A sorting method and device therefor

Abstract

A method of sorting microbubbles comprising: inputting a solution containing a plurality of microbubbles into a sorting device comprising an array of spaced obstacles arranged to differentially direct microbubbles according to their size to separate the plurality of microbubbles in the solution into a first flow and a second flow; and collecting at least one of the first flow and the second flow.

Description

A SORTING METHOD AND DEVICE THEREFORBACKGROUND

[0001] Microbubbles have several biomedical applications both in diagnostics and in treatment of pathologies. For example, microbubbles have been used as contrast agents for ultrasonic scanners. Microbubbles have also been used to enhance drug delivery across the blood-brain barrier.

[0002] Many of the beneficial characteristics of microbubbles are highly dependent on their size. Different ranges of microbubbles are required for different applications. For example, in the case of drug delivery across the blood brain barrier, microbubbles with diameters ranging from 1 pm to 6 pm may be preferred as they can freely flow into the cerebral capillaries, which is where all the nutrient and waste exchange occurs. Larger microbubbles may cause unwanted damage to the blood-brain barrier and be associated with longer cell recovery times.Meanwhile, sub-sized microbubbles may have limited efficacy and their presence can cause unwanted signal attenuation and interfere with the oscillations of nearby microbubbles.

[0003] In order to improve control over treatment, there is a need for microbubbles solutions with mono-sized distributions.

[0004] Current microbubble generation methods, such as mechanical agitation of lipid solutions, create highly polydisperse microbubble solutions. However, current methods for generating mono-sized microbubbles, such as flow focusing, are very time consuming. Such slow production methods are not currently able to produce the quantity of bubbles in the timescale required for biomedical applications.

[0005] One method for isolating specific size ranges of microbubbles is differential centrifugation wherein polydisperse solutions are spun at high speed in a centrifuge to separate the microbubbles by size. However, differential centrifugation is a highly energetic process which may result in the loss of a significant fraction of optimally sized microbubbles. This can reduce the available concentration of optimally sized microbubbles present in the final solution. Where the physical or chemical properties of microbubbles are altered, the product may be regarded as a new formulation of a medicinal product and require full clinical studies.

[0006] In addition, differential centrifugation requires large-scale equipment making it inappropriate for many existing medical facilities. This is particularly problematic given theshort lifetime of microbubbles which makes production of mono-sized microbubbles at the point of use highly desirable.

[0007] It is an aim of the present invention to provide a device and method for microbubble sorting that ameliorates some or all of the abovementioned issues.SUMMARY OF INVENTION

[0008] The present disclosure relates to a device and method for sorting microbubbles according to their size. The disclosure further relates to improvements in microbubble sorting devices.

[0009] An aspect of the invention provides a microbubble sorting device comprising: an inlet for receiving a solution containing a plurality of microbubbles; and an array of spaced obstacles arranged to differentially direct the microbubbles according to their size to separate the plurality of microbubbles in the solution into a first flow and a second flow.

[0010] The microbubble sorting device may include microbubble generator such as a mechanical agitator (e.g. a sonicator). The microbubble sorting device may include a vessel for storing the solution.

[0011] The solution may be a polydisperse microbubble solution.

[0012] The microbubble sorting device may include a mixer for mixing the solution prior to the solution being introduced into the array. For example the mixer may be a stirrer for stirring the solution in the vessel prior to being input into the array. In some examples at least part of the mixer may be located within the vessel (e.g. a magnetic stirring bead). In some examples, the mixer may be external to the vessel. For example, the mixer may comprise a vortex machine.

[0013] The microbubble sorting device may be a passive sorting device (e.g. utilizing channel structures and / or fluidic rheology rather than external force fields to sort the microbubbles). Deterministic lateral displacement is an example of a passive sorting technique. The microbubble sorting device may be configured for sorting microbubbles using deterministic lateral displacement.

[0014] The microbubble sorting device may be configured for sorting microbubbles using Non-equilibrium Inertial Separation. For example, the array may be a Non-equilibrium Inertial Separation Array (NISA).

[0015] Each of the first flow and second flow of microbubbles may be within and / or downstream of the array.

[0016] The first flow of microbubbles may at least partially spatially overlap with the second flow of microbubbles in the array. A net flow direction of the first flow may be different to a net flow direction of the second flow.

[0017] Differentially directing the microbubbles may comprise guiding and / or displacing the microbubbles e.g. laterally.

[0018] The microbubble sorting device may comprise at least one outlet fluidically connected to the inlet by a channel.

[0019] The plurality of spaced obstacles may be received within the channel.

[0020] The channel may be substantially straight.

[0021] The microbubble sorting device may comprise a first outlet for receiving the first flow.

[0022] The microbubble sorting device may comprise a second outlet for receiving the second flow.

[0023] The first outlet may be laterally offset from the second outlet.

[0024] The first outlet may be aligned with the inlet to collect the first flow.

[0025] The second outlet may be laterally offset from the inlet to collect the second flow.

[0026] The first outlet and second outlet may be disposed at an outlet end of the channel.

[0027] The microbubble sorting device may be configured such that in use, there is a net flow of the solution in a flow direction. The flow direction may be parallel to the channel and extend from the inlet to the first outlet.

[0028] A mean microbubble size of the first flow may be smaller than a mean microbubble size of the second flow.

[0029] The microbubble sorting device may comprise a pressure source for pumping the solution through the array. For example, the pressure source may comprise a pump such as an electric pump or a manual pump e.g., including a manually actuatable piston. In otherexamples, the pressure source may comprise a hydrostatic head or pressure (negative or positive) source.

[0030] The microbubble sorting device may comprise a buffer inlet for inputting a buffer solution into the channel.

[0031] The buffer solution may comprise or essentially consist of water.

[0032] For example, the buffer solution may comprise or essentially consist of saline.

[0033] The microbubble sorting device may comprise a pump for pumping the buffer solution into the array. Pumping buffer solution into the array may ensure that the solution is confined to one lateral side of the channel.

[0034] The buffer inlet and the inlet may be disposed at an inlet end of the channel. The inlet end may be substantially opposite the outlet end.

[0035] The microbubble sorting device may be configured such that when the microbubble sorting device is located on a horizontal surface, the array slopes upwards from the inlet to the at least one outlet. Such a slope may beneficially allow microbubbles to travel through the (liquid filled) array by buoyancy.

[0036] The array may be a regular array or an irregular array.

[0037] The array may comprise more than 50, more than 100 or more than 1000 obstacles in total.

[0038] Each obstacle may be a protrusion which extends into the channel. For example, each obstacle may extend from a bottom or top interior wall of the channel.

[0039] In some examples, each obstacle may be a pillar, such as a micropillar, which extends between the top and bottom walls of the channel.

[0040] Each of the obstacles in the array may be identical to each of the other obstacles in the array.

[0041] Each of the obstacles in the array may be regularly spaced from each of the other obstacles in the array.

[0042] The plurality of spaced obstacles may be arranged in rows of obstacles. Each row may comprise a plurality of obstacles. The rows of the array may be angled (i.e. non-parallel or perpendicular) with respect to the flow direction. For example, an angle between the flow direction and the rows of the array may be less than or equal to 10°, 20°, 30°, 40° or 50°. Theangle between the flow direction and the rows of the array may be greater than 5°, 10°, 20°, 30°, 40° or 50°.

[0043] The array may be configured such that microbubbles larger than a critical microbubble size are repeatedly deflected in a lateral direction by each obstacle they encounter to move substantially parallel to the rows of obstacles. For example, the microbubbles may be deflected by direct physical collision with the obstacles or may be deflected away from the obstacles by lift forces and / or fluid inertia (e.g. in examples where a NISA array is used).

[0044] Each of the obstacles may have any substantially convex external profile.

[0045] The obstacles may have a circular external cross-section.

[0046] An external cross-sectional profile of the obstacles may be any regular or irregular shape. For example the external cross-sectional profile of the obstacles may be defined by a circle, ellipse, triangle, quadrilateral, pentagon, hexagon, octagon, or decagon.

[0047] An external cross-sectional profile of the obstacles may be defined by an irregular octagonal shape. The profile may consist of a kite shape with truncated vertices.

[0048] The edges of the kite shape may define four major sides of the profile. The truncated vertices may define four minor sides of the profile.

