Oligoelectrolyte-mediated, pH-triggered release of hydrophobic drugs from non-responsive micelles: Influence of oligo(2-vinyl pyridine)-loading on drug-loading, release and cytotoxicity.

pH-responsive polymeric micelles have been extensively studied for nanomedicine and take advantage of pH differentials in tissues for the delivery of large doses of cytotoxic drugs at specific target sites. Despite significant advances in this area, there is a lack of versatile and adaptable strategies to render micelles pH-responsive that could be widely applied to different payloads and applications. To address this deficiency, we introduce the concept of oligoelectrolyte-mediated, pH-triggered release of hydrophobic drugs from non-responsive polymeric micelles as a highly effective approach with broad scope. Herein, we investigate the influence of the oligoelectrolyte, oligo(2-vinyl pyridine) (OVP), loading and polymer molecular weight on the pH-sensitivity, drug loading/release and cytotoxicity of poly(ethylene glycol-b-ε-caprolactone) (PEG-b-PCL) micelles using copolymers with either short or long hydrophobic blocks (PEG4PCL4 and PEG10PCL10, respectively). The micelles were characterized as a function of pH (7.4 to 3.5). Dynamic light scattering (DLS) revealed narrow particle size distributions (PSDs) for both the blank and OVP-loaded micelles at pH 7.4. While OVP encapsulation resulted in an increase in the hydrodynamic diameter (Dh) (cf. blank micelles), a decrease in the pH below 6.5 led to a decrease in the Dh consistent with the ionization and release of OVP and core collapse, which were further supported by proton nuclear magnetic resonance (1H NMR) spectroscopy and UV-visible (UV-vis) spectrophotometry. The change in zeta potential (ζ) with pH for the OVP-loaded PEG4PCL4 and PEG10PCL10 micelles was different, suggesting that the location/distribution of OVP in the micelles is influenced by the polymer molecular weight. In general, co-encapsulation of drugs (doxorubicin (DOX), gossypol (GP), paclitaxel (PX) or 7-ethyl-10-hydroxycamptothecin (SN38)) and OVP in the micelles proceeded efficiently with high encapsulation efficiency percentages (EE%). In vitro release studies revealed the rapid, pH-triggered release of drugs from OVP-loaded PEG10PCL10 micelles within hours, with higher OVP loadings providing faster and more complete release. In comparison, no triggered release was observed for the OVP-loaded PEG4PCL4 micelles, implying a strong molecular weight dependency. In metabolic assays the drug- and OVP-loaded PEG10PCL10 micelles were found to result in significant enhancement of the cytotoxicity compared to drug-loaded micelles (no OVP) or other controls. Importantly, micelles with low OVP loadings were found to be nearly as effective as those with high OVP loadings. These results provide key insights into the tunability of the oligoelectrolyte-mediated approach for the effective formulation of pH-responsive micelles and pH-triggered drug release.

Increasing surface hydrophilicity with biopolymers: a combined single bubble collision, QCM-D and AFM study.

HYPOTHESIS: Naturally extracted polysaccharides, such as guar gum, are promising candidates for environmentally friendly flotation reagents. It is hypothesized that the kinetics of collision of sub- to millimeter gas bubbles with a hydrophobic graphite surface, and the stability of thin liquid film formed between the bubble and surface is affected by an adsorbed layer of guar gum. EXPERIMENTS: A combination of gravimetric (quartz crystal microbalance with dissipation) and imaging (atomic force microscopy) techniques was used to investigate the adsorption of guar gum on graphite surface, while high-speed camera imaging allowed for direct observation of the bubble collision process with guar gum-modified graphite surfaces with millisecond resolution. FINDINGS: Atomic force microscope topography images revealed a guar gum concentration-dependent interconnected network of guar gum molecules adsorbed at graphite surface. These adsorbed molecules at low surface coverage, changed the wettability of the graphite surface, resulting in a film drainage time longer by an order of magnitude, while at higher surface coverage successfully prevented bubble attachment to the graphite surface. Most importantly, the adsorbed layer changed the strength of the bubble's bouncing off the graphite surface. This enhanced bubble bouncing can be correlated with the film drainage time and used to predict a successful bubble-particle attachment.

Recent advances in studying crystallisation of mono- and di-glycerides at oil-water interfaces.

