Designing capillary tweezers for colloidal micromanipulation

Abstract

Disclosed herein is a device that includes a chamber including one or more walls defining a boundary and is configured to receive a first fluid, a second fluid, and an object. When the contact angle of the interface between the first fluid and the second fluid with the one or more walls is less than 90° and a density of the object is greater than the density of the first fluid, the interface is concave down at the object. When the contact angle of the interface is equal to or greater than 90° and the density of the object is less than the density of the first fluid, the interface is concave up at the object. A change in a shape of the boundary is configured to cause a movement of the object at the interface between the first fluid and the second fluid.

Description

DESIGNING CAPILLARY TWEEZERS FOR COLLOIDAL MICROMANIPULATIONCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application 63 / 599,956, filed November 16, 2023, the entirety of which is hereby incorporated by reference.COPYRIGHT NOTICE

[0002] This patent disclosure may contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves any and all copyright rights.FIELD OF THE INVENTION

[0003] The instant application relates to capillary tweezers for micro-manipulating microscale objects. In particular, the instant application relates to capillary tweezers that can be integrated with a microscope for observing the movement of the object.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0004] This invention was made with government support under 2011754 and 1541959 awarded by National Science Foundation (NSF). The government has certain rights in this invention.BACKGROUND

[0005] Optical tweezers are focused beams of light that are widely used to trap and manipulate colloidal particles in the fields of biological systems and engineering. However, optical tweezers have several drawbacks. Optical tweezers can be large, bulky, and cumbersome because they include various optical components and lasers. More importantly, their large and bulky setup can limit their application in microscopic studies because it is challenging to fit them under a microscope. Optical tweezers can be costly as well because they employ expensive optical components (e.g., expensive high NA objective lenses) andlaser. The laser power used for trapping objects can be too high, especially for micrometerscale (z.e., microscale) samples, causing damage to the samples. In addition, optical tweezer can be a high-maintenance system because the optical components and laser need regular alignment and service. Furthermore, optical tweezers can be suitable for manipulating only one particle at a time. Thus, there remains a need for low-cost and / or non-destructive methods to manipulate microscale objects.SUMMARY

[0006] In one aspect, a device includes a chamber including one or more walls defining a boundary, wherein the chamber is configured to receive a first fluid, a second fluid, and a first object, wherein an interface between the first fluid and the second fluid forms a contact angle with the one or more walls, the contact angle measured along the direction of the first fluid, wherein the device is configured such that at least one of (a) and (b) occurs: (a) when the contact angle is less than 90° and a density of the first object is greater than the density of the first fluid, the interface between the first fluid and the second fluid is concave down at the first object, and (b) when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid, the interface between the first fluid and the second fluid is concave up at the first object, and wherein a change in a shape of the boundary is configured to cause a movement of the first object at the interface between the first fluid and the second fluid, wherein the movement of the first object is confined within the boundary.

[0007] In some embodiments, the movement of the first object includes one or more of a trapping of the first object at a location, a translation of the object, and a rotation of the first object.

[0008] In some embodiments, the movement of the first object includes a trapping of the first object a) at a vertically lowest point on the interface between the first fluid and the second fluid within the boundary, when the contact angle is less than 90° and the density of the first object is greater than the density of the first fluid or b) at a vertically highest point on the interface between the first fluid and the second fluid within the boundary, when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid.

[0009] In some embodiments, the boundary has a width of about 1-3 mm.

[0010] In some embodiments, the boundary has a width of about 1-2 mm.

[0011] In some embodiments, the boundary has a width that is less than or about a capillary length of the interface between the first fluid and the second fluid.

[0012] In some embodiments, the boundary has a width that is less than or equal to 1.1 times a capillary length of the interface between the first fluid and the second fluid.

[0013] In some embodiments, the boundary has a width that is less than or equal to a capillary length of the interface between the first fluid and the second fluid.

[0014] In some embodiments, wherein the shape of the boundary includes a circle, an oval, a triangle, a square, a rectangle, a quadrilateral, a polygon, a rounded triangle, a rounded square, a rounded rectangle, a rounded quadrilateral, a rounded polygon, a circular arc, or a polynomial curve.

[0015] In some embodiments, a force is applied to at least one of the one or more walls to cause the change in the shape of the boundary.

[0016] In some embodiments, the device includes one or more actuators, the one or more actuators operatively connected to at least one of the one or more walls, wherein the one or more actuators, when actuated, is configured to cause a change in a geometry of the one or more walls, causing the change in the shape of the boundary.

[0017] In some embodiments, the device includes a manipulator disposed outside the chamber, the manipulator attached to the one or more actuators, wherein a first movement of the manipulator is configured to cause a second movement of the one or more actuators.

[0018] In some embodiments, the change in the geometry of the one or more walls includes a deformation of at least one of the one or more walls.

[0019] In some embodiments, the change in the geometry of the one or more walls includes one or more of a translation or a rotation of at least one of the one or more walls.

[0020] In some embodiments, the actuation of the one or more actuators includes applying one or more of a mechanical force, an electric potential, an electric current, a magnetic force, a pneumatic pressure, or a hydraulic pressure.

[0021] In some embodiments, at least one of the one or more actuators includes a piezoelectric actuator or a linear force actuator.

[0022] In some embodiments, based on the movement of the first object, a dynamic property of the first object is determined.

[0023] In some embodiments, the actuation of the one or more actuators exerts a force on the first object that is between 1-10 pico Newton.

[0024] In some embodiments, the movement of the first object causes a trapping or a movement of a second object physically connected to the first object.

[0025] In some embodiments, the movement of the first object exerts a force on a second object physically connected to the first object.

[0026] In some embodiments, the one or more actuators includes two actuators.

[0027] In some embodiments, the one or more actuators includes three actuators.

[0028] In some embodiments, the one or more actuators includes four actuators.

[0029] In some embodiments, each wall is connected to at least one actuator.

[0030] In some embodiments, the one or more actuators have a thickness of about 0.5 to about 1 mm.

[0031] In some embodiments, an actuator of the one or more actuators includes one or more supports to reduce a capillary attraction from the other actuators.

[0032] In some embodiments, the one or more supports have a thickness of about 0.5 mm to about 1 mm.

[0033] In some embodiments, the contact angle that the interface between the first fluid and the second fluid forms with the one or more walls is 20-80°.

[0034] In some embodiments, the contact angle that the interface between the first fluid and the second fluid forms with the one or more walls is 50-70°.

[0035] In some embodiments, the one or more walls includes a hydrophilic surface and the first object includes a hydrophobic surface.

[0036] In some embodiments, the one or more walls includes a deformable material.

[0037] In some embodiments, wherein the one or more walls includes an elastomeric material.

[0038] In some embodiments, the one or more walls includes a rigid material.

[0039] In some embodiments, the one or more walls includes a material selected from a group consisting of an elastomeric polymer, polydimethylsiloxane (PDMS), or Formlabs elastic 50A resin, hydrogels, silicone, rubber, polyurethane, or a combination thereof.

[0040] In some embodiments, the one or more walls includes a material selected from a group consisting of a thermoset polymer, polycarbonate, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), or a combination thereof.

[0041] In some embodiments, the one or more walls includes a material selected from a group consisting of a metal, an alloy, a ceramic, or a combination thereof.

[0042] In some embodiments, the first object is selected from a group consisting of polystyrene, silica, or a combination thereof.

[0043] In some embodiments, the first object includes a colloidal particle.

[0044] In some embodiments, the colloidal particle is selected from a group consisting of polystyrene, silica, polymethyl methacrylate (PMMA), glass microspheres, metal microspheres, or a combination thereof.

[0045] In some embodiments, the first object includes an aerosol.

[0046] In some embodiments, the aerosol is selected from a group consisting of hydrocarbons, alkanes, aromatic hydrocarbons, fumed silica, ice crystals, or a combination thereof.

[0047] In some embodiments, the first object includes a biological cell.

[0048] In some embodiments, the biological cell is selected from a group consisting of blood cell, bone cell, stem cell, bacteria, sperm cell, muscle cell, oocyte, neuron, epithelial cell, plant cells, protoplasts, or a combination thereof.

[0049] In some embodiments, the first object has a shape of a bead, a microbead, a sphere, a microsphere, a cylinder, a rod, or a prismoid.

[0050] In some embodiments, the first object has a size of 1-100 pm.

[0051] In some embodiments, the first object has a size of 20-50 pm.

[0052] In some embodiments, the first fluid includes bodily fluid.

[0053] In some embodiments, the first fluid includes water.

[0054] In some embodiments, the first fluid includes a polar liquid.

[0055] In some embodiments, the polar liquid is selected from a group consisting of water, alcohols, ketones, formamide, dimethyl formamide, dimethyl sulfoxide, or a combination thereof.

[0056] In some embodiments, the first fluid includes a nonpolar liquid.

[0057] In some embodiments, the nonpolar liquid is selected from a group consisting of oils, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, fluorinated oils, or a combination thereof.

[0058] In some embodiments, the second fluid includes air.

[0059] In some embodiments, the second fluid includes an oil.

[0060] In some embodiments, the oil is selected from a group consisting of mineral oil, paraffin oil, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, or a combination thereof.

[0061] In some embodiments, a refractive index of the second fluid is matched with the refractive index of the first fluid.

[0062] In some embodiments, the second object is selected from a group consisting of biological cells, colloidal particles, nanoparticles, DNA cell molecules, bacteria, viruses, kinesin motors, microtubules, organelles, chromatin, proteins, or a combination thereof.

[0063] In some embodiments, the device includes a volume chamber, fluidically connected to the chamber.

[0064] In some embodiments, the change in the shape of the boundary does not cause a change in a height of the interface between the first fluid and the second fluid within the chamber.

[0065] In some embodiments, the one or more actuators are at least partially disposed within the volume chamber.

[0066] In some embodiments, the movement of the one or more of the first object and the second object is configured to be observable under a microscope.

[0067] In some embodiments, when the one or more actuators is not actuated, the one or more walls has the geometry of an original geometry and the boundary has the shape of an original shape.

[0068] In one aspect, a system includes a plurality of microfluidic chambers; and a plurality of devices, each of the plurality of the devices fluidically connected to one of the plurality of the microfluidic chambers such that each device is configured to receive the first fluid, the second fluid, and the first object.

[0069] In one aspect, a method includes receiving a first fluid, a second fluid, and a first object in a chamber, wherein the chamber includes one or more walls defining a boundary; and changing a shape of the boundary to cause a movement of the first object at the interface between the first fluid and the second fluid, wherein an interface between the first fluid and the second fluid forms a contact angle with the one or more walls, the contact angle measured along the direction of the first fluid, wherein at least one of (a) and (b) occurs: (a) when the contact angle is than 90° and a density of the first object is greater than the density of the first fluid, the interface between the first fluid and the second fluid is concave down at the first object, and (b) when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid, the interface between the first fluid and the second fluid is concave up at the first object, and wherein the movement of the first object is confined within the boundary.

[0070] In some embodiments, the movement of the first object includes one or more of a trapping of the first object at a location, a translation of the object, and a rotation of the first object.

[0071] In some embodiments, the movement of the first object includes a trapping of the first object a) at a vertically lowest point on the interface between the first fluid and the second fluid within the boundary, when the contact angle is less than 90° and the density of the first object is greater than the density of the first fluid or b) at a vertically highest point on the interface between the first fluid and the second fluid within the boundary, when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid.

[0072] In some embodiments, the boundary has a width of about 1-3 mm.

[0073] In some embodiments, the boundary has a width of about 1-2 mm.

[0074] In some embodiments, the boundary has a width that is less than or about a capillary length of the interface between the first fluid and the second fluid.

[0075] In some embodiments, the boundary has a width that is less than or equal to 1.1 times a capillary length of the interface between the first fluid and the second fluid.

[0076] In some embodiments, the boundary has a width that is less than or equal to a capillary length of the interface between the first fluid and the second fluid.

[0077] In some embodiments, the shape of the boundary includes a circle, an oval, a triangle, a square, a rectangle, a quadrilateral, a polygon, a rounded triangle, a rounded square, a rounded rectangle, a rounded quadrilateral, a rounded polygon, a circular arc, or a polynomial curve.

[0078] In some embodiments, the method includes applying a force to at least one of the one or more walls to cause the change in the shape of the boundary.

[0079] In some embodiments, the method includes actuating one or more actuators to cause a change in a geometry of the one or more walls, causing the change in the shape of the boundary, wherein the one or more actuators is operatively connected to at least one of the one or more walls

[0080] In some embodiments, the method includes causing a first movement of a manipulator to cause a second movement of the one or more actuators, wherein the manipulator is disposed outside the chamber, wherein the manipulator is attached to the one or more actuators,

[0081] In some embodiments, the change in the geometry of the one or more walls includes a deformation of at least one of the one or more walls.

[0082] In some embodiments, the change in the geometry of the one or more walls includes one or more of a translation or a rotation of at least one of the one or more walls.

[0083] In some embodiments, the actuating the one or more actuators includes applying one or more of a mechanical force, an electric potential, an electric current, a magnetic force, a pneumatic pressure, or a hydraulic pressure.

[0084] In some embodiments, at least one of the one or more actuators includes a piezoelectric actuator or a linear force actuator.

[0085] In some embodiments, the method includes determining a dynamic property of the first object based on the movement of the first object.

[0086] In some embodiments, the actuating the one or more actuators exerts a force on the first object that is between 1-10 pico Newton.

[0087] In some embodiments, the movement of the first object causes a trapping or a movement of a second object physically connected to the first object.

[0088] In some embodiments, the movement of the first object exerts a force on a second object physically connected to the first object.

[0089] In some embodiments, the one or more actuators includes two actuators.

[0090] In some embodiments, the one or more actuators includes three actuators.

[0091] In some embodiments, the one or more actuators includes four actuators.

[0092] In some embodiments, each wall is connected to at least one actuator.

[0093] In some embodiments, the one or more actuators have a thickness of about 0.5 to about 1 mm.

[0094] In some embodiments, an actuator of the one or more actuators includes one or more supports to reduce a capillary attraction from the other actuators.

[0095] In some embodiments, the one or more supports have a thickness of about 0.5 mm to about 1 mm.

[0096] In some embodiments, the contact angle that the interface between the first fluid and the second fluid forms with the one or more walls is 20-80°.

[0097] In some embodiments, the contact angle that the interface between the first fluid and the second fluid forms with the one or more walls is 50-70°.

[0098] In some embodiments, the one or more walls includes a hydrophilic surface and the first object includes a hydrophobic surface.

[0099] In some embodiments, the one or more walls includes a deformable material.

[0100] In some embodiments, the one or more walls includes an elastomeric material.

[0101] In some embodiments, the one or more walls includes a rigid material.

[0102] In some embodiments, the one or more walls includes a material selected from a group consisting of an elastomeric polymer, polydimethylsiloxane (PDMS), or Formlabs elastic 50A resin, hydrogels, silicone, rubber, polyurethane, or a combination thereof.

