Buckling-controlled two-way shape memory effect in a ring-shaped bilayer

Shape memory polymers(SMPs)usually have a one-way shape memory effect.In this paper,an easy-operating method to realize a two-way shape memory effect was demonstrated in a ring-shaped bilayer structure where the two layers are SMPs with different thermal transition temperatures.By designing specific thermomechanical processes,the mismatched deformation between the two layers leads to a morphology change of ring-shaped bilayer structures from a smooth ring to a gear-like buckling shape under cooling and a reversible recovery to the smooth shape under heating.Such a morphology change is ascribed to occurrence and recovery of thermoelastic buckling.This method was validated by finite element simulation.We experimentally investigated the influence of pre-strain on buckling,and it was found that both the buckling occurrence and recovery temperature vary with pre-strain.Furthermore,considering a ring-shaped SMP-SMP bilayer structure,finite element analysis was conducted to study the influence of film thickness and modulus ratio of two layers on buckling behavior.The results showed that the critical buckling wavelength was greatly influenced by film thickness and modulus ratio.W e made a theoretical analysis that accorded well with the numerical results.

Modeling size-dependent thermo-mechanical behaviors of shape memory polymer Bernoulli-Euler microbeam

The objective of this paper is to model the size-dependent thermo-mechanical behaviors of a shape memory polymer (SMP) microbeam.Size-dependent constitutive equations,which can capture the size effect of the SMP,are proposed based on the modified couple stress theory (MCST).The deformation energy expression of the SMP microbeam is obtained by employing the proposed size-dependent constitutive equation and Bernoulli-Euler beam theory.An SMP microbeam model,which includes the formulations of deflection,strain,curvature,stress and couple stress,is developed by using the principle of minimum potential energy and the separation of variables together.The sizedependent thermo-mechanical and shape memory behaviors of the SMP microbeam and the influence of the Poisson ratio are numerically investigated according to the developed SMP microbeam model.Results show that the size effects of the SMP microbeam are significant when the dimensionless height is small enough.However,they are too slight to be necessarily considered when the dimensionless height is large enough.The bending flexibility and stress level of the SMP microbeam rise with the increasing dimensionless height,while the couple stress level declines with the increasing dimensionless height.The larger the dimensionless height is,the more obvious the viscous property and shape memory effect of the SMP microbeam are.The Poisson ratio has obvious influence on the size-dependent behaviors of the SMP microbeam.The paper provides a theoretical basis and a quantitatively analyzing tool for the design and analysis of SMP micro-structures in the field of biological medicine,microelectronic devices and micro-electro-mechanical system (MEMS) self-assembling.

A mini review： Shape memory polymers for biomedica applications

Shape memory polymers （SMPs） are smart materials that can change their shape in a pre-defined manner under a stimulus. The shape memory functionality has gained considerable interest for biomedical applications, which require materials that are biocompatible and sometimes biodegradable. There is a need for SMPs that are prepared from renewable sources to be used as substitutes for conventional SMPs. In this paper, advances in SMPs based on synthetic monomers and bio-compounds are discussed. Materials designed for biomedical applica- tions are highlighted.

Recent Progress in Shape Memory Polymers for Biomedical Applications

Shape memory polymers （SMPs） as one type of the most important smart materials have attracted increasing attention due to their promising application in the field of biomedicine, textiles, aerospace et al. Following a brief intoduction of the conception and classification of SMPs, this review is focused on the progress of shape memory polymers for biomedical applications. The progress includes the early researches based on thermo-induced SMPs, the improvement of the stimulus, the development of shape recovery ways and the expansion of the applications in biomedical field. In addition, future perspectives of SMPs in the field of biomedicine are also discussed.

Biomedical applications of shape-memory polymers:how practically useful are they?

