Calcium phosphate coating of biomedical titanium alloys using metal–organic chemical vapour deposition

Abstract

Metal-organic chemical vapour deposition was used to fabricate hydroxyapatite (HAp) and atricalcium phosphate coatings on the surface of representative biomedical titanium alloys: Ti29Nb-13Ta-4?6Zr, commercially pure Ti, and Ti-6Al-4V ELI. The effect of the substrate surface roughness, alloy composition and precursor temperature was investigated in relation to the type of calcium phosphate formed and the morphology and thickness of the HAp coating. The surface roughness of substrates mechanically polished by SiC paper was found to vary depending on the type of alloy, whereas the roughness of substrates buff polished using a colloidal SiO 2 suspension was comparable. The type of calcium phosphate formed could be controlled by the precursor temperature. A coarse, granular microstructure was observed on the surface of the thicker HAp coatings formed on the rough polished substrates, while the thinner HAp coatings formed on the smooth polished substrates had a relatively dense and fine grained microstructure.

There Are over 60 Ways to Produce Biocompatible Calcium Orthophosphate (CaPO4) Deposits on Various Substrates

“…For the first time CaPO 4 was deposited by MOCVD in 1996 [344], followed by other studies [345][346][347][348][349][350][351]. Deposition requires precursors containing Ca and P, and in many cases the inorganic metal precursors containing Ca have rather complex compositions.…”

“…Examples include Ca(tmhd) 2 (where tmhd = 2,2,6,6,-tetramethylheptane-3,5-dione) [344], Ca(hfpd) 2 (tetraglyme) (where hfpd = 1,1,1. 5,5,-hexafluoro-2,4-pentadione) [350], calcium dibenzoylmethane [346] and Ca(dpm) 2 (where dpm = bis-dipivaloylmethanato) [347,349,351], but simpler compounds may also be used, such as calcium lactate [348,350]. Precursors containing P are P 2 O 5 [344], trimethylphosphate [346,348,350] and triphenylphosphate [347,349,351].…”

“…5,5,-hexafluoro-2,4-pentadione) [350], calcium dibenzoylmethane [346] and Ca(dpm) 2 (where dpm = bis-dipivaloylmethanato) [347,349,351], but simpler compounds may also be used, such as calcium lactate [348,350]. Precursors containing P are P 2 O 5 [344], trimethylphosphate [346,348,350] and triphenylphosphate [347,349,351]. Naturally, the precursors must be volatile at relatively low temperatures (<~600 • C), and pressures between 1 Torr and atmospheric pressure.…”

“…To perform MOCVD, precursors containing Ca and P are heated to evaporate and fed with a carrier gas (such as Ar) into a reactor in which a heated substrate is placed [344][345][346][347][348][349][350][351]. To accelerate oxidation of the precursor, oxygen may be separately introduced into the reactor and mixed with the precursor vapor.…”

Titanium for Orthopedic Applications: An Overview of Surface Modification to Improve Biocompatibility and Prevent Bacterial Biofilm Formation

“…Although this method requires highly specialized equipment that requires a high initial investment, it is capable of producing a highly uniform coating on complex geometries. Furthermore, the precursor temperature used in CVD can be used to alter the morphology and thickness of the coating formed, making it highly versatile for commercial use ( Nakai et al., 2015 ). Because of the similarity in technique to PVD, delamination also poses an issue for surface modification of materials using CVD, which must be taken into consideration when applying this technology to orthopedic devices.…”