Water-responsive Shape Memory Research Articles

Environmental-friendly, flexible silk fibroin-based film as dual-responsive shape memory material

Bio-based shape memory materials have attracted wide attention due to their biocompatibility, degradability and safety. However, designing and manufacturing wearable bio-based shape memory films with excellent flexibility and toughness is still a challenge. In this work, silk fibroin substrate with a β-sheet structure was combined with a tri-block shape memory copolymer to prepare a transparent composited shape memory film. The silk fibroin-based film showed a dual-responsive shape memory function, which can respond to both temperature and water stimuli. This film has a sensitive water-responsive shape memory, which starts deforming after exposure to water for 3 s and fully recovers in 30 s. In addition, the composite film shows highly stretchable (>300 %) and could maintain its high tensile properties after 5 cycles of regeneration. The films also exhibited rapid degradation ability. This study provides new insights for the design of dual-responsive shape memory materials by combining biocompatible matrix and multi-block SMP to simultaneously enhance the mechanical properties, which can be used for intelligent packaging, medical supplies, soft actuators and wearable devices.

Shape memory surface adhesion control based on PU-CNC/PS electrospun composite films

Wettability is a fundamental property of solid surfaces. The adhesion of liquids to solid surfaces, especially the intelligent control of surface adhesion, plays an important role in the wettability field, showing broad prospects in self-cleaning, anti-icing, oil–water separation and chemical reactions, etc. In this work, a new shape memory composite film was prepared by electrospinning, consisting of water-responsive shape memory substrate of polyurethane-cellulose nanocrystalline composite fibers and a superhydrophobic polystyrene spindle-fiber surface. Benefiting from the water-responsive shape memory performance of polyurethane-cellulose nanocrystalline substrate, the polystyrene surface spindle-fiber microstructures show sparse-dense switching during the stretching-recovery shape memory cycle, giving rise to smart control of surface adhesive behavior in superhydrophobic high-low adhesion. Given the flexibility and versatility, we demonstrate applications of the shape memory composite film in lossless droplet transfer, selective manipulation of multiple droplets, and smart detection. The composite film would provide potential applications in intelligent platforms, microliquid systems, and wearable fields, etc.

Antimicrobial PVA Hydrogels with Tunable Mechanical Properties and Antimicrobial Release Profiles.

Hydrogels are broadly employed in wound healing applications due to their high water content and tissue-mimicking mechanical properties. Healing is hindered by infection in many types of wound, including Crohn's fistulas, tunneling wounds that form between different portions of the digestive system in Crohn's disease patients. Owing to the rise of drug-resistant infections, alternate approaches are required to treat wound infections beyond traditional antibiotics. To address this clinical need, we designed a water-responsive shape memory polymer (SMP) hydrogel, with natural antimicrobials in the form of phenolic acids (PAs), for potential use in wound filling and healing. The shape memory properties could allow for implantation in a low-profile shape, followed by expansion and would filling, while the PAs provide localized delivery of antimicrobials. Here, we developed a urethane-crosslinked poly(vinyl alcohol) hydrogel with cinnamic (CA), p-coumaric (PCA), and caffeic (Ca-A) acid chemically or physically incorporated at varied concentrations. We examined the effects of incorporated PAs on antimicrobial, mechanical, and shape memory properties, and on cell viability. Materials with physically incorporated PAs showed improved antibacterial properties with lower biofilm formation on hydrogel surfaces. Both modulus and elongation at break could be increased simultaneously in hydrogels after both forms of PA incorporation. Cellular response in terms of initial viability and growth over time varied based on PA structure and concentration. Shape memory properties were not negatively affected by PA incorporation. These PA-containing hydrogels with antimicrobial properties could provide a new option for wound filling, infection control, and healing. Furthermore, PA content and structure provide novel tools for tuning material properties independently of network chemistry, which could be harnessed in a range of materials systems and biomedical applications.

Dual Stimuli-Responsive Orthodontic Aligners: An In Vitro Study.

