Microneedle (MN) delivery system has been greatly developed to deliver drugs into the skin painlessly, noninvasively, and safety. In the past several decades, various types of MNs have been developed by the newer producing techniques. Briefly, as for the morphologically, MNs can be classified into solid, coated, dissolved, and hollow MN, based on the transdermal drug delivery methods of “poke and patch,” “coat and poke,” “poke and release,” and “poke and flow,” respectively. Microneedles also have other characteristics based on the materials and structures. In addition, various manufacturing techniques have been well-developed based on the materials. In this review, the materials, structures, morphologies, and fabricating methods of MNs are summarized. A separate part of the review is used to illustrate the application of MNs to deliver vaccine, insulin, lidocaine, aspirin, and other drugs. Finally, the review ends up with a perspective on the challenges in research and development of MNs, envisioning the future development of MNs as the next generation of drug delivery system.

The flexible control of surface plasmon polaritons (SPPs) is important and intriguing due to its wide application in novel plasmonic devices. Transformation optics (TO) offers the capability either to confine the SPP propagation on rigid curved/uneven surfaces, or to control the flow of SPPs on planar surfaces. However, TO has not permitted us to confine, manipulate, and control SPP waves on flexible curved surfaces. Here, we propose to confine and freely control flexible SPPs using TO and graphene. We show that SPP waves can be naturally confined and propagate on curved or uneven graphene surfaces with little bending and radiation losses, and the confined SPPs are further manipulated and controlled using TO. Flexible plasmonic devices are presented, including the bending waveguides, wave splitter, and Luneburg lens on curved surfaces. Together with the intrinsic flexibility, graphene can be served as a good platform for flexible transformation plasmonics.

Advanced membrane systems with excellent permeance are important for controllable separation processes, such as gas separation and water purification. The ideal candidate materials should be very thin to provide high permeance, be stiff enough to withstand working under high applied pressure, with a large surface area and micro-or nano-pore structure for excellent selectivity. Graphene oxide (GO) nanosheets are graphene with oxygen-containing functional groups, obtained by treating graphite with strong oxidizers. Graphene-based materials, by virtue of their high mechanical strength, large surface area, singleatom-thick unique two-dimensional honeycomb lattice structure, and narrow pore distribution, provide exciting opportunities to assemble novel types of advanced, ultra-thin, high-efficiency membrane devices. In this contribution, we discuss the progress made in the direction of using graphene oxide as high-efficiency membranes for gas separation and water purification. The primary focus will be on introducing the fabrication processes, exceptional properties, and innovative membrane applications of twodimensional graphene oxide materials for controllable separation processes. This state-of-the-art review will provide a platform for understanding the intricate details of gas and water molecular transport through laminar graphene oxide membranes, as well as a summary of the latest process in the field.

A MnCr2O4 spinel coating initially forms at grain boundaries under a H2–H2O gas mixture at high temperature.

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MnCr2O4 spinel coating can significantly affect coke morphology and coke microstructure.

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