Fabrication And Characterization Of Gelatin-based Hydrogel With High Strength

Hydrogels are soft and wet materials with physically or chemically cross-linked three-dimensional?3D?polymeric networks,which are very similar to nature living tissues due to the ability of retaining large amounts of water and are extremely suitable for a variety of biomedical applications such as drug delivery,tissue engineering and cell therapy.However,hydrogels with high water content might be poor in mechanical properties which greatly limits their further application.In recent years,much attention has been paid in the study of hydrogels with high strength and toughness.In this paper,based on the metal coordination between metal ions and gelatin molecular chains,ion crosslinked gelatin hydrogels were prepared by soaking the gelatin hydrogels in different metal ion solutions.The mechanical properties of gelatin hydrogels are greatly influenced by the types of metal ions,soaking temperature,soaking time,and solution concentration.In particular,the gelatin hydrogel soaked in0.5 mol/L Fe³⁺solution can sustain a compression stress of 64.81 MPa at the strain of99%,and it shows good fatigue resistance during the cyclic compression process.The introduction of metal ions also provides the hydrogel good antibacterial properties,metal-crosslinked hydrogels behaved powerful antibacterial effect against E.coli and S.aureus.Based on the metal crosslinked gelatin hydrogel,a physical-chemical double crosslinked gelatin/?polyacrylamide-acrylic acid?-Fe³⁺hydrogel was prepared combined with the design of double network structure.The first network is physically cross-linked gelatin?Gel?hydrogel and the second network is the copolymer of acrylamide?AM?and acrylic acid?AAc?.By immersing the hydrogel in Fe³⁺ion solutions,metal coordination bond is introduced into the network structure,and thus Gel/PAMAAc-Fe³⁺double network hydrogel with high strength,fatigue resistance and good self-recovery ability is obtained.Gelatin/PAMAAc-Fe³⁺hydrogel obtained by this method has high compression strength,which could reach 27.31 MPa at the deformation of 85%.After multiple cycles of compression deformation,the Gel/PAMAAc-Fe³⁺could still maintain good mechanical properties and self-recovery ability.In addition,the response surface methodology?RSM?analysis method was used in the work,and it is found that the swelling behavior of Gel/PAMAAc-Fe³⁺hydrogels is highly depended on Fe³⁺concentration and acrylic acid content.By controlling these factors,hydrogels with controlled swelling properties can be prepared.As a derivative of polyethylene glycol?PEG?,polyethylene glycol diacrylate?PEGDA?was synthesized with PEG and acryloyl chloride.PEGDA hydrogel has good biocompatibility.Based on the theory of double network hydrogel and the metal coordination bond,flexible PEGDA hydrogel was combined with brittle gelatin hydrogel and then treated with Fe³⁺ion solution to prepare Gel/PEGDA-Fe³⁺hydrogel.In order to eliminate the excessive swelling in the iron ion solution,the hydrogel was further immersed in the ammonium sulfate solution to obtain the Gel/PEGDA-Fe³⁺/?NH₄?₂SO₄ hydrogel.Due to the chain entanglement and hydrophobic effect caused by the Hofmeister effect,the mechanical strength of Gel/PEGDA-Fe³⁺/?NH₄?₂SO₄ hydrogel is greatly improved,and the swelling ratio of the hydrogel is also well controlled.