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There is a global epidemic of non-healing wounds. Chronic inflammation, overexpression of pro-inflammatory cytokines, oxidative stress and bacterial infection are implicated in delayed wound healing. Natural extracts are a rich source of bioactive molecules called plant secondary metabolites (PSMs) that include terpenes and phenols. These molecules may facilitate wound healing through their antioxidant, anti-inflammatory, and antibacterial activity. After briefly outlining the process of wound healing and how it is compromised in chronic wounds, this review focuses on investigating how PSMs-based polymers may improve wound healing. Best methods for incorporating PSMs into wound dressings are reviewed and critically compared. The exiting body of literature strongly suggests that PSMs-based polymers incorporated into wound dressings could have clinical value in aiding wound healing. STATEMENT OF SIGNIFICANCE: Chronic wounds develop by the persistence of inflammation, oxidative stress and infection. Chronic wounds affect the worldwide population, by reducing quality of life of patients with significant cost to healthcare systems. To help chronic wounds to heal and overcome this burden, materials with anti-inflammatory, antioxidant and antibacterial properties are required. Plant secondary metabolites (PSMs) are volatile materials that have all these properties. PSMs-based polymers can be fabricated by polymerization techniques. The present review provides an overview of the state-of-the-art of the wound healing mechanisms of PSMs. Current developments in the field of PSMs-based polymers are reviewed and their potential use as wound dressings is also covered., Competing Interests: Declaration of Competing Interest There is no conflict of interest, (Copyright © 2022. Published by Elsevier Ltd.)

Bioconjugation of enzymes on coatings based on polydopamine (PDA) layers is an appealing approach to control biological responses on biomedical implant surfaces. As alternative to PDA wet deposition, a fast, solvent-free, and dynamic deposition approach based on atmospheric-pressure plasma dielectric barrier discharge process is considered to deposit on metallic surfaces acrylic-based interlayers containing highly chemically reactive catechol/quinone groups. A biomimetic approach based on covalent immobilization of Dispersin B, an enzyme with antibiofilm properties, shows the bioconjugation potential of the novel plasma polymer layers. The excellent antibiofilm activity against Staphylococcus epidermidis is comparable to the PDA-based layers prepared by wet chemical methods with slow deposition rates. A study of preosteoblastic MG-63 human cell line viability and adhesion properties on plasma polymer layers demonstrates early interaction required for biomedical applications., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this communication, we report on an innovative solvent‐free method that allows for the design of nano‐/micropatterns with tuneable dimensions. Our approach is based on the spontaneous wrinkling phenomenon taking place in a bilayer system formed by a mechanically responsive bottom plasma polymer layer and a top aluminum thin film. The dimensions of the wrinkles can be adjusted in a wide range (i.e., from nanometer to micrometer range) by modulating the cross‐linking density as well as the thickness of the plasma polymer layer. Finally, it is demonstrated that these wrinkled surfaces could efficiently be used as flexible electrodes. The whole set of our data unambiguously reveals the attractiveness of our method for the fabrication of the micro‐/nanopattern with dimensions on demand. [ABSTRACT FROM AUTHOR]

This study aims at deposition and characterization of antibacterial, hydrophobic and semitransparent metal/plasma polymer nanocomposite coating, containing Ag nanoparticles, onto cotton fabrics intended to be used in medical applications. The nano composite coatings were obtained via a simple, one step and ecofriendly plasma based co-deposition approach where silver was magnetron sputtered simultaneously with plasma polymerization of hexamethyldisiloxane (HMDSO) monomer. The nanocomposite thin films containing different concentration of silver were deposited either by varying silver sputter rate or thickness of the plasma polymer matrix to obtain a good balance between optical properties of the coated fabric and its long term antibacterial performance. The obtained coatings were investigated in detail with respect to their composition, morphology, optical properties, nanoparticle size distribution, silver ion release efficiency, antibacterial performance, water contact angle and washing stability of the coating. The thickness of the plasma matrix was found to be more important in controlling the release of silver ions as well as affecting the optical properties of the coating. The water contact angle on the coated fabric was up to 145°, close to super hydrophobicity. The coating showed effective antibacterial efficacy against Staphylococcus epidermidis (a Gram positive bacterium) which was present even when fabric was subjected to 10 repeated washing cycles indicating good washing stability of the coating. [ABSTRACT FROM AUTHOR]

