Recent Progress in Shape Memory Polymers for Biomedical Applications

Digital Laser Direct Writing of Internal Stress in Shape Memory Polymer for Anticounterfeiting and 4D Printing

Shape memory polymers (SMPs) are a type of smart shape-shifting material that can respond to various stimuli. Their shape recovery pathway is determined by the internal stress stored in the temporary shapes. Thus, manipulating the internal stress is key to the potential applications of SMPs. This is commonly achieved by the types of deformation forces applied during the programming stage. In contrast, we present here a digital laser direct writing method to selectively induce thermal relaxation of internal stress stored in the two-dimensional (2D) shape of a thermoplastic SMP. The internal stress field, while invisible under natural light, can be visualized under polarized light. Consequently, the digital stress pattern can be used for anticounterfeiting. In addition, further uniform heating induces the release of the programmed internal stress within the 2D film. This triggers its transformation into a three-dimensional (3D) shape, enabling 4D printing. The simplicity and versatility of our approach in manipulating internal stress and shape-shifting make it attractive for potential applications.

Thermally and Photothermally Triggered Cytocompatible Triple-Shape-Memory Polymer Based on a Graphene Oxide-Containing Poly(ε-caprolactone) and Acrylate Composite

Triple-shape-memory polymers (triple-SMPs) are a class of polymers capable of fixing two temporary shapes and recovering sequentially from the first temporary shape to the second temporary shape and, last, to the permanent shape. To accomplish a sequential shape change, a triple-SMP must have two separate shape-fixing mechanisms triggerable by distinct stimuli. Despite the biomedical potential of triple-SMPs, a triple-SMP that with cells present can undergo two different shape changes via two distinct cytocompatible triggers has not previously been demonstrated. Here, we report the design and characterization of a cytocompatible triple-SMP material that responds separately to thermal and light triggers to undergo two distinct shape changes under cytocompatible conditions. Tandem triggering was achieved via a photothermally triggered component, comprising poly(ε-caprolactone) (PCL) fibers with graphene oxide (GO) particles physically attached, embedded in a thermally triggered component, comprising a tert-butyl acrylate-butyl acrylate (tBA-BA) matrix. The material was characterized in terms of thermal properties, surface morphology, shape-memory performance, and cytocompatibility during shape change. Collectively, the results demonstrate cytocompatible triple-shape behavior with a relatively larger thermal shape change (an average of 20.4 ± 4.2% strain recovered for all PCL-containing groups) followed by a smaller photothermal shape change (an average of 3.5 ± 0.8% strain recovered for all PCL-GO-containing groups; samples without GO showed no recovery) with greater than 95% cell viability on the triple-SMP materials, establishing the feasibility of triple-shape memory to be incorporated into biomedical devices and strategies.

Study on the Extrusion Molding Process of Polylactic Acid Micro Tubes for Biodegradable Vascular Stents

Polylactic acid (PLA) has been widely used in the field of medical devices. However, few studies have been conducted on the extrusion molding of PLA micro tubes for the preparation of biodegradable vascular stents. In this paper, the extrusion die for PLA single-cavity micro tubes was designed and manufactured by micro-extrusion theory. Taking the outer diameter, wall thickness, wall thickness uniformity and ovality of micro tubes as the evaluation index, the influence of the main extrusion process parameters on the evaluation index was studied. The experimental results show that the outer diameter and wall thickness are significantly affected by screw speed, pulling speed and gas flow rate; extrusion process parameters have little influence on wall thickness uniformity and ovality within a certain range, which mainly depends on the processing accuracy and assembly accuracy of the extrusion die. However, excessively high screw speed and low gas flow rate have significant effects on ovality. Finally, according to the influence of extrusion process parameters on the evaluation index, a series of micro tubes that meet the design requirements are extruded and carved into vascular stent structures.

