Silicon wafer

Silicon wafers (size: 3 inch × 0.387 mm; roughness: 1 nm) (Sigma-Aldrich) and glass slides (size: 76 mm × 26 mm × 1 mm; roughness: <0.15 μm) (MiniMed) were cleaned sequentially with detergent, pure water, acetone, and isopropanol in an ultrasound bath for 15 min. Then, the slides were dried in a flow of nitrogen.

Mono-layer PS templates were prepared following previously described procedure.^{27,34,35 (link)} Silicon wafers (Sigma-Aldrich) were cut into square (∼1.5 × 1.5 cm²) and rectangular (∼1 × 3 cm²) pieces, and sonicated with ethanol. After washing several times with Milli-Q water (Millipore, resistivity of 18.2 MΩ cm⁻¹ at 25 °C) and drying at room temperature, the Silicon wafers were treated with UV/Ozone for 20 minutes to improve wafer hydrophilicity (UV/Ozone ProCleaner™ Plus, BioForce Nanosciences, Inc.). A Petri dish was filled with Milli-Q water, and the PS particle suspension (100 μl, 10 wt%, Bangs Labs) with diameters 280 nm, 210 nm or 99 nm was mixed with an equal amount of ethanol. This mixture was discharged slowly over the rectangular silicon wafer, which was placed in a Petri dish at a sloped plane to the Milli-Q water surface using a micropipette, and the rectangular wafer was then slowly submerged in the water. A sodium dodecyl sulphate (SDS) solution (2%, ∼10 μl) was added to the Petri dish in order to acquire hexagonal close-packed particles. The PS monolayers on the water layer were then lifted off by a square silicon wafer, and dried at room temperature.

Polydimethylsiloxane (PDMS) was obtained by mixing the elastomer base with the curing agent (SYLGARD® 184 silicone elastomer kit, Dow Corning) in a 1:10 weight ratio. The mixture was degassed under vacuum to remove trapped bubbles of air and cast on a custom made aluminum circular mold that hosted a silicon wafer (Sigma Aldrich) at the bottom. After casting, the mold was placed in a laboratory oven at 100°C for 45 minutes, to heat cure the degassed polymer mixture. The heat cured PDMS was removed from the mold and a microchannel ablated with a CO₂ laser (Universal Laser System, V460, 60W) operated with the software CorelDRAW X419. Printing settings were as follow: vector pen mode, power 10%, speed 10%, PPI 1,000. Three PDMS molds were created, each corresponding to a specific microchannel, a specific thin section and a specific flow experiment. The cross section of each channel was triangular (S3 Fig). A summary of the microchannels’ dimensions measured by optical microscopy is given in S1 Table.

Natural silk filaments were provided by Hangzhou Qiantang Silk Company Ltd, Zhejiang, China. The filaments were woven to obtain a 1/1 natural silk fabric. Sodium carbonate (Na₂CO₃) was purchased as a powder from Sinopharm Chemical Reagent Company Ltd, Shanghai, China. The natural silk fabric was degummed 3 times using a 0.05 wt.% Na₂CO₃ solution at 98°C to obtain the SF fabric. Phosphate-buffered saline (PBS) was purchased from the Solarbio Technology Company Ltd, Beijing, China. Alginate (ALG) was purchased as a powder from Sinopharm Chemical Reagent Company Ltd, Shanghai, China. The RSF solution was derived from Bombyx mori cocoons that were dissolved and dialysed (molecular weight cut off 2000) in distilled water for 48 h. Then, the RSF solution was dialysed against a 20 wt.% poly(ethylene glycol) solution (20000 g/mol) for 30 min. The polyelectrolytes were used as received without further purification and were prepared as 1 g/L solutions. silicon wafers were purchased from Ruicai Technology Company Ltd, Suzhou, China. (3-Aminopropyl) triethoxysilane (APTES) was used to form an amination surface on a silicon wafer purchased from Sigma-Aldrich. The chemical structures of the basic materials used to perform the experiments are shown in Fig 1.

Materials in all
synthesis procedures were used without any further purifications.
DA hydrochloride (CAS: 62-31-7, s, >98%), trizma base (CAS: 77-86-1,
s, >99%), hydrochloric acid (CAS: 7647-01-0, l, 25%), copper(II)
sulfate
pentahydrate (CAS: 7758-99-8, s, ≥98.0%), acetic acid (CAS:
64-19-7, l, ≥99%), sodium acetate (CAS: 127-09-3, s, ≥99%),
BA (CAS: 10043-35-3, s, ≥99.5%), sodium hydroxide (CAS: 1310-73-2,
s, ≥98%), and silicon wafer (Si 100, CAS: 7440-21-3, s) from
Sigma-Aldrich and ultrapure deionized water from a Hydrolab Ultra
UV system were used.