GB2472506A

GB2472506A - A Counter-flow filtrating unit and fluid processing device

Info

Publication number: GB2472506A
Application number: GB1013066A
Authority: GB
Inventors: Tao Dong; Henrik Jakobsen; Zhaochu Yang; Qianhua Su; Frank Karlsen; Eirik Bentzen Egeland; Tran Minh Nhut
Original assignee: VESTFOLD UNIVERSITY COLLEGE
Current assignee: VESTFOLD UNIVERSITY COLLEGE
Priority date: 2009-08-03
Filing date: 2010-08-03
Publication date: 2011-02-09
Anticipated expiration: 2030-08-03
Also published as: GB2472506B; GB0913523D0; GB201013066D0

Abstract

A counter flow filtrating unit comprising an output channel 406, a blunt nose section 402 and a barrier section which comprises a series of barrier elements 404 and interposed gaps 409 wherein the barrier elements 404 have a turbine blade-like shape based on streamline design and the interposed gaps 409 define channels so there is fluid communication between an input channel 401 and the output channel wherein fluid travelling along the interposed gaps is at an angle of greater than 90° with respect to the main flow. The elements (fig 1) have a smooth curved shape. In use, the solid nose section bifurcates the incoming fluid into two paths which pass on either side of the barrier section and are filtered so that large particles 407 leave the unit via exit 408 and small particles pass between the barrier elements 404 to the output flow channel 406. The unit forms part of a counter flow processing device (fig 7d;) which comprises a fluid input (fig 7d;701), at least two fluid outlets (fig 7d;703, 707), a cover layer, a processing layer (fig 7d;730)comprising a plurality of counter-flow filtrating units (fig 7d;700), a collecting layer (fig 7d; 740) for collecting the filtered fluid and a residue cleaning port (fig 7d; 409).

Description

Counterfiow-based Filtrating Unit and Fluid Processing Device

FIELD OF THE INVENTION

The present invention relates to a counterfiow-based filtrating unit and fluid processing device, in particular to a device which is compatible with microfabrication

technologies, and can be applied in the fields of

microfluidics and other related technologies.

BACKGROUND

The field of microfluidics is concerned with the

behaviour, control and manipulation of fluids that are geometrically constrained to a small, typically sub-millimetre, dimension, and more typically with volumes of fluid in the millilitre scale, microlitre scale, nanolitre scale or even smaller. Common processing manipulations that one may wish to apply to fluids at all scales include concentrating, separating, mixing and reaction processes.

Over the last few decades miniaturisation technologies have progressed which, in the chemical and biotechnology fields in particular, has resulted in the emergence of lab-on-a-chip devices which are now in common use. For example, micro-chemical devices and microelectromechanical systems (MEMS) such as bio-MEMS devices are known.

However, it is not always feasible to directly miniaturize conventional fluid processing systems designed for relatively large volumes of fluids for use in the microfluidic field where the system would be typically provided on a chip as a lab-on-a-chip device. Take the centrifugation process as an example: the centrifugation process involves a circular plate and comprises complex mechanical and electrical systems, which are only readily applicable for processing relatively large volumes of fluids in at least several tens of millilitre scale. For microfluidics where the volumes of fluid are typically in the micro-or nano-litre scale, such a device would be uneconomical. It would also be extremely difficult from a physical engineering perspective to miniaturize the conventional centrifugation systems on to a chip scale device directly.

The concentration and separation of samples are indispensable for clinical assay and biomedical analysis.

The demand for cell fractionating and isolating for such applications has increased for molecular diagnosis, cancer therapy, and biotechnology applications within the last two decades. Consequently, alternative systems for concentration/ separation of small/micro volumes of fluids, which involve different mechanisms, have been developed.

Among these systems, some utilize the mechanical principles, such as force, geometry, etc.; and others utilize multi physics coupling method, such as magnetic field, electric

field, optics, etc.

For concentration purpose, by utilizing differences in cell size, shape and density, various membrane structure microfilters and microconcentrators have been developed, such as ultrafiltration membranes or nanoporous membranes formed by using ion track-etching technology for separating fluid components. See for example, R. V. Levy, M. W. Jornitz. Types of Filtration. Adv. Biochem. Engin./Biotechnol., vol. 98, 2006, pp. 1-26. and S Metz, C Trautmann, A Bertsch and Ph Renaud. Polyimide microfluidic devices with integrated nanoporous filtration areas manufactured by micromachining and ion track technology.

Journal of Micromechanics and Microengineering, 2004, 14: 8.

Even more, a MEMS filter modules with multiple films (membranes) has been invented, see: Rodgers et al, MEMS Filter Module, US 2005/0184003A1.

However, due to the presence of "dead-ends" in such membranes (films) , clogging is common for microfilters with such flat membrane structures and would be even much more severe in those with multiple films. Moreover, microfilters with flat membrane structures require specialised fabrication processes, which results in difficulties in integrating such thin functional membranes into a lab-on-chip system.