Electroporation in Head-and-Neck Cancer: An Innovative Approach with Immunotherapy and Nanotechnology Combination

Squamous cell carcinoma is the most common malignancy that arises in the head-and-neck district. Traditional treatment could be insufficient in case of recurrent and/or metastatic cancers; for this reason, more selective and enhanced treatments are in evaluation in preclinical and clinical trials to increase in situ concentration of chemotherapy drugs promoting a selectively antineoplastic activity. Among all cancer treatment types (i.e., surgery, chemotherapy, radiotherapy), electroporation (EP) has emerged as a safe, less invasive, and effective approach for cancer treatment. Reversible EP, using an intensive electric stimulus (i.e., 1000 V/cm) applied for a short time (i.e., 100 μs), determines a localized electric field that temporarily permealizes the tumor cell membranes while maintaining high cell viability, promoting cytoplasm cell uptake of antineoplastic agents such as bleomycin and cisplatin (electrochemotherapy), calcium (Ca²⁺ electroporation), siRNA and plasmid DNA (gene electroporation). The higher intracellular concentration of antineoplastic agents enhances the antineoplastic activity and promotes controlled tumor cell death (apoptosis). As secondary effects, localized EP (i) reduces the capillary blood flow in tumor tissue ("vascular lock"), lowering drug washout, and (ii) stimulates the immune system acting against cancer cells. After years of preclinical development, electrochemotherapy (ECT), in combination with bleomycin or cisplatin, is currently one of the most effective treatments used for cutaneous metastases and primary skin and mucosal cancers that are not amenable to surgery. To reach this clinical evidence, in vitro and in vivo models were preclinically developed for evaluating the efficacy and safety of ECT on different tumor cell lines and animal models to optimize dose and administration routes of drugs, duration, and intensity of the electric field. Improvements in reversible EP efficacy are under evaluation for HNSCC treatment, where the focus is on the development of a combination treatment between EP-enhanced nanotechnology and immunotherapy strategies.

Programmable 4D Printing of Photoactive Shape Memory Composite Structures

4D printing is an advanced manufacturing technology combining additive manufacturing with smart materials. Based on light-active shape memory composites, smart medical structures with remote control capability, therapeutic function, and biocompatibility are hopefully fabricated by 4D printing. Here, a multifunctional composite with good mechanical properties, biocompatibility, and light-active shape memory performance is prepared by incorporating gold nanoparticles into a shape memory polyurethane matrix. The composites demonstrate a rapid and stable light-thermal effect, which can achieve localized and controlled breast tumor ablation, providing an approach to hyperthermia treatment for cancer cells. By directly bioprinting the composite melt, a series of 4D-printed structures are manufactured accurately in a convenient, clean, and safe way, which show a fast autonomous light-driven shape recovery process. The examples of a 4D-printed soft tissue scaffold and intraluminal scaffold can expand from a conveniently insertional shape to an expanded shape under light exposure. The proposed strategies provide great inspiration for customized multifunctional light-thermal therapeutic structures for minimally invasive treatment.

Recent Developments in Shape Memory Elastomers for Biotechnology Applications

Shape memory elastomers have revolutionised the world since their introduction in the 20th century. The ability to tailor chemical structures to produce a family of materials in wide-ranging forms with versatile properties has propelled them to be ubiquitous. Recent challenges in the end-of-life management of polymeric materials should prompt us to ask, ‘what innovations in polymeric materials can make a strong case for their use as efficient materials?’ The development of smart elastomers that can acquire, convey, or process a stimulus (such as temperature, pressure, electromagnetic field, moisture, and chemical signals) and reply by creating a useful effect, specifically a reversible change in shape, is one such innovation. Here, we present a brief overview of shape memory elastomers (SMEs) and thereafter a review of recent advances in their development. We discuss the complex processing of structure-property relations and how they differ for a range of stimuli-responsive SMEs, self-healing SMEs, thermoplastic SMEs, and antibacterial and antifouling SMEs. Following innovations in SEMs, the SMEs are forecast to have significant potential in biotechnology based on their tailorable physical properties that are suited to a range of different external stimuli.

