In this blog post, I will explain the manufacturing methods and characteristics of microdevices used in bio-micro/nano-mechanics research in an easy-to-understand manner.
Mechanical Engineering and Bio-Micro/Nano Mechanics
Beyond familiar fields such as hydrogen fuel cell vehicles and AI robots, mechanical engineering encompasses a wide range of areas—including mechanical design, robotics, nanomechanics, mechatronics, applied mechanics, systems control, and combustion—based on the four branches of mechanics: thermal, fluid, solid, and dynamics. Recently, as the boundaries between disciplines have blurred, interdisciplinary research combining ultra-micro nanotechnology and biotechnology has become active. In particular, since the beginning of the 21st century, “Micro” and “Nano” have established themselves as core keywords across various fields, and research related to “Bio-Micro” and “Bio-Nano” is gaining significant attention.
Here, “Bio-Micro/Nano mechanics” is a term combining biology, the prefixes “Micro” and “Nano” (denoting the micro- and nano-scales), and mechanical engineering mechanics. It refers to the field that studies mechanical phenomena and devices at the micro- and nano-scales in relation to humans and living organisms.
The Need for Microdevices for In Vitro Experiments
Research in this field has traditionally relied heavily on animal testing; however, due to significant ethical and financial constraints associated with animal testing, there has been a growing demand for microdevices capable of simulating biological responses in vitro. Engineering-based microdevices enable medical research through cell culture to be conducted with greater precision and in a more ethical manner, playing a crucial role in disease research and treatment development.
Materials Used in Microdevices: PDMS
Microdevices typically include channels capable of culturing cells and primarily use PDMS (polydimethylsiloxane, Sylgard 184) as their main material. PDMS is transparent, elastic, and highly permeable to various liquids and gases, making it suitable for cell culture. Additionally, its ability to adhere stably to relatively large surface areas and to be treated from hydrophobic to hydrophilic makes it advantageous for the fabrication of microfluidic channels.
Microdevice Fabrication Process (Overview of Soft Lithography)
Since microdevices have structures on a very small scale, they are difficult to fabricate by hand and require computer-aided design and microfabrication techniques. The overview of the fabrication process is as follows. 1) The device geometry is determined using computer-aided design (CAD) software. 2) The designed geometry is patterned onto a thin silicon wafer to create a master; at this stage, the features are raised (positive relief). 3) The completed master is placed on a glass substrate, and liquid PDMS is poured over it to cure. 4) The PDMS solidifies after curing for a set period at approximately 80°C. 5) Carefully peeling off the hardened PDMS replicates the master’s shape in relief, forming the channel structure. 6) A PDMS piece cut to the required size is bonded to a glass substrate to complete the channel; to enhance adhesion, the glass and PDMS surfaces are activated via plasma treatment. 7) Surfaces that have become temporarily hydrophilic due to plasma treatment revert to hydrophobicity over time in room-temperature air; heating (e.g., in an 80°C oven for 1–2 days) accelerates this return to their original properties.
The fabricated device consists of a channel and a PDMS body, and cells are cultured and observed inside the channel. At the microscale, the force due to surface tension is relatively greater than that due to channel pressure; therefore, the device can be designed so that fluids do not mix between channels but form an interface, making it suitable for the precise observation of cell-cell interactions.
Applications and Significance
Microdevices capable of reproducing intracellular activity in vitro in this manner help reduce the need for animal testing and contribute to identifying the causes of diseases and developing treatments. Bioengineering focuses on applying engineering principles to biology and medicine to uncover the root causes of diseases and develop necessary therapeutic devices, offering a distinct perspective and value compared to medicine, which is centered on diagnosis and treatment.
