School of Chemistry - Theses
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ItemSonosynthesis of Functional Micro/Nano-structures using Biomolecules( 2022)Malnutrition and access to affordable health services are some of the world’s most urgent problems. The development of nutrient and drug delivery systems by using sub-micro particles as carriers has attained much attention for improving the nutritional value of food and the efficacy of diagnostic/therapeutic treatments. Common methods for synthesizing biofunctional particles usually require many reagents and involve multiple steps. In this regard, a novel and advanced approach for material synthesis needs to be developed and investigated to address those limitations. Ultrasonic techniques have emerged as one-pot and eco-friendly methods for the synthesis of organic and inorganic materials. It has been found that acoustic cavitation derived from sound waves can induce emulsification of liquids to form microcapsules and promote chemical modifications of biomolecules. Protein-shelled microcapsules have been synthesized by using low-frequency ultrasound and reducing agents for food-based applications. However, the direct use of food ingredients for the microencapsulation of microcapsules without resorting to additional external agents was never explored and needs to be investigated further for food-based applications. On another note, drug carriers are usually prepared in nanoscale to enhance interaction with cell membranes for achieving efficient therapeutic treatment. Conventional strategies for preparing drug loaded nanoparticles require matrix materials as carriers, resulting in low drug loading capacity and safety issues. Therefore, synthesis of nanodrugs solely made of antibiotic molecules is a better method for development of drug delivery platforms. Many molecules bearing aromatic groups have been successfully sono-assembled into nanoparticles by high-frequency ultrasound, but they are mainly used as drug carriers. Transforming drug molecules into carrier-free nanodrug has not been widely investigated. As such, I intend to expand new research towards other drug molecules with aromatic moieties. In this regard, my Ph.D. project aims to sono-chemically synthesize various micro and nano structures from biomolecules by tuning the frequency/power of ultrasound without the usage of external reagents. The size of the obtained bio-functional structures is controllable, and their compositions are suitable for use in specific applications such as : i) nutrients delivery in food industries; ii) drug delivery for biomedical applications. The fundamental concepts of sono-chemistry for material synthesis, along with biomolecules (proteins, nutrients and antibiotics) based micro/nano structures and their applications are discussed in Chapter 1. Chapter 2 provides an overview of microencapsulation techniques for food industries and fabrication of nanoparticles for antibiotics delivery. In particular, methodology, formulating materials, current challenges, limitations and innovation are discussed. In Chapter 3, the materials, equipment and methodologies involved in the reactions used in this thesis are thoroughly described. Chapter 4 is the first chapter of result and discussion section. Microcapsules made of egg white protein (EWP), as commonly available biopolymers, were first conceptualized. Oil-soluble nutrients (Vitamin A, D and E) were encapsulated into EWP to form nutrients loaded proteinaceous microcapsules by employing 20 kHz ultrasound. This work primarily points out that high availability of free thiol groups in protein solution is crucial in forming stable microcapsules with robust shells, in order to protect micronutrients from degradation against detrimental effects. In Chapter 5, another two plant-based protein isolates extracted from soybean (SPI) and corn (CPI) were also formulated to form microcapsules. This study provided further insights into the structural, chemical and surface properties of proteins for efficient ultrasonic microencapsulation of micronutrients. A double emulsion technique was further developed to co-encapsulate both oil- (vitamin A and D) and water-soluble (vitamin B, C and minerals) micronutrients. In-vitro digestion study showed that the proteinaceous microcapsules enable sustained release of micronutrients, demonstrating their potential in food fortification applications. In Chapter 6, a sono-chemical strategy for transforming antibiotic doxycycline into carrier-free nanodrugs via high-frequency ultrasound (490 kHz) is reported. This study demonstrates that doxycycline undergoes hydroxylation and dimerization processes upon sonication in an aqueous solution to ultimately self-assemble into nanoparticles. The size of obtained particles could be finely controlled by tuning the applied ultrasonic powers. The nanodrugs exhibited antioxidant properties, along with antimicrobial activity against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacterial strains. These results highlight the feasibility of the ultrasound-based approach for engineering carrier-free nanodrug with multiple controlled bio-functionalities. Chapter 7 provides an overall summary of the entirety of my PhD project as well as my conclusion and thoughts on it.