Poly(lactic acid)/polycaprolactone-based self-programmed photothermal responsive shape memory polymers

Shape memory polymers (SMPs) are evolving intensively in smart materials research. SMPs can undergo large deformations, hold a temporary shape and then recover their original shape upon exposure to a particular external stimulus. The emerging development of fibre reinforced shape memory polymer composites (SMPCs) has improved SMPs’ mechanical properties to be comparable to modern fibre reinforced composites. Moreover, the inclusion of nanoparticles has enhanced the diversity in activation mechanisms and improved structural properties and durability.
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\nToday, the SMPCs are generally viewed as promising substances for engineered applications that have raised intensive interest among the scientists and engineers. Interestingly, stimulation by light enables unique and advanced shape memory effects (SMEs) in SMPCs that can fulfill the sophisticated demands of engineering. The ability to vary the light wavelength, intensity, periodicity, polarization and the irradiated position on the SMP component enables wavelength selective, reversible, sequential and multiple SMEs. Furthermore, light travel long distances in a vacuum, can be focussed onto a certain area, is safe to humans and, can be a control signal carrier and most notably, can be sent through optical fibres to extremely inaccessible areas.
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\nIncorporation of metallic, carbon and organic based photothermal fillers into a SMP matrix is a convenient proven method to prepare light activated shape memory polymer composites (LASMPCs). These photothermal fillers convert electromagnetic radiation into thermal energy that triggers the SMP matrix. The current study comprehensively reviewed the performances, mechanisms, challenges and limitations of the existing LASMPC systems and associated optical technologies. Predominantly this research was intended to develop reinforced LASMPC systems and allied optical technologies applicable for large scale structural engineering applications.
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\nIn this study, styrene and bisphenol A epoxy based thermosets and polylactic acid (PLA) based thermoplastic SMPs were used as polymer matrix materials. Carbon fibre, glass fibre, multiwalled carbon nanotube (MWCNT) and rare earth organic complexes of Nd(TTA)3Phen and Yb(TTA)3Phen were used as reinforcement and photothermal fillers. The samples were produced by means of vacuum bagging, mould casting and 4D printing. Morphological investigations were conducted to identify the microstructure and manufacturability of the LASMPCs. The samples’ mechanical and physical properties were tested by standard test methods for polymer matrix composites. Dynamic mechanical analysis was carried out to determine the thermomechanical characteristics. The photothermal effect was investigated through thermal imaging and associated shape memory behaviours were studied through shape fixing and recovery experiments. A finite element analysis was performed with ABAQUS to simulate the photothermal heating behaviour.
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\nThe current study established a material development framework for LASMPC materials and presented apt manufacturing methods for structural and large scale engineering applications. Different modes of light diffusion such as scattered low intensity light, focussed laser beams and light delivery through fibre optics were proved for structural LASMPCs. Sequential and selective wavelength activation of structural LASMPCs are presented. The FEA simulation provided additional understanding on light exposed LASMPCs’ 3-dimensional heating behaviour. Embedding a D-shaped optical fibre in an LASMPC created a single unit smart actuator, which was remotely activated by light. It was proven that flexible radiation shields can reduce the unanticipated shape recovery of LASMPCs components and protect the LASMPCs from polymer degradation due to radiation.
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\nThe improvements to their structural properties and innovative remote activation methodologies have justified LASMPCs’ aptness for space engineering applications. This study has proven its successful completion by three selected case studies of space applications. An LASMPC solar panel array model was sequentially deployed in four recovery steps. In a vacuum, a space habitat structure model was compressed to a third of its volume and then recovered its original shape. A 4D printed boom structure model was tested, proving customized LASMPC structures for sophisticated space equipment fabrication. The deployable LASMPC structures can reduce the occupied room in spacecraft. The improvements to the structural properties of LASMPCs while keeping the SME, understanding on thermomechanical and photothermal behaviours, remote actuation through optical fibres, radiation shields and the insight to space applications are the most significant novel outcomes of this study. This thesis opens up windows of opportunity for the scientific and engineering communities to provide innovative solutions to realize the sophisticated large scale engineering demands in aerospace and space applications and beyond.