This review focuses on the current understanding regarding lipid crystallisation at oil-water interfaces. The main aspects of crystallisation in bulk lipids will be introduced, allowing for a more comprehensive overview of the crystallisation processes within emulsions. Additionally, the properties of an emulsion and the impact of lipid crystallisation on emulsion stability will be discussed. The effect of different emulsifiers on lipid crystallisation at oil-water interfaces will also be reviewed, however, this will be limited to their impact on the interfacial crystallisation of monoglycerides and diglycerides. The final part of the review highlights the recent methodologies used to study crystallisation at oil-water interfaces.

Teaching an Old Dog New Tricks: A Global Approach to Enhancing the Cytotoxicity of Drug-Loaded, Non-responsive Micelles Using Oligoelectrolytes.

Polymeric micelles have been extensively studied as vectors for the delivery of hydrophobic drugs for the treatment of cancers and other diseases. Despite intensive research, few formulations provide significant benefits, and even fewer have been clinically approved. While many traditional non-responsive micelles have excellent safety profiles, they lack the ability to respond to the intracellular environment and release their cargo in a spatiotemporally defined manner to effectively deliver large doses of cytotoxic drugs into the cytosol of cells that overwhelm efflux pumps. As a novel and adaptable strategy, we hypothesized that well-established non-responsive polymeric micelles could be augmented with a pH-trigger via the co-encapsulation of cytocompatible oligoelectrolytes, which would allow rapid cargo release in the endosome, leading to increased cytotoxicity. Herein, we demonstrate how this strategy can be applied to render non-responsive micelles pH-responsive, resulting in abrupt cargo release at specific and tunable pH values compatible with endosomal delivery, which significantly increased their cytotoxicity up to 3-fold in an ovarian adenocarcinoma (SKOV-3) cell line compared to non-responsive micelles. In comparison, the oligoelectrolyte-loaded micelles were significantly less toxic to healthy 3T3 fibroblasts, indicating a selective cargo release in cancer cell lines. Oligoelectrolytes can be co-encapsulated in the micelles along with drugs at high encapsulation efficiency percentages, which are both ejected from the micelle core upon oligoelectrolyte ionization. Mechanistically, the increase in cytotoxicity appears to also result from the accelerated endosomal escape of the cargo caused by disruption of the endosomal membrane by the simultaneous release of the oligoelectrolytes from the micelles. Furthermore, we show how this approach is broadly applicable to non-responsive micelles regardless of their composition and various classes of hydrophobic chemotherapeutics. The preliminary studies presented here reveal the versatility and wide scope of oligoelectrolyte-mediated, pH-triggered drug release as a compelling and powerful strategy to enhance the cytotoxicity of non-responsive polymeric micelles.

Influence of Lyophilization and Cryoprotection on the Stability and Morphology of Drug-Loaded Poly(ethylene glycol-b-ε-caprolactone) Micelles.

Polymeric micelles are promising carriers for the delivery of poorly water-soluble drugs, providing enhanced drug solubility, blood circulation times, and bioavailability. Nevertheless, the storage and long-term stability of micelles in solution present challenges requiring the lyophilization and storage of formulations in the solid state, with reconstitution immediately prior to application. Therefore, it is important to understand the effects of lyophilization/reconstitution on micelles, particularly their drug-loaded counterparts. Herein, we investigated the use of ß-cyclodextrin (ß-CD) as a cryoprotectant for the lyophilization/reconstitution of a library of poly(ethylene glycol-b-ε-caprolactone) (PEG-b-PCL) copolymer micelles and their drug-loaded counterparts, as well as the effect of the physiochemical properties of different drugs (phloretin and gossypol). The critical aggregation concentration (CAC) of the copolymers decreased with increasing weight fraction of the PCL block (fPCL), plateauing at ~1 mg/L when the fPCL was >0.45. The blank (empty) and drug-loaded micelles were lyophilized/reconstituted in the absence and presence of ß-CD (9% w/w) and analyzed via dynamic light scattering (DLS) and synchrotron small-angle X-ray scattering (SAXS) to assess for changes in aggregate size (hydrodynamic diameter, Dh) and morphology, respectively. Regardless of the PEG-b-PCL copolymer or the use of ß-CD, the blank micelles displayed poor redispersibility (<10% relative to the initial concentration), while the fraction that redispersed displayed similar Dh to the as-prepared micelles, increasing in Dh as the fPCL of the PEG-b-PCL copolymer increased. While most blank micelles displayed discrete morphologies, the addition of ß-CD or lyophilization/reconstitution generally resulted in the formation of poorly defined aggregates. Similar results were also obtained for drug-loaded micelles, with the exception of several that retained their primary morphology following lyophilization/reconstitution, although no obvious trends were noted between the microstructure of the copolymers or the physicochemical properties of the drugs and their successful redispersion.

