Etude de l'autoréparation d'élastomères supramoléculaires

National audienceDes travaux récents ont permis de développer un nouveau type d'élastomère constitué d'un réseau de molécules associées entre elles via des liaisons hydrogènes faibles et réversibles. Cet élastomère supramoléculaire présente un pouvoir autoréparant remarquable : les surfaces formées par pressage ou moulage sont peu autoadhésives ; en revanche, une pièce rompue peut retrouver ses propriétés mécaniques d'origine en mettant simplement en contact les surfaces de fracture. Nous montrons ici au moyen d'une expérience de type « tack » que l'autoréparation de surfaces de fracture et l'autoadhésion de surfaces mises en forme mettent en jeu des mécanismes distincts impliquant des énergies d'adhésion et des échelles de temps très différentes. En particulier, des traitements thermiques révèlent que la désactivation de ce pouvoir autoréparant est fortement accélérée par un recuit des surfaces endommagées. Ces résultats suggèrent l'existence de mécanismes de reconstruction des surfaces gouvernés par la mobilité moléculaire

Poly(vinyl alcohol) hydrogel coatings with tunable surface exposure of hydroxyapatite.

International audienceInsufficient bone anchoring is a major limitation of artificial substitutes for connective osteoarticular tissues. The use of coatings containing osseoconductive ceramic particles is one of the actively explored strategies to improve osseointegration and strengthen the bone-implant interface for general tissue engineering. Our hypothesis is that hydroxyapatite (HA) particles can be coated robustly on specific assemblies of PVA hydrogel fibers for the potential anchoring of ligament replacements. A simple dip-coating method is described to produce composite coatings made of microscopic hydroxyapatite (HA) particles dispersed in a poly(vinyl alcohol) (PVA) matrix. The materials are compatible with the requirements for implant Good Manufacturing Practices. They are applied to coat bundles of PVA hydrogel fibers used for the development of ligament implants. By means of optical and electronic microscopy, we show that the coating thickness and surface state can be adjusted by varying the composition of the dipping solution. Quantitative analysis based on backscattered electron microscopy show that the exposure of HA at the coating surface can be tuned from 0 to over 55% by decreasing the weight ratio of PVA over HA from 0.4 to 0.1. Abrasion experiments simulating bone-implant contact illustrate how the coating cohesion and wear resistance increase by increasing the content of PVA relative to HA. Using pullout experiments, we find that these coatings adhere well to the fiber bundles and detach by propagation of a crack inside the coating. These results provide a guide to select coated implants for anchoring artificial ligaments

A mechano-biological model of multi-tissue evolution in bone

International audienceSuccessfully simulating tissue evolution in bone is of significant importance in predicting various biological processes such as bone remodeling, fracture healing and osseointegration of implants. Each of these processes involves in different ways the permanent or transient formation of different tissue types, namely bone, cartilage and fibrous tissues. The tissue evolution in specific circumstances such as bone remodeling and fracturing healing is currently able to be modeled. Nevertheless, it remains challenging to predict which tissue types and organization can develop without any a priori assumptions. In particular, the role of mechano-biological coupling in this selective tissue evolution has not been clearly elucidated. In this work, a multi-tissue model has been created which simultaneously describes the evolution of bone, cartilage and fibrous tissues. The coupling of the biological and mechanical factors involved in tissue formation has been modeled by defining two different tissue states: an immature state corresponding to the early stages of tissue growth and representing cell clusters in a weakly neo-formed Extra Cellular Matrix (ECM), and a mature state corresponding to well-formed connective tissues. This has allowed for the cellular processes of migration, proliferation and apoptosis to be described simultaneously with the changing ECM properties through strain driven diffusion, growth, maturation and resorption terms. A series of finite element simulations were carried out on idealized cantilever bending geometries. Starting from a tissue composition replicating a mid-diaphysis section of a long bone, a steady-state tissue formation was reached over a statically loaded period of 10,000 h (60 weeks). The results demonstrated that bone formation occurred in regions which are optimally physiologically strained. In two additional 1000 h bending simulations both cartilaginous and fibrous tissues were shown to form under specific geometrical and loading cases and cartilage was shown to lead to the formation of bone in a beam replicating a fracture healing initial tissue distribution. This finding is encouraging in that it is corroborated by similar experimental observations of cartilage leading bone formation during the fracture healing process. The results of this work demonstrate that a multi-tissue mechano-biological model of tissue evolution has the potential for predictive analysis in the design and implementations of implants, describing fracture healing and bone remodeling processes

A 3D in Silico Multi-Tissue Evolution Model Highlights the Relevance of Local Strain Accumulation in Bone Fracture Remodeling

Since 5–10% of all bone fractures result in non-healing situations, a thorough understanding of the various bone fracture healing phases is necessary to propose adequate therapeutic strategies. In silico models have greatly contributed to the understanding of the influence of mechanics on tissue formation and resorption during the soft and hard callus phases. However, the late-stage remodeling phase has not been investigated from a mechanobiological viewpoint so far. Here, we propose an in silico multi-tissue evolution model based on mechanical strain accumulation to investigate the mechanobiological regulation of bone remodeling during the late phase of healing. Computer model predictions are compared to histological data of two different pre-clinical studies of bone healing. The model predicted the bone marrow cavity re-opening and the resorption of the external callus. Our results suggest that the local strain accumulation can explain the fracture remodeling process and that this mechanobiological response is conserved among different mammal species. Our study paves the way for further understanding of non-healing situations that could help adapting therapeutic strategies to foster bone healing

