Studies of air, water, and ethanol vapor atmospheric pressure plasmas for antimicrobial applications.

The generation of air-based plasmas under atmospheric plasma conditions was studied to assess their antimicrobial efficacy against commonly found pathogenic bacteria. The mixture of initial gases supplied to the plasma was found to be critical for the formation of bactericidal actives. The optimal gas ratio for bactericidal effect was determined to be 99% nitrogen and 1% oxygen, which led to a 99.999% reduction of a pathogenic strain of Escherichia coli on stainless steel surfaces. The experimental substrate, soil load on the substrate, flow rate of the gases, and addition of ethanol vapor all were found to affect antimicrobial efficacy of studied plasmas. Optical emission spectroscopy was used to identify the species that were present in the plasma bulk phase for multiple concentrations of nitrogen and oxygen ratios. The collected spectra indicate a unique series of bands present in the ultraviolet region of the electromagnetic spectrum that can be attributed to nitric oxide species known to be highly antimicrobial. This intense spectral profile dramatically changes as the concentration of nitrogen decreases.

Aerosol-assisted plasma deposition of hydrophobic polycations makes surfaces highly antimicrobial.

The currently used multistep chemical synthesis for making surfaces antimicrobial by attaching to them hydrophobic polycations is replaced herein by an aerosol-assisted plasma deposition procedure. To this end, N,N-hexyl,methyl-PEI (HMPEI) is directly plasma-coated onto a glass surface. The resultant immobilized HMPEI coating has been thoroughly characterized and shown to be robust, bactericidal against Escherichia coli, and virucidal against human influenza virus.

Development of antimicrobial coatings by atmospheric pressure plasma using a guanidine-based precursor.

Antimicrobial coatings deposited onto ultra high molecular weight polyethylene (UHMWPE) films were investigated using an atmospheric pressure - plasma enhanced chemical vapor deposition (AP-PECVD) process. Varying concentrations of a guanidine-based liquid precursor, 1,1,3,3-tetramethylguanidine, were used, and different deposition conditions were studied. Attenuated total reflectance - Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS) were used to study the chemical structure and elemental composition of the coatings. Conformity, morphology, and coating thickness were assessed through SEM and AFM. Optimal AP-PECVD parameters were chosen and applied to deposit guanidine coatings onto woven fabrics. The coatings exhibited high antimicrobial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) based on a modified-AATCC 100 test standard, where 2-5 log reductions were achieved.

Modification of silicon carbide surfaces by atmospheric pressure plasma for composite applications.

In this study, we explore the use of atmospheric pressure plasmas for enhancing the adhesion of SiC surfaces using a urethane adhesive, as an alternative to grit-blasting. Surface analysis showed that He-O2 plasma treatments resulted in a hydrophilic surface mostly by producing SiOx. Four-point bending tests and bonding pull tests were carried out on control, grit-blasted, and plasma-treated surfaces. Grit-blasted samples showed enhanced bonding but also a decrease in flexural strength. Plasma treated samples did not affect the flexural strength of the material and showed an increase in bonding strength. These results suggest that atmospheric pressure plasma treatment of ceramic materials is an effective alternative to grit-blasting for adhesion enhancement.

Efficacy of non-toxic surfaces to reduce bioadhesion in terrestrial gastropods.

BACKGROUND: Invasive species are described as the greatest threat to biodiversity, after habitat destruction and climate change, potentially imposing economic impacts and indigenous species impairment. Commonly applied chemical controls present the potential for legacy contamination and non-target organism injury. This study investigated the effects of different substrates and novel topographical surfaces on the behavioral and mechanical associations of the terrestrial gastropod Otala lactea. RESULTS: The gastropod preferentially aestivated on rough glass (61% increase, P < 0.01) relative to smooth glass but avoided a cross-patterned surface tessellation on silicone (82% reduction, P < 0.01) relative to smooth silicone. Significant deviations in turning behavior were found on the cross-patterned topographical surface and hydrophobic Teflon surfaces. The strongest correlation with gastropod adhesion strength to surfaces was found for surface elastic modulus (R = 0.88, P = 0.03), followed by hydrophobicity (R = - 0.71, P = 0.14), but no relationship with roughness (P = 0.36). CONCLUSION: Preliminary data suggest surface roughness controlled aestivation behavior while elastic modulus (surface flexibility) controlled adhesion strength. In spite of greater adhesion to high-modulus materials, surface modulus was not a statistically significant controlling factor on gastropod aestivation preference. Understanding and exploiting the behavioral and mechanistic cues that organisms use while attaching to surfaces may lead to more environmentally benign control approaches.

Accelerated differentiation of osteoblast cells on polycaprolactone scaffolds driven by a combined effect of protein coating and plasma modification.

A combined effect of protein coating and plasma modification on the quality of the osteoblast-scaffold interaction was investigated. Three-dimensional polycaprolactone (PCL) scaffolds were manufactured by the precision extrusion deposition (PED) system. The structural, physical, chemical and biological cues were introduced to the surface through providing 3D structure, coating with adhesive protein fibronectin and modifying the surface with oxygen-based plasma. The changes in the surface properties of PCL after those modifications were examined by contact angle goniometry, surface energy calculation, surface chemistry analysis (XPS) and surface topography measurements (AFM). The effects of modification techniques on osteoblast short-term and long-term functions were examined by cell adhesion, proliferation assays and differentiation markers, namely alkaline phosphatase activity (ALP) and osteocalcin secretion. The results suggested that the physical and chemical cues introduced by plasma modification might be sufficient for improved cell adhesion, but for accelerated osteoblast differentiation the synergetic effects of structural, physical, chemical and biological cues should be introduced to the PCL surface.

Yield of electronically excited CN molecules from the dissociative recombination of HNC+ with electrons.

The authors have studied CN(B-X) and CN(A-X) emissions produced by the dissociative recombination of HNC+ ions with thermal electrons in a flowing afterglow experiment. A separate drift tube study showed that the reaction Ar(+)+HCN, the precursor reaction used in the flow-tube experiment, produces predominantly HNC+ rather than the more energetic HCN+ isomer. Models simulating the ion-chemical processes, diffusion, and gas mixing in the afterglow plasma were fitted to observed position dependent CN(A-X) and CN(B-X) band intensities. Absolute yields of CN(B) and CN(A) were then obtained by comparing the CN band intensities to those of CO bands produced by recombination of CO(2) (+) ions. It was concluded that the 300 K recombination coefficient of HNC+ is close to 2 x 10(-7) cm(3) s(-1), that CN(B) is formed with a yield of 0.22+/-0.08 and CN(A) with a yield of 0.14+/-0.05. By comparison to synthetic spectra, the rotational temperature of CN(B) was estimated to be approximately 2500 K. It was also found that recombination produces CN(B) and CN(A) with far greater vibrational excitation than would be expected from the "impulse model" of Bates [Mon. Not. R. Astron. Soc. 263, 369 (1993)].