Thermo-assisted fabrication of a novel shape-memory hyaluronic acid sponge for non-compressible hemorrhage control.

Hyaluronic acid (HA), a major component of skin extracellular matrix, provides an excellent framework for hemostatic design; however, there still lacks HA materials tailored with superior mechanical properties to address non-compressible hemorrhages. Here, we present a solvent-free thermal approach for constructing a shape-memory HA sponge for this application. Following facile thermal incubation around 130 °C, HA underwent cross-linking via esterification with poly(acrylic acid) within the sponge pre-shaped through a prior freeze-drying process. The resulting sponge system exhibited extensively interconnected macropores with a high fluid absorption capacity, excellent shape-memory property, and robust mechanical elasticity. When introduced to whole blood in vitro, the HA sponges demonstrated remarkable hemostatic properties, yielding a shorter coagulation time and lower blood clotting index compared to the commercial gelatin sponge (GS). Furthermore, in vivo hemostatic studies involving two non-compressible hemorrhage models (rat liver volume defect injury or femoral artery injury) achieved a significant reduction of approximately 64% (or 56%) and 73% (or 70%) in bleeding time and blood loss, respectively, which also outperformed GS. Additionally, comprehensive in vitro and in vivo evaluations suggested the good biocompatibility and biodegradability of HA sponges. This study highlights the substantial potential for utilizing the designed HA sponges in massive bleeding management.

Mechanical and Shape Memory Properties of Additively Manufactured Polyurethane (PU)/Halloysite Nanotube (HNT) Nanocomposites.

This paper investigates the impact of halloysite nanotube (HNT) content on mechanical and shape memory properties of additively manufactured polyurethane (PU)/HNT nanocomposites. The inclusion of 8 wt% HNTs increases their tensile strength by 30.4% when compared with that of virgin PU at 44.75 MPa. Furthermore, consistently significant increases in tensile modulus, compressive strength and modulus, as well as specific energy absorption are also manifested by 47.2%, 34.0%, 125% and 72.7% relative to neat PU at 2.29 GPa, 3.88 MPa, 0.28 GPa and 0.44 kJ/kg respectively. However, increasing HNT content reduces lateral strain due to the restricted mobility of polymeric chains, leading to a decrease in negative Poisson's ratio (NPR). As such, shape recovery ratio and time of PU/HNT nanocomposites are reduced by 9 and 45% with the inclusion of 10 wt% HNTs despite an increasing shape fixity ratio up to 12% relative to those of neat PU.

In vivo biocompatible shape memory polyester derived from recycled polycarbonate e-waste for biomedical application.

From the last few decades, the usage of polycarbonate (PC) has tremendously increased due to its engineering properties such as outstanding mechanical strength, superior toughness, and good optical transparency. Owning to these properties, PC has widespread applications in the field of electronics, construction, data storage, automotive industry and subsequently resulted in an ever-increasing volume of post-consumer PC e-waste, which also increases the environmental pollution with time due to its nonbiodegradability nature. Therefore, recycling of PC has become a significant challenge throughout the globe. Herein, we first time reported synthesis of a family of low-cost biodegradable and biocompatible biopolymers using solvent and catalyst free melt polycondensation reaction of recycled PC e-waste derived monomer bis(hydroxyethyl ether) of bisphenol A (BHEEB) along with other renewable resources such as sebacic acid, citric acid and mannitol. The synthesis of the polyester was confirmed by FTIR spectroscopy, NMR spectroscopy, XRD and DSC. The mechanical properties and biodegradation behaviour of the polyester can be fine-tuned by simply varying the monomer feed ratio. In addition to that, the polyester demonstrated excellent shape memory property in ambient temperature along with outstanding recovery properties. In addition to this, the synthesized polyester showed exceptional in vitro and in vivo cytocompatibility as well as cell proliferation rate against mouse fibroblast cells (NIH-3 T3) and biocompatibility, respectively. Therefore, the novel polyesters derived from recycled PC e-waste may be potential resorbable biomaterial for tissue engineering applications in future.

Degradable photo-crosslinked starch-based films with excellent shape memory property.

