  The sense of touch is fundamental to how we interact with the physical and
digital world. Conventional interactive surfaces and tactile interfaces use
electronic sensors embedded into objects, however this approach poses serious
challenges both for environmental sustainability and a future of truly
ubiquitous interaction systems where information is encoded into everyday
objects. In this work, we present Biodegradable Interactive Materials:
backyard-compostable interactive interfaces that leverage information encoded
in material properties. Inspired by natural systems, we propose an architecture
that programmatically encodes multidimensional information into materials
themselves and combines them with wearable devices that extend human senses to
perceive the embedded data. We combine unrefined biological matter from plants
and algae like chlorella with natural minerals like graphite and magnetite to
produce materials with varying electrical, magnetic, and surface properties. We
perform in-depth analysis using physics models, computational simulations, and
real-world experiments to characterize their information density and develop
decoding methods. Our passive, chip-less materials can robustly encode 12 bits
of information, equivalent to 4096 unique classes. We further develop wearable
device prototypes that can decode this information during touch interactions
using off-the-shelf sensors. We demonstrate sample applications such as
customized buttons, tactile maps, and interactive surfaces. We further
demonstrate the natural degradation of these interactive materials in degrade
outdoors within 21 days and perform a comparative environmental analysis of the
benefits of this approach.
