Surface Severe Plastic Deformation of an Orthopedic Ti–Nb–Sn Alloy Induces Unusual Precipitate Remodeling and Supports Stem Cell Osteogenesis through Akt Signaling

Abstract

This work presents a strategy to augment the bioactivity of a new-generation metastable β-Ti–Nb–Sn alloy through surface severe plastic deformation. Foremost, the alloy was strengthened by precipitation of α phase using a well-designed thermo-mechanical processing route. Subsequently, the surface of the aged alloy was subjected to severe plastic deformation via surface mechanical attrition treatment (SMAT). Upon SMAT, a unique phenomenon of strain-induced precipitate coarsening was observed. A possible mechanism is proposed wherein the precipitates first dissolve due to significant slip transfer across the α/β-interface followed by reprecipitation along the other precipitates thereby leading to coarsening. Coarsening of the precipitates abrogated the strengthening caused by plastic deformation as a result of which the hardness did not increase significantly after SMAT in sharp contrast to other alloys. SMAT led to a decrease in the attachment of human mesenchymal stem cells because of an increase in the roughness-mediated surface hydrophobicity. On the other hand, an increase in the roughness led to the formation of more number of focal adhesions. This in turn enhanced the proliferation rate and more importantly, osteogenic differentiation of stem cells. Detailed investigation into the underlying mechanism revealed that an increase in focal adhesions activated the Akt-mediated mechano-transduction signaling pathway that enhanced the osteogenic differentiation. In summary, the potential of surface severe plastic deformation to impart bioactivity to the next-generation of orthopedic β-Ti alloys is underscored in this work.

Novel ultrafine‐grained β‐type Ti–28Nb–2Zr–8Sn alloy for biomedical applications

“…Our previous studies found that the ultrafine-grained Ti-Nb-Zr-Ta-Si alloy can promote ALP activity in vitro as well as facilitate bone regeneration in vivo. 34,35,45 In this study, higher ALP activity and biomineralization of MC3T3-E1 cells cultured on TNZS was observed compared with that of CP-Ti, suggesting the TNZS alloy would have a positive impact on osteogenesis. 28,43 Rajan et al reported a Ti-Nb-Zr-Si thin film metallic glasses could promote osteoblast differentiation.…”

“…44 Zr, Nb, and Sn had been fabricated with titanium, producing a series of Ti-based alloys with the enhanced osteostimulatory ability and bone regeneration ability. 34,35,45 In this study, higher ALP activity and biomineralization of MC3T3-E1 cells cultured on TNZS was observed compared with that of CP-Ti, suggesting the TNZS alloy would have a positive impact on osteogenesis. The expression level of the osteogenic gene of MC3T3-E1 cells cultured on TNZS is higher than that of CP-Ti.…”

“…33 The good corrosion resistance ability of titanium alloys containing Nb, Zr, and Sn is beneficial for their biological applications. 34,35 Vascular infusion is important for bone formation because it is essential for nutrient transportation. Therefore, it is important to examine the influence of TNZS on angioblasts.…”

Surface engineering of biodegradable implants: emerging trends in bioactive ceramic coatings and mechanical treatments

“…Mechanical surface treatments have been applied successfully to significantly improve biomechanical performance and cellular response of several conventional metallic biomaterials, 36 including stainless steels 222 and titanium alloys 223,224 . Severe plastic deformation is often found to induce nanocrystallization at the surface 225 .…”

Revised Semiempirical Approach to Predict the Occurrence of Twinning in Titanium Alloys

“… 3 , 5 , 6 Therefore, each titanium alloy deforms differently from one another depending on the phases present in the microstructure and their structural parameters. 7 , 8 Furthermore, the type of deformation mechanism, for example, twin, slip and so forth, plays a vital role in tailoring the mechanical properties of titanium alloys. 9 Twin boundaries present in crystalline alloys improve dislocation storage ability.…”