Effect of a new surface-grafting method for nano-hydroxyapatite on the dispersion and the mechanical enhancement for poly(lactide-co-glycolide)

In this paper, a new surface-grafting D, L-lactide (DLLA) for nano-hydroxyapatite (n-HA) with the assist of citric acid was designed. The dispersion of new surface modified n-HA was characterized by Fourier transformation infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and dispersion test, and the mechanical enhancement effect for poly(lactide-co-glycolide) (PLGA) was evaluated by scanning electron microscopy (SEM), differential scanning calorimeter measurements (DSC) and electromechanical universal tester. The results showed that citric acid played a critical role in surface-grafting, which could greatly increase grafting amount and improve dispersion of n-HA, so that it resulted in better interfacial adhesion throughout PLGA matrix, higher crystallinity and better mechanical enhancement for PLGA than the surface-grafting method for n-HA without citric acid, whose bending strength and tensile strength were both over 20% higher than those of pure PLGA when 3 wt% n-HA was added, and it still enhanced 8 and 6% higher than those of pure PLGA even the introduction of 15 wt% n-HA, respectively. The above results suggested that the surface-grafting for n-HA with the aid of citric acid was an ideal novel surface modification method, which could greatly improve the dispersion of n-HA and exhibit excellent mechanical enhancement effect for PLGA, suggesting it has a great potential in the bone fracture internal fixation application in future.