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Sarna-Boś K, Skic K, Boguta P, Adamczuk A, Vodanovic M, Chałas R. Elemental mapping of human teeth enamel, dentine and cementum in view of their microstructure. Micron 2023; 172:103485. [PMID: 37271062 DOI: 10.1016/j.micron.2023.103485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 04/28/2023] [Accepted: 05/21/2023] [Indexed: 06/06/2023]
Abstract
This paper presents a detailed analysis to directly compare the morphology and chemistry of human tooth layers using advanced scanning electron microscopy (SEM) techniques together with supporting data from energy dispersive spectroscopy (EDS) measurements. The aim of this study was to visualise and evaluate the structural and microanalytical differences of the mineralised hard tissues of human teeth. The extracted sound teeth without any pathologies were divided into the following groups: incisors, canines, premolars, and molars. Tooth samples were broken vertically to preserve the primary structures and to visualise individual tooth tissues. Specimens were also used to find variations in the elemental composition of tissues for different tooth groups. The average thickness of the enamel in the tooth groups studied was 1.1 mm and the average width of the enamel prisms was 4.2 µm, with the highest values observed for molars. The analysis of the chemical composition of the enamel showed that Ca and P were among the predominant elements. The average dentine thickness was 1.87 mm, with the highest values determined for molars, and the lowest for canines. The width of the dentinal tubules was less than 2 µm, for molars being significantly smaller. The analysis of the chemical composition of the dentine showed the highest O content of the all tooth tissues analyzed, while a lower P and Ca content was observed compared to the enamel. The cementum thickness averaged 0.14 mm, with the highest values observed for molars and the lowest for incisors. The analysis of the chemical composition of the cementum showed the lowest average O and P content, and the highest average C and N content, compared to the enamel and the dentine. Increasingly accurate imaging and analysis of dental hard tissue structures provides the opportunity for multifactorial evaluation in terms of their clinical application.
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Affiliation(s)
- Katarzyna Sarna-Boś
- Department of Dental Prosthetics, Medical University of Lublin, Chodźki 6, 20-093 Lublin, Poland.
| | - Kamil Skic
- Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland
| | - Patrycja Boguta
- Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland
| | - Agnieszka Adamczuk
- Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland
| | - Marin Vodanovic
- Department of Dental Anthropology, University of Zagreb, School of Dental Medicine, University Hospital Centre Zagreb, Gundulićeva 5, HR-10000 Zagreb, Croatia; Department of Oral Medicine, Medical University of Lublin, Chodźki 6, 20-093 Lublin, Poland
| | - Renata Chałas
- Department of Oral Medicine, Medical University of Lublin, Chodźki 6, 20-093 Lublin, Poland
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Groetsch A, Gourrier A, Casari D, Schwiedrzik J, Shephard JD, Michler J, Zysset PK, Wolfram U. The elasto-plastic nano- and microscale compressive behaviour of rehydrated mineralised collagen fibres. Acta Biomater 2023; 164:332-345. [PMID: 37059408 DOI: 10.1016/j.actbio.2023.03.041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Revised: 03/13/2023] [Accepted: 03/27/2023] [Indexed: 04/16/2023]
Abstract
The hierarchical design of bio-based nanostructured materials such as bone enables them to combine unique structure-mechanical properties. As one of its main components, water plays an important role in bone's material multiscale mechanical interplay. However, its influence has not been quantified at the length-scale of a mineralised collagen fibre. Here, we couple in situ micropillar compression, and simultaneous synchrotron small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) with a statistical constitutive model. Since the synchrotron data contain statistical information on the nanostructure, we establish a direct connection between experiment and model to identify the rehydrated elasto-plastic micro- and nanomechanical fibre behaviour. Rehydration led to a decrease of 65%-75% in fibre yield stress and compressive strength, and 70% in stiffness with a 3x higher effect on stresses than strains. While in agreement with bone extracellular matrix, the decrease is 1.5-3x higher compared to micro-indentation and macro-compression. Hydration influences mineral more than fibril strain with the highest difference to the macroscale when comparing mineral and tissue levels. The effect of hydration seems to be strongly mediated by ultrastructural interfaces while results provide insights towards mechanical consequences of reported water-mediated structuring of bone apatite. The missing reinforcing capacity of surrounding tissue for an excised fibril array is more pronounced in wet than dry conditions, mainly related to fibril swelling. Differences leading to higher compressive strength between mineralised tissues seem not to depend on rehydration while the lack of kink bands supports the role of water as an elastic embedding influencing energy-absorption mechanisms. STATEMENT OF SIGNIFICANCE: Characterising structure-property-function relationships in hierarchical biological materials helps us to elucidate mechanisms that enable their unique properties. Experimental and computational methods can advance our understanding of their complex behaviour with the potential to inform bio-inspired material development. In this study, we close a gap for bone's fundamental mechanical building block at micro- and nanometre length scales. We establish a direct connection between experiments and simulations by coupling in situ synchrotron tests with a statistical model and quantify the behaviour of rehydrated single mineralised collagen fibres. Results suggest a high influence of hydration on structural interfaces, and the role of water as an elastic embedding by outlining important differences between wet and dry elasto-plastic properties of mineral nanocrystals, fibrils and fibres.
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Affiliation(s)
- Alexander Groetsch
- Institute of Mechanical, Process & Energy Engineering, School of Engineering & Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | | | - Daniele Casari
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Thun, Switzerland
| | - Jakob Schwiedrzik
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Thun, Switzerland
| | - Jonathan D Shephard
- Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | - Johann Michler
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Thun, Switzerland
| | - Philippe K Zysset
- ARTORG Centre for Biomedical Engineering Research, University of Bern, Switzerland
| | - Uwe Wolfram
- Institute of Mechanical, Process & Energy Engineering, School of Engineering & Physical Sciences, Heriot-Watt University, Edinburgh, UK.