Aligner therapy for orthodontic tooth movement is gaining importance in orthodontics. The aim of this contribution is to introduce a thermo- and water-responsive shape memory polymer (SMP), which could lay the foundation for a new type of aligner therapy. The thermal, thermo-mechanical, and shape memory properties of thermoplastic polyurethane were studied by means of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and various practical experiments. The glass transition temperature of the SMP relevant for later switching was determined to be 50 °C in the DSC, while the tan δ peak was detected at 60 °C in the DMA. A biological evaluation was carried out using mouse fibroblast cells, which showed that the SMP is not cytotoxic in vitro. On a digitally designed and additively manufactured dental model, four aligners were fabricated from an injection-molded foil using a thermoforming process. The aligners were then heated and placed on a second denture model which had a malocclusion. After cooling, the aligners were in a programmed shape. The movement of a loose, artificial tooth and thus the correction of the malocclusion could be realized by thermal triggering the shape memory effect, at which the aligner corrected a displacement with an arc length of approximately 3.5 mm. The developed maximum force was separately determined to be about 1 N. Moreover, shape recovery of another aligner was realized within 20 h in 37 °C water. In perspective, the present approach can help to reduce the number of orthodontic aligners in therapy and thus avoid excessive material waste.

Dual stimulus response mechanical properties tunable biodegradable and biocompatible PLCL/PPDO based shape memory composites

The aliphatic polyester poly(L-lactide-co-ε-caprolactone)(PLCL) was synthesized successfully in this research. And a temperature-responsive and water-responsive shape memory composite was prepared by the physical blend of PLCL and poly (p-dioxanone) (PPDO) for the first time. The thermal properties, crystallinity, microstructure, mechanical properties, shape memory behavior, and degradation properties of PLCL/PPDO composites were comprehensively investigated. The results showed that the mechanical properties of the composite could be adjusted with the addition ratio of PPDO. All materials possessed excellent shape memory fixation rates: close to 100%. PPDO improved the shape memory recovery ratio of PLCL without affecting the shape memory fixation ratio of PLCL. PL/PP82 showed the best shape memory recovery ratio at 37°C with 91.34 ± 3.56%. A combination of in situ wide-angle X-ray scattering and tensile modes was used to elucidate the unique mechanism of shape memory in the air for this range of composites. PL/PP82 also exhibited excellent thermal and water-induced shape memory effects in water at 37 °C, with a rapid return to the original state of the composite within 19 s. The introduction of PPDO improved the degradation rate of the composite and regulated the rate of degradation. Additionally, the addition of PPDO significantly enhanced the hydrophilicity of the composites, which promoted proliferative adhesion of osteoblasts to the composite surface. Thus, the temperature and water responsive shape memory composites had great potential in bone tissue engineering applications.

Water-induced shape memory cellulose nanofiber-based nanocomposite membrane containing lignin with quick water response and excellent wet mechanical property

Cellulose-based water-responsive shape memory materials have received widespread attention due to their wide range of sources, high response rate, and environmental friendliness. However, fast responsive shape memory polymers (SMPs) tend to lose wet strength due to excessive hydration. Thus, it greatly limits the application range of cellulose-based water-responsive shape memory materials. To address this issue, in this work, a cellulose nanofiber (CNF) nanocomposite membrane with high water-induced shape memory properties was successfully prepared containing polyvinyl alcohol (PVA) and lignin (LIG). Citric acid (CA) was used as the cross-linking agents. Changes in the content ratio of CNF to PVA and the amount of LIG added will change the crosslinked network structure of the CA/LIG/PVA/CNF membrane, leading to changes in the microstructure, water responsiveness and mechanical properties of the membrane. With the addition of LIG, the fracture surface of the microstructure will orient along longitudinal direction and form a densely packed layered structure. The increase content ratio of CNF to PVA can improve the compatibility of each component. The water-induced shape memory recovery rate of the nanocomposite can reach 100% within 4 s. In the dry state, the maximum tensile strength of the film can reach 138.0 MPa, and the maximum tensile modulus of the film can reach 9.0 GPa. After wet swelling, the highest tensile strength and tensile modulus are up to 60 MPa and 0.7 GPa, respectively. The CNF nanocomposite film has excellent performance in blocking ultraviolet and the transmittance value of the membrane is below 8% in the ultraviolet region of 200–400 nm. Hence, the resultant CA/LIG/PVA/CNF membrane will have potential applications in smart science and the provide a framework for developing a cellulose-based shape memory polymer.