To eliminate the dead-ends in membrane filters, the so-called "cross-flow" filters were developed, see for examples: Foster et al., Microfabricated cross flow filter and method of manufacture, US2006/0266692A1 and lida et al., Separating device, analysis system, separation method and method for manufacture of separating device, EP1457251A1. In their inventions, the filtrate barriers are often made with arbitrary shapes, with simple geometrical profiles, i.e., square, trapezoid, and even crescent. These non-streamline profiles of the barriers would cause extra flow resistance, which reduces the filtrate efficiency. Moreover, due to the presence of square corners or cusps in such arbitrary geometrical profiles, clogging is apt to occur in practical use since the target cells or particles may have considerable deformability and adhesiveness.

In this invention, a "counterflow" filtrating unit is developed based on the streamlined turbine blade-like barriers. And a "counterflow" microconcentrator utilizing such units is proposed.

SUMMARY OF THE INVENTION

Consequently, the present invention provides a novel counterfiow filtrating unit, a novel fluid processing device for concentration, filtration or separation with series of couriterfiow units.

Counterfiow Filtrating Unit for Fluid Processing The invention provides a novel separating and filtrating mechanism in the form of a counterfiow filtrating unit comprising: one output flow channel; one blunt nose section facing in an upstream direction towards an incoming fluid; one barrier section facing in a downstream direction; the barrier section comprising a series of barrier elements and interposed gaps; the barrier elements having a turbine blade-like shape based on streamline design and the interposed gaps defining barrier channels providing fluid communication between the input flow channel and the output flow channel; barrier flow occurring wherein the angle between the barrier flow and a main flow is greater than 90 degrees.

Preferably the profile of the counterflow filtrating unit can be any cylindroids, either elliptical or circular cylinder if it is necessary.

Preferably the output flow channel is located on an inside of the elliptic or circular cylinder counterfiow filtrating unit.

Preferably the blunt nose section is solid without gaps. In use, the nose section acts to bifurcate a fluid flow to guide fluid flows that pass on either side of the elliptic or circular cylinder counterflow filtration unit.

It has been found that the turbulence in the flow generated by bifurcation aids the separating process and helps to promote the separating efficiency of the device.

Preferably the barrier section separates the input flow and the output flow, which extends approximately through a degree arc.

Preferably, the barrier elements in the barrier section display a streamlined turbine blade-like profile. But in use, the barrier elements are not necessary to be restrained in the turbine blade-like profile; any other shapes such as simple circle are also applicable if they are suitable.

Preferably the barrier elements described above are spaced apart depending on the characteristic dimension of the target cell. For example, if the characteristic dimension of the target cell is 10pm, the preferred spacing of the barrier elements can be smaller than l0tm. This spacing can be measured by the shortest distance between the two adjacent barrier elements.

Preferably the barrier gaps (barrier channels) between the barrier elements are shaped such that, in use, the flow direction in the barrier channels is at an obtuse angle (90°<180°) to that of the main flow passing the entrance to the barrier channels. The obtuse angle can be measured according to the angle included by the velocity vectors of the local main flow and the barrier flow.

The barrier elements having a turbine blade-like shape based on streamline design is advantageous in providing anti-clogging effect at the entrance to the barrier channels when the device is used for concentration or filtration. The series of turbine blade-like barrier elements, or micro-pillars', act as a barrier to components, such as blood cells, that is, above a desired size, preventing their passage through the barrier channels whilst allowing smaller components and liquid to pass through the barrier. The anti-clogging effect of the turbine blade-like shaped barrier elements is remarkable according to the theoretically analysis, see equation (1) to (3) and relevant paragraphs in

the part of Detailed Description.

Compared with the prior work by Foster et al. (Microfabricated cross flow filter and method of manufacture, US2006/0266692A1), the streamlined profile of the turbine blade-like barrier elements can not only reduce the flow resistance of the filtrate flow but also creates a smoothly continuous flow field around them, thus to improve filtrating efficiency and reduce risks of clogging. And there are no square corners or cusps within the streamlined turbine blade-like barrier elements, which can be applicable to various cells with different shapes. With its bigger end extending deeply into the main flow, the streamlined turbine blade-like barrier element can function as a flow guider for the cells above the desired size.

The counterfiow filtrating units may particularly be used as key components for blood cell concentration, microfluidic filtration of biological samples, and DNA purification. The micro-fabricated counterflow units may also be used in a micro-biochemical reactor, a micro-mixer and wastewater treatment device.

Counterflow Fluid Processing Device The present invention here provides fluid processing embodiments, in the form of counterflow fluid processing devices, such as microconcentrator and micromixter, which are suitable for fabrication by use of microsystems technologies.

