Medical devices are susceptible to biofilm formation which can cause infections in patients. Possible ways to reduce biofilm formation are coatings known as polyelectrolyte multilayers (PEMs); thin films prepared by adsorption of oppositely charged polyelectrolytes to a solid surface. In this study we prepared PEMs out of biocompatible polyelectrolytes, chitosan and pectin, to determine the influence of ionic strength and a precursor layer on their formation and properties. Surface characterization using ellipsometry, tensiometry, and AFM revealed that ionic strength has no significant impact on PEM properties, while the addition of a precursor layer significantly affects the film thickness and morphology. Furthermore, surface coverage with bacteria was determined with SEM demonstrating that the chitosan-terminating multilayer is more efficient against adhesion of E. coli than the pectin-terminating one. The examined multilayers show significant potential in biomedical and related applications due to the material biocompatibility, anti-adhesive properties and inexpensive preparation.

Background Sustainable and low-cost adsorbents are needed for effective removal of organic pollutants from water. However, many high-performance activated carbons require chemical activation, increasing environmental impact and production costs. Insect-farming by-products, such as pupal casings of the black soldier fly (Hermetia illucens), remain largely unexplored as precursors for physically activated carbons. Objective This study evaluated the feasibility of converting Hermetia illucens pupal casings into effective carbon adsorbents using chemical-free physical activation and assessed their ability to remove structurally diverse organic pollutants from water. Methods Activated carbons were produced by direct CO2 activation at 700 and 800 °C using microwave and conventional heating. The materials were characterized by nitrogen adsorption/desorption, X-ray photoelectron spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction. Batch adsorption experiments examined the effects of pH, temperature, adsorbent dose, shaking speed, and pollutant concentration. Adsorption equilibrium, kinetics, and thermodynamics were analyzed using Langmuir and Freundlich isotherms and pseudo-first-, pseudo-second-order models and intraparticle diffusion model. Results The carbons showed basic surface properties and surface areas of 88–355 m2/g. The best sample achieved adsorption capacities of 160 mg/g for ethyl-4-hydroxybenzoate, 214 mg/g for poly(sodium 4-styrenesulfonate), and 155 mg/g for methylene blue. Adsorption followed the Langmuir model and pseudo-second-order kinetics and was spontaneous and endothermic. Regeneration tests confirmed good stability, with second-cycle desorption efficiencies of 67–80%. Conclusions Physically activated carbons derived from Hermetia illucens pupal casings offer competitive adsorption performance without chemical activating agents, providing a sustainable route for insect biomass waste valorization.

STATEMENT OF PROBLEM:Low-pressure airborne-particle abrasion has been used to improve the adhesion of zirconia to resin cement. However, whether a polyelectrolyte multilayer can be used to reduce bacterial adhesion to abraded zirconia is unclear. PURPOSE:The purpose of this in vitro study was to evaluate whether polyelectrolyte multilayers added to airborne-particle abraded zirconia can minimize biofilm development. MATERIAL AND METHODS:Commercially available zirconia powders with yttria content between 3 and 5 mol% were isostatically pressed into Ø20-mm disks and sintered at 1450 °C for 2 hours (n=8). Untreated specimens were compared with airborne-particle abraded ones. Specimens with 3 mol% yttria were further coated with polyelectrolyte multilayers (n=4). The surfaces were characterized by measuring the roughness, hydrophobicity, and surface charge using profilometry, atomic force microscopy, tensiometry, and electrokinetic analyzer, respectively. The extent of bacterial adhesion was determined using spectrophotometry and scanning electron microscopy. Data were analyzed with a single-factor ANOVA and F-test for variance (α=.05). RESULTS:The airborne-particle abrasion of zirconia increased the surface roughness, which led to the pronounced adhesion of Streptococcus mutans. However, polyelectrolyte multilayer coatings made of chitosan and pol(yacrylic acid) reduced the extent of bacterial adhesion, especially in as-sintered specimens, with 70% fewer adhered bacteria than airborne-particle abraded specimens. The effect of polyelectrolyte multilayer coating on the airborne-particle abraded series was greatest with the poly(acrylic acid)-terminating specimens, with 50% fewer adhered bacteria than the uncoated ones. CONCLUSIONS:Airborne-particle abraded zirconia specimens coated with biocompatible polyelectrolyte multilayer coatings with a negatively charged terminating layer were associated with a 50% reduction in bacteria adhesion compared with uncoated specimens.

