An underwater stable and durable gelatin composite hydrogel coating for biomedical applications

Developing underwater stable and durable hydrogel coatings with drag-reducing, drug release, and antibacterial properties is essential for lots of biomedical applications. However, most hydrogel coatings cannot meet the requirement of underwater stability and versatility, which severely limits their widespread use. In this work, an underwater stable, durable and substrate-independent gelatin composite hydrogel (GMP) coating is developed through covalent crosslinks, where a silane coupling agent with an unsaturated double bond is grafted onto a substrate of co-deposited polydopamine and polyethylenimine. GMP coating can be easily coated onto various medical device surfaces, such as artificial joints, catheters, tracheal tubes and titanium alloys, showing excellent structural stability and mechanical tunability under extreme conditions of ultrasonic treatment for 1 h (400 W of ultrasonic power) or underwater shearing for 14 days (400 rpm). Besides, friction experiment reveals that GMP coating exhibits good lubrication properties (coefficient of friction < 0.003). The drug-loading and bacterial inhibition ring tests show that the GMP coating has a tunable drug release ability with the final releasing ratios of 70-95% by changing the content of poly (ethylene glycol) diacrylate. This work offers a scalable approach of fabricating bio-functional and stable hydrogel coatings, which can be potentially used in biomedical applications.

3D-Printed Piezoelectric Scaffolds with Shape Memory Polymer for Bone Regeneration

The application of piezoelectric nanoparticles with shape memory polymer (SMP) to 3D-printed piezoelectric scaffolds for bone defect repair is an attractive research direction. However, there is a significant difference in dielectric constants between the piezoelectric phase and polymer phase, limiting the piezoelectric property. Therefore, novel piezoelectric acrylate epoxidized soybean oil (AESO) scaffolds doped with piezoelectric Ag-TMSPM-pBT (ATP) nanoparticles (AESO-ATP scaffolds) are prepared via digital light procession 3D-printing. The Ag-TMSPM-pBT nanoparticles improve the piezoelectric properties of the AESO scaffolds by TMSPM covalent functionalization and conductive Ag nanoparticles. The AESO scaffolds doped with 10 wt% Ag-TMSPM-pBT nanoparticles (AESO-10ATP scaffolds) exhibit promising piezoelectrical properties, with a piezoelectric coefficient (d33) of 0.9 pC N-1 and an output current of 146.4 nA, which are close to the piezoelectric constants of bone tissue. In addition, these scaffolds exhibit good shape memory function and can quickly recover their original shape under near-infrared (NIR) light irradiation. The results of osteogenesis capability evaluation indicate that the AESO-10ATP scaffolds can promote osteogenic differentiation of BMSCs in vitro and bone defect repair in vivo, indicating the 3D-printed AESO-10ATP piezoelectric scaffolds may have great application potential for bone regeneration.

Barium Titanate Functionalization with Organosilanes: Effect on Particle Compatibility and Permittivity in Nanocomposites

Barium titanate (BT) recently gained new interest in the preparation of dielectric and piezoelectric lead-free materials for applications in sensors, electronics, energy harvesting and storage fields. Barium titanate nanocomposites can achieve attractive performance, provided that the compatibility between ceramic particles and polymeric matrices is enhanced to the benefit of the physical properties of the final composite. Tuning the particle-matrix interface through particle functionalization represents a viable solution. In this work, surface functionalization of BT nanoparticles (NPs), obtained by hydrothermal synthesis, with 3-glycidyloxypropyltrimethoxysilane, 2-[(acetoxy(polyethyleneoxy)propyl]triethoxysilane and triethoxysilylpropoxy(polyethyleneoxy)dodecanoate, was performed after optimizing the hydroxylation process of the NPs to improve their surface reactivity and increase the yield of grafting. Solid-state nuclear magnetic resonance and thermogravimetric analysis were used to quantify the molecules grafted onto the ceramic nanoparticles. Both bare and functionalized particles were employed in the realization of epoxy- and polydimethylsiloxane (PDMS)-based nanocomposites. Functionalization was proven to be beneficial for particle dispersibility and effective for particle alignment in the PDMS matrix. Moreover, the dielectric constant measurements revealed the potential of PDMS-based nanocomposites for applications in the field of dielectric elastomers.

One Soft Step: Bio-Inspired Artificial Muscle Mechanisms for Space Applications

Soft robots, devices with deformable bodies and powered by soft actuators, may fill a hitherto unexplored niche in outer space. All space-bound payloads are heavily limited in terms of mass and volume, due to the cost of launch and the size of spacecraft. Being constructed from stretchable materials allows many possibilities for compacting soft robots for launch and later deploying into a much larger volume, through folding, rolling, and inflation. This morphability can also be beneficial for adapting to operation in different environments, providing versatility, and robustness. To be truly soft, a robot must be powered by soft actuators. Dielectric elastomer transducers (DETs) offer many advantages as artificial muscles. They are lightweight, have a high work density, and are capable of artificial proprioception. Taking inspiration from nature, in particular the starfish podia, we present here bio-inspired inflatable DET actuators powering low-mass robots capable of performing complex motion that can be compacted to a fraction of their operating size.

