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Title: Alginate from brown seaweeds : extraction, characterisation, modification and the studies on its applications for hydrogels
Author: Alshareef, Sohad Abdulkaleg
ISNI:       0000 0004 7972 6225
Awarding Body: Bangor University
Current Institution: Bangor University
Date of Award: 2019
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The aims of the present work are to study alginate extracted from little studied species of brown seaweeds sourced in the local area with the aim of determining the chemical structure, partic-ularly the M/G ratio, and physical properties including gelling, as they relate to commercial and biomedical applications. The M/G ratio is known to be an important indicator of the strength of gels. The obtained alginate was further modified with Poly-lactic-co-glycolic acid (PLGA) and Poly-caprolactone (PCL) to introduce hydrophobic character in an effort to further widen applicability in biomedical uses. Gels prepared from alginate and its derivatives and their properties were studied with respect to swelling and drug release. As the local area (the North wales coast) has an abundance of certain species of brown seaweed these were used to investigate how differences in geographic location affect the alginate con-tent and structure. This study was performed over two years to ascertain the effects of both environment and seasons. As an introduction Chapter 1 details the chemical structure and sources of alginates and their main methods of extraction. The characteristic chemical and physical properties were outlined. Methods of chemical modification to synthesise derivatives, which enhance physical and chemical properties such as gelation were reported. Gelation methods were also detailed. Chapter 2 outlines the main techniques used to characterise the alginates and their derivatives. Chapter 3 details the extraction of alginate from Irish and Welsh seaweeds. The effects of geographic location and other environmental factors such as season of harvesting were studied. as to how they determine yield and chemical structure. The different methods of extraction and their effects on the properties of the extracted alginate were reported. Extraction was performed using the traditional method employing sodium carbonate but also enzymic assisted methods were compared with the finding that extraction temperature is an overriding factor for higher yields. Enzyme extraction of alginate gave the highest yield with the least protein impurity. Hydrolysis using different methods, acidic and enzymatic, was undertaken to compare effect on the M/G ratio. Chapter 4 concerns how alginate was modified by grafting with PCL to introduce increased hydrophobicity and to enhance biodegradation. For the PCL grafts, linear polymers of various molecular weights were used. Hydrogels were then prepared by ionic crosslinking using Ca2+at different concentrations and subsequently the bulk gels were used in swelling studies in de-ionised water and in saline solution. In Chapter 5, description was given for the preparation of spherical beads of both alginate and its more hydrophobic grafted PCL derivatives, which were used as matrix carriers for two model drugs, hydrophilic carmoisine and, hydrophobic β-carotene. The traditional method of external ionotropic gelation was compared to a novel two-step procedure, which uses both in-ternal and external gelation to increase the cross-linking density leading to an improvement in encapsulation efficiency and control of swelling which in turn affect the release profile of the cargo drug. Chapter 6 details the preparation of PLGA/alginate composite microspheres intended for use for delivery of the hydrophilic protein BSA. The microspheres were prepared by a double-emulsion using commercial alginate and Welsh alginate for comparison. The micro-particles were characterised by SEM. The encapsulation efficiency and release of the protein drug from each type of microsphere was compared and release profiles in various media were studied. In conclusion, it was found that the extracted alginates in this study were relatively high in M content. High M content confers higher elasticity in the material that may be of particular value for use as a food additive. It was further found that derivatives synthesised by grafting improved its mechanical properties making for a more rigid gel and this may of particular value in med-ical applications in, for example, as wound dressings. In addition, properties of swelling and drug release can be modified as required and by altering the hydrophilic/hydrophobic nature of such gels can facilitate loading with a wide range of drugs.
Supervisor: Tai, Hongyun Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: carbohydrates ; biopolymers ; seaweeds ; alginate