Candida auris susceptibility on surfaces coated with the antifungal drug caspofungin

Candida auris is known to survive for weeks on solid material surfaces. Its longevity contributes to medical device contamination and spread through healthcare facilities. We fabricated antifungal surface coatings by coating plastic and glass surfaces with a thin polymer layer to which the antifungal drug caspofungin was covalently conjugated. Caspofungin-susceptible and -resistant C. auris strains were inhibited on these surfaces by 98.7 and 81.1%, respectively. Cell viability studies showed that this inhibition was fungicidal. Our findings indicate that C. auris strains can be killed on contact when exposed to caspofungin that is reformulated as a covalently-bound surface layer.

LAY SUMMARY

Candida auris is pathogenic, multidrug resistant yeast with the ability to survive on surfaces and remain transmissible for long periods of time in healthcare settings. In this study, we have prepared an antifungal surface coating and demonstrated its ability to kill adhering C. auris cells on contact.

Candida albicans Can Survive Antifungal Surface Coatings on Surfaces with Microcone Topography

This study demonstrates the ability of Candida albicans, a medically significant human fungal pathogen, to minimize contact with an antifungal surface coating that on a flat surface is lethal on contact by growing on and between micron-sized surface topographical features, thus minimizing the contact area. Scanning electron microscopy showed that cells contacting the "floor" between microcones were killed, whereas cells attached to microcones survived and formed hyphal filaments. These spanned space between cones and avoided contact with the flat surface in-between cones. Thus, fungal cells managed to attach and grow despite the antifungal coating. This ability of Candida albicans to exploit topography features to minimize surface contact yet utilize the solid surface for anchoring reduces the effectiveness of the grafted antifungal surface coating. This suggests that biomedical devices with rough surfaces might be more challenging to protect against fungal biofilm formation via application of an antifungal coating.

Modulation of substrate van der Waals forces using varying thicknesses of polymer overlayers

Thin polymeric coatings are commonly used for altering surface properties and modulating the interfacial performance of materials. Possible contributions from the substrate to the interfacial forces and effects are, however, usually ignored and are not well understood, nor is it established how the coating thickness modulates and eventually eliminates contributions from substrates to the van der Waals (vdW) interfacial force. In this study we quantified, by colloid-probe atomic force microscope (AFM) and by theoretical calculations, the interfacial vdW contributions from substrates acting through ethanol plasma polymer (EtOHpp) coatings of a range of thicknesses on Au and Si bulk materials. In approach force curves against EtOHpp-coated Au substrates the magnitude of the vdW force decreased as the EtOHpp coating thickness increased to 18 nm and then plateaued with further increases in coating thickness, providing direct evidence for a contribution to the total interfacial vdW force from the Au substrate acting through thin coatings. The experimental observations accord with theoretical calculations of the thickness dependence of Hamaker coefficients derived from rigorous simulation using the Lifshitz theory. In addition, the measured forces agree well with theoretical predictions including correction for finite roughness. Thus, our experimental and theoretical results establish how the thickness of polymer thin film coatings modulates the total interfacial vdW force and how this can be used to tune the net vdW force so as to either contain a large substrate contribution or arise predominantly from the polymeric overlayer. Our findings enable rational design of coating thickness to tailor interfacial interactions and material performance.

Bacterial membrane permeability of antimicrobial polymethacrylates: Evidence for a complex mechanism from super-resolution fluorescence imaging

Amphiphilic polymers bearing cationic moieties are an emerging alternative to traditional antibiotics given their broad-spectrum activity and low susceptibility to the development of resistance. To date, however, much remains unclear regarding their mechanism of action. Using functional assays (ATP leakage, cell viability, DNA binding) and super-high resolution structured illumination microscopy (OMX-SR) of fluorescently tagged polymers, we present evidence for a complex mechanism, involving membrane permeation as well as cellular uptake, interaction with intracellular targets and possible complexation with bacterial DNA. STATEMENT OF SIGNIFICANCE: This manuscript details the first study to systematically and directly investigate the mechanism of action of antimicrobial polymers, using super-resolution fluorescence imaging as well as functional assays. While many in the field cite membrane permeation as the sole mechanism underlying the activity of such polymers, we present evidence for multimodal actions including high cellular uptake and interaction with intracellular targets. It is also the first report to show competitive binding of antimicrobial polymers with bacterial DNA in a dose-dependent manner.

