An Injectable Phosphate Releasing Bone Tissue Construct Encapsulating Adipose-Derived Stem Cells and Diphosphate Cleaving Enzymes to Promote Biomineralization in Critical Size Bone Defects

临界尺寸骨缺损（CSBD）是一种不愈合的骨损伤，需要治疗性干预来诱导骨形成。这些损伤是由于创伤、肿瘤切除、发育异常和感染造成的。骨愈合受损，包括延迟愈合或不愈合，在加拿大有15万至20万人住院，每年给医疗保健系统带来12至180亿美元的负担。目前的黄金标准是从患者髂骨上移植自体骨到缺损处。需要进行第二次手术干预增加了术后并发症和伤口感染的风险，并且需要更长的住院时间。一种可通过微创手术实施的注射治疗方式将降低感染风险、住院时间和手术费用。我们成功地证明了在我们实验室开发的可注射壳聚糖海绵具有生物相容性，并在60天内完全生物降解。在壳聚糖海绵中添加酶可以持续释放磷酸盐离子，从而显著增加成骨前MC3T3细胞的生物矿化。此外，成骨因子在海绵中的高包封效率及其在30天内的可控释放可以实现。MC3T3和脂肪源性干细胞（ASCs）的包封表明了支架对细胞存活、增殖和分化的适宜性。在此，我们建议研究海绵作为ASCs包封、酶和成骨因子的输送系统和3d支架，并最终作为CSBD体内生物矿化的组织构建体。为了将这一有前景的技术平台应用于临床，必须在相关的CSBD动物模型中对海绵进行验证。我们将与参与该提案的工业和商业化专家合作，在该CHRP提案中取得成功，从而提供这一机会。

Critical size bone defects (CSBD) are non-healing bone injuries that require a therapeutic intervention to induce bone formation. These injuries occur due to trauma, removal of tumors, developmental anomalies, and infections. Impaired bone healing, including delayed union or non-union, accounts for 150,000 to 200,000 hospitalizations in Canada generating a $12 to$18 B/y burden on the health care system. The current golden standard is to graft autologous bone from the patients iliac crest onto the defect. The need to create a second surgical intervention increases the risk of post-surgical complications and wound infections, and requires longer hospitalization. An injectable therapeutic modality that can be administered using minimally invasive surgery will reduce risk of infection, time of hospitalization and\ surgical costs. We successfully demonstrated, that injectable chitosan sponges developed in\ our laboratory, are biocompatible, and completely biodegrade within 60 days. The addition of enzymes to the chitosan sponges provided a constant release of phosphate ions, which significantly increased biomineralization in pre-osteoblast MC3T3 cells. Further, a high encapsulation efficiency of osteogenic factors in the sponge and its controlled release over a period of 30 days could be achieved. The encapsulation of both MC3T3 and Adipose-Derived Stem Cells (ASCs) indicated the suitability of the scaffold for cells survivability, proliferationand differentiation. Herein, we propose to investigate the sponge as a delivery system and as a 3D-scaffold for ASCs encapsulation, enzymes and osteogenic factors, and ultimately as a tissue construct for in vivo biomineralization in CSBD. To translate this promising technology platform to clinics, it is imperative to validate the sponge in relevant animal model of CSBD. This opportunity will be offered by our success in this CHRP proposal in partnership with industry and commercialization specialists involved in this proposal.