A direct fabrication method capable of producing fully-reversible, tunable nanochannel arrays, without the use of a molding step, is described. It is based on tunnel cracking of a readily-prepared brittle layer constrained between elastomeric substrates. The resulting nanochannels have adjustable cross-sections that can be reversibly opened, closed, widened and narrowed merely by applying and removing tensile strains to the substrate. This permits reversible trapping and release of nanoparticles, and easy priming or unclogging of the nanochannels for user-friendly and robust operations. The ease of fabrication and operation required to open and close the nanochannels is superior to previous approaches.

It is well established that the mechanical environment influences cell functions in health and disease. Here, we address how the mechanical environment influences tumor growth, in particular, the shape of solid tumors. In an in vitro tumor model, which isolates mechanical interactions between cancer tumor cells and a hydrogel, we find that tumors grow as ellipsoids, resembling the same, oft-reported observation of in vivo tumors. Specifically, an oblate ellipsoidal tumor shape robustly occurs when the tumors grow in hydrogels that are stiffer than the tumors, but when they grow in more compliant hydrogels they remain closer to spherical in shape. Using large scale, nonlinear elasticity computations we show that the oblate ellipsoidal shape minimizes the elastic free energy of the tumor-hydrogel system. Having eliminated a number of other candidate explanations, we hypothesize that minimization of the elastic free energy is the reason for predominance of the experimentally observed ellipsoidal shape. This result may hold significance for explaining the shape progression of early solid tumors in vivo and is an important step in understanding the processes underlying solid tumor growth.