The counterflow fluid processing device used as a microconcentrator comprises: at least one input for a fluid to be processed; at least two outputs for the processed fluid; one cover layer for sealing the device; one processing layer (middle layer) containing pluralities of counterfiow filtrating units; one collecting layer (bottom layer) below the processing layer for collecting the filtrate fluid from the processing layer; one port to clean residue in the device.

The details of the counterflow filtrating units included in the middle layer see the section "Novel Counterfiow Unit for Fluid Processing".

Preferably the cover layer provides fluid-tight sealing and can be glass or silicon wafer. Additionally, glass wafer is preferred for the purpose of convenient monitoring.

Preferably in the processing layer, the plurality of counterflow filtrating units are arranged as a regular tessellation, for example, the counterflow filtrating units may be arranged in a fractal configuration, so as to gain a uniform filtrating and concentrating effect.

Preferably in the processing layer, guiding elements are arranged in the inlet region, to give a uniform flow distribution.

Preferably the collecting layer comprises a plurality of collection channels, which receive fluid flow from the output flow channels of the counterflow filtrating units.

The device may further comprise a port to clean the residue in fluid communication with the inlet for discharging fluid. The residue would be the filtrated comprising the components of the fluid, such as larger cells, that are too large to pass through the barrier channels.

Layered micro-structures of this type are now possible using 3-D micro-structure fabrication techniques.

The fluid processing method using the counterfiow fluid processing device as a microconcentrator or microfilter comprises the steps of: a) inputting a fluid to be processed to a microconcentrator; b) passing the fluid through a plurality of counterflow filtrating units in the processing layer; c) in each counterfiow filtrating unit: i) passed by the fluid as a counterflow alongside a barrier section of the counterfiow filtrating unit that comprises a series of barrier elements and interposed gaps, the barrier elements having a streamlined turbine blade-like shape and the interposed gaps defining barrier channels; ii) processing the fluid by passing a portion of the fluid through the barrier channels; and iii) outputting the portion of the fluid from an output flow channel of the counterfiow filtrating unit; d) utilizing the collection layer to collect the portions of fluid from the output flow channels of the counterflow filtrating units in the processing layer; e) releasing the collected portions of fluid from an outlet of the fluid processing device.

Advantageously, the streamlined turbine blade-like barrier elements and counterfiow filtrating units of the present invention devices containing said elements and methods using said element do not require complex electrical or magnetic structures to be included. Therefore, the micro structures proposed in this invention are embeddable in other complex micro-systems such as lab-on-a-chip devices and are particularly suitable for micro-fabrication.

On the other hand, for some special applications, the flow processing devices of the present invention can also supplemented with some auxiliary methods in practical use, such as, the controlled ultrasonic vibration through the channel wall(s), magnetic or electric interactions for fluids, and microscale Optical interactions, etc. In one application the counterfiow devices or methods described above are used to filter or concentrate a fluid.

As the extended application of the embodiment for fluid processing, a similar device can be provide which is particularly suitable for gas-liquid two-phase mixing or reaction wherein the channels between the counterflow filtrating unit are provided for mixing and reaction. Two reagents can be fed into the device via the middle layer and the bottom layer, respectively. The shaped channels between the barrier section of the counterfiow filtrating unit function as jets thus to accelerate the mixing or reaction process.

The embodiment of the counterflow device may particularly be used for blood cell concentration, microfluidic filtration of biological samples, and DNA purification. The micro-fabricated structure may also be used as a micro-biochemical reactor or a micro-mixer.

Furthermore, the device can be used to concentrate different organisms living in the sea, which require, for example, sequencing and full biological mapping. Since the concentration of microorganism in sea water is quite similar -10 -to that of blood samples manipulation, the device of the present invention can be utilised for environmental testing of water quality, marine & fishing technology and innovation, marine microorganism exploration and relevant biological culture.

In one application of the device described above may be a counterflow fluid processing device, which is suitable for micro-fabrication. Preferably the barrier channels are expanded in the flow direction such that, in use, fluid passing through the barrier channels experiences a local pressure increase within the barrier channels.

In another application any of the extended applications of the counterflow fluid processing device described above may be a mixing device, which can also be fabricated by microsystems technologies. Preferably the barrier channels are convergent in the flow direction such that, in use, fluid passing through the barrier channels experiences a pressure reduction. The converging dimensions of the barrier channels causes the fluid passing through the barrier to be formed into jets with high kinetic energy which then jet into the output flow channel. Use of jets improves the mixing effect and improves reaction efficiency.

By the term micro-fabrication as used herein is meant any manufacturing process of the type that is typically, but not exclusively, used for production of semiconductor MEMS (Microelectromechanical systems), and also used for the production of various different polymer micro-devices.

