Microscale Fibers Research Articles

Microscale fibre alignment by a three-dimensional sessile drop on a wettable pad

Fluidic assembly provides solutions for assembling particles with sizes from nanometres to centimetres. Fluidic techniques based on patterned shapes of monolayers and capillary forces are widely used to assemble microfabrication devices. Usually, for self-assembly, the precondition is that the components must be mobile in a fluidic environment. In the present work, a shape-directed fluidic self-assembly of rod-like microstructures, such as an optical fibre on a wettable pad is demonstrated experimentally with submicrometre positioning precision. A model of the process is proposed, which accounts for the following two stages of the orientation of a fibre submerged in a sessile drop: (i) the drop melting and spreading over a wettable pad; (ii) fibre reorientation related to the surface-tension-driven shrinkage of the drop surface area. At the end of stage (ii), the fibre is oriented along the pad. The experimental results for the optical-fibre assembly by a solder joint have been compared to the modelling results, and a reasonable agreement has been found. The major outcome of the experiments and modelling is that surface tension forces on the fibre piercing a drop align the fibre rather than the flow owing to the spreading of the drop over the horizontal pad, i.e. stage (ii) mostly contributes to the alignment.

First Isolation of Individual Silicate Platelets from Clay Exfoliation and Their Unique Self-Assembly into Fibrous Arrays

Thin silicate platelets in a dimension of approximately 80 x 80 x 1 nm(3) are isolated for the first time by a newly developed process involving one-step exfoliation of natural montmorillonite clay and toluene/aqueous NaOH extraction. The platelets are observed to be polygon shape by transmission electron microscopy (TEM) and round bent-leaf shape by dynamic force microscopy (DFM). Individual platelets possessing high-aspect-ratio dimension and ionic character are able to self-assemble into microscale fiber bundles after water evaporation. The self-stacking mechanism indicated strong face-to-face ionic charge stacking propensity in triggering a vertical growth. Regularity of fibrous bundles in an average 5 microm length has been observed.

Characterization of micromanipulator-controlled dry spinning of micro- and sub-microscale polymer fibers

No current microfabrication technique exists for producing room- temperature, high-precision, point-to-point polymer micro- and sub- microscale fibers in three dimensions. The purpose of this work is to characterize a novel method for fabricating interconnected three- dimensional (3-D) structures of micron and sub-micron feature size. Poly- (methyl methacrylate) (PMMA) micro- and sub-microscale fiber suspended bridges are fabricated at room temperature by drawing from pools of solvated polymer using a nano-tipped stylus that is precisely positioned by an ultra-high-precision micromilling machine. The fibers were drawn over a 1.8 mm silicon trench, and as the solvent in the solution bridge rapidly evaporates, a suspended, 3-D PMMA fiber remained between the two pools. The resulting fiber diameters were measured for solutions of PMMA in chlorobenzene with concentrations ranging from 15.5 to 23.0 wt% 495k g mol−1 PMMA and 13.0 to 21.0 wt% 950k g mol−1 PMMA. Fibers were found to increase in diameter from 450 nm to 50 µm, roughly corresponding to the increase in concentration of PMMA. To minimize fiber diameter variance, different stylus materials were investigated, with a Parylene®-coated stylus producing fibers with the lowest variance in diameter. Overall, the fiber diameter was found to increase significantly as the solution concentration and polymer molecular weight increased.

Mesoscopic spatial designs of nano- and microfiber meshes for tissue-engineering matrix and scaffold based on newly devised multilayering and mixing electrospinning techniques

To design a mesoscopically ordered structure of the matrices and scaffolds composed of nano- and microscale fiber meshes for artificial and tissue-engineering devices, two new electrospinning techniques are proposed: multilayering electrospinning and mixing electrospinning. First, the following four kinds of component polymers were individually electrospun to determine the conditions for producing stable nano- and microfibers by optimizing the formulation parameters (solvent and polymer concentration) and operation parameters (voltage, air gap, and flow rate) for each polymer: (a) type I collagen, (b) styrenated gelatin (ST-gelatin), (c) segmented polyurethane (SPU), and (d) poly(ethylene oxide). A trilayered electrospun mesh, in which individual fiber meshes (type I collagen, ST-gelatin, and SPU) were deposited layer by layer, was formed by sequential electrospinning; this was clearly visualized by confocal laser scanning microscopy. The mixed electrospun-fiber mesh composed of SPU and PEO was prepared by simultaneous electrospinning on a stainless-steel mandrel with high-speed rotation and traverse movement. A bilayered tubular construct composed of a thick SPU microfiber mesh as an outer layer and a thin type I collagen nanofiber mesh as an inner layer was fabricated as a prototype scaffold of artificial grafts, and visualized by scanning electron microscopy.

Hydrodynamic microfabrication via “on the fly” photopolymerization of microscale fibers and tubes

A microfluidic apparatus capable of creating continuous microscale cylindrical polymeric structures has been developed. This system is able to produce microstructures (e.g. fibers, tubes) by employing 3D multiple stream laminar flow and "on the fly"in-situ photopolymerization. The details of the fabrication process and the characterization of the produced microfibers are described. The apparatus is constructed by merging pulled glass pipettes with PDMS molding technology and used to manufacture the fibers and tubes. By controlling the sample and sheath volume flow rates, the dimensions of the microstructures produced can be altered without re-tooling. The fiber properties including elasticity, stimuli responsiveness, and biosensing are characterized. Responsive woven fabric and biosensing fibers are demonstrated. The fabrication process is simple, cost effective and flexible in materials, geometries, and scales.

Free-standing silicon microstructures fabricated by laser chemical processing

Laser-assisted chemical-vapor deposition (LCVD) is used for growth in ‘‘free space’’ of microscale fibers and helical structures of silicon. The LCVD technique is also used for fabrication of a tungsten coil on a cylindrical silicon substrate, i.e., a microsolenoid is realized. The microstructure of the silicon deposits is investigated by transmission electron microscopy, and their mechanical strength is evaluated by micromechanical testing in situ in a scanning electron microscope. The resistivity of the tungsten coil is measured, and the magnetic properties of the microsolenoid are investigated by means of superconducting quantum interference device equipment.

Construction and evaluation of a regenerable fluoroimmunochemical-based fibre optic biosensor

A microscale fibre optic biosensor that is capable of in situ regeneration is described and characterized. By combining recently developed fibre optic sensing technology with a capillary column reagent delivery system, it is possible to perform a variety of bench-top affinity assay procedures both repetitively and remotely. The configuration of the sensing chamber at the terminus of the fibre is an important design feature. The construction and operation of the sensor is described and the results of evaluations of the sensor using an antibody–antigen system are presented. Affinity assay steps such as the delivery of solid phase affinity reagents, secondary reagents and rinse solutions are demonstrated. Sampling is accomplished by mild aspiration. Relative standard deviations (RSDs) for these steps are all less than 10%. The capability of selectively measuring fluorescently labelled anti-rabbit immunoglobulin G (lgG), in the presence of a similar protein, by utilizing its immunospecific interaction with rabbit lgG immobilized on silica beads is demonstrated, and exhibits an RSD of 6.2%. A near linear calibration graph is presented over a concentration range of between 0.011 (approximately the limit of detection) and 0.11 mg ml–1.