Helical Microfibers Research Articles

Electrochemically Switchable Circularly Polarized Photoluminescence within Self-Assembled Conducting Polymer Helical Microfibers.

Achieving electrically and/or electrochemically controlled circularly polarized photoluminescence (CPL) is challenging due to the non-electroactive characteristics of most chiral materials and the non-electrosensitive feature of materials' chiroptical signals. Here we found that the CPL of self-assembled conducting polyaniline (PANI) helical microfibers could be reversibly switched by applying an alternating electrical bias. The conducting polymer is not the fluorophore but can transfer its chirality to the coassembled aggregation-induced emission (AIE) fluorescent molecules. The electrochemically switchable CPL is derived from the reversible transformation of the chirality of the polyaniline microfibers, which is probably due to the change in the molecular interchain distance upon doping/dedoping. Subsequently, we have demonstrated double-layer information encryption based on the electrochemically reversible CPL and conductance.

Microfluidic generation of helical micromotors for muscle tissue engineering

Building units play an important and critical role in muscle tissue engineering, which has aroused increasing attention in recent decades. The current muscle units are suffering from over-simplified constructions and complicated fabrication approaches. Thus, we proposed a kind of helical micromotor with the technique of microfluidics to build tissue constructions for muscle tissue engineering. The desired micromotors were achieved by encapsulating muscle cells together with magnetic iron oxide nanoparticles (Fe3O4 NPs) in helical microfibers with biocompatible materials. The helical structures and encapsulated Fe3O4 NPs imparted micromotors with the capacity of advancing in rotation under magnetic fields; while biocompatible components made it possible for cell adhesion, proliferation, and migration. By adjusting the intensity of magnetic fields, the helical pitch of microfibers, or/and the concentration of Fe3O4 NPs, the movement speed of the achieved micromotors could be changed correspondingly. Benefiting from the controllable movement and sufficient cell cultivation, the generated micromotors were capable of assembling together to form a cell mass construction in a relatively safe and convenient environment. Furtherly, fibroblasts could be cultured on the surface of the assembled cell units to achieve complex muscle tissue structures, which would be more similar to in vivo tissue units. These characteristics indicated that the desired helical micromotors had a great application prospect in tissue regeneration, artificial muscle, cell cultured meat and other fields.

High-Throughput and Controllable Fabrication of Helical Microfibers by Hydrodynamically Focusing Flow.

Due to the unique spiral geometry, different functional helical fibers are fabricated to perform vital tasks, including cargo transportation, medical treatment, cell manipulation, and so on. Although microfluidic techniques are widely used to fabricate helical fibers, the problems of channel blockage and spinning instability have not been well solved, which limits the mass preparation and practical application of spiral microfibers. In addition, the spinning mechanism is simply limited to liquid rope coiling, which has little impact on the design of microfluidic devices. Here, new types of microfluidic devices, which were easy to make and exhibited excellent spiral spinning performance, were designed. It was found that adding a sleeve layer outside the inner core needle in a coaxial microfluidic device could effectively promote the stable formation of helical microfibers. This novel microchannel could fabricate helical microfibers of more than 100 m in length continuously at one time with almost no blockage or deformation, and the key parameters of the fibers could be precisely adjusted. Combined with micro-particle image velocimetry (micro-PIV) measurements, it was confirmed that the improvement in the spinning performances was mainly attributed to the emergence of a focusing flow in the presence of the sleeve layer. After loading magnetic nanoparticles, the helical microfibers exhibited excellent motion manipulation capabilities, which showed great potential for drug delivery, cargo transportation, clogging removal, etc. This new design not only realized the high-throughput fabrication of helical microfibers but also provided deeper insights into the underlying mechanisms of spiral generation and new ideas for the design of microfluidic devices.

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

AbstractMicrofluidic 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.

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.

Morphological Hydrogel Microfibers with MXene Encapsulation for Electronic Skin.

