Polymer Microtubes Research Articles

Contactless manipulation of mixed phase fluids in liquid crystal polymer microtubes assisted with light-driven vortex

Smart channels that manipulate liquid motion by anisotropic shape changes represent a promising candidate to construct microfluidics for biochemical analysis. However, the existing systems fail to provide a platform for solid exchange mediums to interact with multiple liquid phases, which is a universal technique to effectively extract, enrich, and precisely detect biomarkers. Herein, a combined photo/magnetic control strategy of mixed phase fluids, which integrates the contactless operations of suspending, depositing, and even separating, is reported for the first time based on a trilayer microtube consisting of a flexible supporting layer, photodeformable liquid crystal polymer, and hydrophilic blocking layer. The asymmetric photodeformation of the liquid crystal polymer generates an internal vortex in the microtube to homogenously disperse solid exchange mediums into various aqueous moving droplets and to enable efficient purification and enrichment of the target biomarkers. A newly constructed homemade portable protein analyzer guided by the combined photo/magnetic control strategy features the advantages of a short detection time (20 min), trace sample consumption (5 μL), and a low detection limit (1 μg mL−1).

Phototuning Energy Transfer in Self‐Organized Luminescent Helical Superstructures for Photonic Applications

AbstractStimuli‐triggered changes in the emission color of functional materials are in demand for a variety of potential applications. Herein, a strategy to reversibly phototune fluorescence color in cholesteric liquid crystal (CLC) with self‐organized luminescent helical superstructure via fluorescence resonance energy transfer (FRET) is developed. This dynamic FRET system is constructed by doping with 1,2‐dithienyldicyanoethene‐based chiral fluorescent photoswitch (switch 7) as an acceptor and a conventional coumarin dye C6 as a donor into a nematic liquid crystal (LC) host. The efficient energy transfer from C6 to switch 7 in the LC media, which is evidenced by both of emission color shift and enhanced circularly polarized luminescence, can be modulated on the basis of reversible trans–cis photoisomerization of switch 7 upon visible/UV light irradiations, leading to the emission color change from orange to green. Noteworthily, the FRET efficiency can be significantly improved when CLCs are confined in the polymer microtubes. Preliminary demonstrations of the LC film and LC microtubes array for information display and encryption with ease of electrical operation between planar, homeotropic, and focal conic states or light manipulation are described.

3D Printing of Vascular Tubes Using Bioelastomer Prepolymers by Freeform Reversible Embedding.

Bioelastomers have been extensively used in tissue engineering applications because of favorable mechanical stability, tunable properties, and chemical versatility. As these materials generally possess low elastic modulus and relatively long gelation time, it is challenging to 3D print them using traditional techniques. Instead, the field of 3D printing has focused preferentially on hydrogels and rigid polyester materials. To develop a versatile approach for 3D printing of elastomers, we used freeform reversible embedding of suspended prepolymers. A family of novel fast photocrosslinakble bioelastomer prepolymers were synthesized from dimethyl itaconate, 1,8-octanediol, and triethyl citrate. Tensile testing confirmed their elastic properties with Young's moduli in the range of 11-53 kPa. These materials supported cultivation of viable cells and enabled adhesion and proliferation of human umbilical vein endothelial cells. Tubular structures were created by embedding the 3D printed microtubes within a secondary hydrogel that served as a temporary support. Upon photocrosslinking and porogen leaching, the polymers were permeable to small molecules (TRITC-dextran). The polymer microtubes were assembled on the 96-well plates custom made by hot-embossing, as a tool to connect multiple organs-on-a-chip. The endothelialization of the tubes was performed to confirm that these microtubes can be utilized as vascular tubes to support parenchymal tissues seeded on them.

Fluorescent sensor of copper(II) ions based on PMBA microtubes with 4-methoxy-1,8-naphthalimide groups

In this article, a high performances hydrophilic tubular fluorescent sensor for Cu(II) detection was fabricated via immobilizing fluorophore 4-methoxy-1,8-naphthalimide groups on poly(N, N′-methylene bisacrylamide) (PMBA) microtubes. The modified polymer microtubes were characterized fully by SEM, FT-IR, EDS mapping, fluorescence microscope and fluorescence spectrometer. This fluorescent sensor displayed high fluorescence emission intensity at 457 nm under irradiation, and exhibited an obvious selective quenching effect in the presence of Cu(II) alone or with a variety of other cations in aqueous solution. Based on the fluorescence intensities before and after quenching, the concentration of Cu(II) could be calculated accurately. Moreover, the fluorescent sensor could be regenerated using ethylene diamine tetraacetic acid (EDTA) as the chelating agent. The regenerated sensor could be reused for many times without performance deteriorate. The mechanism of quenching and regenerating, and the role of the tubes were discussed.

