Development Of Shape Memory Polymers Research Articles

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

Shape memory polymers, based on their unique property that they can automatically revert to their original shape after deformation when subjected to external stimuli, have shown great application prospects and practical value in many fields such as aerospace, automotive and biomedical in recent years. In this study, poly(lactic acid) (PLA)/polycaprolactone (PCL) is used as a substrate, and a graft product, PLA-g-GMA, is prepared by grafting glycidyl methacrylate (GMA) onto PLA as a compatibilizer, and then polymer substrates are prepared by melt extrusion. Then, light-responsive shape memory composites are prepared by loading polypyrrole (PPy) nanoparticles with photothermal conversion functionality into the PLA/PCL substrate, and PPy-coated NdFeB (PPy@NdFeB) is used as the functional phase to prepare auto-responsive shape memory polymers that can be programmed automatically. Among them, the PLA/PCL/PPy composites show shape recovery rate (Rr) and shape fixation rate (Rf) of 81.11% and 98.87%, respectively, at a strain of 85.27% under the programming conditions of a deformation temperature of 65 °C and a stress of 2.14 MPa. The PLA/PCL/PPy@NdFeB composite material, in addition to excellent double and triple shape memory behavior, also has obvious magnetic properties, which can be used to carry out self-programmed temporary shapes. This research aims to solve the limitations of temperature-responsive shape memory polymers in a single stimulus response mode, broaden their application scope, further promote the development of shape memory polymers, and provide realistic guidance for the field of 4D printing.

Shape memory hydrogels with remodelable permanent shapes and programmable cold-induced shape recovery behavior.

Most shape memory polymers apply glass transition or crystallization of domains to fix temporary shapes and shape recovery is induced by heating, which hinders their application under heat-intolerant conditions. Moreover, the permanent shapes of polymers normally cannot be altered arbitrarily after fabrication. Herein, we present a novel shape memory hydrogel with a remodelable permanent shape and programmable cold-induced shape recovery behavior. Poly(acrylic acid) (PAA) hydrogel is prepared in the presence of diethylenetriamine (DETA) and subsequently treated with calcium acetate (Ca(Ac)2). The charge-assisted hydrogen bonding between PAA and DETA imparts the hydrogel with remodelability, while the heat-induced hydrophobic aggregation of polymer chains and acetate groups results in shape fixation by heating and shape recovery by cooling. Afterwards, programmable deformable devices are obtained by assembling hydrogel blocks with different concentrations of Ca(Ac)2. This design strategy promotes the development of shape memory polymers with diverse potential applications.

The effect of Pluronic P123 on shape memory of cross-linked polyurethane/poly(l-lactide) biocomposite

Polyurethane (PU) and poly(l-lactide) (PLLA) have attracted increasing attention in the development of shape memory polymers (SMPs) due to their good biocompatibility and degradability. Although Pluronic P123 can be used to tune polymeric surface hydrophilicity, its effect on SM performance is a mystery. In this study, a soluble cross-linked PU is synthesized as the switching phase and combined with PLLA and P123 to construct a hydrothermally responsive SM composite. The water contact angle of PU/PLLA/P123 decreases from 22.7° to 5.1° within 2 min. PU and P123 form the switching group, which enhances the SM behavior of the composite. The shape fixity (Rf) and shape recovery (Rr) of PU/PLLA/P123 are 94.4 % and 98 % in 55 °C water, respectively, and the shape recovery time is only 10 s. P123 plays the role of “turbine” in the SM process. PU/PLLA/P123 exhibits a balance between stiffness and elasticity, and good degradability. Furthermore, PU/PLLA/P123 is also biocompatible and beneficial to cell proliferation and growth. Therefore, it offers an alternative approach to developing hydrothermally responsive SM biocomposites based on P123, PU and PLLA for biomedical applications.

Polyurethanes Based on Polylactic Acid for 3D Printing and Shape-Memory Applications.

Polylactic acid (PLA) has received increased attention in the development of shape-memory polymers and biomedical materials owing to its excellent physical properties and good biocompatibility and biodegradability. However, the inherent brittleness and high shape-recovery temperature of this material limit its application in the human body. Herein, we fabricated a PLA-based thermoplastic polyurethane (PLA-TPU) prepared from modified PLA-diol, dicyclohexylmethane-4,4'-diisocyanate, and 1,4-butanediol to solve the limitations of pure PLA. The glass transition temperature (Tg) of the designed TPU can be tailored from 6 to 40.5 °C by adjusting the content of hard segments or molecular weight of soft segments. The shape of the designed TPU can be fixed at room temperature and recovered at temperatures above 37 °C. Moreover, the prepared PLA-TPUs exhibited recyclability, three-dimensional printing capability, non-cytotoxicity, blood compatibility, and biodegradability. The shape of PLA-TPU/nano-Fe3O4 composites can be recovered by exposure to near-infrared light. These results collectively indicate that PLA-TPUs and their composites may have potential applications as intelligent flexible medical scaffolds for surgical and medical implantation equipment.

