Friction dans les assemblages de fibres d'hydrogel et applications à la reconstruction des tissus mous

Les assemblages de fibres d'hydrogel offrent des propriétés prometteuses très pertinentes pour leur utilisation dans la reconstruction chirurgicale des tissus mous, telles qu'une bonne biocompatibilité, des propriétés mécaniques proches des tissus natifs et une simplicité de mise en forme en différentes structures à l'aide de techniques textiles. Ce travail de thèse s'intéresse aux phénomènes de friction qui se produisent dans les assemblages de fibres d'hydrogel, à la fois la friction fibre-sur-fibre et la friction avec d'autres surfaces environnantes. Dans une première partie, nous profitons de la friction fibre-sur-fibre pour fabriquer des struc-tures biomimétiques contenant des contraintes résiduelles dont l'intensité et la direction peu-vent être ajustées. Dans une deuxième partie, nous développons un modèle pour prédire l'usure des implants du ligament croisé antérieur (LCA) in vivo. Nous montrons l'application pratique de ce modèle d'usure à une stratégie de planification chirurgicale dans un essai précli-nique d'implants du LCA en fibres d'hydrogel. Enfin, dans une étude ex-vivo des propriétés tribologiques du contact lubrifié entre les fibres d'hydrogel et l'os cortical, nous montrons que le coefficient de friction augmente fortement avec la force normale. Ce travail apporte un nou-vel éclairage sur la conception des matériaux à base d'hydrogel. Il ouvre des perspectives in-téressantes pour la fabrication de structures biomimétiques, et pour l'amélioration des straté-gies de planification chirurgicale dans le cas de la reconstruction des tissus mous.Hydrogel fibre assemblies offer very relevant and promising properties for use in surgical soft tissue reconstruction, such as good biocompatibility, mechanical properties close to native tissues, and simplicity of processing into different structures using textile techniques. This the-sis focuses on the friction phenomena occurring in hydrogel fibre assemblies, both fibre-on-fibre friction and friction with other surrounding surfaces. In a first part, we take advantage of fibre-on-fibre friction to fabricate biomimetic structures containing residual stresses which in-tensity and directionality can be adjusted. In a second part, we develop a model to predict wear damage of anterior cruciate ligament (ACL) implants in vivo. We show the practical appli-cation of the wear model to a surgical planning strategy in a preclinical trial of ACL hydrogel fibre implants. Finally, in an ex-vivo study of the tribological properties of the lubricated contact between hydrogel fibres and cortical bone, we show that the coefficient of friction increases strongly with the normal force. This work brings a novel insight into the design of hydrogel-based materials. It opens interesting perspectives for the fabrication of biomimetic structures, and for the improvement of surgery planning strategies in the case of soft tissue reconstruction

A wear model to predict the damage of ACL implants

International audienc

A wear model to predict damage of reconstructed ACL

International audienc

A wear model to predict damage of reconstructed ACL

International audienc

A wear model to predict damage of reconstructed ACL

Impingement with surrounding tissues is a major cause of failure of anterior cruciate ligament reconstruction. However, the complexity of the knee kinematics and anatomical variations make it difficult to predict the occurrence of contact and the extent of the resulting damage. Here we hypothesise that a description of wear between the reconstructed ligament and adjacent structures captures the in vivo damage produced with physiological loadings. To test this, we performed an in vivo study on a sheep model and investigated the role of different sources of damage: overstretching, excessive twist, excessive compression, and wear. Seven sheep underwent cranial cruciate ligament reconstruction using a tendon autograft. Necropsy observations and pull-out force measurements performed postoperatively at three months showed high variability across specimens of the extent and location of graft damage. Using 3D digital models of each stifle based on X-ray imaging and kinematics measurements, we determined the relative displacements between the graft and the surrounding bones and computed a wear index describing the work of friction forces underwent by the graft during a full flexion-extension movement. While tensile strain, angle of twist and impingement volume showed no correlation with pull-out force (ρ = −0.321, p = 0.498), the wear index showed a strong negative correlation (r = −0.902, p = 0.006). Moreover, contour maps showing the distribution of wear on the graft were consistent with the observations of damage during the necropsy. These results demonstrate that wear is a good proxy of graft damage. The proposed wear index could be used in implant design and surgery planning to minimise the risk of implant failure. Its application to sheep can provide a way to increase preclinical testing efficiency