Plasma-polymerized Hexamethyldisiloxane Research Articles

Silver nanoparticles with plasma-polymerized hexamethyldisiloxane coating on 3D printed substrates are non-cytotoxic and effective against respiratory pathogens.

Due to the emerging resistance of microorganisms and viruses to conventional treatments, the importance of self-disinfecting materials is highly increasing. Such materials could be silver or its nanoparticles (AgNPs), both of which have been studied for their antimicrobial effect. In this study, we compared the biological effects of AgNP coatings with and without a plasma-polymerized hexamethyldisiloxane (ppHMDSO) protective film to smooth silver or copper coatings under three ambient conditions that mimic their potential medical use (dry or wet environments and an environment simulating the human body). The coatings were deposited on 3D printed polylactic acid substrates by DC magnetron sputtering, and their surface morphology was visualized using scanning electron microscopy. Cytotoxicity of the samples was evaluated using human lung epithelial cells A549. Furthermore, antibacterial activity was determined against the Gram-negative pathogenic bacterium Pseudomonas aeruginosa PAO1 and antiviral activity was assessed using human rhinovirus species A/type 2. The obtained results showed that overcoating of AgNPs with ppHMDSO creates the material with antibacterial and antiviral activity and at the same time without a cytotoxic effect for the surrounding tissue cells. These findings suggest that the production of 3D printed substrates coated with a layer of AgNPs-ppHMDSO could have potential applications in the medical field as functional materials.

Structure and chemical composition of thin-film nanocomposites based on silver in organosilicon amorphous matrix prepared by High Target Utilization Sputtering

Thin films based on Ag nanoclusters embedded in an organosilicon polymer matrix were deposited using the High Target Utilization Sputtering technique (HiTUS) by simultaneous sputtering of the Ag target and polymerization of hexamethyldisiloxane (HMDSO) vapors in radiofrequency plasma. The influence of deposition parameters on chemical composition and structure of the deposited nanocomposite films was studied using scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction analytical techniques. The films under investigation exhibit a dense uniform structure with the metallic nanocrystalline silver present in the form of spherical-shaped nanoclusters with dimensions below 10 nm embedded in an amorphous organosilicon plasma polymer. The average size of Ag nanoclusters is increased from 1.8 to 4.4 nm with Ag content increasing from 16 to 57%at. while concentration of nanoclusters is reduced. Incorporation of the metallic silver into the plasma polymerized HMDSO leads to a decrease of carbon and oxygen content as well as a decrease of organosilicon polymer matrix density.

Large-Scale Plasma-Polymerized Hexamethyldisiloxane Thin Films: Role of Interelectrode Distance and Excellent Corrosion Resistance.

In comparison to the more traditional anticorrosion thin film coatings, the plasma polymerization approach offered a more efficient, dry, and straightforward procedure that made it possible to create dense films of several hundred nanometers in thickness, which has potential applications in metallic implant materials. In this paper, large-scale plasma polymerized hexamethyldisiloxane (ppHMDSO) thin film coatings were deposited on stainless steel substrates at different electrode distances to improve their corrosion resistance. The physicochemical properties and corrosion resistance of the ppHMDSO thin films as prepared at different electrode distances were characterized and gauged utilizing various characterization means. The results indicate that decreasing electrode distance accelerates monomer fragmentation and increases the oxidation process. The deposition rate and roughness of the ppHMDSO films both decreased as the electrode distance increased, while the carbonaceous group and hydrophobicity of the films enhanced. The ppHMDSO film prepared at an electrode distance of 40 mm obtained excellent elastic recovery and wear resistance and had an improved corrosion resistance, resulting in a reduction of 75% of the original corrosion behavior against the corrosion in Hank's solution. The resulting large-scale ppHMDSO thin film coatings can be further employed in implants for tissue engineering and biomaterials.

