Plasma-treated Polydimethylsiloxane Research Articles

Surface properties of [formula omitted]m and sub-[formula omitted]m polydimethylsiloxane thin films after oxygen plasma treatment

Polydimethylsiloxane (PDMS) is widely used in many areas of science due to its outstanding properties. The continuous expansion of its applications is evidenced by a large number of research studies dedicated to modifying this soft material, ultimately leading to tailored properties. These studies highlighted the important role of film thickness (in the range of a few micrometers to millimeters) on surface properties, including mechanical properties, wettability, and surface topography. In this work, we investigated these surface properties of pristine as well as oxygen plasma-treated PDMS, in a thickness range of submicrometer and micrometer. We explored the effects of film thickness, dilution ratio, and plasma treatment time on effective Young’s modulus, surface topography (buckling structures), and wettability (hydrophobicity recovery) of the PDMS surfaces by conducting force–distance measurements, atomic force microscopy (AFM) and contact angle (CA) measurements, respectively, over a period of more than one month after the plasma treatment. The results of effective Young’s modulus on pristine PDMS show a high correlation with the dilution ratio and no dependency on the thickness. The characterized waviness (λ) and amplitude (A) of the resulting buckling structures forming on the plasma-treated surfaces reveal a correlation with film thickness, which is not included in the theoretical predictions. The results of CAs show a faster recovery process for the advancing than for the receding condition, and uncover a high correlation with both film thickness and dilution ratio for short-time plasma treatment. Furthermore, the buckling structures as well as the hydrophobicity recovery process in this work revealed a significantly different domain in comparison to the studies in literature, where these properties of PDMS membranes with a thickness ranging from a few micrometers to a few millimeters have been investigated.

Visualization of Flow-Induced Strain Using Structural Color in Channel-Free Polydimethylsiloxane Devices.

Measuring flow of gases is of fundamental importance yet is typically done with complex equipment. There is, therefore, a longstanding need for a simple and inexpensive means of flow measurement. Here, gas flow is measured using an extremely simple device that consists of an Ar plasma-treated polydimethylsiloxane (PDMS) slab adhered on a glass substrate with a tight seal. This device does not even have a channel, instead, gas can flow between the PDMS and the glass by deforming the PDMS wall, in other words, by making an interstice as a temporary path for the flow. The formation of the temporary path results in a compressive bending stress at the inner wall of the path, which leads to the formation of well-ordered wrinkles, and hence, the emergence of structural color that changes the optical transmittance of the device. Although it is very simple, this setup works sufficiently well to measure arbitrary gases and analyzes their flow rates, densities, and viscosities based on the change in color. It is also demonstrated that this technique is applicable to the flow-induced display of a pattern such as a logo for advanced applications.

Surface characterisation reveals substrate suitability for cyanobacterial phototaxis

Cyanobacteria respond to light stimulation, activating localised assembly of type IV pili for motility. The resulting phototactic response is highly dependent on the nature of the incoming light stimulus, and the final motility parameters depend on the surface properties. Conventionally, phototaxis studies are carried out on hydrogel surfaces, such as agarose, with surface properties that vary in time due to experimental conditions. This study considers five substrates, widely utilized in microfluidic technology, to identify the most suitable alternative for performing reliable and repeatable phototaxis assays. The surfaces are characterised via a contact angle goniometer to determine the surface energy, white light interferometry for roughness, zeta-potentials and AFM force distance curves for charge patterns, and XPS for surface composition. Cell motility assays showed 1.25 times increment on surfaces with a water contact angle of 80° compared to a reference glass surface. To prove that motility can be enhanced, polydimethylsiloxane (PDMS) surfaces were plasma treated to alter their surface wettability. The motility on the plasma-treated PDMS showed similar performance as for glass surfaces. In contrast, untreated PDMS surfaces displayed close to zero motility. We also describe the force interactions of cells with the test surfaces using DLVO (Derjaguin-Landau-Verwey-Overbeek) and XDLVO (extended DLVO) theories. The computed DLVO/XDLVO force-distance curves are compared with those obtained using atomic force microscopy. Our findings show that twitching motility on tested surfaces can be described mainly from adhesive forces and hydrophobicity/hydrophilicity surface properties. Statement of significanceThe current article focuses on unravelling the potential Micro-Electro-Mechanical System (MEMS) compatible surfaces for studying phototactic twitching motility of cyanobacteria. This is the first exhaustive surface characterization study coupled with phototaxis experiments, to understand the forces contributing to twitching motility. The methods shown in this paper can be further extended to study other surfaces and also to other bacteria exhibiting twitching motility.

