Elin Törnquist - Academia.edu (original) (raw)

Papers by Elin Törnquist

Research paper thumbnail of Systemically administered zoledronic acid activates locally implanted synthetic hydroxyapatite particles enhancing peri-implant bone formation: A regenerative medicine approach to improve fracture fixation

Acta biomaterialia, Mar 1, 2024

Research paper thumbnail of Bone-implant integration assessed using in-situ mechanical pull-out during synchrotron X-ray tomography

Research paper thumbnail of Exploratory Neutron Tomography of Articular Cartilage

Osteoarthritis and cartilage, Mar 1, 2024

Research paper thumbnail of Nanoscale Characterization of Collagen Structural Responses to <i>in Situ</i> Loading in Rat Achilles Tendons

Social Science Research Network, 2022

Research paper thumbnail of Hydroxyapatite crystal thickness and orientation at the bone implant interface : spatial and temporal evolutions

HAL (Le Centre pour la Communication Scientifique Directe), Jun 26, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Research paper thumbnail of The Osteocyte Lacuno-Canalicular Network at the Bone-Implant Interphase Imaged with Focused Ion Beam -Scanning Electron Microscopy

HAL (Le Centre pour la Communication Scientifique Directe), Jun 26, 2022

Research paper thumbnail of Comparison of small-angle neutron and X-ray scattering for studying cortical bone nanostructure

Scientific Reports, Sep 3, 2020

in this study, we present a combined small-angle neutron and X-ray scattering (SAnS and SAXS) stu... more in this study, we present a combined small-angle neutron and X-ray scattering (SAnS and SAXS) study of the nanoscale structure of cortical bone specimens from three different species. The variation of the scattering cross section of elements across the periodic table is very different for neutrons and X-rays. For X-rays, it is proportional to the electron density while for neutrons it varies irregularly with the atomic number. Hence, combining the two techniques on the same specimens allows for a more detailed interpretation of the scattering patterns as compared to a single-contrast experiment. The current study was performed on bovine, porcine and ovine specimens, obtained in two perpendicular directions with respect to the main axis of the bone (longitudinal and radial) in order to maximise the understanding of the nanostructural organisation. The specimens were also imaged with high resolution micro-computed tomography (micro-ct), yielding tissue mineral density and microstructural orientation as reference. We show that the SANS and SAXS patterns from the same specimen are effectively identical, suggesting that these bone specimens can be approximated as a two-component composite material. Hence, the observed small-angle scattering results mainly from the mineral-collagen contrast, apart from minor features associated with the internal collagen structure.

Research paper thumbnail of Mineralization of cortical bone during maturation and growth in rabbits

Journal of Bone and Mineral Metabolism, Dec 5, 2019

Introduction The composite nature of bone as a material governs its structure and mechanical beha... more Introduction The composite nature of bone as a material governs its structure and mechanical behavior. How the collagenous matrix mineralizes, in terms of both mineral deposition and structure of the mineral crystals, is highly interesting when trying to elucidate the complex structural changes that occur during bone growth and maturation. We have previously looked at mineral deposition and structural evolution of the collagenous matrix, linking both to changes in mechanics. The purpose of this study was to provide specific information on changes in crystal size and organization as a function of growth and maturation. Materials and Methods Using micro-computed tomography (µCT) and micro-focused scanning small-angle X-ray scattering (SAXS) we investigated cortical bone in two orthogonal directions relative to the long axis of the humeri of New Zealand White rabbits spanning from newborn to 6-months of age. We also investigated the changes with tissue age by looking at radial profiles of osteonal structures in the 6-months old rabbits. The findings were compared to our previous compositional, structural and mechanical data on the same sample cohort. Results µCT showed a continuous mineral deposition up until 3-months of age, whilst the SAXS data showed an increase in both crystal thickness and degree of orientation up until 6-months of age. The osteonal profiles showed no statistically significant changes in crystal thickness. Conclusions Comparison to previously collected mechanical data suggests that changes are not only explained by amount of mineral in the tissue but also by the crystal dimensions.

Research paper thumbnail of Characterization of collagen structural response to in situ loading of the rat Achilles tendon

HAL (Le Centre pour la Communication Scientifique Directe), Jul 25, 2021

The collagen response in rat Achilles tendons to in situ tensile loading was studied using small-... more The collagen response in rat Achilles tendons to in situ tensile loading was studied using small-angle X-ray scattering (SAXS), to evaluate the relationship between the elastic and viscoelastic behavior of the tissue and collagen fibrils. The fibril strains were substantially lower than the applied tissue strains. Fibril strains increased linearly before yielding and breaking prior to tissue failure.

