Operations of microfluidic devices often rely on precisely controlled, laminar flow of fluid(s). It is often required that a pressure differential driving a fluid flow within a microfluidic device is stable. As many applications of microfluidic devices are associated with biological fluids that would ideally be kept sterile, a peristaltic pump would preferably be relied upon to drive fluid flow through the microfluidic devices. In this manner, a microfluidic system can be considered a fully closed system whose internal flow channels are kept out of contact with the surrounding atmosphere.
The present disclosure relates to passive pressure wave dampener systems. Microfluidic devices often have a liquid flow or suspension/mixture driven through one or more flow channels by a creation of a pressure gradient between an input port(s) and an output port(s) of the flow channels of the microfluidic devices. Inasmuch as the fluidic streamlines within such devices must be predictable, unchanging, and free of turbulence to enable their proper operation and optimal performance, it is often required that the pressure gradient driving the flow be stable. Many applications of microfluidic devices in particular are associated with biological fluids that would ideally be kept sterile by employing a peristaltic pump in order to drive flow through such devices as a fully closed system, kept out of contact with the surrounding atmosphere. However, the pulsatile nature of peristaltic/hose pumps and similar pumping mechanisms often generates unwanted pulses in the flow stream. To address issues that often limit the practical application of peristaltic pumps to microfluidic devices, embodiments of the present disclosure provide a single, membrane-free chamber that—due to its positioning relative to a flow path of a given microfluidic device and methods of use—serves as (1) a passive pressure pulse dampener, (2) an air bubble catcher, and (3) a clean fluid/buffer reservoir for flushing out residual sample of interest within the given microfluidic device after an input sample has been fully processed.
In one embodiment, the present disclosure provides an example passive pressure wave dampener system. An example system includes an input reservoir, a pump as defined below, a passive dampener device, and a microfluidic device. The input reservoir is configured to hold a sample. The pump is fluidically coupled to the input reservoir. The pump causes a sample fluid flow in the system. The passive dampener device is fluidically coupled to the pump. The passive dampener device is configured to dampen a pressure wave created by the pump in the sample fluid flow. The passive dampener device includes a chamber (e.g., a rigid chamber having a rigid wall or walls or a flexible chamber having a flexible wall or walls) configured to hold a fluid pressurized by the pump. The microfluidic device is fluidically coupled to the passive dampener device. The microfluidic device is configured to separate and sort a particle of interest from the sample fluid flow.
In another embodiment, the present disclosure teaches an example method for dampening a pressure wave to smoothen a pulsatile fluid flow in a microfluidic device. An example method includes pumping, via a pump, a sample from an input reservoir to form a sample fluid flow. The method further includes dampening, via a passive dampener device, pressure waves induced in the sample fluid flow by the pump. The method further includes introducing the sample fluid flow with dampened pressure waves to a microfluidic device for sample sorting.
The foregoing features of the present disclosure will be apparent from the following detailed description of the present disclosure, taken in connection with the accompanying drawings, in which:
The present disclosure relates to passive pressure wave dampener systems. Example systems and methods are described in detail below in connection with
Operation of microfluidic devices often rely on precisely controlled, laminar flow of fluid(s). For example, a microfluidic device can often transport particular cells or particles of interest in a fluid suspension through a network of channels, which may or may not contain obstacles, bifurcations, or other features employed to effectuate a separation or sorting of said cells/particles as the fluid suspension is driven through such a device. To ensure predictable/laminar fluidic streamlines, a pressure differential between an input of the microfluidic device and one or more outputs of the microfluidic device, which drives a flow of fluid, must be essentially non-pulsatile and stable. The pressure differential can be created by simple gravity/hydrostatic pressure, a syringe pump, or other means of producing a compressive force on an input sample and/or a headspace above the input sample. These pressure differential creation approaches are often used with microfluidic and/or other flow-through devices in order to achieve an acceptably stable flow, which allows cell separation features within the microfluidic and other flow-through devices to function as intended. Stable fluid dynamics within the microfluidic and/or other flow-through devices also minimizes shear stress on a flowing sample, which in many cases may contain blood cells and/or other biological material that is inherently susceptible to damage or activation caused by elevated shear stress.