[0103] In some embodiments, the one or more walls includes a material selected from a group consisting of a thermoset polymer, polycarbonate, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), or a combination thereof.

[0104] In some embodiments, the one or more walls includes a material selected from a group consisting of a metal, an alloy, a ceramic, or a combination thereof.

[0105] In some embodiments, the first object is selected from a group consisting of polystyrene, silica, or a combination thereof.

[0106] In some embodiments, the first object includes a colloidal particle.

[0107] In some embodiments, the colloidal particle is selected from a group consisting of polystyrene, silica, polymethyl methacrylate (PMMA), glass microspheres, metal microspheres, or a combination thereof.

[0108] In some embodiments, the first object includes an aerosol.

[0109] In some embodiments, the aerosol is selected from a group consisting of hydrocarbons, alkanes, aromatic hydrocarbons, fumed silica, ice crystals, or a combination thereof.

[0110] In some embodiments, wherein the first object includes a biological cell.[OHl] In some embodiments, the biological cell is selected from a group consisting of blood cell, bone cell, stem cell, bacteria, sperm cell, muscle cell, oocyte, neuron, epithelial cell, plant cells, protoplasts, or a combination thereof.

[0112] In some embodiments, the first object has a shape of a bead, a microbead, a sphere, a microsphere, a cylinder, a rod, or a prismoid.

[0113] In some embodiments, the first object has a size of 1-100 pm.

[0114] In some embodiments, the first object has a size of 20-50 pm.

[0115] In some embodiments, the first fluid includes bodily fluid.

[0116] In some embodiments, the first fluid includes water.

[0117] In some embodiments, the first fluid includes a polar liquid.

[0118] In some embodiments, the polar liquid is selected from a group consisting of water, alcohols, ketones, formamide, dimethyl formamide, dimethyl sulfoxide, or a combination thereof.

[0119] In some embodiments, the first fluid includes a nonpolar liquid.

[0120] In some embodiments, the nonpolar liquid is selected from a group consisting of oils, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, fluorinated oils, or a combination thereof.

[0121] In some embodiments, the second fluid includes air.

[0122] In some embodiments, the second fluid includes an oil.

[0123] In some embodiments, the oil is selected from a group consisting of mineral oil, paraffin oil, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, or a combination thereof.

[0124] In some embodiments, wherein a refractive index of the second fluid is matched with the refractive index of the first fluid.

[0125] In some embodiments, the second object is selected from a group consisting of biological cells, colloidal particles, nanoparticles, DNA cell molecules, bacteria, viruses, kinesin motors, microtubules, organelles, chromatin, proteins, or a combination thereof.

[0126] In some embodiments, the chamber is fluidically connected to a volume chamber.

[0127] In some embodiments, the change in the shape of the boundary does not cause a change in a height of the interface between the first fluid and the second fluid within the chamber.

[0128] In some embodiments, the one or more actuators are at least partially disposed within the volume chamber.

[0129] In some embodiments, the method includes observing the movement of the one or more of the first object and the second object under a microscope.

[0130] In some embodiments, when the one or more actuators is not actuated, the one or more walls has the geometry of an original geometry and the boundary has the shape of an original shape.

[0131] Any one of the embodiments disclosed herein may be properly combined with any other embodiment disclosed herein. The combination of any one of the embodiments disclosed herein with any other embodiments disclosed herein is expressly contemplated.BRIEF DESCRIPTION OF THE DRAWINGS

[0132] The objects and advantages will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

[0133] FIGS. 1 A-1C show schematics of a capillary tweezer, according to certain embodiments.

[0134] FIG. 2 shows a capillary tweezer for trapping an object, according to certain embodiments.

[0135] FIGS. 3 A-3B show schematics of a capillary tweezer for trapping and manipulating movement of microscale objects, according to certain embodiments.

[0136] FIG. 4 shows an integrated device combining microfluidics and capillary tweezers, according to certain embodiments.

[0137] FIG. 5 shows a schematic of a fluid droplet on a flat surface forming a contact angle, according to certain embodiments.

[0138] FIGS. 6A-B show a schematic of a capillary tweezer, according to certain embodiments.

[0139] FIGS. 7A-7D show schematics of a top view of a capillary tweezer, according to certain embodiments.

[0140] FIGS. 8A-8D show schematics of a side view of a capillary tweezer, according to certain embodiments.

[0141] FIGS. 9A-9E show perspective views of capillary tweezers including one or more actuators, according to certain embodiments.

[0142] FIGS. 10A-10C show schematics of capillary tweezers including one or more actuators, according to certain embodiments.

[0143] FIG. 11 shows design process for creating molds for capillary tweezers, according to certain embodiments.

[0144] FIGS. 12A-12C show design of modular molding system for fabricating capillary tweezers, according to certain embodiments.

[0145] FIG. 13 shows design process for creating directly printed capillary tweezers, according to certain embodiments.

[0146] FIGS. 14A-14D show designs of capillary tweezers fabricated using 50A resin, according to certain embodiments.

[0147] FIG. 15A shows a schematic of a top view of a capillary tweezer fabricated using soft lithography, according to certain embodiments.

[0148] FIG. 15B shows a schematic of a side view of a capillary tweezer fabricated using soft lithography, according to certain embodiments.

[0149] FIG. 15C shows a capillary tweezer on a glass coverslip fabricated using soft lithography, according to certain embodiments.

[0150] FIGS. 16A-16C show process steps for fabricating a capillary tweezer using soft lithography, according to certain embodiments.

[0151] FIGS. 17A-17I show fabricated capillary tweezers, according to certain embodiments.

[0152] FIGS. 18A-18B show schematics of capillary tweezers with and without a fabricated bottom, according to certain embodiments.

[0153] FIGS. 19A-19C show designs of capillary tweezers for preventing fluid or water leakage, according to certain embodiments.

[0154] FIG. 20 shows contact angle measurement on exemplary capillary tweezer samples, according to certain embodiments.

[0155] FIG. 21 shows measured contact angles of PDMS samples, according to certain embodiments.

[0156] FIG. 22 shows evaporation of water in fabricated chambers, according to certain embodiments.

[0157] FIGS. 23 A-23B show measured surface tension of water with materials used for fabricated capillary tweezers, according to certain embodiments.

[0158] FIG. 24 shows process for depositing objects inside the chamber of a capillary tweezer, according to certain embodiments.

[0159] FIGS. 25A-25C show self-assembly, as observed by a microscope, of 50 pm silica objects inside the chambers of a capillary tweezer, according to certain embodiments.

[0160] FIG. 26A-26F show trapping, as observed by a microscope, of a single 20 pm polystyrene bead inside the chamber of a capillary tweezer, according to certain embodiments.

[0161] FIG. 27 shows displacement relative to originally trapped position of a single 20 pm polystyrene bead inside a capillary tweezer after the bead is disturbed from its original trapped position, according to certain embodiments.

[0162] FIGS. 28A-28B show self-assembly of 50 micron and 20 micron silica bead rafts inside a capillary tweezers, as observed by a microscope, according to certain embodiments.

[0163] FIGS. 29A-29D show rotation of a raft of 50 micron objects inside a capillary tweezer, as observed by a microscope, according to certain embodiments.

[0164] FIGS. 30A-30B show movement of a raft of 50 micron silica beads inside a capillary tweezer, as observed by a microscope, according to certain embodiments.

[0165] FIG. 30C shows calculated net forces of the raft, according to certain embodiments.

[0166] FIGS. 31 A-31C show the displacement of a raft of 50 micron objects inside a capillary tweezer, as observed by a microscope, according to certain embodiments.

[0167] FIGS. 32 shows displacement of a single 20 micron object inside a capillary tweezer, according to certain embodiments.DETAILED DESCRIPTION

[0168] The present disclosure describes a device including a chamber. In some embodiments, the chamber can include one or more walls defining a boundary. In some embodiments, the chamber can receive a first fluid, a second fluid, and a first object. In some embodiments, an interface between the first fluid and the second fluid can form a contact angle with the one or more walls such that the contact angle is measured along the direction of the first fluid. In some embodiments, the device can be configured such that at least one of (a) and (b) occurs: (a) when the contact angle is less than 90° and a density of the first object is greater than the density of the first fluid, the interface between the first fluid and the second fluid is concave down at the first object, and (b) when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid, the interface between the first fluid and the second fluid is concave up at the first object. In some embodiments, a change in a shape of the boundary can cause a movement of the first object at the interface between the first fluid and the second fluid. In some embodiments, the movement of the first object can be confined within the boundary.

[0169] The present disclosure describes a capillary tweezer (e.g., a capillary machine, a capillary manipulator) for trapping and manipulating the movement of an object floating on the surface of a fluid or at an interface between two fluids. In some embodiments, the capillary tweezers disclosed herein can trap and move the object by changing a shape of a boundary of the fluid. In some embodiments, the change in the shape of the boundary of the fluid causes a change in the capillary forces on the object floating on the surface of the fluid, which can be used to trap or manipulate the movement of the object. In some embodiments, the object can have a size between about 100 nm to 1 mm. In some embodiments, the object can be micrometer-scale (e.g., microscale). In some embodiments, the capillary tweezer disclosed herein can be integrated with an optical microscope for observing the movement of the object as it is being trapped or manipulated.

[0170] To study microscopic biological systems, it is important to have the ability to trap and manipulate the movement of microscopic objects (e.g., particles). One method oftrapping and manipulating microscopic systems is optical tweezers, which are able to trap a single microscopic object at the focal spot of a single laser.

[0171] Despite their use in single-particle research, optical tweezers have several drawbacks. Optical tweezers are often large, bulky, and cumbersome because the setups need to include various optical elements to guide the laser through the sample and create focus. The optical elements and requirement of a laser make the optical tweezer setup more expensive as well. Besides these considerations, “optocution” or two-photon absorption can occur when the laser power is too high, resulting in the biological samples underneath the laser to be damaged.

[0172] 3D machines can be assembled that use capillary forces to manipulate the motion of objects (e.g., floats, particles) floating at an interface between two fluids. By controlling the wettability of these machines, repulsive capillary forces are created between the floating object and the walls of the 3D machine. By varying the shape of the boundary around the floating object, the position of the object in a 2D interface between two fluids can be changed. In some embodiments, various such machines can be made that can rotate and translate objects. Complex compound machines can be built that can manipulate multiple objects at once. Centimeter-scale machines can manipulate microscale objects, or clusters of objects, and can make braids with non-repeating topology out of micrometer-scale filaments. Capillary-based manipulators are distinct from other manipulators such as optical or magnetic tweezers in the fact that the manipulated objects are coupled via a meniscus of the fluid, rather than by an optical or magnetic field. Because of this coupling effect, the shape of the chamber (e.g., a container, a channel), containing the water and floating objects, can be made on the order of the capillary length-scale (which is about a few millimeters for water), while still allowing for the manipulation of a micrometer-scale object.

[0173] While the chamber of the 3D machines can be of the order of a few millimeters to a centimeter, 3D machines with total dimensions on the order of centimeters can be unsuitable for observing the trapping or manipulation of a particle under a microscope. The present disclosure describes capillary tweezers that can have a height on the order of millimeters, such that they can fit between the optical elements and the base of the microscope.

[0174] The present disclosure describes systems, called capillary tweezers, that can manipulate and direct the assembly of microscale objects, including colloidal particles. The capillary tweezers disclosed herein can be small, simple in design, and easy to use as they utilize a chamber and a fluid, in which the microscale objects are deposited, for trapping andmanipulating the objects. In some embodiments, the capillary tweezers can be of millimeter (mm) or sub-mm height, allowing them to be integrated with or fit under a microscope to observe the trapping and manipulation of microscale objects. In some embodiments, the capillary tweezers can be easily and rapidly fabricated using simple 3D printing or soft lithography, which also results in low production cost. In some embodiments, the capillary tweezers can provide a non-destructive method for trapping and manipulating an object (e.g., a particle) because the capillary forces used to trap or manipulate the object do not damage the object, in contrast to high-power laser that can damage the sample in the optical tweezers. In some embodiments, the capillary tweezers can be used for trapping and manipulating a single object as well as multiple objects (e.g., aggregation of particles).

[0175] In some embodiments, by tracking the movement of the objects as they are trapped and manipulated, the capillary tweezers can be used to determine the stiffness and damping factor of trapping and manipulation processes.

[0176] In some embodiments, the capillary tweezers can be integrated with microfluidic devices for lab-on-a-chip and high-throughput applications.

[0177] In some embodiments, the capillary tweezers can be employed in applications including single-molecule measurements, cellular biophysics, measurements of colloidal interactions, microrheology, and the directed assembly of micrometer-scale structures.

[0178] The present disclosure describes capillary tweezers that can trap or manipulate movement of a single object (e.g., a single colloidal particle) in a system having dimensions such that the object can simultaneously be observed (e.g., viewed, imaged, or tracked) under a microscope.

[0179] In some embodiments, the present disclosure describes trapping and manipulating the movement of microscopic objects underneath a microscope for single-particle research. In some embodiments, the millimeter-size capillary tweezer can be used to manipulate the movement of a single micro-scale object (e.g., a particle). For example, the millimeter-size capillary tweezer can be used to manipulate the movement of a single colloidal particle. In some embodiments, the millimeter-size capillary tweezer can be used to manipulate the movement of multiple micro-scale objects. In some embodiments, the capillary tweezer can be used for biophysics applications, for example, for the measurement of spring constants in molecules, manipulation and measurement of the stretching of DNA, and parallelization of experiments. In some embodiments, the capillary tweezer can be built inexpensively and quickly, providing a cheaper and easier to use alternative than optical tweezers. In someembodiments, the application of capillary effects for the manipulation and trapping of microscopic objects can be performed underneath a microscope.

[0180] In some embodiments, the capillary tweezer can manipulate and direct the assembly of micrometer-scale colloidal particles. In some embodiments, a capillary tweezer can be an alternative to optical tweezers that can be used in lab-on-a-chip and high- throughput applications.

[0181] FIGS. 1 A-1C illustrate an exemplary capillary tweezer 100 that uses repulsive capillary forces to trap an object 112 (“floating object”, “float”). In some embodiments, capillary tweezer 100 can include a chamber (e.g., a container, a channel) 102 containing a first fluid 108 and a second fluid 110 forming an interface 120 with the first fluid 108. In some embodiments, capillary tweezer 100 can use water as the first fluid 108 and air as the second fluid 110. Repulsive capillary forces can arise when two objects deform a liquid interface in opposite ways: one bends the interface upward and the other downward. The force is repulsive because the total energy (interfacial and gravitational potential) of the system increases when the two objects approach. As shown in FIG. 1 A, the capillary tweezer 100 forms a meniscus in a container 102 (e.g. a cylindrical container) with size (e.g., diameter) comparable to the capillary length lc= (y / Apg)1 / 2, where y is the interfacial tension, Ap the density difference between the two fluids 108 and 110 and g is the acceleration due to gravity (Zc~2.7 mm for a water-air interface). As shown in FIG. IB, object 112 is then placed at the interface 120. In some embodiments, object 112 can have a dimension of around 1 mm. A repulsive capillary force between the wall 104 and object 112 can arise if the container 102 is hydrophilic, such that it bends the interface upward, and if the object 112 is denser than first fluid 108 but remains bound to the interface by surface tension, such that the object 112 bends the interface 120 downward. As shown in FIG. 1C, displacing the object 112 from its equilibrium position (e.g., the center of the chamber 102) can then give rise to a restoring force that moves the object back to the equilibrium position (e.g., the center of the chamber 102). The restoring force can arise because the walls 104 repel the object 112. The tweezer 100 can work if the inner diameter of the container is not significantly larger than lc. If the inner diameter is significantly larger than Zc, the object 112 does not “feel” the capillary forces of the wall 104.

