Ar 100

The cilia were printed with various combinations of the polymer PCL, graphene, and the solvent DCM. PCL (Sigma Aldrich) and graphene nanoparticles (Sigma Aldrich) were dissolved in DCM (Sigma Aldrich) for a day. Then the mixture was placed into a planetary centrifugal mixer (AR‐100; Thinky) at 1400 rpm for 240 s, removed and stirred well, and then centrifuged for another 240 s. The electrodes and cilia cups were printed with a two‐part silver microparticle ink (Atom adhesives). The dermal rubber layer was printed with Dragon Skin (Smooth‐On). All devices were printed on a flexible tape substrate (Flex‐Tape).
The optimal ratio of PCL to DCM was found to be 30% PCL by weight (prior to adding graphene). This ratio was used for all cases of pure PCL. Four variations of the ink with increasing concentrations of graphene were synthesized and studied. The inks were denoted PCLG1, PCLG2, PCLG3, and PCLG4 corresponding to weight percentages of graphene ≈3.5%, 6.5%, 8.5%, and 10.5%.

The electrode was prepared using the following procedure. A mixture of the carbon powder, 60% PTFE dispersion, 2-propanol, and deionized water was dispersed using a mixer (Thinky AR-100). The slurry was deposited on the surface of a carbon fiber paper (Toray TGP-H-090) using a screen-printing technique and then dried at 120°C in air to remove the solvent. The loading of carbon was adjusted to ca. 4.5 mg cm⁻². Two identical 12 mm diameter electrode disks were punched from the carbon fiber paper. Prior to fabrication of the supercapacitor assembly, these electrodes were immersed in the H₃PO₄ ionomer. A 14 mm diameter electrolyte membrane was sandwiched between the two electrodes attached to stainless steel current collectors. The supercapacitor was then sealed using thermal- and chemical-resistant PTFE tape (Nitto Denko, Nitoflon).

The microfluidic device was fabricated using a typical soft lithography replica molding technique^{35 (link)}. First, a channel mold with a height of 40 μm was fabricated on a silicon wafer (N100, University, USA) with SU-8 photoresist (2025, MicroChem, USA) using maskless lithography (SF-100 Xcel, Intelligent Micro Patterning, LLC, USA). Then, PDMS prepolymer base (Sylgard 184, Dow Corning, USA) was mixed with curing agent at a weight ratio of 10:1 by a conditioning mixer (AR-100, THINKY, JP). The mixture was poured onto the channel mold and cured at 65 °C for 4 h. Subsequently, the PDMS layer was peeled off from the mold, followed by bonding to a glass substrate through oxygen plasma treatment (PDC-002, Harrick, USA) and heating at 90 °C for 2 h. To fabricate the electrodes for droplet coalescence, empty channels were fabricated in the desired shapes on both sides of the main channel. A low-melting-point metal wire (52225, Indium Incorporation, USA) was then inserted into one end of the channel at 95 °C, and negative pressure was applied to another end to fill the whole channel with liquid metal. After further cooling for solidification, the electrodes were formed into desired shapes. The whole channel was treated with aquapel (PPG, USA) to guarantee stable droplet generation and manipulations.

To measure the diffuse reflectance, polymer thin films containing hybrid particles were prepared using an acrylate-type resin containing a photoinitiator. First, 0.5 g of hybrid particles was added to 9.5 g of acrylate resin and mixed using a paste mixer of a revolution/rotation system (AR-100, Thinky, Tokyo, Japan). The mixing process was carried out at a speed of 2200/800 rpm (revolution/rotation) for 30 min. After the mixed resin was applied between two release films (polyethylene terephthalate film coated with silicon), a uniform thin film with a thickness of 150 μm was prepared using a roll-to-roll coater. The prepared film was UV-cured with 4 J cm⁻² using a UV curing machine (KJPHT-101, KJUV, Incheon, Korea). As a result, various thin film samples including pure thin film without any particles, thin films with only organic PMMA particles, thin films with only inorganic TiO₂ particles, and thin films with organic-inorganic hybrid particles were prepared.

First, the pure TiO₂ nanoparticles or the synthesized hybrid nanoparticles were added to an OCA solution and mixed well using a paste mixer (Thinky, AR-100, Tokyo, Japan) at 2000 rpm for 30 min. To prepare a thin film with a thickness of 200 μm, the OCA mixture was applied on a 75 μm thick release film, which was covered with a 50 μm thick release film, and the two release films were bonded using a roll-to-roll coater (MSRTR, SS-1, Seoul, Korea). To cure this bonded film, a UV curing machine (KJUV, KJPHT-101, Incheon, Korea) was used with a UV energy of 4 J cm⁻² and at a UV intensity of 5 mW cm⁻². To evaluate the optical properties of the cured film, the OCA film was cut to a size of 30 mm × 30 mm, and the UV–visible transmittance was measured.