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Softness plays a key role in the deformation of soft elastic substrates at the three-phase contact line, and the acting forces lead to the formation of a wetting ridge due to elastocapillarity. The change in wetting ridge and surface profiles at different softness has a great impact on the droplet behavior in different phenomena. Commonly used materials to study soft wetting are swollen polymeric gels or polymer brushes. These materials offer no possibility to change the softness on demand. Therefore, adjustable surfaces with tunable softness are highly sought-after to achieve on-demand transition between wetting states on soft surfaces. Here, we present a photorheological physical soft gel with adjustable stiffness based on the spiropyran photoswitch that shows the formation of wetting ridges upon droplet deposition. The presented photoswitchable gels allow the creation of reversibly switchable softness patterns with microscale resolution using UV light-switching of the spiropyran molecule. Gels with varying softness are analyzed, showing a decrease in the wetting ridge height at higher gel stiffness. Furthermore, wetting ridges before and after photoswitching are visualized using confocal microscopy, showing the transition in the wetting properties from soft wetting to liquid/liquid wetting.

Elastomeric materials, most prominently polydimethylsiloxane, are of great importance for microfluidic systems. Unfortunately, most elastomeric materials used in these systems so far show poor chemical resistance. Fluorinated elastomers are promising for chemistry-on-chip applications performed on these microfluidic systems, but challenging to shape on the microscale and difficult to bond which is a required step for the fabrication of embedded chips. In this work, a custom-synthesized fluorinated photocurable resin which can be structured using vat photopolymerization 3D printers, and shows a high elasticity combined with a remarkable chemical resistance was demonstrated. The material provides excellent stretchability, with a linear deformation capability of 523% and remains stretchable even after being soaked in tetrahydrofuran for 24 h. By using multi-material printing microfluidic chips with bonded hard and soft segments of different fluorinated resins were fabricated. Also, a variety of chemically resistant microfluidic components including pneumatic valves and peristaltic pumps were proven feasible. This novel fluorine-containing resin is expected to initiate further advancements of chemistry-on-chip application.

Polymeric shape-memory elastomers can recover to a permeant shape from any programmed deformation under external stimuli. They are mostly cross-linked polymeric materials and can be shaped by three-dimensional (3D) printing. However, 3D printed shape-memory polymers so far only exhibit elasticity above their transition temperature, which results in their programmed shape being inelastic or brittle at lower temperatures. To date, 3D printed shape-memory elastomers with elasticity both below and above their transition temperature remain an elusive goal, which limits the application of shape-memory materials as elastic materials at low temperatures. In this paper, we printed, for the first time, a custom-developed shape-memory elastomer based on polyethylene glycol using digital light processing, which possesses elasticity and stretchability in a wide temperature range, below and above the transition temperature. Young’s modulus in these two states can vary significantly, with a difference of up to 2 orders of magnitude. This marked difference in Young’s modulus imparts excellent shape-memory properties to the material. The difference in Young’s modulus at different temperatures allows for the programming of the pneumatic actuators by heating and softening specific areas. Consequently, a single actuator can exhibit distinct movement modes based on the programming process it undergoes.