<p><b>The future of architecture in New Zealand goes hand-in-hand with its ability to adapt to climate change projections. Since the establishment of the modern era, construction materials have remained largely unchanged. Steel, timber, concrete, and brick are all very static in functionality, are the backbone of our built environments. The shifting climate conditions anticipated in the coming decades require adaptable and resilient construction materials. Temperature Rise for New Zealand is 0.3°C to +0.9°C by 2030 and 0.6°C to +2.7°C by 2070, (O’Connell and Hargreaves 1). The expected increase in temperatures around New Zealand homes will negatively affect the internal thermal comfort of occupants. </b></p> <p>The development of shape memory polymers (SMPs) as an auto-responsive and functional system that responds to numerous environmental stimuli becomes a viable option for smart material integration into external building envelopes. The useful properties of SMPs as a lightweight material with reversible shape-changing capabilities, and deformation mechanisms are becoming increasingly realistic for practical implementation into building facades (Mohamed). </p> <p>The implementation of thermo-responsive shape memory polymers into residential building facades allows for a real-time automated response to manage climatic temperature variances for present and future vulnerabilities of buildings and their occupants. Reinventing building envelopes using shape memory polymer application has the potential to create efficient passive cooling methods which may satisfy the demand for architectural climatisation and improve indoor thermal comfort for occupants. Establishing a proof-of-concept for adaptable and resilient design needs to be fast-tracked into New Zealand’s mainstream construction, showcasing smart materials' necessity and innovative capabilities. The reactionary approach to construction is not a viable option for future climate change projection. The damage to buildings without immediate implementation of climate-adaptive design will be irreversible and detrimental for thousands of New Zealanders. The future of building materials within the construction industry must endeavour to steer away from traditional building materials into the inevitable smart material technology.</p>

Shape memory polymers (SMPs) have the capacity of memorizing a temporary shape and recovering their initial shape in response to various external stimuli. As one of promising class of intelligent materials, it has attracted great attention because of its potential applications in many areas, such as biomaterials and biotechnology, automotive industry, and aerospace field. Aliphatic polymers play an important role in the molecular design of SMPs owing to its excellent biodegradability and biocompatibility, and suitable thermal transition temperature range. This review focuses on the recent progress of shape memory polymers based on the aliphatic polyesters such as poly(lactic acid) (PLA), poly ( p -dioxanone) (PPDO), poly(butylene succinate) (PBS), poly( ω -pentadecalactone) (PPDL) and poly( ɛ -caprolactone) (PCL) and so on. From the view of architecture design, different systems are classified by block copolymers, crosslinking networks and interpenetrating networks. The influence of architectural features on the shape memory behaviors is also discussed. The block copolymers have been identified a typical mature system in design of dual-shape material, and the crystalline aliphatic polyesters can be served as the netpiont or the molecular switch in a SMP, depending on its transition temperature range among the binary systems. The thermoplastic feature of block copolymers endows an easy processibility. The various architectures of crosslinking network meet the increasing demand of SMPs design. Constructing network with crystallizable polyester segment such as PCL may achieve SMPs in one-way and two-way mode, and the stress-free two-way mode can also be realized by an elaborate architecture with pre-programed treatment. Embedding two segments in one network may achieve a triple-shape memory effect, meanwhile, incorporating two segments in an interpenetrating polymer network may result in a triple-shape material with improved performance. Recently, the SMPs based on dynamic networks become the new trend, which may combine the self-healing with shape memory effect in one system, and both dynamic covalent bond and non-covalent bond have been concerned. In order to fulfill the increasing requirement of application, the SMPs with multi-shape memory effect, multi-responsibility and multi-functionality are highly expected.

Shape memory polymers are a class of smart materials, which are capable of fixing their deformed shapes, and can return to their original shape in reaction to external stimulus such as heat. Also due to their exceptional properties, they are mostly used in four-dimensional printing applications. To model and investigate thermomechanical response of shape memory polymers mathematically, several constitutive equations have been developed over the past two decades. The purpose of this research is to provide an up-to-date review on structures, classifications, applications of shape memory polymers, and constitutive equations of thermally responsive shape memory polymers and their composites. First, a comprehensive review on the properties, structure, and classifications of shape memory polymers is conducted. Then, the proposed models in the literature are presented and discussed, which, particularly, are focused on the phase transition and thermo-viscoelastic approaches for conventional, two-way as well as multi-shape memory polymers. Then, a statistical analysis on constitutive relations of thermally activated shape memory polymers is carried out. Finally, we present a summary and give some concluding remarks, which could be helpful in selection of a suitable shape memory polymer constitutive model under a typical application.

