Surface functionalization, oxygen depth profiles, and wetting behavior of PET treated with different nitrogen plasmas

Enhancing the Interfacial Strength of Carbon Fiber/Poly(ether ether ketone) Hybrid Composites by Plasma Treatments

As a promising alternative to traditional prepreg, carbon fiber/poly(ether ether ketone) (CF/PEEK) hybrid composites have attracted wide public interest for their flexibility and conformability. However, modification methods focused on the hybrid premix have not been previously studied. In the present work, the interfacial strength of the hybrid composite was improved by treating the carbon and PEEK fibers together in a radiofrequency (RF) plasma containing one of the following gases to achieve surface activation: air, Ar, or Ar–air. After plasma treatment, the increased roughness of CF and the grafted chemical groups of CFs and PEEK fibers were propitious to the mechanical interlocking and interfacial strength. Significant interfacial shear strength (IFSS) enhancement was achieved after Ar 1 min, air 1 min plasma treatment. This study offers an alternative method for improving the interfacial properties of CF/PEEK composites by focusing on the boundary layer and modifying and controlling the fiber–matrix interface.

Composition and Stability of Plasma Polymer Films Exhibiting Vertical Chemical Gradients

Controlling the balance between stability and functional group density in grown plasma polymer films is the key to diverse applications such as drug release, tissue-engineered implants, filtration, contact lenses, microfluidics, electrodes, sensors, etc. Highly functional plasma polymer films typically show a limited stability in air or aqueous environments due to mechanisms like molecular reorganization, oxidation, and hydrolysis. Stabilization is achieved by enhancing cross-linking at the cost of the terminal functional groups such as -OH and -COOH, but also -NH₂, etc. To overcome such limitations, a structural and chemical gradient was introduced perpendicular to the surface plane; this vertical gradient structure is composed of a highly cross-linked base layer, gradually changing into a more functional nanoscaled surface termination layer. This was achieved using CO₂/C₂H₄ discharges with decreasing power input and increasing gas ratio during plasma polymer deposition. The aging behavior and stability of such oxygen-functional vertical gradient nanostructures were studied in air and in different aqueous environments (acidic pH 4, neutral pH ≈ 6.2, and basic pH 10). Complementary characterization methods were used, including angle-resolved X-ray photoelectron spectroscopy (ARXPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) as well as water contact angle (WCA) measurements. It was found that in air, the vertical gradient films are stabilized over a period of months. The same gradients also appear to be stable in neutral water over a period of at least 1 week. Changes in the oxygen depth profiles have been observed at pH 4 and pH 10 showing structural and chemical aging effects on different time scales. The use of vertical gradient plasma polymer nanofilms thus represents a novel approach providing enhanced stability, thus opening the possibility for new applications.

Tackling chemical etching and its mechanisms of polyphenolic composites in various reactive low temperature plasmas

We report a systematic study on the selective polymer composite etching and unravelling the mechanisms in various RF gas plasmas.

Advanced Aromatic Polymers with Excellent Antiatomic Oxygen Performance Derived from Molecular Precursor Strategy and Copolymerization of Polyhedral Oligomeric Silsesquioxane

In this contribution, the advanced aromatic polymers with excellent antiatomic oxygen (AO) performance were designed and synthesized using molecular precursor strategy and copolymerization of polyhedral oligomeric silsesquioxane (POSS). A soluble poly(p-phenylene benzobisoxazole) (PBO) precursor, that is, TBS-PBO (tert-butyldimethylsilyl was denoted as TBS), was designed to overcome the poor solubility of PBO in organic solvents. Then the new copolymer of TBS-PBO-POSS was synthesized by the copolymerization of TBS-PBO and POSS, which possessed good solubility and film-forming ability in common organic solvents, such as N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide. More importantly, the TBS-PBO-POSS films exhibited outstanding antiatomic oxygen properties because of the incorporation of POSS monomers with cagelike structure into the main chain of copolymer, which drastically reduced the AO-induced erosion owing to the formation of the passivating silica layer on the surface of polymers. When the TBS-PBO-POSS films were exposed to AO effective fluences of 1.5495×10(20) atom cm(-2) (5 h) and 4.6486×10(20) atom cm(-2) (15 h), the relative mass loss was merely 0.19% and 0.41%, respectively. This work provides a new perspective and efficient strategy for the molecular design of aromatic heterocyclic polymers possessing excellent combination properties including processing convenience and antioxidative and mechanical properties, which can be employed as potential candidates to endure the aggressive environment encountered in low earth orbits.

