MICROFLUIDIC SAMPLE HOLDER AND METHOD

Abstract

 A microfluidic sample holder is provided, comprising a flow channel (103) for holding a liquid sample comprising a plurality of objects (200, 200a), in particular cellular objects such as cells, and defining a flow path (P). At least part of the channel (103) is defined by a plurality of facets (109, 111, 113, 115), providing the channel (103) with a polygonal shape in cross section perpendicular to the flow path (P). A first facet (109) forms a channel floor and an adjacent second facet (113, 115) forms a channel side wall extending from the floor at an opening angle (α, α') in a range of 100-170 degrees.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a microfluidic sample holder and an associated method. The sample holder comprises a flow channel for holding a fluid sample comprising a plurality of objects, wherein the channel defines a flow path and the channel is defined by a plurality of wall surfaces.

BACKGROUND

[0002] When processing and/or sorting microscopic objects entrained in a fluid, such as e.g. biological cells, often microfluidic devices are used, in which a fluid flow through a channel is used to urge the objects ahead. Movement of the objects through the channel is related to the shear flow force experienced by the objects and to adhesion of the objects to walls of the channel. Inhomogeneities in forces and/or of flow profiles of the fluid may disturb and possibly negatively affect the sorting results. Although some solutions have been provided such as by WO 2022/045892 A1, further improvements are still desired.

SUMMARY

[0003] In view of the above, herewith a microfluidic sample holder is provided, comprising a flow channel for holding a liquid sample comprising a plurality of objects, in particular cellular objects such as cells, and defining a flow path. At least part of the channel is defined by a plurality of facets, providing the channel with a polygonal shape in cross section perpendicular to the flow path. A first facet forms a channel floor and an adjacent second facet forms a channel side wall extending from the floor at an opening angle of 100-170 degrees, in particular in range of 110-160 degrees, more in particular in a range of 120-150 degrees, e.g. 130-140 degrees.

[0004] Such sample holder improves determination and/or controlling shear flow force profile on the objects under flow of the sample liquid. It has been found that a traditional channel wherein the floor and side wall are perpendicular to each other provides a large variation in shear flow force as a function of distance to the side wall along the floor; an object in contact with both the floor and the side wall will experience a flow force significantly less than at a position on the floor far from the side wall, e.g. in a middle of the floor, possibly being even only about 1/3 thereof or lower still. By providing the channel with a side wall at an opening angle of 100-170 degrees, i.e. the side wall being slanted to the floor at an obtuse angle, such drop of flow force profile along the floor is reduced or prevented.

[0005] The larger the opening angle, the smaller the reduction in flow force at or near the side wall becomes; an opening angle in a range 110-160 degrees may therefore be preferred, e.g. in a range 120-150 degrees. An opening angle in a range of 130-140 degrees may be preferred most.

[0006] Herein, a facet refers to a substantially plane wall surface portion separated from an adjacent facet by a bend (which may be straight or curved) in between, which is preferably substantially smaller (in particular: narrower) than the facets. A facet may have any shape, preferably the facet is substantially polygonal. A facet may span most or all of the length of the channel. Typically, in a microfluidic sample holder having a channel length of several millimeters or up to centimeters, a facet may typically have a surface area of at least 100000 square micrometers (0.1 square millimeter) up to a few to a few tens of square millimeters or more, e.g. 1 square millimeter or more such as 100 square millimeter or more. Herein, polygon or polygonal refer to a shape that has three or more corners separating substantially straight sides. A corner may be rounded. Preferably, such bend extends for less than 1/5, more preferably less than 1/10 or even less than 1/25 of a size in a direction perpendicular to the bend of one or more adjacent facet(s), e.g. two facets separated by the bend; likewise, such angle, in particular a rounded angle, may extend for less than 1/5, more preferably less than 1/10 or even less than 1/25 of a length of one or more of the adjacent straight side(s), e.g. two sides separated by the angle.

