Luoran Shang

Spherical colloidal photonic crystals.

CONSPECTUS: Colloidal photonic crystals (PhCs), periodically arranged monodisperse nanoparticles, have emerged as one of the most promising materials for light manipulation because of their photonic band gaps (PBGs), which affect photons in a manner similar to the effect of semiconductor energy band gaps on electrons. The PBGs arise due to the periodic modulation of the refractive index between the building nanoparticles and the surrounding medium in space with subwavelength period. This leads to light with certain wavelengths or frequencies located in the PBG being prohibited from propagating. Because of this special property, the fabrication and application of colloidal PhCs have attracted increasing interest from researchers. The most simple and economical method for fabrication of colloidal PhCs is the bottom-up approach of nanoparticle self-assembly. Common colloidal PhCs from this approach in nature are gem opals, which are made from the ordered assembly and deposition of spherical silica nanoparticles after years of siliceous sedimentation and compression. Besides naturally occurring opals, a variety of manmade colloidal PhCs with thin film or bulk morphology have also been developed. In principle, because of the effect of Bragg diffraction, these PhC materials show different structural colors when observed from different angles, resulting in brilliant colors and important applications. However, this angle dependence is disadvantageous for the construction of some optical materials and devices in which wide viewing angles are desired. Recently, a series of colloidal PhC materials with spherical macroscopic morphology have been created. Because of their spherical symmetry, the PBGs of spherical colloidal PhCs are independent of rotation under illumination of the surface at a fixed incident angle of the light, broadening the perspective of their applications. Based on droplet templates containing colloidal nanoparticles, these spherical colloidal PhCs can be generated by evaporation-induced nanoparticle crystallization or polymerization of ordered nanoparticle crystallization arrays. In particular, because microfluidics was used for the generation of the droplet templates, the development of spherical colloidal PhCs has progressed significantly. These new strategies not only ensure monodispersity, but also increase the structural and functional diversity of the PhC beads, paving the way for the development of advanced optoelectronic devices. In this Account, we present the research progress on spherical colloidal PhCs, including their design, preparation, and potential applications. We outline various types of spherical colloidal PhCs, such as close-packed, non-close-packed, inverse opal, biphasic or multiphasic Janus structured, and core-shell structured geometries. Based on their unique optical properties, applications of the spherical colloidal PhCs for displays, sensors, barcodes, and cell culture microcarriers are presented. Future developments of the spherical colloidal PhC materials are also envisioned.

Bioinspired Multicompartmental Microfibers from Microfluidics

Bioinspired multicompartmental microfibers are generated by novel capillary microfluidics. The resultant microfibers possess multicompartment body-and-shell compositions with specifically designed geometries. Potential use of these microfibers for tissue-engineering applications is demonstrated by creating multifunctional fibers with a spatially controlled encapsulation of cells.

Microfluidic synthesis of barcode particles for multiplex assays.

The increasing use of high-throughput assays in biomedical applications, including drug discovery and clinical diagnostics, demands effective strategies for multiplexing. One promising strategy is the use of barcode particles that encode information about their specific compositions and enable simple identification. Various encoding mechanisms, including spectroscopic, graphical, electronic, and physical encoding, have been proposed for the provision of sufficient identification codes for the barcode particles. These particles are synthesized in various ways. Microfluidics is an effective approach that has created exciting avenues of scientific research in barcode particle synthesis. The resultant particles have found important application in the detection of multiple biological species as they have properties of high flexibility, fast reaction times, less reagent consumption, and good repeatability. In this paper, research progress in the microfluidic synthesis of barcode particles for multiplex assays is discussed. After introducing the general developing strategies of the barcode particles, the focus is on studies of microfluidics, including their design, fabrication, and application in the generation of barcode particles. Applications of the achieved barcode particles in multiplex assays will be described and emphasized. The prospects for future development of these barcode particles are also presented.

Emerging Droplet Microfluidics

Droplet microfluidics generates and manipulates discrete droplets through immiscible multiphase flows inside microchannels. Due to its remarkable advantages, droplet microfluidics bears significant value in an extremely wide range of area. In this review, we provide a comprehensive and in-depth insight into droplet microfluidics, covering fundamental research from microfluidic chip fabrication and droplet generation to the applications of droplets in bio(chemical) analysis and materials generation. The purpose of this review is to convey the fundamentals of droplet microfluidics, a critical analysis on its current status and challenges, and opinions on its future development. We believe this review will promote communications among biology, chemistry, physics, and materials science.

