Ezinwa Elele

Three-dimensional piezoelectric fibrous scaffolds selectively promote mesenchymal stem cell differentiation

The discovery of electric fields in biological tissues has led to efforts in developing technologies utilizing electrical stimulation for therapeutic applications. Native tissues, such as cartilage and bone, exhibit piezoelectric behavior, wherein electrical activity can be generated due to mechanical deformation. Yet, the use of piezoelectric materials have largely been unexplored as a potential strategy in tissue engineering, wherein a piezoelectric biomaterial acts as a scaffold to promote cell behavior and the formation of large tissues. Here we show, for the first time, that piezoelectric materials can be fabricated into flexible, three-dimensional fibrous scaffolds and can be used to stimulate human mesenchymal stem cell differentiation and corresponding extracellular matrix/tissue formation in physiological loading conditions. Piezoelectric scaffolds that exhibit low voltage output, or streaming potential, promoted chondrogenic differentiation and piezoelectric scaffolds with a high voltage output promoted osteogenic differentiation. Electromechanical stimulus promoted greater differentiation than mechanical loading alone. Results demonstrate the additive effect of electromechanical stimulus on stem cell differentiation, which is an important design consideration for tissue engineering scaffolds. Piezoelectric, smart materials are attractive as scaffolds for regenerative medicine strategies due to their inherent electrical properties without the need for external power sources for electrical stimulation.

Measurements of the fluid and particle mobilities in strong electric fields

We present a method for measuring both the fluid and particle velocities in strong electric fields and carefully analyze the repeatability and reproducibility of the measurements. The experiments were conducted in 50-μm capillaries containing dilute aqueous suspensions of 4-μm polystyrene spheres subjected to dc as well as ac (5−50Hz) fields of strengths up to 1 and 0.6kV∕cm, respectively. These measurements indicate that the predictions of classical linear theories for electrokinetic phenomena apply well beyond the range of relatively weak electric fields for which these theories were developed. The results of our studies are critical for the quantification of microanalytical systems which make use of electrokinetic phenomena for the transport, control, and manipulation of fluids and particles.

Electrodeless Electrohydrodynamic Drop-on-Demand Encapsulation of Drugs into Porous Polymer Films for Fabrication of Personalized Dosage Units

Noncontact drop-on-demand (DOD) dosing is a promising strategy for manufacturing of personalized dosage units. However, current DOD methods developed for printing chemically and thermally stable, low-viscosity inks are of limited use for pharmaceuticals due to fundamentally different functional requirements. To overcome their deficiency, we developed a novel electrohydrodynamic (EHD) DOD (Appl, Phys, Lett. 97, 233501, 2010) that operates on fluids of up to 30 Pa·s in viscosity over a wide range of droplet sizes and provides a precise control over the droplet volume. We now evaluate the EHD DOD as a method for fabrication of dosage units by printing drug solutions on porous polymer films prepared by freeze-drying. Experiments were carried out on ibuprofen and griseofulvin, as model poorly water-soluble drugs, polyethylene glycol 400, as a drug carrier, and hydroxypropyl methylcellulose films. The similarities between drug release profiles from different dosage units were assessed by model-independent difference, f(1) , and similarity, f(2) , factors. The results presented show that EHD DOD offers a powerful tool for the evolving field of small-scale pharmaceutical technologies for tailoring medicines to individual patients needs by printing a vast array of predefined amounts of therapeutics arranged in a specific pattern on a porous film.

A novel concept of dielectrophoretic engine oil filter

A novel concept of an alternating current (AC) dielectrophoretic filter with a three‐dimensional electrode array is presented. A filter is constructed by winding into layers around the core tube two sheets of woven metal wire‐mesh with several sheets of woven insulating wire‐mesh sandwiched in between. Contrary to conventional dielectrophoretic devices, the proposed design of electrodes generates a high‐gradient field over a large working volume by applying several hundred volts at a standard frequency of 60 Hz. The operating principle of filtration is based on our recently developed method of AC dielectrophoretic gating for microfluidics. The filtration efficiency is expressed in terms of two non‐dimensional parameters, which describe the combined influence of the particle polarizability and size, the oil viscosity and flow rate, and the field gradient on the particle captivity. The proof‐of‐concept is tested by measuring the single‐pass performance of two filters on positively polarized particles dispersed in engine oil: spherical glass beads, fused aluminum oxide powder, and silicon metal powder, all smaller than the mesh opening. The results obtained are used to consider the potential of using AC dielectrophoretic filtration and provide critical design guidelines for the development of a filter based on the retention capability of challenge particles.

Electrodeless electrohydrodynamic printing of personalized medicines

We report on a method for drop-on-demand printing of personalized medicines. A fluid is infused into an electrically insulating nozzle to form a pendant drop that will serve as a floating electrode that is capacitively coupled to external electrodes during a voltage pulse. An electric force is directly applied to the pendant drop to produce a sessile drop on an insulating polymer film. Versatility is proved on fluids spanning over three orders of magnitude in viscosity and conductivity. Scaling analysis captures the essential physics of drop dynamics and provides critical design guideline.

Single-bubble water boiling on small heater under Earth’s and low gravity

Today’s trends for enhancing boiling heat transfer in terrestrial and space applications focus on removal of bubbles to prevent formation of a vapor layer over the surface at high overheat. In contrast, this paper presents a new boiling regime that employs a vapor–air bubble residing on a small heater for minutes and driving cold water over the surface to provide high heat flux. Single-bubble boiling of water was investigated under normal gravity and low gravity in parabolic flights. Experiments demonstrated a negligible effect of gravity level on the rate of heat transfer from the heater. Due to self-adjustment of the bubble size, the heat flux provided by boiling rose linearly up with increasing heater temperature and was not affected by a gradually rising water temperature. The fast response and stable operation of single-bubble boiling over a broad range of temperatures pave the way for development of new devices to control heat transfer by forming surface domains with distinct thermal properties and wettability. The bubble lifetime can be adjusted by changing the water temperature. The ability of heating water on millimeter scales far above 100 °C without an autoclave or a powerful laser provides a new approach for processing of biomaterials and chemical reactions.Fluids: A quicker way to boil waterA mechanism by which light-weight heaters can more effectively boil water is identified by researchers in the USA. Increasing the rate at which a fluid is heated is hampered by the formation of a layer of vapor on the surface of a heater, which prevents heat flow. This is particularly problematic for small heaters such as those required in space applications. Boris Khusid and his colleagues from the New Jersey Institute of Technology now demonstrate a new boiling regime that takes advantage of an air-vapor bubble that forms on a smaller heater. This bubble drives cold water to the surface and improves the flow of heat. This effect was investigated both under normal gravity and in a low-gravity environment created by parabolic flights, with gravity exhibiting only a negligible influence on the rate of heat transfer.