Thermo-responsive Shape Memory Polymer Research Articles

Two-way thermo-responsive thermoset shape memory polymer based on benzoxazine/urethane alloys using as self-folding structures

A novel two-way shape memory polymers derived from benzoxazine/urethane alloys (poly(BA-a/PU)) are developed in this research. The effect of urethane contents acted as spring elastomer on dynamic mechanical properties and two-way shape memory performance of the alloys was investigated. The experimental test and numerical simulation were also used to study and predict the ability of the developed 2WSMPs. The results showed that shape fixity at room temperature (RT) of poly(BA-a/PU) was enhanced in the range of 80–97% with the addition of PU contents. Shape recovery values to first temporary shape at Tg+20 °C of the specimen were 79–93%, whereas, those to second temporary shape at RT were 82–95%. Furthermore, 2WSMP based on poly(BA-a/PU) was reversely recovered between both temporary shapes more than 7 cycles. The experimental and numerical results revealed that poly(BA-a/PU) exhibited high 2WSMP performance for using as smart materials in self-folding structures application.

4D Printing of Multicomponent Shape-Memory Polymer Formulations

Four-dimensional (4D) printing technology, as a next-generation additive manufacturing method, enables printed objects to further change their shapes, functionalities, or properties upon exposure to external stimuli. The 4D printing of programmable and deformable materials such as thermo-responsive shape-memory polymers (trSMPs), which possess the ability to change shape by exposure to heat, has attracted particular interest in recent years. Three-dimensional objects based on SMPs have been proposed for various potential applications in different fields, including soft robotics, smart actuators, biomedical and electronics. To enable the manufacturing of complex multifunctional 3D objects, SMPs are often coupled with other functional polymers or fillers during or before the 3D printing process. This review highlights the 4D printing of state-of-the-art multi-component SMP formulations. Commonly used 4D printing technologies such as material extrusion techniques including fused filament fabrication (FFF) and direct ink writing (DIW), as well as vat photopolymerization techniques such as stereolithography (SLA), digital light processing (DLP), and multi-photon polymerization (MPP), are discussed. Different multicomponent SMP systems, their actuation methods, and potential applications of the 3D printed objects are reviewed. Finally, current challenges and prospects for 4D printing technology are summarized.

3D printing thermo-responsive shape memory polymer composite based on PCL/TPU blends

3D printing thermo-responsive shape memory polymer composite based on PCL/TPU blends

Influence of humidity on the rheology of thermoresponsive shape memory polymers

Shape Memory Polymers (SMPs) have the inherent ability to maintain a reversible temporary shape and restore a permanent shape under an external trigger. The class of materials has great potential to contribute to smart applications in soft robotics, aerospace, actuation and biomedicine. In these potential application domains, materials are often exposed to large fluctuations due to humidity influences. Therefore, a novel approach is developed to characterize the stronlgy coupled thermal, humidity and time-dependent behavior of polyurethane-based SMP. Weight gain measurements with disk samples of dimension 35,times 35 times 1.5 text {mm}^text {3} and linear expansion tests with rectangular samples of dimension 10 times 40 times 1.0 text {mm}^text {3} at different relative humidity are carried out to perform the isothermal and isohumid dynamic measurements in thermodynamic equilibrium. The time-temperature superposition is used to characterize and compare the viscoelastic properties at different relative humidity. Concerning effective material properties, a major finding of this investigation is the horizontal shift of the material parameter in the temperature space due to the presence of humidity. Thus, the humidity-dependent material behavior is fully described by a humidity-dependent glass transition temperature. The measured experiments provide a full description of the thermal, humidity and mechanical behavior of SMPs.Graphical abstract

Saline-responsive triple-action self-healing coating for intelligent corrosion control

In this work, a triple-action self-healing coating was fabricated to promote the corrosion protection of carbon steel based on a shape memory polymer (SMP) epoxy coating and polyaniline/benzotriazole (PANI/BTA) nanocapsules. The PANI/BTA nanocapsules had dual functions: (1) PANI as a saline (NaCl)-responsive gatekeeper could achieve the controllable release of BTA corrosion inhibitors, which could adsorb on the metal surface to inhibit corrosion; (2) PANI can prompt the formation of Fe2O3 passive layer. Besides, the thermo-responsive SMP coating could narrow the scratch size after heating, which was beneficial to reduce the amount of corrosion inhibitors needed to fully cover the steel surface. Electrochemical impedance spectroscopy (EIS) measurements were performed to investigate the self-healing performance of the coatings containing different contents of PANI/BTA nanocapsules. Furthermore, the synergetic inhibition effects of PANI, BTA and SMP coating were demonstrated using scanning electrochemical microscopy. The results indicated that the healed 0.5 wt% PANI/BTA coating exhibited an excellent self-healing property and its self-healing efficiency was higher than 96%. The XPS results indicated that the Fe2O3 passive layer was formed in the scratched region to resist steel corrosion.