Extrusion as a manufacturing process for polymer micro-tubes for various bio-medical applications

Abstract In various biomedical applications extrusion represents a common manufacturing process for polymeric semi-finished products. Extrusion allows the processing of a wide range of biomaterials, as well as different cross-sectional geometries. The present work focuses on the development of an extrusion process for polymer micro-tubes used for medical devices manufacturing, e.g. microstents for minimally invasive glaucoma therapy. Semi-finished products were manufactured by means of extrusion and dip-coating. Morphology was investigated using biaxial laser measurement and scanning electron microscopy (SEM). For the analysis of mechanical and thermal properties of the specimens uniaxial tensile testing and differential scanning calorimetry (DSC) were performed. While dip-coated micro-tubes reveal a smooth and homogeneous surface, SEM micrographs of extruded micro-tubes exhibit some longitudinal grooves. Mechanical properties of extruded and dip-coated micro-tubes are comparable, so that the presented extrusion process can be regarded suitable for the manufacturing of polymer microtubes in a sub-millimeter scale. A future improvement of nozzle design will allow for a smooth surface of extruded semi-finished products.

Fabrication of carboxyl-functionalized polymer microtubes via RAFT copolymerization of diurea-type xerogel fibers and acrylic acid

A new diurea-type gelator was synthesized from 2-isocyanoethyl acrylate and 4′-diaminodiphenylmethane, which formed supramolecular gel in acetonitrile driven by hydrogen bonds. The xerogel fibers with a smooth lamellar structure were used as templates and monomer source in fabricating polymer microtubes via reversible addition-fragmentation chain transfer polymerization. Because of a very low solubility of the gelator, the polymerization in toluene gave no insoluble product. As suitable amount of methanol was used together with toluene, the polymerization was conducted successfully to obtain ribbon-like polymer tubes with smooth surface. Based on which, acrylic acid was further used as a co-monomer to form carboxyl-functionalized polymer tubes. The resulting products were characterized by multiple techniques. Compared with the ordinary polymer tubes, the carboxyl-functionalized polymer tubes exhibited much improved adsorption capability for methylene blue (MB) at pH 7 and the absorbed MB molecules could be released in both acidic water and acidic ethanol.

Fabrication of functional macroscopic polymer microtubes from N,N′-methylene bisacrylamide crystals and their adsorption for Cr(VI)

Fabrication of functional macroscopic polymer microtubes from N,N′-methylene bisacrylamide crystals and their adsorption for Cr(VI)

Enhanced Flexible Tubular Microelectrode with Conducting Polymer for Multi-Functional Implantable Tissue-Machine Interface.

Implantable biomedical microdevices enable the restoration of body function and improvement of health condition. As the interface between artificial machines and natural tissue, various kinds of microelectrodes with high density and tiny size were developed to undertake precise and complex medical tasks through electrical stimulation and electrophysiological recording. However, if only the electrical interaction existed between electrodes and muscle or nerve tissue without nutrition factor delivery, it would eventually lead to a significant symptom of denervation-induced skeletal muscle atrophy. In this paper, we developed a novel flexible tubular microelectrode integrated with fluidic drug delivery channel for dynamic tissue implant. First, the whole microelectrode was made of biocompatible polymers, which could avoid the drawbacks of the stiff microelectrodes that are easy to be broken and damage tissue. Moreover, the microelectrode sites were circumferentially distributed on the surface of polymer microtube in three dimensions, which would be beneficial to the spatial selectivity. Finally, the in vivo results confirmed that our implantable tubular microelectrodes were suitable for dynamic electrophysiological recording and simultaneous fluidic drug delivery, and the electrode performance was further enhanced by the conducting polymer modification.

