A flexible strain-responsive sensor fabricated from a biocompatible electronic ink via an additive-manufacturing process

Biosensor technologies are of great interest for applications in wearable electronics, soft robotics and implantable biomedical devices. To accelerate the adoption of electronics for chronic recording of physiological parameters in health and disease, there is a demand for biocompatible, conductive & flexible materials that can integrate with various tissues while remaining biologically inert. Conventional techniques used to fabricate biosensors, such as mask lithography and laser cutting, lack the versatility to produce easily customisable, micro-fabricated biosensors in an efficient, cost-effective manner. In this paper, we describe the development and characterisation of an electronic ink made from an environmentally sustainable copolymer - ω-pentadecalactone-co-ε-decalactone, (PDL) incorporating silver nanowires (AgNW), which are known for their antimicrobial and conductive properties. The composites were shown to possess a low percolation threshold (1% w/w of AgNW to PDL), achieve a low electrical resistance (320 ± 9 Ω/sq) and a high electrical capacitance (2.06 ± 0.06 µF/cm²). PDL nanocomposites were biocompatible, demonstrated in vitro through the promotion of neural adhesion and prevention of astrocyte activation. An optimised ink formulation was subsequently used to fabricate strain-responsive biosensors with high spatial resolution (sub – 100 µm) using a direct write additive manufacturing process. Using a customized in vitro set-up, the sensitivity of these biosensors to biologically-relevant strains was assessed under simulated physiological conditions for 21 days. Critically, these 3D printed biosensors have applications in chronic prophylactic monitoring of pressure changes within the body and related pathologies.