Adsorption and viscoelastic properties of fractionated mucin (BSM) and bovine serum albumin (BSA) studied with quartz crystal microbalance (QCM-D)

Thermal Enhanced Electrokinetic Bacterial Transport in Porous Media

Soil bacterial communities are crucial to various ecosystem services, with significant implications for environmental processes and human health. Delivering functional bacterial strains to target locations enhances the preferred ecological features. However, the delivery process is often constrained by limited bacterial transport through low-permeability soil. Although electrokinetics breaks the bottleneck of bacterial transport in thin porous media, its efficiency remains limited. Here, we tested the hypothesis that thermal effects enhance electrokinetic transport by shifting the net force acting on the bacterium. We found that heating significantly increased electrokinetic transport by 2.75-fold at 1 V cm-1 through porous media. Thermal enhancement mechanisms were interpreted by the heating shift of net force integrating matrix attractive and electrokinetic forces and verified by the Quartz Crystal Microbalance with Dissipation Monitoring (QCMD) observed adhesion rigidity shift. Thermal-dependent parameters liquid viscosity and dielectric constant were the primary contributors to the net force shift. Their variations reduce the attractive force and augment the electrokinetic forces, resulting in lower adhesion rigidity and enhanced bacterial transport. A mechanism-based approach interlinking electric field strength, thermal effect, and collision efficiency was established to facilitate the application of thermally enhanced electrokinetic bacterial transport. These findings provide new prospects for improving bacterial transport, hence optimizing soil ecosystem functions.

Mucoadhesion across scales: Towards the design of protein-based adhesives

Mucoadhesion is a special case of bioadhesion in which a material adheres to soft mucosal tissues. This review elucidates our current understanding of mucoadhesion across length, time, and energy scales by focusing on relevant structural features of mucus. We highlight the importance of both covalent and non-covalent interactions that can be tailored to maximize mucoadhesive interactions, particularly concerning proteinaceous mucoadhesives, which have been explored only to a limited extent so far in the literature. In particular, we highlight the importance of thiol groups, hydrophobic moieties, and charged species inherent to proteins as key levers to fine tune mucoadhesive performance. Some aspects of protein surface modification by grafting specific functional groups or coupling with polysaccharides to influence mucoadhesive performance are examined. Insights from this review offer a physicochemical roadmap to inform the development of biocompatible, protein-based mucoadhesive systems that can fulfil dual roles for both adhesion and delivery of actives, enabling the fabrication of advanced biomedical, nutritional and allied soft material technologies.

Layer-by-Layer Deposition of Kraft Lignin and PEDOT:PSS

Kraft lignin (KL) is a sustainable carbon-based substance with a potential use in photovoltaic materials. However, its conductivity is low, but it can be improved via incorporation with a conductive polymer, such as poly(3,4-ethylene dioxythiophene) (PEDOT): poly(styrenesulfonate) (PSS). This study examines the factors affecting the interaction of KL and PEDOT:PSS (PS) in a solution state using a quartz crystal microbalance with dissipation (QCM-D) and a stagnation point refractometer (SPAR). The results confirmed that aqueous environments, e.g., pH and ionic strengths, considerably affected particle size and zeta potential of KL and PS due to protonation, deprotonation, particle aggregation, and charge screening. The polymers exhibited the largest adsorbed mass and thickness at pH 6 and 10 mM NaCl on a solid surface, which was attributed to the relatively linear structure of PEDOT chains, exposing more adsorptive sites for interaction with KL. A 10 mM NaCl concentration facilitated the screening of charges on PS and KL surfaces, diminishing repulsive forces and enabling hydrophobic and cationic-π interaction, which led to increased adsorption. Contact angle and SEM investigations of the adsorbed layer revealed the water contact angle increasing and the morphology changing from a smoother layer to a porous surface, providing further evidence of adsorption. Furthermore, the conductivity was improved by the introduction of a PS adlayer on ITO glass when it was sandwiched between KL adsorbed layers. These findings provide insight into KL and PS interaction and suggest that KL can be used with PS for conductive materials, such as photovoltaics, imparting the waterproofness of the films.

A head-to-head comparison of polymer interaction with mucin from porcine stomach and bovine submaxillary glands

Native mucus is heterogeneous, displays high inter-individual variation and is prone to changes during harvesting and storage. To overcome the lack of reproducibility and availability of native mucus, commercially available purified mucins, porcine gastric mucin (PGM) and mucin from bovine submaxillary gland (BSM), have been widely used. However, the question is to which extent the choice of mucin matters in studies of their interaction with polymers as their composition, structure and hence physicochemical properties differ. Accordingly, the interactions between PGM or BSM with two widely used polymers in drug delivery, polyethylene oxide and chitosan, was studied with orthogonal methods: turbidity, dynamic light scattering, and quartz crystal microbalance with dissipation monitoring. Polymer binding and adsorption to the two commercially available and purified mucins, PGM and BSM, is different depending on the mucin type. PEO, known to interact weakly with mucin, only displayed limited interaction with both mucins as confirmed by all employed methods. In contrast, chitosan was able to bind to both PGM and BSM. Interestingly, the results suggest that chitosan interacts with BSM to a greater extent than with PGM indicating that the choice of mucin, PGM or BSM, can affect the outcome of studies of mucin interactions with polymers.

Comprehensive Characterization of the Viscoelastic Properties of Bovine Submaxillary Mucin (BSM) Hydrogels and the Effect of Additives

This study presents a comprehensive characterization of the viscoelastic and structural properties of bovine submaxillary mucin (BSM), which is widely used as a commercial source to conduct mucus-related research. We conducted concentration studies of BSM and examined the effects of various additives, NaCl, CaCl2, MgCl2, lysozyme, and DNA, on its rheological behavior. A notable connection between BSM concentration and viscoelastic properties was observed, particularly under varying ionic conditions. The rheological spectra could be well described by a fractional Kelvin-Voigt model with a minimum of model parameters. A detailed proteomics analysis provided insight into the protein, especially mucin composition within BSM, showing MUC19 as the main component. Cryo-scanning electron microscopy enabled the visualization of the porous BSM network structure. These investigations give us a more profound comprehension of the BSM properties, especially those pertaining to viscoelasticity, and how they are influenced by concentration and environmental conditions, aspects relevant to the field of mucus research.

Alternative strategies for the recombinant synthesis, DOPA modification and analysis of mussel foot proteins - A case study for Mefp-3 from Mytilus edulis

Mussel foot proteins (Mfps) possess unique binding properties to various surfaces due to the presence of L-3,4-dihydroxyphenylalanine (DOPA). Mytilus edulis foot protein-3 (Mefp-3) is one of several proteins in the byssal adhesive plaque. Its localization at the plaque-substrate interface approved that Mefp-3 plays a key role in adhesion. Therefore, the protein is suitable for the development of innovative bio-based binders. However, recombinant Mfp-3s are mainly purified from inclusion bodies under denaturing conditions. Here, we describe a robust and reproducible protocol for obtaining soluble and tag-free Mefp-3 using the SUMO-fusion technology. Additionally, a microbial tyrosinase from Verrucomicrobium spinosum was used for the in vitro hydroxylation of peptide-bound tyrosines in Mefp-3 for the first time. The highly hydroxylated Mefp-3, confirmed by MALDI-TOF-MS, exhibited excellent adhesive properties comparable to a commercial glue. These results demonstrate a concerted and simplified high yield production process for recombinant soluble and tag-free Mfp3-based proteins with on demand DOPA modification.

