Robert O Ritchie

Publications of Robert O Ritchie

• Directing mesenchymal stem cells to bone to augment bone formation and increase bone mass.

  Authors: Min Guan, Wei Yao, Ruiwu Liu, Kit S Lam, Jan Nolta, Junjing Jia, Brian Panganiban, Liping Meng, Ping Zhou, Mohammad Shahnazari, Robert O Ritchie, Nancy E Lane

  Nature medicine. 01/2012; 18(3):456-62.

  Aging reduces the number of mesenchymal stem cells (MSCs) that can differentiate into osteoblasts in the bone marrow, which leads to impairment of osteogenesis. However, if MSCs could be directedAging reduces the number of mesenchymal stem cells (MSCs) that can differentiate into osteoblasts in the bone marrow, which leads to impairment of osteogenesis. However, if MSCs could be directed toward osteogenic differentiation, they could be a viable therapeutic option for bone regeneration. We have developed a method to direct MSCs to the bone surface by attaching a synthetic high-affinity and specific peptidomimetic ligand (LLP2A) against integrin α4β1 on the MSC surface to a bisphosphonate (alendronate, Ale) that has a high affinity for bone. LLP2A-Ale induced MSC migration and osteogenic differentiation in vitro. A single intravenous injection of LLP2A-Ale increased trabecular bone formation and bone mass in both xenotransplantation studies and in immunocompetent mice. Additionally, LLP2A-Ale prevented trabecular bone loss after peak bone acquisition was achieved or as a result of estrogen deficiency. These results provide proof of principle that LLP2A-Ale can direct MSCs to the bone to form new bone and increase bone strength.

• Mixed-mode toughness of human cortical bone containing a longitudinal crack in far-field compression.

  Authors: Diana Olvera, Elizabeth A Zimmermann, Robert O Ritchie

  Bone. 11/2011; 50(1):331-6.

  Bone is generally loaded under multiaxial conditions in vivo; as it invariably contains microcracks, this leads to complex mixed-mode stress-states involving combinations of tension, compression andBone is generally loaded under multiaxial conditions in vivo; as it invariably contains microcracks, this leads to complex mixed-mode stress-states involving combinations of tension, compression and shear. In previous work on the mixed-mode loading of human cortical bone (using an asymmetric bend test geometry), we found that the bone toughness was lower when loaded in far-field shear than in tension (opposite to the trend in most brittle materials), although only for the transverse orientation. This is a consequence of the competition between preferred mechanical vs. microstructural crack-path directions, the former dictated by the direction of the maximum mechanical "driving force" (which changes with the mode-mixity), and the latter by the "weakest" microstructural path (which in human bone is along the osteonal interfaces or cement lines). As most microcracks are oriented longitudinally, we investigate here the corresponding mixed-mode toughness of human cortical bone in the longitudinal (proximal-distal) orientation using a "double cleavage drilled compression" test geometry, which provides a physiologically-relevant loading condition for bone in that it characterizes the toughness of a longitudinal crack loaded in far-field compression. In contrast to the transverse toughness, results show that the longitudinal toughness, measured using the strain-energy release rate, is significantly higher in shear (mode II) than in tension (mode I). This is consistent, however, with the individual criteria of preferred mechanical vs. microstructural crack paths being commensurate in this orientation.

• The conflicts between strength and toughness.

  Authors: Robert O Ritchie

  Nature materials. 11/2011; 10(11):817-22.

  The attainment of both strength and toughness is a vital requirement for most structural materials; unfortunately these properties are generally mutually exclusive. Although the quest continues forThe attainment of both strength and toughness is a vital requirement for most structural materials; unfortunately these properties are generally mutually exclusive. Although the quest continues for stronger and harder materials, these have little to no use as bulk structural materials without appropriate fracture resistance. It is the lower-strength, and hence higher-toughness, materials that find use for most safety-critical applications where premature or, worse still, catastrophic fracture is unacceptable. For these reasons, the development of strong and tough (damage-tolerant) materials has traditionally been an exercise in compromise between hardness versus ductility. Drawing examples from metallic glasses, natural and biological materials, and structural and biomimetic ceramics, we examine some of the newer strategies in dealing with this conflict. Specifically, we focus on the interplay between the mechanisms that individually contribute to strength and toughness, noting that these phenomena can originate from very different lengthscales in a material's structural architecture. We show how these new and natural materials can defeat the conflict of strength versus toughness and achieve unprecedented levels of damage tolerance within their respective material classes.