Such semiconductor micro-fabrication technologies include, for example, epitaxial growth (e.g. vapour phase, liquid phase, molecular beam, metal organic chemical vapour deposition), lithography (e.g. photo-, electron beam-, x-ray, ion beam-), etching (e.g. chemical, gas phase, plasma), -11 -film growth methods such as evaporation, sputtering and electrodeposition, diffusion doping and ion implantation doping. Non-crystalline materials such as glass may be used.

However, micro-fabricated devices may also be formed on crystalline semiconductor substrates such as silicon or gallium arsenide. Combinations of a micro-fabricated component with one or more other elements such as a glass plate or a complementary micro-fabricated element are frequently used and intended to fall within the scope of the term micro-fabricated used herein. Also intended to fall within the scope of the term micro-fabricated are polymeric replicas made from, for example, a crystalline semiconductor substrate.

Low-cost polymer materials provide an alternative type of materials for micro-fabrication. Advantageously, these material types are cost effective and have good machinability for forming microfluidic type devices.

Examples of these materials include Cyclic olefin Copolymer /Polymer (COC/COP), Polycarbonate (PC), Polymethylmethacrylate (PMMA), Polyethylene terephathalate (PET), Polyetheretherketone (PEEK) , Polyimide (P1), Polydimethylsiloxane (PDMS), Polytetrafluoroethylene (PTFE), and SU-8, etc. Such micro-fabrication technologies for polymer materials include: replication methods, which make use of a template or master from which many identical polymer microstructures can be made with precision (e.g., hot embossing, injection moulding, casting, and Soft lithography), and direct fabrication methods (e.g., mini milling, laser ablation, plasma etching, X-ray lithography, stereo-lithography, SU-8 LIGA, and layering) -12 -The bonding and sealing methods for the aforementioned fluid process devices should also be included within the scope of the term micro-fabrication used herein. For the inorganic materials such as various crystalline semiconductors and glass, the relevant technologies include all kinds of available bonding/sealing techniques used in the microelectronic and MEMS industry. In terms of the different characteristics of the polymers described above and the differing production batch size, the following specific bonding/sealing methods have been developed, for instance, adhesive sealing, 02 plasma irreversible bonding of POMS, reversible bonding of PDMS, ultrasonic welding, thermal bonding, anodic boding and lamination, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows the profile of a streamlined turbine blade-like barrier element of a fluid processing device according to the present invention; Figure 2 exhibits the profile generation of the streamlined turbine blade-like barrier element of Figure 1; Figure 3 illustrates the analysis for microfluidic flow through a barrier channel between two barrier elements of the type shown in Figure 1; Figure 4 shows schematically a counterflow unit for separating and filtrating purpose; Figure 5 illustrates the fractal arrangement of a plurality of counterflow unit of a processing layer of a device according of the present invention; -13 -Figure 6 illustrates the fractal arrangement of a collection layer of said device; Figure 7a shows an assembly drawing of an embodiment according to the present invention comprising a processing layer with an arrangement of counterflow unit of the type shown in Figure 5 and an arrangement of a collection layer of the type shown in Figure 6; Figure 7b illustrates a plan view of the processing layer of the device of Figure 7a; Figure 7c illustrates a perspective view of the collection layer of the device of Figure 7a; Figure 7d shows one embodiment of device according to the prevent invention suitable for mixing or reaction.

DETAILED DESCRIPTION

In this invention, a streamlined turbine blade-like barrier element is proposed for microfluidic separation, concentration, mixing and reaction applications. The profile of a streamline turbine blade-like barrier element 101 is illustrated in Figure 1 comprising two arc-shaped extremities 105, 106, a larger end 105 and a smaller end 106, both of which are connected by two smoothly curved sides 107, 108. The gaps interposed between the blade-like barrier elements provide barrier channels 103.

The term turbine blade-like is used to mean an element having the streamlined shape of an aerofoil as commonly used in the field of fluid turbines. Typically the streamlined shape of a turbine blade has a leading edge and a trailing edge joined by two curved side surfaces, sometimes known as the pressure side and the suction side. Applying this terminology to the profile of Figure 1 when used in a filtering process, the leading edge of the blade is the -14 -larger end 105, the trailing edge is the smaller end 106, the pressure side is curved side 107 and the suction side is curved side 108.

An example of the generation of the turbine blade-like barrier element profile is now described with reference to Figure 2: (a) The width of the element B is first chosen, then two lines L1 and L2 can be drawn perpendicular to B. A line, L, with an angle of inclination (for example, c=30°) to L1 and L2 can be drawn spanning L1 and L2, then two circles, Qi and Q2, can be drawn tangent to L1 and L2 with appropriate radius R1 and R2, respectively.