A multilayer plasma polymer coating was deposited on small glass discs and afterwards treated with ultra violet radiation through a patterned mask to generate a micro-structured substrate with an alternating hydrophilic/hydrophobic surface. The substrate was then immersed in a mother liqueur of the porous, functional material Metal-Organic Framework Ulm-4 (MFU-4) to preferentially grow crystals on the hydrophilic areas of the film. X-ray diffraction and electron microscope analysis showed the formation of MFU-4 single crystals. • Chemically robust micro-structured, multilayer plasma polymer coating • Hydrophobic polytetrafluoroethylene-like coating deposited from trifluoromethane • Spatially directed crystal growth of a porous functional material [ABSTRACT FROM AUTHOR]

In this work, we aimed to understand the key properties that confer antibacterial activity to chlorinated plasma polymers, by investigating plasma polymers deposited from a series of chlorinated precursor molecules and also investigating the effect of plasma conditions. Results revealed that only precursors with a Cl/C ratio ≥1.5 generate effective antibacterial coatings, whereas the coating thickness is irrelevant. Furthermore there is a 'sweet spot' in process conditions to generate coatings with optimal antimicrobial activity. Lastly, we investigated the release of chlorinated fragments and attenuation of the surface-active antibacterial properties of the chlorinated plasma polymers by overcoating them with a perfluorinated plasma polymer. [ABSTRACT FROM AUTHOR]

Amorphous hydrogenated carbon (a-C:H), a polymer-like network typically synthesized by plasma chemical vapor deposition, has long been known to exhibit optical absorption of visible light (λ > 400 nm). Here, we report that this absorption is accompanied by rapid photo-oxidation (within minutes) that behaves in most respects like classic polymer photo-oxidation with the exception that it occurs under visible light illumination rather than ultraviolet illumination. Lower plasma power during deposition produces a-C:H that is less crosslinked, is less absorptive, has longer photoluminescence lifetimes, and has a slower photo-oxidative degradation than a-C:H deposited at higher plasma power. The optical gap of the material deposited here is ∼2.5 eV, and we correspondingly observe photo-oxidation at photon energies of 2.7 and 3.1 eV. A reduced photo-oxidative response is observed at sub-gap energies, suggesting that defect states or absorption tails enable absorption at lower energies. The photo-oxidation depends on both the total accumulated dose as well as the intensity of the illumination, suggesting either a transport limitation of O 2 in the a-C:H or a complex reaction pathway. Under typical laboratory lighting conditions, plasma CVD a-C:H continues to photo-oxidize for more than 20 weeks, demonstrating that any characterization of the long-term behavior of a-C:H under use conditions requires control of not only atmospheric conditions but also ambient lighting environment. [ABSTRACT FROM AUTHOR]

This feature article presents the implementation of a controlled chemical degradation (namely ethanolysis) combined with electrospray tandem mass spectrometry (ESI-MS/MS) as an original analytical strategy to gain insights into the molecular composition of insoluble plasma polymers deposited from hexamethyldisiloxane (HMDSO). Dissociation rules were established for poly(dimethylsiloxane) standards (PDMS) holding trimethylsilyl and/or hydroxy and/or ethoxy end-groups, expected to be found as ethanolysis products released after the cleavage of bonds specifically at cross-linking points of the solid plasma polymer network. Mechanistic investigations were performed on the collision-induced decomposition (CID) of ammonium adducts of the selected standards to derive diagnostic ions typical of a given chain termination. Based on the so-listed diagnostic MS/MS features, the MS/MS analysis of the ethanolyzed samples allowed their structures to be deduced and the architecture of the original plasma polymers to be reconstructed. [ABSTRACT FROM AUTHOR]

Abstract: Research into nanostructured thin films of plasma polymers is driven by applications of these materials in a wide variety of fields. Here, we review work on the preparation of such coatings using low-pressure discharges, with a focus on the different strategies employed. We start with nanostructured plasma polymers prepared by plasma polymerization under special conditions such as at a large distance from the plasma zone and at a high working gas pressure. Then, methods based upon plasma etching and colloidal lithography combined with plasma treatment are described. Finally, dusty plasmas and gas aggregation cluster sources with planar magnetrons are considered for generation of nanoclusters, nanoparticles, and for deposition of nanostructured plasma polymer films. [Copyright &y& Elsevier]

This paper reports a novel approach for surface modification of 100% cotton and 100% polyester fabrics with atmospheric pressure plasma enhanced chemical vapour deposition (APPECVD) of hexamethyldisiloxane (HMDSO). The chemical and structural nature of HMDSO plasma polymers deposited on the fabric surface with respect to discharge power has been studied with FTIR spectroscopy. The functional property such as water repellency imparted to the polyester and cotton fabrics after plasma treatment has been determined by spray test. It is observed that water repellent properties improve after plasma treatment. Moreover, the intrinsic hydrophilic or hydrophobic behaviour of cotton and polyester substrates has been found to have significant effect on the water repellency of the plasma treated samples. Deposition of plasma polymer on the surface of treated samples has been substantiated by scanning electron microscopy. It has been observed that tensile strength of cotton fabric remains unaffected by the given experimental conditions, whereas that of polyester fabric considerably deteriorates at higher discharge powers. [ABSTRACT FROM AUTHOR]

