Fabrication of polymeric microchannels with focused and defocused CO2 lasers

 The control of energy distribution or energy intensity inside a laser spot using a defocusing method enables the formation of high-quality microchannels of multiple cross-sections in polycarbonate. Moreover, a thermal mathematical model of the process was developed to aid understanding of the process and to allow channel topology prediction

Prediction of Poly-methyl-methacrylate Laser Milling Process Characteristics Based on Neural Networks and Fuzzy Data☆

Abstract Laser milling is a recent technology adopted in rapid prototyping to produce tool, mould and polymer-based microfluidic devices. In this process, a laser beam is used to machine a solid bulk, filling the area to be machined with a number of closely spaced parallel lines. Compared to traditional machining, this method has some advantages, such as: greater flexibility of use, no mechanical contact with the surface, a reduction in industrial effluents, a fine accuracy of machining, even with complex forms, and the possibility to work different kind of materials. While it is relatively easy to predict the depth of the area worked, the surface roughness is more difficult to predict due to the materials behaviors at microscopic level. This is truer when polymer processing is considered due to the local thermal effects. The paper addresses the application of an artificial neural network computing technique to predict the depth and the surface roughness in laser milling tests of poly-methyl-methacrylate. The tests were carried out adopting a CO 2 laser working in continuous and pulsed wave mode. The obtained results showed a good agreement between the model and the experimental data. As a matter of fact, despite the thermal degradation that occurs on the PMMA surface, neural network processing offers an effective method for the prevision of roughness parameters as a function of the adopted process parameters

Understanding poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel as a multifunctional membrane in microfluidic cell culture platform

Cell culture technology developed at the turn of 20th century using Petri dish, which is not able to consider the microenvironment that the cells experience in vessels, has remained virtually unchanged for almost a century. However, such microenvironment associated with cell culture which usually consists of soluble factors, extracellular matrix cues, and cellular networks is difficult to reproduce experimentally with the traditional approach. In order to further elaborate complex mechanisms of cell biology through mimicking such microenvironment in vivo, the technical approaches together with developed microdevices are highly demanded within such a context. Microfluidic devices have been extensively developed and used for cell culture in the last two decades, which offer numerous advantages and a great potential for accurate and efficient control of the complex culturing microenvironment at cellular length scale. However, these devices are relatively complex in their fabrication and integration to fulfil multifunctional tasks for cell culture and drug testing simultaneously, which for example requires a membrane between the culture chamber and drug delivery reservoir to control microenvironment at cellular scale. This thesis is to primarily focus on the feasibility and reliability in the attempt of using poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel as an inserted membrane, based on its permeable and flexible tissue-like properties. PHEMA membrane is able to serve dual purposes in the microfluidic systems in cell culture: i) exchanging nutrients between culture chamber and drug delivery reservoir; and ii) sealing the microchannel circuits.</div

Numerical Simulation of Laser Processing Materials: An Engineering Approach

The following chapter aims at giving an overview of the use of numerical simulation in the field of laser processing. Indeed, the past two decades saw an increasing demand for lasers in various areas such as healthcare, microelectronics, cartography, optoelectronics, aeronautics, etc. Thus, the comprehension of the laser-material interaction and the removal mechanism became primordial to predict and improve the efficiency of a process. After a nonexhaustive literature review, two simulation approaches (Finite Element and Design Of Experiment, DOE) will be presented to demonstrate the importance of numerical simulation in laser applications

Flexible stretchable electronics for sport and wellbeing applications

Wearable electronics are becoming increasingly widespread in modern society. Though these devices are intended to be worn, integrated into clothing and other everyday objects, the technologies and processes used to manufacture them is no different than those that manufacture laptops and mobile phones. Many of these devices are intended to monitor the user’s health, activity and general wellbeing, within clinical, recreational and assistive environments. Consequently, the inherent incompatibility of these rigid devices with the soft, elastic structure of the human body can in some cases can be uncomfortable and inconvenient for everyday life. For devices to take the step from a ‘wearable’ to an ‘invisible’, a drastic rethinking of electronics manufacturing is required.The fundamental aim of this research is to establish parameters of usefulness and an array of materials with complimentary processes that would assist in transitioning devices to long term almost invisible items that can assist in improving the health of the wearer. In order to approach this problem, a novel architecture was devised that utilised PDMS as a substrate and microfluid channels of Galinstan liquid alloy for interconnects. CO2 laser machining was investigated as a means of creating channels and vias on PDMS substrates. Trace speeds and laser power outputs were investigated in order to find an optimal combination. The results displayed upper limits for power densities; where surpassing this limit resulted in poor repeatability and surface finish. It was found that there was an optimal set of trace speeds that ranged from approximately 120mm/s to 190mm/s that resulted in the most reliable and repeatable performance. Due to the complex nature of a materials variable energy absorption properties, it is not possible to quantify a single optimal parameter set.To understand the performance of these devices in situ, finite element analysis was employed to model deformations that such a device could experience. The aims here were to investigate the bond strength required to prevent delamination, between the silicon-PDMS and PDMS-PDMS bonds, in addition to the stress applied to the silicone die during these deformations. Based upon the applied loads the required bond strengths would need to be at least ~65kPa to maintain PDMS-PDMS adhesion during these tests, while stress on the silicone-PDMS adhesion required an expected v higher ~160kPa, both of which are within the reach of existing bonding techniques that are capable of withstanding a pressure of ~600kPa before failure occurs. Stress on the silicon die did not exceed ~7.8 MPa during simulation, which is well below the fracture stress.By developing knowledge about how various components of such a system will respond during use and under stress, it allows future engineers to make informed design decisions and develop better more resilient products.</div

