An Experimental and Finite Element Protocol to Investigate the Transport of Neutral and Charged Solutes across Articular Cartilage

Summary

We propose a protocol to investigate the transport of charged and uncharged molecules across articular cartilage with the aid of recently developed experimental and numerical methods.

Abstract

Osteoarthritis (OA) is a debilitating disease that is associated with degeneration of articular cartilage and subchondral bone. Degeneration of articular cartilage impairs its load-bearing function substantially as it experiences tremendous chemical degradation, i.e. proteoglycan loss and collagen fibril disruption. One promising way to investigate chemical damage mechanisms during OA is to expose the cartilage specimens to an external solute and monitor the diffusion of the molecules. The degree of cartilage damage (i.e. concentration and configuration of essential macromolecules) is associated with collisional energy loss of external solutes while moving across articular cartilage creates different diffusion characteristics compared to healthy cartilage. In this study, we introduce a protocol, which consists of several steps and is based on previously developed experimental micro-Computed Tomography (micro-CT) and finite element modeling. The transport of charged and uncharged iodinated molecules is first recorded using micro-CT, which is followed by applying biphasic-solute and multiphasic finite element models to obtain diffusion coefficients and fixed charge densities across cartilage zones.

Introduction

Molecular transport plays a vital role in the homeostasis of articulating joints, delivery of therapeutics to articular cartilage and contrast-enhanced cartilage imaging ^1,2,3. Factors such as cartilage integration and intactness, solute charge and size as well as osmolality and concentration of bath in contact with cartilage may influence the transport rate ^4,5,6. The transport of solutes, either neutral or charged, can be different between articular cartilage zones, because each zo....

Protocol

NOTE: The protocol presented here is adopted from the experimental and computational procedures of recent research papers ^6,8,9. The protocol is illustrated in Figure 1.

The cadaveric materials were collected with permission from veterinary faculty of Utrecht University.

1. Sample and Bath Preparation

1. Drill out cylindrical osteochondral plugs (diameter of 8.5 mm) from cadaveric equine femoral condyles using custom-made drill bit (Figure 1) while spra....

Results

The representative results provided here are adopted from previous research papers ^6,8,9,16.

In OA, articular cartilage undergoes significant changes most importantly GAG loss, and collagen fibril damage ^17,18,19

Discussion

We presented an experimental protocol combined with a finite element modeling procedure to study the diffusion of neutral and charged solutes across articular cartilage. According to our recent studies, the proposed models could accurately describe the transport of both neutral (biphasic-solute) and negatively charged (multiphasic) solutes across different zones of articular cartilage ^8,9. It is widely believed that articular cartilage becomes functionally limite.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Hexabrix	Guerbet	15HX005D	Negatively-charged contrast agent
Visipaque	GE healthcare	12570511	Nuetral contrast agent
PBS (Phosphate-buffered Saline)	Life technologies	10010023	Medium
micro-CT	Perkin Elmer		Monitoring diffusion
Freezing-point osmometer	Advanced instruments		Measuring solution osmolality