Abstract: The control of cell–material interactions is the key to a broad range of biomedical interactions. Gradient surfaces have recently been established as tools allowing the high-throughput screening and optimization of these interactions. In this paper, we show that plasma polymer gradients can reveal the subtle influence of surface chemistry on embryonic stem cell behavior and probe the mechanisms by which this occurs. Lateral gradients of surface chemistry were generated by plasma polymerization of diethylene glycol dimethyl ether on top of a substrate coated with an acrylic acid plasma polymer using a tilted slide as a mask. Gradient surfaces were characterized by X-ray photoelectron spectroscopy, infrared microscopy mapping and profilometry. By changing the plasma polymerization time, the gradient profile could be easily manipulated. To demonstrate the utility of these surfaces for the screening of cell–material interactions, we studied the response of mouse embryonic stem (ES) cells to these gradients and compared the performance of different plasma polymerization times during gradient fabrication. We observed a strong correlation between surface chemistry and cell attachment, colony size and retention of stem cell markers. Cell adhesion and colony formation showed striking differences on gradients with different plasma polymer deposition times. Deposition time influenced the depth of the plasma film deposited and the relative position of surface functional group density on the substrate, but not the range of plasma-generated species. [Copyright &y& Elsevier]

A miniature nonthermal atmospheric plasma jet was used to deposit patterns of plasma polymers on standard Pyrex Petri dishes from an argon/acetylene gas mixture. The injection of the C2H2 monomer through the powered capillary electrode ending in the nozzle section allowed a stable operation of the plasma jet and the successful deposition of plasma-polymer tracks ≈500 μm wide. The line-averaged gas temperature was measured from the OH molecular band emission originating from the entrainment of air into the plasma jet. The gas temperature decreased monotonically from ≈440 K at the nozzle exit to ≈385 K at 5 mm downstream. The emission profiles of the C2 (516 nm) band showed a peak ≈0.5 mm downstream the nozzle exit. The maximum emission for the CH band (431 nm) was obtained at the torch exit. An ATR-FTIR spectroscopy analysis of the deposited plasma-polymer films revealed the presence of C-H, O-H, and C = O functional groups. Mammalian cells grown on the argon/acetylene plasma-treated dishes showed migration and greater density compared to the control and dishes treated with an argon plasma jet. This preliminary study opens the door to the localized enhancement of cell coverage on various substrates (shape and material). [ABSTRACT FROM AUTHOR]

Abstract: Fluorinated amorphous carbon (a-C:F) films e.g. plasma polymerised perfluorocyclobutane have long attracted much consideration due to their low surface energy, hydrophobicity, low refractive index, good electrical and thermal insulation and good thermal stability. Although a-C:F films have many advantages, hydrophobic stability over time in air and water remains a major concern. In this study, the effects of weathering conditions on the hydrophobicity of fluorocarbon films prepared from perfluorocyclobutane precursors were examined using water contact angle measurements. It was found that the high initial hydrophobicity of as-deposited films degrades rapidly in humid conditions. The stability of hydrophobicity can be significantly improved when a suitable treatment such as annealing is employed. The mechanism of weathering was explained with the help of a number of morphological and chemical characterisation techniques such as Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). In particular, XPS results demonstrated that a reduction in the overall amount of –CF3 radical, oxygenation of surface fluorides and the formation of an overlayer all influence the degradation of fluorocarbon in aquatic environment. [Copyright &y& Elsevier]

Complimentary spectroscopic, microscopic and electrochemical studies were performed to characterise the barrier properties as well as the interface structure of model iron substrates covered with thin plasma polymer films. Cathodic plasma polymers were deposited which show high barrier properties. The metal surface was pre-treated by a reducing or oxidising plasma. This allowed the adjustment of the oxidation state of the interface layer. The interface structure was characterised by means of X-ray photoelectron sputter profiles, infrared spectroscopy and the application of a Kelvin probe. The investigations show that the measured Voltapotential on the plasma polymer surface can be correlated with the oxidation state of the interface. Reducing plasmas lead to an almost oxide free surface. After deposition of the plasma polymer, this reduced state of the oxide is sensitive to re-oxidation of the interface by oxygen that diffuses through the plasma polymer. It could be shown that the increase in the plasma polymer thickness leads to an improved barrier effect as indicated by the more negative Voltapotential. The barrier properties of the organosilicon plasma polymer layers on iron were further quantified by means of electrochemical impedance spectroscopy (EIS). The morphology of the plasma polymer surface was studied using atomic force microscopy (AFM) to support the evaluation of the impedance data. A water diffusion coefficient of 4×10-14 cm2/s was found for the plasma polymer. Moreover, the water uptake of the film was measured to be 0.13%. These values illustrate the high barrier properties of these thin films. [Copyright &y& Elsevier]