4D printing of shape memory aliphatic copolyester via UV-assisted FDM strategy for medical protective devices

4D printing, as a booming additive manufacturing technology of smart material, provides a new opportunity for the development of shape memory polymers (SMPs). Meanwhile, the diversity of SMPs structure calls for flexible and well-adapted printing technology. Fused deposition modelling (FDM) is one of the most versatile and cost-effective methods owing to the simplicity of the technique and broad compatibility with a wide variety of materials, but it fails to deal with the fabrication of shape memory networks that possess excellent structural stability as well as shape memory effect (SME). Aiming to personalized or patient-adaptable treatment devices, in this work, we demonstrate a UV-assisted FDM 4D printing strategy to fabricate elbow protector models based on shape memory copolyester networks. First, the linear unsaturated copolyesters were synthesized, amongst, poly(lactic acid) was chosen as hard segment providing the material a good mechanical performance and printability, the poly(ε-caprolactone) with strong crystallizability was employed as switching segment, and a functional coupling agent contained double bonds was used to join the two segments and as the same time. This copolyester can be easily processed into filament, and the in-situ formation of photo-crosslinking network during the UV-assisted FDM printing not only enhances the bonding strength of each layer, but also may guarantee the obtained objects a good shape memory property. Three models with distinctly Chinese characteristics were printed to demonstrate excellent SME. Then, the elbow protectors both in personalized and patient-adaptable treatment strategies were developed, which indicates a great potential in robust applications.

4D printed shape memory polymers and their structures for biomedical applications

Shape memory polymers are smart materials that produce shape changes under external stimulus conditions. Four-dimensional (4D) printing is a comprehensive technology originate from deformable materials and three-dimensional (3D) printing technology. At present, 4D printed shape memory polymers and shape-changing structures have been applied in various fields, especially in the field of biomedical science. 4D printing technology has made a breakthrough of personalized customization in the traditional medical field, providing a new direction for the further development of the biomedical field. In this review, the recent research and development of shape memory polymer, 3D printing technology, 4D printed shape memory polymers and shape-changing structures in biomedical area are present. The examples and applications of 4D printed shape memory polymers and their structures in the area of biomedical are also introduced. Based on 4D printing, stimulated by different conditions, 3D printed objects can be fabricated into various biomedical applications such as cell scaffolds, vascular stents, bone scaffolds, tracheal stents and cardiac stents by different 3D printing techniques. Finally, the application prospects, existing technical restriction and future development directions of 4D printed shape memory polymers and their structures in the biomedical field are summarized.

Thermadapt Shape Memory Polymers with Predictable and Arbitrary Shape Shifting

AbstractThe development of shape memory polymers (SMPs) with a better linear relationship between the shape retention ratio (R ret) and the corresponding stress relaxation (R σ) can address scientific challenges, such that the arbitrary shape shifting can be realized and a desired and accurate strain can be obtained during the procedure of stress relaxation. This method is predictable, accurate, time‐saving, and can prevent the deterioration of materials. However, almost no attention is paid to the predictable and arbitrary shape‐shifting phenomenon. Here, a new phenomenon that the materials exhibit a relatively better linear relationship and the major factor behind the phenomenon—there is a better linear relationship with the decrease in the molecular weight between the cross‐linking points (M c)—are found. Such a one shape memory network with combined catalyst‐free, arbitrary shape shifting, and reprocessability without sacrificing the outstanding shape memory performance, is expected to have a significant and positive impact on the medical device industry, and provides a new strategy for the design of thermadapt SMPs.

Development of shape memory polymers micro/nanofiber membranes in biomedical applications

As a class of smart materials, shape memory polymers (SMPs) can remember the temporary shape and return to the original shape under the condition of the external stimuli. The shape memory micro/nanofibers prepared by electrospinning technology possess a three-dimensional structure which is similar to the natural extracellular matrix. Therefore, it shows great application prospect in the biomedical field, especially in tissue engineering. Moreover, shape memory micro/nanofiber membranes bring more and more opportunities for the rapid development of personalized and smart biomedical devices. This paper reviews of SMP micro/nanofiber membranes, including preparation, structure, morphology and driving methods. We also summarize the applications of SMP micro/nanofiber membranes in the brackets of bone tissue, bone tissue repair, nerve scaffolds and cell culture research. Furthermore, analysis other structures used in the biomedical field are discussed. Finally, we conclude the challenges and the perspectives of SMPs in the future.

