Foued Khoffi

Transcatheter fiber heart valve: Effect of crimping on material performances

Transcatheter aortic valve implantation (TAVI) has become a popular alternative technique to surgical valve replacement. However, the biological valve tissue used in these devices appears to be fragile material in the long term particularly due being folded for low diameter catheter insertion purposes and when released in a calcified environment with irregular geometry. Textile polyester material is characterized by outstanding folding and strength properties combined with proven biocompatibility. It could therefore be considered as a replacement for biological valve leaflets in the TAVI procedure. The folding process associated with crimping, however, may degrade the filaments involved in the fibrous assembly and limit the durability of the device. The purpose of the present work is to study the effect of different crimping conditions on the mechanical performances of textile valve prototypes made from various fabric constructions. Results show that crimping generates some creases in the fabrics, which surface topography varies with fabric construction and crimping configuration. The mechanical properties of the crimped materials are globally slightly reduced. To determine how critical the modifications due to crimping are for prosthesis durability, more detailed long term in vitro and in vivo trials with crimped textile prototypes are needed in addition to this preliminary work.

Mechanical degradation of biological heart valve tissue induced by low diameter crimping: An early assessment

Transcatheter aortic valve implantation (TAVI) has become today an increasingly attractive procedure to relieve patients from aortic valve disease. However, the procedure requires crimping biological tissue within a metallic stent for low diameter catheter insertion purpose. This step induces specific stress in the leaflets especially when the crimping diameter is small. One concern about crimping is the potential degradations undergone by the biological tissue, which may limit the durability of the valve once implanted. The purpose of the present work is to study the effect of low diameter crimping on the mechanical performances of pericardium valve prototypes. The prototypes were compressed to a diameter of 1mm within braided stents for 20 min. SEM observations performed on crimped material show that crimped leaflets undergo degradations characterized by apparent surface defects. Moreover mechanical extension tests were performed on pericardium strips before and after crimping. The strips (15 mm long, 5mm wide) were taken from both crimped and native leaflets considering 2 different valve diameters, 19 and 21 mm. In order to prevent the premature drying of the pericardium tissue during the procedure, the biological tissue was kept in contact with a formaldehyde solution. Results show that the ultimate strength value decreases nearly by up to 50%. The modifications observed in the material may jeopardize the long term durability of the device. However, further tests are necessary with a larger amount of samples to confirm these early results.

Long-Term Biostability of Pet Vascular Prostheses

PET Vascular prostheses are susceptible to physical modification and chemical degradation leading sometimes to global deterioration and rupture of the product. To understand the mechanisms of degradation, we studied 6 vascular prostheses that were explanted due to medical complications. We characterized their level of degradation by comparing them with a virgin prosthesis and carried out physicochemical and mechanical analyses. Results showed an important reduction of the fabric’s mechanical properties in specific areas. Moreover, PET taken from these areas exhibited structural anomalies and was highly degraded even in virgin prostheses. These results suggest that vascular prostheses have weak areas prior to implantation and that these areas are much more prone to in vivo degradation by human metabolism. Manufacturing process could be responsible for these weaknesses as well as designing of the compound. Therefore, we suggest that a more controlled manufacturing process could lead to a vascular prosthesis with enhanced lifespan.

Physico-chemical characteristics of a seed fiber arised from Pergularia Tomentosa L.

In the present paper, we analyze a seed fiber arising from Pergularia tomentosa L. (PTL). It was, primarily, characterized using different techniques. The morphology of the fibers was observed via Scanning Electron Microscopy (SEM). They are also checked in term of decomposition behavior through TGA/DTG instrument. The cristallinity index was determined using XRD and it was about 52 %. The chemical composition in terms of moisture percent, ash, waxes and fats, lignin, hemicellulose and cellulose were, respectively 8.5 %, 2.74 %, 1.88 %, 8.6 %, 16 % and 43.8 %. The contact angle value was measured and the evolution of drop profile was captured with video-camera using GBX Tensiometer Surfaces Sciences Studies. Further, fibers were dyed with Methylene Blue, Direct Red 79, Sumifix supra yellow 3RF and Reactive Blue 198. Color coordinates (ΔL*, Δa*, Δb*, ΔC* and ΔH*) of the samples were so measured. All obtained data were compared to cotton fibers and some other cellulosic fibers. The Results revealed that, based on such properties, PTLF could be a competitive fiber in many applications field (textile weaving, composites, etc).