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3
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Xu M, An B, Zhang D. Competing mechanisms in fracture of staggered mineralized collagen fibril arrays. J Mech Behav Biomed Mater 2023; 141:105761. [PMID: 36905708 DOI: 10.1016/j.jmbbm.2023.105761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 01/17/2023] [Accepted: 03/05/2023] [Indexed: 03/08/2023]
Abstract
Mineralized collagen fibril (MCF) arrays are important structural elements involved in inelastic deformation and fracture process of bone. Recent experiments have shown that MCF breakage has an influence on toughening of bone. Motivated by the experiments, we carry out the analyses of fracture in staggered MCF arrays. The plastic deformation of extrafibrillar matrix (EFM), debonding of the MCF-EFM interface, plastic deformation of MCFs and MCF fracture are accounted for in the calculations. It is found that the fracture of MCF arrays is controlled by competition between MCF breakage and debonding of the MCF-EFM interface. The MCF-EFM interface with high shear strength and large shear fracture energy is capable of activating MCF breakage, which promotes plastic energy dissipation of MCF arrays. In the absence of MCF breakage, damage energy dissipation is higher than plastic energy dissipation and debonding of the MCF-EFM interface provides the major contribution to toughening of bone. We have further revealed that the relative contributions of interfacial debonding mechanism and plastic deformation of MCF arrays are dependent on fracture properties of the MCF-EFM interface in the normal direction. The high normal strength gives rise to enhanced damage energy dissipation and amplified plastic deformation of MCF arrays; while high normal fracture energy of the interface suppresses plastic deformation of MCFs.
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Affiliation(s)
- Min Xu
- Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai Institute of Applied Mathematics and Mechanics, School of Mechanics and Engineering Science, Shanghai University, Shanghai, 200444, China
| | - Bingbing An
- Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai Institute of Applied Mathematics and Mechanics, School of Mechanics and Engineering Science, Shanghai University, Shanghai, 200444, China; Shaoxing Institute of Technology, Shanghai University, Shaoxing, 312074, China.
| | - Dongsheng Zhang
- Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai Institute of Applied Mathematics and Mechanics, School of Mechanics and Engineering Science, Shanghai University, Shanghai, 200444, China; Shaoxing Institute of Technology, Shanghai University, Shaoxing, 312074, China
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4
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Groetsch A, Zysset PK, Varga P, Pacureanu A, Peyrin F, Wolfram U. An experimentally informed statistical elasto-plastic mineralised collagen fibre model at the micrometre and nanometre lengthscale. Sci Rep 2021; 11:15539. [PMID: 34330938 PMCID: PMC8324897 DOI: 10.1038/s41598-021-93505-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 06/23/2021] [Indexed: 11/08/2022] Open
Abstract
Bone is an intriguingly complex material. It combines high strength, toughness and lightweight via an elaborate hierarchical structure. This structure results from a biologically driven self-assembly and self-organisation, and leads to different deformation mechanisms along the length scales. Characterising multiscale bone mechanics is fundamental to better understand these mechanisms including changes due to bone-related diseases. It also guides us in the design of new bio-inspired materials. A key-gap in understanding bone's behaviour exists for its fundamental mechanical unit, the mineralised collagen fibre, a composite of organic collagen molecules and inorganic mineral nanocrystals. Here, we report an experimentally informed statistical elasto-plastic model to explain the fibre behaviour including the nanoscale interplay and load transfer with its main mechanical components. We utilise data from synchrotron nanoscale imaging, and combined micropillar compression and synchrotron X-ray scattering to develop the model. We see that a 10-15% micro- and nanomechanical heterogeneity in mechanical properties is essential to promote the ductile microscale behaviour preventing an abrupt overall failure even when individual fibrils have failed. We see that mineral particles take up 45% of strain compared to collagen molecules while interfibrillar shearing seems to enable the ductile post-yield behaviour. Our results suggest that a change in mineralisation and fibril-to-matrix interaction leads to different mechanical properties among mineralised tissues. Our model operates at crystalline-, molecular- and continuum-levels and sheds light on the micro- and nanoscale deformation of fibril-matrix reinforced composites.
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Affiliation(s)
- Alexander Groetsch
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK
| | - Philippe K Zysset
- ARTORG Centre for Biomedical Engineering Research, University of Bern, Bern, Switzerland
| | - Peter Varga
- AO Research Institute Davos, Davos, Switzerland
| | | | - Françoise Peyrin
- Université de Lyon, CNRS UMR 5220, Inserm U1206, INSA Lyon, UCBL Lyon 1, Creatis, Lyon, France
| | - Uwe Wolfram
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
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5
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Taylor EA, Donnelly E. Raman and Fourier transform infrared imaging for characterization of bone material properties. Bone 2020; 139:115490. [PMID: 32569874 DOI: 10.1016/j.bone.2020.115490] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/24/2020] [Revised: 06/08/2020] [Accepted: 06/11/2020] [Indexed: 12/12/2022]
Abstract
As the application of Raman spectroscopy to study bone has grown over the past decade, making it a peer technology to FTIR spectroscopy, it has become critical to understand their complimentary roles. Recent technological advancements have allowed these techniques to collect grids of spectra in a spatially resolved fashion to generate compositional images. The advantage of imaging with these techniques is that it allows the heterogenous bone tissue composition to be resolved and quantified. In this review we compare, for non-experts in the field of vibrational spectroscopy, the instrumentation and underlying physical principles of FTIR imaging (FTIRI) and Raman imaging. Additionally, we discuss the strengths and limitations of FTIR and Raman spectroscopy, address sample preparation, and discuss outcomes to provide researchers insight into which techniques are best suited for a given research question. We then briefly discuss previous applications of FTIRI and Raman imaging to characterize bone tissue composition and relationships of compositional outcomes with mechanical performance. Finally, we discuss emerging technical developments in FTIRI and Raman imaging which provide new opportunities to identify changes in bone tissue composition with disease, age, and drug treatment.