Microscale investigation on the wettability and bonding mechanism of oxygen plasma-treated PDMS microfluidic chip

The bonding of polydimethylsiloxane (PDMS) microfluidic chip is one of the major concerns during the fabrication process. Plasma treatment can be applied to produce the hydrophilic groups, thus forming an irreversible bonding permanently. The surface wettability and bonding mechanism at the microscale level after plasma treatment need further investigation. In this study, the contact angle, surface morphology and the chemical composition of PDMS surface that were modified by oxygen plasma treatment were experimentally analyzed. Accordingly, molecular dynamics simulation models were constructed to investigate the wettability and bonding mechanism. Experimental results show that the contact angle decreases rapidly with the treatment time. The change in wettability mainly comes from the exposure of hydrophilic OH and CH2OH groups on silicon atoms, while the slight change in surface morphology can be negligible. With the help of hydroxyl groups, the spreading process of water droplet on the PDMS surface becomes much quicker because strong intermolecular interactions are generated. During the bonding process, atoms in both layers are gradually pushed towards the interface and penetrate each other, thus forming a reliable bonding at the interface. It is revealed in the debonding simulation that the plasma treatment on PDMS surface improves the bonding strength.

Detecting zeta potential of polydimethylsiloxane (PDMS) in electrolyte solutions with atomic force microscope

Zeta potential of PDMS-liquid interface is an important parameter for generating electroosmotic flow in a PDMS microchannel. In this paper, the zeta potentials of a PDMS slab in contacting with electrolyte solutions were evaluated with an atomic force microscope (AFM). As a colloidal probe of the AFM approaches to the surface of a PDMS slab in an electrolyte solution, a force curve is obtained and used to calculate the zeta potential of the PDMS. The effects of the plasma treating time and the aging of the electrolyte solutions on the zeta potential of PDMS surfaces were examined. The experimental results show that the air plasma treating time does not change the zeta potential of PDMS appreciably. Furthermore, the decreased zeta potential of a plasma-treated PDMS in an electrolyte solution is due to liquid aging, not the PDMS itself. Such characteristics probed by AFM provide new understanding of the surface charges of PDMS in electrolyte solutions.

Surface modifications to polydimethylsiloxane substrate for stabilizing prolonged bone marrow stromal cell culture

Polydimethylsiloxane (PDMS) has been extensively used as a supporting material for studies of cell mechanobiology, cell micropatterning and microscale-cell analysis in microfluidic chips due to its numerous advantages, such as low cytotoxicity, ease of modification, inexpensive costs and biocompatibility. However, the innate hydrophobicity of PDMS often poses a problem for stable cell adhesion, seriously limiting its applicability for prolonged cell culture. UV exposure and protein coating are suboptimal solutions, while chemical surface functionalization is often associated with laborious procedures and producing environmental toxics. Plasma treatment can render a hydrophilic substrate by altering the surface chemistry, but such effect is often short-lived due to its tendency to hydrophobic recovery. Variation of physical properties of the substratum are known to influence cell behaviour. Nevertheless, the combination of varying PDMS substratum properties via base:curing agent ratio and plasma treatment to stabilize the long-term culture of bone marrow derived stromal cells (BMSCs) still remain poorly understood. In this study, we developed a protocol to maintain the hydrophilicity of the plasma-treated PDMS over a range of substratum properties. This study demonstrated that varying the substratum properties of PDMS can enhance the stability of BMSC culture for at least three weeks, while plasma treatment with or without additional collagen coating further enhanced such effect. The changes in the physical properties of PDMS have rendered difference in BMSCs adhesion, proliferation and in-vitro plasticity, thereby offering a simple and effective strategy for PDMS surface modification to enable long term cell analysis in PDMS-based culture platform.

