Polymer Pen Printing: A Tool for Studying 2D Enzymatic Lithography and Printing 3D Carbon Features

Polymer Pen Lithography (PPL) is a promising molecular printing approach which combines the advantages of both microcontact printing (low cost, high-throughput) and the dip pen lithography (DPN) (arbitrary writing, high-resolution) into one cohesive lithography method to create 2 dimensional (2-D) patterns with micro/nano-features on different substrates. The goal of this dissertation is to design and develop a new tool based upon PPL, which is not limited to forming 2D parallel patterns, but can also create 3D complex microstructures, finding applications in both biotechnology and Micro-Electro-Mechanical systems (MEMS) technology. This novel approach is named Polymer Pen Printing. Different from PPL using traditional dry-ink printing methods, an inking step is added to each printing repetition in the polymer pen printing process. Thus a wide range of ink materials with diverse viscosities can be transferred to substrates to create functional 2D and 3D microstructures. The polymer pen printing apparatus used in this thesis has been accomplished and introduced in Chapter 2. As a preliminary attempt, the single polymer pen printing approach was developed by simply attaching a solid polydimethylsiloxane (PDMS) pen tip to a multi-axis robot for small microarray fabrication. Compared to the single pen printing method, multi-pen printing can create large arrays of features. Therefore, an improved apparatus for polymer pen printing with high-throughput was discussed and built. Silicon molds, which consist of hundreds of uniform pyramidal openings, were photolithographically defined and etched using hydrofluoric acid (HF) followed by potassium hydroxide solution; after surface-modification with fluorosilane, these silicon molds were used to cast arrays of PDMS pyramidal pen tip. The cast PDMS pen array was mounted to a hollow holder with a 45° mirror inside. Therefore, each PDMS pen can be observed and monitored from the microscope on the side. To achieve prints less than 1 micron across, a Z axis stage with nanometer resolution was incorporated; and to control the compression of PDMS pen tips, a force gauge was also incorporated to detect 1 mg of applied force from the tips. The printing process for the multi-pen system is almost the same as single pen system. PDMS pens are coated with ink solution before each printing cycle by dipping into an inkwell and then brought into contact with the substrate surface. Thus multiple patterns, one from each tip, are created in parallel simultaneously. Furthermore, with control of the printing force, feature sizes could be controlled over the range submicron to tens of microns. Three ink candidates have been printed by polymer pen printing approach to fabricate 2D&3D microstructures. The first ink material is Barium Strontium Titanate (BST) nanocrystallites dispersed in a furfuryl alcohol (FA), which was printed by the single PDMS pen with 100 μm tip diameter (Chapter 3). After printing, samples were heated to crosslink FA monomers, forming a stable polymeric matrix with embedded BST nanocrystallites. Without shear-thinning properties, BST/FA ink cannot be used to build 3D posts, but it has the capability to create circular patterns with different thickness by the single or multi-tier deposition method. It was found that the thickness of film increased linearly with the number of deposits without changing the diameter significantly. This encouraging result could enable the formation of microcapacitors with multi-tiered structure. Moreover, the study of printing parameters, including printing height and ink pick-up position, shows that changes to the pen positions in the ink reservoir or substrate have essentially no impact on deposit thickness or diameter. Beyond that, the effect of surface chemistry of PDMS pen and silicon wafer have also been studied. The plasma treated