Engineering novel bio-inspired materials for stem-cell mediated bone regeneration

描述（由申请人提供）：一种模拟天然骨羟基磷灰石（HAP）和胶原蛋白的机械强度、可吸收性和组成的合成生物材料目前还没有上市。在初始强度和可吸收性之间折衷性能的合成移植物对于修复临界尺寸的缺陷是不理想的。因此，目前的合成材料不能很好地解决大骨缺损，导致生物功能、外观和患者生活质量的重大损害。本项目拟开发一种刚性的仿生材料，其原理为：1)明胶分子中HAP纳米晶体的自组织；2)受贻贝黏附蛋白-多巴胺启发，ph诱导钙-配体交联。强有力的试点数据支持所有提出的目标。我们的聚多巴胺掺杂hap -明胶纳米复合材料（PDHG）的抗压和抗拉强度分别接近皮质骨的90%和60%，并且在体外可降解。我们认为掺入多巴胺接枝的长链聚合物可以进一步提高拉伸强度，预示着长链增强PDHG （LcPDHG）多孔支架适用于CSD修复。从支架中释放的多巴胺也对成骨产生积极作用。该团队的长期目标是设计LcPDHG来满足最初的生物力学要求，并最终被内源性骨吸收和取代。在这个特殊的应用中，目的是确定长链聚合物的掺入如何影响LcPDHG的物理性质（例如，拉伸强度，降解），以及天然骨和干细胞如何对LcPDHG释放的游离多巴胺做出反应。核心假设是LcPDHG是一种生物活性材料，具有足够的机械强度、骨导电性和吸收潜力，可作为颅面和其他骨骼区域CSDs的承重移植物。为了验证这一假设，提出了三个具体目标：(1)阐明LcPDHG增强PDHG力学性能的机制，使其接近天然骨，并增加其体外降解；(2)确定多巴胺促进LcPDHG支架骨再生的细胞机制；(3)在大鼠颅骨临界尺寸缺损模型中评估LcPDHG支架的骨形成和移植物材料的替代。初步数据预测了成骨细胞和多巴胺刺激之间有希望的相互作用，并提出了通过多巴胺受体促进干细胞治疗的新信号。本研究具有重要意义，因为它将推进和扩大对多巴胺如何在骨组织工程（TE）中使用的理解，并提供第一个“羟基磷灰石和胶原”人工骨TE支架来修复大型骨缺损。有了这种类型的移植材料，应该可以避免多次手术，简化治疗临界尺寸的颅骨和面部骨缺损。

DESCRIPTION (provided by applicant): A synthetic biomaterial that mimics the mechanical strength, resorbability, and composition of natural bone hydroxyapatite (HAP) and collagen is not currently available. Synthetic grafts compromising properties between initial strength and resorbability are not ideal for repairing critical sized defects. Thus, large bone defects are not well addressed with current synthetic materials leading to significant impairments of biological function, appearance, and patient quality of life. This project proposes to develop a rigid, bio-inspired material using principles of 1) self-organization of HAP nanocrystals in gelatin molecule and 2) pH-induced calcium- ligand cross-links inspired from the mussel adhesive protein - dopamine. Strong pilot data support all of the proposed aims. Our polydopamine laced HAP-gelatin nanocomposite (PDHG) has compressive and tensile strength approximating 90% and 60% of cortical bone, respectively, and is degradable in vitro. We believe that incorporation of a dopamine-grafted long chain polymer can further improve tensile strength and portends the Long Chain enhanced PDHG (LcPDHG) porous scaffold applicable for CSD repair. The dopamine released from the scaffold also produces positive effects on osteogenesis. The long-term goal of this team is to engineer LcPDHG to fulfill the initial biomechanical requirements and to be eventually resorbed and replaced by endogenous bone. The objective in this particular application is to identify how the incorporation of long chain polymers affects the physical properties (e.g., tensile strength, degradation) of LcPDHG, and how the natural bone and stem cells respond to free dopamine released from LcPDHG. The central hypothesis is that the LcPDHG is a bioactive material with adequate mechanical strength, osteoconductivity and resorption potential to serve as a load bearing graft in CSDs in craniofacial and other skeletal areas. To test this hypothesis three specific aims are proposed: (1) Elucidate the mechanism by which LcPDHG enhances mechanical properties of PDHG to approximate natural bone, and increases its in vitro degradation; (2) Determine cellular mechanisms by which dopamine promotes bone regeneration in the LcPDHG scaffold; and (3) Assess bone formation and replacement of graft materials in LcPDHG scaffolds in a rat calvarial critical sized defect model. Preliminary data predict promising interactions between osteoblasts and dopamine stimuli, and suggest novel signaling via dopamine receptors to promote stem cell-based therapy. The proposed research is significant because it will advance and expand the understanding of how dopamine can be used in bone tissue engineering (TE) and provide the first "hydroxyapatite and collagenous" artificial bone TE scaffold to repair large bone defects. With a graft material of thi type, it should be possible to eliminate multiple surgeries and simplify the treatment of critical-size cranial and facial bone defects.