Mark Tracey - Academia.edu (original) (raw)
Papers by Mark Tracey
The authors investigate the application of silicon micromachining techniques to the measurement o... more The authors investigate the application of silicon micromachining techniques to the measurement of erythrocyte deformability, a physiological parameter strongly linked to many aspects of cardiovascular disease. They provide an overview of microscopic blood flow-microhaemorheology, a topic which is intimately related to erythrocyte deformability. The need for refined techniques to measure deformability is derived from a critique of existing techniques. The
Journal of Chemical Technology & Biotechnology, 2015
Microbioreactors have emerged as novel tools for early bioprocess development. Mixing lies at the... more Microbioreactors have emerged as novel tools for early bioprocess development. Mixing lies at the heart of bioreactor operation (at all scales). The successful implementation of micro-stirring methods is thus central to the further advancement of microbioreactor technology. The aim of this study was to develop a micro-stirring method that aids robust microbioreactor operation and facilitates cost-effective parallelization. A microbioreactor was developed with a novel micro-stirring method involving the movement of a magnetic bead by sequenced activation of a ring of electromagnets. The micro-stirring method offers flexibility in chamber designs, and mixing is demonstrated in cylindrical, diamond and triangular shaped reactor chambers. Mixing was analyzed for different electromagnet on/off sequences; mixing times of 4.5 s, 2.9 s, and 2.5 s were achieved for cylindrical, diamond and triangular shaped chambers, respectively. Ease of micro-bubble free priming, a typical challenge of cylindrical shaped microbioreactor chambers, was obtained with a diamond-shaped chamber. Consistent mixing behavior was observed between the constituent reactors in a duplex system. A novel stirring method using electromagnetic actuation offering rapid mixing and easy integration with microbioreactors was characterized. The design flexibility gained enables fabrication of chambers suitable for microfluidic operation, and a duplex demonstrator highlights potential for cost-effective parallelization. Combined with a previously published cassette-like fabrication of microbioreactors, these advances will facilitate the development of robust and parallelized microbioreactors. © 2015 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
1st Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and Biology. Proceedings (Cat. No.00EX451), 2000
A complete instrument for the measurement of erythrocyte (red blood cell) flow in microchannels i... more A complete instrument for the measurement of erythrocyte (red blood cell) flow in microchannels is presented. The instrument measures circa 1500 cells on a cell-by-cell basis in an array of microchannels. Microchannel dimensions and operating pressures are physiologically-analogous. Resulting hi-variate data, obtained by real-time image processing, describes cell flow with a unique volume-velocity space representation which provides detailed insights into both cell flow resistance (independent of cell volume) and the presence of pathological sub-populations. We commence by discussing the instrument's design, with particular attention to the microflnidics. We proceed to report analyses o f the instrument's reproducibility, the characterisation of normal blood, and our ability to detect artificial sub-populations of cells with rigid membranes produced by chemically modifying a fraction o f the analyte. Having validated the performance of the instrument, we then present a clinical result from a transfused thalassaemic displaying highly irregular microrheological metria.
ABSTRACT A generic microfluidic system composed by two single chamber valveless micropumps connec... more ABSTRACT A generic microfluidic system composed by two single chamber valveless micropumps connected to a simple T-type channel intersection is examined numerically. The characteristics of a feasible valveless micropump have been used in the design, where efficient mixing is produced due to the pulsating flow generated by the micropumps. The advantages of using time pulsing inlet flows for enhancing mixing in channels have been harnessed through the activation of intrinsic characteristics of the pumps required to achieve the periodic flows. A parametric study is carried out on this microfluidic system using Computational Fluids Dynamics (CFD) on a design space defined by a Design-of-Experiments (DOE) technique. The frequency f and the phase difference of the periodic fluid velocities (operation parameters) and the angle formed by the inlet channels at the intersection (geometric parameter) are used as design parameters, whereas mixing quality, pressure drop and maximum shear strain rate in the channel are the performance parameters. The study identifies design features for which the pressure drop and shear strain are reduced whereas the mixing quality is increased. The proposed microfluidic system achieves high mixing quality with performance parameters that enable manipulation of biological fluids in microchannels.