[0049] The minor sides may comprise two pairs of opposing sides: a first pair and a second pair. The first pair of minor sides may be oriented substantially parallel to the flow direction. The second pair of minor sides may be oriented substantially perpendicularly to the flow direction.

[0050] The major sides may comprise a pair of long sides and a pair of shorter sides. The pair of long sides may be equal in length to one another. The pair of short sides may be equal in length to one another.

[0051] Each obstacle in the array may have the same orientation as every other obstacle in the array.

[0052] Each obstacle of the array may be oriented such that the pair of long sides approach one another as the lateral direction increases. The lateral direction may bisect the angle between the rows and the flow direction.

[0053] The array may have a spacing between obstacles of 30pm to 3pm, more preferably 10pm to 3pm, more preferably 7.5pm to 3.5pm, more preferably 6.5pm to 3.5pm, more preferably 5.5pm to 3.5pm, yet more preferably 4.5pm to 3.5pm.

[0054] The spacing of the obstacles may be defined by spacings between the nearest neighbors in the lateral and / or flow directions respectively.

[0055] The channel may comprise a hydrophilic surface. The or each array may comprise a hydrophilic surface. The channel and / or the or each array may comprise or essentially consist of a hydrophilic material. The hydrophilic material may comprise tetraethylorthosilicate and / or 2-[acetoxy (polyethyleneoxy) propyl] triethoxysilane and / or polyvinyl alcohol.

[0056] The hydrophilic surface may prevent microbubbles from adhering and agglomerating within the microbubble sorting device.

[0057] The microbubble sorting device may comprise a coating on the channel, such as a hydrophilic coating.

[0058] The microbubble sorting device may comprise a hydrophilic coating on the or each array.

[0059] The hydrophilic coating may comprise a two-layer coating. Each layer of the two-layer coating may comprise a different hydrophilic material.

[0060] The two-layer hydrophilic coating may comprise tetraethylorthosilicate as a base hydrophilic layer. The two layer hydrophilic coating may comprise 2- [acetoxy (polyethyleneoxy) propyl] triethoxysilane as a top hydrophilic layer (to cover the base hydrophilic layer). During manufacture the 2-[acetoxy (polyethyleneoxy) propyl] triethoxysilane may be deposited onto the base hydrophilic layer. Two-layer hydrophilic coatings may beneficially act as a super hydrophilic surface which is particularly effective at preventing microbubble adhesion.

[0061] In other examples, the hydrophilic coating may comprise or essentially consist of other hydrophilic materials such as polyvinyl alcohol.

[0062] In some examples, the base layer may comprise or consist of a non-hydrophilic material while the top layer may comprise or consist of a hydrophilic material. In some examples, a spacing between obstacles in the array may decrease along a length of the channel towards the outlet end.

[0063] The microbubbles may comprise a gas core. For example the gas core may comprise air or perfluorobutane.

[0064] The microbubble sorting device may comprise two or more arrays. Each of the two or more arrays may comprise spaced obstacles arranged to differentially displace themicrobubbles according to their size to separate the plurality of microbubbles in the solution into a first flow and a second flow. Each of the two or more arrays may be a deterministic lateral displacement array.

[0065] Each of the two or more arrays may have any combination of the features discussed above in relation to the array.

[0066] The microbubble sorting device may comprise two arrays, three arrays, four arrays, five arrays, or more than five arrays.

[0067] The two or more arrays may be arranged in a sequence along a length of the channel.

[0068] The obstacles in each of the two or more arrays may be the same.

[0069] The two or more arrays in the sequence may have progressively narrower spacing such that each array in the sequence has a smaller critical microbubble size than the preceding (immediately upstream) array in the sequence.

[0070] The two or more arrays in the sequence may have progressively narrower spacing such that each array in the sequence has a smaller spacing between obstacles than an immediately preceding array in the sequence.

[0071] A final array in the sequence may have a spacing between obstacles of 30pm to 3 pm, more preferably 10pm to 3pm, more preferably 7.5pm to 3.5pm, more preferably 6.5pm to 3.5pm, more preferably 5.5pm to 3.5pm, yet more preferably 4.5pm to 3.5pm.

[0072] In some examples, the arrays may be spaced from one another.

[0073] The microbubble sorting device may comprise two or more lateral outlets. Each of the lateral outlets may be laterally offset relative to the inlet. The lateral outlets may be configured to receive microbubbles that have been laterally offset by a different one of the two or more arrays.

[0074] Each of the lateral outlets may be located along a sidewall of the channel between the inlet end and the outlet end. In other examples, each of the lateral outlets may form part of the outlet end of the microbubble sorting device.

[0075] The second outlet may define a terminal one of the lateral outlets.

[0076] The number of lateral outlets may equal the number of arrays in the channel.

[0077] For example, the microbubble sorting device may comprise two or more lateral outlets (e.g., two lateral outlets, three lateral outlets, four lateral outlets, five lateral outlets, or more than five lateral outlets).

[0078] The microbubble sorting device may comprise one or more additional buffer inlets each for inputting the buffer solution into the array.

[0079] The buffer solution supplied by the additional buffer inlets may be the same buffer solution supplied at the buffer inlet located at the inlet end.

[0080] The number of buffer inlets may equal the number of lateral outlets of the microbubble sorting device.

[0081] Each of the additional buffer inlets may be configured to deliver buffer solution to the channel downstream of a respective one of the lateral outlets (e.g. immediately downstream of a respective one of the lateral outlets).

[0082] Each of the additional buffer inlets may be configured to deliver buffer solution to the channel between two neighbouring arrays in the sequence.

[0083] The microbubble sorting device may be configured to maintain a constant amount of buffer solution at each position along the length of the channel. This may ensure that the solution is confined to one lateral side of the channel.

[0084] The microbubble sorting device may comprise a filter for filtering microbubbles. The filter may be located upstream of the or each array (e.g., upstream of the two or more arrays). For example, the filter may be located in the channel or the inlet. The filter may comprise a matrix of obstacles such as micropillars. The obstacles of the filter may be spaced to provide 50pm, 20pm, 15pm, 10pm or 5pm gaps, measured perpendicular to the flow direction.

[0085] The obstacles of the filter may have any cross-sectional profile. For example the cross- sectional profile may be substantially circular or have any regular or irregular shape such as: triangular, quadrilateral, hexagonal or octagonal.

[0086] In some examples, the filter may comprise a mesh for filtering microbubbles. An aperture size of the mesh may be 50pm, 20pm, 15pm, 10pm or 5 pm.

[0087] A further aspect of the invention provides a device for sorting particles using deterministic lateral displacement, comprising: an inlet for receiving a solution containing a plurality of particles; and an array of spaced obstacles arranged to differentially displace the particles according to their size to separate the plurality of particles in the solution into a first flow and a second flow.

[0088] The solution may comprise a heterogeneous mixture of a liquid and the plurality of particles.

[0089] Each of the plurality of particles may be a solid particle. In other examples, each of the plurality of particles may be fluid particles e.g., gaseous particles such as microbubbles. The solution may be a polydisperse microbubble solution.

[0090] The device may include microbubble generator such as a mechanical agitator (e.g. a sonicator).

[0091] The device may include a vessel for storing the solution.

[0092] The device may include a mixer for mixing the solution prior to the solution being introduced into the array. For example the mixer may be a stirrer for stirring the solution in the vessel prior to being input into the array.

[0093] The device may comprise at least one outlet fluidically connected to the inlet by a channel.

[0094] The plurality of spaced obstacles may be received within the channel.

[0095] The channel may be substantially straight.

[0096] The device may comprise a first outlet for receiving the first flow.

[0097] The device may comprise a second outlet for receiving the second flow.

[0098] The first outlet may be laterally offset from the second outlet.

[0099] The first outlet may be aligned with the inlet to collect the first flow.

[0100] The second outlet may be laterally offset from the inlet to collect the second flow.

[0101] The first outlet and second outlet may be disposed at an outlet end of the channel.

[0102] The device may be configured such that in use, there is a net flow of the solution in a flow direction. The flow direction may be parallel to the channel and extend from the inlet to the first outlet.

[0103] A mean particle size of the first flow may be smaller than a mean particle size of the second flow.

