Ph.D Thesis


Ph.D StudentKaplan Ben
SubjectGuidance of Regenerating Axons in Tissue Engineered
Constructs
DepartmentDepartment of Medicine
Supervisor PROF. Shulamit Levenberg


Abstract

Nerve Injuries including peripheral nerve injuries and spinal cord injuries are common traumatic syndromes with worldwide distribution. Severe cases of peripheral nerve injuries including injuries with skeletal muscle comorbidity are frequently untreatable. Spinal cord injury is currently considered an incurable condition often with devastating effects on patients’ lives. Methods of tissue engineering have been widely explored to encourage regeneration and develop novel treatments for nerve injuries. While some mild progress has been made in pre-clinical settings, translation into clinical practice was not achieved. One limitation of current techniques of tissue engineering is their limited capability to control the organization and orientation of cells and axons and restore preinjury structures. Disorganized axonal growth may lead to generation of painful neuromas and failure of reinnervation of preinjury targets. In the current work we explored the possibility of guiding axonal growth inside implanted engineered scaffolds and alter disoriented and random regeneration into a controlled or linear growth pattern.

In first part of the study, we explored the possibility of innervating engineered muscle grafts transplanted to an abdominal wall defect in vivo, by transferring a native nerve to the graft. The nerve transfer procedure was used to guide axons into the graft and generate neuromuscular connections between the regenerating host nerve and the transplanted muscle graft. Six weeks post-transplantation, nerve conduction studies and electromyography demonstrated increased innervation in engineered grafts neurotized with a native nerve, as compared to non-neurotized grafts. Histological assessments revealed axonal penetration and formation of neuromuscular junctions within the grafts.

In the second part of our study, a fabrication procedure based on 3D printing was carried to generate highly ordered and anatomically personalized, biodegradable polyester scaffolds for nerve regeneration. Scaffolds were customized specifically for spinal cord injury by using an oriented multi-layer printing pattern which established a linear structure in the fabricated scaffold to match the aligned topography of the white matter in the spinal cord. The oriented scaffold was shown to guide regenerating axons to linear confirmations mimicking the preinjury structure of spinal axons and support growth of stem cell derived neurons in vitro and in vivo.

This work demonstrates two novel approaches to enhance control over the directionality and growth patterns of axons regenerating into transplanted engineered scaffolds. The findings may advance the field of tissue engineering and may be applied in future studies to support the potency of additional interventions for axonal regeneration.