Effect of Fluid Flow on Smooth Muscle Cells in a 3-Dimensional Collagen Gel Model

A 3D collagen gel model was developed to simulate interstitial fluid flow and to assess the importance of this flow on the biochemical production rates of vascular smooth muscle cells (SMCs). Rat aortic SMCs were suspended in type I collagen, and the gel was supported by nylon fibers that allowed a 9-cm length of the SMC-gel model to withstand 90 cm H2O differential pressure over a 6-hour period without significant compaction. Up to 1 dyne/cm2 shear stress on the suspended SMCs could be induced by the pressure-driven interstitial flow. The suspended SMCs were globular, had a diameter of ≈10 &mgr;m, and were distributed uniformly throughout the gel. The collagen fibers formed a network that was connected randomly with the surface of SMCs and nylon fibers. The diameter of the collagen fibers was ≈100 nm, and the concentration of collagen was 2.5 mg/mL. Using these parameters, fiber matrix theory predicted a Darcy permeability coefficient (Kp) of 1.22×10−8 cm2, which was close to the measured value of Kp. The production rates of prostaglandin (PG) I2 and PGE2 were used as markers of biochemical responsiveness of SMCs to fluid shear stress. Both PGI2 and PGE2 production rates under 1 dyne/cm2 shear stress were significantly elevated relative to static (no-flow) controls. The production rates, however, were ≈10 times lower than observed when the same cells were plated on collagen-treated glass slides (2D model) and exposed to the same level of shear stress by use of a rotating disk apparatus. The results indicate that interstitial flow can affect SMC biology and that SMCs are more quiescent in 3D cultures than in 2D cultures. The 3D collagen gel model should be useful for future studies of interstitial flow effects on SMC function.