Laurence Meagher - Academia.edu (original) (raw)

Papers by Laurence Meagher

Colloids and Surfaces A: Physicochemical and Engineering Aspects, Mar 1, 2003

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999

The surface charging properties of polycrystalline α-alumina fibres in aqueous electrolyte soluti... more The surface charging properties of polycrystalline α-alumina fibres in aqueous electrolyte solutions have been investigated by direct force and streaming potential measurements. The presence of both Al and Si on the surface of the fibres resulted in a chemically heterogeneous surface. The heterogeneous distribution of Si resulted in large attractive forces between the fibres at moderate to low pH values

Frontiers in Bioengineering and Biotechnology, 2016

Frontiers in Chemistry, Sep 10, 2021

Plasma Processes and Polymers, Feb 7, 2008

Effects of surface oxidation on the properties of amine plasma polymer (pp) films in aqueous medi... more Effects of surface oxidation on the properties of amine plasma polymer (pp) films in aqueous media have not been widely studied, despite their use to control bio‐interfacial properties. Changes in the surface composition of allylamine and heptylamine pp films, on water exposure, were followed by XPS. The surface potential was monitored via AFM measurements and comparison to DLVO theory. Analysis of XPS data implied high initial oxidation rates (rapid quenching of surface radicals). Oxidation of the pp films followed evolution of carbon‐based rather than nitrogen‐based species. Analysis of AFM force data showed changes in the sign of the surface potential with aging from positive to negative. Implications, for example for surface immobilization of molecules in aqueous environments, are also discussed.magnified image

Biointerphases, Jul 5, 2013

Bacterial response to different surface chemistries fabricated by plasma polymerization on electr... more Bacterial response to different surface chemistries fabricated by plasma polymerization on electrospun nanofibers Biointerphases 10, 04A301 (2015);

Biomacromolecules, Apr 17, 2004

Surface-immobilized liposome layers are of interest for various potential applications such as lo... more Surface-immobilized liposome layers are of interest for various potential applications such as localized drug delivery, but their characterization is challenging. We have employed an AFM method and fluorescent dye release to analyze anchored liposomes. In addition, we studied whether the liposomes are surfacebound solely via specific interaction (NeutrAvidin/biotin) or whether physisorptive binding also plays a role. Liposomes containing PEG-biotin lipids were affinity bound to NeutrAvidin molecules which had been immobilized onto solid supports via three different hydrogel interlayers. After liposome docking, approaching the surface with a colloid probe mounted onto an AFM cantilever showed considerable compression behavior, consistent with expectation based on intact, deformable liposomes but not lipid bilayers, thus showing that disruption of liposomes did not occur upon immobilization onto these support surfaces. Plastic deformation suggestive of liposome disruption on compression was not observed. The kinetics of fluorescent dye release also demonstrated that intact liposomes had been successfully immobilized onto all three supports. Blocking surface-immobilized NeutrAvidin molecules with excess biotin in solution before exposure to liposomes showed that the docking of liposomes was dependent largely but not exclusively on biotin-NeutrAvidin affinity binding, with evidence for some nonspecific physisorption, as the extent of liposome binding onto blocked NeutrAvidin surfaces was appreciably lower than for unblocked surfaces but not zero. Finally, consecutive addition of further NeutrAvidin and liposome layers enabled fabrication of multilayers, and this was clearly seen in AFM compressibility and fluorescent dye release measurements.