[0104] The device may comprise a pressure source for pumping the solution through the array. For example the pressure source may comprise a pump such as an electric pump or a manual pump e.g., including a manually actuatable piston. In other examples, the pressure source may comprise a hydrostatic head or pressure (negative or positive) source.

[0105] The device may comprise a buffer inlet for inputting a buffer solution into the channel.

[0106] The buffer solution may comprise or essentially consist of water.

[0107] For example, the buffer solution may comprise or essentially consist of saline.

[0108] The device may comprise a pump for pumping the buffer solution into the array. Pumping buffer solution into the array may ensure that the solution is confined to one lateral side of the channel.

[0109] The buffer inlet and the inlet may be disposed at an inlet end of the channel. The inlet end may be substantially opposite the outlet end.

[0110] The device may be configured such that when the device is located on a horizontal surface, the array slopes upwards from the inlet to the at least one outlet. When the solution contains microbubbles, such a slope may beneficially allow microbubbles to travel through the (liquid filled) array by buoyancy.

[0111] The array may be a regular array or an irregular array.

[0112] The array may comprise more than 50, more than 100 or more than 1000 obstacles in total.

[0113] Each obstacle may be a protrusion which extends into the channel. For example, each obstacle may extend from a bottom or top interior wall of the channel.

[0114] In some examples, each obstacle may be a pillar, such as a micropillar, which extends between the top and bottom walls of the channel.

[0115] Each of the obstacles in the array may be identical to each of the other obstacles in the array.

[0116] Each of the obstacles in the array may be regularly spaced from each of the other obstacles in the array.

[0117] The plurality of spaced obstacles may be arranged in rows of obstacles. Each row may comprise a plurality of obstacles. The rows of the array may be angled (i.e. non-parallel or perpendicular) with respect to the flow direction. For example, an angle between the flow direction and the rows of the array may be less than or equal to 10°, 20°, 30°, 40° or 50°. The angle between the flow direction and the rows of the array may be greater than 5°, 10°, 20°, 30°, 40° or 50°.

[0118] The array may be configured such that particles larger than a critical particle size are repeatedly deflected in a lateral direction by each obstacle they encounter to move substantially parallel to the rows of obstacles.

[0119] Each of the obstacles may have any substantially convex external profile.

[0120] The obstacles may have a circular external cross-section.

[0121] An external cross-sectional profile of the obstacles may be any regular or irregular shape. For example the external cross-sectional profile of the obstacles may be defined by a circle, ellipse, triangle, quadrilateral, pentagon, hexagon, octagon, or decagon.

[0122] An external cross-sectional profile of the obstacles may be defined by an irregular octagonal shape. The profile may consist of a kite shape with truncated vertices.

[0123] The edges of the kite shape may define four major sides of the profile. The truncated vertices may define four minor sides of the profile.

[0124] The minor sides may comprise two pairs of opposing sides: a first pair and a second pair. The first pair of minor sides may be oriented substantially parallel to the flow direction. The second pair of minor sides may be oriented substantially perpendicularly to the flow direction.

[0125] The major sides may comprise a pair of long sides and a pair of shorter sides. The pair of long sides may be equal in length to one another. The pair of short sides may be equal in length to one another.

[0126] Each obstacle in the array may have the same orientation as every other obstacle in the array.

[0127] Each obstacle of the array may be oriented such that the pair of long sides approach one another as the lateral direction increases. The lateral direction may bisect the angle between the rows and the flow direction.

[0128] The array may have a spacing between obstacles of 30pm to 3pm, more preferably 10pm to 3pm, more preferably 7.5pm to 3.5pm, more preferably 6.5pm to 3.5pm, more preferably 5.5pm to 3.5pm, yet more preferably 4.5pm to 3.5pm.

[0129] The spacing of the obstacles may be defined by spacings between the nearest neighbors in the lateral and / or flow directions respectively.

[0130] The channel may comprise a hydrophilic surface. The or each array may comprise a hydrophilic surface. The channel and / or the or each array may comprise or essentially consistof a hydrophilic material. The hydrophilic material may comprise tetraethylorthosilicate and / or 2-[acetoxy (polyethyleneoxy) propyl] triethoxysilane and / or polyvinyl alcohol.

[0131] The hydrophilic surface may prevent particles such as microbubbles from adhering and agglomerating within the device.

[0132] The device may comprise a coating on the channel, such as a hydrophilic coating.

[0133] The device may comprise a hydrophilic coating on the or each array.

[0134] The hydrophilic coating may comprise a two-layer coating. Each layer of the two-layer coating may comprise a different hydrophilic material.

[0135] The two-layer hydrophilic coating may comprise tetraethylorthosilicate as a base hydrophilic layer. The two layer hydrophilic coating may comprise 2- [acetoxy (polyethyleneoxy) propyl] triethoxysilane as a top hydrophilic layer (to cover the base hydrophilic layer).

[0136] During manufacture the 2-[acetoxy (polyethyleneoxy) propyl] triethoxysilane may be deposited onto the base hydrophilic layer.

[0137] Two-layer hydrophilic coatings may beneficially act as a super hydrophilic surface which is particularly effective at preventing particle adhesion.

[0138] In other examples, the hydrophilic coating may comprise or essentially consist of other hydrophilic materials such as polyvinyl alcohol.

[0139] In some examples, the base layer may comprise or consist of a non-hydrophilic material while the top layer may comprise or consist of a hydrophilic material.

[0140] In some examples, a spacing between obstacles in the array may decrease along a length of the channel towards the outlet end.

[0141] The microbubbles may comprise a gas core. For example the gas core may comprise air or perfluorobutane.

[0142] The device may comprise two or more arrays. Each of the two or more arrays may comprise spaced obstacles arranged to differentially displace the particles according to their size to separate the plurality of particles in the solution into a first flow and a second flow. Each of the two or more arrays may be a deterministic lateral displacement array.

[0143] Each of the two or more arrays may have any combination of the features discussed above in relation to the array.

[0144] The device may comprise two arrays, three arrays, four arrays, five arrays, or more than five arrays.

[0145] The two or more arrays may be arranged in a sequence along a length of the channel.

[0146] The obstacles in each of the two or more arrays may be the same.

[0147] The two or more arrays in the sequence may have progressively narrower spacing such that each array in the sequence has a smaller critical particle size than the preceding (immediately upstream) array in the sequence.

[0148] The two or more arrays in the sequence may have progressively narrower spacing such that each array in the sequence has a smaller spacing between obstacles than an immediately preceding array in the sequence.

[0149] A final array in the sequence may have a spacing between obstacles of 30pm to 3 pm, more preferably 10pm to 3pm, more preferably 7.5pm to 3.5pm, more preferably 6.5pm to 3.5pm, more preferably 5.5pm to 3.5pm, yet more preferably 4.5pm to 3.5pm.

[0150] In some examples, the arrays may be spaced from one another.

[0151] The device may comprise two or more lateral outlets. Each of the lateral outlets may be laterally offset relative to the inlet. The lateral outlets may be configured to receive particles that have been laterally offset by a different one of the two or more arrays.

[0152] Each of the lateral outlets may located along a sidewall of the channel between the inlet end and the outlet end. In other examples, each of the lateral outlets may form part of the outlet end of the device.

[0153] The second outlet may define a terminal one of the lateral outlets.

[0154] The number of lateral outlets may equal the number of arrays in the channel.

[0155] For example, the device may comprise two or more lateral outlets (e.g., two lateral outlets, three lateral outlets, four lateral outlets, five lateral outlets, or more than five lateral outlets).

[0156] The device may comprise one or more additional buffer inlets each for inputting the buffer solution into the array.

[0157] The buffer solution supplied by the additional buffer inlets may be the same buffer solution supplied at the buffer inlet located at the inlet end.

[0158] The number of buffer inlets may equal the number of lateral outlets of the device.

[0159] Each of the additional buffer inlets may be configured to deliver buffer solution to the channel downstream of a respective one of the lateral outlets (e.g. immediately downstream of a respective one of the lateral outlets).

[0160] Each of the additional buffer inlets may be configured to deliver buffer solution to the channel between two neighbouring arrays in the sequence.

[0161] The device may be configured to maintain a constant amount of buffer solution at each position along the length of the channel. This may ensure that the solution is confined to one lateral side of the channel.