Cell-Responsive Shape Memory Polymers

Recent decades have seen substantial interest in the development and application of biocompatible shape memory polymers (SMPs), a class of “smart materials” that can respond to external stimuli. Although many studies have used SMP platforms triggered by thermal or photothermal events to study cell mechanobiology, SMPs triggered by cell activity have not yet been demonstrated. In a previous work, we developed an SMP that can respond directly to enzymatic activity. Here, our goal was to build on that work by demonstrating enzymatic triggering of an SMP in response to the presence of enzyme-secreting human cells. To achieve this phenomenon, poly(ε-caprolactone) (PCL) and Pellethane were dual electrospun to form a fiber mat, where PCL acted as a shape-fixing component that is labile to lipase, an enzyme secreted by multiple cell types including HepG2 (human hepatic cancer) cells, and Pellethane acted as a shape memory component that is enzymatically stable. Cell-responsive shape memory performance and cytocompatibility were quantitatively and qualitatively analyzed by thermal analysis (thermal gravimetric analysis and differential scanning calorimetry), surface morphology analysis (scanning electron microscopy), and by incubation with HepG2 cells in the presence or absence of heparin (an anticoagulant drug present in the human liver that increases the secretion of hepatic lipase). The results characterize the shape-memory functionality of the material and demonstrate successful cell-responsive shape recovery with greater than 90% cell viability. Collectively, the results provide the first demonstration of a cytocompatible SMP responding to a trigger that is cellular in origin.

Water-Triggered Stiffening of Shape-Memory Polyurethanes Composed of Hard Backbone Dangling PEG Soft Segments

Shape-memory polymers (SMPs) induced by heat or water are commonly used candidates for biomedical applications. Shape recovery inevitably leads to a dramatic decrease of Young's modulus due to the enhanced flexibility of polymer chains at the transition temperature. Herein, the principle of phase-transition-induced stiffening of shape-memory metallic alloys (SMAs) is introduced to the design of molecular structures for shape-memory polyurethane (SMPUs), featuring all-hard segments composed of main chains that are attached with poly(ethylene glycol) (PEG) dangling side chains. Different from conventional SMPs, they achieve a soft-to-stiff transition when shape recovers. The stiffening process is driven by water-triggered segmental rearrangement due to the incompatibility between the hard segments and the soft PEG segments. Upon hydration, the extent of microphase separation is enhanced and the hard domains are transformed to a more continuous morphology to realize more effective stress transfer. Meanwhile, such segmental rearrangement facilitates the shape-recovery process in the hydrated state despite the final increased glass transition temperature (T_g ). This work represents a novel paradigm of simultaneously integrating balanced mechanics, shape-memory property, and biocompatibility for SMPUs as materials for minimally invasive surgery such as endoluminal stents.

Heterogeneous Solid-State Plasticity of a Multi-Functional Metallo-Supramolecular Shape-Memory Polymer towards Arbitrary Shape Programming

Shape-memory polymers (SMPs) exhibit notable shape-shifting behaviors under environmental stimulations. In a specific shape-memory cycle, the material can be temporarily fixed at diverse geometries while recovering to the same permanent shape driven by the elastic network, which somewhat limits the versatility of SMPs. Via dynamic metallo-supramolecular interactions, herein, we report a multi-functional shape-memory polymer with tunable permanent shapes. The network is constructed by the metallic coordination of a four-armed polycaprolactone with a melting temperature of 54 °C. Owing to the thermo-induced stress relaxation through the bond exchange, the SMPs can be repeatedly programmed into different geometries in their solid state and show the self-welding feature. Via further welding of films crosslinked by different ions, it will present heterogeneous solid-state plasticity, and a more sophisticated shape can be created after the uniform thermal treatment. With elasticity and plasticity in the same network, the SMPs will display programmable shape-shifting behaviors. Additionally, the used material can be recast into a new film which retains the thermo-induced plasticity. Overall, we establish a novel strategy to manipulate the permanent shapes of SMPs through solid-state plasticity and develop a multi-functional shape-shifting material that has many practical applications.

Application and Development of Shape Memory Micro/Nano Patterns

Shape memory polymers (SMPs) are a class of smart materials that change shape when stimulated by environmental stimuli. Different from the shape memory effect at the macro level, the introduction of micro-patterning technology into SMPs strengthens the exploration of the shape memory effect at the micro/nano level. The emergence of shape memory micro/nano patterns provides a new direction for the future development of smart polymers, and their applications in the fields of biomedicine/textile/micro-optics/adhesives show huge potential. In this review, the authors introduce the types of shape memory micro/nano patterns, summarize the preparation methods, then explore the imminent and potential applications in various fields. In the end, their shortcomings and future development direction are also proposed.

