Pressure-Sensitive Supramolecular Adhesives Based on Lipoic Acid and Biofriendly Dynamic Cyclodextrin and Polyrotaxane Cross-Linkers

Self-Adhesive Gelatin/Slide-Ring Double-Network Hydrogel for Human Motion Sensing and Morse Code Communication

Hydrogels emerge as highly promising candidates for wearable electronics due to their moldability and biocompatibility. However, hydrogel-based wearable electronics often suffer from poor mechanical properties and limited adhesion, pose significant challenges to their practical application. Herein, a conductive, stretchable, and self-adhesive gelatin/slide ring hydrogel (SRH) with a double-network (DN) structure is developed by incorporating a polyrotaxane (PR) based cross-linker in the hydrogel with the gelatin (GEL) network. The water-soluble allylic PR (APR) cross-linkers are prepared from the cyclodextrin-based PR via a simple one-step method. Additionally, the effect of APR cross-linkers with different sliding capabilities on the mechanical properties of SRH is further investigated aiming to optimize performance. The optimized SRH achieves a balance between toughness (2226 kJ m-3) and rigidity (154 kPa), along with high stretchability (3048%) and strong adhesion to various substrate materials. More importantly, this DN hydrogel is demonstrated as a human motion sensor capable of Morse code communication. This work not only advances the understanding of slidable PR cross-linker applications but also paves the way for innovative hydrogels tailored for high-performance wearable electronics, broadening their scope and functionality in real-world use.

Versatile Solid-State Medical Superglue Precursors of α-Lipoic Acid

α-Lipoic acid (αLA) is an attractive building block for medical adhesives. However, due to poor water solubility of αLA and high hydrophobicity of poly(αLA), elevated temperatures, organic solvents, or complex preparations are typically required to obtain and deliver αLA-based adhesives to biological tissue. Here, we report αLA-based powder and low-viscosity liquid superglues that polymerize and bond rapidly upon contact with wet tissue. A monomeric mixture of αLA, sodium lipoate, and an activated ester of lipoic acid was used to formulate the versatile adhesives. Stress-strain measurements of the wet adhesives confirmed the high flexibility of the adhesive. Moreover, a small molecule regenerative drug was successfully incorporated into and released from the adhesive without altering the physical and adhesive properties. In vitro and in vivo studies of the developed adhesives confirmed their cell and tissue compatibility, biodegradability, and potential for sustained drug delivery. Moreover, due to the inherent ionic nature of the adhesives, they demonstrated high electric conductivity and sensitivity to deformation, allowing for the development of a tissue-adherent strain sensor.

Light Stimuli-Responsive Degradable and Tough Polymeric Materials with Movable Cross-Links

Both strong and easily dismantlable adhesive systems are required to realize a sustainable society by recovering and reusing substrates. Introducing topological cross-links with cyclodextrins (CDs) into adhesives can improve their adhesive strength. In this study, we prepared movable cross-linked poly(ethyl acrylate) (PEA-TAcγCD) with polymerizable CDs and acid-degradable bonds (TAcγCDAAmMe) for both strong and dismantlable adhesion. The O-amidomethyl bond, which links CD to a polymerizable functional group, can be degraded by mixing Brønsted acid. By combining PEA-TAcγCD with photoacid generators, we successfully controlled the mechanical properties by cleaving the movable cross-links upon light stimulation. The degradation mechanism of TAcγCDAAmMe by photoacid generators was confirmed by mass spectrometry. In addition, the cleavage of movable cross-linking points via light stimulation was demonstrated by both the alteration of mechanical properties and chain relaxation of the system, which were evaluated by utilizing tensile tests and dynamic mechanical analysis, respectively. Therefore, the light-responsive degradable elastomer appeared applicable as an easily dismantled on-demand adhesion system. Using light stimulation, the adhesion strengths with the same or dissimilar substrates were reduced. The easy dismantling of the adhesion system by applying the acid degradability of TAcγCDAAmMe enabled excellent adhesive properties derived from the movable cross-links and easy dismantling by light stimulation. Facilitating the disassembly, collection, and reuse of resources will contribute to the realization of a sustainable society.

