Cannabinoid-Based Bioplastic Conductive Composites for Circular-Lifecycle Medical Electrodes

Establishing bioplastics derived from renewable resources as an alternative to petrochemical-derived plastics is an emergent strategy for combating the effects of plastics on the environment. Current bioplastics exhibit uncertain biocompatibility and limited mechanical and processing characteristics. We prepare poly(cannabinoid)s by step growth polymerization of bifunctional carboxylic acids with hemp-derived cannabinoids containing two hydroxyl groups. The resulting thermoplastic poly(cannabinoid)s are the first of their kind to include cannabinoids directly in their polymeric backbone. Homopolymer and copolymer synthesis utilizing a wide variety of available cannabinoids and dicarboxylic acids enables a large range of mechanical properties, in turn promoting development of application-specific materials. Melt and solution processibility of poly(cannabinoid)s broadens fabrication capabilities. The observed natural anti-inflammatory and anti-oxidative behavior of poly(cannabinoid)s provides improved biocompatibility. Furthermore, the capability of poly(cannabinoid)s to degrade through base-catalyzed hydrolysis facilitates repolymerization and reprocessing of polymer composites.<br/>The healthcare industry, the second largest producer of waste globally, is a suitable gateway for this nascent materials platform. Medical waste is increasing due to the proliferation of single-use devices such as electrocardiogram (ECG) electrodes that are commonly employed for patient monitoring. We fabricate electrodes composed of tungsten particles, a biodegradable and biocompatible metal, dispersed in a homopolymer of poly(cannabinoid)s. Adhesives are prepared from poly(cannabinoid) copolymers with low glass transition temperature. Fabrication is performed using direct-ink-write printing. Ink rheology is optimized using solvents such as di(propylene glycol) methyl ether that have minimal impact on the biosphere compared to other organic solvents. Electrodes exhibiting a volume resistivity of 0.2 ohm-meters are demonstrated functionally using ECG acquisition techniques.<br/>Poly(cannabinoid)s enable chemical recycling of the electrodes after use. Ester linkages in poly(cannabinoid)s provide a path for facile depolymerization via base-catalyzed hydrolysis. Exposure of electrodes to dilute ammonium hydroxide at 80 degrees Celsius yields cannabinoid monomers, dicarboxylic acids, and tungsten. Concurrently, exposure of tungsten to ammonium hydroxide results in selective etching of surface oxide layers, increasing interparticle electrical conductivity resulting in low volume resistivity of new composites. After hydrolysis, components can be easily separated because the high density of tungsten facilitates centrifugation, whereas the hydrophobicity of the cannabinoids and hydrophilicity of the diacids facilitate chemical separation. To assess the lifecycle of materials post-recycling, we repolymerize poly(cannabinoid)s using reclaimed cannabinoids and carboxylic acids and form composites with recycled tungsten particles to show that functional medical electrodes can be reformed. This chemically-driven circular process ensures the preparation of electrodes that meet the required properties for medical devices, including high reproducibility and high materials purity.