Compositionally graded doped hydroxyapatite coating on titanium using laser and plasma spray deposition for bone...

Metallic implants often lack the ability to support bone growth due to poor osteoconductivity. Plasma-sprayed hydroxyapatite (HA) coatings have been used to enhance this property. However, the bond strength between the metal and HA is limited by differences in thermal expansion. This issue has not been fully resolved in prior research. Existing methods have not effectively combined mechanical and antibacterial improvements in a single coating system. The mismatch in thermal expansion leads to coating failure over time. Researchers have explored various additives to improve HA properties, but their effects on bond strength remain unclear. The need for a durable and biocompatible coating remains unmet in clinical settings. This gap motivated the development of a new coating strategy using additive manufacturing techniques.

This study aimed to enhance the mechanical and antibacterial properties of HA coatings on titanium implants. The researchers focused on addressing the weak adhesive bond strength between HA and titanium. They used a two-step coating process involving laser engineering and plasma spray. The goal was to introduce a thermal barrier to reduce thermal mismatch. The study also tested the effects of adding MgO and Ag2O to HA. The researchers sought to determine if these additives could improve biological and antibacterial performance. They wanted to assess whether the new coating method could provide long-term stability. The motivation was to develop a more reliable and functional coating for orthopedic and dental implants.

The researchers applied a gradient HA coating on Ti6Al4V using laser engineered net shaping (LENS™). This was followed by plasma spray deposition to complete the coating. They introduced 1 wt% MgO and 2 wt% Ag2O into the HA to modify its properties. The mechanical strength of the coating was evaluated using adhesive bond strength tests. The release of Ag+ ions was measured to assess antibacterial potential. In vitro experiments used human osteoblast cells to evaluate biocompatibility. The crystallization behavior of the HA layer was analyzed using X-ray diffraction. The study compared the performance of the new coating to conventional plasma-sprayed HA.

The adhesive bond strength increased from 26 ± 2 MPa to 39 ± 4 MPa with the addition of the LENS™ interfacial layer. The presence of MgO and Ag2O did not affect the bond strength. The Ag+ ion release decreased by 70% due to enhanced HA crystallization. In vitro tests showed no harmful effects of Ag2O on osteoblast proliferation or differentiation. The coating exhibited antibacterial activity against E. coli and S. aureus. The mechanical and biological performance of the new coating exceeded that of conventional HA. The gradient structure improved the thermal compatibility between HA and titanium. The study demonstrated the feasibility of combining mechanical and antibacterial enhancements in a single coating.

The study demonstrated that a gradient HA coating using LENS™ and plasma spray improves bond strength and biocompatibility. The addition of MgO and Ag2O did not compromise mechanical performance. The reduction in Ag+ ion release suggests enhanced crystallization of the HA layer. The antibacterial properties of the coating were maintained without affecting cell behavior. The new coating method addresses the limitations of conventional plasma-sprayed HA. The results support the use of this approach for orthopedic and dental implants. The study provides evidence for a novel coating strategy that combines mechanical and biological benefits. The findings suggest that this method could lead to more durable and functional implants.