Smart materials for flexible electronics and devices: hydrogel

In recent years, flexible conductive materials have attracted considerable attention for their potential use in flexible energy storage devices, touch panels, sensors, memristors, and other applications. The outstanding flexibility, electricity, and tunable mechanical properties of hydrogels make them ideal conductive materials for flexible electronic devices. Various synthetic strategies have been developed to produce conductive and environmentally friendly hydrogels for high-performance flexible electronics. In this review, we discuss the state-of-the-art applications of hydrogels in flexible electronics, such as energy storage, touch panels, memristor devices, and sensors like temperature, gas, humidity, chemical, strain, and textile sensors, and the latest synthesis methods of hydrogels. Describe the process of fabricating sensors as well. Finally, we discussed the challenges and future research avenues for flexible and portable electronic devices based on hydrogels.

Rational Design of Intelligent and Multifunctional Dressing to Promote Acute/Chronic Wound Healing

Currently, the clinic's treatment of acute/chronic wounds is still unsatisfactory due to the lack of functional and appropriate wound dressings. Intelligent and multifunctional dressings are considered the most advanced wound treatment modalities. It is essential to design and develop wound dressings with required functions according to the wound microenvironment in the clinical treatment. This work summarizes microenvironment characteristics of various common wounds, such as acute wound, diabetic wound, burns wound, scalded wound, mucosal wound, and ulcers wound. Furthermore, the factors of transformation from acute wounds to chronic wounds were analyzed. Then we focused on summarizing how researchers fully and thoroughly combined the complex microenvironment with modern advanced technology to ensure the usability and value of the dressing, such as photothermal-sensitive dressings, microenvironment dressing (pH-sensitive dressings, ROS-sensitive dressings, and osmotic pressure dressings), hemostatic dressing, guiding tissue regeneration dressing, microneedle dressings, and 3D/4D printing dressings. Finally, the revolutionary development of wound dressings and how to transform the existing advanced functional dressings into clinical needs as soon as possible have carried out a reasonable and meaningful outlook.

Development of green and sustainable smart biochromic and therapeutic bandage using red cabbage (Brassica oleracea L. Var. capitata) extract encapsulated into alginate nanoparticles

Novel multifunctional wound dressing with the ability to protect, cure and sense the healing process, was developed. Red-cabbage extract has been reported to exhibit bioactive compounds with the ability to function as antioxidant, antiinflammatory, anticancer, antibacterial, antifungal, and antiviral agent, as well as a natural pH-sensory chromophoric material. An anthocyanin extract was prepared from Red-cabbage (Brassica oleracea L. Var. capitata). The anthocyanins extract was encapsulated into calcium alginate in the presence of potash alum mordant, which was then applied to the surface of the cotton gauze. Red-cabbage based anthocyanin chromophoric extract was encapsulated at different concentrations into alginate-based hydrogel and immobilized into cotton gauze to provide a smart therapeutic pH-responsive wound dress to function as an antimicrobial and biochromic matrix providing a comfortable dress sensor to monitor the wound status. Decreasing the pH of a wound mimic solution caused a blue shift from 579 to 437 nm. The anthocyanin spectroscopic probe's halochromic activity demonstrated a colorimetric change from purple to pink, which was critical to the dyed cotton diagnostic assay's biochromic performance. The colorimetric parameters of the prepared dressing sensor were proved by UV-Vis absorbance and CIE Lab coordinates. Both mechanical and morphological properties of the prepared dressing were studied using different analytical methods. The effect of anthocyanin concentration on the mechanical, water vapor permeability, water absorption and morphological properties of the wound dressing were investigated. No substantial flaws in air-permeability or bend length were detected after dyeing. The colored cotton gauze samples were tested for their high colorfastness. The cytotoxicity and antimicrobial activity of the prepared biochromic cotton gauze were explored. The dyed cotton samples exhibited no cytotoxicity and improved antimicrobial activity with increasing the anthocyanin ratio on cotton surface.

Photo-Cross-Linked Poly(ethylene glycol) Diacrylate Hydrogels: Spherical Microparticles to Bow Tie-Shaped Microfibers

Bow tie-shaped fibers and spherical microparticles with controlled dimensions and shapes were fabricated with poly(ethylene glycol) diacrylate hydrogel utilizing hydrodynamic shear principles and a photopolymerization strategy under a microfluidic regime. Decreasing the flow rate ratio between the core and sheath fluids from 25 (50:2) to 1.25 (100:80) resulted in increasing the particles size and reducing the production rate by 357 and 86%, respectively. The width of the fibers increased by a factor of 1.4 when the flow rate ratio was reduced from 2.5 to 1 due to the decrease of the shear force at the fluid/fluid interface. The stress at break and Young's modulus of the fibers were enhanced by 32 and 63%, respectively, when the sheath-to-core flow rate ratio decreased from 100:40 to 100:80. The fiber fabrication was simulated using the finite element method, and the numerical and experimental results were in agreement. Adult hippocampal stem/progenitor cells and bone-marrow-derived multipotent mesenchymal stromal cells were seeded onto the fibrous scaffolds in vitro, and cellular adhesion, proliferation, and differentiation were investigated. Microgrooves on the fibers' surface were shown to positively affect cell adhesion when compared to flat fibers and planar controls.