arXiv subjects

Alessio Gizzi

Publications and source records attributed to Alessio Gizzi.

15 recordsLinked to original sources

arXiv2026

Intestinal peristalsis and wrinkling: A novel paradigm

A new computational framework for modeling the intestinal wall as a multi-layered fiber-reinforced continuum is presented. The framework reproduces for the first time physiological motility and overcoming large-displacements limitations (self-contact and volume locking) occurring in classical hyperelastic formulations of soft tissues. We introduce: i) layer-specific functions, segregating active circumferential and longitudinal muscle fibers while maintaining homogeneous passive reinforcement, and ii) a quasi-incompressible volumetric contribution, to handle large peristaltic contractions. Cell electrophysiology is further extended to reproduce both slow waves and spike bursting activities thus mimicking for the first time a localized neural excitation in a three-dimensional geometry of small intestine segment. We introduce a spatio-temporal modulation of contractility to accurately capture activation driven by both slow waves and spike bursts. The overall coupled nonlinear electromechanical boundary valued problem is modeled following the active strain approach. A robust augmented-Lagrangian contact algorithm is also embedded to avoid self-penetration and geometrical instabilities under large displacements. The 8-variables nonlinear governing equations are then discretized using in house P1-P2-P4 finite elements codes implemented within the GetFEM library. Numerical experiments demonstrate the ability of the proposed framework to reproduce physiological peristalsis, i.e., wall contraction greater than 80%, thus allowing full occlusion matching in vivo endoscopic images, and naturally generating wrinkling patterns consistent with experimental observations. We show that an active electromechanics anisotropic heterogeneous modeling strategy is critical for a numerically stable and physiologically accurate representation of gastrointestinal motility.

physics.med-ph↗

arXiv2026

The Remodeling of Fiber Distributions in Biological Tissues: Rotation without Rotation

Collagen remodeling in living tissues exhibits anisotropic orientation patterns commonly described by Von Mises distributions, yet the physical origin of such nonequilibrium organization remains unresolved. In the present work, we demonstrate analytically that the combined action of Malthusian growth dynamics and the introduction of linear relations governing mechanical remodeling naturally gives rise to generalized bimodal Von Mises distributions as emergent states of living matter. The theory reveals a {\it rotation without rotation} mechanism, in which fibers progressively reorient in the absence of angular mechanical coupling via selective deposition and removal along preferred directions. The resulting analytical solutions quantitatively reproduce experimentally observed distributions and establish a direct mechanobiological origin for directional statistics in biological tissues. By interpreting the evolving normalized fiber density as a probability distribution function, we formulate a dynamical Shannon entropy framework that captures the temporal emergence of microstructural organization. The theory further yields closed-form expressions for the drift of the associated Fokker--Planck equation, enabling the corresponding stochastic differential equation to be derived, thus revealing that tissue remodeling is the collective outcome of noisy single-fiber dynamics. These results establish a minimal theoretical framework that connects biomechanics, stochastic processes, and nonequilibrium statistical organization in living matter.

cond-mat.soft↗

arXiv2025

Electromechanical computational model of the human stomach

The stomach plays a central role in digestion through coordinated muscle contractions, known as gastric peristalsis, driven by slow-wave electrophysiology. Understanding this process is critical for treating motility disorders such as gastroparesis, dyspepsia, and gastroesophageal reflux disease. Computer simulations can be a valuable tool to deepen our understanding of these disorders and help to develop new therapies. However, existing approaches often neglect spatial heterogeneity, fail to capture large anisotropic deformations, or rely on computationally expensive three-dimensional formulations. We present here a computational framework of human gastric electromechanics, that combines a nonlinear, rotation-free shell formulation with a constrained mixture material model. The formulation incorporates active-strain, constituent-specific prestress, and spatially non-uniform parameter fields. Numerical examples demonstrate that the framework can reproduce characteristic features of gastric motility, including slow-wave entrainment, conduction velocity gradients, and large peristaltic contractions with physiologically realistic amplitudes. The proposed framework enables robust electromechanical simulations of the whole stomach at the organ scale. It thus provides a promising basis for future in silico studies of both physiological function and pathological motility disorders.

