Ammonia Plasma Treatment Research Articles

Colloidal Monolayers Combined with Cold Plasmas: A Versatile Nanofabrication Tool

New challenges of life science research make nanostructured polymeric surfaces, chemically and spatially resolved, very attractive for biomedical purposes. High costs and unsuitability of polymers processed by the traditional techniques lead to new research routes. In this work, the production of nanostructured polystyrene substrates combining Colloidal lithography and cold plasma processes is shown. Colloidal nanoparticles self-assemble into a regular lattice on the polymers, and are used as physical masks in lithographic processes. Ammonia plasma treatments have been used to improve the suitability of the polymer surface for the entire process. Plasma etching with Ar/O2 discharges have been applied to transfer the patterns.

Surface Amination of Biopolymer Using Surface-Wave Excited Ammonia Plasma

Surface-wave plasma has been used to modify polymer surfaces. The density and selectivity of the functionalizations are very important for biomaterial applications. Low-temperature plasma treatment has been successfully applied to many types of polymers to generate functional surfaces. In this study, we focus on the surface modification of amino groups on chitosan surfaces by ammonia plasma treatment. Chitosan is a nontoxic, biocompatible and biodegradable polymer, which promotes the scarless healing of skin through embolization. The experimental results of X-ray photoelectron spectroscopy measurements showed that the ammonia plasma exposure to the chitosan surface increased the nitrogen incorporation on the surface from 4.67 to 9.92%. The selectivity of amino group functionalizations (–NH2/N) increased from 53.7 to 78.4% after the plasma irradiation.

Surface modification of poly(hydroxybutyrate) films to control cell–matrix adhesion

Tailoring surface properties of degradable polymer scaffolds is key to progress in various tissue engineering strategies. Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) thin films were modified by low pressure ammonia plasma, low pressure water vapour plasma, or immersion in a sodium hydroxide solution to elaborate means to control the cell-matrix adhesion of human umbilical cord vein endothelial cells grown on these materials. Fibronectin (FN) heteroexchange and cell adhesion were correlated to the physicochemical characteristics of the modified polymer surfaces which were investigated by X-ray photoelectron spectroscopy (XPS), scanning force microscopy (SFM), electrokinetic measurements, and contact angle measurements. All treatments increased the hydrophilicity of the polymer samples, which could be accounted to newly created amine or carboxyl functionalities for ammonia plasma or water vapour plasma treatments, respectively, and ester hydrolysis for treatments with alkaline aqueous solutions. Main features of cell adhesion and FN reorganisation-evaluated after 1h and after 5 days-could be attributed to the anchorage strength of pre-coated FN layers at the polymer surface, which was, in turn found to be triggered by the type of modification applied. In line with earlier studies referring to different materials cell adhesion and matrix reorganisation were shown to be sensitively controlled through the physicochemical profile of poly(hydroxybutyrate) surfaces.

Manufacturing and morphology structure of polylactide-type microtubules orientation-structured scaffolds

Tissue engineering using scaffold not only should have biodegradability and a certain 3D structure, but also its morphology structure should be mimetic to that of the repaired natural tissue. So to manufacture the scaffold with a biomimetic structure as the natural tissues is important. In this research, highly porous poly(L-lactic acid) (PLLA) and poly(L-lactic-co-glycolic acid) (PLGA) scaffolds with microtubules orientation structure were designed and fabricated by using dioxane as solvent and an improved thermal-induced phase separation (TIPS) technique. All the factors which will affect solvent crystallization and microtubules orientation structure of the scaffold, such as the type of the solvent and polymer, concentration of the polymer solution, and temperature-gradient of the system have been studied carefully. So the porosity, diameter, tubular morphology and orientation of the microtubules could be controlled by adjusting the concentration of the polymer solution and temperature-gradient of the system. The scaffold with diameter of microtubules from 40 to 240microm and high porosity up to 96% could be obtained by adjusting temperature-gradient during the TIPS process. By increasing concentration of the polymer solution the regularity of the microtubular scaffold has been improved and the thickness of wall of the microtubules has been increased as well. In vitro cell culture results show that after the scaffolds have been improved by the ammonia plasma treatment and then collagen anchorage method, the human transparent cartilage cells H144, could be seeded deeply into the microtubules orientation-structured scaffolds and grew well there.

