Effects of microsphere incorporation on thickness of rings cultured in growth medium. Images of rings seeded with (A) 0, (B) 0.2, or (C) 0.6 mg/106 cells and cultured in growth medium for 14 days and (D) their average wall thicknesses. Scale = 1 mm, n = 6, *p < 0.05. Values are mean ± SD. SD, standard deviation.