Plasma Polymerization Research Articles

New plasma-assisted polymerization/activation route leading to a high density primary amine silanization of PCL/PLGA nanofibers for biomedical applications

Surface modification of hydrophobic nanofibers (NFs) to introduce cell-interactive chemical functionalities remains a challenge in biomedical applications. This study presents a novel three-step plasma-based method for synthesizing coatings with improved chemical selectivity compared to conventional plasma polymers. The process involved hexamethyldisiloxane (HMDSO) plasma polymerization followed by helium plasma activation, both performed in a medium-pressure dielectric barrier discharge. Scanning electron microscopy analysis demonstrated that the plasma-based steps did not cause damage to the NFs. X-ray photoelectron spectroscopy (XPS) and water contact angle measurements revealed the formation of a hydrophilic silanol-rich layer after HMDSO plasma polymerization and helium plasma activation. In the third step, (3-aminopropyl)triethoxysilane (APTES) was grafted onto the plasma polymer to introduce primary amine groups onto the surface, as confirmed by XPS. Although the APTES-based layer exhibited partial removal when exposed to aqueous environments, a stable aminated layer remained on the NF surface, which significantly enhanced Schwann cell responses compared to untreated and HMDSO-based coated NFs. This enhancement was confirmed through fluorescent imaging using live-dead staining, immunostaining, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. These coatings with a high selectivity in their chemical functionality (amines, or other functionalities via silanization agent selection), offer a promising surface functionalization approach for tissue engineering scaffolds.

Delivery of multipotent adult progenitor cells via a functionalized plasma polymerized surface accelerates healing of murine diabetic wounds.

Introduction: Stem cell therapies have been investigated as potential treatment modalities for chronic wounds however there has been limited success to date. Multipotent Adult Progenitor Cells (MAPCs©) have been identified as having potential as an allogenic stem cell product due to their high population doubling number and their characteristic dampening of T-cell proliferation. This helps to prevent autoimmunity and graft/cell rejection. Methods: We have developed a dressing, consisting of medical grade silicone coated with a heptylamine plasma polymer, which supports the growth and transfer of MAPCs to skin. To determine if the dressing can deliver functional stem cells into diabetic wounds, they were loaded with MAPCs and then placed over excisional wounds in both normal and diabetic mice. Results and discussion: Accelerated healing was observed in both the normal and diabetic wounds with wound gape being significantly smaller at day 3 when compared to controls. Wound analysis showed that treatment with the MAPC dressings dampened the inflammatory response with reduced numbers of neutrophils and macrophages observed. Additionally, an increase in pro-angiogenic VEGF and CD31 positive endothelial cells was observed indicating improved new blood vessel formation. The MAPC dressings had no effect on fibrosis with collagen I and III being equally affected in both control and treated wounds. Overall, the functionalized MAPC dressings improve healing responses particularly in diabetic mice with impaired healing responses and therefore, show potential for development as an advanced therapeutic approach for the treatment of chronic diabetic wounds.

An innovative bioactive surface with potential hemocompatibility performance for enhancing osseointegration at early-stage implantation

In the present study, the effectiveness of biomedical titanium (Ti) with plasma oxidation, polymerization, and albumin immobilization in producing a bioactive surface (Ti/rutile TiO2/NH2/protein) that promote hemocompatibility performance was investigated through scanning electron microscopy Raman spectrometry, X-ray photoemission spectroscopy, transmission electron microscopy, wettability examination, and blood clotting time assay. The results indicated that the bioactive surface with uniform island-like immobilized protein clusters was formed on the plasma-oxidized at 240 W specimen. This bioactive surface showed the significantly lowest contact angle as compared with the control (**p < 0.01) and other bioactive surfaces (plasma-oxidized at 80 W and 160 W) (*p < 0.05). In addition, the blood clotting time assay also demonstrated that the bioactive surface with 240 W exhibited the best red blood cell aggregation and adhesion performance. Thus, the fabricated bioactive surface not only increases wettability but also promotes hemocompatibility, thereby could potentially enhancing tissue healing at early-stage post-implantation.