Reduction of core in cage protein for application to electron device

For application to floating nanodots gate memory, ferritin core, ferrihydrite nanodot, array was made and reduced to be conductive. Ammonia plasma treatment was employed to reduce the ferrihydrite cores. X-ray photoelectron spectroscopy analysis confirmed that the plasma treated cores embedded in a SiN film are successfully reduced from ferrihydrite to metal iron. It was elucidated that hydrogen radicals or ions in the plasma combine with oxygen atoms in the core and, consequently, the core is reduced to a conductive state. Transmission electron microscope analysis before and after the treatment showed that the reduced core size was smaller than ferrihydrite core by approximately 2 nm, which is consistent with theoretical calculation of the shrink size accompanying core reduction to α-Fe. The plasma treated cores embedded in SiO 2 film are found to be iron oxides, which indicates that the metal iron nanodots are vulnerable to oxygen and easy to be reoxidized.

Synthetic biodegradable microparticles for articular cartilage tissue engineering

Articular cartilage tissue engineering procedures require the transplantation of chondrocytes that have been expanded in vitro. The expansion is carried out for a considerable time and can lead to a modulation of cell phenotype. However, microcarrier cultures have been shown to allow cell expansion while maintaining the phenotype. Here, we have used the biodegradable polyester poly(lactide-co-glycolide) (PLGA) in the form of microspheres and irregular shaped microparticles with a diameter between 47 and 210 microm. Surface modification of particles was carried out by ammonia plasma treatment and subsequent adsorption of collagen. Alternatively, particles were modified by partial hydrolysis and subsequent immobilization of an amine-terminated dendrimer. Each surface modification step was characterized by X-ray photoelectron spectroscopy. The effectiveness of the surface modification procedures was demonstrated by in vitro cell culture experiments using sheep articular cartilage chondrocytes. A significant influence of both the particle shape and the surface chemistry on the proliferation rate was observed while the phenotype was maintained independent of the surface chemistry or particle shape. Chondrocytes cultured on PLGA microspheres were further assessed for cartilage tissue formation in collagen type I gels in nude mice. The tissue that were formed showed the appearance of a hyaline-like cartilage and the presence of the microspheres substantially reduced the degree of collagen gel contraction over 1-2 months.

Influences of ammonia plasma treatment on modifying depth and degradation of poly( l-lactide) scaffolds

Hydrophobicity of poly( l-lactide) scaffolds is a main drawback in obtaining a sufficient mass of seeded cells for satisfying the requirements of tissue engineering. Plasma treatment is a useful technique to enhance the hydrophilicity of the scaffolds. However, the effect of this technique on the modifying depth and degradation of the scaffolds should be considered. In this paper, the influence of NH 3 plasma treatment on the modifying depth and degradation of scaffolds were investigated. The results showed that the modifying depth of the scaffolds increased with treating time and the plasma power ranging from 20 to 80 W influenced the depth slightly. However, the degradation of the scaffolds increased with increasing treatment time and plasma power. The results also showed that the plasma intruded the scaffolds gradually from top to bottom. For a 4 mm thick scaffold, the optimized treatment condition was 20 W of power in a 30 Pa ammonia atmosphere for 30 min of treating time. Under this condition, the integrity of scaffold could be relatively well kept. NH 3 plasma treatment enabled the penetration of cells into scaffolds and facilitated the proliferation of cells in them.

Introducing Amine Functionalities on a Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Surface: Comparing the Use of Ammonia Plasma Treatment and Ethylenediamine Aminolysis

Amine functionalities were introduced onto the surface of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films by applying radio frequency ammonia plasma treatment and wet ethylenediamine treatment. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS) for chemical composition and Raman microspectroscopy for the spatial distribution of the chemical moieties. The relative amount of amine functionalities introduced onto the PHBV surface was determined by exposing the treated films to the vapor of trifluoromethylbenzaldehyde (TFBA) prior to XPS analysis. The highest amount of amino groups on the PHBV surface could be introduced by use of ammonia plasma at short treatment times of 5 and 10 s, but no effect of plasma power within the range of 2.5-20 W was observed. Ethylenediamine treatment yielded fewer surface amino groups, and in addition an increase in crystallinity as well as degradation of PHBV was evident from Fourier transform infrared spectroscopy. Raman maps showed that the coverage of amino groups on the PHBV surfaces was patchy with large areas having no amine functionalities.