The Physics of Plasma Ion Chemistry: A Case Study of Plasma Polymerization of Ethyl Acetate

Deposition chemistry from plasma is highly dependent on both the chemistry of the ions arriving at surfaces and the ion energy. Typically, when measuring the energy distribution of ions arriving at surfaces from plasma, it is assumed that the distributions are the same for all ionic species. Using ethyl acetate as a representative organic precursor molecule, we have measured the ion chemistry and ion energy as a function of pressure and power. We show that at low pressure (<2 Pa) this assumption is valid; however, at elevated pressures ion-molecule collisions close to the deposition surface affect both the energy and chemistry of these ions. Smaller ions are formed close to the surface and have lower energy than larger ionic species which are formed in the bulk of the plasma. The changes in plasma chemistry therefore are closely linked to the physics of the plasma-surface interface.

Interfacial Forces at Layered Surfaces: Substrate Electrical Double-Layer Forces Acting through Ultrathin Polymer Coatings

Manipulating the surface properties of materials via the application of coatings is a widely used strategy to achieve desired interfacial interactions, implicitly assuming that the interfacial forces of coated samples are determined exclusively by the surface properties of the coatings. However, interfacial interactions between materials and their environments operate over finite length scales. Thus, the question addressed in this study is whether interactions associated with bulk substrate materials could act through thin coatings or, conversely, how thick a coating needs to be to completely screen subsurface forces contributed by underlying substrates. Plasma polymer layers were deposited on silicon wafer substrates from ethanol vapor, with identical chemical composition, ultrasmooth surfaces, and varying thicknesses. Using colloid-probe atomic force microscopy, electrical double-layer forces were determined in solutions of various ionic strengths and fitted using the Derjaguin-Landau-Verwey-Overbeek theory. For the thicker ethanol plasma polymers, the fitted surface potentials reflected the presence of surface carboxylate groups and were invariant with thickness. In contrast, for coatings <18 nm thick, the surface potentials increased steadily with decreasing film thickness; the measured electrical double-layer forces contained contributions from both the coating and the substrate. Theoretical calculations were in agreement with this model. Thus, our observations indicate that the higher surface potential of the underlying SiO₂ surface can influence the interactions between a colloid particle and the multilayer structure if coatings are sufficiently thin. Such superposition needs to be factored into the design of coatings aimed at the control of material interactions via surface forces.

Antifungal Activity in Compounds from the Australian Desert Plant Eremophila alternifolia with Potency Against Cryptococcus spp

Plant metabolites that have shown activity against bacteria and/or environmental fungi represent valuable leads for the identification and development of novel drugs against clinically important human pathogenic fungi. Plants from the genus Eremophila were highly valued in traditional Australian Aboriginal medicinal practices, and E. alternifolia was the most prized among them. As antibacterial activity of extracts from E. alternifolia has been documented, this study addresses the question whether there is also activity against infectious fungal human pathogens. Compounds from leaf-extracts were purified and identified by 1- and 2-D NMR. These were then tested by disk diffusion and broth microdilution assays against ten clinically and environmentally relevant yeast and mould species. The most potent activity was observed with the diterpene compound, 8,19-dihydroxyserrulat-14-ene against Cryptococcus gattii and Cryptococcus neoformans, with minimum inhibition concentrations (MIC) comparable to those of Amphotericin B. This compound also exhibited activity against six Candida species. Combined with previous studies showing an antibacterial effect, this finding could explain a broad antimicrobial effect from Eremophila extracts in their traditional medicinal usage. The discovery of potent antifungal compounds from Eremophila extracts is a promising development in the search for desperately needed antifungal compounds particularly for Cryptococcus infections.

Surface-grafted antimicrobial drugs: Possible misinterpretation of mechanism of action

Antimicrobial surface coatings that act through a contact-killing mechanism (not diffusive release) could offer many advantages to the design of medical device coatings that prevent microbial colonization and infections. However, as the authors show here, to prevent arriving at an incorrect conclusion about their mechanism of action, it is essential to employ thorough washing protocols validated by surface analytical data. Antimicrobial surface coatings were fabricated by covalently attaching polyene antifungal drugs to surface coatings. Thorough washing (often considered to be sufficient to remove noncovalently attached molecules) was used after immobilization and produced samples that showed a strong antifungal effect, with a log 6 reduction in Candida albicans colony forming units. However, when an additional washing step using surfactants and warmed solutions was used, more firmly adsorbed compounds were eluted from the surface as evidenced by XPS and ToF-SIMS, resulting in reduction and complete elimination of in vitro antifungal activity. Thus, polyene molecules covalently attached to surfaces appear not to have a contact-killing effect, probably because they fail to reach their membrane target. Without additional stringent washing and surface analysis, the initial favorable antimicrobial testing results could have been misinterpreted as evidencing activity of covalently grafted polyenes, while in reality activity arose from desorbing physisorbed molecules. To avoid unintentional confirmation bias, they suggest that binding and washing protocols be analytically verified by qualitative/quantitative instrumental methods, rather than relying on false assumptions of the rigors of washing/soaking protocols.

