Fig. 5

Neurotoxicity and neuronal affinity of SPIONs. a HE staining images of nerve tissue sections collected 1, 2, 3, 7, and 14 days after sub-epineurial injection of SPIONs (300 µg/ mL, 20 µL) were used to observe the neurotoxicity of SPIONs. b–e At 1, 3, 7 and 14 days after sub-epineurial injection at the same concentration, the sciatic nerves were harvested, and freshly frozen sections were obtained. The localization and distribution of SPIONs in the nerve tissue were observed through fluorescence using CLSM. The distribution and localization of SPIONs in nerve ultrastructure were observed directly by high-resolution TEM. f SPIONs penetrated the basal membrane of the myelin sheath of Schwann cells and g were distributed in the inner myelin lamina of Schwann cells. h SPIONs were found in unmyelinated nerve fibers. i The iron content of the sciatic nerve at different time points after sub-epineurial injection was quantitatively measured by ICP-AES. Each experiment was carried out in triplicate. The values are represented as the mean ± SD. The long red arrows indicate the SPIONs in panels f–h, and the short red arrowhead indicates the basal membrane of Schwann cells in panel f. *P < 0.05, **P < 0.01