65.3: Quantitative Adhesion Analysis of Sputtered Copper Films on Glass Substrate by Microindentation Measurement

Quantitative adhesion testing of copper films on glass substrates was investigated by microindentation measurement. Due to the weak adhesion and inter-diffusion issues between copper (Cu) and glass substrates, we deposited silicon nitride (SiNx) films on glass substrates initially. Optimizing Cu sputtering parameters and introducing ammonia (NH3) plasma treatment onto SiNx, we obtained the superior adhesion strength of Cu/SiNx/glass structures. Based on the values of critical reduced depth (b) with Cu/SiNx/glass (b=1.311) and with Cu/Mo/glass (b=1.005) structures, we inferred that the adhesion strength of these two kinds of structures was almost the same. Furthermore, the etching profiles of Cu/SiNx structures were excellent. The taper angle was approximately 60 degrees, and critical-dimension loss percent was about 7.

Ammonium chloride complex formation during downstream microwave ammonia plasma treatment of parylene-C

In this work, parylene-C is exposed to the effluent from a microwave ammonia plasma with a goal of producing primary amine groups on the parylene-C. These amine groups are desired as sites for the attachment of various biomolecules that will influence the biocompatibility of the parylene-C. Ammonia plasma treatment is an effective approach for creating amine species on polymers. In this work, attenuated total reflectance infrared spectroscopy studies showed that no primary amine groups resulted from this treatment of parylene-C. Instead, reactive nitrogen-bearing radicals from the plasma appear to have been complexed by chlorine in the polymer. The formation of these complexes scavenged nitrogen-bearing radicals from the plasma and prevented the formation of nitrogenous species, such as the desired primary amines, on the parylene-C. These results are consistent with results of ammonia plasma treatment of other chlorinated polymers and suggest that alternative approaches are required to create nitrogen-bearing species on parylene-C.

Effects of ammonia plasma treatment on the surface characteristics of carbon fibers

Carbon fibers were grown from cobalt catalysts with larger size (> 100 nm), and the size distribution can be controlled by pretreatment. Pretreated cobalt catalytic-layers were observed as islands, which can enhance the growth of carbon fibers. The carbon fibers were treated by ammonia plasma in a PECVD system. High-energy ammonia plasma not only can cause damage but also adsorb on carbon fibers. The ammonia plasma treatment resulted in the etching effect. It is also observed that the more treatment time, the more disorder in structures of carbon fibers. The N–H functional groups were found on the surfaces of ammonia plasma treated carbon fibers and this observation can be further investigated to develop chemical sensor application.

Improving arterial prosthesis neo-endothelialization: Application of a proactive VEGF construct onto PTFE surfaces

The formation of a confluent endothelium on expanded polytetrafluoroethylene (PTFE) vascular prostheses has never been observed. This lack of endothelialization is known to be one of the main reasons leading to the development of thromboses and/or intimal hyperplasia. In this context, several efforts were put forward to promote endothelial cell coverage on the internal surface of synthetic vascular prostheses. The goal of the present study was to immobilize the vascular endothelial growth factor (VEGF) onto Teflon ® PTFE surfaces to generate a proactive polymer construct favoring interaction with endothelial cells. An ammonia plasma treatment was first used to graft amino groups on PTFE films. Subsequent reactions were performed to covalently bind human serum albumin (HSA) on the polymer surface and to load this protein with negative charges, which allows adsorbtion of VEGF onto HSA via strong electrostatic interactions. X-ray photoelectron spectroscopy (XPS) experiments along with surface derivatization strategies were performed between each synthesis step to ascertain the occurrence of the various molecules surface immobilization. Finally, the electrostatic binding of VEGF to the negatively charged HSA matrix was performed and validated by ELISA. Endothelial cell adhesion and migration experiments were carried out to validate the potential of this VEGF-containing biological construct to act as a proactive media toward the development of endothelial cells.

