Microfluidic device prototyping via laser processing of glass and polymer materials

In this thesis, three different processes for the fabrication of microchannels in three different base materials were experimentally and numerically modelled in detail in order to understand the effects of processing conditions on process fabrication capabilities. CO2 and Nd:YAG laser processing systems as well as a xurography technique were employed in this work for the development of microfluidic channels. The effects of CO2 laser processing on the process of directly writing microchannels on surface of four different types of glass: soda lime, fused silica, borosilicate and quartz were studied. Mathematical models were developed to relate the process input parameters to the dimensions of the microchannels. The effect of laser processing on the optical transmission capabilities of the glass was also assessed. A novel method, using Nd:YAG laser system, was employed for the fabrication of internal microchannels inside polymeric materials. Microchannels up to three millimetres long were successfully created inside a polycarbonate within a single laser processing step. Mathematical models were developed to express the relationship between laser processing input parameters and the width of these internal microchannels. The Nd:YAG processing parameters for laser welding of polycarbonate sheets were also determined. A new rapid low-cost prototyping method for the fabrication of multilayer microfluidic devices from cyclic olefin copolymer (COC) films was developed. CO2 laser cutting and xurography techniques were employed for the fabrication of the microfluidic features, followed by multilayer lamination via cyclohexane vapour exposure. Process parameters were optimised including solvent exposure time. Functional UV-transparent microfluidic mixing devices were demonstrated which included internally bound polymer monolithic columns within the microfluidic channels. There is a growing interest to use technologies which are in this thesis, the three different developed processes for the fabrication of microchannels in three different base materials provides the basis for achieving higher dimensional accuracies and novel designs within lab-on-a-chip microfluidic sensing devices

Development of teat sensing system for automated milking

Robotic application of milking cups to the udder of a cow in a rotary high capacity group milking system is a major challenge in automated milking. Application time and reliability are the main constraints. Manual application by an operator of a rotary carousel is of the order of 10 seconds and 100% reliable. In existing non-rotary milking machines, the cups are applied to each teat individually and the process can take up to two minutes. In order to achieve a more rapid simultaneous application of the four cups, the three dimensional locations of the four teats must be known in real time. In this thesis, a multimodal vision system combining optical stereovision and thermal imaging is developed. The overall system is evaluated from the point of view of accuracy and robustness. Laboratory tests have shown that stereovision can rapidly locate teat three dimensional position coordinates, however robust identification of the teats is required. It is shown that this may be achieved using thermal imaging to isolate teats from background objects due to their elevated temperature profile. Further development is necessary to overcome specific situations such as overlapping teats

Effect of laser processing parameters and glass type on topology of micro-channels

Traditional processes to manufacture micro-fluidic devices include standard lithography, electron beam writing and photo-patterning. These techniques are well established but most are limited to surface micro-fabrication. Laser micro-machining provides an alternative for microfabrication of devices. This paper presents Design of Experiment models for the fabrication of micro-channel structures with four different types of glass, soda-lime, fused-silica, borosilicate and quartz. A 1.5kW CO2 laser with 90 μm spot size was used to fabricate micro-channels on the surface of glass sheets. Power, P, pulse repetition frequency, PRF, and translation speed, U, were set as control parameters. The resulting geometry of the channel (depth and width) and transmission capabilities were measured and analyzed. A comparison of the results of this experimental testing with the four glass types showed that quartz and fused-silica glasses would have better channel topologies for chemical sensing applications

Evaluation of use of wearable sensor garment in home screening for sleep apnea events

Sleep apnea is a common condition that seriously degrades sleep quality. Related researches have shown that patients suffering from sleep apnea have higher risks of accidents both at home and at work [1]. In addition, sleep apnea has been associated with an increased risk of cardiovascular related deaths and metabolic conditions, including hypertension, stroke, congestive heart failure, and sudden death [2]. Sleep apnea is estimated to affect 2-4% of middle-aged adults [3]. Up to 80% of these cases are undiagnosed and untreated by the healthcare system [4]. Sleep apnea disease presents also an economical burden on healthcare systems. In this work, the results of clinical trials of evaluating the possibility of using a wearable sensor garment for in-home screening of obstructive sleep apnea and hypoapnea (OSAS) are presented. The garment incorporates ECG, respiration and position signals. The performances of the sensors of the garment were compared to the signal collected during a routine overnight polysomnograph (PSG) in a sleep clinic. The results showed comparable performance of the garment and PSG thus demonstrating the possibility of using the wearable sensor garment as part of an in-home screening system for sleep apnea events

Fast fabrication process of microfluidic devices based on cyclic olefin copolymer

A new low-cost process for fast fabrication of multilayer microfluidic devices using cyclic olefin copolymer film materials is presented. This novel process consists of the fabrication of microfluidic features by xurography, followed by multilayer lamination via cyclohexane vapor exposure. Exposure time to this solvent and compression time were optimized for bond tensile strength. A three-layer microfluidic chip capable of withstanding back pressures up to 23 MPa was fabricated in less than an hour. The suitability of this fast prototyping method for fabrication of functional UV-transparent microfluidic devices was demonstrated by development and testing of a microfluidic mixer and preparation of a polymer monolithic column within the microfluidic channel

Focussed ion beam serial sectioning and imaging of monolithic materials for 3D reconstruction and morphological parameter evaluation

A new characterisation method, based on the utilisation of focussed ion beam-scanning electron microscopy (FIB-SEM), has been employed for the evaluation of morphological parameters in porous monolithic materials. Sample FIB serial sectioning, SEM imaging and image processing techniques were used to extract the pore boundaries and reconstruct the 3D porous structure of carbon and silica-based monoliths. Since silica is a non-conducting material, a commercial silica monolith modified with activated carbon was employed instead to minimise the charge build-up during FIB sectioning. This work therefore presents a novel methodology that can be successfully employed for 3D reconstruction of porous monolithic materials which are or can be made conductive through surface or bulk modification. Furthermore, the 3D reconstructions were used for calculation of the monolith macroporosity, which was in good agreement with the porosity values obtained by mercury intrusion porosimetry (MIP)

From ‘Devices' to 'Self-Aware, Bioinspired MicroSystems': What does the future hold for optical oensing?