Comparative study of the aging behavior of plasma activated hexamethyldisiloxane-based plasma polymers and silicone elastomer thin films

The aging of plasma activated plasma polymer films has been studied to a limited extent, despite the recent application-oriented interest for these coatings. Therefore, the aging of plasma polymerized hexamethyldisiloxane (ppHMDSO) coatings that were subjected to helium or dry air plasma activation was investigated and compared to the aging of plasma activated silicone elastomer (S184) in this work. Water contact angle (WCA) measurements indicated that both materials reached a super-hydrophilic state after both plasma treatments. X-ray photoelectron spectroscopy (XPS) illustrated that this was the result of the introduction of a variety of oxygen-containing functionalities, while atomic force microscopy highlighted that the morphology was not significantly changed. The WCAs of the plasma activated ppHMDSO coating and S184 showed similar aging behavior, as the wettability of both materials significantly decreased. XPS measurements after 11 days of aging indicated that multiple aging processes were occurring in S184, while migration of oxidized short chain fragments was most important for the ppHMDSO coating. All these aged coatings could be silanized with 3-aminopropyltriethoxysilane, although differences in stability were observed. As such, this study provides additional insight in the chemical nature of activated plasma polymers and provides design principles for synthesizing plasma polymers with selective chemical functionalities.

Nanoindentation characterization of nanocomposites coating based on graphene and siloxane matrix deposited by dielectric barrier discharge plasma

Hexamethyldisiloxane (HMDSO)/Graphene nanosheets (GNs) nanocomposite coatings were deposited by a dielectric barrier discharge at atmospheric pressure. Commercially available GNs were incorporated into HMDSO precursor at different concentrations up to 2 wt%. The nanocomposite coatings were analyzed using scanning electron microscopy (SEM) and nanoindentation test. Based on SEM images, it was found that the GNs were well distributed and dispersed in the plasma polymerized hexamethyldisiloxane (ppHMDSO) matrix with no significant agglomeration. The results of nanoindentation tests performed with the continuous stiffness measurements mode showed an increase in the hardness and reduced Young's modulus with the increase of graphene nanosheets percentage. The maximum increase was two orders of magnitude for 2% GNs/ppHMDSO nanocomposite coatings compared to the homopolymer ppHMDSO. Furthermore, the creep compliance analysis showed that the nanocomposite coatings exhibited a viscoelastic behavior compared to the plasma polymer homopolymer.

Effect of Atmospheric Ageing on the Properties of Organosilicon (Pp-HMDSO) Thin Films

This study reports the effect of ageing on plasma polymerized hexamethyldisiloxane (pp-HMDSO) thin films properties during 90 days storage in the atmosphere. The monitoring of the change in thin film chemical structure by FTIR analysis indicates that the general trend in the thin film ageing process is the enhancement of its inorganic chemical nature. A thickness decrease of 35% of the thin film is observed after 90 days ageing time. Thin film ageing has induced surface morphology degradation though the enhancement of both roughness and porosity. The resulted structural and morphological changes have affected different thin film properties, such as electrical resistivity, optical band gap, optical reflectance, and micro-hardness.

Synthetic anionic surfaces can replace microparticles in stimulating burst coagulation of blood plasma.

Biomaterials are frequently evaluated for pro-coagulant activity but usually in the presence of microparticles (MPs), cell-derived vesicles in blood plasma whose phospholipid surfaces allow coagulation factors to set up as functional assemblies. We tested the hypothesis that synthetic anionic surfaces can catalyze burst thrombin activation in human blood plasma in the absence of MPs. In a thromboelastography (TEG) assay with plastic sample cups and pins, recalcified human citrated platelet-poor plasma spontaneously burst-coagulated but with an unpredictable clotting time whereas plasma depleted of MPs by ultracentrifugation failed to coagulate. Coagulation of MP-depleted plasma was restored in a dose-dependent manner by glass microbeads, hydroxyapatite nanoparticles (HA NPs), and carboxylic acid-containing anionic nanocoatings of TEG cups and pins (coated by glow-discharge plasma-polymerized ethylene containing oxygen, L-PPE:O with 4.4 and 6.8 atomic % [COOH]). Glass beads lost their pro-coagulant activity in MP-depleted plasma after their surfaces were nanocoated with hydrophobic plasma-polymerized hexamethyl disiloxane (PP-HMDSO). In FXII-depleted MP-depleted plasma, glass microbeads failed to induce coagulation, however, FXIa was sufficient to induce coagulation in a dose-dependent manner, with no effect of glass beads. These data suggest that anionic surfaces of crystalline, organic, and amorphous solid synthetic materials catalyze explosive thrombin generation in MP-depleted plasma by activating the FXII-dependent intrinsic contact pathway. The data also show that microparticles are pro-coagulant surfaces whose activity has been largely overlooked in many coagulation studies to-date. These results suggest a possible mechanism by which anionic biomaterial surfaces induce bone healing by contact osteogenesis, through fibrin clot formation in the absence of platelet activation.

