Frequency dependent radial compliance of latex tubing

Custom latex tubing is often used in medical device evaluation. Examples include thin-walled devices used to reduce leakage of porous vascular grafts, and thicker-walled prototypes used as mechanically equivalent synthetic arteries. Medical devices such as stents and balloons are introduced into these for mechanically comparable in vitro testing. The three-dimensional mechanical properties of these tubes are critically important, particularly in accelerated testing, since they are primarily designed to replicate the mechanical rather than biological properties of in vivo arteries. This paper explores the instrumentation and protocols necessary to evaluate the frequency dependent radial compliance of precision built latex tubing. Five cm long samples of custom dipped latex tubing 6 mm in diameter with wall thickness from 0.015" to 0.033" were kept dry or soaked in 37 degrees C phosphate buffered saline for 48 or 96 hours before being mounted on a dynamic internal compliance tester. Each tube was tested initially at 70 bpm to establish the internal radial compliance at the physiologically relevant rate. The frequency of the test was then increased incrementally and the radial compliance re-checked. In the most extreme case, tubes were tested up to 2700 bpm. In each case, the volume, pressure, and length of the tube was monitored continuously.