Research paper thumbnail of Segmentation, Analysis, and Modelling of Microstructure in Cortical Bone, based on X-ray Microtomography

The microstructure in cortical bone greatly affect the toughness of the bone and the crack propag... more The microstructure in cortical bone greatly affect the toughness of the bone and the crack propagation during fracture. The two main structural features, Haversian canals and osteons, have been previously studied in order to increase the knowledge of the biomechanics of bone. In studies where X-ray microtomography has been the imaging method of choice, the microstructure has been analysed based on manual segmentation, a method which is difficult and tedious on larger sample volumes. X-ray microtomograms, or µCT images, are gray scale 2D images, which can be rendered into a 3D volume, where the pixel intensity corresponds to the absorption coefficient of the material in the object. Material that absorbs a lot of X-ray radiation will show up as high intensity pixel whilst material that absorbs little will show up as low intensity pixel, just as in a normal radiogram. µCT is best used on samples containing structures with varying absorbtion properties as this will enable good contrast between the structures. In this project, a semi-automatic method for segmenting the microstructures Haversian canals and osteons in µCT images of cortical bovine bone was implemented. Based on this segmentation, a simplified model was built for future Finite Element Modelling. K-means clustering with nine clusters was chosen as segmentation method. By identifying which clusters correspond to what pixel intensities, and hence to what tissue type, it was possible to segment out Haversian canals, and osteons in the µCT images. The simplified model was based on principal component analysis of the segmented canals in 3D, and circle fitting on Haversian canals, and osteons in 2D. The generated segmentations provided enhanced visibility of the microstructure. Based on porosity, and volume analysis, the segmentation pipeline gave good results for the Haversian canals, but was less accurate in differentiating between osteonal tissue and tissue with similar absorption properties embedded in the interstitial bone. Porosity measurements on the segmentations corresponded with previous studies. The radii of the osteons and the Haversian canals, generated by the simplified model, agreed well with previous studies, and the method overcame the issue with unclear osteonal boundaries by using the segmentation of the Haversian canals as a base. This Master's Thesis was carried out during the fall of 2016 and spring of 2017, at the Department of Biomedical Engineering, in collaboration with the Division of Solid Mechanics, both at Lund University. 2 Acknowledgments I would like to thank my supervisors, Anna Gustafsson and Hanna Isaksson, for guiding and assisting me during this project, and also for giving me the opportunity to participate in some activities outside the scope of this project. I would also like to thank Stephen Hall, and the 4D Imaging Lab at the Department of Solid Mechanics, LTH, for the acquisition of the µCT images that are the basis of this project. Lastly, thank you to all the wonderful people in the Biomechanics group, you have made my time spent on this project not only educative but also enjoyable and fun.

Research paper thumbnail of A New Method for Improved Mechanical and Biological Fixation of Fracture Fixation Devices

Orthopaedic Proceedings, Apr 11, 2023

Majority of osteoporosis related fractures are treated surgically using metallic fixation devices... more Majority of osteoporosis related fractures are treated surgically using metallic fixation devices. Anchorage of fixation devices is sometimes challenging due to poor osteoporotic bone quality that can lead to failure of the fracture fixation.Using a rat osteoporosis model, we employed neutron tomography and histology to study the biological effects of implant augmentation using an isothermally setting calcium sulphate/hydroxyapatite (CaS/HA) biomaterial with synthetic HA particles as recruiting moiety for systemically administered bisphosphonates. Using an osteoporotic sawbones model, we then provide a standardized method for the delivery of the CaS/HA biomaterial at the bone-implant interface for improved mechanical anchorage of a lag-screw commonly used for hip fracture fixation. As a proof-of-concept, the method was then verified in donated femoral heads and in patients with osteoporosis undergoing hip fracture fixation.We show that placing HA particles around a stainless-steel screw in-vivo, systemically administered bisphosphonates could be targeted towards the implant, yielding significantly higher peri-implant bone formation compared to un-augmented controls. In the sawbones model, CaS/HA based lag-screw augmentation led to significant increase (up to 4 times) in peak extraction force with CaS/HA performing at par with PMMA. Micro-CT imaging of the CaS/HA augmented lag-screws in cadaver femoral heads verified that the entire length of the lag-screw threads and the surrounding bone was covered with the CaS/HA material. X-ray images from fracture fixation surgery indicated that the CaS/HA material could be applied at the lag-screw-bone interface without exerting any additional pressure or risk of venous vascular leakage.: We present a new method for augmentation of lag-screws in fragile bone. It is envisaged that this methodcould potentially reduce the risk of fracture fixation failure especially when HA seeking “bone active” drugs are used systemically.

