Controllable Microfluidic Fabrication of Microstructured Materials from Nonspherical Particles to Helices

Magnetic Microrobots with Folate Targeting for Drug Delivery

Untethered microrobots can be used for cargo delivery (e.g., drug molecules, stem cells, and genes) targeting designated areas. However, it is not enough to just reach the lesion site, as some drugs can only play the best therapeutic effect within the cells. To this end, folic acid (FA) was introduced into microrobots in this work as a key to mediate endocytosis of drugs into cells. The microrobots here were fabricated with biodegradable gelatin methacryloyl (GelMA) and modified with magnetic metal-organic framework (MOF). The porous structure of MOF and the hydrogel network of polymerized GelMA were used for the loading of enough FA and anticancer drug doxorubicin (DOX) respectively. Utilizing the magnetic property of magnetic MOF, these microrobots can gather around the lesion site with the navigation of magnetic fields. The combination effects of FA targeting and magnetic navigation substantially improve the anticancer efficiency of these microrobots. The result shows that the cancer cells inhibition rate of microrobots with FA can be up to 93%, while that of the ones without FA was only 78%. The introduction of FA is a useful method to improve the drug transportation ability of microrobots, providing a meaningful reference for further research.

Preparation of ethyl cellulose particles with different morphologies through microfluidics

The sizes and shapes of polymer particles determine their performance and application. In this paper, ethyl cellulose particles with different morphologies are generated through extraction and solidification in a microfluidic device with double T-junctions. Droplets of ethyl acetate containing ethyl cellulose are formed first, then, pure water is employed to extract the solvents in the droplets and the ethyl cellulose is solidified to form monodisperse particles. By changing the flow rates of the continuous phase and the dispersed phase and the concentration of ethyl cellulose, red-blood-cell-like, doughnut-like, dimpled and spherical particles are fabricated, and the regime of different particle morphologies is given. The more important is that the physical mechanisms and explanations of the formation of different particle morphologies are clearly disclosed by analyzing the circulation flows outside and inside the droplets. The flow patterns in the microchannel, and the diffusion and solidification properties of the molecules are the key factors that affect the final morphology of particles. Due to the circulation, there are two stagnation points at the front and rear of the droplet, and they are the approximate locations where the dimple in the dimpled particle, the hole in the doughnut-like particle and the two pits in the red-blood-cell-like particles are formed. These analysis and results are useful in flow chemistry, in the fabrication of particle materials, and so on.

Continuous microfluidic fabrication of anisotropic microparticles for enhanced wastewater purification

Anisotropic microparticles containing functional nanomaterials have attracted growing interest due to their enhanced performance in diverse applications ranging from catalysts to environmental remediation. However, the preparation of anisotropic microparticles with highly controlled morphologies and dimensions usually suffers from a limited material choice. Here, we develop a facile strategy to continuously prepare anisotropic microparticles with their shapes changing from spherical to pear-like, maraca-like and rod-like for enhanced water decontamination. Anisotropic microparticles are produced by deforming oil-droplet templates within microfibers and then locking their shapes via thermo/photo-polymerization. The sizes and geometries of the oil-droplet templates are precisely controlled by varying the fluid flow conditions. In addition, porous spherical and rod-like microparticles are functionalized for photocatalytic degradation of organic contaminants by incorporating functional TiO2 and Fe3O4 nanoparticles. Compared to spherical microparticles with equal volume, functionalized rod-like microparticles exhibit better performance in removal of contaminants due to their larger specific surface area, which facilitates the contact between the loaded catalysts and organic pollutants. Moreover, the magnetic rod-like microparticles can be easily recovered and reused without deterioration of catalytic performance. The proposed strategy in this study is useful for producing anisotropic microparticles with well-tailored shapes via different polymerization methods and extending their potential applications.

One-Step Generation of Aqueous-Droplet-Filled Hydrogel Fibers as Organoid Carriers Using an All-in-Water Microfluidic System

Hydrogel fibers are promising carriers for biological applications due to their flexible mechanical properties, well-defined spatial distribution, and excellent biocompatibility. In particular, the droplet-filled hydrogel fibers with the controllable dimension and location of droplets display great advantages to enhance the loading capacity of multiple components and biofunctions. In this work, we proposed a new all-in-water microfluidic system that allows for one-step fabrication of aqueous-droplet-filled hydrogel fibers (ADHFs) with unique morphology and tunable configurations. In the system, the aqueous droplets with equidistance are successfully arranged within the alginate calcium fibers, relying on the design of the pump valve cycle and the select of two immiscible liquids with a stable aqueous interface. The architecture of the ADHF can be flexibly controlled by adjusting the three phase flow rates and the valve switch cycle. The produced ADHFs exhibit high controllability, uniformity, biocompatibility, and stability. The established system enabled the formation of functional human islet organoids in situ through encapsulating pancreatic endocrine progenitor cells within microfibers. The generated islet organoids within droplets exhibit high cell viability and islet-specific function of insulin secretion. The proposed approach provides a new way to fabricate multifunctional hydrogel fibers for materials sciences, tissue engineering, and regenerative medicine.

