Preparation And Performance Of Layered Structure Hydrogel Materials Based On Polyvinyl Alcohol(PVA)

Wet and soft hydrogel materials have been widely used as biomedical materials due to some similarities to soft tissues in biological system.Polyvinyl alcohol(PVA)has many advantages such as good biocompatibility,high water content,degradability and low cost and so on.However,PVA hydrogels,used as substitute for implant devices and soft tissue scaffold,are limited by lacking of functionality and deformation-regulating ability as well as their poor mechanical properties.In view of the above problems,the subject research content of this thesis can be divided into the following three chapters:(1)Preparation of PVA derivative as the active layer of double-layer actuator by means of post-modification,which is utilized to build a bidirectional,reversible,and multi-responsive soft hydrogel actuator;(2)Simple Soaking treatment to induce the remodeling of weak PVA hydrogels and the formation of inert skin layer,effectively improving the toughness and stability of PVA hydrogel.(3)Preparation of the PVA derivative as a hydrop Hilic polymer network by post-modification method and then it is interspersed into the crosslinked LCST-type p NIPAm polymer network to inform a double network structure composite hydrogel.After heating the hydrogel to the phase transition temperature of the thermally responsive p NIPAm,the thermally responsive p NIPAm induces phase separation of the polymer network,thereby achieving enhanced hydrogel mechanical properties.And the concentration gradient distribution of each component in gel precursor solution is due to the evaporation-induced to prepare a polyvinyl alcohol derivative layered hydrogel with strong toughness,multiple shape memory function,and quick response in the process of solvent exchange.The specific research work is summarized as follows:(1)Two-layer soft hydrogel actuator reported has several drawbacks,including non-bidirectional bending,lack of multiple responsive integration,and the case that hydrogel actuator can be bent to form a tubular structure is rare.In this section,we first use N,N-dimethylimide(DEEDA)to post-modify the hydroxyl groups on PVA,which can produce the active layer PVA-DEEDA with multiple stimuli responsiveness;and then,Coating a layer of PVA-DEEDA micro-gel cross-linked with Borax on the biaxially oriented polypropylene(BOPP)substrate to construct a two-layer hydrogel soft actuator with excellent multiple stimuli response,And the decisive mechanism of the actuator' driving performance is revealed,which the introduction of a large number of Borax as crosslinkers are crucial.Under external stimuli such as humidity and temperature,the hydrogel actuator achieves rapid,reversible bidirectional self-curling deformation,forming two-dimensional and three-dimensional tubular,wavy and intersecting shapes.Hydrogels exhibit similar performance to soft artificial muscles and adaptive smart robots,and can lift weights much higher than their own weight,indicating that they have potential application value in small software robots;After exploring the driving mechanism,it was found that PVA-DEEDA and BOPP have significant differences in terms of swelling and thermal expansion behavior,Which provides automatic actuation of the actuator.(2)Significant progress in mechanical properties of synthetic hydrogels has been made.Hydrogels often suffer complex environments in practical applications.However,maintaining mechanical toughness under environmental loads is a big challenge.We created a new class of tough,stable,biocompatible layered PVA hydrogels by simply soaking the preparation PVA hydrogel in sodium silicate.The layered structure of the hydrogel consists of a compact outer layer and a porous center,of which formation mechanism is closely relative to the size effect,salting out and p H effect of sodium silicate.First,the outer layer PVA is preferentially contacted with sodium silicate,and the salting out effect will cause the outer layer of PVA to be first dehydrated to form a dense layer.Meanwhile,due to the strong alkali characteristic of sodium silicate,the-OH in the PVA will be induced to polarize,thereby The hydrogen bond interaction is enhanced to further stabilize the dense structure of the outer layer;subsequently,due to the large molecular size of the sodium silicate,it is difficult to further diffuse into the interior of the PVA hydrogel,and this size effect causes the final layered structure.Due to the protective effect of the outer layer,the PVA hydrogel can also maintain good mechanical properties by immersing it in a high concentration electrolyte with strong acidity/alkalinity and a hydrogen bond cleavage reagent at a high temperature for a long time.The soaking method with the characteristics of high efficiency and simplicity can be further extended to other PVA-based composite hydrogels,so that it is expected to prepare a large class of PVA-based layered hydrogels using it.(3)Shape memory hydrogel(SMH)not only has good adjustability,shape change,biocompatibility and degradability,etc.Which shows a great potential application value and development space in many fields such as biomedicine.However,there are still some inadequacies such as limited shape memory,lack of self-denaturation,stimuli-responsive driving,slow recovery,and weak mechanical properties.A composite hydrogel with double network structure was built by interspersing hydrop Hilic polymer network into a cross-linked LCST-type p NIPAm network,the polymer network p Hase is induced to separate each other above the phase transition temperature of p NIPAm,Which resulted in a significant increase in the mechanical properties of the hydrogel.A polyvinyl alcohol derivative layered hydrogel with strong toughness,multiple shape memory function,and rapid response can be further prepared by evaporation to induce a concentration gradient distribution of each component.In this chapter,we have applied a simple one-step evaporation induced method to prepare a PVA-C3-p NIPAm semi-interpenetrating network hydrogel with a porous layer heterogeneous structure in the vertical direction.The adjustable,fast and tough hydrogel actuator with a heterogeneous structure in the vertical direction is constructed and also has Polymorphic shape memory functions.The porous layer structure has high stability and toughness,and there is no possibility of delamination.The heterogeneous structure caused by evaporation optimizes the thermal response.Through the programming of the heterogeneous structure,various driving such as overall bending,local bending and site-specific folding,orientation bending and chiral torsion are realized,Which are short-lived and reversible and do not cause a significant fatigue after multiple cycles.