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Microfluidic Solutions

Microfluidics is the study of very small volumes of fluid, and in particular, focuses on how we control and manipulate fluid samples.  These fluid samples may vary in their viscosity or they may contain cells, particles or analytes.  Applications for microfluidics have grown substantially in the past 20 years, ranging from millions of reactions being performed in individual droplets (via droplet generation techniques) to cells being grown on-chip with a view to creating

"organs-on-chip"

thereby helping pharma and biotech companies more quickly assess drug candidates.  The possibilities are growing and Cellix is providing solutions aiding researchers' experimental set-up.

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APPLICATIONS

Droplet Generation

Uniform, Stable Droplets

Reliable, steady flow rate and reproducible, consistent volume-size of droplets.

Precise Liquid Control

Hydrodynamic Focusing

Hydrodynamic focusing and precise multichannel mixing are just some of the applications required for the development of your assays...

Organ-on-Chip

Cell culture on-chip

Microfluidic solutions which enable the culture of cells on-chip mimicking some of the key functions of a living organ.

Volatile Organic Compounds

Analysis made easy

Microfluidic solutions for simple VOC sample preparation and analysis.

Applications

HOW DOES IT WORK?

MICROFLUIDIC CHIP

PUMP

APPLICATION

PROTOCOL

Microfluidic Chip

Microfluidic chips are typically fabricated in plastic, glass or PDMS (PolyDimethylSiloxane) and contain a wide variety of simple to complex geometries:  single microchannels or multiple intersecting microchannels with varying dimensions.  Such geometries facilitate mixing, pumping and sorting of samples, cell growth, cell and particle encapsulation etc.  There are many more designs and applications which can be developed but

your choice of microfluidic chip

(material type, channel geometries, channel dimensions etc.) is crucial to your experimental set-up.  When making your own chip or purchasing a chip, it is important to consider the

material type

as this will offer different capabilities.

Many researchers have the capability to fabricate chips in their own labs and usually PDMS is the material of choice because it is quick, easy to fabricate and low-cost.  However, PDMS has a number of well-known disadvantages and as a result, plastic chips are gaining in popularity, particularly as material properties have improved in recent years offering greater optical quality and multi-layer bonding.  Glass chips are more difficult to fabricate and thus, they are often only produced by specialist companies.

Check out our table below

for a summary of some of the key properties for different material types.

Microfluidic Chip

How does it work?

Table - Chip Material Types

Parameter / Material Type

PDMS

Plastic

Glass

Fabrication Difficulty

Easy: Photolithography or machining of moulds with PDMS chips cast and cured on these moulds

Easy - Medium: Thermomoulding or photolithography

Difficult: Photolithography or wet/dry etching typically by specialist companies

Fabrication Cost

Extremely Low

Low - Medium

High

Multi-layer channels (bonding)

Easy: Bonds easily to glass or PDMS substrates

Easy - Medium

Difficult: Requires high temperature & pressure and extremely clean surfaces.

Smallest Channel Size

<1 um

~100 nm

<100 nm

Optical Transparency

High

High

Extremely High

Thermal Stability

Medium

Medium - High

Very High

Solvent Compatibility

Low

Medium - High

Very High

Permeability to Oxygen

Extremely High: Good for gas transport for cellular studies (e.g. cell culture) but bubble formation causes problems with experiments.

Low

Extremely Low

Hydrophobicity

Hydrophobic: Non-specific adsorption and permeation of macromolecules (e.g. proteins) can cause problems.

Plasma treatment possible but typically lasts short time.

Hydrophobic: Plasma treatment possible and can last several years.

Hydrophilic

Pump - choosing the right one

For many years, syringe pumps were the only option for microfluidics and most papers cited use of Harvard Apparatus or KD Scientific syringe pumps.  The market has since developed and there are now many different types of microfluidic pumps to choose from:

Peristaltic pumps

Standard syringe pumps

Microfluidic syringe pumps

Pressure pumps

Recirculation pumps

Each type of pump has pros and cons so it is important to consider the following to help you

choose the right pump for your application

:

What type of microfluidic chip are you connecting the pump to?

The geometry and channel dimensions of your microfluidic chip will offer different fluidic resistances and this needs to be taken into account before choosing your pump.

What flow rates do you wish to use?

What is the viscosity of your sample?

Blood is much more viscous than water and this can impact flow rates in microfluidic channels.