Shape-memory effect(SME) is the ability of a material to change its dimension in a predefined way in response to an external stimulus. Polymers that exhibit SME are an important class of materials in medicine, especially for minimally invasive deployment of devices. However, the rate of translation of the concept to approved products is extremely low, with mostly nitinolbased devices being approved. In this review, the general aspects of the different types of stimuli that can be used to activate SME are reviewed and sterilization issues of shape-memory polymer(SMP)-based medical devices are addressed. In addition, the general usefulness as well as the limitations of the shape-memory effect for biomedical applications are described.

Novel 3D printed shape-memory PLLA-TMC/GA-TMC scaffolds for bone tissue engineering with the improved mechanical properties and degradability

The biodegradable substitution materials for bone tissue engineering have been a research hotspot.As is known to all,the biodegradability,biocompatibility,mechanical properties and plasticity of the substitution materials are the important indicators for the application of implantation materials.In this article,we reported a novel binary substitution material by blending the poly(lactic-acid)-co-(trimethylenecarbonate)and poly(glycolic-acid)-co-(trimethylene-carbonate),which are both biodegradable polymers with the same segment of flexible trimethylene-carbonate in order to accelerate the degradation rate of poly(lactic-acid)-co-(trimethylene carbonate)substrate and improve its mechanical properties.Besides,we further fabricate the porous poly(lactic-acid)-co-(trimethylene-carbonate)/poly(glycolic-acid)-co-(trimethylene-carbonate)scaffolds with uniform microstructure by the 3D extrusion printing technology in a mild printing condition.The physicochemical properties of the poly(lactic-acid)-co-(trimethylenecarbonate)/poly(glycolic-acid)-co-(trimethylene-carbonate)and the 3D printing scaffolds were investigated by universal tensile dynamometer,fourier transform infrared reflection(FTIR),scanning electron microscope(SEM)and differential scanning calorimeter(DSC).Meanwhile,the degradability of the PLLATMC/GA-TMC was performed in vitro degradation assays.Compared with PLLA-TMC group,PLLA-TMC/GATMC groups maintained the decreasing Tg,higher degradation rate and initial mechanical performance.Furthermore,the PLLA-TMC/GA-TMC 3D printing scaffolds provided shape-memory ability at 37℃.In summary,the PLLA-TMC/GA-TMC can be regarded as an alternative substitution material for bone tissue engineering.

4D printing of personalized shape memory polymer vascular stents with negative Poisson’s ratio structure:A preliminary study

Four-dimensional(4D)printing,integrates transformation information into three-dimensional(3D)-printed structures,which means that 3D-printed structures are able to change their shapes,properties,or functionalities over time.Here,two types of shape memory personalized vascular stents with negative Poisson’s ratio structure are developed via 4D printing.The genetic algorithm is used to optimize the structure.Axial compression tests,radial compression tests and three-point bending tests are carried out to study the mechanical properties of the stents.In addition,fluid-structure interaction and stress distribution during the shape recovery process are investigated based on finite element method.The shape memory behaviors of the stents are excellent and in vitro feasibility tests demonstrate that the stents can expand the simulated narrow blood vessel rapidly.Therefore,4D printed shape memory stents with negative Poisson’s ratio structure are highly promising for the treatment of vascular stenosis.

A macro-mechanical constitutive model for shape memory polymer

It is of theoretical and engineering interest to establish a macro-mechanical constitutive model of the shape memory polymer (SMP), which includes the mechanical constitutive equation and the material parameter function, from the viewpoint of practical application. In this paper, a new three-dimensional macro-mechanical constitutive equation, which describes the mechanical behaviors associated with the shape memory effect of SMP, is developed based on solid mechanics and the viscoelasticity theorem. According to the results of the DMA test, a new material parameter function is established to express the relationship of the material parameters and temperature during the glass transition of SMP. The new macro-mechanical constitutive equation and material parameter function are used to numerically simulate the process producing the shape memory effect of SMP, which includes deforming at high temperature, stress freezing, unloading at low temperature and shape recovery. They are also used to investigate and analyze the influences of loading rate and temperature change rate on the thermo-mechanical behaviors of SMP. The numerical results and the comparisons with Zhou’s material parameter function and Tobushi’s mechanical constitutive equation illustrate that the proposed three-dimensional macro-mechanical constitutive model can effectively predict the thermo-mechanical behaviors of SMP under the state of complex stress.