(b) Two circles are copied to the position of next pillar, marked as Q and Q. Then the arc Q can be drawn centred on the centre of circle Q and having a radius (R2-1-R4) (c) According to the given angle /3, a line L3 is drawn through the point Q. According to angle a tangent line of the circle Qi is drawn at point D, which intersects with line L3 at the point C, thus angle cornered by line CD and Line L3, O, equals (/3-Then another tangent line of the circle Qi through the point C, EC, can be drawn, and the angle cornered by line EC and L3, 0, equals (+r/2) (d) Similarly, the line L4 through the point Q can be drawn according to the given angle /32. And the tangent lines of the circle Q2 can be drawn as FG and FF1, with the corner angles of 82=(/32-r2/2) and O4=(/32+/2/2), respectively.

(e) Taking 6i and 02 as the angles of contingence, the back arc GQD (BA) can be drawn using a smooth spline -15 -curve, and let it tangent to the arc Q. Similarly, taking 8 and 84 as the angles of contingence, the inner arc (IA) can be drawn using a smooth spine curve.

(f) Hence, the profile of the blade-like barrier element is obtained. By adjusting the angles a, /3w, 2i r1, and 2# the profile can be adjusted easily.

It is appreciated that whilst the method described above provides an easy and feasible approach to generate the streamlined turbine blade-like profile other methods which are more complicated and precise may be used, such as those described in [11] E. John. Finnemore, Joseph B. Franzini.

Fluid mechanics with engineering applications (10th Edition) . McGraw-Hill, 2001 and Rama S.R. Gorla, Aijaz A. Khan. Turbomachinery: Design and Theory (Mechanical Engineering. CRC, 2003.

To form a barrier, the streamlined turbine blade-like barrier elements 101 are arrayed in a line (straight or curved) with certain spacing. The interposed gaps between the elements 101 form the barrier channels 103. As shown in Figure 3, each barrier channel is formed by two adjacent blade-like elements 101. Consider the fluid flow from cross-section 1 to cross-section 2 in the barrier channel 103.

From the Bernoulli equation for incompressible fluids it is known that: 2 2 2 p 2 p2 (1) where u is the fluid velocity, p is the fluid pressure, and p is the fluid density.

In terms of the continuum equation, that is, -16 -p1A1u1 =p2A2u2 (2) where A is the cross-sectional area of flow.

Assuming P1=P2 and since A<A2, it is clear that Ul>U2. Thus it can be deduced from equation (1) that: pI<p2 (3) According to Equation (3), when the main flow of fluid to be processed is in the direction marked S in Figure 3, clogging is less likely to occur at the entrance of the barrier channel 103. On the one hand, the shear effect of the main flow S reduces clogging near the smaller caput. On the other hand, the local pressure distribution between cross-section 1 and 2 together with the gradually expanding channel width also helps to prevent blocking of the barrier channel 103.

Unlike in the prior art, the angle between the flow in the barrier channel 103 and the main flow S is at an obtuse angle, which is at least larger than 90 degree, and preferably at an angle of at least 110 degrees. The obtuse angle can be measured according to the angle included by the velocity vectors of the main flow and the penetrate flow, as marked by in Figure 3.

Figure 4 illustrates the schematic of the counterfiow unit. As shown the counterflow unit 400 comprises an inlet flow 401 that a fluid to be processed enters, a nose section 402, barrier elements 404, an outlet flow channel 406 and concentrated flow 408.

-17 -The counterflow unit comprises a solid nose section 402 forming the upstream half of the counterfiow unit facing the inlet flow 401 and a porous barrier section 403 formed from a plurality of the turbine blade-like barrier elements 404 with interposed barrier channels 409 of the type described above. It should be noted that the barrier elements 404 in this device are preferably to take a turbine blade-like shape, though other smoothed shapes such as circle, elliptic, etc. are also applicable. Preferably the barrier section extends through an angle, , of the barrier section of approximately 180 degrees, from = 90 degrees to = 270 degrees as viewed in Figure 4.

The overall counterflow unit is in the shape of near elliptical cylinder with its long axis aligned with the flow of fluid entering through the inlet flow 401. Thus, the nose section of the counterflow unit 402 initially presents a blunt body facing the coming flow which causes the flow to bifurcate and pass on both sides of the barrier. It should be noted that the blunt body can be any cylindroids, either cylinder or elliptical cylinder.

All the streamlined barrier elements 404 are located internally tangent to the ellipse of the counterfiow unit.

Barrier channel flow occurs in the interposed gaps 409 sandwiched by adjacent elements 404, with the direction of flow in the channels 409 being at an obtuse angle, counter to the normal direction of the elliptic cylinder at the entrance to each respective barrier channel. As with the channels described above, the angle between the flow around the counterfiow unit and within the channels is preferably at an angle of at least 90 degree. And the obtuse angle can be measured according to the angle included by the velocity -18 -vectors of the main flow and the penetrate flow, marked as 8 in Figure 4.

The filtrate gathers to the centre of the device 400 and exits through outlet flow channel hole 406 where it may then be passed to, for example, a collection layer as described below.

