Josefin Illergård

Interactions of hydrophobically modified polyvinylamines: adsorption behavior at charged surfaces and the formation of polyelectrolyte multilayers with polyacrylic acid.

The structure and adsorption behaviors of two types of hydrophobically modified polyvinylamines (PVAm) containing substituents of hexyl and octyl chains were compared to a native polyvinylamine sample. The conformation of dissolved polyvinylamines was studied in aqueous salt solutions using dynamic light scattering. Modified PVAm showed hydrodynamic diameters similar to native PVAm, which indicated that all PVAm polymers were present as single molecules in solution. The adsorption of the polyvinylamines, both native and hydrophobically modified, from aqueous solution onto negatively charged silica surfaces was studied in situ by reflectometry and quartz crystal microgravimetry with dissipation. Polyelectrolyte multilayers (PEM) with up to nine individual layers were formed together with poly(acrylic acid). Obtained PEM structures were rigid and showed high adsorbed amounts combined with low dissipation, with similar results for both the modified and unmodified PVAm. This suggests that electrostatics dominated the PEM formation. At lower salt concentrations, the hydrophobically modified PVAm produced multilayers with low water contents, indicating that secondary interactions induced by the hydrophobic constituents can also have a significant influence on the properties of the formed layers. The surface structure of PEMs with nine individual layers was imaged in dry state using atomic force microscopy in a dynamic mode. Modified PVAm was found to induce a different structure of the PEM at 100 mM, with larger aggregates compared to those of native PVAm. From these results, it is proposed that modified PVAm can induce aggregation within the PEM, whereas PVAm remains as single molecules in solution.

Bacterial-growth inhibiting properties of multilayers formed with modified polyvinylamine

New methods are needed to fight antibiotic-resistant bacteria. One alternative that has been proposed is non-leaching, permanently antibacterial surfaces. In this study, we test multilayers formed with antibacterial cationic polyvinylamine (PVAm) and polyacrylic acid (PAA) in a growth-inhibition assay. Both hydrophobically modified and native PVAm were investigated. Multilayers did reduce the bacterial growth, as compared to single layers. However, the sampling time in the assay was critical, as the treated surface area is a capacity-limiting factor. After 2h incubation, a maximal growth inhibition of more than 99% was achieved with multilayers. In contrast, after 8h we observed a maximal growth-inhibition of 40%. At longer incubation times, the surface becomes saturated, which explains the observed time-dependent effectiveness. The polymers giving multilayers with the strongest growth-inhibiting properties were native PVAm and PVAm modified with C(8), which also were the polymers with highest charge density. We therefore conclude that this effect is mainly an electrostatically driven process. Viability staining using a fluorescent stain showed a high viability rate of the adhered bacteria. The multilayers are therefore more bacteriostatic than antibacterial.

Contact-active antibacterial multilayers on fibres: a step towards understanding the antibacterial mechanism by increasing the fibre charge

Abstract Contact-active antibacterial materials with irreversibly attached antibacterial agents have been developed as an environmentally friendly alternative to traditional biocide treatments. Of particular interest are materials fabricated through the physical adsorption of charged polymers. This simple method allows for the use of water-based processes and materials originating from renewable sources, e.g., cellulosic fibres. Furthermore, by varying the process parameters, such as ionic strength, it is possible to tune the properties of the adsorbed polymer layer. However, the underlying antibacterial mechanism remains obscure, and this hinders the rational design of antibacterial multilayers. To gain further insight into the antibacterial mechanisms of physically adsorbed multilayers of polyvinylamine and polyacrylic acid, the surface charge of cellulose fibres was increased via radical oxidation. This oxidation increased the amount of polymer that was adsorbed and resulted in increased antibacterial efficacy against both Escherichia coli and Bacillus subtilis compared with polymer-modified unoxidised fibres. Electron microscopy analysis of the E. coli adhered to the fibres revealed that the multilayer treatment resulted in elongated bacteria with deformed cell walls. This work demonstrates the importance of electrostatic interaction to the antibacterial effect of polymer-modified fibres .

Contact-active antibacterial aerogels from cellulose nanofibrils.

The use of cellulose aerogels as antibacterial materials has been investigated by applying a contact-active layer-by-layer modification to the aerogel surface. Studying the adsorption of multilayers of polyvinylamine (PVAm) and polyacrylic acid to aerogels comprising crosslinked cellulose nanofibrils and monitoring the subsequent bacterial adhesion revealed that up to 26mgPVAmgaerogel(-1) was adsorbed without noticeably affecting the aerogel structure. The antibacterial effect was tested by measuring the reduction of viable bacteria in solution when the aerogels were present. The results show that >99.9% of the bacteria adhered to the surface of the aerogels. Microscopy further showed adherence of bacteria to the surfaces of the modified aerogels. These results indicate that it is possible to create materials with three-dimensional cellulose structures that adsorb bacteria with very high efficiency utilizing the high specific surface area of the aerogels in combination with their open structure.