Shape-Memory Polymers Hallmarks and Their Biomedical Applications in the Form of Nanofibers

Shape-Memory Polymers (SMPs) are considered a kind of smart material able to modify size, shape, stiffness and strain in response to different external (heat, electric and magnetic field, water or light) stimuli including the physiologic ones such as pH, body temperature and ions concentration. The ability of SMPs is to memorize their original shape before triggered exposure and after deformation, in the absence of the stimulus, and to recover their original shape without any help. SMPs nanofibers (SMPNs) have been increasingly investigated for biomedical applications due to nanofiber’s favorable properties such as high surface area per volume unit, high porosity, small diameter, low density, desirable fiber orientation and nanoarchitecture mimicking native Extra Cellular Matrix (ECM). This review focuses on the main properties of SMPs, their classification and shape-memory effects. Moreover, advantages in the use of SMPNs and different biomedical application fields are reported and discussed.

Shape Memory Epoxy Resin and Its Composites: From Materials to Applications

Shape memory polymers (SMPs) have historically attracted attention for their unique stimulation-responsive and variable stiffness and have made notable progress in aerospace, civil industry, and other fields. In particular, epoxy resin (EP) has great potential due to its excellent mechanical properties, fatigue resistance, and radiation resistance. Herein, we focus on the molecular design and network construction of shape memory epoxy resins (SMEPs) to provide opportunities for performance and functional regulation. Multifunctional and high-performance SMEPs are introduced in detail, including multiple SMEPs, two-way SMEPs, outstanding toughness, and temperature resistance. Finally, emerging applications of SMEPs and their composites in aerospace, four-dimensional printing, and self-healing are demonstrated. Based on this, we point out the challenges ahead and how SMEPs can integrate performance and versatility to meet the needs of technological development.

Development of Trans-1,4-Polyisoprene Shape-Memory Polymer Composites Reinforced with Carbon Nanotubes Modified by Polydopamine

In this study, which was inspired by mussel-biomimetic bonding research, carbon nanotubes (CNTs) were interfacially modified with polydopamine (PDA) to prepare a novel nano-filler (CNTs@PDA). The structure and properties of the CNTs@PDA were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The CNTs and the CNTs@PDA were used as nanofillers and melt-blended into trans-1,4 polyisoprene (TPI) to create shape-memory polymer composites. The thermal stability, mechanical properties, and shape-memory properties of the TPI/CNTs and TPI/CNTs@PDA composites were systematically studied. The results demonstrate that these modifications enhanced the interfacial interaction, thermal stability, and mechanical properties of TPI/CNTs@PDA composites while maintaining shape-memory performance.

Light-Responsive Soft Actuators: Mechanism, Materials, Fabrication, and Applications

Soft robots are those that can move like living organisms and adapt to the surrounding environment. Compared with traditional rigid robots, the advantages of soft robots, in terms of material flexibility, human–computer interaction, and biological adaptability, have received extensive attention. Flexible actuators based on light response are one of the most promising ways to promote the field of cordless soft robots, and they have attracted the attention of scientists in bionic design, actuation implementation, and application. First, the three working principles and the commonly used light-responsive materials for light-responsive actuators are introduced. Then, the characteristics of light-responsive soft actuators are sequentially presented, emphasizing the structure strategy, actuation performance, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research frontier.

Facile Fabrication of Eucommia Rubber Composites with High Shape Memory Performance

We processed a series of shape memory Eucommia rubber (ER) composites with both carbon–carbon and ionic cross-linking networks via a chemical cross-linking method. The influence of the carbon–carbon cross-linking and ion cross-linking degree of ER composites on curing, mechanical, thermal, and shape memory properties were studied by DSC, DMA, and other analytical techniques. Dicumyl peroxide (DCP) and zinc dimethacrylate (ZDMA) played a key role in preparing ER composites with a double cross-linking structure, where DCP initiated polymerization of ZDMA, and grafted ZDMA onto polymer molecular chains and cross-linked rubber molecular chains. Meanwhile, ZDMA combined with rubber macromolecules to build ionic cross-linking bonds in composites under the action of DCP and reinforced the ER composites. The result showed that the coexistence of these two cross-linking networks provide a sufficient restoring force for deformation of shape memory composites. The addition of ZDMA not only improved the mechanical properties of materials, but also significantly enhanced shape memory performance of composites. In particular, Eucommia rubber composites exhibited outstanding mechanical properties and shape memory performance when DCP content was 0.2 phr.