Towards a methodology for the effective surface modification of porous polymer scaffolds

A novel low-pressure radio-frequency plasma treatment protocol was developed to achieve the effective through-thickness surface modification of large porous poly ( d,l-lactide) (PDLLA) polymer scaffolds using air or water: ammonia plasma treatments. Polymer films were modified as controls. Scanning electron micrographs and maximum bubble point measurements demonstrated that the PDLLA foams have the high porosity, void fraction and interconnected pores required for use as tissue engineering scaffolds. The polymer surface of the virgin polymer does contain acidic functional groups but is hydrophobic. Following exposure to air or water: ammonia plasma, an increased number of polar functional groups and improved wetting behaviour, i.e. hydrophilicity, of wet surfaces was detected. The number of polar surface functional groups increased (hence the decrease in water contact angles) with increasing exposure time to plasma. The change in surface composition and wettablility of wet polymer constructs was characterised by zeta potential and contact angle measurements. The hydrophobic recovery of the treated PDLLA polymer surfaces was also studied. Storage of the treated polymer constructs in ambient air caused an appreciable hydrophobic recovery, whereas in water only partial hydrophobic recovery occurred. However, in both cases the initial surface characteristics decay as function of time.

Enhanced vascular-related cellular affinity on surface modified copolyesters of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx)

Random copolyester of 3-hydroxybutyrate and 3-hydroxyhexanoate, short as PHBHHx, was surface modified by ammonia plasma treatment and/or fibronectin coating, respectively. The improved results were demonstrated by better growth of human umbilical vein endothelial cells (HUVECs) and rabbit aorta smooth muscle cells (SMCs) on the surface of ammonia plasma-treated PHBHHx coated with fibronectin (PFn-PHBHHx), compared with the fibronectin-coated (Fn-PHBHHx) or uncoated PHBHHx, respectively, although XPS analysis and ELISA demonstrated higher fibronectin adsorption on Fn-PHBHHx than on PFn-PHBHHx. Confocal microscopy observation showed that the specific co-localization of fibronectin with F-actin was impaired on PFn-PHBHHx, while it was almost lost on Fn-PHBHHx compared with pristine PHBHHx or plasma-treated PHBHHx (P-PHBHHx). These were attributed to the generation of new nitrogen- and oxygen-containing groups on the PHBHHx surface by the ammonia plasma treatment, which led to increased polar components that enhanced polymer surface energy and hydrophilic properties on P-PHBHHx. The most prominent effect of PFn-PHBHHx was its stimulation of HUVECs proliferation. HUVECs on PFn-PHBHHx formed a confluent monolayer after 3 days of incubation, while SMCs were unable to form a sub-confluent layer. The above evidences revealed that PFn-PHBHHx would benefit endotheliazation rather than SMCs proliferation. We therefore believed that PFn-PHBHHx would be a promising material as a luminal surface of vascular grafts.

Polymeric meshes for internal sutures with differentiated adhesion on the two sides

The aim of this work is to investigate the effects of different plasma treatments on ePTFE abdominal prostheses with the final goal of obtaining a new prosthesis, made of a single strand of ePTFE, with clearly differentiated adhesion properties on the two sides, which should be able to promote tissue ingrowth on one side and prevent post surgical visceral adhesions on the other. Samples obtained from ePTFE Bard Dulex Meshes have been treated sequentially with three different gases (N(2), O(2) and NH(3)) in order to choose the optimal treatment conditions to improve ePTFE wettability. In particular, no modification was induced by N(2) treatment, while the full treatment after the final ammonia gas resulted in the best suitable candidate. As demonstrated by scanning electron microscopy, AFM analyses and contact angle measurements, ammonia plasma treatment increases ePTFE surface roughness and renders it more hydrophilic, thus promoting adhesion without any alteration of the material's bulk properties. The reported results also evidence the possibility to obtain the maximum wettability with a cheap treatment by optimizing plasma exposure time. As a preliminary cell adhesion study, Swiss 3T3 fibroblasts (mouse, embryo) have been seeded on the treated and untreated materials in order to assess whether there was any difference in terms of cell attachment and spreading. Cells seeded on the ammonia plasma treated material showed a better adhesion and spreading when compared to the untreated material.