Due to teeth loss, a large proportion of the elderly rely on full or partial dentures for esthetic, speaking, and eating reasons. A variety of polymers are used in the production of removable prostheses, with poly-(methyl methacrylate) (PMMA) being a widely used material for making denture bases. However, underdenture stomatitis caused by the fungi Candida albicans is still an open problem. The purpose of this work was to consider the impact of polyelectrolyte multilayer (PEM) coating on PMMA surfaces and the effect of the addition of sucrose on the adhesion properties of C. albicans. Two polyelectrolytes were applied for the formation of the PEM coating: poly-(allylamine) hydrochloride (PAH) and poly-(acrylic) acid (PAA). The uncoated and coated surfaces were characterized in terms of topography, surface potential, and hydrophobicity. The extent of adhesion of C. albicans to the surfaces was assessed by scanning electron microscopy. Results show that surfaces coated with negatively charged PAA as the PEM terminating layer adhere less C. albicans than uncoated PMMA or surfaces coated with positively charged PAH as the PEM terminating layer. The addition of sucrose increases the fungal adhesion extent of C. albicans to both types of coated surfaces, lowering the PAA antiadhesion properties. With the addition of sucrose, we were trying to mimic the impact of dentures on patients with a sugar-rich diet.

Polyelectrolyte multilayers are nanofilms often prepared out of polysaccharides with a wide range of applications as anticorrosion, antireflective or antimicrobial coatings. In this study, we prepared films from two biocompatible polysaccharides, chitosan and carboxymethyl cellulose. Such thin films, when prepared on model surfaces such as silicon or glass, change the optical properties of the surface. For this reason, we modified the films postadsorption by immersing them in sodium chloride solution, a process known as salt annealing. By varying the salt concentration and duration of annealing, both surface and optical properties of the multilayer were tuned and improved. The untreated films made the substrate reflect light more diffusely, leading to a clouded appearance of the surface. This effect was reduced via salt annealing, resulting in a film which does not affect the optical properties of the surface. In addition to the changes in optical properties, the wetting behaviour of the films was also studied. This study successfully correlates film roughness and the changes in the diffuse reflectance. Furthermore, as a proof of concept for application, the chitosan/carboxymethyl cellulose film was successfully prepared on a cherry tomato where salt annealing successfully diminished the influence of the film on its reflective properties.

Polyelectrolyte multilayers (PEMs) are nanocoatings with possible applications in various areas, such as biomedicine and food technology. Recently, PEMs have been getting a lot of attention as potential food coatings for the prevention of fruit decay during transportation, storage, and shelf life. In this study, we fabricated thin films made of biocompatible polyelectrolytes, positively charged polysaccharide chitosan (CS), and negatively charged carboxymethyl cellulose (CMC) on apple surface and compared the results with the same multilayers formed on a model silica surface. The aim of our research is to correlate the fundamental aspects of the PEM build-up with their applications and to examine if contact angle measurements could be a useful tool for studying the formation of PEMs on apple surfaces. The influence of various experimental conditions on PEM formation was examined, and it was shown that the PEM build-up and properties such as thickness and hydrophobicity strongly depend on the applied experimental conditions (e.g., pH of the polyelectrolyte solutions). Moreover, for the first time we showed that the PEM build-up on apples could be verified using contact angle measurements. The most dominant zigzag pattern on both silica and apple surfaces at pH(CS) = 5.0 and pH(CMC) = 3.0 highlights the optimal conditions for multilayer formation and suggests that this process can be effectively monitored by using contact angle measurements. All of the results obtained in our study could serve as a basis for obtaining tuned biocompatible transparent polyelectrolyte multilayers on apples with optimized physicochemical properties, which could lead to the enhanced applications of the PEMs in the field of food technology.