Research paper thumbnail of The Hydration State of Bone Tissue Affects Contrast in Neutron Tomographic Images

Frontiers in Bioengineering and Biotechnology, Jun 17, 2022

Neutron tomography has emerged as a promising imaging technique for specific applications in bone... more Neutron tomography has emerged as a promising imaging technique for specific applications in bone research. Neutrons have a strong interaction with hydrogen, which is abundant in biological tissues, and they can penetrate through dense materials such as metallic implants. However, in addition to long imaging times, two factors have led to challenges in running in situ mechanical characterization experiments on bone tissue using neutron tomography: 1) the high water content in specimens reduces the visibility of internal trabecular structures; 2) the mechanical properties of bone are dependent on the hydration state of the tissue, with drying being reported to cause increased stiffness and brittleness. This study investigates the possibility of improving image quality in terms of neutron transmission and contrast between material phases by drying and rehydrating in heavy water. Rat tibiae and trabecular bovine bone plugs were imaged with neutron tomography at different hydration states and mechanical testing of the bone plugs was carried out to assess effects of drying and rehydration on the mechanical properties of bone. From analysis of image histograms, it was found that drying reduced the contrast between bone and soft tissue, but the contrast was restored with rehydration. Contrast-to-noise ratios and line profiles revealed that the contrast between bone tissue and background was reduced with increasing rehydration duration but remained sufficient for identifying internal structures as long as no free liquid was present inside the specimen. The mechanical analysis indicated that the proposed fluid exchange protocol had no adverse effects on the mechanical properties.

Research paper thumbnail of Nanoscale characterization of collagen structural responses to in situ loading in rat Achilles tendons

Matrix Biology, 2023

The specific viscoelastic mechanical properties of Achilles tendons are highly dependent on the s... more The specific viscoelastic mechanical properties of Achilles tendons are highly dependent on the structural characteristics of collagen at and between all hierarchical levels. Research has been conducted on the deformation mechanisms of positional tendons and single fibrils, but knowledge about the coupling between the whole tendon and nanoscale deformation mechanisms of more commonly injured energy-storing tendons, such as Achilles tendons, remains sparse. By exploiting the highly periodic arrangement of tendons at the nanoscale, in situ loading of rat Achilles tendons during small-angle X-ray scattering acquisition was used to investigate the collagen structural response during load to rupture, cyclic loading and stress relaxation. The fibril strain was substantially lower than the applied tissue strain. The fibrils strained linearly in the elastic region of the tissue, but also exhibited viscoelastic properties, such as an increased stretchability and recovery during cyclic loading and fibril strain relaxation during tissue stress relaxation. We demonstrate that the changes in the width of the collagen reflections could be attributed to strain heterogeneity and not changes in size of the coherently diffracting domains. Fibril strain heterogeneity increased with applied loads and after the toe region, fibrils also became increasingly disordered. Additionally, a thorough evaluation of radiation damage was performed. In conclusion, this study clearly displays the simultaneous structural response and adaption of the collagen fibrils to the applied tissue loads and provide novel information about the transition of loads between length scales in the Achilles tendon.

Research paper thumbnail of Dual modality neutron and x-ray tomography for enhanced image analysis of the bone-metal interface

Physics in Medicine and Biology, Jul 7, 2021

The bone tissue formed at the contact interface with metallic implants, particularly its 3D micro... more The bone tissue formed at the contact interface with metallic implants, particularly its 3D microstructure, plays a pivotal role for the structural integrity of implant fixation. X-ray tomography is the classical imaging technique used for accessing microstructural information from bone tissue. However, neutron tomography has shown promise for visualising the immediate bone-metal implant interface, something which is highly challenging with x-rays due to large differences in attenuation between metal and biological tissue causing image artefacts. To highlight and explore the complementary nature of neutron and x-ray tomography, proximal rat tibiae with titanium-based implants were imaged with both modalities. The two techniques were compared in terms of visualisation of different material phases and by comparing the properties of the individual images, such as the contrast-to-noise ratio. After superimposing the images using a dedicated image registration algorithm, the complementarity was further investigated via analysis of the dual modality histogram, joining the neutron and x-ray data. From these joint histograms, peaks with well-defined grey value intervals corresponding to the different material phases observed in the specimens were identified and compared. The results highlight differences in how neutrons and x-rays interact with biological tissues and metallic implants, as well as the benefits of combining both modalities. Future refinement of the joint histogram analysis could improve the segmentation of structures and tissues, and yield novel information about specimen-specific properties such as moisture content.

