A PEDOT: PSS/GO fiber microelectrode fabricated by microfluidic spinning for dopamine detection in human serum and PC12 cells.

Rapid and accurate in situ determination of dopamine is of great significance in the study of neurological diseases. In this work, poly (3,4-ethylenedioxythiophene): poly (styrenesulfonic acid) (PEDOT: PSS)/graphene oxide (GO) fibers were fabricated by an effective method based on microfluidic wet spinning technology. The composite microfibers with stratified and dense arrangement were continuously prepared by injecting PEDOT: PSS and GO dispersion solutions into a microfluidic chip. PEDOT: PSS/GO fiber microelectrodes with high electrochemical activity and enhanced electrochemical oxidation activity of dopamine were constructed by controlling the structure composition of the microfibers with varying flow rate. The fabricated fiber microelectrode had a low detection limit (4.56 nM) and wide detection range (0.01-8.0 µM) for dopamine detection with excellent stability, repeatability, and reproducibility. In addition, the PEDOT: PSS/GO fiber microelectrode prepared was successfully used for the detection of dopamine in human serum and PC12 cells. The strategy for the fabrication of multi-component fiber microelectrodes is a new and effective approach for monitoring the intercellular neurotransmitter dopamine and has high potential as an implantable neural microelectrode.

Tough, Highly Oriented, Super Thermal Insulating Regenerated All-Cellulose Sponge-Aerogel Fibers Integrating a Graded Aligned Nanostructure.

Thermal insulating fibers can effectively regulate the human body temperature and decrease indoor energy consumption. However, designing super thermal insulating fibers integrating a sponge and aerogel structure based on biomass resources is still a challenge. Herein, a flow-assisted dynamic dual-cross-linking strategy is developed to realize the steady fabrication of regenerated all-cellulose graded sponge-aerogel fibers (CGFs) in a microfluidic chip. The chemically cross-linked cellulose solution is used as the core flow, which is passed through two sheath flow channels, containing either a diffusion solvent or a physical cross-linking solvent, resulting in CGFs with a porous sponge outer layer and a dense aerogel inner layer. By regulating and simulating the flow process in the microfluidic chip, CGFs with adjustable sponge thicknesses, excellent toughness (26.20 MJ m-3), and ultralow thermal conductivity (0.023 W m-1 K-1) are fabricated. This work provides a new method for fabricating graded biomass fibers and inspires attractive applications for thermal insulation in textiles.

A Phase Inversion-Based Microfluidic Fabrication of Helical Microfibers towards Versatile Artificial Abdominal Skin.

Microfluidic spinning technology (MST), incorporating microfluidics with chemical reactions, has gained considerable interest for constructing anisotropic advanced microfibers, especially helical microfibers. However, these efforts suffer from the limited material choices, restricting their applications. Here, a new phase inversion-based microfluidic spinning (PIMS) method is proposed for producing helical microfibers. This method undergoes a physicochemical phase inversion process, which is capable of efficiently manufacturing strong (tensile stress of more than 25 MPa), stretchable, flexible and biocompatible helical microfibers. The helical microfibers can be used to fabricate bi-oriented stretchable artificial abdominal skin, preventing incisional hernia formation and promoting the wound healing without conglutination. This research not only offers a universal approach to design helical microfibers but also provides a new insight into artificial skin.

Modulating the Mechanical Performance of Macroscale Fibers through Shear-Induced Alignment and Assembly of Protein Nanofibrils.

Protein-based fibers are used by nature as high-performance materials in a wide range of applications, including providing structural support, creating thermal insulation, and generating underwater adhesives. Such fibers are commonly generated through a hierarchical self-assembly process, where the molecular building blocks are geometrically confined and aligned along the fiber axis to provide a high level of structural robustness. Here, this approach is mimicked by using a microfluidic spinning method to enable precise control over multiscale order during the assembly process of nanoscale protein nanofibrils into micro- and macroscale fibers. By varying the flow rates on chip, the degree of nanofibril alignment can be tuned, leading to an orientation index comparable to that of native silk. It is found that the Young's modulus of the resulting fibers increases with an increasing level of nanoscale alignment of the building blocks, suggesting that the mechanical properties of macroscopic fibers can be controlled through varying the level of ordering of the nanoscale building blocks. Capitalizing on strategies evolved by nature, the fabrication method allows for the controlled formation of macroscopic fibers and offers the potential to be applied for the generation of further novel bioinspired materials.

Microarrays formed by microfluidic spinning as multidimensional microreactors.