hydrophilic PDMS pen can pen transfer more BST/FA than untreated one; and the larger diameters with smaller thickness were obtained on a hydrophilic silicon wafer. The second ink candidate is a dilute aqueous solution of enzyme Candia antartica lipase B (CALB), which is known to catalyze the decomposition of poly (ε-caprolactone) (PCL) films. By bringing enzymes into contact with pre-defined regions of a surface, a polymer film can be selectively degraded to form patterned features that are requited for applications in biotechnology and electronics. This so-called enzymatic lithography is an environmentally friendly process as it does not require any actinic radiation or synthetic chemicals to develop required features. But the need to restrict the mobility of the enzyme in order to maintain control of feature sizes poses a significant challenge. In Chapter 4, after writing 2D enzyme patterns onto a spin-cast PCL film by single pen printing, samples with CALB were incubated at 37 ℃ and 95% relative humidity (RH) for up to 7 days to develop features. The CALB selectively degraded the PCL film during incubation, forming openings through the film. The size of these features (10 to 50 μm diameter) is well suited for use as biocompatible micro-reactors. Previous study of patterning CALB by single polymer pen printing technique resulted in slow etch rates, low throughput and poor image quality. In Chapter 5, I present an improved enzymatic lithography approach, still based on enzyme CALB and PCL system, which can resolve fine-scale features (\u3c 1 μm across) in thick (0.1 - 2.0 μm) polymer films after 5 minutes to 2 hours of incubation at 37 ℃ and 87% RH. Immobilization of the enzyme on the polymer surface was monitored using fluorescence microscopy by labeling CALB with FITC. The crystallite size in the PCL films was systematically varied; small crystallites resulted in significantly faster etch rates (20 nm/min) and the ability to resolve smaller features (as fine as 1 μm). The effect of printing conditions and RH during incubation is also presented. Patterns formed in the PCL film were transferred to an underlying copper foil demonstrating a Green approach to the fabrication of printed circuit boards. In parallel, the third ink material is a mixture of 25 wt% graphite dispersed in a high viscosity phenolic resin n-methyl-2-pyrrolidone (NMP) solution, which can be converted into carbon/carbon composites after a pyrolysis process. The 3D polymeric posts were created by depositing multilayers of thixotropic phenolic ink on a silicon substrate by single polymer pen printing method with a 10 μm radius PDMS pen tip (Chapter 6). After pyrolysis at 1000 ℃ in a nitrogen (N2) atmosphere, the polymeric features were converted to the glassy carbon/graphite features with a high aspect ratio (\u3e2). These features may be used as microelectrodes. Last, arrays of needle-shaped glassy carbon have been developed by a drawing approach using multi-pen printing technique followed by simple pyrolysis process (Chapter 7). To build polymeric needles with ultra-high aspect ratio, the polymeric ink was prepared by dissolving phenolic resin in the high boiling point (204 ℃) solvent NMP without fillers to achieve good printability and suitable viscosity. By slowly lifting up the print head from substrate, liquid needle structures were formed and then solidified on silicon substrates or gold electrodes due to the solvent evaporation. In addition, suspended resin fibers connected to two electrodes have also been fabricated by precisely controlling the movement of the PDMS pen. After pyrolysis, these resin features were converted to glassy carbon and the 3D structures remained. The electrical characterization results showed that glassy carbon made by this method had relatively low resistivity (2.5 x 10-5 Ωm). Therefore the glassy carbon based microneedles are well-suited to be electrodes for electrochemical sensors for biological applications

