Direct Measurment of the Osmotic Pressure of Glycosaminoglycan Solutions at Roomtemperature in Sodium Chloride

INTRODUCTION: Articular cartilage, the load bearing material of synovial joints, can normally withstand loads reaching several times body weight. The presence of proteoglycans in cartilage causes it to swell and enhances its ability to bear compressive load. Previo us studies have measured the osmotic pressure of chondroitin sulfate (CS), the most abundant glycosaminoglycan (GAG) found in cartilage either by sedimentation methods [1] or by equilibration against uncharged macromolecules such as polyethylene glycol, PEG [2-4]. The goal of this study is to measure the osmotic pressure of CS solutions directly with a recently developed custom membrane osmometer [5]. The osmotic pressure of CS solutions in the presence of varying ionic strengths of NaCl is measured at 25°C and compared to ideal Donnan law. The contribution of osmotic pressure to the compressive stiffness of cartilage is estimated from these measurements. Measurements on PEG are also performed to validate this design and technique against prior measurements in the literature.