許旺細胞為周邊神經重要的膠質細胞，能形成多層膜之髓鞘包覆神經軸突，髓鞘的力學行為與髓鞘化過程及許多神經病變有關。本研究以力學角度探討活體神經髓鞘於不同培養階段下的機械性質變化。
首先利用許旺細胞與PC-12類神經細胞共同培養出神經髓鞘，再利用原子力顯微鏡做多點壓痕測試，配合Bilodeau彈性模型估測出視楊氏模數，最後對細胞做免疫螢光染色確認髓鞘位置。此外，利用逆向有限元素法擬合實驗數據，並將其結果與Bilodeau模型結果相互驗證。
結果顯示髓鞘隨著培養天數增加而剛性上升，在M-I、M-II與M-III階段其視楊氏模數分別為3.04±0.27 kPa，4.19±0.12 kPa與5.14±0.26 kPa，中後期高於無髓鞘化之PC-12類神經細胞軸突。於有限元素法模擬中將髓鞘視為超彈性材料，所得到的剛性大小趨勢亦為M-III＞M-II＞M-I，因此推論許旺細胞形成的髓鞘可以保護神經軸突。

Schwann cells play an essential role in peripheral nervous system. They form myelin sheaths wrapping around neuron axons. Many diseases are caused by demyelination. It is believed that mechanical behavior of myelin sheath may be a factor for myelination and demyelination processes. The objective of this study was to investigate mechanical properties of living axons of cultured neurons at different myelination stages.
Myelinated axons were developed from PC-12 cells co-cultured with differentiated Schwann cells. The atomic force microscopy was employed to obtain morphology and multiple force-distance curves of the myelinated axons. Immuno-fluorescence microscopy was also used to validate the formation of myelin sheath. In this study, both Bilodeau model and finite element method were utilized to analyze the experimental relationship between force and indentation depth.
The results showed that the stiffness increased with culturing days. At M-I, M-II and M-III stages, the apparent Young’s modulus of myelin sheath were 3.04±0.27 kPa, 4.19±0.12 kPa and 5.14±0.26 kPa, respectively. As myelin sheath became mature, the apparent Young’s modulus was higher than that of PC-12 cell axons. The results inferred that in addition to increasing conduction velocity, the myelin sheath can protect the axon from damage.

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