Question 1

What is soft lithography and how does it differ from traditional lithography?

Accepted Answer

Soft lithography uses soft elastomeric materials like polydimethylsiloxane (PDMS) to perform microfabrication, making it rapid, simple, and inexpensive compared to traditional methods. While conventional lithography relies on light and light-sensitive polymers on rigid substrates, soft lithography employs flexible elastomeric stamps to pattern complex structures. This approach has successfully fabricated microfluidic systems and other bioengineering devices.

Question 2

What are the main steps in creating a soft lithography stamp?

Accepted Answer

The first step involves fabricating a master mold using traditional photolithography on a silicon substrate. Next, an elastomer mixture of PDMS and curing agent in a 10:1 ratio is prepared and degassed to remove air bubbles. The degassed mixture is poured onto the master mold, baked at 60 degrees Celsius for one hour, then cooled naturally. Finally, the cured PDMS is removed from the mold, creating a flexible elastomeric stamp with relief features.

Question 3

How does the printing technique in soft lithography work?

Accepted Answer

In soft lithography printing, the elastomeric stamp is first coated with a transferable ink such as octadecanethiol (ODT). The inked stamp is then placed on a substrate like gold, transferring only the ink from the raised stamp surface onto the substrate. When the stamp is removed, the result is a direct replication of nano-scale features from the stamp onto the substrate surface.

Question 4

What is the difference between molding and printing in soft lithography?

Accepted Answer

In printing, an inked stamp transfers ink patterns directly onto a substrate surface. In molding, the stamp itself serves as a mold pressed into uncured polymer, which is then cured and peeled away to reveal the pattern. Both techniques achieve direct replication of nano-scale features, but molding creates a negative impression while printing creates a positive transfer of the stamp's raised features.

Question 5

How are multilayer microfluidic systems fabricated using soft lithography?

Accepted Answer

Multilayer microfluidic systems are created by fabricating individual PDMS layers using different master molds. Each PDMS cast is then cleaned, aligned, and layered on top of one another, then baked together. The multiple PDMS layers enable efficient separation of fluids from cells via a semipermeable PDMS membrane, allowing researchers to study how different microenvironments affect mammalian cells through controlled diffusion.

Question 6

What is mechano-profiling and how does soft lithography enable it?

Accepted Answer

Mechano-profiling studies mechanical parameters like forces applied by microorganisms on their environment. Soft lithography creates unconventional structures such as flexible microposts that cells can grow on. As cells interact with these posts, they bend slightly, allowing researchers to measure the bending and calculate the forces exerted by different cell types, providing insights into cellular mechanics.

Question 7

What are the key applications of soft lithography in bioengineering?

Accepted Answer

Soft lithography has applications ranging from molecular analysis to clinical diagnostics and drug development. It fabricates microfluidic channels for biosensing applications, creates flexible microposts for studying cellular forces, and enables multilayer systems for examining microenvironment effects on mammalian cells. These bio microelectromechanical devices represent versatile tools for advancing bioengineering research and medical diagnostics.

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