A sessile droplet can deform the surface of a soft solid not only with its weight. The surface tension pulls up a ridge at the perimeter of the drop, and the capillary pressure embosses a quasi-spherical dimple underneath the drop. This holds for the case of a bulk solid. However, if the solid forms a film with thickness comparable to the deformation scale the shape and the depth of the dimple are strongly distorted. We investigated dimples on elastomer films with a Young's modulus of 25 kPa and thickness in the range 4–104 µm embossed by sessile ionic liquid droplets. The films are supported by an undeformable glass slide. Below a certain critical film thickness, the dimple is shallower and the ridge at the drop rim is less elevated than for the bulk elastomer. The deviations are more pronounced for thinner films. Further, troughs form at the two sides of the ridge. Their distance from the rim is equivalent to the layer thickness. The measurements are qualitatively reproduced by an analytical model and quantitatively by numerical simulations. A consistent physical picture of the deformation on the bulk elastomer and of the distortions on the thin films is given.

Three-dimensional cell and organoid cultures rely on the mechanical support of viscoelastic matrices. However, commonly used matrix materials lack control over key cell-instructive properties. Here we report on fully synthetic hydrogels based on DNA libraries that self-assemble with ultrahigh-molecular-weight polymers, forming a dynamic DNA-crosslinked matrix (DyNAtrix). DyNAtrix enables computationally predictable and systematic control over its viscoelasticity, thermodynamic and kinetic parameters by changing DNA sequence information. Adjustable heat activation allows homogeneous embedding of mammalian cells. Intriguingly, stress-relaxation times can be tuned over four orders of magnitude, recapitulating mechanical characteristics of living tissues. DyNAtrix is self-healing, printable, exhibits high stability, cyto- and haemocompatibility, and controllable degradation. DyNAtrix-based cultures of human mesenchymal stromal cells, pluripotent stem cells, canine kidney cysts and human trophoblast organoids show high viability, proliferation and morphogenesis. DyNAtrix thus represents a programmable and versatile precision matrix for advanced approaches to biomechanics, biophysics and tissue engineering.