Preparation and characterization of calcium sulfate-biomimetic apatite nanocomposites for controlled release of antibiotics.

In the present study, release properties of antibiotic-loaded cement-type nanocomposites of biomimetic apatite and calcium sulfate were studied. Nanocrystalline component of the nanocomposite was synthesized by soaking a mixture of calcium phosphate reactants in tris-buffered simulated body fluid (SBF). The release patterns of cephalexin and gentamicin from both pure calcium sulfate and nanocomposite cements into SBF were collected up to 144 h and fitted by Higuchi and Weibull equations. The effect of loaded antibiotics on physical properties of the cements was also evaluated. Fast release behavior of both antibiotics was obtained from calcium sulfate matrix, in which 80-85% of the loaded antibiotics were liberated during the first 10 h of elution. In contrast, an administered elution was acquired from nanonocomposite materials so that the release was controlled, in all cases, by a combined mechanism; major mechanism was drug diffusion through the matrix and the minor was matrix dissolution. The results showed that the initial setting time and injectability of cements were increased from 7 min and 71% for pure calcium sulfate cement (powder-to-liquid ratio = 2.5 g/mL) to 33 min and 95% for the nanocomposite cement containing 60 wt % apatite, respectively. The compressive strength of nanocomposite was about 0.9 MPa, nearly four times lower than that of pure calcium sulfate. In addition, the use of cephalexin monohydrate did not influence the setting time and compressive strength of the cements, whereas (adding) gentamicin sulfate significantly improved these properties.