We investigated the conversion of optical energy into mechanical energy during nanosecond laser ablation in an underwater regime. Our study analyzed the energy distribution between the shockwave, ...cavitation bubble, and work done by plasma impulse on the solid target, while also examining how laser intensity and absorptive coating affect this distribution. We monitored the evolution of the shockwave and cavitation bubble using the photoelasticity imaging technique and a high-speed laser stroboscopic videography system in the photoelasticity mode. Based on the experimental data, we determined the energy allocated to each process. Our result showed that shockwave energy contributed the most to the energy balance, followed by the cavitation bubble energy. The ratio of shockwave energy to cavitation bubble energy was independent of the laser pulse energy. Coating material helps to convert more optical energy to the thermal energy of the plasma plume, thus increasing the overall optical-to-mechanical energy conversion efficiency.
•When the liquid layer is too thin, part of the plasma plume is formed outside the liquid.•Laser-induced shock wave is reflected back-and-forth between the interfaces.•A bulk cavitation zone is ...formed in the liquid layer due to the shock wave reflection.•The intensity of laser-induced stress depends on the thickness of the liquid layer.•The value of the threshold thickness is dependent on the energy of the ablation pulse.
The dynamics of nanosecond pulsed laser ablation in liquid (ns-PLAL) are significantly altered in the immediate vicinity of a free boundary. To improve the control and efficiency of ns-PLAL, more knowledge is needed on the evolution of the plasma, shock waves, and cavitation bubbles that form when this technique is performed within a thin liquid layer. Here, we present time-resolved photoelastic observations of ns-PLAL using an epoxy resin target covered with a sub-mm liquid paraffin layer. The investigation was conducted on a nanosecond time scale. When the liquid layer thickness approximates the plasma size that is induced in bulk-liquid ablation, part of the plasma plume is formed outside the liquid. This plasma is more extensive than that produced in bulk-liquid ablation, but more compact than in air ablation. At greater liquid layer thicknesses, the plasma is entirely confined within the liquid. The layer surface is elevated due to the expansion of the cavitation bubble on the target. The laser-induced shock wave is reflected back-and-forth between the liquid-air boundary and target surface, causing the formation of a bulk cavitation zone in the liquid layer. This study also discusses the mechanism by which liquid layer thickness affects the strength of laser-induced stress.
•Observations at 1μs interval were carried out for laser ablation in water.•Laser-induced shock wave and cavitation bubble are dynamically observed.•Jet-like shadows are observed during LAL in water ...after multiple-pulse irradiation.•Cloudlike-shadow moving away from the irradiated copper surface was observed.
Laser ablation in liquid (LAL) is utilized in many applications, such as the fabrication of nanoparticles, laser cleaning and laser peening. We have developed a high-speed laser stroboscopic videography system that enables observations at intervals of 1μs. Using this imaging system, we investigated the dynamics of cavitation bubbles induced by LAL to elucidate the timing and location of nanoparticle formation and dispersion into the surrounding liquid. The initial bubble demonstrated a well-defined, smooth boundary during its growth and shrinkage. Although previous studies have reported the ejection of particles at the boundary of the bubble, this was not observed in our images. Intermixing between the gas phase of the bubble and the surrounding liquid occurred when the first bubble collapsed. Jet-like shadows were recorded during LAL in water after multiple-pulse irradiation, but were not observed in freshly filled water that had not yet been irradiated. These shadows disappeared within 10μs and are postulated to be micro-bubbles induced by interactions between nanoparticles suspended in the water and the incoming laser beam.