Electronic skins with distinctive features have attracted remarkable attention from researchers because of their promising applications in flexible electronics. Here, we present novel morphologically conductive hydrogel microfibers with MXene encapsulation by using a multi-injection coflow glass capillary microfluidic chip. The coaxial flows in microchannels together with fast gelation between alginate and calcium ions ensure the formation of hollow straight as well as helical microfibers and guarantee the in situ encapsulation of MXene. The resultant hollow straight and helical MXene hydrogel microfibers were with highly controllable morphologies and package features. Benefiting from the easy manipulation of the microfluidics, the structure compositions and the sizes of MXene hydrogel microfibers could be easily tailored by varying different flow rates. It was demonstrated that these morphologically conductive MXene hydrogel microfibers were with outstanding capabilities of sensitive responses to motion and photothermal stimulations, according to their corresponding resistance changes. Thus, we believe that our morphologically conductive MXene hydrogel microfibers with these excellent features will find important applications in smart flexible electronics especially electronic skins.

Microfluidic-directed biomimetic Bulbine torta-like microfibers based on inhomogeneous viscosity rope-coil effect.

Helical structures are attracting increasing attention owing to their unique typical physical and chemical properties. However, it remains a challenge to construct atypical helical structures at the microscale. This paper proposes a continuous spinning method with a microfluidic-chip-based spinning device to engineer atypical helical microfibers. The strategy causes polymer fluid to form the biomimetic Bulbine torta (BT)-like shape with the aid of the inhomogeneous viscosity rope-coil effect. In particular, the structure parameter of the BT microfibers could be optimized through the synchronous regulation of the microfluidic flow and reaction kinetics, and the obtained microfibers exhibit ultrahigh strain sensitivity, indicating great promise as exceptional candidates for constructing ideal strain sensors. In addition, single- and double-hollow BT microfibers are also prepared by introducing the core flow channel into the microfluidic chip and demonstrate high structural similarity to irregular blood vessels (e.g. varicose veins), which is promising for the actual application of blood vessel tissue engineering.

Photopolymerization with high-order Bessel light beams.

We study photopolymerization with high-order Bessel light beams with phase singularities on-axis. Self-trapping and self-focusing of propagation-invariant light beams in a photopolymer allow the fabrication of extended helical microfibers with a length scale of a centimeter, which is more than an order of magnitude larger than the propagation distance of the Bessel light beams. We show the evolution of microfibers rotating at a rate proportional to the incident optical power, while the periodicity of the helical structures remains constant, irrespective of the laser power. This suggests that optical momentum transfer plays a predominant role in the growth and rotation of such fiber structures.

Wet-spinning of magneto-responsive helical chitosan microfibers.

Helical structures can be found in nature at various length scales ranging from the molecular level to the macroscale. Due to their ability to store mechanical energy and to optimize the accessible surface area, helical shapes contribute particularly to motion-driven processes and structural reinforcement. Due to these special features, helical fibers have become highly attractive for biotechnological and tissue engineering applications. However, there are only a few methods available for the production of biocompatible helical microfibers. Given that, we present here a simple technique for the fabrication of helical chitosan microfibers with embedded magnetic nanoparticles. Composite fibers were prepared by wet-spinning and coagulation in an ethanol bath. Thereby, no toxic components were introduced into the wet-spun chitosan fibers. After drying, the helical fibers had a diameter of approximately 130 µm. Scanning electron microscopy analysis of wet-spun helices revealed that the magnetic nanoparticles agglomerated into clusters inside the fiber matrix. The helical constructs exhibited a diameter of approximately 500 µm with one to two windings per millimeter. Due to their ferromagnetic properties they are easily attracted to a permanent magnet. The results from the tensile testing show that the helical chitosan microfibers exhibited an average Young’s modulus of 14 MPa. By taking advantage of the magnetic properties of the feedstock solution, the production of the helical fibers could be automated. The fabrication of the helical fibers was achieved by utilizing the magnetic properties of the feedstock solution and winding the emerging fiber around a rotating magnetic collector needle upon coagulation. In summary, our helical chitosan microfibers are very attractive for future use in magnetic tissue engineering or for the development of biocompatible actuator systems.

Core–Sheath Wet Electrospinning of Nanoporous Polycaprolactone Microtubes to Mimic Fenestrated Capillaries

Back Cover: In article number 2000180, George Z. Tan and Yingge Zhou present a novel core–sheath wet electrospinning approach to fabricate nanoporous polycaprolactone microtubes as potential functional capillaries for tissue engineering. The solution viscosity and humidity significantly influence the morphology of electrospun polymers, leading to various products including porous microbeads, helical microfibers, and microtubes. The nanoporous microtubes have similar size and morphology to human fenestrated capillary vessels.