cs.CE↗

arXiv2025

Impact of Electric Spatially Discordant Alternans on Cardiac Magnetic Field

Spatially discordant alternans (SDA) play a crucial role in cardiac arrhythmogenesis by creating steep repolarization gradients facilitating conduction block and reentry. While traditionally studied using electrical indicators, this work provides a novel perspective by characterizing SDA through their magnetic field signatures. Using a one-dimensional cardiac fiber model, we demonstrate that magnetic field measurements effectively detect SDA and temperature dependent changes in cardiac action potentials, offering a non-invasive alternative to conventional electrophysiological metrics. Our results reveal that the spatial organization of SDA is mirrored in the magnetic field distribution, with SDA nodes clearly identifiable via spatial mapping. Notably, magnetic restitution curves exhibit a distinct pattern from APD-based indicators, closely following the dynamics of the action potential upstroke. These findings establish the cardiac magnetic field as a powerful diagnostic tool for detecting SDA, opening new avenues for biomagnetic monitoring of arrhythmic risk.

physics.med-ph↗

arXiv2025

A self-contact electromechanical framework for intestinal motility

This study introduces an advanced multiphysics and multiscale modeling approach to investigate intestinal motility. We propose a generalized electromechanical framework that incorporates contact mechanics, enabling the development of a unique and innovative model for intestinal motility. The theoretical framework includes an electromechanical model coupling a microstructural material model, which describes the intestinal structure, with an electrophysiological model that captures the propagation of slow waves. Additionally, it integrates a self-contact detection algorithm based on a nearest-neighbour search and the penalty method, along with boundary conditions that account for the influence of surrounding organs. A staggered finite element scheme implemented in FEniCS is employed to solve the governing equations using the finite element method. The model is applied to study cases of moderate and severe strangulation hernia, as well as intestinal adhesion syndrome. The results demonstrate that low peristalsis takes place in the pre-strangulation zone. At the same time, very high pressure is recorded in the strangulation zone, and peristaltic contractions persisted in the healthy region. For adhesions, the results indicate a complete absence of peristalsis in the adherent region. The model successfully reproduces both qualitatively and quantitatively propagative contractions in complex scenarios, such as pre- and post-surgical conditions, thereby highlighting its potential to provide valuable insights for clinical applications.

physics.med-ph↗

arXiv2024

Magnetic Signature of Thermo-Electric Cardiac Dynamics

Developing new methods for predicting electromagnetic instabilities in cardiac activity is of primary importance. However, we still need a comprehensive view of the heart's magnetic activity at the tissue scale. To fill this gap, we present a model of soft active matter, including thermo-electric coupling, suitably modified to reproduce cardiac magnetic field. Our theoretical framework shows that periodic stimulations of cardiac cells create an external magnetic field evidencing restitution features of nonlinear cardiac dynamics and magnetic restitution curves better discriminate instabilities and bifurcations in cardiac activity. This new framework lays the foundation for innovative, non-invasive diagnostic tools for cardiac arrhythmias.

physics.med-ph↗

arXiv2024

Digital twin model of colon electromechanics for manometry prediction of laser tissue soldering

The present study introduces an advanced multi-physics and multi-scale modeling approach to investigate in silico colon motility. We introduce a generalized electromechanical framework, integrating cellular electrophysiology and smooth muscle contractility, thus advancing a first-of-its-kind computational model of laser tissue soldering after incision resection. The proposed theoretical framework comprises three main elements: a microstructural material model describing intestine wall geometry and composition of reinforcing fibers, with four fiber families, two active-conductive and two passive; an electrophysiological model describing the propagation of slow waves, based on a fully-coupled nonlinear phenomenological approach; and a thermodynamical consistent mechanical model describing the hyperelastic energetic contributions ruling tissue equilibrium under diverse loading conditions. The active strain approach was adopted to describe tissue electromechanics by exploiting the multiplicative decomposition of the deformation gradient for each active fiber family and solving the governing equations via a staggered finite element scheme. The computational framework was fine-tuned according to state-of-the-art experimental evidence, and extensive numerical analyses allowed us to compare manometric traces computed via numerical simulations with those obtained clinically in human patients. The model proved capable of reproducing both qualitatively and quantitatively high or low-amplitude propagation contractions. Colon motility after laser tissue soldering demonstrates that material properties and couplings of the deposited tissue are critical to reproducing a physiological muscular contraction, thus restoring a proper peristaltic activity.