Water-responsive shape memory thermoplastic polyurethane scaffolds triggered at body temperature for bone defect repair

The water-responsive shape memory mechanism model of a TPU specimen was proposed, in which the reversible hydrogen bonding between the water molecules and hard segments formed after wetting and disappeared after drying.

Temperature-sensitive water-responsive shape memory effect in plant leaves

Temperature-sensitive water-responsive shape memory effect in plant leaves

Switchable shape memory wetting surface based on synergistic regulation of surface chemistry and microstructure

Smart control of surface wettability can be obtained by adjusting surface chemistry or regulating surface microstructure, however, coordinated regulation of the two factors on the same surface is still limited. Here, we report a new shape memory composited film consist of a hierarchical pillared polyurethane surface and shape memory polyurethane-cellulose substrate. Reversible switching among multiple wetting states between superhydrophobicity and superhydrophilicity can be realized by synergistic regulation of surface microstructure based on stretching-recovery shape memory effect and surface chemical composition based on O2 plasma-heating. The mild and excellent water-responsive shape memory ability of substrate enables surface microstructure and corresponding wetting to fix at desirable states without keeping continuous external force or stimuli, which is superior to elastomer substrate, responsive molecule modification, or traditional temperature/light triggered shape memory materials. Given the flexibility and versatility, we show its applications in smart platform for creating gradient wettability and patterned micro-reaction.

Rapid water-responsive shape memory films for smart resistive bending sensors

Development of multi-functional water-sensitive shape memory material is crucial for applications in smart textiles, artificial intelligence, and biomedical areas. However, it remains a great challenge to achieve good biocompatibility, rapid water response, and robust mechanical strength in one single material. In this respect, we report a green approach to produce a series of multi-functional water-sensitive memory films (named MCP films) from sisal cellulose microcrystals (MSF-g-COOH), peach gum polysaccharide (PGP), citric acid (CA), and graphene nanosheets (GN). After crosslinking with CA, MCP films exhibit excellent water-induced shape memory and rapid pH stimulus response. More importantly, MCP films can effectively amplify different external motion stimuli by converting them into independent electrical signals to achieve accurate and continuous perception of bending. A high-performance resistive bending sensor was further fabricated from the MCP films to mimic natural human skin. The resistive bending sensor exhibited excellent water-responsive shape memory, self-adhesion, and bending sensitivity, which can be used in electronic skin, human-machine interactions, intelligent wearable devices, personalized health monitoring and other applications. Our work successfully demonstrates the application of the water-sensitive shape memory films in electronic skin and health-monitoring components, and fills the gap between material design and high-performance devices.

Water-responsive shape memory PLLA via incorporating PCL-(PMVS-s-PAA)-PCL-PTMG-PCL-(PMVS-s-PAA)-PCL

Poly(L-lactide) (PLLA) was one of the most well-known biodegradable polyesters. Although its thermo-responsive shape memory (SM) function has been studied by proper program, high transformation temperature is not suitable in some biomedical applications. Water-responsive SM polymer is an alternative choice and exhibits great potential because it is harmless to the cells and tissues of organisms. In the work, a novel PCL-(PMVS-s-PAA)-PCL-PTMG-PCL-(PMVS-s-PAA)-PCL copolymer was devised as an additive to endow PLLA with water-responsive SM capability. The incorporated PLLA was characterized by cross-section, water contact angle, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Inserted PTMG segment and assisted ambient temperature were contributed to its SM behaviors. The shape fixation ratio and shape recovery ratio were 92.0% and 94.2%, respectively. The schematic diagram between internal microstructures and macroscopic properties was proposed. At the same time, the incorporated PLLA showed excellent toughness. So the obtained SM material would be promising for medical and biomimetic fields.

Hybrid Nanocomposites of Cellulose/Carbon-Nanotubes/Polyurethane with Rapidly Water Sensitive Shape Memory Effect and Strain Sensing Performance.

