Stable low-fouling plasma polymer coatings on polydimethylsiloxane

State of the art in nonthermal plasma processing for biomedical applications: Can it help fight viral pandemics like COVID-19?

Plasma processing finds widespread biomedical applications, such as the design of biosensors, antibiofouling surfaces, controlled drug delivery systems, and in plasma sterilizers. In the present coronavirus disease (COVID-19) situation, the prospect of applying plasma processes like surface activation, plasma grafting, plasma-enhanced chemical vapor deposition/plasma polymerization, surface etching, plasma immersion ion implantation, crosslinking, and plasma decontamination to provide timely solutions in the form of better antiviral alternatives, practical diagnostic tools, and reusable personal protective equipment is worth exploring. Herein, the role of nonthermal plasmas and their contributions toward healthcare are timely reviewed to engage different communities in assisting healthcare associates and clinicians, not only to combat the current COVID-19 pandemic but also to prevent similar kinds of future outbreaks.

Inner Surface Design of Functional Microchannels for Microscale Flow Control

Fluidic flow behaviors in microfluidics are dominated by the interfaces created between the fluids and the inner surface walls of microchannels. Microchannel inner surface designs, including the surface chemical modification, and the construction of micro-/nanostructures, are good examples of manipulating those interfaces between liquids and surfaces through tuning the chemical and physical properties of the inner walls of the microchannel. Therefore, the microchannel inner surface design plays critical roles in regulating microflows to enhance the capabilities of microfluidic systems for various applications. Most recently, the rapid progresses in micro-/nanofabrication technologies and fundamental materials have also made it possible to integrate increasingly complex chemical and physical surface modification strategies with the preparation of microchannels in microfluidics. Besides, a wave of researches focusing on the ideas of using liquids as dynamic surface materials is identified, and the unique characteristics endowed with liquid-liquid interfaces have revealed that the interesting phenomena can extend the scope of interfacial interactions determining microflow behaviors. This review extensively discusses the microchannel inner surface designs for microflow control, especially evaluates them from the perspectives of the interfaces resulting from the inner surface designs. In addition, prospective opportunities for the development of surface designs of microchannels, and their applications are provided with the potential to attract scientific interest in areas related to the rapid development and applications of various microchannel systems.

Multitechnique investigation into the aqueous behavior of plasma polymers

Plasma polymers are often used in applications requiring aqueous immersion; therefore, it is important to understand how this exposure affects the physical and chemical properties of the films. Three different plasma polymer films were deposited at different distances from the electrode, and the film properties were characterized using contact angle, ellipsometry, and x-ray photoelectron spectroscopy. The film behaviors in aqueous solutions were studied via quartz crystal microbalance with dissipation (QCM-D). Exposure to buffer solutions produced significant swelling of the plasma polymerized acrylic acid films, with swelling increasing with distance from the powered electrode, results that could be correlated with changes in film chemistry. Plasma polymerized octadiene and allylamine exhibited little swelling. These films exhibited changes in thickness and contact angle with respect to distance from the electrode, but this had little influence on their behavior in aqueous solution. By combining QCM-D with the more traditional surface chemical analysis techniques, the authors have been able to explore both swelling behavior and the effect that sample position and thus deposition parameters have on film properties and aqueous behavior. This approach gives the authors the basis to define deposition parameters to assist the engineering of thin films for applications such as biosensing and tissue engineering applications where specific chemistries and film behaviors are desired.

Restraining non-specific adsorption of protein using Parylene C-caulked polydimethylsiloxane

Non-specific adsorption (NSA) of proteins on surface is a critical issue in polydimethylsiloxane (PDMS)-based microfluidics, which may either considerably decrease the efficiency of a continuous flow reaction or cause a large background noise in a heterogeneous sensing. This work introduced a new method to restrain NSA of protein by caulking PDMS with Parylene C, i.e., forming a Parylene C-caulked PDMS (pcPDMS) surface. The caulking depth of Parylene C inside PDMS matrix was characterized by laser scanning confocal microscopy based on a detectable autofluorescence intensity difference between Parylene C and PDMS after being annealed at 270 °C for 2 h in nitrogen. NSA of bovine serum albumin (BSA) on the inner surfaces of PDMS and pcPDMS microchannels was experimentally compared. The results indicated that the adsorbed BSA on the pcPDMS surface were 35.2% of that on the pristine PDMS surface after the BSA solution flowing through the microchannels at a flow rate of 2000 nL/min, a typical scenario of the continuous flow reaction. In a case mimicking the heterogeneous sensing, after a 60 min washing of phosphate buffered saline flow on a pre-saturated BSA adsorbed surface, the residual BSA on the pcPDMS surface was only 4.5% of that on the pristine PDMS surface. Adsorption/desorption coefficients of BSA on the PDMS and the pcPDMS surfaces were extracted from the experimental results based on the first-order Langmuir model, which indicated that the pcPDMS has a lower adsorption coefficient (Ka ) and a higher desorption coefficient (Kd ), compared to those of the pristine PDMS. A preliminary experiment also indicated that Taq polymerase kept 93.0% activity after flowing through a pcPDMS microchannel, while only 28.9% activity was left after passing a pristine PDMS microchannel under the same operation condition.

Microcontact peeling as a new method for cell micropatterning

Micropatterning is becoming a powerful tool for studying morphogenetic and differentiation processes of cells. Here we describe a new micropatterning technique, which we refer to as microcontact peeling. Polydimethylsiloxane (PDMS) substrates were treated with oxygen plasma, and the resulting hydrophilic layer of the surface was locally peeled off through direct contact with a peeling stamp made of aluminum, copper, or silicon. A hydrophobic layer of PDMS could be selectively exposed only at the places of the physical contact as revealed by water contact angle measurements and angle-resolved X-ray photoelectron spectroscopy, which thus enabled successful micropatterning of cells with micro-featured peeling stamps. This new micropatterning technique needs no procedure for directly adsorbing proteins to bare PDMS in contrast to conventional techniques using a microcontact printing stamp. Given the several unique characteristics, the present technique based on the peel-off of inorganic materials may become a useful option for performing cell micropatterning.

Stable low-fouling plasma polymer coatings on polydimethylsiloxane

Polydimethylsiloxane (DMS) is a popular material for microfluidics, but it is hydrophobic and is prone to non-specific protein adsorption. In this study, we explore methods for producing stable, protein resistant, tetraglyme plasma polymer coatings on PDMS by combining extended baking processes with multiple plasma polymer coating steps. We demonstrate that by using this approach, it is possible to produce a plasma polymer coatings that resist protein adsorption (<10 ng/cm(2)) and are stable to storage over at least 100 days. This methodology can translate to any plasma polymer system, enabling the introduction of a wide range of surface functionalities on PDMS surfaces.