Promiscuous hydrogen in polymerising plasmas

Historically, there have been two opposing views regarding deposition mechanisms in plasma polymerisation, radical growth and direct ion deposition, with neither being able to fully explain the chemistry of the resultant coating. Deposition rate and film chemistry are dependent on the chemistry of the plasma phase and thus the activation mechanisms of species in the plasma are critical to understanding the relative contributions of various chemical and physical routes to plasma polymer formation. In this study, we investigate the roles that hydrogen plays in activating and deactivating reactive plasma species. Ethyl trimethylacetate (ETMA) is used as a representative organic precursor, and additional hydrogen is added to the plasma in the form of water and deuterium oxide. Optical emission spectroscopy confirms that atomic hydrogen is abundant in the plasma. Comparison of the plasma phase mass spectra of ETMA/H₂O and ETMA/D₂O reveals that (1) proton transfer from hydronium is a common route to charging precursors in plasma, and (2) hydrogen abstraction (activation) and recombination (deactivation) processes are much more dynamic in the plasma than previously thought. Consideration of the roles of hydrogen in plasma chemistry may then provide a more comprehensive view of deposition processes and bridge the divide between the two disparate schools of thought.

The importance of fungal pathogens and antifungal coatings in medical device infections

In recent years, increasing evidence has been collated on the contributions of fungal species, particularly Candida, to medical device infections. Fungal species can form biofilms by themselves or by participating in polymicrobial biofilms with bacteria. Thus, there is a clear need for effective preventative measures, such as thin coatings that can be applied onto medical devices to stop the attachment, proliferation, and formation of device-associated biofilms. However, fungi being eukaryotes, the challenge is greater than for bacterial infections because antifungal agents are often toxic towards eukaryotic host cells. Whilst there is extensive literature on antibacterial coatings, a far lesser body of literature exists on surfaces or coatings that prevent attachment and biofilm formation on medical devices by fungal pathogens. Here we review strategies for the design and fabrication of medical devices with antifungal surfaces. We also survey the microbiology literature on fundamental mechanisms by which fungi attach and spread on natural and synthetic surfaces. Research in this field requires close collaboration between biomaterials scientists, microbiologists and clinicians; we consider progress in the molecular understanding of fungal recognition of, and attachment to, suitable surfaces, and of ensuing metabolic changes, to be essential for designing rational approaches towards effective antifungal coatings, rather than empirical trial of coatings.

Facile single-step bioconjugation of the antifungal agent caspofungin onto material surfaces via an epoxide plasma polymer interlayer

We report a facile, one-step, aqueous surface bioconjugation approach for producing an antifungal surface coating that prevents the formation of fungal biofilms.

Synthesis of highly functionalised plasma polymer films from protonated precursor ions via the plasma α–γ transition

Functional group retention in plasma polymers is maximised by tuning the pressure/power to the α to γ transition.

Colloid-probe AFM studies of the surface functionality and adsorbed proteins on binary colloidal crystal layers

We demonstrate the applicability of colloid-probe AFM to detect different surface chemistries on binary colloidal crystal layers of different chemical and protein patterns.

XPS Analysis of Acid Etched Poly (2-Hydroxyethyl Methacrylate) Surfaces

Poly(2-hydroxyethyl methacrylate) (pHEMA) surfaces etched by H2SO 4, chloric acid (HClO4/KClO3), and HF, were analyzed by electron spectros copy (XPS) to study the surface chemical changes that led to good attachment and growth of endothelial cells on the sulfuric acid treated surface, but not on the others. Sulfonation did not occur. With all three acid treatments, the domi nant chemical structures on the new surfaces were not free methacrylic acid groups that might have been produced by hydrolysis of the ester groups. Some of the several possible reactions between the acids and the pHEMA surface are not consistent with the XPS analyses. The acid treated surfaces contain mainly hydroxyl, ether and ester groups, and one or several among these enhance cell attachment and growth. Also, our data indicate caution in using XPS data as predictors of biomedical performance.

