Cold spraying hydroxyapatite: a systematic review

In order to minimise the development of post-surgical complications, it is essential that implants demonstrate excellent biocompatibility, particularly on their surface. Hydroxyapatite (HAP) coating has biological characteristics that are very similar to those of bones. Consequently, such surface modification of an implant can increase its biocompatibility and favor osseointegration processes. Currently, thermal spray technologies are used to produce thin HAP coatings at temperatures close to the melting point of the material. However high temperature reduces biocompatibility properties of the material and limits possibility to incorporate to the coating some bioactive agents. In connection to this, Cold Spray technology may have advantages in comparison to a thermal spraying. However, the brittle nature of HAP complicates producing the coating at low temperature. It is vital to select the appropriate manufacturing process and the correct process parameters in order to ensure that the coating will exhibit the desirable properties and thickness that enhance osseointegration. This study presents a systematic review of published experimental papers with the objective of developing a fundamental approach in selecting process parameters of the powder, substrate, and cold spraying, and produce a high-quality HAP-coating.