Shape Memory Ability Research Articles

In vitro degradation behavior of shape memory PLLA-TMC random copolymers

Poly (lactic acid) (PLA) and poly (trimethylene carbonate) (PTMC) have been in-depth investigated in tissue engineering due to its excellent biocompatibility and controllable biodegradability. However, the acid metabolites of PLA degradation can accelerate the degradation process, resulting in tissue inflammation and postoperative allergy. Here three poly (L-lactide-co-trimethylene carbonate) (PLLA-TMC) random copolymers with L-lactide / 1.3-trimethylene carbonate ratios of 60:40, 70:30, 80:20 (PLTMC64, PLTMC73, PLTMC82 respectively) were synthesized to control the acid degradation and improve the compression resilience. The results showed that LA units on copolymers could improve water uptake and tension strength, reduce weight loss during the degradation (PLTMC82 for 6.53% after 16 weeks in enzymolysis). The crystallization, thermal properties and the surface and section morphology of copolymers were measured in detail for up to 16 weeks. Cell proliferation assay verified that PLLA-TMC copolymers presented excellent biocompatibility. The shape recovered rate of PLTMC73 was the most suitable for surgeons to complete complex implant operation, and 3D bioprinting bone repair scaffolds and 3D structured vascular scaffolds of PLTMC73 both possessed desired shape memory effect. Therefore, PLTMC with appropriate degradation rate and mechanical properties, intrinsically biocompatibility, and excellent shape memory ability, could provide a promising alternative in the field of cardiovascular and bone tissue repair engineering.

Wood-Derived Functional Polymeric Materials.

In recent years, tremendous efforts have been dedicated to developing wood-derived functional polymeric materials due to their distinctive properties, including environmental friendliness, renewability, and biodegradability. Thus, the uniqueness of the main components in wood (cellulose and lignin) has attracted enormous interest for both fundamental research and practical applications. Herein, the emerging field of wood-derived functional polymeric materials fabricated by means of macromolecular engineering is reviewed, covering the basic structures and properties of the main components, the design principle to utilize these main components, and the resulting wood-derived functional polymeric materials in terms of elastomers, hydrogels, aerogels, and nanoparticles. In detail, the natural features of wood components and their significant roles in the fabrication of materials are emphasized. Furthermore, the utilization of controlled/living polymerization, click chemistry, dynamic bonds chemistry, etc., for the modification is specifically discussed from the perspective of molecular design, together with their sequential assembly into different morphologies. The functionalities of wood-derived polymeric materials are mainly focused on self-healing and shape-memory abilities, adsorption, conduction, etc. Finally, the main challenges of wood-derived functional polymeric materials fabricated by macromolecular engineering are presented, as well as the potential solutions or directions to develop green and scalable wood-derived functional polymeric materials.

Shape memory materials promoting cell adhesion and tissue invasion towards the applications requiring minimally invasive implantation

Minimally invasive implantation of porous implants with large volume for in vivo filling proposes high requirements for material preparation. Porous scaffolds based on shape memory polymer (SMP) possess great potential for being delivered as the compact form via minimally invasive surgery. Here, poly (ε-caprolactone)-dienes (PCL-dienes) and crylic acid (AA) were polymerized and cross-linked to fabricate SMP scaffolds, the porous structure of which was created through particle leaching method. Three scaffolds, PAA-PCL20, PAA-PCL50 and PAA-PCL80 were fabricated with different content of PCL-dienes, possessing similar pore size (350 μm) and porosity (85%). PAA-PCL50 scaffold had a Tm of 38 °C, exhibiting shape fixing ability at room temperature and shape recovery ability at body temperature. All scaffolds showed limited interaction with cells. The cell adhesion rate of PAA-PCL50 scaffold was 55%, the highest among the three scaffolds. To promote cellular adhesion, PAA-PCL50 scaffold was mineralized via in situ precipitation, exhibiting CaP particles on the inner surfaces. The mineralized scaffold still exhibited well-performed deformation and shape memory ability, with higher cell adhesion rate (86%) and proliferation rate. In vivo implantation result indicated that the mineralized PAA-PCL50 scaffold better supported tissue invasion, holding a great promise to improve neo-tissue formation.