Proceedings of SPIE, Nov 19, 2001

Journal of Materials Chemistry B, 2016

Degradable polyester fibres with polymer brush coatings improve control of cell adhesion to three... more Degradable polyester fibres with polymer brush coatings improve control of cell adhesion to three-dimensional scaffolds. Please check this proof carefully. Our staff will not read it in detail after you have returned it. Translation errors between word-processor files and typesetting systems can occur so the whole proof needs to be read. Please pay particular attention to: tabulated material; equations; numerical data; figures and graphics; and references. If you have not already indicated the corresponding author(s) please mark their name(s) with an asterisk. Please e-mail a list of corrections or the PDF with electronic notes attached-do not change the text within the PDF file or send a revised manuscript. Corrections at this stage should be minor and not involve extensive changes. All corrections must be sent at the same time. Please bear in mind that minor layout improvements, e.g. in line breaking, table widths and graphic placement, are routinely applied to the final version. Please note that, in the typefaces we use, an italic vee looks like this: n, and a Greek nu looks like this: n. We will publish articles on the web as soon as possible after receiving your corrections; no late corrections will be made.

Journal of Antimicrobial Chemotherapy, Oct 21, 2015

Biofilm-related human infections have high mortality rates due to drug resistance. Cohabitation o... more Biofilm-related human infections have high mortality rates due to drug resistance. Cohabitation of diverse microbes in polymicrobial biofilms is common and these infections present additional challenges for treatment compared with monomicrobial biofilms. Here, we address this therapeutic gap by assessing the potential of a new class of antimicrobial agents, guanylated polymethacrylates, in the treatment of polymicrobial biofilms built by two prominent human pathogens, the fungus Candida albicans and the bacterium Staphylococcus aureus. Methods: We used imaging and quantitative methods to test the antibiofilm efficacy of guanylated polymethacrylates, a new class of drugs that structurally mimic antimicrobial peptides. We further compared guanylated polymethacrylates with first-line antistaphylococcal and anti-Candida agents used as combinatorial therapy against polymicrobial biofilms. Results: Guanylated polymethacrylates were highly effective as a sole agent, killing both C. albicans and S. aureus when applied to established polymicrobial biofilms. Furthermore, they outperformed multiple combinations of current antimicrobial drugs, with one of the tested compounds killing 99.98% of S. aureus and 82.2% of C. albicans at a concentration of 128 mg/L. The extracellular biofilm matrix provided protection, increasing the MIC of the polymethacrylates by 2-4-fold when added to planktonic assays. Using the C. albicans bgl2DD mutant, we implicate matrix polysaccharide b-1,3 glucan in the mechanism of protection. Data for two structurally distinct polymers suggest that this mechanism could be minimized through chemical optimization of the polymer structure. Finally, we demonstrate that a potential application for these polymers is in antimicrobial lock therapy. Conclusions: Guanylated polymethacrylates are a promising lead for the development of an effective monotherapy against C. albicans/S. aureus polymicrobial biofilms.

Colloids and Surfaces B: Biointerfaces, Feb 1, 2002

ABSTRACT Lactoferrin is an important protein found in tear fluid and has been implicated in the f... more ABSTRACT Lactoferrin is an important protein found in tear fluid and has been implicated in the fouling of contact lenses. The interaction forces between lactoferrin layers, adsorbed onto hydrophobic model substrates, as a function of electrolyte concentration, solution pH and protein concentration were investigated using an atomic force microscope (AFM) where the geometry of the scanning tip was modified by attaching a colloid particle. Bovine lactoferrin adsorbed strongly and modified the interaction forces to include both a long-range electrostatic repulsive force, which could be described using the DLVO theory, and a short-range additional repulsion due to compression of the adsorbed protein layers. The adsorption of lactoferrin was verified by XPS analysis of the surfaces and the adsorbed layer was determined to be present as a full monolayer by AFM imaging. At smaller separation distances, deviations from theoretical predictions indicated that there was an adsorbed layer of at least 5 nm on both surfaces. DLVO theory could be used successfully to describe the longer ranged interaction forces in background electrolyte concentrations of 0.0002 and 0.001 M KNO3, at various solution pH values. This analysis yielded effective diffuse electrical double layer potentials, which when plotted against the solution pH, suggested that the point of zero charge (pzc) of the protein coated surfaces was around pH 8, in agreement with literature values of the pI for lactoferrin. At higher electrolyte concentrations, 0.15 M KNO3, the interaction forces could no longer be described using DLVO theory. The interaction forces between the adsorbed lactoferrin layers were purely repulsive, and the range and magnitude varied as a function of solution pH. Variations in the forces as a function of solution pH reflected conformational changes that depend on short ranged electrostatic interactions between the peptide residues within the protein molecules and the peptide residues and the substrate as well as van der Waals and hydrophobic interactions. The range of the interaction forces and the high compressibility of the adsorbed layers indicated that a significant number were present in an end-on orientation.

