Optical fiber is an efficient propagation carrier of laser energy. A short-pulse laser can be focused on the end of a fiber to realize the directional propagation of energy along the carrier path. Therefore, the efficient and high-energy transmission of laser energy can be realized by inducing a plasma detonation wave with an underwater fiber laser. The integration of underwater fiber laser propulsion technology with various scientific and technological advancements holds significant promise in fields such as green ship manufacturing, submarine stealth propulsion, detonation engine performance, and supercavitation weapon systems. In the medical field, vascular embolism and thrombotic disease caused by endovascular thrombus flaking are still intractable diseases. Traditional thrombectomy and interventional hemolysis can cause harmful complications. For example, a thrombectomy can easily cause large-scale bleeding and the embolization of blood vessels. In view of the prominent problems with traditional thrombus removal, the technique of underwater fiber laser propulsion has been applied to the targeted removal of blood vessel thrombi. Based on fiber conduction, a short-pulse laser-induced plasma detonation wave propulsion scheme is proposed as part of the technical research on the noninvasive comprehensive treatment of thrombi. To explore the propagation characteristics of laser-induced plasma detonation waves, the feasibility of the fixed-point and directional noninvasive removal of thrombi using fiber laser-induced plasma detonation waves is verified by combining experiments and simulations.
This study analyzed the mechanism of underwater fiber laser-induced plasma shock wave propulsion. It modeled a thrombus in a human blood vessel, creating two environments for underwater fiber-optic laser propulsion. The study employed numerical simulations to observe the propagation process of plasma shockwaves generated by laser energy. First, the model, propagation mechanism, and absorption mechanism of laser plasma detonation waves were determined. Second, using a numerical simulation method for the energy source term and plasma equation of state, the thrombus propulsion in two blood environments was numerically simulated, and the pressure cloud image and thrust curve of the detonation waves acting on the thrombus were obtained. Then, we analyzed the factors influencing the thrombus progression. These influence factors were determined to be the amount of laser energy and the size and shape of the thrombus, and a corresponding numerical simulation was carried out to obtain the thrust curve conforming to certain rules. Finally, based on the characteristics of the thrombus, experiments that used an underwater fiber laser to push a single microsphere and microsphere cluster were carried out to verify the feasibility of thrombus removal.
The numerical simulation results show that the pressure variation of a plasma detonation wave with 9 mJ of laser energy decreases rapidly with distance and time, and the detonation wave pressure exceeds 108 Pa within 100 μm from the center (Fig. 6). The peak thrust force of a detonation wave on the thrombus first increases and then decreases. In arterial and venous blood environments, the peak thrust forces produced with 20 μJ of laser energy on 2 mm thrombi can reach 1.2 and 1.0 N, respectively (Fig. 10), which can be used for thrombus clearance. The peak thrust on the thrombus is affected by the laser energy and the size and shape of the thrombus. As the laser energy increases from 5 to 25 μJ, the peak thrust on the thrombus increases continuously (Fig. 11). As the size of the thrombus increases from 1 to 3 mm, the peak thrust on the thrombus gradually increases, and the shape of the thrombus also has a significant impact on the peak thrust. A 3 mm square thrombus shows a larger peak thrust than a 3 mm spherical thrombus (Fig. 12). The experimental results show that a laser with an energy of 25 μJ can be used to propel a microsphere particle with a diameter of 50 μm, which has an obvious movement of approximately 300 μm in 4 ms (Fig. 15). A laser with an energy of 36 μJ can be used to break up microsphere clusters of 50 μm microsphere particles into discrete particles that can then be removed (Fig. 16).
With the goal of treating human vascular embolism, this paper discusses the construction of two different human vascular models and numerical simulations of human blood environments. The research shows that when using laser propulsion, the peak thrust on a human thrombus can exceed 1.0 N, and the thrust attenuation is a rapid process. The whole process will cause no harm to human blood vessels, and a human thrombus can be cleared by laser plasma detonation wave propulsion. At the same time, experimental data on how underwater fiber laser plasma detonation waves push microspheres and clusters are collected, and the experimental results are extended to the vascular environment to verify the feasibility of using a fiber laser to move a thrombus. Therefore, fiber laser plasma detonation waves can be used to push and clear a micro-thrombus and break up the thrombus clusters formed by the agglomeration of micro-thrombi.