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Affiliation(s)
- Erik A Taylor
- Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY, United States of America
| | - Eve Donnelly
- Department of Materials Science and Engineering, Cornell University, Ithaca, NY, United States of America; Research division, Hospital for Special Surgery, New York, NY, United States of America.
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6
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Xi L, De Falco P, Barbieri E, Karunaratne A, Bentley L, Esapa CT, Davis GR, Terrill NJ, Cox RD, Pugno NM, Thakker RV, Weinkamer R, Wu WW, Fang DN, Gupta HS. Reduction of fibrillar strain-rate sensitivity in steroid-induced osteoporosis linked to changes in mineralized fibrillar nanostructure. Bone 2020; 131:115111. [PMID: 31726107 DOI: 10.1016/j.bone.2019.115111] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Revised: 10/13/2019] [Accepted: 10/15/2019] [Indexed: 01/29/2023]
Abstract
As bone is used in a dynamic mechanical environment, understanding the structural origins of its time-dependent mechanical behaviour - and the alterations in metabolic bone disease - is of interest. However, at the scale of the mineralized fibrillar matrix (nanometre-level), the nature of the strain-rate dependent mechanics is incompletely understood. Here, we investigate the fibrillar- and mineral-deformation behaviour in a murine model of Cushing's syndrome, used to understand steroid induced osteoporosis, using synchrotron small- and wide-angle scattering/diffraction combined with in situ tensile testing at three strain rates ranging from 10-4 to 10-1 s-1. We find that the effective fibril- and mineral-modulus and fibrillar-reorientation show no significant increase with strain-rate in osteoporotic bone, but increase significantly in normal (wild-type) bone. By applying a fibril-lamellar two-level structural model of bone matrix deformation to fit the results, we obtain indications that altered collagen-mineral interactions at the nanoscale - along with altered fibrillar orientation distributions - may be the underlying reason for this altered strain-rate sensitivity. Our results suggest that an altered strain-rate sensitivity of the bone matrix in osteoporosis may be one of the contributing factors to reduced mechanical competence in such metabolic bone disorders, and that increasing this sensitivity may improve biomechanical performance.
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Affiliation(s)
- L Xi
- Institute of Advanced Structure Technology, Beijing Institute of Technology, Beijing 100081, China; School of Engineering and Material Sciences, Queen Mary University of London, London, E1 4NS, UK.
| | - P De Falco
- School of Engineering and Material Sciences, Queen Mary University of London, London, E1 4NS, UK; Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, D-14424 Potsdam-Golm, Germany.
| | - E Barbieri
- School of Engineering and Material Sciences, Queen Mary University of London, London, E1 4NS, UK; Department of Mathematical Science and Advanced Technology (MAT), Yokohama Institute for Earth Sciences (YES) 3173-25, Showa-machi, Kanazawa-ku, Yokohama-city, Japan.
| | - A Karunaratne
- Department of Mechanical Engineering, University of Moratuwa, Sri Lanka.
| | - L Bentley
- MRC Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell, Harwell Science and Innovation Campus, OX11 0RD, UK.
| | - C T Esapa
- MRC Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell, Harwell Science and Innovation Campus, OX11 0RD, UK; Academic Endocrine Unit, Radcliffe Department of Clinical Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Churchill Hospital, Headington, Oxford, OX3 7JL, UK.
| | - G R Davis
- Dental Physical Sciences Unit, Queen Mary University of London, London, E1 4NS, UK.
| | - N J Terrill
- Beamline I22, Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire, OX11 0DE, United Kingdom
| | - R D Cox
- MRC Mammalian Genetics Unit and Mary Lyon Centre, MRC Harwell, Harwell Science and Innovation Campus, OX11 0RD, UK.
| | - N M Pugno
- Laboratory of Bio-Inspired & Graphene Nanomechanics, Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano, 77, 38123, Trento, Italy; School of Engineering and Material Sciences, Queen Mary University of London, London, E1 4NS, UK; Ket Lab, Edoardo Amaldi Foundation, Via del Politecnico snc, 00133, Rome, Italy.
| | - R V Thakker
- Academic Endocrine Unit, Radcliffe Department of Clinical Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Churchill Hospital, Headington, Oxford, OX3 7JL, UK.
| | - R Weinkamer
- Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, D-14424 Potsdam-Golm, Germany.
| | - W W Wu
- Institute of Advanced Structure Technology, Beijing Institute of Technology, Beijing 100081, China.
| | - D N Fang
- Institute of Advanced Structure Technology, Beijing Institute of Technology, Beijing 100081, China; State Key Laboratory for Turbulence and Complex Systems, College of Engineering, Peking University, Beijing, China.
| | - H S Gupta
- School of Engineering and Material Sciences, Queen Mary University of London, London, E1 4NS, UK.
