Ciara Durcan

Ex vivo experimental investigations and modelling of the layer-dependent, anisotropic, visco-hyperelastic behaviour of the human oesophagus

Characterization of the layer, direction and time-dependent mechanical behaviour of the human oesophagus and the effects of formalin preservation

Journal of the Royal Society interface, Apr 1, 2024

An In Silico-Based Investigation on Anisotropic Hyperelastic Constitutive Models for Soft Biological Tissues

Archives of Computational Methods in Engineering, Jul 24, 2023

Experimental investigations of the human oesophagus: anisotropic properties of the muscular layer in large deformation

bioRxiv (Cold Spring Harbor Laboratory), Jul 19, 2021

Technological advancements in the field of robotics have led to endoscopic biopsy devices able to... more Technological advancements in the field of robotics have led to endoscopic biopsy devices able to extract diseased tissue from between the layers of the gastrointestinal tract. Despite this, the layer-dependent properties of these tissues have yet to be mechanically characterised using human tissue. In this study, the ex vivo mechanical properties of the passive muscularis propia layer of the human oesophagus were extensively investigated. For this, a series of uniaxial tensile tests were conducted. The results displayed hyperelastic behaviour, while the differences between loading the tissue in both the longitudinal and circumferential directions showcased its anisotropy. The anisotropy of the muscular layer was present at different strain rates, with the longitudinal direction being consistently stiffer than the circumferential one. The circumferential direction was found to have little strain-rate dependency, while the longitudinal direction results suggest pronounced strain-rate-dependent behaviour. The repeated trials showed larger variation in terms of stress for a given strain in the longitudinal direction compared to the circumferential direction. The possible causes of variation between trials are discussed, and the experimental findings are linked to the histological analysis which was carried out via various staining methods. Finally, the direction-dependent experimental data was simulated using an anisotropic, hyperelastic model.

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An in silico-based review on anisotropic hyperelastic constitutive models for soft biological tissues

arXiv (Cornell University), Jul 28, 2022

We review nine invariant and dispersion-type anisotropic hyperelastic constitutive models for sof... more We review nine invariant and dispersion-type anisotropic hyperelastic constitutive models for soft biological tissues based on their fitting performance to experimental data from three different human tissues. For this, we used a hybrid multi-objective optimization procedure. A genetic algorithm is devised to generate the initial guesses followed by a gradient-based search algorithm. The constitutive models are then fit to a set of uniaxial and biaxial tension experiments conducted on tissues with differing fiber orientations. For the in silico investigation, experiments conducted on aneurysmatic abdominal aorta, linea alba, and rectus sheath tissues are utilized. Accordingly, the models are ranked with respect to an objective normalized quality of fit metric. Finally, a detailed discussion is carried out on the fitting performance of each model. This work provides a valuable quantitative comparison of various anisotropic hyperelastic models, the findings of which can aid those modeling the behavior of soft tissues in selecting the best constitutive model for their particular application.

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Experimentation and modelling of the human oesophagus

The oesophagus is a primarily mechanical organ which transports food from the pharynx to the stom... more The oesophagus is a primarily mechanical organ which transports food from the pharynx to the stomach through a series of muscular contractions. As of yet, the passive mechanical properties of the human oesophagus have not been established [1]. This is essential for proper investigation into how clinical diseases affect the oesophagus' primary function. Further to this, mechanical data on the oesophagus has applications within tissue engineering [2], and computational models formed from this data can be used to enhance medical device design and surgical simulations [3]. Currently, the vast majority of ex vivo experimentation on the oesophagus has been carried out using animal tissue [2]. While this may give a good representation of how human tissue might behave, it cannot be used to accurately model the human oesophagus for applications within medicine. The oesophagus is one of the few visceral organs that can be separated into two distinct layers; the mucosa-submucosa and the muscularis propria. Currently, outside of this author's work [4], the human oesophagus has not been studied in regard to its layerdependent properties. This work investigates the layer-dependent properties through a series of increasing deformation level cyclic tests performed under uniaxial tension. First, the oesophagus was explanted by means of dissection. Next, the organ was separated into the two main layers. Specimens were then tested in both the longitudinal and circumferential directions to observe any anisotropy. The cyclic tests were conducted at two different strain rates and included two cycles per deformation level to observe the pre-conditioning behaviour. The results displayed anisotropic behaviour, with greater stiffness in the longitudinal direction than the circumferential direction for both of the layers. The mucosa-submucosa was found to be stiffer than the muscularis propria layer in both directions. The observed behaviours were then modelled using two different models. For the first, the first loading path of each deformation level was extracted and an anisotropic, hyperelastic matrix-fibre model based on histological observations was used to simulate the hyperelastic behaviour. Next, the viscoelastic behaviour and stress-softening of the tissue were captured through modelling of the cyclic testing results. Both models produced a good fit with the experimental data.

