Dynamic monitoring of wound healing in spinal cord using a clamp-type imaging window and optical coherence tomography

Abstract

The continuous investigation of wound healing offers intuitive information to study and manage various injuries. It is essential to understand spinal cord (SC) when it has damage to the tight bundle of cells and nerves that sends and receives signals from the brain to and from the rest of the body. Although mouse model and optical imaging are indispensable elements in brain research, there are relatively few studies reported that describe the dynamic monitoring in SC. It is because that in vivo imaging of the spinal cord is certainly limited due to its movement as well as location surrounded by bone and dura mater. In this study, we introduced a new method for in vivo real-time and longitudinal imaging of the spinal cord using a novel spinal cord window chamber and optical coherence tomography (OCT). OCT has been introduced in biomedical imaging modality with various advantages including real-time, non-invasive, and deep tissue imaging. We utilized the OCT to observe three-dimensional structural and functional changes in a SC when incomplete spinal cord injury was recovered. Although its imaging capability is well suited to monitor SC including the wound healing process after injury, it has the challenge to apply to SC study in vivo and the same location because of the motion artifact as well as the lack of an optical imaging window. In order to enable dynamic and long-term imaging of mouse SC, we developed a minimally invasive intervertebral window. Our device is designed as a clamp-type integrated with a round-shaped imaging window, which is readily mounted at the vertebrae. Since our device is fabricated by 3D printing of biocompatible ABS filament and with PDMS material for imaging window, it also has high reproducibility and flexibility to build customized window reflecting the various shape of SC in short period of time. In our preliminary experiment, we successfully imaged the regional and volumetric structure of SC over 20 days, and confirmed that our method provides a reliable platform in various research aiming at interpretation of spinal cord physiology. We also quantified the injured area with home-built software for image processing and generated unique information, which cannot be obtained by conventional optical imaging in vivo. In particular, a ratio of gray and white matter was identified during the recovery phase which is crucial to investigate neural diseases such as multiple sclerosis disability. Through our experimental results, it is expected that a clamp-type window would be widely utilized with various optical imaging modalities including two-photon microscopy to elucidate the recovery process of the spinal cord with neurons and glial cells in future work.