Future Science 1: Microfluidic Lab-on-a-Chips and BioMEMS

Before starting the design of microfluidic devices, make your plan according to final use, fabrication, material, integrations etc.

• What operating conditions for the final device?

• What is the method of fabrication and chip material type?

• What will be the flow type and flow rate?

• 2D or 3D design software related to fabrication method?

• Designing software; AutoCAD, SolidWorks, 3D Builder…

• What is the maximum size of the device?

• What are the channel widths, lengths and heights?

• What is the minimum feature size necessary?

• What will be the connector types and port sizes?

• Whether sensors or actuators are present or not?

• What are the non-channel layers for bonding

• How to make design controls?

Initially making a layout for your microchannel designs and using the same structure for multiple projects advances everything faster. The main challenge in today's microfluidics is the standardization. Make your own standard limits or apply formats for fabrication instruments. Here you can find two approaches

1. Set your design by the sizes of normal microscopy glasses or covers

2. Set your design maximum by photoresist-coated silicon or glass wafer sizes

The software I use for 2D design in DXF in the lecture:

* Nanocad, free version https://nanocad.com/products/nanocad-free/download/

Making designs in 2D format using CAD software is easier and for most of the fabrication methods it is DXF  format is required. Here

1. I summarize the details of how to draw a microfluidic device using CAD software.

2. I show the basics about determining the specs for a gradient generation microfluidic channels.

3. The channel heights will be formed during the fabrication part, not during the design.

The software I use for 2D design, in the lecture is:

* Nanocad, free version https://nanocad.com/products/nanocad-free/download/

Making designs in 2D format using CAD software is easier. If 3D structures are not necessary then converting the 2D into 3D form solves the need. Here

1. I summarize the gradient reservoir device, made in the previous lecture.

2. I converted DXF files into STL with online tools.

3. I arranged the 3D mould using simple 3D Builder software

The software I use for 2D design, conversion, and 3D mould arrangement in the lecture are:

* Nanocad, free version https://nanocad.com/products/nanocad-free/download/

* DXF to STL conversion online tool https://imagetostl.com/convert/file/dxf/to/stl

* Microsoft 3D Builder https://apps.microsoft.com/store/detail/3d-builder/9WZDNCRFJ3T6

Making designs directly in a 3D format using CAD software may be necessary for

• The chosen fabrication method

• simulation of applications related to 3D structures

• publications of computer models of designs

Here in this lecture

1. I summarize the most common CAD software suitable for direct moulding design.

2. Give information about the additional tips about making the designs.

The software I mentioned in the lecture are;

* FreeCad, https://www.freecad.org/index.php

* SolidWorks, https://www.solidworks.com

* Microsoft 3D Builder https://apps.microsoft.com/store/detail/3d-builder/9WZDNCRFJ3T6

* 3DuF, https://3duf.org

After making designs in 2D or 3D with formats of DXF, STL or others, it is possible to analyze the flow characteristics and other physical properties inside channels using Computational Fluid Dynamics (CFD) simulation software. Here you can find the primary ones and their capabilities in a bite.

Here, basic starting point of Comsol lateral flow simulation is described.

Here, basic starting point of Ansys droplet flow simulation is described.

Here, basic starting point of Comsol lateral flow simulation is described.

We previously made a gradient generation microfluidic chip design in this section.

Now we are making control of liquid flow using simulation software. During the simulation, we will edit and update the designs.

Here;

• I summarize the details of how to make CFD simulations of microfluidic device designs in DXF format.

• I show the basics of laminar flow simulation and transport of diluted species simulation.

• The channel heights are neglected during the simulation.

The software I use in the lecture is:

* Nanocad, free version https://nanocad.com/products/nanocad-free/download/

* Comsol Multiphysics, https://www.comsol.com/

This is the second part of the simulation subject previously. We previously made a gradient generation microfluidic chip design in this section.

Now we are making control of liquid flow using simulation software. During the simulation, we will edit and update the designs.

Here;

• I summarize the details of how to make CFD simulations of microfluidic device designs in DXF format.

• I show the basics of laminar flow simulation and transport of diluted species simulation.

• The channel heights are neglected during the simulation.

The software I use in the lecture is:

* Nanocad, free version https://nanocad.com/products/nanocad-free/download/

* Comsol Multiphysics, https://www.comsol.com/

This is the last part of section 2 for microfluidic device design. The artificial intelligence of this year is capable of making channel designs and drawings. GPT4 is not a master but a good learner. Let's see what we can find.

The software I use in the lecture is:

* ChatGPT, free version https://chat.openai.com/

* OPENSCAD, https://openscad.org/

In this lecture, I try to give you the instruments and techniques for setting up your microfluidics laboratory.

I will try to provide you pros and cons of flow control methods together with real application examples.

In microfluidics latency is the time needed by the microfluidic flow controller to react to the set order. 

The settling time includes the response time, plus the rise time and finally, the time needed to be within the specified error margin.

Processing time is the time needed between the reaction of the microfluidic flow controller and the first move in the setup.

Response time is the length of time between an indication of the start of the flow and the display of the first change in flow.

Capillary-driven microfluidics offers a unique approach to fluid manipulation without relying on external forces. Instead, it harnesses the inherent capillary action of materials. When a liquid is introduced at one end of a microchannel, it readily fills the channel, driven by surface interactions. These interactions can be facilitated by materials such as absorbent paper, hydrophilic surfaces, or even microstructured grooves at the bottom of the microchannel, allowing for precise control of fluid movement.

In summary, capillary-driven microfluidics is a versatile and powerful technique that leverages capillary action to control fluid flow in microchannels. Understanding and manipulating parameters such as wettability, contact angles, capillary pressure, corner flow, flow rate, and flow resistance is essential for designing functional and reliable capillary flow systems, with broad applications in fields ranging from diagnostics to analytical chemistry.

In essence, while the designs and methods for achieving power-free flow in microfluidic devices can be sophisticated, the underlying principle remains constant. it is entirely feasible to transport a specific volume of liquid sample through these devices via passive actuators, all without the need for pumps, pulsation, or external power sources.

Among the various types of active pumps, one of the most commonly utilized is the syringe-driven pump. This cost-effective solution is favoured in research laboratories and some industrial instruments equipped with original equipment manufacturer syringe pump actuators.

Syringe pumps can either be readily available off-the-shelf or built through do-it-yourself projects found on the internet. Critical components of these pumps include a drive-screw and a motor responsible for its rotation, while a pusher block keeps the syringe in position to ensure the flow continues. The motor's capacity and the step size of the screw play a pivotal role in determining the system's minimum flow rate and flow resolution, while the maximum flow rate is influenced by the inner diameter of the syringe.

Pressure-regulated pumps are essential tools in microfluidics, offering precise control over fluid flow. They function by maintaining a constant pressure within a closed microfluidic system, ensuring a consistent and stable flow rate.

Peristaltic pumps employ a unique mechanism involving the alternating compression and relaxation of a flexible tube containing the liquid, creating a drawing action that generates fluid flow. Like any technology, peristaltic pumps come with distinct advantages and disadvantages.

Selam Researchers

Microfluidics is all about finely controlling the flow of tiny amounts of fluids, and different valves play a crucial role in achieving this control.

Quake valves are these pneumatic valves that folks use quite often in microfluidics. Now, these valves are crafted in three layers: there's one layer for the control channel, another for the fluid channel, and a bottom layer.

People love using Quake valves in all sorts of microfluidic applications, like PCR, protein separation, and cell sorting. However, there are a couple of quirks to keep in mind.