• Characterization of the effects of x-ray irradiation on the hierarchical structure and mechanical properties of human cortical bone.

  Authors: Holly D Barth, Elizabeth A Zimmermann, Eric Schaible, Simon Y Tang, Tamara Alliston, Robert O Ritchie

  Biomaterials. 08/2011; 32(34):8892-904.

  Bone comprises a complex structure of primarily collagen, hydroxyapatite and water, where each hierarchical structural level contributes to its strength, ductility and toughness. These properties,Bone comprises a complex structure of primarily collagen, hydroxyapatite and water, where each hierarchical structural level contributes to its strength, ductility and toughness. These properties, however, are degraded by irradiation, arising from medical therapy or bone-allograft sterilization. We provide here a mechanistic framework for how irradiation affects the nature and properties of human cortical bone over a range of characteristic (nano to macro) length-scales, following x-ray exposures up to 630 kGy. Macroscopically, bone strength, ductility and fracture resistance are seen to be progressively degraded with increasing irradiation levels. At the micron-scale, fracture properties, evaluated using insitu scanning electron microscopy and synchrotron x-ray computed micro-tomography, provide mechanistic information on how cracks interact with the bone-matrix structure. At sub-micron scales, strength properties are evaluated with insitu tensile tests in the synchrotron using small-/wide-angle x-ray scattering/diffraction, where strains are simultaneously measured in the macroscopic tissue, collagen fibrils and mineral. Compared to healthy bone, results show that the fibrillar strain is decreased by ∼40% following 70 kGy exposures, consistent with significant stiffening and degradation of the collagen. We attribute the irradiation-induced deterioration in mechanical properties to mechanisms at multiple length-scales, including changes in crack paths at micron-scales, loss of plasticity from suppressed fibrillar sliding at sub-micron scales, and the loss and damage of collagen at the nano-scales, the latter being assessed using Raman and Fourier Transform Infrared spectroscopy and a fluorometric assay.

• Age-related changes in the plasticity and toughness of human cortical bone at multiple length scales.

  Authors: Elizabeth A Zimmermann, Eric Schaible, Hrishikesh Bale, Holly D Barth, Simon Y Tang, Peter Reichert, Bjoern Busse, Tamara Alliston, Joel W Ager, Robert O Ritchie

  Proceedings of the National Academy of Sciences of the United States of America. 08/2011; 108(35):14416-21.

  The structure of human cortical bone evolves over multiple length scales from its basic constituents of collagen and hydroxyapatite at the nanoscale to osteonal structures at near-millimeterThe structure of human cortical bone evolves over multiple length scales from its basic constituents of collagen and hydroxyapatite at the nanoscale to osteonal structures at near-millimeter dimensions, which all provide the basis for its mechanical properties. To resist fracture, bone's toughness is derived intrinsically through plasticity (e.g., fibrillar sliding) at structural scales typically below a micrometer and extrinsically (i.e., during crack growth) through mechanisms (e.g., crack deflection/bridging) generated at larger structural scales. Biological factors such as aging lead to a markedly increased fracture risk, which is often associated with an age-related loss in bone mass (bone quantity). However, we find that age-related structural changes can significantly degrade the fracture resistance (bone quality) over multiple length scales. Using in situ small-angle X-ray scattering and wide-angle X-ray diffraction to characterize submicrometer structural changes and synchrotron X-ray computed tomography and in situ fracture-toughness measurements in the scanning electron microscope to characterize effects at micrometer scales, we show how these age-related structural changes at differing size scales degrade both the intrinsic and extrinsic toughness of bone. Specifically, we attribute the loss in toughness to increased nonenzymatic collagen cross-linking, which suppresses plasticity at nanoscale dimensions, and to an increased osteonal density, which limits the potency of crack-bridging mechanisms at micrometer scales. The link between these processes is that the increased stiffness of the cross-linked collagen requires energy to be absorbed by "plastic" deformation at higher structural levels, which occurs by the process of microcracking.

• An equivalent strain/Coffin-Manson approach to multiaxial fatigue and life prediction in superelastic Nitinol medical devices.

  Authors: Amanda Runciman, David Xu, Alan R Pelton, Robert O Ritchie

  Biomaterials. 08/2011; 32(22):4987-93.