Evaluation of dielectric elastomers to develop materials suitable for actuation

Electroactive polymers based on dielectric elastomers are stretchable and compressible capacitors that can act as transducers between electrical and mechanical energies. Depending on the targeted application, soft actuators, sensors or mechanical-energy harvesters can be developed. Compared with conventional technologies, they present a promising combination of properties such as being soft, silent, light and miniaturizable. Most of the research on dielectric elastomer actuators has focused on obtaining the highest strain, either from technological solutions using commercially available materials or through the development of new materials. It is commonly accepted that a high electrical breakdown field, a low Young's modulus and a high dielectric constant are targets. However, the interdependency of these properties makes the evaluation and comparison of these materials complex. In addition, dielectric elastomers can suffer from electromechanical instability, which amplifies their complexity. The scope of this review is to tackle these difficulties. Thus, first, two physical parameters are introduced, one related to the energy converted by the dielectric elastomer and another to its electromechanical stability. These numbers are then used to compare dielectric elastomers according to a general and rational methodology considering their physicochemical and electromechanical properties. Based on this methodology, different families of commercially available dielectric elastomers are first analyzed. Then, different polymer modification methods are presented, and the resulting modified elastomers are screened. Finally, we conclude on the trends enabling the choice of the most suitable modification procedure to obtain the desired elastomer. From this review work, we would like to contribute to affording a quick identification method, including a graphic representation, to evaluate and develop the dielectric materials that are suitable for a desired actuator.

Dual surface modification of carbon materials by polydopamine and phosphomolybdic acid for supercapacitor application

Surface modification of carbon materials is an important issue for its potential application. In this work, this purpose has been successfully achieved by the incorporation of polydopamine (PDA) and phosphomolybdic acid (PMA), forming carbon/PDA/PMA hybrid electrode materials, in which PDA acts both as a linker molecule and as a pseudo-capacitance provider, and PMA contributes to pseudo-capacitive performance. It is revealed that adding PDA and/or PMA results in a decrease of porosity but in an increase of electrical conductivity and thus a suitable combination of porosity, conductivity, and pseudo-capacitance is vital for achieving the optimization of capacitive performance. By using the Trasatti method, we found out that increasing PDA or PMA results in the improvement of pseudo-capacitance proportion and the C-PDA/PMA-1 : 1 sample exhibits a pseudo-capacitance proportion of 32%. In a two-electrode configuration, the C-PDA/PMA-1 : 1 sample delivers a specific capacitance of 101 F g-1 at 1 A g-1, a cycling performance of 108% within 10 000 cycles, and an energy density of 3.5 W h kg-1 (nearly 3.2 times that of the C-blank sample) at 500 W kg-1. Moreover, the dual surface modification of PDA and PMA could be extended to other energy storage systems, highly improving capacitive performance by the synergic effect.

Significantly Enhanced Energy Density by Tailoring the Interface in Hierarchically Structured TiO2-BaTiO3-TiO2 Nanofillers in PVDF-Based Thin-Film Polymer Nanocomposites

Dielectric polymer nanocomposites with a high breakdown field and high dielectric constant have drawn significant attention in modern electrical and electronic industries due to their potential applications in dielectric and energy storage systems. The interfaces of the nanomaterials play a significant role in improving the dielectric performance of polymer nanocomposites. In this work, polydopamine (dopa)-functionalized TiO₂-BaTiO₃-TiO₂ (TiO₂-BT-TiO₂@dopa) core@double-shell nanoparticles have been developed as novel nanofillers for high-energy-density capacitor applications. The hierarchically designed nanofillers help in tailoring the interfaces surrounding the polymer matrix as well as act as individual capacitors in which the core and outer TiO₂ shell function as a capacitor plate because of their high electrical conductivity while the middle BT layer functions as a dielectric medium due to high dielectric constant. Detailed electrical characterizations have revealed that TiO₂-BT-TiO₂@dopa/poly(vinylidene fluoride) (PVDF) possesses a higher relative dielectric permittivity (ε_r), breakdown strength ( E_b), and energy density as compared to those of PVDF, TiO₂/PVDF, TiO₂@dopa/PVDF, and TiO₂-BT@dopa/PVDF polymer nanocomposites. The ε_r and energy density of TiO₂-BT-TiO₂@dopa/PVDF were 12.6 at 1 kHz and 4.4 J cm^-3 at 3128 kV cm^-1, respectively, which were comparatively much higher than those of commercially available biaxially oriented polypropylene having ε_r of 2.2 and the energy density of 1.2 J cm^-3 at a much higher electric field of 6400 kV cm^-1. It is expected that these results will further open new avenues for the design of novel architecture for high-performance polymer nanocomposite-based capacitors having core@multishell nanofillers with tailored interfaces.

