Easy Printing of High Viscous Microdots by Spontaneous Breakup of Thin Fibers.

Electrohydrodynamic jetting is emerging as a successful technique for printing inks with resolutions well beyond those offered by conventional inkjet printers. However, the variety of printable inks is still limited to those with relatively low viscosities (typically <20 mPa s) due to nozzle clogging problems. Here, we show the possibility of printing ordered microdots of high viscous inks such as poly(lactic-co-glycolic acid) (PLGA) by exploiting the spontaneous breakup of a thin fiber generated through nozzle-free pyro-electrospinning. The PLGA fiber is deposited onto a partially wetting surface, and the breakup is achieved simply by applying an appropriate thermal stimulation, which is able to induce polymer melting and hence a mechanism of surface area minimization due to the Plateau-Rayleigh instability. The results show that this technique is a good candidate for extending the printability at the microscale to high viscous inks, thus extending their applicability to additional applications, such as cell behavior under controlled morphological constraints.

Forward electrohydrodynamic inkjet printing of optical microlenses on microfluidic devices.

We report a novel method for direct printing of viscous polymers based on a pyro-electrohydrodynamic repulsion system capable of overcoming limitations on the material type, geometry and thickness of the receiving substrate. In fact, the results demonstrate that high viscosity polymers can be easily manipulated for optical functionalizing of lab-on-a-chip devices through demonstration of direct printing of polymer microlenses onto microfluidic chips and optical fibre terminations. The present system has great potential for applications from biomolecules to nano-electronics. Moreover, in order to prove the effectiveness of the system, the optical performance of such microlenses has been characterized by testing their imaging capabilities when the fibroblast cells were allowed to flow inside the microfluidic channel, showing one of their possible applications on-board a LoC platform.

Active accumulation of very diluted biomolecules by nano-dispensing for easy detection below the femtomolar range.

Highly sensitive detection of biomolecules is of paramount interest in many fields including biomedicine, safety and eco-pollution. Conventional analyses use well-established techniques with detection limits ~1 pM. Here we propose a pyro-concentrator able to accumulate biomolecules directly onto a conventional binding surface. The operation principle is relatively simple but very effective. Tiny droplets are drawn pyro-electro-dynamically and released onto a specific site, thus increasing the sensitivity. The reliability of the technique is demonstrated in case of labelled oligonucleotides diluted serially. The results show the possibility to detect very diluted oligonucleotides, down to a few hundreds of attomoles. Excellent results are shown also in case of a sample of clinical interest, the gliadin, where a 60-fold improved detection limit is reached, compared with standard ELISA. This method could open the way to a mass-based technology for sensing molecules at very low concentrations, in environmental as well as in diagnostics applications.

Spontaneous assembly of carbon-based chains in polymer matrixes through surface charge templates.

Stable chains of carbon-based nanoparticles were formed directly in polymer matrixes through an electrode-free approach. Spontaneous surface charges were generated pyroelectrically onto functionalized ferroelectric crystals, enabling the formation of electric field gradients that triggered the dipole-dipole interactions responsible for the alignment of the particles, while embedded in the polymer solution. The phenomenon is similar to the dielectrophoretic alignment of carbon nanotubes reported in the literature. However, here the electric fields are generated spontaneously by a simple heat treatment that, simultaneously, aligns the particles and provides the energy necessary for curing the host polymer. The result is a polymer sheet reinforced with well-aligned chains of carbon-based particles, avoiding the invasive implementation of appropriate electrodes and circuits. Because polymers with anisotropic features are of great interest for enhancing the thermal and/or the electrical conductivity, the electrode-free nature of this technique would improve the scaling down and the versatility of those interconnections that find applications in many fields, such as electronics, sensors, and biomedicine. Theoretical simulations of the interactions between the particles and the charge templates were implemented and appear in good agreement with the experimental results. The chain formation was characterized by controlling different parameters, including surface charge configuration, particle concentration, and polymer viscosity, thus demonstrating the reliability of the technique. Moreover, micro-Raman spectroscopy and scanning electron microscopy were used for a thorough inspection of the assembled chains.

Graded-size microlens array by the pyro-electrohydrodynamic continuous printing method.

In the present work, the pyro-electrohydrodynamic technique was used for the realization of tunable-size microlens arrays. Poly(methyl methacrylate) dissolved in different solvent mixtures was used as the polymeric material for the realization of the microstructures. By controlling the experimental parameters and in particular, the volume of the drop reservoir, graded-size square arrays of tens of microlenses with focal length in the range 1.5-3 mm were produced. Moreover, the optical quality and geometrical features were investigated by profilometric and interferometric analysis.

Printing of polymer microlenses by a pyroelectrohydrodynamic dispensing approach.

The investigation of a method for fabricating microlenses by a nozzle-free inkjet printing approach is reported. The new method, based on a pyroelectrohydrodynamic mechanism, is also able to dispense viscous liquids and to draw liquid phase drops directly from the reservoir. Specifically, by dispensing optical grade polymer dissolved in different solvent mixtures, microlenses were printed with a pattern defined directly through this deposition method. The reliability of the microlenses and the tunability of their focal properties were demonstrated through profilometric and inteferometric analyses.

Dispensing nano-pico droplets and liquid patterning by pyroelectrodynamic shooting.

Manipulating and dispensing liquids on the micrometre- and nanoscale is important in biotechnology and combinatorial chemistry, and also for patterning inorganic, organic and biological inks. Several methods for dispensing liquids exist, but many require complicated electrodes and high-voltage circuits. Here, we show a simple way to draw attolitre liquid droplets from one or multiple sessile drops or liquid film reservoirs using a pyroelectrohydrodynamic dispenser. Local pyroelectric forces, which are activated by scanning a hot tip or an infrared laser beam over a lithium niobate substrate, draw liquid droplets from the reservoir below the substrate, and deposit them on the underside of the lithium niobate substrate. The shooting direction is altered by moving the hot tip or laser to form various patterns at different angles and locations. Our system does not require electrodes, nozzles or circuits, and is expected to have many applications in biochemical assays and various transport and mixing processes.

Tunable liquid microlens arrays in electrode-less configuration and their accurate characterization by interference microscopy.

A special class of tunable liquid microlenses is presented here. The microlenses are generated by an electrowetting effect under an electrode-less configuration and they exhibit two different regimes that are named here as separated lens regime (SLR) and wave-like lens regime (WLR). The lens effect is induced by the pyroelectricity of polar dielectric crystals, as was proved in principle in a previous work by the same authors (S. Grilli et al., Opt. Express 16, 8084, 2008). Compared to that work, the improvements to the experimental set-up and procedure allow to reveal the two lens regimes which exhibit different optical properties. A digital holography technique is used to reconstruct the transmitted wavefront during focusing and a focal length variation in the millimetre range is observed. The tunability of such microlenses could be of great interest to the field of micro-optics thanks to the possibility to achieve focus tuning without moving parts and thus favouring the miniaturization of the optical systems.

Liquid micro-lens array activated by selective electrowetting on lithium niobate substrates.

Lens effect was obtained in an open microfluidic system by using a thin layer of liquid on a polar electric crystal like LiNbO3. An array of liquid micro-lenses was generated by electrowetting effect in pyroelectric periodically poled crystals. Compared to conventional electrowetting devices, the pyroelectric effect allowed to have an electrode-less and circuit-less configuration. An interferometric technique was used to characterize the curvature of the micro-lenses and the corresponding results are presented and discussed. The preliminary results concerning the imaging capability of the micro-lens array are also reported.