Plasma-Sprayed Hydroxylapatite-Based Coatings: Chemical, Mechanical, Microstructural, and Biomedical Properties

Abstract

This contribution discusses salient properties and functions of hydroxylapatite (HA)-based plasmasprayed coatings, including the effect on biomedical efficacy of coating thickness, phase composition and distribution, amorphicity and crystallinity, porosity and surface roughness, cohesion and adhesion, microand nano-structured surface morphology, and residual coating stresses. In addition, it will provide details of the thermal alteration that HA particles undergo in the extremely hot plasma jet that leads to dehydroxylated phases such as oxyhydroxylapatite (OHA) and oxyapatite (OA) as well as thermal decomposition products such as tri-(TCP) and tetracalcium phosphates (TTCP), and quenched phases such as amorphous calcium phosphate (ACP). The contribution will further explain the role of ACP during the in vitro interaction of the as-deposited coatings with simulated body fluid resembling the composition of extracellular fluid (ECF) as well as the in vivo responses of coatings to the ECF and the host tissue, respectively. Finally, it will briefly describe performance profiles required to fulfill biological functions of osteoconductive bioceramic coatings designed to improve osseointegration of hip endoprostheses and dental root implants. In large parts, the content of this contribution is a targeted review of work done by the author and his students and coworkers over the last two decades. In addition, it is considered a stepping stone toward a standard operation procedure aimed at depositing plasma-sprayed bioceramic implant coatings with optimum properties.

The 2016 Thermal Spray Roadmap

“…As well, studies in biological systems are demanding, as described by some key references (Ref [244][245][246][247][248][249][250][251][252][253][254][255][256][257][258] in the subject area of thermal spray. According to Professor R.B.…”

Plasma-Sprayed Hydroxylapatite Coatings as Biocompatible Intermediaries Between Inorganic Implant Surfaces and Living Tissue

“…Among a plethora of available deposition techniques, atmospheric plasma spraying (APS) was and still is the method of choice (Ref [15][16][17][18][19][20] to deposit hydroxylapatite coatings. Much excellent and groundbreaking work in this field has been performed by De Groot et al It is generally acknowledged that plasma-assisted deposition techniques excel by a fast, well controlled, economically advantageous, and, in its processing technology, mature way to coat almost any substrate with those materials that exhibit a well-defined congruent melting point (Ref 26).…”

“…These properties include coating cohesion and adhesion, phase composition, homogeneous phase distribution, crystallinity, porosity and surface roughness, nano-structured surface morphology, residual coating stress, and coating thickness ( Ref 15,40,41). Comprehensive accounts on optimizing deposition strategies of plasmasprayed hydroxylapatite coatings for medical implants have been recently reviewed by the present author (Ref [18][19][20].…”

“…In particular, maintenance of phase composition at values imposed by national and international norms, and control of coating porosity by implementing novel deposition techniques such as suspension (SPS) or solution precursor plasma spraying (SPPS) are fertile development areas. In the end, careful engineering of hydroxylapatite coatings by appropriately adjusting and fine-tuning of plasma spray parameters will ensure deposition of coatings with optimum mechanical, microstructural, chemical, and biological properties (Ref[15][16][17][18][19][20].…”

The Influence of Process Parameters on the Structure, Phase Composition, and Texture of Micro-Plasma Sprayed Hydroxyapatite Coatings

“…However, with the rapid development of surface technology, HA coatings deposited by using surface technology on a metal substrate provide excellent biocompatibility and good mechanical properties. The plasma spraying technique is a common method for depositing HA coating on metal implants [4][5][6]. However, the overheating of HA particles in the plasma jet can cause the decomposition of the HA powders.…”