Deformable Thermo-Responsive Smart Windows Based on a Shape Memory Polymer for Adaptive Solar Modulations.

Thermo-responsive smart windows that control solar transmission are expected to be the promising solution to excessive building energy consumption and overheating of solar cell devices. The two performance indices, namely, the luminous transmission (Tlum) and the solar modulation (ΔTsol), are often intrinsically limited by conventional thermo-responsive materials, which restrict their applications in smart windows. Alternatively, constructing a deformable surface morphology of smart windows can be an effective strategy to modulate the solar transmission. Here, we report a new category of thermo-responsive smart windows with a deformable surface morphology, which can be custom designed to achieve both desirable ΔTsol and Tlum according to the sunlight incident angles of actual applications. This design is based on a thermo-responsive shape memory polymer and an optical coating, which is termed the butterfly-wing-like smart window (BSW). The BSW reversibly transforms from a temporary shape of flat topography to a predefined original shape of tilted configuration upon heating. It is demonstrated that the BSW has a high ΔTsol of 32.6% and an excellent Tlum(average) of 64.5%. This work provides a new design strategy and mechanism for thermo-responsive smart windows.

Self-sensing shape memory polymer composites reinforced with functional textiles

In this work, thermally reduced graphene oxide coated glass fabric (TRGO-GF) was used as a sensing element and reinforcement to manufacture thermo-responsive polyurethane-based self-sensing shape memory polymer composite (SSMPC). It was demonstrated that the proposed novel functional SSMPC was able to detect changes in temperature and shape recovery at the same time, providing its utility in a number of applications. The temperature sensing capability and the relationship between temperature and electrical resistance of manufactured SSMPC was demonstrated by inducing heating and cooling cycles using a heating film attached to the sample. It was shown that the proposed SSMPC was able to detect any changes in temperature taking place within the composite. The SSMPC showed a negative temperature coefficient (NTC) of resistance of −14.80 × 10−3 (°C)−1 and −7.25 × 10−3 (°C)−1 for testing regime I (30–40 °C) and testing regime II (40–50 °C) respectively. It was demonstrated through experiments that the SSMPC was able to detect the recovery ratio and rate of recovery during the thermally induced shape recovery process. It was also revealed that the extent and rate of shape recovery can be manipulated via controlling the thermal stimulus.

Evaluation of a self-fitting, shape memory polymer scaffold in a rabbit calvarial defect model

Self-fitting scaffolds prepared from biodegradable poly(ε-caprolactone)-diacrylate (PCL-DA) have been developed for the treatment of craniomaxillofacial (CMF) bone defects. As a thermoresponsive shape memory polymer (SMP), with the mere exposure to warm saline, these porous scaffolds achieve a conformal fit in defects. This behavior was expected to be advantageous to osseointegration and thus bone healing. Herein, for an initial assessment of their regenerative potential, a pilot in vivo study was performed using a rabbit calvarial defect model. Exogenous growth factors and cells were excluded from the scaffolds. Key scaffold material properties were confirmed to be maintained following gamma sterilization. To assess scaffold integration and neotissue infiltration along the defect perimeter, non-critically sized (d = 8 mm) bilateral calvarial defects were created in 12 New Zealand white rabbits. Bone formation was assessed at 4 and 16 weeks using histological analysis and micro-CT, comparing defects treated with an SMP scaffold (d = 9 mm x t = 1 or 2 mm) to untreated defects (i.e. defects able to heal without intervention). To further assess osseointegration, push-out tests were performed at 16 weeks and compared to defects treated with poly(ether ether ketone) (PEEK) discs (d = 8.5 mm x t = 2 mm). The results of this study confirmed that the SMP scaffolds were biocompatible and highly conducive to bone formation and ingrowth at the perimeter. Ultimately, this resulted in similar bone volume and surface area versus untreated defects and superior performance in push-out testing versus defects treated with PEEK discs. Statement of significanceCurrent treatments of craniomaxillofacial (CMF) bone defects include biologic and synthetic grafts but they are limited in their ability to form good contact with adjacent tissue. A regenerative engineering approach using a biologic-free scaffold able to achieve conformal fitting represents a potential “off-the-shelf” surgical product to heal CMF bone defects. Having not yet been evaluated in vivo, this study provided the preliminary assessment of the bone healing potential of self-fitting PCL scaffolds using a rabbit calvarial defect model. The study was designed to assess scaffold biocompatibility as well as bone formation and ingrowth using histology, micro-CT, and biomechanical push-out tests. The favorable results provide a basis to pursue establishing self-fitting scaffolds as a treatment option for CMF defects.