In this work, a fast water-responsive shape memory hybrid polymer based on thermoplastic polyurethane (TPU) was prepared by crosslinking with hydroxyethyl cotton cellulose nanofibers (CNF-C) and multi-walled carbon nanotubes (CNTs). The effect of CNTs content on the electrical conductivity of TPU/CNF-C/CNTs nanocomposite was investigated for the feasibility of being a strain sensor. In order to know its durability, the mechanical and water-responsive shape memory effects were studied comprehensively. The results indicated good mechanical properties and sensing performance for the TPU matrix fully crosslinked with CNF-C and CNTs. The water-induced shape fixity ratio (Rf) and shape recovery ratio (Rr) were 49.65% and 76.64%, respectively, indicating that the deformed composite was able to recover its original shape under a stimulus. The TPU/CNF-C/CNTs samples under their fixed and recovered shapes were tested to investigate their sensing properties, such as periodicity, frequency, and repeatability of the sensor spline under different loadings. Results indicated that the hybrid composite can sense large strains accurately for more than 103 times and water-induced shape recovery can to some extent maintain the sensing accuracy after material fatigue. With such good properties, we envisage that this kind of composite may play a significant role in developing new generations of water-responsive sensors or actuators.

Achieving coalesced breathability, mechanical and shape memory properties of collagen fibrous matrix through complexing with chromium (III)

Protein materials evolved in nature for millions of years can display critical structural and functional properties which is difficult for synthetic polymers to surpass. Hence, the combination of multiple components or hierarchies from natural source through a facile method may stand out as a forerunner to materials design and application. Inspired from metalloprotein, this study reported an organic-metal biosystem based on chromium (III) complexed collagen fibrous matrix (Cr-CFM). The obtained Cr-CFM retains inherent conformation of collagen and its fiber morphology in the skin. Compared with pristine CFM, Cr-CFM showed enhanced waterproofness and breathability. Due to coexistence of hydrogen bonds and newly introduced chromium (III) complexing linkages, Cr-CFM exhibited water-adaptive mechanical property. In this organic-metal biosystem, hydrogen bonds show reversible cleavage-reformation under water interference while chromium (III) complexing linkages remains stable. Such combination of “switch” and “netpoint” facilitated water responsive shape memory ability of Cr-CFM with shape fixation and recovery reaching over 80%. The reveal of relationship between structure and coalesced properties of Cr-CFM herein is believed to promote progress of smart protein materials and give inspirations to synthetic polymers.

Two-dimensional membrane and three-dimensional bulk aerogel materials via top-down wood nanotechnology for multibehavioral and reusable oil/water separation

Traditional oil/water separation materials can be divided into two types on the basis of their separation behavior: filtration materials (e.g., meshes, textiles, membranes, etc.) and absorption materials (e.g., sponges, foams, and aerogels). Both types of materials have advantages and disadvantages. Combining the filtration and absorption functions into one and the same material for oil/water separation applications presents a challenge. Prompted by the highly oriented porous structures and anisotropic architectures of wood and its hygro-responsive characteristic, two-dimensional (2D) membrane and three-dimensional (3D) bulk aerogel materials with water-responsive shape memory function, anisotropy, robustness, and superhydrophobicity are prepared using top-down wood nanotechnology for multibehavioral (absorption and filtration) and reusable oil/water separation. Wood aerogel is obtained by partially removing hemicellulose and lignin. Further, it is superhydrophobically treated using a polydimethylsiloxane (PDMS)/curing agent system. As-prepared wood aerogel/PDMS bulk materials possess high oil absorption capacity (about 20 g/g) and can be reused because of their fast water-responsive shape memory function. The prepared wood aerogel/PDMS membrane materials can efficiently separate oil/water mixtures with high separation efficiency (99.5%) and flux (around 2.25 × 104 L/m2·h) by only the driving force of gravity. Top-down wood nanotechnology is low-cost, facile, scalable, green, and efficient, exhibiting potential for application in multibehavioral oil/water separation and ability to handle industrial oily wastewater and oil spillage accidents.

A Biocompatible, Biodegradable, and Functionalizable Copolyester and Its Application in Water-Responsive Shape Memory Scaffold

Shape memory polymers are of great interest for biomedical applications. However, most stimuli used to trigger shape memory processes, including heat, light, electricity, magnetism, and pH are inconvenient and maybe harmful to the body. Here, we designed and fabricated a new shape memory porous scaffold using biocompatible and readily available water as the trigger. This scaffold was based on poly(fumaricacid-co-1,7-octadiene diepoxide-co-terephthalic acid) (PFOT) synthesized via epoxide ring-opening polymerization in one step. The PFOT scaffold promoted the adhesion, spreading, proliferation and function of cardiomyoblast H9C2 cells in a manner comparable to that for the poly(lactic-co-glycolic acid) scaffold. It exhibited an excellent water-responsive shape memory effect with a fixity and recovery ratio >97% and a shape-recovery process of several minutes, suitable for surgery. In addition, the PFOT scaffold presented good in vitro biodegradation. More importantly, PFOT contains extensive free hydroxyl ...