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7
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Groetsch A, Gourrier A, Schwiedrzik J, Sztucki M, Beck RJ, Shephard JD, Michler J, Zysset PK, Wolfram U. Compressive behaviour of uniaxially aligned individual mineralised collagen fibres at the micro- and nanoscale. Acta Biomater 2019; 89:313-329. [PMID: 30858052 DOI: 10.1016/j.actbio.2019.02.053] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2018] [Revised: 02/21/2019] [Accepted: 02/28/2019] [Indexed: 12/17/2022]
Abstract
The increasing incidence of osteoporotic bone fractures makes fracture risk prediction an important clinical challenge. Computational models can be utilised to facilitate such analyses. However, they critically depend on bone's underlying hierarchical material description. To understand bone's irreversible behaviour at the micro- and nanoscale, we developed an in situ testing protocol that allows us to directly relate the experimental data to the mechanical behaviour of individual mineralised collagen fibres and its main constitutive phases, the mineralised collagen fibrils and the mineral nanocrystals, by combining micropillar compression of single fibres with small angle X-ray scattering (SAXS) and X-ray diffraction (XRD). Failure modes were assessed by SEM. Strain ratios in the elastic region at fibre, fibril and mineral levels were found to be approximately 22:5:2 with strain ratios at the point of compressive strength of 0.23 ± 0.11 for fibril-to-fibre and 0.07 ± 0.01 for mineral-to-fibre levels. Mineral-to-fibre levels showed highest strain ratios around the apparent yield point, fibril-to-fibre around apparent strength. The mineralised collagen fibrils showed a delayed mechanical response, contrary to the mineral phase, which points towards preceding deformations of mineral nanocrystals in the extrafibrillar matrix. No damage was measured at the level of the mineralised collagen fibre which indicates an incomplete separation of the mineral and collagen, and an extrafibrillar interface failure. The formation of kink bands and the gradual recruitment of fibrils upon compressive loading presumably led to localised strains. Our results from a well-controlled fibrillar architecture provide valuable input for micromechanical models and computational non-linear bone strength analyses that may provide further insights for personalised diagnosis and treatment as well as bio-inspired implants for patients with bone diseases. STATEMENT OF SIGNIFICANCE: Musculoskeletal diseases such as osteoporosis, osteoarthritis or bone cancer significantly challenge health care systems and make fracture risk prediction and treatment optimisation important clinical goals. Computational methods such as finite element models have the potential to optimise analyses but highly depend on underlying material descriptions. We developed an in situ testing set-up to directly relate experimental data to the mechanical behaviour of bone's fundamental building block, the individual mineralised collagen fibre and its main constituents. Low multilevel strain ratios suggest high deformations in the extrafibrillar matrix and energy dissipation at the interfaces, the absence of damage indicates both an incomplete separation between mineral and collagen and an extrafibrillar interface failure. The formation of kink bands in the fibril-reinforced composite presumably led to localised strains. The deformation behaviour of a well-controlled fibrillar architecture provides valuable input for non-linear bone strength analyses.
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Affiliation(s)
- Alexander Groetsch
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | | | - Jakob Schwiedrzik
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory of Mechanics of Materials and Nanostructures, Thun, Switzerland
| | - Michael Sztucki
- European Synchrotron Radiation Facility (ESRF), F-38043 Grenoble Cedex, France
| | - Rainer J Beck
- Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | - Jonathan D Shephard
- Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | - Johann Michler
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory of Mechanics of Materials and Nanostructures, Thun, Switzerland
| | - Philippe K Zysset
- Institute for Surgical Technology and Biomechanics, University of Bern, Switzerland
| | - Uwe Wolfram
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK.
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Cai J, Burrow MF, Manton DJ, Tsuda Y, Sobh EG, Palamara JEA. Effects of silver diamine fluoride/potassium iodide on artificial root caries lesions with adjunctive application of proanthocyanidin. Acta Biomater 2019; 88:491-502. [PMID: 30776507 DOI: 10.1016/j.actbio.2019.02.020] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 01/29/2019] [Accepted: 02/14/2019] [Indexed: 12/26/2022]
Abstract
Treatment of carious root surfaces remains challenging due to the complex pathological processes and difficulty in restoring the original structure of root dentine. Current treatments targeting the de-/re-mineralisation processes are not entirely satisfactory in terms of the protection of the dentinal organic matrix and the highly organised structure of dentine. In this in vitro study, a cross-linking agent - proanthocyanidin (PA) was used in conjunction with a fluoride-based treatment - silver diamine fluoride/potassium iodide (SDF/KI) to putatively stabilise the organic dentinal framework as well as strengthen the collagen-mineral phase interaction. The effectiveness of this strategy was evaluated 24 h after application in terms of the distribution of ion uptake and microstructure of dentine after treatment as well as analysis of the nano-mechanical properties using a dynamic behaviour model. Results showed that individual use of SDF/KI significantly improved the surface microhardness and integrated mineral density (Z) up to 60 µm depth and the recovery of creep behaviour of demineralised dentine in the surface area compared to that treated with deionised distilled water (DDW). The combined treatment of PA and SDF/KI achieved a more homogenous mineral distribution throughout the lesions than SDF/KI alone; a more significant incremental increase in surface microhardness and Z was observed. Specifically, a superior effect on the subsurface area occurred with PA + SDF/KI, with significant improvements in microhardness, elastic modulus and recovery of creep behaviour of the demineralised dentine. Application of SDF/KI induced small discrete crystal formation distributed over the dentine surface and PA contributed to the formation of slit-shaped orifices of the dentinal tubules that were partially occluded. STATEMENT OF SIGNIFICANCE: Demographic transitions and improved oral health behaviour have resulted in increased tooth retention in elderly people. As a consequence, the risk of root dentine caries is increasing due to the age-associated gingival recession and the related frequent exposure of cervical root dentine. Root caries is difficult to repair because of the complex aetiology and dentine structure. The recovery of dentine quality depends not only on reincorporation of minerals but also an intact dentinal organic matrix and the organic-inorganic interfacial structure, which contribute to the biomechanics of dentine. With the capability of dentine modification, cross-linking agents were applied with a fluoride regimen, which improved its treatment efficacy of root caries regarding the distribution of ion uptake and recovery of dentine biomechanics.
