The Design And Osteoinductive Mechanism Of Biomimetic Bone Repair Scaffold Materials

Bone problems have a highly deleterious impact on society and life. The smallerdefects would heal spontaneously, while the larger bone defects could not do this, itis needed the implant materials helping the damaged tissues to repair and heal.Autogenous bone, xenogenic and artificial bone grafts are currently the mainmethods of clinical treatment of bone defect. One of the most effective methods isautogenous bone graft, but the limited source and functional disorder limited itswidely clinical application. Using the xenogenic bone graft such as Bio-Oss derivedfrom bovine femur, or OsteoBiol derived from porcine bone, the disadvantage ofthese products are their high price and time-consuming manufacturing process.Therefore, designing an ideal bone repair scaffold materials with a highlybiomimetic structure, good biocompatibility and bone regeneration ability is a hottopic in bone tissue engineering. This paper was aimed to design the bionicmesoporous bioactive glass scaffold and PLLA nanofibers scaffold, the materialproperties were detected, and the biological compatibility and bone inductioncapacity were evaluated, the osteogenesis mechanisms were investigated. Finally, wehave implanted them into the animal model of bone defect to evaluate their repaireffects.Firstly, multichannel mesoporous bioactive glass (MBG) microtubes scaffoldmaterials were synthesized using Pluronic P123and wool sponges as templates. Thefine one-dimensional multichannel structures of the biological templates wereduplicated. The wool sponges not only created pores but also helped increase thegrowth rate of hydroxycarbonate apatite in the simulated body fluid (SBF). Thebiocompatibilities were also evaluated by culturing the MC3T3-E1cells on themesoporous bioactive glass microtubes. In addition, dexamethasone (DEX) carryingexperiment proved that the material system with its unique porous structure hold a good load ability, and could provide a continuous release pattern. The MBGmicrotubes exhibited delicate multichannel tubular structures, bioactivities,biocompatibilities and the capability for sustained drug delivery. The data hasdemonstrated that the material had excellent potential for applications in the fields oftissue engineering.In addition to the porous scaffold material, nanofibers scaffold is another hotmaterial system in the field of bone tissue engineering. Nanofibers hold the specificstructure can simulate the extracellular matrix (ECM) of natural bone tissue, whichshow the excellent bone inductivity. Recently, with the deepening of the research onnanofibers scaffold material, different arrangement direction of fiber could determinethe different differentiation of stem cells became a new topic. Therefore, we usepoly-L-lactide (PLLA) as raw material to manufacture random and alignedarrangement nanofibers by electrospinning technique. Here, we investigated theosteogenetic differentiation ability of human bone marrow mesenchymal stem cells(hBMSCs) on different orientation of nanofibers. On random and aligned PLLAnanofibers, hBMSCs showed morphological changes concomitant with variations ofcytoskeleton organization. RT-PCR analysis of osteogenic marker genes, includingBMP2, RUNX2, OPN, COL1A1, SPARC and BSP, showed that random nanofiberssignificantly enhanced osteogenic fate specification of hBMSCs compared withthose on aligned nanofibers. Global gene expression analysis by microarraydemonstrated a similar temporal expression profiles between hBMSCs cultured onrandom nanofibers and those induced with osteogenic supplement (OS). In-depthpathway analysis revealed that focal adhesion kinase, TGF-β, Wnt and MAPKpathways were involved in the osteogenic differentiation of BMSCs on randomnanofibers. These findings imply that BMSCs cultured on random PLLA nanofibersare in an activated state for osteogenic differentiation and highlight the importanceof scaffold topography that can regulate cell behaviors.Based on the above research, we found that the random nanofibers structure ismore advantageous to the osteogenetic differentiation of BMSCs compared with those aligned nanofibers. But their relative hydrophobicity and surface inertia mighthinder their biomedical application. Here, we use low temperature atmosphericplasma to treat random PLLA nanofibers for various times with1,5or10min, tomodify the surface properties and explore the subsequent effects on the behaviors ofrat BMSCs. Our analysis demonstrated that both the amidogen groups on the surfaceand hydrophilicity increased with treatment time. However, the spreading andproliferation of BMSCs were greatest on the5-min-treated nanofibers, followed by1-min and then10-min treatments. qRT-PCR analysis showed that BMSCs on the5-min-treated nanofibers had the highest expression level of osteogenic markergenes, including RUNX2, BMP2, ALP, COL1A1, OPN and OCN. And the5-min-treated nanofibers promoted the highest levels of alkaline phosphatase activityin these cells. These results suggest that atmospheric plasma treatment of PLLAnanofibers is a feasible effective technique to improve biomaterial biocompatibilityand promote osteogenic differentiation of BMSCs.To evaluate the bone repair effect of MBG/DEX materials and nanofibers in vivo,the MBG/DEX samples and5min plasma-treated PLLA nanofibers were implantedinto the rabbit model of mandible defect. At4and12weeks of implantation, wefound that they could provide a favourable role in the bone repair process, and a wellosseointegration between new bone tissue and normal bone was presented after12weeks, the repair effects of MBG/DEX materials and nanofibers were very similarwith the classical repair materials. These results showed that the MBG/DEX materialand plasma-treated PLLA nanofibers could guide bone regeneration significantly,accelerate the process of bone repair, and improve the quality of new bone tissueeffectively.