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Microneedle arrays have been proposed in a wide range of biomedical applications, such as transdermal drug delivery and sensing. However, a scalable manufacturing process of precise microneedle fabrication of the microneedle has been challenged. This paper demonstrates UV-lithography-based one-step fabrication of fine-tuned bell-tip microneedles using a combination of light diffraction and the self-aligned lens effect. Microscale photopatterns can derive the predictive diffraction patterns where the higher light intensity at the center of the photopattern solidifies the liquid photoresist and forms a microlens shape in a self-aligned manner. The light through the microlens focuses down to a sharp point to form a conical shape for the body of the microneedle. Then light propagation through the vertex of the cone causes light emission, creating a fine bell-tip. The described light propagation behavior was characterized and explained in terms of the light intensity distribution from the diffraction based on the extended Fresnel–Kirchhoff diffraction model. The optics finite element analysis software was used to verify the light propagation and the intensity distribution. The step-by-step fabrication process was demonstrated using biocompatible photosensitive resins and validated the light attenuation and the cross-linking energy. The 20 × 20 bell-tip microneedles' array was able to be fabricated from the predicted model. Finally, a microneedle array with various shapes and heights on the same substrate was fabricated by single light exposure, demonstrating numerous achievable shapes using the proposed microneedle fabrication method.

We investigate the ac magnetic behavior of solution processable, non-stoichiometric zinc ferrite nanocrystals with a series of sizes and zinc concentrations. Nearly monodisperse ZnxFe3−xO4 nanocrystals (x = 0–0.25) with an average size ranging from 7.4 nm to 13.8 nm are synthesized by using a solvothermal method. All the nanocrystals are in a superparamagnetic state at 300 K, which is confirmed by Superconductive Quantum Interference Device magnetometry. Due to the doping of non-magnetic Zn2+ into A site of ferrite, the saturation magnetization of nanocrystals increases as the size and Zn concentration increases. The ac magnetic permeability measurements at radio frequencies reveal that the real part of the magnetic permeability of similarly sized ferrite nanocrystals can be enhanced by almost twofold as the Zn2+ doping level increases from 0 to 0.25. The integration of 12.3 nm Zn0.25Fe2.75O4 nanocrystals into a toroidal inductor and a solenoid inductor prepared via a simple solution cast process yields a...