A skin inspired bio-smart composite with water responsive shape memory ability

A skin inspired bio-smart composite was prepared by a facile green “paper-making” method, and it exhibits excellent water responsive shape memory.

A biodegradable functional water-responsive shape memory polymer for biomedical applications.

Shape memory polymers (SMPs) have exhibited great potential in biomedical applications. However, the typical triggers of shape recovery such as heat, UV light, and electricity may be harmful to humans. Accordingly, water-responsive SMPs have become significant, especially for in vivo applications, due to the intrinsic biocompatibility and ready availability of water. However, the reported water-responsive SMPs are limited and relatively complicated. Here, we design a new water-responsive SMP, poly(butanetetrol fumarate) (PBF); the properties of PBF could be modulated by curing. The cured PBF scaffolds exhibited high shape recovery and fixity rates (>95%). PBF showed good biodegradability, and it could support the attachment, viability and alkaline phosphatase activity of osteoblasts. Furthermore, PBF could be readily functionalized via pendant hydroxyl groups, which was demonstrated by the immobilization and controlled release of bone morphogenetic protein 2. We expect that PBF will be useful for various biomedical applications including water-responsive scaffolds, sensors or actuators.

Biodegradable and water-responsive shape memory PHA-based polyurethane for tissue engineering

Abstract We describe the preparation, characterization and evaluation of a biodegradable water-triggered shape memory polyurethane for tissue engineering. A general strategy for fabricating a soft and hard segment self-deformed shape memory polyurethane (SMPU) is presented. Owing to easy processability like the use of solution casting and particulate leaching methods, these materials can be used for vascular stents and bone tissue engineering scaffolds. The unique characteristics of water-responsive SMPU enable shape recovery in the physiological environment and eliminate the temperature constraints for biomedical applications that require no external sample heating. In the field of tissue engineering, complicated defects in tissues have put forward a high demand for the construction of substitutes with diverse shapes. The outstanding properties of tough SMPU will enable the development of small-diameter vascular grafts and increase their application in bone tissue engineering for triggered shape morphing.

A Novel 2,6-Diaminopyridine-base Polymer with Thermo-/Water-responsive Shape Memory Effect

Abstract Shape memory polymers with multiple stimuli have obtained increasing attention. This study illustrates a strategy for synthesizing polymers with thermo-/water-responsive shape memory effect. The novel polymer with excellent nature was proved to synthesized correctly using 2,6-diaminopyridine (DAP), polyethylene glycol (PEG1000) and hexamethylene diisocyanate (HDI). The result shows that the thermal stability of polyurethane can be improved with increasing of the DAP, embed into molecular chain. Moreover, the polymer which possesses excellent thermo-responsive, can be deformed and restored when in contact with water. The finding in this contribution, strongly promote diversified applications of shape-memory polymers, especially in engineering fields.

Fabricating dual-responsive shape memory PVA-based composites via reactive melt-mixing by skillfully utilizing excellent flowability and crosslinking heat of polyethylene

Poly(vinyl alcohol) (PVA) based dual-stimuli responsive shape memory composites were fabricated via a feasible reactive melt mixing with certain content of polyethylene (PE) and crosslinker dicumyl peroxide (DCP). It is found that PE plays many important roles in this method. Firstly, the melting processability of PVA can be improved markedly by skillfully utilizing the excellent flowability and crosslinking heat of PE. Secondly, the PVA composites achieve excellent water/heat dual-induced shape memory property by utilizing PE as fixing domain and heat responsive switching domain and utilizing PVA as water responsive switching domain meanwhile. The fixing ratio is nearly 100% and recovery ratio can reach 90% for both water and heat responsive shape memory. This artful fabricating method achieved the aim of improving the melting processability of PVA and endowing the composites dual-responsive shape memory property simultaneously only by utilizing PE, which is interesting and promising for the development of PVA in the industry application. It shows considerable prospect for PVA composites and their industry application.