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Radiation enhanced diffusion in cartilages as a physical mechanism underlying radiation treatments of osteoarthritis and related disorders

Diana Shvydka, Victor Karpov

TL;DR

The paper addresses diffusion-limited transport in articular cartilage as a key factor in osteoarthritis and explores how low-dose radiotherapy can yield therapeutic benefits. It introduces radiation-enhanced diffusion (RED) as a mechanism to dramatically boost diffusivity through vacancy- and interstitial-mediated processes, with a dose-dependent rise in defect concentrations that can amplify transport by orders of magnitude. It also analyzes radiation-induced electric charge build-up, predicting strong electric fields that drive selective ionic drift and create long-lasting diffusion fluxes, potentially enabling polarity-tailored transport. The work combines physical modeling with quantitative estimates to argue that RED and charge effects could enable curative, rather than solely palliative, OA therapy under controlled irradiation, although experimental verification and objective imaging are essential to confirm these radiophysical mechanisms.

Abstract

Degradation of joint cartilages can result in osteoarthritis (OA) affecting about 10\% of the US population and responsible for significant hospitalization costs. While observations show that low dose radiation treatments (LDRT) bring improvements for a majority of OA patients, the underlying mechanism is not sufficiently understood. Here, we show how the radiation enhanced diffusion (RED) can boost the molecular transport in cartilages promoting cartilage self-healing rendering a mechanism for the observed positive LDRT effects on OA. Along with quantitative estimates for RED, we predict a related phenomenon of the electric charge build up that allows LDRT schedules promoting desirable types of molecular transports dominated by either positive or negative molecular species. Our analyses call upon further experimental verifications and clinical trials with curative rather than palliative intent. In addition to OA applications, our developed approaches can be useful for sports medicine dealing with damage or degeneration of the articular cartilages.

Radiation enhanced diffusion in cartilages as a physical mechanism underlying radiation treatments of osteoarthritis and related disorders

TL;DR

The paper addresses diffusion-limited transport in articular cartilage as a key factor in osteoarthritis and explores how low-dose radiotherapy can yield therapeutic benefits. It introduces radiation-enhanced diffusion (RED) as a mechanism to dramatically boost diffusivity through vacancy- and interstitial-mediated processes, with a dose-dependent rise in defect concentrations that can amplify transport by orders of magnitude. It also analyzes radiation-induced electric charge build-up, predicting strong electric fields that drive selective ionic drift and create long-lasting diffusion fluxes, potentially enabling polarity-tailored transport. The work combines physical modeling with quantitative estimates to argue that RED and charge effects could enable curative, rather than solely palliative, OA therapy under controlled irradiation, although experimental verification and objective imaging are essential to confirm these radiophysical mechanisms.

Abstract

Degradation of joint cartilages can result in osteoarthritis (OA) affecting about 10\% of the US population and responsible for significant hospitalization costs. While observations show that low dose radiation treatments (LDRT) bring improvements for a majority of OA patients, the underlying mechanism is not sufficiently understood. Here, we show how the radiation enhanced diffusion (RED) can boost the molecular transport in cartilages promoting cartilage self-healing rendering a mechanism for the observed positive LDRT effects on OA. Along with quantitative estimates for RED, we predict a related phenomenon of the electric charge build up that allows LDRT schedules promoting desirable types of molecular transports dominated by either positive or negative molecular species. Our analyses call upon further experimental verifications and clinical trials with curative rather than palliative intent. In addition to OA applications, our developed approaches can be useful for sports medicine dealing with damage or degeneration of the articular cartilages.
Paper Structure (6 sections, 16 equations, 3 figures)

This paper contains 6 sections, 16 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Brief survey of cartilage structures
  3. Thermal diffusion in cartilages
  4. Radiation enhanced diffusion
  5. Electric charge build-up
  6. Discussion and conclusions

Figures (3)

  • Figure 1: Schematics of a cartilage structure. Left: A cartilage cell is surrounded by extracellular matrix consisting of proteins (collagen fibers), non-proteoglycan polysaccharides (hyaluronic acid), and proteoglycan (aggrecan). Illustrations downloaded from: Biorender.com . Right: The structure of articular cartilage and the underlying subchondral bone. From articular cartilage surface to the bone there are four zones—superficial, middle, deep, and calcified. Within the zones, there are differences in the orientation of the collagen fibers, the arrangement of the chondrocytes, and the distribution of proteoglycans and their associated GAGs. Downloaded with permission from Ref. davies2019.
  • Figure 2: Sketches of two RED microscopic mechanisms. Left: vacancy mediated diffusion where an ionized atom creates Coulomb repulsion moving nearby ions to vacancy cites. $n_I$ and $n_V$ represent respectively the concentrations of ionized atoms and vacancies. Right: diffusion of ions (dashed circles) through the intersticial positions. The diffusing ions are moved by the electric forces due to a radiation ionized atoms distance $b$ away.
  • Figure 3: Representative data on RED. Left: Experimental diffusivity is compared to literature results for Cr$_2$O$_3$hagel1965 and Fe$_3$O$_4$.castle1969 Overlaid on the results is the predicted self-diffusion of oxygen by the chemical rate-theory model. Here the parameter $k^2$ represents the effect of vacancy sinks, beyond the current scope. The dose rate is described as $2\times 10^{-4}$ dpa/s. Courtesy of ref. yano2021. Right: Radiation-enhanced tracer diffusion coefficients in MgO during 2.0 MeV Kr irradiation. The thermal diffusivity is indicated for comparison. (Reproduced from Ref. sambeek1998 with the permission of AIP Publishing.) See also data from Ref. chen2020 where coefficients for nickel self-ion irradiation at steady state as functions of reverse temperature with damage rates of $10^{-2}$, $10^{-3}$, and $10^{-4}$ displacements per atom per second (dpa/s).