Preparation And Properties Of Environment Responsive Peptide Hydrogels

Environment responsive hydrogel has been regarded as the ideal new materials because it can efficiently response to environmental factors,such as temperature,pH,light,electricity.In this study,we designed some peptides which can form the hydrogels in the presence of enzymes?Plasma Ammonia Oxidase or Tyrosinase?and different environmental factors,including pH and Fe³⁺.These hydrogels could be used as the antibacterial and antitumor agents.?1?Ac-A₉K₂-NH₂ hydrogel formed in the presence of PAO possessed antibacterial activities.Ac-A₉K₂-NH₂ self-assembled into the nanofiber in the presence of PAO.HPLC and MALDI-TOF-MS spectrometry results showed that PAO promoted the oxidation of?-amine of the lysine side chain.Thus the positive charges of Ac-A₉K₂-NH₂ reduced,and the hydrophobic interaction between Ac-A₉K₂-NH₂ molecules enhanced.The two factors promoted the hydrogel formation.The self-supported hydrogel had low cytotoxicity,and did not cause nonspecific immune responses to host cells.The important thing,it could kill both G⁺and G^-bacteria,which can be used as an antimicrobial agent or biological engineering scaffold material.?2?Peptide containing DOPA?L-Dioxyphenylalanine?formed hydrogel under different conditions including tyrosinase,pH and Fe³⁺.We designed a short peptide Ac-I₄K₂Y*-NH₂?Y*=DOPA?,which can self-assemble into nanofiber.After the addition of tyrosinase,it formed hydrogel,and the recovery performance of the hydrogel is good.The secondary structure of the aggregates is mainly the?-sheet.UV-Vis and MALDI-TOF-MS spectra showed that Ac-I₄K₂Y*-NH₂ is oxidated by tyrosinase to quinone which promoted the hydrogel formation.Simultaneously,Ac-I₄K₂Y*-NH₂ could also form the hydrogel in the presence of B16 melanoma cells which can secrete the tyrosinase.Furthermore,the B16 cells were killed after incubation for 24 h.Contrastingly,it had low cytotoxicity to mammalian NIH 3T3 cells.Thus it can be used for detecting and efficiently killing B16 cells.On the other hand,Ac-I₄K₂Y*-NH₂ solution can also form hydrogel at pH 9.5.UV-Vis and MALDI-TOF-MS spectra results showed that the dimer products formed.After adding the Fe³⁺in this system,self-supported hydrogels also formed because of the Fe³⁺-peptide coorditation.Notably,the mechanical strength was higher than that of the hydrogels formed at pH 9.5 without Fe³⁺.?3?The hairpin peptide including DOPA can form dynamic hydrogel in the response of pH and Fe³⁺.Hairpin peptide VY*can not form hydrogel at pH 7.4,while it forms self-supported hydrogel at pH 9.5.It would collaps when FeCl₃ was added into the hydrogel.AFM and TEM images showed that VY*formed short rods nanostructure in the presence of FeCl₃,and its?-sheet structure content decreased significantly.The results suggested that DOPA and Fe³⁺form tri-coordination complex after the addition of FeCl₃,which will lead to the disintegration of the nanofiber structure.Because of VY*'s highly response to Fe³⁺,it can be used for the detection of tumor cells where contains higher Fe³⁺level.