Conference Agenda

Rectal prolapse is a condition in which part of the rectum protrudes through the anus, significantly affecting patients' quality of life. This study aims to characterize the in vivo biomechanical properties of the posterior rectal wall using inverse finite element analysis (FEA). Two patient groups are included: one with rectal prolapse with gel and the other with pelvic prolapse without gel (control group). The goal is to quantify these properties through a minimally invasive approach, utilizing supero-inferior displacement measurements from MRI images acquired in the sagittal plane during the defecatory maneuver.

The study begins by simulating rectal prolapse using finite element analysis, modeling the stages of prolapse with properties from the literature to characterize the rectum, through hyperelastic models, and applying pressure that simulates the defecatory maneuver. These simulations provide insight into how the rectal wall deforms under prolapse conditions.

The supero-inferior displacements obtained from MRI scans are used as input in the inverse finite element analysis to optimize the mechanical parameters of the hyperelastic models. This process allows for the derivation of nonlinear and anisotropic properties of the rectal wall tissues, providing more accurate data on the resilience, elasticity, and deformability of the rectal wall.

By comparing the MRI data with simulation results, this study aims to optimize the in vivo biomechanical properties. The ultimate goal is to improve the understanding of rectal prolapse mechanics and develop personalized treatment strategies, particularly for surgical interventions.

In conclusion, this study integrates numerical simulations with clinical MRI measurements to better understand the biomechanical properties of the rectal wall in rectal prolapse patients. The findings are expected to contribute to more effective therapeutic interventions for prolapse conditions.

Traditional metallic orthopedic screws, despite their high mechanical strength and biocompatibility, often require a secondary surgical removal procedure. Bioabsorbable materials represent a compelling alternative, as they provide the necessary mechanical support during bone healing and progressively degrade in vivo. Among these, Mg-based alloys represent a promising combination of biocompatibility, cytocompatibility, biodegradability, and mechanical properties suitable for orthopedic applications. However, a major challenge of bioabsorbable medical devices lies in the controllability and predictability of their degradation rate and associated mechanical response. In such a scenario, advanced computational modeling represents an essential tool for optimizing the design and tailoring their performance in specific clinical settings. Screw degradation in biological tissue entails the solution of a moving interface problem evolving in a space-time domain. Traditional numerical methods, such as the Finite Element Method (FEM), struggle to handle these problems due to the necessity of dynamically updating the non-smooth contact surface in a complex living environment. Accordingly, alternative approaches, e.g., the phase field formulation, have been proposed but are still limited to specific applications and require a local identification of the contact boundary conditions. In the present contribution, we consider a nonlocal peridynamic formulation naturally enclosing the global solution of multi-field and multi-scale interfaces, circumventing the need to specify local contact boundary conditions and requiring ad hoc numerical procedures. In particular, we adopt and optimize the PeriFast/Corrosion scheme [1], originally developed under the assumption of constant corrosion currents, and generalize the numerical routine to handle time-varying currents proportional to the volume loss rate. We consider as a case study an M2 orthopedic screw made of Mg-10Gd alloy and submerged in a generic biologically-like electrolyte. Model tuning was performed by comparing and contrasting the computed volumetric loss with experimental results [2]. Extensive numerical analyses demonstrated the capability of the proposed PD model to capture the overall trend of the degradation process effectively. Specifically, the degraded screw geometry reveals that the corrosive attack initiates on all the wetted surfaces but affects the threading more significantly, as it is the area most exposed to the electrolyte. The study also analyses the mechanical response of the degraded screw at different time steps under axial and bending loads, thus identifying the critical conditions for orthopedics sustainability. Future studies will focus on coupling the proposed PD degradation model with approaches that simulate the simultaneous bone growth and remodeling process. This will allow to reproduce, among other aspects, individual biochemical pathways, paving the way for a patient-specific customization of these devices.

[1] L. Wang et al., «PeriFast/Corrosion: A 3D Pseudospectral Peridynamic MATLAB Code for Corrosion,» Journal of Peridynamics and Nonlocal Modeling, 2023.

[2] A. Hermann et al., «Combining peridynamic and finite element simulations to capture the corrosion of degradable bone implants and to predict their residual strength,» International Journal of Mechanical Sciences, 2022.