The interparticle gap manipulation of Au-Ag nanoparticle arrays deposited on flexible and atmospheric plasma-treated PDMS substrate for SERS detection

Au-Ag nanoparticle arrays were deposited on a flexible and surface-modified polydimethylsiloxane (PDMS) substrate for surface-enhanced Raman scattering (SERS). The surface of the PDMS substrate was modified to be a hydrophilic layer by nitrogen (N2) atmospheric plasma treatment. When compared to the non-plasma-treated PDMS substrate, the contact angle of the plasma-treated PDMS substrate decreased from 115.4° to 32° to form the hydrophilic surface of the PDMS substrate. The uniform Au-Ag nanoparticle arrays were further deposited by thermal evaporation on the plasma-treated PDMS substrate that was evaluated by scanning electron microscopy (SEM). The results indicate that the Au-Ag@PDMS-N2 substrate exhibited highly sensitive and reproducible SERS spectra of adenine (10−4 M) due to the homogeneous and narrow interparticle gap (~2 nm) between Au-Ag nanoparticles. Particularly, the SERS intensity of 2Au-6Ag@PDMS-N2 substrate increased ~4 times under a bending angle of 5°. This indicated that the flexible behaviors of the PDMS-based SERS substrate can effectively manipulate the interparticle gap between Au-Ag nanoparticles by bending the SERS substrate. Therefore, the flexible and ultrasensitive SERS substrate fabricated by Au-Ag nanoparticles deposited on plasma-treated PDMS substrate provides enormous potential for practical applications in detecting biomolecules and environmental pollutants.

Thickness-dependent wrinkling of PDMS films for programmable mechanochromic responses

We report a remarkable thickness-dependent wrinkling behavior of oxygen plasma-treated polydimethylsiloxane (PDMS) films, in which an energy barrier separates the wrinkling mechanics into two regimes. For thick films, the film wrinkles with a constant periodicity which can be precisely predicted by the classic nonlinear finite mechanics. Reducing the film thickness below 1 mm leads to nonuniform wrinkles with an increasing periodicity which gives rise to random scattering and transparency changes under mechanical strains. By tuning the film thickness, we were able to control both the quality and size of the periodic wrinkles and further design mechanochromic devices featuring brilliant structural colors and programmable colorimetric responses. This work sheds light on the fundamental understanding of the wrinkling mechanics of bilayer systems and their intriguing mechanochromic applications.

Optimization of Geometry Parameters of Inkjet-Printed Silver Nanoparticle Traces on PDMS Substrates Using Response Surface Methodology.

Inkjet printing is an emerging technology with key advantages that make it suitable for the fabrication of stretchable circuits. Specifically, this process is cost-effective and less complex compared to conventional fabrication technologies. Inkjet printing has several process and geometry parameters that significantly affect the electromechanical properties of the printed circuits. This study aims to optimize the geometry parameters of inkjet-printed silver nanoparticle traces on plasma-treated polydimethylsiloxane (PDMS) substrates. The optimization process was conducted for two printed shapes, namely straight line and horseshoe patterns. The examined input factors for the straight line traces were: the number of inkjet-printed layers and line width. On the other hand, the number of cycles and amplitude were the examined input parameters for the horseshoe shape. First, the optimal number of layers and line width were found from the straight line analysis and subsequently were used in the optimization of the horseshoe pattern parameters. The optimization of the input parameters was carried out using the response surface methodology (RSM), where the objective of the optimization was to maximize the breakdown strain of the traces while maximizing the gauge factor and minimizing the ink cost. The results indicate that a 1.78 mm line width and one layer are the optimal geometry parameters for the straight line traces, while for the horseshoe pattern, the optimal parameters are one layer, a line width of 1.78 mm, amplitude of 4 mm and one cycle. The optimal straight line was designed to sustain up to 10% strain while the horseshoe pattern was designed to sustain up to 15% strain.