Investigation of Dow Cyclotene 4026 surface amination by downstream plasma treatment

Dow Cyclotene 4026 surfaces were treated by downstream ammonia cold plasma with and without argon plasma pretreatments. The modified polymer surfaces were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared-attenuated total reflection, and atomic force microscopy (AFM). A 2 fractional factorial design was developed to identify the optimal processing parameters. Further experimental investigation has also been conducted to optimize the operating conditions. The combined results show that the extent of surface amination of Cyclotene grows with increase of power, pressure, and temperature of ammonia plasma treatments both with and without argon plasma pretreatments. For the treatment time effect, the results indicate that N/C (nitrogen/carbon) ratios increase with time and then start to slightly decrease at the ∼4-min point, which may be tentatively explained by a competition between the modification process and the degradation process on the polymer surfaces. AFM results suggest that the upper limit of the operating condition to obtain a desirable surface topography is 175°C. Based on all the results from Design of Experiment, experimental data, and AFM analysis, the optimum processing parameters have been suggested. Finally, the aging effect of aminated surfaces is discussed; further investigation of this effect is still underway. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2418–2427, 2005

Downstream microwave ammonia plasma treatment of polydimethylsiloxane

To control the interactions between surfaces and biological systems, it is common to attach polymers, proteins, and other species to the surfaces of interest. In this case, surface modification of polydimethylsiloxane (PDMS) was performed by exposing PDMS films to the effluent from a microwave ammonia plasma, with a goal of creating primary amine groups on the PDMS. These amine sites were to be used as binding sites for polymer attachment. Chemical changes to the surface of the PDMS were investigated as a function of treatment time, microwave power, and PDMS temperature during plasma treatment. Functional groups resulting from this treatment were characterized using attenuated total reflectance infrared spectroscopy. Plasma treatment resulted in the incorporation of oxygen- and nitrogen-containing groups, including primary amine groups. In general, increasing the treatment time, plasma power and substrate temperature increased the level of oxidation of the films, and led to the formation of imines and nitriles. PDMS samples treated at 100 W and 23 °C for 120 s were chosen for proof-of-concept dextran coating. Samples treated at this condition contained primary amine groups and few oxygen-containing groups. To test the viability of the primary amines for attachment of biopolymers, functionalized dextran was successfully attached to primary amine sites on the PDMS films.

Surface modification of polyethylene powder by nitrogen and ammonia low pressure plasma in a fluidized bed reactor

A combination of a fluidized bed and a low pressure plasma has been employed for the surface modification of low density polyethylene (LDPE) powders. Optical Emission Spectroscopy and Laser Doppler Anemometry has been used for the characterization of the reactor. XPS and contact angle measurements were carried out to reveal surface modification of nitrogen and ammonia plasma treatment of LDPE powders. Both nitrogen and ammonia plasma treatment show an increase of the hydrophilic character of the surface treated LDPE powders. XPS analysis shows the incorporation of new functional moieties including C–N, C–O groups on the surface of treated powders. In this configuration nitrogen plasma treatment leads to a better incorporation of nitrogen containing functional groups when compared to ammonia plasma.

Enhanced tissue-compatibility of polyethylenterephtalat membranes by plasma aminofunctionalisation

Polyethylenterephtalat track-etched membranes were plasma-modified to increase cell-adhesion and tissue-compatibility. Amine functionalities were grafted onto the surfaces by means of ammonia-plasma treatment, and plasma deposition of allylamine. Changes of chemical and physical properties of the samples were followed and in vitro evaluation of biocompatibility was carried out by studying human skin fibroblast interaction with surfaces. We found that fibroblasts adhered and grew better on poly-allylamine coated surfaces with higher amine concentration than on ammonia-plasma treated ones, but both had better cell-adhesive properties than the original membrane.

Surface properties of polyethylene after low-temperature plasma treatment

The effect of oxygen and ammonia plasma treatments on changes of the surface properties of linear high-density polyethylene (HDPE) was studied. Surface energies of the polymer substrates were evaluated by contact angle measurements using Lifshitz-van der Waals acid-base approach. The surface energy of untreated HDPE is mainly contributed by Lifshitz-van der Waals interactions. After 5 min of plasma treatment, hydrogen bonds are formed on the surface, which is reflected in predominant acid-base interactions. The SEM results obtained demonstrate considerable changes of the surface roughness due to different types of the plasma gas used. Evolution of oxygen- or amino-containing moieties was detected by XPS and ATR FT IR. The prepared polyethylene surfaces were used as a basic support for further fabrication of novel hybrid biocomposite sandwich structures.