Mark D. Paine

Fully voltage-controlled electrohydrodynamic jet printing of conductive silver tracks with a sub-100 μm linewidth

Silver microtracks with excellent electrical functionality were created by electrohydrodynamic jet (e-jet) printing of commercial metallo-organic ink. Novel e-jet printing was performed in a fully voltage-controlled fashion. By using a 20 μm nozzle and reducing the printing distance to 50 μm, metallic tracks with a sub-100 μm linewidth were successfully achieved on Si substrates. The physical properties of the printed tracks were characterized by means of scanning electron microscopy, atomic force microscopy, energy-dispersive x-ray spectrum analysis, and electrical measurements. A low resistivity in the range (2–4)×10−8 Ω m, 1.7–2.4 times of the theoretical value of silver, was obtained for the printed microtracks. A uniform fine track with a 35 μm feature size was produced by pulsed jet printing operating at low voltage, and a drop-on-demand capability of ∼7 pl/drop was estimated.

Voltage-Modulated Flow Rate for Precise Thrust Control in Colloid Electrospray Propulsion

We describe a feature of electrospray operation that allows precise control of flow rate through an electrospray emitter by use of the extraction voltage. The effect of extractor voltage on the propellant flow rate through an electrospray emitter has been determined for triethylene glycol and ethylene glycol solutions doped with varying levels of sodium iodide and the ionic liquid 1-ethyl-3-methyl imidazolium tetrafluoroborate using an in-line high-accuracy flow measurement system. In these experiments, a nominally fixed flow rate, obtained by providing a fixed supply pressure, is observed to be influenced by the applied voltage during stable cone-jet electrospray production. The relative sensitivity of flow rate to applied voltage was found to be higher as the nominal flow rate decreased. This method of flow rate control holds particular significance for colloidal electrospray thruster systems, which operate at or near minimum flow rate conditions.

Electrospray deposited fibronectin retains the ability to promote cell adhesion

Scaffolds for tissue engineering require the correct biochemical cues if the seeded cells are to migrate into the scaffold and proliferate. For complex tissues this would require precise patterning of the scaffold structure with the particular biochemical cue required at each location on the scaffold. Electrospray enables the deposition of a wide number of biomolecules onto surfaces and can be used for precise patterning. We assessed the functionality of a key cell-adhesion molecule, fibronectin, after depositing it onto a surface using the electrospray technique. The addition of polypropylene glycol allowed a stable spray to be obtained from solutions with a range of fibronectin concentrations. Immunoassay tests showed that the amount of fibronectin retained on the surface was proportional to that sprayed from the solution. Increasing the surface density of fibronectin deposited onto silicon surfaces enhanced fibroblast attachment. The fibronectin thus appears to have retained its cell attachment functionality after undergoing the electrospray process. Since recent advances allow electrospray to pattern material from solution with micrometre accuracy this may allow materials to be biologically functionalized on a similar scale.