Polymers whose repeating units bear an electrolyte group, so-called polyelectrolytes, are the main building blocks of polyelectrolyte multilayers (PEMs). These thin organicfilms are versatile nanomaterials with applications in many fields. The main reason for their widespread applications lies in the ability to fine-tune their properties simply by adjusting the experimental conditions of their preparation. One of these parameters is the molecular weight of polyelectrolytes utilized for PEM preparation. Although about three decades have passed since the preparation of the first PEM, consensus among scientists about the influence of polyelectrolyte molecular weight on the properties of PEMs still has not been achieved. For example, several studies have shown that PEM thickness increases with the increase of polymer molecular weight, others that PEM thickness decreases with polymer molecularweight, and third that molecularweight does not influence film thickness. To shed some light on these somehow contradictory findings, we report here the results of a study in which we explore the influence of polyelectrolyte molecular weight on the properties of PEM not as an independent parameter but as a variable related to the polyelectrolyte degree of charging. For that purpose, we prepared PEMs via the layer-by-layer assemblywith two distinct molecularweights of poly(allylamine hydrochloride) and poly(acrylic acid) at pH = 5.0, 8.0 (with and without NaCl), and 10.0. In the end, we found that the thickness and, for the most part, the surface roughness of prepared films increased with higher molecular weights of polyelectrolytes in all examined conditions except at pH = 8.0. In that condition, the molecular weight of polymers did not affect the PEM properties because polyelectrolytes are highly charged at that pH and adsorb to a surface in a linear conformation. In other conditions, the impact of polyelectrolyte molecular weight on growth and properties of PEM has been explained by the packing of chain molecules at the film surface (pH = 5.0 and pH = 8.0 with NaCl) or by film erosion thatwas noticed during PEM build up (pH = 10.0).

A study was conducted to investigate the adsorption mechanism of ethyl-4-hydroxybenzoate and poly(sodium 4styrenesulfonate) on activated carbons produced through a two-step process involving carbonization in a nitrogen atmosphere and activation using potassium carbonate. The precursor for the activated carbons was the empty pupal casings of the Hermetia illucens fly. A physicochemical analysis of the materials was conducted during the study. The activated carbons were found to exhibit a slightly acidic surface, with a range of sizes from 979 to 2033 m2/g. The adsorption kinetics of these compounds were found to follow a pseudo-second-order model. The adsorption isotherms of the carbonaceous materials with respect to the tested compounds demonstrated alignment with the Langmuir model. The experimental adsorption capacity of the activated carbons for ethyl-4-hydroxybenzoate was observed to range from 498 to 696 mg/g, while for poly(sodium 4-styrenesulfonate) it was in the range of 343 to 449 mg/g at pH value 6.3 for ethyl-4-hydroxybenzoate and 6.9 for poly (sodium 4-styrenesulfonate and temperature 295 +/- 1 K. In the tested conditions, the adsorption was an endothermic and spontaneous process. The synthesized activated carbons demonstrated the capacity for regeneration. The highest desorption efficiencies for ethyl-4-hydroxybenzoate and poly(sodium 4-styrenesulfonate) after the second cycle were 74 and 79 %, respectively, for the adsorbents tested.

Multilayer films made of strong polyelectrolytes poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate) were built-up on silicon wafer using the layer-by-layer method. The films were built-up in the presence of various divalent cations (Mg2+, Ca2+, Sr2+, Ni2+, Zn2+, and Cu2+) to examine how the nature of cations affects the properties of the film. The results have shown that the thickness, morphology, and roughness of films prepared in the presence of transition metal cations are not significantly different. In contrast, these properties varied for multilayers prepared in the presence of alkaline earth metal cations. The difference in the ion-specific behavior of these two classes of cations was explained by the difference in the hydration of these ions and by the bridging of polyelectrolyte chains with ions. While transition metal cations have similar hydration parameters, alkaline earth cations have different degrees of hydration and a better ability to form bridging bonds with polyelectrolyte monomers.

The prevalence of bacterial infections presents a significant challenge in the medical field, demanding effective strategies to impede bacterial adhesion and growth on various surfaces. The conducted study investigates the efficacy of polyelectrolyte multilayers & horbar;comprising poly(allylamine hydrochloride) (PAH) and alginate (ALG)& horbar;embedded with zinc oxide (ZnO) and copper oxide (CuO) nanoparticles (NPs) to inhibit bacterial adhesion on stainless-steel surfaces. Surface characterization involved zeta potential, contact angle, and roughness assessments. The effect of NP composition, size, and morphology in conjunction with polycation or polyanion terminating multilayers was evaluated against planktonic and surface-adhered Escherichia coli (E. coli) cells. Surfaces with the positively charged PAH-terminating multilayer displayed higher water contact angles (approximate to 63 degrees) than the negatively charged ALG-terminating multilayers (approximate to 45 degrees). Multilayers containing ZnO NPs showed a significant inhibition of planktonic E. coli growth, >99%. Moreover, complete growth inhibition of surface-adhered E. coli was achieved for multilayers containing both ZnO and CuO. Due to their larger specific surface area, rod-like ZnO NPs displayed higher antibacterial activity. The samples with ALG as the terminating layer showed more substantial antibacterial properties than samples with PAH as the terminating layer. Biocompatibility tests on immortalized human keratinocyte cells revealed good compatibility with multilayers incorporating NPs. In summary, this study underscores the potential of ZnO and CuO NPs within PAH/ALG multilayers for antibacterial applications without compromising their cytocompatibility.

