Sustainable Bioinspired Fliers for Environmental Preservation

The aim of my research thesis is to develop biomimetic artificial fliers for environmental preservation applications. My research addresses some of the limitations of conventional Wireless Sensor Networks (WSN) in environmental monitoring, which include low sensor density and the generation of e-waste. A novel approach is proposed that uses Unmanned Aerial Vehicles (UAVs) to disperse self-deployable and ecofriendly sensors (i.e., made from renewable, biocompatible and biodegradable materials), inspired by flying seeds and fruits. Dispersal mechanisms of flying seeds are being researched as they constitute an efficient way of traveling by harnessing the wind. The flying structures evolved in these seeds, as wings or hairy bristles, are passive, since they don’t rely on metabolism, and have adapted to maximize drag to air. This feature is interesting for scientists and engineers who want to develop self-deployable sensors that can spread themselves over targeted areas. In my research work I focus on creating artificial fliers that mimic the aerodynamic properties of various plant seeds, such as Acer campestre, Ailanthus altissima, Tragopogon pratensis, Banksia Attenuata and Banksia prionotes. The choice of these biological models is due to their diverse flight mechanics, that derive from their different structures, leading to different dispersal distances. Through detailed biological analysis of natural fruits, that involves histology, morphology and aerodynamics, key parameters are extracted and applied to the design and fabrication of artificial fliers. For the fabrication, additive manufacturing, such as Fused Deposition Modeling (FDM) and Direct Ink Writing (DIW), is employed, and biocompatible or biodegradable materials such as polylactic acid (PLA), cellulose acetate (CA) and porous-cellulose acetate (p-CA), are used. Each artificial flier that is developed, is integrated with a fluorescent or colorimetric sensor, with the objective of monitoring chemical and physical parameters of top-soil, such as temperature, humidity, pH or nitrates. A flier, inspired to Acer seeds, is developed for temperature sensing and can be 3D printed in a single step, thanks to the embedding, in the polymeric matrix (PLA), of fluorescent particles sensitive to temperature. A porous-cellulose acetate is then developed and characterized in order to find a lightweight and biodegradable solution that serves as the structural material for the fabrication of fliers inspired to Ailanthus altissima and Tragopogon pratensis fruits. The resulting fliers are coupled with colorimetric sensors for humidity and for pH and nitrates, respectively. The Tragopogon-inspired flier is also tested as a carrier for mustard seed in order to explore aerial seeding applications. Finally, the morphology and hygroscopic behavior of winged Banksia seeds is studied with the perspective idea of developing an artificial robotic flier that could actuate with humidity. Interestingly, crystals are found on the seed coat of Banksia seeds. They are characterized and their function is explored with the aim of translating it into the artificial world. By combining a bioinspired approach, additive manufacturing, and sustainable materials, this work contributes to the development of energetically efficient and environmentally friendly solutions for environmental monitoring and preservation through the use of bioinspired sensing fliers.