Negative Poisson ratios and strain-dependent mechanical properties in arterial prostheses

Area of Science:

• Biomaterials Science
• Medical Device Engineering
• Polymer Science

Background:

• Artificial arterial prostheses are used to replace damaged or diseased vessels.
• Understanding the elastic properties of these prostheses is critical for their long-term function and integration with natural tissues.
• Existing assumptions about material behavior may not accurately reflect the performance of novel biomaterials.

Purpose of the Study:

• To measure and analyze the elastic properties of two common artificial arterial prosthesis materials: fibrillar polyurethane (PU) and expanded polytetrafluoroethylene (ex-PTFE).
• To challenge the conventional assumption of incompressibility in these synthetic materials.
• To investigate the strain-dependent behavior and through-thickness Poisson ratios of the prostheses.

Main Methods:

• Direct measurement of the elastic properties of fibrillar polyurethane and expanded polytetrafluoroethylene samples.
• Experimental determination of changes in material thickness under strain.
• Calculation of through-thickness Poisson ratios to quantify volumetric changes.

Main Results:

• The assumption of incompressibility was found to be invalid for both polyurethane and ex-PTFE arterial prostheses.
• Direct measurement of wall thickness changes is necessary for accurate elastic property assessment.
• Expanded polytetrafluoroethylene exhibited highly strain-dependent properties, including large negative through-thickness Poisson ratios (up to -11).

Conclusions:

• The elastic behavior of artificial arterial prostheses, particularly ex-PTFE, deviates significantly from idealized models.
• The incompressibility assumption is inappropriate for these materials, necessitating direct measurement of dimensional changes.
• These findings have critical implications for designing and selecting prostheses that better match the mechanical properties of natural arteries.