[0162] The device may comprise a filter for filtering particles. The filter may be located upstream of the or each array (e.g., upstream of the two or more arrays). For example, the filter may be located in the channel or the inlet. The filter may comprise a matrix of obstacles such as micropillars. The obstacles of the filter may be spaced to provide 50pm, 20pm, 15pm, 10pm or 5pm gaps, measured perpendicular to the flow direction.

[0163] The obstacles of the filter may have any cross-sectional profile. For example the cross- sectional profile may be substantially circular or have any regular or irregular shape such as: triangular, quadrilateral, hexagonal or octagonal.

[0164] In some examples, the filter may comprise a mesh for filtering particles. An aperture size of the mesh may be 50pm, 20pm, 15pm, 10pm or 5pm.

[0165] A further aspect of the invention provides a method of sorting microbubbles comprising: inputting a solution containing a plurality of microbubbles into a microbubble sorting device comprising an array of spaced obstacles arranged to differentially direct microbubbles according to their size to separate the plurality of microbubbles in the solution into a first flow and a second flow, collecting at least one of the first flow and the second flow.

[0166] The microbubble sorting device may be the microbubble sorting device described above.

[0167] In some examples, the solution may be input into the microbubble sorting device while the first flow and / or second flow are collected.

[0168] The method may collecting microbubbles at one or more of the lateral outlets.

[0169] The microbubble sorting device may be configured such that the array slopes upwards from the inlet to the at least one outlet. Such a slope may beneficially allow microbubbles to travel through the (liquid filled) array by buoyancy. For example, the method may involve tilting the microbubble sorting device such that the array slopes upwards from the inlet to the at least one outlet

[0170] The method may be a method of sorting microbubbles using deterministic lateral displacement.

[0171] A further aspect of the invention provides a microbubble solution produced according to the method described above, or produced by the microbubble sorting device described above.

[0172] As used herein, the ‘size’ of a microbubble refers to its diameter. Namely the diameter of the gas core and encapsulating shell of the microbubble where present.

[0173] As used herein, the ‘size’ of a solid particles (which may be non-spherical) may be taken to mean a smallest width measured through a centre of the particle.

[0174] The size of particles and / or microbubbles may be measuring using an optical detection device such as a microscope camera.

[0175] As used herein, ‘lateral’ refers to movement perpendicular to the flow direction of the solution.BRIEF DESCRIPTION OF THE DRAWINGS

[0176] Examples of the invention are described hereinafter with reference to the accompanying drawings, in which:

[0177] FIG. 1 illustrates a device for sorting microbubbles according to their size.

[0178] FIG. 2 illustrates a top cross-sectional view of an array for the device of FIG. 1.

[0179] FIG. 3 illustrates a schematic diagram of a channel of the array of FIG. 1.

[0180] FIG. 4A illustrates an alternate array for use in the device of FIG. 1.

[0181] FIG. 4B illustrates an enlarged view of a section of FIG. 4A.

[0182] FIG. 5 illustrates a filter for use in the device of FIG. 1.

[0183] FIG. 6A illustrates the array of FIG. 2 when the device is in use.

[0184] FIG. 6B illustrates the array of FIG. 2 in use, where an additional hydrophilic coating has been applied to the array.

[0185] FIG. 7A illustrates a multi-stage sorting device for sorting microbubbles according to their size.

[0186] FIG. 7B illustrates a schematic diagram of the channel of the device of FIG. 7A.

[0187] FIG. 7C illustrates a multi-stage sorting device for sorting microbubbles according to their size, having multiple buffer inlets.

[0188] FIG. 8 illustrates a method of sorting microbubbles using deterministic lateral displacement.DETAILED DESCRIPTION

[0189] FIG. 1 shows a device 100 for sorting microbubbles according to their size.

[0190] The device 100 includes a vessel 102 for receiving a polydisperse microbubble solution 104. The solution 104 may be produced by any suitable means. For example, the solution 104 may be produced by mechanical agitation of a lipid solution (e.g., containing a gas phase component).

[0191] Suitable lipid solutions include mixtures of saturated diacyl phosphatidylcholine and polyethylene glycol spacers used to form perflutren lipid microspheres. However, it will be apparent that use of the device 100 and associated method discussed herein is not limited to this specific poly disperse microbubble solution 104.

[0192] In some examples, the device 100 may include microbubble generator (not shown) such as a mechanical agitator (e.g. a sonicator). The microbubble generator may be operatively connected to the vessel to feed polydisperse microbubble solution 104 into the vessel 102. In other examples, the vessel 102 may be integrated into the microbubble generator.

[0193] In this example, the device 100 includes a stirrer 108 to ensure an even distribution of microbubbles throughout the solution 104. In this example, the stirrer 108 is a magnetic stirrer or a vortex mixer.

[0194] The device 100 comprises a body 105 having an inlet 120 for receiving the solution 104 from the vessel 102 and one or more outlets 121, 122. An upwardly tilting connecter may be provided between the vessel 102 and the inlet 120 to smoothly guide microbubbles into the device 100.

[0195] The body 105 includes at least one channel 130 which fluidically connects the inlet 120 to the outlets 121, 122.

[0196] As the solution 104 travels through the channel 130, the microbubbles within the solution 104 are separated into at least two flows according to their size.

[0197] The body 105 comprises a first outlet 121 for receiving the first flow and a second outlet 122 for receiving the second flow. Either or both of the first flow or the second flow may be collected for use in methods of diagnosis or treatment. In other examples, the body 105 may only comprise a single outlet. For example, one flow may be collected for use in treatment while the other flow may be retained in an internal reservoir or recycled into a mechanical agitator.

[0198] The channel 130 comprises a plurality of obstacles (not shown) which spatially separate the microbubbles using deterministic lateral displacement. In other examples, the obstacles (not shown) may separate the microbubbles using a NISA array.

[0199] In this example, the device 100 is configured to sort the solution 104 into a first flow and a second flow. The microbubbles in the first flow are on average smaller than the microbubbles in the second flow.

[0200] Deterministic lateral displacement is a separation method previously used to separate solid particles from a liquid. The device 100 utilises the principles of deterministic lateral displacement to sort microbubbles from the poly disperse microbubble solution 104. This process is described in detail below in relation to FIG. 2.

[0201] FIG. 2 shows a top cross-sectional view of an interior of the channel 130. The channel 130 is configured such that in use, the net flow of the solution 104 is in a flow direction 142 (i.e. from left to right in FIG. 2). In this example the channel 130 is substantially straight and connects the inlet 120 to an outlet end of the channel 130 in which the outlets 121, 122 are disposed.

[0202] As shown, the channel 130 comprises an array 140 of spaced obstacles 141. For example, each obstacle 141 may be a protrusion which extends into the channel 130 (e.g., from a bottom or top interior wall of the channel 130). For example, each obstacle 141 may extend from the bottom surface of the channel to the top surface of the channel to form a pillar, e.g. a micropillar on the order of 1-20 micrometers in diameter. In some examples the micropillars may have a diameter of more than 20 micrometers. The obstacles 141 may be sized according to the target microbubble size.

[0203] In this example, the obstacles 141 have a circular cross-section. However, as will be illustrated in FIG. 4A, the obstacles 141 are not limited to this shape and may instead have anysubstantially convex external profile. For example, the external cross-sectional profile of the obstacles 141 may be any regular or irregular shape, such as an ellipse, triangle, quadrilateral, pentagon, hexagon, octagon, or decagon.

[0204] As shown in FIG. 2, the obstacles 141 in the array 140 are identical to and regularly spaced from one another. In particular, the obstacles 141 are arranged in linear rows of evenly spaced obstacles 141. Each row comprises a plurality of obstacles 141. Only a portion of the array 140 can be seen in FIG. 2. The array 140 may comprise more than 50, more than 100 or more than 1000 obstacles 141 in total.

