# The Role of Extracellular Matrix (ECM) Adhesion Motifs in Functionalised Hydrogels
## 5 ECM-Derived Peptide Sequences and Their Use in Biomimetic Hydrogel Functionalisation
### Laminin: IKVAV Motif  
The pentapeptide sequence IKVAV is derived from the laminin \(\alpha\)1 chain [115], found between residues 2116-2120. The N-terminal isoleucine (I) residue is considered to be vital for promoting cell adhesion activity [116]. Various synthetic peptides from the A chain region of laminin were tested for biological activity and a 19-mer peptide found above the carboxyl globule of the A chain was found to be a promoter of multiple key cellular processes, such as cell adhesion and migration. After testing shorter sequences within this peptide, the pentapeptide IKVAV was confirmed to be an active site for cell adhesion, but more specifically neurite outgrowth. Results concluded that the IKVAV sequence is a principal site within the ECM protein laminin, which serves to regulate cell behaviour [116].  
The pentapeptide motif IKVAV was used to functionalise poly (lactide ethylene oxide fumarate) (PLEOF) and create a hydrogel capable of mimicking the ECM [117]. The regenerative environment created was suitable for neural stem cell (NSC) function. There were more neuronal cells present on the hydrogel surface incorporating IKVAV peptides compared to the pure PLEOF hydrogel surface [117]. The large number of cells on the IKVAV-PLEOF hydrogel were mostly viable following 7 days of incubation. In vivo biocompatibility was also tested, whereby IVVAV-PLEOF hydrogels were successfully integrated into subcutaneous rat tissue and the hydrogel was responsible for increased blood vessel formation [117]. The surface of the IKVAV-PLEOF hydrogel was also more conductive of cell adhesion, which was measured at 60-70% compared with 1-10% on the control PLEOF hydrogel [117]. The capacity for the hydrogels to promote NSC differentiation was evaluated, and more neurons were observed on the surface of IVVAV-PLEOF. Through this work, it is clear that the IKVAV-PLEOF hydrogel can successfully imitate the ECM through its biocompatibility with cells and tissues, along with the ability to stimulate NSC differentiation. These stem cell laden hydrogels may have applications in regenerative spinal cord injury for neural tissue engineering [117].  
[PERSON] et al. [118] investigated the modification of IKVAV onto a silk fibroin-based hydrogel for use as a brain tissue engineering scaffold [118]. NSCs were viable in both the silk fibroin hydrogel modified with IKVAV and the unmodified hydrogel, but the IKVAV modified hydrogel showed a higher viable cell count overall [118]. Cell proliferation data further supported this result, where IKVAV-modified hydrogels showed increased cell proliferation compared to the unmodified hydrogel. The neuronal differentiation potential of both hydrogels was also investigated, with more cells in the IKVAV modified hydrogels being positive for the neuronal differentiation markers \(\beta\)III-tubulin and microtubule-associated protein 2 (MAP-2), compared with those in unmodified hydrogels [118]. These results suggest that silk fibroin hydrogels modified with IKVAV could be used as biomimetic scaffolds for brain tissue engineering applications, following injuries such as trauma and stroke [118].