TiO2 nanotubes constitute very promising nanomaterials for water decontamination by the removal of cations. We combined a range of experimental techniques from structural analyses to measurements of the properties of aqueous suspensions of nanotubes, with (i) continuous solvent modeling and (ii) quantum DFT-based simulations to assess the adsorption of Cs+ on TiO2 nanotubes and to predict the separation of metal ions. The methodology is set to be operable under realistic conditions, which, in this case, include the presence of CO2 that needs to be treated as a substantial contaminant, both in experiments and in models. The mesoscopic model, based on the Poisson-Boltzmann equation and surface adsorption equilibrium, predicts that H+ ions are the charge-determining species, while Cs+ ions are in the diffuse layer of the outer surface with a significant contribution only at high concentrations and high pH. The effect of the size of nanotubes in terms of the polydispersity and the distribution of the inner and outer radii is shown to be a third-order effect that is very small when the nanotube layer is not very thick (ranging from 1 to 2 nm). Besides, DFT-based molecular dynamics simulations demonstrate that, for protonation, the one-site and successive association assumption is correct, while, for Cs+ adsorption, the size of the cation is important and the adsorption sites should be carefully defined.

Goethite was modified by chitosan (CS) or poly(acrylic acid) (PAA) to improve its adsorptive abilities toward components of agrochemicals, i.e., copper ions (Cu), phosphate ions (P), and diuron. The pristine goethite effectively bound Cu (7.68 mg/g, 63.71%) and P (6.31 mg/g, 50.46%) only in their mixed systems. In the one adsorbate solutions, the adsorption levels accounted for 3.82 mg/g (30.57%) for Cu, 3.22 mg/g (25.74%) for P, and 0.15 mg/g (12.15%) for diuron. Goethite modification with CS or PAA did not yield spectacular results in adsorption. The maximum increase in adsorbed amount was noted for Cu ions (8.28%) after PAA modification as well as for P (6.02%) and diuron (24.04%) after CS modification. Both goethite modifications contributed to clear reduction in desorption of pollutants (even by 20.26% for Cu after PAA coating), which was mainly dictated by electrostatic attractive forces and hydrogen bonds formation occurring between macromolecules and impurities. The only exception in this phenomenon was Cu desorption from CS-modified solid-the polymer made it higher (to 95.00%). The Cu adsorption on PAA-modified goethite enhanced solid aggregation and thus facilitated metal cation separation from aqueous media. Consequently, the goethite modification with PAA was considered more promising for environmental remediation.

In this study, the high-resolution ultrasonic spectroscopy (HR-US) technique was applied to examine interpolyelectrolyte neutralization. The mentioned method was tested on the example of complexation between poly(allylammonium) cations and poly(acrylate) anions in aqueous solutions at pH = 7. It was confirmed by HR-US that the type of titration (stepwise or abrupt), the direction of titration, and the type of background salt affect the outcome of interpolyelectrolyte neutralization. The obtained results were explained on the basis of ultrasonic velocity and attenuation changes in the context of suspension compressibility, a parameter that is extremely sensitive to molecular organization and intermolecular interactions. Moreover, the results of HR-US measurements proved to be consistent with previous results obtained by more traditional methods such as dynamic light scattering, microcalorimetry, and electrokinetics. This research demonstrates that HR-US is a convenient and reliable method that can be employed for the investigation of interpolyelectrolyte neutralization and polyelectrolyte-related processes.