[0205] One row of the array 140 is indicated by imaginary line 144 in FIG. 2 which passes through the centre of each obstacle 141 in that row. As shown by line 144, the rows of the array 140 are angled with respect to the flow direction 142. This leads to the creation of separate flow laminae which follow known paths through the array 140. Microbubbles which are less than or equal to the critical size will flow through the array 140 largely unaffected by the obstacles 141. This is shown schematically in FIG. 2 by a first microbubble 151. As shown, the first microbubble 151 is deflected around the obstacles 141 but generally stays in a single streamline path. As such, there is no net lateral movement of the first microbubble 151 as it passes through the array 140. Here ‘lateral’ is used to refer to movement perpendicular to the flow direction 142 of the solution 104 (i.e. vertical as shown in FIG. 2).

[0206] The first outlet 121 is positioned to collect these small microbubbles which form part of the first flow. As shown below in FIG. 3, a receptacle of the first outlet 121 for receiving the first flow from the array 140 may be substantially aligned with the inlet 120 through which solution 104 is delivered into the array 140.

[0207] In contrast, a microbubble which has a size greater than the critical value will be displaced into a different streamline each time it encounters an obstacle 141. Such microbubbles are too large to remain in a single streamline which traverses multiple rows of obstacles 141. Instead these large microbubbles are repeatedly deflected in the same lateral direction by each obstacle 141 they encounter and so move substantially parallel to the rows of obstacles 141. This is illustrated in FIG. 2 by a second microbubble 152. As shown, with each collision the second microbubble 152 is repeatedly displaced by the obstacles 141 in the same lateral direction 154 (upwards in FIG. 2).

[0208] In examples where the array 140 is a NISA array, microbubbles will be deflected away from obstacles by lift forces and fluid inertia rather than direct physical collision.

[0209] There is a net lateral movement of the second microbubble 152 as it travels along a length of the array 140. As a result, as the solution 104 flows through the array 140 microbubbles that are larger than the critical size are displaced laterally and form part of the second flow. A receptacle of the second outlet 122 for receiving the second flow from the array 140 is laterally offset from the inlet 120 in order to collect the second flow.

[0210] Over the length of the array 140, a lateral offset is developed between microbubbles that are larger than the critical size and those that are not. This lateral offset allows the first flow, containing only small microbubbles less than or equal to the critical size, to be extracted from the polydisperse microbubble solution 104. This is advantageous as large microbubbles can be detrimental for some applications. For example, in drug delivery applications large microbubbles may be associated with increased damage to the blood brain barrier and longer recovery times. The device 100 may therefore be used to improve patient safety and offer improved control over diagnostics and treatments.

[0211] A buffer solution may be utilised to ensure that only microbubbles that are larger than the critical size are collected at the second outlet 122. This is shown in FIG. 3 which illustrates a schematic diagram of the channel 130 in use. The obstacles 141 of the array 140 are omitted for clarity.

[0212] As shown, the device 100 may comprise a buffer inlet 160 for inputting a buffer solution 162 into the array 140. The buffer inlet 160 and the inlet 120 may define an inlet end 164 of the channel 130 opposite the outlet end 124.

[0213] As described above, microbubbles which are less than or equal to the critical size (shown as black circles in FIG. 3) will flow through the array 140 largely unaffected by the obstacles 141 and form part of the first flow 171.

[0214] The buffer solution 162 ensures that the solution is confined to one lateral side of the channel 130 (i.e. the bottom half in FIG. 3). The streamlines of the solution 104 travel along the channel 130 in a substantially straight path from the inlet 120 to the first outlet 121. The first outlet 121 is aligned with the inlet 120 to collect the first flow 171.

[0215] Microbubbles that are larger than the critical size are shown as grey circles in FIG. 3. As shown, as these microbubbles travel along the length of the array 140 they are displaced by the obstacles 141 such that there is a net lateral movement of the microbubbles from the solution 104 to the buffer solution 162 to form the second flow 172. The second outlet 122 is aligned with the buffer inlet 160 for receiving the second flow 172.

[0216] As such the device 100 allows microbubbles above the critical size to be removed from the solution 104 while maintaining the population of optimally sized microbubbles.

[0217] Such a device 100 has several advantages over current microbubble sorting techniques such as differential centrifugation. For example, differential centrifugation is a highly energetic process which can result in the loss of a significant number of optimally sized microbubbles. In contrast, deterministic lateral displacement and NISA sorting does not require high centrifugal forces. The microbubbles within the solution 104 may be largely unaffected by the process so fewer optimally sized microbubbles may be lost. Advantageously, this may minimise the expense and time required to collect the required number of optimally sized microbubbles for a therapeutic dose.

[0218] Beneficially, the device 100 may have a smaller footprint and energy requirements than existing sorting devices which require large centrifuges. As such, the device 100 may be better suited for on-site use at the point of care.

[0219] Additionally, the array 140 can be easily tailored to specific microbubble applications which require different microbubbles sizes. In this way, the device 100 can provides a versatile option for sorting microbubbles to be used in various distinct applications.

[0220] FIG. 4A shows a section of an exemplar alternative array 240 which can be used in place of the array 140 shown in FIG. 2. FIG. 4A shows a top cross-sectional view of the alternative array 240 within the interior of the channel 130.

[0221] As shown in FIG. 4A, the obstacles 241 in the array 240 are identical to and regularly spaced from one another. In particular, the obstacles 241 are arranged in linear rows of evenly spaced obstacles 241. Each row comprises a plurality of obstacles 241. Only a portion of the alternative array 240 can be seen in FIG. 4A. The alternative array 240 may comprise more than 50, more than 100 or more than 1000 obstacles 241 in total.

[0222] One row of the alternative array 240 is indicated by imaginary line 244 in FIG. 4A which passes through the centre of each obstacle 241 in that row. As shown by line 244, the rows of the alternative array 240 are angled with respect to the flow direction 142. The general principles through which the alternative array 240 sorts microbubbles in the solution 104 are substantially the same as those described above in relation to FIG. 2. The alternative array 240 is configured to displace microbubbles larger than the critical bubble size in the lateral direction 154 (upwards in FIG. 2).

[0223] The alternative array 240 differs from the array 140 of FIG. 1 by the shape of the obstacles 241. In this example, the obstacles 241 are micropillars whose cross-sectional shape is defined by an irregular octagonal shape.

[0224] The irregular octagonal profile of the obstacles 241 is best shown in FIG. 4B which is an annotated view of a section of FIG. 4A.

[0225] As shown, the profile of each obstacle 241 consists of a kite shape with truncated vertices. The edges of the kite form four major sides 245a, 245b of the irregular octagonal profile while the truncated sides form four minor (i.e., shorter) sides 247a, 247b of the irregular octagonal profile.

[0226] The minor sides 247a, 247b comprise two pairs of opposing sides, a first pair 247a which are each oriented substantially parallel to the flow direction 142, and a second pair 247b which are each oriented substantially perpendicularly to the flow direction 142.

[0227] As will be described in further detail below, the obstacles 241 may be sized and spaced according to the target microbubble size. The size of obstacles 241 may be defined by a micropillar width 251, measured between the first pair 247a of opposing sides, and a micropillar length 252, measured between the second pair 247b of opposing sides. The spacing of the obstacles 241 may be defined by spacings, termed ‘Gap 1 ’ and ‘Gap 2’, between the nearest neighbours in the lateral and flow directions respectively. As shown in FIG. 4B, Gap 1(261) is defined by the minimum spacing between two neighbouring obstacles 241 in neighbouring rows of obstacles 241, measured perpendicular to the flow direction 142. Gap 2(262) is defined by the spacing between two neighbouring obstacles 241 in a row, measured parallel to the flow direction 142.

[0228] In this example, the size and spacings of the obstacles 241 are consistent throughout the whole alternative array 240.

[0229] As shown in FIG. 4B, the major sides 245a, 245b comprise a pair of long sides 245a and a pair of short sides 245b. In this example the pair of long sides 245a are equal in length to one another and the pair of short sides 245b are equal in length to one another. Each obstacle 241 is oriented the same way. In particular, each obstacle 241 is oriented such that the pair of long sides 245a approach one another as the lateral direction 154 increases. The pair of long sides 245a may further assist in directing microbubbles larger than the critical size in the lateral direction 154.

[0230] The irregular octagonal profile may also minimise bubble entrapment along the alternative array 240 by providing asymmetrical spaces between adjacent obstacles 241.

[0231] Bubble entrapment can be detrimental causing clogging which minimises the permeability of the array to microbubbles less than the critical size. This can reduce the effective yield of microbubbles less than the critical size that can be collected.

