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If you are interested in the projects below, please contact Hanna Isaksson.

Modeling Achilles tendon loading during gait

Objective: Investigate the magnitude of loading of the Achilles tendon during gait, by modeling the hindlimb during gait.  

Approach: Physiological musculoskeletal modeling: Investigating physiological loading of the Achilles tendon fascicle using an OpenSim implementation of a Rat hindlimb / alt full rat. Investigate effects of Botox injection/muscle paralysis on the loading.

Background/Relevance/Application: The Achilles tendon transfers load between different calf muscles and the heel [1]. However, the magnitude of loading by the different calf muscles on the Achilles tendon is unknown.

Collaboration opportunities: Potential access to rat gait data [2] by Prof. M. Kersh, university of Illinois.

Figure. A) OpenSim implementation of a rat hindlimb to study muscle-tendon loading under physiological conditions B) Picture of a dissected rat Achilles tendon, displaying the separate fascicle-muscle connections C) CT image of a cross-section of a rat Achilles tendon to identify fascicles

Student background: Basic knowledge in finite computational modeling and mechanics.

Important literature:

[1] Lee AH, Elliott DM (2019) Comparative multi‐scale hierarchical structure of the tail, plantaris, and Achilles tendons in the rat. Journal of anatomy 234:252-262

[2] Song H, Polk JD, Kersh ME (2019) Rat bone properties and their relationship to gait during growth. Journal of experimental biology 222: jeb2035554

For more info, please contact: Biomechanics group, Professor Hanna Isaksson,

Towards dynamic modelling of a fall on the hip

Objective: Create a dynamic model of a human fall on the hip and obtain ground impact force and direction.    

Approach: Adjust an open access model of the human body in OpenSim ( to replicate a fall on the hip. Read out the dynamic impact forces on the hip and use this data as input for a finite element model.

Background/Relevance/Application: In our group we have developed finite element models of the proximal femur (see figure). These models have been validated against mechanical experiments. The boundary conditions in the experiments were set to replicate a fall to the side. However, no 2 falls are exactly the same. People have varying anatomies, not only affecting the strength of the femur, but also the impact during a fall. To obtain a more accurate description of the forces acting on the hip an adjustable model of a human body falling is required

Figure. Left) Finite element model of a femur with boundary conditions replicating ex vivo mechanical testing Right) Image from: [1] showing the concept of including a finite element model in a full body musculoskeletal model.

Student background: Mathematics, basic knowledge in numerical analysis or finite element modeling, and matlab (or strong knowledge in another coding language).

Important literature: [1] Martelli et al. (2014) Strain energy in the femoral neck during exercise, Journal of Biomechanics

For more info, please contact: Biomechanics group, Professor Hanna Isaksson,

Image analysis of phase contrast enhanced synchrotron X-ray tomography of human meniscus

Objective: Characterize the microstructural organization of fibers in human medial menisci statically and when dynamically compressed. Determine the meniscus microstructural response to loading by tracking fiber rearrangements during in situ loading.

Background: Osteoarthritis (OA) is a "wear-and-tear" type of degenerative arthritis that mostly occurs in people above 50 years. Knee OA is associated with the degeneration of the meniscus. The meniscus, a crescent-shaped disc of fibrocartilage that is located between the surfaces of the femur and tibia in the medial and lateral compartments of the joint. It is composed of water and specifically hierarchically arranged collagen, which serves to distribute the load in the knee.  Structural and compositional changes are known to occur in the meniscus due to OA, however, the details of how the degeneration evolves are still unknown. The wide aim of this study is to extend the current understanding of osteoarthritis by combining high resolution imaging with mechanical compression to visualize the altered response of the tissue due to degeneration at the micorscale.

Approach: The candidate will perform the analysis of static and dynamic X-ray phase contrast imaging datasets of human meniscus, acquired with the rheometer setup at the TOMCAT beamline (Paul Scherrer Institute). Focus on the analysis of fiber orientation, and how it changes along the in-situ stress-relaxation protocol applied. Possibility to correlate results to mechanical data and to perform digital image correlation to identify of micro deformations and strain distribution in the tissue.

