Influence of test temperature and test speed on the mechanical strength of absorbable suture anchors

Absorbable implant materials offer various advantages but are mechanically far weaker than metals. Despite known temperature dependence of the biomechanical properties of these materials, mechanical testing has almost exclusively been performed at room temperature in the literature. In this study, the difference in mechanical performance at room and body temperature was assessed in vitro at different test speeds.

Biomechanical bench study.

Five absorbable suture anchor models were held in a metallic holder and loaded under tension using 0.5-mm steel wires until failure. Testing temperature was 20 degrees C +/- 1 degrees C or 37 degrees C +/- 1 degrees C, test speed was 50 mm/min or 5 mm/min. Tensile load at failure and failure mode were recorded. To test creep behavior, a constant load of 100 N was applied, and time to failure was recorded at both temperatures.

Both raising the temperature and decreasing test speed significantly (P <.0001) impaired the mechanical performance of the tested implants. Increase of temperature (20 degrees C to 37 degrees C) resulted in a decrease of the maximal failure strength by up to 40% and decreased time to failure by up to 98% under static load. At 37 degrees, decreasing the test speed from 50 to 5 mm/min lowered the load to failure by up to 18%. Failure of the anchors always occurred by eyelet cutout of the wire.

The lower the test speed, the higher is the influence of the testing temperature. Testing of implants at room temperature instead of body temperature may falsely improve test results by a factor of up to 50 under static load. Therefore, testing absorbable implants at body temperature seems mandatory, preferably at slow test speeds.