Plasma polymer films (PPF), widely used as sensing layers in surface acoustic wave (SAW) based gas and liquid phase sensors, have a major drawback: high concentrations of the sensed analytes easily drive these films into saturation, where accurate measurements are no longer possible. This work suggests a solution to this problem by modifying the PPF with the sensed chemical compound to improve the overall sorption properties and sensor dynamic range. Thin polymer films were synthesized from hexamethyldisiloxane (HMDSO) and triethylsilane (TES) monomers in a plasma-enhanced chemical vapor deposition (PECVD) process using a RF plasma reactor. We used these Si-containing compounds because they are known for their excellent sensing properties. In this work, the layers were deposited onto the active surface of high-Q 438 MHz Rayleigh SAW two-port resonators, used as mass sensitive sensor elements. We call these devices quartz surface microbalances (QSM). In a second step, ammonia plasma modification was applied to the HMDSO and TES films, in order to achieve a higher sensitivity to NH3. The sensors were probed at different NH3 gas concentrations in a computer controlled gas probing setup. A comparison with unmodified films revealed a 74% to 85% improvement in both the sensitivity and sorption ability of the HMDSO sensing layers, and of about 8% for the TES films.

Condensation frosting is an undesired natural phenomenon that could be impeded efficiently using appropriate wettability and morphologically patterned surfaces. The icephobic properties of carbon soot and the fabrication scalability of its synthesis method are a good foundation for anti-frosting applications; however, the fundamentals of frost growth and spreading on sooted surfaces have not been examined yet. In this study, we investigate the anti-frosting performance of three groups of superhydrophobic soot coatings by means of 16 MHz quartz crystal microbalances (QCMs). The analysis of the real-time sensor signal of each soot coated QCM pattern shows that frost formation and its propagation velocity depend on the quantity of oxygen functionalities and structural defects in the material. In turn, the reduction of both parameters shifts the onset of frost growth to temperatures below -20 degrees C, whereas the interdroplet ice bridging is slowed by a factor of four. Moreover, high-resolution scanning electron micrographs of the samples imply delamination upon defrosting of the soot with spherical-like morphology via polar interactions driven mechanism. These results reveal an opportunity for control of frost incipiency on sooted surfaces by adjusting the synthesis conditions and depositing soot coatings with as low as possible content of hydrophilic active sites.

Biofilm development, associated with the adherence of microbial cells on various solid substrates, has an adverse economic impact and is the main reason for the spreading of microbial infections. The present article reports novel findings about the anti-bioadhesion performance of four types of superhydrophobic soot coatings, deposited via combustion flame synthesis and further functionalized using plasma polymerization and/or fluorination, towards a Gram-negative bacterial strain Pseudomonas putida. The real-time sensor response of four representative soot coated 5 MHz quartz crystal microbalances, along with scanning electron microscopy, fluorescence microscopy and contact angle measurements on the model soot surfaces, reveal reversible and irreversible bioadhesion on the soot during the first hour of cell colonization. Each adhesion mode is related to the presence and distribution of morphological features within the size of bacteria, but the prolonged 7-day exposure to the bacterial suspensions unifies the number of attached cells (only 3 times difference from coating-to-coating). Nevertheless, the soot coatings inhibit the proliferation of Pseudomonas species and reduce their quantity by two orders of magnitude compared to an uncoated glass slide, which demonstrates the importance of surface characteristics for precise control of the initial cell attachment and development of multifunctional soot coatings with anti-bioadhesion properties. (C) 2018 Elsevier Ltd.