Research paper thumbnail of Spatio-temporal evolution of hydroxyapatite crystal thickness at the bone-implant interface

Acta Biomaterialia, Oct 1, 2020

A better understanding of bone nanostructure around the bone-implant interface is essential to im... more A better understanding of bone nanostructure around the bone-implant interface is essential to improve longevity of clinical implants and decrease failure risks. This study investigates the spatiotemporal evolution of mineral crystal thickness and plate orientation in newly formed bone around the surface of a metallic implant. Standardized coin-shaped titanium implants designed with a bone chamber were inserted into rabbit tibiae for 7 and 13 weeks. Scanning measurements with microfocused small-angle X-ray scattering (SAXS) were carried out on newly formed bone close to the implant and in control mature cortical bone. Mineral crystals were thinner close to the implant (1.8 ± 0.45 nm at 7 weeks and 2.4 ± 0.57 nm at 13 weeks) than in the control mature bone tissue (2.5 ± 0.21 nm at 7 weeks and 2.8 ± 0.35 nm at 13 weeks), with increasing thickness over healing time (+30 % in 6 weeks). These results are explained by younger bone close to the implant, which matures during osseointegration. Thinner mineral crystals parallel to the implant surface within the first 100 µm close to the implant indicate that the implant affects bone ultrastructure close to the implant, potentially due to heterogeneous interfacial stresses, and suggest a longer maturation process of bone tissue and difficulty in binding to the metal. The bone growth kinetics within the bone chamber was derived from the spatio-temporal evolution of bone tissue's nanostructure, coupled with microtomographic imaging. The findings indicate that understanding mineral crystal thickness or plate orientation can improve our knowledge of osseointegration.

Research paper thumbnail of Analysis of Bone-Implant Integration with Synchrotron X-ray Tomography

HAL (Le Centre pour la Communication Scientifique Directe), Jun 13, 2022

Research paper thumbnail of A quality optimization approach to image Achilles tendon microstructure by phase-contrast enhanced synchrotron micro-tomography

Scientific Reports, Aug 27, 2021

Achilles tendons are mechanosensitive, and their complex hierarchical structure is in part the re... more Achilles tendons are mechanosensitive, and their complex hierarchical structure is in part the result of the mechanical stimulation conveyed by the muscles. To fully understand how their microstructure responds to mechanical loading a non-invasive approach for 3D high resolution imaging suitable for soft tissue is required. Here we propose a protocol that can capture the complex 3D organization of the Achilles tendon microstructure, using phase-contrast enhanced synchrotron micro-tomography (SR-PhC-μCT). We investigate the effects that sample preparation and imaging conditions have on the resulting image quality, by considering four types of sample preparations and two imaging setups (sub-micrometric and micrometric final pixel sizes). The image quality is assessed using four quantitative parameters. The results show that for studying tendon collagen fibers, conventional invasive sample preparations such as fixation and embedding are not necessary or advantageous. Instead, fresh frozen samples result in high-quality images that capture the complex 3D organization of tendon fibers in conditions as close as possible to natural. The comprehensive nature of this innovative study by SR-PhC-μCT breaks ground for future studies of soft complex biological tissue in 3D with high resolution in close to natural conditions, which could be further used for in situ characterization of how soft tissue responds to mechanical stimuli on a microscopic level.

Research paper thumbnail of Segmentation, Analysis, and Modelling of Microstructure in Cortical Bone, based on X-ray Microtomography

The microstructure in cortical bone greatly affect the toughness of the bone and the crack propag... more The microstructure in cortical bone greatly affect the toughness of the bone and the crack propagation during fracture. The two main structural features, Haversian canals and osteons, have been previously studied in order to increase the knowledge of the biomechanics of bone. In studies where X-ray microtomography has been the imaging method of choice, the microstructure has been analysed based on manual segmentation, a method which is difficult and tedious on larger sample volumes. X-ray microtomograms, or mu\mumuCT images, are gray scale 2D images, which can be rendered into a 3D volume, where the pixel intensity corresponds to the absorption coefficient of the material in the object. Material that absorbs a lot of X-ray radiation will show up as high intensity pixel whilst material that absorbs little will show up as low intensity pixel, just as in a normal radiogram. mu\mumuCT is best used on samples containing structures with varying absorbtion properties as this will enable good c...

