Exhibit Shape Memory Properties Research Articles

Multifaceted Shape Memory Polymer Technology for Biomedical Application: Combining Self-Softening and Stretchability Properties.

Thiol-ene polymers are a promising class of biomaterials with a wide range of potential applications, including organs-on-a-chip, microfluidics, drug delivery, and wound healing. These polymers offer flexibility, softening, and shape memory properties. However, they often lack the inherent stretchability required for wearable or implantable devices. This study investigated the incorporation of di-acrylate chain extenders to improve the stretchability and conformability of those flexible thiol-ene polymers. Thiol-ene/acrylate polymers were synthesized using 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO), Trimethylolpropanetris (3-mercaptopropionate) (TMTMP), and Polyethylene Glycol Diacrylate (PEGDA) with different molecular weights (Mn 250 and Mn 575). Fourier Transform Infrared (FTIR) spectroscopy confirmed the complete reaction among the monomers. Uniaxial tensile testing demonstrated the softening and stretching capability of the polymers. The Young's Modulus dropped from 1.12 GPa to 260 MPa upon adding 5 wt% PEGDA 575, indicating that the polymer softened. The Young's Modulus was further reduced to 15 MPa under physiologic conditions. The fracture strain, a measure of stretchability, increased from 55% to 92% with the addition of 5 wt% PEGDA 575. A thermomechanical analysis further confirmed that PEGDA could be used to tune the polymer's glass transition temperature (Tg). Moreover, our polymer exhibited shape memory properties. Our results suggested that thiol-ene/acrylate polymers are a promising new class of materials for biomedical applications requiring flexibility, stretchability, and shape memory properties.

Self‐Healing, Photothermal‐Responsive, and Shape Memory Polyurethanes for Enhanced Mechanical Properties of 3D/4D Printed Objects (Adv. Funct. Mater. 15/2023)

Additive Manufacturing In article number 2211579, Yonglai Lu, Runguo Wang, Xiang Lin, and co-workers design and synthesize new thermoplastic polyurethanes with self-healing, inherent photothermal effects, and excellent printability to address the growing demand for 3D/4D printed objects in terms of performance and precision. The as-prepared materials exhibit shape memory properties, demonstrating their potential for 4D printing. This printing strategy can promote the development for next-generation intelligent devices.

Influence of quadruple hydrogen bonding on polyvinyl butyral resin properties

Herein we report an easily accessible supramolecular polymer readily made from polyvinyl butyral (PVB) by cross-linking with non-covalent self-complementary ureido-pyrimidinone (UPy) dimers. The resulting materials exhibit multifunctional properties, not only self-healing and shape memory, but also enhanced thermo-mechanical resistance. The UPy content, which represents the quadruple hydrogen bonding density, shows an important influence on tuning polymer performances. Moderate UPy content (2.5 mol.%) is important to impart the optimal comprehensive properties. Both infrared analyses and dynamic mechanical analyses indicate that the quadruple hydrogen bonding is stable up to 120 °C, thus enabling the healing process. The healing efficiency highly depends on the glass transition temperature (Tg) of the final polymer, itself being controlled by the UPy content. A 100% healing efficiency can be achieved at 120 °C when the UPy content is controlled up to 2.5 mol.%. Meanwhile, around 90% healing efficiency was achieved in water at 60 °C for all materials. All samples exhibit shape memory properties without obvious dependence on the UPy content. This work illustrates that the physical cross-linking, formed by non-covalent hydrogen bonding, cannot only provide a practical strategy to obtain multi-responsive shape memory polymers with self-healing feature but also offers the possibility to tune the polymer thermal and mechanical properties.

From the synthesis and characterization of methacrylated fatty acid based precursors to shape memory polymers

AbstractFatty acid based precursors were synthesized by a one‐step reaction from oleic or lauric acids and glycidyl methacrylate to be used later in polymer formulations. Different times of reaction, amounts of catalyst and initial ratios of reactants were evaluated, obtaining conversions higher than 0.9 for the best conditions. The monomers obtained are interesting alternatives to synthetics since they combine low cost with environmental advantages (i.e. higher bio‐carbon content). These polymeric precursors were reacted separately in cationic and free radical polymerizations with styrene (50 wt%) to evaluate their potential as greener monomers. The lauric acid precursor and free radical polymerization were the alternatives that produced elastomeric materials with higher glass transition temperatures and storage moduli. These results were related to the lesser plasticizing effect of the shorter fatty acid chain, in comparison with that of the oleic acid based monomer, and to a lower free volume in the formed structure during curing. Moreover, all the obtained polymers exhibited shape memory properties that can be activated by temperature changes. © 2018 Society of Chemical Industry

