Development of oxidized sulfur polymer films through a combination of plasma polymerization and oxidative plasma treatment

Selective Bacterial Growth Inactivation by pH-Sensitive Sulfanilamide Functionalized Carbon Dots

Carbon dots (CDs) were synthesized hydrothermally by mixing citric acid (CA) and an antifolic agent, sulfanilamide (SNM), employed for pH sensing and bacterial growth inactivation. Sulfanilamide is a prodrug; aromatic hetero cyclization of the amine moiety along with other chemical modifications produces an active pharmacological compound (chloromycetin and miconazole), mostly administered for the treatment of various microbial infections. On the other hand, the efficacy of the sulfanilamide molecule as a drug for antimicrobial activity was very low. We anticipated that the binding of the sulfanilamide molecule on the carbon dot (CD) surface may form antibacterial CDs. Citric acid was hybridized with sulfanilamide during the hydrothermal preparation of the CDs. The molecular fragments of bioactivated sulfanilamide molecule play a crucial role in bacterial growth inactivation for Gram-positive and Gram-negative bacteria. The functional groups of citric acid and sulfanilamide were conserved during the CD formation, facilitating the zwitterionic behavior of CDs associated with its photophysical activity. At low concentrations of CDs, the antibacterial activity was apparent for Gram-positive bacteria only. This Gram-positive bacteria selectivity was also rationalized by zeta potential measurement.

On the Effect of Non-Thermal Atmospheric Pressure Plasma Treatment on the Properties of PET Film

The aim of the work was to investigate the effect of non-thermal plasma treatment of an ultra-thin polyethylene terephthalate (PET) film on changes in its physicochemical properties and biodegradability. Plasma treatment using a dielectric barrier discharge plasma reactor was carried out in air at room temperature and atmospheric pressure twice for 5 and 15 min, respectively. It has been shown that pre-treatment of the PET surface with non-thermal atmospheric plasma leads to changes in the physicochemical properties of this polymer. After plasma modification, the films showed a more developed surface compared to the control samples, which may be related to the surface etching and oxidation processes. After a 5-min plasma exposure, PET films were characterized by the highest wettability, i.e., the contact angle decreased by more than twice compared to the untreated samples. The differential scanning calorimetry analysis revealed the influence of plasma pretreatment on crystallinity content and the melt crystallization behavior of PET after soil degradation. The main novelty of the work is the fact that the combined action of two factors (i.e., physical and biological) led to a reduction in the content of the crystalline phase in the tested polymeric material.

WS2/Polyethylene Glycol Nanostructures for Ultra-Efficient MCF-7 Cancer Cell Ablation and Electrothermal Therapy

Developing novel nanostructures and advanced nanotechnologies for cancer treatment has attracted ever-increasing interest. Electrothermal therapy offers many advantages such as high efficiency and minimal invasiveness, but finding a balance between increasing stability of the nanostructure state and, at the same time, enhancing the nanostructure biodegradability presents a key challenge. Here, we modulate the biodegradation process of two-dimensional-material-based nanostructures by using polyethylene glycol (PEG) via nanostructure disrupt-and-release effects. We then demonstrate the development of a previously unreported alternating current (AC) pulse WS₂/PEG nanostructure system for enhancing therapeutic performance. A decrease in cell viability of ∼42% for MCF-7 cells with WS₂/PEG was achieved, which is above an average of ∼25% for current electrothermal-based therapeutic methods using similar energy densities, as well as degradation time of the WS₂ of ∼1 week, below an average of ∼3.5 weeks for state-of-the-art nanostructure-based systems in physiological media. Moreover, the incubation time of MCF-7 cells with WS₂/PEG reached ∼24 h, which is above the average of ∼4.5 h for current electrothermal-based therapeutic methods and with the use of the amount of time harnessed to incubate the cells with nanostructures before applying a stimulus as a measure of incubation time. Material characterizations further disclose the degradation of WS₂ and the grafting of PEG on WS₂ surfaces. These WS₂-based systems offer strong therapeutic performance and, simultaneously, maintain excellent biodegradability/biocompatibility, thus providing a promising route for the ablation of cancer.