For low Reynolds number flow, given a uniform velocity u0 of the inflow, the local velocity distribution around the ellipse shaped counterfiow unit can be described according to the potential flow theory (see I. G. Currie. Fundamental mechanics of fluids, 2nd Ed., McGraw-Hill: New York, 1993.), that is: -u0(1+b/a)sin sin2 + (b/a) cos2 where the parameters a, b, are the major and minor axes of the barrier, respectively, , defined as the angle of local position relative to the inflow. It is noticed that the angle is greater than 90 degree.

As the inflowing fluid containing a solid component, such as blood cells, passes around the counterflow unit 402, 403, the bigger cells with higher mass 407 tend to be forced away from the entrances to the barrier channels 409 due to inertial effects and tend to pass on to the residue outlet 408. In contrast, the smaller cells with lower mass 410 can remain nearer the surface of the counterflow unit and the entrances to the barrier channels and are thereby enabled to be forced through the channels 409 between the elements 404.

Due to the obtuse angle of the channels 409 to the fluid flow around the barrier 403, the flow through the channels -19 - 409 is a contraflow which comprises an upstream element to the main flow direction around the barrier 403. It should be noticed the contraflow is caused by the geometrical design of the counterfiow unit, not by the fluid flow itself.

According to equation (4), there are no stagnant points of flow except for the points =0 and it. Therefore, the clogging can be reduced in such a counterfiow separating unit.

The following example embodiments of device utilize the above-mentioned streamlined turbine blade-like barrier element and the novel concept counterflow.

In the embodiment for microconcentrator of the present invention it has been found beneficial to provide a processing device comprising a plurality of processing elliptical cylinder counterfiow units with each counterflow unit comprising the streamlined turbine blade-like barrier elements as described above. Whilst a number of arrangements of the counterflow units are possible it has been found particularly efficient to arrange the counterflow units in a regular tessellating pattern. For example, the device as shown in Figures 5-7, utilises a fractal configuration based hexagonal tessellating arrangement. It has been proved that the channel network based on fractal theory has a higher efficiency for both heat and mass transport. This illumines that we can design a fractal theory based micro-channel network for the arrangement of the processing device.

Figure 7a provides an assembly overview of the counterfiow processing device which comprises a processing (filtrating, separating or concentrating) layer 710 and a collection (or filtrate) layer 720 which are disposed on top of one another. Normally a cover layer would also be provided on top of the filtering layer 710.

-20 -Figure 5 illustrates how fractal theory can be used to arrange a plurality of counterflow unit in a regular hexagonal tessellating pattern in the processing layer 710.

Dependent on the required number of counterfiow units the number of fractal iterations, k, can be varied.

As shown, each counterfiow unit 700 takes the general form of the filtering device of Figure 4 described above.

Figure 5a presents a base profile of honeycomb, which is marked as zero iteration (k=0) ; as each side of the hexagon (base profile) is replaced a smaller hexagon, a new profile is generated, marked as the first iteration (k=l) shown in Figure 5b. With the generation process going on, we can get the profiles of k=2, 3..., etc. Let the counterfiow unit 700 occupy each hexagon in the k fractal iteration, the fractal arrangement of the processing layer 710 is obtained.

Since the transport characteristics of the processing layer depends on the number and the dimensions of the counterflow unit 700, the numbers of channel segments and hexagon units varying with the fractal iteration k, are listed in Table 1, which can be strictly proved by mathematical induction.

Table 1 The fractal honeycomb network for the counterflow units' configuration Fractal Iteration The Number of Hexagon Units The Number of Channel Segments k N in 1 7(6+1) 3O(25+223x2) 2 37(62+1) 132(27+24-3x22) 3 217=(6�1) 546=(29I263x23) 4 1297=(6+1) 2256=(2hi4283x24) k (6k�1) 22k+3�22k3x2k -21 -According to the generation process of the fractal honeycomb arrangement, the length ratio between two continuous fractal iterations k and (k-i), is (5) 2 Therefore, the fractal dimension can be determined as, InN:=i-2-=2 585 (6) (i 1n2 ml -Given the side length of the base profile a0, the side length of hexagon in k-th iteration can be calculated as, ak=2a0 (7) Therefore, the fractal arrangement can be easily determined when the dimensions of base profile and fractal iteration number are given.

Similarly, the fractal structure of the collection layer 720 (bottom layer) can also realized, as is schematically shown in Figure 6. Contrary to the processing layer 710, each hexagon of the fractal iteration k in the bottom layer is occupied by solid micro-pillar. It should be noticed that the fractal profiles in the processing layer and the collection layer are not coincident in their horizontal location. That is, there is a horizontal deviation between the two projections, for example, the centre points A, B..., G, of the hexagons in the processing layer marked in Figure 5b, are aligned with the vertexes A, -22 -B, ..., G, of the hexagons in the collection layer in Figure 6b. Hence fluid flow discharged from the outlet flow channels 406 of the counterflow unit enters the channels in the collection layer 720.

