טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSarig-Nadir Offra
SubjectA Hydrogel Scaffold Composed of Polyethylene Glycol and
Fibrinogen for in-vitro Peripheral Nerve
Regeneration
DepartmentDepartment of Biomedical Engineering
Supervisor Professor Dror Seliktar
Full Thesis textFull thesis text - English Version


Abstract

Extensive effort is being put in developing new treatments for serious peripheral nerve injury. Many different materials, mostly natural or synthetic have been developed over the years to serve as nerve guidance conduits (NGCs), which help to facilitate a directional axonal sprouting from the proximal end toward the distal end of the injured nerve. In most cases, these NGCs do not achieve the performance of the gold standard treatment, nerve autografts. We apply an alternative biomaterials approach for nerve regeneration using a biosynthetic material comprised of both natural fibrinogen and synthetic poly(ethylene glycol) (PEG) constituents. The purpose of this investigation was to evaluate dorsal root ganglion (DRG) cell outgrowth in PEGylated fibrinogen hydrogels and to asses the potential of this hydrogel as an NGC material. The PEGylated fibrinogen hydrogels readily supported extensive outgrowth of sprouting neurites and invading glial cells from encapsulated DRGs in the presence of nerve growth factor (NGF). By changing the hydrogel composition (i.e. the relative amount of PEG to fibrinogen or the fibrinogen concentration) we were able to control the outgrowth characteristics of DRG cells. In addition, preliminary results showed that the PEGylated fibrinogen hydrogel supports in vitro myelination, a process required for functional nerve regeneration. To further understand the mechanism by which DRG cells penetrate into the PEGylated fibrinogen hydrogel we employed different matrix metalloproteinases (MMPs) inhibitors on DRG-hydrogel cultures and examined the inhibitor’s effect on the DRG cell outgrowth. Our results demonstrate that DRG cell outgrowth into PEGylated fibrinogen hydrogels is inhibited by MMP inhibitors and that the outgrowth characteristics are inhibitor type- and concentration-dependent. Although the PEGylated fibrinogen hydrogel supports extensive outgrowth of DRG it still requires geometric features capable of controlling the direction of the neural outgrowth. By using a commercial laser microdissector microscope we were able to create guidance microchannels within the hydrogel material. These photo-patterned microchannels were characterized and were shown to guide the directional growth of neural cells from DRG explants. To conclude, we demonstrated that the PEGylated fibrinogen hydrogel highly supports the outgrowth of neural cells and with additional physical modifications can serve as a potential NGC material.