The exploration of methods allowing chemical reactions to be carried out at ultrasmall scales is of great scientific and technological interest. We report herein a microfluidic spinning technique for the fabrication of softened-polymer microarrays for use as multidimensional microreactors and the application of these microreactors in the synthesis of fluorescent nanocrystals. Highly aligned microarrays and controlled-angle grids were readily constructed from microfluidically spun polyvinylpyrrolidone (PVP) microfibers. One-zero dimensional (1D-0D), one-one dimensional (1D-1D), and one-two dimensional (1D-2D) microreactors were then produced by the intersections between microfibers and droplets, crossed microfibers, and microfibers and a PVP film, respectively; each component can be doped with different reagents. Specific examples show that these multidimensional microreactors enable the in situ generation of fluorescent nanocrystals without ligands within minutes.

One-Step Microfluidic Fabrication of Bioinspired Microfibers with a Spindle-Knot Structure for Fog Harvest.

Many biomimetic microfibers have been designed from spider silk to collect water efficiently from humid air as a result of its periodic spindle-knot structure, which enhances the direct movement and convergence of captured fog droplets. Here, a hydrodynamic flow-focusing microfluidic device with a theta-shaped tube is designed for the one-step fabrication of bioinspired microfibers with a spindle-knot structure for fog harvest. The morphology of the structured microfibers, including height, width, and spacing of spindle knots, can be adjusted readily by regulating the flow rate of specific phases. The production rate of these structured microfibers can reach 1100 cm/min. Moreover, the capture, transportation, and collection performance of fog droplets on various microfibers are investigated in a fog collection platform. It is demonstrated that our one-step microfluidic device presents a ready method for the fabrication of structured microfibers with spindle knots, which provide a significant facilitation on efficient fog capture and water collection.

Engineered Microfibers for Tissue Engineering.

Hydrogel microfibers are hydrogel materials engineered into fiber structures. Techniques such as wet spinning, microfluidic spinning, and 3D bioprinting are often used to prepare microfibers due to their ability to precisely control the size, morphology, and structure of the microfibers. Microfibers with different structural morphologies have different functions; they provide a flow-through culture environment for cells to improve viability, and can also be used to induce the differentiation of cells such as skeletal muscle and cardiac muscle cells to eventually form functional organs in vitro through special morphologies. This Review introduces recent advances in microfluidics, 3D bioprinting, and wet spinning in the preparation of microfibers, focusing on the materials and fabrication methods. The applications of microfibers in tissue engineering are highlighted by summarizing their contributions in engineering biomimetic blood vessels, vascularized tissues, bone, heart, pancreas, kidney, liver, and fat. Furthermore, applications of engineered fibers in tissue repair and drug screening are also discussed.

Core-Shell Gel Nanofiber Scaffolds Constructed by Microfluidic Spinning toward Wound Repair and Tissue Regeneration.

Growing demand for wound care resulting from the increasing chronic diseases and trauma brings intense pressure to global medical health service system. Artificial skin provides mechanical and microenvironmental support for wound, which is crucial in wound healing and tissue regeneration. However, challenges still remain in the clinical application of artificial skin since the lack of the synergy effect of necessary performance. In this study, a multi-functional artificial skin is fabricated through microfluidic spinning technology by using core-shell gel nanofiber scaffolds (NFSs). This strategy can precisely manipulate the microstructure of artificial skin under microscale. The as-prepared artificial skin demonstrates superior characteristics including surface wettability, breathability, high mechanical strength, strain sensitivity, biocompatibility and biodegradability. Notably, this artificial skin has the capability to deliver medications in a controlled and sustained manner, thereby accelerating the wound healing process. This innovative approach paves the way for the development of a new generation of artificial skin and introduces a novel concept for the structural design of the unique core-shell gel NFSs.

Preparation of Antibacterial Biobased Fibers by Triaxial Microfluidic Spinning Technology Using Ionic Liquids as the Solvents.

Bacterial infections have become a serious threat to public health. The utilization of antibacterial textiles offers an effective way to combat bacterial infections at the source, instead of relying solely on antibiotic consumption. Herein, efficient and durable antibacterial fibers based on quercetin and cellulose were prepared by a triaxial microfluidic spinning technology using ionic liquids (ILs) as the solvents. It was indicated that the structure and properties of the antibacterial fibers were affected by the type of IL and the flow rates during the triaxial microfluidic spinning process. Quercetin regenerated from [Emim]Ac underwent structural transformation and obtained an increased water solubility, while quercetin regenerated from [Emim]DEP remained unchanged, which was proven by FI-IR, XRD, and UV analyses. Furthermore, antibacterial fibers regenerated from [Emim]Ac exhibited the highest antibacterial activity of 96.9% against S. aureus, achieved by reducing the inner-to-outer flow rate ratio to 0 and concentrating quercetin at the center of fibers. On the other hand, when [Emim]DEP was used as the solvent, balancing the inner-to-outer flow rate ratio to concentrate quercetin in the middle layer of the fiber was optimal for achieving the best antibacterial activity of 93.3% because it promised both the higher encapsulation efficiency and release rate. Computational fluid dynamics (CFD) mathematically predicted the solvent exchange process during triaxial spinning, explaining the influence of IL types and flow rates on quercetin distribution and encapsulation efficiency. It was indicated that optimizing the distribution of antibacterial agents within the fibers can fully unleash its antibacterial potential while preserving the mechanical properties of the fiber. Therefore, the proposed simple triaxial spinning strategy provides valuable insights into the design of biomedical materials.

