Surface-modified hydroxyapatite linked by L-lactic acid oligomer in the absence of catalyst

A new surface modification method of hydroxyapatite nanoparticles (n-HA) by surface grafting reaction Of L-lactic acid oligomer with carboxyl terminal (LAc oligomer) in the absence of any catalyst was developed. The LAc oligomer with a certain molecular weight was directly synthesized by condensation Of L-lactic acid. Surface-modified HA nanoparticles (p-HA) were attested by Fourier transformation infrared spectroscopy, P-31 MAS-NMR, and thermal gravimetric analysis (TGA). The results showed that LAc oligomer could be grafted onto the n-HA surface by forming a Ca carboxylate bond. The grafting amount of LAc oligomer was about 13.3 wt %. The p-HA/PLLA composites showed good mechanical properties and uniform microstructure. The tensile strength and modulus of the p-HA/PLLA composite containing 15 wt % of p-HA were 68.7 MPa and 2.1 GPa, respectively, while those of the n-HA/ PLLA composites were 43 MPa and 1.6 GPa, respectively. The p-HA/PLLA composites had better thermal stability than n-HA/PLLA composites and neat PLLA had, as determined by isothermal TGA. The hydrolytic degradation behavior of the composites in phosphate buffered saline (PBS, pH 7.4) was investigated. The p-HA/PLLA composites lost their mechanical properties more slowly than did n-HA/PLLA composites in PBS because of their reinforced adhesion between the HA filler and PLLA matrix. (c) 2005 Wiley Periodicals, Inc.