Preparation of high performance bio-based benzoxazine resin through a green solvent-free strategy for shape memory application

Preparing high performance shape memory bio-based benzoxazine resin through a green solvent-free strategy is an interesting issue with great challenge. Herein, a green solvent-free strategy is setup to synthesize bio-based benzoxazine monomer (VFA-atpe) from amine-terminated polyether and bio-based benzoxazine monomer containing aldehyde group; moreover, cured bio-based benzoxazine resin coded as poly(VFA-atpe) was prepared, of which the integrated performances were studied. Results show that poly(VFA-atpe) not only has high glass transition temperature (280 °C), but also exhibits ultra-high storage modulus (4.2 GPa) and tensile strength (90.4 ± 3.2 MPa), which are much higher than those of all bio-based benzoxazine resins reported so far. In addition, poly(VFA-atpe) shows good shape memory property, its shape recovery efficiency reaches 98%, and thus becomes the first bio-based benzoxazine resin with shape memory ability. These unique integrated performances of poly(VFA-atpe) are attributed to its special structure that simultaneously owns rigid segments and tough polyether.

Synthesis and characterization of mechanical-controllable polyurethane derived from tetramethybiphenyl epoxy acrylate

In this paper, a novel polyurethane copolymer (PU) derived from hexamethylene diisocyanate (HDI), polycaprolactone (PCL) and tetramethyl biphenyl epoxy acrylate (TMBPEA) was synthesized, characterized, and designed to have controllable mechanical properties and shape memory ability. The multifunctional PU contains cystallizable PCL segments, cross-linkable CC bonds in TMBPEA and urethane moieties. Both the PCL crystalline phase and photo-crosslinking of CC bonds play an important role in determining the mechanical properties of PU. Therefore, by adjusting the degree of crystallinity and the degree of crosslinking, the mechanical properties of PU could be easily controlled and varied. Before photo-crosslinking, the crystallinity of PU increases from 33.01% to 78.97%, as the content of PCL in PUs increases. However, after photo-crosslinking, the degree of crystallinity was significantly reduced to 11.09% as the UV irradiation time increased. In this way, the mechanical properties of PUs could be readily controlled by adjusting the ratio of PCL in the PUs and varying the UV irradiation time. As the ratio of PCL in PUs increases, the tensile strength and Young’s modulus of PUs increases from 9.04 ± 1.26 MPa to 12.98 ± 0.33 MPa and 89.79 ± 5.74 MPa to 224.88 ± 5.22 MPa, respectively. Meanwhile, the elongation at break increases from 499.09 ± 88.38% to 776.51 ± 67.39%. After crosslinking, the Young’s modulus of UV-cured PUs decreased from 224.88 ± 5.22 MPa to 18.74 ± 1.30 MPa as the UV irradiation time increased. Moreover, the elongation at break of UV-cured PUs was also dramatically reduced to around 60 MPa after photo-crosslinking compared to pristine PUs. Furthermore, shape memory tests indicated that uncrosslinking PUs samples have shape memory ability.

Star-Shaped Crosslinker for Multifunctional Shape Memory Polyurethane.

Star-shaped cyclophosphazene (ACP) was employed as covalent crosslinker to form a rigid segment in polyurethanes network, to enhance the mechanical performance and to add extra flame retardant property. The effects of different ACP contents on the shape memory ability and fire resistance performance of polyurethane (PU) were studied. Tensile tests suggested high flexibility of the PUs with the maximum elongation-at-break of 161.59%. Dynamic mechanical analysis (DMA) indicated good shape recovery ratio of 72.58% after more than three repeated cycles. Under thermal treatment, the temporary shape could recover to its original state in 10 s. The peak heat release rate (pHRR), total heat released (THR) and temperature at pHRR (Tp) of flame-retardant shape memory polyurethane (FSPU) by micro-combustion calorimeter (MCC) was as low as 183.2 W/g, 21.4 KJ/g, 330.8 °C respectively, suggesting good inherent fire-resistant performance. As amine-containing crosslinkers are one of the most common building units in thermosetting polymers, we anticipate that our finding will have significant benefits beyond shape memory and fire-resistance.

In Situ Reversible Tuning from Pinned to Roll-Down Superhydrophobic States on a Thermal-Responsive Shape Memory Polymer by a Silver Nanowire Film.

Shape memory polymer (SMP) surfaces with tunable wettability have attracted extensive attention due to their widespread applications. However, there have been rare reports on in situ tuning wettability with SMP materials. In this paper, we reported a kind of distinct superhydrophobic SMP microconed surface on the silver nanowire (AgNW) film to achieve in situ reversible transition between pinned and roll-down states. The mechanism is taking advantage of the in situ heating functionality of the silver nanowire film by voltage, which provides the transition energy for SMP to achieve the fixation and recovery of temporary shape. It is noteworthy that the reversible transition could be repeated many times (>100 cycles), and we quantitatively investigate the shape memory ability of microcones with varied height and space under different applied voltages. These results show that the tilted microcones could recover its original upright state under a small voltage (4-11 V) in a short time, and the shortest recovery time is about 0.5 min under an applied voltage of ∼10 V. Finally, we utilize SMP microcone arrays with tunable wettability to realize lossless droplet transportation, and the tilted microconed surface also achieves liquid unidirectional transport due to its anisotropic water adhesion force. The robust microconed SMP surface with reversible morphology transitions will have far-ranging applications including droplet manipulation, reprogrammable fog harvesting, and so on.