Emerging Technology in Fluids, Structures, and Fluid Structure Interactions: Volume 1, Fluid Dynamics and Fluid Structure Interactions, 2004
ABSTRACT
IET Seminar on MEMS Sensors and Actuators, 2006
The user has requested enhancement of the downloaded file.
The Analyst, 2004
We report a reciprocating microfluidic pump, the Micro Throttle Pump (MTP), constructed in a rela... more We report a reciprocating microfluidic pump, the Micro Throttle Pump (MTP), constructed in a relatively uncomplicated manner from glass and microstructured poly(dimethylsiloxane)(PDMS). Unconventionally, the MTP employs throttling of fluid flow as distinct from fully-closing valve structures. Accordingly, this technique offers the prospect of solid-phase suspension tolerance. The reported MTP employs piezoelectrically (PZT) actuated deformation of flow constrictions (throttles) fabricated from PDMS at the two ports of a central, PZT actuated pump chamber. By appropriate time-sequencing of the individual PZTs' actuation, pumping can be induced in either direction. PDMS' elasticity further facilitates throttle operation by virtue of allowing significant PZT flexure that is substantially independent of the underlying PDMS microstructure. In contrast, in a rigid substrate such as silicon, deformation is constrained to where underlying microstructured cavities exist and this restricts design options. We describe the construction and performance of a prototype MTP capable of pumping 300 microl min(-1) or alternatively generating a back-pressure of 5.5 kPa. Preliminary modelling of MTP operation is also presented.
Microvascular Research, 1997
A novel instrument has been developed to study the device incorporating multiple channels of 100 ... more A novel instrument has been developed to study the device incorporating multiple channels of 100 mm length and individual widths ranging between 3.0 and 4.0 mm microrheology of erythrocytes as they flow through channels of dimensions similar to human blood capillaries. are presented. ᭧ 1997 Academic Press The channels are produced in silicon substrates using microengineering technology. Accurately defined, physi-
Microfluidics and Nanofluidics, 2013
We report a simple low-cost magnetic microfluidic device for magnetic bead separation and immobil... more We report a simple low-cost magnetic microfluidic device for magnetic bead separation and immobilisation. One dimensional arrays of localised high magnetic field gradients are constructed at the interfaces between regions magnetised with opposing polarities on the magnetic Fe 2 O 3 composite stripes of credit cards. The localised high magnetic field gradients are employed to trap magnetic beads on the surface of the magnetic stripe, without the need for external magnetic components. A magnetic card writer was used to deterministically pattern the magnetic stripes of credit cards to define arrays of magnetic reversals. The fabrication of the device is based on PDMS to credit card bonding of simple flow channels. Experimental results demonstrate that magnetic beads can be captured with efficiencies of 85 %, 67 % and 27 % at flow rates of 25 µlmin -1 , 50 µlmin -1 and 100 µlmin -1 respectively. The results show that the credit card-based magnetic separator might offer an efficient, simple, low-cost alternative to traditional microfluidic magnetic separators for applications such as immunomagnetic cell separation.
Lab on a Chip, 2005
We report a Micro Throttle Pump (MTP) which has been shown to pump 5 microm diameter polystyrene ... more We report a Micro Throttle Pump (MTP) which has been shown to pump 5 microm diameter polystyrene beads at a concentration of 4.5 x 10(7) beads ml(-1). This new MTP design is constructed in a straightforward manner and actuated by a single piezoelectric (PZT) element. Maximum flow rates at 800 Hz drive frequency of 132 microl min(-1) with water and 108 microl min(-1) with a bead suspension were obtained. Maximum back-pressures of 6 kPa were observed in both cases. The reported MTP employs specific location of distinct internal microfluid structures cast in a single compliant elastomeric substrate to exploit the opposing directions of flexure of regions of a piezoelectric-glass composite bonded to the elastomer. By this novel means, distinct flexural regions, exhibiting compressive and tensile stresses respectively, allow both the pump's integrated input and output throttles and its pump chamber to be actuated concurrently by a single PZT. To support MTP design we also report the characterisation of an individual throttle's resistance as a function of actuator deflection and discuss the underlying mechanism of the throttling effect.