Generation of perfusable hollow calcium alginate microfibers with a double co-axial flow capillary microfluidic device.

This paper describes a highly controllable method to generate hollow calcium alginate microfibers using a double co-axial flow microdevice. The microdevice was fabricated by concentric assembly of two modules; each module consisted of a shortened cone-pulled glass capillary embedded in a polymethylmethacrylate fluidic block. Using this microdevice, cylindrical hollow calcium alginate microfibers with either straight or helical inner walls were stably and continuously generated. The radii of the hollow microfibers were not arbitrary, and in fact, the ratio of the outer to inner diameter was inversely correlated with the combination of core flow rate and the first sheath flow rate. The relationships between the geometrical features of the helix and the flow rates were also analyzed. The helical pitch and the spiral radius of the helical hollow microfibers were strongly influenced by the second sheath flow rate. Finally, guidelines for generating highly controllable straight and helical hollow microfibers and fabricating a seamless flow connector using this microfluidic device are suggested.

Effects of Compatibilizer and Airflow Field on the Formation of Helical Microfibers via Melt Blowing

ABSTRACTWe explore the approaches to improving the fabrication of melt‐blown helical microfibers, which have found the applications in sorption and filtration due to their unique morphology and excellent properties. To explore the effect of compatibilizer on the formation of helical microfiber, polypropylene (PP), polyurethane (TPU), and PP grafted with maleic anhydride (PP‐g‐MAH) are melt blown to fabricate microfibrous nonwovens. The results of rheological test and differential scanning calorimetry show that the addition of PP‐g‐MAH helps to increase the miscibility of the PP/TPU blends. Two die configurations are used to study the effect of airflow filed on the formation of helical microfibers. The computational fluid dynamics simulation results show that the modified swirl die intensifies the swirling strength of the melt blowing airflow. The addition of compatibilizer and modification of the airflow field both benefit the formation of helical microfibers from polymer blends. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1423–1433

Formation of helical alginate microfibers using different G/M ratios of sodium alginate based on microfluidics

The helical structure is one of the most intriguing structures in nature; such an ingenious structure can be found from macromolecules to macroscopic areas, and the fabrication of helical structures has attracted research interest from mechanisms to applications. However, the fabrication of helical microfiber still remains a big challenge. In this study, a coaxial microfluidic device was made to continuously and controllably fabricate helical hydrogel microfibers with flexible shape by simply adjusting the flowrates. Various experimental conditions that can influence the diameter (d), pitch (p) and amplitude (A) of these formed coiled fibers were discussed. For the first time, the effects of G/M ratio of the alginates on the microfiber coiling phenomenon were examined. Additionally, magnetically responsive helical fibers were synthesized, and it is envisioned that hydrogel helical structure microfibers are highly versatile in different area, such as micro sensors, soft actuators and medical applications.

Microfluidic Fabrication of Biomimetic Helical Hydrogel Microfibers for Blood-Vessel-on-a-Chip Applications.

Nature has created many perfect helical microstructures, including DNA, collagen fibrils, and helical blood vessels, to achieve unique physiological functions. While previous studies have developed a number of microfabrication strategies, the preparation of complex helical structures and cell-laden helical structures for biomimetic applications remains challenging. In this study, a one-step microfluidics-based methodology is presented for preparing complex helical hydrogel microfibers and cell-laden helical hydrogel microfibers. Several types of complex helical structures, including multilayer helical microfibers and superhelical hollow microfibers with helical channels, are prepared by simply tuning the flow rates or modifying the geometry of microfluidic device. With the decent perfusability, the hollow microfibers may simulate the structural characteristics of helical blood vessels and create swirling blood flow in a blood-vessel-on-chip setup. Such hydrogel-based helical microstructures may potentially be used in areas such as blood vessel tissue engineering, organ-on-chips, drug screening, and biological actuators.

Bioinspired Polymeric Helical and Superhelical Microfibers via Microfluidic Spinning.