Effect of annealing atmosphere on IGZO thin film transistors on a deformable softening polymer substrate

The effect of annealing atmosphere on indium–gallium–zinc-oxide (IGZO) thin film transistors (TFTs) fabricated on a deformable softening polymer substrate is presented in this work. Different annealing conditions—ambient, oxygen, vacuum and forming gas—are employed in the fabrication of IGZO TFTs and the changes in electrical characteristics are examined. Fabricated devices exhibit shape memory properties due to thiol-ene/acrylate substrates allowing the softening of bioelectronics to demonstrate modulus changes in aqueous conditions at body temperature. Gold (Au) is used as the contact metal for the gate, drain and source for its good adherence and malleability required for this polymer. It is found that annealing treatments at 250 °C can improve the field effect mobility of the TFTs from 10−2 up to 30 cm2 V−1 s−1. These improvements are attributed to the reduction of oxygen concentration in the active film of the TFTs. The contact resistance is also reduced by the annealing treatments from approximately 1 MΩ to 20 kΩ, indicating improvement in physical contact at the IGZO-Au interface. In addition, the contributions of contact resistance and channel resistance to other electrical parameters are analyzed. This study will pave the way for the development and optimization of high-performance bioelectronic devices on smart polymers.

Advances in Ti-Based Systems as High Temperature Shape Memory Alloys

In this study, we investigate the effect of ternary addition on the structural, mechanical properties and temperature dependence of Ti-based as potential shape memory alloys using molecular dynamics approach. We found that binary Ti-Pt alloys exhibit shape memory properties and display possible martensitic transformation from B2 to B19 phases. Partial addition with Zr, Co, Pd, Ir showed preferential ternary high temperature shape memory alloys formation of 6.25 at. % X composition (Ti-Pt-X). We found that the equilibrium lattice constants are in better agreement with the available experimental values. The heats of formation and elastic properties reveal possible composition and phases at temperature above 900 K with good shape memory properties. Their structures were confirmed using the X-ray diffraction patterns at different temperatures.

Shape memory behavior of liquid-crystalline elastomer/graphene oxide nanocomposites

Liquid-crystalline elastomer (LCE) nanocomposites exhibiting shape memory properties were prepared by dispersing a chemically modified graphene oxide (GO) in a smectic, lightly crosslinked epoxy resin obtained by curing p-bis(2,3-epoxypropoxy)-α-methylstilbene (DOMS) with sebacic acid (SA). Chemical grafting of DOMS monomer on GO particle surface improved interfacial adhesion between the epoxy matrix and the filler. The obtained nanocomposite films were characterized in their phase behavior, morphological and thermal properties. Furthermore, their shape memory properties were analyzed through two-way thermomechanical cycling tests. The combination of the LCE liquid crystallinity and the efficient dispersion of functionalized GO resulted in toughened, highly oriented systems endowed with enhanced shape memory response. Incorporation of 0.15 wt.% GO resulted in a significant increase of spontaneous elongation and reduced actuation temperature during cycling thermomechanical tensile testing, demonstrating the potential of these systems as shape memory materials for sensors and actuators.

Micropore Geometry Manipulation by Macroscopic Deformation Based on Shape Memory Effect in Porous PLLA Membrane and its Enhanced Separation Performance.

An effective strategy to tailor the microporous structures has been developed based on the shape memory effect in porous poly(l-lactic acid) membranes in which tiny crystals and amorphous matrix play the roles of shape-fixed phase and reversible-phase, respectively. Our results indicate that not only PLLA membranes but micropores exhibit shape memory properties. The proportional deformations on two scales have been achieved by uniaxial or biaxial tension, providing a facile way to manipulate continuously the size and the orientation degree of pores on microscale. The enhanced separation performance has been validated by taking polystyrene colloids with varying diameters as an example.