Journal of Micromechanics and Microengineering, 2005
Page 1. Continuously variable mixing-ratio micromixer with elastomer valves This article has been... more Page 1. Continuously variable mixing-ratio micromixer with elastomer valves This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2005 J. Micromech. Microeng. 15 1885 (http://iopscience.iop.org/0960-1317/15/10/014) ...
Journal of Micromechanics and Microengineering, 2005
... References [1] Johnston ID, Davis JB, Richter R, Herbert GI and Tracey MC 2004 Elastomerglas... more ... References [1] Johnston ID, Davis JB, Richter R, Herbert GI and Tracey MC 2004 Elastomerglass micropump employing active throttles Analyst 129 82934 [2] Johnston ID, TraceyMC, Davis JB and Tan CKL 2005 Microfluidic solid phase suspension transport with an ...
Journal of Micromechanics and Microengineering, 2014
Polydimethylsiloxane (PDMS) elastomers are extensively used for soft lithographic replication of ... more Polydimethylsiloxane (PDMS) elastomers are extensively used for soft lithographic replication of microstructures in microfluidic and micro-engineering applications. Elastomeric microstructures are commonly required to fulfil an explicit mechanical role and accordingly their mechanical properties can critically affect device performance. The mechanical properties of elastomers are known to vary with both curing and operational temperatures. However, even for the elastomer most commonly employed in microfluidic applications, Sylgard 184, only a very limited range of data exists regarding the variation in mechanical properties of bulk PDMS with curing temperature. We report an investigation of the variation in the mechanical properties of bulk Sylgard 184 with curing temperature, over the range 25 • C to 200 • C. PDMS samples for tensile and compressive testing were fabricated according to ASTM standards. Data obtained indicates variation in mechanical properties due to curing temperature for Young's modulus of 1.32-2.97 MPa, ultimate tensile strength of 3.51-7.65 MPa, compressive modulus of 117.8-186.9 MPa and ultimate compressive strength of 28.4-51.7 GPa in a range up to 40% strain and hardness of 44-54 Sh A .
Journal of Micromechanics and Microengineering, 2010
Fluid transport is accomplished in a micro throttle pump (MTP) by alternating deformation of a mi... more Fluid transport is accomplished in a micro throttle pump (MTP) by alternating deformation of a micro channel cast into a PDMS elastomeric substrate. The active deformation is achieved using a bimorph PZT piezoelectric disk actuator bonded to a glass diaphragm. The bimorph PZT deflects the diaphragm as well as alternately pushing and pulling the elastomer layer providing displacement amplification in the PDMS directly surrounding the micro channel. In order to improve pumping rates we have embedded a PMMA ring into the PMDS substrate which increases the magnitude of the displacement amplification achieved. FEM simulation of the elastomeric substrate deformation predicts that the inclusion of the PMMA ring should increase the channel deformation. We experimentally demonstrate that inclusion of a PMMA ring, having a diameter equal to that of the circular node of the PZT/glass/PDMS composite, increase in the throttle resistance ratio by 40 % and the maximum pumping rate by 90 % compared to an MTP with no ring.
Journal of Micromechanics and Microengineering, 2006
... We also thank our colleague Dr Xian Wei Liu for providing the SEM images of PDMS microdevices... more ... We also thank our colleague Dr Xian Wei Liu for providing the SEM images of PDMS microdevices. References [1] Johnston ID, Davis JB, Richter R, Herbert GI and Tracey MC 2004 Elastomer-glass micropump employing active throttles Analyst 129 82934 ...
Journal of Aerosol Science, 1992
J. Aerosol Sci., Vol. 23, Suppl. I, pp. 201 204, 1992 00218502 92 5.00 + 0.00 Printed in Great Br... more J. Aerosol Sci., Vol. 23, Suppl. I, pp. 201 204, 1992 00218502 92 5.00 + 0.00 Printed in Great Britain. Pergamon Pt.s Ltd THE PRODUCTION OF PRECISION SILICON MICROMACHINED NONSPHERICAL PARTICLES FOR AEROSOL STUDIES. PHKaye, F. Micheli, MCTracey, ...