[0182] FIG. 2 shows a non-limiting example of a capillary tweezer trapping a millimeterscale object.

[0183] The present disclosure describes capillary tweezers for exerting forces on micrometer-scale objects, in addition to the millimeter-scale objects (e.g., floats) as shown in FIG. 2. For example, as shown in FIGS. 3A-3B, the capillary tweezer 300 can be used to trap and manipulate a microscale object 312 at an interface 320 of the first fluid 308 and the second fluid 310 by deforming a boundary 306 of chamber 302 or by otherwise changing the shape of a boundary 306. In some embodiments, microscale object 312 can include colloidal particles. In some embodiments, the microscopic object 312 can have a size of about 10 pm. In some embodiments, boundary 306 can be deformed by applying a force on chamber wall 304. In some embodiments, deforming the boundary 306 can apply a force on the object 312.

[0184] In some embodiments, microscale object 312 can bind to and deform the interface with first fluid 308. In some embodiments, the capillary tweezers 300 can be made of deformable soft material (FIG. 3B).

[0185] In some embodiements, because interfacial deformations are long-ranged, a capillary tweezer that manipulates micrometer-scale objects can be millimeter-scale. In some embodiments, the capillary tweezer can be made through inexpensive approaches such as 3D printing, soft lithography, or large-scale fabrication methods such as roll-to-roll processing.

[0186] FIG. 4 shows an exemplary device 40 including multiple capillary tweezers 400 and a plurality of microfluidic chambers (e.g., microfluidic containers, microfluidic channels). In some embodiments, a device 40 including multiple capillary tweezers 400 can be integrated into a microfluidic device. In some embodiments, in the device 40, the flow through any microfluidic chamber 420 can be diverted to a capillary tweezer 400. The tweezer 400 can then be used for manipulation of objects, e.g., directed assembly or measurement of objects 412. For example, the interfacial rheology can be measured by tracking fluctuations in the positions of the trapped particles 412. In some embodiments, integrated device 40 can include an array of capillary tweezers 400.A. Theoretical Principles1. Basic capillary physics

[0187] The capillary tweezers disclosed herein apply capillary physics to a device configured to move or manipulate an object at an interface. In the capillary tweezers disclosed herein, an object floating at the interface of two fluids inside a chamber (e.g., a container, a channel) can be subject to at least two types of forces that arise from interfacialtension: a force that binds the object (e.g., colloidal particle) to the interface and lateral capillary forces between the object and the boundaries of the chamber.

[0188] If one molecule has a total cohesion energy of U when it is fully surrounded by the molecules of a fluid, the molecule will have an approximate cohesion energy of U / 2 when it is located at an interface between the fluid and air (e.g., a liquid / air interface). If a is the molecule’s size and therefore a2its approximate exposed area, the surface tension is on the order of y ~ UHa1. For water, in which molecules are bonded by hydrogen bonds, its surface tension is y ~ 72 mJ / m2. Surface tension can also be defined as the increase in internal energy U or in free energy F with an increase in surface area, A, with temperature T, volume V, and number of molecules n held constant:

[0189] FIG. 5 depicts a schematic of a fluid droplet 508 placed on a flat surface of a solid 504. In some embodiments, a first fluid 508 can form a fluid-fluid interface 520 with a second fluid 510. In some embodiments, first fluid 508 can include a liquid. In some embodiments, a second fluid 510 can include air, gas, vapor, or liquid. In some embodiments, solid 504 can form a solid-fluid interface 530 (shown as dotted line) with the first fluid 508. In some embodiments, a contact point 540 can be a point where solid 504, first fluid 508, and second fluid 510 meet. In some embodiments, a first tangent on the fluidfluid interface 520 at the contact point 540 (shown by an arrow 542) and a second tangent on the solid-fluid interface 530 at contact point 540 (shown by an arrow 544) can form an angle 0, which is referred to as the contact angle hereinafter. In the present disclosure, the contact angle (e.g., angle ff) of first fluid 508 with solid 504 is the angle between the first tangent 542 and the second tangent 544 measured along the direction of the first fluid 508. In some embodiments, the fluid-fluid interface 520 of first fluid 508 and second fluid 510 can be a meniscus or a surface curvature of the interface. In some embodiments, depending on the type of surface interface, first fluid 508 can be considered wetting or non-wetting. For example, for a wetting fluid, the contact angle 0 < 90°, while for a non-wetting fluid the contact angle Q > 90°. In some embodiments, this contact angle can be derived theoretically using the law of Young-Dupre.

[0190] In a tube or other type of chamber, the pinning of a fluid meniscus at the chamber wall with a certain contact angle can create a curved interface. This curved interface can in turn create a pressure difference between the inside and outside of the fluid. This phenomenon can be described by Laplace’s Theorem, which states that the increase inhydrostatic pressure A / ? that takes place the moment a fluid / fluid or a fluid / gas interface is passed is equal to the product of the surface tension y and the surface curvature C,where R and R’ are the principal radii of the curved interface.

[0191] This effect can cause wetting fluids to rise within tubes, as the surface geometry creates an under-pressure in the fluid. There exist length-scales at which the capillary effects are dominant. Beyond these length-scales, gravity becomes more important. This capillary length, denoted K-1is given byK-1= v / pg - O) where g is gravity, y is the interfacial tension of the fluid-fluid interface and p is the difference in density of the two fluids. For an air-water interface, the capillary length is about 2.7 mm. The capillary length of an oil-water interface can differ from that of an airwater interface based on differences in the interfacial tension between the two fluids and the difference in density between the two fluids.2. Capillary trapping

[0192] FIGS. 6A-B illustrates an exemplary capillary machine or capillary tweezer 600 that can combine the effects of surface tension, gravity / normal and hydrostatic forces to trap an object.

[0193] In some embodiments, an object (e.g., float, floating object, particle) 612 can be trapped at an interface 620 between a first fluid 608 and a second fluid 610. In some embodiments, object 612 is a hydrophobic particle. In some embodiments, object 612 can be a heavy hydrophilic particle that bends the interface 620 downwards but remains at the interface 620 due to the surface tension of first fluid 608. In some embodiments, first fluid 608 can include water and second fluid 610 can include air. In some embodiments, the walls 604 of the chamber (e.g., a container, a channel) 602 can be made hydrophilic such that the interface 620 bends upwards at the chamber wall 604. In some embodiments, to have a stable system, the interface 620 at the wall 604 bends upwards and the interface at the object 612 bends downwards (FIG. 6A). In some embodiments, to have a stable system, the interface 620 at the wall 604 bends downwards and the interface at the object 612 bends upwards (FIG. 6B). In some embodiments, the interface 620 of the first fluid 608 and second fluid 610 at the wall 604 can form a first surface curvature and the interface 620 of the first fluid 608 and second fluid 610 at the object 612 can form a second surface curvature. In someembodiments, the first surface curvature can be correlated to a contact angle between the wall 604 with the interface 620 of the first fluid 608 and the second fluid 610. In some embodiments, the second surface curvature can be correlated to a contact angle between the object 612 with the interface 620 of the first fluid 608 and the second fluid 610.

[0194] In some embodiments, the interface 620 of the first fluid 608 and second fluid 610 at the wall 604 can form a contact angle 0, measured along the direction of the first fluid 608. In some embodiments, wall 604 can form a wall-fluid interface 630 with the first fluid 608. In some embodiments, a wall contact point 640 can be a point where wall 604, first fluid 608, and second fluid 610 meet. In some embodiments, a first tangent 642 (shown by an arrow) of the interface 620 at the wall contact point 640 and a second tangent 644 (shown by an arrow) of the wall-fluid interface 630 at wall contact point 640 can form a contact angle 0, measured along the direction of the first fluid 608.

[0195] As shown in FIG. 6A, in some embodiments, the contact angle can be less than 90° and the interface 620 can concave down at the first object 612, relative to the direction of gravity. In some embodiments, a density of the first object 612 can be greater than the density of the first fluid. In some embodiments, the walls 604 of the chamber can be hydrophilic and the first fluid is aqueous or polar.

[0196] As shown in FIG. 6B, in some embodiments, the contact angle can be equal to or greater than 90° and the interface 620 can concave up at the first object 612, relative to the direction of the gravity. In such embodiments, the density of the first object 612 can be less than the density of the first fluid. In some embodiments, the walls 604 of the chamber can be hydrophobic, and the first fluid is nonpolar.

[0197] In some embodiments, the first surface curvature and the second surface curvature can be different. In some embodiments, the first surface curvature can be positive, while the second surface curvature can be negative. In some embodiments, the first surface curvature can be negative, while the second surface curvature can be positive. In some embodiments, one or more of a density of the object, the surface chemistry of the object, and the surface chemistry of the wall 604 can cause the first surface curvature to be different than the second surface curvature. If both interfaces were to have the same sign of surface curvature, bringing the object 612 closer to the wall 604 can result in a lower total system energy, making the system unstable. Assuming the second fluid 610 is air, the total energy of the system, E, can be described by:where p is the density of the first fluid, g gravity, h the height of the profile of first fluid 608, > the two-dimensional domain of the profile of first fluid 608 with outer boundary cflo and y the surface tension of first fluid 608. The first term in equation 4 represents the total gravitational energy within the height profile of first fluid 608. The second term describes the energy contribution to the total energy of surface tension over the entire interface between first fluid 608 and second fluid 610 (e.g., air). The third term describes the Laplace pressure that forms at the edge of chamber 602. It is negative (e.g., as shown in FIG. 6A) as the surface curvature of the wetting fluid at the wall is negative, creating an underpressure within first fluid 608 at wall 604.

[0198] As the system tries to minimize the free energy available in equation 4, object 612 is pushed towards the center of chamber 602. Movement away from the center is counteracted by a restoring force. This is caused by an increase in gravitational potential energy and interfacial energy (increase in surface tension due to extra created surface and decrease in under-pressure as surface curvature is changed). Therefore, without touching the object 612, the object can be trapped within the geometry of chamber 602. By changing the geometry of the chamber 602, the center of minimum energy can be changed as well, and object 612 can be manipulated. In some embodiments, due to this soft-coupling effect, object 612 can be manipulated on micrometer scale while only having to interact with the larger chamber, usually on the order of millimeters to centimeters.

[0199] In some embodiments, trapping and manipulation of object 612 can cause a trapping and manipulation of a second object that is attached to object 612 (e.g., first object). In some embodiments, trapping and manipulation of object 612 can cause a trapping and manipulation of the second object that is connected to object 612. In some embodiments, the second object can be attached to object 612 via one or more of an electric, a magnetic, a chemical, and a molecular force. In some embodiments, when the object 612 is a colloidal particle and the second object is DNA, a biomolecule, or a cell, then the second object can be chemically bound to the object 612. In such embodiments, the second object can be chemically bound to the object 612 via a covalent bond. In some embodiments, when the object 612 is a colloidal particle, the charge or magnetism of the object 612 can be used to apply forces to the second object.

[0200] In some embodiments, the object 612 can include polystyrene, silica, or a combination thereof. In some embodiments, the first object 612 can include a colloidal particle. Non-limiting examples of the colloidal particle include polystyrene, silica, polymethyl methacrylate (PMMA), glass microspheres, metal microspheres, or a combination thereof. In some embodiments, the first object 612 can include an aerosol. Non-limiting examples of an aerosol include hydrocarbons, alkanes, aromatic hydrocarbons, fumed silica, ice crystals, or a combination thereof. In some embodiments, the first object can include a biological cell. Non-limiting examples of the biological cell include blood cell, bone cell, stem cell, bacteria, sperm cell, muscle cell, oocyte, neuron, epithelial cell, plant cells, protoplasts, or a combination thereof.

[0201] In some embodiments, the first object 612 can have a shape of a bead, a microbead, a sphere, a microsphere, a cylinder, a rod, or a prismoid. In some embodiments, the first object 612 can have a size of 1-100 pm. In some embodiments, the first object can have a size of 20-50 pm.

[0202] In some embodiments, the second object can include biological cells, colloidal particles, nanoparticles, DNA molecules, bacteria, viruses, kinesin motors, microtubules, organelles, chromatin, proteins, or a combination thereof.

[0203] In some embodiments, the capillary tweezers 600 can be used to determine a dynamic property as the first object 612 is trapped and / or manipulated. In some embodiments, the dynamic properties can include one or more of a stiffness and a damping factor of the trapping and manipulation processes.B. Design Principles

[0204] Disclosed herein are design principles behind a capillary tweezer suitable to manipulate objects (e.g., microscopic particles, colloidal particles) underneath a microscope. In some embodiments, the design principles disclosed herein can be applied for fabricating a larger-size capillary tweezer. In some embodiments, the design principles disclosed herein can be applied to fabricate smaller-size capillary tweezer suitable for new applications.

[0205] Disclosed herein are the design principles for capillary tweezers (e.g., smaller-size capillary tweezers) suitable for use underneath a microscope, for example, for manipulating colloidal (or other biological) particles.

[0206] In some embodiments, the capillary tweezer or capillary tweezer can be accommodated or fit under an optical microscope. In some embodiments, the capillarytweezer has a height that enables viewing, imaging, or tracking of the object (e.g., float, particle) within the working distance and depth of field of the microscope. In some embodiments, to fit underneath an optical microscope, the height of a tweezer can be less than one millimeter in general. A larger capillary tweezer that relies on moving the tweezer up and down to change the geometry of the chamber can become impracticable to use under the microscope due to its relatively large height. Accordingly, in some embodiments, the capillary tweezer can remain fixed underneath the microscope while the chamber geometry is changed to manipulate the objects. In some embodiments, space constraints when fitting the capillary tweezer underneath the microscope can also result in limited ability to connect a large body of water to the chamber. Therefore, evaporation and other microfluidic effects within the chamber can cause appreciable change in the vertical position of the object, hindering the viewing, imaging, or tracking of the object as its movement is manipulated (e.g., if an object moves out of a focal plane). Accordingly, in some embodiments, the tweezer can be more isolated from the environment to keep the system stable (e.g., by avoiding evaporation) for a sufficient period of time to carry out experiments.

