Biomimetic Materials - Tissue Engineering

Tissue Engineering

Biomimetic materials in tissue engineering are materials that have been designed such that they elicit specified cellular responses mediated by interactions with scaffold-tethered peptides from extracellular matrix (ECM) proteins; essentially, the incorporation of cell-binding peptides into biomaterials via chemical or physical modification.

Such peptides include both native long chains of ECM proteins as well as short peptide sequences derived from intact ECM proteins. The idea is that the biomimetic material will mimic some of the roles that an extracellular matrix plays in neural tissue. In addition to promoting cellular growth and mobilization, the incorporated peptides could also mediate material degradation by specific protease enzymes or initiate cellular responses not present in a local native tissue. In the beginning, long chains of ECM proteins including fibronectin (FN), vitronectin (VN), and laminin (LN) were used, but more recently the advantages of using short peptides have been discovered. Short peptides are more advantageous because, unlike the long chains that fold randomly upon adsorption causing the active protein domains to be sterically unavailable, short peptides remain stable and do not hide the receptor binding domains when adsorbed. Another advantage to short peptides is that they can be replicated more economically due to the smaller size. A bi-functional cross-linker with a long spacer arm is used to tether peptides to the substrate surface. If a functional group is not available for attaching the cross-linker, photochemical immobilization may be used. In addition to modifying the surface, biomaterials can be modified in bulk, meaning that the cell signaling peptides and recognition sites are present not just on the surface but also throughout the bulk of the material. The strength of cell attachment, cell migration rate, and extent of cytoskeletal organization formation is determined by the receptor binding to the ligand bound to the material; thus, receptor-ligand affinity, the density of the ligand, and the spatial distribution of the ligand must be carefully considered when designing a biomimetic material.