Hydrogels With Tunable Mechanical Properties Based On Photocleavable Proteins

Synthetic hydrogels have been of great interest to biomaterial scientists because of their hydrophilicity and biocompatibility potential.The intelligent hydrogel systems with environmental response are favored by simulating the dynamic and complex environment of organisms.Physical and chemical stimuli are applied to induce various responses in the intelligent hydrogel system,so as to regulate the mechanical properties of hydrogels,release of cells and drugs in hydrogels,and degradation of hydrogels.Comparing to other environment-responsive hydrogels,photo-responsive hydrogels have drawn considerable interest,because their mechanical properties can be remotely and non-invasively controlled upon light illumination.As a natural regulatory element,light can be precisely controlled including the action site,time and intensity.Therefore,photo-responsive hydrogels with tunable mechanical properties can be widely used in biomedicine,including the delivery of bioactive molecules,cell culture,biosensors,tissue engineering,and so on.In the first chapter,we mainly introduce the background knowledge of the whole article.Initially,we introduce several kinds of Phototransformablefluorescent proteins(Pt FPs),including Photoactivatable fluorescent proteins(PA-FPs),Photoconvertible fluorescent proteins(PC-FPs)and Photoswitchable fluorescent proteins(PS-FPs).Their Phototransformation mechanism are briefly described and several typical representative members are listed.Then,we introduce the application of Pt FPs in pulse-chase experiment,super-resolution imaging,photogenetics,fluorescence sensor,etc.Additionally,we introduced two types of photo-responsive hydrogels:one is the photo-responsive hydrogels based on Chemical Group reactions;the other is photo-controllable hydrogels with Pt FPs as a switchable cross-linking agent.In the second chapter,we described a few details of Hydrogels with tunable mechanical properties based on photocleavable proteins.Generally,most reported photo-responsive hydrogels are based on the switch between oligomeric and monomeric states of proteins upon light illumination.Upon the illumination of violet light(~400 nm),the chromophore of Pho Cl undergoes aβ-elimination reaction,leading to the cleavage of the polypeptide backbone.The two fragments of the protein then spontaneously dissociate and become unstructured.We designed two types of Pho Cl mutants which retained the light conversion characteristics and applied them to polyethylene glycol hydrogels respectively.These two types of Pho Cl-PEG hydrogels whose mechanical stability can be lowered or elevated upon photo illumination,respectively.It is desirable to explore new operation mode of photo-controllable hydrogels based on photo-responsive proteins.In the third chapter,we conceived the idea of using Pho Cl-PEG hydrogels to explore the regulation of mechanical force and ligand density on stem cells.To master the modulating factors of stem cell proliferation and differentiation is the only way to explore stem cell engineering and the necessary premise for us to use stem cells to solve medical problems.We used restriction endonuclease method to introduce short peptides with RGD(Arg-Gly-Asp)into the ends of two Pho Cl mutants that we designed(Pho-Weak andPho-Strong).We envisaged that Pho-Weak-RGD and Pho-Strong-RGD were applied to polyethylene glycol hydrogel respectively.These two kinds of photoperiable hydrogels would change the mechanical properties of the hydrogel and the ligand density of RGD respectively after illumination,which can be used to explore the regulation of mechanical force and ligand density on stem cells.Finally,we will make a summary of all the above work,and put forward the prospect of further research based on the above work in the future.