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Affiliation(s)
- Jing Cai
- Melbourne Dental School, The University of Melbourne, 720 Swanston Street, Carlton, VIC 3053, Australia
| | - Michael F Burrow
- Melbourne Dental School, The University of Melbourne, 720 Swanston Street, Carlton, VIC 3053, Australia; Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, Sai Ying Pun, Hong Kong Special Administrative Region
| | - David J Manton
- Melbourne Dental School, The University of Melbourne, 720 Swanston Street, Carlton, VIC 3053, Australia
| | - Yuka Tsuda
- Melbourne Dental School, The University of Melbourne, 720 Swanston Street, Carlton, VIC 3053, Australia
| | - Eman G Sobh
- Melbourne Dental School, The University of Melbourne, 720 Swanston Street, Carlton, VIC 3053, Australia
| | - Joseph E A Palamara
- Melbourne Dental School, The University of Melbourne, 720 Swanston Street, Carlton, VIC 3053, Australia.
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9
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Abstract
PURPOSE OF REVIEW While thinning of the cortices or trabeculae weakens bone, age-related changes in matrix composition also lower fracture resistance. This review summarizes how the organic matrix, mineral phase, and water compartments influence the mechanical behavior of bone, thereby identifying characteristics important to fracture risk. RECENT FINDINGS In the synthesis of the organic matrix, tropocollagen experiences various post-translational modifications that facilitate a highly organized fibril of collagen I with a preferred orientation giving bone extensibility and several toughening mechanisms. Being a ceramic, mineral is brittle but increases the strength of bone as its content within the organic matrix increases. With time, hydroxyapatite-like crystals experience carbonate substitutions, the consequence of which remains to be understood. Water participates in hydrogen bonding with organic matrix and in electrostatic attractions with mineral phase, thereby providing stability to collagen-mineral interface and ductility to bone. Clinical tools sensitive to age- and disease-related changes in matrix composition that the affect mechanical behavior of bone could potentially improve fracture risk assessment.
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Affiliation(s)
- Mustafa Unal
- Department of Orthopaedic Surgery & Rehabilitation, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Vanderbilt Biophotonics Center, Vanderbilt University, Nashville, TN, 37232, USA
| | - Amy Creecy
- Department of Orthopaedic Surgery & Rehabilitation, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, 37232, USA
| | - Jeffry S Nyman
- Department of Orthopaedic Surgery & Rehabilitation, Vanderbilt University Medical Center, Nashville, TN, 37232, USA.
- Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA.
- Vanderbilt Biophotonics Center, Vanderbilt University, Nashville, TN, 37232, USA.
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, 37232, USA.
- Vanderbilt Orthopedic Institute, Medical Center East, South Tower, Suite 4200, Nashville, TN, 37232, USA.
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Vordos N, Drosos G, Kazanidis I, Ververidis A, Ypsilantis P, Kazakos K, Simopoulos C, Mitropoulos AC, Touloupidis S. Hydroxyapatite Crystal Thickness and Buckling Phenomenon in Bone Nanostructure During Mechanical Tests. Ann Biomed Eng 2018; 46:627-639. [DOI: 10.1007/s10439-018-1983-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 01/12/2018] [Indexed: 12/22/2022]
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11
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Georgiadis M, Müller R, Schneider P. Techniques to assess bone ultrastructure organization: orientation and arrangement of mineralized collagen fibrils. J R Soc Interface 2017; 13:rsif.2016.0088. [PMID: 27335222 DOI: 10.1098/rsif.2016.0088] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 05/18/2016] [Indexed: 12/13/2022] Open
Abstract
Bone's remarkable mechanical properties are a result of its hierarchical structure. The mineralized collagen fibrils, made up of collagen fibrils and crystal platelets, are bone's building blocks at an ultrastructural level. The organization of bone's ultrastructure with respect to the orientation and arrangement of mineralized collagen fibrils has been the matter of numerous studies based on a variety of imaging techniques in the past decades. These techniques either exploit physical principles, such as polarization, diffraction or scattering to examine bone ultrastructure orientation and arrangement, or directly image the fibrils at the sub-micrometre scale. They make use of diverse probes such as visible light, X-rays and electrons at different scales, from centimetres down to nanometres. They allow imaging of bone sections or surfaces in two dimensions or investigating bone tissue truly in three dimensions, in vivo or ex vivo, and sometimes in combination with in situ mechanical experiments. The purpose of this review is to summarize and discuss this broad range of imaging techniques and the different modalities of their use, in order to discuss their advantages and limitations for the assessment of bone ultrastructure organization with respect to the orientation and arrangement of mineralized collagen fibrils.