  Medical devices, particularly endovascular stents, manufactured from superelastic Nitinol, a near-equiatomic alloy of Ni and Ti, are subjected to complex mixed-mode loading conditions in vivo,Medical devices, particularly endovascular stents, manufactured from superelastic Nitinol, a near-equiatomic alloy of Ni and Ti, are subjected to complex mixed-mode loading conditions in vivo, including axial tension and compression, radial compression, pulsatile, bending and torsion. Fatigue lifetime prediction methodologies for Nitinol, however, are invariably based on uniaxial loading and thus fall short of accurately predicting the safe lifetime of stents under the complex multiaxial loading conditions experienced physiologically. While there is a considerable body of research documented on the cyclic fatigue of Nitinol in uniaxial tension or bending, there remains an almost total lack of comprehensive fatigue lifetime data for other loading conditions, such as torsion and tension/torsion. In this work, thin-walled Nitinol tubes were cycled in torsion at various mean and alternating strains to investigate the fatigue life behavior of Nitinol and results compared to equivalent fatigue data collected under uniaxial tensile/bending loads. Using these strain-life results for various loading modes and an equivalent referential (Lagrangian) strain approach, a strategy for normalizing these data is presented. Based on this strategy, a fatigue lifetime prediction model for the multiaxial loading of Nitinol is presented utilizing a modified Coffin-Manson approach where the number of cycles to failure is related to the equivalent alternating transformation strain.

• A damage-tolerant glass.

  Authors: Marios D Demetriou, Maximilien E Launey, Glenn Garrett, Joseph P Schramm, Douglas C Hofmann, William L Johnson, Robert O Ritchie

  Nature materials. 02/2011; 10(2):123-8.

  Owing to a lack of microstructure, glassy materials are inherently strong but brittle, and often demonstrate extreme sensitivity to flaws. Accordingly, their macroscopic failure is often notOwing to a lack of microstructure, glassy materials are inherently strong but brittle, and often demonstrate extreme sensitivity to flaws. Accordingly, their macroscopic failure is often not initiated by plastic yielding, and almost always terminated by brittle fracture. Unlike conventional brittle glasses, metallic glasses are generally capable of limited plastic yielding by shear-band sliding in the presence of a flaw, and thus exhibit toughness-strength relationships that lie between those of brittle ceramics and marginally tough metals. Here, a bulk glassy palladium alloy is introduced, demonstrating an unusual capacity for shielding an opening crack accommodated by an extensive shear-band sliding process, which promotes a fracture toughness comparable to those of the toughest materials known. This result demonstrates that the combination of toughness and strength (that is, damage tolerance) accessible to amorphous materials extends beyond the benchmark ranges established by the toughest and strongest materials known, thereby pushing the envelope of damage tolerance accessible to a structural metal.

• Tissue-specific calibration of extracellular matrix material properties by transforming growth factor-β and Runx2 in bone is required for hearing.

  Authors: Jolie L Chang, Delia S Brauer, Jacob Johnson, Carol G Chen, Omar Akil, Guive Balooch, Mary Beth Humphrey, Emily N Chin, Alexandra E Porter, Kristin Butcher, Robert O Ritchie, Richard A Schneider, Anil Lalwani, Rik Derynck, Grayson W Marshall, Sally J Marshall, Lawrence Lustig, Tamara Alliston

  EMBO reports. 10/2010; 11(10):765-71.

  Physical cues, such as extracellular matrix stiffness, direct cell differentiation and support tissue-specific function. Perturbation of these cues underlies diverse pathologies, includingPhysical cues, such as extracellular matrix stiffness, direct cell differentiation and support tissue-specific function. Perturbation of these cues underlies diverse pathologies, including osteoarthritis, cardiovascular disease and cancer. However, the molecular mechanisms that establish tissue-specific material properties and link them to healthy tissue function are unknown. We show that Runx2, a key lineage-specific transcription factor, regulates the material properties of bone matrix through the same transforming growth factor-β (TGFβ)-responsive pathway that controls osteoblast differentiation. Deregulated TGFβ or Runx2 function compromises the distinctly hard cochlear bone matrix and causes hearing loss, as seen in human cleidocranial dysplasia. In Runx2+/⁻ mice, inhibition of TGFβ signalling rescues both the material properties of the defective matrix, and hearing. This study elucidates the unknown cause of hearing loss in cleidocranial dysplasia, and demonstrates that a molecular pathway controlling cell differentiation also defines material properties of extracellular matrix. Furthermore, our results suggest that the careful regulation of these properties is essential for healthy tissue function.

