Preparation And Application Of Functionalized Starch-based Hydrogel

Starch is an environment-friendly natural polysaccharide with rich sources,low price,non-toxic and non-irritant.The hydrogel system prepared with starch as raw material can reduce the production cost and is suitable for large-scale production.Due to its flexible and adjustable physical and chemical properties,such as good biocompatibility,biodegradability and high absorption of solvents,starch hydrogels have attracted extensive attention in biomedical,tissue engineering,water treatment,sensors and other fields.However,starch hydrogel also has some actual problems,such as poor uniformity of network structure,unstable mechanical properties,insufficient research on the interaction between hydrogel molecules,and expansion of application fields.Thus a series of functionalized modified starch hydrogels were designed,which the structure was improved,the intermolecular interaction was explained and the application field was extended.The main contents are as follows:1.Waxy rice amylopectin（WRA）was chose as raw material,and we took the dynamic hydrogen-bonding interaction to bring the WRA element into a polyacrylamide（PAAm）network to elicit a stretchable elastic composite hydrogel through the co-crosslinking reaction.We investigated dynamic interactions between the pre-crosslinked waxy rice amylopectin（PWRA）and PAAm,as well as PWRA themselves,by a series of quantitative reaction models,which revealed the hydrogen-bonding interactions as mainly being built from-OH and-NH₂ groups.The composite hydrogel showed good elasticity and strength,and it was elastically elongated to 520%,and can be repeatedly stretched 100 times without apparent mechanical fatigue in its elasticity.Sodium ions were introduced into the composite network to elicit the hydrogel conductivity（0.18 S/m）.As a pressure of≥10 k Pa was applied to its surface,it could respond to the pressure by generation of a resistance signal in 0.16 s,showing a rapid pressure-responsive capability.This responsive process can reversibly proceed for 100 cycles,while keeping its sensitivity.It is included in a sensing device that can detect pressure from movements of the finger,elbow,and knee.It is capable of recording the variation of the walking pace and revealing the physical conditions of people during running or walking.2.Using natural starch as raw material,a flexible and transparent conductive hydrogel(Starch/Ca²⁺)can be prepared by a simple,green and environmentally friendly one pot method.Only Ca Cl₂ powder,starch and deionized water are used in the whole production process.The raw materials are clean and green,with high conversion ratio and no pollution to the environment.When the mass ratio of starch to Ca Cl₂ is 2:1,the strength,elongation and elastic modulus of Starch/Ca²⁺hydrogel is140 k Pa,90%and 210 k Pa,respectively.It can be recycled repeatedly for 100 times without apparent mechanical fatigue in its elasticity.It is assembled into a sensing device which can be used to detect the variation of pressure signals generated by human motion due to the free ions and channels in the hydrogel.In addition,it can be deduced from infrared spectrum that Ca²⁺ion is complexed with oxygen atom in-CH₂OH in starch chain,forming Starch/Ca²⁺hydrogel.3.Waxy rice amylopectin@polyvinyl alcohol hydrogel（WRA@PVA）with humidity response was introduced into the three-layer polymer film structure,which improved the flexibility and deformation ability of the film.The body of soft robot is composed of three functional layers:polydimethylsiloxane@carbon nanotubes（PDMS@CNT）layer that generates photothermal effect,poly（vinylidene difluoride）（PVDF）layer,able to direct the motion of robot,and waxy rice amylopectin@polyvinyl alcohol（WRA@PVA）layer for humidity response.The humidity-responsive layer improves the shape recoverability of the soft robot during the response to light irradiation,and thus extending its motion lifetime.Introduce elastic awns of Setaria viridis to a soft robot,in which the elastic awn with anisotropic surface structures is capable of giving rise to the anisotropic friction.The elastic-awn legs support the body of robot and push the robot forward by the positive friction.Based on the anisotropic friction,the controllable motion of various soft robots is successfully achieved in response to external stimuli.