Diode laser processing of PMMA and LCP materials for microsystem packaging

The thesis describes the development of laser-assisted bonding methods for assembly of microfluidic devices and MEMS packaging. A laser microwelding technique for assembly of transparent polymer substrates for fabrication of microfluidic devices was studied. The transparent PMMA substrates were bonded together using a high power diode laser system with a broad top-hat beam profile and an intermediate titanium thin film consisting of 0.7 mm diameter spots. A tensile strength of 6 MPa was achieved for this novel method which is comparable to that of the previous work in laser welding of polymers. It has been demonstrated that the method is capable of leak free encapsulation of a microfluidic channel. Furthermore, a novel laser-based method using an LCP film for packaging of MEMS, sensors and other microelectronic devices has been investigated. The results show that it is possible to use a laser based method with an LCP polymer for high quality substrate bonding applications. Glass-glass based cavities allow optical transmission and have potential applications for optical sensors and other photonic devices. For glass-glass bonding, it was shown that thin film titanium material can be used as an effective optical absorber in the laser based LCP bonding technique. Laser bonding of glass and silicon using an LCP film has also been achieved but in this case the silicon substrate acted as the absorber to capture the laser power. Laser bonding of a silicon cap to a molded LCP package has also been demonstrated successfully. The results of temperature monitoring using embedded sensors show that the temperature at the base of the LCP package (~130C) is substantially lower than the bonding temperature (> 280C). The results of shear and leak test show good reliability and hermeticity of the laser bonded microcavities. Both two-dimensional and three-dimensional models of heat transfer are developed and studied using the COMSOL Multiphysics software tool to understand the localised laser heating effects. The results are in good agreement with those of the practical work

Review of Microfluidic Devices and Imaging Techniques for Fluid Flow Study in Porous Geomaterials

Understanding transport phenomena and governing mechanisms of different physical and chemical processes in porous media has been a critical research area for decades. Correlating fluid flow behaviour at the micro-scale with macro-scale parameters, such as relative permeability and capillary pressure, is key to understanding the processes governing subsurface systems, and this in turn allows us to improve the accuracy of modelling and simulations of transport phenomena at a large scale. Over the last two decades, there have been significant developments in our understanding of pore-scale processes and modelling of complex underground systems. Microfluidic devices (micromodels) and imaging techniques, as facilitators to link experimental observations to simulation, have greatly contributed to these achievements. Although several reviews exist covering separately advances in one of these two areas, we present here a detailed review integrating recent advances and applications in both micromodels and imaging techniques. This includes a comprehensive analysis of critical aspects of fabrication techniques of micromodels, and the most recent advances such as embedding fibre optic sensors in micromodels for research applications. To complete the analysis of visualization techniques, we have thoroughly reviewed the most applicable imaging techniques in the area of geoscience and geo-energy. Moreover, the integration of microfluidic devices and imaging techniques was highlighted as appropriate. In this review, we focus particularly on four prominent yet very wide application areas, namely &ldquo;fluid flow in porous media&rdquo;, &ldquo;flow in heterogeneous rocks and fractures&rdquo;, &ldquo;reactive transport, solute and colloid transport&rdquo;, and finally &ldquo;porous media characterization&rdquo;. In summary, this review provides an in-depth analysis of micromodels and imaging techniques that can help to guide future research in the in-situ visualization of fluid flow in porous media

Advances in Micro and Nano Manufacturing: Process Modeling and Applications

Micro- and nanomanufacturing technologies have been researched and developed in the industrial environment with the goal of supporting product miniaturization and the integration of new functionalities. The technological development of new materials and processing methods needs to be supported by predictive models which can simulate the interactions between materials, process states, and product properties. In comparison with the conventional manufacturing scale, micro- and nanoscale technologies require the study of different mechanical, thermal, and fluid dynamics, phenomena which need to be assessed and modeled.This Special Issue is dedicated to advances in the modeling of micro- and nanomanufacturing processes. The development of new models, validation of state-of-the-art modeling strategies, and approaches to material model calibration are presented. The goal is to provide state-of-the-art examples of the use of modeling and simulation in micro- and nanomanufacturing processes, promoting the diffusion and development of these technologies

A generalised approach on kerf geometry prediction during CO2 laser cut of PMMA thin plates using neural networks

This study presents an application of feedforward and backpropagation neural network (FFBP-NN) for predicting the kerf characteristics, i.e. the kerf width in three different distances from the surface (upper, middle and down) and kerf angle during laser cutting of 4 mm PMMA (polymethyl methacrylate) thin plates. Stand-off distance (SoD: 7, 8 and 9 mm), cutting speed (CS: 8, 13 and 18 mm/sec) and laser power (LP: 82.5, 90 and 97.5 W) are the studied parameters for low power CO2 laser cutting. A three-parameter three-level full factorial array has been used, and twenty-seven (33) cuts are performed. Subsequently, the upper, middle and down kerf widths (Wu, Wm and Wd) and the kerf angle (KA) were measured and analysed through ANOM (analysis of means), ANOVA (analysis of variances) and interaction plots. The statistical analysis highlighted that linear modelling is insufficient for the precise prediction of kerf characteristics. An FFBP-NN was developed, trained, validated and generalised for the accurate prediction of the kerf geometry. The FFBP-NN achieved an R-all value of 0.98, in contrast to the ANOVA linear models, which achieved Rsq values of about 0.86. According to the ANOM plots, the parameter values which optimize the KA resulting in positive values close to zero degrees were the 7 mm SoD, 8 mm/s CS and 97.5 W LP