[0207] Another design principle for the capillary tweezer includes the selection of the object (e.g., float, particle) and its properties. In some embodiments, the object can be made heavier or have a different diameter or material composition to tune the trapping stiffness of the capillary tweezer and to ensure proper hydrophilic / hydrophobic properties of the object. In some embodiments, one or more of the size (e.g., diameter, length) of the object, density of the object, surface roughness of the object, contact angle of the interface of the fluid with the object can be optimized to achieve desired trapping stiffness and surface curvature of the fluid interface at the object. Once the object is selected, for example, when a colloidal particle is to be trapped, the design considerations can include selecting the geometry (e.g., radius, width, height) of the chamber of the capillary tweezer and the contact angle of the interface of the fluid at the wall. In some embodiments, the contact angle of the interface of the fluid at the wall can be altered by changing the surface tension properties of the fluid or by changing the material of the chamber.1. Mechanisms to change boundary

[0208] In some embodiments, the boundary of the chamber can be changed, changing capillary forces, thereby moving an object within the chamber.

[0209] In some embodiments, the boundary of the chamber of the capillary tweezer can be changed by deforming the walls of the chamber.

[0210] In some embodiments, the capillary tweezer can include actuators that define the boundary. In some embodiments, the actuators can be actuated to change the boundary of the chamber. a. Deforming the wall geometry

[0211] FIGS. 7A-D illustrate manipulating the movement of an object 712 (e.g., float, particle) by deforming the boundary 706 of a microfluidic chamber (e.g., a microfluidic container, a microfluidic channel) 702 of a capillary tweezer 700. In FIGS. 7A-7D, the intersection of dashed lines represents the center of system and minimum energy before deformation. In some embodiments, boundary 706 can be the edge geometry of microfluidic chamber 702. In some embodiments, the wall of the chamber 702 can be include a deformable material (e.g., elastomer, shape memory alloys). In some embodiments, the wall 704 can be include a deformable material (e.g., elastomer, shape memory alloys, hydrogels). In some embodiments, the wall of the chamber 702 can be include a rigid material (e.g., thermoplastics, thermosets, 3D-printed plastics, UV-cured epoxy resins). In some embodiments, the boundary 706 can include a circle, an oval, a triangle, a square, a rectangle, a quadrilateral, a polygon, a rounded triangle, a rounded square, a rounded rectangle, a rounded quadrilateral, a rounded polygon, a circular arc, or a polynomial curve.

[0212] FIG. 7A shows object 712 located at an interface with fluid 708 when no external force is applied to chamber 702. In some embodiments, chamber 702 can have a circular or round boundary 706 and object 712 can be located at the center of such boundary. In some embodiments, chamber 702 can have a width, along a plane perpendicular to direction of gravity, in the range of 1 mm and 2 mm. In some embodiments, the chamber 702 can have a width of at least about 1 mm, 1.2 mm, 1.6 mm, 1.8 mm, or 2 mm, or the width is in any range bounded by any two values disclosed herein. In some embodiments, chamber 702 can have a width, along a plane perpendicular to the direction of gravity, of about 2-3 mm. In some embodiments, the chamber 702 can have a width of at least about 2 mm, 2.2 mm, 2.6 mm, 2.8 mm, or 3 mm, or the width is in any range bounded by any two values disclosed herein. In some embodiments, chamber 702 can have a width, along a plane perpendicular to direction of gravity, in the range of 0.1 mm and 10 mm. In some embodiments, the chamber 702 can have a width of at least about 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7mm, 8 mm, 9 mm, 10 mm, or the width is in any range bounded by any two values disclosed herein. In some embodiments, chamber 702 can have a width, along a plane perpendicular to the direction of gravity, of about a capillary length of fluid 708.

[0213] FIG. 7B shows that applying a stretching force F on chamber 702 deforms boundary 706, which causes a movement of object 712 from the original position shown in FIG. 7A (e.g. the center of the system and minimum energy before deformation). FIG. 7C shows that applying a squeezing force F on chamber 702 deforms boundary 706, which causes a movement of object 712 from the original position shown in FIG. 7 A. FIG. 7D shows that applying a shear force F on chamber 702 deforms boundary 706, which causes a movement of object 712 from the original position shown in FIG. 7 A. In some embodiments, the applied force F can be one or more of a hydrostatic force, hydraulic force, electrical force, magnetic force, piezoelectric force, and pneumatic force.

[0214] In some embodiments, boundary 706 can be deformed temporally to cause one or more of a linear movement of object (e.g, particle, colloidal particle) 712 and / or a rotation about an axis of object 712. In some embodiments, boundary 706 can be deformed temporally to cause one or more of a linear movement of raft of objects 712 and a rotation about an axis of a raft of objects 712.

[0215] FIGS. 8A-8D illustrate manipulating the movement of an object or object 812 by deforming the boundary 806 of a microfluidic chamber (e.g, a microfluidic container, a microfluidic channel) 802 of a capillary tweezer 800. FIG. 8A shows object 812 suspended within fluid 808 at a location that represents system and minimum energy when no external force is applied to deform chamber 802. In some embodiments, channel 802 can have a width, along a plane perpendicular to direction of gravity, of about 1-2 mm. In some embodiments, the chamber 802 can have a width of at least about 1 mm, 1.2 mm, 1.6 mm, 1.8 mm, or 2 mm, or the width is in any range bounded by any two values disclosed herein. In some embodiments, chamber 802 can have a width, along a plane perpendicular to the direction of gravity, of about 2-3 mm. In some embodiments, the chamber 802 can have a width of at least about 2 mm, 2.2 mm, 2.6 mm, 2.8 mm, or 3 mm, or the width is in any range bounded by any two values disclosed herein. In some embodiments, chamber 802 can have a width, along a plane perpendicular to the direction of gravity, of about a capillary length of fluid 808.

[0216] In FIGS. 8A-8D, the intersection of dashed lines represents the center of system and minimum energy before deformation. FIG. 8B shows trapping of object 812 at the interface 820 between first fluid 808 and second fluid 810 by deforming the boundary 806 ofchamber 802. In some embodiments, deformation of boundary 806 can involve a local, horizontal displacement of the boundary 802. FIG. 8C shows that applying a shear force on chamber 802 deforms boundary 806, causing a movement of object 812 from the original position shown in FIG. 8 A (e.g., the center of the system and minimum energy before deformation). In some embodiments, deformation of boundary 806 can involve a compression of the wall 804 (e.g., sidewall) of the chamber 802. In some embodiments, wall 804 can include a deformable material (e.g., elastomer, shape memory alloys, hydrogels). In some embodiments, the wall of the chamber 802 can be include a rigid material (e.g., thermoplastics, thermosets, 3D-printed plastics, UV-cured epoxy resins).

[0217] In some embodiments, the wall 804 can include an elastomeric polymer. Nonlimiting examples of elastomeric polymers include poly dimethyl siloxane (PDMS), or Formlabs elastic 50A resin, hydrogels, silicone, rubber, and polyurethane, or a combination thereof. In some embodiments, the wall 804 can include a thermoset polymer, polycarbonate, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), or a combination thereof. In some embodiments, the wall 804 can include a metal, an alloy, a ceramic, or a combination thereof.

[0218] In some embodiments, object 812 can move to a position representing minimum energy of the capillary tweezer 800 under deformation. FIG. 8D shows movement of an object 812 in chamber 802 having a slanted geometry. In some embodiments, the level of first fluid 808 (e.g., water) can change within the slanted chamber 802, causing a movement of object 812. In some embodiments, boundary 806 can change as the level of first fluid 808 changes, causing a shift in the location of minimum energy of the system. In some embodiments, object 812 can move to the shifted location of the minimum energy of the system. In some embodiments, the change in the level of first fluid 808 can be driven by one or more of natural evaporation, forced evaporation, and hydrostatic pressure.

[0219] In some embodiments, a deformation of the boundary 806 of the tweezer 800 can cause the movement of object 812. In some embodiments, the deformation of the boundary 806 can deform the interface 820 and shifts the minimum in the potential well. In some embodiments, the magnitude of the shift in the minimum in potential well can be based on one or more of the magnitude and direction of the displacement of the boundary 806. In some embodiments, boundary 806 can be deformed temporally to cause one or more of a linear movement of object 812 and a rotation about an axis of object 812. In some embodiments, boundary 806 can be deformed temporally to cause one or more of a linear movement of raft of objects 812 and a rotation about an axis of a raft of objects 812.

[0220] In some embodiments, the first fluid 808 can include bodily fluid. In some embodiments, the first fluid 808 can include water. In some embodiments, the first fluid 808 can include a polar liquid. Non-limiting examples of polar liquids include water, alcohols, ketones, formamide, dimethyl formamide, dimethyl sulfoxide, or a combination thereof. In some embodiments, the first fluid 808 can include a nonpolar liquid. Non-limiting examples of nonpolar liquids include oils, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, fluorinated oils, or a combination thereof. In some embodiments, the second fluid 810 can include air. In some embodiments, the second fluid 810 can include an oil. Non-limiting examples of the oil include mineral oil, paraffin oil, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, or a combination thereof. In some embodiments, a refractive index of the second fluid 810 can be matched with the refractive index of the first fluid 808.

[0221] Referring to FIGS. 7A-7D and 8A-8D, chamber 702 or 802 has a round geometry. In some embodiments, chamber 702 or 802 can have an arbitrary geometry. In some embodiments, chamber 702 or 802 can have geometry including a circle, an oval, a triangle, a square, a rectangle, a quadrilateral, a polygon, a rounded triangle, a rounded square, a rounded rectangle, a rounded quadrilateral, a rounded polygon, a circular arc, or a polynomial curve. In some embodiments, more complex chamber geometries can be made such that complicated manipulations can be carried out on the object within the chamber. In some embodiments, complicated manipulations include one or more of trapping of object 712 or 812, translation of object 712 or 812, and rotation of object 712 or 812. In some embodiments, the boundary 706 or 806 can be non-circular. In some embodiments, the noncircular boundary 706 or 806 can cause rotation of object 712 or 812. Non-limiting examples of the non-circular boundary include an oval, a rectangle, or a polygon. In some embodiments, a square boundary 706 or 806 can cause rotation of a square object 712 or 812. In some embodiments, a plurality of forces can be applied simultaneously on the capillary tweezer, such as applying shear forces in combination with hydrostatic forces or building other systems interacting with objects with electromagnetic forces. In some embodiments, a radius of the chamber can be smaller than a capillary length of the fluid. In some embodiments, the radius of the chamber can be smaller than the capillary length of the fluid such that the capillary effects dominate. In some embodiments, the fluid can be water and the radius of the chamber can be smaller than the capillary length of water (about 2.7 mm). In some embodiments, the overall size of the capillary tweezer can be small enough to fit or be accommodated under an optical microscope, while keeping the chamber large enough toallow easy preparation and interaction with the fluid interface and the object. In some embodiments, the chamber can be of order of 1-2 mm radius. In some embodiments, the chamber 802 can have a width of at least about 1 mm, 1.2 mm, 1.6 mm, 1.8 mm, or 2 mm, or the width is in any range bounded by any two values disclosed herein.

[0222] In some embodiments, capillary tweezers and baths disclosed herein are small so that they are not cumbersome for manipulating objects. For example, larger systems can be difficult to integrate with an optical microscope, making it challenging to view and quantify the object positions. In some embodiments, the capillary tweezers disclosed herein facilitate measurement of capillary forces in microwells (e.g., microchambers, micro-containers, microchannels) created in an elastomer or other deformable material (e.g., PDMS) and which are filled with fluid, as shown in FIGS. 3A-3B. Such microwells have several advantages over the 3D-printed tweezers: they allow for more controlled experiments over a larger range of length scales; their heights can be limited to a few tens or hundreds of micrometers, making it possible to put them on a microscope and directly image the objects. In some embodiments, the boundary conditions can be manipulated by deforming the boundaries of the microwells. b. Using Actuators

[0223] In some embodiments, capillary tweezers that are designed to be fit under a microscope can have a height of less than a millimeter. For example, the capillary tweezers can include actuators in a constant volume chamber that can move microscale objects around in chambers. In some embodiments, the chambers can have a diameter in the range of 1.5 mm and 2 mm. In some embodiments, the chamber can have a diameter of at least about 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, or 2 mm, or the diameter is in any range bounded by any two values disclosed herein.

[0224] FIGS. 9A-9E show capillary tweezers 900 including actuator 914 that causes a change in the boundary 906 of the chamber (e.g., a container, a channel) 902. In some embodiments, actuator 914 can be actuated to cause a change in boundary 906. In some embodiments, the actuation of actuator 914 can involve one or more of a translation and a rotation of the actuator 914. In some embodiments, the actuation of actuator 914 can involve one or more of a longitudinal movement or a transverse movement of actuator 914. In some embodiments, the actuation of actuator 914 can cause a deformation (e.g., translation or rotation) of chamber wall 904. In some embodiments, when actuator 914 is actuated, aportion of the chamber wall associated with the actuator is translated. In some embodiments, when actuator 914 is actuated, a portion of the chamber wall that is not associated with actuator 904 can be deformed. In some embodiments, capillary tweezer 900 can include support 916 to structurally support actuator 914. In some embodiments, support 916 can enable actuator 914 to suspend within the capillary tweezer 900. In some embodiments, support 916 can be either physically connected to or integrated with actuator 914. In some embodiments, support 916 can hold actuator 914 in place against the capillary attraction between the actuators.

[0225] FIG. 9 A shows capillary tweezer 900 including two actuators 914 and a support916 for each actuator. In some embodiments, chamber 902 of capillary tweezer 900 can have a diameter of 3 mm and a height (e.g., height along z-direction) of 1 mm. In some embodiments, support 916 can have a width of 0.3 mm and a height (e.g., dimension along z- direction) of 0.5 mm. FIG. 9B shows capillary tweezer 900 including two actuators 914 and two support 916 for each actuator.

[0226] FIG. 9C shows capillary tweezer 900 including four actuators 914 and two support 916 for each actuator. In some embodiments, four actuators 914 can be arranged to form a symmetric chamber 902. In some embodiments, a height of channel 902 (height of channel in z-direction) can be more than the height of support 916, allowing the fluid (e.g., water) to flow underneath support 916 and create a constant volume within the capillary tweezer 900 when the actuator 914 moves. Such embodiments are beneficial when capillary tweezer 900 is integrated with an optical microscope for viewing the movement of an object. This is because, in such embodiments, a vertical shift in the water / air interface (e.g., in the z- direction), that is caused when actuator 914 is moved, can be reduced such that the optical plane of the microscope does not need to be adjusted. FIG. 9D shows a perspective view as seen from the bottom of the capillary tweezer shown in FIG. 9D.

[0227] FIG. 9E shows capillary tweezer 900 including four extended actuators 914 and four supports 916 for each extended actuator. In some embodiments, the extended actuators 914 can provide better usability under a microscope by making it easier to apply force. In some embodiments, the actuator 914 can have an extended area of 18 mm x 18 mm to 25 mm x 25 mm.

