Multipurpose platform based on LiNbO3 crystals for novel scenarios in soft matter manipulation

La possibilità di manipolare e dosare la cosiddetta “materia soffice” con tecniche che siano versatili ma anche dotate di elevata risoluzione spaziale, è di grande interesse per una vasta gamma di applicazioni. Questo lavoro di tesi si inserisce in questo contesto proponendo una piattaforma di tipo ferroelettrico in cui la polarizzazione spontanea di cristalli quali il niobato di litio (LiNbO3) è sfruttata ad arte per generare forze di tipo elettro-dinamico su scala micrometrica. Tali forze sono in grado di dosare e indirizzare opportunamente piccoli volumi di materiale fluido di tipo polimerico ma anche di tipo biologico. In particolare, i campi elettrici generati tramite effetto piroelettrico integrato su cristallo sono utilizzati qui per diversi tipi di applicazioni. I risultati mostrano come fluidi polimerici possono essere elettro-filati in modo controllato, evitando le instabilità tipiche dell’electrospinning tradizionale. Polimeri con proprietà ottiche opportune possono essere usati per stampare matrici di microlenti plastiche e versatili. L’energia solare può essere accumulata e sfruttata per sorgenti alternative di campi elettrici. Infine, la morfologia e le proprietà di adesione di cellule di fibroblasti viventi possono essere pilotate tramite le cariche di superficie espresse da tali supporti

Manipulation of polymeric fluids through pyro-electro-hydro-dynamics

This thesis is focused on the manipulation of liquids and polymeric fluids in a non-contact and electrode-free way, exploiting pyro-electro-hydro-dynamic systems. The thesis structure provides an introduction based on the theory and the combination between pyroelectric and electro-hydro-dynamic effect, with a focus on the developed techniques, followed by the presentation of the realized works. It will be presented the fabrication of micro-optical devices, in particular micro-lenses, through pyro-electro-hydro-dynamic effect. The attention will be directed toward the fabrication methods: in fact, they have been obtained by an ink-jet technology or through self-assembly on a micro-engineered pyroelectric crystal. In the first case, a new pyro-ink-jet set-up will be proposed and further modifications of the set-up, which will improve the flexibility of the technique, will be reported. The realized micro-lenses will be optically and geometrically characterized and it will be presented the fabrication of a multi-component device as an example of application of this technique. It will be shown that pyro-ink-jet printing permit to realize very uniform micro-lenses arrays with high resolution (diameter ̴ 300 nm). The second approach is based on the self-assembly of a micro-lenses array on a micro-engineered pyroelectric crystal. It will be showed an array decoration by nano-particles, such as quantum dots, and it will be presented the di-electro-phoretic effect on the employed dots. In particular, the study will focus on the effect of the patterned substrate on the localization of the nano-particles and on the investigation of the dots pattern transfer. Moreover, it will be shown another application of pyro-ink-jet printing: the capability of this system in the highly viscous solution manipulation allows the deposition of polymeric fibers and, in particular, how a fiber like these can be used as a component in a microfluidic channel. That demonstrates pyro-ink-jet printer is also an alternative to the classic electro-spinning system, avoiding electrodes and spiraling effect during the deposition. Produced fibers show great uniformity and reach thicknesses until the nano-metric scale. Moreover, there will be illustrated all the procedures realized to produce the micro-channel

Aerosol-jet printing facilitates the rapid prototyping of microfluidic devices with versatile geometries and precise channel functionalization.