Covalent Binding of Heparin to Functionalized PET Materials for Improved Haemocompatibility

The hemocompatibility of vascular grafts made from poly(ethylene terephthalate) (PET) is insufficient due to the rapid adhesion and activation of blood platelets that occur upon incubation with whole blood. PET polymer was treated with NH_x radicals created by passing ammonia through gaseous plasma formed by a microwave discharge, which allowed for functionalization with amino groups. X-ray photoelectron spectroscopy characterization using derivatization with 4-chlorobenzaldehyde indicated that approximately 4% of the –NH₂ groups were associated with the PET surface after treatment with the gaseous radicals. The functionalized polymers were coated with an ultra-thin layer of heparin and incubated with fresh blood. The free-hemoglobin technique, which is based on the haemolysis of erythrocytes, indicated improved hemocompatibility, which was confirmed by imaging the samples using confocal optical microscopy. A significant decrease in number of adhered platelets was observed on such samples. Proliferation of both human umbilical vein endothelial cells and human microvascular endothelial cells was enhanced on treated polymers, especially after a few hours of cell seeding. Thus, the technique represents a promising substitute for wet-chemical modification of PET materials prior to coating with heparin.

Importance of Poly(lactic-co-glycolic acid) in Scaffolds for Guided Bone Regeneration: A Focused Review

Total or partial tissue damage and loss of function in an organ are two of the most serious and costly issues in human health. Initially, these problems were approached through organ and allogenic tissue transplantation, but this option is limited by the scarce availability of donors. In this manner, new bone for restoring or replacing lost and damaged bone tissue is an important health and socioeconomic necessity. Tissue engineering has been used as a strategy during the 21st century for mitigating this need through the development of guided bone regeneration scaffold and composites. In this manner, compared with other traditional methods, bone tissue engineering offers a new and interesting approach to bone repair. The poly-α-hydroxy acids, which include the copolymers of lactic acid and glycolic acid, have been used commonly in the fabrication of these scaffolds. The objective of our article was to review the characteristics and functions of scaffold with biomedical applications, with special interest in scaffold construction using poly(lactic-co-glycolic acid) polymers, in order to update the current methods used for fabrication and to improve the quality of these scaffolds, integrating this information into the context of advancements made in tissue engineering based on these structures. In the future, research into bone regeneration should be oriented toward a fruitful exchange between disciplines involved in tissue engineering, which is coming very close to filling the gaps in our ability to provide implants and restoration of functionality in bone tissue. Overcoming this challenge will provide benefits to a major portion of the population and facilitate substantial improvements to quality of life.

Effects of plasma surface treatments of diamond-like carbon and polymeric substrata on the cellular behavior of human fibroblasts

Surface properties play an important role in the functioning of a biomaterial in the biological environment. This work describes the influence of the changes that occurred on diamond-like carbon (DLC) and polymeric substrata by different nitrogen and ammonia plasmas treatments and its effects on the cell proliferation on these materials. All substrata were additionally subjected to the effect of neutral beams of nitrogen atoms and NH species for comparison purposes. Results about the proliferation, viability, and morphology of fibroblasts were correlated with surface chemical composition, surface tension, and topography. It was found that the presence of amine groups on the surface and the surface tension are beneficial factors for the cell growth. Surface roughness in DLC also plays a positive role in favoring cell adhesion and proliferation, but it can be detrimental for some of the treated polymers because of the accumulation of low molecular weight fragments formed as a result of the plasma treatments. Analysis of the overall results for each type of material allowed to define a unique parameter called 'factor of merit' accounting for the influence of the different surface characteristics on the cell deployment, which can be used to predict qualitatively the efficiency for cell growth.

Influence of the 316 L stainless steel interface on the stability and barrier properties of plasma fluorocarbon films

Coatings are known to be one of the more suited strategies to tailor the interface between medical devices and the surrounding cells and tissues once implanted. The development of coatings and the optimization of their adhesion and stability are of major importance. In this work, the influence of plasma etching of the substrate on a plasma fluorocarbon ultrathin coating has been investigated with the aim of improving the stability and the corrosion properties of coated medical devices. The 316 L stainless steel interface was subjected to two different etching sequences prior to the plasma deposition. These plasma etchings, with H(2) and C(2)F(6) as gas precursors, modified the chemical composition and the thickness of the oxide layer and influenced the subsequent polymerization. The coating properties were evaluated using flat substrates submitted to deformation, aging into aqueous medium and corrosion tests. X-ray photoelectron spectroscopy (XPS), time of flight-secondary ion mass spectrometry (ToF-SIMS), ellipsometry, and atomic force microscopy (AFM) were performed to determine the effects of the deformation and the aging on the chemistry and morphology of the coated samples. Analyses showed that plasma etchings were essential to promote reproducible polymerization and film growth. However, the oxide layer thinning due to the etching lowered the corrosion resistance of the substrate and affected the stability of the interface. Still, the deformed samples did not exhibited adhesion and cohesion failure before and after the aging.