Effects of Hydration on Nanoscale Structural Morphology and Mechanics of Individual Type I Collagen Fibrils
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Effects of Hydration on Nanoscale Structural Morphology and Mechanics of Individual Type I Collagen Fibrils Joseph M. Wallace1, Chad Harding1 and Arika Kemp1 1
Department of Biomedical Engineering, Indiana University-Purdue University at Indianapolis,
723 W Michigan St. SL220, Indianapolis, IN 46202, U.S.A. ABSTRACT Type I collagen is one of the most vital proteins in our bodies and serves a number of structural roles. Despite collagen’s importance, little is known about its nanoscale morphology in tissues and how morphology relates to mechanical function. This study directly probes nanoscale structure and mechanics in collagen as a function of hydration utilizing atomic force microscopy investigations of the mouse tail tendon. We demonstrate that collagen morphology and mechanical properties at the nanoscale change with dehydration, indicating that hydration is a factor which must be considered when performing studies at any length scale in collagen-based tissues. Studies are underway to further investigate this phenomenon and to determine how these properties change with disease in tendon and other Type I collagen-based tissues. INTRODUCTION Type I collagen is the most abundant protein in the body and forms the structural scaffolding upon which many tissues are built 1. Collagen serves as the principal source of tensile strength in our bodies and is present in a variety of tissues including arterial walls, cornea, tendon, ligament and bone 2. Depending on the tissue being studied, structures based on collagen can be found at various length scales. For instance, tendon is hierarchical and is formed from bundled structures called fascicles. Fascicles are the smallest functional units of the tendon and are composed of fibroblasts (tenoblasts), non-collagenous proteins and collagen fibers. These fibers are then composed of smaller units, the collagen fibril. Bone is also hierarchical but in most cases lacks collagen fibers. Instead, bone has structures at the organ and tissue level (e.g. cortical bone versus trabecular bone) which are composed of microstructural elements (osteons and trabecular packets). The osteons and trabecular packets are made of thin layers of bone tissue known as lamellae which are composed of layers of mineralized collagen fibrils. These two examples highlight that the primary building block of many collagen-based tissues is the nanoscale collagen fibril. Because of the wide-ranging roles that collagen plays in the body and the number of diseases that can strike collagen-based tissues, understanding nanoscale features of collagen is imperative. This need for accurate and quantitative analytical methods prompted our study of collagen using atomic force microscopy (AFM) 3-5. Type I collagen begins as a polypeptide change of amino acids with a characteristic repeating triplet motif of glycine-X-Y (X and Y are most often proline and hydroxyproline, respectively). This chain of amino acids takes a left-handed helical conformation (the helix), and 3 -helices then counter-wind into a right-handed tr
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