Do you require a flow sensor?

Flow sensors provide active feedback maintaining accurate and stable flow control.  However, these are typically calibrated for water or oil and are not compatible with blood.

Check out our table below

for a summary of some of the key properties for different microfluidic pumps including what Cellix can offer.

Parameter / Pump Type

Peristaltic

Standard Syringe

Microfluidic Syringe

Pressure

Recirculating

Technology

Peristaltic

Stepper motor

Stepper motor with damper

Pressure

Solenoid

Flow Stability

Low

High

Extremely High

Extremely High

Medium

Flow Rates

uL/min - L/min. Low - High.

pL/min - mL/min. Low.

Limited by syringe size.

High flow rates difficult to achieve - syringe refilled manually.

nL/min - mL/min. Low - High. High flow rates achieved with optional manifold - refills syringe automatically.

uL/min - mL/min. Low - High

uL/min

Low, Pulsatile

Flow Control

Yes (calibration required)

Yes

Yes (flow sensor for ExiGo optional)

Yes

(with flow sensor)

No

Pressure Control

No

No

No

Yes

No

Switching Response Time

High

Low

Extremely High

Extremely High

Medium

Cell Samples

Yes (cell damage likely with squeezing of tubing)

Yes

Yes

Yes

Yes

Blood Samples

No

Yes

Yes (without flow sensor)

No

No

Gas Sample

No

No

No

Yes

No

Fluid Recirculation

No

No

Yes (possible with optional manifold with ExiGo pump)

No

No

Pump

Table - Pump Types

Application

In addition to choosing the right microfluidic chip and pump, you must also take your application into consideration.  Here are some tips and examples of things you need to think about:

Cell sample type?

Pump flow sensors are not compatible with whole blood samples as they are not calibrated for the viscosity of blood.  There are also issues with build-up of cellular debris from blood on the sensors themselves.  So, if blood is your sample, you need to choose a microfluidic pump which can deliver the flow rates you require

without the need for a flow sensor

.

Sample concentration?

With high concentration of samples (cells or particles) you may risk having blockages in the microchannels of your chip.  Here you must be careful to choose a chip with channel sizes which are large enough to handle high concentrations; or if this is not possible, you must dilute your cell sample.  Depending on your sample concentration, you must also consider the risk of sedimentation.  If your flow rate is too low, you may have issues of sedimentation in your sample reservoir.  If you're not sure and you'd like advice on this, please

contact us

.

Choice of tubing?

Connecting the macro-world to the micro-world is a challenge and you must try to minimise rapid changes in cross-section.  For example, when the tubing is connected to the channel of your chip; if the tubing inner diameter (ID) is very large compared with the dimensions/size of the channel of the chip, there will be a high pressure drop at the connection point (tubing-to-chip) resulting in sample sedimentation and blockages.

Application

Protocol

You've spent some of your valuable budget purchasing microfluidic chips and a microfluidic pump for your application.  You took the time to carefully compare all the microfluidic chips and pumps on the market before you made your purchase, ensuring that it meets all the technical requirements for your application.  Your purchase arrived all shiny and new and you set it up in your lab and then you find

it's not working!

This is a frustrating situation for researchers and Cellix's team works hard to ensure that our customers avoid some common mistakes.

Assay protocol is just as important as all the features and benefits of your new microfluidic chip or pump.    Here are some of the key points to consider relating to protocols for microfluidics:

Priming the channels of the microfluidic chip:

Everyone in microfluidics knows that bubbles in a microfluidic chip can ruin their experiment.  Priming channels correctly is key to avoiding this issue.  Cellix's pump-to-chip

tubing connections

are easily primed and plug directly into our chips.  If you're using your own chip, we can offer advice on best methods.

Order of sample-buffer-sheath fluid injection into the microfluidic chip:

The order of injection of your different fluids (sample, buffer or sheath) is really important depending on what you are trying to achieve.  This must be done in the correct order to achieve your desired results.

Step-by-step assay advice:

For common applications, Cellix provides protocols for experimental set-ups

.  If you don't see your application or protocol listed in our

Resource section

, we can offer advice on how your protocol could be developed.

Cellix's Team has >20 years experience in microfluidics and we have worked with researchers all over the world, assiting them in their experimental set-ups.  If you have a questions,

get in touch now

.

Protocol

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