Layer-by-layer assembly of mucin and chitosan--Influence of surface properties, concentration and type of mucin

Different vehicles containing CaneCPI-5 reduce erosive dentin wear in situ

OBJECTIVE

This study evaluated the protective capacity of a sugarcane-derived cystatin (CaneCPI-5) in different vehicles (1-solution and 2-chitosan gel) against erosive dentin wear in situ.

METHODS

In part-1, 15 volunteers participated in a crossover protocol (solutions): Water; Elmex™ and CaneCPI-5. The volunteers wore an appliance with 4 dentin samples for 5 days. These samples were treated with a drop of the solutions for 1 min (4X/d), then the acquired pellicle (AP) was formed and the samples were subjected to erosive challenges (EROSION: citric acid, for 90 s, 4X/day). 2X/day, half of the samples were also abraded for 15 s (ABRASION). In part-2, 16 volunteers participated in a crossover protocol (gel): No gel, Chitosan gel, Chitosan gel + NaF and Chitosan gel + CaneCPI-5. The volunteers also wore an appliance. The samples were treated once/day with the gel or not for 4 min, then the AP was formed and the samples were subjected to erosive and abrasive challenges, as reported in part-1. Dentin wear was measured by profilometry. Data were analyzed by two-way RM-ANOVA and Sidak's tests (p < 0.05).

RESULTS

Part-1: Elmex™ and CaneCPI-5 significantly reduced dentin loss in comparison with Water for the EROSION/ABRASION conditions (p < 0.05). Part-2, all the treated groups significantly reduced the dentin loss in comparison to the No gel. The greatest reduction was found for the gel + CaneCPI-5 group for the EROSION/ABRASION (p < 0.05).

CONCLUSION

The solution and chitosan gel containing CaneCPI-5 protected against erosive dentin wear in situ.

CLINICAL RELEVANCE

These different vehicles are probably sufficient for protecting people with high risk of developing erosive dentin wear.

Engineering Surfaces with Immune Modulating Properties of Mucin Hydrogels

Hydrogels of cross-linked mucin glycoproteins (Muc-gel) have shown strong immune-modulating properties toward macrophages in vitro, which are translated in vivo by the dampening of the foreign body response to implantation in mice. Beyond mucin hydrogels, other biomaterials such as sensors, electrodes, and other long-term implants would also benefit from such immune-modulating properties. In this work, we aimed to transfer the bioactivity observed for three-dimensional Muc-gels to the surface of two model materials by immobilizing mucin into thin films (Muc-film) using covalent layer-by-layer assembly. We tested how the surface immobilization of mucins affects macrophage responses compared to Muc-gels. We showed that Muc-films on soft polyacrylamide gels mimic Muc-gel in their modulation of macrophage responses with activated gene expression of inflammatory cytokines on day 1 and then dampening them on day 3. Also, the markers of polarized macrophages, M1 and M2, were expressed at the same level for macrophages on Muc-film-coated soft polyacrylamide gels and Muc-gel. In contrast, Muc-film-coated hard polystyrene led to a different macrophage response compared to Muc-gel, having no activated expression of inflammatory cytokines and a different M1 marker expression. This suggested that the substrate mechanical properties and mucin molecular configuration determined by substrate-mucin interactions affect mucin immune-modulating properties. We conclude that mucin immune-modulating properties can be transferred to materials by mucin surface immobilization but will be dependent on the substrate chemical and mechanical properties.

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.

Facile Modification of NF Membrane by Multi-Layer Deposition of Polyelectrolytes for Enhanced Fouling Resistance

Fouling not only deteriorates the membrane structure but also compromises the quality of the permeate and has deleterious consequences on the membrane operation. In the current study, a commercial thin film composite nanofiltration membrane (NF90) was modified by sequentially depositing oppositely charged polycation (poly(allylamine hydrochloride)) and polyanion (poly(acrylic acid)) polyelectrolytes using the layer-by-layer assembly method. The water contact angle was decreased by ~10° after the coating process, indicating increased hydrophilicity. The surface roughness of the prepared membranes decreased from 380 nm (M-0) to 306 nm (M-10) and 366 nm (M-20). M-10 membrane showed the highest permeate flux of 120 L m-2 h-1 with a salt rejection of >98% for MgSO4 and NaCl. The fabricated membranes M-20 and M-30 showed 15% improvement in fouling resistance and maintained the initial permeate flux longer than the pristine membrane.

Effect of TiF4/NaF and chitosan solutions on biofilm formation and prevention of dentin demineralization

OBJECTIVE

This study evaluated the effect of experimental solutions containing TiF₄/NaF and chitosan on bacterial species of microcosm biofilm and on dentin demineralization.