Shape memory polymer (SMP) systems exhibiting semicrystalline- elastomer blends, such as thermoplastic polyurethane and polylactic acid have been well studied, but their use in biomedical shape memory applications has been limited by their high activation temperature. SMPs are capable of deformation and recovery through the activation of an external stimuli, such as temperature. Critical criteria for SMPs used in biomedical applications is achieving a stimulus temperature close to 37°C while still experiencing sufficient shape recovery. A polymer’s glass transition temperature has been well defined as the SMP system’s activation temperature and therefore should be decreased to achieve a decreased activation temperature. In this work, a well-known, biocompatible plasticizer, polyethylene oxide (PEO), was added to thermoplastic polyurethane (TPU) – polylactic acid (PLA) SMP blends to observe the plasticizing effect on the structural, thermal, mechanical, and shape memory properties of the polymer blends. Additionally, the geometry of the fabricated SMP samples was tailored to further enhance the shape memory effect through a bowtie honeycomb structure. Our results suggest that the addition of PEO into the SMP system may be an effective method for decreasing the polymer’s glass transition temperature through the alteration of the polymer chain structure. With the addition of 30% PEO, the glass transition temperature of the TPU/PLA blend was successfully decreased from 62.4°C to 34.6°C while achieving 86.5% shape recovery when activated at 37°C, which is only a 5% decrease in shape recovery when activated at 50°C. These results suggest that the addition of a biocompatible plasticizer may overcome the limitation of employing temperature activated SMP systems in biomedical applications, and enhances the potential of these materials for reconfigurable structures, energy dissipation systems, and SHM in civil engineering applications.

Shape memory polymers (SMPs) possess the remarkable ability to recover their original shape after being severely deformed, triggered by the right stimulus. This chapter reviews recent progress in shape memory materials, focusing on traditional types like shape memory alloys (SMAs) and SMPs, as well as emerging shape memory hybrids, which enable customizable properties for specific applications in a “do-it-yourself” manner. SMPs, in particular, show great promise for morphing aircraft applications due to their temperature- and time-dependent mechanical properties. Tests on SMPs under monotonic loading in high shear demonstrate their ability to recover original shapes while resisting large loads. Advances in SMP composites (SMPCs), which incorporate functional materials and nanostructures, further enhance their deformation recovery, mechanical properties, and controllable actuation. SMPs have broad applications across aerospace, biomedical devices, flexible electronics, and more. This chapter also provides an in-depth analysis of the shape recovery mechanisms, multifunctionality, and potential future directions for SMP development.

Shape memory polymers (SMP) are a class of stimuli-responsive materials that are able to respond to external stimulus such as heat by altering their shape. Bio-compatible SMPs have a number of advantages over static materials and are being studied extensively for biomedical and clinical applications (such as tissue stents and scaffolds). A previous study has demonstrated that the bio-compatible polymer blend of polylactic acid (PLA)/ thermoplastic polyurethane (TPU) (50/50 and 70/30) exhibit good shape memory properties. In this study, the mechanical and thermo-mechanical (shape memory) properties of TPU/PLA SMP blends were characterized; the compositions studied were 80/20, 65/35, and 50/50 TPU/PLA. In addition, porous TPU/PLA SMP blends were fabricated with a gas-foaming technique; and the morphology of the porous structure of these SMPs foams were characterized with scanning electron microscopy (SEM). The TPU/PLA bio-compatible SMP blend was fabricated with melt-blending and compression molding. The glass transition temperature (Tg) of the SMP blends was determined with a differential scanning calorimeter (DSC). The mechanical properties studied were the stress-strain behavior, tensile strength, and elastic modulus; and the thermomechanical (or shape memory) properties studied were the shape fixity rate (Rf), shape recovery rate (Rr), response time, and the effect of recovery temperature on Rr. The porous 80/20 PLA/TPU SMP blend was found to have the highest tensile strength, toughness and percentage extension, as well as the lowest density and uniform pore structure in the micron and submicron scale. The porous 80/20 TPU/PLA SMP blend may be further developed for specific biomedical and clinical applications where a combination of tensile strength, toughness, and low density are required.

This paper explores the concept of reconfigurable compliant mechanisms. We define these to be fully or partially compliant mechanisms whose performance can be modified after they have been fabricated. Specifically, we are interested in the nature and extent of in situ reconfigurability in compliant mechanisms. In other words, we seek to understand the range of performance that can be achieved by these mechanisms without requiring significant reassembly. The material properties such as the storage modulus of a newly studied class of materials — shape memory polymers — vary by over an order of magnitude over a temperature range of 20 – 50 C. These polymers also allow the fixing of moderate to large strains (20 – 75%) experienced at high temperatures for extended periods of time, while retaining the ability to remember their original shape when reheated to the same high temperatures. These two properties make shape memory polymers a natural candidate for the fabrication of reconfigurable compliant mechanisms. We explore various means for introducing reconfigurability in compliant mechanisms, and from these, select a subset that is suitable for in situ reconfiguration. Quasi-static nonlinear finite element simulations are used to study the change in performance due to reconfiguration of four fully compliant mechanisms made of a shape memory polymer. Preliminary results indicate that noticeable qualitative and quantitative changes in performance can be achieved by these mechanisms.

