poly-D-lysine aqueous solution for 2–12 h at 25 °C for surface modification. After
surface modification, electronics was transferred into PBS buffer solution for future
use.
Glass needle andfluidic channel preparation: Glass needle was prepared by
using a conventional pipette puller and glass tube following the parameters: Heat:
Ramp + 25, Pull: 0, Velocity: 140, Time: 100 and Pressure: 200. For a clean-cut
needle with inner diameter from 20 to 200μm, a ceramic tile was used to score the
glass tip checked by optical microscope with subsequent mechanical break.
For the channels used for imaging, the pulling was halted and suspended in the
middle to not completely break the glass tube. The channel size was measured by
confocalfluorescence imaging. Rodamine-6G solution wasfilled into the channel
for imaging. For a channel inner diameter smaller than 300μm, epoxy glue was
used to increase stability of channel preventing channel broken during imaging.
Injection by metal gauge needles: After surface modification, mesh electronics
was transferred into syringe with metal gauge needle by a glass. It is very important
to keep the orientation and unfolded structure of the electronics in the syringe to
prevent any buckles, and allow electronics to be loaded into the needle from its tip
region.
Injection by glass needle: To better control the injection through a small glass
needle, a microinjector and a patch-clamp set-up were used to control the injection
process. Mesh electronics was directly loaded into the glass needle illustrated by
Fig.5.3as following: (1) A plastic tube was connected from the tip end of glass
needle to a syringe. (2) Mesh electronics was drawn in into the rear part of glass
needle. It is very important to load the electronics from its sharp tip to facilitate the
folding of electronics in the glass tube and keep an extended structure to prevent
buckles. (3) The plastic tube was removed from glass needle and the needle was
mounted onto patch-clamp set-up and connected to micro-injector or syringe for
injection.
Injection of mesh electronics in cavity: PDMS pre-polymer components were
prepared in a 10:1 weight ratio atfirst, and diluted by hexane in a 1:3 (PDMS:
hexane) volume ratio. The cavity for injection was formed by two pieces of cured
PDMS. Mesh electronics was transferred from water to ethanol, dissolved in
PDMS/hexane solution and then loaded into glass syringe with a 18 gauge metal
needle. The sensor region of mesh electronics was injected into the cavity and the I/
O region was ejected outside the cavity on a silicon or glass side. Hexane was used
to wash away PDMS residues to unfold I/O region. The interconnect part of mesh
electronics from the PDMS to the substrate wasfixed by Kwik-Sil silicone elas-
tomers to avoid damage during the drying process. Finally, the hybrid structure of
PDMS and electronics was cured at room temperature for 48 h.
Injection of mesh electronics in MatrigelTM: Poly-D-lysine modified mesh
electronics was transferred into PBS solution and then into the NeurobasalTM
medium. Electronics was loaded into metal syringe needle as described above.
MatrigelTMwas diluted into 30% (v/v) with neuron culture medium and poly-
merized at 37 °C. Electronics was injected into polymerized Matrigel. The hybrid
5.2 Experimental 69