US 6929750 B2
The present invention provides a device and a method for separating particles from fluids using ultrasound, laminar flow, and stationary wave effects comprising a micro-technology channel system with an integrated branching point or branching fork, and a single ultrasound source. One of the characteristics of the invention is that the single ultrasound source, which generates the standing waves, excites the complete structure including the channel system. No special reflectors or the like are needed. Extremely thin dividers can separate the flow, thereby enhancing the effectiveness of the device. The device could be manufactured in silicon and the ultrasound energy could preferably be delivered by a piezoelectric element.
1. A device for separating suspended particles from a fluid, comprising a channel unit arranged in a plate having first and second opposing great surfaces, said channel unit including a base stem channel having substantially parallel or near parallel base stem walls perpendicular to said surfaces, said base stem channel having an inlet and, opposite said inlet, a branching point connected to two or more different outlets; and oscillation means for delivering mechanical energy to a fluid in said channel unit, such that said particles are concentrated into laminar layers in the base stem channel, substantially parallel to said base stem walls, wherein said branching point is devised to separate particles, arranged in said laminar layers in a fluid flowing in said base stem channel, to said different outlets, wherein said channel unit is formed as a part of a material layer close to said first great surface, and said oscillation means are arranged in contact with said second great surface for delivering mechanical energy to said plate such that a standing wave field is created between said base stem walls.
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feeding a fluid to a separator unit comprising a plate having first and second opposing great surfaces and a channel unit formed as a part of a material layer close to said first surface, forcing the fluid to a substantially laminar flow in a flow direction;
applying an ultrasound oscillating wave field to said second surface, thereby subjecting said flow to an ultrasound stationary wave field during its flow past a distance in said channel unit, forcing said particles to a non-uniform distribution in a separation direction parallel to said surfaces and perpendicular to the flow direction; and
separating said second laminar flow into a first and a second separated flow in such a way that the concentration of particles is higher in the first separated flow than in the second separated flow.
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The present invention relates to a device and a method for separating a fluid containing suspended particles into fractions of higher and lower concentration of said suspended particles using ultrasonic standing waves and micro-technology.
It is known that when particles in a fluid are subjected to an acoustic standing wave field, the particles are displaced to locations at, or in relation to the standing wave nodes. A number of attempts to use ultrasound standing wave field for the manipulation or separation are known.
In WO 00/04978 is described a device for performing the manipulation of particles suspended in a fluid. It comprises a duct for the flow of a fluid in which particles are suspended, and an acoustic transducer and a reflector for establishing an acoustic standing wave field across the width of said duct, the spacing between the transducer and reflector being 300 μm or less.
In an abstract to the 4th annual European conference on micro & nanoscale technologies for the biosciences (NanoTech 2000), Hawkes and Coakley describes a “force field particle filter, combining laminar flow and ultrasound standing waves” with an acoustic path length at right angles to the flow of 0.25 mm.
In WO 98/50133 is described a device for performing the manipulation of particles suspended in a fluid. It comprises a duct for the flow of a fluid, in which particles are suspended, said duct having means for establishing an acoustic standing wave field so that the particles are displaced to form parallel bands. The duct includes an expansion in width.
In IBM, technical disclosure bulletin vol. 25, No. 1, June 1982, page 192/193 is disclosed an ultrasonic continuous flow plasmapheresis separator comprising two orthogonally mounted ultrasound transducers with one reflector each and a volume between where a dilute suspension is subjected to an acoustic standing wave field.
In JP 06241977 A is described a fine particle measuring instrument that uses a standing ultrasonic wave with a node at the centre of a flow cell to centre and concentrate fine particles.
In EP 0 773 055 A2 and A3 is described a method and an apparatus for handling particles by an acoustic radiation force. The apparatus comprises a chamber for accommodating a fluid containing the particles to be concentrated, filtered or arranged, and a plurality of ultrasound sources disposed to make direct or indirect contact with the fluid. The apparatus also comprises a control device for controlling said ultrasound sources to generate an ultrasound beam obtained by superimposing ultrasound beams from said ultrasound sources on one another, said beams each having a specific intensity, a specific frequency and a specific phase.
In WO 93/19367 A2 and A3 is described a method and an apparatus for particle aggregation, said apparatus comprising a tube for containing of a sample of a liquid, and an ultrasonic transducer arranged to generate a standing wave ultrasound field transverse to the tube. The standing wave exhibiting a progressive change in pressure amplitude transverse to the tube, so that, in use of the apparatus, particles in suspension are displaced transversely of the tube to one or more predetermined regions. After termination of exposure to the standing wave particles are allowed to settle and can then be inspected. Appreciated use of the apparatus includes carrying out immuno-agglutination assays. The document is based on U.S. Pat. Nos. 5,665,605 and 5,912,182.
In JP 07 047259 A is described an apparatus for transporting fine particles in fluid with ultrasonic waves. The apparatus comprises a multitude of ultrasonic wave generating elements two-dimensionally arranged on two flat plates. Between the plates a solution can be deposited.
