Original Full Length Article Symmetrically reduced stiffness and increased extensibility in compression and tension at the mineralized fibrillar level in rachitic bone ☆ , ☆☆ A. Karunaratne a , A. Boyde b , C.T. Esapa c, d , J. Hiller e , N.J. Terrill e, f , S.D.M. Brown d , R.D. Cox d , R.V. Thakker c , H.S. Gupta a, ⁎ a School of Engineering and Material Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK b Dental Physical Sciences, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Mile End Road, London, E1 4NS, UK c Academic Endocrine Unit, Nuffield Department of Clinical Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Churchill Hospital, Headington, Oxford, OX3 7JL, UK d MRC Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell, Harwell Science and Innovation Campus, OX11 0RD, UK e Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire, OX11 0DE, UK f Department of Chemistry, University of Sheffield, Dainton Building, Brookhill, Sheffield, S3 7HF, UK abstract article info Article history: Received 7 August 2012 Revised 12 October 2012 Accepted 24 October 2012 Available online 3 November 2012 Edited by: David Burr Keywords: Bone Nanocomposite Elasticity Mechanical properties In metabolic bone diseases, the alterations in fibrillar level bone-material quality affecting macroscopic mechanical competence are not well-understood quantitatively. Here, we quantify the fibrillar level deforma- tion in cantilever bending in a mouse model for hereditary rickets (Hpr). Microfocus in-situ synchrotron small-angle X-ray scattering (SAXS) combined with cantilever bending was used to resolve nanoscale fibril strain in tensile- and compressive tissue regions separately, with quantitative backscattered scanning electron microscopy used to measure microscale mineralization. Tissue-level flexural moduli for Hpr mice were signif- icantly (p b 0.01) smaller compared to wild-type (~ 5 to 10-fold reduction). At the fibrillar level, the fibril moduli within the tensile and compressive zones were significantly (p b 0.05) lower by ~3- to 5-fold in Hpr mice compared to wild-type mice. Hpr mice have a lower mineral content (24.2 ± 2.1 Ca wt.% versus 27.4 ± 3.3 Ca wt.%) and its distribution was more heterogeneous compared to wild-type animals. However, the average effective fibril modulus did not differ significantly (p > 0.05) over ages (4, 7 and 10 weeks) between tensile and compressive zones. Our results indicate that incompletely mineralized fibrils in Hpr mice have greater deformability and lower moduli in both compression and tension, and those compressive and tensile zones have similar moduli at the fibrillar level. © 2012 Elsevier Inc. All rights reserved. Introduction The deformation and fracture of bone in health and disease, depends on the volume of bone (bone quantity) and the quality of the bone matrix (bone quality). Bone quantity is used to predict osteoporotic fracture risk in patients [1], whereas bone quality is not routinely used to predict outcomes, largely because the parameters that may affect such macroscopic mechanical outcomes are not fully understood. Bone quality is determined by microstructural properties, that include the mineralization distribution and trabecu- lar microarchitecture, and molecular/supramolecular properties, that include the deformability of the ~100 nm diameter mineralized collagen fibrils, the types of non-collagenous proteins present, and collagen cross linking. Mechanisms at the nanometre length scale, such as increased extensibility via extrafibrillar mineralization [2] and stiffening via collagen cross linking [3], will alter the macroscopic deformation and fracture mechanisms of bone in ageing and disease. Nanoscale deformation mechanisms in bone have been investigated in uniaxial tensile [2–4] and compressive loading [5], but not as exten- sively under physiological forces and stress [6], such as bending. Bending deformation of bone involves concurrent compression and tension, in spatially separated zones. In this regard, it is notewor- thy that at the macroscopic scale, direct compressive and tensile deformation behaviours are different [7,8]. It is well known that the post yield zone in compression is shorter, and does not show the linear Bone 52 (2013) 689–698 Abbreviations: Hpr, hypophosphatemic rickets; SAXS, small-angle X-ray scatter- ing; ENU, N-ethyl-N-nitrosourea; PBS, phosphate buffered saline; ρ, mineral particle degree of orientation. ☆ Funding sources: Medical Research Council UK; Diamond Light Source Ltd., Diamond House, Oxfordshire, UK; School of Engineering and Material Sciences, Queen Mary University of London, London, E1 4NS, UK; Engineering and Physical Research Council (EPSRC) UK, Swindon, UK. ☆☆ Conflict of interest statement: All authors have no conflict of interest. ⁎ Corresponding author. Fax: +44 20 7882 3390. E-mail addresses: a.karunaratne@qmul.ac.uk (A. Karunaratne), a.boyde@qmul.ac.uk (A. Boyde), c.esapa@har.mrc.ac.uk (C.T. Esapa), jennifer.bardsley@ndm.ox.ac.uk (J. Hiller), nick.terrill@diamond.ac.uk (N.J. Terrill), s.brown@har.mrc.ac.uk (S.D.M. Brown), r.cox@har.mrc.ac.uk (R.D. Cox), rajesh.thakker@ndm.ox.ac.uk (R.V. Thakker), h.gupta@qmul.ac.uk (H.S. Gupta). 8756-3282/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.bone.2012.10.029 Contents lists available at SciVerse ScienceDirect Bone journal homepage: www.elsevier.com/locate/bone