Figure. A) Human meniscus and a 5mm plug used for imaging and in situ loading. B)setup for in situ loading at the TOMCAT beamline. C) Phase-contrast enhanced synchrotron X-ray volume showing the meniscus internal structure. D) Meniscus during compression. In plane fiber orientation and orientation distribution along the meniscus longitudinal plane.

Student background: knowledge in 3D image analysis and programing.

For more info, please contact: Biomechanics group, Professor Hanna Isaksson,

The effect of viscoelastic properties of ligaments on knee joint mechanics

Objective: Implementation of viscoelastic properties of ligaments into finite element models to estimate their effect on knee joint mechanics.

Background: Ligaments provide stability to the knee joint and play an important role in restraining motion. Knee ligaments have shown intrinsic viscoelastic properties which control the excessive motions in the joint. Simpler material representations have been implemented in 3D finite element knee joint models previously. However, ligament viscoelastic material models have not been studied in those models, and the potential effect of those properties on knee joint mechanics remains unknown.

Approach: The candidate will implement simpler material models as well as a viscoelastic material model for ligaments into a 3D finite element model using the software Abaqus. The kinematics and kinetics of the knee joint as well as cartilage stresses and strains will be evaluated for different ligament material models.

Figure. 3D finite element knee joint model with a solid representation of ligaments. Mechanical response of knee tissues can be estimated as a function of the stance phase of the gait cycle.

Student background: Basic knowledge in material physics. 

Relevant literature: 
[1] Orozco GA et al. (2018). The effect of constitutive representations and structural constituents of ligaments on knee joint mechanics. Scientific reports, (8), 2323.
[2] Räsänen L.P. et al. " Three-dimensional patient-specific collagen architecture modulates cartilage responses in the knee joint during gait." Computer Methods in Biomechanics and Biomedical Engineering 19 (2016): 1225-1240.
[3] Bonifasi-Lista. C., et. al. Viscoelastic properties of the human medial collateral ligament under longitudinal, transverse and shear loading. Journal of Orthopaedic Research, 23, (2005). 67-76.

For more info, please contact: Biomechanics group, Professor Hanna Isaksson,

Nanoscale characterization of collagen structural response to in situ loading in Achilles tendons

Objective: Quantitatively explore the axial and lateral collagen fibril responses to in situ loading in intact Achilles tendons, and their link to overall tissue behavior. 

Background/Relevance: Tendons are responsible for transducing loads from muscles to bone, allowing energy efficient movement. They can withstand high tensile loads and have complex load-dependent biomechanical properties. Their mechanical properties are linked to their hierarchical structure, with collagen as their main load bearing unit. At the nanoscale, collagen molecules periodically arrange into fibrils, which can be studied using X-ray diffraction. The mechanical responses of the nanoscale collagen fibrils and their relation to the overall tissue behavior is not yet fully understood.

Approach: In situ loading combined with small- and wide-angle X-ray scattering (SAXS/WAXS) will be conducted on intact rat Achilles tendons at coSAXS, MAX IV.  From this data, both axial and lateral fibril mechanical response as well as changes in intrafibrillar hydration during loading will be assessed. Additionally, different load rates will be used to evaluate the strain rate dependency of the fibrils. The candidate will participate in preparations before and during the beamtime. After the experiment, the candidate will use existing implementations as well as explore, develop and implement new analysis of the SAXS and WAXS data to quantify fibril strains, changes in hydration, strain rate dependency and the global tissue scale mechanical responses.

Collaboration opportunities: The work is part of a collaborative project between Lund University and MAX IV. 
Figure. Achilles tendons will be mounted in a tensile device at the coSAXS beamline, MAX IV and loaded in different loading scenarios. Simultaneously, SAXS and WAXS patterns will be recorded to study the fibril behavior. The fibril and tissue mechanical responses will be compared. 

Student background: Basic knowledge scattering and diffraction, experimental mechanics and MATLAB.

For more info, please contact: Biomechanics group, Professor Hanna Isaksson,

Automatic segmentation of cortical bone microstructure

Objective: To develop a method for segmenting osteons in high resolution images of cortical bone.