• The significance of crack-resistance curves to the mixed-mode fracture toughness of human cortical bone.

  Authors: Elizabeth A Zimmermann, Maximilien E Launey, Robert O Ritchie

  Biomaterials. 07/2010; 31(20):5297-305.

  The majority of fracture mechanics studies on the toughness of bone have been performed under tensile loading. However, it has recently been shown that the toughness of human cortical bone in theThe majority of fracture mechanics studies on the toughness of bone have been performed under tensile loading. However, it has recently been shown that the toughness of human cortical bone in the transverse (breaking) orientation is actually much lower in shear (mode II) than in tension (mode I); a fact that is physiologically relevant as in vivo bone is invariably loaded multiaxially. Since bone is a material that derives its fracture resistance primarily during crack growth through extrinsic toughening mechanisms, such as crack deflection and bridging, evaluation of its toughness is best achieved through measurements of the crack-resistance or R-curve, which describes the fracture toughness as a function of crack extension. Accordingly, in this study, we attempt to measure for the first time the R-curve fracture toughness of human cortical bone under physiologically relevant mixed-mode loading conditions. We show that the resulting mixed-mode (mode I+II) toughness depends strongly on the crack trajectory and is the result of the competition between the paths of maximum mechanical driving force and "weakest" microstructural resistance.

• On the effect of X-ray irradiation on the deformation and fracture behavior of human cortical bone.

  Authors: Holly D Barth, Maximilien E Launey, Alastair A Macdowell, Joel W Ager, Robert O Ritchie

  Bone. 03/2010; 46(6):1475-85.

  In situ mechanical testing coupled with imaging using high-energy synchrotron X-ray diffraction or tomography is gaining in popularity as a technique to investigate micrometer and even sub-micrometerIn situ mechanical testing coupled with imaging using high-energy synchrotron X-ray diffraction or tomography is gaining in popularity as a technique to investigate micrometer and even sub-micrometer deformation and fracture mechanisms in mineralized tissues, such as bone and teeth. However, the role of the irradiation in affecting the nature and properties of the tissue is not always taken into account. Accordingly, we examine here the effect of X-ray synchrotron-source irradiation on the mechanistic aspects of deformation and fracture in human cortical bone. Specifically, the strength, ductility and fracture resistance (both work-of-fracture and resistance-curve fracture toughness) of human femoral bone in the transverse (breaking) orientation were evaluated following exposures to 0.05, 70, 210 and 630 kGrays (kGy) irradiation. Our results show that the radiation typically used in tomography imaging can have a major and deleterious impact on the strength, post-yield behavior and fracture toughness of cortical bone, with the severity of the effect progressively increasing with higher doses of radiation. Plasticity was essentially suppressed after as little as 70 kGy of radiation; the fracture toughness was decreased by a factor of five after 210 kGy of radiation. Mechanistically, the irradiation was found to alter the salient toughening mechanisms, manifest by the progressive elimination of the bone's capacity for plastic deformation which restricts the intrinsic toughening from the formation "plastic zones" around crack-like defects. Deep-ultraviolet Raman spectroscopy indicated that this behavior could be related to degradation in the collagen integrity.

• How does human bone resist fracture?

  Authors: Robert O Ritchie

  Annals of the New York Academy of Sciences. 03/2010; 1192:72-80.

  The fracture of bone is clearly a major health concern, especially for the elderly. Medical therapies to reduce the possibility of bone fracture to date have principally centered on treating the lossThe fracture of bone is clearly a major health concern, especially for the elderly. Medical therapies to reduce the possibility of bone fracture to date have principally centered on treating the loss in bone mass (bone mineral density) that accompanies aging (i.e., addressing the loss in bone quantity). However, it is now known that there is an additional, perhaps more significant, effect of the degradation in the inherent properties of bone (i.e., a loss in bone quality) with age. To address this issue, we review here the structure and properties of bone, focusing on its strength and fracture resistance from the perspective of the multidimensional hierarchical nature of its structure. We show that bone derives its resistance to fracture from a multitude of deformation and toughening mechanisms at many of these size-scales, ranging from the nanoscale structure of its protein molecules to its macroscopic physiological state.

• Osteopontin deficiency increases bone fragility but preserves bone mass.