(Invited) Tailoring Polymer Structure and Composition for High-Power and High-Charge Capacity Redox Electrodes

Conventional batteries are efficient at delivering a continuous supply of power; however, limited discharge rates prevent their use in high power applications. Many energy systems require sources that can repetitively supply high power bursts, which include electric transportation, utilization of renewable energy sources, and portable electronics. This demand can be addressed using advanced Li-ion batteries and supercapacitors, devices that combine the high power, rapid switching, and exceptional cycle life of a capacitor with the high energy density of a battery. Electroactive conducting polymers are suitable candidates for high-power energy storage, but they are currently limited by i) the lack of nano/micro-structure control over large areas, ii) relatively low charge-capacity, and iii) material stability. In this presentation, we will discuss our group’s recent progress on engineering high-energy and high-power electrode materials for energy storage, including scalable synthesis of nano/micro-structured polymer electrodes and integrating high-charge capacity redox polymers. To increase power, redox polymer microtubes with nanometer thickness are synthesized on large area substrates by controlling gas nucleation density, which guides to formation of nanostructured electrodes. Nanostructured electrodes exhibit superior performance at high charge/discharge rates relative to planar electrodes. To increase electrode charge capacity, redox molecules and polymer are incorporated into conducting polymer electrodes during electrochemical synthesis. The capacitance of polypyrrole electrodes can be increased from 249 F/g to 550 F/g using hydroquinone dopants, and up to 400 F/g using naturally abundant Alkali lignin. We show that the conditions for electrode synthesis, along with the type (and molecular composition) of lignin, exhibit strong correlations with electrode performance.

Fabrication of Fluoropolymer Microtubes via RAFT Copolymerization of N,N'-Methylene Bisacrylamide Gel Fibers and Fluoromonomer.

Fluoropolymer microtubes with a smooth surface were fabricated in more than 70 % yield via reversible addition fragmentation chain transfer (RAFT) co-polymerization of N,N'-methylene bisacrylamide (MBA) gel fibers as both template and monomer, 2-(perfluoro-3-methylbutyl)ethyl acrylate (R-3420) as co-monomer, and pentaerythritol tetraacrylate (PET4A) as cross-linker. The resulting fluoropolymer microtubes were characterized fully by SEM, TEM, EDS, XPS, and FT-IR. The influence of the monomer composition on the yields and morphologies of the tubes were investigated in detail. The results indicated that polymer microtubes with a smooth surface were obtained at suitable amounts of R-3420 and PET4A. Because of the decreased solubility of MBA gel fibers, the wall thickness increased as more R-3420 was used. In the presence of PET4A, the solution polymerization could be facilitated and more R-3420 could be attached onto the tubes based on FT-IR analysis. The water contact angle and swelling ratio measurements both revealed the low hydrophilicity and high lipophilicity of the fluoropolymer microtubes, which made the sample able to absorb toluene selectively in a water/toluene two-phase system.

Preparation of Polymer Microtubes via RAFT Polymerization of Sole MBA Xerogel Fibers

Preparation of Polymer Microtubes via RAFT Polymerization of Sole MBA Xerogel Fibers

Capillarity-induced mechanical behaviors of a polymer microtube surrounded by a droplet

The capillary force of a liquid drop has a great impact on the mechanical behaviors of a polymer microtube. To further explore this capillary effect, we examine the buckling condition and finite deformation of a hollow microfiber surrounded by a droplet. The Eulerian rod model and thin-walled shell model are both adopted to predict the critical value of the capillary force acting on the microfiber. According to the Mooney-Rivlin model, we calculate the true axial stress of the microtube under the combined action of surface tension and Laplace pressure. The numerical results show that the value of the true axial stress is closely related to the Young’s contact angle, droplet volume and characteristic sizes of the microtube. Our findings address that proper control over surface wettability may improve the performance optimization of micro-devices, and these analyses may produce ideas in the areas of nanofabrication, electrospinning and tissue engineering.

Biodegradable and multifunctional polymer micro-tubes for targeting photothermal therapy.

We describe an innovative form of polymer micro-tubes with diverse functions including biodegradation, magnetic manipulation, and photothermal effect that employs and activates photothermal therapy to target cancer cells. The micro-tube comprised soybean protein isolate, poly-l-glutamic acid, magnetite nanoparticles, plus gold nanoparticles. Through electrostatic force, these components, with opposite charges, formed pairs of layers in the pores of the template, various bilayers of soybean protein isolate and poly-l-glutamic acid served as the biodegradable building wall to each micro-tube. The layers of magnetite nanoparticle functionalized micro-tubes enabled the micro-tube manipulate to target the cancer cells by using an external magnetic field. The photo-thermal effect of the layer of gold nanoparticles on the outer surface of the micro-tubes, when under irradiation and when brought about by the near infrared radiation, elevated each sample’s temperature. In addition, and when under the exposure of the near infrared radiation, the elevated temperature of the suspension of the micro-tubes, likewise with a concentration of 0.2 mg/mL, and similarly with a power of 2 W and as well maintained for 10 min, elevated the temperature of the suspension beyond 42 °C. Such temperatures induced apoptosis of target cancer cells through the effect of photothermal therapy. The findings assert that structured micro-tubes have a promising application as a photothermal agent. From this assertion, the implications are that this multifunctional agent will significantly improve the methodology for cancer diagnosis and therapy.