Research paper thumbnail of The Osteocyte Lacuno-Canalicular Network at the Bone-Implant Interphase Imaged with Focused Ion Beam -Scanning Electron Microscopy

HAL (Le Centre pour la Communication Scientifique Directe), Jun 26, 2022

Research paper thumbnail of Hydroxyapatite crystal thickness and orientation at the bone implant interface : spatial and temporal evolutions

HAL (Le Centre pour la Communication Scientifique Directe), Jun 26, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Research paper thumbnail of Systemically administered zoledronic acid activates locally implanted synthetic hydroxyapatite particles enhancing peri-implant bone formation: A regenerative medicine approach to improve fracture fixation

Acta biomaterialia, Mar 1, 2024

Research paper thumbnail of Bone-implant integration assessed using in-situ mechanical pull-out during synchrotron X-ray tomography

Research paper thumbnail of Exploratory Neutron Tomography of Articular Cartilage

Osteoarthritis and cartilage, Mar 1, 2024

Research paper thumbnail of Nanoscale Characterization of Collagen Structural Responses to <i>in Situ</i> Loading in Rat Achilles Tendons

Social Science Research Network, 2022

Research paper thumbnail of Hydroxyapatite crystal thickness and orientation at the bone implant interface : spatial and temporal evolutions

HAL (Le Centre pour la Communication Scientifique Directe), Jun 26, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Research paper thumbnail of The Osteocyte Lacuno-Canalicular Network at the Bone-Implant Interphase Imaged with Focused Ion Beam -Scanning Electron Microscopy

HAL (Le Centre pour la Communication Scientifique Directe), Jun 26, 2022

Research paper thumbnail of Comparison of small-angle neutron and X-ray scattering for studying cortical bone nanostructure

Scientific Reports, Sep 3, 2020

in this study, we present a combined small-angle neutron and X-ray scattering (SAnS and SAXS) stu... more in this study, we present a combined small-angle neutron and X-ray scattering (SAnS and SAXS) study of the nanoscale structure of cortical bone specimens from three different species. The variation of the scattering cross section of elements across the periodic table is very different for neutrons and X-rays. For X-rays, it is proportional to the electron density while for neutrons it varies irregularly with the atomic number. Hence, combining the two techniques on the same specimens allows for a more detailed interpretation of the scattering patterns as compared to a single-contrast experiment. The current study was performed on bovine, porcine and ovine specimens, obtained in two perpendicular directions with respect to the main axis of the bone (longitudinal and radial) in order to maximise the understanding of the nanostructural organisation. The specimens were also imaged with high resolution micro-computed tomography (micro-ct), yielding tissue mineral density and microstructural orientation as reference. We show that the SANS and SAXS patterns from the same specimen are effectively identical, suggesting that these bone specimens can be approximated as a two-component composite material. Hence, the observed small-angle scattering results mainly from the mineral-collagen contrast, apart from minor features associated with the internal collagen structure.

Research paper thumbnail of Mineralization of cortical bone during maturation and growth in rabbits

Journal of Bone and Mineral Metabolism, Dec 5, 2019

Introduction The composite nature of bone as a material governs its structure and mechanical beha... more Introduction The composite nature of bone as a material governs its structure and mechanical behavior. How the collagenous matrix mineralizes, in terms of both mineral deposition and structure of the mineral crystals, is highly interesting when trying to elucidate the complex structural changes that occur during bone growth and maturation. We have previously looked at mineral deposition and structural evolution of the collagenous matrix, linking both to changes in mechanics. The purpose of this study was to provide specific information on changes in crystal size and organization as a function of growth and maturation. Materials and Methods Using micro-computed tomography (µCT) and micro-focused scanning small-angle X-ray scattering (SAXS) we investigated cortical bone in two orthogonal directions relative to the long axis of the humeri of New Zealand White rabbits spanning from newborn to 6-months of age. We also investigated the changes with tissue age by looking at radial profiles of osteonal structures in the 6-months old rabbits. The findings were compared to our previous compositional, structural and mechanical data on the same sample cohort. Results µCT showed a continuous mineral deposition up until 3-months of age, whilst the SAXS data showed an increase in both crystal thickness and degree of orientation up until 6-months of age. The osteonal profiles showed no statistically significant changes in crystal thickness. Conclusions Comparison to previously collected mechanical data suggests that changes are not only explained by amount of mineral in the tissue but also by the crystal dimensions.

Research paper thumbnail of Characterization of collagen structural response to in situ loading of the rat Achilles tendon

HAL (Le Centre pour la Communication Scientifique Directe), Jul 25, 2021

The collagen response in rat Achilles tendons to in situ tensile loading was studied using small-... more The collagen response in rat Achilles tendons to in situ tensile loading was studied using small-angle X-ray scattering (SAXS), to evaluate the relationship between the elastic and viscoelastic behavior of the tissue and collagen fibrils. The fibril strains were substantially lower than the applied tissue strains. Fibril strains increased linearly before yielding and breaking prior to tissue failure.

