Effect of geometrical structure on drug release rate of a three-dimensionally perforated porous apatite/collagen composite cement

To improve the biocompatibility, inter-connective pore structure, and drug delivery ability of self-setting apatite/collagen composite cement (ACC), a three-dimensionally perforated porous apatite/collagen composite cement (TPPACC) containing 3% indomethacin (IMC) was obtained in an arranged multi-cross with 20, 40, and 60 stainless steel needlelike male dies, and stored and hardened at 37°C and 100% relative humidity for 24 h. The mean radius of micro-pores of the TPPACC was evaluated to be 0.125 µm by mercury porosimetry. X-ray powder diffraction and FT-IR spectroscopy suggested that TPPACC consisted of carbonated apatite and had a structure similar to that of natural rat bone. The IMC release rates from a TPPACC block containing the drug were measured in simulated body fluid. The rate of release increased with the number of macro-pores that from planar surface matrix systems followed the Higuchi equation. The relationship between the Higuchi constant and surface area of TPPACC showed a straight line with K = 0.2123 and R2 = 0.9892. These results indicated that the rate of drug release from TPPACC could be controlled by the number of macro-pores for bone cells. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:286-292, 2010