DESIGN

Microcosm biofilm was produced from human saliva mixed with McBain medium (0.2% sucrose) on bovine dentin for 5 days, under 5% CO₂ and 37 °C. From the 2nd day to 5th day, the treatments were applied (1×60s/day) as following: (1) NaF (500 ppm F^-, positive control); (2) TiF₄ and NaF (TiF₄: 190 ppm Ti⁴⁺ and 300 ppm F^-; NaF: 190 ppm F^-); (3) similar to 2 plus 0.5% chitosan (Ch 500 mPa.s, 75% deacetylation); (4) phosphate buffer solution (negative control); and (5) 0.5% chitosan (Ch 500 mPa.s, 75% deacetylation). CFU counting was performed for total microorganism, total streptococci, total lactobacilli and mutans streptococci. Dentin demineralization was measured by transverse microradiography-TMR. The data were compared using ANOVA/Tukey or Kruskal-Wallis/Dunn tests (p < 0.05).

RESULTS

No differences were found between the treatments with respect to CFU counting (p > 0.05). Dentin treated with TiF₄/NaF plus chitosan solution presented the lowest demineralization compared to the negative control and pure chitosan solution. On the other hand, this experimental solution did not significantly differ from TiF₄/NaF solution, being both able to significantly reduce mineral loss.

CONCLUSION

TiF₄/NaF plus chitosan solution, at suitable pH to be clinically applicable, had no antimicrobial effect, but it was able to reduce dentin caries development under this model.

Effect of TiF4/NaF and chitosan solutions on the development of enamel caries under a microcosm biofilm model

OBJECTIVES

To evaluate the effect of experimental solutions containing TiF₄/NaF and chitosan on bacterial species and on enamel caries prevention.

METHODS

Microcosm biofilm was produced from human saliva mixed with McBain saliva (0.2% sucrose) on bovine enamel for five days, under 5% CO₂ and 37 °C. From the second day until the end, the treatments were applied (1 × 60 s/day): (1) NaF (500 ppm F^-, positive control); (2) TiF₄ and NaF (TiF₄: 190 ppm Ti⁴⁺ and 300 ppm F^-; NaF: 190 ppm F^-); (3) similar to 2 plus 0.5% chitosan (Ch 500 mPas, 75% deacetylation); (4) phosphate buffer solution (negative control); and (5) 0.5% chitosan (Ch 500 mPas, 75% deacetylation). CFU counting was performed for total microorganism, total streptococcus, total lactobacillus and Streptococcus mutans. Enamel demineralization was measured by transverse microradiography-TMR. The data were compared using ANOVA/Tukey or Kruskal-Wallis/Dunn tests (p < .050).

RESULTS

No differences were found between the treatments with respect to CFU counting (ANOVA, p > .050). Enamel treated with TiF₄/NaF plus chitosan solution presented the lowest demineralization compared to the negative control and pure chitosan solution. On the other hand, this experimental solution did not significantly differ from TiF₄/NaF and NaF solutions, being all of them able to significantly reduce mineral loss (50-74%), but only TiF₄/NaF plus chitosan reduced lesion depth (55%) compared to the negative control (p = .001).

CONCLUSION

TiF₄/NaF plus chitosan solution had no antimicrobial effect, but it was able to reduce enamel caries development in 79% compared to control under this model.

CLINICAL SIGNIFICANCE

This study showed that TiF₄/NaF plus chitosan solution had no antimicrobial effect, but it was able to reduce enamel caries development under a microcosm biofilm model.

In-office tooth bleaching with chitosan-enriched hydrogen peroxide gels: in vitro results

OBJECTIVE

This study aimed to evaluate the effects of adding chitosan to 35% hydrogen peroxide gels (for in-office bleaching), with or without calcium gluconate, on tooth properties and bleaching efficacy.

METHODS

Bovine enamel/dentin specimens (4 × 4 × 2.5 mm) were randomly allocated into groups (n = 10): negative control (unbleached), bleaching with 35% hydrogen peroxide gel (35% HP, commercial gel); 35% HP with 2% chitosan (% wt) (35% HP + chitosan), 35% HP and calcium (35% HP + Ca, commercial gel), and 35% HP + Ca + 2% chitosan. Variation of surface profile (ΔRa) and color analyses (ΔL*, Δa*, Δb*, ΔE*_ab, ΔE₀₀, and ΔWID) were performed comparing specimens at baseline (initial) and 24 h after of storage in artificial saliva (final). Surface microhardness (KHN) values and scanning electron microscopy (SEM) images were obtained on conclusion. The data were analyzed by ANOVA and Tukey's tests (KHN), generalized linear models (ΔL*, ΔE_ab, ΔE₀₀, ΔWID, ΔRa), and Kruskal-Wallis and Dunn tests (Δa*, Δb*) (α = 0.05).

