Electrospun ultrathin PBAT/nHAp fibers influenced the in vitro and in vivo osteogenesis and improved the mechanical properties of neoformed bone

Abstract

Combining polyester scaffolds with synthetic nanohydroxyapatite (nHAp), which is bioactive and osteoconductive, is a plausible strategy to improve bone regeneration. Here, we propose the combination of PBAT [poly(butylene-adipate-co-terephthalate)] and synthetic nHAp (at 3 and 5wt%). PBAT is a relatively a new polymer with low crystallinity and attractive biodegradability and mechanical properties for orthopedic applications, however, with a still underexplored potential for in vivo applications. Then, we performed a careful biological in vitro and in vivo set of experiments to evaluate the influence of PBAT containing two different nHAp loads. For in vitro assays, osteoblast-like MG63 cells were used and the bioactivity and gene expression related to osteogenesis were evaluated by qRT-PCR. For in vivo experiments, twenty-four male rats were used and a tibial defect model was applied to insert the scaffolds. Micro-computed tomography (Micro-CT) and histological analysis were used to assess e bone neoformation after 6 weeks of implantation. Three point flexural tests measured the mechanical properties of the neoformed bone. All scaffolds showed promising in vitro properties, since they were not cytotoxic against MG-63 cells and promoted high cell proliferation and formation of mineralized nodules. From a mechanistic point-of-view, nHAp loading increased hydrophilicity, which in turn allowed for a better adsorption of proteins and consequent changes in the phenotypic expression of osteoblasts. nHAp induced better cellular responses on/in the scaffolds, which was mainly attributed to its osteoconductive and osteoinductive properties. Micro-CT images showed that nHAp at 3% and 5wt% led to more effective bone formation, presenting the highest bone volume after 6 weeks of implantation. Considering the three point flexural tests, 5wt% of nHAp positively influenced the flexural mode of the neoformed bone, but the stiffiness was similar between the 3% and 5wt% groups. In summary, this investigation demonstrated great potential for the application of these novel scaffolds towards bone regeneration and, thus, should be further studied.

Keywords: Bone regeneration; Electrospinning; Gene expression; Micro-computed tomography; Nanohydroxyapatite; PBAT.