Microstructures and cell reaction of porous hydroxyapatite coatings on titanium discs using a novel vapour-induced pore-forming atmospheric plasma spraying

The surface topography of implants plays an important role in affecting the behaviour of osteoblasts. Previous research has demonstrated that porous hydroxyapatite (HAp) coating surfaces fabricated by vapour-assisted flame spraying enhances osteoblast attachment and differentiation, but flame spraying cannot supply sufficient power for fabricating porous surfaces without cracks. To solve this problem, porous HAp coatings were deposited on titanium (Ti) discs using a novel vapour-induced pore-forming atmospheric plasma spraying (VIPF-APS) technique with a higher amount of energy. A water reservoir was placed behind the Ti discs to serve as the vapour source. Ti discs with three different mean pore diameters, namely, ATi (2.65 μm), BTi (15.65 μm), and CTi (35.33 μm), were used, and the HAp coatings that were deposited on these three discs using the VIPF-APS technique were denoted HAp-ATi, HAp-BTi, and HAp-CTi, respectively. For comparison, the conventional APS technique was used to deposit HAp on ATi, and this sample was named HAp-APS/ATi. The results showed that the VIPF-APS technique effectively produced porous HAp coatings, whereas the conventional APS technique yielded dense coatings that are unfavourable for applications. These porous coatings further contributed to higher osteoblast proliferation and distinctive alkaline phosphatase activity. The VIPF-APS technique thus has great potential for producing bioactive coatings that can be used in implants.