Isolating the interface of an emulsion using X-ray scattering and tensiometry to understand protein-modulated alkylglyceride crystallisation.

HYPOTHESIS: Dairy proteins and mono- and diglycerides (MDG) are often used in unison to tailor the properties of dairy-based emulsions. However, there are significant gaps in our understanding of how proteins affect lipid crystallisation at the oil-water interface. We have used a unique combination of interfacially-sensitive techniques to elucidate the impact of dairy proteins on interfacial MDG crystal formation. EXPERIMENTS: The formation temperature of interfacial MDG crystals was assessed through interfacial tension studies via drop shape analysis. Small and Wide-Angle X-ray Scattering measurements were performed on isolated oil-water interfaces, allowing for in-situ interrogation of MDG crystal structure and concentration at and near the interface. FINDINGS: Dairy proteins are seen to reduce the temperature at which MDG crystals form at the oil-water interface. The displacement of proteins upon interfacial crystal formation was also clearly observed in interfacial tension measurements. For the first time, lipid crystals formed at the oil-water interface have been characterised using X-ray scattering. All scattering studies showed no change to the MDG crystal structures at the oil-water interface in the presence of adsorbed proteins. The results demonstrate that informed selection of emulsifier components is critical to controlling interfacial crystallisation with concomitant impact on emulsion stability.

Microstructure-Thermal Property Relationships of Poly (Ethylene Glycol-b-Caprolactone) Copolymers and Their Micelles.

The crystallinity of polymers strongly affects their properties. For block copolymers, whereby two crystallisable blocks are covalently tethered to one another, the molecular weight of the individual blocks and their relative weight fraction are important structural parameters that control their crystallisation. In the case of block copolymer micelles, these parameters can influence the crystallinity of the core, which has implications for drug encapsulation and release. Therefore, in this study, we aimed to determine how the microstructure of poly(ethylene glycol-b-caprolactone) (PEG-b-PCL) copolymers contributes to the crystallinity of their hydrophobic PCL micelle cores. Using a library of PEG-b-PCL copolymers with PEG number-average molecular weight (Mn) values of 2, 5, and 10 kDa and weight fractions of PCL (fPCL) ranging from 0.11 to 0.67, the thermal behaviour and morphology were studied in blends, bulk, and micelles using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WXRD), and Synchrotron wide-angle X-ray scattering (WAXS). Compared to PEG and PCL homopolymers, the block copolymers displayed reduced crystallinity in the bulk phase and the individual blocks had a large influence on the crystallisation of one another. The fPCL was determined to be the dominant contributor to the extent and order of crystallisation of the two blocks. When fPCL < 0.35, the initial crystallisation of PEG led to an amorphous PCL phase. At fPCL values between 0.35 and 0.65, PEG crystallisation was followed by PCL crystallisation, whereas this behaviour was reversed when fPCL > 0.65. For lyophilised PEG-b-PCL micelles, the crystallinity of the core increased with increasing fPCL, although the core was predominately amorphous for micelles with fPCL < 0.35. These findings contribute to understanding the relationships between copolymer microstructure and micelle core crystallinity that are important for the design and performance of micellar drug delivery systems, and the broader application of polymer micelles.

Injectable Diels-Alder cycloaddition hydrogels with tuneable gelation, stiffness and degradation for the sustained release of T-lymphocytes.

