It is important to make sure only one cell occupies each droplet to be able to attribute each droplet’s behavior, such as fluorescence signal intensity, to a single cell behavior. On the other hand, it is preferred to avoid droplets without any cells to increase the efficiency of the experiment and reduce the reagent consumption.

However, this might be challenging to achieve since cells are randomly distributed in their carrier solution. It has been shown that cell encapsulation follows the Poisson formula in this case.

\[ P(X)=\frac{\lambda^{X}e^{-\lambda}}{X!} \]

In this formula, P shows the fraction of droplets that will contain X cells. \( \lambda \) is the mean number of cells per droplet and is calculated by multiplying cell concentration by the droplet volume. Input the cell concentration and droplet size in the calculator to find the average number of cells and fraction of droplets containing 0, 1, and 2 cells in your experiment.

Hydrogels are hydrophilic polymers that can retain a considerable amount of water within their structure. They have found extensive applications in microfluidics due to their inherent characteristics. Due to their high degree of biocompatibility, they are frequently used as cell-encapsulation matrices, building blocks for biomaterials, PCR medium, materials for drug delivery and protein expression studies, etc.

Hydrogel Types

Hydrogels can be found in both natural and synthetic forms. Natural hydrogels have the advantage of biodegradability while synthetic hydrogels can be customized for specific applications. Click on each group to see more details.

Natural Hydrogels

Natural hydrogels are extensively used in tissue engineering and regenerative medicine. Some of the commonly used natural hydrogels are polysaccharides (such as agarose, alginate, chitosan, hyaluronic acid) or proteins (such as gelatin, collagen, fibrin).

Hydrogel Types

Hydrogels can be found in both natural and synthetic forms. Natural hydrogels have the advantage of biodegradability while synthetic hydrogels can be customized for specific applications. Click on each group to see more details.

Synthetic Hydrogels

Synthetic hydrogels are of paramount interest to researchers since they can be modified with functional groups such as peptides, oligonucleotides, and cleavable linkages. Some of the frequently employed synthetic hydrogels are polyethylene glycol (PEG), polyacrylic acid (PAA), and polyvinyl alcohol (PVA) and polyacrylamide.

Hydrogels are capable of swelling in water and keeping a huge amount of water within their structure. However, hydrogels need to be crosslinked to avoid water dissociation. Crosslinking is a covalent or ionic bond that connects polymeric chains of the hydrogels thus reduces the ability of the individual polymer chains to move. This results in turning the liquid hydrogel into gel or solid phase. Depending on the hydrogel type and the crosslinking method, this process could be reversible or irreversible.

A variety of chemical, photo, and thermal techniques have been employed in microfluidics for cross-linking hydrogels to create particles or cell-laden hydrogels. In chemical crosslinking, molecules of cross-linkers are added to create a bond between polymeric chains upon exposure to UV radiation. Photo crosslinking is possible when a photosensitive group exists that allows the polymer chains to form crosslinkage. Also, some hydrogels can transit from liquid to gel form by changing the temperature. The following table shows some common hydrogels and their corresponding method for crosslinking.

1- B. G. Chung, et al., Microfluidic fabrication of microengineered hydrogels and their application in tissue engineering, Lab. Chip.
2- W. E. Hennink, C.F. van Nostrum, Novel crosslinking methods to design hydrogels, Adv. Drug. Deliv. Rev.

You can use the following calculator to estimate the pressure drop in a rectangular single channel.
The default values are for pressure drop of water at T=20oC in a 10mm rectangular channel with a cross-section of 50µm×100µm.

We have partnered with uFluidix to manufacture droplet generators. Our droplet generators use a simple method for avoiding fittings and connectors. Please watch the video for further instruction.