Modified PDMS Surfaces Research Articles

Biological characterization of the modified poly(dimethylsiloxane) surfaces based on cell attachment and toxicity assays.

Poly(dimethylsiloxane) (PDMS) is a material applicable for tissue and biomedical engineering, especially based on microfluidic devices. PDMS is a material used in studies aimed at understanding cell behavior and analyzing the cell adhesion mechanism. In this work, biological characterization of the modified PDMS surfaces based on cell attachment and toxicity assays was performed. We studied Balb 3T3/c, HMEC-1, and HT-29 cell adhesion on poly(dimethylsiloxane) surfaces modified by different proteins, with and without pre-activation with plasma oxygen and UV irradiation. Additionally, we studied how changing of a base and a curing agent ratios influence cell proliferation. We observed that cell type has a high impact on cell adhesion, proliferation, as well as viability after drug exposure. It was tested that the carcinoma cells do not require a highly specific microenvironment for their proliferation. Cytotoxicity assays with celecoxib and oxaliplatin on the modified PDMS surfaces showed that normal cells, cultured on the modified PDMS, are more sensitive to drugs than cancer cells. Cell adhesion was also tested in the microfluidic systems made of the modified PDMS layers. Thanks to that, we studied how the surface area to volume ratio influences cell behavior. The results presented in this manuscript could be helpful for creation of proper culture conditions during in vitro tests as well as to understand cell response in different states of disease depending on drug exposure.

Mechanical stretching induced alternation of cell attachment and detachment character of poly(N-isopropylacrylamide) gel grafted PDMS surface

Event Abstract Back to Event Mechanical stretching induced alternation of cell attachment and detachment character of poly(N-isopropylacrylamide) gel grafted PDMS surface Yoshikatsu Akiyama1, Miki Matsuyama2, Naoya Takeda2, Masayuki Yamato1 and Teruo Okano1 1 Institute of Advanced Biomedical Engineering and Science, Tokyo Women's Medical University, Japan 2 Department of Life Science and Medical Bioscience, School of Advanced Science and Engineering, Waseda University, Japan Introduction: Temperature-responsive cell culture surface, poly(N-isopropylacrylamide) (PIPAAm) hydrogel grafted tissue culture polystyrene (PIPAAm-TCPS), has been utilized for cell-sheet based tissue-engineering. PIPAAm-TCPS shows temperature-dependent cell attachment and detachment character, which is one of characteristics of PIPAAm-TCPS[1]. Based on a hypothesis that thickness of graft PIPAAm hydrogel layer were altered by applying mechanical stress to PIPAAm gel grafted substrate (Fig. 1), we modified PDMS surfaces with ultra-thin PIPAAm hydrogel (PIPAAm-PDMS) and characterized stretched and unstretched PIPAAm-PDMS surfaces as a new stretchable temperature-responsive cell culture surfaces. Experimental Methods: PIPAAm-PDMS was prepared referring to a previous report[2]. IPAAm monomer dissolved in 2-propanol (monomer concentration, 40 wt%) was spread onto 4-well PDMS cell culture surfaces (each chamber size was 16 mm square), which was purchased from STREX, Inc., followed by O2 plasma and (3-aminoproyl)trimethoxysilane (APTMS) treatments. And then, the surface was subjected to EB irradiation. During EB irradiation, polymerization and grafting polymer on PDMS surface occurred simultaneously. PIPAAm-PDMS was characterized by FT-IR / ATR, XPS analysis, contact angle measurement and cell detachment / attachment assay. For the cell attachment and detachment assay, PIPAA-PDMS with about 10.0 ug/cm2 of PIPAAm graft density was used. Uniaxial mechanical-stress was applied to the PIPAAm-PDMS surfaces with a special device (purchased from STEX, Inc.). In this experiment, 20% of stretch ratio was used for the characterization of stretched PIPAAm-PDMS surface. Results: To prove a hypothesis, PDMS was selected as a model elastic substrate in this experiment. Uniaxially stretched and unstretched PIPAAm-PDMS surfaces were evaluated by a variety of surface analysis methods. By modifying PDMS with PIPAAm hydrogel, contact angle decreased from 110º (unstretched PDMS) to 78º (unstretched PIPAAm-PDMS) at 37ºC (Fig. 2). The stretched and unstrethced PIPAAm-PDMS surfaces showed temperature-dependent contact angles alternation. However, by applying 20% of uniaxial mechanical stretching stress to PIPAAm-PDMS, the contact angles increased form 78º (unstretched PIPAAm-PDMS) to 83º (stretched PIPAAm-PDMS). AFM image of PIPAAm-PDMS surface showed PIPAAm nano-particles, which uniformly covered PDMS surface. The thickness of the graft PIPAAm hydrogel layer decreased from 700 nm to 480 nm (Fig. 3). Considering that temperature-responsive cell culture surfaces with thinner PIPAAm hydrogel layer shows more hydrophobic property, that PIPAAm-PDMS surface properties were altered by the applied mechanical stretching stress. Cell attachment assay also suggested that the stretched PIPAAm-PDMS was more cells adhesive. These results possibly suggest that PIPAAm-PDMS surface properties are controllable by the degree of applied mechanical stress. Grant-in-Aid for Scientific Research (No. 23106009) in Innovative Areas "Bio Assembler" from MEXT