Self-Optimization of the Shape-Memory Effect during Programming Cycle Tests

Thermoresponsive shape-memory polymers (TSMPs) are materials that can memorize temporary shapes and can restore to their permanent shapes upon stimulus. This ability is driven by reversible deformation (εre); however, the deformation of TSMPs inevitably involves unfavorable irreversible deformation (εir). Consequently, avoiding the εir through macromolecular chemistry or/and physical blending has been the currently efficient methodology for designing or fabricating TSMPs. Herein, we report another methodology, programming cycle tests (PCT), which can select and remove unfavorable εir, thus taking the shape-memory performance to its limits. Moreover, PCT is a physical process that only involves a series of successive thermo-mechanical cycles. Therefore, this study provides a simple and efficient methodology for designing and fabricating TSMPs.

Computational Design of Self-Actuated Deformable Solids via Shape Memory Material

The emerging 4D printing techniques open new horizons for fabricating self-actuated deformable objects by combing strength of 3D printing and stimuli-responsive shape memory materials. This article focuses on designing self-actuated deformable solids for 4D printing such that a solid can be programmed into a temporary shape and later recovers to its original shape after heating. To avoid a high material cost, we choose a dual-material strategy that mixes an expensive thermo-responsive shape memory polymer (SMP) material with a common elastic material, which however leads to undesired deformation at the shape programming stage. We model this shape programming process as two elastic models with different parameters linked by a median shape based on customizing a constitutive model of thermo-responsive SMPs. Taking this material modeling as a foundation, we formulate our design problem as a nonconvex optimization to find the distribution of SMP materials over the whole object as well as the median shape, and develop an efficient and parallelizable method to solve it. We show that our proposed approach is able to design self-actuated deformable objects that cannot be achieved by state of the art approaches, and demonstrate their usefulness with three example applications.

Design of high-performance curling mascara through utilization of smart thermoresponsive polymer.

In this study, methoxy poly(ethylene glycol)-b-poly(D,L-lactide), or mPEG-PLA, was used as the smart thermoresponsive polymer in our mascara formulation. The utility of mPEG-PLA in a mascara formulation was investigated by a stepwise build-up in an oil in water (O/W) emulsion. The experimental results may pave the way to a strategy of developing more cosmetic formulation with thermoresponsive shape memory polymers (SMPs). mPEG-PLA was first incorporated in a simple emulsion for rheological evaluation such as shear flow viscosity and small deformation oscillation measurements over the relevant temperature settings to mascara application. Then, wax and pigment were incorporated to complete the basic formulation as an O/W mascara and evaluated rheologically as before. Finally, the formulation was applied by a heated mascara applicator to false lashes to evaluate its curing and lifting effect. With 0.8% concentration of mPEG-PLA, the viscosity was able to increase from 0.20 Pas·s to 1.00 Pas·s. At 1.0% concentration of mPEG-PLA, the emulsion samples with mineral oil were evaluated from 55°C to 25°C for its storage modulus (G') and were found to have a consistent shear-thinning characteristic across all temperature range. The sample containing the polymer (M-1) arrived at a markedly higher elasticity when compared against the sample without (M-0). The same result holds true for the set of samples formulated with beeswax instead of mineral oil. When the formulations were applied with a heated mascara applicator on false eyelashes, the formulation containing mPEG-PLA was found to produce a more pronounced and longer-lasting curl. This preliminary rheological study of an O/W mascara containing mPEG-PLA demonstrated that thermoresponsive SMP can be added to enhance the curl and lifting effect of a mascara formulation.

Crack self-healing of thermo-responsive shape memory polymers with application to control valves, filtration, and drug delivery capsule

Fracture behavior of Shape Memory Polymers (SMPs) and their self-healing property is one of the up-to-date subjects through the literature, where only a few researches have been conducted. Nowadays, because of the exceptional properties of SMPs and their implementation in 4D printing, they are most taken into attention. In this study, thermomechanical coupling effect on 3D fracture analysis of SMPs in large deformation regime has been investigated. Firstly, a thermo-visco-hyperelastic model is implemented to model the thermomechanical cycle of the SMP in the stress-free strain-recovery as well as the fixed-strain-stress-recovery processes. Motivated by fracture analysis and self-healing properties of SMPs, both 2D and 3D fracture analysis are conducted through various feasibility applications, such as flow control valve, pressure control valve, filtration and drug delivery capsule. Moreover, the ability of the analysis is shown through examining different parameters could affect the SMP response, such strain rate (or applied strain), temperature rate and memory recovery. Finally, the results show the ability of the numerical modeling in the aforesaid applications to design, analyze, and fabricate these applications.

