Fig 1.
Fabrication of polydimethylsiloxane (PDMS)/polyimide (PI) neural probe with embedded microchannel.
(a) Channels and probe shape patterned by 1 μm negative photoresist (-PR) and 5 μm positive photoresist (+PR), respectively, on silicon (Si). (b) 20/40 μm channel/probe shape dry etched in Si. (c) Photoresist was removed and trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane (FOTS) was coated on stamp. (d) and (e) 60 μm PDMS was coated on Si stamp and reversely imprinted on FOTS/methacryl oxypropylene trichlorosilane (MOPTS) coated Si and as channel plate. (f) 10 μm PI on poly(methyl methacrylate) (PMMA) coated glass with 1 μm PMMA coating as bonding layer. (g) PDMS channel plate was treated by O2 plasma and bonded to cover plate. (h) Probe shape was defined on cover plate by O2 plasma etching. (i) Released PDMS/PI neural probe with embedded microchannel.
Fig 2.
Stress distribution in neural probe based on finite element method simulation.
(a) Probe geometry. (b) Probe dimensions. (c) Stress distribution on 200 μm wide, 1 cm long, 60/15 μm thick PDMS/PI probe shank with 50 μm wide, 20 μm high embedded channels during buckling. (d) Experimental setup of fluidic pressure control in U-shaped channel. (e) Measured axial force due to displacement of PDMS/PI neural probe with 400 μm probe width and 12.5 μm channel width at 120 kPa fluidic pressure.
Table 1.
Comparison of controlling neural probes flexibility in terms of critical buckling force.
Fig 3.
Critical buckling force of PDMS neural probes at different fluidic pressure.
60 μm thick PDMS neural probes with (a) 200, (b) 300, and (c) 400 μm probe width. Critical buckling force of 60 μm thick PI neural probes with channel width of 12.5, 25, and 50 μm; and probe width of 200, 300, and 400 μm with (d) no pressure and (e) at 240 kPa fluidic pressure. Fluidic pressure at 0 kPa means channel is filled with air while the inlet and outlet were not sealed.
Fig 4.
Measured and simulated critical buckling force of neural probes with channels at different fluidic pressure.
Measured (solid line) and simulated (dash line) critical buckling force of 60/15 μm thick, 1cm long PDMS/PI neural probes with 12.5 μm wide embedded channels at different fluidic pressure for (a) 200, (b) 300, and (c) 400 μm wide probes.
Fig 5.
Measured critical buckling force of PDMS/PI neural probes.
Measured critical buckling force of 60/15 μm PDMS/PI neural probes at (a) different fluidic pressure and (b) different channel width at 120 kPa. (c) Critical buckling force for PI thickness of 10 and 15 μm and probe width of 200 μm and channel width of 12.5 μm.
Fig 6.
Measured axial force of neural probes in gel.
(a) Schematic diagram showing gel movement setup. (b) Measured axial force during insertion in 0.6% agarose gel for 60/15 μm thick PDMS/PI neural probes at different fluidic pressure.