Engineered T-cell therapies have proven highly efficacious for the treatment of haematological cancers, but translation of this success to solid tumours has been limited, in part, due to difficulties in maintaining high doses at specific target sites. Hydrogel delivery systems that provide a sustained release of T-cells at the target site are emerging as a promising strategy. Therefore, in this study we aimed to develop an injectable hydrogel that gels in situ via efficient Diels-Alder cycloaddition (DAC) chemistry and provides a sustained release of T-cells through gradual hydrolysis of the hydrogel matrix. Hydrogels were prepared via the DAC between fulvene and maleimide functionalised poly(ethylene glycol) (PEG) derivatives. By adjusting the concentration and molecular weight of the functionalised PEGs in the hydrogel formulation the in vitro gelation time (Tgel), initial Young's modulus (E) and degradation time (Td) could be tailored from 15-150 min, 5-179 kPa and 7-114 h, respectively. Prior to gelation, the formulations could be readily injected through narrow gauge (26 G) needles with the working time correlating closely with the Tgel. A 5 wt% hydrogel formation with conjugated cyclic RGD motif was found to be optimal for the encapsulation and release of CD3+ T-cells with a near linear release profile and >70% cell viability over the first 4 d and release continuing out to 7 d. With their tuneable Tgel, Td and stiffness, the DAC hydrogels provide the opportunity to control the release period and profile of encapsulated cells.

Long-term adherence of human brain cells in vitro is enhanced by charged amine-based plasma polymer coatings.

Advances in cellular reprogramming have radically increased the use of patient-derived cells for neurological research in vitro. However, adherence of human neurons on tissue cultureware is unreliable over the extended periods required for electrophysiological maturation. Adherence issues are particularly prominent for transferable glass coverslips, hindering imaging and electrophysiological assays. Here, we assessed thin-film plasma polymer treatments, polymeric factors, and extracellular matrix coatings for extending the adherence of human neuronal cultures on glass. We find that positive-charged, amine-based plasma polymers improve the adherence of a range of human brain cells. Diaminopropane (DAP) treatment with laminin-based coating optimally supports long-term maturation of fundamental ion channel properties and synaptic activity of human neurons. As proof of concept, we demonstrated that DAP-treated glass is ideal for live imaging, patch-clamping, and optogenetics. A DAP-treated glass surface reduces the technical variability of human neuronal models and enhances electrophysiological maturation, allowing more reliable discoveries of treatments for neurological and psychiatric disorders.

Interrogating the relationship between the microstructure of amphiphilic poly(ethylene glycol-b-caprolactone) copolymers and their colloidal assemblies using non-interfering techniques.

Understanding the microstructural parameters of amphiphilic copolymers that control the formation and structure of aggregated colloids (e.g., micelles) is essential for the rational design of hierarchically structured systems for applications in nanomedicine, personal care and food formulations. Although many analytical techniques have been employed to study such systems, in this investigation we adopted an integrated approach using non-interfering techniques - diffusion nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS) and synchrotron small-angle X-ray scattering (SAXS) - to probe the relationship between the microstructure of poly(ethylene glycol-b-caprolactone) (PEG-b-PCL) copolymers [e.g., block molecular weight (MW) and the mass fraction of PCL (fPCL)] and the structure of their aggregates. Systematic trends in the self-assembly behaviour were determined using a large family of well-defined block copolymers with variable PEG and PCL block lengths (number-average molecular weights (Mn) between 2 and 10 and 0.5-15 kDa, respectively) and narrow dispersity (Ð < 1.12). For all of the copolymers, a clear transition in the aggregate structure was observed when the hydrophobic fPCL was increased at a constant PEG block Mn, although the nature of this transition is also dependent on the PEG block Mn. Copolymers with low Mn PEG blocks (2 kDa) were observed to transition from unimers and loosely associated unimers to metastable aggregates and finally, to cylindrical micelles as the fPCL was increased. In comparison, copolymers with PEG block Mn of between 5 and 10 kDa transitioned from heterogenous metastable aggregates to cylindrical micelles and finally, well-defined ellipsoidal micelles (of decreasing aspect ratios) as the fPCL was increased. In all cases, the diffusion NMR spectroscopy, DLS and synchrotron SAXS results provided complementary information and the grounds for a phase diagram relating copolymer microstructure to aggregation behaviour and structure. Importantly, the absence of commonly depicted spherical micelles has implications for applications where properties may be governed by shape, such as, cellular uptake of nanomedicine formulations.

The effect of emulsifier type on the secondary crystallisation of monoacylglycerol and triacylglycerols in model dairy emulsions.

