Dichlorodimethylsilane

2-Hydroxyethyl methacrylate (2-HEMA) was supplied by Merck (Darmstadt, Germany); ethylene glycol dimethacrylate (EGDMA), Dulbecco’s Modified Eagle’s Medium (DMEM) and dichlorodimethylsilane were from Sigma-Aldrich (Steinheim, Germany); N-(3-aminopropyl) methacrylamide hydrochloride (APMA) was from Polysciences Inc. (Warrington, PA, USA); D(+)-sucrose (99.7%) and 2,2′-azo-bis(isobutyronitrile) (AIBN) from Acros (Geel, Belgium). The Cy3 Ab Labeling Kit was supplied from Amersham/GE Healthcare (Munich, Germany). The AAV Titration ELISA was from Progen (Heidelberg, Germany) and the IGF-1 ELISA kit (Insuline like Growth Factor 1) from R&D Systems (Nordenstadt, Germany); the Beta-Glo^® Assay System was from Promega (Mannheim, Germany); the β-gal staining kit and cell proliferation reagent WST-1 were obtained from Roche Applied Science (Mannheim, Germany). Vectastain ABC HRP kit (Peroxidase, Standard) and Biotynilated Dolichos Biflorus Agglutinin (DBA) were from Vector Laboratories (Burlingame, CA, USA). The antibody anti-IGF-I (AF-291-NA) was from R&D Systems (Nordenstadt, Germany). Ultra-pure water (resistivity > 18.2 MΩ·cm) was obtained by reverse osmosis (MilliQ^®, Millipore Ibérica, Madrid, Spain) and water for cell culture was from Sigma-Aldrich (Steinheim, Germany). All other reagents were analytical grade.

For preparing polyacrylamide (PA) gel substrates, glass bottom dishes were sequentially treated with 3‐Aminopropyltrimethoxysilane (281 778, APTMS, Sigma‐Aldrich, MO, USA) for 10 min and 0.5% glutaraldehyde (G6257, Sigma‐Aldrich, MO, USA) for 30 min. The PA‐gel premixture was prepared using acrylamide (A8887, Sigma‐Aldrich, MO, USA) and N,N'‐methylene bisacrylamide (M7279, Sigma‐Aldrich, MO, USA) in a 1:1 ratio. Then, 0.05% ammonium persulfate (A3678, Sigma‐Aldrich, MO, USA) and 0.15% N,N,N´,N´‐tetramethylethylenediamine (T9281, Invitrogen, MA, USA) were added into the mixture. PA hydrogel stiffness was determined by concentrations of acrylamide and bisacrylamide.^[81
] The mixed PA solution was incubated in pre‐treated glass bottom dishes and covered with a dichlorodimethylsilane (Sigma‐Aldrich, MO, USA)‐treated glass coverslip to flatten the gel. After polymerization, the coverslip was removed from the PA gel. For functionalization of the PA hydrogel surface, 50 mm sulfosuccinimidyl‐6‐(4′‐azido‐2′‐nitrophenylamino) hexanoate (22 589, sulfo‐SANPAH, Thermo Fisher Scientific, MA, USA), a heterobifunctional cross‐linker, was supplemented on the PA hydrogel and exposed to UV light for 5 min. After washing in 200 mm HEPES, the PA hydrogel was coated with 50 µg ml⁻¹ FN and left overnight. Experiments were performed after washing with PBS before use.

Negative photoresist SU-8 3035 and the corresponding developer mr-dev 600 were acquired from Microchem and used as received. PDMS in the form of Sylgard 184 (base and crosslinking curing agent) was obtained from Dow Corning and was mixed in the ratio 10:1 before use. Pyrrole was purchased from Sigma-Aldrich and was distilled and stored at −20 °C before use. Sodium dodecylbenzenesulfonate (NaDBS) and dichlorodimethylsilane were acquired from Sigma-Aldrich and used as received. As a substrate for the SU-8 design template in photolithography, standard 4-in. silicon wafers were used. The reference electrode (model RE-5B) used for electropolymerization and electrical characterizations was purchased from BASi.