Turning peptides into bioactive nylons

Rational design of poly(peptide-ester) block copolymers for enzyme-specific surface resorption

Tissue resorption and remodeling are pivotal steps in successful healing and regeneration, and it is important to design biomaterials that are responsive to regenerative processes in native tissue. The cell types responsible for remodeling, such as macrophages in the soft tissue wound environment and osteoclasts in the bone environment, utilize a class of enzymes called proteases to degrade the organic matrix. Many hydrophobic thermoplastics used in tissue regeneration are designed to degrade and resorb passively through hydrolytic mechanisms, leaving the potential of proteolytic-guided degradation underutilized. Here, we report the design and synthesis of a tyrosol-derived peptide-polyester block copolymer where protease-mediated resorption is tuned through changing the chemistry of the base polymer backbone and protease specificity is imparted through incorporation of specific peptide sequences. Quartz crystal microbalance was used to quantify polymer surface resorption upon exposure to various enzymes. Aqueous solubility of the diacids and the thermal properties of the resulting polymer had a significant effect on enzyme-mediated polymer resorption. While peptide incorporation at 2 mol% had little effect on the final thermal and physical properties of the block copolymers, its incorporation improved polymer resorption significantly in a peptide sequence- and protease-specific manner. To our knowledge, this is the first example of a peptide-incorporated linear thermoplastic with protease-specific sensitivity reported in the literature. The product is a modular system for engineering specificity in how polyesters can resorb under physiological conditions, thus providing a potential framework for improving vascularization and integration of biomaterials used in tissue engineering.

Embedding Peptides into Synthetic Polymers: Radical Ring-Opening Copolymerization of Cyclic Peptides

Biopolymers such as proteins and nucleic acids are the key building blocks of life. Synthetic polymers have nevertheless revolutionized our everyday life through their robust synthetic accessibility. Combining the unmatched functionality of biopolymers with the robustness of tailorable synthetic polymers holds the promise to create materials that can be designed ad hoc for a wide array of applications. Radical polymerization is the most widely applied polymerization technique in both fundamental science and industrial polymer production. While this polymerization technique is robust and well controlled, it generally yields unfunctional all-carbon backbones. Combinations of natural polymers such as peptides, with synthetic polymers, are thus limited to tethering peptides onto the side chains or chain ends of the latter. This synthetic limitation is a critical restraint, considering that the function of biopolymers is programmed into the sequence of their main chain (i.e., primary structure). Here, we report the radical copolymerization of peptides and synthetic comonomers yielding synthetic polymers with defined peptide sequences embedded into their main chain. Key was the development of a solid-phase peptide synthesis (SPPS) approach to generate synthetic access to peptide conjugates containing allylic sulfides. Following cyclization, the obtained peptide monomers can be readily copolymerized with N,N-dimethylacrylamide (DMA)─controlled by reversible addition-fragmentation chain transfer (RAFT). Importantly, the developed synthetic strategy is compatible with all 20 standard amino acids and uses exclusively standard SPPS chemicals or chemicals accessible in one-step synthesis─prerequisite for widespread and universal application.