  Authors: Philipp J Thurner, Carol G Chen, Sophi Ionova-Martin, Luling Sun, Adam Harman, Alexandra Porter, Joel W Ager, Robert O Ritchie, Tamara Alliston

  Bone. 02/2010; 46(6):1564-73.

  The ability of bone to resist catastrophic failure is critically dependent upon the material properties of bone matrix, a composite of hydroxyapatite, collagen type I, and noncollagenous proteins.The ability of bone to resist catastrophic failure is critically dependent upon the material properties of bone matrix, a composite of hydroxyapatite, collagen type I, and noncollagenous proteins. These properties include elastic modulus, hardness, and fracture toughness. Like other aspects of bone quality, matrix material properties are biologically-defined and can be disrupted in skeletal disease. While mineral and collagen have been investigated in greater detail, the contribution of noncollagenous proteins such as osteopontin to bone matrix material properties remains unclear. Several roles have been ascribed to osteopontin in bone, many of which have the potential to impact material properties. To elucidate the role of osteopontin in bone quality, we evaluated the structure, composition, and material properties of bone from osteopontin-deficient mice and wild-type littermates at several length scales. Most importantly, the results show that osteopontin deficiency causes a 30% decrease in fracture toughness, suggesting an important role for OPN in preventing crack propagation. This significant decline in fracture toughness is independent of changes in whole bone mass, structure, or matrix porosity. Using nanoindentation and quantitative backscattered electron imaging to evaluate osteopontin-deficient bone matrix at the micrometer level, we observed a significant reduction in elastic modulus and increased variability in calcium concentration. Matrix heterogeneity was also apparent at the ultrastructural level. In conclusion, we find that osteopontin is essential for the fracture toughness of bone, and reduced toughness in osteopontin-deficient bone may be related to the increased matrix heterogeneity observed at the micro-scale. By exploring the effects of osteopontin deficiency on bone matrix material properties, composition and organization, this study suggests that reduced fracture toughness is one mechanism by which loss of noncollagenous proteins contribute to bone fragility.

• Microindentation for in vivo measurement of bone tissue mechanical properties in humans.

  Authors: Adolfo Diez-Perez, Roberto Güerri, Xavier Nogues, Enric Cáceres, Maria Jesus Peña, Leonardo Mellibovsky, Connor Randall, Daniel Bridges, James C Weaver, Alexander Proctor, Davis Brimer, Kurt J Koester, Robert O Ritchie, Paul K Hansma

  Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research. 02/2010; 25(8):1877-85.

  Bone tissue mechanical properties are deemed a key component of bone strength, but their assessment requires invasive procedures. Here we validate a new instrument, a reference point indentationBone tissue mechanical properties are deemed a key component of bone strength, but their assessment requires invasive procedures. Here we validate a new instrument, a reference point indentation (RPI) instrument, for measuring these tissue properties in vivo. The RPI instrument performs bone microindentation testing (BMT) by inserting a probe assembly through the skin covering the tibia and, after displacing periosteum, applying 20 indentation cycles at 2 Hz each with a maximum force of 11 N. We assessed 27 women with osteoporosis-related fractures and 8 controls of comparable ages. Measured total indentation distance (46.0 +/- 14 versus 31.7 +/- 3.3 microm, p = .008) and indentation distance increase (18.1 +/- 5.6 versus 12.3 +/- 2.9 microm, p = .008) were significantly greater in fracture patients than in controls. Areas under the receiver operating characteristic (ROC) curve for the two measurements were 93.1% (95% confidence interval [CI] 83.1-100) and 90.3% (95% CI 73.2-100), respectively. Interobserver coefficient of variation ranged from 8.7% to 15.5%, and the procedure was well tolerated. In a separate study of cadaveric human bone samples (n = 5), crack growth toughness and indentation distance increase correlated (r = -0.9036, p = .018), and scanning electron microscope images of cracks induced by indentation and by experimental fractures were similar. We conclude that BMT, by inducing microscopic fractures, directly measures bone mechanical properties at the tissue level. The technique is feasible for use in clinics with good reproducibility. It discriminates precisely between patients with and without fragility fracture and may provide clinicians and researchers with a direct in vivo measurement of bone tissue resistance to fracture.

• Prolonged Treatments with Anti-Resorptive Agents and PTH Have Different Effects on Bone Strength and the Degree of Mineralization in Old Estrogen Deficient Osteoporotic Rats.

