“…Moreover, animals can die during the surgery and the optical window can break or detach after successful implantation. These problems can be overcome by the use of optical fibres that provide access to sites deeper within the organ [ 141 , 142 ], or with micro-endoscopic probes employed to provide a less invasive observation mode of cellular-level features in colon [ 143 , 144 ], oesophagus [ 145 , 146 ], and trachea [ 147 ]. Fluorescent micro-endoscopy is a powerful technique for imaging the internal structure of a hollow organ; however, it can have a lower resolution and smaller field of view compared to high-resolution microscopes used in the techniques above.…”