Effect of intermittent applications of continuous ultrasound on the viability, proliferation, morphology and matrix production of chondrocytes in 3-D matrices
Document Type Article
Published in J. Acoust. Soc. Am., Vol. 121, No. 5, Pt. 2, May 2007. Used by permission.
Chondrocytes, the cellular component of articular cartilage, have long been recognized as strain-sensitive cells, have the ability to sense mechanical stimulation through surface receptors and intracellular signaling pathways. This response has been exploited to facilitate chondrocyte culture in in vitro systems such as those that use hydrostatic pressure, dynamic compression, hydrodynamic shear, as well as low-intensity pulsed ultrasound (US). While the ability of US to influence chondrogenesis has been documented, the precise mechanisms of US induced stimulation are unclear. Thus, a critical need remains to evaluate the impact of US on chondrocytes in 3-D cultures, a necessary microenvironment for maintaining chondrocyte phenotype. Here, chondrocytes seeded in 3-D scaffolds were subjected to continuous ultrasound stimulation at several frequencies for the same number of cycles, applied twice in a 24-hour period. Non-US stimulated scaffolds served as the control. Both groups were maintained in culture for 10 days and were assayed at the conclusion of the culture period (total DNA content, morphology, and cartilage specific gene expression). Our results show that chondrocytes stimulated with continuous US for predetermined time intervals possessed 1.2 to 1.4-times higher cellular viability than the control as well as higher levels of type-II collagen and aggrecan mRNA expression.