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Hydrogels are promising material for wound dressing and tissue engineering. However, owing to their low tissue adhesion in a moist environment and lack of flexibility, hydrogels are still not widely applied in movable parts, such as joints. Herein, we report a dual-crosslinked hydrogel adhesive using a dopamine-modified and acrylate-terminated crosslinker, tri(ethylene glycol) diacrylate-dopamine crosslinker (TDC). The covalent crosslinking was formed by photopolymerization between acrylic acid (AA) and TDC, and the noncovalent crosslinking was formed by intermolecular dopamine-dopamine and dopamine-AA interactions. Our resultant hydrogel demonstrated strong tissue adhesion in a moist environment (approximately 71 kPa) and high mechanical resilience (approximately 94%) with immediate recovery at a 200% strain rate. Moreover, it accelerated wound healing upon dressing the wound site properly. Our study provides the potential for advanced polymer synthesis by introducing a functional crosslinking agent.

Cross-linking is an essential element in enhancing polymers’ mechanical properties in adhesives, elastomers, and hydrogels. However, covalent cross-linking introduces a trade-off relationship betwe...

Materials that can switch adhesive properties based on external stimuli are required in several industries for temporary bonding or transfer processes. Previously studied materials achieve this under restricted conditions (hydration, heat, and long switching times), and some materials have limitations related to reuse because of irreversible reactions or residue formation on substrates. Herein, a rapid photoresponsive switchable pressure-sensitive adhesive (PSA) fabricated using an acrylic polymer and an aliphatic monomer containing azobenzene is reported. The adhesion force of the proposed PSA can be switched by photoisomerizing the azobenzene moiety. The process induces the transition of surface energy and modulus of the PSA. Ultraviolet and visible light irradiation can switch the probe tack force from 200 to 4 kPa within 15-30 s. Adhesion switching is possible in a state wherein the PSA remains adhered to a substrate. Mini-LEDs are selectively transferred from the carrier PSA to a polydimethylsiloxane substrate following the process of partial adhesion switching of the PSA. The novel and switchable PSA, which exhibits a selective and repeatable adhesion switching property and high switching ratio when stimulated by light stimuli, may be potentially used to realize the mini-LED or micro-LED transfer processes.

Unlike traditional adhesives with a fixed adhesive force, switchable adhesives, which have an adhesive force that can be adjusted by external stimuli, are specifically designed to be released according to user demand, or to enable the transfer of fine electronic devices. Previously developed switchable adhesives have limitations such as a slow switching rate, narrow adhesion modulation range, or the lack of reusability. Thus, we fabricated switchable pressure-sensitive adhesives (PSAs) that can overcome these limitations. The adhesive force of each switchable PSA, which comprises an azobenzene-containing acrylic polymer and low molecular weight compounds, was designed to be activated/deactivated via ultraviolet (UV) and visible light irradiation. The adhesive force and UV intensity required for the switch were found to be dependent on the aliphatic chain length of the compound. The adhesive force of the SP-C10, i.e., a switchable PSA containing a azobenzene compound with an aliphatic chain of 10 hydrocarbons, increased to 3.5 N from nearly zero in response to only 30 s of low-level (25 mW cm−2) UV irradiation. Additionally, SP-C10 did not lose its adhesive force even after 30 cycles of repeated adhesion switching. The mechanism of adhesion switching influenced by UV intensity and the structure of low molecular weight azobenzene compounds are also reported.

A polymer-ZnO colloidal solution was prepared as the organic-inorganic composite electron transport layer of inverted polymer solar cells (i-PSCs) by successive modification of ZnO particles with organic dispersant and polyethyleneimine (PEI), which offers an alternative to previously used complicated processes such as high temperature annealing or multi-layer coatings. The modification of ZnO surfaces with 2-(2-methoxyethoxy) acetic acid (MEA) provides colloidal stability and prevents aggregation of ZnO particles after adding PEI into the ZnO colloidal solution. The amount of incorporated PEI was increased to ~10 wt%, and the cell performance parameters of Jsc and fill factor (FF) were enhanced proportional to PEI content because of its contribution in decreasing the work function of ZnO ETL. By fabrication of i-PSCs with the modified ZnO ETL, the power conversion efficiency (PCE) was increased by ~40% from 5.10% to 7.51% in the ITO/ETL/PV-D4610:PC60BM/MoO3/Ag structure. The multi-functionalized ZnO ETL provides a more facile process for preparation of an organic-inorganic composite ETL to improve the performance of i-PSCs.