Antimicrobial property of polyethersulfone (PES) membrane by plasma copolymerization of TEOS and oxazoline for organic dyes filtration

Plasma-based surface modification has been regarded as a green method to avoid the usage of toxic solvents in order to introduce various functional groups on the filtration membrane. In this paper, we employ plasma polymerization on the polyethersulfone (PES) ultrafiltration membrane by using simultaneously Tetraethyl orthosilicate (TEOS) and Oxazoline precursor exhibiting superhydrophilic and antibacterial properties to be used for organic dyes filtration. The addition of nanoscale coatings produced by the proposed plasma copolymerization of TEOS and Oxazoline could enhance the overall performance of the membrane in terms of pure water flux and antimicrobial properties compared to untreated sample. We evaluate its chemical composition by using Attenuated Total Reflectance Fourier Transform Infrared (FTIR/ATR) and XPS spectroscopy to ensure the presence of Oxazoline ring and Silicate functional group. Thus, our proposed plasma-modified membrane could be promising to solve specific issues regarding antibiofouling and improve simultaneously its overall performance.

Plasma polymers as targets for laser-driven proton-boron fusion

Laser-driven proton-boron (pB) fusion has been gaining significant interest for energetic alpha particles production because of its neutron-less nature. This approach requires the use of B- and H-rich materials as targets, and common practice is the use of BN and conventional polymers. In this work, we chose plasma-assisted vapour phase deposition to prepare films of oligoethylenes (plasma polymers) on Boron Nitride BN substrates as an advanced alternative. The r.f. power delivered to the plasma was varied between 0 and 50 W to produce coatings with different crosslink density and hydrogen content, while maintaining the constant thickness of 1 μm. The chemical composition, including the hydrogen concentration, was investigated using XPS and RBS/ERDA, whereas the surface topography was analyzed using SEM and AFM. We triggered the pB nuclear fusion reaction focusing laser pulses from two different systems (i.e., the TARANIS multi-TW laser at the Queen’s University Belfast (United Kingdom) and the PERLA B 10-GW laser system at the HiLASE center in Prague (Czech Republic)) directly onto these targets. We achieved a yield up to 108 and 104 alpha particles/sr using the TARANIS and PERLA B lasers, respectively. Radiative-hydrodynamic and particle-in-cell PIC simulations were performed to understand the laser-target interaction and retrieve the energy spectra of the protons. The nuclear collisional algorithm implemented in the WarpX PIC code was used to identify the region where pB fusion occurs. Taken together, the results suggest a complex relationship between the hydrogen content, target morphology, and structure of the plasma polymer, which play a crucial role in laser absorption, target expansion, proton acceleration and ultimately nuclear fusion reactions in the plasma.

Eucalyptus globulus essential oil thin film polymerized by cold plasma on Ti6Al4V: Sterilization effect, antibacterial activity, adhesion, and viability of mesenchymal stem cells

AbstractThis work aims to evaluate the characterization, antibacterial activity, and mesenchymal stem cell (MSC) viability in films obtained by cold plasma polymerization, from the essential oil of Eucalyptus globulus on Ti6Al4V alloy. The film presented low roughness values and a contact angle of 85°. The process incorporated a coating with oxygenated functional groups (OH and C═O). The effect of ultraviolet radiation, ethylene oxide, autoclave, and air plasma sterilization on polymer degradation was evaluated. Biofilm formation by Staphylococcus aureus was reduced on the film surface with no toxicity to MSCs. These effects can be attributed to functional groups, combined with the surface roughness and contact angle. These results suggest a potential for the application of this coating in biomaterials.

Correcting Hohlraum Drive Asymmetry with Glow Discharge Polymerization Coated Capsule Shims

In inertial confinement fusion target design, the shape discrepancy between the cylindrical hohlraum and the spherical capsule creates a low mode asymmetry in the implosion. One way to correct such asymmetry is to shim the target capsule surface with extra mass in specific locations following a three-dimensional P4 Legendre mode. Previously, the desired surface pattern was precision machined out of the capsule. The resulting 2DConA experiments that investigated the implosion’s shape demonstrated the shimming method’s success. However, machining leaves large defects on the capsule surface that will degrade neutron yield in a DT implosion. An alternative shimming approach is to grow the pattern on the capsule surface using a glow discharge polymerization coating process in a stencil lithography application. In this paper, we discuss the fabrication, characterization, and challenges of making shimmed target capsules with this new method.

PTFE-Containing Coating Obtained on Ti by Spraying and PEO Pretreatment

In case of using titanium alloys in equipment exposed to aggressive media (for example, sea water), it is necessary to take into account and, first of all, prevent the formation of a galvanic couple of titanium and another metal/alloy, which in most cases leads to the corrosion destruction of the latter. Another significant problem of using titanium is its low wear-resistance and poor tribological characteristics. To impart the necessary properties to titanium and its alloys, a composite coating was formed on the top of titanium. For the coating formation, a combination of the plasma electrolytic treatment and polymer spraying was used. The SEM, EDS and XRD analyses established morphological features, elemental and phase composition of the composite coatings. Contact angles and the wettability parameters of the composite coatings were investigated. An analysis of the data obtained showed that composite coatings have better protective properties than untreated material and base PEO coatings.

