InterPore2025

Measurement of permeability coefficient of biological very soft matter

21 May 2025, 09:50

15m

Oral Presentation (MS20) Biophysics of living porous media MS20

Speaker

Junghwa Hong (Dept. Control & Instrumentation Eng, Korea University)

Description

The human skeletal sponge bone is composed of hard porous materials (pore diameters of 100 to 500 $\mu$m) filled with the red marrow (BM). BM provides microenvironments for bone remodeling and hematopoietic function. BM cells form the marrow extracellular space, which is filled with intramarrow fluid (IF) and is flexible enough to allow migration, deformation, interaction, and metabolism of the BM cells. For the interaction and metabolism of BM cells, intramarrow fluid flow (IFF) must occur in the BM. The IFF is caused by pressure of sinusoids (1.78 to 2.73 kPa), which regulate intramarrow fluid pressure gradients (IFP).
The IFF is governed by permeability of the BM ($\kappa$) and the IFP. Changes in $\kappa$ could affect changes in the BM extracelluar space and IFF (IFF shear stress and BM cell migration). Therefore, changes in $\kappa$ could result in changes in structural interaction, metabolism, hematopoiesis, and osteogenesis of the BM cells. However, $\kappa$ is never measured since the BM has an extremely soft matter and is fragile in vitro.
An apparatus was applied to 16 bovine vertebral trabecular cylinders 10 mm in diameter and length to induce the caudal-cephalic IFF during compressive loading (0.3% strain). A pressure transducer was placed at the bottom of the samples to monitor IFP. Two electrodes were inserted at the bottom and top of each sample to measure the streaming potential gradient (SPG).
The measured IFP and SPG were 2500 $\pm$ 268 Pa/0.01m and 11.85 $\pm$ 3.21 mV/0.01m. The permeability was 3.82 $\times$ 10${}^{-12}$ $\pm$ 2.44 $\times$ 10${}^{-11}$ m${}^2$/Pa$\cdot$s based on the poro-electrokinetic: $\kappa$ = ${\sigma }_0$ ($\frac{\underset{―}{\mathrm{\nabla }}v}{\underset{―}{\mathrm{\nabla }}p}$)${}^2$ where ${\sigma }_0$ is BM electric conductivity of 0.17 [S/m] [Balmer, et.al, 2018], $\underset{―}{\mathrm{\nabla }}v$ is SPG [V/m], and $\underset{―}{\mathrm{\nabla }}p$ is IFP [Pa/m].
The value of $\kappa$ could depend on the stiffness, shape, and distribution of the BM cells as well as the ECM. For example, a higher proportion and clustering of adipocytes significantly reduces $\kappa$, which significantly reduces the IFF. A pathological remodeling of the ECM such as myelofibrosis could lower the value of $\kappa$, which results in changes in the fluid-to-porous solid properties of the BM. As a result, changes in $\kappa$ could cause changes in the metabolism, differentiation, proliferation, and migration of BM cells as well as the metabolism and bone remodel signaling of the osteocytes in trabeculae. It could be suggested that measuring changes in $\kappa$ using MRI [Daldrup-Link, et.al, 2000] may be used as a noninvasive early detection tool for diagnosing pathologies related to hematopoiesis and osteogenesis.