Atmospheric Pressure Plasma Jet Treatment of Polymers Enables Reagent-Free Covalent Attachment of Biomolecules for Bioprinting

Three-dimensional (3D) bioprinting, where cells, hydrogels, and structural polymers can be printed layer by layer into complex designs, holds great promise for advances in medicine and the biomedical sciences. In principle, this technique enables the creation of highly patient-specific disease models and biomedical implants. However, an ability to tailor surface biocompatibility and interfacial bonding between printed components, such as polymers and hydrogels, is currently lacking. Here we demonstrate that an atmospheric pressure plasma jet (APPJ) can locally activate polymeric surfaces for the reagent-free covalent attachment of proteins and hydrogel in a single-step process at desired locations. Polyethylene and poly-ε-caprolactone were used as example polymers. Covalent attachment of the proteins and hydrogel was demonstrated by resistance to removal by rigorous sodium dodecyl sulfate washing. The immobilized protein and hydrogel layers were analyzed using Fourier transform infrared and X-ray photoelectron spectroscopy. Importantly, the APPJ surface activation also rendered the polymer surfaces mildly hydrophilic as required for optimum biocompatibility. Water contact angles were observed to be stable within a range where the conformation of biomolecules is preserved. Single and double electrode designs of APPJs were compared in their characteristics relevant to localized surface functionalization, plume length, and shape. As a proof of efficacy in a biological context, APPJ-treated polyethylene functionalized with fibronectin was used to demonstrate improvements in cell adhesion and proliferation. These results have important implications for the development of a new generation of 3D bioprinters capable of spatially patterned and tailored surface functionalization performed during the 3D printing process in situ.

Sulfur and nitrogen containing plasma polymers reduces bacterial attachment and growth

Role of sulfur (S) and nitrogen (N) groups in promoting cell adhesion or commonly known as biocompatibility, is well established, but their role in reducing bacterial attachment and growth is less explored or not well-understood. Natural sulfur-based compounds, i.e. sulfide, sulfoxide and sulfinic groups, have shown to inhibit bacterial adhesion and biofilm formation. Hence, we mimicked these surfaces by plasma polymerizing thiophene (ppT) and air-plasma treating this ppT to achieve coatings with S of similar oxidation states as natural compounds (ppT-air). In addition, the effects of these N and S groups from ppT-air were also compared with the biocompatible amine-amide from n-heptylamine plasma polymer. Crystal violet assay and live and dead fluorescence staining of E. coli and S. aureus showed that all the N and S coated surfaces generated, including ppHA, ppT and ppT-air, produced similarly potent, growth reduction of both bacteria by approximately 65% at 72 h compared to untreated glass control. The ability of osteogenic differentiation in Wharton's jelly mesenchymal stem cells (WJ-MSCs) were also used to test the cell biocompatibility of these surfaces. Alkaline phosphatase assay and scanning electron microscopy imaging of these WJ-MSCs growths indicated that ppHA, and ppT-air were cell-friendly surfaces, with ppHA showing the highest osteogenic activity. In summary, the N and S containing surfaces could reduce bacteria growth while promoting mammalian cell growth, thus serve as potential candidate surfaces to be explored further for biomaterial applications.

Surface-Charged Zirconia Nanoparticles Prepared by Organophosphorus Surface Functionalization with Ammonium or Sulfonate Groups

Organophosphorus coupling agents bearing permanently charged functional groups (either cationic quaternary ammonium or anionic sulfonates) were synthesized and used for the modification of zirconia nanoparticles with a diameter <10 nm. Surface functionalization was confirmed by FTIR and solid-state NMR spectroscopy. Surface coverages up to 2.3-2.4 molecules/nm² were achieved for modification with these charged coupling agents. The pH-dependent charge measurements of homogeneously modified particles showed stable surface charges over a wide range of pH for both ammonium- and sulfonate-functionalized particles. Surface charge measurements of particles co-functionalized with charged coupling molecules and uncharged methyl phosphonic acid revealed a decreasing charge density with increasing amount of uncharged coupling agent. Thus, an adjustment of charges by co-functionalization was obtained on the particle surface. The thus-formed surface-charged colloids were used in a second step for electrostatic-driven aggregation phenomena necessary for layer-by-layer processes. Sulfonate-modified negatively charged SiO₂ submicrometer particles of 506 nm in diameter were decorated with ammonium-modified ZrO₂ nanoparticles. In addition, a layer-by-layer deposition of alternating charge-modified TiO₂ nanoparticles was proven by optical spectroscopy. Due to the broad applicability of organophosphorus coupling agents for surface modification, particularly for transition-metal oxides, the shown route represents a general method for the creation of almost pH-independent charges on the surface of nanoparticles.