The barrier properties of thin model organosilicon plasma polymers layers on iron are characterised by means of electrochemical impedance spectroscopy (EIS). Tailored thin plasma polymers of controlled morphology and chemical composition were deposited from a microwave discharge. By the analysis of the obtained impedance diagrams, the evolution of the water uptake ϕ, coating resistance and polymer capacitance with immersion time were monitored and the diffusion coefficients of the water through the films were calculated. The impedance data correlated well with the chemical structure and morphology of the plasma polymer films with a thickness of less than 100 nm. The composition of the films were determined by means of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of the plasma polymer surface and the interface between the plasma polymer and the metal were characterised using atomic force microscopy (AFM). It could be shown that, at higher pressure, the film roughness increases which is probably due to the adsorption of plasma polymer nanoparticles formed in the plasma bulk and the faster film growth. This leads to voids with a size of a few tens of nanometers at the polymer/metal interface. The film roughness increases from the interface to the outer surface of the film. By lowering the pressure and thereby slowing the deposition rate, the plasma polymers perfectly imitate the substrate topography and lead to an excellent blocking of the metal surface. Moreover, the ratio of siloxane bonds to methyl-silyl groups increases which implies that the crosslink density is higher at lower deposition rate. The EIS data consistently showed higher coating resistance as well as lower interfacial capacitance values and a better stability over time for the film deposited at slower pressure. The diffusion coefficient of water in thin and ultra-thin plasma polymer films could be quantified for the smooth films. The measurements show that the quantitative evaluation of the electrochemical impedance data requires a detailed understanding of the film morphology and chemical composition. In addition, the measured diffusion coefficient of about 1.5×10−14 cm2 s−1 shows that plasma polymers can act as corrosion resistant barrier layers at polymer/metal interfaces. [Copyright &y& Elsevier]

Plasma polymer coatings fabricated from Melaleuca alternifolia essential oil and its derivatives have been previously shown to reduce the extent of microbial adhesion on titanium, polymers, and other implantable materials used in dentistry. Previous studies have shown these coatings to maintain their performance under standard operating conditions; however, when used in e.g., a dental implant, these coatings may inadvertently become subject to in situ cleaning treatments, such as those using an atmospheric pressure plasma jet, a promising tool for the effective in situ removal of biofilms from tissues and implant surfaces. Here, we investigated the effect of such an exposure on the antimicrobial performance of the Melaleuca alternifolia polymer coating. It was found that direct exposure of the polymer coating surface to the jet for periods less than 60 s was sufficient to induce changes in its surface chemistry and topography, affecting its ability to retard subsequent microbial attachment. The exact effect of the jet exposure depended on the chemistry of the polymer coating, the length of plasma treatment, cell type, and incubation conditions. The change in the antimicrobial activity for polymer coatings fabricated at powers of 20–30 W was not statistically significant due to their limited baseline bioactivity. Interestingly, the bioactivity of polymer coatings fabricated at 10 and 15 W against Staphylococcus aureus cells was temporarily improved after the treatment, which could be attributed to the generation of loosely attached bioactive fragments on the treated surface, resulting in an increase in the dose of the bioactive agents being eluted by the surface. Attachment and proliferation of Pseudomonas aeruginosa cells and mixed cultures were less affected by changes in the bioactivity profile of the surface. The sensitivity of the cells to the change imparted by the jet treatment was also found to be dependent on their origin culture, with mature biofilm-derived P. aeruginosa bacterial cells showing a greater ability to colonize the surface when compared to its planktonic broth-grown counterpart. The presence of plasma-generated reactive oxygen and nitrogen species in the culture media was also found to enhance the bioactivity of polymer coatings fabricated at power levels of 10 and 15 W, due to a synergistic effect arising from simultaneous exposure of cells to reactive oxygen and nitrogen species (RONS) and eluted bioactive fragments. These results suggest that it is important to consider the possible implications of inadvertent changes in the properties and performance of plasma polymer coatings as a result of exposure to in situ decontamination, to both prevent suboptimal performance and to exploit possible synergies that may arise for some polymer coating-surface treatment combinations. [ABSTRACT FROM AUTHOR]