  Authors: Zhiqiang Cheng, Wei Yao, Elizabeth A Zimmermann, Cheryl Busse, Robert O Ritchie, Nancy E Lane

  Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research. 12/2009;

  Introduction: Current approved medical treatments for osteoporosis reduce fracture risk to a greater degree than predicted from change in bone mineral density (BMD) in women with postmenopausalIntroduction: Current approved medical treatments for osteoporosis reduce fracture risk to a greater degree than predicted from change in bone mineral density (BMD) in women with postmenopausal osteoporosis. We hypothesize that bone active agents improve bone strength in osteoporotic bone by altering different material properties of the bone.Methods: 18-month-old female Fischer rats were ovariectomized (OVX) or sham-operated and left untreated for 60 days to induce osteopenia before they were treated with single doses of either risedronate (iv., 500mug/kg), zoledronic acid (iv., 100mug/kg), raloxifene (2mg/kg, po., 3x/wk), hPTH (1-34) (25mug/kg, sc., 3x/wk) or vehicle (NS 1ml/kg 3x/wk). Groups of animals were sacrificed after day 60 and day 180 of treatment and either the proximal tibial metaphysis or lumbar vertebral body were studied. Bone volume and architecture were assessed by microCT and histomorphometry. Measurements of bone quality included the degree of bone mineralization (DBM), localized elastic modulus, bone turnover by histomorphometry, bone compression testing of the LVB and three-point bending testing of the femur.Results: The trabecular bone volume, DBM, elastic modulus and compressive bone strength were all significantly lower at day 60 post-OVX (pretreatment, day 0 study) than at baseline. After 60 days of all of the bone active treatments, bone material measurements (BV/TV, DBM, EM, maximum compression and bending bone strengths) were restored. However, after 180 days of treatment, the OVX+PTH group further increased BV/TV (+30% from day 60, p <0.05 within group and between groups). In addition, after 180 days of treatment, there was more highly mineralized cortical and trabecular bone, and increased cortical bone size and whole bone strength in OVX+PTH compared to other OVX+ anti-resorptives.Conclusions: Treatment of estrogen deficient aged rats with either anti-resorptive agents or PTH rapidly improved many aspects of bone quality including microarchitecture, bone mineralization, turnover and bone strength. However, prolonged treatment for 180 days with PTH resulted in additional gains in bone quality and bone strength suggesting that the maximal gains in bone strength in cortical and trabecular bone sites may require a longer treatment period with PTH.

• Higher doses of bisphosphonates further improve bone mass, architecture, and strength but not the tissue material properties in aged rats.

  Authors: Mohammad Shahnazari, Wei Yao, Weiwei Dai, Bob Wang, Sophi S Ionova-Martin, Robert O Ritchie, Daniel Heeren, Andrew J Burghardt, Daniel P Nicolella, Michael G Kimiecik, Nancy E Lane

  Bone. 11/2009;

  We report the results of a series of experiments designed to determine the effects of ibandronate (Ibn) and risedronate (Ris) on a number of bone quality parameters in aged osteopenic rats to explainWe report the results of a series of experiments designed to determine the effects of ibandronate (Ibn) and risedronate (Ris) on a number of bone quality parameters in aged osteopenic rats to explain how bone material and bone mass may be affected by the dose of bisphosphonates (BP) and contribute to their anti-fracture efficacy. Eighteen-month old female rats underwent either ovariectomy or sham surgery. The ovariectomized (OVX) groups were left untreated for 2 months to develop osteopenia. Treatments started at 20 months of age as follows: sham and OVX control (treated with saline), OVX + risedronate 30 and 90 (30 or 90 mug/kg/dose), and OVX + ibandronate 30 and 90 (30 or 90 mug/kg/dose). The treatments were given monthly for 4 months by subcutaneous injection. At sacrifice at 24 months of age the 4th lumbar vertebra was used for muCT scans (bone mass, architecture, and degree of mineralization of bone, DMB) and histomorphometry, and the 6th lumbar vertebra, tibia, and femur were collected for biomechanical testing to determine bone structural and material strength, cortical fracture toughness, and tissue elastic modulus. The compression testing of the vertebral bodies (LVB6) was simulated using finite-element analysis (FEA) to also estimate the bone structural stiffness. Both Ibn and Ris dose-dependently increased bone mass and improved vertebral bone microarchitecture and mechanical properties compared to OVX control. Estimates of vertebral maximum stress from FEA were correlated with vertebral maximum load (r=0.5, p<0.001) and maximum stress (r=0.4, p<0.005) measured experimentally. Tibial bone bending modulus and cortical strength increased compared to OVX with both BP but no dose-dependent effect was observed. DMB and elastic modulus of trabecular bone were improved with Ibn 30 compared to OVX but were not affected in other BP-treated groups. DMB of tibial cortical bone showed no change with BP treatments. The fracture toughness examined in midshaft femurs did not change with BP even with the higher doses. In summary, the anti-fracture efficacy of BP is largely due to their preservation of bone mass and while the higher doses further improve the bone structural properties do not improve the localized bone material characteristics such as tissue strength, elastic modulus, and cortical toughness.

