Esophagus stretch tests: Biomechanics for tissue engineering and possible implications on the outcome of esophageal atresia repairs performed under excessive tension

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

The mechanical characterization of the oesophagus is essential for applications such as medical device design, surgical simulations and tissue engineering, as well as for investigating the organ's pathophysiology. However, the material response of the oesophagus has not been established ex vivo in regard to the more complex aspects of its mechanical behaviour using fresh, human tissue: as of yet, in the literature, only the hyperelastic response of the intact wall has been studied. Therefore, in this study, the layer-dependent, anisotropic, visco-hyperelastic behaviour of the human oesophagus was investigated through various mechanical tests. For this, cyclic tests, with increasing stretch levels, were conducted on the layers of the human oesophagus in the longitudinal and circumferential directions and at two different strain rates. Additionally, stress-relaxation tests on the oesophageal layers were carried out in both directions. Overall, the results show discrete properties in each layer and direction, highlighting the importance of treating the oesophagus as a multi-layered composite material with direction-dependent behaviour. Previously, the authors conducted layer-dependent cyclic experimentation on formalin-embalmed human oesophagi. A comparison between the fresh and embalmed tissue response was carried out and revealed surprising similarities in terms of anisotropy, strain-rate dependency, stress-softening and hysteresis, with the main difference between the two preservation states being the magnitude of these properties. As formalin fixation is known to notably affect the formation of cross-links between the collagen of biological materials, the differences may reveal the influence of cross-links on the mechanical behaviour of soft tissues.

Mechanical experimentation of the gastrointestinal tract: a systematic review

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 sophisticated in vivo testing methods which allow for both the layer- and direction-dependent characterisation of the GI organs. The findings of this review can also be used to identify experimental data for the readers' own constitutive or FE modelling as the experimental studies have been grouped in terms of organ (oesophagus, stomach, small intestine, large intestine or rectum), test condition (ex vivo or in vivo), number of directions studied (isotropic or anisotropic), species family (human, porcine, feline etc.), tissue condition (intact wall or layer-dependent) and the type of test performed (biaxial tension, inflation-extension, distension (pressure-diameter), etc.). Furthermore, the studies that investigated the time-dependent (viscoelastic) behaviour of the tissues have been presented.

Ultrastructural changes in esophageal tissue undergoing stretch tests with possible impact on tissue engineering and long gap esophageal repairs performed under tension

Esophageal biomechanical studies are being performed to understand structural changes resulting from stretches during repair of esophageal atresias as well as to obtain biomechanical values for tissue-engineered esophagus. The present study offers insights into ultrastructural changes after stretching of the ovine esophagus using uniaxial stretch tests. In vitro uniaxial stretching was performed on esophagi (n = 16) obtained from the abattoir within 4-6 h of 1-month-old lambs. Esophagi were divided into 4 groups (4 esophagi/group): control, Group1 (G1), Group2 (G2), Group3 (G3) stretched to 20%, 30% and 40% of their original length respectively. Force and lengthening were measured with 5 cycles performed on every specimen. Transmission electron microscopic (TEM) studies were performed on the 4 groups. During observational TEM study of the control group there were no significant differences in muscle cell structure or extracellular matrix. In all stretched groups varying degrees of alterations were identified. The degree of damage correlated linearly with the increasing level of stretch. Distance between the cells showed significant difference between the groups (control (μ = 0.41 μm, SD = 0.26), G1 (μ = 1.36 μm, SD = 1.21), G2 (μ = 2.8 μm, SD = 1.83), and G3 (μ = 3.01 μm, SD = 2.06). The diameter of the cells (control μ = 19.87 μm, SD = 3.81; G1 μ = 20.38 μm, SD = 4.45; G2 μ = 21.7 μm, SD = 6.58; G3 μ = 24.48 μm, SD = 6.69) and the distance between myofibrils (control μ = 0.23 μm, SD = 0.08; G1 μ = 0.27 μm, SD = 0.08; G2 μ = 0.4 μm, SD = 0.15; G3 μ = 0.61 μm, SD = 0.2) were significantly different as well ( p < 0.05 was considered to be significant). Esophageal stretching > 30% alters the regular intracellular and extracellular structure of the esophageal muscle and leads to disruption of intra- and extracellular bonds. These findings could provide valuable insights into alterations in the microscopic structure of the esophagus in esophageal atresias repaired under tension as well as the basis for mechanical characterization for tissue engineering of the esophagus.

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

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\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{-1}$$\end{document}-1 and 10% s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{-1}$$\end{document}-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.

Balloon dilatation complications during esophagogastric anastomotic stricture treatment under fluoroscopy: Risk factors, prevention, and management

BACKGROUND

Balloon dilatation (BD) is a common treatment for esophagogastric anastomotic stricture (EAS), but with complications. This study investigates the risk factors, prevention, and management of BD complications to provide clinical guidance.

METHODS

We retrospectively analyzed the clinical data of 378 patients with EAS treated by BD from March 2011 to June 2021. The association between esophagogastric anastomotic rupture outcome and patient and stricture characteristics and treatment were analyzed by logistic regression.

RESULTS

BD was performed 552 times and technical success, 98.0%; overall clinical success, 97.8%; major adverse events, 1.3%; minor adverse events, 9.4%; mortality, 0.3%. Logistic regression showed that age (p = 0.080), sex (p = 0.256), interval from surgery to stricture development (p = 0.817), number of dilatations (p = 0.054), cause of stricture (p ≥ 0.168), and preoperative chemotherapy (p = 0.679) were not associated with anastomotic rupture. Balloon diameter (p < 0.001), preoperative radiotherapy (p = 0.003), and chemoradiotherapy (p = 0.021) were correlated with anastomotic rupture. All patients with type I and II ruptures resumed oral feeding without developing into type III rupture. Type III rupture occurred in six cases, who resumed oral feeding after 7-21 days of nasal feeding and liquid feeding. One patient died of massive bleeding after BD.

CONCLUSIONS

Symptomatic treatment for type I and II ruptures and transnasal decompression and jejunal nutrition tubes for type III rupture, are suggested pending rupture healing. Tumor recurrence, preoperative radiotherapy, and balloon diameter affected the anastomotic rupture outcome.

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

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.

Safety and efficacy of large balloon dilatation under fluoroscopy

The maximum diameter of the balloon used for balloon dilatation(BD) of esophagogastric anastomotic stricture (EAS) is generally 20 millimeters. This study aimed to evaluate the safety and efficacy of BD under fluoroscopy, using balloons with a diameter of 25-30 millimeters. We retrospectively analyzed the data of patients with benign EAS treated by large BD (balloon diameter, 25-30 mm) under fluoroscopy. The Cox proportional hazards model (PHM) was used to identify the factors associated with stricture-free survival. The results show that a total of 127 patients were included in this study, and 204 BDs were performed. The technical success rate was 96.6%, and the clinical success rate was 99.2%. The incidence of serious adverse events was 3.4% (7/204). One patient died of massive hemorrhage during BD, and nine patients were lost to follow-up. For the remaining 117 patients, the median stricture-free survival period was 14.9 months. In multivariable analysis using the Cox PHM, only balloon diameter was significantly associated with stricture-free survival. The stricture-free survival period tended to increase as balloon diameter increased. Large BD under fluoroscopy appears to be safe and effective for the treatment of benign EAS after esophagectomy.