An in vivo evaluation of the biocompatibility of anodic plasma chemical (APC) treatment of titanium with calcium phosphate.

Implant loosening is an unresolved complication associated with prosthetics. Previous studies report improved osseointegration with hydroxyapatite (HA) or tri-calcium phosphate coatings. Unfortunately, the brittleness and low strength of these coatings in adhesion to the implant or internal cohesion is problematic, restricting their use. Anodic plasma-chemical (APC) treatment, an advanced anodisation method, allows for porous oxide layer formation with incorporation of calcium and phosphate directly into the oxide. This produces superior adhesive strength than a conventional coating of calcium phosphate offering potential for long-term osseointegration. Although the cytocompatibility of several APC treatments have been previously shown, this study was the first to investigate the biocompatibility and osteoconductivity of APC surfaces in vivo when compared with standard HA coated and noncoated commercially pure titanium implant cortical screws. Sample screws were implanted in female Swiss alpine sheep for 12 weeks. Bone remodelling in situ, differences in bone apposition resulting in cortical thickening as well as peak removal torque measurements were assessed. We found no significant differences between the tested coatings and no delamination was observed with any of the APC-treated surfaces. The results suggest that APC-treated samples have similar biological performance to HA-coated screws. In our opinion, APC treatment, which also has superior binding strength to the base metal compared with standard HA coatings as well as similar biocompatibility as shown here, holds great potential for biomedical applications. Now that the in vivo biocompatibility has been proven, the work is being extended to more challenging in vivo models.

Anodic plasma chemical treatment of titanium Schanz screws reduces pin loosening.

OBJECTIVE: This study was designed to assess the benefits of a new Anodic Plasma Chemical calcium-phosphate (APC-CaP) surface treatment on reducing pin track infection and pin loosening in comparison to anodized titanium (Ti) during external fracture fixation. METHODS: A tibial midshaft, transverse, 6-mm gap osteotomy was created in 17 adult female Swiss alpine sheep. The tibia was stabilized with an external fixator and 4 Schanz screws of Ti or APC-CaP-treated Ti. The sheep were examined during a 12-week observation period. Infection was assessed with weekly clinical pin track grading and microbiologic assessment at sacrifice. Pin loosening was assessed by grading for radiolucency on biweekly radiographs and by measuring extraction torque on pin removal. In vivo bending stiffness measurements were performed to determine gap healing. A qualitative histologic assessment of the tissue adjacent to pin sites was also performed. RESULTS: A trend (P = 0.056) for less infection around APC-CaP pins was found at 6 weeks, but the strength of this difference diminished with time. Significantly more radiolucency was found around Ti pins after 8 (P = 0.011) and 12 (P < 0.001) weeks. At all pin sites, the extraction torque for APC-CaP pins was higher than for Ti pins (P = 0.007). No difference in the progression of gap healing was found. Histology showed bone growth at the implant surface in the form of distance osteogenesis for Ti and contact osteogenesis for APC-CaP. CONCLUSIONS: This study has shown that the APC-CaP surface improves the clinical performance of Ti pins with respect to pin loosening and pin track infection.

Anodic plasma-chemical treatment of CP titanium surfaces for biomedical applications.

The anodic plasma-chemical (APC) process was used to modify CP titanium surfaces for biomedical applications. This technique allows for the combined chemical and morphological modification of titanium surfaces in a single process step. The resulting conversion coatings, typically several micrometer thick, consist mainly of titanium oxide and significant amounts of electrolyte constituents. In this study, a new electrolyte was developed containing both calcium-stabilized by complexation with EDTA-and phosphate ions at pH 14. The presence of the Ca-EDTA complex, negatively charged at high pH, favors incorporation of high amounts of calcium into the APC coatings during the anodic (positive) polarization. The coating properties were evaluated as a function of the process variables by XPS, GD-OES, Raman spectroscopy, SEM and tensile testing, and compared to those of calcium-free APC coatings and uncoated CP titanium surfaces. The maximal Ca/P atomic ratio in the coating produced with the new APC electrolyte was approximately 1.3, with higher Ca concentrations than reported in conventional APC coatings. The dissolution behavior of the incorporated, amorphous CaP phases was investigated by exposure to a diluted EDTA solution. The coatings produced in the new electrolyte system exhibit favorable mechanical stability. The new APC technology is believed to be a versatile and cost-effective coating technique to render titanium implant surfaces bioactive.