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Affiliation(s)
| | - Ralph Müller
- Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | - Philipp Schneider
- Institute for Biomechanics, ETH Zurich, Zurich, Switzerland Bioengineering Science Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, UK
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12
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Time dependent deformation behavior of dentin. Arch Oral Biol 2017; 76:20-29. [DOI: 10.1016/j.archoralbio.2017.01.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Revised: 11/15/2016] [Accepted: 01/03/2017] [Indexed: 11/23/2022]
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13
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Lin L, Samuel J, Zeng X, Wang X. Contribution of extrafibrillar matrix to the mechanical behavior of bone using a novel cohesive finite element model. J Mech Behav Biomed Mater 2016; 65:224-235. [PMID: 27592291 DOI: 10.1016/j.jmbbm.2016.08.027] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Revised: 07/19/2016] [Accepted: 08/21/2016] [Indexed: 12/21/2022]
Abstract
The mechanical behavior of bone is determined at all hierarchical levels, including lamellae (the basic building block of bone) that are comprised of mineralized collagen fibrils and extrafibrillar matrix. The mechanical behavior of mineralized collagen fibrils has been investigated intensively using both experimental and computational approaches. Yet, the contribution of the extrafibrillar matrix to bone mechanical properties is poorly documented. In this study, we intended to address this issue using a novel cohesive finite element (FE) model, in conjunction with the experimental observations reported in the literature. In the FE model, the extrafibrillar matrix was considered as a nanocomposite of hydroxyapatite (HA) crystals bounded through a thin organic interface modeled as a cohesive interfacial zone. The parameters required by the cohesive FE model were defined based on the experimental data reported in the literature. This hybrid nanocomposite model was tested in two loading modes (i.e. tension and compression) and under two hydration conditions (i.e. wet and dry). The simulation results indicated that (1) the failure modes of the extrafibrillar matrix predicted using the cohesive FE model were closely coincided with those experimentally observed in tension and compression tests; (2) the pre-yield deformation (i.e. internal strain) of HA crystals with respect to the applied strain was consistent with that obtained from the synchrotron X-ray scattering measurements irrespective of the loading modes and hydration status; and (3) the mechanical behavior of the extrafibrillar matrix was dictated by the properties of the organic interface between the HA crystals. Taken together, we postulate that the extrafibrillar matrix plays a major role in the pre-yield deformation and the failure mode of bone, thus, giving rise to important insights in the ultrastructural origins of bone fragility.
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Affiliation(s)
- Liqiang Lin
- Department of Mechanical Engineering, University of Texas at San Antonio, TX 78249, United States
| | - Jitin Samuel
- Department of Mechanical Engineering, University of Texas at San Antonio, TX 78249, United States
| | - Xiaowei Zeng
- Department of Mechanical Engineering, University of Texas at San Antonio, TX 78249, United States.
| | - Xiaodu Wang
- Department of Mechanical Engineering, University of Texas at San Antonio, TX 78249, United States.
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14
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Abstract
The interface between collagen and the mineral reinforcement phase, carbonated hydroxyapatite (cAp), is essential for bone's remarkable functionality as a biological composite material. The very small dimensions of the cAp phase and the disparate natures of the reinforcement and matrix are essential to the material's performance but also complicate study of this interface. This article summarizes what is known about the cAp-collagen interface in bone and begins with descriptions of the matrix and reinforcement roles in composites, of the phases bounding the interface, of growth of cAp growing within the collagen matrix, and of the effect of intra- and extrafibrilar mineral on determinations of interfacial properties. Different observed interfacial interactions with cAp (collagen, water, non-collagenous proteins) are reviewed; experimental results on interface interactions during loading are reported as are their influence on macroscopic mechanical properties; conclusions of numerical modeling of interfacial interactions are also presented. The data suggest interfacial interlocking (bending of collagen molecules around cAp nanoplatelets) and water-mediated bonding between collagen and cAp are essential to load transfer. The review concludes with descriptions of areas where new research is needed to improve understanding of how the interface functions.
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Affiliation(s)
- S R Stock
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, 303 E. Chicago Ave., Chicago, IL, 60611-3008, USA,
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15
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Katsamenis OL, Jenkins T, Thurner PJ. Toughness and damage susceptibility in human cortical bone is proportional to mechanical inhomogeneity at the osteonal-level. Bone 2015; 76:158-68. [PMID: 25863123 DOI: 10.1016/j.bone.2015.03.020] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Revised: 03/18/2015] [Accepted: 03/27/2015] [Indexed: 01/16/2023]
Abstract
Limitations associated with current clinical fracture risk assessment tools highlight the need for increased understanding of the fracture mechanisms of the bone and, ideally, a means of assessing this in vivo. Being a multi-layered hierarchical structure, the overall properties of the bone are dictated by its structural and compositional properties over multiple length scales. In this study, we investigate the osteonal-, micro- and tissue-level mechanical behaviour of cortical bone tissue samples from young and elderly donors through atomic force microscope (AFM) cantilever-based nanoindentation, reference point microindentation (RPI) and fracture toughness experiments respectively. We demonstrate that bone's fracture toughness and crack growth resistance at the tissue-level are significantly correlated to damage susceptibility at the micro-level, and mechanical inhomogeneity between lamellae and interlamellar areas at the osteonal-level. In more detail, reduced nanoelasticity inhomogeneity of lamellar/interlamellar layers within the osteons correlated to increased indentation depth at the micro-level and an overall reduction in crack-growth toughness and fracture toughness of the tissue. Our data also suggest that deterioration of bone's mechanical properties is expressed concurrently at these three levels, and that mechanical inhomogeneity between the principal structural units of the cortical tissue holds a key role on bone's toughness behaviour. We hypothesise that the reduction in nanoelasticity inhomogeneity is--at least to some extent--responsible for the inability of the microstructure to effectively adapt to the applied load, e.g. by redistributing strains, in a non-catastrophic manner preventing damage formation and propagation. Our hypothesis is further supported by synchrotron radiation micro-computed tomography (SRμCT) data, which show that failure of tougher bone specimens is governed by increased deflection of the crack path and broadly spread damage around the crack-tip. In contrast, shorter and more direct crack paths as well as less-distributed damage were evidenced during failure of the weaker specimens. Overall, this multi-scale study highlights the importance of elasticity inhomogeneity within the osteon to the damage susceptibility and consequently to the fracture resistance of the tissue.