Micro-structure and tensile properties of microfluidic spinning konjac glucomannan and sodium alginate composite bio-fibers regulated by shear and elongational flow: experiment and multi-scale simulation.

Microfluidic spinning has been widely used to produce bio-fibers with excellent tensile performances by regulating the conformation of biological macromolecules. However, the effect of channel shapes on fiber tensile performances is unclear. In this study, bio-fibers were prepared using konjac glucomannan and sodium alginate by five channels. The micro-morphology and tensile performance of fibers were characterized and measured. Then, the dynamical behaviours of macromolecule clusters in flow fields were simulated by multi-scale numerical methods. The results show that the elongational flow with increasing extension rates produced fibers with a tensile strength of 32.34 MPa and a tensile strain of 18.72 %, which were 1.37 and 1.55 times that for a shear flow, respectively. The difference in tensile performances was attributed to the micro-morphology regulated by flow fields. The continuously increasing extension rate of flow was more effective than the shear rate or the maximum extension rate for the stretching of macromolecule clusters. We conclude that the channel shapes significantly influence flow fields, dynamical behaviours of molecule clusters, the morphology of fibers, and tensile performances. This study provides a novel numerical method and understanding of microfluidic spinning, which will promote the optimization and applications of bio-fibers.

Microfiber Fabricated via Microfluidic Spinning toward Tissue Engineering Applications.

Microfibers, a type of long, thin, and flexible material, can be assembled into functional 3D structures by folding, binding, and weaving. As a novel spinning method, combining microfluidic technology and wet spinning, microfluidic spinning technology can precisely control the size, morphology, structure, and composition of the microfibers. Particularly, the process is mild and rapid, which is suitable for preparing microfibers using biocompatible materials and without affecting the viability of cells encapsulated. Furthermore, owing to the controllability of microfluidic spinning, microfibers with well-defined structures (such as hollow structures) will contribute to the exchange of nutrients or guide cell orientation. Thus, this method is often used to fabricate microfibers as cell scaffolds for cell encapsulation or adhesion and can be further applied to biomimetic fibrous tissues. In this review, the focus is on different fiber structures prepared by microfluidic spinning technology, including solid, hollow, and heterogeneous structures, generated from three essential elements: spinning platform, fiber composition, and solidification methods. Furthermore, the application of microfibers is described with different structures in tissue engineering, such as blood vessels, skeletal muscle, bone, nerves, and lung bronchi. Finally, the challenges and future development prospects of microfluidic spinning technology in tissue engineering applications are discussed.

Dissolvable Calcium Alginate Microfibers Produced via Immersed Microfluidic Spinning.

Fabrication of micro- and nanofibers are critical for a wide range of applications from microelectronics to biotechnology. Alginate microfibers with diameters of tens to hundreds of microns play an important role in tissue engineering and fibers of these diameters are impossible to fabricate via electrospinning and can only be produced via fluidic spinning. Typically, microfluidic spinning based on photopolymerization produces fibers that are not easily dissolvable, while fluidic spinning with chemical cross-linking employs complex setups of microfabricated chips or coaxial needles, aimed at precise control of the fiber diameter; however, fluidic spinning introduces significant cost and complexity to the microfluidic setup. We demonstrate immersed microfluidic spinning where a calcium alginate microfiber is produced via displacement of alginate solution through a single needle that is immersed in a cross-linking bath of calcium chloride solution. The resulting diameter of the fiber is characterized and the fiber diameter and topology of the deposited fiber is related to the concentration of the alginate solution (2 wt%, 4 wt%, and 6 wt%), needle gauge (30 g, 25 g, and 20 g), and the volumetric flow rate of the alginate solution (1 mL/min, 2 mL/min, and 2.7 mL/min). The resulting fiber diameter is smaller than the internal diameter of the needle and this dependence is explained by the continuity of the flow and increased rate of fall of the liquid jet upon its issuing from the needle. The fiber diameter (demonstrated diameter of fibers range from 100 microns to 1 mm) depends weakly on the volumetric flow rate and depends strongly on the needle diameter. It also seems that for a smaller needle size, a greater concentration of alginate results in smaller diameter fibers and that this trend is not evident as the needle diameter is increased. In terms of topology of the deposited fiber, the higher wt% alginate fiber produces larger loops, while smaller wt% alginate solution yields a denser topology of the overlaid fiber loops. These fibers can be dissolved in DMEM/EDTA/DSC solution in 20-30 min (depending on the fiber diameter), leaving behind the hollow channels in the hydrogel matrix. We believe that the demonstrated simple setup of the immersed microfluidic spinning of the calcium alginate microfibers will be useful for creating tissue constructs, including the vascularized tissue implants.

