Construction Of Neurotransmission Function Hydrogel And Its Application In Spinal Cord Injury Repair

Spinal cord injury often results in the loss of all or part of the patient's motor and sensory functions,causing a heavy burden of life and psychological burden on the patient,and there are currently no effective methods and methods for treating spinal cord injury.Therefore,how to promote nerve repair and regeneration after spinal cord injury has been a research hotspot.The transplantation of tissue engineering scaffolds and the associated cells or active factors are a promising tool for the treatment of spinal cord injury.Although numerous reports indicate that natural or synthetic materials can be applied to central nervous tissue engineering.However,simply simulating the extracellular matrix does not satisfy the need for nerve cell growth.Central nervous tissue has certain neurotransmission properties,and nerve cells can maintain the development,homeostasis,and function of the central nervous system(CNS)through chemical substances and electrical signals.Therefore,CNS biomaterials not only need good biocompatibility,but also have certain neurotransmission function to facilitate cellcell signaling.On the other hand,some currently used stent biomaterials have problems with the mismatch of the mechanical properties of the CNS,which can easily cause stress stimuli,leading to the occurrence of inflammatory reactions and ultimately the failure of transplantation repair.Hydrogel is a kind of hydrophilic colloid material which is closest to human soft tissue.Through the regulation of components and structure,the elastic modulus of material and spinal cord can be highly matched.Therefore,from the point of view of bionics,this article simulates the neurotransmission function and soft mechanical properties of spinal cord tissue,and designs and prepares a neurotransmission functional hydrogel based on neurotransmitter dopamine,electrically conductive hydrogel and exosome as nerves tissue engineering scaffold for the repair of spinal cord injury.1.Neurotransmitter dopamine-functionalized hydrogel loaded with neural stem cells for spinal cord injury repairThe effectiveness of stem cell therapies has been hampered by poor cell survival and the unwanted differentiation of transplanted stem cells.These problems can be partially solved by using functionalized three-dimensional hydrogels that improve the survival of transplanted stem cells and provide biochemical cues to direct cell differentiation.Neurotransmitters,a family of chemical signaling molecules,play a critical role in neuronal outgrowth during embryonic development,and dopamine is a key factor in mediating cell–cell interactions during signal transmission,which is essential for neurogenesis.In this study,we functionalized gelatin hydrogels with dopamine and evaluated their role in regulating the neurogenesis of encapsulated neural stem cells(NSCs).Our results show that compared with the unmodified controls,gelatin hydrogels conjugated with dopamine promote neurite outgrowth and the differentiation of encapsulated NSCs into mature neurons.When the functionalized hydrogels were used to transplant NSCs,the hydrogels also promoted neuronal connectivity repair and axonal regeneration while inhibiting glial scarring after spinal cord injury,resulting in significant hindlimb functional improvement compared with the controls.Our findings show that cell–cell interaction cues can be harnessed to direct therapeutic NSC fate.2.Preparation of highly electroactive conductive hydrogel and their role in regulating differentiation of neural stem cellsMimicking soft tissue mechanical properties and the high conductivity required for electrical transmission in the native spinal cord is critical in nerve tissue regeneration scaffold designs.However,fabricating scaffolds of high conductivity,tissue-like mechanical properties and excellent biocompatibility simultaneously remains a great challenge.Here,a soft,highly electroactive,biocompatible conducting polymer hydrogel(CPH)based on a plant-derived polyphenol,tannic acid(TA),crosslinking and doping conducting polypyrrole(PPy)chains is developed to explore its therapeutic efficacy after a spinal cord injury(SCI).The developed hydrogels exhibit an excellent electronic conductivity(0.05-0.18 S/cm)and appropriate mechanical properties(0.3-2.2 kPa),which can be achieved by controlling TA concentration.In vitro,a CPH with a higher electroactivity accelerated the differentiation of neural stem cells(NSCs)into neurons while suppressing the development of astrocytes.3.High electroactive hydrogels promote repair of spinal cord injuryThe hydrogel scaffold material can be implanted as a “bridge” and connected to the spinal cord injury area,and serves to guide the nerve cells to grow into the injury area and promote functional recovery.Spinal cord tissue is an electrically conductive human tissue.Traditional hydrogel stents lack the ability of conducting electroactivity,which is not conducive to conduct electrical signals between cells,and can not construct a suitable conductive micro-environment for nerve cells,which limits the application of hydrogel stents in central nervous tissue engineering.In this study,the TA-PPy conducting polymer hydrogel developed as described above was used as a scaffold material.The hydrogel scaffold material was implanted to bridge both ends of the lesion.Studies have found that TA-PPy conducting polymer hydrogel scaffolds can improve the micro-environment of nerve regeneration in vivo,promote nerve tissue repair and functional recovery.4.Electroconductive hydrogels loaded with exosomes to repair spinal cord injuryIn recent years,exosomes as intercellular signaling carriers have attracted more and more attention from researchers.In this paper,exosome was further loaded with a highly electroactive hydrogel synthesized.It was found that loading exosome hydrogel can inhibit the thawing of macrophages to maintain their resting state.In addition,the loading of exosome hydrogels does not affect the survival of NSCs and is very suitable for neural differentiation and growth of NSCs.By constructing an animal model of spinal cord injury and performing in vivo implantation experiments,it was found that loaded exosome hydrogel can significantly promote nerve tissue regeneration and inhibit reactive astrocyte-mediated scar tissue formation,improving mouse hindlimb motor function.