Effect of polypeptide block length on nano-assembly morphology and thermo-sensitivity of methyl poly (ethylene glycol)-poly (L-valine) copolymer aqueous solutions

The delicacy of nature prompted scientists to create functional or responsive biomaterials using existing natural components. Here we reported novel thermo-gelling hydrogels based on methyl poly (ethylene glycol)-poly (L-valine) (mPEG-L-PV) diblock copolymer solutions, which exhibited well-defined sol-gel transition at a temperature range from 10 degrees C to 40 degrees C. The beta-sheet was the dominant secondary structure for poly(L-PV) block when the molecular weight of the polypeptide ranged from 277 Da to 1138 Da. The formation of mPEG-L-PV clear sol solutions was related to the stable nanostructures that were aggregated clusters of poly(L-PV) beta-sheet filaments and stabilized by the hydrophilic PEG segments. The block length of poly(L-PV) significantly affected the secondary structures of polypeptide and the morphology of assembled filaments, which resulted in different thermo-gelling behavior of the copolymer solutions. The occurrence of sol-gel transition with temperature was primarily due to the dehydration effect of PEG block, whereas in the case of the copolymer with a lower molecular weight of poly(L-PV) block, the change of polypeptide secondary structures also contributed to the formation of the gel. This paper provides fundamental information about the strong dependence of polypeptide block length on the nano-assembly morphology as well as thermosensitive behavior of polypeptide-based hydrogels. The block length of poly(L-PV) significantly affected the secondary structures of polypeptide and the morphology of assembled filaments, which resulted in different thermo-gelling behavior of the copolymer solutions.