Research paper thumbnail of Segmentation, Analysis, and Modelling of Microstructure in Cortical Bone, based on X-ray Microtomography

The microstructure in cortical bone greatly affect the toughness of the bone and the crack propag... more The microstructure in cortical bone greatly affect the toughness of the bone and the crack propagation during fracture. The two main structural features, Haversian canals and osteons, have been previously studied in order to increase the knowledge of the biomechanics of bone. In studies where X-ray microtomography has been the imaging method of choice, the microstructure has been analysed based on manual segmentation, a method which is difficult and tedious on larger sample volumes. X-ray microtomograms, or µCT images, are gray scale 2D images, which can be rendered into a 3D volume, where the pixel intensity corresponds to the absorption coefficient of the material in the object. Material that absorbs a lot of X-ray radiation will show up as high intensity pixel whilst material that absorbs little will show up as low intensity pixel, just as in a normal radiogram. µCT is best used on samples containing structures with varying absorbtion properties as this will enable good contrast between the structures. In this project, a semi-automatic method for segmenting the microstructures Haversian canals and osteons in µCT images of cortical bovine bone was implemented. Based on this segmentation, a simplified model was built for future Finite Element Modelling. K-means clustering with nine clusters was chosen as segmentation method. By identifying which clusters correspond to what pixel intensities, and hence to what tissue type, it was possible to segment out Haversian canals, and osteons in the µCT images. The simplified model was based on principal component analysis of the segmented canals in 3D, and circle fitting on Haversian canals, and osteons in 2D. The generated segmentations provided enhanced visibility of the microstructure. Based on porosity, and volume analysis, the segmentation pipeline gave good results for the Haversian canals, but was less accurate in differentiating between osteonal tissue and tissue with similar absorption properties embedded in the interstitial bone. Porosity measurements on the segmentations corresponded with previous studies. The radii of the osteons and the Haversian canals, generated by the simplified model, agreed well with previous studies, and the method overcame the issue with unclear osteonal boundaries by using the segmentation of the Haversian canals as a base. This Master's Thesis was carried out during the fall of 2016 and spring of 2017, at the Department of Biomedical Engineering, in collaboration with the Division of Solid Mechanics, both at Lund University. 2 Acknowledgments I would like to thank my supervisors, Anna Gustafsson and Hanna Isaksson, for guiding and assisting me during this project, and also for giving me the opportunity to participate in some activities outside the scope of this project. I would also like to thank Stephen Hall, and the 4D Imaging Lab at the Department of Solid Mechanics, LTH, for the acquisition of the µCT images that are the basis of this project. Lastly, thank you to all the wonderful people in the Biomechanics group, you have made my time spent on this project not only educative but also enjoyable and fun.

Research paper thumbnail of A New Method for Improved Mechanical and Biological Fixation of Fracture Fixation Devices

Orthopaedic Proceedings, Apr 11, 2023

Majority of osteoporosis related fractures are treated surgically using metallic fixation devices... more Majority of osteoporosis related fractures are treated surgically using metallic fixation devices. Anchorage of fixation devices is sometimes challenging due to poor osteoporotic bone quality that can lead to failure of the fracture fixation.Using a rat osteoporosis model, we employed neutron tomography and histology to study the biological effects of implant augmentation using an isothermally setting calcium sulphate/hydroxyapatite (CaS/HA) biomaterial with synthetic HA particles as recruiting moiety for systemically administered bisphosphonates. Using an osteoporotic sawbones model, we then provide a standardized method for the delivery of the CaS/HA biomaterial at the bone-implant interface for improved mechanical anchorage of a lag-screw commonly used for hip fracture fixation. As a proof-of-concept, the method was then verified in donated femoral heads and in patients with osteoporosis undergoing hip fracture fixation.We show that placing HA particles around a stainless-steel screw in-vivo, systemically administered bisphosphonates could be targeted towards the implant, yielding significantly higher peri-implant bone formation compared to un-augmented controls. In the sawbones model, CaS/HA based lag-screw augmentation led to significant increase (up to 4 times) in peak extraction force with CaS/HA performing at par with PMMA. Micro-CT imaging of the CaS/HA augmented lag-screws in cadaver femoral heads verified that the entire length of the lag-screw threads and the surrounding bone was covered with the CaS/HA material. X-ray images from fracture fixation surgery indicated that the CaS/HA material could be applied at the lag-screw-bone interface without exerting any additional pressure or risk of venous vascular leakage.: We present a new method for augmentation of lag-screws in fragile bone. It is envisaged that this methodcould potentially reduce the risk of fracture fixation failure especially when HA seeking “bone active” drugs are used systemically.

