Utilising the AFM nanoindentation technique for the study of hair cross- and longitudinal sections, the mechanical anisotropy of human hair fibres affected by a rare congenital condition, Monilethrix, has been investigated for the first time. Supported by X-ray microdiffraction data, and applying a model based on an ideal composite material consisting of rods (KIFs) and matrix (KAPs) to Monilethrix affected fibres, it has been shown that the results could be grouped into clearly different classes, namely: almost isotropic behaviour for Monilethrix affected hairs and anisotropic behaviour for Control hair. Moreover, AFM nanoindentation of hair cross sections has demonstrated, also for the first time that hairs affected by Monilethrix have a continuous, and not periodic, weakness within the cortex. This has been attributed to disruptions in the KIF-KIF, KIF-intermacrofibrillar matrix or KIF-desmosome complexes within the hair shaft, as suggested by X-ray microdiffraction examination. Hairs from a patient exhibiting no obvious phenotype exhibited similar mechanical weakness despite the otherwise normal visual appearance of the fibre. This further supports a hypothesis that the beaded appearance of Monilethrix hair is a secondary factor, unrelated to the inherent structural weakness.

利用 AFM 纳米压痕技术研究头发的横断面和纵断面，首次研究了受罕见先天性疾病 Monilethrix 影响的人发纤维的机械各向异性。在 X 射线微衍射数据的支持下，并将基于由棒 (KIF) 和基体 (KAP) 组成的理想复合材料的模型应用于受 Monilethrix 影响的纤维，结果表明可以将结果分为明显不同的类别，即：Monilethrix 影响毛发的几乎各向同性行为和Control 的各向异性行为头发。此外，头发横截面的 AFM 纳米压痕也首次证明受 Monilethrix 影响的头发在皮质内具有连续而非周期性的弱点。这归因于毛干内的 KIF-KIF、KIF-大原纤维间基质或 KIF-桥粒复合物的破坏，正如 X 射线微衍射检查所表明的那样。尽管纤维的其他视觉外观正常，但未表现出明显表型的患者的头发表现出类似的机械弱点。这进一步支持了一个假设，即 Monilethrix 头发的串珠外观是次要因素，与固有的结构弱点无关。