RESULTS

Considering ΔL*, Δa*, Δb*, ΔE*_ab, ΔE₀₀, and ΔWID values, the bleached groups differed from negative control. For ΔRa, chitosan-based groups showed lower variation in surface roughness compared to 35% HP, without significant difference from negative control. For KHN, chitosan groups did not differ from negative control (unbleached control = chitosan groups > 35% HP + Ca > 35% HP). For SEM, slight surface changes were observed in all bleached groups, but the intensity varied according to gel used (35% HP > gels with Ca > gels with chitosan).

CONCLUSION

Chitosan-enriched hydrogen peroxide gels can reduce negative impacts on tooth properties without affecting bleaching efficacy.

CLINICAL RELEVANCE

Although commercial gels containing remineralizing agents such as calcium reduce the negative effects on the properties of teeth, the addition of chitosan appears to be a promising approach to preservation of dental properties without interfering in bleaching efficacy.

Polyelectrolyte Multilayers on Soft Colloidal Nanosurfaces: A New Life for the Layer-By-Layer Method

The Layer-by-Layer (LbL) method is a well-established method for the assembly of nanomaterials with controlled structure and functionality through the alternate deposition onto a template of two mutual interacting molecules, e.g., polyelectrolytes bearing opposite charge. The current development of this methodology has allowed the fabrication of a broad range of systems by assembling different types of molecules onto substrates with different chemical nature, size, or shape, resulting in numerous applications for LbL systems. In particular, the use of soft colloidal nanosurfaces, including nanogels, vesicles, liposomes, micelles, and emulsion droplets as a template for the assembly of LbL materials has undergone a significant growth in recent years due to their potential impact on the design of platforms for the encapsulation and controlled release of active molecules. This review proposes an analysis of some of the current trends on the fabrication of LbL materials using soft colloidal nanosurfaces, including liposomes, emulsion droplets, or even cells, as templates. Furthermore, some fundamental aspects related to deposition methodologies commonly used for fabricating LbL materials on colloidal templates together with the most fundamental physicochemical aspects involved in the assembly of LbL materials will also be discussed.

Impact of mucin on the anti-erosive/anti-abrasive efficacy of chitosan and/or F/Sn in enamel in vitro

The application of stannous ions in combination with fluoride (F/Sn) is one of the central strategies in reducing erosive tooth wear. F/Sn efficacy can be enhanced by adding chitosan, a positively charged biopolymer. For patients with low saliva flow, this efficacy, however, is not sufficient, making further improvement desirable. This could be achieved by combining chitosan with other molecules like mucin, which together might form multilayers. This in-vitro study aimed to investigate the effect of chitosan, mucin, F/Sn and combinations thereof on enamel erosion and erosion-abrasion. Human enamel samples (n = 448, 28 groups) were cyclically eroded or eroded-abraded (10 days; 6 × 2 min erosion and 2 × 15 s/200 g abrasion per day). Samples were treated 2 × 2 min/day with solutions containing either, chitosan (50 or 500 mPas), porcine gastric mucin, F/Sn or combinations thereof after abrasive challenge. Tissue loss was measured profilometrically, interaction between hard tissue and active agents was assessed with energy dispersive spectroscopy and scanning electron microscopy. Chitosan and F/Sn showed the expected effect in reducing tissue loss under erosive and under erosive-abrasive conditions. Neither mucin alone nor the combinations with mucin showed any additional beneficial effect.

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.

Layer-By-Layer Assemblies of Biopolymers: Build-Up, Mechanical Stability and Molecular Dynamics

Rapid development of versatile layer-by-layer technology has resulted in important breakthroughs in the understanding of the nature of molecular interactions in multilayer assemblies made of polyelectrolytes. Nowadays, polyelectrolyte multilayers (PEM) are considered to be non-equilibrium and highly dynamic structures. High interest in biomedical applications of PEMs has attracted attention to PEMs made of biopolymers. Recent studies suggest that biopolymer dynamics determines the fate and the properties of such PEMs; however, deciphering, predicting and controlling the dynamics of polymers remains a challenge. This review brings together the up-to-date knowledge of the role of molecular dynamics in multilayers assembled from biopolymers. We discuss how molecular dynamics determines the properties of these PEMs from the nano to the macro scale, focusing on its role in PEM formation and non-enzymatic degradation. We summarize the factors allowing the control of molecular dynamics within PEMs, and therefore to tailor polymer multilayers on demand.

