Extracellular matrix proteins like collagen promote regeneration as implants in clinical studies. However, collagens are large and unwieldy proteins, making small functional peptide analogs potentially ideal substitutes. Self-assembling collagen-like-peptides conjugated with PEG-maleimide were assembled into hydrogels. When tested pre-clinically as corneal implants in mini-pigs, they promoted cell and nerve regeneration, forming neo-corneas structurally and functionally similar to natural corneas.
IntroductionResident stem cells capable of regeneration are present in almost every organ in the body but frequently cannot achieve the repair needed after damage by injury or disease. The limiting factor is often the extracellular matrix (ECM) surrounding the cells. During damage, the ECM is frequently replaced by scar tissue, which does not provide the required structural integrity and inhibits regeneration of functional tissue. 1 The replacement of scar tissue with ECM or biomaterials that mimic its structure and function could therefore promote regeneration. 1,2 Regenerating damaged tissues and organs, including corneas, could potentially mitigate the need for organ transplantation, which currently faces acute worldwide shortage and immune rejection issues. We have previously shown in human corneal transplantation clinical studies that cell-free corneal ECM mimics made from recombinant human collagen (RHC) stimulated regeneration of the human cornea, an organ that normally does not regenerate on its own. 3,4 However, RHC replicates human collagen, which, like many other ECM biopolymers, is comprised of large proteins and is difficult to manipulate. Smaller units of complex proteins, particularly those capable of self-assembly have been examined as controllable ECM mimics, as they can form a wide range of structures including nanofibres. 5 Collagen-like peptides (CLPs), also known as collagen-mimetic peptides (CMPs), have recently been investigated as potential alternatives to collagen, as they can self-assemble and form triple helical nanofibers like collagen. [6][7][8][9][10][11][12][13][14] In order to stabilize the triple helices of CLPs, polymer templates that can link the three peptide chains together with sufficient flexibility to allow for proper packing of the chains with correct amino acid register have been tested. 7 More recent designs have used collagen peptides as the physical crosslinks for the polymer system through triple helix formation. 6,7 CLPs and CLP-polymer systems have now been tested in vitro as engineered 3D scaffolds on their own, 8 conjugated to polyethylene glycol (PEG) backbones, 9-11 and complexed with bioactive factors 12,13 or localization agents such as gold nanoparticles. 14 However, the majority of studies have been confined to in vitro testing with cells.The trend in regenerative medicine is now towards the use of complex, naturally derived ECM macromolecules, as intact decellularised scaffolds or as processed and purified concentrated liquids or finely ground powder that are the...