Unfortunately, both gravity-driven and syringe-driven fluid pressurization approaches suffer from drawbacks that limit their usefulness in practice. For example, it is difficult to achieve more than a few feet of hydrostatic pressure (i.e., about 2-3 pounds per square inch (PSI)) if using gravity/height alone. In addition, many applications of microfluidic devices are associated with biological fluids that must be kept sterile. However, because a large portion of the inside of a syringe barrel of a standard syringe ‘touches’ the surrounding air when the syringe is initially empty, a standard syringe is by nature a non-sterile system unless it is used in a fully sterile environment such as a biocontainment hood or cleanroom, which limits its utility for applications requiring sample sterility. Further, there are upper limits to how much fluid a syringe can hold. Syringe pumps are often not capable of handling syringes larger than 60 milliliters (mL), in rare cases up to 120 mL, in volume. These limitations are particularly restrictive in applications involving biological samples such as blood cell suspensions, in which several hundred milliliters of an input sample may need to be processed and kept completely sterile while driven through a microfluidic device.
While alternative approaches have been developed to sterilely drive blood cell samples through microfluidic devices, a particularly desirable method for creating a pressure differential across a microfluidic device is the use of a peristaltic pump, which functions completely external to the sample itself. The peristaltic pump acts only upon an outer surface of a tubing that connects an input sample to a microfluidic device. The input sample can be often housed in a container (e.g., a flexible bag or other closed container). However, the peristaltic pump unfortunately creates a series of pressure waves with each revolution of the rotating pump-head of the peristaltic pump, as its rollers drive fluid through the tubing. These pressure waves typically render peristaltic pumping unsuitable for driving flow through microfluidic devices.
Two additional practical considerations associated with the use of microfluidic devices are (i) catastrophic results that can occur if one or more flow channels become occluded with an air bubble, as precise/uninterrupted flow conditions are often essential to proper functioning of a microfluidic device, and (ii) an ability to flush the dead volume (as defined below) of a microfluidic device at the conclusion of processing of an input sample, as in many cases it is desirable to minimize a loss of cells or particles of interest within the channels of the microfluidic device itself and/or within its attendant tubing connections.
To address issues that often limit the practical utility of microfluidic devices, embodiments of the present disclosure provide a single, membrane-free chamber that—due to its positioning relative to the flow path of a given microfluidic device and methods of use—serves as a (1) passive pressure pulse dampener, (2) air bubble catcher, and (3) clean fluid/buffer reservoir for flushing out residual sample within the given microfluidic device after an input sample has been fully processed via a peristaltic, or other pulsatile, pumping mechanism as described with respect to
As used herein, a “pump” refers to a device that moves fluids (liquids, suspensions, or gases) in a pulsating manner. Examples of a pump can include a peristaltic pump, a pulsatile pump or other pump that creates pulses in fluids moved by the pump.
As used herein, “passive pressure wave dampener” refers to a dampening system/device/component that operates without electrical power to dampen pressure waves in a fluid flow.
As used herein, a “chamber” refers to a container having a rigid wall(s) or a flexible wall(s) for holding a fluid.
As used herein, a “dead volume” refers to an internal volume in a microfluidic device and its attendant tubing.
As used herein, a “pulse volume” refers to a volume delivered by a pump-head per a periodic pulse generated by a rotation or other mechanism of a pump.
Turning to the drawings,
The passive pressure wave dampener system 100A includes an input reservoir 110A, a pump 120, a passive dampener device 130, and a microfluidic device 140.
The input reservoir 110A is configured to provide an input liquid mixture, such as a priming fluid (e.g., aqueous fluid or buffer) and/or an input sample having a plurality of particles or cells in a fluid (e.g., particulate or cellular suspension), to the microfluidic device 140. The input reservoir 110A includes a container 112A, an input channel or inlet 116A, an output channel or outlet 114A, a flow path 118, and in some embodiments a valve or clamp 122A.