physics.med-ph↗

arXiv2023

Phase field modelling and simulation of damage occurring in human vertebra after screws fixation procedure

The present endeavor numerically exploits the use of a phase-field model to simulate and investigate fracture patterns, deformation mechanisms, damage, and mechanical responses in a human vertebra after the incision of pedicle screws under compressive regimes. Moreover, the proposed phase field framework can elucidate scenarios where different damage patterns, such as crack nucleation sites and crack trajectories, play a role after the spine fusion procedure, considering several simulated physiological movements of the vertebral body. A convergence analysis has been conducted for the vertebra-screws model, considering several mesh refinements, which has demonstrated good agreement with the existing literature on this topic. Consequently, by assuming different angles for the insertion of the pedicle screws and taking into account a few vertebral motion loading regimes, a plethora of numerical results characterizing the damage occurring within the vertebral model has been derived. Overall, the phase field results may shed more light on the medical community, which will be useful in enhancing clinical interventions and reducing post-surgery bone failure and screw loosening.

cs.CE↗

arXiv2023

A numerical model of the human cornea accounting for the fiber-distributed collagen microstructure

We present a fiber-distributed model of the reinforcing collagen of the human cornea. The model describes the basic connections between the components of the tissue by defining an elementary block (cell) and upscaling it to the physical size of the cornea. The cell is defined by two sets of collagen fibrils running in sub-orthogonal directions, characterized by a random distribution of the spatial orientation and connected by chemical bonds of two kinds. The bonds of the first kind describe the lamellar crosslinks, forming the ribbon-like lamellae; while the bonds of the second kind describe the stacking crosslinks, piling up the lamellae to form the structure of the stroma. The spatial replication of the cell produces a truss structure with a considerable number of degrees of freedom. The statistical characterization of the collagen fibrils leads to a mechanical model that reacts to the action of the deterministic intraocular pressure with a stochastic distribution of the displacements, here characterized by their mean value and variance. The strategy to address the solution of the heavy resulting numerical problem is to use the so-called stochastic finite element improved perturbation method combined with a fully explicit solver. Results demonstrate that the variability of the mechanical properties affects in a non-negligible manner the expected response of the structure to the physiological action.

physics.bio-ph↗

arXiv2019

An orthotropic electro-viscoelastic model for the heart with stress-assisted diffusion

We propose and analyse the properties of a new class of models for the electromechanics of cardiac tissue. The set of governing equations consists of nonlinear elasticity using a viscoelastic and orthotropic exponential constitutive law (this is so for both active stress and active strain formulations of active mechanics) coupled with a four-variable phenomenological model for human cardiac cell electrophysiology, which produces an accurate description of the action potential. The conductivities in the model of electric propagation are modified according to stress, inducing an additional degree of nonlinearity and anisotropy in the coupling mechanisms; and the activation model assumes a simplified stretch-calcium interaction generating active tension or active strain. The influence of the new terms in the electromechanical model is evaluated through a sensitivity analysis, and we provide numerical validation through a set of computational tests using a novel mixed-primal finite element scheme.

math.NA↗

arXiv2018

Modelling thermo-electro-mechanical effects in orthotropic cardiac tissue

In this paper we introduce a new mathematical model for the active contraction of cardiac muscle, featuring different thermo-electric and nonlinear conductivity properties. The passive hyperelastic response of the tissue is described by an orthotropic exponential model, whereas the ionic activity dictates active contraction incorporated through the concept of orthotropic active strain. We use a fully incompressible formulation, and the generated strain modifies directly the conductivity mechanisms in the medium through the pull-back transformation. We also investigate the influence of thermo-electric effects in the onset of multiphysics emergent spatiotemporal dynamics, using nonlinear diffusion. It turns out that these ingredients have a key role in reproducing pathological chaotic dynamics such as ventricular fibrillation during inflammatory events, for instance. The specific structure of the governing equations suggests to cast the problem in mixed-primal form and we write it in terms of Kirchhoff stress, displacements, solid pressure, electric potential, activation generation, and ionic variables. We also propose a new mixed-primal finite element method for its numerical approximation, and we use it to explore the properties of the model and to assess the importance of coupling terms, by means of a few computational experiments in 3D.