A closer physico-chemical look to the Layer-by-Layer electrostatic self-assembly of polyelectrolyte multilayers

The fabrication of polyelectrolyte multilayer films (PEMs) using the Layer-by-Layer (LbL) method is one of the most versatile approaches for manufacturing functional surfaces. This is the result of the possibility to control the assembly process of the LbL films almost at will, by changing the nature of the assembled materials (building blocks), the assembly conditions (pH, ionic strength, temperature, etc.) or even by changing some other operational parameters which may impact in the structure and physico-chemical properties of the obtained multi-layered films. Therefore, the understanding of the impact of the above mentioned parameters on the assembly process of LbL materials plays a critical role in the potential use of the LbL method for the fabrication of new functional materials with technological interest. This review tries to provide a broad physico-chemical perspective to the study of the fabrication process of PEMs by the LbL method, which allows one to take advantage of the many possibilities offered for this approach on the fabrication of new functional nanomaterials.

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.

Mucin adsorption on vaterite CaCO3 microcrystals for the prediction of mucoadhesive properties

Porous vaterite CaCO₃ crystals are widely used as containers for drug loading and as sacrificial templates to assemble polymer-based nano- and micro-particles at mild conditions. Special attention is paid nowadays to mucosal delivery where the glycoprotein mucin plays a crucial role as a main component of a mucous. In this work mucoadhesive properties of vaterite crystals have been tested by investigation of mucin binding to the crystals as a function of (i) time, (ii) glycoprotein concentration, (iii) adsorption conditions and (iv) degree of mucin desialization. Mucin adsorption follows Bangham equation indicating that diffusion into crystal pores is the rate-limiting step. Mucin strongly binds to the crystals (ΔG = -35 ± 4 kJ mol^-1) via electrostatic and hydrophobic interactions forming a gel and thus giving the tremendous mucin mass content in the crystals of up to 16%. Despite strong intermolecular mucin-mucin interactions, pure mucin spheres formed after crystal dissolution are unstable. However, introduction of protamine, actively used for mucosal delivery, makes the spheres stable via additional electrostatic bonding. The results of this work indicate that the vaterite crystals are extremely promising carriers for mucosal drug delivery and for development of test-systems for the analysis of the mucoadhesion.

Strategies to overcome the polycation dilemma in drug delivery

Because of polycationic auxiliary agents such as chitosan, polyethyleneimine and cell penetrating peptides as well as cationic lipids assembling to polycationic systems, drug carriers can tightly interact with cell membranes exhibiting a high-density anionic charge. Because of these interactions the cell membrane is depolarized and becomes vulnerable to various uptake mechanisms. On their way to the target site, however, the polycationic character of all these drug carriers is eliminated by polyanionic macromolecules such as mucus glycoproteins, serum proteins, proteoglycans of the extracellular matrix (ECM) and polyanionic surface substructures of non-target cells such as red blood cells. Strategies to overcome this polycation dilemma are focusing on a pH-, redox- or enzyme-triggered charge conversion at the target site. The pH-triggered systems are making use of a slight acidic environment at the target site such as in case of solid tumors, inflammatory tissue and ischemic tissue. Due to a pH shift from 7.2 to slightly acidic mainly amino substructures of polymeric excipients are protonated or shielding groups such as 2,3 dimethylmaleic acid are cleaved off unleashing the underlying cationic character. Redox-triggered systems are utilizing disulfide linkages to bulky side chains such as PEGs masking the polycationic character. Under mild reducing conditions such as in the tumor microenvironment these disulfide bonds are cleaved. Enzyme-triggered systems are targeting enzymes such as alkaline phosphatase, matrix metalloproteinases or hyaluronidase in order to eliminate anionic moieties via enzymatic cleavage resulting in a charge conversion from negative to positive. Within this review an overview about the pros and cons of these systems is provided.

Self-Assembled Mucin-Containing Microcarriers via Hard Templating on CaCO₃ Crystals

Porous vaterite crystals of CaCO₃ are extensively used for the fabrication of self-assembled polymer-based microparticles (capsules, beads, etc.) utilized for drug delivery and controlled release. The nature of the polymer used plays a crucial role and discovery of new perspective biopolymers is essential to assemble microparticles with desired characteristics, such as biocompatibility, drug loading efficiency/capacity, release rate, and stability. Glycoprotein mucin is tested here as a good candidate to assemble the microparticles because of high charge due to sialic acids, mucoadhesive properties, and a tendency to self-assemble, forming gels. Mucin loading into the crystals via co-synthesis is twice as effective as via adsorption into preformed crystals. Desialylated mucin has weaker binding to the crystals most probably due to electrostatic interactions between sialic acids and calcium ions on the crystal surface. Improved loading of low-molecular-weight inhibitor aprotinin into the mucin-containing crystals is demonstrated. Multilayer capsules (mucin/protamine)₃ have been made by the layer-by-layer self-assembly. Interestingly, the deposition of single mucin layers (mucin/water)₃ has also been proven, however, the capsules were unstable, most probably due to additional (to hydrogen bonding) electrostatic interactions in the case of the two polymers used. Finally, approaches to load biologically-active compounds (BACs) into the mucin-containing microparticles are discussed.

