[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The pyro-electrohydrodynamic (EHD) manipulation of liquids has been discovered and demonstrated recently as a high resolution printing technique avoiding the use of nozzles and external electrodes. The activation of the pyro-electric effect is usually achieved on ferroelectric crystals by an external heating source or by an infrared laser. Here, we show an original modality for triggering the pyro-EHD process through a light-absorbing polymer
nanocomposite thin layer deposited on the ferroelectric substrate, thus overcoming some limitations of the previous configuration. Significant simplification and compactness of the set-up is achieved thanks to the nanocomposite coating, since a commercial low-cost white-light halogen lamp can be adopted to trigger the pyro-jetting process from a liquid reservoir. Remarkably, high resolution is achieved in dispensing very high viscous liquids. Practical demonstrations in polymer optical microlenses direct printing using polydimethylsiloxane and poly(methyl methacrylate) are finally reported to validate the approach in handling high-viscous polymers for practical applications.
Full-text · Article · Jun 2015 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Electrical conductivity and viscosity play a major role in the tip jetting behaviour of liquids subjected
to electrohydrodynamic (EHD) forces, thus influencing significantly the printing performance.
Recently, we developed a nozzle- and electrode-free pyro-EHD system as a versatile alternative to
conventional EHD configurations and we demonstrated different applications, including inkjet printing
and three-dimensional lithography. However, only dielectric fluids have been used in all of those
applications. Here, we present an experimental characterization of the pyro-EHD jetting regimes,
induced by laser blasts, of sessile drops in case of dielectric and conductive liquids in order to extend
the applicability of the system to a wider variety of fields including biochemistry and biotechnology
where conductive aqueous solutions are typically used.
Full-text · Article · Jan 2015 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: In this paper, we introduce a single-step self-assembling process aimed at forming two-dimensional (2-D) array microstructures made from a nanocomposite polymer layer in which are dispersed CdSe-CdS nanocrystals. The novelty of the process reported here is that it operates simultaneously as a two-fold process where the liquid polymer matrix is self-shaped by electrohydrodynamic pressure as a 2-D array of microstructures, while at the same time, the nanocrystals are self-assembled by dielectrophoretic forces. The proposed approach could inspire future smart fabrication techniques for producing self-assembled lensed nanocomposite layers. In principle, the method is scalable down to diameter lens up to few micrometers.
No preview · Article · Jan 2015 · IEEE Journal of Selected Topics in Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: Manipulation of liquids on micro- and nanoscale is a key issue in many fields of technology and biotechnology. Electric field induced formation of micro-liter and nanoliter droplets is very useful in lab-on-chip applications and would represent a new and contact-less way for functionalizing smart materials [1–3]. Ink-jet printing, manipulation of biomolecules, deposition of inorganic, organic and biological inks [4, 5], dispensing of small amounts of material into well-defined areas would be a further possibility for functionalizing sensing area for lab-on-a-fiber devices and related applications.
Full-text · Article · Jan 2015 · Springer Series in Surface Sciences
[Show abstract][Hide abstract] ABSTRACT: A novel scheme for solar energy harvesting based on the pyro-electric effect has been demonstrated. The proposed harvester is based on an optical system focusing solar radiation onto a ferroelectric crystal (i.e. lithium niobate). The face exposed to the heating source is coated with a nanocomposite material (i.e. carbon black and graphene particles) that greatly improves the adsorption of solar radiation. The solar energy focused onto the crystal through a simple optical system allows one to induce a thermal gradient able to generate electric charges. Experiments have been carried out indoor as well as outdoor (in Pozzuoli, Naples, Italy, on December). Results show that two configurations appear to be preferable: (a) pyro-electric element with carbon black-based coating and a Fresnel lens (surface of about 100 cm2); (b) pyro-electric element with graphene-based coating and a Fresnel lens (surface of about 600 cm2). In both experimental arrangements the maximum temperature variation reached locally onto the lithium niobate substrate is relatively high with peaks greater than 250 °C. The maximum electrical power peak is of about 90 μW and about 50 μW for (a) and (b) respectively. The results of this first investigation are encouraging for further development of more efficient harvesting devices.
