Browsing by Author "Attia, Usama M."

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    Creating movable interfaces by micro-powder injection moulding
    (Elsevier, 2013-09-09) Attia, Usama M.; Hauata, M.; Walton, I.; Annicchiarico, Daniele; Alcock, Jeffrey R.
    This paper presents a novel in situ technique to produce articulated components with high-precision, micro-scale movable interfaces by micro-powder injection moulding (μPIM). The presented process route is based on the use of micro-scale sacrificial layer between the movable subcomponents which is eliminated during the debinding step, creating a dimensionally-controlled, micro-scale mobile interface. The fabrication technique combines the advantages of micro-powder overmoulding, catalytic debinding and sintering. The demonstrated example was a finger bone prosthesis joint consisting of two sub-components with an interface between components of 200 μm in size. The geometries of the sub-components were designed such that they are inseparable throughout the process whilst allowing them to move relative to each other after the debinding stage. The components produced showed the feasibility of the process route to produce readily-assembled meso-, and potentially micro-, scale articulated systems
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    Design and fabrication of a three-dimensional microfluidic device for blood separation using micro-injection moulding
    (Sage, 2013-12-03) Attia, Usama M.; Marson, Silvia; Alcock, Jeffrey R.
    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 highthroughput 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.
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    Evaluating and controlling process variability in micro-injection moulding
    (Springer Science Business Media, 2011-01-31T00:00:00Z) Attia, Usama M.; Alcock, Jeffrey R.
    Microsystem technologies require relatively strict quality requirements. This is because their functionalities are usually dependent on stringent requirements of dimensions, masses or tolerances. When mass-producing micro-components, e.g. replication of disposable microfluidic diagnostics devices, the consistency of the produced components could be significantly affected by process variability. The variability could be associated with a specific process parameter or could be a result of process noise. This paper presents a methodology to assess and minimise process variability in micro-injection moulding, an example of well- established mass-production techniques for micro-components. A design-of- experiments approach was implemented, where five process parameters were investigated for possible effects on the process variability of two components. The variability was represented by the standard deviation of the replicated part mass. It was found that melt temperature was a significant source of variability in part mass for one of the components, whilst the other was affected by unsystematic variability. Optimisations tools such as response surfaces and desirability functions were implemented to minimise mass variability by more than 40%.
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    An evaluation of process-parameter and part-geometry effects on the quality of filling in micro-injection moulding
    (Springer Science Business Media, 2009-12-01T00:00:00Z) Attia, Usama M.; Alcock, Jeffrey R.
    This paper addresses the use of micro-injection moulding for the fabrication of polymeric parts with microfeatures. Five separate parts with different micro- feature designs are moulded of Polymethylmethacrylate. The design-of-experiments approach is applied to correlate the quality of the parts to the processing parameters. Five processing parameters are investigated using a screening half- factorial experimentation plan to determine their possible effect on the filling quality of the moulded parts. The part mass is used as an output parameter to reflect the filling of the parts. The experiments showed that the holding pressure is the most significant processing parameter for all the different shapes. In addition, the experiments showed that the geometry of the parts plays a role in determining the significant processing parameters. For a more complex part, injection speed and mould temperature became statistically significant. A desirability function approach was successfully used to improve the filling quality of each part.
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    Fabrication of ceramic micro-scale hollow components by micro-powder injection moulding
    (Elsevier Science B.V., Amsterdam., 2012-06-30T00:00:00Z) Attia, Usama M.; Alcock, Jeffrey R.
    Rapid developments in microsystem technologies demand ceramic microcomponents of increasing geometrical complexity. State-of-the-art microfabrication routes of ceramics are either limited in geometrical complexity and/or high volume capabilities. This paper presents a process route by which ceramic microcomponents with relatively complex three-dimensional architectures could be realised by a high-volume technique. The proposed strategy, in which yttria- stabilised zirconia was implemented, combines the capabilities of insert- micromoulding, powder micro-overmoulding, catalytic debinding and sintering. The produced architectures demonstrate the capability of the technique to combine the high performance of ceramic materials with the dimensional accuracy and mass manufacturability of powder micromoulding.
