Conformal Mechanics of Serpentine Meshes for Millimeter-Scale Neural Probes

Abstract

The mechanical reliability of implantable neural probes depends on their ability to accommodate large deformations during implantation and chronic operation while limiting stress concentrations within conductive interconnects. Despite extensive studies of serpentine interconnects in stretchable electronics, their mechanics under loading conditions relevant to cylindrical neural probes remain poorly understood. This work investigates the mechanics of two stretchable neural interface architectures, Single Serpentine Traces and Interconnected Mesh networks, designed with gold (Au) interconnects encapsulated in polyimide (PI) and embedded within a soft elastomeric substrate. Finite element analysis and experiments are used to characterize their response under stretching, conformal wrapping onto cylindrical neural probes, and bending of the wrapped structure. Deformation in both architectures is accommodated primarily through bending and rotation of the serpentine segments, with localized metal yielding initiating at strains of approximately 5.5–8.25% depending on loading direction and topology. During conformal wrapping onto probes with radii as small as 0.4 mm, the Single Serpentine Traces architecture remains below the Au yield stress, reaching a maximum stress of 145 MPa, whereas the Interconnected Mesh develops localized yielding at interconnection junctions with peak stresses exceeding 215 MPa. Subsequent bending produces only modest stress amplification, although the Interconnected Mesh exhibits approximately twofold greater stress sensitivity than the Single Serpentine Traces. The results demonstrate that rotational compliance governs stress redistribution, while geometric constraints at interconnection junctions control failure initiation. These findings reveal a fundamental tradeoff between electrical connectivity and stress concentrations and provide mechanics guidelines for conformal neural probes and related stretchable bioelectronic systems.