In the present study we demonstrated that composite PPHMDS/DND coatings with elastic moduli close to those of mature bone tissue (0.2-2.8 GPa) stimulated growth and osteogenic differentiation of human adipose-derived mesenchymal stem cells (hAD-MSCs). Composite coatings were prepared by a method of plasma polymerization (PP) where detonation nanodiamond (DND) particles in different amounts (0.1, 0.5, and 1 mg/mL) were added to hexamethyldisiloxane (HMDS) before plasma deposition. This method allows variation only in the reduced elastic modulus (Er') with increase in the particle concentration, while the other surface properties, including surface wettability and topography, did not change. The response of hAD-MSCs to the increasing stiffness showed an effect on adhesion and osteogenic differentiation but not on cell proliferation. Matrix mineralization and cell spreading were maximized on PPHMDS/DND coatings with the highest elastic modulus (2.826 GPa), while the differences in proliferation rates among the samples were negligible. In general, PPHMDS/DND coatings provide better conditions for growth and osteogenic differentiation of hAD-MSCs in comparison to glass coverslips, confirming their suitability for osteo-integration applications. Additionally, our findings support the hypothesis that biomaterials with elasticity similar to that of the native tissue can improve the differentiation potential of mesenchymal stem cells.

With the present research we describe several alternative approaches aimed at polymer-on-polymer coatings, produced by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique. The depositions were made using two different plasma systems: plasma chamber unit B 30.2 (precursor pentane, hexamethyldisiloxane, perfluorhexane) and PECVD system "Oxford Nanofab Plasmalab System 100" (precursor methane-argon and acetylene-argon). Applying between 3 and 40 min-long cold plasma treatments, in common more than 100 different samples were modified: hydrophobic nanofiltration membranes of type PEEK, as well as ultrafiltration membranes of type PAN and Ultem. Structural and chemical characterisations of the deposited nano-thick functional layers were implemented through SEM imaging, ATR-FTIR, EDX, XPS, AFM and contact angle measurements, which proved the methods' feasibility and properties of the plasma-polymerised coatings. Membrane filtration performance was evaluated by using an 8-position cross-flow filtration system, in terms of permeate flux and rejection characteristics and with styrene oligomers of different molecular weights as markers.

Thin composite layers from polymer/nanoparticles (Ag-nanoparticles and detonation nanodiamonds) were prepared by plasma polymerization process on the base of hexamethyldisiloxane. The variation of the layer composition was achieved by changing the type of nanoparticles. The optical measurement techniques used were UV-VIS-NIR ellipsometry (SE), Fourier-transformed infrared spectroscopy (FTIR) and Raman spectroscopy. The values of the refractive index determined are in the range 1.30 to 1.42. All samples are transparent with transmission between 85-95% and very smooth. The change in Raman and FTIR spectra of the composites verify the expected bonding between polymer and diamond nanoparticles due to the penetration of the fillers in the polymer matrix. The comparison of the spectra of the corresponding NH3 plasma treated composites revealed that the composite surface becomes more hydrophilic. The obtained results indicate that preparation of layers with desired compositions is possible at a precise control of the detonation nanodiamond materials.

With this paper we describe several alternative approaches aimed at polymer-onpolymer coatings, produced by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique. In our case three types of input compounds were applied for varied "cold plasma" PECVD deposition of nano-thick functional layers: namely hexamethyldisiloxane (HMDSO), pentane and toluene onto plastic substrates. The output characterisations through SEM imaging, ATR-FTIR, EDX, AFM and contact angle measurements, proved the methods' feasibility and properties of the plasma-polymerised coatings.

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 similar to 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 degrees 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.

The organic vapor sensitivity of a quartz crystal microbalance (QCM) with an epoxy resin-carbon soot coating designed to be tolerant to humidity is reported. This is achieved using nonengulfed, but attached, hydrophobic carbon soot nanoparticles, coated in an irregular surface topography composed of islands and cavities. The root mean square roughness (R-rms) of 130 nm, together with the hydrophobic soot, convert the epoxy surface to a superhydrophobic (SH) one with high static contact angle (similar to 151 degrees) and low contact angle hysteresis (similar to 1.1 degrees). The frequency shift of the SH QCM at 100% relative humidity is similar to 7 times lower compared with an uncoated device, and thus indicating low water vapor adsorption due to superhydrophobicity. In addition, the SH QCM shows between three and six times higher gas sensitivity and lower detection limit compared with the conventional polymer coated QCMs. These results correlate well with the Rrms and surface topography of the coating, which ensure enhanced sensing area. Furthermore, the sensor demonstrates reproducibility, reversibility, and fast response-recovery time (similar to 10 s) to ethanol, methanol, and isopropanol vapor. These experiments reveal that superhydrophobicity increases the organic vapor sorption at the expense of water vapor sorption, and thus allowing operation of the QCM gas sensors in an uncontrolled humidity environment.