With the increasingly serious plastic pollution, people's demand for the multi-functional biodegradable plastics is becoming more and more urgent. Inspired by the crosslinked shape memory polymers, the crosslinked starch films were synthesized by inducing the decomposition of benzophenone into free radical and depriving hydrogen on starch macromolecules under UV irradiation, in order to gain a high shape memory performance. The results showed that a three-dimensional crosslinking network between starch macromolecule chains was formed. Compared with the uncrosslinked starch films, the photo-crosslinked films not only had higher mechanical property (tensile strength increased by 154%), but also had better water resistance (water contact angle from 60° to 87°) due to the reduction of free hydroxyl groups. In addition, the stable covalent bonds serving as netpoints endow photo-crosslinked films with great improvement in shape memory property, with nearly 180° bending recovery. More importantly, the maximum shape memory fixity ratio (Rf) and shape memory recovery ratio (Rr) under stretch deformation were 96.5% and 99.8%, respectively. And the Rf and Rr could reach 94.6% and 79.8% even at higher strain. In all, the excellent shape memory performance and good degradability crosslinked starch films, which have great potential application in disposable heat-shrinkable packaging materials.

Digital Light Processing 4D Printing of Transparent, Strong, Highly Conductive Hydrogels.

Hydrogels have excellent biocompatibility, transparency, stretchability, and ionic conductivity, but their fabrication through photopolymerization-based 3D printing is limited due to the low solubility of hydrophobic photoinitiators and lack of efficient hydrophilic photoinitiators. Herein, a type of microemulsion is synthesized and the common hydrophobic photoinitiator can be adopted and finally, a series of transparent hydrogels with high strength (up to 22.9 MPa), elasticity (up to 583%), and ionic conductivity (up to 9.64 S m-1) are fabricated through digital light processing 3D printing technology. Objects with complex structures and a high printing resolution are printed. Hydrogels with both high strength and high ionic conductivity are obtained through chemical crosslinking and ion coordination effect. Dual-material 3D printing is applied to package the hydrogel with elastomers. Due to the high sensitivity and reliability under both stretching and compressive deformation, the hydrogel sensors are applied to monitor various human motions. In addition, the hydrogel exhibits solvent-induced dehydration and excellent water-activated shape memory properties, which are greatly beneficial for its storage and applications in the biomedical field.

Bioinspired Shape Memory Hydrogel Artificial Muscles Driven by Solvents.

Although hydrogels containing large amounts of water are similar to natural muscles, they are a challenge to be used in artificial muscles because of their poor mechanical properties and low work capacities. The current paper describes the design and fabrication of tendril-inspired hydrogel artificial muscles via a consecutive shaping process. Tunicate cellulose nanocrystals (TCNCs) are incorporated into polymeric networks via host-guest interactions to reinforce the hydrogel. Tendril-inspired hydrogels are obtained by treating the TCNC-reinforced hydrogels with a consecutive stretching, twisting, and coiling process and locking the shaped structure through Fe3+/-COO- ionic coordination. These hydrogel muscles exhibit a high actuation rate, large actuation strain, and shape memory property in response to solvents. The actuation performances of hydrogel muscles are affected by their chirality, twist density, applied stress, and temporary shape. Moreover, a homochiral hydrogel muscle with temporary shape II shows comparable contractile work capacity with a natural muscle, which can be applied as the engine to actuate the movement of a car model. This work demonstrates a simple and effective strategy for the fabrication of hydrogel artificial muscles that have great potential for biomedical application as a result of their comparable water content and contractile work capacity with natural muscles.

Hydrogel Production Platform with Dynamic Movement Using Photo-Crosslinkable/Temperature Reversible Chitosan Polymer and Stereolithography 4D Printing Technology.