Mantis shrimp-inspired functionalized plant fibers to fabricate a soy protein adhesive with high strength and mildew resistance

Soy protein-based adhesives present a promising alternative to petroleum-based adhesives in the wood industry. Nevertheless, their limitations, including insufficient water resistance, low bonding strength, and inadequate mold resistance, constrain their industrial applications. Plant fiber-reinforced composites find extensive applications across various sectors, including furniture, automotive, and aerospace. However, the smooth surfaces of the fibers adversely impact the reinforcement effect. Inspired by the multilayered microscale structure of peacock mantis shrimp chelipeds, this work presents an eco-friendly method to develop hierarchical functionalized kenaf fibers (KF) for reinforcing soybean meal (SM) adhesive. Specifically, ZnO was deposited onto the KF surface to impart micro-nano roughness, thereby enhancing their mechanical interlocking effect with the SM matrix. Bio-based lipoic acid (LA) and limonene (LIM) were employed to create a highly reactive layer on the fiber surface, facilitating the formation of multiple chemical crosslinking structures with the SM matrix. The synergistic mechanical and chemical effects between KF and SM endowed adhesive with improved performance. The wet shear strength of the three-layer plywood prepared with the synthetic adhesive was remarkably increased by 450 % to 1.21 MPa. Additionally, the combined anti-mold effects of ZnO, LA, LIM, and triglyceride amine (TGA) extend the adhesive's storage time to 7 days. This sustainable and eco-friendly design of multilayered bionically functionalized KF offers an efficient approach for the high-value utilization of agroforestry residues, presenting broad application prospects in SM-based adhesives.

High Refractive Index, Low Birefringence Holographic Materials via the Homopolymerization of 1,2-Dithiolanes

High refractive index, low birefringence photopolymers were created via the radical-mediated, ring opening homopolymerization of 1,2-dithiolane functionalized monomers and were subsequently evaluated as holographic recording media. This investigation systematically characterized the reaction kinetics, thermodynamics, and volume shrinkage of the 1,2-dithiolane homopolymerization as well as the optical transparency, refractive index, birefringence, and holographic performance of multifunctional 1,2-dithiolane functionalized monomers and their resultant polymers. Real-time kinetic and thermodynamic analyses of a monofunctional 1,2-dithiolane monomer, lipoic acid methyl ester (LipOMe), indicated rapid monomer conversion, exceeding 90% in 60 s, with an overall enthalpy of reaction of 18 ± 1 kJ/mol. The ring-opening polymerization resulted in low shrinkage (10.6 ± 0.3 cm3/mol dithiolane) and a significant bulk refractive index increase (0.030 ± 0.003). The resulting photopolymers exhibited high optical transparency, minimal haze, and negligible birefringence, suggesting the potential of 1,2-homopolymers as optical materials. To further explore the specific capabilities for use as high-performance holographic recording applications, several multifunctional monomers were synthesized with the ethanedithiol lipoic acid monomer (EDT-Lip2) selected for experimentation. Holographic diffraction gratings written using this monomer achieved a peak-to-mean refractive index modulation of 0.008 with minimal haze and birefringence.

Recyclable surgical, consumer, and industrial adhesives of poly(α-lipoic acid)

Polymer adhesives play an important role in many medical, consumer, and industrial products. Polymers of α-lipoic acid (αLA) have the potential to fulfill the need for versatile and environmentally friendly adhesives, but their performance is plagued by spontaneous depolymerization. We report a family of stabilized αLA polymer adhesives that can be tailored for a variety of medical or nonmedical uses and sustainably sourced and recycled in a closed-loop manner. Minor changes in monomer composition afforded a pressure-sensitive adhesive that functions well in dry and wet conditions, as well as a structural adhesive with strength equivalent to that of conventional epoxies. αLA surgical superglue successfully sealed murine amniotic sac ruptures, increasing fetal survival from 0 to 100%.

Sustainable polymers that stick inside and out

A naturally occurring fatty acid yields a set of adhesives with different properties.

