Development of Multidomain Peptide Hydrogels for Tissue Engineering Applications

Abstract

Over the past decade, multidomain peptides (MDP) have been designed, synthesized, and customized for tissue engineering applications. The goals of this work were twofold: 1) to develop novel MDP hydrogels with unique chemical properties 2) to evaluate previously developed MDP hydrogels for biocompatibility. By utilizing the principle of covalent capture, an MDP hydrogel with enhanced rheological properties was developed and characterized. The incorporation of cysteine residues into the MDP sequence allowed for covalent bonding between adjacent peptide nanofibers, which ultimately resulted in a hydrogel with increased rheological properties. Through in vitro, ex vivo, and in vivo experimentation, biological response to several MDP hydrogels was evaluated. This work highlights the immense importance of systemic factors in the physiological response to the MDP. Ex vivo experiments performed on the dental pulp of extracted rat mandibles showed little cellular infiltration, and sequestration of key proteins in the MDP hydrogel was noted. Hydrogels injected near odontoblast cells absorbed dentin sialophosphoprotein, a protein with key applications in regenerative dentistry. When MDP hydrogel was injected into the core of pulpal soft tissue, extracellular matrix deposition, scaffold remodeling, and biodegradation were seen. These results support potential use of the MDP as a scaffold for tissue engineering of the dental pulp. In vivo subcutaneous injection experiments contrasted ex vivo results with rapid cellular infiltration of the MDP hydrogel. The MDP hydrogel quickly becomes highly vascularized, and a high density of nerve fascicles from the peripheral nervous system are found within the MDP implant. A cytokine array elucidated key proteins secreted by cells into the MDP hydrogel that may be responsible for these effects, and it is hypothesized that the immune system plays a significant role in defining these responses. Lastly, an attempt to mimic the function of bone morphogenetic protein-2 (BMP-2) using the MDP hydrogel is described. The BMP-2 mimetic MDP hydrogel demonstrated cytocompatibility with pre-osteoblast cells, but failed to induce ectopic calcification after subcutaneous injection. Through a variety of experiments, including ex vivo, in vitro, and in vivo analysis, advances were made in understanding the physiological response to MDPs and its dependency on MDP sequence.