Ion-Transfer Engineering via Janus Hydrogels Enables Ultrahigh Performance and Salt-Resistant Solar Desalination

Emerging solar interfacial evaporation offers the most promising response to the severe freshwater crisis. However, the most challenging bottleneck is the conflict between resisting salt accumulation and maintaining high evaporation performance since conventional salt-resistant evaporators enhance water flow to remove salt, leading to tremendous heat loss. Herein, an ion-transfer engineering is proposed via a Janus ion-selective hydrogel that enables ion-electromigration salt removal, breaking the historical dependence on water convection, and significantly lowering the heat loss. The hydrogels drive cations downward and anions upward, away from the evaporation surfaces. An electrical potential is thus established inside the evaporator and salt in 15 wt% brine is removed stably for seven days. A record-high evaporation rate of 6.86 kg m^-2  h^-1 in 15 wt% brine, 2.5 times the previously reported works, is achieved. With the from-scratch salt-resistant route, comprehensive water-thermal analysis, and record-high performance, this work holds great potential for the future salt-resistant evaporators.

Self-Pumping Janus Hydrogel with Aligned Channels for Accelerating Diabetic Wound Healing

Excessive exudate secreted from diabetic wounds often results in skin overhydration, severe infections, and secondary damage upon dressing changes. However, conventional wound dressings are difficult to synchronously realize the non-maceration of wound sites and rapid exudate transport due to their random porous structure. Herein, a self-pumping Janus hydrogel with aligned channels (JHA) composed of hydrophilic poly (ethylene glycol) diacrylate (PEGDA) hydrogel layer and hydrophobic polyurethane (PU)/graphene oxide (GO)/polytetrafluoroethylene (PTFE) layer is designed to rapidly export exudate and accelerate diabetic wound healing. In the design, the ice-templating process endows the hydrophilic hydrogel layer with superior liquid transport ability and mechanical strength due to the formation of aligned channel structure. The hydrophobic layer with controlled thickness functions as an effective barrier to prevent exudate from wetting the skin surface. Experiments in diabetic rat model show that JHA can significantly promote re-epithelialization and collagen deposition, shorten the inflammation phase, and accelerate wound healing. This unique JHA dressing may have great potential for real-life usage in clinical patients.

Strain-sensitive alginate/polyvinyl alcohol composite hydrogels with Janus hierarchy and conductivity mediated by tannic acid

To construct conductive hydrogels with a conductive and a non- or weakly conductive layer for comfortable and safe electronic application, marine biobased anionic polysaccharide sodium alginate (SA) and neutral polyvinyl alcohol (PVA) were employed as the hydrogel matrixes. Tannic acid (TA) was exploited to mediate the demixing of the miscible aqueous solution of SA and PVA in view of the much larger interaction strength of TA with PVA than both of TA with SA and PVA with SA calculated from the density functional theory (-40.21, -29.77 and -21.00 kcal·mol^-1 respectively). The finally-fabricated alginate/PVA composite hydrogels not only possess a "Janus" hierarchy but manifest asymmetrical conductivity, i.e., one layer strongly conductive and another weakly conductive. The strongly conductive layer achieves a conductivity of more than 2.95 S·m^-1, facilitating their application in soft electronic areas like human-machine interfaces, smart wearable devices and soft robots. The weakly conductive layer with the conductivity less than 0.60 S·m^-1 and the thickness adjustable, constitutes a protective screen for another layer. The Janus hydrogels exhibit good mechanical performance, excellent strain-sensing performance and fatigue-resistant mechanics, conductivity and sensitivity.

Intelligent Paper-Free Sprayable Skin Mask Based on an In Situ Formed Janus Hydrogel of an Environmentally Friendly Polymer

Traditional skin care masks usually use a piece of paper to hold the aqueous essences, which are not environmentally friendly and not easy to use. While a paper-free mask is desired, it is faced with a dilemma of moisture holding and rapid release of encapsulated bioactive substances. Herein, a paper-free sprayable skin mask is designed from an intelligent material-a thermogel which undergoes sol-gel-suspension transitions upon heating-to solve this dilemma. A synthesized block copolymer of poly(ethylene glycol) and poly(lactide-co-glycolide) with appropriate ratios can be dissolved in water, and thus easily mixed with a biological substance. The mixture is sprayable. After spraying, a Janus film is formed in situ with a physical gel on the outside and a suspension on the inside facing skin. Thus, both moisture holding and rapid release are achieved. Such a thermogel composed of biodegradable amphiphilic block copolymers loaded with nicotinamide as a skin mask is verified to reduce pigmentation on a 3D pigmented reconstructed epidermis model and further in a clinical study. This work might be stimulating for investigations and applications of biodegradable and intelligent soft matter in the fields of drug delivery and regenerative medicine.