Hyperthermal Intact Molecular Ions Play Key Role in Retention of ATRP Surface Initiation Capability of Plasma Polymer Films from Ethyl α-Bromoisobutyrate

We report a systematic study of the plasma polymerization of ethyl α-bromoisobutyrate (EBIB) to produce thin film coatings capable of serving as ATRP initiation surfaces, for which they must contain α-bromoisobutyryl functional groups. In the deposition of polymeric coatings by plasma polymerization there generally occurs considerable fragmentation of precursor ("monomer") molecules in the plasma; and the retention of larger structural elements is challenging, particularly when they are inherently chemically labile. Empirical principles such as low plasma power and low pressure are usually utilized. However, we show that the α-bromoisobutyryl structural moiety is labile in a plasma gas phase and in low pressure plasma conditions, below the collisional threshold, there is little retention. At higher pressure, in contrast, fragmentation of this structural motif appears to be reduced substantially, and coatings useful for ATRP initiation were obtained. Mass spectrometry analysis of the composition of the plasma phase revealed that the desired structural moiety can be retained through the plasma, if the plasma conditions are steered toward ions of the precursor molecule. Whereas at low pressure the plasma polymer assembles mainly from various neutral (radical) fragments, at higher pressure the deposition occurs from hyperthermal ions, among which the protonated intact molecular ion is the most abundant. At higher pressure, a substantial population of ions has low kinetic energy, leading to "soft landing" and thus less fragmentation. This study demonstrates that relatively complex structural motifs in precursor molecules can be retained in plasma polymerization if the chemical and physical processes occurring in the plasma phase are elucidated and controlled such that desirable larger structural elements play a key role in the film deposition.

Antibacterial constituents of Eremophila alternifolia: An Australian aboriginal traditional medicinal plant

ETHNOPHARMACOLOGICAL RELEVANCE

For traditional medicinal purposes Aboriginal Australians have utilised numerous plant species, Eremophila alternifolia is among the most prominent. Traditionally, fresh leaves, leaf-infusions and handmade leaf-pastes have been used as both external and internal preparations to provide relief from a variety of conditions. Preparations of the species have been used to treat various infections of skin, eyes and throat including the treatment of septic wounds. These usages suggest that the plant contains antibacterial compounds; however, to date they have not been isolated and identified.

AIM OF THE STUDY

The present study aimed to identify antibacterial compounds from this important traditionally recorded medicinal species.

MATERIALS AND METHODS

Bioassay-guided fractionation was used to isolate compounds from the crude leaf-extract. Antibacterial activity of pure compounds was assessed through broth microdilution method by determining both minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs). Structure elucidation was performed using spectroscopic techniques such as 1D and 2D nuclear magnetic resonance spectroscopy and high resolution mass spectrometry.

RESULTS

Four compounds have been isolated from the leaf-extract; they include previously known flavanones [pinobanksin (1), pinobanksin-3-acetate (2) and pinobanksin-3-cinnamate (3)] and a serrulatane diterpene, 8-hydroxyserrulat-14-en-19-oic acid (4). While compound 4 had been found in other Eremophilas, flavanones 2 and 3 are identified for the first time from the genus Eremophila. The flavanone 3 is the most promising antibacterial compound with significant activity (10-20µM) against strains of the Gram-positive bacterium Staphylococcus aureus including methicillin resistant and biofilm forming strains. No activity was observed for any isolated compounds against the Gram-negative bacterium Escherichia coli.

CONCLUSION

The antibacterial activity of the crude extract of E. alternifolia and of the isolated compounds against Gram-positive bacteria provides a Western scientific explanation of the therapeutic modality of this plant species in traditional Aboriginal medicinal practice.

"Thunderstruck": Plasma-Polymer-Coated Porous Silicon Microparticles As a Controlled Drug Delivery System

Controlling the release kinetics from a drug carrier is crucial to maintain a drug's therapeutic window. We report the use of biodegradable porous silicon microparticles (pSi MPs) loaded with the anticancer drug camphothecin, followed by a plasma polymer overcoating using a loudspeaker plasma reactor. Homogenous "Teflon-like" coatings were achieved by tumbling the particles by playing AC/DC's song "Thunderstruck". The overcoating resulted in a markedly slower release of the cytotoxic drug, and this effect correlated positively with the plasma polymer coating times, ranging from 2-fold up to more than 100-fold. Ultimately, upon characterizing and verifying pSi MP production, loading, and coating with analytical methods such as time-of-flight secondary ion mass spectrometry, scanning electron microscopy, thermal gravimetry, water contact angle measurements, and fluorescence microscopy, human neuroblastoma cells were challenged with pSi MPs in an in vitro assay, revealing a significant time delay in cell death onset.

Photo-doping of plasma-deposited polyaniline (PAni)

Although polyaniline (PAni) has been studied extensively in the past, little work has been done on producing films of this material via plasma deposition.