Improvement in Cohesive Properties of Adhesion Systems Using Movable Cross-Linked Materials with Stress Relaxation Properties

A strong, tough, and stable adhesion system used in various environments must be developed. A long-lasting adhesion system should effectively perform in the following five aspects: adhesion strength, toughness, energy dissipation property, self-restoration property, and creep resistance property. However, these properties are difficult to balance using conventional adhesives. Here, a new topological adhesion system using single-movable cross-network (SC) materials [SC(DMAAm) Adh] was designed. 3-(Trimethoxysilyl) propyl acrylate was used as the anchor, N,N-dimethyl acrylamide (DMAAm) was used as the main chain monomer, and γ-cyclodextrin (γ-CD) units acted as movable cross-links. The movable cross-links provided SC(DMAAm) Adh with energy dissipation properties, thereby improving its toughness. The γ-CD units also acted as bulky stoppers that provided a high adhesion strength and self-restoration properties. Moreover, the combination of the movable cross-links and bulky stoppers provided creep resistance to SC(DMAAm) Adh. The performance of the adhesion systems under different mobilities of the polymer chains was examined by adjusting the water content. In proper water-containing states, all mechanical properties of SC(DMAAm) Adh were better than those of the adhesion systems using homopolymers [P(DMAAm) Adh] and polymers with covalent cross-linking points [CP(DMAAm) Adh].

α-Lipoic acid improves mitochondrial biogenesis and dynamics by enhancing antioxidant and inhibiting Wnt/Ca2+ pathway to relieve fluoride-induced hepatotoxic injury

Fluoride (F), widely present in water and food, poses a serious threat to liver health, and oxidative damage and mitochondrial damage are its main causes. As a natural mitochondrial protector and antioxidant, α-lipoic acid (ALA)'s alleviating effect on fluorosis liver injury and its underlying mechanism are still unclear. Therefore, this study established a fluorosis ALA intervention mice model to explore the mechanism of mitochondrial biogenesis, mitochondrial dynamics, and Wnt/Ca2+ pathway in ALA attenuating fluorosis liver injury. The results showed that ALA mitigated F-induced weight loss, hepatic structural and functional damage, hepatocytes mitochondrial damage, and decreased antioxidant levels. However, ALA did not reduce F accumulation in the femur. Further mRNA and protein detection results showed that F increased the expression levels of key genes in the mitochondrial fission (Drp1, Mff, and Fis1), mitophagy (Parkin, Pink1, and Prdx3), Wnt/Ca2+ pathway (Wnt5a and CaMK2), and rised the number and intensity of fluorescent spots of Drp1, but decreased the expression levels of key genes in the mitochondrial biogenesis (Sirt1, Sirt3, and PGC-1α) and fusion (OPA1, Mfn2, and Mfn1), and reduced the number and intensity of fluorescent spots of PGC-1α in the liver. However, the intervention of ALA relieved the F-induced changes in the expressions of the above genes. In conclusion, ALA mitigated F-induced hepatic injury through enhancing antioxidant capacity and inhibiting Wnt/Ca2+ pathway to improve mitochondrial biogenesis and dynamics disturbance. This study further reveals the hepatotoxic mechanism of F and the protective mechanism of ALA, and provides a theoretical basis for ALA as a potential preventive and palliative agent for F-induced hepatotoxic injury.

Micromechanics and damage in slide-ring networks

We explore the mechanics and damage of slide-ring gels by developing a discrete model for the mechanics of chain-ring polymer systems that accounts for both crosslink motion and internal chain sliding. The proposed framework utilizes an extendable Langevin chain model to describe the constitutive behavior of polymer chains undergoing large deformation and includes a rupture criterion to innately capture damage. Similarly, crosslinked rings are described as large molecules that also store enthalpic energy during deformation and thus have their own rupture criterion. Using this formalism, we show that the realized mode of damage in a slide-ring unit is a function of the loading rate, distribution of segments, and inclusion ratio (number of rings per chain). After analyzing an ensemble of representative units under different loading conditions, we find that failure is driven by damage to crosslinked rings at slow loading rates, but polymer chain scission at fast loading rates. Our results indicate that increasing the strength of the crosslinked rings may improve the toughness of the material.