Rapid Processing and Drug Evaluation in Glioblastoma Patient-Derived Organoid Models with 4D Bioprinted Arrays

SummaryGlioblastoma is the most common and deadly primary brain malignancy. Despite advances in precision medicine oncology (PMO) allowing the identification of molecular vulnerabilities in glioblastoma, treatment options remain limited, and molecular assays guided by genomic and expression profiling to inform patient enrollment in life-saving trials are lacking. Here, we generate four-dimensional (4D) cell-culture arrays for rapid assessment of drug responses in glioblastoma patient-derived models. The arrays are 3D printed with thermo-responsive shape memory polymer (SMP). Upon heating, the SMP arrays self-transform in time from 3D cell-culture inserts into histological cassettes. We assess the utility of these arrays with glioblastoma cells, gliospheres, and patient derived organoid-like (PDO) models and demonstrate their use with glioblastoma PDOs for assessing drug sensitivity, on-target activity, and synergy in drug combinations. When including genomic and drug testing assays, this platform is poised to offer rapid functional drug assessments for future selection of therapies in PMO.

Effect of pore size and spacing on neovascularization of a biodegradble shape memory polymer perivascular wrap.

Neointimal hyperplasia (NH) is a main source of failures in arteriovenous fistulas and vascular grafts. Several studies have demonstrated the promise of perivascular wraps to reduce NH via promotion of adventitial neovascularization and providing mechanical support. Limited clinical success thus far may be due to inappropriate material selection (e.g., nondegradable, too stiff) and geometric design (e.g., pore size and spacing, diameter). The influence of pore size and spacing on implant neovascularization is investigated here for a new biodegradable, thermoresponsive shape memory polymer (SMP) perivascular wrap. Following an initial pilot, 21 mice were each implanted with six scaffolds: four candidate SMP macroporous designs (a-d), a nonporous SMP control (e), and microporous GORETEX (f). Mice were sacrificed after 4 (N = 5), 14 (N = 8), and 28 (N = 8) days. There was a statistically significant increase in neovascularization score between all macroporous groups compared to nonporous SMP (p < .023) and microporous GORETEX (p < .007) controls at Day 28. Wider-spaced, smaller-sized pore designs (223 μm-spaced, 640 μm-diameter Design c) induced the most robust angiogenic response, with greater microvessel number (p < .0114) and area (p < .0055) than nonporous SMPs and GORETEX at Day 28. This design also produced significantly greater microvessel density than nonporous SMPs (p = 0.0028) and a smaller-spaced, larger-sized pore (155 μm-spaced, 1,180 μm-sized Design b) design (p = .0013). Strong neovascularization is expected to reduce NH, motivating further investigation of this SMP wrap with controlled pore spacing and size in more advanced arteriovenous models.

Design-to-fabrication with thermo-responsive shape memory polymer applications for building skins

Smart materials are studied for climate-responsive building skins due to internal changeable properties stimulated by material-specific input. This research focuses on shape memory polymer (SMP) and temperature as its activating stimulus for dynamic shading devices with mechanisms of opening and closing. From case-studies, four design strategies are presented in this paper. Design research and 3D printing fabrication tests of SMP prototypes were conducted by the research-through-design approach. Prototypes were comparatively analyzed for development and optimization in architectural applications. It is challenging to train permanent shapes, to program temporary shapes and to design repetitive material behaviours. Measures to achieve reversible reiterative shape-changing materials are required for practical implementation. For further design-fabrication research on the actual temperature and the material behaviours of designed elements, the SMP with glass transition at 35°C was applied. Later, it would be necessary to simulate the environmental effects and validate the performance of thermo-responsive SMP building skins.

Two-Way and Multiple-Way Shape Memory Polymers for Soft Robotics: An Overview

Shape memory polymers (SMPs) are smart materials capable of changing their shapes in a predefined manner under a proper applied stimulus and have gained considerable interest in several application fields. Particularly, two-way and multiple-way SMPs offer unique opportunities to realize untethered soft robots with programmable morphology and/or properties, repeatable actuation, and advanced multi-functionalities. This review presents the recent progress of soft robots based on two-way and multiple-way thermo-responsive SMPs. All the building blocks important for the design of such robots, i.e., the base materials, manufacturing processes, working mechanisms, and modeling and simulation tools, are covered. Moreover, examples of real-world applications of soft robots and related actuators, challenges, and future directions are discussed.