Iterative synthesis of monodisperse pendants for making comb-like polyurethanes

Polyurethanes grafted with well-defined polar pendants were synthesized and investigated. A series of linear and dendritic poly(urea/malonamide)s with uniform chain length were first prepared from an iterative synthesis route, which is based on a dual-functional building block, 4-isocyanate-4´-(3,3-dimethyl-2,4-dioxo-azetidine)diphenyl methane (IDD). Moreover, side chain polyurethanes (SPUs) bearing azetidine-2,4-dione functional groups were prepared from one pot reaction for following post-functionalization of poly(urea/malonamide)s when IDD-diols were added to polyurethane prepolymers as chain extenders. Subsequently, the azetidine-2,4-dione functional groups on the SPUs underwent addition reactions with amino functional group containing dendritic or linear poly(urea/malonamide)s under mild condition, without the need of catalyst and protection/deprotection procedure to achieve polyurethanes grafted with well-defined pendants. Mechanical properties of these comb-like polyurethanes strongly depend on the architecture and the molecular length of poly(urea/malonamide) pendants, which could be adjusted by the grafting fractions of the dendritic or linear poly(urea/malonamide)s with various generations. These poly(urea/malonamide) pendants provided strong hydrogen bonding interactions to achieve physical crosslinking effects in the polyurethanes. Consequently, the polyurethanes with improved mechanical properties and sustained phase transition exhibit shape memory properties.

Shape Memory Polymers Synthesised For Controllable Switching Temperatures

Shape memory polymers (SMPs) have been synthesized by various diisocyanates and polyols for specific transition temperatures. But these types of shape memory polymers don’t have a control in varying temperatures and fail to exhibit shape memory properties. Hence it is necessary to synthesize a shape memory polymer which suits for specific applications even if there is a variation in operating temperatures which have a control on switching temperatures. This paper mainly concentrates on synthesis of shape memory polymers for controllable switching temperatures. The shape memory properties of the shape memory polymers were studied by bend test. It is found that shape memory polymers exhibits 100% shape memory effect. The shape memory properties, thermal properties and morphological characteristics are investigated by Xray difractogram (XRD), Differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) and SEM.

Shape Memory Cellulose-Based Photonic Reflectors

Biopolymer-based composites enable to combine different functionalities using renewable materials and cost-effective routes. Here we fabricate novel thermoresponsive photonic films combining cellulose nanocrystals (CNCs) with a polydiolcitrate elastomer exhibiting shape memory properties, known as hydroxyl-dominant poly(dodecanediol-co-citrate) (PDDC-HD). Iridescent films of CNCs are first made by evaporation-induced self-assembly, then embedded in the PDDC-HD prepolymer, and finally cured to obtain a cross-linked composite with shape memory properties. The fabricated samples are characterized by polarized optical microscopy, scanning electron microscopy, and thermomechanical cycling. The obtained hybrid material combines both intense structural coloration and shape memory effect. The association of stiff cellulose nanocrystals and soft polydiolcitrate elastomer enhances the overall mechanical properties (increased modulus and reduced brittleness). This hybrid nanocomposite takes advantage of two promising materials and expands their possibilities to cover a wide range of potential applications as multiresponsive devices and sensors. As they perform from room to body temperatures, they could be also good candidates for biomedical applications.

Synthesis and characterization of new polydiolcitrates with tunable properties

ABSTRACTPolydiolcitrates are an emerging class of biocompatible polyesters with a great potential in the field of biomedicine and packaging for food and drug materials. In this work, a new type of (co‐)polydiolcitrates made of citric acid (CA) and ethylene glycol (EG) and/or poly(ethylene glycol) (PEG) is investigated. By varying both the EG/PEG and the CA/diol molar ratios, materials exhibiting very different swelling behavior, mechanical and thermal properties are obtained. In particular, the substitution of EG segments with longer and flexible PEG ones results in an increase in crosslinking density, with remarkable effects on swelling capacity, glass transition temperature, and Young modulus. Moreover, polyesters with CA/diol molar ratio equal to 1:1 exhibit shape memory properties, with full capacity of keeping the temporary shape and high capacity of recovering the original shape. This work demonstrates that the appropriate choice of polyester composition allows modulating the sample properties, that permits to these materials to cover a wide range of possible applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3713–3720

Elastic chitosan/chondroitin sulfate multilayer membranes

Freestanding multilayered films were obtained using layer-by-layer (LbL) technology from the assembly of natural polyelectrolytes, namely chitosan (CHT) and chondroitin sulfate (CS). The morphology and the transparency of the membranes were evaluated. The influence of genipin (1 and 2 mg ml−1), a naturally-derived crosslinker agent, was also investigated in the control of the mechanical properties of the CHT/CS membranes. The water uptake ability can be tailored by changing the crosslinker concentration that also controls the Young’s modulus and ultimate tensile strength. The maximum extension tends to decrease upon crosslinking with the highest genipin concentration, compromising the elastic properties of CHT/CS membranes: nevertheless, when using a lower genipin concentration, the ultimate tensile stress is similar to the non-crosslinked one, but exhibits a significantly higher modulus. Moreover, the crosslinked multilayer membranes exhibited shape memory properties, through a simple hydration action. The in vitro biological assays showed better L929 cell adhesion and proliferation when using the crosslinked membranes and confirmed the non-cytotoxicity of the developed CHT/CS membranes. Within this research work, we were able to construct freestanding biomimetic multilayer structures with tailored swelling, mechanical and biological properties that could find applicability in a variety of biomedical applications.

