Preparation And Swelling Kinetics Of P(Maleyl Gelatin-Isopropylacrylamide) Hydrogel

Poly?N-isopropylacrylamide??PNIPAAm?hydrogel,as a typical thermo-responsive system,has been most frequently studied.PNIPAAm hydrogels are applied in biotechnology and bioengineering fields due to their unique properties of the lower critical solution temperature?LCST?close to human body temperature.Poor bioactivity and biodegradability of PNIPAAm hydrogels undoubtedly limit their further applications.Our group has been dedicating to solving this problem by incorporating the biomolecules facilely into the PNIPAAm systems.Because of their similarity to many tissues in softness and elasticity,hydrogels have been applied in numerous fields including drug delivery,cell encapsulation and artificial organs.In this paper,natural polymer gelatin is modified and introduced into PNIPAAm hydrogel with methylidene bisacrylamide?BIS?as crosslinker,persulfate?APS?as initiator and tetramethylethylenediamine?TEMED?as promoter.A series of P?MAGEL-NIPAAm?hydrogels were synthesized,and their synthesis conditions were optimized by studying their thermo-sensitivity,mechanical property and swelling property,which not only ensured the thermo-sensitivity of the hydrogel,but also improved the mechanical property and swelling property of hydrogel.The effects of MAGEL content,BIS content and different valence ions(Na⁺,Mg²⁺and Al³⁺)on swelling kinetics,swelling type,swelling ratio and de-swelling kinetics of P?MAGEL-NIPAAm?hydrogel were studied in detail.It lays a foundation for further practical application of such hydrogel.1.When the content of APS was less than 0.96‰,the content of BIS was less than1.2‰,and the content of MAGEL was less than 30%,the P?MAGEL-NIPAAm?hydrogel had kept a good thermo-responsive behavior.With the increase of APS dosage,the swelling ratio and strength of the hydrogel first increase and then decrease,and reach a maximum when the APS content is 0.84‰.With the increase of BIS dosage,the swelling ratio of the hydrogel decreases,and strength of the hydrogel first increase and then decrease.With the increase of MAGEL dosage,the swelling ratio of the hydrogel gradually increases,and strength of the hydrogel does not change much.The optimum synthesis conditions for the hydrogel were as follows:MAGEL accounted for 30%of the monomer,the initiator APS content was 0.84‰,and the BIS content was 1.2‰.2.The compression ratio of hydrogel is 76.6%under the optimal synthesis conditions,and it has good toughness.The P?MAGEL-NIPAAm?hydrogel shape memory ratio is more than 96%,which lays a theoretical foundation for the practical application of hydrogel.3.With the increase of MAGEL content,the equilibrium swelling ratio and the swelling rate of P?MAGEL-NIPAAm?hydrogel increased.P?MAGEL-NIPAAm?hydrogel without MAGEL and little content of MAGEL?10%?belongs to the first-order swelling model.When the P?MAGEL-NIPAAm?hydrogel containing 20%,30%,40%and 50%MAGEL,the swelling kinetics of hydrogel belongs to the second-order swelling model.The value of the swelling rate constant k_s of the second-order kinetics reaches a maximum at MAGEL content of 30%,indicating that the hydrogel has the fastest swelling rate at this time.4.Analysis of swelling mechanism of P?MAGEL-NIPAAm?hydrogel in water showed that P?MAGEL-NIPAAm?hydrogel containing 0%⁵0%MAGEL belongs to Fickian swelling,the obtains index n at 30%content of MAGEL.It obtain the highest value of the index n and the proportionality constant k at 30%of MAGEL.The diffusion coefficient D increases with the increase of MAGEL content,indicating that the addition of MAGEL can effectively increase the water absorption rate of the hydrogel.5.With the BIS content increased,the equilibrium swelling ratio decreased and the swelling rate decreased.When the BIS content is 0.4‰to 2.4‰,the swelling kinetics of P?MAGEL-NIPAAm?hydrogels belong to the second-order swelling model,which also belong to Fickian swelling.The values of the swelling rate constant k_s,the Fickian swelling index n,the proportional constant k and the circular hydrogel diffusion coefficient D decrease with the increase of the BIS content.6.The swelling kinetics of P?MAGEL-NIPAAm?hydrogel in NaCl solution showed that the swelling of P?MAGEL-NIPAAm?hydrogel containing 30%MAGEL in NaCl solution below 0.2 M belongs to second-order swelling.With the NaCl solution concentration increases,the values of the swelling rate constant k_s,the Fickian swelling index n and the proportional constant k decrease.It shows that NaCl not only reduces the equilibrium swelling ratio of the hydrogel,but also reduces the swelling rate of the hydrogel.7.The hydrogel conformed to the second-order kinetic model in 0⁰.3 M MgCl₂solution,and the swelling ratio and swelling rate decrease as the concentration of the MgCl₂ solution increases.The hydrogel did not conform to the second-order kinetic model in 0⁰.3 M AlCl₃ solution.The swelling ratio and swelling rate decreased with the increase of AlCl₃ solution concentration.And the swelling rate and the equilibrium swelling ratio in the AlCl₃ solution are smaller than those in the NaCl and MgCl₂solutions of the same concentration.8.Through the kinetic analysis of the de-swelling of P?MAGEL-NIPAAm?hydrogels,it is shown that:the addition of MAGEL increases the water retention ratio of the hydrogel;the increase of BIS will also improve the water retention ratio of hydrogel.With the concentration of NaCl solution increases,the water retention ratio of hydrogel decreases.When the concentration of salt solution is 0.1M,the deswelling ratio of P?MAGEL-NIPAAm?hydrogel is Al³⁺>Mg²⁺>Na⁺,the water retention ratio is Al³⁺<Na⁺?Mg²⁺.When the concentration of salt solution is 0.3 M,the deswelling ratio of P?MAGEL-NIPAAm?hydrogel is Al³⁺>Na⁺>Mg²⁺,and the water retention ratio is Al³⁺<Na⁺<Mg²⁺.