Programmable Shapeshifting Hydrogels And Their Biomedical Applications

Hydrogels with hydrophilic three-dimensional polymer networks can swell and maintain specific shapes in the water.The composition and mechanical properties are similar to natural biological tissues,showing unique benefits in the biomedical fields including contact lens,drug delivery and tissue culture.Besides these conventional characteristics,hydrogels providing various stimuli responsivenesses have blossomed in recent years.The hydrogels with rational molecular designs can response to the surrounding environment and change their macroscopic shapes by swelling or deswelling.Despite the elegance,the deformation of hydrogel is generally determined at the stage of material synthesis.It means one hydrogel sample is restricted by single deformation mode after the fabrication,which brings great difficulty in face of complex and changeable practical application scenarios.Except for constrained deformation modes,the hydrogel shapeshifting kinetics at time scale also lacks post-programming regulation capabilities,which prohibits the controllable and precise deployment of hydrogels.A more ideal solution is that a hydrogel can be programmed on demand after synthesis to flexibly suit various scenarios.This work is dedicated to developing novel programmable shapeshifting hydrogels whose deformation modes or dynamics can be manipulated by spatial-temporal programming methods,and the potentials in biomedical devices are then explored.A photo-programmable thermosensitive hydrogel with reversible shapeshifting actuation is first developed.Dynamic disulfide bonds are introduced into the PNIPAM network to endow the hydrogel with anisotropic alignment and shape reconfiguration through the bond exchange.The programmed gel achieves ultrafast reversible actuation by thermal-induced anisotropic change of polymer conformation,which is greatly different from the typical mass-transfer-dominated mechanism.This kind of programming method exhibits high spatial selectivity and allows on-demand postmanipulation of complex actuation modes in one sample.In addition to the above-mentioned spatial programming of complex deformation modes,this work further focuses on the potential of temporal programming.Orthogonal dynamic covalent bonds and ionic bonds are combined to prepare temporal programming shape memory hydrogels.The exchange of dynamic covalent bonds promises spatially shape reconfiguration,while the time-dependent dynamic exchange of ionic bonds becomes the molecular basis for temporal programming.The internal entropic driving force of the hydrogel dissipates with time according to the ionic bond exchange.Thereafter the hydrogels with different programming times can achieve multiscale shapeshifting kinetics during the recovery process without any external triggers,which is different from traditional stimuli-responsive hydrogels.However,this autonomous shapeshifting mode lacks on-demand onset,which means the deformation can not start at any wanted time.To solve this issue,an autonomous shape memory hydrogel with programmable delayed onset is developed for the first time.Owing to the strong phase separation at high temperature,the hydrogel can be fixed at a temporal shape.When it comes to the ambient water,it can keep stable in a customizable delay period and then start to recovery autonomously due to the slow internal water redistribution along with the phase evolution process.The delay period of the hydrogel can be regulated by adjusting the material formula or programming time,which ensures the flexible adjustment of shapeshifting onset towards different medical scenarios.On this basis,this work incorporates DLP printing technology to fabricate 4D printed delayed shape memory medical devices towards different clinical needs like lacrimal plug and effusion draining catheter.This kind of delayed device promises sufficient operation window to pass through channel or barrier,exhibiting great strengths in vivo and in vitro experiments.