In situ acid production by organic matter induced with trace homogeneous Fenton reagent for membrane fouling control

The homogeneous Fenton process involves both coagulation and oxidation, but it requires added acidity, so it is rarely used to control membrane fouling. This work found that the pH of neutral simulated wastewater sharply declined to 4.1 after pre-treatment with 0.1 mM Fenton reagent (Fe2+:H2O2=1:1) without added acidity. This occurred mainly because the trace homogeneous Fenton reagent induced in situ acid production by organic matter in the wastewater, which supplied the acidic conditions required for the Fenton reaction and ensured that the reaction could proceed continuously. Then, oxidation during the pre-Fenton process enhanced the electrostatic repulsion forces and effectively weakened the hydrogen bonds of organic matter at the membrane surface by altering the net charge and hydroxyl content of organic matter, while coagulation caused the foulants to gather and form large aggregates. These changes diminished the deposition of foulants onto the membrane surface and resulted in a looser fouling layer, which eventually caused the membrane fouling rate to decline from 83 % to 24 % and the flux recovery rate to increase from 44 % to 98 % during 2 h of filtration. This membrane fouling mitigation ability is much superior to that of pre-H2O2, pre-Fe2+ or pre-Fe3+ processes with equivalent doses.

Investigation of the mucin-nanoparticle interactions via real-time monitoring by microbalance and kinetic model simulation

Interactions between nanoparticles and the mucus layer are crucial to understand the behaviours in biological environments and design drug delivery systems. In this study, we developed a kinetic deposition model for the dynamic mucin-nanoparticle interactions using quartz crystal microbalance with dissipation (QCM-D). We investigated the effects of the physiochemical properties of several nanoparticles (including size, charge, and shape) and the physiological conditions on the mucin-nanoparticle interaction. Interestingly, layered double hydroxide (LDH) nanoparticles showed stronger interactions with the mucus layer compared to other types of nanoparticles due to their unique plate-like morphology. In specific for sheet-like LDH nanoparticles, our model found that their equilibrium adsorption capacity (Qe) followed the Langmuir adsorption isotherm, and the adsorption rate (k1) increased proportionally with the nanoparticle concentration. In addition, the particle size and thickness affected Qe and the surface coverage. Furthermore, bovine serum albumin (BSA) coating dramatically increased k1 of LDH nanoparticles. We proposed a novel mechanism to elucidate mucin-nanoparticle interactions, shedding light on the synergistic roles of drag force (Fd), repulsive force (Fr), and adsorptive force (Fa). These findings offer valuable insights into the complex mucin-nanoparticle interactions and provide guidance for the design of drug delivery systems.

Drivers of the In-Mouth Interaction between Lupin Protein Isolate and Selected Aroma Compounds: A Proton Transfer Reaction-Mass Spectrometry and Dynamic Time Intensity Analysis

Plant proteins often carry off-notes, necessitating customized aroma addition. In vitro studies revealed protein-aroma binding, limiting release during consumption. This study employs in vivo nose space proton transfer reaction-time-of-flight-mass spectrometry and dynamic sensory evaluation (time intensity) to explore in-mouth interactions. In a lupin protein-based aqueous system, a sensory evaluation of a trained "green" attribute was conducted simultaneously with aroma release of hexanal, nonanal, and 2-nonanone during consumption. Results demonstrated that enlarging aldehyde chains and relocating the keto group reduced maximum perceived intensity (Imax_R) by 71.92 and 72.25%. Protein addition decreased Imax_R by 30.91, 36.84, and 72.41%, indicating protein-aroma interactions. Sensory findings revealed a perceived intensity that was lower upon protein addition. Aroma lingering correlated with aroma compounds' volatility and hydrophobicity, with nonanal exhibiting the longest persistence. In vitro mucin addition increased aroma binding four to 12-fold. Combining PTR-ToF-MS and time intensity elucidated crucial food behavior, i.e., protein-aroma interactions, that are pivotal for food design.

Probing Relative Humidity Impact on Biological Protein Bovine Serum Albumin and Bovine Submaxillary Gland Mucin by Using Contact Resonance Atomic Force Microscopy

In biomaterials, a substantial amount of research has been placed on the mechanical properties of biomolecules and their interactions with body fluids. Bovine serum albumin (BSA) is a widely studied model protein, while bovine submaxillary gland mucin (BSM) is another cow-derived protein frequently employed in research. Films were examined with contact resonance atomic force microscopy (CR-AFM), and the results showed that the mechanical characteristics of the films were affected by the relative humidity. We quantitatively analyze the viscoelasticity of these proteins after they have been subjected to humidity by measuring the resonance frequency and quality factor. The findings indicate that prolonged humidity exposure has a different effect on the mechanical properties of BSA and BSM films. The results show that after exposure to humidity, the resonance peaks of BSA shift to the left, indicating stiffness, while those of BSM shift to the right, indicating hydration. Moreover, BSM's hydration is caused by relative humidity, leading to a constant increase in resonance frequency and material softness. Contrarily, BSA showed a decrease in contact resonance frequency due to ongoing strain-induced deformation, indicating increased material stiffness. The findings have significance for the design and development of biomaterials for a variety of applications, such as the delivery of drugs, the engineering of tissue, and the development of biosensors. Our research demonstrates that CR-AFM has the potential to become a non-invasive and sensitive method that can be used to characterize the mechanical characteristics of biomolecules and their interactions with bodily fluids.

Interaction Mechanisms and Predictions of the Biofouling of Polymer Films: A Combined Atomic Force Microscopy and Quartz Crystal Microbalance with Dissipation Monitoring Study

Biofouling of polymeric membranes is a severe problem in water desalination and treatment applications. A fundamental understanding of biofouling mechanisms is necessary to control biofouling and develop more efficient mitigation strategies. To shed light on the type of forces that govern the interactions between biofoulants and membranes, biofoulant-coated colloidal AFM probes were employed to investigate the biofouling mechanisms of two model biofoulants, BSA and HA, toward an array of polymer films commonly used in membrane synthesis, which included CA, PVC, PVDF, and PS. These experiments were combined with quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The Derjaguin, Landau, Verwey, and Overbeek (DLVO) and the extended-DLVO (XDLVO) theoretical models were applied to decouple the overall adhesion interactions between the biofoulants and the polymer films into their component interactions, i.e., electrostatic (El), Lifshitz-van der Waals (LW), and Lewis acid-base (AB) interactions. The XDLVO model was found to predict better the AFM colloidal probe adhesion data and the QCM-D adsorption behavior of BSA onto the polymer films than the DLVO model. The ranking of the polymer films' adhesion strengths and adsorption quantities was inversely proportional to their γ- values. Higher normalized adhesion forces were quantified for the BSA-coated colloidal probes with the polymer films than the HA-coated colloidal probes. Similarly, in QCM-D measurements, BSA was found to cause larger adsorption mass shifts, faster adsorption rates, and more condensed fouling layers than HA. A linear correlation (R2 = 0.96) was obtained between the adsorption standard free energy changes (ΔGads°) estimated for BSA from the equilibrium QCM-D adsorption experiments and the AFM normalized adhesion energies (WAFM/R) estimated for BSA from the AFM colloidal probe measurements. Eventually, an indirect approach was presented to calculate the surface energy components of biofoulants characterized by high porosities from Hansen dissolution tests to perform the DLVO/XDLVO analyses.