Surface and subsurface film growth of titanium dioxide on polydimethylsiloxane by atomic layer deposition

There has been increasing interest in polymers for biomaterial applications. Researchers have been trying to incorporate metal oxides or metals into polymers in order to attain significantly enhanced desirable properties of the resulting polymer material such as conductivity and antimicrobial activity. One promising technique for such materials is atomic layer deposition (ALD). By depositing a very thin film of metal or metal oxide, one can take advantage of these material properties without losing the unique bulk properties of the polymer; however, deposition of such a material on polymers becomes challenging in part due to the availability of both surface and subsurface film growth.In this study, atomic layer deposition (ALD) of TiO2 on polydimethylsiloxane (PDMS) is investigated at the early stages of nucleation and growth of TiO2 on both O2-plasma treated and non-plasma treated PDMS. X-ray absorption near edge structure, scanning electron microscopy/energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy are used for material characterization. Results indicate that ALD-like surface growth of TiO2 takes place on plasma-treated PDMS; for non-plasma treated pristine PDMS, apparent favorable diffusion/infiltration of TiO2 into the subsurface of the polymer is obtained, without noticeable external surface deposition for at least the first 25 ALD cycles.

Adhesion between Hydrophobic Elastomer and Hydrogel through Hydrophilic Modification and Interfacial Segregation.

Recent progress in the printing of soft materials has made it possible to fabricate soft stretchable devices for a range of engineering applications. These devices tend to be heterogeneous systems, and their reliability depends to a large extent on the integrity of the interfaces between the various materials in the system. Previous studies on the printing of hydrogels have highlighted the need to investigate the adhesion between extrusion printable dielectric elastomers and hydrogels. Here we consider polydimethylsiloxane (PDMS) and a polyacrylamide hydrogel that contains lithium chloride and a nonionic rheological modifier. We show that the adhesion between oxygen plasma-treated PDMS and the hydrogel increases with time to reach a stable value of 15 J m-2 after ∼6 days. During that time, the contact angle of water on the PDMS interface remains constant at ∼30°, suggesting that hydrophobic recovery of plasma-treated PDMS is suppressed by the presence of the hydrogel. It is further observed that a thin viscous layer develops at the interface between PDMS and hydrogel, which results in energy dissipation upon debonding and which allows full recovery of the adhesion after debonding and rejoining. This viscous layer develops only in the presence of the rheological modifier in the hydrogel and the hydrophilic surface treatment of the PDMS.

Study on surface structure of plasma‐treated polydimethylsiloxane (PDMS) elastomer by slow positron beam

In this paper, the variations in surface structure of polydimethylsiloxane elastomers before and after argon plasma treatments have been investigated by X‐ray photoelectron spectroscopy, slow positron beam, and scanning electron microscope. An inorganic silica‐like layer was probed by X‐ray photoelectron spectroscopy after 3 minutes or longer time of treatments, and the sample surface turned into totally hydrophilic. Short time (1 and 2 min) plasma exposure mainly removed preexisting low molecular weighted (LMW) siloxanes on sample surface. By using slow positron beam, the thicknesses of silica‐like layer for 3‐, 5‐, and 10‐minute–treated samples were estimated to be around 30, 66, and 91 nm, respectively. Beneath the silica‐like layer, a loose polymeric structure was also detected, which was ascribed to the accumulation of LMW siloxanes. Scanning electron microscope images showed that the silica‐like layer cracked after 10 minutes of plasma treatment, which provided direct diffusion pathways for LMW siloxanes. Hence, 10‐minute–treated sample showed rather low organic composition near surface. Slow positron beam provides valuable depth profile information for evaluating the surface aging condition of polydimethylsiloxane composite.

