Strontium-incorporated mineralized PLLA nanofibrous membranes for promoting bone defect repair

Mineralized scaffolds, which are fabricated by electrodeposition, mimic the chemistry of natural bone and have attracted a great amount of attention due to their rapid and simple production. In this study, mineralized electrospun polylactic acid (PLLA) nanofibrous membranes containing different amounts of strontium (Sr) were fabricated by an electrodeposition method for potential use in bone regeneration applications. In vitro assays, including cell proliferation and osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (BMSCs) grown on these membranes and in vivo cranial bone defect repair assays, were carried out. It was found that mineral crystals could be uniformly deposited onto the electrospun nanofibrous membranes, while the morphologies of the formed crystals were affected by the amount of Sr. By analysis of the X-ray diffraction (XRD) measurements, the formed crystalline phase was dramatically affected by the incorporation of Sr, which drove a conversion from the hydroxyapatite (HA) phase to the dicalcium phosphate dehydrate (DCPD) phase. The release of Sr²⁺ from the Sr/PLLA nanofibrous membranes was monitored over 20 d, and the release rates of Ca²⁺ and PO₄^3- from the Sr-incorporated samples were higher compared with those of the mineralized sample without Sr. In vitro cell proliferation experiments demonstrated that mineralized Sr/PLLA nanofibrous membranes could facilitate BMSC proliferation. Furthermore, the mineralized Sr/PLLA nanofibrous membranes induced a higher degree of osteogenic differentiation in the BMSCs compared with those of pure PLLA and mineralized PLLA, as determined by the results of alkaline phosphatase (ALP) activity, alizarin red (AR) and osteocalcin (OCN) staining and the expression of osteogenesis-related genes. More importantly, in vivo cranial defect experiments revealed that mineralized Sr/PLLA nanofibrous membranes promoted bone regeneration. These findings indicated that mineralized Sr/PLLA nanofibrous membranes are a promising material for bone tissue engineering.