The investigation of deposited organic carbon‐silicon films using cyclonic atmospheric pressure plasma polymerization

AbstractBackgroundThe upgrading of atmospheric‐pressure plasma polymerization process, the detailed investigation of atmospheric‐pressure plasma polymerization deposited organic carbon‐silicon film features is essential to obtain the further understandings into the optimizing coating techniques.AimThis investigation demonstrates plasma cyclone deposited film features with adjusting argon gas flow rate and HMDSN monomer flow rate.MethodThis study utilized the plasma cyclone system to polymerize a carbon‐silicon film. In this study, Optical Emission Spectroscopy (OES) was employed as a diagnostic tool to indirectly inspect the chemical composition of the atmospheric‐pressure plasma polymerization's glow discharge by detecting the photo‐emitting species. The Contact Angle Goniometer, ATR‐FTIR, AFM, and XPS were used to measure the surface properties of the films deposited by plasma cyclone.ResultsThe static contact angle results show that most of the deposited films obtain the divergent contact angle values with adjusting argon gas flow rate and HMDSN monomer flow rate. ATR‐FTIR results show that argon gas flow rate and HMDSN monomer flow rate dominate the porosity of plasma cyclone deposited film surface. XPS and AFM analyses also detect the comparable trend of physicochemical characteristics of organic carbon‐silicon film with adjusting argon gas flow rate and HMDSN monomer flow rate. In summary, the organic carbon‐silicon films can be successfully polymerized by plasma cyclone.ConclusionsThe results refer that the organic carbon‐silicon film deposition on vanadium redox flow battery separator surface improved the electrolyte uptake of the cyclonic‐plasma‐coated separators was larger than that of a commercial separator.

Foundations of plasma enhanced chemical vapor deposition of functional coatings

Since decades, the PECVD (‘plasma enhanced chemical vapor deposition’) processes have emerged as one of the most convenient and versatile approaches to synthesize either organic or inorganic thin films on many types of substrates, including complex shapes. As a consequence, PECVD is today utilized in many fields of application ranging from microelectronic circuit fabrication to optics/photonics, biotechnology, energy, smart textiles, and many others. Nevertheless, owing to the complexity of the process including numerous gas phase and surface reactions, the fabrication of tailor-made materials for a given application is still a major challenge in the field making it obvious that mastery of the technique can only be achieved through the fundamental understanding of the chemical and physical phenomena involved in the film formation. In this context, the aim of this foundation paper is to share with the readers our perception and understanding of the basic principles behind the formation of PECVD layers considering the co-existence of different reaction pathways that can be tailored by controlling the energy dissipated in the gas phase and/or at the growing surface. We demonstrate that the key parameters controlling the functional properties of the PECVD films are similar whether they are inorganic- or organic-like (plasma polymers) in nature, thus supporting a unified description of the PECVD process. Several concrete examples of the gas phase processes and the film behavior illustrate our vision. To complete the document, we also discuss the present and future trends in the development of the PECVD processes and provide examples of important industrial applications using this powerful and versatile technology.

Heteroatom Introduction to Reconstruct Interfacial Chemical Structures for High-Reliability CFRTP/A6061-T6 Hybrid Structures.

The application of carbon-fiber-reinforced thermoplastic (CFRTP)/metal hybrid structures is a vital step for realizing the lightweight design concepts in aerospace. However, the CFRTP/metal hybrid structures are usually not reliable enough in practical applications due to the high differences in chemical and physical properties between these two materials. The current work provides a bottom-up strategy of introducing heteroatoms into CFRTP/metal interfaces to reconstruct the interfacial chemical structures and thus manufacture high-reliability hybrid structures. Based on the principle of utmost using reaction sites at metal surfaces, the heteroatoms of oxygen and hydrogen are specially designed and introduced to the CFRTP/A6061-T6 (6061) interfaces by simple and green plasma polymerization. The introduced oxygen and hydrogen heteroatoms react with the aluminum and oxygen of the oxidation film at 6061 surfaces to produce great interfacial Al-O covalencies and hydrogen bonds. The reconstructing interfacial chemical structures strengthen the joint strength of CFRTP/6061 hybrid structures from 8.82 to 23.97 MPa. Our heteroatom introduction strategy is expected to get a fresh insight into the interfacial design concept and has several important implications for the future application of high-reliability CFRTP/metal hybrid structures.