The present invention provides a device and a method for separating particles from fluids using ultrasound, laminar flow, and stationary wave effects comprising micro-technology channels formed in the surface portion of a plate, having integrated branching points or branching forks, and an ultrasound source arranged in close contact to an opposing surface of said plate.
Standing waves are generated in the channels so that particles suspended in the fluid are brought into certain lamina of said fluid, and that one or more lamina are formed devoid of particles, or are formed carrying particles of different properties than the first mentioned ones. Said laminae are thus arranged perpendicular to said plate, this is important because the branching of a channel must take place within the plate, so that a connection with another channel can take place also within the same plate. The advantages of this will be obvious below.
One of the characteristics of the invention is that the ultrasound source is arranged in perpendicular contact with the plate, conveying ultrasound energy in a direction that is perpendicular the plate. The inventors have tested and proved that in the present invention, as a result of the dimensions of the channels and the properties of the plate and the ultrasound transmitter, a standing wave is generated that reaches from one side wall of a channel to the opposing side wall of the same channel. It would normally be expected that such an arrangement would generate (only) a standing wave reaching from a bottom wall to a top wall of said channel, continuing in a direction of the original energy flow.
The inventors have also realised the great importance of this idea. Because, according to the invention, the ultrasound source now do not have to be a part of the plane or layer where the channels reside, and space becomes available for packing more channels into a limited space, greatly enhancing the possibilities of manufacturing devices with a multitude of parallel channels providing high capacity particle separation. A high degree of particle separation could also easily be provided by a serial arrangement of separation units, as will be further explained below. The capability of high yield parallel and serial processing of a fluid using ultrasound is thus a central part and consequence of the inventive concept.
The above is possible because the channels and branching points are formed in a plate comprising one piece of material or in a few pieces of material closely bonded together. No special reflectors or the like are used. It may also be possible to use more than one ultrasound source. Thin dividers are arranged to separate the laminar flows after the branching points, thereby enhancing the effectiveness of the device. The device is preferably manufactured using silicon technology benefiting from the possibility of small precise dimensions, and the ultrasound energy could preferably be delivered by a piezoelectric element, which in turn could be driven from a control unit capable of delivering electrical energy of certain shape, frequency and power.
The invention is defined in the accompanying claim 1, while preferred embodiments are set forth in the dependent claims.
The invention will be described below with reference to the accompanying drawings, in which:
At the back of the plate 51, means for delivering ultrasound energy to the plate is arranged in the form of a piezoelectric element 150, 853. The device will function as follows:
A fluid with suspended particles entering the base stem 110 at the inlet 160 will flow towards the branching point 175 because of an arranged pressure gradient, which gradient could be created by e.g. a suction pump, a pressure pump, a syringe or by gravity. By controlling the frequency of the ultrasound and use of certain frequencies suitable to the dimensions of the base stem 110, particularly the width 185 of said stem 110, a stationary wave pattern is formed in the fluid inside said stem 110. Especially there will form a stationary wave pattern orthogonal to the direction of the flow between a left 810 and a right 820 side wall of the base stem 110. Pressure nodes will form in greater numbers in the middle part of the channel than at the walls, where pressure antinodes will form. During said flow, particles in the fluid will tend to accumulate in nodes of said stationary wave-pattern, or in certain layers in relation to the nodes depending on the particles' density/densities/acoustic impedance relative to the surrounding fluid. Particles with a higher density than said surrounding fluid will tend to accumulate in the nodes, whereas particles with a density lower than the surrounding fluid will tend to accumulate in the antinodes. The layers of fluid discussed in the following are the layers parallel to the sidewalls 810, 820 of the base stem 110.
Depending on the density/acoustic impedance, size and weight of the particles, certain patterns of accumulations of particles will be formed. This is an advantage when separating out particles of a certain weight and/or size from a medium containing a spectrum of particles of different density/acoustic impedance. Generally, particles having a density higher than the density of the surrounding fluid, accumulates in the nodes, and particles having a density lower than the fluid without particles, accumulate in the antinodes. By providing a branching fork with two side branches or arms and one central branch or arm 140 as shown in
Depending on the resonance conditions, confer
By controling the frequency of the uitrasound that creates the standing wave field it is possible to generate a standing wave between the side walls of the base stem 110 with a standing wave length 0.5, 1.5, 2.5 etc. wavelengths, i.e., n times 0.5 wavelengths, n-1, 3. 5, 7 . . . cf.
Preferred embodiments of the invention therefore include means for controlling the frequency of the ultrasound generating means. In
Other embodiments of the invention include bifurcation and “trifurcation” of different shape, integrated on the same piece of material, and with the overall purpose to divide the laminar flow of fluid.
Parallel arrangements of single or serial structures according to
Returning now to
Preferred embodiments include embodiments with channel systems integrated with a single substrate or deposited on a substrate by a continuous series of compatible processes.
The device according to the present invention can be manufactured for example in silicon. The requirement to make the walls of the base stem (810, 820) essentially perpendicular to the plate and parallel or near parallel to each other is easily fulfilled by using silicon of a <110> crystal structure and well known etching techniques. The desired channel wall structure described may also be realised by deep reactive ion etching, DRIE.
