Synergistic and additive effects of hydrostatic pressure and growth factors on tissue formation

Background: Hydrostatic pressure (HP) is a significant factor in the function of many tissues, including cartilage, knee meniscus, temporomandibular joint disc, intervertebral disc, bone, bladder, and vasculature. Though sutdies have been performed in assessing the role of HP in tissue biochemistry, to the best of our knowledge, not studies have demonstrated enhanced mechanical properties from HP application in any tissue. Methodology/Principal Findings: The objective of this study was to determine the effects of hydrostatic pressure (HP), with and without growth factors, on the biomechanical and biochemical properties of engineered articular cartilage constructs, using a two-phased approach. In phase 1, a 3×3 full-factorial design of HP magnitude (1, 5, 10 MPa) and frequency (0, 0.1, 1 Hz) was used, and the best two treatments were selected for use in phase II. Static HP at 5 MPa and 10 MPa resulted in significant 95% and 96% increases, respectively, in aggregate modulus (H_A), with corresponding increases in GAG content. These regimens also resulted in significant 101% and 92% increases in Young's modulus (Eγ), with corresponding increases in collagen content. Phase II employed a 3×3 full-factorial design of HP (no HP, 5 MPa static, 10 MPa static) and growth factor application (no GF, BMP-2+IGF-I, TGF-β1). The combination of 10 MPa static HP and TGF-β1 treatment had an additive effect on both H_A and E_Y, as well as a synergistic effect on collagen content. This group demonstrated a 16% increase in H_A, a 231% increase in E_Y, an 85% increase in GAG/wet weight (WW), and a 173% increase in collagen/WW, relative to control. Conclusions/Significance: To our knowledge, this is the first study to demonstrate increases in the biomechanical properties of tissue from pure HP application, using a cartilage model. Furthermore, it is the only study to demonstrate additive or synergistic effects between HP and growth factors on tissue function properties. These findings are exciting as coupling HP stimulation with growth factor application has allowed for the formation of tissue engineered constructs with biomechanical and biochemical properties spanning native-tissue values.