Robust, reprocessable and shape-memory vinylogous urethane vitrimer composites enhanced by sacrificial and self-catalysis Zn(II)–ligand bonds

Endowing thermoset polymers with reinforcement, reprocessability and multi-functions shows great potential in practice. Herein, we describe the facile synthesis of robust, healable and reprocessable aminated silica/polydimethylsiloxane (PDMS) composites by engineering dynamic vinylogous urethane crosslinks and sacrificial Zn(II)-amine coordination bonds into the matrix simultaneously. These dynamic dual cross-links are constructed not only between polymer chains but also on the interface of fillers and matrix due to the surface modification of silica. Vinylogous urethane crosslinks endow the vitrimers with good healing ability and reprocessability at elevated temperature, and Zn(II) ions could enhance the mechanical properties of composites significantly by sacrificial bonds. Besides, silica can further increase the energy dissipation ratio of sacrificial bonds. Furthermore, these Zn(II) ions could also act as Lewis acid catalysts to accelerate the exchange reactions of vinylogous urethane crosslinks and thereby improve the reprocessability and healable ability of PDMS composites. Moreover, the composites also had attractive shape-memory ability, showing great application potential in smart material fields.

New Chain-Extended Bismaleimides with Aryl-Ether-Imide and Phthalide Cardo Skeleton (II): Creep, Stress Relaxation, Shape Memory and Self-Repairing Properties

In Part I of the paper, we have focused on the synthesis, characterization and solubility of three chain-extended bismaleimides containing aryl-ether-imide and phthalide cardo skeleton with different molecular weight (MPEIBMI-2.0, MPEIBMI-1.5 and MPEIBMI-1.25) and the thermal stability and thermal mechanical properties of their cured resins. In Part II of the paper, their high-temperature static viscoelasticity, shape memory (SM) performance and self-repairing behavior for micro-damages were investigated by dynamic mechanical analyzer and optical microscope. The creep test results exhibit the MPEIBMI-2.0 cured film has the strongest creep resistance at the same testing temperature due to the highest stiffness of its network structure, and the maximum allowable load of MPEIBMI-1.25 film at 200 °C reaches 15 MPa for 60 min creep experiment. The rate of stress relaxation for MPEIBMI-1.25 film is slower in spite of having relatively lower stress level. The MPEIBMI-1.25 film has the largest ultimate elongation at high temperature and this deformability confers it excellent shape memory (SM) ability. The shape fixity ratio reaches above 98% and the recovery rate is increased to above 96% from 94.5% after one SM cycle. The micro-damages on the surface of cured films could be repaired when heated to the temperature above their glass transition temperature, and the repairing temperature is increased with their crosslinking density to obtain perfect repairing efficiency.

Enhanced strength and toughness of κ-carrageenan/polyacrylic acid physical double-network hydrogels by dual cross-linking of the first network

Double network (DN) hydrogels with high strength and toughness have been developed as promising materials. In this paper, we prepared a novel κ-carrageenan/polyacrylic acid (κ-CG/PAA) DN hydrogel with excellent mechanical performances, which was achieved by dual cross-linking of the stiff first network. The obtained DN-1.956-0.1-2-15 hydrogels exhibited exceptional mechanical properties with fracture tensile stress of 2.53 MPa, fracture strain of 1381.91% and toughness of 13.40 MJ/m3. The results showed that dual cross-linking of κ-CG (double-helical junctions and metal coordination bonds) was conductive to high strength and toughness. Moreover, due to their totally physically cross-linking structures, the hydrogels showed 67% recovery of toughness after 2 min. Furthermore, the DN hydrogels showed self-healing capability, shape-memory ability, as well as excellent cytocompatibility and biodegradability. Such a designed DN hydrogel realizes the essential integration of improved mechanical properties, good biocompatibility and biodegradation for developing a desired scaffold material for potential tissue engineering applications.