The container 112A (e.g., a flexible bag or any other suitable container) is configured to hold the input liquid mixture. The input channel or inlet 116A is configured to introduce the liquid mixture, which in some embodiments may be performed via sterile tubing weld to one or more bags containing the fluid(s) to be processed, and the output channel or outlet 114A is configured to is in communication with the pump 120. The flow path 118 fluidically couples the input reservoir 110A, the pump 120, the passive dampener device 130, and the microfluidic device 140. The valve or clamp 122A may be used to control a fluid flow entering the pump 120. In some embodiments, multiple input reservoirs can be used as further described with respect to
The pump 120 is configured to pump/pressurize the liquid mixture. The pump 120 can be in communication with tubing forming a portion of the flow path 118 by compressing the flow path 118 in such a manner that the liquid mixture is pressurized, thereby causing a pulsatile output fluid flow from the pump 120. For example, a peristatic pump can compress the flow path 118 as the flow path 118 is acted upon by two or more rotating rollers of the peristatic pump-head 120. Other pulsatile, pumping mechanisms can be used to pump/pressurize the liquid mixture.
The passive dampener device 130 is configured to dampen the series of pressure waves created by the pump 120 in a pulsatile fluid flow in order to smoothen the pulsatile fluid flow. The passive dampener device 130 is disposed downstream of the pump 120 and upstream of the microfluidic device 140. The passive dampener device 130 is external to the pump 120 and microfluidic device 140.
The passive dampener device 130 includes a chamber 132 and a connector 134 (e.g., a T connector). The chamber 132 is configured to hold fluid pressurized by the pump 120. The chamber 132 includes a port 136. Examples of the chamber 132 can include a rigid walled chamber, a flexible walled chamber or any other suitable chamber configured to contain fluid and/or air. The connector 134 is configured to fluidically couple the chamber 132 (e.g., via the port 136), the pump 120 (e.g., via the flow path 118), and the microfluidic device 140 (e.g., via an inlet 142). When the passive dampener device 130 is partially filled by a pressurized fluid, the chamber 132 includes an air headspace 138 (shown in
The microfluidic device 140 is configured to process (e.g., perform cell separation or sorting, or other operations, on) the input sample provided by the input reservoir 110A. The microfluidic device 140 includes an inlet 142, two or more outlets 144, and a flow path (e.g., shown in
The input reservoir 110B is configured to hold and provide an input sample. The input reservoir 110B includes the container 112B, the input channel or inlet 116B, the output channel or outlet 114B, and the valve or clamp 122B. The container 112B holds the input sample. The output channel or outlet 114B outputs the input sample into the flow path 126. The valve or clamp 122B is used to control a fluid flow entering the connector 124.
The input reservoir 110C is configured to hold and provide a priming fluid. The input reservoir 110C includes the container 112C, the input channel or inlet 116C, the output channel or outlet 114C, and the valve or clamp 122C. The container 112C holds the priming fluid. The output channel or outlet 114C outputs the priming fluid into the flow path 126. The valve or clamp 122C is used to control a fluid flow entering the connector 124.
The connector 124 is fluidically couple to the input reservoir 110B, the input reservoir 110C, and the flow path 126. The flow path 126 fluidically couples the input reservoirs 110B and 110C (e.g., via the connector 124), the pump 120, the passive dampener device 130 (e.g., via the connector 134), and the microfluidic device 140 (e.g., via the connector 134 and inlet 142). The valve or clamp 122D is used to control a fluid flow entering the pump 120.
As can be seen in
The chamber 132 can be disposed in an orientation such that errant air bubbles pulled from the input reservoir(s) 110A-110C by the pump 120 and driven toward the inlet 142 of the microfluidic device 140 can flow up into the chamber 132 due to gravity, rather than entering the microfluidic device 140. Further, the pressurized fluid in the chamber 132 acts to push residual particles or cells through the microfluidic device 140 when the sample from the input reservoir(s) 110A-110C is no longer being pumped through the microfluidic device 140 (e.g., when the pump 120 is turned off once the input reservoir 110A/110B has been emptied to the desired degree), as further described with respect to
In preferred embodiments, while the system is in operation the chamber 132 may be disposed such that a longitudinal axis 152 of the chamber 132 and the connector 134 is directed approximately toward the center of the Earth (e.g., along the direction of gravity) and/or in operation the longitudinal axis 152 is substantially perpendicular to the microfluidic device 140.