[0007] Preferably, on an opposite side of the floor another one of such side walls slanted to the floor at an obtuse angle as explained above may be provided, preferably both angles are the same, in opposite directions. The channel may be symmetric in the cross sectional plane.

[0008] Further, associated with the preceding, herewith is provided an assembly comprising such sample holder and comprising a liquid sample comprising a plurality of objects, in particular cells.

[0009] Note that in this text, "cellular objects" and "cells" refer to biological cellular objects and biological cells, respectively, such as single cells (e.g. blood cells, T-cells, immune cells of any kind, tumor cells, etc.), clumps of cells bound together, yeasts, organelles, etc.

[0010] The objects may have an average diameter.

[0011] In the sample holder, the opening angle may be formed by a transition between the first and second facets.

[0012] The transition may be at most 1/2 of the average diameter, preferably at most 1/3 more preferably about 1/4 of the average diameter, and/or the transition may be at most 10 micrometers, preferably at most 5 micrometers, more preferably be at most 3 micrometers, most preferably about 1 micrometer.

[0013] Also or alternatively, the transition may be formed by a fillet having a fillet radius of curvature of at most 1/3 of the average diameter, preferably at most 1/4 more preferably about 1/5 of the average diameter, and/or the transition may be formed by a fillet having a fillet radius of curvature of at most 5 micrometers, preferably be at most 3 micrometers more preferably about 1 micrometer.

[0014] At least the floor and the side wall, preferably all channel facets, may be smooth to within 0,1 times the average diameter, preferably to within 0,05 such as to within 0,02 or even 0,01 times the average diameter; and/or at least the floor and the side wall, preferably all channel facets, may be smooth to within 1 micrometer, preferably to within 0,1 micrometer such as to within 0,01 micrometer.

[0015] At least the first and second facet, possibly any facet, may be plane, at least at length scales larger than 10 micrometer, preferably at length scales larger 5 micrometer, more preferably at length scales larger than 3 micrometer, most preferably larger than 1 micrometer.

[0016] Such transition, and/or such surface conditions, and/or such planarity may be provided by one or more of moulding of glass and/or polymer, wet etching of glass or polymer, and liquid coating a glass and/or polymer surface with a surface layer.

[0017] The transition assists one or more of determining the flow profile of a fluid through the channel, determining a small contact surface of an object, in particular a biological cell, with the floor and the side wall, and promoting that objects collect at the floor rather than adhere to, or remain stuck to, the side wall and/or transition.

[0018] It is noted that a fillet radius of curvature on the order of 1/2 the average diameter of round and/or deformable objects allows an objects to contact the fillet over a significant surface area, therewith, not only shear flow forces are affected but also surface adhesion of such object may be significantly higher than when only a comparably small contact surface area is provided; hence, a small fillet radius of curvature provides improvements to the desired effects.

[0019] The smoothness may spare biological cells and/or may prevent interfering with flow profiles and/or object movement at least to an extent.

[0020] A further facet of the channel may form a ceiling and the channel may have a height between the floor and ceiling. The floor and ceiling may be parallel.

[0021] The side wall may span at least 1/4 of the height, preferably at least 1/3 more preferably at least 1/2 of the height or substantially the entire height. Thus, various polygonal shapes can be contemplated.

[0022] The height may be at least 5 times the average diameter, preferably at least 7 times such as 10 times, 15 times or more. Also or alternatively, the height may be 50 micrometer or larger, such as 75 micrometer or larger, e.g. 100 micrometer or several hundreds of micrometers up to a millimeter. This accommodates use with biological cells that tend to have an average diameter of about 10 micrometer, assuming a generally globular shape of the cell.

[0023] The floor and possibly the ceiling may have a width perpendicular to the flow path of about 1,0 millimeter or more, e.g. 1,5 millimeter or 2,0 millimeter up to several millimeters. Also or alternatively, The floor and possibly the ceiling may have a length along to the flow path of several millimeters or several tens of millimeters, e.g. 10 millimeter or more, e.g. 25 millimeter or more, 50 millimeter, and possibly up to several centimeters, e.g. up to 20 cm. The channel may be bent in the sample holder, providing a bent flow path from an inlet to an outlet of the channel for filling the channel with a liquid. In some embodiments, a channel width varies along the channel length.

