Multiscale materials from microcontinuous-flow synthesis: ZnO and Au nanoparticle-filled uniform and homogeneous polymer microbeads

Four-Level Structural Hierarchy: Microfluidically Supported Synthesis of Polymer Particle Architectures Incorporating Fluorescence-Labeled Components and Metal Nanoparticles

Hierarchical assemblies of functional polymer particles are promising due to their surface as well as physicochemical properties. However, hierarchical composites are complex and challenging to form due to the many steps necessary for integrating different components into one system. Highly structured four-level composite particles were formed in a four-step process. First of all, gold (Au) nanoparticles, poly(methyl methacrylate) (PMMA) nanoparticles, and poly(tripropylene glycol diacrylate) (poly-TPGDA) microparticles were individually synthesized. By applying microfluidic techniques, polymer nano- and microparticles were formed with tunable size and surface properties. Afterwards, the negatively charged gold nanoparticles and PMMA particles functionalized with a positively charged surface were mixed to form Au/PMMA assemblies. The Au/PMMA composites were mixed and incubated with poly-TPGDA microparticles to form ternary Au/PMMA/poly-TPGDA assemblies. For the formation of composite-containing microparticles, Au/PMMA/poly-TPGDA composites were dispersed in an aqueous acrylamide-methylenebisacrylamide solution. Monomer droplets were formed in a co-flow microfluidic device and photopolymerized by UV light. In this way, hierarchically structured four-level composites consisting of four different size ranges─0.025/0.8/30/1000 μm─were obtained. By functionalizing polymer nano- and microparticles with different fluorescent dyes, it was possible to visualize the same composite particle under two different excitation modes (λ_ex = 395-440 and λ_ex = 510-560 nm). The Au/PMMA/poly-TPGDA composite-embedded polyacrylamide microparticles can be potentially used as a model for the creation of composite particles for sensing, catalysis, multilabeling, and biomedical applications.

Multi-size control of homogeneous explosives by coaxial microfluidics

A coaxial microfluidic platform was developed for the multi-size control of homogeneous explosives.

Microfluidic strategy for rapid and high-quality control of crystal morphology of explosives

A new strategy based on a microfluidic platform is proposed for the rapid and high-quality control of explosives' crystal morphology.

Macroporous materials: microfluidic fabrication, functionalization and applications

This article provides an up-to-date highly comprehensive overview (594 references) on the state of the art of the synthesis and design of macroporous materials using microfluidics and their applications in different fields.

Microfluidic Synthesis of Actuating Microparticles from a Thiol-Ene Based Main-Chain Liquid Crystalline Elastomer

In this article the microfluidic synthesis of strongly actuating particles on the basis of a liquid crystalline main-chain elastomer is presented. The synthesis is carried out in a capillary-based co-flow microreactor by photo-initiated thiol-ene click chemistry of a liquid crystalline monomer mixture. These microparticles exhibit a deformation from a spherical to a rod-like shape during the thermal-initiated phase transition of the liquid crystalline elastomer (LCE) at which the particles' aspect ratio is almost doubled. Repeated contraction cycles confirm the complete reversibility of the particles' actuation properties. The transition temperature of the LCE, the temperature range of the actuation process as well as the magnitude of the particles' aspect ratio change are studied and controlled by the systematic variation of the liquid crystalline crosslinker content in the monomer mixture. Especially the variable actuation properties of these stimuli-responsive microparticles enable the possibility of an application as soft actuators or sensors.

Applications of Continuous-Flow Photochemistry in Organic Synthesis, Material Science, and Water Treatment

Continuous-flow photochemistry in microreactors receives a lot of attention from researchers in academia and industry as this technology provides reduced reaction times, higher selectivities, straightforward scalability, and the possibility to safely use hazardous intermediates and gaseous reactants. In this review, an up-to-date overview is given of photochemical transformations in continuous-flow reactors, including applications in organic synthesis, material science, and water treatment. In addition, the advantages of continuous-flow photochemistry are pointed out and a thorough comparison with batch processing is presented.

