Printing and encapsulation of electrical conductors on polylactic acid (PLA) for sensing applications

This paper presents the printing of resistive and interdigitated (IDE) capacitive devices for temperature and humidity sensing applications, respectively, on biodegradable polylactic acid (PLA) substrates. Inkjet and gravure printing were evaluated to transfer silver-based nanoparticles inks. Flash photonic ink sintering methodologies were employed to maintain the PLA mechanical integrity due to its low glass transition temperature (58 °C). Between the two printing techniques investigated, gravure-printed devices on 200 μm-thick PLA sheets were shown to have better resolution and higher sensitivities to temperature and humidity (1100 ppmK-1 and 5.6 fF/%RH). Additionally, we demonstrated the inkjet printing of IDE onto thin (25 μm) dissolved-PLA spin-coated substrates, to enhance the mechanical flexibility and to reduce the response time to humidity (from 238 s to 70 s). Finally, a low temperature encapsulation is proposed by embedding the printed structures within PLA sheets.