Graphene-based advanced nanoplatforms and biocomposites from environmentally friendly and biomimetic approaches

Environmentally friendly and biomimetic approaches to fabricate graphene-based advanced nanoplatforms and biocomposites for biomedical applications are summarized in this review.

Arginine-Based Polymer Brush Coatings with Hydrolysis-Triggered Switchable Functionalities from Antimicrobial (Cationic) to Antifouling (Zwitterionic)

Arginine polymer based coatings with switchable properties were developed on glass slides (GS) to demonstrate the smart transition from antimicrobial (cationic) to fouling-resistant (zwitterionic) surfaces. l-Arginine methyl ester-methacryloylamide (Arg-Est) and l-arginine-methacryloylamide (Arg-Me) polymer brushes were grafted from the GS surface via surface-initiated reversible addition-fragmentation chain-transfer (SI-RAFT) polymerization. In comparison to the pristine GS and Arg-Me graft polymerized GS (GS-Arg-Me) surfaces, the Arg-Est polymer brushes-functionalized GS surfaces exhibit a superior antimicrobial activity. Upon hydrolysis treatment, the strong bactericidal efficacy switches to good resistance to adsorption of bovine serum albumin (BSA), the adhesion of Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Escherichia coli, as well as the attachment of Amphora coffeaeformis. In addition, the switchable coatings are proven to be biocompatible. The stability and durability of the switchable coatings are also ascertained after exposure to filtered seawater for 30 days. Therefore, deposition of the proposed "smart coatings" offers another environmentally friendly alternative for combating biofouling.

Substrate-Regulated Growth of Plasma-Polymerized Films on Carbide-Forming Metals

Although plasma polymerization is traditionally considered as a substrate-independent process, we present evidence that the propensity of a substrate to form carbide bonds regulates the growth mechanisms of plasma polymer (PP) films. The manner by which the first layers of PP films grow determines the adhesion and robustness of the film. Zirconium, titanium, and silicon substrates were used to study the early stages of PP film formation from a mixture of acetylene, nitrogen, and argon precursor gases. The correlation of initial growth mechanisms with the robustness of the films was evaluated through incubation of coated substrates in simulated body fluid (SBF) at 37° for 2 months. It was demonstrated that the excellent zirconium/titanium-PP film adhesion is linked to the formation of metallic carbide and oxycarbide bonds during the initial stages of film formation, where a 2D-like, layer-by-layer (Frank-van der Merwe) manner of growth was observed. On the contrary, the lower propensity of the silicon surface to form carbides leads to a 3D, island-like (Volmer-Weber) growth mode that creates a sponge-like interphase near the substrate, resulting in inferior adhesion and poor film stability in SBF. Our findings shed light on the growth mechanisms of the first layers of PP films and challenge the property of substrate independence typically attributed to plasma polymerized coatings.

Inhomogeneous Growth of Micrometer Thick Plasma Polymerized Films

Plasma polymerization is traditionally recognized as a homogeneous film-forming technique. It is nevertheless reasonable to ask whether micrometer thick plasma polymerized structures are really homogeneous across the film thickness. Studying the properties of the interfacial, near-the-substrate (NTS) region in plasma polymer films represents particular experimental challenges due to the inaccessibility of the buried layers. In this investigation, a novel non-destructive approach has been utilized to evaluate the homogeneity of plasma polymerized acrylic acid (PPAc) and 1,7-octadiene (PPOD) films in a single measurement. Studying the variations of refractive index throughout the depth of the films was facilitated by a home-built surface plasmon resonance (SPR)/optical waveguide (OWG) spectroscopy setup. It has been shown that the NTS layer of both PPAc and PPOD films exhibits a significantly lower refractive index than the bulk of the film that is believed to indicate a higher concentration of internal voids. Our results provide new insights into the growth mechanisms of plasma polymer films and challenge the traditional view that considers plasma polymers as homogeneous and continuous structures.