Composite Sensor Particles for Tuned SERS Sensing: Microfluidic Synthesis, Properties and Applications

Surface-enhanced Raman scattering (SERS) is a promising platform for particle-based sensor signaling, and droplet-based microfluidic systems are particularly advantageous for control of the size and composition of micro- and nanoparticles. For controlled sensing application, a high homogeneity of the sensor particles is a key requirement, and the particles with functional properties demand for the preparation in a minimum number of synthesis steps. Frequently used coflow and flow focusing arrangements, however, produce the microparticles of only larger size. To address such concern for downscaling of particle size, which is crucial for strong sensing outcome, we have used a peculiar micro cross-flow arrangement here for generating the polymer microparticles of broad size range between 30 and 600 μm along with in situ embedded silver nanoparticles. Embedded silver acts as nuclei for additional silver enforcement via silver-catalyzed silver deposition in order to realize the composite microparticles for SERS sensing. The homogeneous size and spatial distribution of silver nanoparticles inside the matrix and enforcement over the surface together with controlled pore size provides a high and homogeneous loading of polymer composite sensor. Moreover, different parameters such as analytes concentration and particles size have been studied here for SERS sensing application of biochemical molecules (amino acids and vitamins). Overall, the platform for size-tuned droplets generation, synthesis of composite microparticles, mechanism for synchronized photopolymerization-photoreduction, tuned silver enforcement, and the impacts of different analytes on differently composed microparticles are systematically investigated in this paper.

Control of shape and size of polymer nanoparticles aggregates in a single-step microcontinuous flow process: a case of flower and spherical shapes

Controlled aggregation of polymer nanoparticles for building anisotropic nano- and microstructures via a self-assembling bottom-up process is an important strategy. Therefore, in this work, the formation of structured poly(methyl methacrylate) (PMMA) particles with diameters between lower micrometer and submicrometer range by use of a microcontinuous flow arrangement was investigated in the presence of nonionic water-soluble polymer polyvinylpyrrolidone (PVP). The investigations show that the microreaction strategy is well applicable and allows a tuning of size and shape of nanoparticles in dependence on reactant concentrations and flow rate ratios. Larger and complex structured polymer particles have been found at lower PVP concentration, whereas more compact submicron-sized particles were formed at higher PVP concentrations. The addition of ionic surfactants modulates the generation of characteristic particle shapes. The observation of intermediate states between complex flowerlike particles and simple spheres in dependence on the applied concentration of low molecular weight surfactants supports the explanation of particle formation by a mechanism with superposition of particle growth and assembling. When mixed surfactants (PVP-SDS or PVP-CTAB) are used, the final particles shape depends on the concentration of individual concentrations of surfactants and on the competition between mobility, solvation, and micelle formations.

Three-dimensional hydrodynamic focusing method for polyplex synthesis

Successful intracellular delivery of nucleic acid therapeutics relies on multiaspect optimization, one of which is formulation. While there has been ample innovation on chemical design of polymeric gene carriers, the same cannot be said for physical processing of polymer-DNA nanocomplexes (polyplexes). Conventional synthesis of polyplexes by bulk mixing depends on the operators' experience. The poorly controlled bulk mixing process may also lead to batch-to-batch variation and consequent irreproducibility. Here, we synthesize polyplexes by using a three-dimensional hydrodynamic focusing (3D-HF) technique in a single-layered, planar microfluidic device. Without any additional chemical treatment or postprocessing, the polyplexes prepared by the 3D-HF method show smaller size, slower aggregation rate, and higher transfection efficiency, while exhibiting reduced cytotoxicity compared to the ones synthesized by conventional bulk mixing. In addition, by introducing external acoustic perturbation, mixing can be further enhanced, leading to even smaller nanocomplexes. The 3D-HF method provides a simple and reproducible process for synthesizing high-quality polyplexes, addressing a critical barrier in the eventual translation of nucleic acid therapeutics.

