Micromotors from Microfluidics.

Inspired by the motions of natural objects, attention and efforts have been paid and devoted to fabricate micromotors of spherical, tubular, helical or other shapes for applications in emerging fields including delivery, remediation, and other biomedical applications. Among the proposed methods, the microfluidic technology offers an opportunity to fabricate micromotors with different microstructures. This review presents research progress on micromotors, especially those from microfluidics. The morphologies of the micromotors were firstly outlined. Then, the microfluidic technology used to fabricate different micromotors was discussed. Finally, the applications of these micromotors were briefly introduced, followed by their challenges and future developments.

A responsive porous hydrogel particle-based delivery system for oncotherapy.

Liver cancer is one of the malignant cancers that seriously threatens human health. Although some common treatments including chemotherapy have been applied in oncotherapy, there are often serious shortcomings such as frequent and uncontrollable drug infusion. To overcome these limitations, here, we introduced responsive porous hydrogel microparticles loaded with 5-fluorouracil and metformin for oncotherapy. Because of the interconnected porous structures, various forms of active molecules could be loaded into the particles. In addition, the relatively higher temperature of the tumor site and the temperature-responsive shape transition of pNIPAM hydrogel enabled controllable drug release. The porous pNIPAM particles not only exhibited large loading efficiency and sustained release for the 5-fluorouracil and metformin co-delivery, but also protected drugs from being resolved. Thus, it can be anticipated that the porous microparticles will have great potential in oncotherapy.

Composite Multifunctional Micromotors from Droplet Microfluidics.

Inspired by natural biological machines, lots of effort has been invested in developing artificially functional micromotors which can convert energy into movement for carrying out tasks in diverse areas. Here, we present a capillary microfluidic system with dual inner injections for one-step generation of composite structured polymer micromotors with two distinct cores of platinum (Pt) nanoparticle-integrated and iron oxide (Fe3O4) nanoparticle-dispersed hydrogels. Because the flow rates of the prepolymerized fluids can be precisely tuned in the microfluidics, the diameters of the micromotors as well as the sizes and numbers of the inner cores can be well tailored to optimize the parameters of the resultant micromotors. When exposed to a hydrogen peroxide (H2O2) medium, the Pt-integrated cores of the micromotors could provide propulsion by expelling bubbles produced from the catalytic decomposition of H2O2, while the Fe3O4-dispersed cores could impart magnetic guidance for the micromotors. Benefiting from the close cooperation of these two types of cores, the micromotors were imparted with a strong propulsion and prominent recyclability for the delivery of both microscale and macroscale objects. These results manifest that this kind of composite micromotor has great diversity in various applications.

Programmable wettability on photocontrolled graphene film.

Surface materials with specific wettability play important roles in a wide variety of areas from science to industry. We present a novel paraffin-infused porous graphene film (PIPGF) with programmable wettability. Because of graphene's photothermal property, the paraffin in the PIPGF was in transition between liquid and solid in response to near-infrared (NIR) light irradiation. Thus, we imparted the film with a dynamic and reversible transition between a slippery and a rough surface as the remotely tunable wettability. In addition, with the integration of NIR masks, the paraffin could melt at corresponding patterns on the PIPGF, which formed special flow pathways for the slipping droplets. Therefore, the PIPGF could provide programmable wettability pathways for the spatiotemporal droplet manipulation by flexibly changing the NIR masks. We demonstrated these programmable wettability pathways to not only simplify liquid handling in the microplates and droplet microarrays technology but also to provide distinctly microfluidic microreactors for different purposes, such as practical blood grouping diagnosis. These features indicated that the photocontrollable PIPGF would be amenable to a variety of applications, such as microfluidic systems, laboratory-on-a-chip settings, and droplet manipulations.

Graphene oxide hydrogel particles from microfluidics for oil decontamination.

In this work, we present a simple droplet microfluidic approach for generating graphene oxide (GO) hydrogel composite particles for oil decontamination. By stepwise solvent exchanges, the resulted hydrophilic GO hydrogel composite particles were transferred into organic media without any chemical modifications. As the GOs were locked tightly in hydrogel network, they were hardly changed during the processes of solvent exchanges. Thus, their polar surfaces remained in direct contact with the exchanged organic media, which indicated that the transferred GO particles were capable of effectively adsorbing polar impurities. Attractively, by encapsulating hollow cores and additional magnetic nanoparticles into the emulsion templates during the fabrication, the GO hydrogel composite particles were imparted with hierarchical porous structures and controllable movement capability, both of which could improve their efficiency of impurities adsorbing. These features make the GO hydrogel composite particles described here ideal for oil decontamination.

Bioinspired shape-memory graphene film with tunable wettability.

Functional materials with specific surface wettability play an important role in a wide variety of areas. Inspired by nature's Nepenthes pitcher plant, we present a novel slippery film with tunable wettability based on a shape-memory graphene sponge. The porous graphene sponge coated with shape-memory polymer was used to lock in inert lubricants and construct slippery surfaces to repel different liquids. The superelasticity and high strength, together with good electrical conductivity, of the graphene sponge imparted the graphene/polymer hybrid films with fast recoverable shape-memory properties. Various droplets could slip on the compressed film with a lubricant-covered surface, but the droplets would be pinned when the shape-memory graphene film rebounded due to electrical stimulation, which caused the penetration of the infused lubricant into the pores and the exposure of rough topography film surfaces. The electrothermally dynamic tuning approach was stable and reversible; thus, the shape-memory graphene film was imparted with controlled slippery properties and functions that would be amenable to a variety of applications, such as liquid handling for microplates.