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Journal of the Mechanics and Physics of Solids 53 (2005) 1552–1573 www.elsevier.com/locate/jmps

Remodeling of biological tissue: Mechanically induced reorientation of a transversely isotropic chain network Ellen Kuhla,, Krishna Garikipatib, Ellen M. Arrudab,c, Karl Groshb a

Chair for Applied Mechanics, University of Kaiserslautern, D-67653 Kaiserslautern, Germany Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA c Macromolecular Science and Engineering Program, University of Michigan, Ann Arbor, MI 48109, USA b

Received 21 October 2004; received in revised form 9 March 2005; accepted 11 March 2005

Abstract A new class of micromechanically motivated chain network models for soft biological tissues is presented. On the microlevel, it is based on the statistics of long chain molecules. A wormlike chain model is applied to capture the behavior of the collagen microfibrils. On the macrolevel, the network of collagen chains is represented by a transversely isotropic eight chain unit cell introducing one characteristic material axis. Biomechanically induced remodeling is captured by allowing for a continuous reorientation of the predominant unit cell axis driven by a biomechanical stimulus. To this end, we adopt the gradual alignment of the unit cell axis with the direction of maximum principal strain. The evolution of the unit cell axis’ orientation is governed by a first-order rate equation. For the temporal discretization of the remodeling rate equation, we suggest an exponential update scheme of Euler-Rodrigues type. For the spatial discretization, a finite element strategy is applied which introduces the current individual cell orientation as an internal variable on the integration point level. Selected model problems are analyzed to illustrate the basic features of the new model. Finally,

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E-mail addresses: [email protected] (E. Kuhl), [email protected] (K. Garikipati), [email protected] (E.M. Arruda), [email protected] (K. Grosh). 0022-5096/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jmps.2005.03.002