A green approach toward epoxy-benzoxazine copolymers with shape-memory ability

In the frame of green-based chemistry, advanced shape memory polymers are designed from benzoxazine (RSBOX) and epoxy (R-EP) resins basing on potential natural raw materials, such as resorcinol and stearylamine. Thermal curing, investigated by differential scanning calorimetry, shows several overlapping peaks suggesting a complex curing mechanism. Dynamic mechanical analysis of cured RS-BOX/R-EP copolymers demonstrates an increase in the glass temperature and narrower glass transition by the increase of the RS-BOX ratio. In contrast, crosslinking density increases with higher epoxy resin content. All investigated materials possess one-way dual shape memory ability triggered by glass transition temperature with excellent shape fixity, while the shape recovery values ranged between 95 and 100%. The duration of the recovery process is significantly influenced by the RS-BOX amount. Additionally, the mechanical and shape memory properties of fully bio-based SMPs might be suitably tailored for advanced applications by merely varying the initial composition.

A novel thermoplastic shape memory polymer with solid-state plasticity derived from exchangeable hydrogen bonds.

A novel thermoplastic shape memory polymer (SMP) was synthesized by partly modifying the double bonds of trans-1,4-polybutadiene (TPB) and subsequently introducing mono-isocyanate as pendant groups. The comb-like chains consisted of abundant hydrogen bonds on their side groups, which could readily assemble into dynamic non-covalent polymer networks. The physical crosslink net-points formed by the hydrogen bonds were utilized to anchor the permanent shape of PBTP, while the soft trans-1,4-polybutadiene segments served as a switching phase to afford the temporary shape, and the glass transition temperature (Tg) was taken as the switching temperature. The optimal result was obtained with the sample with 30% modification, which showed an excellent shape fixity ratio and inferior shape recovery ratio of 100% and 89.57%, respectively. According to the results of the stress relaxation test, the relaxation time for this sample is 27 s when heated at 70 °C, implying that the dynamic network inside the sample can undergo topological rearrangement rapidly while maintaining the network integrity during the process. The high density of exchangeable hydrogen bonds constitutes a highly crosslinked non-covalent network, the dynamic nature of which is responsible for this outstanding network topological structure rearrangement behaviour, and endows this SMP with solid-state plasticity to reconfigure its permanent shape in the absence of catalysts or moulds. The highly complex permanent shape reconfiguration at a moderate temperature within a rational period will greatly promote the practical use of SMPs, and enable a wide variety of future engineering applications.

Shape-Memory Metallopolymer Networks Based on a Triazole-Pyridine Ligand.

Shape memory polymers represent an interesting class of stimuli-responsive polymers. With their ability to memorize and recover their original shape, they could be useful in almost every area of our daily life. We herein present the synthesis of shape-memory metallopolymers in which the switching unit is designed by using bis(pyridine–triazole) metal complexes. The polymer networks were synthesized via free radical polymerization of methyl-, ethyl- or butyl-methacrylate, tri(ethylene glycol) dimethacrylate and a methacrylate moiety of the triazole–pyridine ligand. By the addition of zinc(II) or cobalt(II) acetate it was possible to achieve metallopolymer networks featuring shape-memory abilities. The successful formation of the metal-ligand complex was proven by Fourier transform infrared (FT-IR) spectroscopy and by 1H NMR spectroscopy. Furthermore, the shape-recovery behavior was studied in detailed fashion and even triple-shape memory behavior could be revealed.

A new class of vitrimers based on aliphatic poly(thiourethane) networks with shape memory and permanent shape reconfiguration

Vitrimers are a new promising class of polymeric materials which are attracting increasing attention thanks to their thermosetting characteristics with their capability of being reprocessed and recyclable, which make them more environmentally friendly in reference to the conventional thermosets. In the present study, we report a new class of vitrimeric materials consisting in poly(thiourethane) networks. These materials can be easily prepared from readily available isocyanate and thiol monomers in the presence of dibutyltin dilaurate (DBTDL) as the catalyst. The reaction has a click nature and therefore leads to highly homogeneous networks. The materials studied behave as conventional thermosets until topological rearrangement started. Freezing topological temperatures (Tv) between 132 and 95 °C were determined depending on the amount of catalyst in the material. The vitrimers prepared showed good shape memory and welding abilities and a high optical transparency and therefore they have a great potentiality in advanced engineering applications. The occurrence of the trans-thiocarbamoylation reaction, responsible of the rearrangement, has been confirmed by using model compounds. The materials remained unaltered after reprocessing, which was proved by means of FTIR and thermomechanical studies.