Microfluidics has emerged as a powerful analytical tool for biology and biomedical research, with uses ranging from single-cell phenotyping to drug discovery and medical diagnostics, and only small sample volumes required for testing. The ability to rapidly prototype new designs is hugely beneficial in a research environment, but the high cost, slow turnaround, and wasteful nature of commonly used fabrication techniques, particularly for complex multi-layer geometries, severely impede the development process. In addition, microfluidic channels in most devices currently play a passive role and are typically used to direct flows. The ability to "functionalize" the channels with different materials in precise spatial locations would be a major advantage for a range of applications. This would involve incorporating functional materials directly within the channels that can partake in, guide or facilitate reactions in precisely controlled microenvironments. Here we demonstrate the use of Aerosol Jet Printing (AJP) to rapidly produce bespoke molds for microfluidic devices with a range of different geometries and precise "in-channel" functionalization. We show that such an advanced microscale additive manufacturing method can be used to rapidly design cost-efficient and customized microfluidic devices, with the ability to add functional coatings at specific locations within the microfluidic channels. We demonstrate the functionalization capabilities of our technique by specifically coating a section of a microfluidic channel with polyvinyl alcohol to render it hydrophilic. This versatile microfluidic device prototyping technique will be a powerful aid for biological and bio-medical research in both academic and industrial contexts

Digital Holography Microscopy at Lab-on-a-Chip scale: novel algorithms and recording strategies

Il lavoro presentato è mirato allo sviluppo di nuove tecniche di microscopia olografica digitale (Digital Holography Microscopy, DHM), e di opportuni algoritmi numerici per lo studio di biomateriali in ambiente microfluidico. Nello specifico vengono affrontate due problematiche di imaging particolarmente rilevanti nello studio di sistemi Lab-on-a-Chip (LoC). Dapprima è stato studiato il problema della microscopia quantitativa di oggetti biologici osservati attraverso mezzi complessi, come soluzioni torbide e substrati diffondenti, dove la formazione dell’immagine è ostacolata da processi di scattering. Lo studio condotto è stato mirato all’analisi di processi di diffusione da layer statico e da mezzo liquido di tipo colloidale, in regime quasi-statico e dinamico. Sono stati sviluppati a tale scopo dei metodi di registrazione e nuovi algoritmi di ricostruzione dell’immagine olografica (Multi-Look Digital Holography, MLDH) che consentono di fornire un imaging quantitativo dei campioni in esame. Di particolare interesse è il caso di volumi di liquido costituiti da globuli rossi: nel lavoro presentato viene dimostrata la possibilità di studiare, mediante MLDH, processi di adesione cellulare di materiale biologico situato in presenza di flussi di globuli rossi ad alta concentrazione. La possibilità di visualizzare e analizzare quantitativamente materiale biologico all’interno di un capillare o una vena, compensando l’effetto di diffusione del sangue, potrebbe in futuro consentire di studiare la formazione all’interno del vaso di coaguli e placche di colesterolo, sintomatici dell’insorgere di malattie cardiache. La stessa tecnica è in grado di recuperare l’informazione distorta a causa della presenza all’interno del canale di ostacoli statici o quasi-statici (dovuti alla formazione di bio-film o sospensioni batteriche, o causata da processi di fabbricazione del canale microfluidico), aumentando così notevolmente la varietà dei processi biologici analizzabili su piattaforme LoC. Nel lavoro viene anche dimostrato come la presenza di un mezzo torbido possa essere sfruttata vantaggiosamente al fine di migliorare la qualità dell’immagine in sistemi di imaging basati su luce coerente. Parallelamente è stata messa a punto una tecnica interferometrica che, sfruttando il movimento dei campioni nei canali microfluidici, consente di sostituire un sensore convenzionale 2D con un sensore lineare, più compatto e integrabile a bordo del chip, e capace di fornire prestazioni superiori in termini di velocità di acquisizione. Il lavoro presentato descrive il processo di sintesi di un nuovo tipo di ologramma (Space-Time Digital Hologram, STDH), che consente di ottenere un Field-of-View (FoV) illimitato nella direzione del flusso e, quindi, di superare il trade-off esistente tra fattore di ingrandimento e FoV, comune ad ogni tecnica di microscopia convenzionale. Viene inoltre dimostrato che un STDH mantiene le caratteristiche e i vantaggi di un ologramma digitale standard, quali la focalizzazione numerica flessibile, che permette di analizzare contemporaneamente tutti gli oggetti presenti in un volume di liquido, e la possibilità di estrarre la segnatura di fase degli stessi

Wrinkling prediction, formation and evolution in thin films adhering on polymeric substrata