Boronic Acid-Tethered Silk Fibroin for pH-Dependent Mucoadhesion

Mucus lines all surfaces of the human body not covered by skin and provides lubrication, hydration, and protection. The properties of mucus are influenced by changes in pH that may occur due to physiological conditions and pathological circumstances. Reinforcing the mucus barrier with biopolymers that can adhere to mucus in different conditions can be a useful strategy for protecting the underlying mucosae from damage. In this work, regenerated silk fibroin (silk) was chemically modified with phenyl boronic acid to form reversible covalent complexes with the 1,2- or 1,3-diols. The silk modified with boronic acid pendant groups has an increased affinity for mucins, whose carbohydrate component is rich in diols. These results offer new applications of silk in mucoadhesion, and the ability to bind diols to the silk lays the foundation for the development of silk-based sugar-sensing platforms.

Mucoadhesive Dendrons Conjugated to Mesoporous Silica Nanoparticles as a Drug Delivery Approach for Orally Administered Biopharmaceuticals

Biological drugs are increasingly important for patients and industry due to their application in the treatment of common and potentially life-threatening diseases such as diabetes, cancer, and obesity. While most marketed biopharmaceuticals today are injectables, the potential of mucoadhesive delivery systems based on dendron-coated mesoporous silica nanoparticles for oral delivery of biological drugs is explored in this project. We hypothesize that specifically designed dendrons can be employed as mucoadhesive excipients and used to decorate the surface of nanoparticles with properties to embed a drug molecule. We initially tested a novel synthesis method for the preparation of dendrons, which was successfully validated by the chemical characterization of the compounds. The interaction between dendrons and mucin was studied through isothermal titration calorimetry and quartz crystal microbalance with dissipation monitoring and proved to be spontaneous and thermodynamically favorable. Dendrons were conjugated onto 244.4 nm mesoporous silica nanoparticles and characterized for chemical composition, size, and surface charge, which all showed a successful conjugation. Finally, dynamic light scattering was used to study the interaction between nanoparticles and porcine gastric mucin, whereas the interaction between nanoparticles and porcine intestinal mucus was characterized by rheological measurements. This study shows a deeper biophysical understanding of the interaction between nanoparticles and mucin or native porcine intestinal mucus, further leveraging the current understanding of how dendrons can be used as excipients to interact with mucin. This will provide knowledge for the potential development of a new generation of mucoadhesive nanoformulations for the oral delivery of biopharmaceuticals.

Surface-Functionalized Polystyrene Nanoparticles Alter the Transmembrane Potential via Ion-Selective Pores Maintaining Global Bilayer Integrity

Although nanoplastics have well-known toxic effects toward the environment and living organisms, their molecular toxicity mechanisms, including the nature of nanoparticle-cell membrane interactions, are still under investigation. Here, we employ dynamic light scattering, quartz crystal microbalance with dissipation monitoring, and electrophysiology to investigate the interaction between polystyrene nanoparticles (PS NPs) and phospholipid membranes. Our results show that PS NPs adsorb onto lipid bilayers creating soft inhomogeneous films that include disordered defects. PS NPs form an integral part of the generated channels so that the surface functionalization and charge of the NP determine the pore conductive properties. The large difference in size between the NP diameter and the lipid bilayer thickness (∼60 vs ∼5 nm) suggests a particular and complex lipid-NP assembly that is able to maintain overall membrane integrity. In view of this, we suggest that NP-induced toxicity in cells could operate in more subtle ways than membrane disintegration, such as inducing lipid reorganization and transmembrane ionic fluxes that disrupt the membrane potential.

LL37 and collagen-binding domain-mediated LL37 binding with type I collagen: Quantification via QCM-D

Antimicrobial peptide (AMP)-loaded biomaterials may represent a viable alternative for stimulating wound healing while protecting against infections. Previously, to develop an efficient delivery system for the cathelicidin antimicrobial peptide, LL37, our lab modified LL37 with a collagen-binding domain derived from collagenase (cCBD) as an anchoring unit to collagen-based wound dressings. However, a direct quantification of unmodified LL37 and cCBD-LL37 binding with collagen has not been performed. In this study, we used quartz crystal microbalance with dissipation monitoring (QCM-D), immunohistochemistry (IHC), and atomic force microscopy (AFM) to establish and characterize an adsorbed layer of type I collagen on the QCM-D sensor and quantify peptide-collagen binding. A collagen deposition protocol was successfully established by measuring concentration-dependent deposition of collagen in QCM-D, and collagen self-assembly was observed by IHC and AFM. Hydrophobicity is known to affect the behavior of collagen adsorption. Therefore, we compared the deposition of collagen on hydrophilic SiO₂-coated sensors vs. hydrophobic polystyrene (PS)-coated sensors via QCM-D, and found that the hydrophobic surface yielded more collagen adsorption, which suggested that hydrophobic surfaces are preferable for collagen layer establishment. There was no significant difference between LL37 and cCBD-LL37 binding with collagen, but the cCBD-LL37 showed better retention on the collagen after washing with PBS, indicating that there is an advantage to using cCBD as an anchoring unit to collagen. Collectively, these results provide important information on cCBD-mediated AMP-binding mechanisms and establish an effective method for quantifying peptide-collagen binding.

Can polyphenolic surface modifications prevent fungal colonization of titanium dental implants?

Oral biofilms can be a major health problem causing infections and chronic inflammation of mucosal tissue. While much effort is put in the investigation of bacteria in biofilms, the role of fungi is often neglected, despite Candida albicans playing a key role in the formation of multispecies oral biofilms. With the rise of antibiotic resistance, new strategies to reduce microbial growth need to be found. Therefore, plant derived polyphenolic molecules have been suggested to reduce both adhesion and growth of pathogenic bacteria and fungi. In this study, we investigated the use of polyphenolic coatings to reduce adhesion and biofilm formation of C. albicans BWP17 on titanium implants. Tannic acid and pyrogallol coatings altered the hydrophobic and charge properties of titanium surfaces, and both compounds were gradually released as active molecules over time. Despite such effects, we found no significant inhibition on growth and biofilm formation of C. Albicans, indicating that the release of active molecules from the coatings did not reach relevant inhibitory concentrations. However, a potential antibiofilm effect was observed by the pH-dependent disassembly of the polyphenolic layer, which caused the biofilm to detach. Hence, further efforts are required to create tailored implant surfaces, which sustainably reduce microbial growth and adhesion.

Mucosomes: Intrinsically Mucoadhesive Glycosylated Mucin Nanoparticles as Multi-Drug Delivery Platform

Mucus is a complex barrier for pharmacological treatments and overcoming it is one of the major challenges faced during transmucosal drug delivery. To tackle this issue, a novel class of glycosylated nanoparticles, named "mucosomes," which are based on the most important protein constituting mucus, the mucin, is introduced. Mucosomes are designed to improve drug absorption and residence time on the mucosal tissues. Mucosomes are produced (150-300 nm), functionalized with glycans, and loaded with the desired drug in a single one-pot synthetic process and, with this method, a wide range of small and macro molecules can be loaded with different physicochemical properties. Various in vitro models are used to test the mucoadhesive properties of mucosomes. The presence of functional glycans is indicated by the interaction with lectins. Mucosomes are proven to be storable at 4 °C after lyophilization, and administration through a nasal spray does not modify the morphology of the mucosomes. In vitro and in vivo tests indicate mucosomes do not induce adverse effects under the investigated conditions. This study proposes mucosomes as a ground-breaking nanosystem that can be applied in several pathological contexts, especially in mucus-related disorders.

