ch13_bone - Harvard-MIT Division of Health Sciences and...

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Unformatted text preview: Harvard-MIT Division of Health Sciences and Technology HST.523J: Cell-Matrix Mechanics Prof. Myron Spector Massachusetts Institute of Technology Harvard Medical School Brigham and Women's Hospital VA Boston Healthcare System 2.785j/3.97J/BEH.411/HST523J BONE M. Spector, Ph.D. Several slides have been removed from this presentation for copyright reasons. Sources: (1) American Academy of Orthopaedic Surgeons (AAOS). "Orthopaedic Basic Science Slide Set," CD-ROM, 2nd ed., 1999. Slides on bone structure, types of bone, Haversian System, osteoblasts and osteocytes, bone chemistry and mechanical properties. (2) Frank Netter illustrations, Ciba. Figure by MIT OCW. Cortical Bone Properties Property Human Bovine Elastic Modulus Transverse 17.4 GPa 20.4 GPa Elastic Modulus Long 9.6 GPa 11.7 GPa Shear Modulus 3.5 GPa 4.1 GPa Tensile Yield Stress Long 115 M Pa 141 MPa Tensile Ult Stress Long 133 M Pa 156 MPa Tensile Ult Stress Trans 51 M Pa 50 MPa Comp Yield Stress Long 182 M Pa 196 MPa Comp Yield Stress Trans 121 M Pa 150 MPa Comp Ult Stress Long 195 M Pa 237 MPa Comp Ult Stress Trans 133 M Pa 178 MPa Tensile Ultimate Strain 2.9 - 3.2% 0.67 - 0.72% Compressive Ult. Strain 2.2 - 4.6% 2.5 - 5.2% Martin, et al. (1998) Osteon Properties Ascenzi and Bonucci Osteon Type* Longitudinal Transverse Alternating Longitudinal Alternating Longitudinal Transverse Alternating Mechanical Elastic Ultimate Test Modulus(GPa) Stress (MPa) Compression 6.3 110 Compression 9.3 164 Compression 7.4 134 Tension 11.7 114 Tension 5.5 94 Shear 3.3 46 Shear 4.2 57 Shear 4.1 55 *Orientation of the collagen fiber bundles with respect to the plane of the osteon section. Collagen fiber bundles oriented with the direction of testing produce a higher normal stiffness while collagen fiber bundles oriented out of the plane of testing produce a lower stiffness but a higher shear stiffness. Correlation Between Trabecular Bone Compressive Modulus and Density R2 for Linear and Power Models Region Linear Power Proximal Femur 0.50 0.55 Distal Femur 0.65 0.65 Proximal Tibia 0.41 0.40 Proximal Humerus 0.65 0.66 Distal Radius 0.17 0.13 Ciarelli et al. (1991) Effects of biomechanical stress on bones in animals Diagram removed for copyright reasons. When bone is subjected to bending, fluid is forced through the canalicular channels from regions of greater compression toward regions of lesser compression (or from more concave surfaces to more convex surfaces). This gradient of flow is proportional to the strain gradient across the cortex of the bone. The magnitude of the fluid shear stress on osteocytes lying within the lacunae is proportional to the rate at which fluid is forced through these channels, which in turn is proportional to the strain rate. DB Burr, et al., Bone 30:781 (2002) See the following two papers - images have been removed for copyright reasons. (1) Turner, J. and F.M. Pavalko. "Mechanotransduction and functional response of the skeleton to physical stress: the mechanisms and mechanics of bone adaptation." J Orthop Sci 3:346 (1998) (2) Burr, D.B., A.G. Robling and C.H. Turner. "Effects of biomechanical stress on bones in animals." 30:5 (May 2002)781-6 Effects of Spaceflight on Bone RT Turner, et al., Proc Soc Exp Biol Med 180:544 (1985) RT Turner, et al;. Physiologist 24:S-97 (1981) Photos removed for copyright reasons. BONE CELLS: OSTEOBLASTS Contraction of osteoblasts Expression of -smooth muscle actin in osteoblasts in vivo Fracture healing Distraction osteogenesis CONTRACTILE CONNECTIVE TISSUE CELLS Express SMA in vivo Capable of contracting collagen-GAG matrices in vitro SMA-positive cells retain differentiated phenotype SMA trait derived from the stem cell Amount of contraction correlated with the SMA content SMA and contraction up-regulated by TGF-1 Roles have yet to be determined, but may be both positive and negative POSSIBLE ROLES FOR SMA-ENABLED CONTRACTION OF MS CELLS Closure of skin wounds; fx. heal? Tensioning of a healing ligament Retraction of the ends of torn ligaments/tendons that do not heal Disease processes Contracture Tissue formation Modeling of ECM architecture and remodeling (e.g., crimp in ligament/tendon?) Tissue engineering Contracture of scaffolds Healing See the following papers - images have been removed for copyright reasons. (1) Menard, C.G., S. Mitchell and M. Spector. "Contractile behavior of smooth muscle actin-containing osteoblasts in collagen-GAG matrices in vitro: implant-related cell contraction." Biomaterials 21:18 (2000 Sept) 1867-77. (2) Kinner, B. et al. JOR 2002;20:622-632 (3) Kinner, B. et al. "Expression of smooth muscle actin in connective tissue cells participating in fracture healing in a murine model." Bone 30:738 (2002). (4) B. Kinner, et al., JOR 21:20 (2003) SMA AND CONTRACTION OF MUSCULOSKLETAL CELLS Many Questions to be Answered What are the roles of SMA-enabled contraction in normal and pathological processes? What therapeutic approaches can be taken for its regulation? How does the SMA-enabled contraction impact musculoskeletal tissue engineering? ...
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