|Institution:||Hong Kong University of Science and Technology|
|Keywords:||Drug delivery systems; Ultrasonics in ophthalmology; Sclera; Diseases; Treatment|
|Full text PDF:||http://dx.doi.org/10.14711/thesis-b1584202|
Ultrasound-mediated transscleral delivery of high molecular weight compounds is an emerging yet challenging technique for treating eye disease. Our group has successfully demonstrated in live animal study that the application of 40 kHz ultrasound with a mechanical index (MI) = 0.20 could overcome the ocular barriers to deliver macromolecules into the eye. In this thesis, I mainly focus on: 1) exploring the effect of ultrasound on the scleral collagen arrangement and its correlation to the transscleral transport enhancement; 2) understanding the mechanism of the macromolecules diffusivity enhancement during and after ultrasound by quantitative analysis using a mathematical model; and 3) evaluating the effect of ultrasound on the barrier properties and transport activities in the retinal pigment epithelium cells in vitro. Transscleral transport of macromolecules could be enhanced by ultrasound without disturbing the scleral collagen network. Both low intensity and high intensity ultrasound at 40 kHz did not induce statistical significant changes to the collagen fibril arrangement in the scleral matrix. Ultrasound at the low intensity regime, i.e. stable cavitation regime, was identified as the optimal regime to maximize the transport enhancement along the transscleral route. The transport enhancement was most significant during ultrasound application and was mainly due to the ultrasound-induced chaotic mixing in the stable cavitation regime. As the MI of the system reached transient cavitation regime, the partition of the BSA molecules was significantly enhanced. The transport of macromolecules across the retinal pigment epithelium (RPE) cell layer was achieved by temporary tight junction disruptions post sonication. 40 kHz ultrasound has the most prominent effect on the temporary tight junction disruption and thus significantly enhanced the transport of macromolecules across the RPE cells along the paracellular pathways. In addition, folic transport across the RPE cells was upregulated post sonication. Intracellular calcium concentration was transiently upregulated after sonication, which could be the result of the activation of mechano-sensitive ion channels in the cells by ultrasound.