Aqueous Lubrication, Structure and Rheological Properties of Whey Protein Microgel Particles.

Aqueous lubrication has emerged as an active research area in recent years due to its prevalence in nature in biotribological contacts and its enormous technological soft-matter applications. In this study, we designed aqueous dispersions of biocompatible whey-protein microgel particles (WPM) (10-80 vol %) cross-linked via disulfide bonding and focused on understanding their rheological, structural and biotribological properties (smooth polydimethylsiloxane (PDMS) contacts, Ra < 50 nm, ball-on-disk set up). The WPM particles (Dh = 380 nm) displayed shear-thinning behavior and good lubricating performance in the plateau boundary as well as the mixed lubrication regimes. The WPM particles facilitated lubrication between bare hydrophobic PDMS surfaces (water contact angle 108°), leading to a 10-fold reduction in boundary friction force with increased volume fraction (ϕ ≥ 65%), largely attributed to the close packing-mediated layer of particles between the asperity contacts acting as "true surface-separators", hydrophobic moieties of WPM binding to the nonpolar surfaces, and particles employing a rolling mechanism analogous to "ball bearings", the latter supported by negligible change in size and microstructure of the WPM particles after tribology. An ultralow boundary friction coefficient, μ ≤ 0.03 was achieved using WPM between O2 plasma-treated hydrophilic PDMS contacts coated with bovine submaxillary mucin (water contact angle 47°), and electron micrographs revealed that the WPM particles spread effectively as a layer of particles even at low ϕ∼ 10%, forming a lubricating load-bearing film that prevented the two surfaces from true adhesive contact. However, above an optimum volume fraction, μ increased in HL+BSM surfaces due to the interpenetration of particles that possibly impeded effective rolling, explaining the slight increase in friction. These effects are reflected in the highly shear thinning nature of the WPM dispersions themselves plus the tendency for the apparent viscosity to fall as dispersions are forced to very high volume fractions. The present work demonstrates a novel approach for providing ultralow friction in soft polymeric surfaces using proteinaceous microgel particles that satisfy both load bearing and kinematic requirements. These findings hold great potential for designing biocompatible particles for aqueous lubrication in numerous soft matter applications.

Study on the surface energy characteristics of polydimethylsiloxane (PDMS) films modified by C4F8/O2/Ar plasma treatment

We conducted plasma treatment on polydimethylsiloxane (PDMS) films using inductively coupled C4F8/O2/Ar gas mixture plasma to modify their surface properties. We investigated the relationship between plasma characteristics and the changes in PDMS surfaces in order to understand the surface modification mechanism. The surface characteristics of PDMS films were evaluated in detail by surface energy measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Using contact angle measurements, it was confirmed that the surface, polar, and dispersive energies of the plasma-treated PDMS films increased as the O2 gas ratio increased. AFM analysis showed that the roughness of plasma-treated PDMS surfaces increased when the O2 gas ratio increased. XPS analysis confirmed the presence of a functional group CFx (X=1, 2, and 3) in C4F8-rich plasma and a functional group OH in O2-rich plasma. It was confirmed that the surface energy of the PDMS films could be controlled by controlling the C4F8/O2/Ar plasma treatment parameters which should be required for applying the direct transfer technique in each material having different surface energy.

Adhesive Stretchable Printed Conductive Thin Film Patterns on PDMS Surface with an Atmospheric Plasma Treatment.

