Crack-driven electrical response in stretchable electronics: an original multi-scale characterization

Emerging applications in electronics require devices capable of conforming to complex three-dimensional geometries, such as wearable systems. Stretchable electronics must remain functional under mechanical deformation. In this work, stretchable conductive inks with innovative formulation are proposed, using silver flakes as the conductive material and bio-based binders, namely hydroxypropylmethyl cellulose (HPMC) and TEMPOoxidized cellulose nanofibrils (CNFt). The choice of binder significantly influences the stretchability of the printed conductive tracks and the crack formation under strain. To investigate the initiation and evolution of microcracks over deformations, we employ an original experimental approach combining in-situ SEM tensile testing with direct observation of microstructural evolution. This technique provides key insights into the underlying mechanisms governing crack pattern formation under realistic loading conditions. The results show that HPMC promotes the formation of a limited number of large cracks, whereas CNFt leads to the formation of numerous thin cracks. Combining both binder materials enables control over crack formation (morphology and distribution). This is critical, as microstructural evolution under strain is the predominant factor governing the relative change in electrical resistance. Overall, this approach establishes a powerful methodology for linking microstructural evolution to functional electrical performance, thereby enabling the rational design of highly reliable stretchable conductive materials.