[0024] The side wall facet may span at least 50% of the channel height, preferably at least 75% such as more than 80%, e.g. more than 90%.

[0025] The at least part of the channel may be defined by an even number of facets. The polygonal cross sectional shape of the channel may have an even number of angles and facets. The polygonal shape of the channel may be trapezoidal, hexagonal, or octagonal and/or may preferably be symmetric with respect to the floor and/or axisymmetric with respect to an axis along the flow path.

[0026] At least the first and second facet, possibly any facet, may be plane at length scales larger than 10 micrometer, preferably at length scales larger 5 micrometer, more preferably at length scales larger than 3 micrometer, most preferably larger than 1 micrometer. Also or alternatively, at least the first and second facet, possibly any facet, may be plane at length scales larger than 100 micrometer, preferably at length scales larger than 1 millimeter, more preferably at length scales larger than 5 millimeter, most preferably larger than 10 millimeter. This facilitates provision of smooth and/or predictable liquid flow. This may also or alternatively prevent hindrance to the objects and provide predictable force application to the objects. The channel, at least part of the floor and/or side wall thereof, may be provided with one or more of a functionalisation layer, an antifouling layer, a target cell layer; the objects may comprise target cells or effector cells interacting with the target cells, e.g. binding to the target cells. This facilitates assessing interaction of the cells with reduced or no effects from (adhesion to) the side wall(s) .

[0027] The shape of the channel simplifies positioning substances or objects on the floor or in desired portion of the floor by flowing a liquid through the channel.

[0028] It is understood that such functionalization layer may be coated to promote attachment of cells (e.g. target cells), and that such antifouling layer may have antifouling properties to reduce cell binding and attachment. A functionalization layer may preferably be provided on the floor. An antifouling layer may preferably be provided on the side walls and/or ceiling.

[0029] For suitable layers, suitable coating agents for attachment of cells are known in the art. Such coatings preferably comprise a polypeptide. Polypeptides can be naturally occurring polypeptides and/or synthetic. Such a coating may comprise a polypeptide selected from the group consisting of fibronectin, poly-L-lysine, poly-D-lysine, poly-L-ornithine, laminin, collagen, fibronectin, fibrinogen, vitronectin, osteopontin, thrombospondin, VEGF, VCAM-1, ICAM. In another embodiment, the coating may comprise one or more from the group consisting of fibronectin, poly-L-lysine, poly-D-lysine, poly-L-ornithine, laminin, collagen, fibronectin, fibrinogen, vitronectin, osteopontin, thrombospondin, VEGF, VCAM-1, and ICAM. These polypeptides may attach to the surface and in their turn subsequently attach with target cells thereby attaching the target cells to the surface. In any case, a suitable coating may be selected such that the target cells that are attached to the surface allow for the target cells to remain attached to the surface when applying a force on the effector cells that are bound thereto. In other words, when a shear flow force or another force (such as e.g. an acoustic or centrifugal force) is applied on the effector cells which allows for these cells to detach from the target cells, the target cells are to substantially remain attached to the surface.

[0030] Further, it is noted that a hydrophobic surface may be coated by applying an aqueous solution containing a PEG block co-polymer e.g. Pluronic-F127 that physisorbs and presents a PEG-brush surface with low biofouling properties. Chemical functionalization may also be achieved by first attaching a chemically reactive linker to the surface, and then solution coating the device with an anti-fouling molecule that reacts with the activated linker molecule. Pattered coating may be achieved by using a photoactivatable linker and using a photo mask and UV illumination to activate the linker only in select regions of the device. In any case, suitable antifouling agents or antifouling properties of at least the side walls can be appropriately selected and applied in the Microfluidics sample holder as described herein.