Experimental data on the temperature behavior of quartz crystal microbalances (QCMs) rigidly coated with solid polymer films of hexamethyldissiloxane (HMDSO) for gas and liquid-phase sensor applications are provided. 16 MHz AT-cut quartz resonators used as QCMs are coated at seven different HMDSO thicknesses in the 70-400 nm range by using a RF-plasma polymerization process. Their quasi cubic temperature frequency characteristics (TFCs) are measured over a temperature of -50 degrees C to 90 degrees C for each film thickness. A cubic spline approximation of the experimental data reveals a periodic oscillating behavior of the temperature coefficients of the TFC, while its inflection point oscillates between 24 degrees C and 28 degrees C in the above thickness range. Devices coated at 150, 260 and 380 nm, i.e. at a thickness period of 110-120 nm, were found to have identical thermal stability and TFC behavior. A simple practical method for correcting the sensor readings for thermally induced frequency shifts, based on an additional temperature measurement at each sensor reading, is suggested and verified experimentally. (C) 2015 Elsevier B.V. All rights reserved.

The successful osseointegration of a bone implant is greatly dependent on its ability to support cellular adhesion and functions. Deposition of thin composite coatings onto the implant surface is a promising approach to improve interactions with cells without compromising implant bulk properties. In this work, we have developed composite coatings, based on hexamethyldisiloxane (HMDS) and detonation nanodiamond (DND) particles and have studied adhesion, growth and function of osteoblast-like MG-63 cells. PPHMDS/DND composites are of interest for orthopedics because they combine superior mechanical properties and good biocompatibility of DND with high adherence of HMDS to different substrata including glass, metals and plastics. We have used two approaches of the implementation of DND particles into a polymer matrix: pre-mixture of both components followed by plasma polymerization and layer-by-layer deposition of HMDS and DND particles and found that the deposition approach affects significantly the surface properties of the resulting layers and cell behaviour. The composite, prepared by subsequent deposition of monomer and DND particles was hydrophilic, with a rougher surface and MG-63 cells demonstrated better spreading, growth and function compared to the other composite which was hydrophobic with a smooth surface similarly to unmodified polymer. Thus, by varying the deposition approach, different PPHMDS/DND composite coatings, enhancing or inhibiting osteoblast adhesion and functions, can be obtained. In addition, the effect of fibronectin pre-adsorption was studied and was found to increase greatly MG-63 cell spreading.

Mesenchymal stem cells (MSCs) hold a great promise for use in many cell therapies and tissue engineering due to their remarkable potential to replicate indefinitely and differentiate into various cell types. Many efforts have been put to study the factors controlling stem cell differentiation. However, still little knowledge has been gained to what extent biomaterials properties influence stem cell adhesion, growth and differentiation. Research utilizing bone marrow-derived MSCs has concentrated on development of specific materials which can enhance specific differentiation of stem cells e.g. osteogenic and chondrogenic.In the present work we have modified an organosilane, hexamethyldisiloxane (HMDS) with detonation nanodiamond (DND) particles aiming to improve adhesion, growth and osteodifferentiation of rat mesenchymal stem cells. HMDS/DND films were deposited on cover glass using two approaches: premixing of both compounds, followed by plasma polymerization (PP) and PP of HMDS followed by plasma deposition of DND particles. We did not observe however an increase in rMSCs adhesion and growth on DND-modified PPHMDS surfaces compared to unmodified PPHMDS. When we studied alkaline phosphatase (ALP) activity, which is a major sign for early osteodifferentiation, we found the highest ALP activity on the PPHMDS/DND material, prepared by consequent deposition while on the other composite material ALP activity was the lowest. These results suggested that DND-modified materials were able to control osteodifferention in MSCs depending on the deposition approach. Modification of HMDS with DND particles by consequent plasma deposition seems to be a promising approach to produce biomaterials capable to guide stem cell differentiation toward osteoblasts and thus to be used in bone tissue engineering.