Shape memory polymers (SMPs) are known as smart polymer materials which can be deformed and fixed in a temporary shape and can recover to its original shape upon an external stimulus such as temperature which is the main stimulus for general SMPs. In this research, a renewable natural resource based on vanillin-furfurylamine benzoxazine (V-fa) and eugenol-furfurylamine benzoxazine (E-fa) are developed to substitute the use of petroleum based polybenzoxazine. The as-synthesized V-fa and E-fa show the degradation temperature at 5% weight loss to be as high as 343 and 310?C and char content to be 66 and 54%, respectively. Effects of epoxidized castor oil (ECO) content at 10-50wt% filled in bio-based polybenzoxazine on thermal, mechanical and shape memory properties of bio-based polybenzoxazine/bio-based epoxy SMPs are thoroughly investigated. The results reveal that with increase in ECO content, storage modulus and glass transition temperature of V-fa/ECO and E-fa/ECO copolymer decreased providing the values of 2.27 GPa to 1.60 GPa and 158?C to 100?C, respectively for V-fa/ECO copolymer and 1.53 GPa to 1.16 GPa and 40?C to -17?C, respectively for E-fa/ECO copolymer. In shape memory properties, the V-fa/ECO SMPs show shape fixity values at a room temperature of 86-94% and the values decrease with increasing ECO content, while the temporary shape at room temperature of the E-fa/ECO SMPs cannot fixed. Additionally, the V-fa/ECO SMPs provided the shape recovery values at Tg+20?C of 81-96% and the values increase with increasing of ECO content. Furthermore, it was observed that the V-fa/ECO copolymer having 40wt% of V-fa content exhibits good balance properties between shape memory performance and thermomechanical properties and it can be greatly recovered to the original shape for 5 cycles.

Role of thermal property and interface in shape memory polymers

Personalized 4D printing of bioinspired tracheal scaffold concept based on magnetic stimulated shape memory composites

Shape memory polymers (SMPs) are stimuli‐response materials known for their ability to be actuated from temporary shape into original shape. Because of this unique functionality SMPs are promising materials for diverse applications fields, including smart biomedical devices, aviation, automobile, structures or coatings. In this article, the work has been focused on the chemical modification of an epoxy monomer Bisphenol A diglycidyl ether (DGEBA) which was carried out by using allyl amines as curing agents and a thiol. When both systems Epoxy‐Amine/Tiol‐Ene were photopolymerized, a soft phase is introduced through a thiol‐ene system and a rigid phase is given by the polymerization of the epoxy polymer when it reacts with the curing agent allyl amine. One of the main requirements in SMPs is the presence of soft and rigid phases. The study of the effect of the concentration of three different curing agents, allyl amine type, over the capacity of the conformed polymers to return to their original shape was evaluated. DMA analysis was used to determine the Tg in the polymers, once obtained, the polymers were treated on a hot water bath above 10 °C their Tg, then the evaluation of the memory shape was carried out by two tests, bending and torsion. SMPs were obtained and specimens with 20% of concentration of allyl amine as curing agent showed an improvement in their ability of memory shape with a 99% of recovery.

Stimuli-responsive materials are smart materials capable to adjust their properties (e.g. shape and size) in response to an external or internal stimulus including temperature, light, magnetic field, mechanical stress, and pH. Shape memory polymers (SMPs) are attractive class of stimuli-responsive, programmable smart materials with shape-memory behavior: memorize their original, permanent shape; deform and fix into a secondary, temporary shape; and recover the original, permanent shape upon applying an external stimulus. In recent years, advancing intelligent supercapacitors and batteries have attracted significant attention whereas stimuli-responsive materials were integrated to induce stimuli-responsive properties to introduce new properties or mitigate some of the existing issues such as thermal management, mitigating volume change-induced performance degradation, recovery from a mechanical deformation, self-healing, electrochromism. Indeed, integrating energy storage technologies with a variety of stimuli are a fascinating method to realize smart functions [1-3].Herein, we aim to develop a heat-responsive battery capable of mitigating the impact of incidental mechanical abuse or deformation. To achieve this, a shape-memory solid polymer electrolyte (SMSPE) is engineered and incorporated into lithium metal batteries (LMBs). In response to an external heat, the engineered SMSPEs recover their original shape and size from mechanical deformations such as bending and elongation. This study opens-up a promising approach for engineering intelligent batteries responsive to unfavorable internal or external stimuluses, with potential to have a broad impact on other energy storage technologies in different sizes and shapes. The Li|SPSPEs|LFP full cell batteries display a long-term cycle life with a discharge capacity of ~120 mAh g−1 at C/10 in ambient temperature with around 90% capacity retention after 100 cycles. Moreover, the Li|SPSPEs|Li symmetrical cells exhibit a long-term stability with a low voltage polarization at a current density of 0.05 mAh cm−2 for up to 1000 cycles.Overall, the proposed approach shows a promising design principle which can open up new possibilities for the next-generation batteries and their safe operation. With vast range of available SMPs with tunable chemistries, transition temperatures, and high shape-memory performance, and opens up new frameworks to address a variety of detrimental, unresolved issues such as thermal runaway, with potential expansion to the other energy storage technologies.

