Florence Dieval

Influence of the Textile Structure on the Degradation of Explanted Aortic Endoprostheses

OBJECTIVES To investigate mechanisms of textile failure in explanted human aortic endoprostheses. MATERIALS AND METHODS Endoprostheses (n31) underwent optical and scanning electron microscopy, filament dynamometry, and saturation index measurement. RESULTS The macroscopic lesions observed in the Stentor and Vanguard devices were holes at the extremities of the stents and slipping of the warp yarns at the level of sutures or of the longitudinal seams. The macroscopic lesions observed in AneurX endoprostheses were holes, slipping of the warp yarns and ruptures of the ligatures. The macroscopic lesions observed in the two Talent endoprostheses were sections of fibers at the level of the suture holes and few areas lesions of wear, with sometimes holes at the contact of the stent extremities. Stentor, Vanguard and AneurX all demonstrated low saturation indexes of the fabric (44-59%) with an important anisotropy. Whereas the Talent endograft demonstrated a high index of saturation (124-131%) with a low anisotropy. We did not demonstrate significant polymer degradation in any of the endoprostheses. CONCLUSIONS It is essential to take into account the saturation index to optimally choose a woven textile for the construction of an endoprosthesis since this property of the textile may contribute to explain the macroscopic lesions observed. We did not observe significant polymer degradation by filament dynamometry but further studies are needed to confirm these data.

Mechanisms of Rupture of Knitted Polyester Vascular Prostheses: An In vitro Analysis of Virgin Prostheses

OBJECTIVES Previous explant retrieval studies have shown ruptures occurring on the remeshing line and the guide line of two types of warp-knitted grafts. The aim of our study was to characterize the mechanisms these ruptures. MATERIALS AND METHODS We performed an in vitro study of the mechanical and chemical characteristics of virgin prostheses. We studied 2 virgin polyester warp-knitted grafts models: the Cooley Double Velour and the Microvel Double Velour constructed by Meadox (USA), using the following techniques: characterization and de-knitting of the textile structure, circumferential tensile strength, filament dynamometry, critical dissolution time of the filaments and scanning electron microscopy. RESULTS Both prostheses were constructed in the same way but the texturized yarns of the Cooley graft included twice as many filaments (54) than the Microvel (27). There was more adsorbed tension in the Cooley structure than in the Microvel. The circumferential tensile strength test demonstrated that the Cooley graft always ruptured on the remeshing line and the Microvel graft always ruptured at the interface between the remeshing line and the standard line. Filament dynamometry demonstrated a heterogeneous behavior of the filaments inside the yarns, mainly at the remeshing line of the Cooley graft (27.1 cN/tex +/- 11.5% versus 26.1 cN/tex +/- 2.2% for the guide line and 28 cN/tex +/- 6.7% for the standard knit). Critical dissolution time of the filaments was significantly lower for the Microvel grafts (2.5 sec versus 17.2 sec for the Cooley). CONCLUSIONS Rupture of knitted polyester prostheses are probably an underestimated phenomenon. They may occur at specific areas of the graft. Further studies are required to determine whether all grafts of this type are at risk.

Design, Degradation Mechanism and Long-Term Cytotoxicity of Poly(l-lactide) and Poly(Lactide-co-ϵ-Caprolactone) Terpolymer Film and Air-Spun Nanofiber Scaffold

Degradable nanofiber scaffold is known to provide a suitable, versatile and temporary structure for tissue regeneration. However, synthetic nanofiber scaffold must be properly designed to display appropriate tissue response during the degradation process. In this context, this publication focuses on the design of a finely-tuned poly(lactide-co-ϵ-caprolactone) terpolymer (PLCL) that may be appropriate for vascular biomaterials applications and its comparison with well-known semi-crystalline poly(l-lactide) (PLLA). The degradation mechanism of polymer film and nanofiber scaffold and endothelial cells behavior cultured with degradation products is elucidated. The results highlights benefits of using PLCL terpolymer as vascular biomaterial compared to PLLA.

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.