[0228] In some embodiments, capillary tweezer 900 can include one or more actuators 914. In some embodiments, one or more actuators 914 can be operatively connected to at least one of the one or more walls 904. In some embodiments, when one or more actuator914 is actuated, a geometry of the one or more walls 904 can change, causing a change in the shape of the boundary 906.

[0229] In some embodiments, the actuation of actuators 914 can include applying one or more of a mechanical force, an electric potential, an electric current, a magnetic force, a pneumatic pressure, or a hydraulic pressure. In some embodiments, the actuator 914 can include a piezoelectric actuator or a linear force actuator. In some embodiments, the capillary tweezer 900 can include one, two, three, or four actuators. In some embodiments, each wall 904 can be connected to at least one actuator. In some embodiments, the actuator 914 can include one or more supports 916 to reduce a capillary attraction force from the other actuators 914. In some embodiments, the actuator 914 can have a thickness of about 0.5 mm to about 1 mm. In some embodiments, the one or more supports 916 can have a thickness of about 0.5 mm to about 1 mm. In some embodiments, the actuation of actuator 914 can exert a force on the first object that is between 5-15 pN. In some embodiments, the actuation of actuator 914 can exert a force on the first object that is between 1-10 pN.

[0230] FIGS. 10A-10C show designs of capillary tweezers 1000 including one, two, and four actuators 1014, respectively. In some embodiments, one or more actuators 1014 can be operatively connected to at least one of the one or more walls 1004. In some embodiments, when one or more actuator 1014 is actuated, a geometry of the one or more walls 1004 can change, causing a change in the shape of the boundary 1006. In some embodiments, the capillary tweezer 1000 can include support 1016 to provide structural support for one or more actuators 1014. In some embodiments, as shown on right side schematics of FIGS. 10A-10C, when the one or more actuators 1014 are moved (e.g., as shown along the directions shown by arrows), the height of the fluid 1008 within the chamber (e.g., a container, a channel) 1002 of these capillary tweezers 1000 does not change appreciably, allowing viewing of the manipulation of objects when capillary tweezer is integrated with an optical microscope.

[0231] In a non-limiting example, FIGS. 9A-9E show design process for a general set of complex capillary tweezers. In a non-limiting example, FIGS. 10A-10C show the geometrical specifications of the common capillary tweezers. FIGS. 9A-9E and FIGS. 10A- 10C highlight an important design consideration: the central chamber (e.g., 902, 1002) in which objects are deposited is connected to a larger volume which stays constant. In the embodiments shown in FIGS. 9A-9E and 10A-10C, the central chamber walls (e.g., 904, 1004) can be moved like actuators. These actuators (e.g., 914, 1014) are inside the larger volume, so any movement of the actuators does not change the total volume, keeping the height of the fluid interface (e.g., water-air interface, water-oil interface) constant. Thisallows the user to keep the optical plane of the microscope constant while objects are manipulated.2. Measurement of capillary forces and interaction using capillary tweezer

[0232] In some embodiments, capillary tweezers can be used to measure the capillary force and interaction of micrometer-scale spherical objects (e.g., colloidal particles). In some embodiments, the micrometer-scale spherical objects can be bound to the fluid interfaces and their movement tracked by a microscope to measure the capillary forces and interactions on the objects. In some embodiments, Brownian motion of the objects can be used to quantify forces and interactions. In some embodiments, tracking the motion of the objects in a capillary tweezer can be used to quantify the dynamic properties of objects relating to their motion. In some embodiments, dynamic properties can include one or more of a stiffness of the repulsive capillary interaction and a damping factor of the object being trapped or manipulated using the capillary tweezer. In some embodiments, if the objects are charge- stabilized, the electrostatic interactions between the objects can be screened by adding salt to the fluid when measuring the capillary force and interactions. In some embodiments, the electrostatic interactions between a charged object and a charged fluid interface can be screened by adding salt to the fluid when measuring the capillary force and interactions.C. Material Selection

[0233] In some embodiments, the material for the capillary tweezer (e.g., chamber, chamber walls) can be deformable, structurally durable, optically transparent, and / or can have surface properties suitable to cause trapping or manipulation of an object.1. Deformable

[0234] In some embodiments, the material for the capillary tweezer can be deformable. In some embodiments, the material for the capillary tweezer can be flexible and can resist tearing or breaking up. In some embodiments, the material is fabricated easily using readily available and industry standard techniques such as compression molding or 3D-printing. In some embodiments, the material of the capillary tweezer can be selected based on the elastic modulus and tensile strength that allows desired flexibility, structural integrity, and control of the chamber boundary when in operation.

[0235] In some embodiments, the material for the capillary tweezer can be elastomeric. In some embodiments, the material for the capillary tweezer can be repeatedly stretched and deformed without substantially changing its original shape.

[0236] In some embodiments, the material for the capillary tweezer can be rigid to provide structural stability to the capillary tweezer.

[0237] Non-limiting examples of materials for the chamber (e.g., a container, a channel) include an elastomeric polymer, polydimethylsiloxane (PDMS), Formlabs elastic 50A resin, hydrogels, silicone, rubber, polyurethane, polyethylene, polypropylene, nylon, or a combination thereof.

[0238] Non-limiting examples of materials for the chamber include a thermoset polymer, polycarbonate, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), or a combination thereof.

[0239] Non-limiting examples of materials for the chamber include a metal, an alloy, a ceramic, shape memory alloys, or a combination thereof.2. Optically Clear

[0240] In some embodiments, the material of the capillary tweezer can be optically clear. In some embodiments, the material of the capillary tweezer can be optically transparent or translucent. In some embodiments, the material is optically clear to facilitate viewing and / or tracking of an object (e.g., colloidal particles) that is trapped within the boundary of the chamber.

[0241] Non-limiting examples of optically clear materials for the chamber include glass, polycarbonate, poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), PVC, polyethylene, ionomer resin, fluorinated ethylene propylene, or a combination thereof.3. Surface Properties

[0242] In some embodiments, the material of a wall of the chamber can be hydrophilic (e.g., having a contact angle smaller than 90 degrees) and the object can be hydrophobic. In some embodiments, the material of the wall of the chamber can be wettable by the fluid in which the object is floating, and the object can be non-wettable by the fluid. In some embodiments, the fluid can spread on the wall of the chamber, while the fluid cannot spread on the surface of the object. In some embodiments, in which the material of the wall of thechamber is hydrophilic and the object is hydrophobic, the contact angle of the fluid at the chamber wall is small to promote a strong trapping effect within the capillary tweezers. In some embodiments, the wall of the chamber can be surface treated with a hydrophilic coating. In some embodiments, the chamber can be surface modified to have a hydrophilic wall.

[0243] In some embodiments, the wall of the chamber can be surface treated with plasma, hydroxyl groups, amine groups, nanopatterning, micropatterning, nanostructures, microstructures, particle deposition, vapor deposition, sol-gel treatment, and combinations thereof.

[0244] In some embodiments, the wall of the chamber can be surface modified with amino, polyethylene oxide, epoxy silanes, or a combination thereof.4. Initial Selection & Elastic Properties

[0245] Disclosed herein are the materials suitable to fabricate the capillary tweezers selected based on their elastic modulus and tensile strength. In some embodiments, the material for capillary tweezer, including the chamber, can include agarose hydrogels (lwt% and 4.5wt% gels), Formlabs 50A resin and polydimethylsiloxane (PDMS). In some embodiments, the material for capillary tweezer, including the chamber, can include polyacrylamide (PAM) because it is widely used within biological research, optically clear, and flexible. In some embodiments, the material for fabricating the capillary tweezer can include a soft elastic material. The elastic properties of the materials used for fabricating capillary tweezer are given in Table 1.Table 1: Overview of elastic properties of various materials.Criterium Agarose hydrogels PDMS 50A ResinUltimate Tensile Strength 1% gel: 0.048; 4.5% gel: 0.302 3.51-5.13 3.23 [MPa] [Normand et al. [Ariati et al. [Formlabs]Biomacromolecules, 2000] Polymers,2021]Elastic Modulus [MPa] 1% gel: ~0.01; 4.5% gel: ~1 2.34 [Ariati 3.43[Mori et al. Materials Sciences et al. [Formlabs, and Applications, 2013] Polymers, DOW2021, DOW Chemical]Chemical]EXAMPLES

[0246] Certain embodiments will now be described in the following non-limiting examples.A. Fabrication Methods

[0247] Depending on the material, samples of capillary tweezer (e.g., capillary machine) can be created using open / compression molding techniques. For example, agarose & PDMS samples were created using open / compression molding, while Formlabs 50A resin sample was fabricated using direct 3D-printing. Each sample was subject to certain specific postcuring steps to make the material more usable.1. Sample creation: Agarose Hydrogels & PDMS via molding

[0248] FIG. 11 shows exemplary design process for creating open / compression molds for agarose hydrogel and PDMS capillary tweezer samples. To create these samples via molding techniques, first a mold is created. These design processes can accommodate various inserts that can create samples with varying chamber geometry. In Step 1101, design molds (e.g., negatives of the mold design) are created using AutoCAD design program. Next, mold models are preformed using Preform 3D printing software in step 1102 and then printed using Formlabs 3 3D printers in step 1103. The printed molds are then cleaned in two isopropyl alcohol (IP A) baths for 15 mins in step 1104. Next, the cleaned molds are cured in an oven at 60°C for 30 min in step 1105. The cured molds are sanded down to ensure fit of the components in step 1106. Further cleaning of the molds to remove the excess dust using DI water is performed in step 1107. Finally, the molds are dried out in the air in step 1108.

[0249] FIGS. 12A-12C show examples of the compression, open molds, and the resulting design of samples that can be fabricated. Table 2 provides dimensions of sample geometry fabricated using the various inserts shown in FIGS. 12A-12C. FIG. 12A shows a design of a modular molding system for creating samples of various thicknesses and geometries by utilizing various inserts. FIG. 12B shows a design of a modular system for creating samples using open molding. FIG. 12C shows design parameters used for designating chamber geometry provided in Table 2.

[0250] The molds were designed in AutoCAD 2024 and were printed using a Formlabs 3 printer with Clear resin V4 and the PreForm software (layer thickness set at 25 pm with automatically generated supports). The molds were cleaned by soaking in 2 isopropylalcohol (IP A) baths for 15 minutes each. Molds were then post-cured in an oven at 60 °C for 30 minutes. Molds were sanded down to ensure proper fit of components and cleaned by rinsing with de-ionized (DI) water to prevent sample contamination. Molds were then left to dry on a lab-bench until completely dry.Table 2: Overview of chamber geometries of PDMS / agarose hydrogel samples. All chambers are circular.Agarose-specific creation methods

[0251] To fabricate agarose samples, 1 wt% and 4.5 wt% liquid agarose-DI water mixtures were made by dissolving powdered agarose (VWR type II agarose for biotechnology) in DI water and heating in a microwave until completely dissolved. 4.5wt% gels are stronger but less optically transparent. 4.5wt% gels were chosen, as opposed to for example 5wt% or 4wt%, as elastic information is more readily available in published papers.

[0252] The viability of the creation of agarose-based samples was tested by pouring the liquid 1 wt% and 4.5 wt% agarose-DI water mixture in compression molds with insert sample types 1,2 & 5-7 (see Table 2), pressing down the top and waiting until the mixture had solidified. Samples with sloped chambers (e.g., sloped containers, sloped channels) (insert sample type 3,4) were made with an open mold. After the pouring process, any excess liquid was scraped off the top of the open mold with a razor blade before any significant solidification has taken place. Samples were removed from the inserts with tweezers. The quality of the resulting samples were evaluated with a Dino-Lite Edge 3.0 AM73915MZT digital microscope.

[0253] Agarose hydrogels were stored in a beaker with DI water until used for experiments, as to prevent any swelling or drying-related changes in moisture content and size of the gels in the time period between the creation and the usage of the gels. The gels were tapped dry with a KIMTECH kimwipe before being used for any experiments after being stored to prevent a water meniscus from being formed on the top of the sample as opposed to only in the chamber.PDMS-specific sample creation methods

[0254] Liquid PDMS is created using a 10:1 PDMS elastomer kit (available from Sylgard). PDMS was poured in similar open / compression molds as for agarose hydrogels. Initial experiments showed that PDMS tends to stick to the 3D-printed compression molds. Therefore, various additional protocols were recommended to promote release from compression molds in addition to the design process highlighted in FIG. 11. These protocols were tested using compression molds using a type 1 insert. These protocols are highlighted below.1. Carry out no additional steps promoting mold release [Control experiment],2. Spray molding systems with Smooth-on Universal Mold Release as per instructions on can before pouring PDMS.3. Treat molding systems for 24 hrs in DI water to release residues from mold and drying until fully dry in oven at 60 °C before pouring PDMS.

[0255] Open mold tests were also conducted using a type 1 insert. In all protocols, the liquid PDMS was thoroughly degassed in a vacuum chamber as to prevent bubble formation in the curing process before pouring in the molds.2. Sample creation: 50A resin

[0256] FIG. 13 shows the design process for fabricating directly printed 50A samples. Elastic samples including Formlabs 50A resin were printed directly via a Formlabs 3 3D printer without requiring molds to be made first. As a result, the production process for these samples therefore was simplified. Examples of chamber designs are highlighted in FIGS. 14A-D (e.g., design types 6 A, 7 A, 4 A, and 2 A with extended wings) while an overview of all created design geometries is provided in Table 3.

[0257] Samples were designed in AutoCAD and printed using a Formlabs 3 printer (steps 1301, 1302, and 1303). Samples were cleaned in two IPA baths for 15 minutes each (step 1304). The samples were blown dry with a nitrogen blower and kept in a fume hood tocompletely dry out overnight (step 1305). Samples were post-cured in CL-1000 UV Crosslinker for 30 min and heated in an oven at 60 °C for 30 minutes (steps 1306 and 1307). Samples were removed from the supporting print structure with pliers. These last two steps were especially important to optimize the 50A strength and remove any tackiness that was present on the material.Table 3: Overview of chamber geometries of 50A samples. All chambers are circular.Sam Chamber ra- Chamber Chamber Chamber Total thick- Total top typ dius (mm) slope (de- height bottom ness (mm) area (mm x grees from (mm) thickness mm) horizontal) (mm)1A 2 0 1 0 1 18 x 182A 2 0 0.5 0.5 1 18 x 183A 2 26.57 1 0 1 18 x 184A 2 26.57 0.5 0 1 18 x 185A 2 14.04 1 0 1 18 x 186A 2 0 0.5 0 0.5 18 x 187A 1 0 0.5 0 0.5 18 x 188A 2 0 0.3 0.2 0.5 18 x 183. Sample fabrication using soft lithography

[0258] FIGS. 15A-15B show top view and side view schematics of a capillary tweezer 1500 fabricated using soft lithography methods. In some embodiments, capillary tweezers 1500 can include a channel (e.g., a container, a channel) 1502 that contains a wall 1504. In some embodiments, chamber 1502 can be filled with a first fluid 1508. In some embodiments, a second fluid 1510 can form an interface with first fluid 1508. In some embodiments, coverslip 1560 can be attached to one or more of a top or bottom of capillary tweezer 1500. In some embodiments, coverslip 1560 allows viewing under a microscope and / or prevents contamination of sample when viewed under the microscope. In some embodiments, when an object 1512 is deposited at the interface of the first fluid 1508, object 1512 can be trapped on interface with the first fluid 1508. In some embodiments, chamber 1502 can include a 265 pm tall layer of PDMS with a circular hole through it. In some embodiments, the hole can have a dimension of about 2-4 mm. In some embodiments, first fluid 1508 can include water and second fluid 1510 can include air. In some embodiments,chamber 1502 can be filled with about a microliter of water and object 1512 is deposited at the interface of first fluid 1508. FIG. 15C shows a photograph of a fabricated capillary tweezer 1500 fabricated using soft lithography as discussed in FIGS. 15A-15B.