[0031] Also or alternatively, herewith a method is provided comprising providing the assembly or the microfluidic sample holder described herein, and providing a liquid sample flow through the channel, for urging objects contained in the sample liquid through the channel. The flow force profile across the floor is more even than in traditional channels. Therefore, studies involving the objects' movement in the presently provided (device comprising the) channel may provide improved results.

[0032] Also or alternatively, herewith a method is provided comprising providing an assembly of the microfluidic sample holder described herein with a liquid sample comprising objects in the channel, and subjecting the assembly to a controllable force in a direction perpendicular to the floor.

[0033] Such methods may comprise allowing and/or promoting adhesion of at least part of the objects to the floor, preferably also preventing adhesion of at least part of the objects to the side wall. Objects that may adhere to the side wall may be urged to the floor, in case the controllable force acting on the object is larger than the adhesion force. Note that also gravity may suffice for overcoming adhesion to the side wall and allow any adhered object to move to the floor rather than stick to the side wall.

[0034] Also or alternatively, any method herein may also comprise providing a first part of the objects as target cells, allowing and/or promoting adhesion of at least part of the first objects to the floor; providing a second part of the objects as effector cells, allowing and/or promoting adhesion of at least part of the second objects to the first objects; and studying at least one adhesion characteristic of at least some of the second objects to the first objects. The at least one adhesion characteristic may in particular comprise adhesion strength and/or also survival of the first and/or second object.

[0035] Adhesion of cells to each other may be indicative of cell-cell interaction. Thus, interaction between the cells can be studied. Due to the slanted side wall(s) effects of adhesion of the objects, e.g. effector cells to the target cells, may be studied as a function of shear flow force, also or alternatively, use of a liquid flow may facilitate sorting first and/or second objects, e.g. on the basis of adhesion under particular flow conditions. The sorting may comprise sorting on the basis of adhesion of the objects to the floor and/or on the basis of adhesion of part of the objects to another part of the objects, e.g. sorting effector cells on the basis of adhesion of the effector to target cells; weaker bound cells may become detached and entrained in the liquid flow and may be removed from (at least part of) the channel, whereas stronger bound cells may remain attached and in place in the channel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above-described aspects will hereafter be more explained with further details and benefits with reference to the drawings showing a number of embodiments by way of example.

Fig. 1 indicates a microfluidic flow cell;

Fig. 2 indicates a cross section of a traditional microfluidic flow cell;

Fig. 3 indicates a cross section of an improved microfluidic flow cell according to the present concepts;

Fig. 4 shows simulated results of shear flow force at a position between the floor and a side wall of an improved microfluidic flow cell according to the present concepts, as a function of the opening angle α (see also Fig. 3).

DETAILED DESCRIPTION OF EMBODIMENTS

[0037] It is noted that the drawings are schematic, not necessarily to scale and that details that are not required for understanding the present invention may have been omitted. The terms "upward", "downward", "below", "above", "left", "right" and the like relate to the embodiments as oriented in the drawings, unless otherwise specified. Further, elements that are at least substantially identical or that perform an at least substantially identical function are denoted by the same numeral, where helpful individualised with alphabetic suffixes.

[0038] Further, unless otherwise specified, terms like "detachable" and "removably connected" are intended to mean that respective parts may be disconnected essentially without damage or destruction of either part, e.g. excluding structures in which the parts are integral (e.g. welded or moulded as one piece), but including structures in which parts are attached by or as mated connectors, fasteners, releasable self-fastening features, etc. The verb "to facilitate" is intended to mean "to make easier and/or less complicated", rather than "to enable".

[0039] Fig. 1 shows a microfluidic sample holder 1 comprising a flow channel 3 for holding a liquid sample comprising a plurality of objects (not shown) via inlet/outlet connectors 5,7. The objects may in particular be cellular objects such as cells. The connectors 5, 7 define a flow path P through the channel 3 for liquid flown into the channel 3 via one of the connectors, e.g. 5, and removed from the channel via the other connector, e.g. 7. In some cases, not shown, a flow cell may comprise plural inlet/outlet connectors, in combination defining different flow paths.