Natamycin-Loaded Ethyl Cellulose/PVP Films Developed by Microfluidic Spinning for Active Packaging.

The preparation of active packaging loaded with antimicrobial, antioxidant, and other functional agents has become a hot topic for food preservation in recent years. In this field, active fiber films based on spinning methods have attracted the interest of researchers owing to their high specific surface area, high porosity, high loading capacity, and good controlled release capacity. In the present work, neatly arranged ethyl cellulose (EC)/polyvinyl-pyrrolidone (PVP) fibrous films loaded with natamycin as an antimicrobial agent were prepared by microfluidic spinning. The encapsulation efficiency of natamycin was more than 90% in each group and the loading increased with increasing natamycin content. According to the characterization results of the natamycin-loaded EC/PVP fibrous films, hydrogen bonding was formed between natamycin and EC and PVP in the fibrous films. Meanwhile, the water contact angle of the fibrous films was increased, suggesting the improved hydrophobicity of the films. In the in vitro bacterial inhibition experiments, the active fiber films loaded with natamycin showed good antimicrobial activity, which could significantly inhibit the growth of gray mold. In conclusion, N-EC/PVP fibrous films with antimicrobial activity prepared by microfluidic spinning showed good potential in the field of active packaging.

Axially Encoded Mechano-Metafiber Electronics by Local Strain Engineering.

Multimaterial integration, such as soft elastic and stiff components, exhibits rich deformation and functional behaviors to meet complex needs. Integrating multimaterials in the level of individual fiber is poised to maximize the functional design capacity of smart wearable electronic textiles, but remains unfulfilled. Here, this work continuously integrates stiff and soft elastic components into single fiber to fabricate encoded mechano-metafiber by programmable microfluidic sequence spinning (MSS). The sequences with programmable modulus feature the controllable localization of strain along metafiber length. The mechano-metafibers feature two essential nonlinear deformation modes, which are local strain amplification and retardation. This work extends the sequence-encoded metafiber into fiber networks to exhibit greatly enhanced strain amplification and retardation capability in cascades. Local strain engineering enables the design of highly sensitive strain sensors, stretchable fiber devices to protect brittle components and the fabrication of high-voltage supercapacitors as well as axial electroluminescent arrays. The approach allows the scalably design of multimaterial metafibers with programmable localized mechanical properties for woven metamaterials, smart textiles, and wearable electronics.

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.

Hollow Microfiber Assembly-Based Endocrine Pancreas-on-a-Chip for Sugar Substitute Evaluation.

With the increasing demand for low-sugar, low-calorie healthy diets, artificial sweeteners are widely used as substitutes for sugar in the food industry. Therefore, developing models that can better predict the effects of sugar substitutes on the human body is necessary. Here, a new type of endocrine pancreas-on-a-chip is developed based on a microfiber assembly and its stimulation of pancreatic secretion by glucose or sugar substitutes is evaluated. This new endocrine pancreas-on-a-chip is assembled using two components: (1) a cell-loaded hollow methacrylate gelatin (GelMA)/calcium alginate (CaA) composite microfiber prepared by microfluidic spinning to achieve vascular simulation and material transport, and (2) a 3D pancreatic islet culture layer, which also serves as a fiber assembly microchip. Using this established organ chip, the effects of five sweeteners (glucose, erythritol, xylitol, sodium cyclamate, and sucralose) were investigated on pancreatic islet cell viability and insulin and glucagon secretion. The constructed endocrine pancreas-on-a-chip has potential for the safety evaluation of sugar-substituted food additives, which can expand the application of organ chips in the field of food safety and provide a new platform for evaluating various food additives.

Oriented ascorbic acid onto zeolitic metal-organic framework-8 membrane via microfluidic spinning for biomedical care.