Adsorption of SARS CoV-2 spike proteins on various functionalized surfaces correlates with the high transmissibility of Delta and Omicron variants

The SARS-CoV-2 virus emerged at the end of 2019 and rapidly developed several mutated variants, specifically the Delta and Omicron, which demonstrate higher transmissibility and escalating infection cases worldwide. The dominant transmission pathway of this virus is via human-to-human contact and aerosols which once inhaled interact with the mucosal tissue, but another possible route is through contact with surfaces contaminated with SARS-CoV-2, often exhibiting long-term survival. Here we compare the adsorption capacities of the S1 and S2 subunits of the spike (S) protein from the original variant to that of the S1 subunit from the Delta and Omicron variants on self-assembled monolayers by Quartz Crystal ​Microbalance. The results clearly show a significant difference in adsorption capacity between the different variants, as well as between the S1 and S2 subunits. Overall, our study demonstrates that while the Omicron variant is able to adsorb much more successfully than the Delta, both variants show enhanced adsorption capacity than that of the original strain. We also examined the influence of pH conditions on the adsorption ability of the S1 subunit and found that adsorption was strongest at pH 7.4, which is the physiological pH. The main conclusion of this study is that there is a strong correlation between the adsorption capacity and the transmissibility of the various SARS-CoV-2 variants.

The detection and characterization techniques for the interaction between graphene oxide and natural colloids: A review

The high dispersibility of graphene oxide (GO) and the universality of natural colloids (clay minerals, (hydr)oxides of Al, Fe, silica, etc.) make them interact easily. Many kinds of analytical methods have been used to study the interaction between GO and natural colloids. This review provides a comprehensive overview of analytical methods for the detection and quantification of interaction process. We highlighted the influence of the most relevant environmental factors (ionic strength, pH, etc.) on batch experiment, quartz crystal microbalance with dissipation monitoring measurements, and column experiments. Besides, the benefits and drawbacks of spectroscopic, microscopic techniques, theoretical models, calculation and time-resolved dynamic light scattering methods also have discussed in this work. This review can give some guidance to researchers in their selection and combination of the technique for the research of the interaction between GO and natural colloids.

Real-time changes of the adsorption process and conformation of marine dissolved organic matters on the solid-liquid interface

In this study, the adsorption characteristics of marine dissolved organic matters (MDOMs) on the solid-liquid interface in the coastal waters was investigated. The results showed that the organic macromolecules with adsorption ability in MDOMs are not rigid molecules. However, the macromolecules have viscoelasticity properties. At different dilution ratios, the MDOMs adsorption process includes rapid (0-200 s) and slow adsorption (200 s later) periods. MDOMs adsorption in the solid-liquid interface is a dynamic process in which adsorption and hydration occur simultaneously. MDOMs concentration is an important driving force for adsorption. The three macromolecules of acid polysaccharides, protein-like, and polycarboxylate-type humic acids in MDOMs are rich in functional groups and they have the ability to absorb to solid surface. Acidic polysaccharides exhibit a sustained adsorption ability, while the adsorption of other macromolecules occurred only in the initial rapid adsorption period. In addition, the acid polysaccharides show weak thixotropy during the adsorption process. It would cause the stretching of macromolecular structure of the adsorption layer, enhancing the hydration of the adsorption layer. The study shows the adsorption process of MDOMs at the solid-liquid interface and the structural characteristics of the adsorption layer. It can provide helpful information for the inhibition and removal of MDOMs pollution during the actual development of marine resources.

Comparative Degradation Kinetics Study of Polyamide Thin Films in Aqueous Solutions of Chlorine and Peracetic Acid Using Quartz Crystal Microbalance

Polyamide thin film composite membranes are widely used in water reclamation. Peracetic acid (PAA) is an emerging wastewater disinfectant with a potential for membrane cleaning and disinfection; however, its interaction with polyamide remains poorly understood. This study employs quartz crystal microbalance with dissipation (QCM-D) to determine the PAA-induced degradation kinetics of polyamide thin films, in comparison with the conventional disinfectant-free chlorine (HOCl). Polyamide films showed a sorption phase followed by a degradation phase when exposed to PAA (1000 mg L^-1) and HOCl (100 mg L^-1) solutions. While the sorption phase in HOCl experiments was short (1.4-3.5 min) and followed a Boltzmann-sigmoidal model, it spanned over 3-33 h in PAA experiments and displayed a two-stage behavior. The latter kinetics are attributed to sequential processes of the physical sorption of PAA in polyamide films followed by PAA-induced polyamide oxidation. In the degradation phase, the HOCl-exposed films followed a rapid, two-step exponential decay reaching an equilibrium mass of ∼50% of the initial (wet) mass after ∼5 h of exposure. In contrast, the PAA-exposed films followed a Boltzmann-sigmoidal decay, with ∼80% of the initial (wet) mass remaining intact after >10 h of exposure. Fast force maps generated using atomic force microscopy showed a progressive increase in the morphological heterogeneity of the polyamide films in HOCl solution due to pitting, cracking, bulging, and eventual delamination under both flow and no-flow conditions. In contrast, PAA only formed small pits on the polyamide film under flow; in a stagnant PAA solution, the film had no visible changes even after ∼148 h of exposure. This is the first comparative study on the chemical and morphological changes in polyamide films induced by PAA and HOCl. The much higher compatibility of polyamide with PAA than with chlorine supports the potential of PAA being used as a halogen-free membrane cleaning/disinfecting agent.

Construction and characterization of Juglans regia L. polyphenols nanoparticles based on bovine serum albumin and Hohenbuehelia serotina polysaccharides, and their gastrointestinal digestion and colonic fermentation in vitro

Herein, we report the construction and characterization of nanoparticles based on bovine serum albumin and Hohenbuehelia serotina polysaccharides for the delivery of polyphenols isolated from the shells of Juglans regia L. (BSA-JRP-HSP NPs). We also systematically investigated their gastrointestinal digestion and colonic fermentation characteristics in vitro. BSA-JRP-HSP NPs, with amorphous properties and regular spherical morphological features, have a high encapsulation efficiency of 88.47 ± 0.04%, average particle size of 285.7 ± 3.1 nm, and zeta potential of -12.20 ± 0.61 mV, and they exhibit excellent photothermal stabilities and strong mucin adhesion capacity. Through measurements of gastrointestinal digestion and colonic fermentation in vitro, the results suggest that BSA-JRP-HSP NPs presented well-sustained release characteristics for preventing the biodegradation of JRP during gastrointestinal digestion. After gastrointestinal digestion, BSA-JRP-HSP NPs could modulate the composition and structure of gut microbiota, promoting the growth of beneficial bacterial (e.g. Prevotella, Dialister, Akkermansia, etc.) and inhibiting the growth of pathogenic bacteria (e.g. Bacteroides, Phascolarctobacterium, Lachnospiracea incertae sedis, etc.). The production of short-chain fatty acids (SCFAs) including acetic acid, propionic acid, and butyric acid was remarkably enhanced by treatment with BSA-JRP-HSP NPs. This study has proved that BSA-JRP-HSP NPs can serve as a novel candidate for improving the bioavailability of JRP.