Right now, there is real excitement across the broad area of materials science research, as the quality of the work improves and the potential for new levels of impact becomes more tangible. Furthermore, access to more powerful characterisation tools enables new materials to be more fully and rapidly profiled. Enhanced characterisation coupled with improved ability to control and manipulate material structure from the atomic/molecular level presents unparalleled opportunities for researchers. New modelling techniques can establish correlations between theory and practice, while innovative approaches to molecular self-assembly and 3D printing allows full control over the spatial arrangement of materials from the molecular to the macro scale. A clearer understanding of surface and interfacial behaviour will be essential to underpin fundamental breakthroughs that in turn produce truly disruptive technologies. Stimuli-responsive materials that exhibit changes in optical (colour, absorbance, fluorescence, reflectivity), electrical/electrochemical (resistance, redox behaviour), chemical (binding-release) or physical (dielectric constant, viscosity, rigidity, volume) characteristics are opening up new concepts in so-called 4D-materials science, in which the 4th dimension is the ability to change materials characteristics over time in a controlled manner using external stimuli. These tremendous advances in materials science will provide the foundations for entirely new concepts in sensing – concepts that draw inspiration from biological sources and models, enabling the creation of autonomous devices that are able to monitor and manage their own condition, as well as that of their surrounding environment. New capabilities such as programmed motility, switchable selective uptake and release of molecular agents, self-maintenance/repair, and remote reporting will be commonplace, and ultimately, the ability to self-assemble, replicate, and disassemble will enable these devices to manifest many of the features of biological entities. Assembling these capabilities into new platforms based on bioinspired concepts could open the way to devices with performance specifications well beyond the current state of the art. For example, smart implantable devices capable of sensing, reporting and responding to changes in an individual’s health status, and that can function reliably within the body for many years, could dramatically improve the quality of life for many millions of people suffering from chronic conditions. Achieving this goal is arguably one of the most important global challenges for modern science. In this lecture I will explore how some of these features, albeit still at a relatively primitive stage of development, are already beginning to move from concept to demonstration. In particular, I will focus on the important role of light as a means to enable and control stimuli-responsive materials, and discuss how these might provide initial building blocks for creating these futuristic devices and platforms

‘Can biomimetic principles coupled with advanced fabrication technologies and stimuli-responsive materials drive revolutionary advances in wearable and implantable biochemical sensors?’

Since the initial breakthroughs in the 1960’s and 70’s that led to the development of the glucose biosensor, the oxygen electrode, ion-selective electrodes, and electrochemical/optochemical diagnostic devices, the vision of very reliable, affordable chemical sensors and bio-sensors capable of functioning autonomously for long periods of time (years), and providing access to continuous streams of real-time data remains unrealized. This is despite massive investment in research and the publication of many thousands of papers in the literature. It is over 40 years since the first papers proposing the concept of the artificial pancreas, by combining the glucose electrode with an insulin pump. Yet even now, there is no chemical sensor/biosensor that can function reliably inside the body for more than a few days, and such is the gap in what can be delivered (days), and what is required (minimum 10 years) for implantable devices, it is not surprising that in health diagnostics, the overwhelmingly dominant paradigm for reliable measurements is single use disposable sensors. Realising disruptive improvements in chem/bio-sensing platforms capable of long-term (months, years) independent operation requires a step-back and rethinking of strategies, and considering solutions suggested by nature, rather than incremental improvements in available technologies

Next generation autonomous sensing platforms based on biomimetic principles

Imagine a world in which issues related to long-term (months to years) reliability of chem/bio-sensing platforms have been solved, and devices capable of carrying out complex chem/bio-functions in an autonomous manner are ubiquitously available. The potential impact of these technologies socially and economically is enormous, and the demand will be universal, driven by an infinite range of applications. Devices will perform complex analytical measurements while located in remote and environmentally hostile locations, such as the deep oceans, or inside the human body. Their capabilities will go far beyond those of existing devices; chemical sensors, biosensors, lab-on-chip (LOC) systems or autonomous analysers, that cannot deliver the price-performance required for reliable long-term (years) autonomous in-situ operation. Revolutionary device improvements are required to meet this vision, and it is becoming clear that these improvements require a fundamental move towards devices based on bio-inspired approaches. For example, future instrument fluidics will have a much more active role beyond the current tasks of transporting samples, mixing reagents, and cleaning. Much like the circulation systems in living entities, these circulation systems will perform advanced functions, like using mobile micro-scaled biomimetic agents to detect, spontaneously migrate to, and repair damaged channels or fluidic components in order to maintain functional integrity of the device. These strategies, if successful, will be broadly disruptive across many application domains, from chronic disease management to environmental monitoring. In this paper, I will present ideas and strategies through which this exciting vision might be advanced via an exciting combination of stimuli-responsive materials, emerging technologies for precise control of 3D materials morphology (to nanoscale dimensions), and state of the art characterization and visualization techniques