HYDROPHOBIC SURFACE MODIFICATION OF SILK FABRIC USING PLASMA-POLYMERIZED HMDSO

In this work, we study the hydrophobic properties of silk fabrics by deposition of plasma-polymerized (pp) hexamethyldisiloxane (HMDSO) using low-pressure plasma-enhanced chemical vapor deposition. Recently, hydrophobic properties are under active research in textile industry. The effects of coating time and power on the HMDSO-coated silk fabrics are investigated. Water contact angle of pp-HMDSO-coated silk fabric surface is measured as a function of power and coating time. Fabric surface shows an enhancement in hydrophobicity after coating. Attenuated total reflectance-Fourier transform infrared spectroscopy reveals the surface chemistry, and scanning electron microscopy shows the surface morphology of the uncoated and HMDSO-coated fabrics, respectively. In the case of uncoated fabric, water droplet absorbs swiftly, whereas in the case of HMDSO-coated fabric, water droplet remains on the fabric surface with a maximum contact angle of 140[Formula: see text]. The HMDSO-deposited silk surface is found to be durable after detergent washing. Common stains such as ink, tea, milk, turmeric and orange juice are tested on the surface of both fabrics. In HMDSO-coated fabrics, all the stains are bedded like ball droplet. In order to study the self-cleaning property, the fabric is tilted to 45[Formula: see text] angle; stain droplets easily roll off from the fabric.

Bacterial adhesion on conventional and self-ligating metallic brackets after surface treatment with plasma-polymerized hexamethyldisiloxane.

ABSTRACTIntroduction: Plasma-polymerized film deposition was created to modify metallic orthodontic brackets surface properties in order to inhibit bacterial adhesion. Methods: Hexamethyldisiloxane (HMDSO) polymer films were deposited on conventional (n = 10) and self-ligating (n = 10) stainless steel orthodontic brackets using the Plasma-Enhanced Chemical Vapor Deposition (PECVD) radio frequency technique. The samples were divided into two groups according to the kind of bracket and two subgroups after surface treatment. Scanning Electron Microscopy (SEM) analysis was performed to assess the presence of bacterial adhesion over samples surfaces (slot and wings region) and film layer integrity. Surface roughness was assessed by Confocal Interferometry (CI) and surface wettability, by goniometry. For bacterial adhesion analysis, samples were exposed for 72 hours to a Streptococcus mutans solution for biofilm formation. The values obtained for surface roughness were analyzed using the Mann-Whitney test while biofilm adhesion were assessed by Kruskal-Wallis and SNK test. Results: Significant statistical differences (p< 0.05) for surface roughness and bacterial adhesion reduction were observed on conventional brackets after surface treatment and between conventional and self-ligating brackets; no significant statistical differences were observed between self-ligating groups (p> 0.05). Conclusion: Plasma-polymerized film deposition was only effective on reducing surface roughness and bacterial adhesion in conventional brackets. It was also noted that conventional brackets showed lower biofilm adhesion than self-ligating brackets despite the absence of film.