[0040] Fig. 2 indicates a part of a channel 3 of a traditional microfluidic flow cell, being defined by four facets forming a floor 9, a ceiling 11 and opposite side walls 13, 15. The channel 3 has a rectangular cross section about the flow path P, the side walls 13, 15 extending perpendicular to the floor 9 and ceiling 11.

[0041] Fig. 3 shows a cross sectional view of a channel 103 of an improved microfluidic sample holder like sample holder 1 of Fig. 1. Here, part of the channel 103 is defined by a plurality of facets 109, 111, 113, 115, providing the channel 103 with a polygonal shape in cross section perpendicular to the flow path P. A first facet 109 forms a channel floor and adjacent second facets 113, 115 form channel side walls extending from the floor 109 at corners A, A' each at an opening angle α, α' of about 135 degrees. In the shown channel 103 the floor 109 and ceiling 111 are parallel and the channel 103 is left-right symmetric with α and α' being equal although in opposite directions (a middle of the floor 109 is indicated with the letter M). The floor 109 may have any suitable size, e.g. having a width W₁₀₉ in a range of 1,5 to 2,5 millimeters, e.g. 2,0 mm. The channel 103 has height H₁₀₃ typically in a range of 50-500 micrometer, e.g. about 100 micrometer. In the shown channel 103, the side walls 113, 115 span the height H₁₀₃ of the channel 103, providing a width W_S. The sizes of the channel 103, in particular the width W₁₀₉, may be selected for allowing microscopy of contents of the channel 103.

[0042] In Fig. 3, a direction of the force of gravity is indicated as F_Z for a preferred use orientation of the sample holder. In the corners A, A', a transition between the floor 109 and the side wall 113, 115 may be formed by a fillet (not shown) but preferably is as small as possible. An object such as a biological effector cell 200 (not to scale) may therefore lie on the floor 109 and not be obstructed at the corner A. An object 200a in contact with the side wall 113 will tend to travel down towards the floor 109 through gravity. If so desired, a controllable force such as acceleration in a centrifuge may be used as well. This may improve removal of objects 200a from the side walls 113, 115.

[0043] Part of the floor 109 is, as an option, provided with a functionalisation layer 117, which here is also provided with a layer of target cells 250 (not to scale), and part of a side wall 113 is provided with an antifouling layer 119 to which cells 200a tend not to adhere. Note that more or less such layers may be provided and that size and/or position of a functionalisation layer 117 and/or an antifouling layer 119 may differ from the ones indicated in Fig. 3, e.g. the floor being provided with plural different functionalisation layers, and/or both side walls and/or the ceiling being provided with one or more antifouling layers,

[0044] When a liquid is flown through the channel 103 along the flow path P, any objects 200, 200a may be entrained associated with the shear force experiences by the respective object 200, 200a. The shear force may separate objects from the surface to which they adhere, e.g. effector cells 200 adhering to target cells 250. Adhesion strength may be used to identify and possibly qualify cellular processes. The better the adhesion force may be known, the better and/or more useful information regarding adhesion behaviour, e.g. being indicative of cell-cell mechanics, may be obtained.

[0045] Fig. 4 shows simulated results of shear flow force at a position A between the floor 109 and a side wall 113 of a microfluidic flow cell according to Fig. 3 as a function of the opening angle α, and relative to a shear flow force in the middle of the floor 109. For the simulation, channel sizes are selected as follows (see Fig. 3) : W₁₀₉ = 2000 micrometer; H₁₀₃ = 100 micrometer; W_S = variable, spanning the height of the channel 103 as a hypotenuse between the floor 109 and the ceiling 111 depending on the angle α.

[0046] At an opening angle α of 90 degrees, the known configuration of Fig. 2 is achieved (and W_S = 0). An object (such as e.g. an effector cell) in the corner in such geometry will experience a shear flow force of less than 30% of the shear flow force experienced in the middle M of the floor 109, i.e. the flow force differs by well over 70% across the width of the floor 109.