The size of the chamber 132 can be calculated based at least in part on the type of the pump, the pressure range of a pressure wave produced by the pump, the volume of the chamber to be filled, and the volume per periodic pulse generated by the pump as further described with respect to the Section of “Passive Dampener Volume Calculation.”
The passive pressure wave dampener system 100A or 100B can serve as (1) an effective passive pulse dampener of pressure waves arising from the pump 120 that drives flow of the particulate/cellular sample from the input reservoirs 110A-110C through the microfluidic device 140, (2) a ‘bubble catcher’ to divert and incorporate any unwanted air that may otherwise flow into, and confound operation of, the microfluidic device 140, and (3) a reservoir of clean fluid/buffer to be used to flush residual particulates/cells through the microfluidic device 140 following the desired degree of emptying of the input reservoirs 110A-110C, as further described in
In step 202, the pump 120 pumps a priming fluid from a first input reservoir. For example, the input reservoir 110A shown in
In step 204, the chamber 132 automatically fills with the priming fluid pumped out of the input reservoir 110A or 110C until the chamber 132 reaches a steady state at which a pressure in the chamber 132 matches a maximum pressure created by the pump 120. Errant air bubbles can be pulled from the input reservoir 110A or 110C by the pump 120 and driven toward the inlet 142 of the microfluidic device 140 and flow up into the chamber 132 due to gravity rather than entering the microfluidic device 140.
The two or more outlets 144 of the microfluidic device 140 can be occluded (e.g., via clamping) to allow a resulting increase in pressure within the microfluidic device 140 to raise the air solubility of the priming fluid, thereby increasing the dissolution rate of any air that had been trapped within the microfluidic device 140 during priming. Examples are described with
In step 206, the pump 120 pumps a sample (e.g., a particulate/cellular suspension of interest) from the first input reservoir or a second input reservoir. For example, a sample can be injected, or introduced via a sterile tubing weld, into the input reservoir 110A shown in
In step 208, the passive dampener device 130 dampens pressure waves induced in the sample fluid flow by the pump 120. The pump 120 can cause a sample fluid flow in the system and create a pressure wave in the sample fluid flow. The passive dampener device is disposed downstream of the pump and upstream of the microfluidic device.
In step 210, the sample fluid flow with dampened pressure waves is introduced to the microfluidic device 140 for sample sorting. The outlets 144 of the microfluidic device 140, if previously occluded, will have been opened, and the sample can be driven though the microfluidic device 140. As the chamber 132 has reached the steady state during the priming stage described in steps 202 and 204, the sample (having particulates/cells with a density higher than that of water) are completely or almost completely directed into the microfluidic device 140 instead of being diverted into the chamber 132. Any small amount of sample diverted to the dampening chamber 132 during pumping would largely be expelled and driven through the downstream device once the pumping mechanism is halted during step 212. Examples are described with
In step 212, when the sample is no longer being pumped through the microfluidic device 140, the chamber 132 automatically releases the priming fluid to flush residual particles or cells from the dead volume of the microfluidic device 140 and into one or more downstream output collection vessels (not shown) via the outlets 144 of the microfluidic device 140. Examples are described with
The passive dampener device 130 can serve as an air bubble catcher. For example, during and after this priming stage, any errant air bubbles 420 that may be pulled from the input reservoir 110A by the pump 120 and driven toward the inlet 142 of the microfluidic device 140 will flow up into the chamber 132 due to gravity, rather than entering the microfluidic device 140. The errant air bubbles 420 are trapped within the chamber 132, merging with the air of its headspace 138. As shown in
The pump (e.g., a peristaltic/hose pump) can be used in a sterile environment, because the pump can provide a mechanism to drive unlimited amounts of input sample for device processing in a manner that maintains the sterility of a sterile input sample, provided that the interior of the input reservoir (e.g., the input reservoirs 110A-110C in
A size of a passive dampening chamber (e.g., the chamber 132 in
One skilled in the art will appreciate that peristaltic pumps can have a known number of rollers which are spaced a known distance apart around a circular pump-head. These dimensions along with knowledge of the internal diameter of the tubing that is being periodically squeezed by the pump-head rollers, to generate a peristaltic flow, allows for a calculation of the so-called ‘pulse volume’ (as defined above) of a pump/tubing combination. In general, the larger the pulse volume the larger the amplitude of the pressure waves generated by the pump, and the larger the amount of trapped/pressurized air that needs to be housed by the dampening chamber of the present disclosure.
