Preparation And Properties Of Conductive Hydrogel Based On The Properties Of Polysuccinimide And Its Application In Flexible Strain Sensors

Flexible strain sensors(FSSs)have proved to be a promising candidate for smart wearable devices due to their flexibility,light weight and biocompatibility.Compared with the traditional flexible strain sensor with poor tensile property,the conductive hydrogel has the characteristics of tensile property,flexibility,light weight,fast response and so on.Conductive hydrogels mainly include ionic conductive hydrogels,conductive nanomaterial conductive hydrogels and conductive polymer-based conductive hydrogels.Conductive polymer-based conductive hydrogels have become one of the most important research hotspots due to the unique doping mechanism of conductive materials in conductive hydrogels,good electrical and electrochemical properties and good environmental stability.However,there are still some challenges in the development of conductive hydrogel sensors so far.First,most conductive hydrogel sensors do not adhere directly to human skin and usually require tape or medical bandages to hold them in place;Secondly,conductive hydrogels usually have poor mechanical properties(such as low strength and fragility).Therefore,it is urgent to develop conductive hydrogels with adhesion properties and good mechanical properties to monitor human motion signals.Polyethylene pyrrolidone(PVP)has both hydrophilic and hydrophobic groups and is a good dispersant(template)for the synthesis of conductive polymers.Polyaspartic acid(PASP)has been widely studied in biomedical field due to its biocompatibility,biodegradability and functionability.In this context,polyvinylpyrrolidone was selected as the template for the synthesis of polypyrrole,and PASP was modified and grafted to prepare a composite conductive hydrogel with good mechanical properties and adhesion properties.First,polypyrrole(PPy)synthesized in polyethylene pyrrolidone was used as the conducting polymer,acrylamide(AAm)was used as the monomer,N,N-methylene formamide(MBA)was used as the crosslinking agent,and ammonium persulfate(APS)was used as the initiator.The semi-interpenetrating structure of PAAm/PPy/PASP composite conductive hydrogel was formed by the introduction of polyaspartic acid(PASP)from the hydrolysis of PSI.The results show that the introduction of PASP into PAAM hydrogels can not only improve the electrical conductivity of the composite hydrogels,but also significantly improve their mechanical properties.When PASP content is 10%,the conductivity increases from 0.75 S /m to 1.19 S/m,the elongation at break increases from 110% to 633%,and the tensile strength increases from 55 k Pa to 117.5 k Pa.However,the addition of PPy improved the conductivity of PAAm/PASP hydrogel.When PPy content was 0.6wt% and PASP content was 10%,the composite conductive hydrogel prepared had the best comprehensive performance,and the conductivity was 1.19 S/m at this time.When the strain is 400%,the Gaugefactor(GF)can reach 1.88.The results of applying the composite conductive hydrogel as a strain sensor to monitor human motion show that the sensor has high sensitivity,stability and reproducibility no matter in the large strain of finger bending or in the small strain of throat swallows.Secondly,polyaspartic acid(PASP)was grafted with ethanolamine(EA)and dopamine(DA)to obtain biodegradable macromolecular binder PDAEA.Using AAM as monomer,MBA as crosslinking agent,APS as initiator,and also using PPY synthesized in polyethylene pyrrolidone as conducting polymer,PAAm/PPy/PDAEA composite conductive hydrogel with adhesion was prepared by free radical polymerization in aqueous solution.The results show that the addition of PDAEA can not only improve the elongation at break of the composite conductive hydrogel,but also make the hydrogel adhesion.When the grafting amount of DA in PDAEA was 8%,the adhesion of hydrogel increased from 39.75 N/m to 274.05 N/m.In addition,the relationship between strain-electrical properties and sensitivity of PAAm/PPy/PDAEA composite conducting hydrogels was also studied.There is a linear relationship between the resistance change rate and the strain and sensitivity of the composite conductive hydrogel.With the increase of strain,the sensitivity and resistance change rate of hydrogel increase.When the strain is 900%,the resistance change rate is 1115%.The strain sensor based on PAAm/PPy/PDAEA composite conductive hydrogel has the characteristics of responsiveness,stability and repeatability in monitoring the motion of human joints.