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Biomechanics

Biomechanics - Poster Session E

Poster P10 - Computational simulation of neonatal and adult esophageal atresia repair using a bioresorbable elastomer sleeve

Saturday, October 26, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Esophageal atresia (EA), a birth defect marked by discontinuity between the proximal and distal esophagus, affects 1 in 4100 live births​[1]​. This discontinuity can be classified as short- or long-gap (>3 cm)​[2]​, and current surgical management involves primary anastomosis. There is a greater incidence of post-operative complications following long-gap primary repair such as strictures and anastomotic leakage ascribed to tension at the anastomotic site​[3]​. For short-gap repair, short-term repair outcomes and survivability have improved considerably, but long-term management into adulthood presents challenges requiring surgical interventions​[2]​. Based on our prior clinical successes with patient-specific manufacture of devices assisting soft tissue repair​[4]​, we proposed a computational model suggesting an elastomeric sleeve sutured around a primary anastomosis would further reduce anastomotic tensions compared to primary anastomosis alone​[1]​. This model utilized esophageal mechanical properties derived from adult pigs​[5]​. Although esophageal anatomy is frequently studied, there is limited data on esophageal mechanics, specifically changes with different age groups. To develop a repair strategy for EA, predicting anastomotic forces for both neonatal and adult tissue is critical. Esophageal nonlinear elasticity changes with age, impacting anastomotic tension prediction. In this study we 1) mechanically test neonatal and adult sheep tissues; 2) develop constitutive parameters ascribed to these tissues mechanics; and 3) computationally verify differences across neonatal and adult sleeve-assisted repair and the consequent anastomotic tension reduction compared to primary repair. This study uses computational modeling to estimate how mechanical property changes during growth from neonatal to adulthood would affect anastomotic tension under suture alone and suture-plus-sleeve repair.

Materials and

Methods:  Animal tissues were acquired after sacrifice procedures in accordance with Johns Hopkins and GT IACUC. Neonatal(n=2) and adult(n=3) sheep esophagi were resected and longitudinal segments (adult muscle: 20 x 5 x 800 | adult mucosa: 20 x 5 x 400 | neonatal 15 x 5 x 400) were prepared for mechanical testing. Samples were preconditioned at 1Hz and 5% strain for 30 cycles in buffered saline at 37oC. Samples were tested to failure at 5% strain. A finite element model of the uniaxial test was fit to experimental data and constitutive model parameters were derived for an incompressible nonlinear elastic Ogden one-term model (FEBio Studio v 1.8)​[6]​. The adult esophagi were modeled as a bilayer structure for the mucosa and muscle layers, while the neonatal esophagi were modeled as a single layer and ascribed to aforementioned Ogden parameters. Sutures were modeled as nonlinear elastic springs, and the sleeve was modeled as a poly(glycerol dodecanedioate) (PGD) material with an opening arc of 90 degrees using an Ogden constitutive model. Eight radial sutures were added to the models for primary anastomosis, and two mattress sutures and four radial sutures attached the sleeve to the esophageal layers. The displacement magnitude, effective LaGrangian strain, and strain energy density for each model was analyzed over 2 seconds of axial loading using the nonlinear finite element code. After running FEBio programs for the neonatal and adult suture and sleeve-augmented repair models, nodes 2 mm and 4 mm from the anastomosis were selected for two different measurements.

Results, Conclusions, and Discussions: A one-term Ogden constitutive model fit stress-strain data (r2 > 0.99) for adult muscle, adult mucosa and neonatal sheep tissues. A body force of 0.005 N and 0.003 N was applied to the adult and neonatal models respectively to simulate the tension force in the esophagus generated when pulling the ends together​[1]​. The adult tissue is stiffer compared to the neonatal, necessitating an increased body force. In future experiments, the relationship between tissue stiffness at different ages and the required body force to simulate anastomotic tension may be explored. All sleeve assisted repair models had a reduction in Lagrangian strain compared to primary anastomosis (Fig. 1A, 1C). At 2 mm, the neonatal models had an average of about 37%, 42%, and 65% reduction and at 4 mm, a 39%, 46%, and 64% reduction in displacement magnitude, effective Lagrangian strain, and strain energy density data, respectively (Fig. 1B-D). At 2 mm, the adult models had an average of about 65% (p < 0.0001), 65% (p=0.0002), and 78% (p < 0.0001) reduction in displacement magnitude, effective Lagrangian strain, and strain energy density data, respectively (Fig. 1B-D). At 4 mm, the adult models had an average of about 71%, 78%, and 87% reduction in displacement magnitude, effective Lagrangian strain, and strain energy density data, respectively (p < 0.0001) (Fig. 1B-D). Stiffer tissues benefit more with the sleeve. The reduction in displacement magnitude and strain in the sleeve-assisted models in comparison to the suture models was greater in the adults compared to the neonatal group at both distances. With the additional sleeve, the adults had similar displacement and strain data to the neonates with the sleeve (Fig. 1B-D). However, due to these initial values being higher for the adults with primary anastomosis, this led to a greater percent reduction compared to the neonates. The adult models had higher strain to failure due to its thicker, bilayer structure combined with stiffer nonlinear elastic properties. Overall, tissue structure and material properties due to age can significantly impact the mechanics of repair and should therefore be considered when developing EA repair mechanisms.

Acknowledgements (Optional):  Funded in part by NIHR21HD110874-02
​​1. Ramaraju H, et al . J Mech Behav Biomed Mater 2022;133:105349.
​2. Hamilton-Hall MN, et al. J Pediatr Surg 2023;58(6):1213–8.
​3. Chang EY et al. J Korean Surg Soc 2012;83(1):43–9.
​4. Les AS, et al. Laryngoscope 2019;129(8):1763–71.
​5. Sommer G, et al. Acta Biomater 2013;9(12):9379–91.
​6. Maas SA, et al. FEBio. J Biomech Eng 2012;134(1).