BACKGROUND: Three-dimensional (3D) printing using hydrogel has made great strides when it comes to mimicking 3D artificial tissue in the medical field. However, most structures do not mimic the dynamic movement of the tissues. Without imitating dynamic movements, there are limitations on the extent to which the proper implementation of the tissue's own functions can be achieved. METHOD: In this study, we intend to present an approach to solving this problem using hydroxybutyl methacrylated chitosan (HBC-MA), a photo-crosslinkable/temperature reversible chitosan polymer. In addition, stereolithography-3D (SLA-3D) printing technology was used, which is more likely to mimic the complex microstructure. As a control, a 3D structure made with pristine poly(ethylene glycol) dimethacrylate (PEG-DMA) was created, and a 4D structure was prepared by adding HBC-MA to poly(ethylene glycol) dimethacrylate (PEG-DMAP) resin. RESULTS: HBC-MA caused the expansion of water into the polymer matrix at low temperature, and the 4D structure resulted in expansion of the polymer volume, generating dynamic movement due to the expansion of water. Conversely, as the temperature rose, deswelling occurred, followed by a decrease in the volume, showing a shape memory property of returning to the existing structure. Morphological, swelling, and mechanical analysis further confirmed the principle of dynamic movement. In addition, parameters were provided through calculation of the bending ratio angle (θ). CONCLUSION: Through this, it is suggested that HBC-MA can be applied as a core polymer for SLA-4D printing, and has high potential for realizing the dynamic movement of tissue.

Study of Shape Memory and Tensile Property of 3D Printed Sinusoidal Sample/Nylon Composite Focused on Various Thicknesses and Shape Memory Cycles.

This study evaluated the shape memory and tensile property of 3D-printed sinusoidal sample/nylon composite for various thickness and cycles. Sinusoidal pattern of five thicknesses: 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, and 1.0 mm were 3D-printed on nylon fabric by the fused deposition modeling (FDM) 3D printer using shape memory thermoplastic polyurethane (SMTPU). Afterward, shape memory and tensile property was investigated up to 50 shape memory cycles. The study found that 3D-printed sinusoidal sample/nylon composite had a 100% shape recovery ratio for various thicknesses up to 50 cycles. The average shape recovery rate gradually decreased from 3.0°/s to 0.7°/s whereas the response time gradually increased with the increase of a 3D-printed pattern thickness. The stress and initial modulus gradually increased with the increase of the cycle's number. Thus, the shape memory property had a similar tendency for various cycles whereas the tensile property gradually increased with the increase of the cycle number. Moreover, this study demonstrated that this 3D-printed sinusoidal sample/nylon composite can go through more than 50 cycles without losing its tensile or shape memory property. This 3D-printed sinusoidal sample/nylon composite has vast potential as smart, reinforced, and protective clothing that requires complex three-dimensional shapes.

Melamine Foam-Supported Form-Stable Phase Change Materials with Simultaneous Thermal Energy Storage and Shape Memory Properties for Thermal Management of Electronic Devices.

Paraffin wax (PW) is widely used as a phase change material (PCM) in the thermal energy storage field, whereas the leakage and strong rigidity of PW have hindered its practical applications. In this work, binary melamine foam (MF)/PW blends with simultaneous thermal energy storage and shape memory properties were prepared through vacuum impregnation. Herein, PW performs as a latent heat storage material and as a switching phase for shape fixation and MF serves as a supporting material to prevent the leakage and as a permanent phase for shape recovery. Due to the light weight and super-elasticity of MF, the MF/PW PCMs possess not only good encapsulation ability and a high latent heat, but also excellent shape-fixing and recovery properties (shape-fixing and recovery ratios are about 100%). Besides, the MF/PW PCMs can be fabricated into arbitrary shapes using MF as a template, and they exhibit excellent shape memory cyclic performance and thermal reliability. A temperature-sensitive and temperature-controlled deployable panel is further established, which can be installed in the electronic device and used for temperature protection. With high thermal energy storage capability, excellent shape memory properties, shape designability, and stable cycling reliability, this multifunctional MF/PW PCM shows a promising application in thermal energy management systems.

Enhancement in Mechanical and Shape Memory Properties for Liquid Crystalline Polyurethane Strengthened by Graphene Oxide.

Conventional shape memory polymers suffer the drawbacks of low thermal stability, low strength, and low shape recovery speed. In this study, main-chain liquid crystalline polyurethane (LCPU) that contains polar groups was synthesized. Graphene oxide (GO)/LCPU composite was fabricated using the solution casting method. The tensile strength of GO/LCPU was 1.78 times that of neat LCPU. In addition, shape recovery speed was extensively improved. The average recovery rate of sample with 20 wt % GO loading was 9.2°/s, much faster than that of LCPU of 2.6°/s. The enhancement in mechanical property and shape memory behavior could be attributed to the structure of LCPU and GO, which enhanced the interfacial interactions between GO and LCPU.