[0047] Upon providing the side wall 113 at a larger opening angle α to the floor 109, the relative drop in shear flow force becomes less, i.e. the shear flow force differs less over the width of the floor 109 between positions A and M. At an angle α of 145 degrees, the shear flow force at the corner A is about 75% of the maximum force at or near position M, i.e. te shear flow force differs less than 25% across the width of the floor 109. Hence, homogeneity of the fore distribution is significantly increased.

[0048] A typical example of a method of using a sample holder according to the present concepts may comprise one or more of the following steps, see also Fig. 3.

[0049] A sample holder 103 as described herein may be provided with a functionalisation layer 117 formed by a polypeptide coating, or other coating promoting cell attachment, and possibly also being provided and with side walls coated with an antifouling layer 119. A thus prepared sample holder 103 may be shipped to a user. Inlet/outlet connectors to the channel 103 may be provided with closures, e.g. for one or more of protecting any layers 117, 119, preventing contamination, etc.

[0050] In such sample holder, target cells 200 may be introduced into the channel 103, in particular in a sample liquid. Due to the slanted side walls 113, 115 by the angle α, target cells 250 that sedimented initially onto the side walls 113, 115 (not shown but compare with cell 200a) roll down the side walls 113, 115 to end on the floor 109. This may be promoted by the antifouling layer 119 preventing adhesion of the target cell to the side wall. Collection of target cells 250 on the floor 109 (and any layer on that) may possibly be assisted by application of a controllable force towards the floor. The cells 250 are then optionally cultured for a while on the floor 109 in order to form a well-attached target cell layer.

[0051] Thereafter effector cells 200 may be introduced into the channel 103 and these may be allowed to attach, or: made to attach, to the target cells 250. Again the antifouling layer 119 and the slope of the side walls 113, 115 promote the effector cells 200a to land on the floor 109, and any layer on the floor 109, and prevent adhesion of effector cells to the side walls 113, 115. Then (the sample holder with) the effector cells 200 may be incubated for a desired period.

[0052] Then, if applicable after the optional incubation, sample liquid may be flown through the channel 103 along the flow path P, providing shear flow forces. By controlling the flow, a controllable force may be applied to the effector cells 200. This allows observing position stability and/or motion of effector cells, e.g. using optical detection such as involving (microscopy) imaging as a function of the flow and/or the shear flow force. The shear flow force may be sufficient to break adhesion between effector cells and target cells. Thus, effector cell - target cell binding strength may be measured qualitatively and/or quantitatively, allowing insight into cell-cell interaction. Also or alternatively, effector cells may be sorted based on the effector cell - target cell binding strength.

[0053] The reduced variation of the shear flow force provided by the present concepts compared to a traditional sample holder channel design, i.e. improved homogeneity of the shear flow force profile across the floor, allows for improved determination of the breaking force and/or improved sorting. Also or alternatively, increased homogeneity of the flow profile result in reduced velocity variations between objects entrained in the fluid flow and/or in reduced dispersion of objects entrained in the liquid flow. Thus, chances of re-settling of objects entrained in the liquid and/or any associated redistribution of objects may be reduced or prevented, and/or sorting of fractions of objects may be improved.

[0054] The disclosure is not restricted to the above-described embodiments which can be varied in a number of ways within the scope of the claims.

[0055] For instance, elements and aspects discussed for or in relation with a particular embodiment may be suitably combined with elements and aspects of other embodiments, unless explicitly stated otherwise.

Claims

1. A microfluidic sample holder comprising a flow channel (103) for holding a liquid sample comprising a plurality of objects (200, 200a), in particular cellular objects such as cells, and defining a flow path (P),

wherein at least part of the channel (103) is defined by a plurality of facets (109, 111, 113, 115), providing the channel (103) with a polygonal shape in cross section perpendicular to the flow path (P),

wherein a first facet (109) forms a channel floor and an adjacent second facet (113; 115) forms a channel side wall extending from the floor at an opening angle (α, α') in a range of 100-170 degrees, in particular in range of 110-160 degrees, more in particular in a range of 120-150 degrees, e.g. 130-140 degrees.