[0232] Clogging can be exacerbated by a small fraction of very large microbubbles which may be present in the solution 104. For example, the solution 104 may comprise a small fraction of microbubbles which are larger than the spacing between adjacent rows of obstacles 241 (e.g. larger than Gap 1 (261) in the alternative array 240). These very large microbubbles can body the entrances to the array leading to diminished yields of optimally sized microbubbles collected.

[0233] FIG. 5 illustrates a filter 400 for use in the device 100. The filter 400 will be described with reference to the array 140 as an example. However it will be understood that the filter 400 is not dependent on the configuration of the array and is suitable for use with a variety of differently configured arrays such as the alternative array 240.

[0234] In some examples, the filter 400 may form part of the inlet 120 or be disposed in the channel 130 upstream of the array 140. Alternately, the filter 400 may be a standalone device configured to receive the solution 104 from the vessel 102 and provide a filtered solution to the inlet 120 of the body 105.

[0235] In this example, the filter 400 forms part of the body 105 and is positioned upstream of the array 140 (not shown). The filter 400 comprises a regular matrix of micropillars 404.

[0236] Unlike the array 140, the rows of the example filter 400 are not angled with respect to the flow direction. The filter 400 defines a series of straight flow paths through the filter 400 which are parallel to the flow direction 142.

[0237] In use, the filter 400 receives solution 104 from the vessel 102. Very large microbubbles are blocked by the matrix and thereby filtered from the solution 104. The filtered solution 104 feeds into the array 140 which is downstream of the filter 400.

[0238] The specific geometry of the filter 400 may be varied to tailor the device 100 to different applications where different microbubble sizes are required. For example, the micropillars 404 of the filter 400 may be spaced to provide 50pm, 20pm, 15pm, 10pm or 5pm gaps (perpendicular to the flow direction 142).

[0239] The micropillars 404 of the filter 400 may have any cross-sectional profile. For example the cross-sectional profile may be substantially circular or have any regular or irregular shape such as: triangular, quadrilateral, hexagonal or octagonal. In some examples, the matrix may comprise one or more rows of elongate micropillars which extend along the flow direction 142.

[0240] In other examples the filter 400 may not comprise a matrix of micropillars. For example, the filter may instead comprise a mesh for filtering microbubbles. An aperture size of the mesh may be selected to tailor the device 100 for different applications. For example, the aperture size of the mesh may be 50pm, 20pm, 15pm, 10pm or 5 pm.

[0241] FIG. 6A and FIG. 6B illustrate a further way of minimising microbubble clogging, utilising a hydrophilic coating. The array 140 is shown in these figures as an example. However, it will be understood that the hydrophilic coating is not dependent on the configuration of the array and is suitable for use with a variety of differently configured arrays such as the alternative array 240.

[0242] The array 140 and channel 130 may be formed from a plastic material such as PDMS (Polydimethylsiloxane). During use of the device, the microbubbles may become attached to the walls of the channel 130 or the obstacles 141 themselves. This is illustrated in FIG. 6A which shows an image of the array 140 during use. As shown, even microbubbles 402 which are smaller than the spacing between rows of obstacles 141 can become blocked in the array 140. The microbubbles collect together and form a larger agglomerate that may at least partially block the array 140.

[0243] A hydrophilic coating can be applied to the channel 130 and the array 140 to prevent microbubbles adhering and agglomerating within the device 100. Beneficially this may maximise the yield of optimally sized microbubbles that can be collected from the device 100.

[0244] This is illustrated in FIG. 6B which shows the array of FIG. 6A with an additional hydrophilic coating applied to the channel 130 and the array 140. As shown, by providing a hydrophilic coating, microbubble clogging within the array 140 can be reduced. The hydrophilic coating may ensure an insulating layer of solvent from the solution 104 lines the channel 130 and acts to prevent microbubble adhesion.

[0245] In some examples, the hydrophilic coating may comprise a two-layer coating. Each layer may comprise a different hydrophilic material. For example, tetraethylorthosilicate may be used as a base hydrophilic layer while 2- [acetoxy (polyethyleneoxy) propyl] triethoxysilanemay be deposited on top of the base hydrophilic layer to form the two-layer hydrophilic coating.

[0246] Two-layer hydrophilic coatings may beneficially act as a super hydrophilic surface which is particularly effective at preventing microbubble adhesion.

[0247] In other examples, the hydrophilic coating may comprise or essentially consist of other hydrophilic materials such as polyvinyl alcohol.

[0248] Additionally or alternately, microbubble clogging may be minimised by employing an incline to the array 140 of the device 100. The device 100 may be configured such that when the device 100 is located on a horizontal surface, the array 140 slopes upwards from the inlet 120 to the outlet end. In this way, the inherent buoyancy of the microbubbles can assist in progressing the microbubbles through the array 140. This can help to prevent microbubbles from becoming static and agglomerating within the array 140.

[0249] The device 100 may comprise a pump (not shown) for pumping the solution 104 from the vessel 102 through the array 140 to the outlets 121, 122.

[0250] FIG. 7A illustrates a schematic diagram of a sorting device 700. The device 700 is configured to sort a particles, such as microbubbles or solid particles, within a solution using deterministic lateral displacement. In this example, the device 700 is substantially similar to the device 100 of Figures 1-6, and is used to sort microbubbles within a polydisperse solution according to their size. Reference numerals have been repeated for features of the device 700 which correspond to analogous features of device 100.

[0251] The device 700 differs from the device 100 in that it comprises multiple arrays of obstacles as opposed to a single array 140.

[0252] In this example the device 700 comprises four arrays: a first array 710, a second array 720, a third array 730 and a fourth array 740. Each of the arrays 710, 720, 730, 740 form part of the body 105 and are located in the channel 130 between the inlet 120 and the outlet end 124. The device 700 is configured such that the solution 104 is passed through each of the four arrays 710, 720, 730, 740 sequentially.

[0253] Each of the arrays are 710, 720, 730, 740 deterministic lateral displacement arrays. In this example, each of the arrays 710, 720, 730, 740 have the general configuration of the alternative array 240 shown in FIG. 4 A (having obstacles 241 with an irregular octagonal profile). The obstacles 241 of the each of the arrays 710, 720, 730, 740 are the same. In otherexamples, different obstacles may be used in the arrays 710, 720, 730, 740. For example, one or more of the arrays 710, 720, 730, 740 may instead have the general configuration of the array 140 shown in FIG. 2 (having obstacles 141 with a circular profile).

[0254] The spacing between obstacles in the arrays 710, 720, 730, 740 may decrease sequentially along the length of the channel 130. I.e., the first array 710 has the largest spacing of any of the arrays 710, 720, 730, 740 while the second array 720 has a spacing smaller than the spacing of the first array 710 and larger than the spacing of the third array 730. The fourth array 740 has the smallest spacing of any of the arrays 710, 720, 730, 740.

[0255] This is shown below in Table 1 which illustrates example spacings, Gap 1 (261) and Gap 2 (262), between neighbouring obstacles 241 in the arrays 710, 720, 730, 740.

[0256] In this example the micropillar width 251 is equal to the micropillar length 252. This value is indicated in the row titled 'Pillar size'.First ThirdSecond Fourth array array array 720 array 740710 730Gap 1 (261) 20pm 12pm 8pm 5.5pmPillar size 10pm 10pm 10pm 10pmGap 2 (262) 11pm 8pm 5.5pm 4.5pmCriticalMicrobubble 10pm 6pm 4.5pm 3.5pmSizeNumber of rows 42 42 42 42Table 1: table of array configurations for the device 700 shown in FIG. 7A.

[0257] As shown, the arrays 710, 720, 730, 740 in the sequence have progressively narrower spacing such that each array 710, 720, 730, 740, has a smaller critical microbubble size than the previous array 710, 720, 730, 740 in the sequence.

[0258] In this example, the first array 710 removes microbubbles greater than 10pm in diameter from the solution 104. The second array 720 removes microbubbles greater than 6pm in diameter from the remaining solution 104. The third array 730 removes microbubbles greater than 4.5pm in diameter from the remaining solution 104. The fourth array 740 removes microbubbles greater than 3.5pm in diameter from the remaining solution 104.

