Biodegradable electronics is a rapidly growing field, and the development of controllably biodegradable, high-conductivity materials suitable for additive manufacturing under ambient conditions remains a challenge. In this report, printable conductive pastes that employ poly­(lactic acid) (PLA) as a binder and tungsten as a conductor are demonstrated. These composite conductors can provide enhanced stability in applications where moisture may be present, such as environmental monitoring or agriculture. Post-processing the printed traces using a solvent-aging technique increases their conductivity by up to 2 orders of magnitude, with final conductivities approaching 5000 S/m. Such techniques could prove useful when thermal processes including heating or laser sintering are limited by the temperature constraints of typical biodegradable substrates. Both accelerated oxidative and hydrolytic degradation of the printed composite conductors are examined, and a fully biodegradable capacitive soil moisture sensor is fabricated and tested.

Efficient removal of CO2 from enclosed environments is a significant challenge, particularly in human space flight where strict restrictions on mass and volume are present. To address this issue, this study describes the use of a multimaterial, layer-by-layer, additive manufacturing technique to directly print a structured multifunctional composite for CO2 sorption with embedded, intrinsic, heating capability to facilitate thermal desorption, removing the need for an external heat source from the system. This multifunctional composite is coprinted from an ink formulation based on zeolite 13X, and an electrically conductive sorbent ink formulation, which includes metal particles blended with the zeolite. The composites are characterized using analytical and imaging tools and then tested for CO2 adsorption/desorption. The resistivity of the conductive sorbent is <2 mΩ m, providing a temperature increase up to 200 °C under 7 V applied bias, which is sufficient to trigger CO2 desorption. The CO2 adsorption capability of the conductive zeolite ink appears to be unaffected by the presence of the conductive particles, meaning a large fraction of the total mass of the structured composite device is functional.

Printed biodegradable electronics potentially enable the monitoring of various soil parameters at a high spatial density while minimizing cost and waste. A tunable degradable encapsulant is a critical component in a soil-degradable electronic device, as it acts to delay the ingress of water, microbes, and other agents responsible for degradation of underlying functional materials. Here, blends of beeswax and commercial soy wax are presented as tunable biodegradable encapsulant materials for transient soil sensors. Using differential scanning calorimetry, we first show that the blends of the two waxes have limited miscibility, which enables programming of degradation times. Laboratory degradation tests in soil revealed that the longevity of encapsulated devices can be controlled by the ratio of the component soy and beeswax, with up to 100 days with 100% beeswax and less than 10 days with the addition of 25% soy wax by mass. Thicker coatings of 1.6 mm of 10% soy wax in beeswax blends are shown to protect devices for 12 weeks. Additionally, melt-processed beeswax encapsulants are used as a simple method to delay the degradation of otherwise rapidly biodegradable materials, such as wooden stakes, that could be used to house soil-degradable electronic devices.