The authors investigate the application of silicon micromachining techniques to the measurement o... more The authors investigate the application of silicon micromachining techniques to the measurement of erythrocyte deformability, a physiological parameter strongly linked to many aspects of cardiovascular disease. They provide an overview of microscopic blood flow-microhaemorheology, a topic which is intimately related to erythrocyte deformability. The need for refined techniques to measure deformability is derived from a critique of existing techniques. The
Journal of Chemical Technology & Biotechnology, 2015
Microbioreactors have emerged as novel tools for early bioprocess development. Mixing lies at the... more Microbioreactors have emerged as novel tools for early bioprocess development. Mixing lies at the heart of bioreactor operation (at all scales). The successful implementation of micro-stirring methods is thus central to the further advancement of microbioreactor technology. The aim of this study was to develop a micro-stirring method that aids robust microbioreactor operation and facilitates cost-effective parallelization. A microbioreactor was developed with a novel micro-stirring method involving the movement of a magnetic bead by sequenced activation of a ring of electromagnets. The micro-stirring method offers flexibility in chamber designs, and mixing is demonstrated in cylindrical, diamond and triangular shaped reactor chambers. Mixing was analyzed for different electromagnet on/off sequences; mixing times of 4.5 s, 2.9 s, and 2.5 s were achieved for cylindrical, diamond and triangular shaped chambers, respectively. Ease of micro-bubble free priming, a typical challenge of cylindrical shaped microbioreactor chambers, was obtained with a diamond-shaped chamber. Consistent mixing behavior was observed between the constituent reactors in a duplex system. A novel stirring method using electromagnetic actuation offering rapid mixing and easy integration with microbioreactors was characterized. The design flexibility gained enables fabrication of chambers suitable for microfluidic operation, and a duplex demonstrator highlights potential for cost-effective parallelization. Combined with a previously published cassette-like fabrication of microbioreactors, these advances will facilitate the development of robust and parallelized microbioreactors. © 2015 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
1st Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and Biology. Proceedings (Cat. No.00EX451), 2000
A complete instrument for the measurement of erythrocyte (red blood cell) flow in microchannels i... more A complete instrument for the measurement of erythrocyte (red blood cell) flow in microchannels is presented. The instrument measures circa 1500 cells on a cell-by-cell basis in an array of microchannels. Microchannel dimensions and operating pressures are physiologically-analogous. Resulting hi-variate data, obtained by real-time image processing, describes cell flow with a unique volume-velocity space representation which provides detailed insights into both cell flow resistance (independent of cell volume) and the presence of pathological sub-populations. We commence by discussing the instrument's design, with particular attention to the microflnidics. We proceed to report analyses o f the instrument's reproducibility, the characterisation of normal blood, and our ability to detect artificial sub-populations of cells with rigid membranes produced by chemically modifying a fraction o f the analyte. Having validated the performance of the instrument, we then present a clinical result from a transfused thalassaemic displaying highly irregular microrheological metria.
ABSTRACT A generic microfluidic system composed by two single chamber valveless micropumps connec... more ABSTRACT A generic microfluidic system composed by two single chamber valveless micropumps connected to a simple T-type channel intersection is examined numerically. The characteristics of a feasible valveless micropump have been used in the design, where efficient mixing is produced due to the pulsating flow generated by the micropumps. The advantages of using time pulsing inlet flows for enhancing mixing in channels have been harnessed through the activation of intrinsic characteristics of the pumps required to achieve the periodic flows. A parametric study is carried out on this microfluidic system using Computational Fluids Dynamics (CFD) on a design space defined by a Design-of-Experiments (DOE) technique. The frequency f and the phase difference of the periodic fluid velocities (operation parameters) and the angle formed by the inlet channels at the intersection (geometric parameter) are used as design parameters, whereas mixing quality, pressure drop and maximum shear strain rate in the channel are the performance parameters. The study identifies design features for which the pressure drop and shear strain are reduced whereas the mixing quality is increased. The proposed microfluidic system achieves high mixing quality with performance parameters that enable manipulation of biological fluids in microchannels.