Durable superhydrophobic carbon soot coatings for sensor applications

A novel approach for the fabrication of durable superhydrophobic (SH) carbon soot coatings used in quartz crystal microbalance (QCM) based gas or liquid sensors is reported. The method uses modification of the carbon soot through polymerization of hexamethyldisiloxane (HMDSO) by means of glow discharge RF plasma. The surface characterization shows a fractal-like network of carbon nanoparticles with diameter of ~50 nm. These particles form islands and cavities in the nanometer range, between which the plasma polymerized hexamethyldisiloxane (PPHMDSO) embeds and binds to the carbon chains and QCM surface. Such modified surface structure retains the hydrophobic nature of the soot and enhances its robustness upon water droplet interactions. Moreover, it significantly reduces the insertion loss and dynamic resistance of the QCM compared to the commonly used carbon soot/epoxy resin approach. Furthermore, the PPHMDSO/carbon soot coating demonstrates durability and no aging after more than 40 probing cycles in water based liquid environments. In addition, the surface layer keeps its superhydrophobicity even upon thermal annealing up to 540 °C. These experiments reveal an opportunity for the development of soot based SH QCMs with improved electrical characteristics, as required for high-resolution gas or liquid measurements.

Angiogenic tube formation of bovine aortic endothelial cells grown on patterns formed by H2/He plasma treatment of the plasma polymerized hexamethyldisiloxane film.

Angiogenesis, the process to generate new vessels, is necessary for normal development in children as well as the wound healing and the tumor growth in adults. Therefore, it is physiologically and/or pathophysiologically significant to monitor angiogenesis. However, classical in vitro methods to evaluate angiogenesis take a long time and are expensive. Here, the authors developed a novel method to analyze the angiogenesis in a simple and economical way, using patterned films. In this study, the authors fabricated a plasma polymerized hexamethyldisiloxane (PPHMDSO) thin film deposited by capacitively coupled plasma chemical vapor deposition system with various plasma powers. The patterned PPHMDSO film was plasma treated by 10:90 H2/He mixture gas through a metal shadow mask. The films were characterized by water contact angle, atomic force microscopy, x-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy analyses. Our results show that the PPHMDSO film suppresses the cell adhesion, whereas surface modified PPHMDSO film enhances the cell adhesion and proliferation. From cell culture experiments, the authors found that the patterned film with 300 μm line interval was most efficient to evaluate the tube formation, a sapient angiogenic indicator. This patterned film will provide an effective and promising method for evaluating angiogenesis.

Dental implants coated with a durable and antibacterial film

Bacterial adhesion to the surface of implants in bone tissue may result in serious peri-implant diseases and cannot always be avoided by sterilization prior to implantation. For this reason, different strategies to confer the implant surfaces with intrinsic antibacterial properties are being developed. A major difficulty is that effective antibacterial materials may be detrimental to the adhesion of eukaryotic cells, and be poorly integrated into the host tissue. Here, we develop and characterize a composite coating material comprising silver nanoparticles deeply buried inside a matrix of plasma-polymerized hexamethyldisiloxane. Applied to titanium dental screws, the coating shows a good resistance against stresses from sterilization with β-irradiation and drilling into bone tissue. By varying the parameters of the plasma-depositing process, we are able to either induce or hinder the adhesion of epithelial cells. Through a fluorescence microscopy analysis, we demonstrate that the inclusion of silver nanoparticles in the polymer matrix does not influence the adhesion of fibroblasts and osteoblasts. However, the presence of silver in the coating layer results in dramatically reduced adhesion of Escherichia coli bacteria with respect to uncoated or silver-free coated surfaces.

Studying the influence of nanodiamonds over the elasticity of polymer/nanodiamond composites for biomedical application