The helix and superhelix play critical roles in the achievement of tissue functions. These fascinating structures have attracted increasing interest due to their potential biomimicking applications. However, continuous and controlled fabrication of these structures, especially the superhelical structures, from various polymers for different practical applications still remains a big challenge. Here, a novel and versatile microfluidic spinning strategy is presented for generation of both helical and superhelical microfibers from either hydrophilic, hydrophobic, or amphiphilic polymers. The diameter (d ), wavelength (λ), and amplitude (A) of these microfibers could be highly controlled. The helical microfibers show outstanding elongations and potential applications in magnetic responsive elastic microactuators. It is envisioned that these results will greatly enrich the possibility of generating new multiple-ordered structures from various polymers for applications in different areas.

Controllable Microfluidic Fabrication of Magnetic Hybrid Microswimmers with Hollow Helical Structures

Controllable magnetic hybrid microswimmers with hollow helical structures are fabricated, by a facile strategy based on microfluidic template synthesis and biosilicification, to achieve enhanced rotation-based locomotion for cargo transport. The magnetic hybrid microswimmers are fabricated by first synthesizing Fe3O4-nanoparticles-containing helical Ca-alginate microfibers from microfluidics, followed with biosilicification and controllable dicing to engineer their rigid hollow helical structures. The microswimmers show hollow helical structures consisting of a rigid, biocompatible alginate/protamine/silica shell embedded with Fe3O4 nanoparticles. Their helical structures can be engineered into open tubular structures or closed compartmental structures by using microfibers or diced microfibers as templates for biosilicification. Powered by a simple rotating magnet, the microswimmers can achieve enhanced rotation-based locomotion and provide good mechanical strength for supporting cargo for transportation....

Fabrication of helical microfibers from melt blown polymer blends

ABSTRACTHelical fibers in micro/nanoscale resembling plant tendrils have been of increasing interest due to their unique characteristics. Fabrication of helical microfibers from polymer blends using melt blowing technique is reported in this study. An elastomeric and a stiff polymer are chosen as the raw materials, and a designed swirl‐die melt‐blowing device is used to prepare the microfibrous nonwovens. Focusing on the interfacial interaction between the polymer components induced by the polymer structure and intrinsic properties, airflow field characteristics, and processing parameters, we explore the effects of various parameters on helical fiber formation. Differential scanning calorimeter is employed to examine the rigidity of polymer chains, and the three‐dimensional airflow field simulation is carried out to reveal the airflow field characteristics. This work can provide a promising technique for producing stretchable microfibrous materials which have potential applications in field such as filtration materials and oil sorbents. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2018,56, 970–977

Compartmentalized Microhelices Prepared via Electrohydrodynamic Cojetting.

Anisotropically compartmentalized microparticles have attracted increasing interest in areas ranging from sensing, drug delivery, and catalysis to microactuators. Herein, a facile method is reported for the preparation of helically decorated microbuilding blocks, using a modified electrohydrodynamic cojetting method. Bicompartmental microfibers are twisted in situ, during electrojetting, resulting in helical microfibers. Subsequent cryosectioning of aligned fiber bundles provides access to helically decorated microcylinders. The unique helical structure endows the microfibers/microcylinders with several novel functions such as translational motion in response to rotating magnetic fields. Finally, microspheres with helically patterned compartments are obtained after interfacially driven shape shifting of helically decorated microcylinders.

Coiled Plant Tendril Bioinspired Fabrication of Helical Porous Microfibers for Crude Oil Cleanup.

Fabrication of the helical fibers with sheath/core structure comprising 3D interconnected porous polystyrene (PS) and ductile polyvinylidene fluoride is inspired by coiled plant tendril. The key innovation point applied in this study is to produce a helical porous system based on sheath/core structure that can come into being a huge storage space in the sorption process for crude oil. More importantly, the mechanical properties confirm to have a more excellent improvement than that of the initial PS fibers, which make it become a possible candidate for the large‐area sorption and reuse of crude oil from the ocean or industry. The bioinspired fabricating strategy opens a significant avenue between the coaxial electrospinning and crude oil contamination cleanup. It is also expected that the unique structure can make it a promising candidate for applications in energy conversion, tissue engineering, and intelligent devices.

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.