Purified mucins in drug delivery research

One of the main challenges in the field of drug delivery remains the development of strategies to efficiently transport pharmaceuticals across mucus barriers, which regulate the passage and retention of molecules and particles in all luminal spaces of the body. A thorough understanding of the molecular mechanisms, which govern such selective permeability, is key for achieving efficient translocation of drugs and drug carriers. For this purpose, model systems based on purified mucins can contribute valuable information. In this review, we summarize advances that were made in the field of drug delivery research with such mucin-based model systems: First, we give an overview of mucin purification procedures and discuss the suitability of model systems reconstituted from purified mucins to mimic native mucus. Then, we summarize techniques to study mucin binding. Finally, we highlight approaches that made use of mucins as building blocks for drug delivery platforms or employ mucins as active compounds.

Effect of albumin, urea, lysozyme and mucin on the triboactivity of Ti6Al4V/zirconia pair used in dental implants

The titanium implant/zirconia abutment interface can suffer failure upon mechanical and biological issues, ultimately leading to the loss of the artificial tooth. The study of the effect of the organic compounds present in saliva on the tribological behavior of these systems is of utmost importance to understand the failure mechanisms and better mimic the in vivo conditions. The aim of the present work is to evaluate the effect of the addition of albumin, urea, lysozyme and mucin to artificial saliva, on the triboactivity of Ti6Al4V/zirconia pair commonly used in dental implants and then, compare the results with those obtained with human saliva. The solutions' viscosity was measured and the adsorption of the different biomolecules to both Ti6Al4V and zirconia was accessed. Tribological tests were performed using Ti6Al4V balls sliding on zirconia plates inside of a corrosion cell. Friction and wear coefficients were determined, and the open circuit potential (OCP) was monitored during the tests. Also, the wear mechanisms were identified. The presence of mucin in the artificial lubricant led to the lowest wear coefficients. The main wear mechanism was abrasion, independently of the used lubricant. Adhesive wear was observed for the systems without mucin. Tribocorrosion activity and wear coefficient were lower in the presence of mucin. None of the studied artificial lubricants mimicked the effect of human saliva (HS) on the tribological behavior of the studied pair since this lubricant led to the lowest friction coefficient and highest corrosion activity.

Development of an open-source thermally stabilized quartz crystal microbalance instrument for biomolecule-substrate binding assays on gold and graphene

The interaction of biomolecules, such as proteins, with biomaterial surfaces is key to disease diagnostic and therapeutic development applications. There is a significant need for rapid, low-cost, field-serviceable instruments to monitor such interactions, where open-source tools can help to improve the accessibility to disease screening instruments especially in low- and middle-income countries. We have developed and evaluated a low-cost integrated quartz crystal microbalance (QCM) instrument for biomolecular analysis based on an open-source QCM device. The custom QCM instrument was equipped with a custom-made electronically controlled isothermal chamber with a closed-loop control routine. A thermal coefficient of 5.6 ppm/°C was obtained from a series of evaluations of the implemented control. Additionally, a custom-designed data acquisition system and a mathematical processing and analysis tool is implemented. The quartz crystal detection chips used here incorporate gold and reduced graphene oxide (rGO) coated surfaces. We demonstrate the system capability to monitor and record the biomolecular interaction between a typical protein bovine serum albumin (BSA) and these two substrates. This instrument was compared to a commercial QCM, demonstrating good correspondence between the computed mass adsorption density responses using the Sauerbrey model. For both Au and rGO surfaces, the custom QCM significantly outperforms the commercial system in limit of detection, sensitivity and linear range. The instrument presented here has the potential to serve as a ubiquitous bioelectronic tool for point-of-care disease screening and rapid therapeutics development.

Adsorption and Conformation Behavior of Lysozyme on a Gold Surface Determined by QCM-D, MP-SPR, and FTIR

The physicochemical properties of protein layers at the solid–liquid interface are essential in many biological processes. This study aimed to link the structural analysis of adsorbed lysozyme at the water/gold surface at pH 7.5 in a wide range of concentrations. Particular attention was paid to the protein’s structural stability and the hydration of the protein layers formed at the interface. Complementary methods such as multi-parameter surface plasmon resonance (MP-SPR), quartz crystal microbalance with energy dissipation (QCM-D), and infrared spectroscopy (FTIR) were used for this purpose. The MP-SPR and QCM-D studies showed that, during the formation of a monolayer on the gold surface, the molecules’ orientation changes from side-on to end-on. In addition, bilayer formation is observed when adsorbing in the high-volume concentration range >500 ppm. The degree of hydration of the monolayer and bilayer varies depending on the degree of surface coverage. The hydration of the system decreases with filling the layer in both the monolayer and the bilayer. Hydration for the monolayer varies in the range of 50–70%, because the bilayer is much higher than 80%. The degree of hydration of the adsorption layer has a crucial influence on the protein layers’ viscoelastic properties. In general, an increase in the filling of a layer is characterized by a rise in its rigidity. The use of infrared spectroscopy allowed us to determine the changes taking place in the secondary structure of lysozyme due to its interaction with the gold surface. Upon adsorption, the content of II-structures corresponding to β-turn and random lysozyme structures increases, with a simultaneous decrease in the content of the β-sheet. The increase in the range of β-turn in the structure determines the lysozyme structure’s stability and prevents its aggregation.

Bulk Phase Behavior vs Interface Adsorption: Specific Multivalent Cation and Anion Effects on BSA Interactions

Proteins are ubiquitous and play a critical role in many areas from living organisms to protein microchips. In humans, serum albumin has a prominent role in the foreign body response since it is the first protein which will interact with, e.g., an implant or stent. In this study, we focused on the influence of salts (i.e., different cations (Y³⁺, La³⁺) and anions (Cl^-, I^-) on bovine serum albumin (BSA) in terms of its bulk behavior as well as the role of charges for protein adsorption at the solid-liquid interface in order to understand and control the underlying molecular mechanisms and interactions. This is part of our group's effort to gain a deeper understanding of protein-protein and protein-surface interactions in the presence of multivalent ions. In the bulk, we established two new phase diagrams and found not only multivalent cation-triggered phase transitions, but also a dependence of the protein behavior on the type of anion. The attractive interactions between proteins were observed to increase from Cl^- < NO₃^- < I^-, resulting in iodide preventing re-entrant condensation and promoting liquid-liquid phase separation in bulk. Using ellipsometry and a quartz-crystal microbalance with dissipation (QCM-D), we obtained insight into the growth of the protein adsorption layer. Importantly, we found that phase transitions at the substrate can be triggered by certain interface properties, whether they exist in the bulk solution or not. Through the use of a hydrophilic, negatively charged surface (native silica), the direct binding of anions to the interface was prevented. Interestingly, this led to re-entrant adsorption even in the absence of re-entrant condensation in bulk. However, the overall amount of adsorbed protein was enhanced through stronger attractive protein-protein interactions in the presence of iodide salts. These findings illustrate how carefully chosen surface properties and salts can directly steer the binding of anions and cations, which guide protein behavior, thus paving the way for specific/triggered protein-protein, protein-salt, and protein-surface interactions.

