PEO coatings design for Mg-Ca alloy for cardiovascular stent and bone regeneration applications.

Four bioactive PEO (plasma electrolytic oxidation) coatings were generated on Mg0.8Ca alloy using a Ca/P-based electrolyte and adding Si or Fas necessary. Surface characteristics, chemical composition and ion liberation of the coatings were characterized using SEM/EDS (Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy), X-ray diffraction, optical profilometry and ICP-OES (inductively coupled plasma optical emission spectrometry). Direct biocompatibility studies were performed by seeding premyoblastic, endothelial and preosteoblastic cell lines over the coatings. Biocompatibility of the coatings was also evaluated with respect to murine endothelial, preosteoblastic, preosteoclastic and premyoblastic cell cultures using extracts obtained by the immersion degradation of the PEO-coated specimens. The coatings reduced the degradation of magnesium alloy and released Mg Ca, P, Si and F. Of all the studied compositions, the Si-containing PEO coating exhibited the optimal characteristics for use in all potential applications, including bone regeneration and cardiovascular applications. Coatings with high F content negatively influenced the endothelial cells. RAW 264.7, MC3T3 and co-culture differentiation studies using extracts of PEO coated Mg0.8Ca demonstrated improved osteoclastogenesis and osteoblastogenesis processes compared to bare alloy.

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.

Metal release from ceramic coatings for dental implants.

OBJECTIVES: Two types of ceramic coatings on commercially pure titanium for dental implant applications with different Ca/P ratios in the range from 1.5 to 4.0, and two different thicknesses (∼5 and ∼15µm) were examined with the aim of underpinning the effect of coating composition, thickness and microstructure on the corrosion behavior and hydroxyapatite forming ability in SBF. METHODS: Bioactive coatings were formed on Ti by plasma electrolytic oxidation (PEO). The composition, structure, and morphology of the materials were characterized before and after the immersion in simulated body fluid solution (SBF) at 37°C for up to 4 weeks. All the materials were screened with respect to metal ion release into SBF. RESULTS: Only thick PEO coating with overstoichiometric Ca/P ratio of 4.0 exhibited capacity to induce the precipitation of hydroxyapatite over the short period of 1 week. Long term Ti(4+) ion release from all PEO-coated materials was 2-3 times lower than from the uncoated Ti. Metal ion release is attributed mostly to chemical dissolution of the coating at initial stages of immersion. SIGNIFICANCE: The long term stability was greater for thin PEO coating with overstoichiometric Ca/P ratio of 2.0, which exhibited ∼95ngcm(-2) of Ti(4+) ions release over 4 weeks. Thin PEO coatings present economically more viable option.

Bioactive plasma electrolytic oxidation coatings--the role of the composition, microstructure, and electrochemical stability.

A Plasma electrolytic oxidation (PEO) process was used to produce bioactive coatings on Ti. PEO coatings with Ca/P atomic ratio of 1.7 and 4.0 were fabricated and characterized with respect to their morphology, composition, and microstructure. AC and DC electrochemical tests were used to evaluate the effect of (i) organic additives (amino acids, proteins, vitamins, and antibiotics) in alpha-minimum essential medium (α-MEM) on electrochemical stability of noncoated and PEO-coated Ti and (ii) coating composition, microstructure, and corrosion behavior on the cell response in α-MEM. PEO-coated Ti showed higher corrosion resistance than the noncoated Ti in MEM with and without organic additives by an order of magnitude. The corrosion resistance in α-MEM decreased with time for nonmodified Ti and increased for PEO-coated Ti; the latter was because of the adsorption of the proteins in the coating pores which increased the diffusion resistance. The presence of Ca and P in titanium oxide coating at the Ca/P ratio exceeding that of any stoichiometric Ca-P-O and Ca-P-O-H compounds facilitates faster osteoblast cell adhesion.

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.

Calcium and titanium release in simulated body fluid from plasma electrolytically oxidized titanium.

The release of titanium and calcium species to a simulated body fluid (SBF) at 37 degrees C has been investigated for titanium treated by dc plasma electrolytic oxidation (PEO) in three different electrolytes, namely phosphate, silicate and calcium- and phosphorus-containing. The average rate of release of titanium over a 30 day period in immersion tests, determined by solution analysis, was in the range approximately 1.5-2.0 pg cm(-2) s(-1). Calcium was released at an average rate of approximately 11 pg cm(-2) s(-1). The passive current densities, determined from potentiodynamic polarization measurements, suggested titanium losses of a similar order to those determined from immersion tests. However, the possibility of film formation does not allow for discrimination between the metal releases due to electrochemical oxidation of titanium and chemical dissolution of the coating.

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.