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A multifunctional system comprised of hyaluronic acid microneedles was developed as an effective transdermal delivery platform for rapid local delivery. The microneedles can regulate the filling amount on the tip, by controlling the concentration of hyaluronic acid solution. Ultrasonication induces dissolution of the HA microneedles via vibration of acoustic pressure, and AC iontophoresis improves the electrostatic force-driven diffusion of HA ions and rhodamine B. The effect of ultrasound on rhodamine release was analyzed in vitro using a gelatin hydrogel. the frequency and voltage dependence of the Ac on the ion induction transfer was also evaluated experimentally. the results showed that the permeability of the material acts as a key material property. The delivery system based on ultrasonication and iontophoresis in microneedles increases permeation, thus resulting in shorter initial delivery time than that required by delivery systems based on passive or ultrasonication alone. This study highlights the significance of the combination between ultrasonic waves and iontophoresis for improving the efficiency of the microneedles, by shortening the reaction duration. We anticipate that this system can be extended to macromolecular and dependence delivery, based on drug response time.

The growing interest in wearable devices has drawn increased attention to smart textiles, and various transfer methods have therefore been introduced to realize the desired functions using textiles as substrates. However, the existing transfer techniques are not suited for the production of sophisticated nanoscale patterns on textiles, as textile roughness and difficulty of precise pattern size control hinder miniaturization, deteriorate device performance, and complicate the use of optical phenomena such as surface plasmon resonance. To address these limitations, we have developed a method based on simple dissolution of a water-soluble nanopatterned polymer film for the facile transfer of nanostructures of on-film-deposited functional materials onto textile substrates. The above method tolerates a variety of functional materials, e.g., metals and SiO2, and nano/microscale structures, e.g., nanoscale lines, dots, holes, and mesh patterns with a minimum pattern width of 50 nm. The proposed technique is employed to fabricate a palladium nanoscale line array (utilized as a highly sensitive and selective hydrogen sensor) and is shown to be suitable for the production of security patterns on textiles, as it allows the printing of complex nanostructure patterns with electrical and optical functionalities.

The fabrication of large-area and flexible nanostructures currently presents various challenges related to the special requirements for 3D multilayer nanostructures, ultrasmall nanogaps, and size-controlled nanomeshes. To overcome these rigorous challenges, a simple method for fabricating wafer-scale, ultrasmall nanogaps on a flexible substrate using a temperature above the glass transition temperature (Tg) of the substrate and by layer-by-layer nanoimprinting is proposed here. The size of the nanogaps can be easily controlled by adjusting the pressure, heating time, and heating temperature. In addition, 3D multilayer nanostructures and nanocomposites with 2, 3, 5, 7, and 20 layers were fabricated using this method. The fabricated nanogaps with sizes ranging from approximately 1 to 40 nm were observed via high-resolution transmission electron microscopy (HRTEM). The multilayered nanostructures were evaluated using focused ion beam (FIB) technology. Compared with conventional methods, our method could not only easily control the size of the nanogaps on the flexible large-area substrate but could also achieve fast, simple, and cost-effective fabrication of 3D multilayer nanostructures and nanocomposites without any post-treatment. Moreover, a transparent electrode and nanoheater were fabricated and evaluated. Finally, surface-enhanced Raman scattering substrates with different nanogaps were evaluated using rhodamine 6G. In conclusion, it is believed that the proposed method can solve the problems related to the high requirements of nanofabrication and can be applied in the detection of small molecules and for manufacturing flexible electronics and soft actuators.

In this study, a combined system of microneedles and a triboelectric nanogenerator (TENG) has been developed for drug delivery. A triboelectric device, which converts mechanical energy into alternating current (AC), was chosen to replace the electrophoresis (EP) effect. To directly generate triboelectricity from salmon deoxyribonucleic acid (SDNA)-based microneedles, a triboelectric series of SDNA film and chargeable polymers (polyimide and Teflon) was studied. The electrical output of the two charged polymers was compared to find a material that could be highly charged with SDNA. The electrical output was also compared as a function of the concentration of a drug embedded in the SDNA film, and the results confirmed that drug intercalation affected the carrier diffusion. The mechanical strength of the microneedles was assessed by histological analysis of their penetration into porcine cadaver skin. Furthermore, the output voltage of a system incorporating microneedles and TENG in cadaver skin, and in vitro drug release into gelatin were evaluated to examine potential application as an electrically active drug delivery system. The electrical output voltage of this system was ∼95 V. The mechanism of triboelectric perturbation to the skin has also been discussed. The system developed in this work is a new, facile approach toward effective drug delivery that replaces the existing EP method and expands the application of TENGs.

