Silvia Marson

Flatness optimization of micro-injection moulded parts: the case of a PMMA microfluidic component

Micro-injection moulding (µ-IM) has attracted a lot of interest because of its potential for the production of low-cost, miniaturized parts in high-volume. Applications of this technology are, amongst others, microfluidic components for lab-on-a-chip devices and micro-optical components. In both cases, the control of the part flatness is a key aspect to maintaining the components functionality. The objective of this work is to determine the factors affecting the flatness of a polymer part manufactured by µ-IM and to control the manufacturing process with the aim of minimizing the in-process part deformation. As a case study, a PMMA microfluidic substrate with overall dimensions of 10 mm diameter and 1 mm thickness was investigated by designing a µ-IM experiment having flatness as the experimental response. The part flatness was measured using a micro-coordinate measuring machine. Finite elements analysis was also carried out to study the optimal ejection pin configuration. The results of this work show that the control of the µ-IM process conditions can improve the flatness of the polymer part up to about 15 µm. Part flatness as low as 4 µm can be achieved by modifying the design of the ejection system according to suggested guidelines.

Design and fabrication of a three-dimensional microfluidic device for blood separation using micro-injection moulding

Micro-manufacturing is a fast developing area due to the increasing demand for components and systems of high precision and small dimensions. A number of challenges are yet to be overcome before the full potential of such techniques is realised. Examples of such challenges include limitations in component geometry, material selection and suitability for mass production. Some micro-manufacturing techniques are still at early development stages, while other techniques are at higher stage of manufacturing readiness level but require adaptation in part design or manufacturing procedure to overcome such limitations. This article presents a case study, where the design of a micro-scale, biomedical device is adapted for functionality and manufacturability by a high-volume micro-fabrication technique. Investigations are described towards a disposable three-dimensional, polymer-based device for the separation of blood cells and plasma. The importance of attempting a three-dimensional device design and fabrication route was to take advantage of the high-throughput per unit volume that such systems can, in principle, allow. The importance of a micro-moulding fabrication route was to allow such blood-containing devices to be cheaply manufactured for disposability. Initial device tests showed separation efficiency up to approximately 80% with diluted blood samples. The produced prototype indicated that the process flow was suitable for high-volume fabrication of three-dimensional microfluidics.

Computational modelling and optimisation of the fabrication of nano-structures using focused ion beam and imprint forming technologies

Focused Ion Beam (FIB) and Nano-Imprint Forming (NIF) have gained recently major interest because of their potential to enable the fabrication of precision engineering parts and to deliver high resolution, low-cost and high-throughput production of fine sub-micrometre structures respectively. Using computational modelling and simulation becomes increasingly important in assessing capabilities and risks of defects with respect to product manufacturability, quality, reliability and performance, as well as controlling and optimising the process parameters. A computational model that predicts the milling depth as function of the ion beam dwell times and a number of process parameters in the case of FIB milling is investigated and experimentally validated. The focus in the NIF study is on modelling the material deformation and the filling of the pattern grooves during the mould pressing using non-linear large deformation finite element analysis with hyperelastic non-compressive material behaviour. Simulation results are used to understand the risk of imperfections in the pattern replication and to identify the optimal process parameters and their interaction.

Biofluid behaviour in 3D microchannel systems: Numerical analysis and design development of 3D microchannel biochip separators

This paper describes the design and development cycle of a 3D biochip separator and the modelling analysis of flow behaviour in the biochip microchannel features. The focus is on identifying the difference between 2D and 3D implementations as well as developing basic forms of 3D microfluidic separators. Five variants, based around the device are proposed and analysed. These include three variations of the branch channels (circular, rectangular, disc) and two variations of the main channel (solid and concentric). Ignoring the initial transient behaviour and assuming steady state flow has been established, the efficiencies of the flow between the main and side channels for the different designs are analysed and compared with regard to relevant bio-microfluidic laws or effects (bifurcation law, Fahraeus effect, cell-free phenomenon, bending channel effect and laminar flow behaviour). The modelling results identify flow features in microchannels, a constriction and bifurcations and show detailed differences in flow fields between the various designs. The manufacturing process using injection moulding for the initial base case design is also presented and discussed. The work reported here is supported as part of the UK funded 3D-MINTEGRATION project.

Modelling and process capability analysis of Focused Ion Beam

Focused Ion Beam (FIB) machining is a dynamic process whereby atoms can be removed from the surface of a substrate by an accelerated stream of ions, focused into a small area purely by electronic and electrical control. In the fabrication of 3D features such as miniaturised objects, masks and moulds for various microsystems, the control of the depth variation is a critical parameter. A modelling framework integrating computational models for simulation of the FIB milling of predefined shapes, risk analysis, process capability and optimisation that can aid the optimal control of key process parameters is developed and demonstrated. The modelling methodology is based on numerical techniques for discretisation of the FIB process governing equations, statistical analysis, reduced order modelling through response surface approach and non-gradient numerical optimisation.

Conductive Polymers for Plastic Electronics

Since the discovery of conductive polymers, scientists have devoted great efforts to successfully synthesizing conductive polymers, which combine the processing and mechanical properties of “conventional insulating polymers” with the electrical and optical properties of metals. Nowadays the use of conductive polymers in commercial products is still limited, due to the partial success achieved in producing materials with high conductivity and real plastic characteristics. Once better conductive plastics are developed, the potential applications can be endless, ranging from organic bioelectronics to plastic electronic components for sensors and biosensors. The difficulty in trying to process conductive polymers using the methods normally utilized by the polymer industry (e.g., injection molding) arises from the fact that these materials are not intrinsically thermoplastic. Over the last two to three decades, scientists have tried different approaches to produce thermoplastic polymers with high conductivity. In this chapter, after a brief history of conductive polymers, these approaches are reviewed, with particular emphasis on polyaniline. A section that describes micro-injection molding and highlights the thermoplastic characteristics required by the material used for the process is also included. Finally, possible improvements of such materials (e.g., molecular recognition) achieved by applying the molecular imprinting technology are also mentioned.

Model assisted process control in micro- and nano-fabrication using Focused Ion Beam

The major interest in Focused Ion Beam (FIB) has been driven by the potential of the process to enable the fabrication of precision engineering parts, high resolution patterns and micro-moulds required in applications such as the manufacturing of miniaturised components for various heterogeneous systems, micro-fluidics, bio-medical, MEMS, and embedded electronic test devices. A major issue with realising the milling capability of FIB is associated with the ability to accurately control the depth variation. A computational model that predicts the milling depth as function of the ion beam scanning frequency and a number of process parameters is investigated and experimentally validated. The model can assist in specifying optimal FIB process parameters for achieving accurate shapes of the intended micro- or nano-features.