[0259] FIGS. 16A-16C show steps for fabricating the capillary tweezer using soft lithography. FIG. 16A shows the design of a photomask with appropriate lateral dimensions of a chamber e.g., a container, a channel). In some embodiments, a soft lithography technique can be used to prepare molds. In some embodiments, molds can be prepared using SU-8 photoresist. In some embodiments, molds prepared using SU-8 can provide precise control over the height of the tweezers and their wall smoothness, which affects pinning and the applied force. FIG. 16B shows filling the mold with PDMS (or other elastomers, hydrogels) and curing it in an oven. FIG. 16C shows the plasma cleaning of the cured PDMS and a coverslip for bonding to each other and making the PDMS hydrophilic.B. Fabrication Results

[0260] An overview of successful and unsuccessful fabrication results is given in Table 4. Examples of the fabricated samples are shown in FIGS. 17A-17I. FIG. 17A shows a top view of compression molded PDMS, having 1 mm radius chamber (e.g., a container, a channel). FIG. 17B shows a top view of printed 50A sample having 2 mm radius chamber with bottom. FIG. 17C shows a top view of compression molded 4.5wt% agarose hydrogel having 2 mm radius chamber. FIG. 17D shows a compression molded PDMS. FIG. 17E shows a printed 50A sample. FIG. 17F shows a compression molded 4.5wt% agarose hydrogel. FIG. 17G shows an open molded PDMS using DI mold pre-treatment process. FIGS. 17H-17I show views of agarose hydrogel on mold insert.

[0261] Due to the very low elastic modulus and tensile strength of the 1 wt% agarose gel, reliable sample creation proved unfeasible at this wt%. Sloped chambers could not be fabricated with any agarose gels, as samples would rip during the removal process from the sloped compression mold insert (types 3,4). 4.5wt% agarose hydrogels could, however, produce all other proposed types of chamber geometries. All types of chambers could reliably be made using the directly printed 50A methods. Compression molding using PDMS proved unfeasible as bubble-formation would nonetheless take place in the compression molds independent of the specific protocol used (see FIGS. 17 A, 17D). Treating the molds with Smooth-on Universal Mold Release stopped the PDMS from curing in its entirety. Treating molding systems in DI water improved the results if used with open molds.

[0262] Several microfluidic effects were observed under the Dino- Lite Edge 3.0 AM73915MZT digital microscope relevant to further fabrication of the capillary tweezers: samples were deposited on a clean glass microscopic coverslip and tapped dry before being evaluated under the microscope. 5-10 pL of water were deposited in the chambers. As shown in FIG. 18 A, a sample with a bottom can hold the water within the chamber without any leaking of any water from the bottom. However, as shown in FIG. 18B, a sample without a bottom that is deposited on a glass coverslip can experience a large volume of water getting pulled between the interface of the sample and glass as soon as the water is supplied to the sample.Table 4: Overview of successful and unsuccessful sample creation methods with various chamber geometries. • / represents successful fabrication methods, / represents unsuccessful fabrication methods and empty cells represent untested methods.

[0263] Referring to FIGS. 18A-B, the high wettability of glass contributed to the effect of pulling of water between the interface of the sample and glass. Energy minimization prefers to have a double interface between the glass-water and water-sample instead of having adirect, singular, sample-glass interface. Water therefore gets pulled underneath the sample to wet the glass, creating undesired microfluidic flows. In order to prevent this effect, the samples can include a fabricated bottom, although this may reduce the optical clarity of the capillary tweezer because the light from the microscope has to pass through the additional fabricated bottom layer as well. Preferably, samples with an open bottom can be sealed to the glass, which can reduce the risk of both the water leakage from the bottom and loss in optical clarity that would otherwise be caused by the fabricated bottom.C. Sample Properties Methods1. Contact Angle Measurements

[0264] To test the hydrophilic properties of the materials used in fabrication, contact angles of water on various samples were measured using the sessile drop method using a flat stage and a camera. 50-60 pL DI water drops were deposited on the flat, horizontal interface of the sample.

[0265] To make PDMS permanently hydrophilic, a polyvinyl alcohol (PVA)-deposition protocol developed by Trantidou, T. et al. Microsystems & Nanoengineering (2017) is used after samples were cured in the molding systems. The protocol included oxidizing the sample using a plasma cleaner and then immersing the sample in a PVA solution (e.g., 1 wt% PVA in water). The solutions were kept immersed in the PVA solution for 10 minutes and then dried with nitrogen and heated in an oven at 110°C for 15 min to remove residual moisture.

[0266] To create the PVA solution, first the PVA was added to deionized water (1 wt%) and stirred at room temperature for 40 min, and then at 100°C for 40 minutes. The temperature was then decreased to 65°C for several hours.

[0267] Contrary to the 100W plasma-machine used in Trantidou, T. et al., an 18W plasma-cleaner was used. Samples were plasma-cleaned for 2 minutes. This same protocol was applied to the 50A. Experiments were repeated 3 times using the same sample. The following samples were prepared:• 4.5 wt% agarose hydrogel (no additional treatment)• 50A (no additional treatment)• Open-molded PDMS (no additional treatment)• Plasma-cleaned 50A• Plasma-cleaned and PVA-treated 50APlasma-cleaned and PVA-treated PDMS

[0268] Besides these measurements, the stability of the contact angle at the wall of the PVA-treated PDMS was investigated by re-measuring the contact angle of the same PDMS sample over various days. In order to investigate the dependence of plasma-treatment time on the contact-angle, 3 PDMS samples were plasma-treated for 2, 6 and 10 minutes respectively and PVA-coated. Contact angles were then measured once.2. Evaporation Measurements

[0269] To test the temporal stability of the capillary tweezers, evaporation effects were quantified. This was accomplished by taking videos of various samples using a Dino-Lite Edge 3.0 AM73915MZT digital microscope. The samples contained 5 pL of water in their chambers and evaporation time was measured from the moment the chamber is filled to the point the meniscus of the water touched the bottom of the well. Experiments were repeated 3 times for each sample.

[0270] If there is a leakage of water from the bottom of the chamber (or well, container, channel), it can interfere with the proper measurement of the evaporation effects (e.g., evaporation time for the water in the chamber). FIGS. 19A-19C show various options that were considered to prevent water leaking from the bottom of the chamber as highlighted in FIG. 18.

[0271] FIG. 19A shows a sample that can be glued to glass coverslips, for example, using a water-resistant silicone DOW Coming Vacuum lubricant or epoxy solution. The advantage of this method is that the bottom of the chamber is not glued and includes only the glass coverslip, having good optical qualities. FIG. 19B shows a sample that has a bottom by design. FIG. 19C shows a sample that can be directly cured on a pre-treated coated / functionalized glass coverslips. In this method, 60 pL of poly-l-lysine solution was spin-coated for 30 seconds at 4000 RPM after which a type 2 insert with an open mold is used to cure the 4.5wt% agar gel directly to the glass coverslip. The following samples were prepared for the evaporation tests, all having a chamber radius of 2 mm:• Poly-l-lysine treated agarose hydrogel with dry outer edges• Poly-l-lysine treated agarose hydrogel with wet outer edges (20 pL water added on the outer regions of the hydrogel to prevent evaporation from the gel surface itself).• Untreated agarose hydrogel with a bottom, dry edges• Untreated agarose hydrogel with a bottom, wet edgesPlasma-cleaned (2 min) 50A sample with bottomPlasma-cleaned (2 min) PVA treated PDMS.3. Surface Tension Measurements

[0272] Surface tension measurements were carried out using a Sigma 700 / 701 Force Tensiometer using Wilhelmy plate measurements. These measurements were especially important as the materials used to fabricate the capillary tweezers can release surfactants in the water solution decreasing the surface tension of water, reducing the trapping strength of the tweezers. Two distinct experiments were conducted. In the first experiment, PVA- treated PDMS and 50A (post-cured in an oven for 30 min, no UV curing) samples were prepared. These samples were deposited in 500 mL of DI water. Surface tension measurements were taken 1 hour after preparation of the material and again after 2 days.

[0273] For the second experiment, the exact treatment protocols of 50A are investigated. The following samples are prepared:• Post-cured 50 A in oven for 30 min• Post-cured 50 A in UV-curer for 30 min, then oven for 30 min• Post-cured 50 A in oven for 30 min, then UV-curer for 30 min• Post-cured 50 A in UV-curer for 30 min, then oven for 30 min. Treated in two water baths for 24 hrs each, first water bath being tap water, second begin DI water• Post-cured 50A in oven for 30 min, then UV-curer for 30 min. Treated in two water baths for 24 hrs each, first water bath being tap water, second begin DI water• Plasma cleaned PVA treated PDMS using the standard protocol highlighted in previous sections.

[0274] In each experiment, each sample consisted of a 1 cm x 1 cm x 1 cm cube of material that were left in a 500 ml volume of water 24 hrs before the measurement. As the exact material composition of 50A is unknown, various ways to post-cure the 50A were performed as opposed to the general fabrication procedure highlighted in EXAMPLES, section A “Fabrication Methods”).D. Sample Properties Results1. Contact Angle Measurements

[0275] FIG. 20 shows measured contact angle on the following samples:• 4.5 wt% agarose hydrogel (no additional treatment)• 50A (no additional treatment)• Open-molded PDMS (no additional treatment)• Plasma-cleaned 50A• Plasma-cleaned and PVA-treated 50A• Plasma-cleaned and PVA-treated PDMS

[0276] It is preferred that the sample capillary tweezer has a low contact angle. The agarose hydrogel exhibited the lowest contact angle. This is expected as 95.5% of the gel itself consisted of water. The importance of plasma treating PDMS was also observed, resulting in an average decrease of 30 degrees of the contact angle, bringing it to approximately the same contact angle as that of 50A. Plasma treating 50A was not found to improve the contact angle of 50A.

[0277] FIG. 21 demonstrates the importance of plasma cleaning time of PDMS. Contact angles of PDMS samples were measured over time, as well as after various plasma-treatment times (dotted lines, measured on day 0). A cleaning time of 2 minutes yielded the lowest contact angle. Cleaning longer yielded an inferior contact angle. An explanation of this effect is that with longer plasma cleaning time the surface of the PDMS becomes too rough. This surface roughness overcomes the benefit of oxidizing the PDMS surface that promotes the hydrophilic nature, giving rise to a larger contact angle compared to shorter cleaning time. A large variability of the PDMS contact angle is also seen, eventually settling around 60-70 degrees.2. Evaporation Measurements

[0278] FIG. 22 shows the results of the evaporation times (time until total evaporation) of water in the following samples (as described in EXAMPLES, section 3.C.2 “Evaporation Measurements”):• Poly-l-lysine treated agarose hydrogel with dry outer edges• Poly-l-lysine treated agarose hydrogel with wet outer edges (20 pL water added on the outer regions of the hydrogel to prevent evaporation from the gel surface itself).• Untreated agarose hydrogel with a bottom, dry edges• Untreated agarose hydrogel with a bottom, wet edges• Plasma-cleaned (2 min) 50A sample with bottom• Plasma-cleaned (2 min) PVA treated PDMS

[0279] The plasma cleaned 50A sample showed the best material properties among the tested samples, having the lowest degree of evaporation, followed by the 50A sample. The difference in evaporation time can be explained by comparing the swelling rates of the 50A and PDMS in water. The weight increase of PDMS in water is twice as fast as for 50A (2.3 wt% for 50A, 5wt% for PDMS in 24 hrs). Agarose hydrogels had the fastest evaporation times and therefore were the least stable. While wetting the edges of the hydrogel resulted in slight increase in the evaporation time, the PDMS and 50A still remained better quality than the hydrogel because they had the lowest evaporation times of the tested samples. The fast evaporation times of the hydrogel can be explained by water evaporating from the hydrogel surface. As the hydrogel has tendency to keep its water content stable, it absorbs water from the channel, increasing evaporation related effects significantly. Using poly-l-lysine treated coverslips as opposed to using agarose hydrogels with a bottom showed no significant improvement relating to evaporation time.3. Surface Tension Measurements

[0280] FIG. 23 A shows surface tension measurements of water in contact with PDMS and 50A measured at 1 hour and 2 days after depositing material in water. FIG. 23B shows surface tension measurements of 50A using various post-treatment options, measured 1 day after production stored in water (WT stands for water treatment and DI water measurements are included as baseline). Using plasma-treated and PVA treated PDMS had no observable effect on the surface tension of water. Using untreated 50 A, however, decreased the surface tension of water by about 12% from baseline. This effect however was not immediate, as seen from FIG. 23 A, where it takes the sample 2 days to cause a 9% decrease. This effect may be caused by uncured photo-initiator or acrylate monomer leaching into the water, acting as surfactants. Post-treatment of the 50A by making use of UV light reduces this effect slightly. Post-curing the 50A in beakers of water or reversing the order of the UV and oven post-treatment had no noticeable positive effect, as seen in FIG. 23B.

[0281] A summary of material properties is provided in Table 5.Table 5: Summary of material properties and usability.Criterium Agarose hydrogels PDMS 50A Resin

[0282] Although the agarose hydrogels have the lowest contact angle and are most hydrophilic, their low evaporation time and absorption of water in the gel causing unwanted microfluidic flows, combined with fragility of the material makes them a less suitable candidate for making capillary tweezers among the fabricated samples. Both PDMS and 50Ahave similar contact angles and therefore similar order of trapping strength. 50A however causes a slight decrease in the surface tension of water as opposed to PDMS. However, as this effect is not very large (a 12% difference after 2 days), the trapping strengths should not deviate significantly. As 50A has longer evaporation time, leading to better system stability and more complex geometries that can be prototyped faster using direct 3D printing, 50A is the best material in this example for designing capillary tweezers among the fabricated samples. PDMS, however, can be molded and thus is better suited for larger industrial scale fabrication and can be considered another suitable option. Another benefit of testing the design of capillary tweezers made out of 50A is that if the testing shows that the design can operate as a capillary tweezer, the design is most likely expected to operate as a capillary tweezer made of PDMS as well because PDMS has a higher associated surface tension with water.E. Capillary Tweezers Testing

[0283] Capillary tweezers fabricated from 50A resin were selected for qualitative testing to see if the capillary tweezer can trap and manipulate the movement of object (e.g., particles, floats). First, simple samples of 50A resin were used (as described in the EXAMPLES, sections A and B) to see if and how objects of various sizes can be trapped. Best practices for designing simple samples were then developed. Next, more complicated capillary tweezers were developed and manipulation of various objects was tested.1. Simple particle trapping methods

[0284] To test simple trapping of object (e.g., particle) trapping in chambers (e.g., a container, a channel) fabricated using 50A resin (50A chambers), various chamber designs were used. These being straight chamber type 1 A (without a bottom), straight chamber type 8A (with bottom) and sloped chamber type 2A (without bottom) as given in Table 3.