In this study, we developed a variable-stiffness and deformable link using shape-memory material and the jamming transition phenomenon. Above its glass transition temperature (Tg), a shape-memory polymer (SMP) can be deformed by applying a small load. SMPs maintain the deformed shape after they have been cooled below Tg, and they return to their original shape when heated above Tg. The reversible change in the elastic modulus between the glassy and rubbery states of SMPs can be on the order of 100–1000 times. We exploited the characteristics of SMPs to develop robot components with variable stiffness and sensitivity. The jamming transition phenomenon for granular material has been widely used as a method to change the stiffness of robots. This phenomenon is the change from fluid-like to solid-like conditions by removing air from a space containing particles. In this study, we developed a variable-stiffness link by combining the SMP and the jamming transition phenomenon. Moreover, by replacing the SMP with shape-memory alloys (SMAs), whose recovery force and elastic modulus are larger than those of SMPs, we prepared a second prototype with variable stiffness. We evaluated the performance of both prototypes, using the SMP or the SMA, with experiments and confirmed the motion principle of the proposed link (e.g., shape recovery and shape fixity). Moreover, it was confirmed that the stiffness of these links can be changed among four states.

Shape memory polymers (SMPs) are a new type of smart material, they perform large reversible deformation with a certain external stimulus (e.g., heat and electricity). The properties (e.g., stiffness, strength and other mechanically static or quasi-static load-bearing capacity) are primarily considered for conventional resin-based composite materials which are mainly used for structural materials. By contrast, the mechanical actuating performance with finite deformation is considered for the shape memory polymers and their composites which can be used for both structural materials and functional materials. For shape memory polymers and their composites, the performance of active deformation is expected to further promote the development in smart active deformation structures, such as deployable space structures and morphing wing aircraft. The shape memory polymer composites (SMPCs) are also one type of High Strain Composite (HSC). The space deployable structures based on carbon fiber reinforced shape memory polymer composites (SMPCs) show great prospects. Considering the problems that SMPCs are difficult to meet the practical applications in space deployable structures in the recent ten years, this paper aims to research the mechanics of deformation, and failure of SMPCs. In the overall view of the shape memory polymer material’s nonlinearity (nonlinearity and stress softening in the process of pre-deformation and recovery, relaxation in storage process, irreversible deformation), by the multiple verifications among theory, finite element and experiments, one obtains the deformation and mechanism for the process of “pre-deformation, energy storage and actuation and its non-fracture constraint domain. Then, the parameters of SMPCs will be optimized. Theoretical analysis is realized by the strain energy function, additionally considering the interaction strain energy between the fiber and the matrix. For the common resin-based or soft-material-based composites under pure bending deformation, we expect to uniformly explain the whole process of buckling occurrence, evolution and finally failure, especially for the early evolution characteristics of fiber microbuckling inside the microstructures. The research results are meaningful for the practical applications for SMPC deployable structures in space. Considering the deformation mechanisms of SMPCs, the local post-microbuckling is required for the unidirectional fiber reinforced composite materials, at the conditions of its large geometrical deflection. The cross section of SMPC is divided into three areas: non-buckling stretching area, non-buckling compressive area, and buckling compressive area. Three variables are considered: critical buckling position, and neutral plane, the fiber buckling half-wavelength. Considering the condition of the small strain and large displacement, the strain energy expression of the SMP/fiber system was derived, which contains two types, e.g., strain energy of SMP and fiber. According to the minimum energy principle, the expression for all key parameters were derived, including the critical buckling curvature, neutral plane position, the buckling half-wavelength, fiber buckling amplitude, and strain.