| Self-assemblies of peptide amphiphiles（PAs） that are bioactive, biocompatible,biodegradable and friendly to the environment have potential applications in template for biomimetic mineralization, chiral separation, antimicrobial agents, tissue engineering, drug delivery and so on. PA hydrogels have application in cell culture due to the fact that three-dimensional network structures and pores can provide mechanical support and permeability. And the stiffness of PA hydrogels could influence cell behavior. Preparation and stiffness of PA hydrogels have become a hot spot in the field of biomaterials. So we designed two series of peptide amphiphiles consisting of the lysine, triggered hydrogelation, and visualized self-assembled structures. We investigated the relation of PA gelation and stiffness with molecular structures including the number of carbon in the alkyl and the arrangement mode of charged amino acids, pH, and ionic strength. And change pH or ionic strength to trigger hydrogelation of C12H23O-V4EGS2,C12H23O-V4KGS4,C12H23O-VEVKVEVKGS2.The CMC values of PA molecules(C12H23O-KV3K-NH2, C14H27O-KV3K-NH2, and C16H31O-KV3K-NH2) decreased with the increase of the carbon numbers in the alkyl or pH.It was due to stronger hydrophobic interaction or weaker electrostatic repulsion. As for C16H31O-KV3K-NH2, the lowest concentration of hydrogelation was between 8m M and10 m M.C12H23O-KV3K-NH2, C14H27O-KV3K-NH2, and C16H31O-KV3K-NH2 could form hydrogel at 10 mM and pH 8.4. They self-assemblied into nanoribbons which crosslinked each other. C12H23O-KV3K-NH2, C14H27O-KV3K-NH2 had（α+β） secondary structure while C16H31O-KV3K-NH2 owned β-sheet.PA C12H23O-V3K2-NH2, C14H27O-V3K2-NH2, and C16H31O-V3K2-NH2 self-assembled into hydrogels with the similar stiffness at 10 m M and pH 8.4. They all self-assemblied into nanoribbons and had β-sheet secondary structures Similarly, C14H27O-KV3K-NH2 andC16H31O-KV3K-NH2 formed hydrogels with the similar stiffness under the same conditions.So we reached the conclusion that the number of carbon in the alkyl wasn’t a significant factor that affected formation and stiffness of hydrogels.Compared with C16H31O-KV3K-NH2, C16H31O-V3K2-NH2 could form gel and stiffer at 10 m M and pH 7.8. We compared formation and stiffness of CnH2n-1O-KV3K-NH2 hydrogels and Cn H2n-1O-V3K2-NH2 hydrogels. PA CnH2n-1O-KV3K-NH2 self-assembled into semi-transparent hydrogels at 10 mM and pH 8.4, while PA CnH2n-1O-V3K2-NH2 hydrogels were turbid.Agreeing with the phenomena, rheological data indicated that CnH2n-1O-KV3K-NH2 gels were stiffer than CnH2n-1O-V3K2-NH2 gels. It was concluded that PA with charged amino acids arranged at the C terminus formed hydrogels more easily and the lowest pH of hydrogelation was smaller. The fact indicated that arranging charged amino acids at the C terminus was helpful for stiffness when no PA precipitated.10 mM PA C12H23O-V3K2-NH2 solution became hydrogel when pH was increased from 5to 7.8. The hydrogel was stiffer at pH 8.3. Similarly, 10 mM PA C14H27O-V3K2-NH2 solution became hydrogel when pH was increased from 3 to 7.8. But PA C12H23O-V3K2-NH2 and C14H27O-V3K2-NH2 precipitated at pH 8.4.CD demonstated that secondary structures changed into β-sheet from the combination of random-coil and β-sheet when pH was increased from 3to 8.4. AFM found more nanoribbons.So we reached the conclusion that PA C12H23O-V3K2-NH2 and C14H27O-V3K2-NH2 formed hydrogel more easily and hydrogel was stiffer when pH was increased at a certain pH range.PA C16H31O-KV3K-NH2 solution at 10 mM and pH 6 became hydrogel when 35 mM NaCl were present. The hydrogel was stiffer when 50 mM NaCl were present. And there was precipitate in the hydrogel at 64 mM NaCl. So we reached the conclusion that PA C16H31O-KV3K-NH2 formed hydrogel when NaCl were present,and PA gel was stiffer with the concentration of NaCl increased.But too much NaCl led to PA precipitation.10 mM PA C12H23O-（VEVK）2GS2 became hydrogel at pH 6. AFM and CD demonstated nanofibers and β-sheet secondary structures. 10 m M PA C12H23O-V4KGS4 solution became hydrogel when pH was decreased from 11.2 to 9.5. 10 mM PA C12H23O-V4EGS2 solution at pH 10.5 became hydrogel when same molar Ca2+was present. The fact indicated that pH or salt could trigger C12H23O-V4EGS2,C12H23O-V4KGS4 and C12H23O-（VEVK）2GS2 to formhydrogel. |