Wrinkling has recently attracted an increasing interest by suggesting a number of unforeseeable applications in many emerging material science and engineering fields. If guided and somehow designed, wrinkles could be in fact used as an alternative printing way for realizing complex surface geometries and thus employed as an innovative bottom-up process in the fabrication of nano- and micro-devices. For these reasons, the prediction of wrinkles of films adhering on flat as well as on structured substrata is a challenging task, genesis and development of the phenomenon being not yet completely understood both when thin membranes are coupled with soft supports and in cases where the geometry of the surfaces are characterized by complex three-dimensional profiles. Here we investigate the experimental formation of new intriguing and somehow unforeseeable wrinkled patterns achieved on periodic structures, by showing prediction through a new hybrid analytical-numerical strategy capable to overcome some common obstacles encountered in modeling film wrinkling on flat and 3D-shaped substrata. The proposed approach, which drastically reduces the computational effort, furnishes a helpful way for predicting both qualitative and quantitative results in terms of wrinkling patterns, magnitude and wavelength, by also allowing to follow the onset of film instabilities and the progressive evolution of the phenomenon until its final stage. Keywords: Thin film, Wrinkling, PDMS substrates, Lithium niobate crystals, FEM simulation

A prototype for 3D electrohydrodynamic printing

Electrohydrodynamic direct writing is a flexible cost effective alternative technique that is capable of producing a very fine jet of liquid in the presence of an external electric field. This jet can then be used to pattern surfaces in an ordered and controlled fashion and offers a robust route to low cost large area micro and nano-manufacturing. Unlike other types of direct writing techniques, the liquid in electrohydrodynamic printing is subjected to both pushing and pulling forces. The pushing force is brought about by the constant flow rate that is maintained via high precision mechanical pumps while a pulling force is applied through a potential difference that is applied between the nozzle and the ground electrode and as a result a fine jet can be generated to pattern surfaces. The impracticality of use and the cost of building micrometre and sub-micrometre sized nozzles to print narrow line widths warrant an investigation into alternative means of dispensing printing inks using nozzles that are cheap to produce, easy to handle and consistent in delivery. The enormous capillary pressures that would have to be overcome in order to print highly viscous materials with micrometre and sub-micrometre sized nozzles may also limit the types of feed that could be used in printing narrow line widths. Thus, the initial work described is focused on improving print head design in an attempt to electrohydrodynamic print pattern narrow line widths using silk fibroin. This is followed by work where we attempt to design and construct of a new electrohydrodynamic printing machine with the sole purpose of expediting research in electrohydrodynamic printing in a flexible, feasible and user friendly manner. To achieve this, replicating rapid prototype technology is merged with conventional electrohydrodynamic printing phenomena to produce a EHD printing machine capable of print depositing narrow line widths. In order to validate the device the work also describes an attempt to print a fully formed human ear out of polycaprolactone. Finally, we investigate an approach to the electohydrodynamic printing of nasal septal scaffolds using the microfabrication system that was developed and optimized in our laboratory. In these initial stages we were successful in showing the degree of control and flexibility we possess when manufacturing constructs out of a biodegradable polymer ( polycaprolactone) from the micro to macro scale through manipulation of just one process parameter (concentration). This work also features characterization of scaffold mechanical properties using a recently invented Atomic force microscopy technique called PeakForce QNM (Quantitative Nanomechanical Property Mapping)

Investigations on the Processing of Ceramic Filled Inks for 3D InkJet Printing

3D inkjet printing is moving from a technology of rapid prototyping to rapid manufacturing. The introduction of ultraviolet curable composites filled with functional ceramics could expand the possibilities of this technology. In this work, a simple and scalable process was investigated as a template for the production of inkjet printable functional ceramics. Pyrogenic alumina particles with an average size of 13 nm, 35 nm and 100 nm were used as fillers in an acrylate mixture. The physical coating of the ceramics with 2‐[2‐(2‐methoxyethoxy)ethoxy] acetic acid results in a low‐viscosity dispersion with a ceramic content of up to 2 vol%, Newtonian behavior and surface tension within the limits allowed for inkjet printing. The material has sufficient stability for printing tensile specimens. Tensile tests have shown that modulus of elasticity, tensile strength and toughness can be kept constant despite the light scatter caused by the particles. The final production steps could be reduced to grinding and drying of the powders, their resuspension in the organic matrix and inkjet printing. The process can be used in an industrial