In this study, a plasma surface modification with printing process was developed to fabricate printed flexible conductor patterns or devices directly on polydimethylsiloxane (PDMS) surface. An atmospheric plasma treatment was first used to oxidize the PDMS surface and create a hydrophilic silica surface layer, which was confirmed with photoelectron spectra. The plasma operating parameters, such as gas types and plasma powers, were optimized to obtain surface silica layers with the longest lifetime. Conductive paste with epoxy resin was screen-printed on the plasma-treated PDMS surface to fabricate flexible conductive tracks. As a result of the strong binding forces between epoxy resin and the silica surface layer, the printed patterns showed great adhesion on PDMS and were undamaged after several stringent adhesion tests. The printed conductive tracks showed strong mechanical stability and exhibited great electric conductivity under bending, twisting, and stretching conditions. Finally, a printed pressure sensor with good sensitivity and a fast response time was fabricated to demonstrate the capability of this method for the realization of printed electronic devices.

Simple surface engineering of polydimethylsiloxane with polydopamine for stabilized mesenchymal stem cell adhesion and multipotency.

Polydimethylsiloxane (PDMS) has been extensively exploited to study stem cell physiology in the field of mechanobiology and microfluidic chips due to their transparency, low cost and ease of fabrication. However, its intrinsic high hydrophobicity renders a surface incompatible for prolonged cell adhesion and proliferation. Plasma-treated or protein-coated PDMS shows some improvement but these strategies are often short-lived with either cell aggregates formation or cell sheet dissociation. Recently, chemical functionalization of PDMS surfaces has proved to be able to stabilize long-term culture but the chemicals and procedures involved are not user- and eco-friendly. Herein, we aim to tailor greener and biocompatible PDMS surfaces by developing a one-step bio-inspired polydopamine coating strategy to stabilize long-term bone marrow stromal cell culture on PDMS substrates. Characterization of the polydopamine-coated PDMS surfaces has revealed changes in surface wettability and presence of hydroxyl and secondary amines as compared to uncoated surfaces. These changes in PDMS surface profile contribute to the stability in BMSCs adhesion, proliferation and multipotency. This simple methodology can significantly enhance the biocompatibility of PDMS-based microfluidic devices for long-term cell analysis or mechanobiological studies.

Mechanically robust, electrically stable metal arrays on plasma-oxidized polydimethylsiloxane for stretchable technologies

Certain applications of evolving flexible technologies demand that metallic features remain both mechanically robust (crack-free) and electrically stable for large macroscopic mechanical deformation. Examples of this are flexible radio frequency transmission line technologies and soft metamaterials where electromagnetic properties (e.g., functionality and losses), which rely on the integrity of metallic features, are highly sensitive to shape and resistance variation. In this context, we demonstrate here the ability to deposit crack-free chromium/gold metallized mesa structures on polydimethylsiloxane (PDMS) substrates using thermal evaporation. In order to achieve this, the PDMS is exposed to an optimized oxygen plasma prior to the metallization. A shadow mask allowed us to define specific arrays of metallic mesa features having different sizes (100–600 μm) and surface filling factors on plasma-treated and non-treated PDMS. In contrast to non-treated PDMS, we demonstrate for a loading strain &amp;gt;45% that the local metal mesa strain is &amp;lt;2% (crack-free) and the electrical resistance variation is &amp;lt;2 for plasma-treated substrates. Such a result is achieved by tailoring the filling factor and the equivalent stiffness ratio of the layers. The relationship between the filling factor, the equivalent stiffness ratio, and the local strain reduction is analytically modelled. This allows one to understand the role of the key parameters in the behavior of the overall flexible system and, in principle, to design optimized systems such as those mentioned above.