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Affiliation(s)
- Orestis L Katsamenis
- μVIS X-ray Imaging Centre, Faculty of Engineering and the Environment, University of Southampton, SO17 1BJ Southampton, UK; Bioengineering Sciences Research Group, Faculty of Engineering and the Environment, University of Southampton, SO17 1BJ Southampton, UK.
| | - Thomas Jenkins
- Bioengineering Sciences Research Group, Faculty of Engineering and the Environment, University of Southampton, SO17 1BJ Southampton, UK
| | - Philipp J Thurner
- Bioengineering Sciences Research Group, Faculty of Engineering and the Environment, University of Southampton, SO17 1BJ Southampton, UK; Institute for Lightweight Design and Structural Biomechanics, Vienna University of Technology, 1040 Vienna, Austria.
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Gu C, Katti DR, Katti KS. Dynamic nanomechanical behaviour of healthy and OI human cortical bone. BIOINSPIRED BIOMIMETIC AND NANOBIOMATERIALS 2015. [DOI: 10.1680/bbn.14.00018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Viscoelasticity of bone has been of interest for many years because this time-dependent mechanical property relates to the fracture risk of bone under dynamic loading. Several factors have been claimed to contribute to this property including the nature of different constituents of bone and their interactions, as well as moisture content. In the present study, intact normal human cortical bone was demineralised, and molecular structures were identified using infrared spectroscopy. Osteogenesis imperfecta (OI) human cortical bone was also selected for comparison because OI bone has severe defects in collagen molecules, while its mineral phase is almost identical to that of normal bone. The dynamic nanomechanical behaviours of the intact, demineralised and OI human cortical bone specimens were examined using dynamic nanoindentation. Loss tangent, tan δ, was considered as a measure of the degree of the viscoelastic response. Variable dynamic load tests show that the viscoelastic responses of all bone specimens increase with frequency. With demineralisation, bone specimens show greater viscoelastic response than intact specimens. OI bone shows similar viscoelastic response as normal bone. Results suggest that the viscoelasticity of bone is mostly attributable to the mineral phase. The present study adds to the understanding of the viscoelastic response of bone material. In addition, the dynamic mechanical properties of OI bone are firstly reported here.
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Affiliation(s)
- Chunju Gu
- Research Assistant, Department of Civil and Environmental Engineering, North Dakota State University, Fargo, ND, USA
| | - Dinesh R. Katti
- Professor, Department of Civil and Environmental Engineering, North Dakota State University, Fargo, ND, USA
| | - Kalpana S. Katti
- University Distinguished Professor, Department of Civil and Environmental Engineering, North Dakota State University, Fargo, ND, USA
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Effect of cyclic loading on the nanoscale deformation of hydroxyapatite and collagen fibrils in bovine bone. Biomech Model Mechanobiol 2014; 13:615-26. [PMID: 23958833 DOI: 10.1007/s10237-013-0522-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Accepted: 08/07/2013] [Indexed: 01/15/2023]
Abstract
Cyclic compressive loading tests were carried out on bovine femoral bones at body temperature (37 °C), with varying mean stresses (-55 to -80 MPa) and loading frequencies (0.5-5 Hz). At various times, the cyclic loading was interrupted to carry out high-energy X-ray scattering measurements of the internal strains developing in the hydroxyapatite (HAP) platelets and the collagen fibrils. The residual strains upon unloading were always tensile in the HAP and compressive in the fibrils, and each increases in magnitude with loading cycles, which can be explained from damage at the HAP–collagen interface and accumulation of plastic deformation within the collagen phase. The samples tested at a higher mean stress and stress amplitude, and at lower loading frequencies exhibit greater plastic deformation and damage accumulation, which is attributed to greater contribution of creep. Synchrotron microcomputed tomography of some of the specimens showed that cracks are produced during cyclic loading and that they mostly occur concentric with Haversian canals.
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Importance of age on the dynamic mechanical behavior of intertubular and peritubular dentin. J Mech Behav Biomed Mater 2014; 42:229-42. [PMID: 25498296 DOI: 10.1016/j.jmbbm.2014.11.021] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Revised: 11/20/2014] [Accepted: 11/22/2014] [Indexed: 11/23/2022]
Abstract
An experimental evaluation of human coronal dentin was performed using nanoscopic dynamic mechanical analysis (nanoDMA). The primary objectives were to quantify any unique changes in mechanical behavior of intertubular and peritubular dentin with age, and to evaluate the microstructure and mechanical behavior of the mineral deposited within the lumens. Specimens of coronal dentin were evaluated by nanoDMA using single indents and in scanning mode via scanning probe microscopy. Results showed that there were no significant differences in the storage modulus or complex modulus between the two age groups (18-25 versus 54-83 yrs) for either the intertubular or peritubular tissue. However, there were significant differences in the dampening behavior between the young and old dentin, as represented in the loss modulus and tanδ responses. For both the intertubular and peritubular components, the capacity for dampening was significantly lower in the old group. Scanning based nanoDMA showed that the tubules of old dentin exhibit a gradient in elastic behavior, with decrease in elastic modulus from the cuff to the center of tubules filled with newly deposited mineral.