Smart scaffolds: shape memory polymers (SMPs) in tissue engineering

Smart scaffolds based on shape memory polymer (SMPs) have been increasingly studied in tissue engineering. The unique shape actuating ability of SMP scaffolds has been utilized to improve delivery and/or tissue defect filling. In this regard, these scaffolds may be self-deploying, self-expanding, or self-fitting. Smart scaffolds are generally thermoresponsive or hydroresponsive wherein shape recovery is driven by an increase in temperature or by hydration, respectively. Most smart scaffolds have been directed towards regenerating bone, cartilage, and cardiovascular tissues. A vast variety of smart scaffolds can be prepared with properties targeted for a specific tissue application. This breadth of smart scaffolds stems from the variety of compositions employed as well as the numerous methods used to fabricated scaffolds with the desired morphology. Smart scaffold compositions span across several distinct classes of SMPs, affording further tunability of properties using numerous approaches. Specifically, these SMPs include those based on physically cross-linked and chemically cross-linked networks and include widely studied shape memory polyurethanes (SMPUs). Various additives, ranging from nanoparticles to biologicals, have also been included to impart unique functionality to smart scaffolds. Thus, given their unique functionality and breadth of tunable properties, smart scaffolds have tremendous potential in tissue engineering.

Intelligent Polymers, Fibers and Applications

Intelligent materials, also known as smart materials, are capable of reacting to various external stimuli or environmental changes by rearranging their structure at a molecular level and adapting functionality accordingly. The initial concept of the intelligence of a material originated from the natural biological system, following the sensing–reacting–learning mechanism. The dynamic and adaptive nature, along with the immediate responsiveness, of the polymer- and fiber-based smart materials have increased their global demand in both academia and industry. In this manuscript, the most recent progress in smart materials with various features is reviewed with a focus on their applications in diverse fields. Moreover, their performance and working mechanisms, based on different physical, chemical and biological stimuli, such as temperature, electric and magnetic field, deformation, pH and enzymes, are summarized. Finally, the study is concluded by highlighting the existing challenges and future opportunities in the field of intelligent materials.

Biodegradable shape-memory polymers and composites

Polymers have recently been making media headlines in various negative ways. To combat the negative view of those with no polymer experience, sustainable and biodegradable materials are constantly being researched. Shape-memory polymers, also known as SMPs, are a type of polymer material that is being extensively researched in the polymer industry. These SMPs can exhibit a change in shape because of an external stimulus. SMPs that are biodegradable or biocompatible are used extensively in medical applications. The use of biodegradable SMPs in the medical field has also led to research of the material in other applications. The following categories used to describe SMPs are discussed: net points, composition, stimulus, and shape-memory function. The addition of fillers or additives to the polymer matrix makes the SMP a polymer composite. Currently, biodegradable fillers are at the forefront of research because of the demand for sustainability. Common biodegradable fillers or fibers used in polymer composites are discussed in this chapter including Cordenka, hemp, and flax. Some other nonbiodegradable fillers commonly used in polymer composites are evaluated including clay, carbon nanotubes, bioactive glass, and Kevlar. The polymer and filler phase differences will be evaluated in this chapter. The recent advances in biodegradable shape-memory polymers and composites will provide a more positive perspective of the polymer industry and help to attain a more sustainable future.

Electrospun Shape Memory Polymer Micro-/Nanofibers and Tailoring Their Roles for Biomedical Applications

Shape memory polymers (SMPs) as a relatively new class of smart materials have gained increasing attention in academic research and industrial developments (e.g., biomedical engineering, aerospace, robotics, automotive industries, and smart textiles). SMPs can switch their shape, stiffness, size, and structure upon being exposed to external stimuli. Electrospinning technique can endow SMPs with micro-/nanocharacteristics for enhanced performance in biomedical applications. Dynamically changing micro-/nanofibrous structures have been widely investigated to emulate the dynamical features of the ECM and regulate cell behaviors. Structures such as core-shell fibers, developed by coaxial electrospinning, have also gained potential applications as drug carriers and artificial blood vessels. The clinical applications of micro-/nanostructured SMP fibers include tissue regeneration, regulating cell behavior, cell growth templates, and wound healing. This review presents the molecular architecture of SMPs, the recent developments in electrospinning techniques for the fabrication of SMP micro-/nanofibers, the biomedical applications of SMPs as well as future perspectives for providing dynamic biomaterials structures.

