Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The design and construction of transient electronic sensors face significant constraints, primarily due to the scarcity of degradable materials capable of meeting the criteria for safe degradation, adequate physicochemical properties, and compatibility with existing fabrication and processing methods. Materials-related challenges become particularly pronounced when direct contact between the electrically conductive component of the sensing element and the aqueous electrolyte medium is required for measurements,1 as is the case in the electrochemical determination of various (bio)chemical analytes. In such scenarios, conductive films based on biodegradable metals frequently dissolve in an insufficiently controlled manner,2 leading to compromised structural integrity and disruption of the measurement process. Here, we introduce highly conductive, flexible, and free-standing composite films comprised of polycaprolactone and molybdenum (PCL/Mo). These PCL/Mo films are well-suited for use in conductive lines, interconnects, and degradable electrodes within transient sensors. The films are fabricated using conventional solution processing techniques, commencing with a viscous ink formulation that includes PCL and fine Mo microparticles. The PCL/Mo films exhibit electrical conductivities of up to ~10 kS/m and maintain a flat impedance profile that resembles an ideal resistor at frequencies up to 100 kHz. Furthermore, they remain stable after undergoing hundreds of bending cycles. When tested in a simulated physiological medium in vitro, the PCL/Mo films degrade gradually due to Mo corrosion and PCL hydrolysis, while still retaining their electrical and mechanical properties for up to 2 months. The desired patterning of PCL/Mo films can be achieved through laser cutting or printing approaches. Additionally, patterned PCL/Mo films can be joined with flexible PCL films using biodegradable glue or thermal bonding to create fully biodegradable sensors. Therefore, PCL/Mo films are excellent candidates for the construction of impedance-based degradable sensors and reliable flexible interconnects in transient electronic devices, unlocking the opportunity to address challenging applications such as fully biodegradable electrochemical biosensors for point-of-care testing or implantable transient devices for healthcare monitoring. As a proof-of-concept application of PCL/Mo films, we demonstrate a fully biodegradable impedimetric sensor for the detection of amylase, relying on monitoring the degradation of thin glycogen (polysaccharide) coatings.