2. Microfluidic sample holder according to claim 1, wherein a transition between the floor (109) and the side wall (113, 115) is at most 10 micrometer, preferably at most 5 micrometers, more preferably at most 3 micrometers, most preferably about 1 micrometer.

3. Microfluidic sample holder according to any preceding claim, wherein a (the) transition between the floor (109) and the side wall (113, 115) is formed by a fillet having a fillet radius of curvature of at most 5 micrometers, preferably be at most 3 micrometers more preferably about 1 micrometer.

4. Microfluidic sample holder according to any preceding claim, wherein at least the floor (109) and the side wall (113, 115), preferably all channel facets (109, 111, 113, 115), are smooth to within 1 micrometer, preferably to within 0,1 micrometer such as to within 0,01 micrometer.

5. Microfluidic sample holder according to any preceding claim, wherein at least the first and second facet (109; 113, 115), possibly any facet, is plane, at length scales larger than 10 micrometer, preferably at length scales larger 5 micrometer, more preferably at length scales larger than 3 micrometer, most preferably larger than 1 micrometer, and/or at length scales larger than 100 micrometer, preferably at length scales larger than 1 millimeter, more preferably at length scales larger than 5 millimeter, most preferably larger than 10 millimeter.

6. Microfluidic sample holder according to any preceding claim, wherein at least part of the floor (109) and/or side wall (113, 115) is provided with one or more of a functionalisation layer, an antifouling layer, a target cell layer.

7. Assembly comprising the sample holder according to any preceding claim and comprising a liquid sample comprising a plurality of objects (200, 200a), in particular cellular objects such as cells.

8. Assembly according to claim 7, wherein the objects (200, 200a) have an average diameter; wherein a transition between the floor (109) and the side wall (113, 115) is at most 1/2 of the average diameter, preferably at most 1/3 more preferably about 1/4 of the average diameter.

9. Assembly according to any one of claims 7-8, wherein the objects (200, 200a) have an (the) average diameter;
wherein a (the) transition between the floor (109) and the side wall (113, 115) is formed by a fillet having a fillet radius of curvature of at most 1/3 of the average diameter, preferably at most 1/4, more preferably about 1/5 of the average diameter.

10. Assembly according to any one of claims 7-9, wherein the objects (200, 200a) have an (the) average diameter;
wherein at least the floor (109) and the side wall (113, 115), preferably all channel facets (109, 111, 113, 115), are smooth to within 0,1 times the average diameter, preferably to within 0,05 such as to within 0,02 or even 0,01 times the average diameter.

11. Assembly according to any one of claims 7-10, wherein at least part of the floor (109) and/or side wall (113, 115) is provided with one or more of a functionalisation layer (117), an antifouling layer (119), a target cell (250) layer; and wherein the objects (200, 200a) comprise target cells (250) and/or in case of a target cell layer (117; 250) comprise effector cells (200, 200a) interacting with target cells (250) of the target cell layer (117, 250).

12. Method comprising providing the assembly according to any one of claims 7-11, and providing a liquid sample flow through the channel (103) along the flow path (P), for urging the objects (200, 200a) through the channel (103).

13. Method according to claim 12, further comprising subjecting at least part of the assembly to a controllable force in a direction perpendicular to the floor (109) for urging the objects towards the floor (109) and/or away from the floor (109) .

14. Method according to any one of claims 12-13, comprising providing a first part of the objects (250) as target cells, allowing and/or promoting adhesion of at least part of the first objects (250) to the floor (109); providing a second part of the objects (200, 200a) as effector cells, allowing and/or promoting adhesion of at least part of the second objects (200) to the first objects (250); and studying at least one adhesion characteristic of at least some of the second objects (200) to the first objects (250).

15. Method according to any one of claims 12-14, further comprising sorting at least a part of the objects (200, 200a), preferably on the basis of adhesion of the objects (200, 200a) to the floor (109) and/or to another part of the objects (250) .

Drawing