Hydrogel delivery of DBM and exosome mimetics for bone repair

点击翻译按钮获取中文摘要

Abstract Congenital and acquired craniofacial defects are not uncommon. Demineralized bone matrix (DBM) has been widely used for the orthopedic repair. However, more extensive use of DBM is limited due to its particulate nature after demineralization and rapid particle dispersion following irrigation, resulting in unpredictable osteoinductivity. Viscous excipients are often employed to produce stable suspension of DBM particles, but such carriers are rapidly dissolved in a body and the localized effect of osteogenic components present in DBM such as bone morphogenetic proteins (BMPs) may not expect at the defect site. Although exogenous BMPs can be combined to enhance DBM capacity, its clinical application requires supraphysiological doses and has revealed significant adverse effects. Thus, there is a need to develop alternative strategies that can enhance the osteogenic potency of DBM. This study seeks to enhance bone regeneration capacity by incorporating DBM into a self-healing dynamic polymer network that combines physiological stability and pro-osteogenic properties. Upon BMP stimulation, BMP efficacy is greatly reduced due to the enhanced expression of natural BMP antagonists such as noggin. Thus, this study will further enhance the potency of BMPs present in DBM by abrogation of BMP antagonism through RNA interference for noggin. Cell-derived exosome mimetics (EM) will be applied as a bio- vector to deliver RNA interference molecules in a localized and efficient manner. The overall objective of this proposal is to devise a robust bone graft composite that can effectively repair bone defects by integrating DBM and noggin-silencing EM into polymeric carrier systems. To achieve this goal, we propose three aims. In Aim 1, we will develop a malleable and self-healing hydrogel based on the self-assembly of phytochemical-grafted chitosan with silica-rich nanoclays, where the decorated phytochemical drives dynamic intermolecular interactions for gelation and nanoclay works as physical crosslinker with osteoinductive property. By varying the ratio of phytochemical to nanoclay and the content of DBM particles, hydrogel/DBM composites will be designed and prepared by evaluating gelation kinetics, injectability and self-healing characteristics. The osteoinductive activity of the developed composite will be determined in vitro and in a rat calvarial defect. Next in Aim 2, we will harvest EM from MSCs transfected with noggin-directed siRNA and evaluate the synergistic effect of EM on DBM-induced bone formation. We will also conjugate EM to hydrogels via a click crosslinking reaction for more localized and prolonged noggin silencing effects. Finally in Aim 3, we will integrate DBM and EM loaded with noggin siRNA into self-healing hydrogels of phytochemical and nanoclay developed from Aim 1 and evaluate the ability of the bone graft composite to promote bone regeneration in more challenging environments using a mandibular defect model. Successful bone formation will be evaluated compared with commercial DBM products and recombinant BMP-2. Successful completion of these studies will identify a new strategy to improve clinical efficacy of current bone grafting by maximizing activity of BMP signaling in DBM-mediated bone regeneration.