Smart and Covalently Cross-Linked: Hybrid Shape Memory Materials Reinforced through Covalent Bonds by Zirconium Oxoclusters.

The first examples of organic-inorganic hybrid materials reinforced by transition-metal oxoclusters that exhibit shape memory properties, based on the covalent incorporation of zirconium-based inorganic building blocks, are reported. Methacrylate-functionalized zirconium oxoclusters Zr4 O2 (OMc)12 and [Zr6 O4 (OH)4 (OOCCH2 CH3 )3 {OOCC(CH3 )=CH2 }9 ]2 , with the covalent incorporation in a butyl acrylate (BA)/polycaprolactone dimethacrylate (PCLDMA) copolymer and the noncovalent incorporation of [Zr6 O4 (OH)4 (OOCCH2 CH3 )12 ]2 are focused upon herein. Shape recovery and fixity rates are studied to observe if the shape memory properties are preserved upon going from a simple copolymer to noncovalent or covalent-based hybrids. These rates display values higher than 90 %, which provides evidence that the oxocluster does not hinder the shape memory properties in the hybrid materials. The introduction of an inorganic phase and the progressively more stable interactions between organic and inorganic parts lead to an enhancement of the thermomechanical properties. The materials are characterized through FTIR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and swelling tests. Dynamic-mechanical analyses are used to investigate whether the hybrid materials display thermally activated shape memory properties. The stability of the hybrid materials are evaluated by a combined spectroscopic approach based on FTIR, solid-state NMR, and X-ray absorption spectroscopy.

Light Responsive Microstructured Surfaces of Liquid Crystalline Network with Shape Memory and Tunable Wetting Behaviors.

Using adaptive soft materials to fabricate microstructured surfaces renders them with tunable topographic feature and thus controllable physical properties. Here, light responsive microstructured surfaces are reported with shape memory and tunable wetting behaviors; the surfaces are covered with micropillar arrays and constructed by lightly crosslinked azo-containing liquid crystalline network (LCN). UV light irradiation induces 25% contraction in length of the micropillars along their long axes and, as a consequence, the variations of topographic feature and wetting behavior of the surfaces. In addition, the LCNs exhibit shape memory properties, which can freeze the temporary topographic feature of microstructured surfaces (formed under UV irradiation and relatively high temperature) and enable application of their functionalities at mild conditions. This light responsiveness makes it feasible to remotely and precisely tune the local regions of microstructured surfaces, which should broaden the applications of adaptive surfaces in regulating the wetting, optical, and adhesion properties in selected regions.

Magnetically Multilayer Polysaccharide Membranes for Biomedical Applications.

Self-standing nanocomposite films based on biopolymers and functional nanostructures have been widely used due to their potential applications as active elements in biomedical devices. The coupling between chitosan (CHI) and alginate (ALG) multilayered films and magnetic nanoparticles (MNPs) allowed to fabricate magnetic responsive freestanding membranes with a high structural control along the thickness, using the layer-by-layer (LbL) methodology. The mechanical characterization evidenced a trend for an increase of both Young modulus, and ultimate tensile strength with the inclusion of MNPs, or by cross-linking with genipin. Additionally, the multilayered membranes exhibited shape memory properties triggered by hydration. The in vitro biological performance studies showed that cells were more viable and adherent with higher proliferation rates when MNPs were included in the membranes. Our results suggested the potential of the developed magneto-active freestanding membranes for biomedical applications, such as in tissue engineering and biomedical applications.

