Most people consider PDMS or Polydimethylsiloxane when they think about microfluidics or microfabrication. However, since George Whitesides introduced PDMS in microfluidics for the first time in 1998, it has been the material of choice and has grown crucial to the field.
Functional Principles of Microfluidics and PDMS Bonding
PDMS is an inert silicone that can be cast and will conform to the microfluidic structures and channels of the mold where fabricators place it. Engineers create these cast constructions from elevated shapes made in a mold’s cavity. The figures in the mold’s bottom are transferred into the cast component when the PDMS is cast in the mold and removed.
People who handle the glass or silicon-containing matching portions then put in oxygen plasma with the cast components. These parts will bond when precisely assembled after being ignited with oxygen plasma – the covalent nature of the interaction results in a solid binding between the PDMS and mating parts.
Deciding whether you need equipment for a quick proof of concept or gear to streamline and repeat the process in large quantities when bonding PDMS devices is crucial.
A variety of materials are available for PDMS plasma bonding. Moreover, it’s critical to comprehend the tiny variances to ensure the success of your plasma treatment application.
PDMS Material Specifications
Polydimethylsiloxane, also called dimethicone or dimethylsiloxane, is a chemical compound with the acronym PDMS. It belongs to the so-called organosilicon combinations because it is a silicon-based organic polymer.
Since PDMS is optically clear, chemically inert, and thus non-flammable, non-toxic, and biocompatible, its properties are genuinely outstanding. Numerous applications are made possible by these characteristics.
PDMS’s other features include transparency, flexibility, low dielectric constant, gas permeability, biocompatibility, low surface tension, and low solubility.
Food sectors employ it to prevent liquids from foaming. The medical industry uses it to produce medical equipment like contact lenses. PDMS is a critical component of skin lotions and hair treatments in the cosmetics industry.
Additionally, it works as a treatment for pet fleas and head lice. Sol-gel techniques or plasma deposition can both be used to create PDMS coatings, depending on the application.
Both low-pressure and atmospheric plasma can be used for the latter. Depending on the plasma conditions, the polydimethylsiloxane on a PDMS surface can either be hydrophobic or hydrophilic after treatment. The feed gas’s composition is the most crucial factor.
Microfluidics Industries & Uses & PDMS Plasma Bonding
With applications in companies undertaking process evaluation of fluid chemistry, producing microfluidic devices is a relatively recent technology.
The main factors influencing the sector are the ability to use microfluidics to minimize the size of the fluid testing gear and the volume of fluid needed to test.
These essential criteria determine the requirement for the medical sector, biotech sector, and others to continuously apply these design characteristics to their particular needs.
The following list of sectors that frequently use PDMS in conjunction with plasma surface treatment or plasma coating technologies is more comprehensive:
Biomedicine
There are a ton of PDMS-related applications in the realm of biomedicine. Microfluidic devices, microchannels, and high-tech surfaces are all included. These surfaces can exhibit improved cytocompatibility and decreased genotoxicity.
Depending on the preconceived use, the type of plasma treatment might be either surface modification ( activation or coating) or even plasma-aided ion implantation. The oxygen plasma treatment of a PDMS surface can also increase the substrate’s biocompatibility.
Sensors
Engineers can use PDMS and plasma to create a wide range of sensors. One intriguing instance is a composite sensor for sensing physical activity made of carbon nanotubes and PDMS that has been plasma etched.
Stretchable PDMS sensors are another option; for these, the surface is plasma-treated first, then covered with silver and carbon nanotubes.
Textiles
PDMS in this industry is either done to manufacture innovative materials for various uses or to make fabrics more resilient and hydrophobic. Different fibers have had plasma treatment and PDMS coating.
They employ some of those fibers in the prolonged administration of certain drugs, including caffeine. Others should develop oleophobic or superhydrophobic properties and self-cleaning abilities.
Microelectronics
PDMS has been widely used to either coat PDMS substrates with other materials or deposit PDMS on microchip substrates. This is possible by combining PDMS with plasma surface treatment.
Additionally, surface activation or cleaning is a regular practice. A hydrophilic surface is preferred for various microelectronics related activities because it improves surface wettability. This is relevant when a printing technique gets involved in the fabrication process.
Nanofiltration
It demonstrates that plasma treatment of such membranes affects the flow of liquids and gases across them. Today, nanomembranes may be made from PDMS. The working gas mixture significantly influences.
For instance, pure argon and combinations of argon, oxygen, and hydrogen have been examined.
PDMS Plasma Surface Modification
Following replica molding from a master mold to pattern a PDMS substrate, the PDMS is oxidized in air or oxygen (O2) plasma. Organic and hydrocarbon material is eliminated by air or oxygen plasma by chemical interaction with highly reactive oxygen radicals and ablation by energizing oxygen ions. As a result, silanol (SiOH) groups are left on the surface, making it more hydrophilic and wettable.
The PDMS is instantly touched by another oxidized PDMS or glass surface after plasma activation to produce a bridging Si-O-Si connection at the interface, forming an irreversible seal. The creation and operation of microchannels benefit significantly from this water-tight covalent connection.
The manufacturing of microfluidic devices facilitated by plasma treatment for uses like:
- Study of micron-scale fluid flow and chemical reactions
- The identification of biological or chemical species
- Drug testing and clinical diagnosis for medical research
- Fluid manipulation at the cellular level
- Organoid studies, tissue culture, and cell culture
- Using droplet isolation, single-cell sequencing
In a nutshell, PDMS has demonstrated its potential in realizing a wide range of microfluidic applications, especially in custom industrial plasma systems. It’s now possible to manufacture devices with simple designs to devices with extremely complicated features using PDMS microfabrication.
The fact that researchers thoroughly investigate PDMS makes it possible for everyone to maximize its qualities per their needs.
