Multifunctional calcium phosphate based coatings on titanium implants with integrated trace elements.

For decades, the main focus of titanium implants developed to restore bone functionality was on improved osseointegration. Additional antimicrobial properties have now become desirable, due to the risk that rising antibiotic resistance poses for implant-associated infections. To this end, the trace elements of copper and zinc were integrated into calcium phosphate based coatings by electrochemically assisted deposition. In addition to their antimicrobial activity, zinc is reported to attract bone progenitor cells through chemotaxis and thus increase osteogenic differentiation, and copper to stimulate angiogenesis. Quantities of up to 68.9 ± 0.1 µg cm- 2 of copper and 56.6 ± 0.4 µg cm- 2 of zinc were deposited; co-deposition of both ions did not influence the amount of zinc but slightly increased the amount of copper in the coatings. The release of deposited copper and zinc species was negligible in serum-free simulated body fluid. In protein-containing solutions, a burst release of up to 10 µg ml-1 was observed for copper, while zinc was released continuously for up to 14 days. The presence of zinc was beneficial for adhesion and growth of human mesenchymal stromal cells in a concentration-dependent manner, but cytotoxic effects were already visible for coatings with an intermediate copper content. However, co-deposited zinc could somewhat alleviate the adverse effects of copper. Antimicrobial tests with E. coli revealed a decrease in adherent bacteria on brushite without copper or zinc of 60%, but if the coating contained both ions there was almost no bacterial adhesion after 12 h. Coatings with high zinc content and intermediate copper content had the overall best multifunctional properties.

Silver and copper addition enhances the antimicrobial activity of calcium hydroxide coatings on titanium.

Electrochemically assisted deposition of Ca(OH)2 (Portlandite) coatings on titanium surfaces has been proven as a promising method to provide the substrate with a most desirable combination of significant bacterial growth reduction on one hand and good biocompatibility on the other. Due to the rapid in vivo transformation of Ca(OH)2 to hydroxyapatite, the antimicrobial activity will be an ephemeral property of the coating when implanted into the human body. In this study, the ability to reduce bacterial growth of such portlandite coatings was significantly enhanced by an ionic modification with copper and silver ions. Antibacterial tests revealed a noticeably elevated reduction of bacterial growth, especially for copper and even at a relatively low copper content of about 0.3 wt.%. In addition, the cytocompatibility, a crucial prerequisite for potential in vivo biocompatibility, of the copper-modified coating was comparable to pure calcium hydroxide coatings.

Electrochemically assisted deposition of strontium modified magnesium phosphate on titanium surfaces.

Electrochemically assisted deposition was utilized to produce ceramic coatings on the basis of magnesium ammonium phosphate (struvite) on corundum-blasted titanium surfaces. By the addition of defined concentrations of strontium nitrate to the coating electrolyte Sr(2+) ions were successfully incorporated into the struvite matrix. By variation of deposition parameters it was possible to fabricate coatings with different kinetics of Sr(2+) into physiological media, whereas the release of therapeutically relevant strontium doses could be sustained over several weeks. Morphological and crystallographic examinations of the immersed coatings revealed that the degradation of struvite and the release of Sr(2+) ions were accompanied by a transformation of the coating to a calcium phosphate based phase similar to low-crystalline hydroxyapatite. These findings showed that strontium doped struvite coatings may provide a promising degradable coating system for the local application of strontium or other biologically active metal ions in the implant-bone interface.

Real-time measurement of protein adsorption on electrophoretically deposited hydroxyapatite coatings and magnetron sputtered metallic films using the surface acoustic wave technique.

Surface acoustic wave (SAW) biosensors are highly sensitive for mass binding and are therefore used to detect protein-protein and protein-antibody interactions. Whilst the standard surface of the chips is a thin gold film, measurements on implant- or bone-like surfaces could significantly enhance the range of possible applications for this technique. The aim of this study was to establish methods to coat biosensor chips with Ti, TiN, and silver-doped TiN using physical vapor deposition as well as with hydroxyapatite by electrophoresis. To demonstrate that protein adsorption can be detected on these surfaces, binding experiments with fibronectin and fibronectin-specific antibodies have been performed with the coatings, which successfully proved the applicability of PVD and EPD for SAW biosensor functionalization.

Tetracalcium phosphate: Synthesis, properties and biomedical applications.

Monoclinic tetracalcium phosphate (TTCP, Ca(4)(PO(4))(2)O), also known by the mineral name hilgenstockite, is formed in the (CaO-P(2)O(5)) system at temperatures>1300 degrees C. TTCP is the only calcium phosphate with a Ca/P ratio greater than hydroxyapatite (HA). It appears as a by-product in plasma-sprayed HA coatings and shows moderate reactivity and concurrent solubility when combined with acidic calcium phosphates such as dicalcium phosphate anhydrous (DCPA, monetite) or dicalcium phosphate dihydrate (DCPD, brushite). Therefore it is widely used in self-setting calcium phosphate bone cements, which form HA under physiological conditions. This paper aims to review the synthesis and properties of TTCP in biomaterials applications such as cements, sintered ceramics and coatings on implant metals.