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    Flatness optimization of micro-injection moulded parts: the case of a PMMA microfluidic component
    (Institute of Physics Publishing; 1999, 2011-10-20T00:00:00Z) Marson, Silvia; Attia, Usama M.; Lucchetta, G.; Wilson, A.; Alcock, Jeffrey R.; Allen, David M.
    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 component's 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
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    Integration of functionality into polymer-based microfluid devices produced by high-volume micromoulding techniques
    (Springer, 2010) Attia, Usama M.; Alcock, Jeffrey R.
    Microfluidic devices with integrated functional elements have gained increasing attention in the recent years. Many prototypes covering a wide range of applications have been fabricated and tested, especially in the fields of chemical and biomedical sciences. Nevertheless, integrated microfluidic devices are still far from being widely used as cost-efficient commercial products, often because they are produced by fabrication methods that are not suitable for mass production. Several methods have been recently introduced for cost-efficient high-volume production of micro-featured plastic parts, such as micro-injection moulding and hot-embossing. These methods have been widely used for fabricating simple disposable microfluidic chips on a commercial scale, but have not yet been similarly applied for producing integrated microfluidic devices. This review paper aims at presenting the state of the art in integrated microfluidic devices produced by cost-efficient high-volume replication processes. It takes micro-injection moulding and hot-embossing as its two process examples. Several types of elements are classified according to their functions, defined relative to their physical inputs and outputs. Their level of integration is reviewed. In addition, elements are discussed from a manufacturing viewpoint, in terms of being readily produced by replication techniques or by back-end processes. Current and future challenges in integration are presented and discussed.
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    A methodology for shrinkage measurement in micro-injection moulding
    (Elsevier Science B.V., Amsterdam., 2013-06-01T00:00:00Z) Annicchiarico, Daniele; Attia, Usama M.; Alcock, Jeffrey R.
    The aim of this paper is to provide a method for measuring shrinkage in micro injection moulded (μ-IM) parts - no standardised approach being reported as yet in the literature. This study investigates the feasibility of implementing the international standards used to investigate shrinkage in conventional (macro) moulding at the micro-scale. Following a similar experimental procedure to the relevant standards, micro-moulded polyoxymethylene (POM) specimens were produced, and the influence of processing parameters on their shrinkage was analysed using the design of experiment (DoE) approach. The analysis results showed that the methodology was capable of detecting factors that had a statistically significant effect on shrinkage at the micro-scale, in both parallel to, and normal to, the flow directions for moulding, post-moulding and total shrinkage.
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    Micro-Injection Moulding of Polymer Microfluidic Devices
    (Springer Science Business Media, 2009-07-01T00:00:00Z) Attia, Usama M.; Marson, Silvia; Alcock, Jeffrey R.
    Microfluidic devices have several applications in different fields, such as chemistry, medicine and biotechnology. Many research activities are currently investigating the manufacturing of integrated microfluidic devices on a mass- production scale with relatively low costs. This is especially important for applications where disposable devices are used for medical analysis. Micromoulding of thermoplastic polymers is a developing process with great potential for producing low-cost microfluidic devices. Among different micromoulding techniques, micro-injection moulding is one of the most promising processes suitable for manufacturing polymeric disposable microfluidic devices. This review paper aims at presenting the main significant developments that have been achieved in different aspects of micro-injection moulding of microfluidic devices. Aspects covered include device design, machine capabilities, mould manufacturing, material selection and process parameters. Problems, challenges and potential areas for research are highlighted.
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    Micro-Injection Moulding Of Three-Dimensional Integrated Microfluidic Devices
    (Cranfield University, 2009) Attia, Usama M.; Alcock, Jeffrey R.