Urushiol-functionalized mesoporous silica nanoparticles and their self-assembly into a Janus membrane as a highly efficient hemostatic material

Quick hemostasis plays a very important role in preventing hemorrhagic shock and death by controlling blood loss from trauma in civil and military accidents. An ideal quick hemostat should have tissue-adhesive functional groups, clotting factor activating components, and a plasma non-permeable hydrophobic layer. Inspired by the adhesive behavior of mussels, a novel efficient hemostat of urushiol-functionalized mesoporous silica nanoparticles (MSN@U) with a core-shell structure was synthesized and their hemostatic performance was evaluated for the first time. MSN@U could form an amphipathic Janus membrane (a hydrophobic layer and a hydrophilic layer in one membrane) by interfacial self-assembly. The morphology and structure of MSN@U were characterized. The results showed that MSN@U possessed a large specific surface area of 448.91 m2 g-1 and a rich porous structure with an average pore diameter of 3.94 nm. The hydrophilic catechol groups and the long hydrophobic alkyl groups of urushiol allowed MSN@U to self-assemble at the blood/air interface. The former made MSN@U tightly adhere onto blood vessel tissue through covalent bonds, while the latter formed a hydrophobic barrier layer which hindered blood from oozing. Meanwhile, MSN@U would accelerate clotting cascade reactions. These three effects made MSN@U a very quick hemostat with a hemostatic time of 22 ± 2 s on a rat liver laceration. Both in vitro and in vivo tests showed that they had a better hemostatic effect and blood compatibility than MSN. Cell viability evaluations indicated that MSN@U had no cytotoxicity. MSN@U will be a safe and promising hemostatic agent for clinical applications.

Intrinsic Tuning of Poly(styrene-butadiene-styrene)-Based Self-Healing Dielectric Elastomer Actuators with Enhanced Electromechanical Properties

The electromechanical properties of a thermoplastic styrene-butadiene-styrene (SBS) dielectric elastomer was intrinsically tuned by chemical grafting with polar organic groups. Methyl thioglycolate (MG) reacted with the butadiene block via a one-step thiol-ene "click" reaction under UV at 25 °C. The MG grafting ratio reached 98.5 mol % (with respect to the butadiene alkenes present) within 20 min and increased the relative permittivity to 11.4 at 10³ Hz, with a low tan δ. The actuation strain of the MG-grafted SBS dielectric elastomer actuator was 10 times larger than the SBS-based actuator, and the actuation force was 4 times greater than SBS. The MG-grafted SBS demonstrated an ability to achieve both mechanical and electrical self-healing. The electrical breakdown strength recovered to 15% of its original value, and the strength and elongation at break recovered by 25 and 21%, respectively, after 3 days. The self-healing behavior was explained by the introduction of polar MG groups that reduce viscous loss and strain relaxation. The weak CH/π bonds through the partially charged (δ+) groups adjacent to the ester of MG and the δ- center of styrene enable polymer chains to reunite and recover properties. Intrinsic tuning can therefore enhance the electromechanical properties of dielectric elastomers and provides new actuator materials with self-healing mechanical and dielectric properties.

Fabrication of Dielectric Elastomer Composites by Locking a Pre-Stretched Fibrous TPU Network in EVA

Dielectric elastomer (DE) composites with high electrical breakdown strength and large voltage-induced deformation were developed by retaining pre-stretched thermoplastic polyurethane (TPU) fibers in ethylene vinyl acetate copolymer (EVA). The microstructure of the candidate E-TPU fiber membrane and EVA coated E-TPU (E-TPU/EVA) film were characterized by scanning electron microscopy (SEM). The quasi-static and dynamic mechanical property, and the electromechanical properties, including the dielectric constant, dielectric loss tangent, and electromechanical sensitivity, of the DE composites were evaluated. Initially, tensile tests demonstrated that the DE composites based on E-TPU/EVAs had a higher elongation at break of above 1000% but a low elastic modulus of approximately 1.7 MPa. Furthermore, dielectric spectroscopy showed that the E-TPU/EVA had a dielectric constant of 4.5 at the frequency of 1000 Hz, which was 1.2 times higher than that of pure EVA film. Finally, it was found from electromechanical test that the voltage induced strain of E-TPU/EVA rose to 6%, nearly 3 times higher than that of pure TPU film, indicating an excellent electromechanical property. The DE composites developed have demonstrated the potential to be good candidate materials in the fields of artificial intelligence, biomimicry and renewable energy.

S. K, Jayalakshmy MS, Thomas S, Rouxel D, Philip J, Bhowmik RN, Kalarikkal N. Dopamine functionalization of BaTiO3: an effective strategy for the enhancement of electrical, magnetoelectric and thermal properties of BaTiO3-PVDF-TrFE nanocomposites

Electro-active polymer–ceramic composites are emerging materials in the fields of nano/macro electronic and microelectromechanical device applications.

Improved electromechanical properties of brominated butyl rubber filled with modified barium titanate

Barium titanate (BT) particles, BT-KH570 particles, and polar plasticizer tri-n-butyl phosphate (TBP) were added into BIIR matrix to form a dielectric elastomer composite, which had a high dielectric constant, good mechanical properties, and large actuated strain.