Supplementary Material
Fabricating small-scale, curved, polymeric structures for biological applications using a combination of photocurable/ thermocurablepolydimethylsiloxane and phase interactions

Ting-YaChang1•Chun-Yen Sung1•MichinaoHashimoto2•Chao-Min Cheng3

1Institute of Nanoengineering and Microsystems, National TsingHua University, Hsinchu 30013, Taiwan.

2The pillar of Engineering Product Development, Singapore University of Technology and Design, 487372,Singapore.

3Institute of Biomedical Engineering, National TsingHua University, Hsinchu 30013, Taiwan.

Corresponding Author: Chao-Min Cheng E-mail: Phone:+886-35162402 Fax:+886-35745454

Ting-Ya Chang and Chun-Yen Sung contributed equally to this work.

Supplementary Figure

Fig.S1. Contact angle formation and measurement on different paper-based substrates. Figures show top view, cross section, and contact angle of photocurablePDMS in desired patterns with four kinds of paper bases: (a) filter paper; (b) calligraphy paper; (c)chromatography paper; and, (d) rice paper. (e)Bar graph comparingphotocurablePDMS contact angle for each of the four paper bases.

Materials and methods

1 Materials

Liquid-phase photocurablePDMS (i.e., UV-activated PDMS) consists ofprepolymer, 2-3% (methacryloxypropyl)methylsiloxanedimethyl-siloxane (RMS-033, Gelest, PA, USA), and 3%photoinitiator, 2,2-dimethoxy-2-phenylacetophenone(No. 196118, Sigma Aldrich, St. Louis, MO, USA). Highly viscous photocurablePDMS mixture was heated in a boiling water bath to reduce viscosity. Heated photocurablePDMS solution can be transferred more easily and, owing to greater flow properties, leaves less remaining product on the wall of a pipette tip during transfer. A predesigned pattern was printed ontoour chosen substrate (i.e., filter papers or transparent films),usinga commercialwax or ink printer, to establishhydrophilic test zones for the placement ofphotocurablePDMS droplets. Whatmanqualitative paper (Whatman grade No. 1 filter paper, Sigma Aldrich, St. Louis, MO, USA,No.:1001-185) and a wax printer (Xerox Phaser 8560DN, Fuji, Japan) were used tomanufacture our paper device. Tape adhered to the opposite side of the paper facilitated the lateral flow of PDMS droplets so that liquid-phase photocurablePDMSwas trapped in test zones of the assembled substrate (using a combination of substrate, ink/wax, and tape).

2 Contact angle measurement

To obtain different structure curvatures, patterns of photocurablePDMS droplets ware created on four types of paper: 1) filter paper(Whatman, Maidstone, UK); 2) chromatography paper (Whatman, Maidstone, UK); 3) calligraphy paper: and, 4) rice paper.Calligraphy paper and rice paper were purchased from a general bookstore. After wax printing the desired pattern of 55 mm circular wells onto each type of paper, we dropped 10 μLof photocurablePDMSinto each of the 55 mm circular well shapes. We then immediately placed the paper into a UV incubator for 30 seconds. Patterns were made on each paper type nine times. Following this, PDMS droplet contact angles(i.e., the contact angles of each droplet to the paper substrate) were measured by a machine we designed that combined an optical lens, a camera, a microscope stage, and a white lightbulb; paper patterned with PDMS was pasted onto the microscope stage. The lens position and light strength were optimized to take photographic images showing the cross section of each contact interface. These images were then analysed by FAT32 software to determine contact angle.

3 Cell-based assay

To examinedevice performancespecifically for cell culturing, PDMS blocks (i.e., concave structure)manufactured in a 4x4 format were immersed into 75% ethanol and then 1 μg/mL fibronectin solution in phosphate-buffered saline (PBS) for surface modification (i.e., a protein can enhance cell adhesiveness) and incubated at 37C in a humidified 5% CO2incubator for one hour.Madin-Darby canine kidney (MDCK) and mouse embryonic fibroblast (NIH3T3) cells were maintained in 90% Dulbecco’s modified Eagle’s medium with 10% fetal bovine serum (FBS) and 100 U/mL penicillin/streptomyocin at 37C in a humidified 5% CO2 incubator.We used 0.25% trypsin-ethylenediaminetetraacetic acid (EDTA) to trypsinize cultures and plated separated cells on concave PDMS blocks at a density of1 x 104cells/mL. Theseinoculated thermocurablePDMS blocks were incubated at 37C in a humidified 5% CO2 incubator for two days before cells were fixed over different time durationsin 3.7% formaldehyde solution in PBS for 13 minutes at 37C, and permeabilized with 0.3% Triton-X-100 in PBS for 13 minutes at room temperature. F-actin and nucleiwere labeled with 6 μMAlexaFlour®488 phalloidin (Molecular Probes, USA) and 4, 6-diamidino-2-phenylindole (DAPI) (Invitrogen, USA). Cells were subsequently observed through a fluorescent microscope (Zeiss Axiovert) using a 20X objective or a confocal microscope (LSM700, Zeiss).

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