    This thesis investigates the use of micro-injection moulding (μIM), as a high-volume process, for producing three-dimensional, integrated microfluidic devices. It started with literature reviews that covered three topics: μIM of thermoplastic microfluidics, designing for three-dimensional (3-D) microfluidics and functional integration in μIM. Research gaps were identified: Designing 3-D microfluidics within the limitations of μIM, process optimisation and the integration of functional elements. A process chain was presented to fabricate a three-dimensional microfluidic device for medical application by μIM. The thesis also investigated the effect of processing conditions on the quality of the replicated component. The design-of-experiments (DOE) approach is used to highlight the significant processing conditions that affect the part mass taking into consideration the change in part geometry. The approach was also used to evaluate the variability within the process and its effect on the replicability of the process. Part flatness was also evaluated with respect to post-filling process parameters. The thesis investigated the possibility of integrating functional elements within μIM to produce microfluidic devices with hybrid structures. The literature reviews highlighted the importance of quality control in high-volume micromoulding and in-line functional integration in microfluidics. A taxonomy of process integration was also developed based on transformation functions. The experimental results showed that μIM can be used to fabricate microfluidic devices that have true three-dimensional structures by subsequent lamination. The DOE results showed a significant effect of individual process variables on the filling quality of the produced components and their flatness. The geometry of the replicated component was shown to have effect on influential parameters. Other variables, on the other hand, were shown to have a possible effect on process variability. Optimization statistical tools were used to improve multiple quality criteria. Thermoplastic elastomers (TPE) were processed with μIM to produce hybrid structures with functional elements.
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    Optimising process conditions for multiple quality criteria in micro-injection moulding
    (Springer Science Business Media, 2010-09-30T00:00:00Z) Attia, Usama M.; Alcock, Jeffrey R.
    This paper presents a statistical technique to optimise process conditions for multiple quality criteria in micro-injection moulding. A sample hierarchical component with micro-features was replicated where it was required to improve the process conditions for both complete mould filling and variability in mass. A design-of-experiments approach was used to investigate the effect of five processing parameters on both criteria. It was found that holding pressure, melt temperature and injection velocity were statistically significant for part mass, whereas injection velocity alone was significant for mass variation. Desirability functions were used to predict processing conditions that improved both requirements within pre-set conditions. The technique was validated by experiment and it was shown to be applicable for process parameters for multiple criteria.
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    Part mass and shrinkage in micro injection moulding: statistical based optimisation using multiple quality criteria
    (Elsevier Science B.V., Amsterdam., 2013-09-30T00:00:00Z) Annicchiarico, Daniele; Attia, Usama M.; Alcock, Jeffrey R.
    Purpose: The aim of this paper is to optimise process conditions in micro injection moulding (m-IM) to minimise shrinkage whilst maximising part mass. Method: A Design of Experiment (DoE) approach was implemented for studying the effect of five processing parameters on shrinkage and part mass. A multiple quality criteria based analysis was used to optimise the process. Results: Significant factors were found for shrinkage and part mass. Conclusions: The multi quality criteria could be optimized, and this optimization validated experimentally.
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    A process chain for integrating microfluidic interconnection elements by micro- overmoulding of thermoplastic elastomers
    (Institute of Physics Publishing; 1999, 2010-04-14T00:00:00Z) Attia, Usama M.; Alcock, Jeffrey R.
    This paper presents a process chain for in-line integration of microfluidic interconnection elements by a variant of micro-injection moulding (mu IM). A SEBS-based thermoplastic elastomer (TPE) was moulded over polymethylmethacrylate (PMMA) to produce a hybrid microfluidic structure with an aspect ratio of 2. The process chain implemented micro-milling for fabricating micro-structured tool inserts, and mu IM and micro-overmoulding was used for replication. A two-plate mould was used for moulding the substrate, whilst a three-plate mould with a replaceable insert was used for TPE overmoulding. The presented application was an interconnect system for a microfluidic device, which enabled direct fitting of standard tubes into microfluidic substrates. A leakage test showed that the interconnection was leak-proof within a range of flow rates between 0.32 and 0.62 ml min(-1).
