Hydroxyapatite/poly(ethylene glutarate) (HAp/PEG) biomaterial composites were prepared by ring-opening polymerization (ROP) of cyclic oligo(ethylene glutarate) (C-PEG) in porous HAp scaffolds. The HAp/C-PEG precomposites were prepared by immersing the porous HAp scaffolds in the mixture solution of C-PEG and dibutyl tinoxide catalyst overnight and polymerizing at 200 degrees C for 24, 48, and 72 h under vacuum. The successful ROP of C-PEG in the porous HAp scaffolds was corroborated by the signals of hydroxyl end-group of PEG shown in the (1)H NMR spectrum of the ROP-products extracted from the composites. PEG in the composites was present as a thin layer coating on the HAp grains and was evenly distributed throughout the samples. The PEG content was about 13-16 wt % and decreased with increasing polymerization time. Its molecular weight (M(w), weight average) measured by gel permeation chromatography was in the range of 4300-6800 g/mol. Compressive strength of the HAp/PEG composites was significantly increased from 3 MPa of the porous HAp scaffold to 11-15 MPa, depending on the PEG content in the composites. In vitro bioactivity of the HAp/PEG composites was studied by soaking in simulated body fluid (SBF) at 36.5 degrees C for 7-28 days. After prolonged soaking, the HAp nanocrystals precipitated from the SBF solution and formed as a layer of globular aggregates, coated on the composite surfaces. This result suggested that the HAp/PEG composite was a bioactive material.

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A study of the influence of filler volume fraction on the strain-rate dependence of CaCO 3 -reinforced polyethylene was carried out. Tensile tests were done at different strain rates ranging from 0.008 to 2.0 min Ϫ1 , whereas the CaCO 3 amount was varied from 0.10 to 0.40. In the range of strain rates in this study, it was found that increasing strain rate generally increased yield stress and Young's modulus, but decreased yield strain for both unfilled and filled polyethylene. The increase in the filler volume fraction resulted in the decrease in the degree of strain-rate dependence of yield stress and strain. The decrease in strain-rate dependence of the composite changed into strain-rate independence when the filler content was beyond 0.20, and more pronounced at a high strain rate than a low strain rate.

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