Serrulatane Diterpenoid from Eremophila neglecta Exhibits Bacterial Biofilm Dispersion and Inhibits Release of Pro-inflammatory Cytokines from Activated Macrophages

The purpose of this study was to assess the biofilm-removing efficacy and inflammatory activity of a serrulatane diterpenoid, 8-hydroxyserrulat-14-en-19-oic acid (1), isolated from the Australian medicinal plant Eremophila neglecta. Biofilm breakup activity of compound 1 on established Staphylococcus epidermidis and Staphylococcus aureus biofilms was compared to the antiseptic chlorhexidine and antibiotic levofloxacin. In a time-course study, 1 was deposited onto polypropylene mesh to mimic a wound dressing and tested for biofilm removal. The ex-vivo cytotoxicity and effect on lipopolysaccharide-induced pro-inflammatory cytokine release were studied in mouse primary bone-marrow-derived macrophage (BMDM) cells. Compound 1 was effective in dispersing 12 h pre-established biofilms with a 7 log10 reduction of viable bacterial cell counts, but was less active against 24 h biofilms (approximately 2 log10 reduction). Compound-loaded mesh showed dosage-dependent biofilm-removing capability. In addition, compound 1 displayed a significant inhibitory effect on tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) secretion from BMDM cells, but interleukin-1 beta (IL-1β) secretion was not significant. The compound was not cytotoxic to BMDM cells at concentrations effective in removing biofilm and lowering cytokine release. These findings highlight the potential of this serrulatane diterpenoid to be further developed for applications in wound management.

Packed Bed Bioreactor for the Isolation and Expansion of Placental-Derived Mesenchymal Stromal Cells

Large numbers of Mesenchymal stem/stromal cells (MSCs) are required for clinical relevant doses to treat a number of diseases. To economically manufacture these MSCs, an automated bioreactor system will be required. Herein we describe the development of a scalable closed-system, packed bed bioreactor suitable for large-scale MSCs expansion. The packed bed was formed from fused polystyrene pellets that were air plasma treated to endow them with a surface chemistry similar to traditional tissue culture plastic. The packed bed was encased within a gas permeable shell to decouple the medium nutrient supply and gas exchange. This enabled a significant reduction in medium flow rates, thus reducing shear and even facilitating single pass medium exchange. The system was optimised in a small-scale bioreactor format (160 cm²) with murine-derived green fluorescent protein-expressing MSCs, and then scaled-up to a 2800 cm² format. We demonstrated that placental derived MSCs could be isolated directly within the bioreactor and subsequently expanded. Our results demonstrate that the closed system large-scale packed bed bioreactor is an effective and scalable tool for large-scale isolation and expansion of MSCs.

Comparison of Plasma Polymerization under Collisional and Collision-Less Pressure Regimes

While plasma polymerization is used extensively to fabricate functionalized surfaces, the processes leading to plasma polymer growth are not yet completely understood. Thus, reproducing processes in different reactors has remained problematic, which hinders industrial uptake and research progress. Here we examine the crucial role pressure plays in the physical and chemical processes in the plasma phase, in interactions at surfaces in contact with the plasma phase, and how this affects the chemistry of the resulting plasma polymer films using ethanol as the gas precursor. Visual inspection of the plasma reveals a change from intense homogeneous plasma at low pressure to lower intensity bulk plasma at high pressure, but with increased intensity near the walls of the chamber. It is demonstrated that this occurs at the transition from a collision-less to a collisional plasma sheath, which in turn increases ion and energy flux to surfaces at constant RF power. Surface analysis of the resulting plasma polymer films show that increasing the pressure results in increased incorporation of oxygen and lower cross-linking, parameters which are critical to film performance. These results and insights help to explain the considerable differences in plasma polymer properties observed by different research groups using nominally similar processes.

Colloid-probe AFM studies of the interaction forces of proteins adsorbed on colloidal crystals

In recent years, colloid-probe AFM has been used to measure the direct interaction forces between colloidal particles of different size or surface functionality in aqueous media, as one can study different forces in symmerical systems (i.e., sphere-sphere geometry). The present study investigates the interaction between protein coatings on colloid probes and hydrophilic surfaces decorated with hexagonally close packed single particle layers that are either uncoated or coated with proteins. Controlled solvent evaporation from aqueous suspensions of colloidal particles (coated with or without lysozyme and albumin) produces single layers of close-packed colloidal crystals over large areas on a solid support. The measurements have been carried out in an aqueous medium at different salt concentrations and pH values. The results show changes in the interaction forces as the surface charge of the unmodified or modified particles, and ionic strength or pH of the solution is altered. At high ionic strength or pH, electrostatic interactions are screened, and a strong repulsive force at short separation below 5 nm dominates, suggesting structural changes in the absorbed protein layer on the particles. We also study the force of adhesion, which decreases with an increment in the salt concentration, and the interaction between two different proteins indicating a repulsive interaction on approach and adhesion on retraction.