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.

Plasma polymers are synthesized from hexamethyldisiloxane by capacitively coupled glow discharge. The effect of current density and monomer flow rate on the polymer structure is investigated by FTIR spectroscopy. The influence of the same parameters on the NO2 sensing properties of the polymers is studied by a quartz crystal microbalance.

Cell morphology and organisation of actin cytoskeleton are closely related to all essential for cells processes including adhesion, growth and differentiation. Therefore, both cell characteristics can be used to assess the tissue compatibility of a biomaterial. Many approaches have been used to modify biomaterials surface in order to improve their interactions with cells. In the present work, we have modified the surface of a synthetic polymer, plasma polymerised hexamethyldisiloxane (PPHMDS) using two approaches: treatment in ammonia plasma and plasma deposition of detonation nanodiamond (DND) particles, and have studied the alteration in cell morphology, adhesion and actin cytoskeleton organisation in rat mesenchymal stem cells (rMSCs) in order to assess suitability of plasma modified polymer films as cell adhesion substrata for tissue engineering application.

Abstract. Plasma polymers and composites based on hexamethyldisilox ane (PPHMDSO) were synthesized and studied by FTIR. By varying p lasma polymerization parameters, fillers with various nanodiamond pa rticles (DNDs) and post ammonia plasma modification the changes in the structur e we e achieved. At higher current density an elongation of the polymer chain and high crosslinking were observed. The decrease of the monomer flow rate l ed to a longchain and branched polysiloxane network. The structure of t he composites contained DND particles distributed in the polymer matrix. The ammonia modification led to a higher degree of cross-linking due to the additi onal decrease of hydrocarbon groups. This work demonstrates the possibility t o produce composites with controlled chemical structure by changing plasma parameters, DND nanofillers and post treatment in ammonia plasma.

Temperature induced frequency shifts may compromise the sensor response of polymer coated acoustic wave gas-phase sensors operating in environments of variable temperature. To correct the sensor data with the temperature response of the sensor the latter must be known. This study presents and discusses temperature frequency characteristics (TFCs) of solid hexamethyldisiloxane (HMDSO) polymer coated sensor resonators using the Rayleigh surface acoustic wave (RSAW) mode on ST-cut quartz. Using a RF-plasma polymerization process, RSAW sensor resonators optimized for maximum gas sensitivity have been coated with chemosensitive HMDSO films at 4 different thicknesses: 50, 100, 150 and 250 nm. Their TFCs have been measured over a (−100 to +110) °C temperature range and compared to the TFC of an uncoated device. An exponential 2,500 ppm downshift of the resonant frequency and a 40 K downshift of the sensor’s turn-over temperature (TOT) are observed when the HMDSO thickness increases from 0 to 250 nm. A partial temperature compensation effect caused by the film is also observed. A third order polynomial fit provides excellent agreement with the experimental TFC curve. The frequency downshift due to mass loading by the film, the TOT and the temperature coefficients are unambiguously related to each other.

The possibility is presented of producing thin plasma polymers with desired properties by using nanofillers. Composite films are synthesized from a mixture of hexamethyldisiloxane (HMDSO) and detonation nanodiamond particles (DNDs). The chemical structure of the composite consists of DNDs distributed in the polymer matrix. The effect of DNDs on the humidity and ammonia sorptive properties of the polymers obtained is studied by measuring the mass changes as a result of gas sorption by using a quartz crystal microbalance (QCM). The results show that, in view of building a sensing element for measuring humidity, ammonia or other gases, it is possible to maximize the sensor sensitivity to a certain gas by using an appropriate concentration of DNDs in HMDSO. Thus, a high degree of sensor sensitivity, together with short response time and minimum hysteresis, can be achieved. Composites of plasma-polymerized HMDSO with DNDs can be used as gas sensitive layers for the development of quartz resonator sensors.