Atmospheric Pressure Plasma Polymerization of Carvone: A Promising Approach for Antimicrobial Coatings

Medical devices are often vulnerable to colonization by nosocomial pathogens (bacteria), leading to infections. Traditional sterilization methods may not always be effective, and as a result, alternative options are being explored to prevent microbial contamination. Recently, scientists are emphasizing using plant-derived essential oils that possess inherent antibacterial properties to produce antimicrobial coatings using plasma polymerization technology carried out at atmospheric pressure (AP). This approach shows promise compared to other coating strategies that need several processing steps, including a high-vacuum system, and are laborious, such as the immobilization of antimicrobial materials on precoated layers in the low-pressure plasma polymerization approach. The present study demonstrates the potential of AP plasma polymerization for producing thin films with excellent antibacterial properties and surface characteristics. The resulting coatings are stable, smooth, and have high wettability, making them ideal for repelling bacteria. The calculated zeta potential and deposition rate for the films are also favorable. These AP plasma-polymerized thin films created from carvone show a reduction rate of more than 90% for Escherichia coli and Staphylococcus aureus bacteria. Our computational docking studies also reveal strong binding interactions between the original carvone monomer and both bacteria. The study suggests that these AP plasma-produced coatings have great potential as antibacterial coatings for biomedical devices.

Plasma polymerization of biogenic precursors

AbstractPlasma‐enhanced chemical vapor deposition is a highly promising tool for coating deposition due to its versatility, tunability, low chemical consumption, and cost‐effectiveness, with an increasing scope of deposition methods at both low and atmospheric pressure. Adhering to green chemistry principles, biobased precursors have recently shifted into the focus of research interests. This review gives an overview of the main biogenic substance classes that have been used for the deposition of plasma polymer coatings, including natural oils, terpenes, enzymes, and lactic acid‐based precursors. The common feature of these precursors is not only their biogenic origin, but additionally the manifold properties of the resulting plasma‐deposited thin films, ranging from antimicrobial properties to tunable surface‐wetting characteristics, electrical conductivity, or biodegradability. This combination of unique features makes plasma‐derived polymers based on natural precursors immensely attractive for manifold applications.

Comprehensive Analysis of Different Coating Materials on the POM Substrate.

This study presents a comprehensive analysis of different coating materials on the POM substrate. Specifically, it investigated physical vapour deposition (PVD) coatings of aluminium (Al), chromium (Cr), and chromium nitride (CrN) of three various thicknesses. The deposition of Al was accomplished through a three-step process, particularly plasma activation, metallisation of Al by magnetron sputtering, and plasma polymerisation. The deposition of Cr was attained using the magnetron sputtering technique in a single step. For the deposition of CrN, a two-step process was employed. The first step involved the metallisation of Cr using magnetron sputtering, while the second step involved the vapour deposition of CrN, obtained through the reactive metallisation of Cr and nitrogen using magnetron sputtering. The focus of the research was to conduct comprehensive indentation tests to obtain the surface hardness of the analysed multilayer coatings, SEM analyses to examine surface morphology, and thorough adhesion analyses between the POM substrate and the appropriate PVD coating.

Challenges in the deposition of plasma polymer nanoparticles using gas aggregation source: Rebounding upon impact and how to land them on a substrate

AbstractPlasma polymer nanoparticles (pp‐NPs) are relatively easy to produce by plasma‐based gas aggregation sources. However, as experimentally evidenced in this study for the case of C:H:N:O pp‐NPs, pp‐NPs are unlike metal/metal oxide nanoparticles prone to reflection from the substrate if they hit it with too high a speed. This may result in little or no deposition rate even though the nanoparticle beam is very intense. As is shown, the deposition of pp‐NPs can be promoted either by the adjustment of their speed before they reach the substrate or by a proper selection of a substrate. Concerning the latter, enhanced capturing of pp‐NPs was observed on structured or liquid substrates.

Noble gas effect on ACL etching selectivity to SiO2 films

AbstractIn this study, we investigated the effect of Ar/He mixing ratio in the tetrafluoromethane/perfluorocyclobutane/Ar/He gas mixture on plasma parameters, SiO2 etching kinetics, and etching selectivity with respect to the amorphous carbon layer (ACL) mask in the inductively coupled plasma system with the low frequency (2 MHz) bias source. It was found that the type of dominant carrier gas does influence the output process characteristics through changes in both ion flux and CFx/F ratio determining the plasma polymerizing ability. In particular, He‐rich plasmas exhibited better performance with respect to the faceting of ACL mask and SiO2/ACL etching selectivity.

