The effect of dynamic shear force on chondrocyte biosynthesis in agarose gels

Abstract

The dense extracellular matrix (ECM) within the articular cartilage derives its compressive modulus from the electrostatic and osmotic interactions between highly charged glycosaminoglycan (GAG) chains. Furthermore, the structural integrity of the ECM comes from the tightly interwoven collagen network, which accounts for the tensile and shear stiffness of the cartilage. Due to the avascular, aneural, and alymphatic nature of cartilage, its native cells (chondrocytes) have limited regeneration capabilities after injury. Previous investigators discovered that dynamic compressive loading can increase cell biosynthesis in cartilage explants as well as in hydrogels such as agarose and self-assembling peptides. Also, recent research has revealed that biosynthesis in cartilage explants can be increased by dynamic tissue shear loading as well. Thus, the purpose of this study was to investigate whether dynamic tissue shear loading could affect chondrocyte biosynthesis in agarose gels. Chondrocytes from 1-2 week old bovine knee cartilage were seeded into 3% agarose gel slabs, and 2-mm thick by 4-mm diameter cylindrical disks were cored from these gels. Groups of disks were maintained in free swelling control culture, or subjected to 5% static compression control, or 3% sinusoidal shear strain (0.1 Hz) superimposed on a 5% static compressive offset.

(cont.) After loading, specimens were examined to measure total GAG concentration and DNA content (cell number) over the days of culture + 24 hours of loading. However, the rate of GAG synthesis using ³⁵S-sulfate and the rate of protein synthesis using ³H-proline were only observed for the 24 hours of loading. We found that on any given day during a time course study, dynamic shear loading caused a statistically significant increase in chondrocyte biosynthesis when compared to the controls. The data suggests that the effect of dynamic shear loading on biosynthesis can be optimized by considering factors such as the state of the cell-gel construct, the supplements added to the culture medium, and the shear loading protocol. In conclusion, the experiments, presented in this study, show that dynamic tissue shear loading, which isolates mechanical deformation from fluid flow, also has the potential to stimulate chondrocyte biosynthesis of GAG and protein in tissue engineered hydrogel scaffolds.