Sustainable Cannabinoid-Derived Biopolymers for Biopotential Electrodes

M. Sotzing, J. Toribio, A. Pollock, G. Sotzing, A. Chortos
Purdue University,
United States

Keywords: biopolymer, sustainable, biodegradable, depolymerization, medical, green technology


An increasing use of plastics and an understanding of the harm that discarded plastics can cause to the environment and human health necessitates improved bio-derived and biodegradable polymers. Cannabinoids, a natural oil derived from hemp, provides numerous benefits to the environment throughout its lifecycle. During cultivation, hemp is capable of sequestering approximately 4x the CO2 than trees while improving topsoil quality. Hemp, specifically its fibers, has been used in a variety of industries such as paper making and construction. In contrast, cannabinoids have not been fully realized in such industries despite the unique properties that they possess. Cannabinoids have been polymerized to form plastics that possess many of these unique properties for a range of applications. Cannabinoids are a class of molecules that include several chemical structures, such as cannabidiol or cannabigerol, which can be condensation polymerized with dicarboxylic acids to form polycannabinoids. A large range of thermal and mechanical properties have been achieved with just a few cannabinoids, such as a glass transition ranging from -30 C to 160 C. In this work, cannabinoids present the capacity to infiltrate the one-time use medical biopotential monitoring market. This is achieved with a proof-of-concept electrocardiogram (ECG) electrode made entirely from sustainably source biopolymers and bioresorbable metals. A rigid plastic made from cannabidiol, exhibiting glass transition of ~30 C is used to formulate conductive 3D-printing inks when combined with bioresorbable metal microparticles. Biodegradable/bioresorbable particles are dispersed in a homopolymer polycannabinoid with a compatible green solvent, printed using direct-ink-write printing method, and cured at high temperature, yielding a composite with a volume resistivity of ~0.2 ohm-meters. A sustainable biomedical adhesive is also developed through a random copolymerization of low and high glass transition polycannabinoids exhibiting mechanical adhesion to the skin. ECG electrodes demonstrated similar performance to commercial silver chloride electrodes. Additionally, electrodes were tested in submersion ECG acquisition, a notable shortcoming of commercial hydrogel-based electrodes. Owing to the high hydrophobicity of polycannabinoids, ranging from 80 to 120 degree water contact angle, polycannabinoid ECG electrodes were able to perform stably for over an hour exhibiting lower baseline drift and higher Q-peak potential by the end of the testing period when compared to silver chloride electrodes. Ester linkages in polycannabinoids provide a path for facile depolymerization via base-catalyzed hydrolysis, which could provide significant value in comparison to one-time use electrodes. Exposure of electrodes to dilute ammonium hydroxide at elevated temperatures successfully depolymerized polycannabinoids, yielding monomers and metal additives. This capability could enable future repolymerization for a circular economy in the biomedical field without concerns of contamination.