[0259] In other examples, the relative angles between obstacles (141) in the first array (710) may differ from that of the second array (720) and so on to define decreasing critical diameters. In this way, the arrays (710, 720, 730, 740) may have different characteristic critical diameters to each other even where the same sized obstacles (141) are used in each array (710, 720, 730, 740).

[0260] The microbubbles which are greater than the critical size may be output as a waste product or collected for use (e.g. in a therapeutic or diagnostic method). This is illustrated in FIG. 7B which shows a schematic diagram of the channel 130 in use. The obstacles 141 of the arrays 710, 720, 730, 740 are omitted for clarity.

[0261] Like the device 100, the device 700 comprises multiple outlets. In this example, the device 700 comprises a first outlet 121, which is aligned with the inlet 120, and a series of lateral outlets 751, 752, 753, 754 configured to receive microbubbles that are laterally offset by the deterministic lateral displacement arrays 710, 720, 730, 740.

[0262] As the solution 104 flows through the channel 130, large microbubbles will be removed by the lateral outlets 751, 752, 753, 754. There will be no net lateral movement of microbubbles which are less than or equal to the critical size of each of the arrays 710, 720, 730, 740. These microbubbles form part of the first flow 171 which travels in a substantially straight path from the inlet 120 to the first outlet 121.

[0263] The first flow may be collected or may be discarded as a waste product. In some examples, the device 700 may be configured to feed the first flow 171 into a microbubble generator such as a mechanical agitator.

[0264] Each of the lateral outlets 751, 752, 753, 754 may be laterally offset relative to the inlet 120 in a similar manner to the second outlet 122 of device 100. The number of lateral outlets 751, 752, 753, 754 may equal the number of deterministic lateral displacement arrays 710, 720, 730, 740 in the channel 130. In this example, the device 700 comprises four lateral outlets: a first lateral outlet 751, a second lateral outlet 752, a third lateral outlet 753 and a fourth lateral outlet 754.

[0265] Each lateral outlet 751, 752, 753, 754 is configured to receive microbubbles displaced by a respective one of the arrays 710, 720, 730, 740. I.e. The first lateral outlet 751 is configured to receive microbubbles laterally displaced by the first array 710, the second lateral outlet 752 is configured to receive microbubbles laterally displaced by the second array 720, and so on.

[0266] By tailoring the critical size of the arrays 710, 720, 730, 740, the size distribution of microbubbles collected at each of the lateral outlets can be selected. For example, microbubbles collected at the second lateral outlet 752:• must be less than or equal to the critical size of the first array 710 to have passed through the first array 710; and• must be larger than the critical size of the second array 720 to have been displaced laterally by the second array 720, i.e., Ci>d2>C2where Ci represents the critical size of the first array 710, C2represents the critical size of the second array 720, and d2represents the diameter of the microbubbles collected at the second lateral outlet 752.

[0267] By using multiple deterministic lateral displacement arrays 710, 720, 730, 740, a series of refined solutions with narrow size distributions of microbubbles can be extracted from a poly disperse solution 104.

[0268] The microbubbles output at the lateral outlets 751, 752, 753, 754 may be collected for use in diagnostics or treatment or may be discarded as a waste product e.g. depending on the application. In this example, the application requires microbubbles that are between 4.5 and 3.5 micrometers in diameter so the microbubbles at the fourth lateral outlet 754 may be collected while the microbubbles at the first, second and third lateral outlet 751, 752, 753 may be discarded. The first, second and third array 710, 720, 730 may help to prevent clogging by removing large microbubbles before they reach the fourth array 740.

[0269] In this way, the multistage sorting device 700 may allow microbubble solutions with mono-sized distributions to be collected by removing both oversized and undersized microbubbles from a poly disperse solution 104. Such refined solutions with a narrow microbubble size distribution may provide improved control over treatment.

[0270] The example devices 700 described above comprise multiple discrete arrays 710, 720, 730, 740, arranged sequentially in the channel 130. The arrays 710, 720, 730, 740 may bespaced apart from one another along the length of the channel 130. In other examples, there may be no spacing between neighbouring arrays 710, 720, 730, 740.

[0271] In some examples the channel 130 may not comprise multiple discrete arrays and may instead comprise a single deterministic lateral displacement array wherein the spacing between obstacles decreases along the length of the channel 130 towards the outlet end 124.

[0272] Table 2 and Table 3 below provide further example array spacings and their associated critical bubble size.First ThirdSecond Fourth array array array 720 array 740710 730Gapl 20pm 12pm 8pm 4.5pmPillar size 10pm 10pm 10pm 10pmGap 2 11pm 8pm 4.5pm 3.5pmCritical microbubble 10pm 6pm 3.5pm 2.5pm sizeNumber of 42 42 42 42 rowsTable 2: table of alternate array configurations for the device 700.First Second Third Fourth array array 720 array 730 array 740 710Gap 1 20pm 12pm 8pm 6.5pmPillar size 10pm 10pm 10pm 10pmGap 2 11pm 8pm 6.5pm 5.5pmCritical microbubbl 10pm 6pm 5.5pm 4.5pm e sizeNumber of42 42 42 42 rowsTable 3: table of alternate array configurations for the device 700.

[0273] In the example shown in FIG. 7B, the device 700 comprises four arrays 710, 720, 730, 740. In other examples, the device 700 may comprise two or more deterministic lateral displacement arrays. For example, the device 100 may comprise two arrays, three arrays, four arrays or five or more arrays.

[0274] A minimum of two arrays may be required to produce a refined solution where both oversized and undersized microbubbles have been removed. Tables 4 to 7 provide example spacings for examples where the device 700 comprises only two deterministic lateral displacement arrays. In these examples the third array 730, third lateral outlet 753, fourth array 740 and fourth lateral outlet 754 have been removed.First Second array 710 array 720Gap 1 20pm 4.5pmPillar10pm 10pm sizeGap 2 4.5pm 3.5pmCritical microbub 3.5 pm 2.5 pm ble sizeNumber 4 5 of rowsTable 4 : table of alternate array configurations for the device 700.First Second array 710 array 720Gap 1 20pm 5.5 pmPillar 10pm 10pm sizeGap 2 5.5pm 4.5pmCritical microbub 4.5 pm 3.5 pm ble sizeNumber 4 5 of rowsTable 5 : table of alternate array configurations for the device 700.First Second array 710 array 720Gap 1 20pm 6.5pmPillar10pm 10pm sizeGap 2 6.5pm 5.5pmCritical microbub 5.5 pm 4.5 pm ble sizeNumber7 8 of rowsTable 6 : table of alternate array configurations for the device 700.First Second array 710 array 720Gap 1 20pm 7.5pmPillar 10pm 10pm sizeGap 2 7.5pm 5.5pmCritical microbub 6.5pm 4.5pm ble sizeNumber 9 10 of rowsTable 7 : table of alternate array configurations for the device 700.

[0275] As shown in FIG. 7B, like the device 100, the device 700 comprises a single buffer inlet 160 which is located at the inlet end 164 of the channel 130. The buffer inlet 160 inputs a buffer solution 162 such as water into the channel 130.

[0276] The buffer solution 162 is repeatedly removed from the channel 130 at each of the lateral outlets 751, 752, 753, 754. This may cause some lateral migration of the first flow 171 along the length of the channel 130.

[0277] This is shown in FIG. 7B where microbubbles that are larger than the critical size of any of the arrays 710, 720, 730, 740 are shown as grey circles while ‘sub-sized’ microbubbles which are less than or equal to the critical size of the fourth array 740 are shown as black circles. As shown, the sub-sized microbubbles flow as part of the solution 104 unaffected by the arrays 710, 720, 730, 740. Some of the solution 104 migrates laterally to accommodate for the buffer solution 162 lost to the lateral outlets 751, 752, 753. As a result, some of the subsized microbubbles in the solution 104 migrate laterally with the solution 104 and are collected at the fourth lateral outlet 754.

[0278] Unfortunately, this may broaden the size distribution of the microbubbles collected at the fourth lateral outlet 754.

[0279] One way to prevent this effect is to introduce buffer solution 162 at multiple points along the length of the device 700. This is demonstrated in FIG. 7C which illustrates a modified device 700' for sorting a species, such as microbubbles or solid particles, from a solution using deterministic lateral displacement.