The combined unique properties offered by organic and inorganic constituents within a single material on a nanoscale level make nanocomposites attractive for the next generation of biocompatible materials. The composite materials of the detonation nanodiamond/polymer type possess spatial organization of components with new structural features and physical properties, as well as complex functions due to the strong synergistic effects between the nanoparticles and the polymer [1]. The plasma polymerization (PP) method was chosen to obtain composites of silicon-based polymers, in which detonation generated nanodiamond (DND) particles were incorporated. The composite layers are homogeneous, chemically resistant, thermally and mechanically stable, thus allowing a large amount of biological components to be loaded onto their surface and to be used in tissue engineering, regenerative medicine, implants, stents, biosensors and other medical and biological devices. Mesenchymal stem cells (MSCs) are the main focus of research in regenerative medicine due to their extraordinary potential to differentiate into different kinds of cells including osteoblasts, which are needed for various bone disease treatments. However, for optimal usage of MSCs knowledge about the factors that influence their initial distribution in the human system, tissue-specific activation and afterwards differentiation into osteoblasts is required. In recent studies it was found that one of these factors is the elasticity of the substrates [2]. The choice of the proper material which specifically guides the differentiation of stem cells even in the absence of growth factors is very important when building modern strategy for bone regeneration. One of the reasons for there not being many studies in this area worldwide is the lack of suitable biomaterials which support these kinds of experiments. The goal of this study is to create substrates suitable for cell culture with a range of mechanical properties (namely elasticity and hardness) using composite layers (PPHMDS-DND) of plasma polymerized (PP) hexamethyldisiloxane (HMDS) and detonation generated nanodiamond (DND). The samples' elastic modulae and hardness were measured by CSM Ultra Nanoindentation Tester.

Nanostructured self-cleaning lyocell fabrics with asymmetric wettability and moisture absorbency (part I)

A single-faced superhydrophobic lyocell fabric maintaining its inherent high moisture absorbing bulk property was produced by oxygen plasma-based nanostructuring and a subsequent coating with a low-surface-energy material. After 5 minutes of oxygen plasma etching, followed by 30 seconds of a plasma polymerized hexamethyldisiloxane coating, the treated surface of lyocell turned into a superhydrophobic surface with a static contact angle greater than 160° and a sliding angle less than 2°; however, the backside was hydrophilic, untreated lyocell fabric. As a result of oxygen plasma etching, dual hierarchical roughness was formed on the lyocell fabric as nano scale pillars or hairs were added onto the lyocell fabric surface with micro scale roughness. Extremely opposite wetting behavior was observed, when a water droplet was deposited on the face and backside of the plasma-treated lyocell fabric. A water droplet was immediately absorbed and spread out on the untreated backside, while it rolled off the treated surface, demonstrating a bouncing effect.

Water permeability of quarry stone superficially modified by plasma polymerization of hexamethyldisiloxane at atmospheric pressure

The surface of quarry stone was modified with a thin film of plasma-polymerized hexamethyldisiloxane (PPHMDSO) deposited at atmospheric pressure. The surface of the treated stone turned hydrophobic as shown by water contact angle measurements. FTIR characterization showed CH3 and Si-CH3 bands characteristic of HDMSO functional groups. Finally, the water absorption of untreated and PPHMDSO-modified stones was studied. In both cases, the water absorption profile was consistent with Fickian diffusion but the treated stone absorbed 8 times less water than the untreated stone.

Characterization of Plasma Polymerized Hexamethyldisiloxane Films Prepared by Arc Discharge

Herein, we present a simple method for fabricating plasma polymerized hexamethyldisiloxane films (pp-HMDSO) possessing superhydrophobic characteristics via arc discharge. The pp-HMDSO films were deposited on a soda–lime–silica float glass using HMDSO monomer vapor as a precursor. A detailed surface characterization was performed using scanning electron microscopy and atomic force microscopy. The growth process of the pp-HMDSO films was investigated as a function of deposition time from 30 to 300 s. The non-wetting characteristics of the pp-HMDSO films were evaluated by means of contact angle (CA) measurements and correlated with the morphological characteristics, as obtained from microscopy measurements. The deposited films were found to be nano-structured and exhibited dual-scale roughness with the static CA values close to 170°. Fourier transform infrared spectroscopy analysis was carried out to investigate chemical and functional properties of these films. Methyl groups were identified spectroscopically to be present within the pp-HMDSO films and were proposed to result in the low surface energy of material. The synergy between the dual-scale roughness and low surface energy resulted in the superhydrophobic characteristics of the pp-HMDSO films. A possible mechanism for the pp-HMDSO film formation is proposed.

