Researchers propose cost-effective techniques of making microcontact printing stamps to print protein and grow cells.

Adherent cells—group of cells that stick to and grow on a surface—can help repair damaged skin, cartilage or retina. It is possible to control the shape and size of adherent cells by growing them on substances, such as proteins, that enable or inhibit growth. To study the growth and behaviour of such cells in the lab, researchers grow cells on proteins, printed in different shapes on glass or plastic. The protein is printed on the surface using stamps, and the method is called microcontact printing.

In a recent study, researchers from the Indian Institute of Technology (IIT) Bombay have created a novel method for producing such stamps using which patterns of proteins can be printed. The new approach is cost-effective and addresses many drawbacks of conventional protein-printing methods.

Microcontact printing is used in biology to study cell functions, like differentiation and migration, which depend on the shape of a cell. Differentiation is the ability of cells to change from one type to another. The information gathered from these studies can help us develop therapies against disease-causing cells.

“This technique has applications in the fields of diagnostics, virus identification and understanding of basic biology,” says Prof Abhijit Majumder from IIT Bombay, who led the study.

The study was published in the journal Scientific Reports and was funded by Wellcome Trust-DBT India Alliance.

To print proteins of different patterns, we need stamps with those patterns. Photolithography, a technique that employs light as a chisel to etch, is usually used to fabricate these stamps. However, this method requires expertise and is quite expensive. It also needs high-end, sophisticated equipment and depends on using light-sensitive material.

The researchers of the current study made two types of stamps using readily available materials. For the first type, they used polystyrene beads—like those found inside bean bags—measuring about half a millimetre. When the beads were kept in a puddle of water on a glass surface and the water was allowed to dry slowly, the beads being spherical in shape got hexagonally packed. They then covered the beads surface with a thin layer of polydimethylsiloxane (PDMS), a soft and elastic material, to make the stamp. This approach fixed the beads in place and preserved the hexagonal design.



Stamps made using polystyrene beads, protein islands (green) made using stamps and, cells grown on these islands

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The second type of stamp was made by injecting PDMS into cylindrical needles of different sizes and allowed the PDMS to solidify. The researchers then pulled out these cylinders and arranged them in the desired pattern on a surface. Like in the previous method, they covered the surface of these arranged PDMS cylinders with thin PDMS layer to make the stamp with cylindrical impressions that looked like a series of tightly-packed speed-breakers on the road. These stamps could also be bent to create patterns with curves.

Stamp fabricated using PDMS cylinders without and with curvatures

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The researchers used these stamps to create protein patterns on flat surface and grew mouse cells on these patterns to test the reliability of these stamps. They found that the adherent cells, cultured on these patterns, were healthy and viable. On comparing the uniformity in protein deposition, they discovered that this novel approach was also accurate and the stamps were reproducible similar to traditional photolithography. The proposed method is also easy to carry out and requires less expertise.

However, the most significant advantage of the proposed approach is its low cost. The PDMS stamps made using novel approach cost mere ₹350 with no requirements for maintenance of equipment. On the contrary, stamps made using photolithography cost around ₹1500 a piece, with additional equipment costs adding to lakhs of rupees annually. An additional advantage of using stamp fabrication methods described in this study is that same stamp can be used to print patterns of varying sizes as they can be flattened by applying pressure, thus increasing their surface area.

“Creating stamps with curved surfaces is quite challenging in conventional lithography,” remarks Akshada Khadpekar, a research scholar at IIT Bombay and the first author of this study, highlighting yet another advantage of the proposed method.

Importing expensive lab equipment could be a significant hurdle to doing research. Hence, developing affordable, homegrown technologies, as proposed in the current study, can ease the burden.

“Our method will substantially reduce the cost associated with stamp fabrication and micro-contact printing,” says Dr Abhijit Majumder. “This will help research labs with low funding to expand their field of research, ” he concludes.

This article has been run past the researchers, whose work is covered, to ensure accuracy.