Free-Radical-Induced Grafting from Plasma Polymer Surfaces

With the advances in science and engineering in the second part of the 20th century, emerging plasma-based technologies continuously find increasing applications in the domain of polymer chemistry, among others. Plasma technologies are predominantly used in two different ways: for the treatment of polymer substrates by a reactive or inert gas aiming at a specific surface functionalization or for the synthesis of a plasma polymer with a unique set of properties from an organic or mixed organic-inorganic precursor. Plasma polymer films (PPFs), often deposited by plasma-enhanced chemical vapor deposition (PECVD), currently attract a great deal of attention. Such films are widely used in various fields for the coating of solid substrates, including membranes, semiconductors, metals, textiles, and polymers, because of a combination of interesting properties such as excellent adhesion, highly cross-linked structures, and the possibility of tuning properties by simply varying the precursor and/or the synthesis parameters. Among the many appealing features of plasma-synthesized and -treated polymers, a highly reactive surface, rich in free radicals arising from deposition/treatment specifics, offers a particular advantage. When handled carefully, these reactive free radicals open doors to the controllable surface functionalization of materials without affecting their bulk properties. The goal of this review is to illustrate the increasing application of plasma-based technologies for tuning the surface properties of polymers, principally through free-radical chemistry.

Effect of H₂S Plasma Treatment on the Surface Modification of a Polyethylene Terephthalate Surface

H₂S plasma created by an electrode-less radio-frequency discharge was used to modify the surface properties of the polymer polyethylene terephthalate. X-ray photoelectron spectroscopy, secondary ion mass spectrometry and atomic force microscopy were used to determine the evolution of the surface functionalities and morphology. A very thin film of chemically bonded sulfur formed on the surface within the first 10 s of treatment, whereas treatment for more than 20 s caused deposition of higher quantities of unbonded sulfur. The sulfur concentration reached a maximum of between 40 and 80 s of plasma treatment; at longer treatment times, the unbonded sulfur vanished, indicating instability of the deposited sulfur layer. Large differences in the surface morphology were observed.

Plasma polymer-functionalized silica particles for heavy metals removal

Highly negatively charged particles were fabricated via an innovative plasma-assisted approach for the removal of heavy metal ions. Thiophene plasma polymerization was used to deposit sulfur-rich films onto silica particles followed by the introduction of oxidized sulfur functionalities, such as sulfonate and sulfonic acid, via water-plasma treatments. Surface chemistry analyses were conducted by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. Electrokinetic measurements quantified the zeta potentials and isoelectric points (IEPs) of modified particles and indicated significant decreases of zeta potentials and IEPs upon plasma modification of particles. Plasma polymerized thiophene-coated particles treated with water plasma for 10 min exhibited an IEP of less than 3.5. The effectiveness of developed surfaces in the adsorption of heavy metal ions was demonstrated through copper (Cu) and zinc (Zn) removal experiments. The removal of metal ions was examined through changing initial pH of solution, removal time, and mass of particles. Increasing the water plasma treatment time to 20 min significantly increased the metal removal efficiency (MRE) of modified particles, whereas further increasing the plasma treatment time reduced the MRE due to the influence of an ablation mechanism. The developed particulate surfaces were capable of removing more than 96.7% of both Cu and Zn ions in 1 h. The combination of plasma polymerization and oxidative plasma treatment is an effective method for the fabrication of new adsorbents for the removal of heavy metals.

Development of negatively charged particulate surfaces through a dry plasma-assisted approach

A completely dry method has been introduced for the development of negatively charged oxidized sulfur-terminated particles.