[0285] The objects to be trapped were 20 pm monodisperse fluorescent polystyrene beads (1060 kg / m3) and 50 pm monodisperse silica beads (2320 kg / m3). All objects were washed 2x by centrifugation in a DI water bath before use. FIG. 24 shows a process flow diagram for depositing objects at the fluid interface for simple 50A samples.

[0286] First, 50A samples of capillary tweezers were created. The samples were then adhered to thoroughly cleaned glass coverslips. This was done either with five-minute epoxy or DOW vacuum grease and a swab. Only the outside edges of the sample were treated,ensuring that no epoxy or vacuum grease reaches within the chamber. Next, 4-9 pL of DI water were pipetted in the chamber to form a meniscus. Two methods were investigated to deposit the beads on the interface: 1) objects were diluted in a 2: 1 IPA:DI water solution until single objects can be pipetted onto a prepared sample with a water meniscus, 2) the objects were attached to a blunt needle by poking the needle in the prepared solution with objects. The needle was left to dry after which the needle was submerged slightly in the chamber to attach objects to the water / air interface. Videos were then taken with a Dino-Lite Edge 3.0 AM73915MZT digital microscope to observe the particle movement.

[0287] For the fluorescent objects the samples were illuminated with a UV flashlight. A script was developed based on Trackpy and IPY parallel computational packages to track these objects based on videos. Velocities and related viscous forces as well as accelerations and related net forces on objects can then be calculated by determining inter-frame object displacement and using velocity-Verlet central difference schemes.2. Simple particle trapping results

[0288] FIGS. 25A-25C show a successful trapping of 50 pm silica bead objects. Silica beads having 50 pm size were deposited in a 4 mm wide 50A chamber (or 50A channel). As soon as the objects were deposited at the interface, migration towards the center begins to take place in the order of seconds. Single-object (e.g., single particle) trapping was achieved (FIG. 25A), while multiple 50 pm silica beads were found to self-assemble and align in the center of the chamber as rafts of 3 objects (FIG. 25B) and 9 objects (FIG. 25C) with minimal outside surface to minimize the total energy of the system.

[0289] Following approach for depositing objects was developed: depositing objects using a blunt needle on the air / water interface is preferred over using the IPA solution method as the IPA creates violent surface flows disturbing measurements until all IPA has evaporated. To prevent any contamination by the needle, the needle should be thoroughly cleaned with IPA and blown dry with nitrogen. The use of epoxy as opposed to vacuum grease is preferred to bond samples to coverglass slips as DI water is not contaminated and systems have better re-usability.

[0290] FIGS. 26A-26F illustrate trapping of a single 20 pm polystyrene (PS) bead inside the chamber of capillary tweezer described in FIGS. 15A-15C. The 20 pm PS bead was deposited at the interface of water in the chamber and attains a position at the center of the chamber. It was then perturbed out of the center using an optical tweezer. The bead was firsttrapped in the focus of the optical tweezer and then moved out of the center of the capillary tweezer. The optical tweezer was then turned off, and movement of the bead was observed under a microscope. The snapshots of the movement of the bead with increasing time showed that the bead moved back to the capillary trap center highlighted as dotted circle. A return to the capillary trap center is indicative of a restoring force and stable trapping of the bead.

[0291] FIG. 27 illustrates estimating magnitude of trap stiffness for the single 20 pm polystyrene (PS) bead trapped as shown in FIGS. 26A-26F. The information gained from tracking the PS bead motion as in FIGS. 26A-26F is used to estimate the trap stiffness. The motion of the PS bead can be treated as Brownian motion in a harmonic potential because a) for small displacements from the trap center xc, the capillary tweezer functions like a Hookean spring with a trap stiffness k, and 2) the bead is diffusing in a viscous medium having a damping y with a diffusion coefficient D. The object (e.g., particle) tracking data of the PS bead is fit to this model, where ( (t) is a Gaussian white noise, = fc / y is the mean regression rate, xois the object initial position, and xcis the position of the center of the capillary trap:

[0292] The bead tracking data is fit using a spring constant whose magnitude is 10‘2pN / um, which is smaller than the stiffness of an optical tweezer on a similar sized object. As a comparison, maximum stiffness for trapping using an optical tweezer is 100 pN / um.3. Complex manipulation methods

[0293] More complex capillary tweezers were designed to test manipulation (e.g., 2D movement) of a colloidal particle within a capillary. These tweezers follow the fabrication procedure as highlighted in FIG. 13. The object or particle deposition process was similar to the process highlighted in FIG. 24 where the needle deposition method was used and samples were adhered to coverglass slips using 5 minute epoxy. Trapping and manipulation of 5, 20 and 50 pm monodisperse silica beads were tested.

[0294] The actuators of the flexible capillary tweezers made of 50A were controlled by making use of a handheld metal mechanical tweezers. Images and videos of the capillary tweezers were taken using a Dino-Lite Edge 3.0 AM73915MZT digital microscope or a Nikon TE2000-E optical microscope with Ph-1 phase contrast condenser and 4x optics. Aparticle tracking script was developed that is able to track particles / objects from the phasecontrast optical microscope and determine net forces on objects from a velocity-Verlet like central difference scheme on object displacements.4. Complex manipulation results

[0295] FIGS. 28-32 show the testing results on the capillary tweezers fabricated from 50A resin and fit underneath an optical microscope for viewing of the trapping and manipulation of the movement of the objects. Silica objects (e.g., particles) of size 50 micron (z.e., 50 pm) and 20 micron (z.e., 20 pm) beads were deposited on the water interface in a 4 mm wide 50A chamber. The testing results show that 20 and 50 micron objects (both single objects and rafts consisting of multiple objects) can be trapped inside flexible, 3D printed capillary tweezers that fit underneath an optical microscope. The results show that by making use of multiple actuators at once, rafts can be rotated or displaced linearly.

[0296] Due to the constant volume design of these capillary tweezers, no significant adjustments were needed to be made to the focus plane of the Dinoscope digital microscope, while only minor adjustments were made to the focus plane of the Phase-contrast Nikon TE- 2000E optical microscope. This shift in optical plane can be caused by the object slightly moving upwards on the slope of the meniscus while the flexible actuators were brought closer together, which can be challenging to avoid for capillary tweezers. The testing results also demonstrate that the trapping and movement of the 20 and 50 micron objects (both single objects and rafts consisting of multiple objects) can be viewed by the optical microscope, without moving the capillary tweezer.

[0297] FIGS. 28A-28B show that both 50 micron (FIG. 28A) and 20 micron silica beads (FIG. 28B), once deposited on to the water interface (left side images in FIGS. 28A-28B), self-assembled into rafts near the center of the chamber (right side images in FIGS. 28 A- 28B). The movement of raft was captured using a Dinoscope digital microscope without moving the capillary tweezer.

[0298] FIGS. 29A-D show rotation of a raft of 50 micron objects (e.g., particles) when two actuators of the capillary tweezer are squeezed together. FIG. 29A shows the selfassembled raft of deposited 50 micron beads. Next, the two opposing actuators (indicated by arrows) were squeezed towards each other. FIGS. 29B-29D show that when the two opposing actuators (indicated by arrows) were squeezed towards each other, the raft of beads rotates clockwise relative to the original orientation of the beads in FIG. 29A. FIGS. 29B-29D show images taken with increasing time and demonstrate that the raft of beads continued to rotate over time. The rotation of the raft of beads was viewed under the Dinoscope digital microscope, without moving the capillary tweezer.

[0299] FIGS. 30A-30B depict tracking of object (e.g., particle) trajectory (e.g., movement of the particle) using a microscope and without moving the capillary tweezer. 50 micron silica beads were deposited on the water interface inside the capillary tweezer that was fit under a Nikon TE-2000E microscope. FIG. 30A, which is a composite image of 40 individual phase-contrast images taken by the Nikon microscope, shows that when the bottom actuator was moved up, a raft of 50 micron silica beads self-assembled in the middle of the capillary tweezers. FIG. 3 OB shows the trajectories of the tracked objects when the bottom actuator was moved up (indicated by an arrow) (image shows beginning frame of the video).

[0300] FIG. 30C shows calculated net force on the raft of 50 micron beads when the bottom actuator of the capillary tweezer was moved up. Considering that the capillary tweezers experience highly over-damped motion and assuming that the objects are at terminal velocity when travelling, the capillary forces can be determined by: 1) determining velocities from inter-frame movement; 2) calculating Stokes force on the object from the velocity; and 3) noting that the capillary force is (almost) equal and opposing the Stokes force. Using this method, it is estimated that for single 50 micron objects, capillary forces are between 101 1- 1012N. This agrees well with net force calculations from FIG. 30C which estimates a net force on the order of 1012on a single 50 micron object (shown as legends 1-11 in FIG. 30C) and 101 1N on rafts of 11 objects (shown as legend “total” in FIG. 30C). For 20 micron silica objects, this capillary force is estimated between 1012-1013N, assuming that the force scales down with the volume of the object.

[0301] FIGS. 31 A-C show the displacement of a raft of 50 micron silica beads when the two actuators of the capillary tweezer are moved in the same direction (in the direction of the arrows). FIG. 31 A shows the original position. FIG. 3 IB shows that the raft of beads is displaced along the direction of the movement of the two actuators compared to the original position in FIG. 31 A. FIG. 31C, which is taken at a later time than FIG. 3 IB, shows the raft of beads return to its original orientation as the two actuators return to their initial positions. The images are taken using a Dinoscope digital microscope, without moving the capillary tweezer.

[0302] FIG. 32 illustrates the displacement of a single 20 micron silica bead as the right actuator (shown by an arrow) of the capillary tweezer is pushed inwards. The image is anoverlay of four frames from the video taken by a Dinoscope digital microscope. The circles around the object represent the shift in position of the object. The total time for displacement is approximately 8 seconds.

[0303] Testing of fabricated capillary tweezers shows that 20 and 50 micron silica beads and 20 micron polystyrene beads can be trapped and manipulated using capillary tweezers. 5 micron silica beads could not be trapped by the fabricated capillary tweezers. This can be attributed to the weight of these objects being too small to cause any significant deformation of the surface of the water.

[0304] It is also observed that adhering the outer edges of the capillary tweezers to the glass coverslip prevents water leakage. As the actuators themselves are not adhered to the glass, a film of water develops between these actuators and the glass. This is beneficial as it reduces friction and introduces better usability and can be considered as a design consideration and feature in future designs.

[0305] It will be appreciated that while one or more particular materials or steps have been shown and described for purposes of explanation, the materials or steps may be varied in certain respects, or materials or steps may be combined, while still obtaining the desired outcome. Additionally, modifications to the disclosed embodiment and the invention as claimed are possible and within the scope of this disclosed invention.

[0306] Those skilled in the art would readily appreciate that all parameters and configurations described herein are meant to be exemplary and that actual parameters and configurations will depend upon the specific application for which the systems and methods of the present invention are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that the invention may be practiced otherwise than as specifically described. The present invention is directed to each individual feature, system, or method described herein. In addition, any combination of two or more such features, systems or methods, if such features, systems or methods are not mutually inconsistent, is included within the scope of the present invention.

Claims

CLAIMSWhat is claimed is:

1. A device comprising: a chamber comprising one or more walls defining a boundary, wherein the chamber is configured to receive a first fluid, a second fluid, and a first object, wherein an interface between the first fluid and the second fluid forms a contact angle with the one or more walls, the contact angle measured along the direction of the first fluid, wherein the device is configured such that at least one of (a) and (b) occurs:(a) when the contact angle is less than 90° and a density of the first object is greater than the density of the first fluid, the interface between the first fluid and the second fluid is concave down at the first object, and(b) when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid, the interface between the first fluid and the second fluid is concave up at the first object, and wherein a change in a shape of the boundary is configured to cause a movement of the first object at the interface between the first fluid and the second fluid, wherein the movement of the first object is confined within the boundary.

2. The device of claim 1, wherein the movement of the first object comprises one or more of a trapping of the first object at a location, a translation of the object, and a rotation of the first object.

3. The device of claim 1, wherein the movement of the first object comprises a trapping of the first object a) at a vertically lowest point on the interface between the first fluid and the second fluid within the boundary, when the contact angle is less than 90° and the density of the first object is greater than the density of the first fluid or b) at a vertically highest point on the interface between the first fluid and the second fluid within the boundary, when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid.

4. The device of any one of claims 1-3, wherein the boundary has a width of about 1-3 mm.

5. The device of any one of claims 1-3, wherein the boundary has a width of about 1-2 mm.

6. The device of any one of claims 1-3, wherein the boundary has a width that is less than or about a capillary length of the interface between the first fluid and the second fluid.

7. The device of any one of claims 1-3, wherein the boundary has a width that is less than or equal to 1.1 times a capillary length of the interface between the first fluid and the second fluid.

8. The device of any one of claims 1-3, wherein the boundary has a width that is less than or equal to a capillary length of the interface between the first fluid and the second fluid.

9. The device of any one of claims 1-8, wherein the shape of the boundary comprises a circle, an oval, a triangle, a square, a rectangle, a quadrilateral, a polygon, a rounded triangle, a rounded square, a rounded rectangle, a rounded quadrilateral, a rounded polygon, a circular arc, or a polynomial curve.

10. The device of any one of claims 1-9, wherein a force is applied to at least one of the one or more walls to cause the change in the shape of the boundary.

11. The device of any one of claims 1-10, the device comprising one or more actuators, the one or more actuators operatively connected to at least one of the one or more walls, wherein the one or more actuators, when actuated, is configured to cause a change in a geometry of the one or more walls, causing the change in the shape of the boundary.

12. The device of any one of claims 11, the device comprising: a manipulator disposed outside the chamber, the manipulator attached to the one or more actuators, wherein a first movement of the manipulator is configured to cause a second movement of the one or more actuators.

13. The device of any one of claims 11-12, wherein the change in the geometry of the one or more walls comprises a deformation of at least one of the one or more walls.

14. The device of any one of claims 11-12, wherein the change in the geometry of the one or more walls comprises one or more of a translation or a rotation of at least one of the one or more walls.

15. The device of any one of claims 11-14, wherein the actuation of the one or more actuators comprises applying one or more of a mechanical force, an electric potential, an electric current, a magnetic force, a pneumatic pressure, or a hydraulic pressure.

