Abstract

Growth factors are attractive for their ability to drive proliferation, differentiation and other biological programs critical for tissue repair. In many cases, growth factors are used to improve cell survival and integration of transplanted cells such as Mesenchymal Stromal Cells (MSC) within host tissue. However, growth factors, either alone or in combination with cells like MSC, are typically administered at supraphysiological doses that can lead to dangerous off-target effects when the growth factors diffuse away from the site where they are originally delivered. Short peptide mimics of full-length peptides can be a promising alternative since they can be covalently conjugated to biomaterials and therefore localized to the site of interest. However, these short peptide “mimetics” often lack the potency of their full-length counterparts. In this dissertation, I sought to improve the potency of growth factor mimicking and cell adhesive peptides to encourage differentiation of MSC. I focused on a peptide that mimics the knuckle epitope (KE) of Bone Morphogenetic Protein 2 (BMP-2). KE is from the region of BMP2 thought to bind the BMP receptor. I used orthogonal click chemistries (strain promoted-azide alkyne cycloaddition (SPAAC) and maleimide-thiol) to graft either KE or integrin binding cyclo-RGD (cRGD) peptides to alginate hydrogels. I first optimized SPAAC for grafting cRGD to alginate hydrogels, and found that cRGD grafted in this manner, through a heterobifunctional crosslinker (BCN-amine) was more potent than cRGD that was directly grafted to alginate via carbodiimide chemistry. I then sought to increase the potency of the KE peptide. MSC expressed key markers of osteogenesis (RUNX2, Alkaline Phosphatase, ALP and osteocalcin, OCN) in a KE-dose dependent manner. Interestingly, when co-presented with cRGD, KE at a high concentration partially mimicked the activity of full length BMP-2. To investigate the possibility that the mechanism through which high KE dose induced MSC osteogenesis was through close proximity between KE and cRGD, I used the orthogonal chemistries to create alginate polymers grafted with both KE and cRGD (bivalent), forcing the peptides to be closer to one another than when the peptides were grafted to different alginate chains (monovalent) at a constant overall peptide concentration. In these studies, I found that close proximity between cRGD and KE can explain much, but not all, of the need for high KE dosage to induce MSC osteogenesis. The methodology and results gained these studies could be used as a guideline for future models, either as a platform for studying another kind of growth factor and/or integrin binding peptide, or as an application for safer growth factor delivery.

Committee Chair

Nathaniel Huebsch

Committee Members

Cory Berkland; Lori Setton; Marcus Foston; Matthew Silva

Degree

Doctor of Philosophy (PhD)

Author's Department

Biomedical Engineering

Author's School

McKelvey School of Engineering

Document Type

Dissertation

Date of Award

3-3-2025

Language

English (en)

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