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    Reconfigurable micro-mould for the manufacture of truly 3D polymer microfluidic devices
    (Cranfield University, 2009-03-31) Marson, Silvia; Attia, Usama M.; Allen, David M.; Tipler, P.; Jin, T.; Hedge, J.; Alcock, Jeffrey R.; Rajkumar Roy; Essam Shehab
    This paper concerns the concept, the design and the manufacturing steps for the fabrication of a precision mould for micro-injection moulding of truly three dimensional microfluidic devices. The mould was designed using the concept of replaceable cavities to enable the flexible development of the complex microfluidic device and to reduce machining time and therefore costs during the prototyping, testing and subsequent production phase. The precision machining technique used for the cavity manufacture was micromilling.
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    A review of micro-powder injection moulding as a microfabrication technique
    (Institute of Physics Publishing; 1999, 2011-03-01T00:00:00Z) Attia, Usama M.; Alcock, Jeffrey R.
    Micro-powder injection moulding (µPIM) is a fast-developing micro-manufacturing technique for the production of metal and ceramic components. Shape complexity, dimensional accuracy, replication fidelity, material variety combined with high- volume capabilities are some of the key advantages of the technology. This review assesses the capabilities and limitations of µPIM as a micro- manufacturing technique by reviewing the latest developments in the area and by considering potential improvements. The basic elements of the process chain, variant processes and simulation attempts are discussed and evaluated. Challenges and research gaps are highlighted, and potential areas for improvement are presente
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    Study of blood flow behavior in microchannels
    (2008-06-01T00:00:00Z) Marson, Silvia; Benade, M.; Attia, Usama M.; Allen, David M.; Kersaudy, Kerhoas M.; Hedge, J.; Morgan, S. L.; Larcombe, L. D.; Alcock, Jeffrey R.; van Brussel, H.; Brinksmeier, E.; Spaan, H.; Burke, T.
    Microfluidic (also known as lab-on-a-chip) devices offer the capability ofmanipulating very low volumes of fluids (of the order of micro litres) for severalapplications including medical diagnostics. This property makes microfluidicdevices very attractive when the fluid, such as blood, has a limited supply becausethe patients cannot easily and frequently provide a large sample. This is typically thecase for aged, diseased patients that do require frequent sampling during acute careor of older people that have the option of being treated and cared for at home [1].Prototype lab-on-a-chip devices for medical diagnostics comprise a number ofelements which separately perform different functions within the system. Activitywithin the research community is focusing on the better integration of devicefunctionalities with the long term goal of creating fully integrated, portable,affordable clinical devices. However, engineering these solutions for the largevolume production of lab-on-a-chip devices requires design rules which are not yetentirely available.This paper describes the results obtained from a set of experiments run to drawgeneric design rules for the manufacture of a cells/plasma micro separator [2]. Thecells/plasma micro separator was selected for investigation because it is a strategicelement required in the preparation of blood samples for many different analyticaldevices. The experiments focused on the study of the behaviour of whole bloodpassing through micro constrictions which are required for enhancing the separationeffect [3].The test microfluidic device was an aluminium specimen designed andmanufactured to incorporate micro constrictions of different width and length. The metallic aluminium test device was designed for manufacturing by micromilling anddiamond cutting processes in view of applying these techniques to the manufactureof micro-moulds for the high-volume production of plastic microfluidic devices viamicro-injection moulding.The widths of the constrictions were 23, 53 and 93µm and the lengths were 300 and700µm. The blood flow pattern and the level of haemolysis generated in the wholeblood were determined for flow rates between 0.2 and 1 ml/min. Initial resultssuggested that the above conditions generate a stable flow and do not cause bloodhaemolysis following passage through the narrow constrictions. This result impliesthat constrictions as narrow as 23 µm and as long as 700µm can be safely used inblood microfluidic devices under appropriate flow conditions without the risk ofdamaging the blood compone