Shape Memory Polyurethane and its Composites for Various Applications

The inherent capability to deform and reform in a predefined environment is a unique property existing in shape memory polyurethane. The intrinsic shape memory ability of the polyurethane is due to the presence of macro domains of soft and hard segments in its bulk, which make this material a potential candidate for several applications. This review is focused on manifesting the applicability of shape memory polyurethane and its composites/blends in various domains, especially to human health such as shielding of electromagnetic interference, medical bandage development, bone tissue engineering, self-healing, implants development, etc. A coherent literature review highlighting the prospects of shape memory polyurethane in versatile applications has been presented.

A novel mechanical robust, self-healing and shape memory hydrogel based on PVA reinforced by cellulose nanocrystal

Fabrication of multifunctional hydrogel with excellent mechanical property, self-healing and shape memory ability is still a challenging issue. In this study, a mechanical robust multifunctional hydrogel based on PVA reinforced by cellulose nanocrystal using nanofiller reinforcement strategy was reported. Owing to the hydrogen bonding and supramolecular interaction between PVA and CNC, the prepared hydrogel exhibited satisfying mechanical property. The obtained multifunctional PVA hydrogel could be potentially applied in biomedical or artificial skins fields.

Effects of Hard Segment of Polyurethane with Disulfide Bonds on Shape Memory and Self-Healing Ability

Self-healing polyurethane with disulfide bonds was synthesized using polycarbonate diol as a soft segment, and methylene diphenyl diisocyanate and 2-hydroxyethyl disulfide as a hard segment. Well-developed phase separation as the hard segments increased was confirmed by Fourier transform infrared spectra. The X-ray diffraction data showed that the crystallinity of the polycarbonate with a semicrystalline structure decreased as the HS increased, which affected the thermal, mechanical, and thermomechanical properties of the PU block copolymer. As the hard segments increased, the yield point on the strain-stress curve disappeared, and the mechanical properties (elongation at break and breaking stress) and the shape recovery rate of SHPU improved. The increase in the physical crosslinking between the hard segments contributed to improving shape recovery and mechanical properties. In particular, self-healing polyurethane with 30, and 35 wt% hard segments showed excellent self-healing ability at 80 C, while the self-healing ability for self-healing polyurethane with 40 wt% hard segments was decreased. The increase of the hard segment restricted the movement of the soft segment, thus the self-healing ability of SHPU with 40 wt% HS was decreased. It could be concluded that self-healing polyurethane synthesized using semicrystalline PC diol has a significant effect on shape recovery and self-healing efficiency due to the crosslinks between the hard segments.

Dual-responsive shape memory and self-healing ability of a novel copolymer from epoxy/cashew nut shell liquid and polycaprolactone

In this work, the blends of epoxy (EP) and polycaprolactone (PCL) with a bio-based curing agent, viz. cashew nut shell liquid (CNSL) were studied for their dual-responsive shape memory and self-healing behaviors. The suitable EP/CNSL weight ratio was observed at 70/30. The increase of PCL content up to 20 wt% in EP-CNSL matrix significantly enhanced the shape memory response to both thermal and chemical stimuli. All specimens showed 100% thermo-responsive shape recovery and the recovery time decreased with increasing PCL content. In the case of chemo-responsive shape memory, the immersion times spent for 100% shape recovery in water and methanol substantially decreased when PCL was added. Moreover, after thermal treatment, the EP-CNSL matrix with 20 wt% PCL showed significant self-healing ability with high tensile strength recovery at 93.70%. The EP-CNSL/PCL copolymer could be a promising alternative bio-related smart material for various applications such as dual-activated sensors and coatings with self-healing ability.

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.

Chitosan‐based double network hydrogels with self‐healing and dual‐responsive shape memory abilities

ABSTRACTChitosan‐based single network hydrogels with imine bonds have excellent self‐healing capability, while poor mechanical properties limit their applications. Here, chitosan‐polyacrylamide‐based double network hydrogels were prepared via in situ free‐radical polymerization of acrylamide in the presence of N‐carboxyethyl chitosan (CEC) and dibenzaldehyde‐terminated telechelic poly(ethylene glycol), which had excellent mechanical properties, self‐healing, and dual‐responsive shape memory abilities. The maximum tensile strength and elongation at break could reach 460 kPa and 4600%, respectively. Meanwhile, owing to the reversibility of imine bonds, elongation and strength at break of hydrogels could heal by 84.2 and 93.2% under alkali stimulation at 35 °C, respectively. Furthermore, the hydrogels also had good shape memory abilities for pH‐stimuli responsiveness of the imine bonds and metal ions stimuli responsiveness of CEC. The prepared chitosan‐based functional hydrogels have great potential application prospects in tissue scaffolds, actuators, and wearable devices. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48247.