The device of Figure 7 can be easily realized by micro-fabrication. The cover plate can be made of transparent material so that the visualization of the separating process is possible. The sample inlet 701 is provided in the processing layer 710 and collection layer 720 or may alternatively be provided by an aperture in the cover plate.

The residue outlet 703 (for concentrated residue that has not passed through the barriers of the counterflow unit) and is provided both through the processing layer 710 and collection layer 720, the filtrate outlet 705 is arranged in the collection layer 720. Further more, a port 709 is used to clean and discharge the residue by communicating with the inlet 701 of the processing layer.

In Figure 7b, the details of the processing layer 710 are shown. To maintain stable counterflow in the processing layer, several guiding micro-pillars 712 are arranged around the counterflow unit 700. As the sample fluid flows through the honeycomb-like tessellation of counterflow unit 700 and in the channels 714, the flow field is perturbed due to the combined effects of bifurcated flow and confluent flow.

Therefore, the filtrating effectiveness of the filtering device is enhanced.

Fluid discharged from one counterfiow unit 700 is passed into a neighbouring unit for further processing or filtering. In the arrangement shown, seven guiding elements 712 are arranged near the inlet 701 of the processing layer 710. Of course, the general flow direction is from the -23 -sample inlet 701 to the concentrated fluid outlet 703 and the collection layer 720 for the filtrate.

In the collection layer 720, a fractal micro-channel network 722 is designed for filtrate flow, in which hexagon micro-pillars 724 are used to form a channel network. The width of the micro-channel can be adjusted in terms of the dimension of the bio-particle and the pressure difference between the adjacent two arrays of separating units, thus to prevent filtrate from being forced by up into the processing layer 710.

As shown in Figure 7a, the centre hole (marked as 406 in Figure 4) of each counterfiow unit in processing layer 710 should match with the micro-channel 722 in the collection layer 720, as has been discussed above with reference to Figure 5b and Figure 6b.

As an extended application of the fluid processing device described in Figure 7a to Figure 7c, one embodiment of device suitable for multiphase mixing and reaction is shown in Figure 7d. As shown, the device for mixing also comprises of two basic layers, namely a reacting layer 730 and a reagent layer, whose configuration is exactly the same as that of the device for filtrating and concentrating.

According to Figure 7d, two reagents Ri and R2 enter the device from the reagent inlet 701 and 709, respectively.

Reagent R2 flows through the fractal microchannel network 722 and the central holes of the counterflow units in turn before feeding into the reaction layer via the barrier channels of the oounterflow units. Mixing and reaction occurs in the channels between the counterfiow units. Due to the uniform tessellation of the counterfiow units, the device can provide a good mixing efficiency. Besides, the -24 -shaped barrier channel works as a jet to promote the mixing and reaction efficiency.

This device can be used for liquid-liquid fluids mixing and reaction. Moreover, the device is also suitable for gas-liquid two-phase mixing and reaction, with the gas reagent input from the inlet 709 in the reagent layer.

It should be noted that in Figure 7d, the two reagent inlets are collocated in the adverse-flow type, that is, the inlet 709 located opposite to the inlet 701. The cocurrent-flow type of the two reagents is also applicable, i.e., the reagent layer 740 rotates with the angle 180 degree in plane.

The appropriate collocation depends on the characteristics of reagents in practical use.