Herein, a nanowelding technique is adopted to fabricate three-dimensional layer-by-layer Pd-containing nanocomposite structures with special properties. Nanowires fabricated from noble metals (Pd, Pt, Au, and Ag) were used to prepare Pd− Pd nanostructures and Pd−Au, Pd−Pt, Pd−Ag, and Pd−Pt−Au nanocomposite structures by controlling the welding temperature. The recrystallization behavior of the welded composite materials was observed and analyzed. In addition, their excellent mechanical and electrical properties were confirmed by performing 10,000 bending test cycles and measuring the resistances. Finally, flexible and wearable nanoheaters and gas sensors were fabricated using our proposed method. In comparison with conventional techniques, our proposed method can not only easily achieve sensors with a large surface area and flexibility but also improve their performance through the addition of catalyst metals. A gas sensor fabricated using the Pd−Au nanocomposites demonstrated 3.9-fold and 1.1-fold faster H 2 recovery and response, respectively, than a pure Pd−Pd gas sensor device. Moreover, the Pd−Ag nanocomposite exhibited a high sensitivity of 5.5% (better than that of other fabricated gas sensors) for 1.6% H 2 concentration. Therefore, we believe that the fabricated nanocomposites appear promising for wide applications in wearable gas sensors, flexible optical devices, and flexible catalytic devices.

Herein, we develop an adhesive-free double-faced nanotransfer lithography (ADNT) technique based on the surface deformation of flexible substrates under the conditions of temperature and pressure control and thus address the challenge of realizing the mass production of large-area nanodevices in the fields of optics, metasurfaces, and holograms. During ADNT, which is conducted on a flexible polymer substrate above its glass transition temperature in the absence of adhesive materials and chemical bonding agents, nanostructures from the polymer stamp are attached to the deformed polymer substrate. Various silicon masters are employed to prove our method applicable to arbitrary nanopatterns, and diverse Ag and Au nanostructures are deposited on polymer molds to demonstrate the wide scope of useable metals. Finally, ADNT is used to (i) produce a flexible large-area hologram on the defect-free poly­(methyl methacrylate) (PMMA) film and (ii) fabricate a metasurface hologram and a color filter on the front and back surfaces of the PMMA film, respectively, to realize dual functionality. Thus, it is concluded that the use of ADNT can decrease the fabrication time and cost of high-density nanodevices and facilitate their commercialization.

A novel method for fabricating shape-controlled and well-arrayed heterogeneous nanostructures by altering the melting point of the metal thin film at the nanoscale is proposed. Silver nanofilms (AgNFs) are transformed into silver nanoislands (AgNIs), silver nanoparticles (AgNPs), and silver nanogaps (AgNGs) that are well-ordered and repositioned inside the gold nanoholes (AuNHs) depending on the diameter of the AuNHs, the thickness of the AgNF, and the heating temperature (120–200 °C). This method demonstrates the ability to fabricate uniform, stable, and unique structures with a fast, simple, and mass-producible process. For demonstrating the diverse applicability of the developed structures, high-density AgNGs inside the AuNHs are utilized as surface-enhanced Raman spectroscopy (SERS) substrates. These AgNGs-based SERS substrates exhibit a performance enhancement, which is 1.06 × 106 times greater than that of a metal film, with a relative standard deviation of 19.8%. The developed AgNP/AgNI structures are also used as nonreproducible anti-counterfeiting signs, and the anti-counterfeiting/readout system is demonstrated via image processing. Therefore, our method could play a vital role in the nanofabrication of high-demand nanostructures.