3D Printing‐Enabled Design and Manufacturing Strategies for Batteries: A Review

Lithium-ion batteries (LIBs) have significantly impacted the daily lives, finding broad applications in various industries such as consumer electronics, electric vehicles, medical devices, aerospace, and power tools. However, they still face issues (i.e., safety due to dendrite propagation, manufacturing cost, random porosities, and basic & planar geometries) that hinder their widespread applications as the demand for LIBs rapidly increases in all sectors due to their high energy and power density values compared to other batteries. Additive manufacturing (AM) is a promising technique for creating precise and programmable structures in energy storage devices. This review first summarizes light, filament, powder, and jetting-based 3D printing methods with the status on current trends and limitations for each AM technology. The paper also delves into 3D printing-enabled electrodes (both anodes and cathodes) and solid-state electrolytes for LIBs, emphasizing the current state-of-the-art materials, manufacturing methods, and properties/performance. Additionally, the current challenges in the AM for electrochemical energy storage (EES) applications, including limited materials, low processing precision, codesign/comanufacturing concepts for complete battery printing, machine learning (ML)/artificial intelligence (AI) for processing optimization and data analysis, environmental risks, and the potential of 4D printing in advanced battery applications, are also presented

Sustainable Robots 4D Printing

Nature frequently serves as an inspiration for modern robotics innovations that emphasize secure human–machine interaction. However, the advantages of increased automation and digital technology integration conflict with the global environmental objectives. Accordingly, biodegradable soft robots have been proposed for a range of intelligent applications. Biodegradability provides soft robotics with an extraordinary functional advantage for operations involving intelligent shape transformation in response to external stimuli such as heat, pH, and light. Soft robot fabrication using conventional manufacturing techniques is inflexible, time-consuming, and labor-intensive. Recent advances in 3D and 4D printing of soft materials and multi-materials have become the key to enabling the direct manufacture of soft robotics with complex designs and functions. This review comprises a detailed survey of 3D and 4D printing advances in biodegradable soft sensors and actuators (BSSA), which serve as the most prominent parts of each robotic system. In addition, a concise overview of biodegradable materials for the fabrication of 3D-printed flexible devices with medical along with industrial applications is provided. A complete summary of current additive manufacturing techniques for BSSA is discussed in depth. Moreover, the concept of biodegradable 4D-printed soft actuators and sensors and biohybrid soft robots is reviewed

INVESTIGATION OF PYROELECTRIC EFFECT GENERATED BY LITHIUM NIOBATE CRYSTALS INDUCED BY INTEGRATED MICROHEATERS

This thesis work focuses on the investigation of the pyroelectric effect from the –Z surface of Lithium (LiNbO3) crystal using different microheater (µH) designs fabricated on the +Z surface of the crystal. Thermal analyses of the microheater designs were performed both theoretically and experimentally using COMSOL™ Multiphysics and FLIR SC7000 thermocamera respectively. The pyroelectric effect was investigated analysing the current impulses detected using a metallic probe detector connected to an oscilloscope. The temperature variation induced by the microheater causes a spontaneous polarization in the crystal resulting in the formation surface bound charges. The electric field generated between the probe and the crystal surface causes the charge emission that appears as a voltage impulse on the oscilloscope. In an ambient condition, the air layer act as a dielectric thin film layer at few hundreds of microns between the detector probe and crystal surface gap spacing. It was demonstrated and validated that the threshold field strength require to generate the PE was near the dielectric breakdown of air. The pyroelectric emission shows a higher dependency on the rate of thermalization of the microheater and also the electric field generated between the probes to surface gap spacing’s of crystal. The deep characterization of µHs is investigated, in order to demonstrate the reliability and the effectiveness of these microdevices for all those applications where compact and low-power consuming electrical field sources are highly desirable