Emerging Technology in Fluids, Structures, and Fluid Structure Interactions: Volume 1, Fluid Dynamics and Fluid Structure Interactions, 2004
ABSTRACT
IET Seminar on MEMS Sensors and Actuators, 2006
The user has requested enhancement of the downloaded file.
The Analyst, 2004
We report a reciprocating microfluidic pump, the Micro Throttle Pump (MTP), constructed in a rela... more We report a reciprocating microfluidic pump, the Micro Throttle Pump (MTP), constructed in a relatively uncomplicated manner from glass and microstructured poly(dimethylsiloxane)(PDMS). Unconventionally, the MTP employs throttling of fluid flow as distinct from fully-closing valve structures. Accordingly, this technique offers the prospect of solid-phase suspension tolerance. The reported MTP employs piezoelectrically (PZT) actuated deformation of flow constrictions (throttles) fabricated from PDMS at the two ports of a central, PZT actuated pump chamber. By appropriate time-sequencing of the individual PZTs' actuation, pumping can be induced in either direction. PDMS' elasticity further facilitates throttle operation by virtue of allowing significant PZT flexure that is substantially independent of the underlying PDMS microstructure. In contrast, in a rigid substrate such as silicon, deformation is constrained to where underlying microstructured cavities exist and this restricts design options. We describe the construction and performance of a prototype MTP capable of pumping 300 microl min(-1) or alternatively generating a back-pressure of 5.5 kPa. Preliminary modelling of MTP operation is also presented.
Microvascular Research, 1997
A novel instrument has been developed to study the device incorporating multiple channels of 100 ... more A novel instrument has been developed to study the device incorporating multiple channels of 100 mm length and individual widths ranging between 3.0 and 4.0 mm microrheology of erythrocytes as they flow through channels of dimensions similar to human blood capillaries. are presented. ᭧ 1997 Academic Press The channels are produced in silicon substrates using microengineering technology. Accurately defined, physi-
Microfluidics and Nanofluidics, 2013
We report a simple low-cost magnetic microfluidic device for magnetic bead separation and immobil... more We report a simple low-cost magnetic microfluidic device for magnetic bead separation and immobilisation. One dimensional arrays of localised high magnetic field gradients are constructed at the interfaces between regions magnetised with opposing polarities on the magnetic Fe 2 O 3 composite stripes of credit cards. The localised high magnetic field gradients are employed to trap magnetic beads on the surface of the magnetic stripe, without the need for external magnetic components. A magnetic card writer was used to deterministically pattern the magnetic stripes of credit cards to define arrays of magnetic reversals. The fabrication of the device is based on PDMS to credit card bonding of simple flow channels. Experimental results demonstrate that magnetic beads can be captured with efficiencies of 85 %, 67 % and 27 % at flow rates of 25 µlmin -1 , 50 µlmin -1 and 100 µlmin -1 respectively. The results show that the credit card-based magnetic separator might offer an efficient, simple, low-cost alternative to traditional microfluidic magnetic separators for applications such as immunomagnetic cell separation.
Lab on a Chip, 2005
We report a Micro Throttle Pump (MTP) which has been shown to pump 5 microm diameter polystyrene ... more We report a Micro Throttle Pump (MTP) which has been shown to pump 5 microm diameter polystyrene beads at a concentration of 4.5 x 10(7) beads ml(-1). This new MTP design is constructed in a straightforward manner and actuated by a single piezoelectric (PZT) element. Maximum flow rates at 800 Hz drive frequency of 132 microl min(-1) with water and 108 microl min(-1) with a bead suspension were obtained. Maximum back-pressures of 6 kPa were observed in both cases. The reported MTP employs specific location of distinct internal microfluid structures cast in a single compliant elastomeric substrate to exploit the opposing directions of flexure of regions of a piezoelectric-glass composite bonded to the elastomer. By this novel means, distinct flexural regions, exhibiting compressive and tensile stresses respectively, allow both the pump's integrated input and output throttles and its pump chamber to be actuated concurrently by a single PZT. To support MTP design we also report the characterisation of an individual throttle's resistance as a function of actuator deflection and discuss the underlying mechanism of the throttling effect.
