Development of hydroxyapatite bone scaffold for controlled drug release via poly(epsilon-caprolactone) and hydroxyapatite hybrid coatings

Abstract

A scaffold-coating design, the hydroxyapatite (HA) porous bone scaffold coated with poly(epsilon-)caprolactone (PCL) and HA powder hybrids, was developed for use as tissue-regeneration and controlled-release system. An antibiotic drug, tetracycline hydrochloride (TCH), was encapsulated within the hybrid coating layer through a dip-coating and solvent-casting method. Coating cycle and drug loading amount differed to control the level of drug-release rate. The HA scaffold framework, obtained by a polymeric foam reticulate method, exhibited a highly porous structure, with porosity and pore size of approximately 87% and 180 microm, respectively. The hybrid layer, consisting of PCL sheet and HA fine powders, was uniformly coated on the scaffold surface. The coating layer exhibited only PCL and HA phases and structures, revealing no chemical interaction among the coating components, as observed by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses. The coated-HA scaffolds showed an effective stress distribution behavior in response to an applied load, as confirmed by the compressive stress-strain curve. The mechanical properties of the coated scaffolds were improved highly with coatings; the compressive strength and elastic modulus of the cyclic coated scaffolds were approximately 3-4 times, and the energy absorption were approximately 8 times, higher than those without coating. These improvements were attributed mainly to the shielding of framework flaws by a flexible coating layer and partially to the thicker stems (porosity reduction). The dissolution of the coated scaffolds in a phosphate-buffered saline (PBS) solution increased with incubation time. The drug was released sharply within the initial several hours ( approximately 2 h), but the rate decreased further, showing a sustained release. The release amount was well controlled via coating-cycle and initial drug loading amount, suggesting the effectiveness of the coating-scaffold design as a drug-delivery system.