Photonic Crystal Microbubbles as Suspension Barcodes

A novel suspension array was developed that uses photonic crystal (PhC) microbubbles as barcode particles. The PhC microbubbles have an outer transparent polymeric shell, a middle PhC shell, and an inner bubble core, and they were achieved by extraction-derived self-assembly of colloidal nanoparticles in semipermeable solid microcapsules. The encoded elements of the microbubbles originated from their PhC structure with a coated shell, which not only improved the stability of the codes but also provided a flexible surface for bioassays. By using multicompartmental microcapsule templates, PhC microbubbles with substantial coding levels and controllable movement could also be achieved. In addition, as the size of the encapsulated bubbles could be tailored, the overall density of the PhC microbubbles could be adjusted to match the density of a detection solution and to remain in suspension. These remarkable properties make the PhC microbubbles excellent barcode particles.

Photonic Crystal Encoded Microcarriers for Biomaterial Evaluation

Photonic crystal encoded biomaterials microcarriers made from silica-hybrid photonic crystal beads are reported. The characteristic reflection peak originating from the physical periodic structure is used as the code of the microcarriers. They are stable during cell adhesion and culture on their surface. Based on this method, Different biomaterials are incorporated into different PCBs and used as encoded microcarriers for the multiplex evaluation of the interaction of cells and materials in a single culture experiment. These encoded microcarriers are ideal for multiplex bioevaluation of biomaterials or drug applications.

Controlled Fabrication of Bioactive Microfibers for Creating Tissue Constructs Using Microfluidic Techniques.

The fabrication of heterogeneous microstructures, which exert precise control over the distribution of different cell types within biocompatible constructs, is important for many tissue engineering applications. Here, bioactive microfibers with tunable morphologies, structures, and components are generated and employed for creating different tissue constructs. Multibarrel capillary microfluidics with multiple laminar flows are used for continuously spinning these microfibers. With an immediate gelation reaction of the cell dispersed alginate solutions, the cell-laden alginate microfibers with the tunable morphologies and structures as the designed multiple laminar flows can be generated. The performances of the microfibers in cell culture are improved by incorporating bioactive polymers, such as extracellular matrix (ECM) or methacrylated gelatin (GelMA), into the alginate. It is demonstrated that a series of complex three-dimensional (3D) architectural cellular buildings, including biomimic vessels and scaffolds, can be created using these bioactive microfibers.

Bioinspired Helical Microfibers from Microfluidics

Helical objects are among the most important and landmark structures in nature, and represent an emerging group of materials with unique spiral geometry; because of their enriched physical and chemical properties, they can have multiple functionalities. However, the fabrication of such complex helical materials at the micro- or nanoscale level remains a challenge. Here, a coaxial capillary microfluidic system, with the functions of consecutive spinning and spiraling, is presented for scalable generation of helical microfibers. The generation processes can be precisely tuned by adjusting the flow rates, and thus the length, diameter, and pitch of the helical microfibers are highly controllable. Varying the injection capillary design of the microfluidics enables the generation of helical microfibers with structures such as the novel Janus, triplex, core-shell, and even double-helix structures. The potential use of these helical microfibers is also explored for magnetically and thermodynamically triggered microsprings, as well as for a force indicator for contraction of cardiomyocytes. These indicate that such helical microfibers are highly versatile for different applications.

Bio-inspired self-healing structural color hydrogel

Significance Structural color hydrogels have been widely studied and used in different applications, such as in switches, optical devices, etc. However, because the deterioration and accumulation of damage of these materials are inevitable during applications, the creation of bio-inspired structure color materials with increased survivability is still desired for both fundamental research and practical applications. In this study, inspired by creatures in nature with spontaneous healing from injury and recovering of functionality, we demonstrated a self-healing structural color hydrogel by filling a healable protein hydrogel into an inverse opal scaffold. A series of new structural color materials with 1D linear microfiber, 2D pattern, and 3D photonic path structures could be constructed by assembling and healing the composite structural color hydrogel elements. Biologically inspired self-healing structural color hydrogels were developed by adding a glucose oxidase (GOX)- and catalase (CAT)-filled glutaraldehyde cross-linked BSA hydrogel into methacrylated gelatin (GelMA) inverse opal scaffolds. The composite hydrogel materials with the polymerized GelMA scaffold could maintain the stability of an inverse opal structure and its resultant structural colors, whereas the protein hydrogel filler could impart self-healing capability through the reversible covalent attachment of glutaraldehyde to lysine residues of BSA and enzyme additives. A series of unprecedented structural color materials could be created by assembling and healing the elements of the composite hydrogel. In addition, as both the GelMA and the protein hydrogels were derived from organisms, the composite materials presented high biocompatibility and plasticity. These features of self-healing structural color hydrogels make them excellent functional materials for different applications.

Microfluidic Generation of Porous Particles Encapsulating Spongy Graphene for Oil Absorption

Porous particles encapsulating spongy graphene are generated from a microfluidic device and used as adsorbents for water treatment. The amphiphilic surface characteristics result from hydrophobic graphene cores and hydrophilic shells and, together with the porous structure, ensure that the particles have the ability to absorb oils that are either floating on the water or under water.