Preparation and characterization of hydroxyapatite/poly(ethylene glutarate) biomaterials

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.