Effect of zinc substitution in hydroxyapatite coating on osteoblast and osteoclast differentiation under osteoblast/osteoclast co-culture

Zinc is an essential trace element required for bone remodelling process,but its role in such process remains to be elucidated.In particular,inconsistent results have been reported on the effect of Zn on osteoclastic responses,and supplement of receptor activator of nuclear factor kappa-B ligand(RANKL)factors has been commonly adopted.Co-culture is a suitable approach to elucidating the role of Zn in bone remodelling process,by better imitating the cellular environment as the presence of osteoblasts plays critical role in modulating osteoclastic functions.In this study,zincsubstituted HA coatings have been deposited using a liquid precursor plasma spraying process at two different concentrations(1,2 wt.%).The effect of zinc substitution on osteoblastic and osteoclastic differentiation has been studied in vitro.In particular,a cultivation regime was designed to first induce osteoblastic differentiation of rat bone marrow stromal cells(BMSCs)for 14 days,and then induce osteoclastic differentiation of osteoclast-like precursor RAW 264.7 cells through the aid of the osteoblasts formed for additional 14 days,in the absence of the external addition of RANKL.The results showed that Zn substitution moderately promoted the BMSC differentiation into the osteoblasts and reduced the osteoclastic activity in early time(1 day co-culture).However,promotion of the osteoclastic activity were observed at later stages,as indicated by the significantly enhanced expressions of trap5b and IL-1(8-and 15-day co-culture)and moderate stimulation of the nucleus integration and formation of the multinucleated cells(14-day co-culture).Such stimulating effect of the osteoclastic activity was absent under mono-culture of RAW 264.7 cell,with simple RANKL supplementation.The results suggest that both the zinc and the presence of MSC/osteoblast play profound and highly interacted roles on osteoclast differentiation and activity,which is critical in modulating the bone remodelling process.

Critical Role of Silicon in Directing the Bio-inspired Mineralization of Gelatin in the Presence of Hydroxyapatite

Significant progress has been made on understanding the critical role of organic components in directing the collagen mineralization.We hypothesize that the inorganic trace elements might also play important role in the mineralization of collagenous matrix.To this aim,we systematically compared the in-vitro biomineralization behaviors of gelatin,gelatin-HA and gelatin-SiHA electrospun membranes.The results indicated that the presence of Si ions played a striking influence on the nucleation behaviors and mineralized structures.The gelatin-SiHA samples demonstrated more homogeneous nucleation within the gelatin fiber and growth along the fiber direction,in comparison with the heterogeneous nucleation and growth of spherulitic clusters on top of the nanofiber surface,i.e.extrafibrillar mineralization.The likely shift of the nucleation mode to the intrafibrillar mineralization in the presence of Si ions led to good alignment of apatite c-axis with the long axis of the nanofiber,resulting in a mineralization process and microstructure that were closer to those in natural bone.Cellular response analysis indicated that Si incorporation improved the MSC attachment and cytoskeleton organization.Such findings might have important implication in both understanding the complex mechanisms involved in collagen mineralization and optimal designing of advanced bio-inspired materials with potential superior mechanical and biological properties.