Compounds from Geijera parviflora with prostaglandin E2 inhibitory activity may explain its traditional use for pain relief

ETHNOPHARMACOLOGICAL RELEVANCE

Australian Aboriginal people used crushed leaves of Geijera parviflora Lindl. both internally and externally for pain relief, including for toothache (Cribb and Cribb, 1981). This study tested the hypothesis that this traditional use might be at least in part explained by the presence of compounds with anti-inflammatory activity.

MATERIALS AND METHODS

A crude extract (95% EtOH) was prepared from powdered dried leaves. From the CH3Cl fraction of this extract compounds were isolated by bioassay-guided fractionation and tested for: (1) cytotoxicity in RAW 264.7 murine leukemic monocyte-macrophages, (2) prostaglandin E2 (PGE2) inhibitory activity in 3T3 Swiss albino mouse embryonic fibroblast cells, as well as (3) nitric oxide (NO) and (4) tumour necrosis factor alpha (TNFα) inhibitory activity in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Isolated compounds were also tested for (5) antibacterial activity against a panel of Gram-positive (Staphylococcus aureus ATCC 29213 and ATCC 25923, Staphylococcus epidermidis ATCC 35984, biofilm-forming) and Gram-negative (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853) strains by broth microdilution.

RESULTS

Eleven compounds were isolated, including one new flavone and one new natural product, with a further four compounds reported from this species for the first time. Some of the compounds showed good anti-inflammatory activity in vitro. In particular, flindersine (1) and N-(acetoxymethyl) flindersine (3) inhibited PGE2 release with IC50 values of 5.0μM and 4.9μM, respectively, without any significant cytotoxicity. Several other compounds showed moderate inhibition of NO (5, 6, 7) and TNF-α (6), with IC50 in the low micromolar range; however much of this apparent activity could be accounted for by the cytotoxicity of these compounds. None of the compounds showed anti-bacterial activity.

CONCLUSIONS

The inhibition of PGE2, an important mediator of inflammation and pain, by flindersine and a derivative thereof, along with the moderate anti-inflammatory activity shown by several other compounds isolated from Geijera parviflora leaf extract, support the traditional use of this plant for pain relief by Australian Aboriginal people.

Cellular micromotion monitored by long-range surface plasmon resonance with optical fluctuation analysis

Long-range surface plasmon resonance (LRSPR) is a powerful biosensing technology due to a substantially larger probing depth into the medium and sensitivity, compared with conventional SPR. We demonstrate here that LRSPR can provide sensitive noninvasive measurement of the dynamic fluctuation of adherent cells, often referred to as the cellular micromotion. Proof of concept was achieved using confluent layers of 3T3 fibroblast cells and MDA-MB-231 cancer cells. The slope of the power spectral density (PSD) of the optical fluctuations was calculated to determine the micromotion index, and significant differences were measured between live and fixed cell layers. Furthermore, the performances of LRSPR and conventional surface plasmon resonance (cSPR) were compared with respect to micromotion monitoring. Our study showed that the micromotion index of cells measured by LRSPR sensors was higher than when measured with cSPR, suggesting a higher sensitivity of LRSPR to the micromotion of cells. To investigate further this finding, simulations were conducted to establish the relative sensitivities of LRSPR and cSPR to membrane fluctuations. Increased signal intensity was predicted for LRSPR in comparison to cSPR, suggesting that membrane fluctuations play a significant role in the optical micromotion measured in LRSPR. Analogous to cellular micromotion measured using impedance techniques, LRSPR micromotion has the potential to provide important biological information on the metabolic activity and viability of adherent cells.

Surface coatings with covalently attached caspofungin are effective in eliminating fungal pathogens

In this work we have prepared surface coatings formulated with the antifungal drug caspofungin, an approved pharmaceutical lipopeptide compound of the echinocandin drug class.

Nitric oxide releasing plasma polymer coating with bacteriostatic properties and no cytotoxic side effects

We report a stable plasma polymer coating which releases nitric oxide, inhibiting bacterial growth without cytotoxic side effects.