Role of alloying additions on the properties of Cu–Al–Mn shape memory alloys

The effect of alloying seven different elements [Zn, Si, Fe, Ni, Mg, Cr and Ti] on the microstructure, hardness, phase precipitation and transformation temperature in a Cu–12.5Al–5Mn alloy with a view to possible improvements as a result of these additions is the focus of the reported study. The base alloy has been chosen keeping in mind its ability to exhibit shape memory properties and improved ductility over other Cu-based SMAs. The objective was to ascertain changes or improvements attained due to the individual tertiary additions.The samples were prepared through liquid metallurgy route using pure copper, aluminum, manganese and the respective quaternary alloying elements in right quantities to weigh 1000g of the alloy in total and were melted together. Samples from the cast alloys were subject to homogenisation treatment at 200°C for 2h in a muffle furnace and furnace cooled. Samples from the homogenised alloys were heated and held for 2h at 920°C followed by ice quenching to obtain the desired martensitic structure for shape memory behaviour. The alloys in the cast, homogenised and quenched conditions were metallographically polished to observe the martensitic phase formation mainly in quenched samples which is a pre requisite for exhibiting shape memory properties in these alloys. X-ray Diffraction studies were carried out on the cast and quenched samples using Cu Kα target; and the phases identified indicate martensitic phase precipitation; however in some cases the precipitation is incomplete. Differential Scanning Calorimetric [DSC] studies were carried out on quenched samples from room temperature to 600°C maintaining a constant rate of 10°C/min. Results indicate clear transformation peaks in all the samples which are significantly high than conventionally reported except with the addition of Mg in which case no distinct peaks have been recorded. The range of martensite retention is the maximum in ternary Cu–Al–Mn alloys; addition of quaternary elements decreases this range significantly. Presence of Ni delays austenite formation and completion [As and Af] significantly as compared to the ternary alloys; whereas with other additions the As and Af temperatures are brought forward. This means that whereas the alloys without quaternary additions would be better suited for its shape memory properties, ternary alloys would be better suited for higher transition temperatures.The role of different alloying additions has been highlighted in the findings. Variations in properties have been attained due to different additions and improvements attained in terms of higher transformation temperatures and martensite formation due to the alloying additions.

Shape-memory behavior of bisphenol A-type cyanate ester/carboxyl-terminated liquid nitrile rubber coreacted system

Bisphenol A-type cyanate ester (BACE) was modified by carboxyl terminated liquid nitrile rubber (CTBN) exhibiting shape memory properties. Shape memory BACE/CTBN copolymer was a new kind of smart materials, which has huge development potential and promising future. A series of shape memory BACE/CTBN copolymers were prepared by varying mass ratio of BACE and CTBN. The mechanical performance, thermal properties, and shape memory effect of the BACE/CTBN copolymers were systematically investigated. It was found that the BACE/CTBN copolymers have excellent shape-memory behavior, and the glass transition temperature (T g ) of the copolymers can be adjusted with the content of CTBN. The shape recovery speed increases with the increment of the content of CTBN and the shape fixed ratio and shape recovery ratio are almost 100 %.

Synthesis and characterization of shape memory epoxy-anhydride system

Thermoset polymers exhibiting shape memory properties were derived on reacting digycidyl ether of bisphenol A (DGEBA) with pyromellitic dianhydride (PMDA) in presence of a shape memory polymer precursor i.e. carboxyl telechelic poly(tetramethylene oxide) (PTAC) that was synthesized. Cure characteristics of the blends were investigated by differential scanning calorimetry and FTIR. Blends with varying proportions of DGEBA/PTAC/PMDA were studied for their flexural, dynamic mechanical and shape memory properties. The flexural strength and modulus decreased with increase in concentration of PTAC. The storage modulus and the transition temperatures (Ttrans) of the systems also showed a similar trend. These polymers showed good shape memory properties. PTAC increased the modulus ratio (Eg/Er) which in turn increased the extent of shape recovery with a concomitant diminution in the shape recovery time. An increase in temperature results in faster recovery with an increase in the extent of shape recovery. The epoxy-anhydride system possesses adequate thermal, mechanical and shape memory characteristics for possible use in smart actuator systems.

Shape memory segmented polyurethanes: dependence of behavior on nanocellulose addition and testing conditions

AbstractThe response of synthesized shape memory segmented polyurethanes (PUs) was affected by the addition of cellulose nanocrystals, as well as by the various conditions selected to carry out thermomechanical cyclic tests. The PUs were synthesized from an α‐hydro‐ω‐hydroxy‐poly(ethylene oxide), tolylene‐2,4‐diisocyanate and 1,4‐butanediol as chain extender. Nanocomposites were prepared by mixing a suspension of cellulose nanocrystals in N,N‐dimethylformamide with the thermoplastic PU dissolved in the same organic solvent. The thermal properties of the neat PU and resulting composites were examined using differential scanning calorimetry. It was found that cellulose addition increases the PU soft segment melting and crystallization temperatures and the degree of crystallinity of this phase. Shape memory behavior was studied using cyclic thermal tensile tests. Both neat PU and composites exhibit shape memory properties, with fixity and recovery values that depend on heating temperature, imposed deformation, deformation rate and nanofiller addition. Copyright © 2011 Society of Chemical Industry