It is also possible to form the layers in plastic materials, for instance by using a silicon matrix. Many plastics have good chemical properties. The silicon layer structure can be produced by means of well-known technologies. Channels and cavities can be produced by means of anisotropic etching or plasma etching techniques. The silicon layer may be protected against etching by an oxide layer that is by forming a SiO2 layer. Patterns may be arranged in the SiO2 layer by means of lithographic technologies. Also, etching may be selectively stopped by doping the silicon and using p.n. etch stop or other etch stop techniques. Since all these process steps are well known in the art they are not described in detail here.
The above described technology is also suitable for producing a matrix or mould for moulding or casting devices of the invention in e.g. plastic.
The piezoelectric element providing the mechanical oscillations is preferably of the so-called multi-layer type, but a bimorph piezoceramic element may also be used as well as any other kind of ultrasound generating element with suitable dimensions.
An appreciated application of an embodiment of the invention is in the field of cleaning a patient's blood during surgical operations. The object in this field is to sort out the red blood cells from the contaminated plasma. Contamination could include air bubbles, fat particles, coagulation products and other not desirable biological material. The red cells will thereafter be brought back to the patient's circulation. One disadvantage with prior art in the form of centrifuges is that the red blood cells can become deformed, a disadvantage that is not present with a device according to the present invention.
Depending on the application, the shape and dimensions of the channel, the length of the stem 110 and the arms 120, 130, 140, and the frequency of the ultrasound may vary. In an application for separating out red blood cells from diluted blood recovered from a patient during a surgical operation, the channel is preferably rectangular in cross-section and the stem part of the channel has a width of 700 μm for a one-node standing wave ultrasound field. Greater widths will be appropriate for standing wave ultrasound fields with more nodes.
The mechanical tolerance of the width of the channel is important. The difference should preferably be less than a few percent of half the wavelength of the frequency used in the material/the fluid concerned.
A first outlet tube 1631 is providing a connection from the nine intermediate outlets 1531-1539 via a first collecting manifold to a free end 1641 of said first outlet tube 1631. A second outlet tube 1632 is providing a connection from the eight central outlets 1541-1548 via a second collecting manifold to a free end 1642 of said second outlet tube 1632.
When fluid flows in the direction of the arrow 1804, ultrasound-standing waves are separating the particles in the channel unit into three fluid layers 1801-1803. The position of the ultrasound source is indicated by the rectangle 1810.
The described process separating two types of particles is illustrating a solution to the need within the field of medical technology to separate blood components from each other, i.e. red and white blood cells and platelets (erythrocytes, leukocytes and thrombocytes), also called the formed elements of the blood.
Known art in the field comprises mainly or solely solutions based on centrifugation. A disadvantage is that it is very difficult to obtain a complete separation of the formed elements, instead a so-called “buffy coat” is obtained. This buffy coat comprises a high concentration of thrombocytes, leukocytes and a low concentration of erythrocytes. In this context one should bear in mind that the sensitive thrombocytes have been centrifugated and subjected to high g-forces, which probably have induced an impaired function within said erythrocytes.
An embodiment of the present invention can be used to separate thrombocytes and leukocytes from erythrocytes, because they possess different densities as can be seen in table 1. Blood consists of plasma and formed elements.
Other solutions possible, iodine control agents.
As can be seen in table 1, different components have different density. The variation in density is very small for the table entries. When ordinary blood is separated, a channel unit will separate all formed elements in the same way, because their density is higher than the medium they are suspended in, i.e. the plasma.
As an alternative embodiment, the medium is modified, i.e. the plasma is modified so that its density is altered, giving the possibility to separate the different blood cells. This is achieved by adding an amount of denser liquid to the plasma and thereby dilute the plasma to a lower concentration, but with a higher density.
Take 100 ml blood with a haematocrit of 40%. This entails that 60% (=60 ml) of the blood is plasma. The plasma has a density of 1.0269. By adding 30 ml of 50% glucose solution we get according to the formula:
v1 is the volume of the first fluid
d1 is the density of the first fluid
v2 is the volume of the second fluid
d2 is the density of the second fluid
dtot is the density of the mix
The density of the mix medium becomes 1.0746.
When this mixture is entered in an embodiment, a separation is achieved where thrombocytes and erythrocytes are directed into separate branches, because now the thrombocytes are lighter than the medium.
This is of course just an example. It is also possible to separate out leukocytes because they have a specific weight, different from the one of erythrocytes and thrombocytes. It should also be possible to separate out bacteria and virus with this method. The method can be used on all solutions except those solutions where it is impossible or otherwise inappropriate to manipulate the density of the solution. It is also possible to separate out bacteria and stem cells from cultures of the same, having them suspended in a suitable solution.
FIG. 19 and
It will be appreciated by persons skilled in the art that the structure of the device according to the present invention has several advantages including ease of manufacture and solving of the problem of separating particles liable to disintegration in filtering and centrifugation processes.