Claims

-25 -CLAIMS1. A counterflow filtrating unit, which is suitable for being used as a unit for fluid concentration, filtration, purification or mixture,the counterfiow filtrating unit comprising: one output flow channel; one blunt nose section facing in an upstream direction towards an incoming fluid; one barrier section facing in a downstream direction; the barrier section comprising a series of barrier elements and interposed gaps; the barrier elements having a turbine blade-like shape based on streamline design and the interposed gaps defining barrier channels providing fluid communication between an input flow channel and the output flow channel; barrier flow occurring wherein the angle between the barrier flow and a main flow is greater than 90 degrees.
2. A counterflow fluid processing device, which is suitable for fabrication by use of microsystems technologies, comprising: at least one input for a fluid to be processed; at least two outputs for the processed fluid; one cover layer for sealing the device; one processing layer (middle layer) containing pluralities of counterflow filtrating units as claimed in claim 1; one collecting layer (bottom layer) below the processing layer for collecting the filtrate fluid from the processing layer; -26 -one port to clean residue in the device.
3. A counterflow filtrating unit as claimed in claim 1, wherein the unit is in the shape of any blunt body, such as an elliptic or circular cylinder, etc.
4. A counterflow filtrating unit as claimed in claims 1 and 3, wherein the output flow channel of the counterflow filtrating unit is located on an inside of the blunt body, such as elliptic or circular cylinder shape.
5. A counterfiow filtrating unit as claimed in claims 1, 3 and 4, wherein the nose section is solid and without gaps and the barrier section comprises the plurality of barrier elements and the interposed gaps.
6. A counterfiow filtrating unit as claimed in claims 1, 3 to 5, wherein the nose section faces in an upstream direction towards the incoming fluid and the barrier section of the counterflow filtrating unit faces in a downstream direction.
7. A counterflow filtrating unit as claimed in claims 1, 3 to 6, wherein the nose section, in use, acts to bifurcate a fluid flow entering through the input flow channel to form two fluid flows that pass on either side of the counterfiow unit.
8. A counterflow filtrating unit as claimed in any of claims 1, 3 to 7, wherein the barrier section extends approximately through a 180 degree arc.-27 -
9. A counterflow filtrating unit as claimed in any of claims 1, 3 to 8, wherein the barrier elements in the barrier section take a streamlined turbine blade-like profile.
10. A counterflow filtrating unit as claimed in claim 9, wherein the turbine blade-like barrier element is designed in a streamline profile, comprising two curved edges (ends) the larger is a leading edge (end) and the smaller is a trailing edge (end), both of which are connected by smoothed curves; in which there are not any sharp corners or cusps.
11. A counterfiow filtrating unit as claimed in any of claims 1, 3 to 10, wherein the barrier channels between the barrier elements are shaped such that fluid flowing, in use, through the barrier channels is directed at an obtuse angle (from 90 to 180 degree) to the direction of a fluid flow passing an entrance to the barrier channels.
12. A counterflow filtrating unit as claimed in claims 1, 3 to 11, wherein the barrier elements are spaced depending on a characteristic dimension of a target cell; this spacing being measured by the shortest distance between two adjacent barrier elements.
13. A counterfiow fluid processing device as claimed in claim 2, wherein the collecting layer is disposed below the processing layer.
14. A counterflow fluid processing device as claimed in claims 2 and 13, further comprising guiding elements located -28 -in the inlet region of the processing layer, to give a uniform flow distribution.
15. A counterflow fluid processing device as claimed in claims 2, 13 and 14, comprising a processing layer wherein the plurality of counterflow filtrating units as claimed in claims 1, 3 to 12 are arranged as a regular tessellation.
16. A counterfiow fluid processing device as claimed in any of claims 2, 13 to 15, wherein there is a collecting layer comprising a plurality of collection channels for receiving fluid flow from the output flow channels of the counterfiow filtrating units as claimed in claims 1, 3 to 12, and the output.
17. A counterfiow fluid processing device as claimed in any of claims 2, 13 to 16, wherein the device is a micro-fabricated filtering or concentrating device.
18. A counterfiow fluid processing device as claimed in any of claims 2, 13 to 16, wherein the device is a micro-fabricated mixing device.
19. A counterfiow fluid processing device as claimed in any of claims 2, 13 to 18, wherein any auxiliary methods are combined into, e.g., controlled ultrasonic vibration through the channel wall(s), magnetic or electric interactions for fluids, and microscale optical interactions, etc.
20. A counterfiow method of processing a fluid using the counterflow fluid processing device as claimed in claims 2, 13 to 16 comprising the steps of: -29 -a) inputting a fluid to be processed to a counterfiow fluid processing device as claimed in claims 2, 13 to 16; b) passing the fluid through a plurality of counterflow filtrating units as claimed in claims 1, 3 to 12 in the processing layer; c) in each counterflow filtrating unit as claimed in claims 1, 3 to 12: i) passing the fluid as a counterflow alongside a barrier section of the counterflow filtrating unit that comprises a series of barrier elements and interposed gaps, the barrier elements having a streamlined turbine blade-like shape and the interposed gaps defining barrier channels; ii) processing the fluid by passing a portion of the fluid through the barrier channels; and iii) outputting the portion of the fluid from an output flow channel of the counterflow filtrating unit; d) utilizing the collecting layer to collect the portions of fluid from the output flow channels of the counterflow filtrating units in the processing layer; e) releasing the collected portions of fluid from an outlet of the fluid processing device.
21. A method as claimed in claim 20 wherein fluid that does not pass through the barrier of a counterfiow filtrating unit is passed to the flow channels of a neighbouring counterflow filtrating unit or to a residue outlet of the fluid processing device.
22. A method as claimed in claim 20 used to filter or concentrate a fluid.-30 -
23. Use of a micro-fabricated counterflow fluid processing device as claimed in any of claims 2, 13 to 16 as a micro-filter for a medical assay.
24. Use of a micro-fabricated couriterflow fluid processing device as claimed in any of claims 2, 13 to 16 as a micro-concentrator for biomedical analysis.
25. Use of a micro-fabricated counterfiow fluid processing device as claimed in any of claims 2, 13 to 16 as a micro-reactor for chemical reactions.