Evaluation of an air spinning process to produce tailored biosynthetic nanofibre scaffolds

We optimised the working parameters of an innovative air spinning device to produce nanofibrous polymer scaffolds for tissue engineering applications. Scanning electron microscopy was performed on the fibre scaffolds which were then used to identify various scaffold morphologies based on the ratio of surface occupied by the polymer fibres on that covered by the entire polymer scaffold assembly. Scaffolds were then produced with the spinning experimental parameters, resulting in 90% of fibres in the overall polymer construct, and were subsequently used to perform a multiple linear regression analysis to highlight the relationship between nanofibre diameter and the air spinning parameters. Polymer solution concentration was deemed as the most significant parameter to control fibre diameter during the spinning process, despite interactions between experimental parameters. Based on these findings, viscosity measurements were performed to clarify the effect of the polymer solution property on scaffold morphology.

In Vitro Approach to the Dilative Behavior of Knitted Vascular Prosthetic Grafts

The purpose of this report is to propose an in vitro approach to predicting the long-term dilative behavior of knitted polyester prosthetic grafts. Various techniques were applied to five warp knitted fabric prosthetic grafts in order to determine the following fabric properties: knitted fabric structure, textile structure, number and respective linear density of threads and strands, and length of yarn in each stitch. Following these investigations, the prosthetic grafts underwent testing to determine specific strength at break, breaking extension, and stress-strain curve. On two prosthetic grafts, image analysis was performed during circumferential tensile strength testing in order to monitor changes in structural features as a function of stress. Changes in the distance between two wales and two courses of stitches and stitch surface were measured. In addition to surface deformation, thickness was measured, using an induction sensor. Study of fabric structure showed many differences between the five models made by different manufacturers. Knit fabric structure was Indeforma in three cases and half-tricot in two. Strand number and size varied greatly from one model to another. Pattern also varied from one model to another, with knit stitch density varying from 1 to 3. Specific strength at break testing showed great differences in the mechanical properties of the grafts. These differences were especially obvious in the first part of the rheograms, which reflects the ability of the graft to comply in response to low-strength forces, i.e., much lower than those necessary to cause rupture. Image analysis of stitch behavior under stress further confirmed differences in graft behavior depending on the fabric structure adopted by the manufacturers. The in vitro approach proposed in this study to analyze the fabric characteristics of knitted prosthetic grafts effectively revealed differences in construction and behavior. These differences could account for differences in the dilative behavior of grafts in vivo.

Voluminal reconstruction of the bodies applied to the cloth trade

The clothes industry in the developed countries must generate sufficient value added to justify a higher price than the articles produced in great quantity and at low prices in the countries with good wages. The offer of clothing made to measure, at a reasonable price compared with mass‐produced clothing, can constitute an interesting opportunity for the clothes trade. The use of data processing can help to achieve this goal. This assumes that the manufacturer has a virtual model of the customer. This model combined with the knowledge of the behaviour of the support/clothing couple allows the data‐processing creation of clothing specific to the customer. It is necessary to have a precise and instantaneous acquisition technique. Whatever the principle of measurement, several sensors are necessary to measure the totality of a human body. The results obtained are then like a scatter plot. Moreover, this scatter plot has a non‐uniform density according to the measured zone. The surface reconstruction finds these limits in such a situation. In addition, the voluminal reconstruction allows adaptation to this situation by linking spatially the elements describing the shape of the body. Moreover, the use of tetrahedrons allows a modeling of the deformation of the human body. To adapt to the diversity of the scatter plot a method has been developed called the sculptor method. Initially a triangulation gives the convex shape of the scatter plot. It is necessary to remove the superfluous tetrahedrons. To carry out this operation, this form is produced by spheres whose size is adapted. This makes possible a convex solid, which sticks to the scatter plot. This operation shows that this method allows one to reconstruct a body clothed or not with good fidelity.

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.

Les polymères synthétiques résorbables : caractéristiques et applications pour les prothèses artérielles

Impregnation of textile vascular prosthetics has been suggested in order to replace the precoagulation of the prosthetic at the time of implantation, as this technique is mandatory to make the prosthetic leak-proof. Currently these matrix are biologic and may potentially be responsible for infectious transmission. This infectious risk and the results of previous healing studies of impregnated prosthetics led us to take into account a further use of an essentially synthetic matrix. The main advantage of these matrix consisted in providing a reproducible degradation rate without submitting the patients to the not well known risk of infectious transmission due to their chemical synthesis. These matrices may provide a well-controlled variation of porosity of the prostheses after implantation. We conducted a literature review of the main synthetic resorbable polymers used as biomaterials which may also be potentially used for the impregnation of textile vascular prosthetics. We observed the main chemical characteristics and the absorption rate of these polymers.