Dairy emulsions contain an intrinsically heterogeneous lipid phase, whose components undergo crystallisation in a manner that is critical to dairy product formulation, storage, and sensory perception. Further complexity is engendered by the diverse array of interfacially-active molecules naturally present within the serum of dairy systems, and those that are added for specific formulation purposes, all of which interact at the lipid-serum interface and modify the impact of lipid crystals on dairy emulsion stability. The work described in this article addresses this complexity, with a specific focus on the impact of temperature cycling and the effect of emulsifier type on the formation and persistence of lipid crystals at lipid-solution interfaces. Profile analysis tensiometry experiments were performed using single droplets of the low melting fraction of dairy lipids, in the presence and absence of emulsifiers (Tween 80 and whey protein isolate, WPI) and during the temperature cycling, to study the formation of monoacylglycerol (MAG) crystals at the lipid-solution interface. Companion experiments on the same lipid systems, and at the same cooling and heating rates, were undertaken with synchrotron small angle X-ray scattering, to specifically analyse the effect of emulsifier type on the formation of triacylglycerol (TAG) crystals at the lipid-solution interface of a model dairy emulsion. These two complementary techniques have revealed that Tween 80 molecules delay MAG and TAG crystal formation by lowering the temperature at which the crystallisation occurs during two cooling cycles. WPI molecules delay the crystallisation of MAGs and TAGs during the first cooling cycle, while MAG crystals form without delay during the second cooling cycle at the same temperature as MAG crystals in an emulsifier free system. The crystallisation of TAGs is inhibited during the second cooling cycle. The observed differences in crystallisation behaviour at the interface upon temperature cycling can provide further insight into the impact of emulsifiers on the long-term stability of emulsion-based dairy systems during storage.

Can small air bubbles probe very low frother concentration faster?

The existing literature on the rise velocities of air bubbles in aqueous surfactant solutions adsorbing at the water-air interface focuses mainly on large bubbles (D > 1.2 mm). In addition, due to the way the bubbles in rising bubble experiments are formed, their size is dependent on interfacial tension (the lower the interfacial tension the smaller the bubble). In this paper, smaller air bubbles (D < 505 ± 3 µm) are used to investigate the effect of the bubble size on the detection of two flotation frothers of different adsorption kinetics via bubble rise velocity measurements. We use an alternative method for bubble generation, allowing us to compare the rise velocity of bubbles of the same size in solutions of frothers of varying bulk concentration. The approach taken (ensuring consistent bubble size) ascertains that the buoyancy force component is kept constant when comparing the different solutions. As a consequence, any variations in the bubble rise velocity can be related to changes in the hydrodynamic drag force acting on a rising bubble. The interfacial behavior of frothers, i.e. the adsorption kinetics, interfacial activity and the maximum amount of molecules adsorbed at the interface, are determined from interfacial tension measurements and adsorption isotherms. The differences in the degree of tangential immobilisation caused by two different frothers are discussed in the context of differences in the structure of the dynamic adsorption layer, which is formed during the bubble rise.

Incorporation and antimicrobial activity of nisin Z within carrageenan/chitosan multilayers.

An antimicrobial peptide, nisin Z, was embedded within polyelectrolyte multilayers (PEMs) composed of natural polysaccharides in order to explore the potential of forming a multilayer with antimicrobial properties. Using attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR), the formation of carrageenan/chitosan multilayers and the inclusion of nisin Z in two different configurations was investigated. Approximately 0.89 µg cm-2 nisin Z was contained within a 4.5 bilayer film. The antimicrobial properties of these films were also investigated. The peptide containing films were able to kill over 90% and 99% of planktonic and biofilm cells, respectively, against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) strains compared to control films. Additionally, surface topography and wettability studies using atomic force microscopy (AFM) and the captive bubble technique revealed that surface roughness and hydrophobicity was similar for both nisin containing multilayers. This suggests that the antimicrobial efficacy of the peptide is unaffected by its location within the multilayer. Overall, these results demonstrate the potential to embed and protect natural antimicrobials within a multilayer to create functionalised coatings that may be desired by industry, such as in the food, biomaterials, and pharmaceutical industry sectors.

Influence of Aqueous Phase Composition on Double Emulsion Stability and Colour Retention of Encapsulated Anthocyanins.