Research paper thumbnail of The Hydration State of Bone Tissue Affects Contrast in Neutron Tomographic Images

Frontiers in Bioengineering and Biotechnology, Jun 17, 2022

Neutron tomography has emerged as a promising imaging technique for specific applications in bone... more Neutron tomography has emerged as a promising imaging technique for specific applications in bone research. Neutrons have a strong interaction with hydrogen, which is abundant in biological tissues, and they can penetrate through dense materials such as metallic implants. However, in addition to long imaging times, two factors have led to challenges in running in situ mechanical characterization experiments on bone tissue using neutron tomography: 1) the high water content in specimens reduces the visibility of internal trabecular structures; 2) the mechanical properties of bone are dependent on the hydration state of the tissue, with drying being reported to cause increased stiffness and brittleness. This study investigates the possibility of improving image quality in terms of neutron transmission and contrast between material phases by drying and rehydrating in heavy water. Rat tibiae and trabecular bovine bone plugs were imaged with neutron tomography at different hydration states and mechanical testing of the bone plugs was carried out to assess effects of drying and rehydration on the mechanical properties of bone. From analysis of image histograms, it was found that drying reduced the contrast between bone and soft tissue, but the contrast was restored with rehydration. Contrast-to-noise ratios and line profiles revealed that the contrast between bone tissue and background was reduced with increasing rehydration duration but remained sufficient for identifying internal structures as long as no free liquid was present inside the specimen. The mechanical analysis indicated that the proposed fluid exchange protocol had no adverse effects on the mechanical properties.

Research paper thumbnail of Nanoscale characterization of collagen structural responses to in situ loading in rat Achilles tendons

Matrix Biology, 2023

The specific viscoelastic mechanical properties of Achilles tendons are highly dependent on the s... more The specific viscoelastic mechanical properties of Achilles tendons are highly dependent on the structural characteristics of collagen at and between all hierarchical levels. Research has been conducted on the deformation mechanisms of positional tendons and single fibrils, but knowledge about the coupling between the whole tendon and nanoscale deformation mechanisms of more commonly injured energy-storing tendons, such as Achilles tendons, remains sparse. By exploiting the highly periodic arrangement of tendons at the nanoscale, in situ loading of rat Achilles tendons during small-angle X-ray scattering acquisition was used to investigate the collagen structural response during load to rupture, cyclic loading and stress relaxation. The fibril strain was substantially lower than the applied tissue strain. The fibrils strained linearly in the elastic region of the tissue, but also exhibited viscoelastic properties, such as an increased stretchability and recovery during cyclic loading and fibril strain relaxation during tissue stress relaxation. We demonstrate that the changes in the width of the collagen reflections could be attributed to strain heterogeneity and not changes in size of the coherently diffracting domains. Fibril strain heterogeneity increased with applied loads and after the toe region, fibrils also became increasingly disordered. Additionally, a thorough evaluation of radiation damage was performed. In conclusion, this study clearly displays the simultaneous structural response and adaption of the collagen fibrils to the applied tissue loads and provide novel information about the transition of loads between length scales in the Achilles tendon.

Research paper thumbnail of Dual modality neutron and x-ray tomography for enhanced image analysis of the bone-metal interface

Physics in Medicine and Biology, Jul 7, 2021

The bone tissue formed at the contact interface with metallic implants, particularly its 3D micro... more The bone tissue formed at the contact interface with metallic implants, particularly its 3D microstructure, plays a pivotal role for the structural integrity of implant fixation. X-ray tomography is the classical imaging technique used for accessing microstructural information from bone tissue. However, neutron tomography has shown promise for visualising the immediate bone-metal implant interface, something which is highly challenging with x-rays due to large differences in attenuation between metal and biological tissue causing image artefacts. To highlight and explore the complementary nature of neutron and x-ray tomography, proximal rat tibiae with titanium-based implants were imaged with both modalities. The two techniques were compared in terms of visualisation of different material phases and by comparing the properties of the individual images, such as the contrast-to-noise ratio. After superimposing the images using a dedicated image registration algorithm, the complementarity was further investigated via analysis of the dual modality histogram, joining the neutron and x-ray data. From these joint histograms, peaks with well-defined grey value intervals corresponding to the different material phases observed in the specimens were identified and compared. The results highlight differences in how neutrons and x-rays interact with biological tissues and metallic implants, as well as the benefits of combining both modalities. Future refinement of the joint histogram analysis could improve the segmentation of structures and tissues, and yield novel information about specimen-specific properties such as moisture content.