Polyelectrolyte multilayers are nanofilms with vast applications in numerous areas such as medicine and food industry. Recently, they have been getting a lot of attention as potential food coatings for the prevention of fruit decay during transportation and storage, and therefore the coatings need to be biocompatible. In this study, we fabricated thin films made of biocompatible polyelectrolytes, positively charged polysaccharide chitosan, and negatively charged carboxymethyl cellulose on a model silica surface. Typically, to enhance the properties of the prepared nanofilms, the first layer (precursor layer) of poly(ethyleneimine) is used. However, for the construction of completely biocompatible coatings, this could be problematic due to potential toxicity. This study offers an option for a viable candidate as a replacement precursor layer: chitosan itself was adsorbed from a more concentrated solution. In the case of chitosan/carboxymethyl cellulose films, using chitosan over poly(ethyleneimine) as a precursor layer has shown a twofold increase in film thickness, as well as an increase in film roughness. In addition, these properties can be tuned by the presence of a biocompatible background salt (e.g., sodium chloride) in the deposition solution that has proven to change the film thickness and surface roughness depending on the salt concentration. Such a straightforward way of tuning the properties of these films combined with their biocompatibility makes this precursor material a prime candidate for use as a potential food coating.

Thin films made of weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) have been fabricated on silicon wafers using the layer-by-layer (LbL) method. To study the influence of counteranion type on the growth and properties of PAH/PAA multilayers, the nature of the supporting sodium salt was varied from cosmotropic to chaotropic anions (F-, Cl-, and ClO4 -). Results of ellipsometry and AFM measurements indicate that the film thickness and surface roughness systematically increase on the order F- < Cl- < ClO4 -. Furthermore, we found that the hydrophobicity of the PAH/PAA multilayer also follows the described trend when a polycation is the terminating layer. However, the heating of PAH/PAA multilayers to 60 °C during the LbL assembly suppressed the influence of background anions on the multilayer formation and properties. On the basis of the obtained results, it could be concluded that thermal annealing induces changes at the polymer-air interface in the sense of reorientation and migration of polymer chains.

Thin films called polyelectrolyte multilayers could be formed by alternate adsorption of positively and negatively charged polyelectrolytes. In the case of adsorption on nanoparticles followed by the dissolution of the template, it is possible to prepare hollow polyelectrolyte capsules. Due to a large number of available polymeric compounds and easily tunable multilayer properties, these systems find their application in various fields such as biomedicine and catalysis. In this study we focused on the design, synthesis and characterization of capsules of nanometer dimensions made of nontoxic weak polyelectrolytes, poly(allylamine) and poly(acrylic acid) in a water medium using fully biocompatible hydroxyapatite nanoparticles as template. The formation of the polyelectrolyte multilayer was monitored by measuring the electrophoretic mobility of particles. After the optimization of the core decomposition conditions, hollow polyelectrolyte capsules were prepared by dissolution of the template in the presence of HCl. Further characterization was performed using Fourier-transform infrared spectroscopy, energy dispersion X-ray spectroscopy, dynamic light scattering, scanning electron microscopy, and atomic force microscopy. With these techniques, the chemical composition, structure, size, morphology and stability of obtained nanocapsules were determined. It was found that the capsules are of a rather narrow size distribution ranging from 100 to 250 nm with a flexible capsule wall being only a few tens of nanometers thick which is very important in the case of future applications in the field of drug delivery. Moreover, the dispersions of nanocapsules were stable for at least 40 days. This extreme stability of nanocapsules could be probably attributed to their low mass, small dimensions, and high surface charge.

Polyelectrolyte multilayers are coatings formed by the alternate deposition of polycations and polyanions on a charged surface. In this study we examined how the type of substrate affects a multilayer prepared from poly(allylamine hydrochloride) and poly(acrylic acid). Silicon and titanium wafers were used as substrates. Their properties were systematically studied using ellipsometry, tensiometry, atomic force microscopy and streaming potential measurements. Multilayers were built up at pH = 7 with tetramethylammonium chloride as the background salt. The growth of films was monitored by ellipsometry, while the morphology and surface roughness were determined by atomic force microscopy. It was found that the thickness of multilayers containing 10 layers on silicon is 10 nm, whereas the thickness of the same film on titanium is three times higher. It was shown that multilayers formed on silicon display a grain-like structure, which was not the case for a film formed on titanium. Such morphological properties are also reflected in the surface roughness. Finally, it was shown that, in addition to the electrostatic interactions, the hydrophobicity of the substrate also plays an important role in the polyelectrolyte multilayer formation process and influences its thickness and properties.