Miya Ishihara

Photoacoustic (PA) imaging offers the potential for deep‐tissue visualization, but the development of dyes specifically responsive to diverse lesion environments remains insufficient. To address this problem, we synthesized cyanine dyes incorporating various aryl‐piperazinyl groups at the central carbon of the polymethine chain, aiming to modulate their PA signals in response to various biological processes such as enzyme activity or reactions induced by reactive oxygen species (ROS). When various aryl substituents were incorporated into the piperazinyl cyanine scaffold, each dye showed a distinct absorption spectrum depending on the electron‐donating/withdrawing ability of the substituents. Density functional theory (DFT) optimization and natural population analysis (NPA) revealed that dyes with highly electron‐withdrawing aryl substituents exhibit reduced electron localization in the conjugated system and reduced bond‐length alternation. Conformational analysis further showed substituent‐dependent preferences for different low‐energy conformers, suggesting that both electronic structure and molecular conformation contribute to the observed absorption spectral changes. PA spectra of these dyes also changed depending on the aryl substituents, suggesting that the mechanism of these aryl‐piperazinyl cyanine dyes could serve as a design principle for environment‐responsive PA dyes in the future.

Although second near-infrared (NIR-II) photoacoustic (PA) imaging affords deep tissue penetration, developing efficient contrast agents remains challenging due to a lack of suitable optical absorbers. Herein, we report semiconducting polymer nanoparticles (SPNs) for dual-modal PA and NIR fluorescence imaging, featuring a high optical absorption coefficient at 1064 nm that facilitates excitation via high-power Nd:YAG lasers. Phantom evaluations revealed a linear PA signal correlation, with a low detection limit of 0.05 cm ⁻¹ . In vivo studies in tumor-bearing mice demonstrated passive SPN accumulation in tumor tissue, successfully visualized by both PA and NIR fluorescence imaging. These results indicate that SPNs are promising contrast agents for dual-modal imaging.

Background: The effectiveness of negative‐pressure wound therapy (NPWT) in skin graft fixation has been demonstrated in several clinical studies. However, in vitro and in vivo studies on skin graft fixation with NPWT have been scarce. In this in vivo study, we aimed to determine whether NPWT fixation enhances skin graft survival and how it contributes to improving skin graft survival biologically. Materials and methods: We harvested skin from the bilateral abdominal wall of 88 mice after anesthetizing them. Full‐thickness skin grafts (FTSGs) were performed on contralateral harvest sites, and grafts were fixed using NPWT (continuous and intermittent modes), conventional compression methods, and wrapping with polyurethane foam as a control group. On days 5 and 10 of grafting, the survival rates of the FTSGs were evaluated. Immunohistopathological analysis and measurement of the expression levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (FGF‐2), and epidermal growth factor (EGF) were performed. Results: The survival rates of FTSG in the continuous NPWT group were significantly higher than those in the other groups. The number of capillaries in the dermis was significantly higher in the continuous NPWT group than in the other groups. In the wound bed, VEGF levels were significantly higher in both NPWT groups than in the other groups. Conclusion: Continuous NPWT increases the survival rate of FTSGs and shortens the duration of skin graft survival.

SignificanceWe developed a high-speed optical-resolution photoacoustic microscopy (OR-PAM) system using a high-repetition-rate supercontinuum (SC) light source and a two-axes Galvano scanner. The OR-PAM system enabled real-time imaging of optical absorbers inside biological tissues with excellent excitation wavelength tunability.AimIn the near-infrared (NIR) wavelength range, high-speed OR-PAM faces limitations due to the lack of wavelength-tunable light sources. Our study aimed to enable high-speed OR-PAM imaging of various optical absorbers, including NIR contrast agents, and validate the performance of high-speed OR-PAM in the detection of circulating tumor cells (CTCs).ApproachA high-repetition nanosecond pulsed SC light source was used for OR-PAM. The excitation wavelength was adjusted by bandpass filtering of broadband light pulses produced by an SC light source. Phantom and in vivo experiments were performed to detect tumor cells stained with an NIR contrast agent within flowing blood samples.ResultsThe newly developed high-speed OR-PAM successfully detected stained cells both in the phantom and in vivo. The phantom experiment confirmed the correlation between the tumor cell detection rate and tumor cell concentration in the blood sample.ConclusionsThe high-speed OR-PAM effectively detected stained tumor cells. Combining high-speed OR-PAM with molecular probes that stain tumor cells in vivo enables in vivo CTC detection.

