Figure 9.

Effect of collagen polymerization on acoustic attenuation (a) Aliquots of soluble collagen solution (2.0 mg ml⁻¹, solid lines) or vehicle control (dashed lines) were prepared under either neutralized (red, DMEM) or acidic (black, 0.02 N acetic acid in PBS) conditions. Cold samples were placed in a 4-cm long cylindrical sample holder with Saran membranes on either side. Acoustic attenuation measurements were obtained by a pulse-echo technique using a 28 ns ultrasound pulse (38 MHz center frequency) reflected by a steel disk placed at the bottom of the propagation path. The amplitude of the signal received from the reflector was recorded every 30 s and plotted beginning 6 min after sample addition (e.g., prior to collagen polymerization), as the normalized mean ± SEM for n ⩾ 3 replicates per condition. (b) Echo amplitude at 20 min normalized to initial amplitude (6 min) for vehicle control (white), or 2.0 mg ml⁻¹ collagen (black) samples. Data are presented as mean ± SEM for n ⩾ 3 replicates per condition. Significantly different means, *P < 0.05 by t-test with Holm-Sidak’s post-hoc test for multiple comparisons.