Self-Healing Structural Materials

Self-healing materials have been developed since the 1990s and are currently used in various applications. Their performance in extreme environments and their mechanical properties have become a topic of research interest. Herein, we discuss cutting-edge self-healing technologies for hard materials and their expected healing processes. The progress that has been made, including advances in and applications of novel self-healing fiber-reinforced plastic composites, concrete, and metal materials is summarized. This perspective focuses on research at the frontier of self-healing structural materials

Blister-like Soft Nano-textured Thermo-pneumatic Actuator as an Artificial Muscle

Here, model blister-like soft thermo-pneumatic artificial muscles with the embedded nanofibers impregnated with ethanol are developed. The muscles are essentially blister-like thermo-pneumatic soft actuators (BTSAs), which deflect in response to heat supplied to their bottom. The resulting deflections are on the scale of 1 cm, and the BTSAs are operational for several cycles. They are able to raise the artificial rigid scales, spines or fur/thin fibers attached to them emulating such animals as pangolin, hedgehog and porcupine. They are also capable of removing the stickiest adhesive tapes attached to them, and thus hold great promise for biomedical applications where artificially grown skin patches should be removed from an underlying substrate without being damaged. The theory of the BTSA proposed in this work is in reasonable agreement with the acquired experimental data

Natural Biopolymer-based Triboelectric Nanogenerators via Fast, Facile, Scalable Solution Blowing

Here, we fabricated nanofiber (NF)-based triboelectric nanogenerators (TENGs) from natural biopolymers using the industrially scalable solution blowing. This technique eliminates severe restrictions on solutions to be used, and allows one to achieve biocompatible devices. Here solutions of soy protein and lignin were blown into continuous monolithic NFs of hundreds of nanometers in diameter. The technique we employed yields large-area NF mats within tens of minutes, and has never been employed to form TENGs. Furthermore, in contrast to electrospun and meltblown fiber mats, solution–blown NF mats are much fluffier/porous, which is beneficial for achieving higher voltages by means of triboelectricity. In particular, triboelectricity generated by our biopolymer-based TENGs revealed that they hold great promise as sustainable and environmentally-friendly self-powered devices for biomedical applications with the highest efficiency in their class. Moreover, these are the first nano-textured plant-derived biopolymer-made TENGs

Programmable Soft Robotics Based on Nano-Textured Thermo-Responsive Actuators

Soft robotic systems are increasingly emerging as robust alternatives to conventional robotics. Here, we demonstrate the development of programmable soft actuators based on volume expansion/retraction accompanying liquid-vapor phase transition of a phase-change material confined within an elastomer matrix. The combination of a soft matrix (a silicone-based elastomer) and an embedded ethanol-impregnated polyacrylonitrile nanofiber (PAN NF) mat makes it possible to form a sealed compound device that can be operated by changing the actuator temperature above/below the boiling point of ethanol. The thermo-responsive actuators based on this principle demonstrate excellent bending ability at a sufficiently high temperature (>90 °C) - comparable with compressed air-based soft actuators. The actuator using the mechanism presented here is easy to manufacture and automate and is recyclable. Finally, the actuation mechanism can be incorporated into a wide variety of shapes and configurations, making it possible to obtain tunable and programmable soft robots that could have a wide variety of industrial applications

Self-healing three-dimensional bulk materials based on core-shell nanofibers

In this study, electrospun core-shell nanofibers containing healing agents are embedded into a three-dimensional bulk matrix in a simple versatile process. Two types of the healing agents (resin monomer and cure) are encapsulated inside the nanofiber cores. The core-shell fibers are encased in the macroscopic three-dimensional bulky material. To achieve this goal, the electrospun core-shell fibers containing two components of PDMS (either resin monomer or cure) are directly embedded into an uncured PDMS bath and dispersed there, essentially forming a monolithic composite. For the evaluation of the self-healing features, the interfacial cohesion energy is measured at the cut surface of such a material. Namely, the bulk of the prepared self-healing material is entirely cut into two parts using a razor blade and then re-adhered due to the self-curing process associated with the released healing agents. The results reveal that the self-healing fiber network works and releases a sufficient amount of resin monomer and cure at the cut surface to facilitate self-healing. In addition, chopped into short filaments core-shell fibers were embedded into highly porous sponge-like media. After a mechanical damage in compression or shearing fatigue, this sponge-like material also revealed restoration of stiffness due to the released self-healing. The sponges revealed a 100% recovery and even enhancement after being damage in the cyclic compression and shearing tests, even though only 0.086% of the healing agents were embedded per sponge mass and finely dispersed in it

Characterization of Biological Properties of Dental Pulp Stem Cells Grown on an Electrospun Poly(<span style="font-variant: small-caps">l</span>-lactide-<i>co</i>-caprolactone) Scaffold

Poly(l-lactide-co-caprolactone) (PLCL) electrospun scaffolds with seeded stem cells have drawn great interest in tissue engineering. This study investigated the biological behavior of human dental pulp stem cells (hDPSCs) grown on a hydrolytically-modified PLCL nanofiber scaffold. The hDPSCs were seeded on PLCL, and their biological features such as viability, proliferation, adhesion, population doubling time, the immunophenotype of hDPSCs and osteogenic differentiation capacity were evaluated on scaffolds. The results showed that the PLCL scaffold significantly supported hDPSC viability/proliferation. The hDPSCs adhesion rate and spreading onto PLCL increased with time of culture. hDPSCs were able to migrate inside the PLCL electrospun scaffold after 7 days of seeding. No differences in morphology and immunophenotype of hDPSCs grown on PLCL and in flasks were observed. The mRNA levels of bone-related genes and their proteins were significantly higher in hDPSCs after osteogenic differentiation on PLCL compared with undifferentiated hDPSCs on PLCL. These results showed that the mechanical properties of a modified PLCL mat provide an appropriate environment that supports hDPSCs attachment, proliferation, migration and their osteogenic differentiation on the PLCL scaffold. The good PLCL biocompatibility with dental pulp stem cells indicates that this mat may be applied in designing a bioactive hDPSCs/PLCL construct for bone tissue engineering

Wetting of inclined nano-textured surfaces by self-healing agents

Experiments were conducted to study spreading of droplets of liquid healing agents on tilted nanofiber mats, which is relevant in the framework of self-healing engineered materials with vascular networks. In the present situation the effect of gravity on drop spreading is important, as well as the inclination angle and the mat thickness. In the control case of gravity-driven spreading of droplets on an inclined polydimethylsiloxane (PDMS) surface the results agreed fairly well with the theoretical predictions in the framework of the lubrication theory for the intact surfaces. However, spreading on the inclined nanofiber mats revealed significant deviations from the theory due to the imbibition of liquid into the inter-fiber pores. The imbibition effect, which stems from the wettability-driven suction, increased as the mat thickness increased. Notably, the imbibition effect also increased as the inclination angle increased