Lab-on-a-chip synthesis of inorganic nanomaterials and quantum dots for biomedical applications

The past two decades have seen a dramatic raise in the number of investigations leading to the development of Lab-on-a-Chip (LOC) devices for synthesis of nanomaterials. A majority of these investigations were focused on inorganic nanomaterials comprising of metals, metal oxides, nanocomposites and quantum dots. Herein, we provide an analysis of these findings, especially, considering the more recent developments in this new decade. We made an attempt to bring out the differences between chip-based as well as tubular continuous flow systems. We also cover, for the first time, various opportunities the tools from the field of computational fluid dynamics provide in designing LOC systems for synthesis inorganic nanomaterials. Particularly, we provide unique examples to demonstrate that there is a need for concerted effort to utilize LOC devices not only for synthesis of inorganic nanomaterials but also for carrying out superior in vitro studies thereby, paving the way for faster clinical translation. Even though LOC devices with the possibility to carry out multi-step syntheses have been designed, surprisingly, such systems have not been utilized for carrying out simultaneous synthesis and bio-functionalization of nanomaterials. While traditionally, LOC devices are primarily based on microfluidic systems, in this review article, we make a case for utilizing millifluidic systems for more efficient synthesis, bio-functionalization and in vitro studies of inorganic nanomaterials tailor-made for biomedical applications. Finally, recent advances in the field clearly point out the possibility for pushing the boundaries of current medical practices towards personalized health care with a vision to develop automated LOC-based instrumentation for carrying out simultaneous synthesis, bio-functionalization and in vitro evaluation of inorganic nanomaterials for biomedical applications.

Joining plasmonics with microfluidics: from convenience to inevitability

Along the advances in optofluidics, functionalities based on the surface plasmon-polariton have also been finding an increasing level of involvement within micro/nano-fluidic systems, gradually forming a new field of plasmo-fluidics. This survey of the burgeoning field reveals that judicious selection and combination of plasmonic and micro/nano-fluidic features render the plasmo-fluidic integration useful and mutually beneficial to the point of inevitability. We establish categories for the level of integration and utilize them as a framework for surveying existing work and extracting future perspectives.

Mass production and size control of lipid-polymer hybrid nanoparticles through controlled microvortices

Lipid-polymer hybrid (LPH) nanoparticles can deliver a wide range of therapeutic compounds in a controlled manner. LPH nanoparticle syntheses using microfluidics improve the mixing process but are restricted by a low throughput. In this study, we present a pattern-tunable microvortex platform that allows mass production and size control of LPH nanoparticles with superior reproducibility and homogeneity. We demonstrate that by varying flow rates (i.e., Reynolds number (30-150)) we can control the nanoparticle size (30-170 nm) with high productivity (∼3 g/hour) and low polydispersity (∼0.1). Our approach may contribute to efficient development and optimization of a wide range of multicomponent nanoparticles for medical imaging and drug delivery.

Molecular Imaging Probe Development using Microfluidics

In this manuscript, we review the latest advancement of microfluidics in molecular imaging probe development. Due to increasing needs for medical imaging, high demand for many types of molecular imaging probes will have to be met by exploiting novel chemistry/radiochemistry and engineering technologies to improve the production and development of suitable probes. The microfluidic-based probe synthesis is currently attracting a great deal of interest because of their potential to deliver many advantages over conventional systems. Numerous chemical reactions have been successfully performed in micro-reactors and the results convincingly demonstrate with great benefits to aid synthetic procedures, such as purer products, higher yields, shorter reaction times compared to the corresponding batch/macroscale reactions, and more benign reaction conditions. Several 'proof-of-principle' examples of molecular imaging probe syntheses using microfluidics, along with basics of device architecture and operation, and their potential limitations are discussed here.

Some recent advances in the design and the use of miniaturized droplet-based continuous process: applications in chemistry and high-pressure microflows

This mini-review focuses on two different miniaturizing approaches: the first one describes the generation and use of droplets flowing within a millifluidic tool as individual batch microreactors. The second one reports the use of high pressure microflows in chemistry. Millifluidics is an inexpensive, versatile and easy to use approach which is upscaled from microfluidics. It enables one to produce hierarchically organized multiple emulsions or particles with a good control over sizes and shapes, as well as to provide a convenient data acquisition platform dedicated to slow or rather fast chemical reactions, i.e., from hours to a few minutes. High-pressure resistant devices were recently fabricated and used to generate stable droplets from pressurized fluids such as supercritical fluid-liquid systems. We believe that supercritical microfluidics is a promising tool to develop sustainable processes in chemistry.