Plasma sprayed hydroxyapatite coatings applied on Ti-6Al-4 V substrates have been widely used in joint prosthesis and dentistry applications, owing to the combination of the excellent mechanical properties of Ti alloys and the favorable osteoconductive and bioactive properties of the HA coatings . However, due to the favorable bioactive property and the proper body nutrition and temperature, they are usually in favor of the bacteria adherence and colonization on the implant, which cause the failure of the implant . Therefore, antibacterial materials have been added into the HA coating to effectively reduce the postoperative infection. However, the addition of antimicrobial materials would generally lead to cytotoxicity and be detrimental for bone formation and growth, while bone ingrowth at early stage is critical for implant/bone fixation and patient recuperation.
Among all the antibacterial materials, chitosan is a widely used natural polymer, generated by deacetylation of chitin, with combined biodegradability, non-toxicity, antibacterial and hemostasis properties. The combination of chitosan and HA has drawn much attention in antimicrobial applications. The intrinsic antibacterial activity of chitosan lies in the interference of its cationic amino group with the negatively charged residues of macromolecules at the surface of bacterial wall, which affects the permeability of the bacterial membrane. However, its electrostatic interaction with anionic glycosaminoglycans (GAG) and other negatively charged molecules would also likely promote the adhesion of osteoblast cells. Moreover, due to its cationic nature and predictable degradation rate, chitosan based materials are also suitable to bind growth factors and release them in a controlled fashion. Therefore, it is logical to hypothesize that dual function of chitosan (antibacterial activity and promotion of osteoblast cell proliferation) may be achieved through the selective destruction of the bacterial cell, since bacteria and osteoblastic cells vary significantly in their size and properties.
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