Microfluidics (NanoAssemblr©) as a potential platform for nanocarrier formation

• Main Author: Lim, Shaun Wen Zheng
• Other Authors: Czarny Bertrand Marcel Stanislas
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Science::Biological sciences::Biochemistry; Engineering::Nanotechnology; Science::Medicine::Biomedical engineering
• Online Access: https://hdl.handle.net/10356/153123
• Institution: Nanyang Technological University

Since the inception of nanocarriers as drug delivery agents, liposomes stood out as a suitable candidate due to its non-toxic and biodegradable characteristics. Over the past five decades, much research efforts have attempted to elucidate the drug delivery potential of liposomes with some achieving clinical success. However, more work can be put towards refining drugs/bioactives loading, and fabrication methods. Herein a new technique, microfluidics, serves to revolutionise liposome fabrication method to improve the desired research outcomes. This thesis is divided into three parts, namely: investigating the role of lipid compositions and process parameters on liposomal self-assembly, understanding the mechanism of liposome formation as well as optimizing encapsulation of actives in liposomes. Microfluidics involve precise mixing of solvents and manipulation of chip architecture to achieve changes in liposome size. In this work, the method known as mixer-assisted microfluidics was used. It involves a staggered herringbone mixer (SHM) to promote rapid and controlled mixing. In the first part of the thesis, different types of lipid composition such as length, saturation, solvent choice and additives were explored to evaluate their effect on size and polydispersity if liposomal assembly was successful using microfluidics as compared to thin film hydration. Results showed that liposomal assembly was most successful with lipids with unsaturation in at least one hydrocarbon chain. Fully saturated lipids with lipid carbon chains more than 14 were unable to form liposomes. It was clear that the method may not be universally suited for all lipid types so varied operating conditions must be involved together with investigation towards the actual cause of this aggregation. A phenomenon known as membrane interdigitation was discovered in the first part. Interdigitation refers to the phenomenon where two opposing leaflets of a bilayer interpenetrate into one another and form a single layer. When this happens, aggregation results as the single layer is not thermodynamically stable. It was discovered that saturated double chained lipids with transition temperature (Tm) below room temperature were especially susceptible to lipid interdigitation. Strategies to prevent interdigitation is to either remove ethanol above the lipid’s main transition temperature (Tm), preventing the formation of interdigitated structures and subsequent aggregated states or by the incorporation of the inhibiting additives, such as cholesterol. In the second part of the thesis, the process parameters such as effects of flow or ratio of organic solvent on liposome formation were explored. Results showed that the higher the ratio of aqueous phase to organic solvent is, the smaller the particle size is. The same trend was shown for higher flow rates of the streams. One possible explanation is because of the shearing effect used in the mixer-assisted microfluidics. As more aqueous buffer is used, the organic layer containing the lipid has lesser time to assemble into the liposomes before being exposed to an aqueous environment, leading to a smaller size. With the results from part 1 and 2, further exploration of microfluidics were performed. 2 model drugs, dextran FITC and latanoprost were used as hydrophilic and lipophilic model drug respectively. Results showed that unsaturated lipid, EggPC showed encapsulation of 27% for dextran FITC and 40% for latanoprost. Drug release profiles show sustained release for both types of drug. The drug loadings were similar to that produced using conventional thin film hydration method. As conventional thin film hydration are constantly plagued with reproducibility and ease of handling issues, microfluidic technology is poised to resolve these problems. The advantages of using microfluidics include ease of handling, high reproducibility, size control without involving additional size reduction steps, as well as a fully automated mixing process. With these benefits mentioned above, this shows great promise as an alternative liposome fabrication method. Thus, the novelty of this project lies in establishing a relationship between microfluidics and the formation of liposomes. Various studies on liposomal work with microfluidics do not explicitly describe the conditions for successful liposome formation, so the work in this project serves to complete the knowledge gap by understanding how and why different lipid types are able to form liposomes.