Biodegradable sheets loaded with basic fibroblast growth factor (bFGF) are prepared as novel bFGF‐releasing systems from polyglycolic acid nonwoven fabric by oxygen plasma treatment followed by bFGF ...adsorption. In the present study, we investigated the therapeutic effects of this system on a focal cerebral infarction model (CB‐17 mouse). A preliminary in vitro study showed that this system released bFGF in an acellular culture medium, thereby keeping the bFGF concentration in the medium at ≥5 ng/ml for a prolonged period of 7 days. The released bFGF from this system retained its biological activity to enhance endothelial tube formation in vitro. In a mouse model of subacute focal cerebral infarction, this system increased the expression of endogenous vascular endothelial growth factor in the peri‐infarct cortex and subventricular zone, promoted angiogenesis in the striatum, and increased neural progenitor cells in the peri‐infarct cortex. Thus, this bFGF‐releasing system has the potential to be a novel therapeutic approach for cerebral infarction.
Immediate postcraniotomy headache frequently occurs within the first 48 h after surgery. The mechanisms underlying immediate postcraniotomy headache are not yet fully understood, and effective ...treatments are not yet established. This study aimed to identify the factors associated with immediate postcraniotomy headache in patients who underwent clipping surgery with frontotemporal craniotomy and to examine the effects of these factors on postcraniotomy headache. A total of 51 patients were included in this study. Immediate postcraniotomy headache was defined as pain with numerical rating scale score ≥4 on postoperative day 7. Sixteen patients (31.4%) had immediate postcraniotomy headache. The headache-positive group had a higher incidence of preoperative analgesic use (50.0% vs. 5.7%, respectively, p < 0.001), increased temporal muscle swelling ratio (137.0%±30.2% vs. 112.5%±30.5%, respectively, p = 0.01), and higher postoperative analgesic use (12.9±5.8 vs. 6.7±5.2, respectively, p < 0.001) than the headache-negative group. The risk factors independently associated with immediate postcraniotomy headache were preoperative analgesic use and temporal muscle swelling by >115.15% compared with the contralateral side in the receiver operating characteristic analysis. Postcraniotomy headache was significantly more common in patients with preoperative analgesic use and temporal muscle swelling than in those without (p < 0.001 and p = 0.002, respectively). Altogether, patients with immediate postcraniotomy headache had greater preoperative analgesic use, greater temporal muscle swelling ratio, and higher postoperative analgesic use than those without. Thus, temporal muscle swelling is a key response to immediate postcraniotomy headache.
Evolution of free-electron density in internal modification of glass by fs-laser pulses at high pulse repetition rates is simulated based on rate equation model, which is coupled with thermal ...conduction model in order to incorporate the effect of thermal ionization. Model shows that highly absorbing small plasma generated near the geometrical focus moves toward the laser source periodically to cover the region, which is much larger than focus volume. The simulated results agree qualitatively with dynamic motion of plasma produced in internal modification of borosilicate glass by fs-laser pulses at 1 MHz through the observation using high-speed video camera. The paper also reveals the physical mechanism of the internal modification of glass when heat accumulation is significant.
The effects of an absorptive coating on the dynamics of underwater laser-induced shock process have been observed from the end of laser pulse to hundreds of microseconds after irradiation by ...time-resolved imaging techniques. A laser pulse of 13 ns at 1,064 nm was focused by a 40-mm focal length lens onto the surface of epoxy-resin blocks immersed in water to induce the shock process in the confining regime. A custom-designed time-resolved photoelasticity imaging technique and a high-speed laser stroboscopic videography technique in photoelasticity mode were used to analyze the evolution of shock waves in the water phase, the strength of stress waves in the solid phase, the oscillation of cavitation bubbles, and the generation of bubble-collapse-induced shock waves. We showed that black paint coating enhances the strength of laser-induced stress wave inside the solid, drives faster shock waves traveling in the water phase, and produces higher-energy cavitation bubbles. We propose that even at power densities of 1 GW/cm
2
and above, an absorptive coating can intensify the shock process by enhancing the absorption of laser energy by plasma.
