Study On The Effect Of Polar Grafting On The Electrical Response Properties Of Gelatin Hydrogels

Smart hydrogels can respond to various physical stimulis and change their physical and chemical properties.The electro-response hydrogel uses electric field as stimulus,which can change the size,shape and other properties of the hydrogels after the electric field was applied.Natural polymer like gelatin has excellent chemical and physical properties,but its electro-response was poor.In order to improve its response under electric field,this paper used protein as polymer backbone,and four grafting copolymers were successfully synthesized by graft copolymerization and polymer reaction:gelatin-graft-polyaniline(Gelatin-g-PANI),gelatin-graft-polypyrrole(Gelatin-g-PPy)and gelatin-graft-monomethyl polyethylene glycol(Gelatin-g-MPEG Mw=2000 and 1000).The composition and structures of copolymers were characterized by FT-IR,UV-Vis and 'H NMR.Glutaraldehyde(GA)was selected as the crosslinking agent,and a DC electric field(E=0.4 and 0.8kV/mm)was applied during the gelation of the hydrogel to prepare a new type of hydrogel.The influence of electric field on the mechanical properties of hydrogel was evaluated by measuring the storage modulus through dynamic viscoelastic spectroscopy(DMA),and the electro-response of hydrogels was evaluated by introducing ?G and ?G/G0.Scanning electron microscopy(SEM),thermogravimetry(TGA)and dielectric analysis(DA)were used to characterize the response mechanism of electric field to polymer solution.The mainly content as follows:1.The Gelatin-g-PANI copolymer was synthesized by grafting copolymerization in the acidic solution,and the copolymers with different PANI grafting amount were prepared respectively.Then the suitable crosslinking agent concentration and gelation temperature were selected to prepare the Gelatin-g-PANI hydrogels with excellent elasticity.The experimental results showed that the hydrogel had a positive response to the electric field,and the storage modulus of the hydrogel decreased significantly with the increase of grafting amount.Studies have shown that the poor water solubility of PANI leads to the decrease of the solubility of PANI in water and decrease the storage modulus.However,the hydrogels showed a positive response to the electric field.Comparing the storage modulus of hydrogel prepared with and without electric field,the ?G and ?G/G0 of the hydrogel showed a tendency that increase first and then decrease with the grafting amount.When the PANI grafting amount was 3.74 wt%,the response of hydrogel reached maximum.2.The gelatin-g-PPy copolymers were synthesized by graft copolymerization,and the copolymers with different grafting amount of PPy were prepared.Similar to gelatin-g-PANI hydrogel,the storage modulus of hydrogel decreased rapidly with the increase of grafting amount.The ?G and ?G/G0 of the hydrogel also showed a trend of first increase and then decrease with the grafting amount subsequently,and the maximum response was achieved when the PPy grafting amount was 0.31 wt%.3.MPEG was selected as the grafting unit,and the terminal hydroxyl groups of MPEG(Mw=1000 or 2000)were modified by aldehydes and then the peptide skeleton connected to MPEG-CHO was through of aldol-condensation reaction.It was found that after the grafting of MPEG2000 and MPEG1000,the storage modulus of hydrogels were gradually decreased with the increase of grafting content,while ?G and ?G/G0 tends to increase first and then decrease with the increase of grafting amount.The hydrogel reached maximum when grafting amount of MPEG2000 and MPEG 1000 was 4.53 wt%and 3.52 wt%respectively.4.Comprehensive analysis of the four kinds of graft modified gelatin hydrogels The maximum response of the hydrogels were Gelatin-g-PANI>Gelatin-g-MPEG2000>Gelatin-g-PPy>Gelatin-g-MPEG1000>pure gelatin.Electro-response properties revealed that grafting polar polymers onto the side of protein backbone could significantly improve the dielectric permittivity of the hydrogel,enhancing the polarization ability of the polymer under the electric field,and increase the electro-response properties of the hydrogels.