Three-dimensional (3D) cell cultures have contributed to a variety of biological research fields by filling the gap between monolayers and animal models. The modern optical sectioning microscopic methods make it possible to probe the complexity of 3D cell cultures but are limited by the inherent opaqueness. While tissue optical clearing methods have emerged as powerful tools for investigating whole-mount tissues in 3D, they often have limitations, such as being too harsh for fragile 3D cell cultures, requiring complex handling protocols, or inducing tissue deformation with shrinkage or expansion. To address this issue, we proposed a modified optical clearing method for 3D cell cultures, called MACS-W, which is simple, highly efficient, and morphology-preserving. In our evaluation of MACS-W, we found that it exhibits excellent clearing capability in just 10min, with minimal deformation, and helps drug evaluation on tumor spheroids. In summary, MACS-W is a fast, minimally-deformative and fluorescence compatible clearing method that has the potential to be widely used in the studies of 3D cell cultures.

Diabetes mellitus (DM) is a kind of metabolic disorder characterized by chronic hyperglycemia and glucose intolerance due to absolute or relative lack of insulin, leading to chronic damage of vasculature within various organ systems. These detrimental effects on the vascular networks will result in the development of various diseases associated with microvascular injury. Modern optical imaging techniques provide essential tools for accurate evaluation of the structural and functional changes of blood vessels down to capillaries level, which can offer valuable insight on understanding the development of DM-associated complications and design of targeted therapy. This review will briefly introduce the DM-induced structural and functional alterations of vasculature within different organs such as skin, cerebrum and kidneys, as well as how novel optical imaging techniques facilitate the studies focusing on exploration of these pathological changes of vasculature caused by DM both in-vivo and ex-vivo.

The 9th Chinese–Russian Workshop on Biophotonics and Biomedical Optics was held online on 28–30 September 2020. The bilateral workshop brought together both Russian and Chinese scientists, engineers, and clinical researchers from a variety of disciplines engaged in applying optical science, photonics, and imaging technologies to problems in biology and medicine. During the workshop, 2 plenary lectures, 35 invited presentations, 5 oral presentations, and 8 internet reports were presented. This special issue selects some papers from the attendees and includes both research and review articles.

