Optimizing the tensile properties of polyvinyl alcohol hydrogel for the construction of a bioprosthetic heart valve stent

Abstract

Although bioprosthetic heart valves offer the benefits of a natural opening and closing, better hemodynamics, and avoidance of life-long anticoagulant therapy, they nevertheless tend to fail in 10-15 years from tears and calcification. Several authors, including the present ones, have identified the rigid stent as a factor contributing to these failures. The ultimate solution is an artificial heart valve that has mechanical properties that allow it to move in conformity with the aortic root during the cardiac cycle, has superior hemodynamics, is nonthrombogenic, will last more than 20 years, and mitigates the need for anticoagulants. We have identified a polymer, polyvinyl alcohol (PVA) hydrogel, that has mechanical properties similar to soft tissue. The purpose of this research is to match the tensile properties of PVA to the porcine aortic root and to fabricate a stent prototype for a bioprosthetic heart valve with the use of the PVA hydrogel. Specimens of 15% w/w PVA were prepared by processing through 1-6 cycles of freezing (-20 degrees C) at 0.2 degrees C/min freeze rate and thawing (+20 degrees C) at different thawing rates (0.2 degrees C/min and 1 degrees C/min), for different holding times (1 and 6 h) at -20 degrees C. Subsequently tensile tests and stress-relaxation tests were conducted on the specimens. The different holding times at -20 degrees C demonstrated no difference in the result. The slower thawing rate improved the tensile properties but did not produce significant changes on the stress-relaxation properties. The nonlinear stress-strain curve for the PVA after the fourth freeze-thaw cycle matched the porcine aortic root within the physiological pressure range. The stress-relaxation curve for PVA also approximated the shape of the aortic root. The complex geometry of an artificial heart valve stent was successfully injection molded. These results, in combination with other preliminary findings for biocompatibility and fatigue behavior, suggest that PVA hydrogel is a promising biomaterial for implants, catheters, and artificial skin.

SANS Characterization of an Anisotropic Poly(vinyl alcohol) Hydrogel with Vascular Applications

“…15,17,18 SANS Data Analysis. 2-D patterns of absolute scattering intensity were obtained for each sample and each q range.…”

“…[11][12][13][14] The mechanical properties of PVA are similar to the characteristics of soft tissues, displaying an exponential stress-strain curve that can be altered by changing several physical cross-linking parameters. 15, 16 Wan et al 15 reported PVA samples that matched the circumferential direction in porcine aortic root up to 35% strain. Millon et al 17 reported a PVA-bacterial cellulose nanocomposite that was able to closely match the mechanical properties of porcine aorta in either circumferential or axial directions up to 70% strain as well as a nanocomposite with high composition of both components which fell within the range displayed by heart valve tissues.…”

Measurements of Dynamic Viscoelasticity of Poly (vinyl alcohol) Hydrogel for the Development of Blood Vessel Biomodeling

“…Such factors may influence the motion of the biomodeling when there is pulsatile flow in its lumen, as may the mechanical interaction between the biomodeling and the interventional devices during the training of endovascular intervention. Methods of representing these factors of a blood vessel with PVA-H have been reported by Wan et al (23) and Millon et al (24), (25) . Wan et al first indicated that PVA-H can represent the nonlinearity of a blood vessel in a tensile test by performing freeze-thaw cycles, which is a method in which PVA gel is repeatedly frozen and thawed.…”

Development of a Vessel-Mimicking Material for use in Anatomically Realistic Doppler Flow Phantoms

“…The strain applied to the uniaxial S2-shaped PVA-C + BC samples was optically measured using the extensometer on the Zwick tensile testing machine by tracking the two reflective points to the sample. The system was fitted with a 50 N load cell and a comprehensive uniaxial test protocol was developed which incorporated methodology utilized by Wan et al (2002), Dineley et al (2006) and Fromageau et al (2007) to mechanically characterize the PVA-C samples. A feed rate of 5 mm min -1 , which was common to all three studies, was selected and the samples prepared from each freeze-thaw cycle were subjected to 6 stress strain cycles to a maximum displacement of 80 % of the gauge length.…”