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Mechanical analyses of trabecular bone and its interaction with implants
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (BioMaterial Systems)ORCID iD: 0000-0002-2594-0213
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bone substitute materials or implants are commonly used in the surgical treatment of bone fractures. However, severe complications are sometimes reported. In order to improve fracture treatment where the interior, porous trabecular bone is involved, it is important to better understand the mechanical properties of this bone and how it interacts with the substitutes/implants, and this was the aim of this thesis.

Since one of the key mechanical properties of trabecular bone, i.e. the elastic moduli at the tissue level, was not consistently reported in the literature, the results from four widely applied methods were first summarized and presented in a review paper.

Furthermore, to improve the analysis of the mechanical behavior of bone and its interaction with implants, a new digital volume correlation (DVC) technique was proposed based on higher-order finite elements.

We further proposed a method to estimate the elastic modulus at the tissue level by compression of single trabeculae within a synchrotron radiation micro-computed tomograph (SRµCT). Full-field displacements were estimated by DVC, which also provided boundary conditions for a finite element model. The proposed method shows potential to estimate trabecular mechanical properties at the tissue level.

Further, strains and cracks of a trabecular structure under compression till fracture were characterized at the single trabecular level, with DVC applied on high-resolution images from SRµCT.

The effect of augmentation materials on the engagement of screws inserted into trabecular bone was evaluated in human femoral bone, with and without real-time SRµCT. A newly developed tissue adhesive indicated a potential benefit of this material to the primary implant stability compared to a cement and no augmentation.

Finally, a trabecular structure of PLA/HA composite material was printed using a fused deposition modelling method as a preliminary step towards better synthetic models of trabecular bone. The synthetic trabecular structure was evaluated using micro-CT, compression and screw pull-out testing.

In conclusion, methods to estimate strains and mechanical properties of trabecular bone were proposed, insights into interactions between trabecular bone and augmentation/implants were gained, as well as a first step towards a synthetic trabecular model, which may contribute to further mechanical analyses and/or improved clinical treatments of trabecular bone.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 65
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1836
Keywords [en]
Trabecular bone, Elastic modulus, Digital volume correlation, Pullout resistance, Micro-computed tomography.
National Category
Other Materials Engineering Applied Mechanics
Identifiers
URN: urn:nbn:se:uu:diva-385143ISBN: 978-91-513-0715-2 (print)OAI: oai:DiVA.org:uu-385143DiVA, id: diva2:1342155
Public defence
2019-09-18, Ångström 8001, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2019-08-28 Created: 2019-08-12 Last updated: 2019-09-17
List of papers
1. Young’s modulus of trabecular bone at the tissue level: A review
Open this publication in new window or tab >>Young’s modulus of trabecular bone at the tissue level: A review
2018 (English)In: Acta Biomaterialia, ISSN 1742-7061, E-ISSN 1878-7568, Vol. 78, p. 1-12Article, review/survey (Refereed) Published
Abstract [en]

The tissue-level Young’s modulus of trabecular bone is important for detailed mechanical analysis of bone and bone-implant mechanical interactions. However, the heterogeneity and small size of the trabecular struts complicate an accurate determination. Methods such as micro-mechanical testing of single trabeculae, ultrasonic testing, and nanoindentation have been used to estimate the trabecular Young’s modulus. This review summarizes and classifies the trabecular Young’s moduli reported in the literature. Information on species, anatomic site, and test condition of the samples has also been gathered. Advantages and disadvantages of the different methods together with recent developments are discussed, followed by some suggestions for potential improvement, for future work. In summary, this review provides a thorough introduction to the approaches used for determining trabecular Young’s modulus, highlights important considerations when applying these methods and summarizes the reported Young’s modulus for follow-up studies on trabecular properties.

Keywords
trabecular bone; tissue-level Young’s modulus; single trabeculae, struts
National Category
Medical Materials Biomaterials Science Medical Image Processing
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-364424 (URN)10.1016/j.actbio.2018.08.001 (DOI)000445990200001 ()30081232 (PubMedID)
Funder
Göran Gustafsson Foundation for Research in Natural Sciences and Medicine, 1729Swedish Research Council, 2016-04608
Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2019-08-12Bibliographically approved
2. A global digital volume correlation algorithm based on higher-order finite elements: Implementation and evaluation
Open this publication in new window or tab >>A global digital volume correlation algorithm based on higher-order finite elements: Implementation and evaluation
2019 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 168, p. 211-227Article in journal (Refereed) Published
Abstract [en]

We propose a DVC technique that is based on higher-order finite-element discretization of the displacement field and a global optimization procedure. We use curvature penalization to suppress non-physical fluctuations of the displacement field and resulting erroneous strain concentrations. The performance of the proposed method is compared to the commercial code Avizo using trabecular bone images and found to perform slightly better in most cases. In addition, we stress that the performance of a DVC method needs to be evaluated using double scans (zero strain), virtual deformation (imposed deformation) and real deformation. Double scans give insight into the presence of noise and artifacts whereas virtual deformation benchmarks allows evaluation of the performance without noise and artifacts. Investigation of the performance for actual deformed heterogeneous materials is needed for evaluation with noise, artifacts and non-zero strains. We show that both decreasing the resolution of the displacement field (increasing subvolume size) as well as (increasing) curvature penalization (regularization) have a similar effect on the performance of evaluated DVC methods: Decreasing the detrimental effect of noise, artifacts and interpolation errors, but also decreasing the sensitivity of a DVC method to displacement peaks, discontinuities and strain concentrations. The needed amount of regularization is a trade-off between accuracy and precision of the estimated strain fields and their resolution. The obtainable accuracy and precision of the estimated displacement fields are influenced by interpolation errors in the DVC procedure and the relative amount of detail, noise and artifacts in the images. Errors in the displacement field are typically magnified during the strain calculation. Based on the tests and subvolume sizes (16-50 voxels) in this study, the expected order of magnitude of the accuracy and precision is 0.1 micro-voxels and 1 milli-voxels for the displacements and 0.1 and 1 milli-strains of the strain fields. 

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Digital volume correlation, Accuracy, Precision, Benchmarks, Evaluation, Trabecular bone
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-387714 (URN)10.1016/j.ijsolstr.2019.03.024 (DOI)000469906300017 ()
Funder
Swedish Research Council, 2016-04608Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-08-12Bibliographically approved
3. A combined experimental and numerical method to estimate the elastic modulus of single trabeculae
Open this publication in new window or tab >>A combined experimental and numerical method to estimate the elastic modulus of single trabeculae
Show others...
2017 (English)Manuscript (preprint) (Other academic)
National Category
Other Materials Engineering Applied Mechanics
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-330457 (URN)
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-12
4. Quantification of strains and cracks in trabecular bone by digital volume correlation: A case study
Open this publication in new window or tab >>Quantification of strains and cracks in trabecular bone by digital volume correlation: A case study
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-390619 (URN)
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-15
5. The effect of augmentation materials on screw pullout resistance from human trabecular bone
Open this publication in new window or tab >>The effect of augmentation materials on screw pullout resistance from human trabecular bone
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Ceramics Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-389555 (URN)
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-12
6. 3D-printed PLA/HA composite structures as synthetic trabecular bone: a feasibility study using Fused Deposition Modelling
Open this publication in new window or tab >>3D-printed PLA/HA composite structures as synthetic trabecular bone: a feasibility study using Fused Deposition Modelling
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-390621 (URN)
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-13

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