From polyelectrolyte complexes to polyelectrolyte multilayers: Electrostatic assembly, nanostructure, dynamics, and functional properties

Polyelectrolyte complexes (PECs) are three-dimensional macromolecular structures formed by association of oppositely charged polyelectrolytes in solution. Polyelectrolyte multilayers (PEMs) can be considered a special case of PECs prepared by layer-by-layer (LbL) assembly that involves sequential deposition of molecular-thick polyelectrolyte layers with nanoscale control over the size, shape, composition and internal organization. Although many functional PEMs with novel physical and chemical characteristics have been developed, the current practical applications of PEMs are limited to those that require only a few bilayers and are relatively easy to prepare. The viability of such engineered materials can be realized only after overcoming the scientific and engineering challenges of understanding the kinetics and transport phenomena involved in the multilayer growth and the factors governing their final structure, composition, and response to external stimuli. There is a great need to model PEMs and to connect PEM behavior with the characteristics of the PEC counterparts to allow for prediction of performance and better design of multilayered materials. This review focuses on the relationship between PEMs and PECs. The constitutive interactions, the thermodynamics and kinetics of polyelectrolyte complexation and PEM formation, PEC phase behavior, PEM growth, the internal structure and stability in PEMs and PECs, and their response to external stimuli are presented. Knowledge of such interactions and behavior can guide rapid fabrication of PEMs and can aid their applications as nanocomposites, coatings, nano-sized reactors, capsules, drug delivery systems, and in electrochemical and sensing devices. The challenges and opportunities in future research directions are also discussed.

Influence of Glycosylation on Interfacial Properties of Recombinant Mucins: Adsorption, Surface Forces, and Friction

Interfacial properties of two brush-with-anchor mucins, C-P55 and C-PSLex, have been investigated at the aqueous solution/poly(methyl methacrylate) (PMMA) interface. Both are recombinant mucin-type fusion proteins, produced by fusing the glycosylated mucin part of P-selectin glycoprotein ligand-1 (PSLG-1) to the Fc part of a mouse immunoglobulin in two different cells. They are mainly expressed as dimers upon production. Analysis of the O-glycans shows that the C-PSLex mucin has the longer and more branched side chains, but C-P55 has slightly higher sialic acid content. The adsorption of the mucins to PMMA surfaces was studied by quartz crystal microbalance with dissipation. The sensed mass, including the adsorbed mucin and water trapped in the layer, was found to be similar for these two mucin layers. Atomic force microscopy with colloidal probe was employed to study surface and friction forces between mucin-coated PMMA surfaces. Purely repulsive forces of steric origin were observed between mucin layers on compression, whereas a small adhesion was detected between both mucin layers on decompression. This was attributed to chain entanglement. The friction force between C-PSLex-coated PMMA is lower than that between C-P55-coated PMMA at low loads, but vice versa at high loads. We discuss our results in terms of the differences in the glycosylation composition of these two mucins.

Do Abrasives Play a Role in Toothpaste Efficacy against Erosion/Abrasion?

Abrasives may counteract the efficacy of anti-erosion toothpastes either due to physical effects or due to interaction with active agents. This study aimed to investigate whether the amount of abrasives is a determinant for the efficacy of Sn2+-containing toothpastes with or without chitosan additive. Enamel samples were eroded (0.50 wt% citric acid, pH 2.5; 6 × 2 min/day) on a shaking desk - 30/min in experiment 1 (E1) and 35/min in experiments 2 (E2) and 3 (E3) - and immersed in toothpaste slurries (2 × 2 min). Half of the samples were additionally brushed (15 s, load 200 g) within the immersion time. The toothpastes contained 0, 5, 10, 15, and 20% silica. In E1 and E2 the active ingredients were F- (700 ppm as amine fluoride, 700 ppm as NaF) and Sn2+ (3,500 ppm as SnCl2); in E3 chitosan (0.5%) was additionally added. The placebo contained 20% silica. Tissue loss was determined profilometrically. In E1, slurries completely inhibited tissue loss; distinct surface deposits occurred. With brushing, tissue loss significantly increased up to an abrasive content of 10%, but decreased significantly with higher amounts; 20% silica revealed similar values as the abrasive-free formulation. In E2, all slurries inhibited tissue loss distinctly irrespective of the amounts of abrasives. With brushing, a similar trend as in E1 was observed but with much less efficacy. The chitosan-containing formulations in E3 were much more effective; similar results as in E1 were found. In conclusion, the amount of abrasives had no effect when toothpastes were applied as slurries, but played an important role with brushing.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

