Multi-Axial Peripheral Stent (MAPS) Testing

Peripheral artery disease (PAD) is an atherothrombotic condition reducing blood flow to the lower limbs. In addition to vascular surgery and angioplasty, arterial stenting is a primary intervention for alleviating the effects of stenotic or occluded vessels. A significant clinical challenge in PAD is the large number of reported stent fractures that have led to reduced stent performance, in-stent restenosis vessel reocclusion, and need for re-intervention.

Figure 1. Example of the complex multi-axial loading conditions (Bending, Torsion, Extension/Contraction, Compression) that occur during leg flexion in a femoral artery.

A contributing factor to the failure of peripheral artery stents is the complex biomechanical environment for which the stents are placed. For example in the superficial femoral artery, stents can undergo pulsatile distention, axial shortening, axial elongation, bending, twisting, and pinching (Figure 1). Taking these multi-axial loading conditions into consideration during stent development is therefore critical for improving stent performance and durability. While computational simulations can provide insight into the multi-modal loading scenarios, bench top evaluations of peripheral stents have largely been restricted to isolated loading directions.

Exponent uses an ElectroForce® 9400 Multiaxial Peripheral Stent (MAPS) Test Instrument to replicate multi-axial in-vivo stent loading conditions. This system is capable of combining dynamic bending, rotation, extension/compression, and radial distention on multiple stents under controlled conditions at physiological temperature. The instrument is capable of testing an accelerated 10 year simulated life, or performing fatigue to fracture studies.

Figure 2. A. Bose Electroforce 9400 Multi-Axial Peripheral Stent (MAPS) tester; B. Eight stents can be tested within physiologically compliant vessels under simultaneous multi-axial loading as depicted in window C.

Located in Exponent’s Biomedical Engineering laboratory, this unique machine is capable of providing custom multi-axial loading for stents designed for the superficial femoral artery, femoropopliteal artery, renal artery, carotid artery, and coronaries among others. Stents may be placed in isolation or in an overlapped configuration. These capabilities can significantly enhance and accelerate stent development, evaluation, and aid in regulatory submission.

Exponent’s MAPS procedures are included on the laboratory’s accreditation to ISO 17025 (A2LA Certificate: 2561.01) and the lab conducts testing in accordance with U.S. FDA guidance and industry standards:

  • Guidance for Industry and FDA Staff - Non-Clinical Engineering Tests and Recommended Labeling for Intravascular Stents and Associated Delivery Systems
  • ASTM F2477 Standard Test Methods for in vitro Pulsatile Durability Testing of Vascular Stents
  • ASTM F2942-13 Standard Guide for In vitro Axial, Bending, and Torsional Durability Testing of Vascular Stents
  • ISO 25539 - Cardiovascular implants - Endovascular devices - Part 2: Vascular Stents.

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