Preparation of chitosan/hydroxyapatite composite coating obtained from crab shells on hierarchical micro/nano-textured Ti surface

In this study, crab shell bio-waste was used to fabricate chitosan/hydroxyapatite (CS/HA) coatings on the surface of pure titanium (Ti). HA is the main inorganic component in human bone; it has favorable biocompatibility, bioactivity, and osteoconductivity. CS can promote cell adhesion, proliferation, and differentiation and is highly antibacterial. Additionally, acid etching plus alkaline treatment was adopted to create micro/nano-textured hierarchical topographical features on the surface of Ti samples, and the CS/HA composite coating was then prepared through hydrothermal treatment and added to the chemically pretreated Ti surfaces. A nanoporous network structure was formed after alkali treatment, and the micropores remained after acid etching. The CS/HA layer coated on the strut surface of the porous network structure was thin and did not entirely fill and block the nanoporous network structure. Therefore, this surface contained a favorable three-dimensional microenvironment for cell attachment. The Ti surface exhibited the highest roughness (482.2 nm) after acid etching and alkali treatment, and it presented a superhydrophilic surface (contact angle of less than 10 degrees). Subsequently, when the surface was coated with CS/HA, the roughness slightly decreased to 400.7 nm, and the water contact angle slightly increased to 21.6 degrees. After the CS/HA-coated sample was immersed in simulated body fluid for 7 days, many apatite particles were deposited on the surface, indicating that the coating had favorable bioactivity.