Date of Graduation

12-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Chemical Engineering

Advisor/Mentor

Almodovar, Jorge

Committee Member

Servoss, Shannon L.

Second Committee Member

Thompson, Audie K.

Third Committee Member

Wolchok, Jeffrey C.

Fourth Committee Member

Nayani, Karthik

Keywords

Biomaterials; Layer-by-layer method; Schwann cells; Tissue regeneration

Abstract

When a peripheral nerve injury (PNI) occurs, the gold standard for tissue regeneration is the use of autografts. However, due to the secondary effects produced by multiple surgeries involved in the removal and implantation of autografts for very small lesions, it is possible to replace them with the use of Nerve Guide Conduits (NGCs). However, NGCs are limited to short lesions (less than 1 cm). This limitation is caused by the absence of compounds in the extracellular matrix (ECM) that autografts can provide. Since much of the regenerative process takes place on the NGC surface, our work aims to modify its surface using heparin and collagen coatings, two natural polymers present in the ECM. Heparin/collagen bilayers (HEP/COL) will increase biocompatibility, cell adhesion and migration, and allow the incorporation of neurotrophic factors such as Nerve Growth Factor (NGF). This research evaluates the effects on human Schwann cells (hSCs) when cultured on a commercial collagen NGC under four conditions: without coatings and with six heparin/collagen bilayers (HEP/COL)6 with and without NGF supplemented to the culture medium (10 ng/ml). We have exhaustively characterized (HEP/COL)6 coatings. The chemical structures of the polymers, the morphology, and the surface charge of the coatings could be determined. Real-time analysis of hSCs behavior showed three main phases: adhesion, proliferation, and adaptation. The adhesion phase was increased in the conditions with (HEP/COL)6, and the viability studies showed an increase of up to 250% compared to cells grown on polystyrene without coatings. The cell morphology has never been altered by (HEP/COL)6, as well as the morphology of the coated NGC. Cell migration was favored, and (HEP/COL)6 also increased the expression of some proteins such as BDNF, which promotes the duration of the myelination process, or TNF alpha, which is a mediator of inflammatory and immune functions. Concerning the surface modification of a commercial NGC, these studies showed an increase of more than 200% in cell viability when compared to uncoated NGCs. We also determined the presence of heparin and evidenced the cell adhesion on (HEP/COL)6 coated NGCs. In conclusion, (HEP/COL)6 seems to be a promising strategy to improve the performance of NGCs.

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