Research paper thumbnail of Spatio-temporal evolution of hydroxyapatite crystal thickness at the bone-implant interface

Acta Biomaterialia, Oct 1, 2020

A better understanding of bone nanostructure around the bone-implant interface is essential to im... more A better understanding of bone nanostructure around the bone-implant interface is essential to improve longevity of clinical implants and decrease failure risks. This study investigates the spatiotemporal evolution of mineral crystal thickness and plate orientation in newly formed bone around the surface of a metallic implant. Standardized coin-shaped titanium implants designed with a bone chamber were inserted into rabbit tibiae for 7 and 13 weeks. Scanning measurements with microfocused small-angle X-ray scattering (SAXS) were carried out on newly formed bone close to the implant and in control mature cortical bone. Mineral crystals were thinner close to the implant (1.8 ± 0.45 nm at 7 weeks and 2.4 ± 0.57 nm at 13 weeks) than in the control mature bone tissue (2.5 ± 0.21 nm at 7 weeks and 2.8 ± 0.35 nm at 13 weeks), with increasing thickness over healing time (+30 % in 6 weeks). These results are explained by younger bone close to the implant, which matures during osseointegration. Thinner mineral crystals parallel to the implant surface within the first 100 µm close to the implant indicate that the implant affects bone ultrastructure close to the implant, potentially due to heterogeneous interfacial stresses, and suggest a longer maturation process of bone tissue and difficulty in binding to the metal. The bone growth kinetics within the bone chamber was derived from the spatio-temporal evolution of bone tissue's nanostructure, coupled with microtomographic imaging. The findings indicate that understanding mineral crystal thickness or plate orientation can improve our knowledge of osseointegration.

Research paper thumbnail of Analysis of Bone-Implant Integration with Synchrotron X-ray Tomography

HAL (Le Centre pour la Communication Scientifique Directe), Jun 13, 2022

Research paper thumbnail of A quality optimization approach to image Achilles tendon microstructure by phase-contrast enhanced synchrotron micro-tomography

Scientific Reports, Aug 27, 2021

Achilles tendons are mechanosensitive, and their complex hierarchical structure is in part the re... more Achilles tendons are mechanosensitive, and their complex hierarchical structure is in part the result of the mechanical stimulation conveyed by the muscles. To fully understand how their microstructure responds to mechanical loading a non-invasive approach for 3D high resolution imaging suitable for soft tissue is required. Here we propose a protocol that can capture the complex 3D organization of the Achilles tendon microstructure, using phase-contrast enhanced synchrotron micro-tomography (SR-PhC-μCT). We investigate the effects that sample preparation and imaging conditions have on the resulting image quality, by considering four types of sample preparations and two imaging setups (sub-micrometric and micrometric final pixel sizes). The image quality is assessed using four quantitative parameters. The results show that for studying tendon collagen fibers, conventional invasive sample preparations such as fixation and embedding are not necessary or advantageous. Instead, fresh frozen samples result in high-quality images that capture the complex 3D organization of tendon fibers in conditions as close as possible to natural. The comprehensive nature of this innovative study by SR-PhC-μCT breaks ground for future studies of soft complex biological tissue in 3D with high resolution in close to natural conditions, which could be further used for in situ characterization of how soft tissue responds to mechanical stimuli on a microscopic level.

Research paper thumbnail of Segmentation, Analysis, and Modelling of Microstructure in Cortical Bone, based on X-ray Microtomography

The microstructure in cortical bone greatly affect the toughness of the bone and the crack propag... more The microstructure in cortical bone greatly affect the toughness of the bone and the crack propagation during fracture. The two main structural features, Haversian canals and osteons, have been previously studied in order to increase the knowledge of the biomechanics of bone. In studies where X-ray microtomography has been the imaging method of choice, the microstructure has been analysed based on manual segmentation, a method which is difficult and tedious on larger sample volumes. X-ray microtomograms, or mu\mumuCT images, are gray scale 2D images, which can be rendered into a 3D volume, where the pixel intensity corresponds to the absorption coefficient of the material in the object. Material that absorbs a lot of X-ray radiation will show up as high intensity pixel whilst material that absorbs little will show up as low intensity pixel, just as in a normal radiogram. mu\mumuCT is best used on samples containing structures with varying absorbtion properties as this will enable good c...

Research paper thumbnail of The Osteocyte Lacuno-Canalicular Network at the Bone-Implant Interphase Imaged with Focused Ion Beam -Scanning Electron Microscopy

HAL (Le Centre pour la Communication Scientifique Directe), Jun 26, 2022

Research paper thumbnail of Hydroxyapatite crystal thickness and orientation at the bone implant interface : spatial and temporal evolutions

HAL (Le Centre pour la Communication Scientifique Directe), Jun 26, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.