Study on Thermal and Mechanical Properties of SBS/PCL Based Thermo-Responsive Shape Memory Polymer Nanocomposite Actuator

The present paper study the thermal, electrical and shape memory behavior of Polystyrene-block-Polybutadiene-block-Polystyrene (SBS) and Polycaprolactone (PCL) blend reinforced with Carbon nanofibers (CNF). Here SBS acts as an elastomer, PCL behaves as switch polymer and CNF is used as a conductive filler which facilitates shape memory polymer Nano Composite (SMPNC). The immiscibility between the microstructures is demonstrated in DSC results. Characterization techniques such as, TGA, Shape memory test etc. were also conducted. The results show that this is an optimized SMP system with good shape recovery and fixing performances.

One-way thermo-responsive shape memory polymer nanocomposite derived from polycaprolactone and polystyrene-block-polybutadiene-block-polystyrene packed with carbon nanofiber

Shape-memory polymer nanocomposite (SMPNC) blends with thermoresponsive shape memory capability have received increasing interests and have been a grooming research area due to its potential applications. In the present study, the polymer blend comprising of Polycaprolactone (PCL) and Polystyrene-block-Polybutadiene-block-Polystyrene (SBS) is prepared by melting and blending method, followed by the addition of carbon nanofibers (CNF), to provide the blend with excellent shape memory property stimulated by temperature. In this polymeric blend SBS, PCL, and CNF are acted as an elastomer, switch polymer and conductive filler, respectively. The two-phase morphology of components in the blend is confirmed using Scanning Electrode Microscopic (SEM) images, Polarised Optical Microscopic (POM) images, and stress-strain plots. The immiscibility between the microstructures is revealed from the Differential Scanning Calorimetric (DSC) results. Characterization techniques such as X-Ray Diffraction (XRD), Thermo Gravimetric Analysis (TGA) and shape memory test are also conducted. The crystallinity of the synthesized composite is influenced by the PCL content. As the PCL content increases, crystalline nature also increases. From TGA results, the thermal stability of the composites is found to be decreasing from PCL 5 to PCL 100. The tensile and shape memory results show an optimized one-way SMPNC system with good shape recovery and fixing performances.

Pre-Programmed Tri-Layer Electro-Thermal Actuators Composed of Shape Memory Polymer and Carbon Nanotubes.

Due to their high deformability, lightness, and safe interaction with the surrounding environment, flexible actuators are key ingredients in soft robotics technologies. Among these, electro-thermal actuators (ETAs), based on carbon nanotubes (CNTs), are used to generate agile movements when current is applied. The extent of movement is determined mostly by the coefficient of thermal expansion (CTE) of the materials arranged in a bi-/tri-layer structure. However, current CNT-based ETAs usually accomplish only simple actions with limited movements. In this work, we successfully developed novel ETAs that are capable of carrying out various controllable movements, such as extremely high bending curvature or unique actuations mimicking a wheel and a worm. These superior functionalities are achieved by adding a third layer or hinges composed of a thermo-responsive shape memory polymer (SMP) onto a bi-layer CNT-kapton ETA. To predict the unique movements of the "triangle" and "worm" actuators, finite element simulations were performed. The combination of SMP and electro-thermal behavior demonstrates its potential for applications in the field of soft actuators and robotics.

Shape memory polymer resonators as highly sensitive uncooled infrared detectors

Uncooled infrared detectors have enabled the rapid growth of thermal imaging applications. These detectors are predominantly bolometers, reading out a pixel’s temperature change due to infrared radiation as a resistance change. Another uncooled sensing method is to transduce the infrared radiation into the frequency shift of a mechanical resonator. We present here highly sensitive resonant infrared sensors, based on thermo-responsive shape memory polymers. By exploiting the phase-change polymer as transduction mechanism, our approach provides 2 orders of magnitude improvement of the temperature coefficient of frequency. Noise equivalent temperature difference of 22 mK in vacuum and 112 mK in air are obtained using f/2 optics. The noise equivalent temperature difference is further improved to 6 mK in vacuum by using high-Q silicon nitride membranes as substrates for the shape memory polymers. This high performance in air eliminates the need for vacuum packaging, paving a path towards flexible non-hermetically sealed infrared sensors.