High release of antibiotic from a novel hydroxyapatite with bimodal pore size distribution

We developed a novel hydroxyapatite (HA) cylinder (HA-A) and compared the slow release of antibiotic in vitro as well as osteoconduction of the material in vivo to a commercially produced porous hydroxyapatite cylinder (HA-B). HA-A (4 x 4 mm) was synthesized by mixing HA powder, gelatin, and vegetable oil. The material had a bimodal pore size distribution, with intragranular (10 nm to 10 microm) and intergranular (100 microm) pores, and porosity of 40 vol %, while HA-B had pore sizes ranging from 50 to 300 microm and identical porosity. In vitro drug release was tested using antibiotics (isepamicin sulfate, vancomycin hydrochloride, and flomoxef sodium) soaked on the HA cylinders using a vacuum system. The mean adsorption efficiency was higher for HA-A (46%) than for HA-B (26%) and higher levels of antibiotic were released from HA-A. Of the antibiotics, ISP showed the longest release duration. Bone ingrowth into the pores was observed for both materials. Because the novel HA showed both the slower release of antibiotic (nanosize pores) and supported excellent osteoconduction (microsize pores), it could be useful for the treatment of osteomyelitis.