脊髓损伤治疗依然是世界性的一大医学难题，本项目通过3D仿生打印技术构建定位、梯度、长效释药系统并应用于大鼠脊髓损伤修复。研究内容包括：脊髓再生药物筛选；凝胶材料的选择与胶凝研究； 3D打印定位释药系统、皮质脊髓束导管梯度释药系统；制备PLGA-蛋白微球、EMSCs自交联凝胶以及Minicircle-DNA纳米凝胶，并打印长效缓释系统；体内外观测EMSCs在不同部位、不同作用凝胶中增殖、迁移和神经分化；采用荧光金逆行示踪和BDA顺向示踪等技术，考察灰质区神经接力网络的形成、纵向导管中皮质脊髓束（CST）轴突的下行延伸以及神经接力网络与CST神经纤维之间的突触连接，优化生物墨水组方与打印工艺；BBB评价大鼠的功能恢复并探讨其可能机理。本项目拟与美国哈佛大学医学院合作，通过优势互补协同研究，为新型释药系统构建、脊髓损伤修复和3D打印技术的创新应用提供新思路、新技术、新载体。

Spinal cord injury (SCI) often results in persistent functional deficits, and nerve repair after SCI remains to be a difficult problem in whole world. This multidisciplinary joint research project will focus on constructing biomimic 3D printed self-crosslinking gels for local, gradient, and long-term drug delivery and spinal cord regeneration, including screening drugs for spinal cord regeneration based on 3D printing technique; screening of potential ink formulations and comprehensive studies on degree of crosslinking, rheological and mechanical properties and degradation ability of the resultant gels; 3D printing of site-specific drug delivery systems in grey and white matter, as well as the gradient release system in the conduits for the corticospinal tract; preparation of protein-encapsulated poly(lactide-co-glycolide) (PLGA) microspheres, ectodermal mesenchymal stem cells (EMSCs) self-crosslinking gels and Minicircle-DNA nanogels for long-term delivery of the factors in the 3D-printed drug release systems; in vitro evaluation of EMSCs proliferation, migration and neural differentiation when embedded in gels site-specifically deposited with various factors; evaluation of the formation of a relay neuronal network and the descending of corticospinal tract (CST) axons; examination of the connection between the relay neuronal network and the CST fibers by the formation of synapses, so as to further optimize the bioink formulations for 3D printing; evaluation of functional recovery after gel transplantation to the lesion site of transected SCI using BBB locomotor rating scale and exploration of the possible mechanisms for nerve regeneration. Altogether, in collaboration with Harvard Medical School, this multidisciplinary joint research project has complementary advantages and will provide new insights and technologies for the application of 3D printing technique in developing novel drug delivery systems and nerve regeneration after SCI.