[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Nov 2014 · Nature Communications
[Show abstract][Hide abstract] ABSTRACT: In this work we introduce an easy multiscale approach for the fabrication of polymer microlens arrays through a self-assembling process driven by the electrohydrodynamic (EHD) pressure. This method represents a simple alternative to the conventional soft lithography techniques. A thin layer of liquid polymer is deposited on a micro-engineered ferroelectric crystal and can be self-assembled and cross-linked in a single step process as a consequence of the pyro-electric effect activated by simply heating the substrate. Although the EHD instability induced by the pyroelectric effect was discovered in principle few years ago, here we demonstrate a systematic investigation for fabrication of microlens arrays in a multiscale range (i.e. between 25 ???m to 200 ???m diameter) with high degree of uniformity. By controlling the polymer instability driven by EHD, we report on two different micro-optical shapes can be obtained spontaneously, i.e. spherical or toroidal. Here we show how the geometrical properties and the focal length of the lens array are modulated by controlling two appropriate parameters. Such microlenses can be useful also as polymer patterned arrayed microstructures for optical data interconnections, OLEDs efficient light extraction, concentrating light in energy solar cells, imaging and 3D display solutions and other photonics applications.
Full-text · Article · Nov 2014 · IEEE Journal of Selected Topics in Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: Here, we report on a single step approach for fabricating free-standing polymer membranes reinforced with arrayed self-assembled carbon nanotubes (CNTs). The CNTs are self-assembled spontaneously by electrode-free DC dielectrophoresis based on surface charge templates. The electrical charge template is generated through the pyroelectric effect onto periodically poled lithium niobate ferroelectric crystals. A thermal stimulus enables simultaneously the self-assembly of the CNTs and the cross-linking of the host polymer. Examples of thin polydimethylsiloxane membranes reinforced with CNT patterns are shown.
No preview · Article · Oct 2014 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: A study was conducted to demonstrate tethered pyro-electrohydrodynamic spinning (TPES) for patterning well-ordered structures at micro- and nanoscale. The TPES was introduced in wireless modality without electric circuit, electrodes, and voltage supply. This novel approach definitively simplified the electrospinning (ES) apparatus extending the nanofiber spinning to active organic polymers preserving at the same time all the properties of conventional systems. Fiber drawing from the liquid polymer was driven through the pyroelectric charge generated into a ferroelectric crystal able to induce the electrohydrodynamics (EHD) pressure required for polymer manipulation without wires. The approach was highly flexible, simple, compact, and cost-effective when compared with classical ES and allowed working safely, avoiding the use of high-voltage equipment at kVolts scale.
Full-text · Article · Jun 2014 · Chemistry of Materials
[Show abstract][Hide abstract] ABSTRACT: Hypodermic needle injection is still the most common method of drug delivery despite its numerous limitations and drawbacks, such as pain, one-shot administration, and risk of infection. Seeking a viable, safe, and pain-free alternative to the over 16 billion injections per year has therefore become a top priority for our modern technological society. Here, a system that uses a pyroelectric cartridge in lieu of the syringe piston as a potential solution is discussed. Upon stimulation, the cartridge electro-draws, at room temperature, an array of drug-encapsulated, biodegradable polymer microneedles, able to deliver into hypodermic tissue both hydrophobic and hydrophilic bioactive agents, according to a predefined chrono-programme. This mould-free and contact-free method permits the fabrication of biodegradable polymer microneedles into a ready-to-use configuration. In fact, they are formed on a flexible substrate/holder by drawing them directly from drop reservoirs, using a controlled electro-hydrodynamic force. Tests of insertion are performed and discussed in order to demonstrate the possibility to prepare microneedles with suitable geometric and mechanical properties using this method.
Full-text · Article · Jun 2014 · Advanced Functional Materials
[Show abstract][Hide abstract] ABSTRACT: In the case of light emitting semiconducting polymers, different techniques have been used for the fabrication of electroluminescent devices. Experiments and characterizations have been carried out at different operating voltages and for voltage dependent emission color also combining the processability of organic materials with efficient luminescence displayed by inorganic nanocrystals (NCs). In fact, the experimental perspective to disperse emitting colloidal NCs into polymers has allowed to further engineer hybrid organic-inorganic materials introducing innovative functionalities as for instance photoluminescence conversion capabilities. This has proved of great interest for novel applications such as the fabrication of photonic crystals and, notably, of innovative solar cells showing enhanced efficiency. Here we report on the fabrication of novel active micro-optical elements made by a mixture of rod-shaped inorganic NCs dispersed into poly-dimethylsiloxane.