Water-in-oil-in-water (W1/O/W2) emulsions (double emulsions) have often been used for the encapsulation of bioactive compounds such as anthocyanins. Instability of both anthocyanins and double emulsions creates a need for a tailored composition of the aqueous phase. In this work, double emulsions with a gelled internal water phase were produced and monitored over a 20-day storage period. The effect of the electrolyte phase composition (varying electrolyte components, including adipic acid, citric acid, and varying concentration of potassium chloride (KCl)) on anthocyanin and double emulsion stability was analysed using colour analysis, droplet sizing, and emulsion rheology. The effect of electrolytes on colour retention was shown to differ between the primary W1/O emulsion and the secondary W1/O/W2 emulsion. Furthermore, droplet size analysis and emulsion rheology highlighted significant differences in the stability and structural behaviour of the emulsions as a function of electrolyte composition. In terms of colour retention and emulsion stability, a citrate-buffered system performed best. The results of this study highlight the importance of strict control of aqueous phase constituents to prevent anthocyanin degradation and maximise double emulsion stability. Additional experiments analysed the effect of pectin chemistry on the anthocyanin colour retention and leakage, finding no conclusive difference between the unmodified and amidated pectin.

Incorporation of FGF-2 into Pharmaceutical Grade Fucoidan/Chitosan Polyelectrolyte Multilayers.

Biopolymer polyelectrolyte multilayers are a commonly studied soft matter system for wound healing applications due to the biocompatibility and beneficial properties of naturally occurring polyelectrolytes. In this work, a popular biopolymer, chitosan, was combined with the lesser known polysaccharide, fucoidan, to create a multilayer film capable of sequestering growth factor for later release. Fucoidan has been shown to act as a heparin-mimic due to similarities in the structure of the two molecules, however, the binding of fibroblast growth factor-2 to fucoidan has not been demonstrated in a multilayer system. This study assesses the ability of fucoidan to bind fibroblast growth factor-2 within a fucoidan/chitosan polyelectrolyte multilayer structure using attenuated total internal reflectance infrared spectroscopy and quartz crystal microbalance with dissipation monitoring. The fibroblast growth factor-2 was sequestered into the polyelectrolyte multilayer as a cationic layer in the uppermost layers of the film structure. In addition, the diffusion of fibroblast growth factor-2 into the multilayer has been assessed.

Lysozyme uptake into pharmaceutical grade fucoidan/chitosan polyelectrolyte multilayers under physiological conditions.

Polyelectrolyte multilayers composed of pharmaceutical grade fucoidan and chitosan have been assembled and studied in terms of their response to physiological solution conditions and the presence of lysozyme. The influence of phosphate buffered saline (PBS) solution on the multilayer was interrogated using attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). The combination of the techniques reveal that the polyelectrolyte multilayers swell when exposed to PBS after build-up and may include a small degree of mass loss as the film swells. The degree of swelling was influenced by the terminating layer of the multilayer. Upon exposure to lysozyme, it was observed that some deswelling occurred, as the enzyme adsorbed onto and permeated into the multilayer. The behaviour of the multilayer as a potential reservoir for lysozyme contrasts with the interaction with bovine serum albumin, which did not penetrate into the multilayer, indicating either exclusion by size or due to the overall net negative charge of the film.

Adsorption of Carboxymethyl Cellulose onto Titania Particle Films Studied with in Situ IR Spectroscopic Analysis.

Adsorption of carboxymethyl cellulose (CMC) in aqueous solution onto a titania nanoparticle film has been studied using in situ attenuated total reflectance infrared spectroscopy (ATR-IR). CMC was adsorbed onto the positively charged titania surface in neutral, partially charged, and fully charged state. The response of the adsorbed polyelectrolyte layer was monitored upon changing the electrolyte pH and ionic strength. The degree of dissociation of the CMC increased upon adsorption onto the titania surface and changed with the surface coverage. Ionic strength change was observed to influence the degree of dissociation of the adsorbed CMC similar as when in solution. No significant peak shifts were observed in the spectrum of the adsorbed CMC during adsorption or in response to changing solution conditions; therefore, inner-sphere complexation between the carboxyl groups and the titania could not be confirmed. The effect of ion identity on the adsorption process was studied using soft and hard cations and mono- and divalent cations. The presence of a divalent counterion was observed to cause changes in the carboxymethyl vibrations, which can be related to formation of intra- or interchain linkages.

Odd-even effects on hydration of natural polyelectrolyte multilayers: An in situ synchrotron FTIR microspectroscopy study.

