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Printable feedstocks that can produce lightweight, robust, and ductile structures with tunable and switchable conductivity are of considerable interest for numerous application spaces. Combining the specific properties of commodity thermoplastics with the unique electrical and redox properties of conducting polymers (CPs) presents new opportunities for the field of printed (bio)electronics. Here, we report on the direct ink write (DIW) printing of ink formulations based on polyaniline-dinonylnaphthalene sulfonic acid (PANI-DNNSA), which has been synthesized in bulk quantities (∼400 g). DNNSA imparts solubility to PANI up to 50 mg mL −1 , which allows the use of various additives to tune the rheological behavior of the inks without significantly compromising the electrical properties of the printed structures, which reach conductivities in the range of <10 −7 –10 0 S cm −1 as a function of ink formulation and post treatment used. Fumed silica (FS) and ultra-high molecular weight polystyrene (UHMW-PS) additives are leveraged to endow printability and shape retention to inks, as well as to compare the use of traditional rheological modifiers with commodity thermoplastics on CP feedstocks for tailored DIW printing. We show that the incorporation of UHMW-PS into these ink formulations is critical for obtaining high crack resistance in printed structures. This work serves as a guide for future ink designs of CPs with commodity thermoplastics and their subsequent DIW printing to yield conductive architectures and devices for various applications. 

Shape-changing objects are prized for applications ranging from acoustics to robotics. We report sub-millimetre bubbles that reversibly and rapidly change not only their shape but also their topological class, from sphere to torus, when subjected to a simple pressure treatment. Stabilized by a solid-like film of nanoscopic protein “particles”, the bubbles may persist in toroidal form for several days, most of them with the relative dimensions expected of Clifford tori. The ability to cross topological classes reversibly and quickly is enabled by the expulsion of protein from the strained surfaces in the form of submicron assemblies. Compared to structural modifications of liquid-filled vesicles, for example by slow changes in solution osmolality, the rapid inducement of shape changes in bubbles by application of pressure may hasten experimental investigations of surface mechanics, even as it suggests new routes to lightweight materials with high surface areas. 

While studies have shown that oral exams are a valuable method of assessment, their use has been limited due to concerns about scalability, examiner bias, and student anxiety. This paper presents preliminary results on incorporating oral exams into two large undergraduate engineering courses, examining the potential viability of these assessment strategies. This work was done when the courses were offered remotely due to COVID-19, but the results offer valuable insights that could carry over to in-person instruction as well.