Extended Data Fig. 6: Mechanical testing of PFPE-DMA films under various conditions.
From: 3D spatiotemporally scalable in vivo neural probes based on fluorinated elastomers
(a-e) Tensile testing of PFPE-DMA films. a, Stress-stretch curve in uniaxial tension to rupture. The data are from Fig. 2h. b, Stress-stretch curve in uniaxial tension, with a maximum stretch of 1.1 to determine the elastic modulus (strain rate of 0.2 s−1). c, Cyclic testing with a progressive increase in the maximum stretch. d, Cyclic testing with a progressive increase in strain rate to show the rate-dependency of the hysteresis. e, Pure shear test of two specimens with a pre-crack to determine fracture toughness. We estimate a fracture toughness of 128 and 261 J/m2 for each specimen. (f-k) Adhesion energy measurements between PFPE-DMA layers. (f, g) PFPE-DMA – PFPE-DMA adhesion energies measured with the 90° peel test for two samples (using a stainless-steel microwire mesh in (f) and a Nylon mesh in (g)) as a function of displacement. As the displacement first increases, the crack blunts but does not grow, and the force increases (thus the energy measured) until the crack starts to propagate. The plateau characterizes the adhesion energy. Higher peeling rates correspond to higher adhesion energy values, due to the viscoelasticity of PFPE-DMA. h, PFPE-DMA – glass adhesion energy is lower than PFPE-DMA - PFPE-DMA adhesion energy in (f, g). i, Schematic of the 90° peel test. A microwire mesh (stainless steel or Nylon) lays on top of the first layer of PFPE-DMA solvent cast and hard-baked on a glass slide. The second layer of PFPE-DMA, thicker than the microwire mesh, is solvent casted and hard-baked on top of the mesh. Polyimide tape prevents the adhesion of the microwire mesh to the bottom layer of PFPE-DMA on one side, to initiate the pre-crack. j, Photograph of a sample, tweezers show the side with the polyimide tape for the pre-crack. k, Photograph taken during the 90° peel test. l, Delamination-free large deformation of multilayer PFPE-DMA neural probes. Photograph of a 4-metal layer PFPE-DMA neural probe on a thick, stretchable H-SEBS substrate before, during, and after uniaxial stretching. m, Resistance of metal interconnects in PFPE-DMA neural probes before and after uniaxial stretch. Relative changes in the resistance of the metal interconnects before (n = 3 interconnects) and after (n = 3 interconnects) releasing the device from the fabrication substrate and applied 2% (n = 1 sample) and 5% (n = 1 sample) uniaxial stretch (value = mean ± S.D. when n > 1 samples). (n-t) SEM images of a multilayer soft neural probe after undergoing an accelerated aging test in 1x PBS at 65 °C for 10 days. SEM overview of the probe (n) with three FIB-cut positions labeled in green, orange, and red, corresponding to cross-sections along the interconnect direction at the interface of electrode and interconnect (o, r), (p, s) parallel to the interconnects, (q, t) perpendicular to the interconnects.
