A microfluidic approach to synthesizing high-performance microfibers with tunable anhydrous proton conductivity

Tailoring micro/nano-fibers for biomedical applications

Nano/micro fibers have evoked much attention of scientists and have been researched as cutting edge and hotspot in the area of fiber science in recent years due to the rapid development of various advanced manufacturing technologies, and the appearance of fascinating and special functions and properties, such as the enhanced mechanical strength, high surface area to volume ratio and special functionalities shown in the surface, triggered by the nano or micro-scale dimensions. In addition, these outstanding and special characteristics of the nano/micro fibers impart fiber-based materials with wide applications, such as environmental engineering, electronic and biomedical fields. This review mainly focuses on the recent development in the various nano/micro fibers fabrication strategies and corresponding applications in the biomedical fields, including tissue engineering scaffolds, drug delivery, wound healing, and biosensors. Moreover, the challenges for the fabrications and applications and future perspectives are presented.

How Does a Microfluidic Platform Tune the Morphological Properties of Polybenzimidazole Nanoparticles?

Microfluidic synthesis methods are among the most promising approaches for controlling the size and morphology of polymeric nanoparticles (NPs). In this work, for the first time, atomistic mechanisms involved in morphological changes of polybenzimidazole (PBI) NPs in microfluidic media are investigated. The multiscale molecular dynamic (MD) simulations are validated with the literature modeling and experimental data. A good agreement is obtained between the molecular modeling results and experimental data. The effects of mixing time, solvent type, dopant, and simulation box size at the molecular level are investigated. Mixing time has a positive impact on the morphology of the PBI NPs. Microfluidic technology can control the mixing time well and engineer the morphology of the NPs. In the process of morphological changes, at the optimum time (about 11.5 ms), the attraction energy between the polymer molecules is at the highest level (-37.65 kJ/mol). The size of the polymer NPs is minimal (2.3 nm), and the aspect ratio and entropy are at the lowest level, equal to 1.07 and 11.024 kJ/mol·K, respectively. It was found that the presence of water leads to the precipitation of polymeric NPs owing to the dominance of hydrophobic forces. Both dimethylacetamide (DMA) and phosphoric acid (PA) improve the control of the size and morphology of NPs. However, the addition of PA has a greater impact; PA acts as a cross-linker, making PBI NPs finer and more spherical. In addition, MD simulation reveals that PA increases the proton diffusion coefficient in PBI and enhances its efficiency in fuel cells. This study paves a new efficient way for morphological engineering of polymeric NPs using microfluidic technology.

Multifunctional Micro/Nanoscale Fibers Based on Microfluidic Spinning Technology

Superfine multifunctional micro/nanoscale fibrous materials with high surface area and ordered structure have attracted intensive attention for widespread applications in recent years. Microfluidic spinning technology (MST) has emerged as a powerful and versatile platform because of its various advantages such as high surface-area-to-volume ratio, effective heat transfer, and enhanced reaction rate. The resultant well-defined micro/nanoscale fibers exhibit controllable compositions, advanced structures, and new physical/chemical properties. The latest developments and achievements in microfluidic spun fiber materials are summarized in terms of the underlying preparation principles, geometric configurations, and functionalization. Variously architected structures and shapes by MST, including cylindrical, grooved, flat, anisotropic, hollow, core-shell, Janus, heterogeneous, helical, and knotted fibers, are emphasized. In particular, fiber-spinning chemistry in MST for achieving functionalization of fiber materials by in situ chemical reactions inside fibers is introduced. Additionally, the applications of the fabricated functional fibers are highlighted in sensors, microactuators, photoelectric devices, flexible electronics, tissue engineering, drug delivery, and water collection. Finally, recent progress, challenges, and future perspectives are discussed.

Synthesis of Biomaterials Utilizing Microfluidic Technology

Recently, microfluidic technologies have attracted an enormous amount of interest as potential new tools for a large range of applications including materials synthesis, chemical and biological detection, drug delivery and screening, point-of-care diagnostics, and in-the-field analysis. Their ability to handle extremely small volumes of fluids is accompanied by additional benefits, most notably, rapid and efficient mass and heat transfer. In addition, reactions performed within microfluidic systems are highly controlled, meaning that many advanced materials, with uniform and bespoke properties, can be synthesized in a direct and rapid manner. In this review, we discuss the utility of microfluidic systems in the synthesis of materials for a variety of biological applications. Such materials include microparticles or microcapsules for drug delivery, nanoscale materials for medicine or cellular assays, and micro- or nanofibers for tissue engineering.

Highly tuneable proton-conducting coordination polymers derived from a sulfonate-based ligand

Three highly proton-conducting coordination compounds have been synthesized via the HCl steaming-assisted conversion approach by using multiple functional groups including the sulfonate group and the Cl⁻ or HPO₄²⁻ group.

Polycaprolactone Microfibrous Scaffolds to Navigate Neural Stem Cells

Fibrous scaffolds have shown promise in tissue engineering due to their ability to improve cell alignment and migration. In this paper, poly(ε-caprolactone) (PCL) fibers are fabricated in different sizes using a microfluidic platform. By using this approach, we demonstrated considerable flexibility in ability to control the size of the fibers. It was shown that the average diameter of the fibers was obtained in the range of 2.6-36.5 μm by selecting the PCL solution flow rate from 1 to 5 μL min^-1 and the sheath flow rate from 20 to 400 μL min^-1 in the microfluidic channel. The microfibers were used to create 3D microenvironments in order to investigate growth and differentiation of adult hippocampal stem/progenitor cells (AHPCs) in vitro. The results indicated that the 3D topography of the PCL substrates, along with chemical (extracellular matrix) guidance cues supported the adhesion, survival, and differentiation of the AHPCs. Additionally, it was found that the cell deviation angle for 44-66% of cells on different types of fibers was less than 10°. This reveals the functionality of PCL fibrous scaffolds for cell alignment important in applications such as reconnecting serious nerve injuries and guiding the direction of axon growth as well as regenerating blood vessels, tendons, and muscle tissue.