In general, if one knows a degree of pressure variation that occurs in a system (with a given pump, passive dampener device, and microfluidic device), in which a system pressure varies between a minimum pressure (Pmin) and a maximum pressure (P max), and a dampening chamber total volume is Vd when the dampening chamber is empty, and the dampening chamber is filled to a fraction of ffilled during operation of the particle processing system, a common, isentropic process assumption is made in which a ‘pump dampener factor’ fd (e.g., a constant associated with a given type of a pump) for the system can be calculated using the Equation (1) as follows:
Where Vp is a pulse volume (e.g., a fluidic volume per periodic pulse generated by the associated pump), and n is a constant that is specific to the gas being used within such a dampener (e.g., for air or nitrogen at room temperature, n≈1.4).
Different pumps generally show different values of fd. Based on available literature, values of several pump types are shown in the table below, with ‘hose pump’ a synonym of peristaltic pump:
Syringe pumps may also benefit from the use of the present disclosure, though their degree of pressure fluctuation (due to intermittent operation of a stepper motor compressing the syringe) is often significantly smaller than that of peristaltic pumps, and therefore when using a syringe-based pumping approach a correspondingly-smaller dampening chamber can be employed.
Once a pump dampener factor fd is known for a given pump, the known fd value can be used to estimate the total volume Vd of the passive dampening chamber that can be used in the same system to generate an acceptably small pressure variation, ΔP, to ensure acceptable performance of the downstream microfluidic device. The total volume Vd of a passive dampening chamber can be calculated using the Equation (2) as follow:
In practice, however, due to the aforementioned complexities in a given pump/device system setup, some degree of trial and error may be needed to determine an appropriately-sized passive dampener for a given application.
For a microfluidic device intended to separate/filter cells in a flowing suspension by size, in which individual device output tubing effluent streams are intended to carry different-sized cell cohorts to corresponding collection vessels, any pressure fluctuations may cause unwanted mixing of the fluidic streams carrying cells of different sizes (or one or more cell-free streams), particularly near the exit of the microfluidic device. The passive dampener device taught herein can dampen fluidic sample pressure waves to reduce or eliminate such unwanted mixing such that cells within the sample can be properly sorted by the internal channels of the microfluidic device, as described with respect to
As shown in
As shown in
It should be understood that the operations and processes described above and illustrated in the figures can be carried out or performed in any suitable order as desired in various implementations. Additionally, in certain implementations, at least a portion of the operations can be carried out in parallel. Furthermore, in certain implementations, less than or more than the operations described can be performed.
In describing example embodiments, specific terminology is used for the sake of clarity. For purposes of description, each specific term is intended to at least include all technical and functional equivalents that operate in a similar manner to accomplish a similar purpose. Additionally, in some instances where a particular example embodiment includes multiple system elements, device components or method steps, those elements, components or steps may be replaced with a single element, component or step. Likewise, a single element, component or step may be replaced with multiple elements, components or steps that serve the same purpose. Moreover, while example embodiments have been shown and described with references to particular embodiments thereof, those of ordinary skill in the art will understand that various substitutions and alterations in form and detail may be made therein without departing from the scope of the present disclosure. Further still, other embodiments, functions and advantages are also within the scope of the present disclosure.