Structure–activity relationships of guanylated antimicrobial polymethacrylates

Host-defense antimicrobial peptides (AMPs) are a promising lead in the search for novel antibiotics. Many of these peptides exhibit broad-spectrum antibacterial ability, low toxicity toward human cells, and little susceptibility to induction of bacterial resistance. Our research focuses on the development of synthetic polymers that are able to mimic the amphiphilic and cation-rich characteristics of AMPs. This derives bioactive polymers that retain the activity profile of AMPs while utilizing a construct that is less expensive and easier to produce and manipulate chemically. This review details structure–activity relationships (SARs) of a new class of arginine-rich, synthetic AMP mimicking polymers (SAMPs), the guanylated polymethacrylates. These are contrasted with those of amine-based polymers that are mimics of lysine-rich AMPs. The ideal composition for candidates for practical applications was identified as those containing guanidines as a cation source, having a low molecular weight and a low level of lipophilicity. This gave polymers with high potency against Gram-positive strains of bacteria (e.g., Staphylococcus epidermidis MIC = 10 μg/mL) and low toxicity towards human red blood cells (<4% hemolysis at given MIC). This work emphasizes the need to rationalize observed biological activities based not purely on the global lipophilic and cationic character of polymers but rather to consider the profound effect that specific pendant functional groups may have on the potency, selectivity, and mechanisms behind the action of antimicrobial polymers.

A solid-state nuclear magnetic resonance study of post-plasma reactions in organosilicone microwave plasma-enhanced chemical vapor deposition (PECVD) coatings

Plasma-polymerized organosilicone coatings can be used to impart abrasion resistance and barrier properties to plastic substrates such as polycarbonate. Coating rates suitable for industrial-scale deposition, up to 100 nm/s, can be achieved through the use of microwave plasma-enhanced chemical vapor deposition (PECVD), with optimal process vapors such as tetramethyldisiloxane (TMDSO) and oxygen. However, it has been found that under certain deposition conditions, such coatings are subject to post-plasma changes; crazing or cracking can occur anytime from days to months after deposition. To understand the cause of the crazing and its dependence on processing plasma parameters, the effects of post-plasma reactions on the chemical bonding structure of coatings deposited with varying TMDSO-to-O2 ratios was studied with (29)Si and (13)C solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) using both single-pulse and cross-polarization techniques. The coatings showed complex chemical compositions significantly altered from the parent monomer. (29)Si MAS NMR spectra revealed four main groups of resonance lines, which correspond to four siloxane moieties (i.e., mono (M), di (D), tri (T), and quaternary (Q)) and how they are bound to oxygen. Quantitative measurements showed that the ratio of TMDSO to oxygen could shift the chemical structure of the coating from 39% to 55% in Q-type bonds and from 28% to 16% for D-type bonds. Post-plasma reactions were found to produce changes in relative intensities of (29)Si resonance lines. The NMR data were complemented by Fourier transform infrared (FTIR) spectroscopy. Together, these techniques have shown that the bonding environment of Si is drastically altered by varying the TMDSO-to-O2 ratio during PECVD, and that post-plasma reactions increase the cross-link density of the silicon-oxygen network. It appears that Si-H and Si-OH chemical groups are the most susceptible to post-plasma reactions. Coatings produced at a low TMDSO-to-oxygen ratio had little to no singly substituted moieties, displayed a highly cross-linked structure, and showed less post-plasma reactions. However, these chemically more stable coatings are less compatible mechanically with plastic substrates, because of their high stiffness.

Antimicrobial Polymethacrylates Synthesized as Mimics of Tryptophan-Rich Cationic Peptides

This study describes a facile and high yielding route to two series of polymethacrylates inspired by the naturally occurring, tryptophan-rich cationic antimicrobial polymers. Appropriate optimization of indole content within each gave rise to polymers with high potency against Staphylococcus epidermidis (e.g., PGI-3 minimum inhibitory concentration (MIC) = 12 μg/mL) and the methicillin-resistant strain of Staphylococcus aureus (e.g., PGI-3 MIC = 47 μg/mL) with minimal toxicity toward human red blood cells. Future work will be directed toward understanding the cooperative roles that the cationic and indole pendant groups have for the mechanism of these polymers.

Direct imaging of mechanical and chemical gradients across the thickness of graded organosilicone microwave PECVD coatings

The characterization of variations in the chemical composition and ensuing mechanical properties across the thickness of coatings with continuously varying compositions through their thickness (graded coatings) presents considerable challenges for current analytical techniques in materials science. We report here the direct imaging of nanomechanical and chemical gradients across cross-sections of an organosilicone coating fabricated via microwave plasma enhanced chemical vapor deposition (PECVD). Cross-sectional nanoindentation was used to determine the mechanical properties of uniform and graded organosilicone coatings. Both hardness and modulus across the coatings were directly measured. Additionally, "modulus mapping" on cross-sections was used to map the complex modulus. For the graded coating, it was found that variations in the complex modulus was predominantly due to varying storage modulus. It was observed that at the interface with the substrate there was a low storage modulus, which linearly increased to a relatively high storage modulus at the surface. It is proposed that the increase in stiffness, from the substrate interface to the outer surface, is due to the increasing content of a cross-linked O-Si-O network. This mechanical gradient has been linked to a change in the Si:O ratio via direct compositional mapping using ToF-SIMS. Direct mapping of the mechanical and compositional gradients across these protective coatings provides insight into the changes in properties with depth and supports optimization of the critical mechanical performance of PECVD graded coatings.

