See through large animal tissues: overcoming biological barriers

Tissue optical clearing is a fundamental technique that enhances light penetration deep into biological samples by reducing light scattering through refractive index homogenization. This process renders tissues transparent, enabling high-resolution three-dimensional imaging of intact organs and revealing complex cellular architectures that are otherwise inaccessible to optical microscopy.

Prof. Dan Zhu’ group at Huazhong University of Science and Technology (HUST), China, have been focusing on tissue optical clearing imaging, and developed serial tissue optical clearing methods and obtaining neuro-vasculature of whole organ of mouse. Actually, the anatomical structure and physiological function of larger animals like pigs and non-human primates, are closer to humans. However, there are challenge of the tissue optical clearing technology for large animal models. In this review, they systematically clarify the challenges on transition of current methods from rodent models to larger animals, which include substantially longer reagent penetration times due to larger organ sizes and different components. Thus, it is necessary to overcome stronger light scattering of tissue caused by factors like higher myelin content in neural tissues.

They outline how existing protocols, such as 3DISCO, CUBIC, and specialized methods like BoneClear, require specific modifications to effectively clear large-animal tissues. Examples include the mapping of neural circuits in primate brains and the imaging of cochlear structures in pig inner ears. The technology facilitates the study of organ development and disease mechanisms in models that more closely resemble humans.

The researchers suggest that future work should focus on standardizing sample preparation, enhancing reagent penetration efficiency, and improving cross-species compatibility. They also note that emerging methods, including intelligent imaging and AI-assisted analysis, could support further advances in the field. The work entitled “Advances in Tissue Optical Clearing for 3D Imaging in Large Animals” was published on Frontiers of Optoelectronics (published on Aug. 18, 2025).