Preparation Of Shape Memory Polymer With Separate Temperature Switch And Actuator And Its Application

Shape memory polymer（SMP）has attracted more and more attention in biomedical materials due to its excellent biocompatibility and degradability.When the temperature reaches its glass transition temperature（T_g）or crystallization temperature（T_m）,the shape memory of SMP materials will occur.The storage modulus of SMP materials will decrease by several orders of magnitude,and the shape recovery force of SMP will be weakened.The storage modulus of SMP materials decreases by several orders of magnitude,and the shape recovery force weakens.In addition,in order to meet the appropriate response temperature in human body,T_g or T_m of SMP need to be designed around the range of human body temperature,resulting in its weak mechanical properties.Therefore,compared with shape memory alloy,SMP still has the problems of weak shape recovery force and low elastic modulus,resulting in its limited application.In order to solve the problem that SMP cannot meet the comprehensive performance requirements of low temperature excitation,high elastic modulus and high shape memory recovery,SMP shape memory behavior can be divided into two independent actions:temporary shape memory（temperature switch）and permanent shape memory（actuator）.In this study,inspired by the principle of bow and string,temperature switch and actuator of SMP were designed separately,and temperature response SMP with different temperature response and memory effect was prepared,and its structure and performance were studied.At the same time,the application of this kind of SMP is explored.（1）Due to the good physiological inertia of polyethylene glycol（PEG）,SMP（SMP-H）of crosslinked polymer actuator with honeycomb capsule structure was innovatively synthesized by PEG spherulite self-template method.Meanwhile,SMP（SMP-L）of loofah-like crosslinked polymer actuator was synthesized by interpenetrating network（IPN）method as comparison.The shape memory effect and shape recovery force of SMP were studied by introducing PEG with different melting points as different temperature response switches.The results show that the shape recovery stress of SMP-H with honeycomb actuator is three times higher than that of SMP-L with loofah-like IPN structure obtained by IPN method.The SMP-H can lift up to 400times its own weight,while the SMP-L can lift only 200 times.For actuators with the same honeycomb structure,the introduction of a PEG-10K prepared SMP-H sample below the melting point of the actuator（61℃）can occur at a lower temperature（58℃）to achieve a maximum shape recovery stress of 45KPa.Compared with SMP-L,SMP-H with honeycomb actuator has higher energy storage modulus and mechanical properties.SMP-H improves the storage modulus of the actuator and the shape recovery force of the SMP by introducing a temperature switch PEG that is lower than the melting point of the actuator.In addition,SMP-H has good thermal reversible self-healing and repeatable machining performance due to various ionic and hydrogen bond interactions in the internal network.（2）In order to further improve the shape recovery force and mechanical properties of SMP,polylactic acid（PLA）with high elastic modulus was selected as the actuator of SMP.PEG is introduced into the molecular chain and chemically crosslinked to form a crosslinked polymer（CPA）,which acting as the temperature switch of SMP.Using polyacrylate as the interface layer between PLA and CPA,composite SMP was successfully prepared.At the same time,for comparison,PLA materials were modified by introducing wood fiber（WF）and glyceride triacetate（TAC）by melting blending method,respectively,to obtain PLA/WF and PLA/TAC,which were used as different actuators to prepare different composite SMPs.The shape memory effect and shape recovery force of composite SMP were studied.The results showed that CPA and PLA interface achieved good composite effect when polyacrylate was used as the interface layer between PLA and CPA.Meanwhile,the prepared composite SMP had shape memory effect at 52℃.Tensile and DMA tests show that PLA/WF has higher tensile strength and storage modulus than pure PLA,and its corresponding composite SMP has higher shape restoring force.As the T_g of PLA/TAC drops to 45℃,the energy storage modulus plummets near the transition temperature,resulting in weak mechanical properties and weak recovery force of the corresponding composite SMP shape.The spring-like composite SMP sample has more than600 times its own weight shape recovery force,which further improves the shape recovery force of composite SMP.（3）In order to meet the application requirements of the stent material,PLA/WF was selected as the actuator to synthesize CPA with T_m of 40℃,and Fe₃O₄ was introduced as the magnetic medium,as the non-contact electromagnetic induction heating-temperature switch,and polyacrylate was used as the interface layer between PLA/WF and CPA.The magnetic response composite SMP was successfully prepared.It was made into shape memory scaffold and put into the transparent tube of simulating colorectal for application exploration.The results show that the composite SMP has a good shape memory effect as a scaffold driven by electromagnetic heating.