Chemical & Biomolecular Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2219
Formerly known as the Department of Chemical Engineering.
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Item Microvessel rupture induced by high-intensity therapeutic ultrasound—a study of parameter sensitivity in a simple in vivo model(Springer Nature, 2017-03-02) Kim, Yeonho; Nabili, Marjan; Acharya, Priyanka; Lopez, Asis; Myers, Matthew R.Safety analyses of transcranial therapeutic ultrasound procedures require knowledge of the dependence of the rupture probability and rupture time upon sonication parameters. As previous vessel-rupture studies have concentrated on a specific set of exposure conditions, there is a need for more comprehensive parametric studies. Probability of rupture and rupture times were measured by exposing the large blood vessel of a live earthworm to high-intensity focused ultrasound pulse trains of various characteristics. Pressures generated by the ultrasound transducers were estimated through numerical solutions to the KZK (Khokhlov-Zabolotskaya-Kuznetsov) equation. Three ultrasound frequencies (1.1, 2.5, and 3.3 MHz) were considered, as were three pulse repetition frequencies (1, 3, and 10 Hz), and two duty factors (0.0001, 0.001). The pressures produced ranged from 4 to 18 MPa. Exposures of up to 10 min in duration were employed. Trials were repeated an average of 11 times. No trends as a function of pulse repetition rate were identifiable, for either probability of rupture or rupture time. Rupture time was found to be a strong function of duty factor at the lower pressures; at 1.1 MHz the rupture time was an order of magnitude lower for the 0.001 duty factor than the 0.0001. At moderate pressures, the difference between the duty factors was less, and there was essentially no difference between duty factors at the highest pressure. Probability of rupture was not found to be a strong function of duty factor. Rupture thresholds were about 4 MPa for the 1.1 MHz frequency, 7 MPa at 3.3 MHz, and 11 MPa for the 2.5 MHz, though the pressure value at 2.5 MHz frequency will likely be reduced when steep-angle corrections are accounted for in the KZK model used to estimate pressures. Mechanical index provided a better collapse of the data (less separation of the curves pertaining to the different frequencies) than peak negative pressure, for both probability of rupture and rupture time. The results provide a database with which investigations in more complex animal models can be compared, potentially establishing trends by which bioeffects in human vessels can be estimated.Item Solute Release from Polymer Capsules Loaded With Liposomes(2017) Acharya, Priyanka; Raghavan, Srinivasa; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polymer capsules and lipid vesicles (liposomes) are two types of containers that have been extensively studied for their applications in drug delivery. In this thesis, we explore a hybrid of these two structures (i.e. polymer capsules bearing encapsulated liposomes) and study the release of solute from these structures. The capsules are made by contacting the anionic biopolymer alginate with multivalent cations such as calcium (Ca2+) or holmium (Ho3+), which crosslink the alginate chains. Liposomes prepared from conventional phospholipids are loaded with a model solute (an aromatic dye) and then encapsulated in the alginate capsules. We study the effects of different variables on solute release, including the capsule size and architecture, crosslinking ion type and concentration, and crosslinking time. In addition, we compare release from the bare capsules (not containing liposomes) with that from capsules containing liposomes. A key finding is that the latter releases solute over a much longer time compared to the former. Overall, the results from this study will guide the design of new structures for drug delivery applications.