Incorporation of tobramycin into biomimetic hydroxyapatite coating on titanium

Calcium phosphate coatings containing an antibiotic were produced on titanium alloy (Ti6Al4V) implants using a biomimetic approach. Thin, amorphous calcium phosphate (ACP) coatings were first deposited onto Ti6Al4V plates by immersion in 5 times concentrated simulated body fluid (SBF), for 24 h at 37°C. The ACP-coated implants were then immersed in a supersaturated calcium phosphate (SCP) solution containing 0, 100, 200, 400, 600 or 800 mg/l of tobramycin for 48 h at 37°C. A carbonated hydroxyapatite (CHA) layer, approximately 40 μm thick, was formed. Approximately 3 μg/mg of tobramycin was co-precipitated with the CHA crystals onto titanium alloy plates, using 800 mg/l tobramycin in the coating solution. For comparison, plasma-sprayed calcium phosphate coatings were also immersed in solutions containing 100, 200, 400 or 1000 mg/l of tobramycin for 10, 40 min, or 48 h. A maximum of about 0.3 μg/mg could be adsorbed onto the plasma-sprayed calcium phosphate coating with the comparable concentration of 800 mg/l in solution. The dissolution of coating and release of tobramycin were also measured in vitro using saline solution buffered at pH 5.0 or 7.3 at 37°C. The release rate of tobramycin was faster at pH 7.3 than at pH 5, with 50 and 4 μg/ml/min, respectively. Tobramycin released from the biomimetic-coated plates could inhibit growth of Staphylococcus aureus bacteria. The result of this study, therefore, indicates that the biomimetic CHA coatings containing antibiotics could be used to prevent post-surgical infections in orthopaedic or trauma.