Fiber heart valve prosthesis: Early in vitro fatigue results

Transcatheter aortic valve replacement has become today a largely considered alternative technique to surgical valve replacement in patients with high risk for open chest surgery. Biological valve tissue used in the transcatheter devices has shown success over 5 years now, but the procedure remains expensive. Moreover, different studies point out potential degradations that the tissue can undergo when folded to lower diameter and released in calcified environment with irregular geometry, which may jeopardize the durability of the device. The use of synthetic materials, like textile in particular, to replace biological valve leaflets would help reducing the procedure costs, and limit the degradations when the valve is crimped. Textile polyester material has been extensively used in the vascular surgery and is characterized by outstanding folding and strength properties combined with proven biocompatibility. However, the friction effects that occur between filaments and between yarns within a fabric under flexure loading could be critical for the resistance of the material on the long term. The purpose of this study was to assess the early fatigue performances of textile valve prototypes under accelerated cyclic loading up to 200 Mio cycles. Durability tests show that the fibrous material undergoes rearrangements between fibrous elements within the textile construction and the mechanical properties are modified on the long term. But testing is not complete with 200 Mio cycles. The material should be tested up to a higher number of cycles in future work to test the effective long-term durability.

Compliance properties of collagen-coated polyethylene terephthalate vascular prostheses

Background Compliance mismatch between native artery and a prosthetic graft used for infrainguinal bypass is said to be a factor for graft failure. The aim of this study was to develop a technique for measuring the compliance of collagen-coated polyethylene terephthalate (PET) vascular prostheses and to analyze the influence of several key properties on the elastic behavior of the grafts. Methods Compliance testing was performed on 3 prostheses with and without internal compliant membrane (ICM). The principle of this test was to study the dimensional changes of prostheses submitted to internal pressure from 30 to 240 mm Hg at intervals of predetermined values. Results We demonstrated that the ICM created links with the inner surface of the crimps and considerably modified the graft behavior when submitted to internal pressure. The results showed that compliance properties were dependent on the wall thickness and the crimping geometry of textile vascular prostheses. Mechanical analysis predicts the circumferential tensile behavior of these arterial grafts and validates tests for measuring compliance.

Effect of finishing resins on mechanical and surface properties of cotton Denim fabrics

Abstract The effect of two famous finishing resins; acrylic resin (Resacryl M), and Glyoxal resin (Resinol AM), applied by the same Pad Dry Cure Process PDC but according to various conditions, on the mechanical and surface properties of different cotton denim fabrics is studied in this paper. The treated samples which are characterized at two steps of the treatment process: before and after washing (BW and AW) were characterized in terms of surface morphology observations by SEM, geometrical roughness measurements with Kawabata Evaluation System KES, thickness and Dry crease recovery angle DCRA measurements, and mechanical testing properties. It resulted that Resinol AM improves dry crease recovery angle, but causes a loss of strength in the warp direction. Nevertheless, Resacryl M improves handless and preserves the mechanical properties fabric before and after washing. Studying the effect of resins type, concentrations and curing temperature on the mechanical behavior and surface of the cotton fabrics is very important in textile laundering, because it allows choosing the best finishing agents and conditions. Furthermore, the results of this report will be in workable data to predict the properties of the treated fabrics after resin finishing.

Kenaf fibre-reinforced polyester composites: flexural characterization and statistical analysis

Abstract This paper deals with the effect of the chemical treatment, fibre ratio and fibre reinforcement structure on the flexural properties of kenaf-polyester composites. Composites were made from an unsaturated polyester matrix reinforced with an alkali-treated and virgin kenaf fibres in a loose fibres and nonwovens. Results reveal that alkali treatment improves the flexural properties of composites expect elongation. The same result was obtained when using a nonwoven structure us reinforcement. The best flexural properties were observed for 11.1% fibre weight ratio with the nonwoven structure reinforce composite. The flexural strength and the flexural modulus were 69.5 MPa and 7.11 GPa, respectively, for this composite while it was 42.24 MPa and 3.61, respectively, for polyester samples (no fibre reinforcement). A statistical study was carried out in order to study the effect of the alkali treatment, reinforcement structure and the reinforcement weight ration on the composite properties. This study proved that the parameter with most impact on the measured properties is the fibre-to-matrix weight ratio. And also this study aims to determine the optimum parameters allowing maximising all measured properties and we found that when using a nonwoven structure made with chemically-treated fibre at 11.10% fibre weight ratio, is the optimum solution.