Negative-pressure wound therapy (NPWT) promotes wound healing by applying negative pressure to the wound surface. A quarter of a century after its introduction, NPWT has been used in various clinical conditions, although molecular biological evidence is insufficient due to delay in basic research. Here, we have summarized the history of NPWT, its mechanism of action, what is currently known about it, and what is expected to be known in the future. Particularly, attention has shifted from the four main mechanisms of NPWT to the accompanying secondary effects, such as effects on various cells, bacteria, and surgical wounds. This chapter will help the reader to understand the current status and shortcomings of NPWT-related research, which could aid in the development of basic research and, eventually, clinical use with stronger scientific evidence. Keywords Angiogenesis Biofilm Epithelial-mesenchymal transition Mechanotransduction Microdeformational wound therapy Surgical site infection Topical negative pressure Vacuum-assisted closure Vacuum sealing drainage Wound healing

Photobiomodulation studies have reported that blue light irradiation induces the production of reactive oxygen species. We investigated the effect of blue laser (405 nm) irradiation on the ATP levels in mouse skin and determined the types of reactive oxygen species and reactive nitrogen species using cultured mouse fibroblasts. Blue laser irradiation caused a decrease in the ATP level in the mouse skin and triggered the generation of superoxide anion and hypochlorous acid, whereas nitric oxide and peroxynitrite were not detected. Moreover, blue laser irradiation resulted in reduced cell viability. It is believed that the decrease in the skin ATP level due to blue light irradiation results from the increased levels of oxidative stress due to the generation of reactive oxygen species. This method of systematically measuring the levels of reactive oxygen species and reactive nitrogen species may be useful for understanding the effects of irradiation conditions.

T2 mapping is an MRI method particularly reflective of the collagen arrangement in the cartilage, and diffusion tensor (DT) imaging captures the diffusion of water molecules. Laser-induced photoacoustic measurement (LIPA) makes it possible to assess not only the thickness of the cartilage layer but also its viscoelastic properties. By assessing cartilage damage assessment using LIPA and 3.0 Tesla MRI (T2 mapping and DT imaging), this study investigates the usefulness of the various methods. The International Cartilage Repair Society (ICRS) classification was used to classify 29 bone cartilage pieces excised during surgical procedures. At the same time, LIPA was performed at sites matching the area of cartilage damage. MRI was performed preoperatively to measure the T2 and the apparent diffusion coefficient. In addition, tissue sections for histological assessment using the Mankin score were prepared for each ICRS grade, and the results with the various methods were compared. With DT imaging, significant differences were observed in all grades (P < 0.01). With T2 mapping, significant differences were observed in all grades except for grade 1 versus grade 2 (P < 0.01). With LIPA, significant differences were observed in ICRS grade 1 versus grade 3 (P < 0.05), grade 1 versus grade 4 (P < 0.01), grade 2 versus grade 4 (P < 0.01), and grade 3 versus grade 4 (P < 0.05). With the Mankin score, significant differences were observed in ICRS grade 1 versus grade 3 (P < 0.01), grade 1 versus grade 4 (P < 0.01), grade 2 versus grade 4 (P < 0.01), and grade 3 versus grade 4 (P < 0.01). Correlations were observed in all combinations of ICRS grade with DT imaging, T2 mapping, LIPA, and Mankin score. Correlations were observed between the degree of histological degeneration and DT imaging, T2 mapping, and ICRS grade, but LIPA had a weaker correlation than MRI. In the assessment of knee osteoarthritis, there are instances where it is difficult to assess the damaged cartilage site with MRI alone, and we believe that it is desirable to use a combination of LIPA and MRI.

Intraoperative thermographic confirmation of the extent of carotid plaque distribution using an uncooled infrared camera was assessed during carotid endarterectomy (CEA). This camera was small, light, and provided high temperature resolution (<0.022 degrees), thus allowing detection of the changes in thermal radiation induced by surface temperature differences. Vascular flow of the artery appeared as a light color, and absence of flow as a dark color. Vascular re-flow was recognized as a bright color. Therefore, vascular flow could be evaluated using the uncooled infrared camera during CEA. The uncooled infrared camera offers real-time information on vascular patency and extent of plaque. Spatial resolution and image quality are satisfactory, and the procedure can be repeated easily and safely. We have shown that the uncooled infrared camera could be a new and feasible technology for intraoperative imaging of the vascular flow, and isconsidered to be clinically useful during CEA.

Like all mammalian cells, normal adult chondrocytes have a limited replicative life span, which decreases with age. To facilitate the therapeutic use of chondrocytes from older donors, a method is needed to prolong their life span.

A light-scattering signal, which is sensitive to cellular/subcellular structural integrity, is a potential indicator of brain tissue viability because metabolic energy is used in part to maintain the structure of cells. We previously observed a unique triphasic scattering change (TSC) at a certain time after oxygen/glucose deprivation for blood-free rat brains; TSC almost coincided with the cerebral adenosine triphosphate (ATP) depletion. We examine whether such TSC can be observed in the presence of blood in vivo, for which transcranial diffuse reflectance measurement is performed for rat brains during hypoxia induced by nitrogen gas inhalation. At a certain time after hypoxia, diffuse reflectance intensity in the near-infrared region changes in three phases, which is shown by spectroscopic analysis to be due to scattering change in the tissue. During hypoxia, rats are reoxygenated at various time points. When the oxygen supply is started before TSC, all rats survive, whereas no rats survive when the oxygen supply is started after TSC. Survival is probabilistic when the oxygen supply is started during TSC, indicating that the period of TSC can be regarded as a critical time zone for rescuing the brain. The results demonstrate that light scattering signal can be an indicator of brain tissue reversibility.