Basic Approaches to the Design of Intrinsic Self-Healing Polymers for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) as a revolutionary system for harvesting mechanical energy have demonstrated high vitality and great advantage, which open up great prospects for their application in various areas of the society of the future. The past few years have seen exponential growth in many new classes of self-healing polymers (SHPs) for TENGs. This review presents and evaluates the SHP range for TENGs, and also attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Among the most widely used SHPs for TENGs, the analysis of non-covalent (hydrogen bond, metal-ligand bond), covalent (imine bond, disulfide bond, borate bond) and multiple bond-based SHPs in TENGs has been performed. Particular attention is paid to the use of SHPs with shape memory as components of TENGs. Finally, the problems and prospects for the development of SHPs for TENGs are outlined.

A near-infrared light-triggered shape-memory polymer for long-time fluorescence imaging in deep tissues

Implanting a stent in the body through a minimally invasive operation and tracking its location in real-time is still a challenge. Herein, a near-infrared (NIR) light-triggered shape-memory polymer possessing a long-time fluorescence imaging function has been developed by cross-linking 6-arm poly(ethylene glycol)-poly(ε-caprolactone) using a croconate dye YHD798 as the chemical crosslinker and NIR-absorption perssad. Due to the extraordinary photothermal conversion property of YHD798, the temperature of the material raised from 20 °C to 120 °C under 808 nm near-infrared irradiation at 0.4 W cm^-2, leading to shape recovery in 50 s in a programmed shape-transition process. YHD798 also exerted an aggregation-induced emission effect, endowing the polymer with a clear NIR fluorescence imaging function even when covered by a 2 mm pork slab and could be used for the real-time visualization of the implanted device fabricated from this polymer in deep tissues of the body. When a tubular stent that was fabricated from this polymer, was implanted into the carotid artery of a Sprague-Dawley rat, it could recover to its permanent shape under 808 nm laser irradiation in 60 s owing to the shape-memory function and facilitated NIR-I fluorescence imaging after implantation for a week owing to the croconate dye. This work provides a new strategy for designing and developing smart polymers with NIR-light-triggered shape-memory effect and long-term fluorescence imaging function for biomedical applications.

3D printed biodegradable functional temperature-stimuli shape memory polymer for customized scaffoldings

Shape memory polymers (SMPs) and their composites have become the prominent choice of the various industries owing to the unique inherent characteristics which can be stimulated through the exposure of external stimuli. The use of SMPs in the three-dimensional (3D) technologies has produced enormous advantages. However, the potential of SMPs in 3D printing has limitedly explored. In the present study, an investigation was performed to study the shape memory effect (SME) of the fused filament fabricated (FFF) chitosan (CS) reinforced poly-lactic-acid (PLA) based porous scaffolds. Firstly, the composite filaments, with 1, 1.5, and 2% wt. of CS, were fabricated by using the twin-screw extrusion process, which was later used to print the test specimens at different infill density. The printed samples were selectively pre-elongated to 2.5 mm and then processed through direct heating, at 60-70 °C, for enabling the SME. It has been observed that the CS particles acted as rigid phases and interrupted the re-ordering of PLA chain. However, the scaffoldings showed 18.8% shape recovery at optimized process parametric settings. In addition, wettability and biocompatibility analyses of developed scaffoldings have also been performed to investigate the biological aspects of the developed scaffoldings. The stimulated samples found to be possessed with good wettability and cell proliferation. Overall, the 3D printed PLA/CS porous scaffoldings have shown significant shape recovery characteristics and are biologically active to be used as self-healing implants for acute bone deficiencies.

An investigation on electro-induced shape memory performances of CE/EP/CB/SCF composites applied for deployable structure

The objective of this work is to investigate the thermomechanical, electrical, and shape-memory properties of bisphenol A-type cyanate ester (BACE)/polybutadiene epoxy (PBEP)/carbon black (CB) composite and assess its feasibility applied for deployable structure. Using a BACE/PBEP polymer as matrix and superconducting carbon black (CB) and short carbon fibers (SCFs) as reinforcing material, the shape memory composite was prepared by compression molding. The effects of CB and SCF content on the shape memory properties of the composites were investigated. The results demonstrate that the glass transition temperature (Tg) and the storage modulus of the composites increases as SCFs content increase. Because of the synergic effect of CB and SCFs, the shape memory composites exhibit excellent shape memory performance, and the shape recovery ratio is about 100%. With the increase in SCF content, the recovery time decreased, and the volume electrical resistivity of the composite could decrease by adding a small amount of SCFs. According to the above results, a shape memory polymer composite deployable structure was prepared.