q-bio.TO↗

arXiv2018

Spatiotemporal correlation uncovers fractional scaling in cardiac tissue

Complex spatiotemporal patterns of action potential duration have been shown to occur in many mammalian hearts due to a period-doubling bifurcation that develops with increasing frequency of stimulation. Here, through high-resolution optical mapping and numerical simulations, we quantify voltage length scales in canine ventricles via spatiotemporal correlation analysis as a function of stimulation frequency and during fibrillation. We show that i) length scales can vary from 40 to 20 cm during one to one responses, ii) a critical decay length for the onset of the period-doubling bifurcation is present and decreases to less than 3 cm before the transition to fibrillation occurs, iii) fibrillation is characterized by a decay length of about 1 cm. On this evidence, we provide a novel theoretical description of cardiac decay lengths introducing an experimental-based conduction velocity dispersion relation that fits the measured wavelengths with a fractional diffusion exponent of 1.5. We show that an accurate phenomenological mathematical model of the cardiac action potential, fine-tuned upon classical restitution protocols, can provide the correct decay lengths during periodic stimulations but that a domain size scaling via the fractional diffusion exponent of 1.5 is necessary to reproduce experimental fibrillation dynamics. Our study supports the need of generalized reaction-diffusion approaches in characterizing the multiscale features of action potential propagation in cardiac tissue. We propose such an approach as the underlying common basis of synchronization in excitable biological media.

physics.bio-ph↗

arXiv2017

A modeling framework for contact, adhesion and mechano-transduction between excitable deformable cells

Cardiac myocytes are the fundamental cells composing the heart muscle. The propagation of electric signals and chemical quantities through them is responsible for their nonlinear contraction and dilatation. In this study, a theoretical model and a finite element formulation are proposed for the simulation of adhesive contact interactions between myocytes across the so-called gap junctions. A multi-field interface constitutive law is proposed for their description, integrating the adhesive and contact mechanical response with their electrophysiological behavior. From the computational point of view, the initial and boundary value problem is formulated as a structure-structure interaction problem, which leads to a straightforward implementation amenable for parallel computations. Numerical tests are conducted on different couples of myocytes, characterized by different shapes related to their stages of growth, capturing the experimental response. The proposed framework is expected to have impact on the understanding how imperfect mechano-transduction could lead to emergent pathological responses.

cond-mat.soft↗

arXiv2017

A note on stress-driven anisotropic diffusion and its role in active deformable media

We propose a new model to describe diffusion processes within active deformable media. Our general theoretical framework is based on physical and mathematical considerations, and it suggests to use diffusion tensors directly coupled to mechanical stress. A proof-of-concept experiment and the proposed generalised reaction-diffusion-mechanics model reveal that initially isotropic and homogeneous diffusion tensors turn into inhomogeneous and anisotropic quantities due to the intrinsic structure of the nonlinear coupling. We study the physical properties leading to these effects, and investigate mathematical conditions for its occurrence. Together, the experiment, the model, and the numerical results obtained using a mixed-primal finite element method, clearly support relevant consequences of stress-assisted diffusion into anisotropy patterns, drifting, and conduction velocity of the resulting excitation waves. Our findings also indicate the applicability of this novel approach in the description of mechano-electrical feedback in actively deforming bio-materials such as the heart.

q-bio.TO↗

arXiv2014

On the coherent behavior of pancreatic beta cell clusters

Beta cells in pancreas represent an example of coupled biological oscillators which via communication pathways, are able to synchronize their electrical activity, giving rise to pulsatile insulin release. In this work we numerically analyze scale free self-similarity features of membrane voltage signal power density spectrum, through a stochastic dynamical model for beta cells in the islets of Langerhans fine tuned on mouse experimental data. Adopting the algebraic approach of coherent state formalism, we show how coherent molecular domains can arise from proper functional conditions leading to a parallelism with "phase transition" phenomena of field theory.

cond-mat.soft↗