Bioactivation of Plane and Patterned PDMS Thin Films by Wettability Engineering

This study shows how surface properties of polydimethylsiloxane (PDMS) thin films, such as wettability and cellular adhesive behavior, can be influenced by surface modification and patterning, to improve the suitability of such modified PDMS for biomedical applications. For that purpose, different types of PDMS (i.e., soft (S-) and hard (H-) PDMS) and differently patterned surfaces were prepared by a commercially available tool which is originally used to produce patterned PDMS stamps for substrate conformal imprint lithography. To increase surface wettability and cellular adhesive behavior, PDMS surfaces were modified by O2, Ar/O2, Ar, and forming gas (N2/H2) plasma treatment. It is shown that, especially, plasma treatment using N2/H2 is a promising method to modify PDMS surfaces towards enhanced wettability. Such modified PDMS surfaces exhibit water contact angle values (WCA) of nearly 0° and demonstrate enhanced attachment of melanoma cells. Differences between as-prepared and plasma-treated S- and H-PDMS can be observed, where H-PDMS shows smaller WCA than S-PDMS. Even plasma-treated PDMS surfaces, however, exhibit only temporary hydrophilicity, due to hydrophobic recovery. To overcome this problem, plasma-treated PDMS films were stored in ethanol and water, where low and constant WCAs for several months could be achieved. Finally, the influence of surface topography of different patterned PDMS thin films on the adhesion behavior of melanoma cells was investigated. It can be concluded that chemical as well as structural modifications of PDMS enable to gradually control the adhesive properties of cells on their surfaces. This has a high technological impact since regulated and topologically stable adhesion and repulsion of cells by their scaffolds has high potency for in vitro as well as in vivo applications.

Control of adhesion of human induced pluripotent stem cells to plasma-patterned polydimethylsiloxane coated with vitronectin and γ-globulin

Human induced pluripotent stem cells (hiPSCs) are a promising source of cells for medical applications. Recently, the development of polydimethylsiloxane (PDMS) microdevices to control the microenvironment of hiPSCs has been extensively studied. PDMS surfaces are often treated with low-pressure air plasma to facilitate protein adsorption and cell adhesion. However, undefined molecules present in the serum and extracellular matrix used to culture cells complicate the study of cell adhesion. Here, we studied the effects of vitronectin and γ-globulin on hiPSC adhesion to plasma-treated and untreated PDMS surfaces under defined culture conditions. We chose these proteins because they have opposite properties: vitronectin mediates hiPSC attachment to hydrophilic siliceous surfaces, whereas γ-globulin is adsorbed by hydrophobic surfaces and does not mediate cell adhesion. Immunostaining showed that, when applied separately, vitronectin and γ-globulin were adsorbed by both plasma-treated and untreated PDMS surfaces. In contrast, when PDMS surfaces were exposed to a mixture of the two proteins, vitronectin was preferentially adsorbed onto plasma-treated surfaces, whereas γ-globulin was adsorbed onto untreated surfaces. Human iPSCs adhered to the vitronectin-rich plasma-treated surfaces but not to the γ-globulin-rich untreated surfaces. On the basis of these results, we used perforated masks to prepare plasma-patterned PDMS substrates, which were then used to pattern hiPSCs. The patterned hiPSCs expressed undifferentiated-cell markers and did not escape from the patterned area for at least 7 days. The patterned PDMS could be stored for up to 6 days before hiPSCs were plated. We believe that our results will be useful for the development of hiPSC microdevices.

Plasma treatment of PDMS for applications of in vitro motility assays

In vitro motility assays are readily used to simplify the complex environments within the cell and in muscle tissue. These assays have afforded considerable insight into the fundamentals of their underlying biophysics, interactions with cargo, intracellular regulation, and motor cooperation/competition. Extension of the standard in vitro motility assay into a more automated and cost-effective fluidic design while providing availability to the scientific community without expertise in lithographic fabrication is critical for the continued advancement of the field. In this work, we utilized a standard plasma cleaner to oxidize the widely prevalent material polydimethylsiloxane (PDMS) to create flow cells that could be used for in vitro motility assays. Our analysis indicated that a 40min pre-treatment of the PDMS with plasma exposure resulted in optimal bundle motility. This finding was attributed to the condition at which the least amount of oxygen permeates the PDMS slab, enters the motility buffer, and oxidizes the motor proteins. Based on these findings, we developed a method for constructing microfluidic devices from glass and plasma-treated PDMS molds in which motility could be observed.