Pelvic Organ Prolapse (POP) is a prevalent condition among women globally, arising from weakened pelvic floor structures. Traditional surgical treatments frequently utilize synthetic meshes for reinforcement; however, these materials can cause complications such as erosion and chronic pain. Consequently, biodegradable mesh implants have emerged as promising alternatives due to their improved mechanical biocompatibility. This study investigates the mechanical properties of biodegradable polycaprolactone (PCL) meshes through experimental analyses and computational modeling, aiming to enhance their efficacy for POP repair.
The primary objective of the study is to evaluate the mechanical behavior of biodegradable PCL meshes compared to native vaginal tissue. This involves both experimental testing and numerical simulations. A key focus is assessing how different mesh geometries influence mechanical performance and validating computational models to enhance predictive accuracy for future POP repair applications.
In the methodology, biodegradable PCL meshes with quadratic and cross-shaped geometries were fabricated via melt electrowriting (MEW), with a filament thickness of 240 µm. Uniaxial tensile tests and ball burst tests were conducted on these meshes, alongside comparative tests on sow vaginal tissue. Numerical simulations using Abaqus/Explicit software were developed to replicate ball burst tests, allowing an evaluation of tissue-mesh interaction. Validation of these computational models was performed by comparing them with experimental data.
Results from ball burst testing demonstrated that biodegradable PCL meshes increased the maximum force resistance by approximately 14–20% compared to native vaginal tissue alone. Specifically, the cross-shaped mesh significantly outperformed the quadratic mesh, providing enhanced mechanical reinforcement by up to 30%. Numerical simulations closely matched the experimental results, with discrepancies of around 6% for vaginal tissue, 7% for mesh implants alone, and approximately 14% for mesh-reinforced tissue. These computational models effectively predicted mechanical behavior, indicating their potential in reducing the reliance on extensive in vivo testing.
The study concludes that biodegradable PCL meshes present a highly promising alternative to conventional synthetic meshes for POP treatment. Optimized mesh geometries significantly enhance mechanical support, potentially mitigating complications associated with current synthetic implants. Additionally, validated computational models offer a reliable framework for preclinical assessments, decreasing the dependence on animal testing and accelerating the development of future urogynecological implants. Future research should prioritize in vivo studies to evaluate long-term biocompatibility, degradation profiles, and clinical outcomes.

Understanding the mechanical properties of the spinal dura mater is essential for accurate computational modeling of the spinal cord complex. Despite its importance, characterizing this membrane poses unique challenges due to its high anisotropy, thin geometry, and sensitivity to various experimental conditions. This study present a comprehensive evaluation of how measurement technique selection and test protocols - specifically, digital image correlation (DIC) and paint application for speckle generation, crosshead displacement tracking, and preconditioning - impact the resulting mechanical parameters of human spinal dura mater.

In this experiment, spinal dura mater was collected from human donors, from which standardized samples were cut in both longitudinal and transverse orientations. Some of the specimens were coated with a high-contrast paint to enable DIC, while the remaining ones were measured conventionally, based on the crosshead displacement of a universal testing machine. In addition, selected specimens underwent preliminary cyclic loading (preconditioning). The stress in the samples was expressed in terms of I Piola-Kirchhoff stress (PK1) relative to the stretch ratio, and the results were statistically analyzed with consideration of potential demographic and anthropometric factors. Poisson’s ratio was determined from the ratio of the Hencky (logarithmic) strain measured in the transverse direction to that in the longitudinal direction.

Comparisons between crosshead displacement and DIC revealed that the choice of measurement approach significantly influences the extracted mechanical parameters. For longitudinal specimens measured by DIC, elastic moduli were up to 70% higher than values derived from crosshead data, while ultimate strain was up to 35% lower. Further, paint application itself altered tissue behavior, particularly affecting stiffness. In contrast, preconditioning did not emerge as a strong factor in modifying the stress-stretch results. After applying correction factors for these effects, we obtained averaged values for longitudinal extension of approximately 282 MPa (elastic modulus), 25 MPa (failure stress), and 1.10 (failure stretch). In the transverse orientation, these parameters were around 15.6 MPa, 1.56 MPa, and 1.12, respectively.
Notably, Poisson’s ratios ranged from about 2.6 to 4.3, underscoring the tissue’s anisotropic and potentially volume-altering behavior under load.

The findings highlight the necessity of carefully standardizing experimental protocols for testing anisotropic tissues like spinal dura mater. Methodological choices - particularly regarding strain tracking (DIC vs. crosshead), sample preparation, and paint application - can significantly influence stiffness and ultimate strain measurements. These results provide input parameters and correction guidelines for computational models, aiding in the development of more reliable simulations of spinal biomechanics.