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19
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Sui T, Korsunsky AM. Hierarchical Modeling of Elastic Behavior of Human Dental Tissue Based on Synchrotron Diff raction Characterization. Adv Healthc Mater 2014. [DOI: 10.1002/9781118774205.ch7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Sui T, Sandholzer MA, Baimpas N, Dolbnya IP, Walmsley A, Lumley PJ, Landini G, Korsunsky AM. Multiscale modelling and diffraction-based characterization of elastic behaviour of human dentine. Acta Biomater 2013; 9:7937-47. [PMID: 23602879 DOI: 10.1016/j.actbio.2013.04.020] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Revised: 04/10/2013] [Accepted: 04/11/2013] [Indexed: 10/26/2022]
Abstract
Human dentine is a hierarchical mineralized tissue with a two-level composite structure, with tubules being the prominent structural feature at a microlevel, and collagen fibres decorated with hydroxyapatite (HAp) crystallite platelets dominating the nanoscale. Few studies have focused on this two-level structure of human dentine, where the response to mechanical loading is thought to be affected not only by the tubule volume fraction at the microscale, but also by the shape and orientation distribution of mineral crystallites, and their nanoscale spatial arrangement and alignment. In this paper, in situ elastic strain evolution within HAp in dentine subjected to uniaxial compressive loading along both longitudinal and transverse directions was characterized simultaneously by two synchrotron X-ray scattering techniques: small- and wide-angle X-ray scattering (SAXS and WAXS, respectively). WAXS allows the evaluation of the apparent modulus linking the external load to the internal HAp crystallite strain, while the nanoscale HAp distribution and arrangement can be quantified by SAXS. We proposed an improved multiscale Eshelby inclusion model that takes into account the two-level hierarchical structure, and validated it with a multidirectional experimental strain evaluation. The agreement between the simulation and measurement indicates that the multiscale hierarchical model developed here accurately reflects the structural arrangement and mechanical response of human dentine. This study benefits the comprehensive understanding of the mechanical behaviour of hierarchical biomaterials. The knowledge of the mechanical properties related to the hierarchical structure is essential for the understanding and predicting the effects of structural alterations that may occur due to disease or treatment on the performance of dental tissues and their artificial replacements.
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Deymier-Black AC, Singhal A, Yuan F, Almer JD, Brinson LC, Dunand DC. Effect of high-energy X-ray irradiation on creep mechanisms in bone and dentin. J Mech Behav Biomed Mater 2013; 21:17-31. [DOI: 10.1016/j.jmbbm.2013.01.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Revised: 01/08/2013] [Accepted: 01/23/2013] [Indexed: 10/27/2022]
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22
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Effect of stress and temperature on the micromechanics of creep in highly irradiated bone and dentin. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2013; 33:1467-75. [DOI: 10.1016/j.msec.2012.12.069] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Revised: 08/12/2012] [Accepted: 12/14/2012] [Indexed: 11/20/2022]
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Deymier-Black AC, Singhal A, Almer JD, Dunand DC. Effect of X-ray irradiation on the elastic strain evolution in the mineral phase of bovine bone under creep and load-free conditions. Acta Biomater 2013; 9:5305-12. [PMID: 22871638 DOI: 10.1016/j.actbio.2012.07.046] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Revised: 07/16/2012] [Accepted: 07/27/2012] [Indexed: 11/16/2022]
Abstract
Both the load partitioning between hydroxyapatite (HAP) and collagen during compressive creep deformation of bone and the HAP residual strain in unloaded bone have been shown in previous synchrotron X-ray diffraction studies to be affected by the X-ray irradiation dose. Here, through detailed analysis of the X-ray diffraction patterns of bovine bone, the effect of X-ray dose on (i) the rate of HAP elastic strain accumulation/shedding under creep conditions and (ii) the HAP lattice spacing and average root mean square (RMS) strain under load-free conditions are examined. These strain measurements exhibit three stages in response to increasing X-ray dose. Up to ∼75 kGy (stage I) no effect of dose is observed, indicating a threshold behavior. Between ∼75 and ∼300 kGy (stage II) in unloaded bone the HAP d-spacing increases and the RMS strain decreases with dose, indicating strain relaxation of HAP. Furthermore, under constant compressive load creep conditions, the rate of compressive elastic strain accumulation in HAP decreases with increasing dose until, at ∼115 kGy, it changes sign, indicating that the HAP phase is shedding load during creep deformation. These stage II behaviors are consistent with HAP-collagen interfacial damage, which allows the HAP elastic strain to relax within both the loaded and unloaded samples. Finally, for doses in excess of ∼300 kGy (stage III, measured up to 7771 kGy) the HAP lattice spacing and RMS strain for load-free samples and the rate of HAP elastic strain shedding for crept samples remain independent of dose, suggesting a saturation of damage and/or stiffening of the collagen matrix due to intermolecular cross-linking.
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Affiliation(s)
- Alix C Deymier-Black
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.
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Singhal A, Almer J, Dunand D. Variability in the nanoscale deformation of hydroxyapatite during compressive loading in bovine bone. Acta Biomater 2012; 8:2747-58. [PMID: 22465576 DOI: 10.1016/j.actbio.2012.03.036] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Revised: 03/10/2012] [Accepted: 03/21/2012] [Indexed: 11/27/2022]
Abstract
High-energy synchrotron X-ray diffraction is used to study in situ elastic strains in hydroxyapatite (HAP) for bovine femur cortical bone subjected to uniaxial compressive loading. Load-unload tests at room temperature (27°C) and body temperature (37°C) show that the load transfer to the stiff nanosized HAP platelets from the surrounding compliant protein matrix does not vary significantly (p<0.05) with temperature. This emphasizes that the stiffness of bone is controlled by the stiffness of the HAP phase, which remains unaffected by this change in temperature. Both the extent of hysteresis and the residual value of internal strains developed in HAP during load-unload cycling from 0 to -100 MPa increase significantly (p<0.05) with the number of loading cycles, indicative of strain energy dissipation and accumulation of permanent deformation. Monotonic loading tests, conducted at body temperature to determine the spatial variation of properties within the femur, illustrate that the HAP phase carries lower strain (and thus stresses) at the anterio-medial aspect of the femur than at the anterio-lateral aspect. This is correlated to higher HAP volume fractions in the former location (p<0.05). The Young's modulus of the bone is also found to correlate with the HAP volume fraction and porosity (p<0.05). Finally, samples with a primarily plexiform microstructure are found to be stiffer than those with a primarily Haversian microstructure (p<0.05).
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