Designing highly structured polycaprolactone fibers using microfluidics

Microfibers are becoming increasingly important for biomedical applications such as regenerative medicine and tissue engineering. We have used a microfluidic approach to create polycaprolactone (PCL) microfibers in a controlled manner. Through the variations of the sheath fluid flow rate and PCL concentration in the core solution, the morphology of the microfibers and their cross-sections can be tuned. The microfibers were made using PCL concentrations of 2%, 5%, and 8% in the core fluid with a wide range of sheath-to-core flow rate ratios from 120:5µL/min to 10:5µL/min, respectively. The results revealed that the mechanical properties of the PCL microfibers made using microfluidic approach were significantly improved compared to the PCL microfibers made by other fiber fabrication methods. Additionally, it was demonstrated that by decreasing the flow rate ratio and increasing the PCL concentration, the size of the microfiber could be increased. Varying the sheath-to-core flow rate ratios from 40:5 to 10:5, the tensile stress at break, the tensile strain at break, and the Young׳s modulus were enhanced from 24.51MPa to 77.07MPa, 567% to 1420%, and 247.25MPa to 539.70MPa, respectively. The porosity and roughness of microfiber decreased when the PCL concentration increased from 2% to 8%, whereas changing the flow rate ratio did not have considerable impact on the microfiber roughness.

On-chip synthesis of fine-tuned bone-seeking hybrid nanoparticles

Aims: Here we report a one-step approach for reproducible synthesis of finely tuned targeting multifunctional hybrid nanoparticles (HNPs). Materials & methods: A microfluidic-assisted method was employed for controlled nanoprecipitation of bisphosphonate-conjugated poly(D,L-lactide-co-glycolide) chains, while coencapsulating superparamagnetic iron oxide nanoparticles and the anticancer drug Paclitaxel. Results: Smaller and more compact HNPs with narrower size distribution and higher drug loading were obtained at microfluidic rapid mixing regimen compared with the conventional bulk method. The HNPs were shown to have a strong affinity for hydroxyapatite, as demonstrated in vitro bone-binding assay, which was further supported by molecular dynamics simulation results. In vivo proof of concept study verified the prolonged circulation of targeted microfluidic HNPs. Biodistribution as well as noninvasive bioimaging experiments showed high tumor localization and suppression of targeted HNPs to the bone metastatic tumor. Conclusion: The hybrid bone-targeting nanoparticles with adjustable characteristics can be considered as promising nanoplatforms for various theragnostic applications.

Enhanced osteogenic differentiation of stem cells via microfluidics synthesized nanoparticles

Advancement of bone tissue engineering as an alternative for bone regeneration has attracted significant interest due to its potential in reducing the costs and surgical trauma affiliated with the effective treatment of bone defects. We have improved the conventional approach of producing polymeric nanoparticles, as one of the most promising choices for drug delivery systems, using a microfluidics platform, thus further improving our control over osteogenic differentiation of mesenchymal stem cells. Molecular dynamics simulations were carried out for theoretical understanding of our experiments in order to get a more detailed molecular-scale insight into the drug-carrier interactions. In this work, with the sustained intracellular delivery of dexamethasone from microfluidics-synthesized nanoparticles, we explored the effects of particle design on controlling stem cell fates. We believe that the insights learned from this work will lead to the discovery of new strategies to tune differentiation for in situ differentiation or stem cell therapeutics.

FROM THE CLINICAL EDITOR

The use of mesenchymal stem cells has been described by many researchers as a novel therapy for bone regeneration. One major hurdle in this approach is the control of osteogenic differentiation. In this article, the authors described elegantly their microfluidic system in which dexamethasone loaded nanoparticles were produced. This system would allow precise fabrication of nanoparticles and consequently higher efficiency in cellular differentiation.

Microfluidic spinning of micro- and nano-scale fibers for tissue engineering

Microfluidic technologies have recently been shown to hold significant potential as novel tools for producing micro- and nano-scale structures for a variety of applications in tissue engineering and cell biology. Over the last decade, microfluidic spinning has emerged as an advanced method for fabricating fibers with diverse shapes and sizes without the use of complicated devices or facilities. In this critical review, we describe the current development of microfluidic-based spinning techniques for producing micro- and nano-scale fibers based on different solidification methods, platforms, geometries, or biomaterials. We also highlight the emerging applications of fibers as bottom-up scaffolds such as cell encapsulation or guidance for use in tissue engineering research and clinical practice.

Microfluidic-assisted self-assembly of complex dendritic polyethylene drug delivery nanocapsules

Microfluidic platform for the synthesis of complex nanocapsules is presented via a controlled self-assembly. The monodisperse nanocapsules in the range of 50-200 nm consist of a dendritic polyethylene core and a Pluronic copolymer shell. The resultant nanocarriers encapsulate large amount of hydrophobic anticancer drug like paclitaxel while providing a low complement activation as well as sustained release profile with high tunability.