羽毛是自然界中最複雜的皮膚衍生物。羽毛複雜的成長過程所產生外觀上的階層分支、高度組織化的內外層結構，及在鳥類生活中所扮演的多樣功性，讓羽毛成為近代跨研究領域的重要課題。羽毛早期的研究以解剖學分析為主；近年因恐龍羽毛的史前化石出土，啟發了更多人由演化及羽毛形成過程的觀點來探究羽毛課題。新穎羽毛演化模型的發表，和羽毛形態發生過程中關鍵分子生物訊號的確認，是近年來羽毛研究重要的里程碑。從經典研究結果得知，在毛囊這個高度不對稱環境中所生成的羽毛，應具有材質上的非均性，但前人卻鮮少深入探討此一非均性對羽毛力學性質的影響。本論文將探討：羽軸內部微結構的非均性及演化上不同鳥種所展現的羽毛微結構差異，對於羽軸力學性質的影響。
我們首先量測羽軸髓質和皮質不同徑向方位的彎曲彈性模量，以探討組成羽軸的皮質及羽髓，於彎曲測試上是否存在非均向性。我們利用自行設計的彎曲試驗機所量測的結果得知，由單一物種、部位所取得羽髓多孔微結構，其微結構的非均性，並不會造成非均向的羽髓彈性模量。然而，於橫跨五種不同鳥種羽皮質和羽髓彎曲彈性模量研究，我們發現相異物種羽髓的彈性模量差別甚大：鴕鳥羽髓的彈性模量比其他近代鳥種大一倍以上；但不同物種羽毛皮質部位的彈性模量差異不大。
我們亦研究羽軸含水量對微結構形態所產生的影響，以了解羽毛由生長到成熟過程中羽毛脫水過程的微觀圖像：藉由螢光顯微鏡觀察五種鳥類羽軸厚片的橫截面，並解析皮質及羽髓的形態於吸水與脫水過程的變化發現，每種羽軸吸水後皆會有明顯的膨脹，且多數會呈現以羽軸側支方向為主的非均向的膨脹；無皮質包覆羽髓的吸水膨脹主要方向，與其內部孔洞週期性的結構排列方向相垂直；微結構越明顯的羽髓，隨含水量變化所導致的整體形變比例也越大。

Feathers are the most complex integumentary appendage found in nature. The complex feather regeneration leads to its hierarchical branching, highly organized inner-outer structure, and multifunction in avian daily life. The feather has become an important topic in modern interdisciplinary research field. In contrast to early anatomy research of feathers, the excavation of prehistoric dinosaur feather fossils have inspired scientists to explore feathers in the perspective of evolution and regeneration recently. The novel feather development model and the confirmation of crucial biochemical signals during feather morphogenesis are important milestones in the modern feather research.
The feather regeneration in an asymmetric avian follicle makes the composition of a feather exhibits non-uniform material properties. However, former researchers rarely investigate how the non-uniform composition of feather may contribute to its mechanical properties. In this thesis, we investigate the effect of non-uniform inner microstructure in the feather rachis among species, and study the influence of microstructure on rachis mechanical properties. We use a home-made bending test system to measure the bending elastic modulus of the rachis medulla and cortex in different bending direction. The result indicates that the non-uniform microstructure of the porous medulla from a single species do not introduce the anisotropy of the elastic modulus. However, the measured elastic modulus of medulla have a distinctive difference among feathers from various species.
We also investigate the influence of the moisture to the rachis microstructure in order to understand the impact of the dehydration during feather development microscopically. We use the fluorescent microscopy to observe the morphology of medulla and cortex during hydration and dehydration of the rachis. We observe the swelling of the feather rachis associated with the hydration. The rachis prefer expanding anisotropically towards the barbs direction. The hydrated rachis medulla without cortex tends to expand perpendicularly to the direction of microstructure pattern.

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