Bacterial adhesion to polyvinylamine-modified nanocellulose films

Cellulose nanofibril (CNF) materials have been widely studied in recent years and are suggested for a wide range of applications, e.g., medical and hygiene products. One property not very well studied is the interaction between bacteria and these materials and how this can be controlled. The current work studies how bacteria adhere to different CNF materials modified with polyelectrolyte multilayers. The tested materials were TEMPO-oxidized to have different surface charges, periodate-oxidized to vary the water interaction and hot-pressed to alter the surface structure. Then, multilayers were constructed using polyvinylamine (PVAm) and polyacrylic acid. Both the material surface charge and water interaction affect the amount of polymer adsorbed to the surfaces. Increasing the surface charge decreases the adsorption after the first PVAm layer, possibly due to conformational changes. Periodate-oxidized and crosslinked films have low initial polymer adsorptions; the decreased swelling prevents polymer diffusion into the CNF micropore structure. Microscopic analysis after incubating the samples with bacterial suspensions show that only the materials with the lowest surface charge enable bacteria to adhere to the surface because, when adsorbing up to 5 layers PVAm/PAA, the increased anionic surface charge appears to decrease the net surface charge. Both the amounts of PVAm and PAA influence the net surface charge and thus the bacterial adhesion. The structure generated by the hot-pressing of the films also strongly increases the number of bacteria adhering to the surfaces. These results indicate that the bacterial adhesion to CNF materials can be tailored using polyelectrolyte multilayers on different CNF substrates.

Tailoring the effect of antibacterial polyelectrolyte multilayers by choice of cellulosic fiber substrate

Abstract There is a need for new, antibacterial cellulose-based materials. Antibacterial cellulosic fibers with irreversibly attached polyvinylamine (PVAm) and polyacrylic acid (PAA) in multilayers were developed based on a water-based physical adsorption process. The antibacterial substance is thus prevented from leaching, in contrast to materials containing, for example, silver. It was shown on fibers from different sources that the antibacterial effect against both Escherichia coli and Bacillus subtilis can be tailored. The efficiency correlated with the initial fiber charge, which in turn correlated with the amount of adsorbed PVAm. In the case of highly charged fibers, the antibacterial efficacy was more than 99.9%. A sustainable antibacterial material can be obtained in a simple way based on a water-based process.

Water Purification Using Functionalized Cellulosic Fibers with Nonleaching Bacteria Adsorbing Properties

Portable purification systems are easy ways to obtain clean drinking water when there is no large-scale water treatment available. In this study, the potential to purify water using bacteria adsorbing cellulosic fibers, functionalized with polyelectrolytes according to the layer-by-layer method, is investigated. The adsorbed polyelectrolytes create a positive charge on the fiber surface that physically attracts and bonds with bacteria. Three types of cellulosic materials have been modified and tested for the bacterial removal capacity in water. The time, material-water ratio and bacterial concentration dependence, as well as the bacterial removal capacity in water from natural sources, have been evaluated. Freely dispersed bacteria adsorbing cellulosic fibers can remove greater than 99.9% of Escherichia coli from nonturbid water, with the most notable reduction occurring within the first hour. A filtering approach using modified cellulosic fibers is desirable for purification of natural water. An initial filtration test showed that polyelectrolyte multilayer modified cellulosic fibers can remove greater than 99% of bacteria from natural water. The bacteria adsorbing cellulosic fibers do not leach any biocides, and it is an environmentally sustainable and cheap option for disposable water purification devices.

Effect of cationic polyelectrolytes in contact-active antibacterial layer-by-layer functionalization

Abstract Contact-active surfaces have been created by means of the layer-by-layer (LbL) modification technique, which is based on previous observations that cellulose fibers treated with polyelectrolyte multilayers with polyvinylamine (PVAm) are perfectly protected against bacteria. Several different cationic polyelectrolytes were applied, including PVAm, two different poly(diallyl dimethyl ammonium chloride) polymers and two different poly(allylamine hydrochloride) polymers. The polyelectrolytes were self-organized in one or three layers on cellulosic fibers in combination with polyacrylic acid by the LbL method, and their antibacterial activities were evaluated. The modified cellulose fibers showed remarkable bacterial removal activities and inhibited bacterial growth. It was shown that the interaction between bacteria and modified fibers is not merely a charge interaction because a certain degree of bacterial cell deformation was observed on the modified fiber surfaces. Charge properties of the modified fibers were determined based on polyelectrolyte titration and zeta potential measurements, and a correlation between high charge density and antibacterial efficiency was observed for the PVAm and PDADMAC samples. It was demonstrated that it is possible to achieve antibacterial effects by the surface modification of cellulosic fibers via the LbL technique with different cationic polyelectrolytes.