Development of Protein-Displaying Peptide Hydrogels for Tissue Engineering

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Abstract The development of novel bio-materials for tissue engineering is a burgeoning research field with broad impact on public health in the United States. Advances in the field have the potential to treat myriad medical conditions such as dermal injuries (i.e. lacerations and burns), cardiac trauma, severe spinal injuries, and bone breaks. Currently, most synthetic materials used for tissue engineering are polymers that incorporate growth factors or peptides into a material matrix. The mode of incorporation ranges from covalent (for small peptides) to adsorptive (for larger proteins of interest). The field would be significantly advanced if full-length proteins could be incorporated and displayed within tissue engineering platforms both with high affinity and specificity. Stimulus-responsive peptide hydrogels have received increasing attention in the materials science and tissue engineering communities of late. These types of materials assemble into nano-scale fibers that are hydrated to form rigid gel materials. The advantages of these materials include, facile access to pure monomer units, non- toxicity, injectability, and in certain cases, anti-bacterial properties. What lacks, however, is the ability to incorporate and display functional proteins through high-affinity non-covalent binding interactions. In the mentored phase of the proposed research program, phage display technology will be developed using virus- like particles (VLPs) derived from bacteriophage Q¿, a viral nanoparticle principally utilized by the Finn laboratory for myriad bio-technological applications. The proposal aims to develop a platform for the display of peptide libraries on the exterior surfaces of Q¿ VLPs for use in directed evolution experiments to identify variants that interact specifically with a gel-forming peptide, MAX8. We will display the selected peptides on the surface of Q¿ VLPs and evaluate how binding affinity and gel-incorporation are correlated. The material properties of the newly synthesized materials will then be rigorously characterized. The independent phase of the proposed research will grow directly from the results of the mentored phase. The research program initiated in my group will use information garnered about the use of peptide affinity tags for incorporation of macromolecules into hydrogels to develop a novel tissue engineering approach. The peptide affinity tags identified in the mentored phase will be fused to bone morphogenetic protein 2 (BMP2) at one or both termini, and act as nucleation sites for gel fibril formation. The modified BMP2 proteins will be integrated into peptide hydrogels and the materials evaluated for relevant properties such as protein release and loading capacity. These new materials will serve as scaffolds in tissue culture experiments to promote the growth and differentiation of osteo-progenitor cells. An advantage of this particular approach is that materials are formulated by simple mixing of gelling components, thus making incorporation of multiple growth factors facile. This will be extended in future incarnations to include multiple growth factors to better mimic the native extracellular matrix.