Spinal cord injury triggers a series of complex biochemical alterations of nervous tissue. Up to now, such cellular events could not be studied without conventional tissue staining. The development of optical, label-free imaging techniques could provide powerful monitoring tools with the potential to be applied in vivo. In this work, we assess the ability of vibrational spectroscopy to generate contrast at molecular level between normal and altered regions in a rat model of spinal cord injury. Using tissue sections, we demonstrate that Fourier transform infrared (FT-IR) spectroscopy and spontaneous Raman spectroscopy are able to identify the lesion, the surrounding scar, and unharmed normal tissue, delivering insight into the biochemical events induced by the injury and allowing mapping of tissue degeneration. The FT-IR and Raman spectroscopic imaging provides the basis for fast multimodal nonlinear optical microscopy (coherent anti-Stokes Raman scattering, endogenous two-photon fluorescence, and second harmonic generation). The latter proves to be a fast tool for imaging of the lesion on unstained tissue samples, based on the alteration in lipid content, extracellular matrix composition, and microglia/macrophages distribution pattern. The results establish these technologies in the field of regeneration in central nervous system, with the long-term goal to extend them to intravital use, where fast and nonharmful imaging is required.

Implantation of soft alginate hydrogel in small spinal cord lesions improved functional recovery. Possible underlying mechanisms include the mechanical stabilization of the wound, reduction of secondary damage and inhibition of fibrous scarring.

Spinal cord injury (SCI) induces complex biochemical changes, which result in inhibition of nervous tissue regeneration abilities. In this study, Fourier-transform infrared (FT-IR) spectroscopy was applied to assess the outcomes of implants made of a novel type of non-functionalized soft calcium alginate hydrogel in a rat model of spinal cord hemisection (n = 28). Using FT-IR spectroscopic imaging, we evaluated the stability of the implants and the effects on morphology and biochemistry of the injured tissue one and six months after injury. A semi-quantitative evaluation of the distribution of lipids and collagen showed that alginate significantly reduced injury-induced demyelination of the contralateral white matter and fibrotic scarring in the chronic state after SCI. The spectral information enabled to detect and localize the alginate hydrogel at the lesion site and proved its long-term persistence in vivo. These findings demonstrate a positive impact of alginate hydrogel on recovery after SCI and prove FT-IR spectroscopic imaging as alternative method to evaluate and optimize future SCI repair strategies.