In this study, we demonstrated the light-driven control of the flow-rate inside a microchannel within a temperature-responsive hydrogel by fabricating metal microstructures by multiphoton photoreduction. When CW light was illuminated onto the microstructures, significant alteration in the flow-rate was confirmed. The change in flow-rate is attributable to the light-stimulated deformation of the microchannel associated with the shrinkage of the PNIPAm hydrogel. This method allows for the spatially-selective control of the flow-rate simply via light illumination since the light absorbers can be fabricated at a targeted position by multiphoton photoreduction.
We demonstrate the fabrication of double-network (DN) hydrogel microstructures inside a hydrogel by multi-photon cross-linking induced by focused femtosecond laser pulses. Two different poly(ethylene glycol) diacrylate (PEGDA, Mw=700 and 4000) solutions were prepared. A cross-linked PEGDA hydrogel molded into block-shape was immersed in PEGDA hydrogel prepolymer solutions of different molecular weight. Then the DN microstructures were fabricated by spatially-selective photo cross-linking of the polymer chains by femtosecond laser pulse irradiation. The mechanical strength of DN microstructures were enhanced which was confirmed by uniaxial compression test, suggesting the potential of our method for controlling spatial distribution of strength and stiffness.
The scope of utilizing soft materials is expanding further in recent years because of the flexibility and the good biocompatibility. In this presentation, laser direct writing of microstructures that exhibits optical and/or electrical properties in and on soft materials by means of photoreduction and graphitization will be described. The fabrication of metal microstructures by multi-photon photoreduction within PEGDA and pNIPAM hydrogels will be reviewed in addition to recent results on applications toward soft actuators. Femtosecond laser direct writing of highly crystalline graphene from native PDMS as well as cellulose nanofiber films, a sustainable biomass, and its application for a highly sensitive piezoresistive sensor will also be presented.
We demonstrated the fabrication of gold microstructures inside a PEG-based hydrogel with different charged fluorophores by multi-photon photoreduction. By adding an anionic charged FITC-dextran or a cationic charged Rhodamine110 to the metal ion solution, line width of the fabricated gold microstructures increased compared to that of the structures fabricated in fluorophore-free hydrogel. The photobleaching could enhanced the reduction of gold ions accompanying the oxidation of the fluorophores. Notably, the inhibition of reduction of gold ions at a site other than the focal point was observed with FITC-dextran, which may be attributable to the coordination of gold ions to FITC-dextran.
We demonstrate the microfabrication of double-network (DN) hydrogels by multi-photon polymerization induced by focused femtosecond laser pulses. Two different poly (ethylene glycol) diacrylate (PEGDA) solutions (Mw=700 and 4000) were cured as both structures were crossing each other, allowing overlapped structure to form double networks composed of both employed polymer chains. This method allows the spatially-selective microfabrication of DN hydrogels inside the microfabricated hydrogel structures, which would realize the hydrogel microstructures showing spatially varied distribution of strength and stiffness.
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