaluated the possibility of creating new stiff and bioactive composites based on both: (i) novel biodegradable starch based polymers (starch/ethylene-vinyl alcohol blends -SEVA-C), and (ii) high molecular weight polyethylene (HMWPE), for temporary and permanent applications respectively. Both polymers were reinforced with bioactive glasses (BGE1) and glass-ceramics (BGE1C), with 90percent of the particles below 10 mu m in the SiO_2-3CaOP_2O_5-MgO system. These fillers were incorporated, in weight fractions up to 40percent wt. into both types of matrixes. The composites were compounded by twin-screw extrusion (TSE) and then injection moulded. The mechanical properties of the composites were evaluated in tensile tests, and their bioactivity was assessed by analysing the respective surfaces (SEM/EDS) after different immersion periods in a simulated body fluid (SBF). Ca, P, Si and Mg concentrations were followed vs. time by induced-coupling plasma (ICP) spectroscopy, and x-ray diffraction (XRD) was used to identify the crystalline phases present on the films formed at the materials surfaces. The obtained results indicated that the modulus of the composites increased for higher amounts of BGE1 and specially BGE1C, while the strains at break decreased. For the BGE1C filler it was possible to produce composites matching the stiffness of human cortical bone. The bioactivity of SEVA-C composites become relevant for BGE1 amounts of only 20percent wt., for immersion periods higher than 30 days. On the contrary, for the HMWPE matrix composites weight fractions of at least 40percent wt. were necessary to confer a bioactive character to the composites.