Inertial cavitation of lyophilized and rehydrated nanoparticles of poly(L-lactic acid) at 835 kHz and 1.8 MPa ultrasound

Nanoparticles of poly-L-lactic acid dispersed in water and of approximately 120 nm diameter were prepared by a nanoprecipitation method followed by lyophilization together with trehalose. After rehydration, the nanodispersion was exposed to ultrasound at 835 kHz frequency and 1.8 MPa peak negative sound pressure. Substantial levels of broadband noise were surprisingly detected which are attributed to the occurance of inertial cavitation of bubbles present in the dispersion. Inertial cavitation encompasses the formation and growth of gas cavities in the rarefaction pressure cycle which collapse in the compression cycle because of the inwardly-acting inertia of the contracting gas-liquid interface. The intensity of this inertial cavitation over 600 s was similar to that produced by Optison microbubbles used as contrast agents for diagnostic ultrasound. Non-lyophilized nanodispersions produced negligible broadband noise showing that lyophilization and rehydration are requirements for broadband activity of the nanoparticles. Photon correlation spectroscopy indicates that the nanoparticles are not highly aggregated in the nanodispersion and this is supported by scanning (SEM) and transmission (TEM) electron micrographs. TEM visualized non-spherical nanoparticles with a degree of irregular, non-smooth surfaces. Although the presence of small aggregates with inter-particulate gas pockets cannot be ruled out, the inertial cavitation activity can be explained by incomplete wetting of the nanoparticle surface during rehydration of the lyophilizate. Nano-scale gas pockets may be trapped in the surface roughness of the nanoparticles and may be released and coalesce to the size required to nucleate inertial cavitation on insonation at 835 kHz/1.8 MPa

Organische und Hybrid-Nanopartikel für die kontrollierte Auslösung von transienter Kavitation mittels therapeutischem Ultraschall

The search for new and innovative methods of cancer treatment is a major research field in pharmaceutics and biomedical engineering. Besides the development of new cancer drugs for systemic chemotherapy as well as improvements in radiotherapy and surgery, targeted drug delivery to tumour tissue using drug loaded colloidal vehicles is a major approach to increase efficacy and decrease possible side effects of chemotherapy. This strategy usually attempts to exploit the EPR effect to allow passive accumulation of a drug loaded vehicle inside the tumour tissue. A limitation of this strategy however is that the release of the encapsulated drug is primarily controlled by degradation of the vehicle or diffusion of the drug, which can take up to several weeks for complete release. Another approach to improve chemotherapy is using external triggers for an immediate release of an encapsulated drug on-site. External triggers which should be preferably non-invasive such as laser light, electromagnetic fields, changes in pH or ultrasound are discussed in the literature. The current work concentrates on the use of ultrasound as an external trigger. Publications on US-triggered drug release work with so-called microbubbles. Microbubbles are stabilised gas bubbles that can interact with ultrasonic waves and are commercially used as contrast agents in ultrasound diagnostics. A key mechanism of how microbubbles can be used for drug release is the so-called phenomenon of inertial cavitation. Inertial cavitation describes an event where a bubble in a liquid expands and collapses implosively, emitting shock waves of high energy. This energy may be used for drug delivery. A major limitation of the microbubble approach is that the systemic distribution of MBs in the body is restricted solely to the vascular system. Owing to their size they are not able to accumulate inside tumour tissue. To overcome these obstacles, a combination of nanomedicine and ultrasound triggered drug release is presented in this thesis. This combination leads to so-called sonosensitive nanoparticles. These particles should be able to accumulate in the tumour and release their payload by an externally applied ultrasonic field. This approach has the potential to improve common systemic chemotherapy substantially, as a localised drug delivery can be achieved. The concept of this work is based on recent findings that nanoparticles with highly rough and lipophilic surfaces are able to decrease the inertial cavitation threshold of water. Inertial cavitation is the key mechanism for ultrasound triggered drug delivery. The aim of this thesis is therefore the development of different preparation techniques for nanoparticles that can cause inertial cavitation in an ultrasonic field. The ultrasound used for the initiation of cavitation must lie in the therapeutic or diagnostic region, i.e. frequencies ≥ 0.5 MHz or 2 MHz, respectively. The thesis is divided into three main sections that present and discuss different preparation methods and the physical and acoustic characterisation of the prepared nanostructures. The three principles are a Layer-by-Layer approach, the “Grand Canyon” approach and the “Hub Cap” approach. Briefly, all of them produce nanoparticles of specific morphology that should be capable to adsorb tiny air bubbles on their surface. These air bubbles are required for the instigation of inertial cavitation. The mechanism is proposed to be as follows. First, nanoparticles of a specific shape are prepared. Subsequently, adsorption of tiny air bubbles on their surface is allowed e.g. by drying and reconstitution. The attached bubbles can grow, oscillate and cavitate inertially in an ultrasonic field which can be measured by passive acoustic detection. Air adsorption on rough and hydrophobic surfaces for causing cavitation in an ultrasonic field is a generally accepted concept but has never been proven directly on nanoparticles. As part of this work it is therefore intended to obtain evidence of the adsorption of air bubbles on the surface of the prepared nanoparticles

Analysis and Concretization of Fuzziness in the U-space Regulation

The U-space Regulation will come applicable on January 26, 2023, and it will allow EU Member States to designate U-space airspaces as well as to establish infrastructure. If UAS operators - private and commercial - wish to fly in a U-space airspace, they must use U-space services to maintain safety and an efficient airspace utilization. While the technical basis for the U-space services is included in the U-space Regulation, it omits some crucial details regarding the relationship between its key stakeholders like the U-space service provider and the UAS operator, imposing challenges on the technical implementation. Therefore, a plurality of legally abstract requirements and partially ambiguous provisions (henceforth referred to as fuzziness) need to be concretized in a first step. Subsequently, the derived legal interpretation needs to be tested for its technical practicability in order to practically realise an efficient drone traffic management in U-space. In doing so, this contribution addresses identified fuzziness of the UAS flight authorisation service according to Article 10 of the U-space Regulation and shows the concretization needs for this service in order to fulfil its extensive tasks, such as the authorisation and activation of UAS flights