Low-cost polymeric photocatalytic microreactors: Catalyst deposition and performance for phenol degradation

The feasibility of using flexible polymer microtubes as photocatalyst supports was investigated by using PFA tubes of various inner diameters (i.d.). Catalyst immobilisation was performed by loading a prepared TiO2 suspension into the tubes, which were then subjected to a quick thermal treatment at 285°C. The presence of the catalyst on the inner walls of the tubes was confirmed by SEM-EDS analysis, and the thicknesses of the resulting catalytic layers were evaluated by SEM for different catalyst precursor concentrations. The performances of the reactors were investigated by the photocatalytic degradation of phenol. The apparent reaction rates observed on these reactors were found to be one order of magnitude larger than found in a small batch vessel operating with suspended slurry. The effects of the number of catalytic coatings, the concentration of the catalyst precursor suspension, the reactor inner diameter and the initial pH of the solutions on the performance of the reactor were investigated.

One-step synthesis of polymer micro-tubes tethered by polymer nanowire networks via RAFT polymerization of N ,N ′-methylene bisacrylamide xerogel fibers in toluene and ethanol mixed solution

One-step synthesis of polymer micro-tubes tethered by polymer nanowire networks via RAFT polymerization of <i>N</i> ,<i>N</i> ′-methylene bisacrylamide xerogel fibers in toluene and ethanol mixed solution

Template-Free Synthesis of Polypyrrole Microtubes

Interest in new energy storage technologies, especially to support transportation and renewable energy generation, is increasing at a rapid rate. New technologies face many challenges, such as material abundance, efficiency, charge storage capacity and long term cycle-ability. Emerging devices, like supercapacitors, have the potential to provide high energy storage capacity and fast charge-discharge rates to bridge the gap between traditional batteries and high-power capacitors.In a supercapacitor, many types of electrode material can be used, ranging from high surface area, inert carbon nanomaterials to Faradaic metal oxides and conducting polymers. Porous carbon nanomaterials rely upon electrical double layer capacitance, in which charged are stored physically at the electrode interfaces rather than through charge transfer with the electrode (Faradaic). While EDLC devices can discharge at high rates (high power), they are limited by low energy densities. Electroactive conductive polymers (ECPs) are promising materials, since they are conductive, possess moderate to high energy storage capacity, and can be synthesized using low cost and large scale methods.In this work, we investigate a simple approach to preparing large quantities of conducting polymer microtubes without the need for a solution or substrate based template. Due to its fairly high specific power and energy, polypyrrole is studied as the electrode material for microtube-based devices. However, since the mechanism for electrochemical synthesis is similar for various monomers, we expect this approach can be applied to other materials relative ease. In this presentation, we will discuss how to control the polymer assembly and microtube synthesis by changing the substrate geometry. Figure 1. Polypyrrole microtubes on 200x200 stainless steel mesh. Deposition at 10mA/s for 30C.Electrodes prepared using our template-free synthesis with polypyrrole to achieve microtube structures is shown in Figure 1. Polypyrrole was electrochemically polymerized on various stainless steel mesh substrates (40x40, 200x200, 400x400, among others) with various mass, current density and monomer concentration. Electrodes were studied to understand the growth mechanism and microtube formation, and how the electrode structure affects the charge storage properties.Variations in the substrate surface structure resulted in an easy tool to manipulate the microtube size (100μm up to 1 mm), shape (cone-like or tube-like structure) and density of microtubes along the electrode. The finer meshes (200x200 and 400x400) gave the highest density (about 350 microtubes/cm2) and the best electrochemical performance (200 F/g) measured by cyclic voltammetry, electrochemical impedance spectroscopy and galvanodynamic cycling.The microtube’s formation and growth mechanism was studied using scanning electron microscopy (SEM) on samples prepared through different stages of growth (1C up to 30C). Figure 2 shows how the tube structures evolve from an initial nucleus, which forms at the intersection of two metal wires in the mesh, to the final tube. Figure 2. Microtubes growth mechanism.Polypyrrole microtubes exhibit similar electrochemical properties compared to thin films. Electrodes prepared on 200x200 and 400x400 mesh displayed a high density of microtubes and good electrochemical properties, as shown in Figure 3. It should be noted that some microtubes exhibited poor electrochemical performance due to the high potentials required during synthesis (e.g. large mesh sizes, 40x40). Figure 3. Cyclic voltammetry of 8.26mg polypyrrole microtube electrodes.These results led us to understand the influence of the substrate, current density and concentration in the template-free assembly and electrochemical performance of polypyrrole, as well as new ways to manipulate the physical structure of redox materials for supercapacitor electrodes. Importantly, this approach has been used to synthesis tens of milligrams of material per square centimeter, and is amenable for scale to large systems.