Latest Advancements in Micro Nano Molding Technologies – Process Developments and Optimization, Materials, Applications, Key Enabling Technologies

Micro- and nano-molding technologies are continuously being developed due to enduring trends like increasing miniaturization and higher functional integration of products, devices, and systems. Furthermore, with the introduction of higher performance polymers, feedstocks, and composites, new opportunities in terms of material properties can be exploited, and, consequently, more micro-products and micro/nano-structured surfaces are currently being designed and manufactured.Innovations in micro- and nano-molding techniques are seen in the different processes employed in production (injection molding, micro injection molding, etc.); on the use of new and functional materials; for an ever-increasing number of applications (health-care devices, micro-implants, mobility, and communications products, optical elements, micro-electromechanical systems, sensors, etc.); in several key enabling technologies that support the successful realization of micro and nano molding processes (micro- and nano-tooling technologies, process monitoring techniques, micro- and nanometrology methods for quality control, simulation, etc.) and their integration into new manufacturing process chains.This Special Issue reprint showcases research papers and review articles that focus on the latest developments in micro-manufacturing and key enabling technologies for the production of both micro-products and micro-structured surfaces

Development of on-farm diagnostic devices

The global population, currently 7.7 billion, is expected to grow to 9.7 billion by 2050. This is expected to lead to a 70% increase in demand for animal-based protein. Irish beef and dairy products account for over 50% of our agricultural output and DAFM’s Food Wise 2025 strategy aims to position Ireland as a world leader in sustainable agri-food production. However, the high percentage of livestock that are lost due to infectious diseases (20%), poses a challenge to achieving this sustainability, in addition to more sustainable use of antimicrobials, smarter livestock diagnostics and treatments are therefore required. The goal of this thesis was to develop a low-cost disposable biosensor that would permit point-of-care (POC) detection of diseases in bovines, through cost-effective, scalable microfabrication techniques. Such devices could enable real-time determination of the health status of animals on farm and contribute to more informed therapeutic interventions. Electrochemistry presents a viable option for POC devices in this regard and allows easy integration with portable electronics. Electrochemical Impedance Spectroscopy (EIS) is a surface sensitive technique that measures the resistive and capacitive behaviour of an electrochemical system. It lends itself to serological immunosensor development as it allows label-free detection. For the purposes of this research, silicon devices were fabricated with six microband working electrodes, gold counter, and platinum pseudo-reference electrodes. The microband working electrodes were modified with a biocompatible co-polymer. This co-polymer supported the cross-linking of a bioreceptor (e.g., anti-bovine IgG) to electrode surface, which selectively bound to the target biomolecule (bovine IgG) in serum. This EIS device could distinguish between seronegative and seropositive samples in 15 minutes making it suitable for POC applications. Additionally, the presence of six working electrodes allowed for testing of multiple samples at a time. Often, however, only a single test is required. As such, silicon presents an expensive option for disposable sensors. Hence, polymer replication methods were also investigated in this thesis. This process allowed a single silicon wafer to be repeatedly used to produce polymer structures. A microneedle format was chosen to eliminate the need for taking samples on-farm and provide a pain-free method of in vivo measurements in interstitial fluid in interstitial fluid. The fabrication method used a double-sided micro-moulding process to move towards mass manufacturing. COMSOL simulations were performed to explore the active layer on the microneedle tip surface, ensuring no diffusional overlap between electrodes and providing the most effective tip design. The microneedle structures also presented the opportunity for novel fabrication of nanoring arrays, by removing part of the protruding structure and exposing underlying nanorings. These have the potential to be highly sensitive electrochemical devices due to enhanced mass transport and high current densities, while maintaining the scalable cost-effective fabrication process of the microneedles. Devices produced steady-state CVs in a known redox molecule, with currents in the nA range

Micro/Nano Structures and Systems

Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability is a comprehensive guide that explores the various aspects of micro- and nanostructures and systems. From analysis and design to manufacturing and reliability, this reprint provides a thorough understanding of the latest methods and techniques used in the field. With an emphasis on modern computational and analytical methods and their integration with experimental techniques, this reprint is an invaluable resource for researchers and engineers working in the field of micro- and nanosystems, including micromachines, additive manufacturing at the microscale, micro/nano-electromechanical systems, and more. Written by leading experts in the field, this reprint offers a complete understanding of the physical and mechanical behavior of micro- and nanostructures, making it an essential reference for professionals in this field

Theranostic Gelatin Nanoparticles for Antigen Delivery and Combined Strategies for Transcutaneous Application

Transcutaneous application of vaccines is a promising strategy to enhance the effectiveness of vaccination using a reachable route of administration. Additionally, replacing the conventional needles with skin mechanical penetration techniques as microneedles or skin laser microporation will offer great advantages. This transcutaneous delivery techniques are pain-free and will help to avoid the hazards of needles. For the delivery of antigens, nanocarriers are so promising to enhance and modulate their immune response. The nanocarriers offer merits such as antigen protection from degradation, and controlling the release rate of the antigen. Additionally, due to the particulate nature of the nanocarriers, they can potentially display the antigen in a way that better mimics pathogens. For this aim, ovalbumin as a model antigen has been delivered using functionalized theranostic gelatin nanoparticles to bone marrow-derived dendritic cells (BMDCs). The nanoparticles were rendered fluorescent by using a novel imaging agent (gold and silver alloy nanoclusters) that emits near-infra red light. This was beneficial to study the nanoparticles uptake by BMDCs and also to image the nanoparticles within the skin tissue. Finally, the developed theranostic nanocarriers induced the maturation of the BMDCs and enhanced the proliferation of both helper T cells (CD4+) and cytotoxic T cells (CD8+). This indicates the potential efficacy of the delivery system for vaccination either against allergy or viruses and tumors

