{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T01:21:56Z","timestamp":1760059316025,"version":"build-2065373602"},"reference-count":28,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2025,6,5]],"date-time":"2025-06-05T00:00:00Z","timestamp":1749081600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Science and Technology Council, Taiwan","award":["111-2811-B-039-002","112-2112-M-039-001","113-2112-M-039-001","CMU111-MF-18","CMU113-MF-02"],"award-info":[{"award-number":["111-2811-B-039-002","112-2112-M-039-001","113-2112-M-039-001","CMU111-MF-18","CMU113-MF-02"]}]},{"DOI":"10.13039\/501100012544","name":"China Medical University, Taiwan","doi-asserted-by":"publisher","award":["111-2811-B-039-002","112-2112-M-039-001","113-2112-M-039-001","CMU111-MF-18","CMU113-MF-02"],"award-info":[{"award-number":["111-2811-B-039-002","112-2112-M-039-001","113-2112-M-039-001","CMU111-MF-18","CMU113-MF-02"]}],"id":[{"id":"10.13039\/501100012544","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>The flight feather rachis is a lightweight, anisotropic structure that must withstand asymmetric aerodynamic loads generated during flapping flight\u2014particularly under unidirectional compression during the wing downstroke. To accommodate this spatiotemporal loading regime, the rachis exhibits refined internal organization, especially along the dorsoventral axis. In this study, we used finite element modeling (FEM) to investigate how dorsoventral polarization in cortical keratin allocation modulates the mechanical performance of shaft-like structures under bending. All models were constructed with conserved second moments of area and identical material properties to isolate the effects of spatial material placement. We found that dorsal-biased reinforcement delays yield onset, enhances strain dispersion, and promotes elastic recovery, while ventral polarization leads to premature strain localization and plastic deformation. These outcomes align with the dorsally thickened rachises observed in flight-specialized birds and reflect their adaptation to asymmetric aerodynamic forces. In addition, we conducted a conceptual exploration of radial (cortex\u2013medulla) redistribution, suggesting that even inner\u2013outer asymmetry may contribute to directional stiffness tuning. Together, our findings highlight how the flight feather rachis integrates cortical material asymmetry to meet directional mechanical demands, offering a symmetry-informed framework for understanding biological shaft performance.<\/jats:p>","DOI":"10.3390\/sym17060880","type":"journal-article","created":{"date-parts":[[2025,6,5]],"date-time":"2025-06-05T03:58:52Z","timestamp":1749095932000},"page":"880","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Structural Mechanics of the Flight Feather Rachis: The Role of Cortical Keratin Asymmetry"],"prefix":"10.3390","volume":"17","author":[{"ORCID":"https:\/\/orcid.org\/0009-0008-5843-3593","authenticated-orcid":false,"given":"Hao","family":"Wu","sequence":"first","affiliation":[{"name":"Graduate Institute of Biomedical Sciences, China Medical University, Taichung 404328, Taiwan"},{"name":"Department of Life Sciences, National Chung Hsing University, Taichung 402202, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ju-Cheng","family":"Hsiao","sequence":"additional","affiliation":[{"name":"Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung 404328, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0005-0964-9812","authenticated-orcid":false,"given":"Wan-Chi","family":"Liao","sequence":"additional","affiliation":[{"name":"Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung 404328, Taiwan"},{"name":"Master Program for Biomedical Engineering, China Medical University, Taichung 404328, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"You-Sian","family":"Wang","sequence":"additional","affiliation":[{"name":"Master Program for Biomedical Engineering, China Medical University, Taichung 404328, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xiang-Ning","family":"Xie","sequence":"additional","affiliation":[{"name":"Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung 404328, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7195-4384","authenticated-orcid":false,"given":"Wen-Tau","family":"Juan","sequence":"additional","affiliation":[{"name":"Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung 404328, Taiwan"},{"name":"Department of Medical Research, China Medical University Hospital, Taichung 404327, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1038\/nmat4089","article-title":"Bioinspired structural materials","volume":"14","author":"Wegst","year":"2015","journal-title":"Nat. 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