The aim of this project was to investigate the possibility of achieving pH triggered drug release through electrostatic repulsion of charged functionalities within ordered polymer films. As a general introduction to the focus of the research, Chapter 1 outlines the various approaches currently in use or under development in the field of drug delivery. The two principle methods of forming monolayer assemblies and the electrochemical techniques used to characterize the structures are also described.
Chapter 2 details the investigations into the effect of pH on Langmuir monolayers of c/s-11-Eicosenoic acid (EA). Results show that electrostatic repulsion between deprotonated acid groups causes the monolayer to expand, suggesting that pH-induced structural changes may influence the films permeability. However, due to monolayer instability, EA was unsuitable for the production of Langmuir-Blodgett films (LB) and efforts were focused on 10, 12-Tricosadiynoic acid (TDA).
Chapter 3 describes the fabrication of polymeric LB films of TDA on Indium-Tin oxide (ITO) coated glass substrates. Capacitance studies reveal that a compact monolayer with an estimated dielectric constant of 4.8 is formed. Diffusion of the hydrophilic Fe(CN)63' complex through the polymer is impeded further suggesting that the layer is compact.
Chapter 4 deals with the permeation studies conducted on Self- Assembled Monolayers of Thioctic Acid (TA). The shorter, less dense TA monolayers were found to be permeable, in the protonated state, to the Ru(NH3)63+ and Fe(CN)63' probes studied. Upon ionization, an apparent reduction in monolayer permeability was observed, but only in the case of the negatively charged complex suggesting that electrostatic repulsion between the charged monolayer and the similarly charged probe screened it from the monolayer interior.
There are two important conclusions to this work; First, if such an approach is to become viable it will be essential to strike a compromise between monolayer association and the degree of freedom necessary for rearrangement. Second, as a consequence of the surface charge density required to expand the film, the application of such a system will be limited by the charge of the compound to be released.
Metadata
Item Type:
Thesis (Master of Science)
Date of Award:
1998
Refereed:
No
Supervisor(s):
Forster, Robert J.
Uncontrolled Keywords:
Drugs (controlled release); Drug delivery systems; Monolayer assemblies; Electrochemical techniques