A comparative outlook of corrosion behaviour and chlorophyll assisted growth kinetics of various carbon nano-structure reinforced hydroxyapatite-calcium orthophosphate coating synthesized in-situ through pulsed electrochemical deposition

Abstract

Chlorophyll functionalised carbon nanostructures namely exfoliated graphene, reduced graphene oxide (RGO) and multi-walled carbon nanotube (MWCNT) have been successfully co-deposited from aqueous media along with in-situ formed hydroxyapatite-calcium orthophosphate phases to develop a biocompatible coating, which eventually can increase the overall coating strength as reinforcement. Chlorophyll disperses and functionalised carbon nanostructure in aqueous media excluding the need of surfactant during pulsed electrochemical deposition, which was earlier not possible for defect-free graphene as well as carbon nanotubes. It also controls the growth kinetics of these coatings which eventually responsible for the overall characteristics of the composite material.The lattice parameter of calcium phosphate phase remain unchanged in all the composite coating whereas, the lattice parameter and weight percentage (35–73%) of hydroxyapatite crystal are found changing with the type of reinforcement on account of difference in growth kinetics controlled via chlorophyll amphiphilicity along with defect state over nano-graphene. The osteoconduction performance is mostly related with the surface characteristics along with corrosion properties which lead to the formation of different shapes and size of porous apatite scaffold starting from sub-micron spherical shape to lamellar structure with varying Ca/P ratio. The gradual evolution of lamellar structure in RGO and exfoliated graphene, and increased surface porosity in exfoliated graphene compare to other reinforcements, predicts their increased probability of successful adaption over implant surfaces by surrounding tissues. RGO reinforcement forms higher amount of stable hydroxyapatite phase over the surface leading to a better corrosion protection which is on account of faster reactions kinetics associated with a quantitative increase of carbon within the given deposition parameter. These results suggest that chlorophyll functionalized carbon reinforcements can be exploited to craft a range of strategies for the development of functional biocompatible layer over metallic implant surfaces where chlorophyll plays a significant role in controlling overall nano carbon phases reinforcement.