Journal of Micromechanics and Microengineering, 2005
Page 1. Continuously variable mixing-ratio micromixer with elastomer valves This article has been... more Page 1. Continuously variable mixing-ratio micromixer with elastomer valves This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2005 J. Micromech. Microeng. 15 1885 (http://iopscience.iop.org/0960-1317/15/10/014) ...
Journal of Micromechanics and Microengineering, 2005
... References [1] Johnston ID, Davis JB, Richter R, Herbert GI and Tracey MC 2004 Elastomerglas... more ... References [1] Johnston ID, Davis JB, Richter R, Herbert GI and Tracey MC 2004 Elastomerglass micropump employing active throttles Analyst 129 82934 [2] Johnston ID, TraceyMC, Davis JB and Tan CKL 2005 Microfluidic solid phase suspension transport with an ...
Journal of Micromechanics and Microengineering, 2014
Polydimethylsiloxane (PDMS) elastomers are extensively used for soft lithographic replication of ... more Polydimethylsiloxane (PDMS) elastomers are extensively used for soft lithographic replication of microstructures in microfluidic and micro-engineering applications. Elastomeric microstructures are commonly required to fulfil an explicit mechanical role and accordingly their mechanical properties can critically affect device performance. The mechanical properties of elastomers are known to vary with both curing and operational temperatures. However, even for the elastomer most commonly employed in microfluidic applications, Sylgard 184, only a very limited range of data exists regarding the variation in mechanical properties of bulk PDMS with curing temperature. We report an investigation of the variation in the mechanical properties of bulk Sylgard 184 with curing temperature, over the range 25 • C to 200 • C. PDMS samples for tensile and compressive testing were fabricated according to ASTM standards. Data obtained indicates variation in mechanical properties due to curing temperature for Young's modulus of 1.32-2.97 MPa, ultimate tensile strength of 3.51-7.65 MPa, compressive modulus of 117.8-186.9 MPa and ultimate compressive strength of 28.4-51.7 GPa in a range up to 40% strain and hardness of 44-54 Sh A .
Journal of Micromechanics and Microengineering, 2010
Fluid transport is accomplished in a micro throttle pump (MTP) by alternating deformation of a mi... more Fluid transport is accomplished in a micro throttle pump (MTP) by alternating deformation of a micro channel cast into a PDMS elastomeric substrate. The active deformation is achieved using a bimorph PZT piezoelectric disk actuator bonded to a glass diaphragm. The bimorph PZT deflects the diaphragm as well as alternately pushing and pulling the elastomer layer providing displacement amplification in the PDMS directly surrounding the micro channel. In order to improve pumping rates we have embedded a PMMA ring into the PMDS substrate which increases the magnitude of the displacement amplification achieved. FEM simulation of the elastomeric substrate deformation predicts that the inclusion of the PMMA ring should increase the channel deformation. We experimentally demonstrate that inclusion of a PMMA ring, having a diameter equal to that of the circular node of the PZT/glass/PDMS composite, increase in the throttle resistance ratio by 40 % and the maximum pumping rate by 90 % compared to an MTP with no ring.
Journal of Micromechanics and Microengineering, 2006
... We also thank our colleague Dr Xian Wei Liu for providing the SEM images of PDMS microdevices... more ... We also thank our colleague Dr Xian Wei Liu for providing the SEM images of PDMS microdevices. References [1] Johnston ID, Davis JB, Richter R, Herbert GI and Tracey MC 2004 Elastomer-glass micropump employing active throttles Analyst 129 82934 ...
Journal of Aerosol Science, 1992
J. Aerosol Sci., Vol. 23, Suppl. I, pp. 201 204, 1992 00218502 92 5.00 + 0.00 Printed in Great Br... more J. Aerosol Sci., Vol. 23, Suppl. I, pp. 201 204, 1992 00218502 92 5.00 + 0.00 Printed in Great Britain. Pergamon Pt.s Ltd THE PRODUCTION OF PRECISION SILICON MICROMACHINED NONSPHERICAL PARTICLES FOR AEROSOL STUDIES. PHKaye, F. Micheli, MCTracey, ...