Effects of Electrokinetic Phenomena on Bacterial Deposition Monitored by Quartz Crystal Microbalance with Dissipation Monitoring

Bacterial deposition is the first step in the formation of microbial biofilms in environmental technology, and there is high interest in controlling such deposition. Earlier work indicated that direct current (DC) electric fields could influence bacterial deposition in percolation columns. Here, a time-resolved quartz crystal microbalance with dissipation monitoring (QCM-D) and microscopy-based cell counting were used to quantify DC field effects on the deposition of bacterial strains Pseudomonas putida KT2440 and Pseudomonas fluorescens LP6a at varying electrolyte concentrations and weak electric field strengths (0-2 V cm^-1). DC-induced frequency shifts (Δf), dissipation energy (ΔD), and ratios thereof (Δf/ΔD) proved as good indicators of the rigidity of cell attachment. We interpreted QCM-D signals using a theoretical approach by calculating the attractive DLVO-force and the shear and drag forces acting on a bacterium near collector surfaces in a DC electric field. We found that changes in DC-induced deposition of bacteria depended on the relative strengths of electrophoretic drag and electro-osmotic shear forces. This could enable the prediction and electrokinetic control of microbial deposition on surfaces in natural and manmade ecosystems.

A comparison between the structures of reconstituted salivary pellicles and oral mucin (MUC5B) films

HYPOTHESIS

Salivary pellicles i.e., thin films formed upon selective adsorption of saliva, protect oral surfaces against chemical and mechanical insults. Pellicles are also excellent aqueous lubricants. It is generally accepted that reconstituted pellicles have a two-layer structure, where the outer layer is mainly composed of MUC5B mucins. We hypothesized that by comparing the effect of ionic strength on reconstituted pellicles and MUC5B films we could gain further insight into the pellicle structure.

EXPERIMENTS

Salivary pellicles and MUC5B films reconstituted on solid surfaces were investigated at different ionic strengths by Force Spectroscopy, Quartz Crystal Microbalance with Dissipation, Null Ellipsometry and Neutron Reflectometry.

FINDINGS

Our results support the two-layer structure for reconstituted salivary pellicles. The outer layer swelled when ionic strength decreased, indicating a weak polyelectrolyte behavior. While initially the MUC5B films exhibited a similar tendency, this was followed by a drastic collapse indicating an interaction between exposed hydrophobic domains. This suggests that mucins in the pellicle outer layer form complexes with other salivary components that prevent this interaction. Lowering ionic strength below physiological values also led to a partial removal of the pellicle inner layer. Overall, our results highlight the importance that the interactions of mucins with other pellicle components play on their structure.

Understanding and Improving Microplastic Removal during Water Treatment: Impact of Coagulation and Flocculation

The efficacy of plastic particle removal by municipal water treatment plants is currently uncertain, and the mechanisms involved in microplastic (MP) coagulation and flocculation have only been superficially investigated. The removal of pristine versus weathered plastic debris and the impact of plastic particle size on removal remain largely unexplored. In this study, coagulation, flocculation, and settling performances were investigated using pristine and weathered MPs (polyethylene (PE) and polystyrene (PS) microspheres, and polyester (PEST) fibers). Weathering processes that changed the surface chemistry and roughness of MPs impacted MP affinity for coagulants and flocculants. A quartz crystal microbalance with dissipation monitoring was used to identify the mechanisms involved during MP coagulation and flocculation. Measured deposition rates confirmed the relatively low affinity between plastic surfaces and aluminum-based coagulants compared to cationic polyacrylamide (PAM). In every case examined, coagulant efficiency increased when the plastic surface was weathered. Removals of 97 and 99% were measured for PEST and weathered PE, respectively. Larger pristine PE MPs were the most resistant to coagulation and flocculation, with 82% removal observed even under enhanced coagulation conditions. By understanding the interaction mechanisms, the removal of weathered MPs was optimized. Finally, this study explored the use of settled water turbidity as a possible indicator of MP removal.

Characterization of nano-layered solid-contact ion selective electrodes by simultaneous potentiometry and quartz crystal microbalance with dissipation

Nano-layered solid-contact potassium-selective electrodes (K⁺-ISEs) were explored as model ion-selective electrodes for their practical use in clinical analysis. The ultra-thin ISEs ought to be manufactured in a highly reproducible manner, potentially making them suitable for mass production. Thus, their development is pivotal towards miniaturised sensors with simplified conditioning/calibration protocols for point-of-care diagnostics. To study nano-layered ISEs, the ultra-thin nature of ISEs for the first time enabled to combine potentiometry-quartz crystal microbalance with dissipation (QCM-D) to obtain value-added information on the ISE potentiometric response regarding their physical state such as mass/thickness/viscoelastic properties/structural homogeneity. Specifically, the studies were focused on real-time observations of the ISE potentiometric response in relation to changes of their physicochemical properties during the ISE preparation (conditioning) and operation (including biofouling conditions) to identify the occurring processes that may accordingly be critical for potential instability of the ISEs, impeding their practical application. The K⁺-ISEs were prepared on a QCM-D gold sensor by electrodepositing poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) layer serving as an ion-to-electron transducer subsequently covered by a spin-coated poly(vinyl chloride) based K⁺-ion selective membrane (K⁺-ISM). The studies demonstrated that the performance of the nano-layered design of K⁺-ISEs is detrimentally affected by such processes as water layer formation accordingly causing the instability of the electrode potential. The changes in the ISE physical state such mass/viscoelastic properties associated with water layer formation and origin of the potential instability was already observed at the ISE conditioning stage. The potential instability of nano-layered ISEs limits their practical applicability, indicating the need of new solutions in designing ISEs, for instance, exploiting new water-resistant materials and modifying preparation protocols.

Enhanced protein adsorption upon bulk phase separation

In all areas related to protein adsorption, from medicine to biotechnology to heterogeneous nucleation, the question about its dominant forces and control arises. In this study, we used ellipsometry and quartz-crystal microbalance with dissipation (QCM-D), as well as density-functional theory (DFT) to obtain insight into the mechanism behind a wetting transition of a protein solution. We established that using multivalent ions in a net negatively charged globular protein solution (BSA) can either cause simple adsorption on a negatively charged interface, or a (diverging) wetting layer when approaching liquid-liquid phase separation (LLPS) by changing protein concentration (cp) or temperature (T). We observed that the water to protein ratio in the wetting layer is substantially larger compared to simple adsorption. In the corresponding theoretical model, we treated the proteins as limited-valence (patchy) particles and identified a wetting transition for this complex system. This wetting is driven by a bulk instability introduced by metastable LLPS exposed to an ion-activated attractive substrate.

Mechanism of lysozyme adsorption onto gold surface determined by quartz crystal microbalance and surface plasmon resonance

In this study, the physicochemical characterization of lysozyme adsorbed on gold was investigated. Through the use of MP-SPR it was possible to establish that the orientation of molecules changes from side-on to between or end-on with increasing surface coverage. The data confirms that the process of adsorption is driven primarily by electrostatic interactions but also by hydrophobic forces. MP-SPR data was compared with the Random Sequential Adsorption model for a molecule with an ellipsoidal shape. Contact angle measurements showed that higher surface coverage also translates in more hydrophilic properties of obtained lysozyme layer. Comparison of CD and PM-IRRAS spectra in solution and adsorbed state respectively showed changes in the secondary structures of lysozyme. These changes are dependent on pH, but fundamentally they go in the direction of the increase of β-turn/random content with a simultaneous decrease in β-sheet fraction, which suggests that aggregation is not occurring. The combination of MP-SPR and QCM-D measurements allowed the estimation of the number of water molecules associated with the lysozymes films. It has been observed that hydration decreases from 70% in pH = 4 to 30% in pH = 11. This data indicates that hydration is driven mainly by the degree of protonation of lysozyme molecules.