Adhesion of MRC-5 and A549 cells on poly(dimethylsiloxane) surface modified by proteins.

PDMS is a very popular material used for fabrication of Lab-on-a-Chip systems for biological applications. Although PDMS has numerous advantages, it is a highly hydrophobic material, which inhibits adhesion and proliferation of the cells. PDMS surface modifications are used to enrich growth of the cells. However, due to the fact that each cell type has specific adhesion, it is necessary to optimize the parameters of these modifications. In this paper, we present an investigation of normal (MRC-5) and carcinoma (A549) human lung cell adhesion and proliferation on modified PDMS surfaces. We have chosen these cell types because often they are used as models for basic cancer research. To the best of our knowledge, this is the first presentation of this type of investigation. The combination of a gas-phase processing (oxygen plasma or ultraviolet irradiation) and wet chemical methods based on proteins' adsorption was used in our experiments. Different proteins such as poly-l-lysine, fibronectin, laminin, gelatin, and collagen were incubated with the activated PDMS samples. To compare with other works, here, we also examined how ratio of prepolymer to curing agent (5:1, 10:1, and 20:1) influences PDMS hydrophilicity during further modifications. The highest adhesion of the tested cells was observed for the usage of collagen, regardless of PDMS ratio. However, the MRC-5 cell line demonstrated better adhesion than A549 cells. This is probably due to the difference in their morphology and type (normal/cancer).

Bioinspired dry adhesive: Poly(dimethylsiloxane) grafted with poly(2-ethylhexyl acrylate) brushes

In this report we demonstrate that modification of poly(dimethylsiloxane) (PDMS) surfaces with polymer brushes offers a promising route towards materials with improved, bioinspired dry adhesive surfaces. To that end, poly(2-ethylhexyl acrylate) brushes were grafted from PDMS surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP) and also on silicon wafers in the presence of a structurally similar sacrificial initiator. Attenuated Total Reflection-Fourier Transformed Infrared spectroscopy (ATR-FTIR), Nuclear Magnetic Resonance Spectroscopy (NMR), Gel Permeation Chromatography (GPC) and ellipsometric studies confirmed the presence and regular growth of polymer chains both in solution and on PDMS and silicon surfaces respectively. Adhesion of the modified PDMS surfaces was tested using Hysitron TI-950 Triboindenter at indentation depths of 50–500nm and retraction rates of 5–50nm/s. Finally, micro-fabricated pillars (diameter=18μm) were grafted with the polymer brushes. All samples showed a significant increase in adhesion after grafting. Micro patterned PDMS surface has also shown a marked increase in adhesion after grafting of the polymer brushes as compared to non-grafted PDMS.

Chemical modification of PDMS surface without impacting the viscoelasticity: Model systems for a better understanding of elastomer/elastomer adhesion and friction

Abstract The influence of both viscoelastic and interfacial parameters on the surface properties of elastomers is difficult to study. Here, we describe a simple route to achieve surface modification of PDMS without impacting the viscoelastic properties of the bulk. PEG modified PDMS surfaces were synthesized by two step surface modification based on hydrosilylation. The covalent grafting of PEG on the surface has been evidenced by AFM and ATR-FTIR, and its effect on the hydrophilicity characterized by static and dynamic contact angle. The static water contact angle of the PEG-modified PDMS decreases from 110° (for unmodified PDMS) to 65°. Dynamic contact angles also show a significant decrease in both advancing and receding contact angles, along with a significant increase in the contact angle hysteresis, which can be related to an increase in the surface energy as estimated by JKR measurements. The viscoelastic properties of modified PDMS are found to be quantitatively comparable to those of the unmodified PDMS. This simple method is an efficient way to prepare model materials which can be used to get a better understanding of the exact contribution of the surface chemistry on surface properties of elastomers.

