Design and characterisation of novel peptide-based hydrogel for controlled delivery of therapeutics

Peptide-based hydrogels are widely applied in biomedical applications because they possess good biocompatibility, biodegradability, injectability, and non-toxicity. Peptides with short chains (< 20 amino acids) can self-assembled into nano fibrous hydrogels with secondary structures including alpha helices, beta-sheets and coiled-coils. Chemically cross-linked peptide hydrogels may be harmful to the human body because their toxic cross-linkers are difficult to degrade, which poses limitations in biomedical applications. To overcome these issues, physically cross-linked hydrogels have been designed with adjustable properties to suit different purposes. In this PhD project, peptide KFEFKFEFK and EFKFEFKFE were designed with beta-sheet structures and self-assembled into hydrogels at pH 7. KFEFKFEFK carried +1 net charge and EFKFEFKFE carried -1 net charge. The mechanical properties of these two hydrogels depended on the concentration of peptides. Both of them exhibited injectability according to the shear thinning/recovery test. Besides, hydrogels with different charges exhibited apparently different 3D cell culture abilities according to the mechanical properties test over 14 days. The biocompatibility of hydrogels depended on the type of cell lines according to the cell viability. In addition, large molecular weight polymeric probes with different charges (fluorescein-dextran, FITC-Poly-L-Lysine) were encapsulated into these two peptide hydrogels to study how electrostatic interactions can be exploited for controlled release kinetics. Based on the diffusion coefficient DE, it has been revealed that the large diffusivities of probes were induced by electrostatic repulsion in hydrogel system. Furthermore, recombinant human interleukine-2/21 (rhIL-2/21) were selected as large drug molecules to encapsulate into peptide hydrogels for the assessment of drug delivery application. The long-term (21days) controlled release of rhIL-21 in EFKFEFKFE hydrogel demonstrated that EFKFEFKFE was a promising drug delivery system for cancer immunotherapy.