Biopolymeric Mucin and Synthetic Polymer Analogs: Their Structure, Function and Role in Biomedical Applications

Mucin networks are viscoelastic fibrillar aggregates formed through the complex self-association of biopolymeric glycoprotein chains. The networks form a lubricious, hydrated protective shield along epithelial regions within the human body. The critical role played by mucin networks in impacting the transport properties of biofunctional molecules (e.g., biogenic molecules, probes, nanoparticles), and its effect on bioavailability are well described in the literature. An alternate perspective is provided in this paper, presenting mucin’s complex network structure, and its interdependent functional characteristics in human physiology. We highlight the recent advances that were achieved through the use of mucin in diverse areas of bioengineering applications (e.g., drug delivery, biomedical devices and tissue engineering). Mucin network formation is a highly complex process, driven by wide variety of molecular interactions, and the network possess structural and chemical variations, posing a great challenge to understand mucin’s bulk behavior. Through this review, the prospective potential of polymer based analogs to serve as mucin mimic is suggested. These analog systems, apart from functioning as an artificial model, reducing the current dependency on animal models, can aid in furthering our fundamental understanding of such complex structures.

Covalently-crosslinked mucin biopolymer hydrogels for sustained drug delivery

The sustained delivery of both hydrophobic and hydrophilic drugs from hydrogels has remained a challenge requiring the design and scalable production of complex multifunctional synthetic polymers. Here, we demonstrate that mucin glycoproteins, the gel-forming constituents of native mucus, are suitable for assembly into robust hydrogels capable of facilitating the sustained release of hydrophobic and hydrophilic drugs. Covalently-crosslinked mucin hydrogels were generated via exposure of methacrylated mucin to ultraviolet light in the presence of a free radical photoinitiator. The hydrogels exhibited an elastic modulus similar to that of soft mammalian tissue and were sensitive to proteolytic degradation by pronase. Paclitaxel, a hydrophobic anti-cancer drug, and polymyxin B, a positively-charged hydrophilic antibacterial drug, were retained in the hydrogels and released linearly with time over seven days. After four weeks of drug release, the hydrogels continued to release sufficient amounts of active paclitaxel to reduce HeLa cell viability and sufficient amounts of active polymyxin B to prevent bacterial proliferation. Along with previously-established anti-inflammatory, anti-viral, and hydrocarbon-solubilizing properties of mucin, the results of this study establish mucin as a readily-available, chemically-versatile, naturally-biocompatible alternative to complex multifunctional synthetic polymers as building blocks in the design of biomaterials for sustained drug delivery.

Sugar-mediated disassembly of mucin/lectin multilayers and their use as pH-Tolerant, on-demand sacrificial layers

The layer-by-layer (LbL) assembly of thin films on surfaces has proven to be an extremely useful technology for uses ranging from optics to biomedical applications. Releasing these films from the substrate to generate so-called free-standing multilayer films opens a new set of applications. Current approaches to generating such materials are limited because they can be cytotoxic, difficult to scale up, or have undesirable side reactions on the material. In this work, a new sacrificial thin film system capable of chemically triggered dissolution at physiological pH of 7.4 is described. The film was created through LbL assembly of bovine submaxillary mucin (BSM) and the lectin jacalin (JAC) for a (BSM/JAC) multilayer system, which remains stable over a wide pH range (pH 3-9) and at high ionic strength (up to 5 M NaCl). This stability allows for subsequent LbL assembly of additional films in a variety of conditions, which could be released from the substrate by incubation in the presence of a competitive inhibitor sugar, melibiose, which selectively disassembles the (BSM/JAC) section of the film. This novel multilayer system was then applied to generate free-standing, 7 μm diameter, circular ultrathin films, which can be attached to a cell surface as a "backpack". A critical thickness of about 100 nm for the (BSM/JAC) film was required to release the backpacks from the glass substrate, after incubation in melibiose solution at 37 °C for 1 h. Upon their release, backpacks were subsequently attached to murine monocytes without cytotoxicity, thereby demonstrating the compatibility of this mucin-based release system with living cells.

Use of dentifrices to prevent erosive tooth wear: harmful or helpful?

