Scaffold mediated delivery of drugs/genes for promoting nerve regeneration via gene silencing/pathway inhibition after traumatic nerve injuries

• Main Author: Zhang, Na
• Other Authors: CHEW Sing Yian
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Bioengineering
• Online Access: https://hdl.handle.net/10356/146233
• Institution: Nanyang Technological University

Axons damaged by traumatic injuries are unable to spontaneously regenerate in the adult central nervous system (CNS). Although the peripheral nervous system (PNS) has some regenerative capabilities, the ability of growth is often limited due to scar tissue formation that hinders axonal regeneration. Various biomolecules (i.e. genes/drugs) offer strategies for improving regeneration by enhancing the intrinsic growth capability of neurons and overcoming the inhibitory environment that prevents neurite outgrowth. Unfortunately, several bottlenecks remain and has been preventing the successful utilization of drugs/genes. First and foremost, is the lack of robust delivery platforms to deliver drugs/genes effectively in vitro and in vivo. Secondly and equally important, is the fact that despite the plethora of in vitro drug screening platforms available, such as micropillars and microfluidic devices, it remains difficult to translate in vitro outcomes to in vivo applications with good correlations. Consequently, the development of effective therapeutics, particularly targeting tissue regeneration, remains slow. Objectives: This thesis aims to explore the synergistic effects of biochemical signals and topographical cues in enhancing nerve regeneration. Specifically, effective therapeutics which promote robust axon regeneration after traumatic nerve injuries are investigated. Besides that, efficient drug/gene delivery platforms which are able to provide sustained biochemical signals and topographical cues to enhance nerve regeneration are also explored. Methodologies: In order to find effective therapeutic candidates for promoting axon regeneration after traumatic nerve injuries, both in vitro and in vivo works were carried out. The in vitro works includes aligned fibrous scaffold design and characterizations, drug/gene screening using cortical/DRG neurons by evaluating the length of neurite growth. The in vivo works include establishing animal injury models, in vivo scaffold fabrication and characterizations, scaffold implantation as well as morphometric and functional assessments. Key findings: A biomimicking aligned fiber substrate that provides sustained and effective non-viral delivery of miRs for in vitro and in vivo miR screening was successfully established. With this platform, we discovered that a three miR cocktail (i.e. miR-132/miR-222/miR-431) is able to promote significant axon regeneration and functional recovery. Additionally, a laser-induced axotomy model on biomimicking aligned fiber substrates which provided a sustained delivery of therapeutics for in vitro drug/gene screening was also been established. By adopting this platform, the distance of axotomy can be precisely controlled. We found that miR-132/miR-222/miR-431 cocktail stimulated the most robust neurite outgrowth. More importantly, distance effects on neurite outgrowth were overcome by the effects of miRs. Conclusions: Given that the miR-132/miR-222/miR-431 cocktail promotes neurite outgrowth in both intact neurons and axotomized neurons, as well as exhibits robust axon regeneration after spinal cord injury, we conclude that the cocktail of miR-132/miR-222/miR-431 is a promising therapeutic for spinal cord injury treatment.