Plasma polymerization of 1,1,1-trichloroethane yields a coating with robust antibacterial surface properties

Novel, highly chlorinated surface coatings were produced via a one-step plasma polymerization (pp) of 1,1,1-trichloroethane (TCE), exhibiting excellent antimicrobial properties against the vigorously biofilm-forming bacterium Staphylococcus epidermidis.

Rhodomyrtals A–D, four unusual phloroglucinol-sesquiterpene adducts from Rhodomyrtus psidioides

Four unusual phloroglucinol-sesquiterpene adducts, rhodomyrtals A–D (1–4), representing two unprecendented carbon frameworks of phloroglucinol coupled eudesmane with the linkage at C-12′, were isolated from Rhodomyrtus psidioides.

RAFT-derived antimicrobial polymethacrylates: elucidating the impact of end-groups on activity and cytotoxicity

We report the use of RAFT polymerization to obtain eight cationic methacrylate polymers bearing amine or guanidine pendant groups, while varying the R- and Z-RAFT end-groups.

Biomaterials surfaces capable of resisting fungal attachment and biofilm formation

Microbial attachment onto biomedical devices and implants leads to biofilm formation and infection; such biofilms can be bacterial, fungal, or mixed. In the past 15 years, there has been an increasing research effort into antimicrobial surfaces but the great majority of these publications present research on bacteria, with some reports also testing resistance to fungi. Very few studies have focused exclusively on antifungal surfaces. However, with increasing recognition of the importance of fungal infections to human health, particularly related to infections at biomaterials, it would seem that the interest in antifungal surfaces is disproportionately low. In studies of both bacteria and fungi, fungi tend to be the minor focus with hypothesized antibacterial mechanisms of action often generalized to also explain the antifungal effect. Yet bacteria and fungi represent two Distinct biological Domains and possess substantially different cellular physiology and structure. Thus it is questionable whether these generalizations are valid. Here we review the scientific literature focusing on surface coatings prepared with antifungal agents covalently attached to the biomaterial surface. We present a critical analysis of generalizations and their evidence. This review should be of interest to researchers of "antimicrobial" surfaces by addressing specific issues that are key to designing and understanding antifungal biomaterials surfaces and their putative mechanisms of action.

Parvifloranines A and B, two 11-carbon alkaloids from Geijera parviflora

Two novel alkaloids (parvifloranines A and B), possessing an unusual 11-carbon skeleton linked with amino acids, were isolated from Geijera parviflora, an endemic Australian Rutaceae. Their structures were elucidated by extensive spectroscopic measurements including 2D NMR analyses. Parvifloranine A was found to be a mixture of two enantiomers, (S)-1 and (R)-1, in a ratio of 1:4, based on their separation using a chiral column. Parvifloranine B is also believed to be a mixture of enantiomers. Proposed biosynthetic pathways are discussed. Parvifloranine A inhibited the synthesis of nitric oxide in LPS-stimulated RAW 264.7 macrophages with an IC50 value of 23.4 μM.

Grafting of poly(ethylene glycol) on click chemistry modified Si(100) surfaces

Poly(ethylene glycol) (PEG) is one of the most extensively studied antifouling coatings due to its ability to reduce protein adsorption and improve biocompatibility. Although the use of PEG for antifouling coatings is well established, the stability and density of PEG layers are often inadequate to provide optimum antifouling properties. To improve on these shortcomings, we employed the stepwise construction of PEG layers onto a silicon surface. Acetylene-terminated alkyl monolayers were attached to nonoxidized crystalline silicon surfaces via a one-step hydrosilylation procedure with 1,8-nonadiyne. The acetylene-terminated surfaces were functionalized via a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction of the surface-bound alkynes with an azide to produce an amine terminated layer. The amine terminated layer was then further conjugated with PEG to produce an antifouling surface. The antifouling surface properties were investigated by testing adsorption of human serum albumin (HSA) and lysozyme (Lys) onto PEG layers from phosphate buffer solutions. Detailed characterization of protein fouling was carried out with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with principal component analysis (PCA). The results revealed no fouling of albumin onto PEG coatings whereas the smaller protein lysozyme adsorbed to a very low extent.