[Show abstract][Hide abstract] ABSTRACT: In the recent years many commercial applications such as optoelectronics, photonic and biomedical devices, as well as image processing require the fabrication of adaptive and adjustable micro-lens array. A lot of attempts have been conducted in order to support the growing interest in the production of lens arrays for sensors or optical communications devices for parallel data transmission. Several fabrication techniques and a large variety of process have been proposed for polymer based microlenses and their incorporation into technological devices with a large area of application, but, the preparation of moulds, masks or metal layers with very accurate dimensions and shapes is generally required. Here we present the application of a pyro-electrohydrodynamic (Pyro-EHD)-dispenser for the fabrication of polymer microlens arrays overpassing the viscosity limit of the conventional ink-jet printing systems and working in a nozzle-less modality. The results regarding the fabrication procedure and the characterization of polymer micro-lens arrays of different shapes and heights are examined.
[Show abstract][Hide abstract] ABSTRACT: In this work we present a direct printing of microlenses using high viscous polymer materials. In particular the pyro-electric effect activated onto a Lithium Niobate crystal is exploited for the fabrication on demand of microlens array.
[Show abstract][Hide abstract] ABSTRACT: Novel and intriguing lithographic approaches based on instabilities of liquid polymers and electro-hydro-dynamic at nanoscale have been developed. The unusual fabrication methods were aimed at fabricating 3D polymeric microstructures. A variety of microstructures were fabricated and tested for applications in different fields 1. LIQUID NANO DISPENSER A new opto-nanofluidic approach named Pyro-EHD is presented for dispensing liquid nano-pico-droplets through pyroelectric effect activated by hot tip source or an IR laser into a dielectric crystal using a non-invasive simple and powerful electrode-less configuration. The manipulation of small amounts of liquids at micro to nanometer scale is of great interest in many fields of technology: biotechnology, patterning by deposition of inorganic, organic and biological inks and photnics [1-4]. We show a new and simple system where the liquid actuation and dispensing has been achieved through electrode-less configurations using polar dielectric crystals such as Lithium Niobate (LN) crystal and by exploiting the pyroelectric effect [5,6]. The technique presented allows one to avoid the use of high-voltage power supplies and electrical circuits, and moreover there is no need to design and fabricate nanocapillary nozzles. The functionalization of the lithium niobate (LN) is obtained by micro-engineering the ferroelectric domains and by inducing the pyroelectric effect through the use of appropriate heat sources such as a IR laser beam . The set-up consists basically of a polished 500-µm thick z-cut LN substrate (from Crystal Technology, Inc.) placed over a microscope glass slide at a specific distance fixed by appropriate spacers (Figure 1). A liquid drop or film is first deposited on the glass slide and successively the upper surface of the LN wafer is placed in contact with an heated-tip that can be scanned in order to induce point-wise thermal stimuli. The heated-tip is in axis with the droplet reservoir on the microscope glass slide. A conventional heated soldering tip was used as heated-tip-source. LN reacts to the thermal-stimuli by building-up an electric potential across the z-cut LN crystal's surfaces because of the pyroelectric effect, that consists in the spontaneous polarization change ∆Ps following to a temperature gradient ∆T. At equilibrium, the crystal Ps is fully screened by the external screening charge and no electric field exists . When the heating source locally heats the crystal, a sudden surface charge density σ immediately appears given by neglecting losses, where Pc is the material-specific pyroelectric coefficient (Pc= -8.3 x 10 -5C/°C/m2 for LN @ 25°C). The electric field exerts an attractive force on the liquid . When the liquid starts to deform under the action of the electric field, two evolutions are possible. Case (I): if the liquid volume and the separation distance D between the two Invited Paper
[Show abstract][Hide abstract] ABSTRACT: Carbon nanoparticles are becoming ubiquitous in many fields of science and technology. However, a grand challenge remains in assembling, patterning, and positioning or even simple manipulation of CNTs for complex functional assemblies. CNTs have in fact enormous perspectives for application in biotechnologies as bactericide agents or as prominent tools for investigating cell mechanisms, or more in general as functionalized nanoparticle-vectors, but their exploitation requires viable technology at the lab-on-a-chip scale. Many approaches have been attempted in developing technologies for manipulating CNTs. One elective approach is based on electric fields driven mechanisms such as DEP forces. A variety of chips have been designed and realized with this aim. Here we report on a novel hybrid microfluidic chip made by assembling a polar-dielectric crystal with polymeric microfluidic channels. One challenging feature of such a hybrid device approach, based on an electrode-free dielectrophoretic (DEP) approach, is that it makes use of surface charge templates for self-assembling and manipulation of CNTs in liquid media directly into a microfluidic channel. Here various examples of self-assembly in microfluidic channels as well as separation and collection of two classes of nano/microparticles are reported. The method can open the way to novel fabrication protocols for the realisation of future flexible devices with new and more complex functionalities, highly desirable in electronics as well as in biotechnology at the lab-on-a-chip scale.