16. The device of any one of claims 11-15, wherein at least one of the one or more actuators comprises a piezoelectric actuator or a linear force actuator.

17. The device of any one of claims 1-16, wherein, based on the movement of the first object, a dynamic property of the first object is determined.

18. The device of any one of claims 11-17, wherein the actuation of the one or more actuators exerts a force on the first object that is between 1-10 pico Newton.

19. A device of any one of claims 1-18, wherein the movement of the first object causes a trapping or a movement of a second object physically connected to the first object.

20. The device of any one of claims 1-19, wherein the movement of the first object exerts a force on a second object physically connected to the first object.

21. The device of any one of claims 11-20, wherein the one or more actuators comprises two actuators.

22. The device of any one of claims 11-21, wherein the one or more actuators comprises three actuators.

23. The device of any one of claims 11-22, wherein the one or more actuators comprises four actuators.

24. The device of any one of claims 11-23, wherein each wall is connected to at least one actuator.

25. The device of any one of claims 11-24, wherein the one or more actuators have a thickness of about 0.5 to about 1 mm.

26. The device of any one of claims 11-25, wherein an actuator of the one or more actuators comprises one or more supports to reduce a capillary attraction from the other actuators.

27. The device of claim 26, wherein the one or more supports have a thickness of about 0.5 mm to about 1 mm.

28. The device of any one of claims 1-27, wherein the contact angle that the interface between the first fluid and the second fluid forms with the one or more walls is 20-80°.

29. The device of claim 1-28, wherein the contact angle that the interface between the first fluid and the second fluid forms with the one or more walls is 50-70°.

30. The device of any one of claims 1-29, wherein the one or more walls comprises a hydrophilic surface and the first object comprises a hydrophobic surface.

31. The device of any one of claims 1-29, wherein the one or more walls comprises a deformable material.

32. The device of any one of claims 1-29, wherein the one or more walls comprises an elastomeric material.

33. The device of any one of claims 1-29, wherein the one or more walls comprises a rigid material.

34. The device of any one of claims 1-29, wherein the one or more walls comprises a material selected from a group consisting of an elastomeric polymer, polydimethylsiloxane (PDMS), or Formlabs elastic 50A resin, hydrogels, silicone, rubber, polyurethane, or a combination thereof.

35. The device of any one of claims 1-29, wherein the one or more walls comprises a material selected from a group consisting of a thermoset polymer, polycarbonate, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), or a combination thereof.

36. The device of any one of claims 1-29, wherein the one or more walls comprises a material selected from a group consisting of a metal, an alloy, a ceramic, or a combination thereof.

37. The device of any one of claims 1-36, wherein the first object is selected from a group consisting of polystyrene, silica, or a combination thereof.

38. The device of any one of claims 1-36, wherein the first object comprises a colloidal particle.

39. The device of claim 38, wherein the colloidal particle is selected from a group consisting of polystyrene, silica, polymethyl methacrylate (PMMA), glass microspheres, metal microspheres, or a combination thereof.

40. The device of any one of claims 1-39, wherein the first object comprises an aerosol.

41. The device of claim 40, wherein the aerosol is selected from a group consisting of hydrocarbons, alkanes, aromatic hydrocarbons, fumed silica, ice crystals, or a combination thereof.

42. The device of any one of claims 1-39, wherein the first object comprises a biological cell.

43. The device of claim 42, wherein the biological cell is selected from a group consisting of blood cell, bone cell, stem cell, bacteria, sperm cell, muscle cell, oocyte, neuron, epithelial cell, plant cells, protoplasts, or a combination thereof.

44. The device of any one of claims 1-43, wherein the first object has a shape of a bead, a microbead, a sphere, a microsphere, a cylinder, a rod, or a prismoid.

45. The device of any one of claims 1-43, wherein the first object has a size of 1-100 pm.

46. The device of any one of claims 1-43, wherein the first object has a size of 20-50 pm.

47. The device of any one of claims 1-46, wherein the first fluid comprises bodily fluid.

48. The device of any one of claims 1-46, wherein the first fluid comprises water.

49. The device of any one of claims 1-46, wherein the first fluid comprises a polar liquid.

50. The device of claim 49, wherein the polar liquid is selected from a group consisting of water, alcohols, ketones, formamide, dimethyl formamide, dimethyl sulfoxide, or a combination thereof.

51. The device of any one of claims 1-46, wherein the first fluid comprises a nonpolar liquid.

52. The device of claim 51, wherein the nonpolar liquid is selected from a group consisting of oils, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, fluorinated oils, or a combination thereof.

53. The device of any one of claims 47-52, wherein the second fluid comprises air.

54. The device of any one of claims 47-52, wherein the second fluid comprises an oil.

55. The device of claim 54, wherein the oil is selected from a group consisting of mineral oil, paraffin oil, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, or a combination thereof.

56. The device of any one of claims 1-55, wherein a refractive index of the second fluid is matched with the refractive index of the first fluid.

57. The device of any one of claims 19-56, wherein the second object is selected from a group consisting of biological cells, colloidal particles, nanoparticles, DNA cell molecules, bacteria, viruses, kinesin motors, microtubules, organelles, chromatin, proteins, or a combination thereof.

58. The device of any one of claims 1-57, the device comprising: a volume chamber, fluidically connected to the chamber.

59. The device of claim 58, wherein the change in the shape of the boundary does not cause a change in a height of the interface between the first fluid and the second fluid within the chamber.

60. The device of any one of claims 11-59, wherein the one or more actuators are at least partially disposed within the volume chamber.

61. The device of any one of claims 19-60, wherein the movement of the one or more of the first object and the second object is configured to be observable under a microscope.

62. The device of any one of claims 11-61, wherein, when the one or more actuators is not actuated, the one or more walls has the geometry of an original geometry and the boundary has the shape of an original shape.

63. A system comprising: a plurality of microfluidic chambers; anda plurality of devices claimed in claim 1, each of the plurality of the devices fluidically connected to one of the plurality of the microfluidic chambers such that each device is configured to receive the first fluid, the second fluid, and the first object.

64. A method comprising: receiving a first fluid, a second fluid, and a first object in a chamber, wherein the chamber comprises one or more walls defining a boundary; and changing a shape of the boundary to cause a movement of the first object at the interface between the first fluid and the second fluid, wherein an interface between the first fluid and the second fluid forms a contact angle with the one or more walls, the contact angle measured along the direction of the first fluid, wherein at least one of (a) and (b) occurs:(a) when the contact angle is than 90° and a density of the first object is greater than the density of the first fluid, the interface between the first fluid and the second fluid is concave down at the first object, and(b) when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid, the interface between the first fluid and the second fluid is concave up at the first object, and wherein the movement of the first object is confined within the boundary.

65. The method of claim 64, wherein the movement of the first object comprises one or more of a trapping of the first object at a location, a translation of the object, and a rotation of the first object.

66. The method of claim 64, wherein the movement of the first object comprises a trapping of the first object a) at a vertically lowest point on the interface between the first fluid and the second fluid within the boundary, when the contact angle is less than 90° and the density of the first object is greater than the density of the first fluid or b) at a vertically highest point on the interface between the first fluid and the second fluid within the boundary, when the contact angle is equal to or greater than 90° and the density of the first object is less than the density of the first fluid.

67. The method of any one of claims 64-66, wherein the boundary has a width of about 1- 3 mm.

68. The method of any one of claims 64-66, wherein the boundary has a width of about 1- 2 mm.

69. The method of any one of claims 64-66, wherein the boundary has a width that is less than or about a capillary length of the interface between the first fluid and the second fluid.

70. The method of any one of claims 64-66, wherein the boundary has a width that is less than or equal to 1.1 times a capillary length of the interface between the first fluid and the second fluid.

71. The method of any one of claims 64-66, wherein the boundary has a width that is less than or equal to a capillary length of the interface between the first fluid and the second fluid.

72. The method of any one of claims 64-71, wherein the shape of the boundary comprises a circle, an oval, a triangle, a square, a rectangle, a quadrilateral, a polygon, a rounded triangle, a rounded square, a rounded rectangle, a rounded quadrilateral, a rounded polygon, a circular arc, or a polynomial curve.

73. The method of any one of claims 64-72, the method comprises applying a force to at least one of the one or more walls to cause the change in the shape of the boundary.

74. The method of any one of claims 64-73, the method comprising actuating one or more actuators to cause a change in a geometry of the one or more walls, causing the change in the shape of the boundary, wherein the one or more actuators is operatively connected to at least one of the one or more walls75. The method of any one of claims 74, the method comprising causing a first movement of a manipulator to cause a second movement of the one or more actuators, wherein the manipulator is disposed outside the chamber, wherein the manipulator is attached to the one or more actuators,76. The method of any one of claims 74-75, wherein the change in the geometry of the one or more walls comprises a deformation of at least one of the one or more walls.

77. The method of any one of claims 74-75, wherein the change in the geometry of the one or more walls comprises one or more of a translation or a rotation of at least one of the one or more walls.

78. The method of any one of claims 74-77, wherein the actuating the one or more actuators comprises applying one or more of a mechanical force, an electric potential, an electric current, a magnetic force, a pneumatic pressure, or a hydraulic pressure.

79. The method of any one of claims 74-78, wherein at least one of the one or more actuators comprises a piezoelectric actuator or a linear force actuator.

80. The method of any one of claims 64-79, the method comprises determining a dynamic property of the first object based on the movement of the first object.

81. The method of any one of claims 64-80, wherein the actuating the one or more actuators exerts a force on the first object that is between 1-10 pico Newton.

82. A method of any one of claims 64-81, wherein the movement of the first object causes a trapping or a movement of a second object physically connected to the first object.

83. The method of any one of claims 64-82, wherein the movement of the first object exerts a force on a second object physically connected to the first object.

84. The method of any one of claims 74-83, wherein the one or more actuators comprises two actuators.

85. The method of any one of claims 74-84, wherein the one or more actuators comprises three actuators.

86. The method of any one of claims 74-85, wherein the one or more actuators comprises four actuators.

87. The method of any one of claims 74-86, wherein each wall is connected to at least one actuator.

88. The method of any one of claims 74-87, wherein the one or more actuators have a thickness of about 0.5 to about 1 mm.

89. The method of any one of claims 74-88, wherein an actuator of the one or more actuators comprises one or more supports to reduce a capillary attraction from the other actuators.

90. The method of claim 89, wherein the one or more supports have a thickness of about 0.5 mm to about 1 mm.

91. The method of any one of claims 64-90, wherein the contact angle that the interface between the first fluid and the second fluid forms with the one or more walls is 20-80°.

92. The method of claim 64-91, wherein the contact angle that the interface between the first fluid and the second fluid forms with the one or more walls is 50-70°.

93. The method of any one of claims 64-92, wherein the one or more walls comprises a hydrophilic surface and the first object comprises a hydrophobic surface.

94. The method of any one of claims 64-92, wherein the one or more walls comprises a deformable material.

95. The method of any one of claims 64-92, wherein the one or more walls comprises an elastomeric material.

96. The method of any one of claims 64-92, wherein the one or more walls comprises a rigid material.

97. The method of any one of claims 64-92, wherein the one or more walls comprises a material selected from a group consisting of an elastomeric polymer, polydimethylsiloxane(PDMS), or Formlabs elastic 50A resin, hydrogels, silicone, rubber, polyurethane, or a combination thereof.

98. The method of any one of claims 64-92, wherein the one or more walls comprises a material selected from a group consisting of a thermoset polymer, polycarbonate, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), or a combination thereof.

99. The method of any one of claims 64-92, wherein the one or more walls comprises a material selected from a group consisting of a metal, an alloy, a ceramic, or a combination thereof.

100. The method of any one of claims 64-99, wherein the first object is selected from a group consisting of polystyrene, silica, or a combination thereof.

101. The method of any one of claims 64-99, wherein the first object comprises a colloidal particle.

102. The method of claim 101, wherein the colloidal particle is selected from a group consisting of polystyrene, silica, polymethyl methacrylate (PMMA), glass microspheres, metal microspheres, or a combination thereof.

103. The method of any one of claims 64-102, wherein the first object comprises an aerosol.

104. The method of claim 103, wherein the aerosol is selected from a group consisting of hydrocarbons, alkanes, aromatic hydrocarbons, fumed silica, ice crystals, or a combination thereof.

105. The method of any one of claims 64-103, wherein the first object comprises a biological cell.

106. The method of claim 105, wherein the biological cell is selected from a group consisting of blood cell, bone cell, stem cell, bacteria, sperm cell, muscle cell, oocyte, neuron, epithelial cell, plant cells, protoplasts, or a combination thereof.

107. The method of any one of claims 64-106, wherein the first object has a shape of a bead, a microbead, a sphere, a microsphere, a cylinder, a rod, or a prismoid.

108. The method of any one of claims 64-107, wherein the first object has a size of 1-100 pm.

109. The method of any one of claims 64-107, wherein the first object has a size of 20-50 pm.

110. The method of any one of claims 64-109, wherein the first fluid comprises bodily fluid.

111. The method of any one of claims 64-109, wherein the first fluid comprises water.

112. The method of any one of claims 64-109, wherein the first fluid comprises a polar liquid.

113. The method of claim 112, wherein the polar liquid is selected from a group consisting of water, alcohols, ketones, formamide, dimethyl formamide, dimethyl sulfoxide, or a combination thereof.

114. The method of any one of claims 64-109, wherein the first fluid comprises a nonpolar liquid.

115. The method of claim 114 wherein the nonpolar liquid is selected from a group consisting of oils, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, fluorinated oils, or a combination thereof.

116. The method of any one of claims 110-115, wherein the second fluid comprises air.

117. The method of any one of claims 110-115, wherein the second fluid comprises an oil.

118. The method of claim 117, wherein the oil is selected from a group consisting of mineral oil, paraffin oil, hydrocarbons, alkanes, aromatic hydrocarbons, silicone oils, or a combination thereof.

119. The method of any one of claims 64-118, wherein a refractive index of the second fluid is matched with the refractive index of the first fluid.

120. The method of any one of claims 82-119, wherein the second object is selected from a group consisting of biological cells, colloidal particles, nanoparticles, DNA cell molecules, bacteria, viruses, kinesin motors, microtubules, organelles, chromatin, proteins, or a combination thereof.

121. The method of any one of claims 64-120, wherein the chamber is fluidically connected to a volume chamber.

122. The method of claim 121, wherein the change in the shape of the boundary does not cause a change in a height of the interface between the first fluid and the second fluid within the chamber.

123. The method of any one of claims 74-122, wherein the one or more actuators are at least partially disposed within the volume chamber.

124. The method of any one of claims 82-123, the method comprising observing the movement of the one or more of the first object and the second object under a microscope.

125. The method of any one of claims 74-124, wherein, when the one or more actuators is not actuated, the one or more walls has the geometry of an original geometry and the boundary has the shape of an original shape.

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