生物降解性形状记忆聚合物的研究进展

形状记忆聚合物(SMP)可以在特定的刺激下改变形状,是一类应用前景广阔的智能材料。生物降解性SMP可以在人体内分解。这种材料符合生物医学应用中的严格要求,是微创手术和可触发生物医学设备的理想选择,对其中部分材料已经进行了深入的研究,并有着广泛的用途。文中综述了聚乳酸(PLA)、聚己内酯(PCL)、聚三亚甲基碳酸酯(PTMC)、聚十二烷甘油酯(PGD)、聚(ω-十五酸内酯)(PPDL)等几种主要的生物降解性形状记忆聚合物的研究进展,并对其形状记忆效应的机理进行了分析和介绍。

动态热机械分析技术在高分子形状记忆效应表征中的应用进展

形状记忆高分子(SMP)是指能够感知外界环境变化的刺激并响应这种变化,对其自身状态参数进行调整,从而回复到预先设定状态的一类高分子材料。目前SMP除能够实现研究最为广泛的不可逆双重形状记忆效应外,也能够展现复杂的三重形状记忆效应、多重形状记忆效应、恒定外力下的可逆双向形状记忆效应、无外力的可逆双向形状记忆效应及其形状可重构效应。通常聚合物的形状记忆效应能够使用动态热机械分析技术进行表征,通过控制SMP的应力、应变和温度能够实现变形、暂时形状的固定和形状的回复,从而得到应力-应变-温度循环热机械曲线,实现定量形状记忆性能,包括形状固定率(R_(f))、形状回复率(R_(r))、形状回复速率(V_(r))和形状回复力等。本文综述了动态热机械分析仪(TA-Q800)的拉伸模式在各种形状记忆效应表征中的应用,包括测试程序的选择、程序设置及其相对应的热机械循环曲线、参数计算和测试条件对形状记忆效应的影响,最后分析了研究中存在的问题并展望了未来发展方向。

Unique two-way free-standing thermo-and photo-responsive shape memory azobenzene-containing polyurethane liquid crystal network

In this work,azobenzene-containing polyurethane liquid crystal networks(PULCN(AZO)s)were synthesized using a one-pot strategy to demonstrate excellent two-way free-standing thermo-/photo-responsive shape memory effects.Based on the step-growth nature of hydroxyls and isocyanates,the architectures of the networks were adjusted by controlling the stoichiometries of chemical materials.A uniform monodomain sample was prepared by external stress relaxation via a reversible addition reaction of a dynamic carbamate bond.Two independent transition temperatures assigned to glass transition temperature/melting temperature and liquid crystal phase transition temperature were employed to thermally trigger triple shape memory effects and two-way autonomous actuation.In addition,taking advantage of the trans-cis photoisomerization of azobenzene,the programmed network showed a reversible bending and unbending shape change upon irradiation by visible light at450 and 550 nm,respectively.Coupling the autonomously thermo-induced contraction/extension actuation and reversible photo-induced bending/unbending behaviors of PULCN(AZO)s in one system will expand their potential applications in emerging multifunctional devices.

光响应形状记忆聚合物的研究进展

光响应形状记忆聚合物是一类刺激响应智能材料,它可以根据光照变化做出相应的形状改变。相比于传统的热响应形状记忆聚合物,光响应形状记忆聚合物具有远程控制、非接触式操作、局部驱动等优点。通过综述光响应形状记忆聚合物的研究进展,介绍光响应形状记忆聚合物的定义、机理、研究现状,以及光响应形状记忆聚合物在自修复材料、柔性电子器件和传感驱动领域的应用前景。总结了光响应形状记忆聚合物的优点,提出所面临的问题并进行了展望。