Dental erosion is the loss of dental hard tissues caused by non-bacterial acids. Due to acid contact, the tooth surface becomes softened and more prone to abrasion from toothbrushing. Dentifrices containing different active agents may be helpful in allowing rehardening or in increasing surface resistance to further acidic or mechanical impacts. However, dentifrices are applied together with brushing and, depending on how and when toothbrushing is performed, as well as the type of dentifrice and toothbrush used, may increase wear. This review focuses on the potential harmful and helpful effects associated with the use of dentifrices with regard to erosive wear. While active ingredients like fluorides or agents with special anti-erosive properties were shown to offer some degree of protection against erosion and combined erosion/abrasion, the abrasive effects of dentifrices may increase the surface loss of eroded teeth. However, most evidence to date comes from in vitro and in situ studies, so clinical trials are necessary for a better understanding of the complex interaction of active ingredients and abrasives and their effects on erosive tooth wear.

Randomised in situ study on the efficacy of a tin/chitosan toothpaste on erosive-abrasive enamel loss

Tin is a notable anti-erosive agent, and the biopolymer chitosan has also shown demineralisation-inhibiting properties. Therefore, the anti-erosive/anti-abrasive efficacy of the combination of both compounds was tested under in situ conditions. Twenty-seven volunteers were included in a randomised, double-blind, three-cell crossover in situ trial. Enamel specimens were recessed on the buccal aspects of mandibular appliances, extraorally demineralised (6 × 2 min/day) and intraorally treated with toothpaste slurries (2 × 2 min/day). Within the slurry treatment time, one-half of the specimens received additional intraoral brushing (5 s, 2.5 N). The tested toothpastes included a placebo toothpaste, an experimental NaF toothpaste (1,400 ppm F(-)) and an experimental F/Sn/chitosan toothpaste (1,400 ppm F(-), 3,500 ppm Sn(2+), 0.5% chitosan). The percentage reduction of tissue loss (slurry exposure/slurry exposure + brushing) compared to placebo was 19.0 ± 47.3/21.3 ± 22.4 after use of NaF and 52.5 ± 30.9/50.2 ± 34.3 after use of F/Sn/chitosan. F/Sn/chitosan was significantly more effective than NaF (p ≤ 0.001) and showed good efficacy against erosive and erosive-abrasive tissue loss. This study suggests that the F/Sn/chitosan toothpaste could provide good protection for patients who frequently consume acidic foodstuffs.

Recombinant supercharged polypeptides restore and improve biolubrication

Recombinant supercharged polypeptides (SUPs) with low cytotoxicity are developed and applied to rejuvenate the lubrication of naturally occurring salivary conditioning films (SCFs). SUPs with 72 positive charges adsorbed and rigidified the SCFs and recruited mucins to form a hydrated layer. These SCFs with SUPs have higher mechanical strength and sustain lubricating effect for longer duration compared with only SCFs.

Affinity based multilayered polymeric self-assemblies for oral wound applications

Oral mucositis, a painful and debilitating ulcerative wound condition, is a frequently occurring complication following chemo- and/or radiotherapy. While the current standards of therapy (e.g., gels and mouth rinses) provide temporary relief, there is still an unmet need for a robust, long acting barrier that can provide lubricating protection in oral wounds, thereby enhancing the wound healing response. It is proposed that an affinity based layer-by-layer (LBL) self-assembly that can be administered as a series of mouth rinses could permit the formation of protective barriers, providing a modular approach to regenerative oral therapy. In this study, biotinylated poly(acrylic acid) was synthesized for developing LBL assemblies using biotin-streptavidin affinity linkages. To explore the ability of developed LBL assemblies to potentially resist the harsh intraoral environment, in vitro chemical and ex vivo mechanical tests were performed. The stability results demonstrated significant LBL barrier stability with wear resistance. From statistical analyses, it was deduced that polymer MW and the number of LBL layers contributed significantly to chemical barrier stability. Also, the extent of biotin conjugation played a key role for LBL development and in mechanical barrier stability. Thus, the proposed affinity based LBLs with their excellent barrier properties offer a modular treatment approach in oral mucosal injuries.

Mucin multilayers assembled through sugar-lectin interactions

Multilayer films of biopolymers are attractive tools to exploit the extraordinary properties of certain biomacromolecules and introduce new functionalities to surfaces. Mucins, the gel-forming constituents of mucus, are versatile glycoproteins that have potential as new building blocks for biomaterial surface coatings. Multilayer films have mostly been assembled through the electrostatic pairing of polyelectrolytes, which results in limited pH and salt stability and screens charges otherwise available for useful payload binding. Here, we aim at assembling mucin multilayer films that differ from conventional paired polyelectrolyte assemblies to obtain highly stable and functional surface modifications. Using the lectin wheat germ agglutinin (WGA) to cross-link mucin-bound sugar residues, we show that (Mucin/WGA) films can grow into hydrated films and sustain exceptional resistance to extreme salt conditions and a large range of pH. Furthermore, we show that the addition of soluble N-acetyl-d-glucosamine can induce the controlled release of WGA from (Mucin/WGA) films. Last, we show that (Mucin/WGA) films can repeatedly incorporate and release a positively charged model cargo. The lubricating, hydration, barrier, and antimicrobial properties of mucins open multiple applicative perspectives for these highly stable mucin-based multilayer films.