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Experimental investigations of the human oesophagus: anisotropic properties of the embalmed mucosa–submucosa layer under large deformation

Biomechanics and Modeling in Mechanobiology, Aug 28, 2022

Mechanical characterisation of the layer-specific, viscoelastic properties of the human oesophagu... more Mechanical characterisation of the layer-specific, viscoelastic properties of the human oesophagus is crucial in furthering the development of devices emerging in the field, such as robotic endoscopic biopsy devices, as well as in enhancing the realism, and therefore effectiveness, of surgical simulations. In this study, the viscoelastic and stress-softening behaviour of the passive human oesophagus was investigated through ex vivo cyclic mechanical tests. Due to restrictions placed on the laboratory as a result of COVID-19, only oesophagi from cadavers fixed in formalin were allowed for testing. Three oesophagi in total were separated into their two main layers and the mucosa-submucosa layer was investigated. A series of uniaxial tensile tests were conducted in the form of increasing stretch level cyclic tests at two different strain rates: 1% s −1 and 10% s −1. Rectangular samples in both the longitudinal and circumferential directions were tested to observe any anisotropy. Histological analysis was also performed through a variety of staining methods. Overall, the longitudinal direction was found to be much stiffer than the circumferential direction. Stress-softening was observed in both directions, as well as permanent set and hysteresis. Strain rate-dependent behaviour was also apparent in the two directions, with an increase in strain rate resulting in an increase in stiffness. This strain rate dependency was more pronounced in the longitudinal direction than the circumferential direction. Finally, the results were discussed in regard to the histological content of the layer, and the behaviour was modelled and validated using a visco-hyperelastic matrix-fibre model.

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Experimental investigations of the human oesophagus: anisotropic properties of the embalmed muscular layer under large deformation

Biomechanics and Modeling in Mechanobiology, Apr 27, 2022

The oesophagus is a primarily mechanical organ whose material characterisation would aid in the i... more The oesophagus is a primarily mechanical organ whose material characterisation would aid in the investigation of its pathophysiology, help in the field of tissue engineering, and improve surgical simulations and the design of medical devices. However, the layer-dependent, anisotropic properties of the organ have not been investigated using human tissue, particularly in regard to its viscoelastic and stress-softening behaviour. Restrictions caused by the COVID-19 pandemic meant that fresh human tissue was not available for dissection. Therefore, in this study, the layer-specific material properties of the human oesophagus were investigated through ex vivo experimentation of the embalmed muscularis propria layer. For this, a series of uniaxial tension cyclic tests with increasing stretch levels were conducted at two different strain rates. The muscular layers from three different cadaveric specimens were tested in both the longitudinal and circumferential directions. The results displayed highly nonlinear and anisotropic behaviour, with both time-and history-dependent stress-softening. The longitudinal direction was found to be stiffer than the circumferential direction at both strain rates. Strain rate-dependent behaviour was apparent, with an increase in strain rate resulting in an increase in stiffness in both directions. Histological analysis was carried out via various staining methods; the results of which were discussed with regard to the experimentally observed stress-stretch response. Finally, the behaviour of the muscularis propria was simulated using a matrix-fibre model able to capture the various mechanical phenomena exhibited, the fibre orientation of which was driven by the histological findings of the study.

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Mechanical experimentation of the gastrointestinal tract: a systematic review

Biomechanics and Modeling in Mechanobiology

The gastrointestinal (GI) organs of the human body are responsible for transporting and extractin... more The gastrointestinal (GI) organs of the human body are responsible for transporting and extracting nutrients from food and drink, as well as excreting solid waste. Biomechanical experimentation of the GI organs provides insight into the mechanisms involved in their normal physiological functions, as well as understanding of how diseases can cause disruption to these. Additionally, experimental findings form the basis of all finite element (FE) modelling of these organs, which have a wide array of applications within medicine and engineering. This systematic review summarises the experimental studies that are currently in the literature (n = 247) and outlines the areas in which experimentation is lacking, highlighting what is still required in order to more fully understand the mechanical behaviour of the GI organs. These include (i) more human data, allowing for more accurate modelling for applications within medicine, (ii) an increase in time-dependent studies, and (iii) more sophi...

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An In Silico-Based Investigation on Anisotropic Hyperelastic Constitutive Models for Soft Biological Tissues

Archives of Computational Methods in Engineering

An in silico-based review on anisotropic hyperelastic constitutive models for soft biological tissues

Cornell University - arXiv, Jul 28, 2022

We review nine invariant and dispersion-type anisotropic hyperelastic constitutive models for sof... more We review nine invariant and dispersion-type anisotropic hyperelastic constitutive models for soft biological tissues based on their fitting performance to experimental data from three different human tissues. For this, we used a hybrid multi-objective optimization procedure. A genetic algorithm is devised to generate the initial guesses followed by a gradient-based search algorithm. The constitutive models are then fit to a set of uniaxial and biaxial tension experiments conducted on tissues with differing fiber orientations. For the in silico investigation, experiments conducted on aneurysmatic abdominal aorta, linea alba, and rectus sheath tissues are utilized. Accordingly, the models are ranked with respect to an objective normalized quality of fit metric. Finally, a detailed discussion is carried out on the fitting performance of each model. This work provides a valuable quantitative comparison of various anisotropic hyperelastic models, the findings of which can aid those modeling the behavior of soft tissues in selecting the best constitutive model for their particular application.

