Electrospinning is a versatile tool used to produce highly customizable nonwoven nanofiber mats of various fiber diameters, pore sizes, and alignment. It is possible to create electrospun mats from synthetic polymers, biobased polymers, and combinations thereof. The post-processing of the end products can occur in many ways, such as cross-linking, enzyme linking, and thermal curing, to achieve enhanced chemical and physical properties. Such multi-factor tunability is very promising in applications such as tissue engineering, 3D organs/organoids, and cell differentiation. While the established methods involve the use of soluble small molecules, growth factors, stereolithography, and micro-patterning, electrospinning involves an inexpensive, labor un-intensive, and highly scalable approach to using environmental cues, to promote and guide cell proliferation, migration, and differentiation. By influencing cell morphology, mechanosensing, and intracellular communication, nanofibers can affect the fate of cells in a multitude of ways. Ultimately, nanofibers may have the potential to precisely form whole organs for tissue engineering, regenerative medicine, and cellular agriculture, as well as to create in vitro microenvironments. In this review, the focus will be on the mechanical and physical characteristics such as porosity, fiber diameter, crystallinity, mechanical strength, alignment, and topography of the nanofiber scaffolds, and the impact on cell proliferation, migration, and differentiation.
A novel electrochemical deposition method for manufacturing functionally graded, oxide-dispersion strengthened metal matrix nanocomposites will be presented. Using a rotating disk electrode and depositing from an electrolyte containing a suspension of oxide nanoparticles, metal-ceramic nanocomposites have been produced. This method leads to precise control over the volume fraction of the oxide in the nanocomposite and allows for the manufacturing of compositionally uniform, periodically layered, or functionally graded structures. In the higher order structures the composition variation can be finely tuned with nanometer resolution, and the characteristic microstructural length scale (e.g., individual layer thickness) can range from microns up to millimeters. Using indentation methods, the nanocomposites are shown to display enhanced and tunable mechanical properties.
Rare-earth telluride compounds are characterized by their high performance thermoelectric properties that have been applied to the development of functional materials [1]. Recently, May and co-workers reported that nanostructured bulk lanthanum telluride (La3-xTe4, 0 ≤ x ≤ 1/3) by mechanical ball-milling exceeded the figure of merit (ZT) of 1 at high temperatures near 1300K [2-3]. Since the increased thermoelectric efficiency of nanostructured materials is due to the enhancement of phonon scattering introduced by quantum confinement, thin films have also generated significant scientific and technological interest [4-6]. Here, we report on the electrodepostion of lanthanum telluride and lanthanum thin films in ionic liquids in ambient conditions. Surface morphologies varied from needle-like to granular structures and depend on deposition conditions. This novel electrochemical synthesis approach is a simple, inexpensive and laboratory-environment friendly method of synthesizing nanostructured thermoelectric materials.
Thermoelectric devices allow for conversion between electrical and thermal energy and have a great deal of potential as both cooling devices and alternative energy sources. Currently they are limited by their low efficiency, and so are only used in very specialized applications. Some potential materials for use in high temperature thermoelectric devices include rare earth telluride compounds. One such material is bulk lanthanum telluride, La3-xTe4, 0 ≤ x ≤ 1/3, which was found to have a ZT greater than unity at temperatures near 1000 C [1]. Lanthanum is already commonly used in many industrial applications, including as lanthanum hydride in the cathode of nickel metal hydride batteries [2]. Nanostructured materials have been shown to have a higher thermoelectric efficiency relative to bulk materials due to the enhancement of phonon scattering through quantum confinement [3]. This has generated a great deal of interest in low-dimensional and nanostructured thermoelectric devices. Since lanthanum telluride is usually made by ball milling, the creation of complex nanostructures or thin films with traditional methods is difficult. We have developed a technique to electrochemically deposit lanthanum telluride thin films from an ionic liquid at low temperatures (approximately 70 C). The films were deposited on noble metal substrates from 1-ethyl-3-methylimidazolium bromide ionic liquid based electrolytes containing to 0.05 M to 0.25 M lanthanum nitrate and 0.025M (HTeO2)+. The ratios of lanthanum to tellurium in the deposited films were determined by relative concentrations of the anions and cations in the electrolyte. The technique used for the deposition of these thin films could ultimately be used in the synthesis of nanostructured lanthanum telluride. This electrochemical method promises to be simpler, less expensive, and more efficient than current techniques. 1. A. May, J-P. Fleurial and G. J. Snyder, Phys. Rev. B, 78, 125205 (2008). 2. T. Sakai et al., J. Less-Common Met., 161, 193-202 (1990). 3. L. D. Hicks and M. S. Dresselhaus, Phys. Rev. B, 47, 12727 (1993).
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