Sylard 184

All commercial reagents were obtained from Aldrich Chemical Co. and used without further purification unless otherwise specified. Hard PDMS components: (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer (VDT-731), platinum-divinyltetramethyldisiloxane (SIP6831.2), 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (SIT7900.0), and (25-30% methylhydrosiloxane)-dimethylsiloxane copolymer (HMS-301) were purchased from Gelest. The soft PDMS elastomer kit (Sylard 184) was ordered from Dow corning. The alkanethiol solution was prepared by dissolving 1-octadecylthiol in ethanol to obtain a concentration of 5mM. The amine backfilling solution was prepared by dissolving 10 mg ml⁻¹ 3,6-diaminoacridine hydrochloride in a mixture of ethanol and diacetone alcohol and then immediately filtered through 0.22 μm syringe filters before use.

Fiber implants were fabricated with four different materials: stainless steel (steel), silica, polycarbonate (PC), and HydroMed D4 (hydrogel) (Figure 2). All fiber implants were manufactured to a similar diameter in the range of 400 ± 30 μm. The steel implants were obtained by purchasing microwires from Goodfellow FF215135 (Huntingdon, UK), and the silica implants were obtained by stripping the cladding from commercial silica-core optical fibers (FT400UMT, Thorlabs, Newton, NJ, USA). For the PC implant preparation, after degassing at 80 °C for 2 weeks, 10-mm-thick rods were thermally drawn into a fiber using a custom-built fiber drawing tower at a drawing temperature of 150–160 °C. HydroMed D4, an ether-based polyurethane hydrogel (AdvanSource Biomaterials Corp., Wilmington, MA, USA), was selected for its thermoplasticity, as it ensures the stable manufacturing of the hydrogel fibers. The preform was prepared by solvent casting the Hydromed D4 into a thin sheet and then rolling it into a 10-mm-thick rod. Preforms were then drawn using the same custom tower at drawing temperatures of 80–90 °C. To eliminate the effect of surface properties including the mechanical friction and chemical adhesion, all implants were dip-coated with polydimethylsiloxane (PDMS, Sylard 184, Dow Corning Midland, MI, USA). The base and curing agents of the PDMS were mixed to a 10:1 ratio.

A mixture of polydimethyl-siloxane elastomer (PDMS, Sylard 184, Dow Corning) and curing agent at ratio of 10:1 were prepared to make the microfluidic channels. The elastomer mixture was poured onto a SU-8 patterned silicon wafer (SU-8 photoresist, Microchem) and baked in an oven at 65 °C for 1 hour in order to mold the PDMS channels. The channels were then placed onto PDMS-coated glass slides, where the PDMS layer is partially cured at 65 °C for 20 minutes. The assembled channels were then baked for another 1 hour for full cure of the PDMS channels and the coated layers.