Polysaccharides Thin Film Based On Interfacial Complexation And Its Application

Polysaccharides are abundant natural polymers, due to their unique properties such as hydrophilicity, stability, safety, biodegradability and non-toxicity and are inexpensive. These exceptional structural and functional properties of polysaccharides are the main reasons to why they are used as biomaterials and for surface modification of biomedical devices. Being natural constituents, they are ideal building blocks for creating systems mimicking the structural and biochemical properties in vivo cellular environment. In the past 15 years, many attempts have been made to assemble polysaccharides into poly electrolyte multilayers （PEMs） films via polymer interfacial complexation, i.e. layer-by-layer （LbL） assembly based on electrostatic interactions as the main driving force.Most polysaccharides are negatively charged and are thus used as polyanion constituents, unless they are chemically modified to render them polycationic. This was actually the case for amide modified Hyaluronan acid （HA） and for quaternized chitosan. The choice to use a polycationic polysaccharide is very limited. Indeed, only chitosan （CHI）, a de-acetylated form of chitin, is currently available and used in PEMs films. Due to its many unique properties, including wider availability, biocompatibility, wound-healing and anti-bacterial properties, Chitosan is the most widely used polysaccharide in LbL assembly. However chitosan has low solubility in aqueous solutions with pH values above 6. This limits its use as an absorption enhancer in many applications, for example, nasal or peroral delivery systems. A further restriction of chitosan is that, it quickly adsorbs water and shows a high degree of swelling in aqueous environments, which reduces its suitability and use in thin films based on chitosan in a number of applications such as drug delivery systems.In this current study, the aim of the research work is to use new polysaccharides with positive charge such as quaternized cellulose and cationic guar gum instead of chitosan to fabricate thin films based on LbL assembly. In Addition, their interaction with anionic polysaccharide and synthetic polyelectrolyte was investigated by studying the influence of physical parameters such as pH, ionic strength and temperature. The anti-fogging, anti-frosting and anti-bacterial behavior of polysaccharides thin film was also studied.To achieve the above mentioned objectives, numerous techniques were applied to characterize the polysaccharides thin film prepared using LbL assembly. Ultraviolet-visible spectroscopy （UV-Vis）, optical reflectometry （OR）, and Fourier transform infrared （FT-IR） spectroscopy were applied to monitor the complexation process, film thickness growth and interaction of thin film with metal ions. Quartz crystal microbalance-with dissipation （QCM-D） was applied to determine the growth mode and calculate the adsorbed mass of polyelectrolyte pairs. Atomic force microscopy （AFM） was used to observe the film morphologies, and water contact angle measurement was utilized to determine hydrophilicity of polysaccharide thin film. A zone of inhabitation （ZOI） experiment was utilized to realize the anti-bacterial behavior of the polysaccharides thin film.The first part of this thesis is about the preparation of the thin films of oppositely charged cellulose derivatives, quaternized cellulose （QC） and carboxymethyl cellulose （CMC）, alternatively deposited on silicon or quartz substrates. The factors of pH value, ionic strength and temperature as solution parameters and dipping-and rinsing time as operational parameters on the thin film growth and morphology, were investigated. The main chains of QC and CMC, composed of glucose rings, are hydrophilic and rigid, and hence, QC and CMC show different assembly behavior compared with synthetic vinyl polyelectrolytes such as polystyrene sulfonate （PSS） and poly （diallyldimethyl-ammonium） （PDDA）. As the pH value increases, in the region from pH 3 to pH 5, QC and CMC can be LbL assembled to prepare the thin film. In the neutral pH region, QC and CMC are very hard to assemble. When the pH value is higher than 10, QC and CMC can be deposited again to fabricate the thin film. The LbL assembly of QC and CMC is very sensitive to ionic strength. Adding 0.1 M NaCl into the assembling solution, the thin film growth tremendously decreases, while increasing temperature of assembly solution accelerates the thickness growth of the film. The thickness of QC/CMC increases with increase of dipping time, whereas increasing of rinsing time lead to decrease of thin film growth.Initially, QC was used as cationic polysaccharides to fabricate a thin film. Therefore, the goal of the present chapter is to determine the possibility of preparing a thin film of cationic guar gum （CGG） with weak polyacids such as CMC and poly （acrylic acid） （PAA） via LbL assembly based on electrostatic interactions. The dependence of thin film growth and morphology on pH value, ionic strength and temperature were evaluated. Increasing the pH value in the region from pH 3 to pH 4, CGG and weak polyacids can be LbL assembled to prepare the thin film. In the neutral pH region and high pH value, CGG and weak polyacids are very difficult to assemble. In contrast to synthetic polyelectrolyte complex thin film, such as PSS/PDDA and PSS/PAH, the LbL assembly of CGG/CMC and CGG/PAA are very sensitive to high salt concentration. Ionic strength favors the growth of CGG/CMC and CGG/PAA thin film when salt concentration is low, while increasing salt concentration is unfavorable for the growth of CGG/CMC multilayer. The increase of temperature in the deposition process was shown to have a considerable effect on the thickness growth of CGG/ weak polyacids. Increases of dipping time offer enough time to adsorb polyelectrolyte chain on thin film surface and rearrangement, which lead to diffuse more polyelectrolyte chain into thin film and therefor increase thin film thickness. However, increasing of rinsing time decrease the thickness growth of CGG/weak polyacids by immigration of polyelectrolyte chain from thin film surface to solution.In chapter 4, the anti-fogging and anti-frosting behavior of the polysaccharides assembled films was studied. Polysaccharides thin films exhibited anti-fogging and anti-frost behavior whereas the LbL assembled films, of the combination of polysaccharides and synthetic polyelectrolyte such as the QC/PAA, QC/PSS, CGG/PAA and CGG/PSS did not display anti-fogging and anti-frost properties. The anti-fogging and anti-frosting properties of polysaccharides films are attributed to the fact that water molecules can be quickly adsorbed into the matrix of the film as a result of strong interactions of the polar groups in the polymer and water molecule via hydrogen bonding, which prohibiting condensation of water droplets. This investigation indicates that polysaccharides can be LbL assembled to produce an optical thin film, with anti-fogging-, anti-frosting properties.Finally, the interpenetration of metal ions in the polysaccharide thin film was investigated, accordingly the anti-bacterial behavior was researched. Using several types of PEM films constructed using QC and CGG as polycations and CMC and PAA or as polyanions, we found that binding of Cu²⁺, Fe²⁺ and Ag+ metal ions with a PEM matrix can occur through coordination with polyacids groups. CGG/PAA containing Cu²⁺, Fe²⁺ and Ag+ metal ions are chosen to study antibacterial behavior due to their good interaction with metal ions. The bacterial inhibition experiments demonstrated that CGG/PAA-Ag show a good anti-bacterial behavior. The anti-bacterial behavior of CGG/PAA containing Ag+ ion attributed to the fact that Ag+ ion can be released from CGG/PAA thin film and interact with bacterial in many different ways leads to killing the bacteria.Therefore, we successfully fabricated polysaccharides thin film based on interfacial complexation from these new cationic polysaccharides with excellent properties such as anti-fogging, anti-frosting and antibacterial behavior. These films offer a promise for future applications in different sectors such as biomedical, drug delivery system and filtration.