The goal of the project is to study the failure modes of a novel textile heart valve prothesis dedicated to non invasive implantation. The project adresses 2 issues: 1/ the mechanical behavior of the valve under accelerated cyclic loading 2/the behavior of the textile material in vivo.
Non invasive aortic valve implantation has become an alternative technique to surgical valve replacement in patients with high risk for open chest surgery. With over 100 000 procedures already performed clinically, the technology is expected to be extended to less critical patients in a coming future. Biological valve tissue is however fragile material when folded for low diameter catheter insertion purpose. Textile polyester is less fragile material, which could be an alternative solution to replace valve leaflets. However, no result is available today about the long term behavior of fabric used as heart valve material. The purpose of the present project is to assess the degradation modes of textile from both a mechanical and biological point of view. Different fabrics were solicited in vitro under fatigue conditions and implanted in vivo in sheep models. The results analysis helps comparing the different fabrics and identify, which textile construction provides the best results.
In vitro tests were carried out using a commercial heart valve fatigue tester. Valve prototypes were manufactured with different designs using a dedicated sample weaving machine. The parameters that vary from one prototype to the other are the following: construction (plain weave, twill, satin), saturation index, yarn type (mono or multifilament), calendering level, surface treatment. Cycling was performed at 13 Hz up to material rupture. Rupture modes have been studied for each prototype at macroscopic and microscopic levels. Moreover, the changes in the mechanical properties were analyzed as well by comparing the strength of some materials before and after cycling.
Regarding the In Vivo tests, these were carried out on sheep models considering a 6 months implantation time. After that period of time, the animals were sacrificed and histological analysis was performed on the prototypes for comparison purpose. In particular 2 aspects were studied: (1) calcification level, (2) fibrin deposition. Actually, these 2 substances are critical for the valve durability.
The first fatigue tests performed on multifilament material allowed reaching 200 Mio cycles. It appears that the material seems to adapt to the applied stress. The textile structure relaxes with cycling, while yarns tend to flatten in order to limit inter-filament friction. Conversely, monofilament and calendered constructions underwent degradations after 50 Mio cycles, while non woven material was ruptured already after 5 Mio cycles. Mechanical characterization of these materials underline that ruptures are friction ruptures in the calendered construction, and flexure fatigue in the monofilament. With regard to the in vivo behavior, 6 months survival time has been reached successfully with several prototypes.It will now be possible,from the obtained results, to develop a specific textile construction more adapted to the effective need.
The obtained results demonstrate that the valve durability depends on the fabric contruction. Multifilament material seems to present an advantage. Other fabric constructions are still under test. After the cycling, it will be possible to identify, which textile is the most appropriate to the application. With regard to the in vivo tests, the observed results tend to open new perspectives for developing hybrid textiles.
The results obtained in vivo and under fatigue in vitro allowed submitting 4 publications (see below). Moreover, 7 communications were presented in international meetings and 1 patent is going to be written in the coming months about a specific textile.
1. VAESKEN A, KHOFFI F, HEIM F, DIEVAL F, CHAKFE N. Fiber Heart Valve Prosthesis: Early In Vitro Fatigue Results. JBMR-Part B, 2015 May; DOI: 10.1002/jbm.b.33393
2. VAESKEN A, HEIM F, CHAKFE N. Fiber Heart Valve Prosthesis: Influence of the Fabric Construction Parameters on the Valve Fatigue Performances. JMBBM, 2014; 40: 69-74
3. KHOFFI F, HEIM F, CHAKFE N. Transcatheter Fiber Heart Valve: Effect of Crimping on Material Performances. JBMR-Part B, 2014 Nov ; DOI:10.1002/jbm.b.33330
4. HEIM F, GASSER B, KHOFFI F, BLONDEL P. Textile Heart Valve: First In-Vivo Experiment in the Aortic Position. The Journal of Heart Valve Disease, 2014; 23(3):316-8
Today more than 300,000 procedures are run worldwide every year to replace diseased heart valves. In order to limit the surgical risks, simplify the procedure and reduce costs, the transcatheter surgery (minimally invasive surgery) becomes more and more popular among the valve scientific community and the surgeons. To date, over 20.000 transcatheter valve replacements have already been performed worldwide. However the biological tissue used to produce the valve leaflets in the existing devices is not suitable for the procedure. Basically, transcatheter valve implantation generates specific stresses in the leaflet tissue, which tend to weaken the material and reduce its durability. Today the procedure is limited to patients who are critically ill, with reduced life expectancy. However there's strong interest in extending the procedure to a larger part of the diseased population. This requires the use of more durable materials for the valve leaflets. Polyester fabric could be an suited candidate to replace biological tissue. It is strong, flexible, biocompatible and perfectly pliable for catheter insertion purpose. First textile valve prototypes have already been manufactured and tested in vitro in the LPMT laboratory at UHA university. The short-term performances of the textile prostheses that have been measured in vitro are similar to those obtained for other prostheses. Furthermore, a first successfull animal implantation, that has already been carried out with a 2 months survival time, has aroused the interest of valve manufacturers. The overall results obtained yet show the potential of the concept. However, proof of concept will be definitively given only when it is shown that textile material is durable. The purpose of the Provatex project is to test the textile lifetime and to identify the possible failure modes that the valve will undergo on the long term. Only then the technological transfer to the industry may be considered. The failure of the textile prosthesis will be studied at 2 levels. First, through fatigue tests in vitro, it will be possible to evaluate the mechanical degradation of the material. Second, with some in vivo tests it will be possible to explore valve failures caused by the interaction between the textile and the biological tissues.
Monsieur HEIM FREDERIC (Laboratoire de Physique et Mécanique Textiles) – firstname.lastname@example.org
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
LPMT Laboratoire de Physique et Mécanique Textiles
SATT Conectus SATT Conectus Alsace
Help of the ANR 279,760 euros
Beginning and duration of the scientific project: September 2012 - 24 Months