Advanced Electrohydrodynamic Atomisation Engineered Microneedle Coatings

Transdermal drug delivery (TDD) is an emerging field in the pharmaceutical remit compared to conventional methods (oral and parenteral). Microneedle (MN) based devices have gained significant interest as a strategy to overcome the skins formidable barrier; the stratum corneum and enhance drug delivery. The research presented here shows the successful coating of MNs with polymeric dye composites using Electrohydrodynamic atomisation (EHDA). Initially the rheological behaviours of polymeric solutions and morphological characterisation was carried out. This was followed by Quality by Design (QBD) implementation for the optimisation of the key process parameters in EHDA. Here, the electrosprayed nanoparticles and electrospun nano/micro fibres consisted of a polymeric matrix and dye. Eight formulations were assessed consisting of 5% w/v of polycaprolactone (PCL) in dichloromethane (DCM) and 5% w/v polyvinylpyrrolidone (PVP) in ethanol. A full factorial Design of Experiments (DoE) was used to assess the various parameters (applied voltage, deposition distance and flow rate). Further particle and fibre analysis was carried out using Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), particle/fibre size distribution. In addition to this, in vitro release studies were carried out using fluorescein (FL) and rhodamine B (RhB) as model dyes and in vitro permeation studies were applied. From optimising EHDA more than 52% of particles were under 500 nm and fibres were in the micron range. In vitro drug release studies showed 100% drug release after 7 days for PCL particles and fibres. It also showed 100% drug release within 120 min for PVP particles and 300 minutes for PVP fibres. The release kinetics and the permeation study showed that the MN successfully pierced the membrane and the Es and Esp MN coatings released a large amount of the loaded drug within 6 hours for all formulations. This study has demonstrated the capability of these robust MNs to encapsulate a diverse range of drugs within a polymeric matrix giving rise to the potential of developing personalised medical devices

Development of Facile Microfabrication Technologies for the Fabrication and Characterization of Multimodal Impedimetric, Plasmonic, and Electrophysiological Biosensors

The objective of this dissertation was to develop novel methods of patterning inorganic and organic materials, develop biocompatibility evaluations, and subsequently apply these methods toward developing biosensors and lab-on-a-chip devices, such as Interdigitated Electrodes (IDEs) and Microelectrode Arrays (MEAs) on non-traditional (such as nanostructured and plasmonic) polymer substrates or deploy these methods to enhance precision cellular placement on traditional (glass) MEA substrates. It was hypothesized that a combination of such facile microfabrication techniques and patterning technologies on traditional and non-traditional substrates would increase the sensitivity and selectivity of such sensor platforms by several orders of magnitude, and potentially introduce new modalities for cell-based biosensing. In order to demonstrate the biological functionality of these new IDEs and MEAs, a variety of cell cultures were used (cardiac, stem cell, and endothelial cells) to study the growth, proliferation, modes of increasing sensitivity and response to various compounds in vitro (outside the body)

Functional surface microstructures inspired by nature : From adhesion and wetting principles to sustainable new devices

In the course of evolution nature has arrived at startling materials solutions to ensure survival. Investigations into biological surfaces, ranging from plants, insects and geckos to aquatic animals, have inspired the design of intricate surface patterns to create useful functionalities. This paper reviews the fundamental interaction mechanisms of such micropatterns with liquids, solids, and soft matter such as skin for control of wetting, self-cleaning, anti-fouling, adhesion, skin adherence, and sensing. Compared to conventional chemical strategies, the paradigm of micropatterning enables solutions with superior resource efficiency and sustainability. Associated applications range from water management and robotics to future health monitoring devices. We finally provide an overview of the relevant patterning methods as an appendix