## 4 Potential Applications of Peptide-Synthetic Polymer Hybrids
### Crosslinked Hydrogels and Scaffolds for Tissue Engineering
Furthermore, the indicated temperature enhanced the fibril assembly of peptide via an antiparallel arrangement of the \(\beta\)-sheets through hydrophobic interactions. These interactions were established between the alanine residues laterally stabilized by hydrogen bonding between lysine and peptide carbonyls of adjacent polypeptide chains. To assess the applicability of the hybrid hydrogels for vocal fold tissue engineering, the stiffness (_i.e._, elastic modulus) and the degree of elasticity (_i.e._, loss tangent) of the gels were tested by torsional wave analysis showing good mechanical resistance and stability. However the major drawback was the incompatibility of the crosslinking process with mammalian cells. The indicated limitation was subsequently overcome by just adjusting the peptide sequence [105] and specifically by adding arginylglycylaspartic acid groups (RGD) that enhanced cell adhesion. Thus, elastin-mimetic hybrid polymers (EMHPs) with an alternating multiblock architecture were again obtained by a step-growth polymerization method. In this case, PEG was employed as a synthetic polymer that was covalently linked to different AK2 peptides that incorporated the indicated RGD sequences. Crosslinking between lysine amine groups was performed by using hexamethylene diisocyanate and hydrogels with a compressive modulus of \(1.06\pm 0.1\) MPa were subsequently derived. Interestingly, EMHPs having RGD groups exhibited increased helical structure compared with the peptides alone, likely owing to H-bonding between the arginine residues with the oxygen atoms in PEG. It was also observed that neonatal human dermal fibroblasts (NHDFs) were able to adhere to the hydrogels within 1 h of culture and to spread and develop F-actin filaments after 24 h. Furthermore, NHDF proliferation was only observed on hydrogels containing RGD domains, demonstrating the importance of integrin engagement for cell growth. In this way, the synthesized cell-instructive hybrid copolymers are promising candidates as elastomeric scaffolds for tissue engineering since not only were strong and elastic but also could support cell adhesion and growth. Finally, another interesting and recent work related to smart biohydrogels was conducted by [PERSON] _et al._[106], who reported the preparation of peptide-saccharide hydrogels through a vinyl sulfone-thiol conjugated addition under mild conditions. In order to evaluate the viability of mesenchymal stem cells (MSCs) in the hydrogels a qualitative Live/Dead staining analysis (Invitrogen) was performed. After 1, 7 and 14 days _in vitro_ at pH 7, the viability of MSCs encapsulated in the hydrogels was found to be greater than 90%, which was directly related to differentiation potential and metabolic activity. Thus, due to the non-cytotoxicity (_i.e._, good cell viability) of the 3D samples and biodegradability (_i.e._, they were composed of natural building blocks), the peptide-saccharide hydrogels can be used as a platform for culturing MSCs. Furthermore, the new hydrogels have the potential to be further functionalized to provide biophysical and biochemical cues to encapsulated cells and precisely control cell function and fates.