Control of PLA Stereoisomers-Based Polyurethane Elastomers as Highly Efficient Shape Memory Materials

Poly(lactic acid) (PLA) has received increasing attention in the development of shape memory polymers (SMPs) due to its excellent physical properties and good biocompatibility. However, the intrinsically increased crystallinity of PLA at higher deformation ratios still remains a significant challenge, which remarkably restricts the chain mobility and reduces shape recovery efficiency. Being different from other types of biodegradable polymers, the diverse isomeric forms of PLA have provided great opportunities for modulation of PLA toward a favorable property by incorporating different PLA stereoisomers in one macromolecular architecture. In this paper, we report a completely amorphous PLA poly(ester urethane) elastomer that exhibits excellent shape fixity (>99%) and shape recovery (>99%) in a time frame of seconds. By means of adjusting the stereoisomeric ratios and control over architecture, the resultant poly(PLLA/PDLLA urethane)s (PLDU) elastomers show a single glass transition temperature (Tg), as th...

Micro-vascular shape-memory polymer actuators with complex geometries obtained by laser stereolithography

In our work we present the complete development process of geometrically complex micro-vascular shape-memory polymer actuators. The complex geometries and three-dimensional networks are designed by means of computer aided design resources. Manufacture is accomplished, in a single step, by means of laser stereolithography, directly from the computer-aided design files with the three dimensional geometries of the different actuators under development. To our knowledge, laser stereolithography is applied here for the first time to the development of shape memory polymer devices with complex geometries and inner micro-vasculatures for their activation using a thermal fluid. Final testing of the developed actuators helps to validate the approach and to put forward some present challenges.

Shape memory effect on the formation of oxazoline and triazine rings of BCC/DGEBA copolymer

The development of shape memory polymer by the copolymerization of 1,3-bis(4-cyanatophenyl) cyclohexane cyanate ester and DGEBA through the formation of oxazoline and triazine ring without using any external flexibilizer/plasticizer.

Electroactive shape memory polymer based on optimized multi-walled carbon nanotubes/polyvinyl alcohol nanocomposites

The development of shape memory polymers (SMPs) has gained remarkable attention due to their wide range of applications, from biomedical to electromechanical. In this work, we have developed and optimized an electroactive SMP based on polyvinyl alcohol/multi-walled carbon nanotubes (PVA/MWNTs) composites. When a constant voltage of 60V was applied to the optimized sample, the polymer shape could be recovered to the original form within 35s. Different weight fractions of MWNT/PVA composites were prepared by using a simple solution blending and transitional solution casting method, and their microstructures, electrical conductivities, thermal conductivities, and electroactive shape memory properties were investigated. According to our systematic analysis, the enhanced performance can be attributed to the reinforcement of MWNTs that led to the improved electrical and thermal conductivities of the PVA matrix.

Shape memory epoxy: Composition, structure, properties and shape memory performances

Due to the intrinsic properties of polymers, medical applications have been the primary targets for the development of shape memory polymers (SMPs) exhibiting softness at body temperature, biocompatibility, high deformability, good shape recovery (Rr) and good shape fixity (Rf). However, there is an increasing need for developing smart materials that would meet the drastically different requirements imposed by applications where, instead, high strength well above room temperature, durability, stability, and high thermo-mechanical endurance are necessary. Here, we present results obtained on a series of shape memory (SM) epoxies that appear promising base materials for such applications. The influence of molecular and structural design on their physical and SM properties were studied. The impact of various SM programming conditions (i.e., deformation load, recovery heating rate, number of cycles, and isothermal holding times in the hot and cold deformed shapes) was also investigated. The instantaneous SM behavior was found similar for all the networks with Rf and Rr values nearing 100% above 6 to 7% strain. The SM performances strongly depended on the strain-dependent thermal expansion/contraction of the materials during thermo-mechanical cycling. Networks with lower crosslink density, higher chain flexibility and/or mobility showed reduced SM performances, further diminished by more stringent thermo-mechanical cycling conditions.

Shape‐Memory Polymer in Response to Solution

Significant advances have recently been made in the development of shape-memory polymers (SMP) that are able to undergo solution-induced shape changes. The main challenge in the development of such polymer systems is the conversion of solution-induced effects at the molecular level to macroscopic movement of working pieces. This paper presents a systematic study on the effects of solution on the glass transition temperature (Tg). In addition, it provides a new approach that the SMP can be induced by applying non-energy stimulus.