Jun Tan

Substantial enhancement of recombinant tissue plasminogen activator (rt-PA) mediated thrombolysis can be achieved with exposure of a thrombus to pulsed ultrasound. However, the mechanism of this interaction has not yet been elucidated. In this work cavitation is investigated as a possible mechanism for enhancement in 120-kHz pulsed ultrasound-assisted thrombolysis. Porcine blood clots were immersed in plasma as control and exposed to rt-PA, ultrasound (0.35 MPa, 80% duty cycle, 1667 Hz pulse repetition frequency), or a combination of rt-PA and ultrasound. A confocally aligned active and passive cavitation detection system was employed to detect subharmonic emissions from stable cavitation and broadband superharmonic emissions from inertial cavitation. After exposure, clot mass loss was determined, and clots were subjected to immunohistochemical analysis of fibrin degradation. Spatial investigation of cavitation thresholds inside the clot, on the clot surface, and in the fluid surrounding the clot showed the threshold to be lowest on the clot surface. Stable cavitation was detected in clots exposed to ultrasound alone and a combination of rt-PA and ultrasound. Curiously, inertial cavitation was detected only in samples containing rt-PA. The presence of both stable and inertial cavitation correlated with increased clot mass loss and a distinct pattern of fibrin degradation on histologic evaluation.

In this project, a solvent-free membrane fabrication technique was being investigated to study the physical and chemical properties of the membrane fabricated by this method. This membrane is to be served as a scaffold for tissue engineering applications. Different characterisation tests were being carried out on two different average particle size of Polycaprolactone (PCL) powder, 100 μm and 500 μm, and also their respective membranes fabricated by the solvent-free membrane fabrication method. Various modes of heating were also tested to check how different kinds of heating will affect the rate of melting the PCL powder and also study how the end product will differ from each other. In addition, patterning and shaping experiments were carried out to examine whether it is possible to form patterns on PCL membranes and also whether PCL membranes of customised shapes can be produced. The results showed that the solvent-free membrane fabrication technique did not change any of the chemical properties of PCL and it is proven that this method is simple, fast and does not require any organic solvent. Most importantly, this fabrication method was able to produce a porous PCL membrane in just a single step process, without any post process required.