Promising vaccine adjuvants of self-assembling peptide hydrogels for protein ovalbumin (OVA) are introduced in this study. The hydrogels are formed by the enzyme of phosphatase, and the vaccine adjuvant potency of both l- and d-peptide hydrogels is evaluated. The results indicate that, compared with the clinically used alum adjuvant, both l- and d-peptide hydrogels can increase the IgG production of OVA for about 1.3 and 3.8 times, respectively. Both gels can enhance antigen uptake and induce dendritic cell maturation, and promote and prolong accumulation of antigen in lymph node, as well as evoke germinal center formation. However, the d-peptide hydrogel with OVA exhibits a slightly more efficient accumulation of OVA in the lymph nodes and seems preventing tumor growth more significantly than its l-counterpart. With the good biocompatibility and degradability of peptide hydrogels, the hydrogels described in this study have big potential for the production of protein vaccines for immunotherapy against different diseases.

We demonstrate that the incorporation of one or two amino acids of phenylalanine (F) or 4-fluoro phenylalanine (^fF) will greatly lower the background fluorescence intensities of conventional quenched probes with quenchers. This enhanced quenching effect was due to the synergetic effect of the aggregation caused quenching and the presence of a quencher. Such strategy will not greatly affect the enzyme recognition properties to the probes. We also demonstrated that our self-assembled nanoprobe with the enhanced quenching effect showed a better performance in cells for the detection of cell apoptosis than the unassembled probes. Our study demonstrates that using molecular self-assembly can optimize and improve the performance of molecular probes and it provides a simple but very useful strategy to boost the signal-to-noise ratios of fluorescence probes.

We demonstrate that the incorporation of one or two amino acids of phenylalanine (F) or 4-fluoro phenylalanine (^fF) will greatly lower the background fluorescence intensities of conventional quenched probes with quenchers. This enhanced quenching effect was due to the synergetic effect of the aggregation caused quenching and the presence of a quencher. Such strategy will not greatly affect the enzyme recognition properties to the probes. We also demonstrated that our self-assembled nanoprobe with the enhanced quenching effect showed a better performance in cells for the detection of cell apoptosis than the unassembled probes. Our study demonstrates that using molecular self-assembly can optimize and improve the performance of molecular probes and it provides a simple but very useful strategy to boost the signal-to-noise ratios of fluorescence probes.

A hetero-hexameric protein system is developed in this study, which not only functions as cross-linkers for hydrogel formation but also offers docking sites for controlled delivery of bioactive molecules. First, a hexameric protein with two, four, and six tax-interacting protein-1 (TIP-1), respectively (named as 2T, 4T, and 6T), is designed and obtained. As the hexapeptide ligand (WRESAI) can specifically bind to TIP-1 with high affinity, the hexameric proteins of 2T, 4T, and 6T can be used to crosslink the self-assembling nanofibers of Nap-GFFYGGGWRESAI, leading to formation of injectable biohybrid hydrogels with tunable mechanical properties. Furthermore, a hetero-hexameric protein containing four TIP-1 and two C-terminal moiety of the pneumococcal cell-wall amidase LytA (C-LytA) proteins is designed and engineered (named as 4T2C). The 4T2C proteins can not only serve as cross-linkers for hydrogel formation but also provide docking sites for loading and controlled release of model drug Rhoda-GGK′. This study opens up new opportunities for further development of multifunctional hetero- recombinant protein-based hydrogels for biological applications.

Enzyme-responsive hydrogels have great potential in applications of controlled drug release, tissue engineering, etc. In this study, we reported on a supramolecular hydrogel that showed responses to two enzymes, phosphatase which was used to form the hydrogels and esterase which could trigger gel-sol phase transitions. The gelation process and visco-elasticity property of the resulting gel, morphology of the nanostructures in hydrogel, and peptide conformation in the self-assembled nanostructure were characterized by rheology, transmission electron microscope (TEM), and circular dichroism (CD), respectively. Potential application of the enzyme-responsive hydrogel in drug release was also demonstrated in this study. Though only one potential application of drug release was proved in this study, the responsive hydrogel system in this study might have potentials for the applications in fields of cell culture, controlled-drug release, etc.

Enzymatic hydrogelation is a totally different process to the heating-cooling gelation process, in which the precursors of the gelators can be involved during the formation of self-assembled structures. Using thixotropic hydrogels formed by a super gelator as our studied system, we demonstrated that the enzyme concentration/conversion rate of enzymatic reaction had a strong influence on the morphology of resulting self-assembled nanostructures and the property of resulting hydrogels. The principle demonstrated in this study not only helps to understand and elucidate the phenomenon of self-assembly triggered by enzymes in biological systems, but also offers a unique methodology to control the morphology of self-assembled structures for specific applications such as controlled drug release.

Self-assembly prevails in nature and learning from nature will lead to biofunctional materials. Inspired by the protein of elastin, we reported in this study on a supramolecular hydrogel bearing the elastin repeating peptide of VPGAG. The visco-elasticity property, morphology of the nanostructures, and aromatic stacking in the self-assembled nanostructure were characterized by a rheometry, transmission electron microscope (TEM), and fluorescence microscope, respectively. The biocompatibility of the gelator was also proved by an MTT assay. Though the supramolecular hydrogel failed to exhibit a high elasticity like elastin, the thixotropic hydrogel might have potentials for the applications in fields of cell culture, controlled-drug release, etc.