Plasma-polymerized HMDSO coatings to adjust the silver ion release properties of Ag/polymer nanocomposites

In the current work, we study the silver ion release potential and the water uptake through a SiO x C y H z -polymer which is grown from the precursor hexamethyldisiloxane (HMDSO) in radiofrequency (RF) plasma. These layers were deposited on top of two dimensional (2D) ensembles of silver nanoparticles (AgNPs) with nominal thickness of 2 nm on a 20 nm RF-sputtered polytetrafluoroethylene (PTFE) thin film. The composition of the plasma-polymerized HMDSO barriers was varied by changing the oxygen flow during the polymerization process and their thickness was varied as well. Morphology and optical properties of the nanocomposites were investigated using transmission electron microscopy (TEM) and UV–Visible spectroscopy (UV–Vis), respectively. The concentration of the silver ions released from the nanocomposites after immersion in water for several time intervals was measured using inductively coupled plasma mass spectrometry (ICP-MS). Contact angle analysis and electrochemical impedance spectroscopy (EIS) measurements were also performed and results show a strong dependence of the coatings properties and their water uptake on the oxygen content in the coating films and their thickness. Plasma polymerization with increasing the oxygen flow leads to the formation of more hydrophilic thin films with a higher Ag ion release potential. Increasing the thickness of the coatings reduced the amount of the released ions and the rate of the release process was slowed down. This indicates that by tailoring the structure and the thickness of the plasma-polymerized coating films, one can tune the silver ion release properties of Ag/polymer nanocomposites.

The ice repellency of plasma polymerized hexamethyldisiloxane coating

A superhydrophobic thin film was deposited on an aluminium oxide substrate by low pressure plasma polymerization of hexamethyldisiloxane (HMDSO). The coating was determined to be superhydrophobic due to its high water contact angle (∼158°) and low contact angle hysteresis. The aim of this work is to verify the icephobic properties of the HMDSO thin films obtained under simulated atmospheric conditions in a wind tunnel at sub-zero temperature and subsequent centrifugal adhesion test. The results obtained showed that the ice adhesion strength of the superhydrophobic HMDSO coating was 3.5 times lower than that on an aluminium substrate as reference tests. Although ice adhesion strength of the surface increased after 15 times icing/de-icing cycles, the surface kept its icephobic properties (ice adhesion strength 1.4 times lower than untreated aluminium).

Plasma deposition of a silicone-like layer for the corrosion protection of magnesium

Magnesium (Mg) and its alloys are widely used for biodegradable implant materials due to their degradability and mechanical properties similar to bone. However, the high corrosion rate and release of hydrogen gas hinder its clinical application. In this study, plasma-polymerization was used to deposit the hexamethyldisiloxane (HMDSO) polymeric films on Mg surface using low temperature radio frequency discharge plasma. The chemical and physical properties of the HMDSO films were characterized by contact angle measurements, field emission scanning electron microscope, and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Contact angle results show that the contact angle and the plasma discharge powers are strongly correlated. ATR-FTIR results indicate that plasma-polymerized HMDSO films have a chemical structure close to polydimethylsiloxane (PDMS). The weight loss test and electrochemical impedance spectroscopy were performed immersion in 0.9% NaCl solution in order to investigate corrosion protective properties of the coating layer. It was found that HMDSO plasma-polymerized coating layer showed good anti-corrosion properties than that of untreated samples. These results that the polymeric films coated on Mg may be potentially applied for clinical use.

Organic-Inorganic Behavior of Plasma-Polymerized Hexamethyldisiloxane Films Studied by Electron and Photon Induced Ion Desorption

In the present work two thin films, fabricated by plasma-polymerization of hexamethyldisiloxane (HMDSO) monomer, were studied by a combination of electron (ESID) and photon (PSID) stimulated ion desorption techniques. The organic character of the polymer film is evidenced by the high contribution of C2Hn+ species and the absence of high mass fragments in its ESID spectrum. On the other hand, the inorganic character is elucidated by the presence of high mass silicon ionic fragments. NEXAFS and PSID spectra also show clear differences between organic and inorganic films. The marked reduction of CH3+ species for PSID spectra of the organic–polymeric film is in accordance with ESID analysis and may be interpreted by a screening effect of its cross-linked organic structure.