Poly (Vinyl Butyral-Co-Vinyl Alcohol-Co-Vinyl Acetate) Coating Performance on Copper Corrosion in Saline Environment

Poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate) named further PVBA was investigated as a protective coating for copper corrosion in 0.9% NaCl solution using electrochemical measurements such as, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization associated with atomic force microscopy (AFM). The PVBA coating on the copper surface (Cu-PVBA) was modeled in methanol containing PVBA. Its inhibitory properties against corrosion was comparatively discussed with those of the copper sample treated in methanol without polymer (Cu-Me) and of untreated sample (standard copper). A protective performance of PVBA coating of 80% was computed from electrochemical measurements, for copper corrosion in NaCl solution. Moreover, AFM images designed a specific surface morphology of coated surface with PVBA, clearly highlighting a polymer film adsorbed on the copper surface, which presents certain deterioration after corrosion, but the metal surface was not significantly affected compared to those of untreated samples or treated in methanol, in the absence of PVBA.

Self-healing and shape memory metallopolymers: state-of-the-art and future perspectives

Recent achievements and problems associated with the use of metallopolymers as self-healing and shape memory materials are presented and evaluated.

Bioperspectives for Shape-Memory Polymers as Shape Programmable, Active Materials

Within the natural world, organisms use information stored in their material structure to generate a physical response to a wide variety of environmental changes. The ability to program synthetic materials to intrinsically respond to environmental changes in a similar manner has the potential to revolutionize material science. By designing polymeric devices capable of responsively changing shape or behavior based on information encoded into their structure, we can create functional physical behavior, including a shape-memory and an actuation capability. Here we highlight the stimuli-responsiveness and shape-changing ability of biological materials and biopolymer-based materials, plus their potential biomedical application, providing a bioperspective on shape-memory materials. We address strategies to incorporate a shape-memory (actuation) function in polymeric materials, conceptualized in terms of its relationship with inputs (environmental stimuli) and outputs (shape change). Challenges and opportunities associated with the integration of several functions in a single material body to achieve multifunctionality are discussed. Finally, we describe how elements that sense, convert, and transmit stimuli have been used to create multisensitive materials.

Photonic actuators with predefined shapes

Developing actuators with multi-responsibility, large deformation, and predefined shapes is critical for the application of actuators in the field of artificial intelligence. Herein, we report the preparation of a new type of unimorph actuators containing phenol-formaldelyde resin (PFR) and graphene oxide (GO) using the chiral nematic structure of cellulose nanocrystals (CNCs) as the template. The so-obtained PFR/GO films have a unimorph structure with an asymmetric distribution of GO across the film. They exhibit synchronous responses of both photonic properties and actuation to humidifying/dehumidifying. Moreover, PFR/GO films can be forged into desired shapes by aldehyde treatment, and thereby are able to produce complex movements. In addition, the objects with predetermined shapes show good shape recovery capability upon many wetting-drying cycles, especially through the treatment with formaldehyde. A mechanism model for shape predetermination by aldehyde treatment is suggested based on experimental details. By further designing the predetermined shapes and patterns, such PFR/GO actuators may hold great promise for smart actuation devices of highly complex movements.

Biocompatible thermo- and magneto-responsive shape-memory polyurethane bionanocomposites

Thermo- and magneto-responsive shape-memory bionanocomposites based on a bio-based polyurethane and magnetite nanoparticles were prepared. Due to the structure of the reactants, the behavior of the polyurethane matrix differs from common polyurethanes, since the soft segment was formed by a diisocyanate and a chain extender, whereas the macrodiol served as hard segment. The influence of the magnetite nanoparticles on the thermal and mechanical properties and the shape-memory behavior was studied. It was observed that magnetite nanoparticles interacted with macrodiol-rich domains and decreased the overall crystallinity of the material, although their presence did not affect the mechanical properties to a great extent. At the same time, the magnetite nanoparticles increased the shape fixity and contributed to shape recovery. The bionanocomposites exhibited magnetic behavior and could be easily heated in an alternating magnetic field, allowing fast and almost complete shape recovery. Preliminary cytotoxicity, hemocompatibility, and cell adhesion analysis suggest that the new materials are benign and potentially useful for biomedical applications.