Protective Coating for the Lithium Metal Anode Prepared by Plasma Polymerization

The demand for batteries with higher energy densities for energy storage and electric vehicles motivates research for a stable and reversible lithium metal anode. The native passivation layer on commercial lithium foils does not enable stable cycling in liquid electrolytes due to inhomogeneities in the layer composition and impurities. These inhomogeneities and impurities result in locally varying current densities, which often lead to dendrite growth and ultimately cell failure. Artificial protection layers are one promising option to overcome these issues and enable the reversible operation of lithium metal anodes. In this study, we used plasma polymerization of 1.4 bis(trifluoromethyl)benzene to form an artificial passivation layer on top of plasma-cleaned lithium metal. The layer was characterized with time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. The mechanical properties of the layer were examined by nanoindentation. Symmetric cell tests showed stable cycling behavior for over 300 h, with overpotentials below 0.1 V at current densities between 0.1 and 1 mA/cm2. 18O2 isotope exchange experiments were used to get an estimation of the diffusion coefficients of oxygen in the native passivation layer of lithium foils at room temperature and for oxygen in the plasma polymer at room temperature. The combination of layer thickness and diffusion coefficient of the plasma polymer is sufficient to protect the lithium metal against oxygen for at least 30 min, which makes it a suitable protective coating.

Nanomaterial‐Incorporated Membrane Distillation Membranes: Characteristics, Fabrication Techniques, and Applications

AbstractMembrane distillation (MD), a temperature‐driven membrane separation process, is used for various applications due to its less complicated design. MD operations encounter major issues such as permeate flux decrease, membrane fouling, and wetting. A lot of research has been conducted in the past years on the modification of MD membranes by incorporating nanomaterials to overcome these obstacles and considerably increase their performance. Nanomaterials incorporated into the membranes improve the water permeability, mechanical strength, and fouling. The incorporation of next‐generation nanomaterials like metal oxide nanoparticles, carbon‐based nanomaterials, graphene‐based membranes, quantum dots, and metal‐organic frameworks in the MD membranes is investigated. Essential membrane properties for MD operations are comprehensively studied, including higher liquid entry pressure, permeability, porosity, hydrophobicity, thermal stability, mean pore size, and low fouling rate. Significant advances in the application of nanomaterials to the modification of MD membranes as well as other membrane fabrication techniques adopted for the incorporation of nanoparticles like surface grafting, interfacial polymerization, plasma polymerization, and dip coating are reviewed. Important future aspects are discussed.

Polishing of Metal, Foam, and Si-Doped GDP Capsules for Use as ICF Targets

Spherical targets with a smooth uniform surface are required for inertial confinement fusion experiments. This paper examines polishing as a method of decreasing the surface roughness of tungsten (W) capsules, chromium (Cr) capsules, SiCH [Si-doped glow discharge polymer (GDP)] capsules, and GDP-coated General Atomics–Carbon Hydrogen (GA-CH) foam beads. As expected, increasing the time spent polishing metal (W, Cr) capsules corresponded to decreasing roughness. Despite the decrease in overall surface roughness of Cr capsules, defects present in the batch initially were amplified through polishing. For SiCH capsules, increasing polishing time decreased the surface roughness, though the yield of usable capsules was affected by cracks induced through polishing. While polishing results for GDP-coated foam beads did not show consistent decrease in roughness, the polishing process did not result in the collapse of any of the foams, demonstrating the potential for polishing as a method of decreasing roughness.

Electrochemical behavior of oxazoline‐based plasma polymers for biosensing applications

AbstractPlasma‐polymerized polyoxazoline (POx) thin films offer a fast, scalable, and solvent‐free method of electrode functionalization through the unique chemistry of the oxazoline ring. However, for POx to be a viable green alternative to existing surface modification approaches, the films should be able to withstand the processing steps involved in biosensing. Here, the effects that current exposure, extended incubation, and repeated electrode rinses have on the electrochemical and physical stability of polymethyloxazoline thin films are investigated. The films are observed to become more diffusive after incubation and rinse steps. While no significant changes in chemistry were observed, a marked change in nanotopography occurred after exposure to current, suggesting a change in the polymer film structure.