The influence of aneurysm size on the outcomes of endovascular management (EM) for aneurysmal subarachnoid hemorrhages (aSAH) is poorly understood. To evaluate the outcomes of EM for ruptured large ...cerebral aneurysms, we retrospectively analyzed the medical records of patients with aSAH that were treated with coiling between 2013 and 2020 and compared the differences in outcomes depending on aneurysm size. A total of 469 patients with aSAH were included; 73 patients had aneurysms measuring ≥10 mm in diameter (group L), and 396 had aneurysms measuring <10 mm in diameter (group S). The median age; the percentage of patients that were classified as World Federation of Neurological Surgeons grade 1, 2, or 3; and the frequency of intracerebral hemorrhages differed significantly between group L and group S (p = 0.0105, p = 0.0075, and p = 0.0458, respectively). There were no significant differences in the frequencies of periprocedural hemorrhagic or ischemic events. Conversely, rebleeding after the initial treatment was significantly more common in group L than in group S (6.8% vs. 2.0%; p = 0.0372). The frequency of a modified Rankin Scale score of 0-2 at discharge was significantly lower (p = 0.0012) and the mortality rate was significantly higher (p = 0.0023) in group L than in group S. After propensity-score matching, there were no significant differences in complications and outcomes between the two groups. Rebleeding was more common in large aneurysm cases. However, propensity-score matching indicated that the outcomes of EM for aSAH may not be affected markedly by aneurysm size.
In the transsylvian (TS) approach, as characterized by clipping surgery, the presurgical visualization of the superficial middle cerebral vein (SMCV) can help change the surgical approach to ensure ...safe microsurgery. Nevertheless, identifying preoperatively the venous structures that are involved in this approach is difficult. In this study, we investigated the venous structures that are involved in the TS approach using three-dimensional (3D) rotational venography (3D-RV) and evaluated the effectiveness of this method for presurgical simulation. Patients who underwent 3D-RV between August 2018 and June 2020 were involved in this retrospective study. The 3D-RV and partial maximum intensity projection images with a thickness of 5 mm were computationally reconstructed. The venous structures were subdivided into the following three portions according to the anatomic location: superficial, intermediate, and basal portions. In the superficial portion, predominant frontosylvian veins were observed on 31 (41%) sides, predominant temporosylvian veins on seven (9%) sides, and equivalent fronto- and temporosylvian veins on 28 (37%) sides. The veins in the intermediate (deep middle cerebral and uncal veins) and basal portions (frontobasal bridging veins) emptied into the SMCV on 57 (75%) and 34 (45%) sides, respectively. The 3D-RV images were highly representative of the venous structures observed during microsurgery. In this study, 3D-RV was utilized to capture the details of the venous structures from the superficial to the deep portions. Presurgical simulation of the venous structures that are involved in the TS approach using 3D-RV may increase the safety of microsurgical approaches.
Laser-induced cavitation has mostly been studied in bulk liquid or at a two-dimensional wall, although target shapes for the particle synthesis may strongly affect bubble dynamics and interfere with ...particle productivity. We investigated the dynamics of the cavitation bubble induced by pulsed-laser ablation in liquid for different target geometries with high-speed laser microsecond videography and focus on the collapse behaviour. This method enables us observations in a high time resolution (intervals of 1 μs) and single-pulse experiments. Further, we analyzed the nanoparticle productivity, the sizes of the synthesized nanoparticles and the evolution of the bubble volume for each different target shape and geometry. For the ablation of metal (Ag, Cu, Ni) wire tips a springboard-like behaviour after the first collapse is observed which can be correlated with vertical projectile motion. Its turbulent friction in the liquid causes a very efficient transport and movement of the bubble and ablated material into the bulk liquid and prevents particle redeposition. This effect is influenced by the degree of freedom of the wire as well as the material properties and dimensions, especially the Young's modulus. The most efficient and largest bubble movement away from the wire was observed for a thin (500 μm) silver wire with velocities up to 19.8 m s
−1
and for materials with a small Young's modulus and flexural rigidity. We suggest that these observations may contribute to upscaling strategies and increase of particle yield towards large synthesis of colloids based on targets that may continuously be fed.
Productivity of laser ablation in liquids we found that the productivity is enhanced for a wire tip laser ablation due to a springboard-like effect of the flexible target releasing the cavitation bubble.
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