Bioactive multi-elemental PEO-coatings on titanium for dental implant applications

Bioactive PEO (Plasma Electrolytic Oxidation) coatings were generated on Grade I commercially pure titanium for dentistry applications using a Ca/P-based electrolyte with added Si, Mg, Zn or F species. Surface characteristics, chemical composition and ion liberation of the coatings were characterized using SEM/EDS, X-ray diffraction, optical profilometry, contact angle and ICP-OES. Corrosion resistance (OCP and DC polarization) was evaluated in SBF. Osteoblastogenesis and osteoclastogenesis processes on PEO-coated Ti and non-coated Ti controls were assessed after 7 days and 5 days of cell culture, respectively. Monolayer formation and metabolic activity were evaluated for the MC3T3 preosteoblastic cell line. All PEO coatings favoured differentiation processes over proliferation and presented three times greater quantity of secreted collagen than non-coated Ti control. All coating enabled osteoclast differentiation, with differences in number and size of the osteoclasts between the materials.

Stability of plasma electrolytic oxidation coating on titanium in artificial saliva

Bioactive PEO coating on titanium with high Ca/P ratio was fabricated and characterized with respect to its morphology, composition and microstructure. Long-term electrochemical stability of the coating and Ti(4+) ion release was evaluated in artificial saliva. Influence of the lactic acid and fluoride ions on corrosion protection mechanism of the coated titanium was assessed using AC and DC electrochemical tests. The PEO-treated titanium maintained high passivity in the broad range of potentials up to 2.5 V (Ag/AgCl) for up to 8 weeks of immersion in unmodified saliva and exhibited Ti(4+) ion release <0.002 µg cm(-2) days(-1). The high corrosion resistance of the coating is determined by diffusion of reacting species through the coating and resistance of the inner dense part of the coating adjacent to the substrate. Acidification of saliva in the absence of fluoride ions does not affect the surface passivity, but the presence of 0.1 % of fluoride ions at pH ≤4.0 causes loss of adhesion of the coating due to inwards migration of fluoride ions and their adsorption at the substrate/coating interface in the presence of polarisation.

Transmission electron microscopy of coatings formed by plasma electrolytic oxidation of titanium

Transmission electron microscopy and supporting film analyses are used to investigate the changes in composition, morphology and structure of coatings formed on titanium during DC plasma electrolytic oxidation in a calcium- and phosphorus-containing electrolyte. The coatings are of potential interest as bioactive surfaces. The initial barrier film, of mixed amorphous and nanocrystalline structure, formed below the sparking voltage of 180 V, incorporates small amounts of phosphorus and calcium species, with phosphorus confined to the outer approximately 63% of the coating thickness. On commencement of sparking, calcium- and phosphorus-rich amorphous material forms at the coating surface, with local heating promoting crystallization in underlying and adjacent anodic titania. The amorphous material thickens with increased treatment time, comprising almost the whole of the approximately 5.7-microm-thick coating formed at 340 V. At this stage, the coating is approximately 4.4 times thicker than the oxidized titanium, with a near-surface composition of about 12 at.% Ti, 58 at.% O, 19 at.% P and 11 at.% Ca. Further, the amount of titanium consumed in forming the coating is similar to that calculated from the anodizing charge, although there may be non-Faradaic contributions to the coating growth.