• A novel biomimetic approach to the design of high-performance ceramic-metal composites.

  Authors: Maximilien E Launey, Etienne Munch, Daan Hein Alsem, Eduardo Saiz, Antoni P Tomsia, Robert O Ritchie

  Journal of the Royal Society, Interface / the Royal Society. 10/2009;

  The prospect of extending natural biological design to develop new synthetic ceramic-metal composite materials is examined. Using ice-templating of ceramic suspensions and subsequent metalThe prospect of extending natural biological design to develop new synthetic ceramic-metal composite materials is examined. Using ice-templating of ceramic suspensions and subsequent metal infiltration, we demonstrate that the concept of ordered hierarchical design can be applied to create fine-scale laminated ceramic-metal (bulk) composites that are inexpensive, lightweight and display exceptional damage-tolerance properties. Specifically, Al(2)O(3)/Al-Si laminates with ceramic contents up to approximately 40 vol% and with lamellae thicknesses down to 10 microm were processed and characterized. These structures achieve an excellent fracture toughness of 40 MPa radicalm at a tensile strength of approximately 300 MPa. Salient toughening mechanisms are described together with further toughening strategies.

• Mixed-mode fracture of human cortical bone.

  Authors: Elizabeth A Zimmermann, Maximilien E Launey, Holly D Barth, Robert O Ritchie

  Biomaterials. 07/2009;

  Although the mode I (tensile opening) fracture toughness has been the focus of most fracture mechanics studies of human cortical bone, bones in vivo are invariably loaded multiaxially. Consequently,Although the mode I (tensile opening) fracture toughness has been the focus of most fracture mechanics studies of human cortical bone, bones in vivo are invariably loaded multiaxially. Consequently, an understanding of mixed-mode fracture is necessary to determine whether a mode I fracture toughness test provides the appropriate information to accurately quantify fracture risk. In this study, we examine the mixed-mode fracture of human cortical bone by characterizing the crack-initiation fracture toughness in the transverse (breaking) orientation under combined mode I (tensile opening) plus mode II (shear) loading using samples loaded in symmetric and asymmetric four-point bending. Whereas in most structural materials, the fracture toughness is increased with increasing mode-mixity (i.e., where the shear loading component gets larger), in the transverse orientation of bone the situation is quite different. Indeed, the competition between the maximum applied mechanical mixed-mode driving force and the weakest microstructural paths in bone results in a behavior that is distinctly different to most homogeneous brittle materials. Specifically, in this orientation, the fracture toughness of bone is markedly decreased with increasing mode-mixity.

• Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses.

  Authors: Maximilien E Launey, Douglas C. Hofmann, William L. Johnson, Robert O Ritchie

  Proceedings of the National Academy of Sciences of the United States of America. 04/2009; 106(13):4986-91.

  The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength andThe recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of approximately 2 mum, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these "designed" composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems.

• Pharmacologic inhibition of the tgf-Beta type I receptor kinase has anabolic and anti-catabolic effects on bone.

  Authors: Khalid S Mohammad, Carol G Chen, Guive Balooch, Elizabeth Stebbins, C Ryan McKenna, Holly Davis, Maria Niewolna, Xiang Hong Peng, Daniel H. N. Nguyen, Sophi S Ionova-Martin, John W. Bracey, William R Hogue, Darren H Wong, Robert O Ritchie, Larry J Suva, Rik Derynck, Theresa A Guise, Tamara Alliston

  PLoS ONE. 02/2009; 4(4):e5275.