[0280] The modified device 700' is substantially similar to the device 700 differing only in the number of the buffer solution inlets. Like the device 700, the modified device 700' comprises a buffer inlet 160 located at the inlet end 164. Unlike the device 700, the modified device 700' further comprises one or more additional buffer inlets 761, 762, 763. Each of the additional buffer inlets 761, 762, 763 are configured to deliver buffer solution 162 to the channel 130 between two neighbouring arrays 710, 720, 730, 740 in the sequence.

[0281] In this example the modified device 700' comprises three additional buffer inlets: a first additional buffer inlet 761, a second additional buffer inlet 762, and a third additional buffer inlet 763. The first additional buffer inlet 761 inputs buffer solution 162 into the channel 130 downstream of the first array 710, upstream of the second array 720. The second additional buffer inlet 762 inputs buffer solution 162 into the channel 130 downstream of the second array 720, upstream of the third array 730.

[0282] By introducing buffer solution after each lateral outlet 751, 752, 753, a constant amount of buffer solution can be maintained along the length of the channel 130. A constant amount of buffer solution 162 ensures that the solution 104 is confined to one lateral side of the channel 130 (i.e., the bottom half in FIG. 7C). The streamlines of the solution 104 travel along the channel 130 in a substantially straight path from the inlet 120 to the first outlet 121. This can prevent lateral migration of sub-sized microbubbles thereby improving the yield of subsized microbubbles at the first outlet 121 and maintaining narrow size distributions of microbubbles collected at the lateral outlets 751, 752, 753, 754.

[0283] The ideal pressure drop for additional buffer to off-set the flow can be calculated and implemented on chip passively or controlled by an external pressure regulator actively.

[0284] While the device 700 and the modified device 700' are discussed in relation to microbubbles, it will be appreciated that the advantages of multi-stage sorting are not limited to microbubble applications. In some examples the device 700 and the modified device 700' may instead be particle sorting devices for sorting solid particles.

[0285] FIG. 8 shows a method 800 of sorting microbubbles using deterministic lateral displacement.

[0286] The method 800 comprises a first step 801 of inputting a solution containing a plurality of microbubbles into a sorting device. The sorting device comprises an array of spaced obstacles arranged to differentially displace microbubbles according to their size to separate the plurality of microbubbles in the solution into a first flow and a second flow. In some examples, the sorting device may be any one of the deterministic lateral displacement sorting devices described herein (e.g., the device 100 of FIG. 1, the device 700 of FIG. 7B, or the modified device 700' of FIG. 7C).

[0287] In some examples, the array may be any of the deterministic lateral displacement arrays described herein such as the array 140, or alternative array 240.

[0288] The method 800 further comprises a second step 802 of collecting at least one of the first flow and the second flow.

[0289] The first step 801 may be completed before the second step 802. In some examples the first step 801 and the second step may be completed simultaneously.

Claims

CLAIMS1. A microbubble sorting device comprising: an inlet for receiving a solution containing a plurality of microbubbles; and an array of spaced obstacles arranged to differentially direct the microbubbles according to their size to separate the plurality of microbubbles in the solution into a first flow and a second flow.

2. The microbubble sorting device of claim 1, further comprising at least one outlet fluidically connected to the inlet by a channel, wherein the plurality of spaced obstacles are received within the channel.

3. The microbubble sorting device of claim 2, wherein the microbubble sorting device comprises a first outlet for receiving the first flow, and a second outlet for receiving the second flow.

4. The microbubble sorting device of claim 3, wherein the first outlet is aligned with the inlet to collect the first flow, and the second outlet is laterally offset from the inlet to collect the second flow.

5. The microbubble sorting device of any one of claims 2 to 4, wherein the microbubble sorting device is configured such that when the microbubble sorting device is located on a horizontal surface, the array slopes upwards from the inlet to the at least one outlet.

6. The microbubble sorting device of any one of claims 2 to 5, wherein the channel comprises a hydrophilic surface, optionally wherein the array comprises a hydrophilic material.

7. The microbubble sorting device of claim 6, comprising a hydrophilic coating on the channel and optionally the array.

8. The microbubble sorting device of claim 7, wherein the hydrophilic coating comprises a two- layer coating and each layer of the two-layer coating comprises a different hydrophilic material, optionally wherein the two-layer hydrophilic coating comprises tetraethylorthosilicate34as a base hydrophilic layer and 2- [acetoxy (polyethyleneoxy) propyl] triethoxysilane as a top hydrophilic layer to cover the base hydrophilic layer.

9. The microbubble sorting device of any one of claims 2 to 8, comprising a buffer inlet for inputting a buffer solution into the channel.

10. The microbubble sorting device of any one of claims 2 to 9, wherein the microbubble sorting device comprises two or more arrays arranged in a sequence along a length of the channel, optionally wherein the microbubble sorting device comprises two arrays, three arrays, four arrays, five arrays, or more than five arrays.

11. The microbubble sorting device of claim 10, wherein the two or more arrays in the sequence may have progressively narrower spacing such that each array in the sequence has a smaller spacing between obstacles than an immediately preceding array in the sequence.

12. The microbubble sorting device of claim 10 or 11, wherein a final array in the sequence has a spacing between obstacles of 30pm to 3pm, 10pm to 3pm, 7.5pm to 3.5pm, 6.5pm to 3.5pm, 5.5pm to 3.5pm, or 4.5pm to 3.5pm.

13. The microbubble sorting device of any one of claims 10 to 12, comprising two or more lateral outlets configured to receive microbubbles that have been laterally offset by a different one of the two or more arrays.

14. The microbubble sorting device of claim 13, wherein the microbubble sorting device comprises one or more additional buffer inlets each for inputting a buffer solution into the array, wherein each of the additional buffer inlets is configured to deliver buffer solution to the channel downstream of a respective one of the lateral outlets.

15. The microbubble sorting device of any one of claims 1 to 14, comprising a pressure source for pumping the solution through the array.

16. The microbubble sorting device of any one of claims 1 to 15, wherein the plurality of spaced obstacles are arranged in rows of obstacles, and wherein the array is configured such that microbubbles larger than a critical microbubble size are repeatedly deflected in a lateral direction by each obstacle they encounter to move substantially parallel to the rows of obstacles.3517. The microbubble sorting device of claim 16, wherein the microbubble sorting device is configured such that in use, there is a net flow of the solution in a flow direction, and wherein the rows of the array are angled with respect to the flow direction, optionally wherein an angle between the flow direction and the rows of the array is greater than 5° and less than or equal to 30°.

18. The microbubble sorting device of any one of claims 1 to 17, wherein an external cross- sectional profile of the obstacles is defined by a circle.

19. The microbubble sorting device of any one of claims 1 to 18, wherein an external cross- sectional profile of the obstacles is defined by an irregular octagonal shape.

20. The microbubble sorting device of claim 19, wherein the profile consists of a kite shape with truncated vertices.

21. The microbubble sorting device of claim 20, wherein the edges of the kite shape define four major sides of the profile, and the truncated vertices define four minor sides of the profile, wherein the major sides comprise a pair of long sides and a pair of shorter sides, and wherein each obstacle of the array is oriented such that the pair of long sides approach one another as the lateral direction increases.

22. The microbubble sorting device of any one of claims 2 to 21, comprising a filter for filtering microbubbles, located upstream of the or each array, optionally wherein the filter comprises a matrix of obstacles such as micropillars and wherein the obstacles of the filter are spaced to provide 50pm, 20pm, 15pm, 10pm or 5pm gaps, measured perpendicular to the flow direction.

23. A method of sorting microbubbles, comprising: inputting a solution containing a plurality of microbubbles into a microbubble sorting device comprising an array of spaced obstacles arranged to differentially direct microbubbles according to their size to separate the plurality of microbubbles in the solution into a first flow and a second flow; and collecting at least one of the first flow and the second flow.

24. The method of claim 23, wherein the microbubble sorting device is the microbubble sorting device according to any one of claims 1 to 22.

25. The method of claim 23, wherein the microbubble sorting device is the microbubble sorting device according to claim 13 or 14, and wherein the method further includes collecting microbubbles at one or more of the lateral outlets.

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