HYPOTHESIS: Odd-even effects in polysaccharide polyelectrolyte multilayers influence their hydration content and the chemical environment of the water within them. EXPERIMENTS: Polysaccharide polyelectrolyte multilayers (PEMs) composed of pharmaceutical grade fucoidan and chitosan were studied under confinement using synchrotron FTIR microspectroscopy at increasing pressure, in order to isolate and measure infrared spectra of water within the PEM, without interference from bulk water. Complementary studies of the PEMs were carried out using lab-based in situ attenuated total reflectance Fourier transform spectroscopy (ATR FTIR) and quartz crystal microbalance with dissipation monitoring (QCM-D), as well as zeta potential measurements, to determine the quantity of adsorbed polymer, hydration content, film thickness, viscoelastic properties and surface charge during layer-by-layer deposition. FINDINGS: The hydration of the PEM followed a saw-tooth profile, known as the odd-even effect, where the film increased hydration with fucoidan adsorption and dehydrated/densified with chitosan adsorption. The water structure within the film showed a lower degree of hydrogen bonding than water in the bulk electrolyte. However, the water structure/environment was independent of the terminating layer of the PEM, in spite of the alteration in percentage hydration water, indicating only a partial proof of the initial hypothesis for this multilayer system (hydration amount changes, hydration water environment does not).

Antibiofilm Nitric Oxide-Releasing Polydopamine Coatings.

The growing number of patient morbidity related to nosocomial infections has placed an importance on the development of new antibacterial coatings for medical devices. Here, we utilize the versatile adhesion property of polydopamine (pDA) to design an antibacterial coating that possesses low-fouling and nitric oxide (NO)-releasing capabilities. To demonstrate this, glass substrates were functionalized with pDA via immersion in alkaline aqueous solution containing dopamine, followed by grafting of low-fouling polymer (poly(ethylene glycol) (PEG)) via Michael addition and subsequent formation of N-diazeniumdiolate functionalities (NO precursors) by purging with NO gas. X-ray photoelectron spectroscopy confirmed the successful grafting of PEG and formation of N-diazeniumdiolate on polydopamine-coated substrates. NO release from the coating was observed over 2 days, and NO loading is tunable by the pDA film thickness. The antibacterial efficiency of the coatings was assessed using Gram-negative Pseudomonas aeruginosa (i.e., wild-type PAO1 and multidrug-resistant PA37) and Gram-positive Staphylococcus aureus (ATCC 29213). The NO-releasing PEGylated pDA film inhibited biofilm attachment by 96 and 70% after exposure to bacterial culture solution for 24 and 36 h, respectively. In contrast, films that do not contain NO failed to prevent biofilm formation on the surfaces at these time points. Furthermore, this coating also showed 99.9, 97, and 99% killing efficiencies against surface-attached PAO1, PA37, and S. aureus bacteria. Overall, the combination of low-fouling PEG and antibacterial activity of NO in pDA films makes this coating a potential therapeutic option to inhibit biofilm formation on medical devices.

The influence of pH on the interfacial behaviour of Quillaja bark saponin at the air-solution interface.

The interfacial behavior of surfactants present in a natural extract from Quillaja saponaria Molina bark at the air-solution interface is studied by measurements of interfacial tension, interfacial elasticity, and interfacial reflectance FTIR spectroscopy. The active molecule, saponin, is observed directly at the air-solution interface (via reflectance FTIR spectroscopy) above and below the pKa of the molecule, and spectra confirm the altered charge of the interfacial layer at the two solution conditions. For all concentrations of saponin studied, and at pH values below and above pKa (i.e. pH 3 and 7), a reduction in interfacial tension as a function of time is observed, with some differences in early time-scale adsorption and with lower values of quasi-equilibrium interfacial tension for pH 3. The interfacial layer is seen to be elastic, as determined from measurements of hydrostatic expansion, with some variation at the two pH values, and as a function of concentration. In addition to interfacial layer characterisation, the interaction between two air-solution interfaces is probed using bubble collisions with an air-solution interface. This experiment allows for observation of thin film drainage kinetics and determination of the final foam film thickness for the case when one of the interfaces is at equilibrium while the dynamic adsorption layer is being established at the other. This is the first time when the interactions between such interfaces (i.e. only one being at equilibrium) have been studied. This is of particular importance for the formation stage of foams, during which time many of the interfaces are not at equilibrium. When two interfaces interact across a thin liquid film, pH is seen to significantly influence foam film thickness.