Vdt 731

To prepare the hPDMS mixture we used 3.4 g of VDT-731 (Gelest, Inc., Cat# VDT-731), 18 μL of Pt catalyst (Platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane complex solution) (Sigma-Aldrich, Cat# 479543), and one drop of cross-linking modulator 2,4,6,8-Tetramethyl-2,4,6,8 -tetravinylcyclotetrasiloxane (Sigma-Aldrich, Cat# 396281). All components were thoroughly mixed in a 50 mL conical bottom centrifuge tube on the vortex mixer for at least 30 sec. Before use, we added 1 g of HMS-301 (Gelest, Inc., Cat# HMS-301) to the mixture, promptly mixed it for 30 sec on a vortex mixer, degassed in a high-speed centrifuge (3 minutes, 3000 rpm), and immediately used it for the mold coating. The detailed protocol is described elsewhere (74 , 76 ).

To observe the surface deformation of PCEs on exposure to H₂ via SEM, we have to duplicate the surface morphology via hard PDMS molding because the surface recovers to its original state in a short period after the removal of H₂. First, a PCE was placed in a homemade flow cell with 4% H₂ ventilation maintained for 3 h to increase its dehydrogenation time. To prepare hard PDMS, 3.4 g of (7–8% vinylmethylsiloxane)–(dimethylsiloxane) copolymer (VDT-731, Gelest, USA), 100 mg of 1,3,5,7-tetramethylcyclotetrasiloxane (SIT7900.0, Gelest, USA), and 50 mg of platinum divinyltetramethyldisiloxane (SIP6831.1, Gelest, USA) were mixed and degassed for 5 min. One gram of copolymer (HMS-301, Gelest, USA) (25–30% methylhydrosiloxane)–(dimethylsiloxane) was then added into the above mixture and quickly stirred within 1 min. Immediately, the PCE was placed in the copy device (Supplementary Figure S10) with hard PDMS in the dropper. After saturation of the hydrogenation of the PCE (within 1 min), the hard PDMS was dropped on the PCE, with H₂ kept on until the hard PDMS was solidified (within 30 min). Finally, the hard PDMS was peeled from the surface of the PCE. A duplication of the surface morphology of the PCE in a fully hydrogenated state was obtained.

ZrO₂ nanocomposites were prepared from a solution with 30 wt% 10 nm ZrO₂ NPs dispersed in MIBK, which were purchased from Ditto Technology (DT-ZROSOL-30MIBK (N10)). Dipentaerythritol penta-/hexa-acrylate and 1-hydroxycyclohexyl phenyl ketone were purchased from Sigma‒Aldrich and used as a monomer and a photoinitiator, respectively. MIBK, MEK, and acetone were purchased from Duksan General Science. h-PDMS, a vinylmethyl copolymer (VDT-731), a platinum catalyst (SIP6831.2), and a siloxane-based silane reducing agent (HMS-301) were purchased from Gelest. 2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane and toluene, which were used as a modulator and a solvent, were purchased from Sigma‒Aldrich and Samchun Chemicals, respectively. PDMS, a silicone elastomer base, and a silicone elastomer curing agent were purchased from Dow Corning (SYLGARD™ 184 Silicone Elastomer Kit). The trichloro(1H,1H,2H,2H-perfluorooctyl)silane used for hydrophobic coating was purchased from Sigma‒Aldrich. toluene and n-hexane were purchased from Samchun Chemicals.

The reagents were used as received without further purification unless otherwise specified. Spin-on-glass (SOG) 315F was purchased from Filmtronics and was filtered twice sequentially using 0.22 μm (Millipore) and 0.02 μm (Whatman Anotop 10) syringe filters immediately before use in order to remove nanoparticles in the SOG sol formed by hydrolysis [26 (link)]. Polydimethylsiloxane (soft PDMS; Sylgard 184, Dow corning) was prepared in a 10:1 ratio of PDMS base with curing agent. Hard PDMS components, poly(25–30% methylhydrosiloxane)-(dimethylsiloxane) (HMS-301), poly(7–8% vinylmethylsiloxane)-(dimethylsiloxane), (VDT-731), platinum divinyltetramethyldisiloxane (SIP6831.1) and (1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) (7900), were purchased from Gelest. Polyethylene glycol (PEG, M_W = 10,000 g/mol) and benzenethiol (BT) (99.99 %) were purchased from Aldrich. 100% ethyl alcohol (Decon) was used to solvate benzenethiol. Ultrapure water (18.2 MΩ·cm) was generated using a Millipore Milli-Q Academic A-10 system and used to prepare the PEG buffer (0–5.6 wt %) solutions.

The master mold was treated with a vaporized silane coupling agent (Sigma Aldrich, Trichloro-1H, 1H, 2H, 2H-Perfluorooctyl-silane) to form a surface self-assembled monolayer (SAM) for 10 min at 140 °C to improve the demolding. The h-PDMS solution was prepared by mixing 1.7 g of vinylmethyl copolymers (Gelest, VDT-731), 9 μL of platinum-catalyst (Gelest, SIP6831.2), 0.05 g of the modulator (Sigma Aldrich, 2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane), 1 g of toluene, and 0.5 g of siloxane-based silane reducing agent (Gelest, HMS-301). The h-PDMS was spin-coated on the master mold at 2000 rpm for 60 s, and then baked at 80 °C for 2 h. A degassed mixture 10:1 weight ratio of a PDMS (Dow corning, Sylgard 184 A) and curing agent (Dow corning, Sylgard 184 B) was poured on the h-PDMS layer then baked at 80 °C for 3 h. The soft mold was demolded carefully from the master mold, then treated identically to a self-assembled monolayer (SAM) as reported above.

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.

Fabrication of elastic collagen nano- and micro-patterns is a challenging task due to the susceptibility of type-I collagen to undergo rapid gelation, and van-der-waals and capillary interactions between the nano-stamp and the printed surface that provoke a collapse of the soft PDMS nano-stamps onto the glass surface. To address these issues and achieve high precision micro- and nano-patterns on elastic platforms we (i) substituted regular PDMS nano-stamps with composite stamps, veneered with a submillimeter-thick hard PDMS (hPDMS) for non-collapsing high-definition printing surfaces (Schmid and Michel, 2000 ; Tabdanov et al., 2015 ), and (ii) substituted collagen with a-collagen-1 rabbit pAb (AbCam, Cambridge, UK), conjugated with biotin and a fluorescent tag, to ensure cross-linking of the antibody to PAA gels and for fluorescence visibility, respectively. For hPDMS we mixed 3.4g of VDT-731 (Gelest, Inc.), 18mL of Pt catalyst (Platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane complex solution) (Sigma-Aldrich) and one drop of cross-linking modulator (2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane) (Sigma-Aldrich). Next, immediately before use, we added 1g of HMS-301 (Gelest, Inc.) and thoroughly mixed it for 30sec on vortex mixer (Odom et al., 2002 ).