Electrochemically assisted deposition of nanostructured hydroxyapatite coatings as a novel method to prepare drug-eluting devices

Controlled drug delivery implies the ability of controlling the distribution of biologically active molecules both in space and time: it embodies both control of drug release rate, and the delivery of this drug to a specific body organ or tissue. This research effort finds interesting applications in medical devices such as ceramic coated metallic implants or drug-eluting stents which nowadays work by a drug loaded polymer coating their metallic surface. In order to overcome problems deriving from the in vivo polymers degradation there is at least theoretical advantage of materials that are derived from, or adequately mimic substances endogenous to the body with known biocompatibility. Moreover approaches aimed to imprint to such materials the ability of transferring information and as a consequence of it of acting selectively onto the biological environment, are currently under investigation. In this sense hydroxyapatite nano-crystals represent an elective material, because they are not only similar to the mineral component of bone but have a chemical reactivity which can be modified and driven. In the study, a novel method to perform drug-eluting nano-hydroxyapatite coatings was developed. Carbonate HA nanocrystals coatings have been first obtained by electrochemically-assisted deposition on Ti plate from diluted calcium and phosphate solutions . The local pH variation rate, induced by the electrochemical process, controls the HA nucleation and crystallization which, in these experimental conditions, bring to the formation of HA nanocrystals with a morphology and crystallinity degree very close to the biological ones. The use of different molecular weight heparin molecules (whose anticoagulant effect has been extensively studied), as co-reagents during the electrochemically assisted HA crystallization deposition allowed to entrap these drug molecules into the coating structure