Motivation: The fracture resistance of cortical bone is closely related to the microstructure of the tissue and extrinsic toughening mechanisms arise when growing cracks interact with the osteons. In our research, we use a combination of experimental and numerical techniques to understand how the underlying microstructure is related to the fracture resistance of cortical bone tissue. To succeed, it is crucial to have a realistic description of the bone microstructure, including osteons and Haversian canals, in 3D.

Approach: In this project, high resolution tomography will be used to visualize the microstructure of cortical bone. A data set containing tomographic images of 10 different samples acquired at the 4D Imaging Lab, Division of Solid Mechanics, LTH, will be used as a starting point.

Application: The candidate will develop a protocol for segmenting osteons in cortical bone by exploring different image analysis techniques, e.g., clustering methods (Matlab) and machine learning methods (Ilastik). Different options for improving image contrast will be evaluated, e.g., using different filters and phase retrieval algorithms.

Figure. A) Cortical bone specimens with different microstructural orientations. B) Image slice of cortical bone showing the osteons. C) Hand segmentation of osteons.

Student background: Basic knowledge in image analysis.

For more info, please contact: Biomechanics group, Professor Hanna Isaksson,

Crack propagation in single bone trabeculae

Objective: Develop a computational finite element (FE) model to study damage and crack propagation in single bone trabeculae. The goal is to evaluate how the internal microstructure affects the crack path and the fracture resistance of the bone locally.

Background: Damage in trabecular bone starts as microcracks inside individual trabeculae. These are believed to be important for the overall mechanical integrity and for the remodeling of the trabecular bone tissue. Experimental studies have shown that microcracks tend to follow the internal tissue structure inside the trabeculae, however, how that affects the mechanical response or the resistance to fracture is not known.

Approach: The candidate will develop FE models of single trabeculae based on microscopy images. Starting from a homogeneous geometry, models with increasing complexity will be developed to analyze e.g. the effect of the lamellar microstructure, heterogeneous material distributions and anisotropy on crack propagation.  

Application: A modelling framework based on the extended finite element method (XFEM) in Abaqus will be used as a starting point. This framework has been previously developed in the research group and used to simulate crack propagation at the microscale in cortical bone models. Within the master’s project, alternative approaches to simulate crack propagation can also be evaluated, such as using zero-thickness cohesive elements. The results in terms of crack patterns and mechanical response will be evaluated. 

Figure. Schematic representation of project approach. A single trabecula is segmented and converted to a FE-model. The XFEM method is used to simulate crack propagation under tensile loading.  

Student background: Knowledge of finite element modeling (FHL066 or analogous course is highly valued), solid mechanics and fracture mechanics.

For more info, please contact: Biomechanics group, Professor Hanna Isaksson,

High definition 3D tracking of tendon collagen fibers

Objective: Develop a computer algorithm to 3D track fibers inside the complex Achilles tendon tissue. Determine how fiber sizes change in different regions of the tendon and under different loading conditions. Determine the (dis)continuity of fibers (which is currently under debate).

Background: Tendons are soft tissues composed of hierarchically arranged collagen fibers (30%) and water (70%). Achilles tendons are mechanoresponsive, i.e. they actively adapt to their in vivo mechanical loading environment over time. Using high-resolution tomography and automized 3D computer analysis this experiment aims to investigate how the microstructure is affected by altered in vivo mechanical loading/unloading. To date the full relationships between structure and function throughout the tendon hierarchy is yet to be elucidated. Understanding how loading influence the tendon tissue is essential to preserve a correct mechanical function of tendons which, in turns, affect the overall skeletal health. The data that will be analyzed in this project are high resolution volumesacquired by phase-contrast enhanced synchrotron X-ray tomography. To our knowledge this cutting-edge technique was never use before to study Achilles tendon structure before.

Approach: The candidate will develop and validate an algorithm to segment single fibers, calculate fiber sizes and fiber geometries, and follow fiber trajectories three-dimensionally.


Figure: A) schematic representation of an Achilles tendon. B) Phase-contrast enhanced synchrotron X-ray volume showing the tendon internal structure. C) volume rendering showing some collagen fibers.

Student background:
knowledge in 3D image analysis and programing.

For more info, please contact: Biomechanics group, Professor Hanna Isaksson,

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