(100μm, ID) to 98% (400μm, ID) with less than 10% impedance change in
average. Altogether, results show robustness of mesh electronics for
syringe-injection through a wide range of needle ID.
5.3.2 Parameters for Syringe Injectable Electronics
We believe this submicron thickness and mesh network design for electronics are
very critical to the success of injection. First, this design increases the
surface-to-volume ratio of electronics from 0.2μm−^1 (thinfilm electronics with 10-
μm thickness) to 3.25μm−^1 (mesh electronics with 5-μm-wide and 800-nm-thick
ribbon). Second, combining with the polyelectrolyte surface modifications, this
design reduces the effective density of electronics (due to the forming of electric
double layers) allowing electronics to be unfold andfloating in solution. Third, this
design increases the drag force from solution motion to mesh electronics enabling
effective injection. Finally, the mesh design reduce the effective bending stiffness of
electronics from 0.0602 nN m (thinfilm electronics) to 0.0025 nN m (mesh elec-
tronics) so that electronics can be readily folded to pass throughfine needles.
To further understand the structure design parameters for injection, we carried
out imaging experiments using confocalfluorescence imaging to 3D reconstruct the
structure of injectable electronics inside a glass needle. Glass tube was pulled into a
fluidic channel (Fig.5.10a), with the same geometry and inner diameter as the
metal and glass needle used for applications. The channel inner diameter is 200–
600 μm measured by confocalfluorescence imaging and the length is 0.1–0.5 mm.
We injected mesh electronics with different structures into channel. SU-8 in mesh
electronics was doped by Rodamine-6G for imaging and 3D reconstruction.
We call the ribbons along the injection direction as longitudinal ribbons and the
ribbons perpendicular to the injection direction as transverse ribbons. Longitudinal
and transverse ribbons together form mesh with a periodic unit cells structure. All the
Fig. 5.9 Yield of injection.aYield (blue) and impedance change (red) of electronics containing
metal electrode injected through different gauge needles inset: brightfield image of metal electrode
on mesh electronics.bYield (blue) and conductance change (red) of electronics containing
nanowirefield-effect transistor injected through different gauge needles. Solid spot: 5 mm wide
mesh, hollow spot: 2 mm wide mesh. Inset: brightfield image of nanowire FET (highlighted by
green arrows) on mesh electronics. Scale bar: 10lm
5.3 Results and Discussion 81