Shape Memory Materials for Biomedical Applications

Shape memory properties provide a very attractive insight into materials science, opening unexplored horizons and giving access to unconventional functions in every material class (metals, polymers, and ceramics). In this regard, the biomedical field, forever in search of materials that display unconventional properties able to satisfy the severe specifications required by their implantation, is now showing great interest in shape memory materials, whose mechanical properties make them extremely attractive for many biomedical applications. However, their biocompatibility, particularly for long‐term and permanent applications, has not yet been fully established and is therefore the object of controversy. On the other hand, shape memory polymers (SMPs) show promise, although thus far, their biomedical applications have been limited to the exploration. This paper will first review the most common biomedical applications of shape memory alloys and SMPs and address their critical biocompatibility concerns. Finally, some engineering implications of their use as biomaterials will be examined.     

Controlling Malleability of Metamaterials through Programmable Memory

Malleability, the ability to adapt materials to specific shapes, is necessary in applications where a form closure is requested. The material should be easily deformable between desired stable shapes. Such stability can be obtained through bistable elements that act as memory in metamaterials. Herein, a material with memory behavior programmed by the local temperature is presented. The behavior can be switched between a permanent shape change and a complete elastic recovery after removing an applied mechanical load. Additionally, a deformed material can be forced to recover its shape by heating. Through an adaption of the mesostructure and the used polymers, the characteristic behavior (switching time and temperature) can be adjusted. Furthermore, heating can be applied locally that only certain parts are able to change. A unit cell design based on analytical and numerical analyses is demonstrated that considers not only the mesostructure but also the combination of polymeric materials with specific thermoresponsive mechanical behavior. Unit cells and structures of several cells are additively manufactured to validate the programmable behavior. The concept is extended to indirect heating with an alternating magnetic field, using a compound made from a polymeric material and magnetic particles.     

发展形状记忆材料的展望

根据马氏体相变的特征:代位原子无扩散切变,以不变平面应变进行形状改变,以及按群论应用于马氏体相变的表述式,导出材料具有形状记忆效应的条件,即只要形成单变体或接近单变体马氏体,防止阻碍形状记忆效应因素如位错的形成和材料通过马氏体相变及其逆相变就能显示形状记忆效应。     

增强形状记忆聚合物材料研究进展

本文介绍了增强形状记忆聚合物的最新研究进展,详细探讨了各种增强材料对形状记忆聚合物的形状记忆效应的影响,总结了增强形状记忆聚合物研究的若干热点问题.     

Magnetic Shape Memory Polymers with Integrated Multifunctional Shape Manipulation

Shape-programmable soft materials that exhibit integrated multifunctional shape manipulations, including reprogrammable, untethered, fast, and reversible shape transformation and locking, are highly desirable for a plethora of applications, including soft robotics, morphing structures, and biomedical devices. Despite recent progress, it remains challenging to achieve multiple shape manipulations in one material system. Here, a novel magnetic shape memory polymer composite is reported to achieve this. The composite consists of two types of magnetic particles in an amorphous shape memory polymer matrix. The matrix softens via magnetic inductive heating of low-coercivity particles, and high-remanence particles with reprogrammable magnetization profiles drive the rapid and reversible shape change under actuation magnetic fields. Once cooled, the actuated shape can be locked. Additionally, varying the particle loadings for heating enables sequential actuation. The integrated multifunctional shape manipulations are further exploited for applications including soft magnetic grippers with large grabbing force, reconfigurable antennas, and sequential logic for computing.     

Photonic Devices Out of Equilibrium: Transient Memory,Signal Propagation,and Sensing

Soft photonic materials are important for sensors, displays, or energy management and have become switchable under static equilibrium conditions by integration of responsive polymer features. The next step is to equip such materials with the ability for autonomously dynamic and self‐regulating behavior, which would advance their functionality and application possibilities to new levels. Here, this study shows the system integration of a nonlinear, biocatalytic pH‐feedback system with a pH‐responsive block copolymer photonic gel, and demonstrates autonomous transient memories, remotely controlled signal propagation, and sensing. This study utilizes an enzymatic switch to program the lifetime of the reflective state of a photonic gel, and induces propagation of pH‐waves extinguishable by illumination with UV‐light. The described combination of nonlinear chemistry and responsive photonic gels opens pathways toward out‐of‐equilibrium photonic devices with active and autonomous behavior useful for sensing, computation, and communication.     

ZnO基电阻存储材料的研究与进展

在电阻存储技术的快速发展中,电阻存储材料是其发展的关键基础。因此探索新型、高效、环保的电阻存储材料是推进电阻存储技术发展的研究热点。ZnO自身具备优异的光学特性,结合可调控的电学、磁学特性,被誉为最有应用潜力的电阻存储材料。扼要介绍了ZnO基电阻存储材料的研究概况,结合大数据时代信息存储的背景回顾了ZnO基存储材料的研究进展、物理机制,对以往的研究工作进行了归纳与总结,并阐述了未来的发展趋势。     

TiNi形状记忆合金及其多孔体

综述了TiNi形状记忆合金的研究开发与应用现状,包括三元TiNiCu、TiNiNb、TiNiHf合金,并介绍了用自蔓高温合成法制备一种新型人造骨科材料——TiNi多孔体的最新研究进展。     

Organic Nonvolatile Memory Devices Based on Ferroelectricity

A memory functionality is a prerequisite for many applications of electronic devices. Organic nonvolatile memory devices based on ferroelectricity are a promising approach toward the development of a low‐cost memory technology. In this Review Article we discuss the latest developments in this area with a focus on three of the most important device concepts: ferroelectric capacitors, field‐effect transistors, and diodes. Integration of these devices into larger memory arrays is also discussed.     

On the Indeterminacy in Hardness of Shape Memory Alloys

The present communication addresses an interesting problem related to the indeterminacy in hardness of superelastic NiTi reported by Xu et al. The origin of the indeterminacy is attributed to the inadequacy of the conventional Vickers hardness testing measurement which does not record elastic deformation, and thus the indeterminacy may be removed with suitable techniques. Concepts of hardness in relation to deformation are clarified. Recommendations for measuring the hardness of NiTi and other elastic-plastic materials are suggested, together with comments on the advantages and disadvantages of each of these methods.     

Thinnest Nonvolatile Memory Based on Monolayer h‐BN

2D materials have attracted much interest over the past decade in nanoelectronics. However, it was believed that the atomically thin layered materials are not able to show memristive effect in vertically stacked structure, until the recent discovery of monolayer transition metal dichalcogenide (TMD) atomristors, overcoming the scaling limit to sub‐nanometer. Herein, the nonvolatile resistance switching (NVRS) phenomenon in monolayer hexagonal boron nitride (h‐BN), a typical 2D insulator, is reported. The h‐BN atomristors are studied using different electrodes and structures, featuring forming‐free switching in both unipolar and bipolar operations, with large on/off ratio (up to 10⁷). Moreover, fast switching speed (<15 ns) is demonstrated via pulse operation. Compared with monolayer TMDs, the one‐atom‐thin h‐BN sheet reduces the vertical scaling to ≈0.33 nm, representing a record thickness for memory materials. Simulation results based on ab‐initio method reveal that substitution of metal ions into h‐BN vacancies during electrical switching is a likely mechanism. The existence of NVRS in monolayer h‐BN indicates fruitful interactions between defects, metal ions and interfaces, and can advance emerging applications on ultrathin flexible memory, printed electronics, neuromorphic computing, and radio frequency switches.