Journal of Controlled Release, Apr 1, 2002

Liposomes were immobilized onto the surface of perfluorinated polymer tape samples and tissue cul... more Liposomes were immobilized onto the surface of perfluorinated polymer tape samples and tissue culture polystyrene well-plates using a multilayer immobilization strategy. In the first step, a thin interfacial bonding layer with surface aldehyde groups was deposited from a glow discharge struck in acetaldehyde vapour. Polyethylenimine was then covalently bound onto the aldehyde groups by reductive amination, followed by covalent binding of NHS-PEG-biotin molecules onto the surface amine groups by carbodiimide chemistry. Next, NeutrAvidin protein molecules were bound onto the PEG-biotin layer. Finally, liposomes containing PEG-biotinylated lipids were docked onto the remaining binding sites of the surface-immobilized NeutrAvidin molecules. AFM was used to image surface-bound liposomes and revealed a density well below close packing. The release characteristics of the surface-bound liposomes were measured by the fluorescence intensity changes of carboxyfluorescein upon release. Liposomes filled with sodium orthovanadate were surface immobilized and used in two in vitro angiogenesis assays. Marked differences compared to various control samples were observed, demonstrating the utility of drug-filled, surface-bound liposomes for evoking localized, controlled biological host responses proximal to an implanted biomedical device.

Journal of Colloid and Interface Science, Nov 1, 2020

Thin polymeric coatings are commonly used for altering surface properties and modulating the inte... more 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.

Langmuir, Aug 13, 2019

Manipulating the surface properties of materials via the application of coatings is a widely used... more 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 (AFM), electrical double layer forces were determined in solutions of various ionic strengths and fitted using Derjaguin-Landau-Verwey-Overbeek (DLVO) 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 SiO 2 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.

European Cells & Materials, Sep 1, 2005

Understanding the mechanisms of snow adhesion to surfaces and its subsequent shedding provides me... more Understanding the mechanisms of snow adhesion to surfaces and its subsequent shedding provides means to search for active and passive methods to mitigate the issues caused by snow accumulation on surfaces. Here, a novel setup is presented to measure the adhesion strength of snow to various surfaces without altering its properties (i.e., liquid water content (LWC) and/or density) during the measurements and to study snow shedding mechanisms. In this setup, a sensor is utilized to ensure constant temperature and liquid water content of snow on test substrates, unlike inclined or centrifugal snow adhesion testing. A snow gun consisting of an internal mixing chamber and ball valves for adjusting air and water flow is designed to form snow with controlled LWC inside a walk-in freezing room with controlled temperatures. We report that snow adheres to surfaces strongly when the LWC is around 20%. We also show that on smooth (i.e., RMS roughness of less than 7.17 µm) and very rough (i.e., RMS roughness of greater than 308.33 µm) surfaces, snow experiences minimal contact with the surface, resulting in low adhesion strength of snow. At the intermediate surface roughness (i.e., RMS of 50 µm with a surface temperature of 0 • C, the contact area between the snow and the surface increases, leading to increased adhesion strength of snow to the substrate. It is also found that an increase in the polar surface energy significantly increases the adhesion strength of wet snow while adhesion strength decreases with an increase in dispersive surface energy. Finally, we show that during shedding, snow experiences complete sliding, compression, or a combination of the two behaviors depending on surface temperature and LWC of the snow. The results of this study suggest pathways for designing surfaces that might reduce snow adhesion strength and facilitate its shedding.