What is Microfluidic and Lab-on-a-chip?
Posted by Nazım Yılmaz on
This is introductory writing to the field. Microfluidics and lab-on-a-chip is a very broad field with many researchers. Often the research is very application-specific and therefore there is no area to fit in this specific writing.
What is microfluidic?
It is the field of engineering that copes with fluids so that it can be caused by liquids, plasma, or fluidized particles but typically it is going to be liquid and these fluids are geometrically constrained on the micro-scale. That means typically it is inside microchannels. The fluid is at least either in two dimensions or in one dimension between two plates. It’s like if you have to plated are very close to each other, let’s say 50 micrometers the liquid that’s in that slits will behave microfluidics and therefore this is kind of part of microfluidics. So it’s a liquid that is within a very small solid domain. It combines the field of physics, fluid mechanics, manufacturing technologies, the application of biomedical engineering, etc. We are interested in small things in fluids and let’s first have a look here at the size of things to be mentioned, so here you can see the length scale going down in size 1 centimeter to 1milimeter .. etc. If we make a cube out of this a 1 cubic millimeter or one cubic centimeter it is what we call a millimeter. When going ten times smaller in size, it is a thousand times smaller in volume, so 10 times more in size a cubic millimeter is a microliter. A cube of 100 by 100 micrometers is a nanoliter.
Microfluidic is typically the field where the channel sizes or recipient sizes between below 1 millimeter down to say micrometer size. When we go 100 nanometers or below, it is called nanofluidics. So it’s a bit of a gray zone what’s the difference between micro and nanofluidics, but you’ll see that the physics on the microfluidics scales is quite specific, and these specific effects are going to be dominating different effects done on the macro scale. The reason for that is that physics again on that scale is again gonna be different than the ones on the micro-scale. It’s gonna be much more electro-fluidic effects are gonna be dominating. The size 100 micrometers that’s the size of an over a cell, 10 micrometers is the size of a blood cell, 1-micrometer size of a bacterium, 100-nanometer size of a virus, and you go smaller than you gained like this is the size of a DNA strand or protein. And if we go even small then you get that nucleation of raindrops in that sense. You go now to a website called http://htwins.net/scale2/ to zoom in and zoom out from the meter scale to the scale of neutrinos and again up to the scale of the galaxy clusters and so you see on different scales how different objects are what objects that we encounter typically in the world.
What is a lab on a chip?
It's an analytical or bioanalytic laboratory that is downscaled to the size of a chip of a small chip-sized object. Think about a device where you tried to integrate all functions that are normally happening in a micro lab or a laboratory and try to integrate on a very small microfluidic scale. LOC is about credit card-sized formats either in class or in plastics very often one has a disposable cartridge together with some kind of readout system. The form of arrays for example on them often there’s some kind of an optofluidic or some electronic detection scheme attached. LOC is a microfluidic device for the optical detection, PDMS, cells using flow or particles of some kind of you know these are kind of the keywords that's always come back. Also, when we check the applications of LOC research, we can look have a closer look at these keywords and maybe first look at what kind of applications people are talking about. It’s about cancer, cells, cytotoxicity, tissue, analysis, array, sensor, blood, bacterial detection. This is kind of the application that we can find back in this word clouds.
The importance of usage LOC devices
When should one use microfluidics or lab-on-chip technologies? I think there are three main reasons why or when one should consider going to microfluidics or the microscale to do things. The first reason is that the application demands that one have a small-scale or micro-scale device. For example, if one wants to monitor something with a wearable or point of care for example one wants to make it implantable like a pacemaker or an insulin pump and implanted in the human body. Also, another thing is that sometimes the thing to handle is very unique for example handling single cells or viruses or DNA, these objects are so small that it is needed a small scale device to be able to analyze them properly. Other reasons can the multiple function integration on a small-scale device, the increased performance of a single analysis, and/or the decrease in cost but let's first look at the increased performance. Microchannels have a large surface-per-volume, low-inertia, and surface effects that are dominating which means that things affect differently on the micro-scale than on the macroscale and that can be beneficial. Let's make a large thermal gradient for doing special chemistry and we need a gradient of 100°C degrees of a very short distance. So if we have 100°C degrees, this is at 0°C degrees at 100°C degrees and microchannels have a certain special temperature gradient. One can generate very easily very high electrical field gradients on the micro-scale. Another fact is surface effects become dominant because when on a micro-scale molecules are always close to the surface thus it can make things very small and precise. In microfluidics that can be due to two reasons, it can be due to manufacturing so if one uses as in other applications if one makes a lot of different devices like if one makes like 100 or thousand devices at the same time, of course, your cost the batch manufacturing. So the fact that you can do everything in parallel gonna drive down the per-device costs. Also, the number of materials that you're going to use is going to be much cheaper if you make it on a micro-scale. But in microfluidics that’s not always the driving force very often the driving force is not a material cost of manufacturing but it’s the consumables. So if one makes a device ten times smaller in size the volume is going to be a thousand times smaller.
So these are the three reasons why people want to downscale and so in my application benefits strongly from one of these or one of these three reasons or a combination of them then one should consider going to the macroscale if see no benefit in these three regions then no reason to go to the micro-scale.
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