Download

Mechanical Characterisation of the Human Oesophagus

Experimentation and modelling of the human oesophagus

The oesophagus is a primarily mechanical organ which transports food from the pharynx to the stom... more The oesophagus is a primarily mechanical organ which transports food from the pharynx to the stomach through a series of muscular contractions. As of yet, the passive mechanical properties of the human oesophagus have not been established [1]. This is essential for proper investigation into how clinical diseases affect the oesophagus’ primary function. Further to this, mechanical data on the oesophagus has applications within tissue engineering [2], and computational models formed from this data can be used to enhance medical device design and surgical simulations [3]. Currently, the vast majority of ex vivo experimentation on the oesophagus has been carried out using animal tissue [2]. While this may give a good representation of how human tissue might behave, it cannot be used to accurately model the human oesophagus for applications within medicine. The oesophagus is one of the few visceral organs that can be separated into two distinct layers; the mucosa-submucosa and the muscul...

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Experimental investigations of the human oesophagus: anisotropic properties of the muscular layer in large deformation

by Ciara Durcan and Mokarram Hossain

Technological advancements in the field of robotics have led to endoscopic biopsy devices able to... more Technological advancements in the field of robotics have led to endoscopic biopsy devices able to extract diseased tissue from between the layers of the gastrointestinal tract. Despite this, the layer-dependent properties of these tissues have yet to be mechanically characterised using human tissue. In this study, the ex vivo mechanical properties of the passive muscularis propia layer of the human oesophagus were extensively investigated. For this, a series of uniaxial tensile tests were conducted. The results displayed hyperelastic behaviour, while the differences between loading the tissue in both the longitudinal and circumferential directions showcased its anisotropy. The anisotropy of the muscular layer was present at different strain rates, with the longitudinal direction being consistently stiffer than the circumferential one. The circumferential direction was found to have little strain-rate dependency, while the longitudinal direction results suggest pronounced strain-rate...

Download

Experimental investigations of the human oesophagus: anisotropic properties of the embalmed mucosa–submucosa layer under large deformation

Biomechanics and Modeling in Mechanobiology

Mechanical characterisation of the layer-specific, viscoelastic properties of the human oesophagu... more Mechanical characterisation of the layer-specific, viscoelastic properties of the human oesophagus is crucial in furthering the development of devices emerging in the field, such as robotic endoscopic biopsy devices, as well as in enhancing the realism, and therefore effectiveness, of surgical simulations. In this study, the viscoelastic and stress-softening behaviour of the passive human oesophagus was investigated through ex vivo cyclic mechanical tests. Due to restrictions placed on the laboratory as a result of COVID-19, only oesophagi from cadavers fixed in formalin were allowed for testing. Three oesophagi in total were separated into their two main layers and the mucosa–submucosa layer was investigated. A series of uniaxial tensile tests were conducted in the form of increasing stretch level cyclic tests at two different strain rates: 1% s$$^{-1}$$ - 1 and 10% s$$^{-1}$$ - 1 . Rectangular samples in both the longitudinal and circumferential directions were tested to observe a...

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Experimental investigations of the human oesophagus: anisotropic properties of the embalmed muscular layer under large deformation

Biomechanics and Modeling in Mechanobiology, Apr 27, 2022

The oesophagus is a primarily mechanical organ whose material characterisation would aid in the i... more The oesophagus is a primarily mechanical organ whose material characterisation would aid in the investigation of its pathophysiology, help in the field of tissue engineering, and improve surgical simulations and the design of medical devices. However, the layer-dependent, anisotropic properties of the organ have not been investigated using human tissue, particularly in regard to its viscoelastic and stress-softening behaviour. Restrictions caused by the COVID-19 pandemic meant that fresh human tissue was not available for dissection. Therefore, in this study, the layer-specific material properties of the human oesophagus were investigated through ex vivo experimentation of the embalmed muscularis propria layer. For this, a series of uniaxial tension cyclic tests with increasing stretch levels were conducted at two different strain rates. The muscular layers from three different cadaveric specimens were tested in both the longitudinal and circumferential directions. The results displayed highly nonlinear and anisotropic behaviour, with both time-and history-dependent stress-softening. The longitudinal direction was found to be stiffer than the circumferential direction at both strain rates. Strain rate-dependent behaviour was apparent, with an increase in strain rate resulting in an increase in stiffness in both directions. Histological analysis was carried out via various staining methods; the results of which were discussed with regard to the experimentally observed stress-stretch response. Finally, the behaviour of the muscularis propria was simulated using a matrix-fibre model able to capture the various mechanical phenomena exhibited, the fibre orientation of which was driven by the histological findings of the study.

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