• High helium flow is required to generate stable plasma in SDBDs. • Mesh electrode DBD can cause formation of local electric field in the discharge. • The DBD design can influence the plasma polymer topography. In this article, an atmospheric pressure surface dielectric barrier discharge (SDBD) generated in helium has been studied for its discharge characteristics and its ability to generate amine functionalised polymer coatings for application in cell therapy. The electrical and optical properties of the surface plasma generated SDBD consisting of a mesh electrode are presented. Current-voltage measurements and intensified charge coupled device (ICCD) camera images showed that the plasma device is able to generate glow like discharge structures that are stable over the area of the electrodes at applied voltages ranging from 3.5 kV to 5 kV pk-pk. Most importantly, the plasma images show evidence of high electric fields around the hexagonal grid of the mesh electrode. Through the helium line ratio method, the density and temperature of electrons in the discharge was estimated between 1011–1012 cm3 and 0.3–0.8 eV respectively as a function of gas flow. Surface characterisation of the allylamine plasma polymer coating (ppAAm) with X‐ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed that the coating is rich in amine functionality. However, atomic force microscopy (AFM) analysis show that the thickness of the coating is spatially nonuniform. From the results, it is predicted that the high amine functionality of the coating could be applied in cell adhesion and growth. [ABSTRACT FROM AUTHOR]

To combat infections on biomedical devices, antimicrobial coatings have attracted considerable attention, including coatings comprising naturally occurring antimicrobial peptides (AMPs). In this study the aim was to explore performance upon extended challenge by bacteria growing in media above samples. The AMPs LL37, Magainin 2, and Parasin 1 were selected on the basis of well-known membrane disruption activity in solution and were covalently grafted onto a plasma polymer platform, which enables application of this multilayer coating strategy to a wide range of biomaterials. Detailed surface analyses were performed to verify the intended outcomes of the coating sequence. Samples were challenged by incubation in bacterial growth media for 5 and 20 h. Compared with the control plasma polymer surface, all three grafted AMP coatings showed considerable reductions in bacterial colonization even at the high bacterial challenge of initial seeding at 1 × 107 CFU, but there were increasing numbers of dead bacteria attached to the surface. All three grafted AMP coatings were found to be non-toxic to primary fibroblasts. These coatings thus could be useful to produce antibacterial surface coatings for biomaterials, though possible consequences arising from the presence of dead bacteria need to be studied further, and compared to non-fouling coatings that avoid attachment of dead bacteria. [ABSTRACT FROM AUTHOR]

The amount and distribution of metal nanoparticles in a plasma polymer matrix are studied according to the chemical structure of the polymer and the nature of the metal. The structure of the polymer (polyallylalcohol) is modified by varying the plasma parameters such as polymerization time, input power and discharge time. This study, done with silver, shows that when the polymer contains a lot of functional groups (here hydroxyl ones) with a rough surface, a high amount of silver, homogeneously distributed is inserted into the polymer. Moreover, three metals are studied: Ag, Cu and Sn. A higher quantity of silver and tin ions is inserted into the matrix compared to copper. Finally, two routes for the incorporation of silver nanoparticles are studied where the impregnation with the metallic salt and its reduction are done either in two stages or in one step with a single solution containing both the metallic salt and the reducing agent. The first method allows obtaining a higher amount of loaded silver with a homogeneous dispersion in the matrix. • High amount of embedded silver if high amount of polymer functional groups. • Homogeneous silver distribution with a rough matrix surface rich in functional groups. • Elaboration of polymer/metal composite with impregnation and reduction in two steps. • Reduction of most of metal ions by the polymer: the reduction step can be avoided. • Dependence of the loaded metal amount on its chemical properties. [ABSTRACT FROM AUTHOR]

New trends toward green technologies and broad utilization of polymers have led to intense research on surfaces with controlled wettability. This study demonstrates an easy method to control the wettability (estimated by static water contact angle [WCA]) of a polymer surface by introducing a proper ratio of C–F, C–H, and N–H bonds. The preparation method combines magnetron sputtering from a polytetrafluoroethylene (PTFE) target and plasma‐enhanced chemical vapor deposition (PECVD) from a nitrogen/acetylene mixture, making it environment‐friendly, unlike PECVD from hydrocarbons/fluorocarbons. The proposed method allows depositing plasma polymers with WCAs from 110° to 17° by varying only the gas composition. The corresponding plasma polymers consist of C:F (magnetron sputtering of PTFE), C:F:N:H (reactive magnetron sputtering and PECVD), and a‐C:H (PECVD from acetylene). [ABSTRACT FROM AUTHOR]