A cost-effective two-step method for enhancing the hydrophilicity of PDMS surfaces

Poly(dimethylsiloxane) (PDMS) is commonly used for fabricating micro- and nanofluidic devices due to its low cost and ease of fabrication. The major disadvantage to using PDMS for these applications is its hydrophobic properties. The current methods that enhance the hydrophilicity of elastomers used for micro- and nanofluidic applications are intricate and cost-inefficient. This contribution demonstrates how the hydrophobic PDMS surface can be chemically modified in 5 minutes using a two-step silanization method in an oxygen-saturated environment to provide a highly stable hydrophilic surface for irreversible PDMS to PDMS bonding and PDMS to borosilicate glass bonding. The surface wettabilities of the modified and pristine PDMS were characterized over a wide range of time using static contact angle measurements. The modified PDMS surfaces exhibit enhanced stable hydrophilicity with a contact angle of 87° for 5 days. Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectra of the modified and pristine PDMS surfaces confirmed the presence of hydroxyl groups of water molecules in the modified PDMS at 3150 cm−1 in addition to the characteristic peaks of pristine PDMS. This reliable silane beaker chemistry-based method allows easy bonding of the PDMS surfaces for liquid containment and irreversible bonding to borosilicate glass. This approach can effectively be adapted for enhancing the hydrophilicity of PDMS, which ensure relevance for current and future micro- and nanofluidic applications.

Surface Chemical Modification of Poly(dimethylsiloxane) for the Enhanced Adhesion and Proliferation of Mesenchymal Stem Cells

The surface chemistry of materials has an interactive influence on cell behavior. The optimal adhesion of mammalian cells is critical in determining the cell viability and proliferation on substrate surfaces. Because of the inherent high hydrophobicity of a poly(dimethylsiloxane) (PDMS) surface, cell culture on these surfaces is unfavorable, causing cells to eventually dislodge from the surface. Although physically adsorbed matrix proteins can promote initial cell adhesion, this effect is usually short-lived. Here, (3-aminopropyl)triethoxy silane (APTES) and cross-linker glutaraldehyde (GA) chemistry was employed to immobilize either fibronectin (FN) or collagen type 1 (C1) on PDMS. The efficiency of these surfaces to support the adhesion and viability of mesenchymal stem cells (MSCs) was analyzed. The hydrophobicity of the native PDMS decreased significantly with the mentioned surface functionalization. The adhesion of MSCs was mostly favorable on chemically modified PDMS surfaces with APTES + GA + protein. Additionally, the spreading area of MSCs was significantly higher on APTES + GA + C1 surfaces than on other unmodified/modified PDMS surfaces with C1 adsorption. However, there were no significant differences in the MSC spreading area on the unmodified/modified PDMS surfaces with FN adsorption. Furthermore, there was a significant increase in cell proliferation on the PDMS surface with APTES + GA + protein functionalization as compared to the PDMS surface with protein adsorption only. Therefore, the covalent surface chemical modification of PDMS with APTES + GA + protein could offer a more biocompatible platform for the enhanced adhesion and proliferation of MSCs. Similar strategies can be applied for other substrates and cell lines by appropriate combinations of self-assembly monolayers (SAMs) and extracellular matrix proteins.

Surface modification of poly(dimethylsiloxane) and its applications in microfluidics-based biological analysis

Poly(dimethylsiloxane) (PDMS)-based microfluidic systems have been gaining popularity in various applications, particularly for biological analyses because of their non-toxicity, easy fabrication, practical scalability, optical transparency, and low cost. However, because of the inherent hydrophobicity of PDMS-based material, biological samples easily and strongly interact with PDMS surfaces in biological environments, which prevents the immediate use of PDMS-based microfluidics without any surface processing. To date, various surface modification methods and different materials have been utilized to improve the repelling properties of the PDMS surface and to introduce new functional groups. Based on the recent advances in this field, we outline the main strategies utilized in PDMS surface modification in this review. We also present several applications of modified PDMS surfaces in biological analysis, such as biomolecule separation, immunoassay, cell culture, and DNA hybridization.

Fabrication of Reversible Poly(dimethylsiloxane) Surfaces via Host–Guest Chemistry and Their Repeated Utilization in Cardiac Biomarker Analysis