Nowadays, the hydrogen dressing and electrostatic spun films widely used on wounds do not facilitate the permeability of the wound area and fail to achieve controlled drug delivery. Therefore, finding a wound dressing with both breathability and targeted drug delivery has remained an unmet challenge. Here, an oriented microstructure membrane with sustained drug release and robust antibacterial performance was constructed through the microfluidic spinning method. The multifunctional oriented membrane was prepared by loading ascorbic acid onto the zeolitic metal-organic framework-8 to develop drug delivery nanomaterial zeolitic metal-organic framework-8 @ascorbic acid (ZIF-8 @AA) and then mixing ZIF-8 @AA with polyvinyl pyrrolidone (PVP) solution via microfluidic technology, which produced an oriented microfiber member. In addition, the spinning parameters, including the fluid content, rotation speed, and flow rate, on microfiber diameter were evaluated. The constructed oriented membrane had bactericidal efficiencies of 82.94% ± 2.79% and 95.96% ± 1.54% against E. coli and S. aureus, respectively. After five days, the membrane still has a sustained release. Moreover, the fabricated membrane also has good biocompatibility and hemocompatibility in vitro. The oriented arrangement strategy provides a promising approach for wound healing materials in targeted drug delivery. Furthermore, this strategy offers a feasible idea for loading active materials into substrates for disease treatment in the biomedical field.

Coaxial microfluidic spinning design produced high strength alginate membranes for antibacterial activity and drug release.

Directional drug delivery and sufficient strength are two conditions that need to be met for wound dressing. In this paper, an oriented fibrous alginate membrane with sufficient strength was constructed via coaxial microfluidic spinning, and zeolitic imidazolate framework-8/ascorbic acid was used to realize drug delivery and antibacterial activity. The effects of the process parameters of the coaxial microfluidic spinning on the mechanical properties of the alginate membrane were discussed. In addition, it was found that the antimicrobial activity mechanism of zeolitic imidazolate framework-8 was attributed to the disruptive effect of reactive oxygen species (ROS) on bacteria, and the quantitative amount of generated ROS were evaluated by detecting •OH and H2O2. Furthermore, a mathematical drug diffusion model was established and showed high consistency with the experimental data (R2 = 0.99). This study provides a new idea for the preparation of dressing materials with high strength and directional drug delivery and also provides some guidance for the development of coaxial microfluidic spin technology to be used in functional materials for drug release.

Antibacterial and hemostatic polyvinyl alcohol/microcrystalline cellulose reinforced sodium alginate breathable dressing containing Euphorbia humifusa extract based on microfluidic spinning technology.

Antibacterial hemostatic medical dressings have become feasible solutions in response to the challenging wound-healing process. In this study, a novel fiber-type medical dressing with excellent breathable, antibacterial, and hemostatic qualities was created using sodium alginate (SA), microcrystalline cellulose (MCC), polyvinyl alcohol (PVA), and Euphorbia humifusa Willd (EHW) based on microfluidic spinning technology, and the properties of the dressing were characterized. The orthogonal test demonstrates that PVA and MCC can enhance the mechanical properties of the fiber, which is a crucial requirement for fiber assembly to form the dressing. Moreover, the presence of EHW enhances the dressing's antibacterial and hemostatic qualities. The dressings have been proven to have potent antibacterial and hemostatic properties as well as the ability to considerably speed up wound healing and skin tissue regeneration in the in-vitro and in-vivo tests. In conclusion, this innovative fiber-type medical dressing containing SA, MCC, PVA, and EHW has enormous potential for managing wounds caused by bacteria.

3D printing of heterogeneous microfibers with multi-hollow structure via microfluidic spinning.

Tissues with tubular structures play important roles in the human bodies, such as mass transport, nutrition exchange, and waste filtration. However, it remains a challenge to generate micro-scaffolds with well-defined luminal structure in biomedical field. In this study, we proposed a novel method to fabricate multi-component microfibers with multi-hollow structure via microfluidic spinning, which can subsequently be integrated with 3D printing for tissue-like block assembling. To achieve this goal, we fabricated a microchip using a 3D printed template with adjustable heights. Utilizing this microchip, we successfully generated the Calcium alginate microfibers with multi-components and defined hollow structures in a controllable manner. Then this microfluidic spinning method was integrated with a 3D mobile platform to assemble the microfibers into a grid-like 3D architecture. The resulted 3D scaffolds exhibited good organization and maintained the hollow structure of the fibers. Furthermore, we successfully developed a bronchus model utilizing this strategy by loading pulmonary bronchial epithelium cells and endothelial cells into microfibers with two hollow structures. The present strategy provides a potential platform to rebuild the lumen-like tissues using microfibers.