Study of the Human Albumin Role in the Formation of a Bacterial Biofilm on Urinary Devices Using QCM-D

Catheter-associated urinary tract infections (CAUTIs) are the most common health care-associated infections due to rapid bacterial colonization+ and biofilm formation in urinary catheters. This behavior has been extensively documented in medical devices. However, there is a few literature works on CAUTI providing a model that allows the exhaustive study of biofilm formation in a urinary environment. The development of an effective model would be helpful to identify the factors that promote the biofilm formation and identify strategies to avoid it. In this work, we have developed a model to test biofilm formation on urinary medical device surfaces by simulating environmental and physical conditions using a quartz crystal microbalance with dissipation (QCM-D) module with an uropathogenic strain. Moreover, we used the developed model to study the role of human albumin present in artificial urine at high concentrations because of renal failure or heart-diseases in patients. Despite model limitations using artificial urine, these tests show that human albumin can be considered as a promoter of biofilm formation on hydrophobic surfaces, being a possible risk factor to developing a CAUTI.

Swelling of mucoadhesive electrospun chitosan/polyethylene oxide nanofibers facilitates adhesion to the sublingual mucosa

Mucoadhesive chitosan-based electrospun nanofibers are promising candidates for overcoming challenges associated with sublingual drug delivery, yet studies focusing on evaluating the mucoadhesive properties of nanofibers for sublingual administration are limited. The aim was to elucidate the mucoadhesive properties of chitosan/polyethylene oxide (PEO) nanofibers focusing on how the degree of deacetylation (DDA, 53-96 %) of chitosan influenced their morphological and mucoadhesive properties. The mechanism of mucoadhesion was explained by the intermolecular interactions of chitosan with mucin from bovine submaxillary glands using quartz-crystal microbalance with dissipation monitoring and by adhesion of the nanofibers to ex vivo porcine sublingual mucosa. An increase in chitosan DDA improved the morphological stability of the nanofibers in water, but did not contribute to altered mucoadhesive properties. This study demonstrates excellent mucoadhesive properties of chitosan/PEO nanofibers and shows that the strong mucoadhesiveness of the nanofibers is attributed to their swelling ability.

A free-floating mucin layer to investigate the effect of the local microenvironment in lungs on mucin-nanoparticle interactions

Respiratory tract mucus represents an important barrier for pulmonary drug delivery. Understanding of mucin-nanoparticle interactions is a prerequisite for rational design of inhalable nanoparticles. In the present study, in order to establish a reliable quartz crystal microbalance with dissipation (QCM-D) approach to reveal the effect of the lung microenvironment on the mucin-nanoparticle interactions, we investigated the intrinsic features of the mucin layers immobilized onto sensors via chemical conjugation or physical adsorption by using atomic force microscopy (AFM) and QCM-D. Our results demonstrated that the covalently-grafted mucin layer responded more sensitively than the physically-adsorbed mucin layer to the local microenvironment shifting from PBS (pH 7.35 and ionic strength 30 mM) to PBS (pH 6.25 and ionic strength 150 mM) and resulted in a softer mucin layer with more hydrophobic areas exposed. Furthermore, using the QCM-D approach with the covalently-grafted mucin layer, we demonstrated the significant influence of the local microenvironment on the interaction of mucin with poly (lactic-co-glycolic acid)-based nanoparticles with different surface hydrophilicity. The present work underlines the QCM-D approach with a covalently-grafted mucin layer as a potent tool to elucidate the potential influence of local microenvironment on mucin-nanoparticle interactions. STATEMENT OF SIGNIFICANCE: Studying interactions between nanoengineered materials and biological systems plays a vital role in development of biomedical applications of nanoengineered materials. In this work, by employing a more biologically relevant, 'free-floating' mucin layer model, we demonstrate the significant impact of the lung microenvironment on the nature and the extent of the interaction between the mucin and the nanoparticles with different surface hydrophilicity. To the best of our knowledge, this is the first work describing the nanoscale properties of immobilized mucin layers and investigating the mucin-nanoparticle interactions with emphasis on the impact of local microenvironment in lungs. Thus, it is expected to have important consequences in rational design of inhalable nanoparticle delivery systems.

Human saliva and model saliva at bulk to adsorbed phases - similarities and differences

Human saliva, a seemingly simple aqueous fluid, is, in fact, an extraordinarily complex biocolloid that is not fully understood, despite many decades of study. Salivary lubrication is widely believed to be a signature of good oral health and is also crucial for speech, food oral processing and swallowing. However, saliva has been often neglected in food colloid research, primarily due to its high intra- to inter-individual variability and altering material properties upon collection and storage, when used as an ex vivo research material. In the last few decades, colloid scientists have attempted designing model (i.e. 'saliva mimicking fluid') salivary formulations to understand saliva-food colloid interactions in an in vitro set up and its contribution on microstructural aspects, lubrication properties and sensory perception. In this Review, we critically examine the current state of knowledge on bulk and interfacial properties of model saliva in comparison to real human saliva and highlight how far such model salivary formulations can match the properties of real human saliva. Many, if not most, of these model saliva formulations share similarities with real human saliva in terms of biochemical compositions, including electrolytes, pH and concentrations of salivary proteins, such as α-amylase and highly glycosylated mucins. This, together with similarities between model and real saliva in terms of surface charge, has led to significant advancement in decoding various colloidal interactions (bridging, depletion) of charged emulsion droplets and associated sensory perception in the oral phase. However, model saliva represents significant dissimilarity to real saliva in terms of lubricating properties. Based on in-depth examination of properties of mucins derived from animal sources (e.g. pig gastric mucins (PGM) or bovine submaxillary mucin (BSM)), we can recommend that BSM is currently the most optimal commercially available mucin source when attempting to replicate saliva based on surface adsorption and lubrication properties. Even though purification via dialysis or chromatographic techniques may influence various physicochemical properties of BSM, such as structure and surface adsorption, the lubricating properties of model saliva formulations based on BSM are generally superior and more reliable than the PGM counterpart at orally relevant pH. Comparison of mucin-containing model saliva with ex vivo human salivary conditioning films suggests that mucin alone cannot replicate the lubricity of real human salivary pellicle. Mucin-based multi-layers containing mucin and oppositely charged polyelectrolytes may offer promising avenues in the future for engineering biomimetic salivary pellicle, however, this has not been explored in oral tribology experiments to date. Hence, there is a strong need for systematic studies with employment of model saliva formulations containing mucins with and without polycationic additives before a consensus on a standardized model salivary formulation can be achieved. Overall, this review provides the first comprehensive framework on simulating saliva for a particular bulk or surface property when doing food oral processing experiments.