自组装核壳纳米微域交联的聚丙烯酸酯基聚合物的制备、性能及形状记忆机理

以双键封端的活性Pluronic F127三嵌段共聚物自组装形成的活性核壳纳米胶束作为多功能纳米交联剂,丙烯酸羟乙酯和丙烯酸为共单体,通过紫外光引发交联剂和单体的自由基聚合,制备了自组装核壳纳米微域交联的聚丙烯酸酯基形状记忆聚合物.利用差示扫描量热仪、动态热机械分析仪和万能拉力试验机对聚丙烯酸酯基形状记忆聚合物的热性能、动态热机械性能和力学性能进行了表征.结果表明,随着丙烯酸酯单体浓度的降低,其玻璃化转变温度、室温模量、玻璃态模量与橡胶态模量的比值、拉伸强度和断裂伸长率都逐渐降低,表现出兼具高强度和高韧性的特点.对聚丙烯酸酯基形状记忆聚合物的形状固定率、回复率和回复速率进行了定量表征.结果表明,当单体浓度超过1.97 mol/L时,聚丙烯酸酯基形状记忆聚合物展现出优异的形状记忆性能,形状固定率超过97%,回复率超过98%,回复速率超过8.8%/min.最后,通过应力松弛对该形状记忆聚合物体系的形状记忆机理进行了分析.

磁响应形状记忆聚合物在医学中的应用与研究进展

磁响应形状记忆聚合物(Shape Memory Polymer,SMP)是在SMP的基础上,通过引入磁性粒子以实现磁响应的新型材料,其远程非接触的传导控制方式为临床治疗和新型智能医疗器材的研发提供了新的方案。本文介绍磁热效应概念,并对磁热响应形状记忆机理进行阐述,综述磁响应SMP在不同医学领域中的研究进展,尤其是与4D打印技术的创新性结合,分析磁响应SMP的优点与所面临的问题,并对今后的应用进行展望。

形状记忆聚合物及其应用前景

介绍了形状记忆聚合物的形状记忆效应机理,对其不同驱动方式进行比较和评价,并且系统介绍了形状记忆聚合物在航天航空、生物医疗、纺织、温度指示、防伪指示以及微流体混合器等工程领域的应用。针对形状记忆聚合物目前开发和应用的大趋势,分析了形状记忆聚合物的多功能化研究现状,通过比较本征型和复合型导电形状记忆聚合物,说明了本征型导电形状记忆聚合物材料的优越特性和广阔的应用前景。

形状记忆聚合物复合材料的研究进展

形状记忆聚合物复合材料已成为形状记忆材料的研究热点和重点,文中针对近年来形状记忆聚合物复合材料的最新研究进行了综述。分别对颗粒增强、纤维增强和颗粒纤维混合3类增强材料制备的形状记忆聚合物复合材料的结构与性能特点进行了分析和评述;着重阐述了形状记忆聚合物复合材料形状记忆效应的机理以及影响形状记忆行为的因素;分析了形状记忆聚合物复合材料研究中存在的问题,同时对形状记忆聚合物复合材料的应用前景进行了展望。

EVA形状记忆效应的综合评价和分析

用 DCP可对 EVA进行适度交联 ,控制二者组分结构 ,从而控制 EVA的交联程度 ,可使 EVA具有优异的记忆功能特性 ,如形状回复率和形状固定率均可达 95 %以上 ,并对交联 EVA的微观交联程度进行分析 ,结果表明 ,EVA的记忆性能主要取决于交联点间分子量 ,其交联程度与 EVA的记忆特性存在着某种内在的必然联系 ;进一步结合 DMTA等热分析技术 ,分析发现其形状固定性与室温和熔融模量的比值呈线性关系 。

纺织用形状记忆聚合物研究进展

综述形状记忆聚合物纤维和织物的应用,介绍形状记忆聚合物纤维和织物的开发以及聚合物乳液整理织物的形状记忆效果。