Controllable microfluidic fabrication of microstructured functional materials

Microstructured functional materials such as microfibers and microparticles are widely used for a myriad of applications. Precise manipulation of the functional components and structure is important for the microstructured functional materials to achieve desired functions for advanced application. This review highlights the recent progress on the controllable microfluidic fabrication of microstructured functional materials from liquid templates. First, microfluidic strategies for controllable generation of liquid templates including laminar jets and emulsion droplets are introduced. Then, strategies for fabricating microfibers and microparticles with diverse structures and advanced functions from the liquid templates are highlighted. These strategies mainly focus on precisely engineering the functional components and microstructures of the microfibers and microparticles by tailoring those of their liquid templates to achieve desired advanced functions. Finally, future development of microfluidic techniques for industrial-scale production of the microstructured functional materials is discussed.

Controllable Fabrication of Functional Microhelices with Droplet Microfluidics

Microhelices with unique three-dimensional (3D) helical structures have attracted great attention due to applications in various fields, especially magnetic microhelices can be applied as microrobots for removal of clogging substance in microchannels, cargo transport, cell manipulation, and so on. Here, a facile and flexible strategy is developed to controllably fabricate microhelices with droplet microfluidics. On-flow fabrication of microhelices is simply achieved by generating monodisperse droplets first, transforming the spherical droplets into helical templates subsequently due to the liquid rope coiling effect, followed by polymerizing monomers in the templates via on-line UV irradiation and then degrading the shells of helical fibers. Benefitting from the flexible controllability of microfluidics, the morphologies of microhelices can be precisely controlled by adjusting the flow rates of fluids and the structures of microfluidic devices. Functional microhelices can be easily prepared by introducing functional components or elements into inner fluids. By introducing magnetic nanoparticles into inner fluids, magnetic microhelices are easily fabricated as microrobots that featured with magnetic-field-driven corkscrew-like motion for efficient cargo transport and removal of clogging substance in microchannels. This novel microfabrication method allows a precise morphological control and easy functionalization of microhelices, providing a flexible and versatile strategy for fabricating designer functional microhelices for diverse applications.

Electrocoiling-guided printing of multiscale architectures at single-wavelength resolution

The rope coiling observed in liquid ink with high viscosity has been exploited in additive printing to fabricate architectures with periodically curled structures and tune their mechanical properties. However, the control over the coiling path relying on mechanical motion restricts the spatiotemporal resolution. We develop an electrically assisted high-resolution technique to manipulate coiling paths of viscous ink and structures of the deposited filament. By spatially programming the voltage applied onto the viscous ink, we show that the switching between different filament structures can be accomplished at single wavelength resolution, facilitating the rapid and accurate construction of sophisticated patterns. Furthermore, translational guiding of the electrocoiling enables rapid printing of filaments with complex structures at a line speed of 10² mm s^-1. With a simplified trajectory of the printing head, large-area and multiscale patterns can be printed at an unprecedented speed; for instance, centimeter-sized architectures constructed from nanofibers with micron-sized curled structures can be completed in a few minutes. By enabling the printing of complex fiber networks with tunable shape and density, our work provides a route towards custom-design of fiber architectures with unique features such as spatially varying mechanical properties.

Rapid preparation of auto-healing gels with actuating behaviour

Gels with multiple stimuli-responsive actuating behaviour have shown great potential in many applications. Nevertheless, facile approaches to rapidly preparing gel actuators are still highly needed, and obtaining gels possessing both actuating and auto-healing capabilities remains a challenge. Herein, we report the rapid preparation of gel actuators with a self-healing ability. Dual-component gels, composed of poly(BA-co-VI-co-AM) (G-1) and poly(BA-co-AA-co-AM/β-CD) (G-2) (BA = butyl acrylate, VI = N-vinyl imidazole, AM = acrylamide, AA = acrylic acid, β-CD = β-cyclodextrin), are prepared within 10 minutes (min) via biphase frontal polymerization (FP). Both G-1 and G-2 gels show excellent intrinsic self-healing properties based on hydrogen bonds, with healing efficiencies of 91% and 97%, respectively; self-healing between G-1 and G-2 also occurs due to hydrogen bonding and host-guest interactions. Moreover, dual-component gels, in terms of G-1 and G-2 bilayer gel flowers and strips, heterogeneous healed bilayer gel strips, and microfluidic-directed bilayer gel microsphere ensembles, all show actuating behaviour in acidic, alkaline and organic solutions, with actuation degrees up to 96% in 5 min. The actuation mechanism is also proposed. This work might provide new insights into fast synthesis of self-healing dual-component gels towards application in the actuator field.

Silk Fibroin Microparticles with Hollow Mesoporous Silica Nanocarriers Encapsulation for Abdominal Wall Repair

Therapeutic vascularization appears to be an effective way of repairing abdominal wall defects. Attempts to implement this treatment tend to focus on the generation of featured drug carriers with the ability effectively to encapsulate the angiogenesis-stimulating agents and control their release to maintain an appropriate concentration at the injured area. Here, a new type of composite microparticle (CM) composed of silk fibroin (SF) and hollow mesoporous silica nanocarriers (HMSNs) is presented for therapeutic agent delivery. The CMs are generated by drying microfluidic emulsion templates of HMSN-dispersed SF solution. The resultant CMs have a distinctive micro-nanostructure, in which two barriers control the drug release. The encapsulated HMSNs increase the drug-carrying capacity of the CMs, and also form the first barrier via physical absorption. The microfluidic SF microparticles not only provide a shell with excellent monodispersity and biocompatibility but also form the second barrier via efficient encapsulation. Because of these superior properties of the CMs, the loaded drugs can be delivered with a satisfactory activity at the required rate, making them ideal for implementing therapeutic vascularization and repairing abdominal wall defects.