The 9th Chinese–Russian Workshop on Biophotonics and Biomedical Optics was held online on 28– 30 September 2020. The bilateral workshop brought together both Russian and Chinese scientists, engineers, and clinical researchers from a variety of disciplines engaged in applying optical science, photonics, and imaging technologies to problems in biology and medicine. During the workshop, 2 plenary lectures, 35 invited presentations, 5 oral presentations, and 8 internet reports were presented. This special issue selects some papers from the attendees and includes both research and review articles.The papers from this special issue will provide the readers an update on the latest developments in biophotonics and biomedical optics. This issue includes two reviews, focusing on the application of optical nanoprobes in bacterial infection by Ding et al. and the application of tissue optical clearing in diabetes-induced pathological changes by Zhu et al. In addition, thirteen original research articles are presented, covering the topics of optical imaging, tissue optical clearing, optical interactions with tissue and cells, optical techniques for clinical application.Specifically, many advanced optical imaging techniques have been developed in recent years and applied to various biomedical applications. In this issue, Wang et al. described a two-photon nonlinear SIM (2P-SIM) technique using a multiple harmonics scanning pattern that employs a composite structured illumination pattern, which can produce a higher order harmonic pattern based on the fluorescence nonlinear response in a 2P process. Kazachkina et al. performed a pilot study of the dynamics of tumor oxygenation determination using phosphorescence lifetime imaging of mesotetra (sulfopheny1) tetrabenzoporphyrin Pd (II) (TBP), and observed a low oxygen content with increased phosphorescence lifetime of TBP in the tumor. Mylnikov et al. used the fluorescence imaging methods to reveal the indicated forms of tumor cell death under the combined effect of flavonoidcontaining extract of Gratiola officinalis and cytostatic, and found that the combination with a concentration ratio of the extract and cyclophosphamide of 3:1 has the greatest effectiveness due to stimulation of the cytostatic effect and cytotoxic effect. In addition, for the label-free imaging, Dyachenko et al. used laser speckle contrast imaging to monitor acute pancreatitis at ischemia-reperfusion of pancreas in rats. Zou et al. applied the OCT to investigate the influence of different sized nanoparticles and thermal coagulation-induced changes in the optical properties of normal, benign, and cancerous human breast tissues. Liu et al. presented an adaptive Watershed algorithm to automatically extract foveal avascular zone (FAZ) from retinal optical coherence tomography angiography (OCTA) images. Liang et al. revealed the underlying mechanisms of artifacts for thermoacoustic imaging (TAI) by investigating the specific absorption rate (SAR) distribution inside tissue phantoms, and showed its high dependence with the geometries of the imaging targets and the polarizing features of the microwave.Tissue optical clearing technique has become a powerful tool in deep tissue detection. The underlying mechanisms of optical clearing will help better understanding and application of the clearing protocols. In this issue, Genin et al. performed complex study of glycerol effects on rat skin tissue from different aspects involving the optical, weight and geometrical properties, and discussed the possible mechanism under the action of glycerol solutions. Jaafar et al. presented an investigation of optical clearing agents’ in°uence on probing depth using porcine skin with confocal Raman microspectroscopy (CRM). In addition, Kozintseva et al. studied the time dependence of optical clearing by monitoring the luminescence intensity of the upconverting particles (UCNPs), and demonstrated the possibility to use the UCNPs for studying the dynamics of optical clearing of biological tissues under local compression.The optical interactions with tissue and cells are hotspots in biomedical photonics. In this issue, Gyulkhandanyan et al. determined and tested the most effective meso-substituted cationic pyridylporphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. Kapkov et al. also used the laser tweezers for quantitative measurement of interaction forces between red blood cells (RBSs) and endothelial cells (ECs) in stationary conditions. They showed that the interaction force raises along with increasing concentration of fibrinogen and dextran in all considered cases of ECs interaction with RBCs.The photonics plays important roles in not only fundamental researches but also clinical diagnosis. In this issue, Hou et al. applied the Muller matrix microscope to distinguish microstructural features between high-grade cervical squamous intraepithelial lesion (HSIL) and cervical squamous cell carcinoma (CSCC), and presented results from 37 clinical patients with analysis regions of cervical squamous epithelium. This work provides an efficient method for digital pathological diagnosis and points out a new way for automatic screening of pathological sections.This issue provides a broad and frontier view about the recent developments in biophotonics and biomedical optics, hence we strongly recommend this issue.It should be noted that this special issue is just a part of the Chinese–Russian workshop on Biophotonics and Biomedical Optics 2020. Some of the above papers will be published in the first issue of next year. Finally, we thank all the contributing authors for making this issue possible.

现代光学成像技术与荧光标记技术不断发展,为高分辨地获取生物组织三维结构信息提供了重要的工具。然而,大多数生物组织具有不透明特性,限制了光在组织中的穿透深度,进而限制了光学成像技术在大组织或整体器官成像中的应用。近年兴起的组织光透明技术通过多种物理、化学手段降低组织对光的衰减,增加光穿透深度,从而提高光学成像的成像深度与成像质量,为整体组织器官的三维成像提供了全新的思路。本文从离体组织光透明方法、大组织器官标记方法、三维整体成像技术三个方面,对整体器官的光透明成像方法进行综述。

We present a three-dimensional (3D) isotropic imaging of mouse brain using light-sheet fluorescent microscopy (LSFM) in conjunction with a multi-view imaging computation. Unlike common single view LSFM is used for mouse brain imaging, the brain tissue is 3D imaged under eight views in our study, by a home-built selective plane illumination microscopy (SPIM). An output image containing complete structural information as well as significantly improved resolution (～4 times) are then computed based on these eight views of data, using a bead-guided multi-view registration and deconvolution. With superior imaging quality, the astrocyte and pyramidal neurons together with their subcellular nerve fibers can be clearly visualized and segmented. With further including other computational methods, this study can be potentially scaled up to map the connectome of whole mouse brain with a simple light-sheet microscope.