Emerging Patterns in Soft Materials from Geometric Confinement

Geometric confinement of soft materials has a significant impact on how they behave and organize.  Different from a sphere, a toroidal confinement is characterized by having a handle and a varying curvature. I will describe a recently developed templating method that enables rapid generation of stable 3D/toroidal confinements. I will discuss the effect of geometry and topology on the structure of several out-of-equilibrium systems. Biofilms of B. subtilis bacteria, when confined in toroidal droplets, grow on both the inner saddle and the outer regions. Compared to biofilms growing on a flat substrate, the relative coverage is an order of magnitude higher and the biofilm roughness almost doubled. Biofilm architecture is also quantitatively distinctive. The final biofilm structure demonstrate a heavy dependency on geometry-dependent oxygen accessibility. The templating method also allow us to generate soft solid structures like toroidal hydrogels. Thermo-responsive toroidal hydrogel swell and deswell isotropically via uniform shrinkage in all dimensions in the quasistatic case. In contrast, non-quasistatic shrinkage leads to mechanical instabilities and shape changes. Finally, I will discuss some experimental results on the organization and proliferation pattern of tissue cells on curved toroidal surfaces.