CARS imaging of therapeutic alginate implants after spinal cord injury in the rat

Label-free multiphoton microscopy probes the morphochemistry of tissue and constitutes a promising technology for biomedical research. Here, we used a multimodal approach to monitor de- and regeneration after spinal cord hemisection in the rat. Furthermore, the effects of a therapeutic implant consisting of unfunctionalized soft calcium alginate hydrogel were assessed. Coherent anti-Stokes Raman scattering (CARS) was used to visualize axonal structures, two-photon excited fluorescence to visualize the activation of microglia/macrophages and second harmonic generation to visualize collagenous scarring. CARS/multiphoton imaging revealed a decreased inflammatory response, reduced scarring, increased presence of axons at the site of injury and decreased demyelination of contralateral white matter in treated animals. The reduction of chronic inflammation and the increase of axons in the lesion correlated with improved hind limb functions. Therefore, CARS/multiphoton microscopy qualified as diagnostically relevant technique with the potential to be applied in vivo for therapeutic monitoring.