Photochemistry for Advanced Nanoengineering: Polymer Microtubes with Inner Walls Coated with Silver Nanoparticles

Micro-capillaries with an engineered hidden surface were produced via the self-rolling of polymer thin films whose surface was photochemically modified so as to coat it with silver nanoparticles. The polymer films consisted of a poly(4-vinyl pyridine) (P4VP) layer top-coated with a polystyrene layer. When immersed in acid water, they underwent self-rolling due to selective swelling of the poly(4-vinyl pyridine) layer. The generation of Ag nanoparticles at the inner structure of the 40 μm-wide capillaries was carried out by a photochemically initiated reduction process. It was confirmed by UV-VIS spectroscopy, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) analysis. The possibility of designing non-uniform distributions of silver particles at the inner surface of the tubes was also established. It consists of photopatterning the top of the film - the polystyrene side - prior to the swelling/self-rolling step. This approach provides new opportunities for the design of micro-compartments for micro-biological research and for micro-fluidics applications.

High-aspect-ratio conducting polymer microtube synthesis by light-activated electropolymerization on microstructured silicon

Synthesis of conducting polymer (CP) microtubes with characteristic size and period of a few micrometers, height from 5 to 50 micrometers, and aspect-ratio from 1 to 10, is demonstrated by light-activated electropolymerization on microstructured silicon for poly(3,4-ethylendioxythiophene), poly(3-methylthiophene) and polythiophene. Electrochemical characterization by cyclic voltammetry demonstrates that the entire surface of microstructured CPs is electroactive and can be effectively exploited in electrochemical processes without detaching CP films from the silicon substrate, thus directly and easily taking advantage of the increased polymer surface area. Such a successful merging of CP and silicon microstructuring technologies would break new grounds in different analytical/technological fields connected to microstructured CPs.

Direct Transformation of N,N′‐Methylene Bisacrylamide Self‐Assembled Fibers Into Polymer Microtubes via RAFT Polymerization

A novel fabrication method of polymer tubes with simple operation process and high yield is presented. N,N'-methylene bisacrylamide (MBA) polymer microtubes are fabricated via reversible addition-fragmentation chain transfer (RAFT) polymerization using MBA self-assembled fibers as both the template and monomer source. The resulting products are characterized by SEM, TEM, FTIR, and element analysis. The mechanical properties of the gel-like product and the MBA organogel are measured by rheometer. The morphology of the polymer tubes obtained via RAFT polymerization is compared with the sample obtained via conventional radical polymerization. Based on the current investigations, the fabrication mechanism of this method is initially proposed.

Solvothermal Synthesis of Nickel Glycolate Polymer and NiO Microtubes and Their Cr(VI) Absorbing Properties

In this work, nickel glycolate polymer microtubes (NGPMs) were prepared via a facile solvothermal method using hydrous nickel nitrate and anhydrous sodium acetate as starting materials, and ethylene glycol as solvent. Furthermore, nickel oxide (NiO) microtubes were obtained by a high-temperature treatment of NGPMs in air atmosphere. The morphology and phase of the products were characterized by scanning electron microscope (SEM), Transmission electron microscope (TEM) and X-ray diffractometer (XRD). The results show that NGPMs are of hierarchical structure, which are composed of a lot of nanolamellas. The morphology of NiO microtubes directly derived from that of NGPMs. In addition, the experiments were conducted with atomic absorption spectrometer for adsorption of Cr2O72- in ultrapure water using these microtubes obtained as absorbers. The results reveal that NGPMs obviously possess a better ability of chromium absorption with a maximum absorbing value of 14.6 mg/g at pH of 4 than NiO microtubes. Thus, the as-prepared of NGPMs may be promising as a new type of absorber for heavy metal ion for water treatment.