Interactions of Transition Metal Dichalcogenide Nanosheets With Mucin: Quartz Crystal Microbalance With Dissipation, Surface Plasmon Resonance, and Spectroscopic Probing

Ultrathin 2-dimensional transition metal dichalcogenides (TMDs) have become a class of high-potential materials in biomedicine due to their intriguing properties. They have been applied to solve biomedical challenges, such as biosensing, bioimaging, drug delivery, and cancer therapy. However, studies of the interactions between these materials and biomolecules are insufficient. Mucous tissue serves as a barrier to foreign hazardous substances and a gel layer for substance exchange. The main organic matter of mucous tissue is mucin, so it was selected as a model biomolecule to study its interactions with six different TMD nanosheets (NSs), including single-layered (SL), few-layered (FL), and small few-layered (SFL) MoS2 and WS2 NSs, using quartz crystal microbalance (QCM) with a dissipation monitor (QCM-D) and surface plasmon resonance (SPR). Additionally, UV absorption, fluorescence, and circular dichroism (CD) spectroscopy were applied to investigate the mechanism of the interactions and to study the conformational change of mucin. We found that the TMD NSs could adsorb on the mucin layer and affect its viscoelasticity. The results indicated that the SL WS2 NSs exhibited the highest initial absorption rate and the maximum absorption amount, while the SL MoS2 NSs exhibited the highest initial desorption rate. During the adsorption, the viscoelasticity variations of the mucin layer caused by the WS2 nanosheets were weaker than those caused by the MoS2 nanosheets. Furthermore, the conformational changes of mucin caused by the SL MoS2, SL WS2, and SFL MoS2 NSs were higher than those resulting from other TMD NSs. These findings provide important information on the interactions between TMD NSs and mucin and provide useful insights into the interfacial behavior of TMD NSs before they enter tissues.

Qualitative and quantitative analysis of the biophysical interaction of inhaled nanoparticles with pulmonary surfactant by using quartz crystal microbalance with dissipation monitoring

Understanding the interaction between inhaled nanoparticles and pulmonary surfactant is a prerequisite for predicting the fate of inhaled nanoparticles. Here, we introduce a quartz crystal microbalance with dissipation monitoring (QCM-D)-based methodology to reveal the extent and nature of the biophysical interactions of polymer- and lipid-based nanoparticles with pulmonary surfactant. By fitting the QCM-D data to the Langmuir adsorption equation, we determined the kinetics and equilibrium parameters [i.e., maximal adsorption (Δm_max), equilibrium constant (K_a), adsorption rate constant (k_a) and desorption rate constant (k_d)] of polymeric nanoparticles adsorption onto the pulmonary surfactant (e.g., an artificial lipid mixture and an extract of porcine lung surfactant). Furthermore, our results revealed that the nature of the interactions between lipid-based nanoparticles (e.g., liposomes) and pulmonary surfactant was governed by the liposomal composition, i.e., incorporation of cholesterol and PEGylated phospholipid (DSPE-PEG₂₀₀₀) into DOPC-based liposomes led to the adsorption of intact liposomes onto the pulmonary surfactant layer and the mass exchange between the liposomes and pulmonary surfactant layer, respectively. In conclusion, we demonstrate the applicability of the QCM-D technique for qualitative and quantitative analysis of the biophysical interaction of inhaled nanoparticles with pulmonary surfactant, which is vital for rational design and optimization of inhalable nanomedicines.

Novel grafted electrochemical interface for covalent glucose oxidase immobilization using reactive pentafluorophenyl methacrylate

One of the most important factors for the proper functioning of enzymatic electrochemical biosensors is the enzyme immobilization strategy. In this work, glucose oxidase was covalently immobilized using pentafluorophenyl methacrylate (PFM) by applying two different surface modification techniques (plasma polymerization and plasma-grafting). The grafted surface was specifically designed to covalently anchor enzyme molecules. It was observed using QCM-D measurements the PFM plasma-grafted surfaces were able to retain a higher number of active enzyme molecules than the PFM polymerized surfaces. An amperometric glucose biosensor using titanium dioxide nanotubes array (TiO₂NTAs) modified by PFM plasma-grafted surface was prepared. The resulting biosensor exhibited a fast response and short analysis time (approximately eight minutes per sample). Moreover, this biosensor achieved high sensitivity (9.76 μA mM^-1) with a linear range from 0.25 to 1.49 mM and a limit of detection (LOD) equal to 0.10 mM of glucose. In addition, the glucose content of 16 different food samples was successfully measured using the developed biosensor. The obtained results were compared with the respective HPLC value and a deviation smaller than 10% was obtained in all the cases. Therefore, the biosensor was able to overcome all possible interferences in the selected samples/matrices.

Interactions of salivary mucins and saliva with food proteins: a review

Mucins are long glycoprotein molecules responsible for the gel nature of the mucous layer that covers epithelial surfaces throughout the body. Mucins, as the major salivary proteins, are also important proteins for the food oral processing and digestion. The interactions of salivary mucins and saliva with several food proteins and food protein emulsions, as well as their functional properties related to the food oral processing were reviewed in this paper. The target food proteins of focus were whey proteins (lactoferrin and beta-lactoglobulin) and non-whey proteins (casein, gelatin, galectin/lectin, and proline-rich proteins). Most of the studies suggest that electrostatic attraction (between positively charged food proteins with negatively charged moieties of mucin mainly on glycosylated region of mucin) is the major mode of interaction between them. On the other hand, casein attracts the salivary proteins only via non-covalent interactions due to its naturally self-assembled micellar structure. Moreover, recent studies related to β-lactoglobulin (BLG)-mucin interactions have clarified the importance of hydrophobic as well as hydrophilic interactions, such as hydrogen bonding. Furthermore, in vitro studies between protein emulsions and saliva observed a strong aggregating effect of saliva on caseinate and whey proteins as well as on surfactant-stabilized emulsions. Besides, the sign and the density of the charge on the surface of the protein emulsion droplets contribute significantly to the behavior of the emulsion when mixed with saliva. Other studies also suggested that the interactions between saliva and whey proteins depends on the pH in addition to the flow rate of the saliva. Overall, the role of interactions of food proteins and food protein emulsions with mucin/saliva-proteins in the oral perception, as well as the physicochemical and structural changes of proteins were discussed.

Interactions of Fly Ash Particles with Mucin and Serum Albumin

Fly ash particles can contribute to haze and adverse health outcomes. In this study, two mucins, one from bovine submaxillary glands (bovine submaxillary mucin, BSM) and one from porcine stomach (porcine gastric mucin), as well as bovine serum albumin (BSA), which served as the physical barriers against foreign substances entering the tissues and the blood protein, respectively, were chosen as models for the investigations of the interactions between the proteins and the fly ash particles. Their adsorption behaviors were studied using spectroscopy and a quartz crystal microbalance with a dissipation monitor (QCM-D). The results indicated that the fly ash particles can induce the loosening of mucins and BSA, probably via the formation of complexes. Further, the secondary structure of proteins changed in the presence of fly ash particles. The α-helix content decreased with an increasing fly ash particle concentration. The addition of fly ash particles into protein solutions led to fluorescence quenching, which suggested that there were interactions between these particles and the mucins and BSA. The association constants ( K_a) for BSM and BSA were 5.35 and 4.18 L/g, respectively. Furthermore, the results of QCM-D analyses showed that the amount decreased on the mucin surface but increased slightly on the BSA surface, which indicated that the fly ash particles disrupted the mucin layer upon adsorption. These findings provide clear evidence of the interactions between the fly ash particles and the mucins and BSA, which can lead to structural changes. This study contributes to a better understanding of the interactions and adsorptions of atmospheric particulate pollutants with the proteins in the human body.