Needle-less skin immunisation using low-frequency ultrasound

Low-frequency ultrasound (20 kHz) was investigated as an alternative to the needle for skin immunisation due to inherent problems associated with needle usage. Due to degradation of BSA, a model antigen, when exposed to ultrasound, it was decided that the skin will be pre-treated with ultrasound before vaccine application. Ultrasound was applied to skin via a 13 mm diameter probe immersed in coupling medium. in vitro permeation studies using rat skin were conducted to determine effects of machine controlled parameters such as ultrasound pulse length (i.e. pulse interval), intensity and nature of wave (i.e. continuous / pulse wave) and non-machine controlled parameters such as probe distance, and the nature and volume of coupling medium volume (e.g. presence of surfactant) on vaccine permeation into and through the skin, with the aim of using the optimal parameters for subsequent in vivo immunisation. The optimised ultrasound settings were first tested for tolerability in vivo in mice and rats using various techniques such as transepidermal water loss, blood flow and histology. Ultrasound settings were then adjusted based on the skin responses to avoid irreversible skin damage without compromising the effectiveness of ultrasound on skin permeability. Skin barrier properties following ultrasound exposure were found to be repaired upon application of liposomes in in vitro and in vivo experiments. Subsequently, groups of mice were immunised using several optimised ultrasound protocols to establish the potential of low-frequency ultrasound for skin immunisation. High immune responses were elicited in mice immunised using ultrasound. in vivo challenge tests showed that the antibody produced in the mice were functional and would afford protection against tetanus toxin. Immunisation experiments were also conducted in rats to test synergistic effects between ultrasound and sodium dodecyl sulphate (SDS) and these showed the showed potential of lower SDS concentrations in combination with ultrasound. In conclusion, this research has established the potential of low-frequency ultrasound for needle-free skin immunisation