  During development, growth factors and hormones cooperate to establish the unique sizes, shapes and material properties of individual bones. Among these, TGF-beta has been shown to developmentallyDuring development, growth factors and hormones cooperate to establish the unique sizes, shapes and material properties of individual bones. Among these, TGF-beta has been shown to developmentally regulate bone mass and bone matrix properties. However, the mechanisms that control postnatal skeletal integrity in a dynamic biological and mechanical environment are distinct from those that regulate bone development. In addition, despite advances in understanding the roles of TGF-beta signaling in osteoblasts and osteoclasts, the net effects of altered postnatal TGF-beta signaling on bone remain unclear. To examine the role of TGF-beta in the maintenance of the postnatal skeleton, we evaluated the effects of pharmacological inhibition of the TGF-beta type I receptor (TbetaRI) kinase on bone mass, architecture and material properties. Inhibition of TbetaRI function increased bone mass and multiple aspects of bone quality, including trabecular bone architecture and macro-mechanical behavior of vertebral bone. TbetaRI inhibitors achieved these effects by increasing osteoblast differentiation and bone formation, while reducing osteoclast differentiation and bone resorption. Furthermore, they induced the expression of Runx2 and EphB4, which promote osteoblast differentiation, and ephrinB2, which antagonizes osteoclast differentiation. Through these anabolic and anti-catabolic effects, TbetaRI inhibitors coordinate changes in multiple bone parameters, including bone mass, architecture, matrix mineral concentration and material properties, that collectively increase bone fracture resistance. Therefore, TbetaRI inhibitors may be effective in treating conditions of skeletal fragility.

• Glucocorticoid-induced bone loss in mice can be reversed by the actions of parathyroid hormone and risedronate on different pathways for bone formation and mineralization.

  Authors: Wei Yao, Zhiqiang Cheng, Aaron Pham, Cheryl Busse, Elizabeth A Zimmermann, Robert O Ritchie, Nancy E Lane

  Arthritis and rheumatism. 12/2008; 58(11):3485-97.

  OBJECTIVE: Glucocorticoid excess decreases bone mineralization and microarchitecture and leads to reduced bone strength. Both anabolic (parathyroid hormone [PTH]) and antiresorptive agents are usedOBJECTIVE: Glucocorticoid excess decreases bone mineralization and microarchitecture and leads to reduced bone strength. Both anabolic (parathyroid hormone [PTH]) and antiresorptive agents are used to prevent and treat glucocorticoid-induced bone loss, yet these bone-active agents alter bone turnover by very different mechanisms. This study was undertaken to determine how PTH and risedronate alter bone quality following glucocorticoid excess. METHODS: Five-month-old male Swiss-Webster mice were treated with the glucocorticoid prednisolone (5 mg/kg in a 60-day slow-release pellet) or placebo. From day 28 to day 56, 2 groups of glucocorticoid-treated animals received either PTH (5 mug/kg) or risedronate (5 mug/kg) 5 times per week. Bone quality and quantity were measured using x-ray tomography for the degree of bone mineralization, microfocal computed tomography for bone microarchitecture, compression testing for trabecular bone strength, and biochemistry and histomorphometry for bone turnover. In addition, real-time polymerase chain reaction (PCR) and immunohistochemistry were performed to monitor the expression of several key genes regulating Wnt signaling (bone formation) and mineralization. RESULTS: Compared with placebo, glucocorticoid treatment decreased trabecular bone volume (bone volume/total volume [BV/TV]) and serum osteocalcin, but increased serum CTX and osteoclast surface, with a peak at day 28. Glucocorticoids plus PTH increased BV/TV, and glucocorticoids plus risedronate restored BV/TV to placebo levels after 28 days. The average degree of bone mineralization was decreased after glucocorticoid treatment (-27%), but was restored to placebo levels after treatment with glucocorticoids plus risedronate or glucocorticoids plus PTH. On day 56, RT-PCR revealed that expression of genes that inhibit bone mineralization (Dmp1 and Phex) was increased by continuous exposure to glucocorticoids and glucocorticoids plus PTH and decreased by glucocorticoids plus risedronate, compared with placebo. Wnt signaling antagonists Dkk-1, Sost, and Wif1 were up-regulated by glucocorticoid treatment but down-regulated after glucocorticoid plus PTH treatment. Immunohistochemistry of bone sections showed that glucocorticoids increased N-terminal Dmp-1 staining while PTH treatment increased both N- and C-terminal Dmp-1 staining around osteocytes. CONCLUSION: Our findings indicate that both PTH and risedronate improve bone mass, degree of bone mineralization, and bone strength in glucocorticoid-treated mice, and that PTH increases bone formation while risedronate reverses the deterioration of bone mineralization.