Proteomic profiling of the planarian Schmidtea mediterranea and its mucous reveals similarities with human secretions and those predicted for parasitic flatworms

The freshwater planarian Schmidtea mediterranea has been used in research for over 100 years, and is an emerging stem cell model because of its capability of regenerating large portions of missing body parts. Exteriorly, planarians are covered in mucous secretions of unknown composition, implicated in locomotion, predation, innate immunity, and substrate adhesion. Although the planarian genome has been sequenced, it remains mostly unannotated, challenging both genomic and proteomic analyses. The goal of the current study was to annotate the proteome of the whole planarian and its mucous fraction. The S. mediterranea proteome was analyzed via mass spectrometry by using multidimensional protein identification technology with whole-worm tryptic digests. By using a proteogenomics approach, MS data were searched against an in silico translated planarian transcript database, and by using the Swiss-Prot BLAST algorithm to identify proteins similar to planarian queries. A total of 1604 proteins were identified. The mucous subproteome was defined through analysis of a mucous trail fraction and an extract obtained by treating whole worms with the mucolytic agent N-acetylcysteine. Gene Ontology analysis confirmed that the mucous fractions were enriched with secreted proteins. The S. mediterranea proteome is highly similar to that predicted for the trematode Schistosoma mansoni associated with intestinal schistosomiasis, with the mucous subproteome particularly highly conserved. Remarkably, orthologs of 119 planarian mucous proteins are present in human mucosal secretions and tear fluid. We suggest planarians have potential to be a model system for the characterization of mucous protein function and relevant to parasitic flatworm infections and diseases underlined by mucous aberrancies, such as cystic fibrosis, asthma, and other lung diseases.

Influence of the percentage of acetylation on the assembly of LbL multilayers of poly(acrylic acid) and chitosan

The Layer-by-Layer (LbL) self-assembly of polyelectrolyte multilayers (PEMs) formed by poly(acrylic acid) (PAA) and chitosan (CHI) of two different percentages of acetylation (AC) has been studied by dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The results point out that the non-linear growth (exponential growth) of the films is not modified by the percentage of acetylation of the CHI (AC). The comparison of the thickness obtained by D-QCM and by ellipsometry has allowed us to calculate the water content of the films showing that the multilayers are highly hydrated. This agrees with the values of the complex shear modulus obtained from the analysis of D-QCM data that are in the MPa range, and show a transition from a viscous to mainly elastic behavior depending on the charge density of the CHI chains. The monomer surface density in each layer (obtained from the combination of ellipsometry and differential refractive index measurements) indicated that the mechanism of charge compensation depends on the percentage of acetylation of the CHI. It was found that the adsorption kinetics is a bimodal process with characteristic times that depend on the number and nature of each layer. The load capacity of the multilayers for a β-blocker, propranolol, was found to be higher for the lowest acetylation degree.

pH-induced changes in the fabrication of multilayers of poly(acrylic acid) and chitosan: fabrication, properties, and tests as a drug storage and delivery system

Multilayers of poly(acrylic acid), PAA, and chitosan, CHI, have been built by the layer-by-layer (LbL) method from aqueous solutions at different pH values and analyzed by the dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The results showed that under all of the assembly conditions considered the growth of the films is nonlinear. The thickness of the PAA layers increases as the pH of the assembling solutions decreases, whereas the adsorption of CHI is almost unaffected by the pH conditions. The comparison of the thickness obtained by D-QCM and by ellipsometry has allowed us to calculate the water content of the films, showing that the multilayers are highly hydrated, with an average water content higher than 20%. The analysis of D-QCM data has provided high-frequency values of the complex shear modulus that are in the megapascal range and shows a transition from mainly viscous to mainly elastic behavior for the added PAA layers, depending on the pH. The monomer surface density in each layer (obtained from the combination of ellipsometry and differential refractive index measurements) indicated that the monomer density depends on the assembly conditions. It was found that the adsorption kinetics is a bimodal process, with characteristic times that depend on the number and nature of the layers. Finally, the possibility of using of these multilayers as a drug storage and delivery system has been evaluated.