(333g) Preparation of Tissue Plasminogen Activator Loaded Microbubbles for Potential Application in Ischemic Stroke Treatment

Microbubbles are well known as ultrasound contrast agents for medical ultrasound imaging due to their ability to scatter and reflect ultrasound. By incorporating drugs into their shell layers, microbubbles could be used as drug carriers. Ultrasound could serve as a trigger which facilitates the release and local delivery of drugs from the microbubbles. The only FDA approved thrombolytic agent for ischemic stroke patients is tissue plasminogen activator (tPA). However, due to the small therapeutic time-window and side effect of intracerebral haemorrhage, the proportion of patients that has received intravenous injection of tPA is fairly low. In this study, we aim to fabricate tPA-loaded microbubbles as combination therapy agent to overcome the small therapeutic time frame and reduce the dose of tPA which could make the thrombolytic agents safer. Coaxial electrohydrodynamic atomization (CEHDA) method was explored to produce the tPA-loaded microbubbles. First, bovine serum albumin (BSA) was used as shell layer material. The effects of operating conditions such as voltage, core and shell flow rate ratio and tPA/BSA volume ratio on the microbubbles size were investigated. Moreover, phospholipid was explored as the shell materials of microbubbles to carry tPA. The results showed coaxial electrohydrodynamic atomization (CEHDA) has the capability to fabricate tPA-loaded microbubbles. BSA microbubbles with mean diameter of ~41 um can be obtained under optimal operating conditions. Above the optimum applied voltage of 12.8kV, no further decrease of mean microbubble diameter can be observed. However, the bubble size can be further decreased to ~38 um and ~28 um by increasing the conductivity and adding 1,3-propanediol into shell layer, respectively. The results also showed that by using lipid as shell material, the tPA-loaded microbubbles size can be further diminished to ~8 um. The acoustic performance was examined and the results showed that the burst of fabricated phospholipid microbubbles can be triggered by ultrasound with 2MHz frequency. Compared with BSA microbubbles, lipid microbubbles with tPA loaded in shell layer showed a higher potential for the ischemic stroke treatment.