Md Walid Hassan, University of Hawai‘i at Manoa
https://doi.org/10.64861/CFBS7967
Keywords: Radiation-induced fibrosis, Space radiation environment, Tissue remodeling dynamics, Acoustic radiation force, Directional anisotropy, Physics-informed modeling, Situational awareness
Abstract:
Chronic ionizing radiation during long-duration spaceflight progressively induces fibrotic tissue remodeling, a delayed mechanical consequence that onboard dosimeters cannot detect and for which no noninvasive, spaceflight-suitable monitoring tool currently exists. This paper presents a physics-informed model that maps radiation exposure history to a latent tissue remodeling state variable, r(t), through directional tissue stiffness, converting a static, single-time-point stiffness descriptor into a longitudinal representation of tissue-remodeling dynamics.
Starting from a generalized tissue balance law, we derive a mean-field remodeling ordinary differential equation (ODE) via spatial averaging and a mean-field closure, then introduce a radiation-driven source term that couples dose rate and radiation quality to the remodeling rate. A linearized constitutive mapping connects r(t) to the longitudinal and transverse directional stiffnesses and to the tissue’s degree of anisotropy, a directional-stiffness observable whose quantitative recovery from acoustic radiation force impulse peak-displacement ratios has been established by prior empirical and machine-learning methods.
An algebraic inversion recovers r(t) from degree-of-anisotropy measurements, with a first-order finite-difference estimator of the remodeling rate, dr/dt, enabling classification of tissue state as aggressive progression, mild progression, stabilized adaptation, or post-exposure recovery. A local identifiability analysis establishes parameter-recoverability conditions.
A 365-day mission and additional post-mission numerical example demonstrates all three active tissue-response regimes with quantitative verification at every computational step. A reproducible extended-time fiber-field animation translates the modeled state into localized disorganization and post-exposure realignment, providing a structural visualization of the predicted progression and recovery regimes.
Date of Conference: September 15-18, 2026
Track: Atmospherics/Space Weather