On the basis of the host-guest interactions between azobenzenes and cyclodextrins, a new strategy for the preparation of a dually functionalized poly(dimethylsiloxane) (PDMS) surface was investigated using surface-initiated atom-transfer radical polymerization (SI-ATRP) and click chemistry. The PDMS substrates were first oxidized in a H(2)SO(4)/H(2)O(2) solution to transform the surface Si-CH(3) groups into Si-OH groups. Then, the SI-ATRP initiator 3-(2-bromoisobutyramido)propyl(trime-thoxy)silane was grafted onto the substrates through a silanization reaction. Sequentially, the poly(ethylene glycol) (PEG) units were introduced onto the PDMS-Br surfaces via SI-ATRP reaction using oligo(ethylene glycol) methacrylate. Afterward, the bromide groups on the surface were converted to azido groups via nucleophilic substitution reaction with NaN(3). Finally, the azido-grafted PDMS surfaces were subjected to a click reaction with alkynyl and PEG-modified β-cyclodextrins, resulting in the grafting of cyclodextrins onto the PDMS surfaces. The composition and chemical state of the modified surfaces were characterized via X-ray photoelectron spectroscopy, and the stability and dynamic characteristics of the cyclodextrin-modified PDMS substrates were investigated via attenuated total reflection-Fourier transform infrared spectroscopy and temporal contact angle experiments. The surface morphology of the modified PDMS surfaces was characterized through imaging using a multimode atomic force microscope. A protein adsorption assay using Alexa Fluor594-labeled bovine serum albumin, Alexa Fluor594-labeled chicken egg albumin, and FITC-labeled lysozyme shows that the prepared PDMS surfaces possess good protein-repelling properties. On-surface studies on the interactions between azobenzenes and the cyclodextrin-modified surfaces reveal that the reversible binding of azobenzene to the cyclodextrin-modified PDMS surfaces and its subsequent release can be reversibly controlled using UV irradiation. Sandwich fluoroimmunoassay of the cardiac markers myoglobin and fatty acid-binding protein demonstrates that the cyclodextrin-modified PDMS surfaces can be repeatedly utilized in disease biomarker analysis.

Recent developments in PDMS surface modification for microfluidic devices

PDMS is enjoying continued and ever increasing popularity as the material of choice for microfluidic devices due to its low cost, ease of fabrication, oxygen permeability and optical transparency. However, PDMS's hydrophobicity and fast hydrophobic recovery after surface hydrophilization, attributed to its low glass transition temperature of less than -120 degrees C, negatively impacts on the performance of PDMS-based microfluidic device components. This issue has spawned a flurry of research to devise longer lasting surface modifications of PDMS, with particular emphasis on microfluidic applications. This review will present recent research on surface modifications of PDMS using techniques ranging from metal layer coatings and layer-by-layer depositions to dynamic surfactant treatments and the adsorption of amphipathic proteins. We will also discuss significant advances that have been made with a broad palette of gas-phase processing methods including plasma processing, sol-gel coatings and chemical vapor deposition. Finally, we will present examples of applications and future prospects of modified PDMS surfaces in microfluidics, in areas such as molecular separations, cell culture in microchannels and biomolecular detection via immunoassays.

Convenient Method for Modifying Poly(dimethylsiloxane) with Poly(ethylene glycol) in Microfluidics

This report describes a convenient and reproducible method for the covalent modification of poly(dimethylsiloxane) (PDMS) with poly(ethylene glycol) (PEG) chains to suppress nonspecific protein adsorption. PEG additives terminated with a vinyl group are added into the PDMS prepolymer; when the PDMS is thermally cured, the vinyl group reacts with the silane groups on the PDMS, which covalently link the PEG group to the PDMS network. The PEG-modified PDMS surfaces are characterized with FT-IR, X-ray photoelectron spectroscopy (XPS), and contact angle measurement. We also examined the modified PDMS for on-chip capillary electrophoresis and its capability of resisting nonspecific protein adsorption using bovine serum albumin (BSA) as a model. Based on our study, a molecular mechanism is given to successfully explain the surface properties of the modified PDMS surfaces.

In vitro blood compatibility of modified PDMS surfaces as superhydrophobic and superhydrophilic materials

AbstractThe surface of polydimethylsiloxane rubber (PDMS) was irradiated by a CO2‐pulsed laser. The irradiated surfaces were grafted by hydroxyethylmethacrylate phosphatidylcholine (HEMAPC) by using the preirradiation method. The laser‐treated surfaces and HEMAPC‐grafted PDMS surfaces were characterized by using a variety of techniques including ATR‐FTIR spectroscopy, scanning electron microscopy (SEM), and wettability, which was measured by a water‐drop contact angle. Different surfaces with different wettability were prepared. These surfaces, including untreated PDMS (hydrophobic), laser‐treated PDMS (superhydrophobic), and HEMAPC‐grafted surfaces (superhydrophilic), were used for a platelet adhesion study. Results from in vitro testing indicated that chemical structures, such as negative‐charge polar groups and wettability, are important factors in blood compatibility of these surfaces and the superhydrophilic (the most wettable) and the superhydrophobic (the most unwettable) of modified PDMS surfaces have excellent blood compatibility compared to the unmodified PDMS. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91:2042–2047, 2004