Measurement of radial and axial forces of biliary self-expandable metallic stents.

Background: Efforts to understand the properties of self-expandable metallic stents (SEMSs) through their mechanical properties have progressed. Among them, radial force (RF) is well known as an expanding force, but axial force (AF) has not been measured before. Correlations of these properties to clinical results are not well known.

Objective: We measured RF and AF of 14 different SEMSs and discussed the results in terms of clinical implications.

Design: Experimental study.

Subjects: Measurement of RF and AF of 14 different covered and uncovered SEMSs.

Methods: RF was measured with an RF measurement machine manufactured by Machine Solution, and AF was measured with in-house equipment.

Results: Measurements of RF in the process of expansion showed characteristic patterns closely related to the structures and materials of SEMSs. Results of AF measurement can be classified into 3 groups: high, medium, and low AF, depending on the type of SEMS. AF decreased with an increase of the length of stents. A plot of RF against AF revealed 3 distinguished RF/AF combinations and indicated the importance of understanding the properties by not only RF or AF individually but also by RF/AF combination.

Limitations: In vitro study using measurement equipment.

Conclusion: It was demonstrated that a combination of RF and AF is more effective than RF or AF individually in understanding the clinical implications of SEMSs. More work is needed to correlate mechanical properties with clinical results by designing model experiments.