Plasma sprayed hydroxyapatite coatings: Understanding process relationships using design of experiment analysis

Abstract

24The biocompatibility and osteoconductivity of hydroxyapatite (HA) coatings have led to 25 their use in a wide range of applications in dentistry and orthopaedics. One such application 26 is for the uncemented fixation of implants, where coatings are commonly applied to 27 titanium implants using a plasma thermal spraying process. The spraying process is 28 affected by a large number of parameters leading to highly complex process -property -29 structure relationships. In a step forward from one-at-a-time analyses, this study used 30Design of Experiment (DOE) methodology to investigate the simultaneous effects of key 31 plasma spray process parameters on hydroxyapatite coatings for biomedical applications. 32The effects of five plasma spray process parameters (current, gas flow rate, powder feed 33 rate, spray distance and carrier gas flow rate) on the roughness, crystallinity and purity of 34 hydroxyapatite coatings was determined using a fractional factorial design. The results of 35 this study enabled identification of consistent and competing influences within the process 36 and the identification of some first order interactions. In particular, the diffuse particle size 37 of the HA feedstock powder was found to influence the responses observed within the 38 parameter range investigated. The roughness of HA coatings was found to relate to the 39 particle velocity and the degree of particle melting occurring, withhigher coating roughness 40 resulting when current was high, gas flow rate was low and powder feed rate was high. 41Highest coating crystallinity resulted at high current, low spray distance and low carrier 42 gas flow rate. Under these conditions deposition of larger HA particles resulted leading to 43 higher amounts of bulk crystalline material and the low spray distance increased the 44 substrate temperature allowing amorphous material to recrystallise. Coating purity relates 45 directly to thermal decomposition of the particles within the plasma jet with a high purity 46 3 coating resulting at low particle temperatures i.e at the lower ranges of powder feed rate, 47 spray distance and carrier gas flow rate. This study thus brings greater clarity on the effects 48 of plasma spray process parameters on the properties of resultant hydroxyapatite coatings. 49 50 Keywords 51Plasma spraying, hydroxyapatite, Design of Experiment (DOE) 52 53

Hydroxyapatite-Based Coating on Biomedical Implant

“…The APS, HVOF and HVSFS methods are extensively practised for HAp coating processes especially the one involves Ti metal as substrates [111,112]. The processing parameters such as gas flow, air-fuel ratio, electric arc current and spray distance are the primary factor in determining the coating properties performance concerning the adhesion strength between substrate and coating of these thermal spraying techniques [113,114].…”

EIS, Mott Schottky and EFM analysis of the electrochemical stability and dielectric properties of Ca-P-Ag and Ca-P-Si-Ag coatings obtained by plasma electrolytic oxidation in Ti6Al4V

“…Coatings obtained showed in Figure 1 presented a morphology of interconnected pores with an average size of 1 µm, and smaller pores with a mean size ranging from 428 nm to 681 nm. These different pore sizes will stimulate fluid exchange and cells signaling and will make possible the occurrence of high surface energy sites [1]. Pore sizes described are related to the spark discharges produced by the high electrolytic and dielectric breakdown voltage, which can be controlled with the corresponding variables in the electrolyte assembly [6,8].…”

“…In this perspective, many techniques have been employed for performing coatings on metallic materials such as plasma spraying [1], electrophoretic deposition [2], ion implantation [3], sol-gel [4], plasma electrolytic oxidation [5], among others [6]. Plasma electrolytic oxidation (PEO) is one of the techniques for this purpose to enhance the mechanical properties, wear resistance, and the good adhesion with the substrate exhibited by the coatings.…”

“…Additionally, it has been investigated coatings no obtained by PEO with constituent agents that help to prevent infection in implanted devices, preventing the growth of bacterial biofilms. These constituents such as chitosan and silver ions [11], even pure titanium have presented antibacterial activity [1,6]. Different techniques have been used for the evaluation of electrochemical stability in the coating as potentiodynamic curves, electrochemical impedance spectroscopy and Mott-Schottky [12].…”

Corrosion Resistance Evaluation of HVOF Produced Hydroxyapatite and TiO2-hydroxyapatite Coatings in Hanks' Solution

“…The EIS has the advantage of to be a non-destructive and transient technique, is able to separate the resistance of electrolyte from the processes occurring at the electrode/electrolyte interface, explores a great frequency range allowing to detect events occurring in a large time constants interval [27][28][29] . [30][31][32][33] using plasma spray, microplasma, and vacuum cold spray to deposit hydroxyapatite for biological purposes have studied different properties, but no electrochemical investigation was performed.…”