Effect of thermomechanical processing on the mechanical biofunctionality of a low modulus Ti-40Nb alloy.

Different hardening strategies were evaluated regarding their potential to improve the mechanical biofunctionality of the cast and solution-treated low modulus ß-Ti alloy Ti 40Nb. The strategies are based on thermomechanical treatments comprised of different hot- and cold-rolling steps, as well as annealing treatments aiming at the successive exploitation of different hardening mechanisms (grain boundary hardening, work hardening and precipitation hardening). Quasi-static tensile testing revealed that grain refinement by one order of magnitude has only a small impact on improving the mechanical biofunctionality of Ti-40Nb. However, work hardening effectively improves the tensile strength by 30% to a value of 650MPa, while retaining Young׳s modulus at 60GPa. The α-phase precipitation hardening was verified to have an increasing effect on both, strength and Young׳s modulus. Thereby, the change of Young׳s modulus dominates the change of the strength, even at low α-phase fractions. The pseudo-elastic behavior of Ti 40Nb is discussed under consideration of the microstructural changes due to the thermomechanical treatment. The texture changes evolving upon cold-rolling markedly influence the recrystallization behavior. However, the present results do not show a significant effect of the texture on the mechanical properties of Ti-40Nb.

Chemical nanoroughening of Ti40Nb surfaces and its effect on human mesenchymal stromal cell response.

Samples of low modulus beta-type Ti40Nb and cp2-Ti were chemically treated with 98% H2 SO4 + 30% H2 O2 (vol. ratio 1:1) solution. Surface analytical studies conducted with HR-SEM, AFM, and XPS identified a characteristic nanoroughness of the alloy surface related with a network of nanopits of ∼25 nm diameter. This is very similar to that obtained for cp2-Ti. The treatment enhances the oxide layer growth compared to mechanically ground states and causes a strong enrichment of Nb2 O5 relative to TiO2 on the alloy surface. The in vitro analyses clearly indicated that the chemical treatment accelerates the adhesion and spreading of human mesenchymal stromal cells (hMSC), increases the metabolic activity, and the enzyme activity of tissue non-specific alkaline phosphatase (TNAP). Surface structures which were generated mimic the cytoplasmic projections of the cells on the nanoscale. Those effects are more pronounced for the Ti40Nb alloy than for cp2-Ti. The relation between alloy surface topography and chemistry and cell functions is discussed.

A novel strontium(II)-modified calcium phosphate bone cement stimulates human-bone-marrow-derived mesenchymal stem cell proliferation and osteogenic differentiation in vitro.

In the present study, the in vitro effects of novel strontium-modified calcium phosphate bone cements (SrCPCs), prepared using two different approaches on human-bone-marrow-derived mesenchymal stem cells (hMSCs), were evaluated. Strontium ions, known to stimulate bone formation and therefore already used in systemic osteoporosis therapy, were incorporated into a hydroxyapatite-forming calcium phosphate bone cement via two simple approaches: incorporation of strontium carbonate crystals and substitution of Ca(2+) by Sr(2+) ions during cement setting. All modified cements released 0.03-0.07 mM Sr(2+) under in vitro conditions, concentrations that were shown not to impair the proliferation or osteogenic differentiation of hMSCs. Furthermore, strontium modification led to a reduced medium acidification and Ca(2+) depletion in comparison to the standard calcium phosphate cement. In indirect and direct cell culture experiments with the novel SrCPCs significantly enhanced cell proliferation and differentiation were observed. In conclusion, the SrCPCs described here could be beneficial for the local treatment of defects, especially in the osteoporotic bone.