Joining mechanically dissimilar materials is a challenge throughout engineering, with spectacular and often devastating failures. This challenge also underlies one of the worst procedures in all of medical practice, the surgical reattachment of tendon to bone. The body presents a highly effective attachment prior to injury, but the tissue regenerated following healing is vastly inferior mechanically and surgical outcomes can be abject failures, with recurrence of tears as high as 94 percent following surgical repair of massive rotator cuff tears in elderly patients.Our group studies how the natural tendon-to-bone attachment develops, functions, and heals, and how healing might be improved through tissue engineered augmentation. Although much of the basic physiology is still debated, it is clear that choreographed, nanoscale-to-milliscale toughening mechanisms are at play, and that mechanical factors play a central role in developing and sustaining these mechanisms. Hierarchical toughening mechanisms involve tailoring of the collagen lattice upon which the entire tendon-to-bone attachment is constructed, and accommodation by this lattice of a relatively stiff hydroxyl apatite phase. Toughening strategies include cross-scale functional grading of the mineral component within collagen, macro-scale interdigitation of bony and tendinous tissue, and shape optimization to distribute stresses.Central challenges are understanding how mineral accumulates on the collagen lattice underlying tendon, bone, and its connection, and quantifying the mechanical consequences of adding prescribed amounts of mineral, both to this collagen lattice and to potential scaffolds for guiding healing. This talk will focus on our recent efforts to characterize and reconstitute the nano-to-milliscale physiology of the tendon-to-bone attachment at the humeral head of the rotator cuff.
Guy Genin (Washington University) received B.S.C.E. and M.S. degrees in engineering mechanics from Case Western Reserve University in 1992, and S.M. and Ph.D. degrees in applied and solid mechanics from Harvard University in 1993 and 1996, and post-doctoral training at Cambridge and Brown. He is Professor of Mechanical Engineering and Materials Science at Washington University in St. Louis, and of Neurological Surgery at Washington University School of Medicine. His professional interests involve study of interfaces and adhesion in physiology, nature, and engineering. His current research focuses on connections between tendon and bone, and on interactions between plant and animal cells with their mechano-electric environment.
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