Self-Organized Criticality in Sheared Suspensions

Recent studies reveal that suspensions of neutrally buoyant non-Brownian particles driven by slow periodic shear can undergo a dynamical phase transition between a fluctuating irreversible steady state and an absorbing reversible state. Using a computer model, we show that such systems exhibit self-organized criticality when a finite particle sedimentation velocity vs is introduced. Under periodic shear, these systems evolve, without external intervention, towards the shear-dependent critical concentration ϕc as vs is reduced. This state is characterized by power-law distributions in the lifetime and size of fluctuating clusters. Experiments exhibit similar behavior and, as vs is reduced, yield steady-state values of ϕ that tend towards the ϕc corresponding to the applied shear

Triatominos (Reduviidae: Triatominae) en un foco de enfermedad de Chagas en Talaigua Nuevo (Bolívar, Colombia).

Introduction. The epidemiological importance and ecological characteristics of triatomines were investigated in a Chagas disease focus in Talaigua Nuevo, Bolivar Province.Objective. To describe and correlate the ecological characteristics of triatomines in a Chagas disease focus.Materials And Methods. Triatomines were collected in 300 domiciles located in the urban zone of Talaigua Nuevo. This included inspection of microhabitats in and around the domestic environment, and also wine palms, woodpiles and firewood.Results. Among the 103 triatomines collected, four species were identified--Triatoma maculata, Eratyrus cuspidatus, Panstrongylus geniculatus, and Rhodnius prolixus. T. maculata was the most abundant species (92.23%). The majority (93%) were collected in the intradomiciliary environment.Conclusion. Individuals of T. maculata naturally infected with Trypanosoma were recorded for the first time in Bolivar Province. The distribution range of P. geniculatus and R. prolixus was expanded. Using a multiple correspondence analysis, no relationship was discerned between the house type and occurrence of triatomines.Introducción. Se describen las características e importancia epidemiológica de los triatominos presentes en un foco de enfermedad de Chagas en el municipio de Talaigua Nuevo, departamento de Bolívar. Objetivo. Determinar y correlacionar características ecológicas de los triatominos presentes en un foco de Chagas en el municipio de Talaigua Nuevo, Bolívar. Materiales y métodos. La captura de los triatominos se realizó en 300 domicilios del casco urbano en los que se revisaron el intra y peridomicilio, así como ambientes extradomésticos (palmas de vino y cúmulos de madera y leña). Resultados. Se capturaron 103 triatominos pertenecientes a cuatro especies: Triatoma maculata, Eratyrus cuspidatus, Panstrongylus geniculatus y Rhodnius prolixus. T. maculata, fue la especie predominante (92,3%). El 93% de los triatominos fueron capturados en ambientes intradomiciliarios. Conclusión. Se reporta por primera vez en Bolívar la captura de individuos de T. maculata infectados naturalmente con Trypanosoma sp. Se amplía la distribución geográfica de P. geniculatus y R. prolixus. El análisis de correspondencias múltiples no encontró ninguna relación significativa entre las características físicas de las viviendas y la presencia de triatominos dentro de ellas

Evidencias de su transformación educacional por los impactos de la formación académica de posgrado

The paper contains the analysis of part of the evidence of the educational transformations experimented by the educational field and by society in the province of Granma, derived from the influence of the post-graduate academic formation received by teachers and professors from educational institutions here. It presents the main actions of the strategy developed under the leadership of the Center of Studies of Education in Granma (CEdEG) Fausto Santisteban Pons of the present-day University of Granma. These achievements are largely the results of the institutional research projects carried out by CEdEG and its competent staff of collaborators. The high quality of the work already has done grants the progressive and stable development of this activity in the years to come, in order to fulfill the demands of the educational improvement process and the institutional evaluation of the university.La ponencia contiene un análisis de algunas de las principales evidencias de transformaciones educacionales acontecidas en el sector educacional y la sociedad granmenses, como resultado de la incidencia de la formación académica de posgrado recibida por los maestros y profesores de sus instituciones educacionales. Se presentan las principales acciones desarrolladas como parte de la estrategia, fundamentalmente lideradas por el Centro de Estudios de Educación de Granma (CEdEG) Fausto Santisteban Pons, de la hoy Universidad de Granma. Los logros alcanzados son resultados, en buena medida, de los proyectos institucionales de investigación desarrollados por el CEdEG y su amplio claustro de colaboradores, unido a la política establecida por las direcciones educacionales implicadas. El trabajo desarrollado propicia la continuidad sostenida y creciente de esta actividad en los próximos años, lo cual constituye una necesidad imperiosa ante las exigencias del proceso de Acreditación universitaria de las diferentes carreras universitarias y del propio proceso de formación doctoral, así como de dar continuidad a la calidad educacional en el territorio como parte y aspiración del actual proceso de Perfeccionamiento Educacional que se lleva a cabo en Cuba.   &nbsp

Augmentation of Bone Tunnel Healing in Anterior Cruciate Ligament Grafts: Application of Calcium Phosphates and Other Materials

Bone tunnel healing is an important consideration after anterior cruciate ligament (ACL) replacement surgery. Recently, a variety of materials have been proposed for improving this healing process, including autologous bone tissue, cells, artificial proteins, and calcium salts. Amongst these materials are calcium phosphates (CaPs), which are known for their biocompatibility and are widely commercially available. As with the majority of the materials investigated, CaPs have been shown to advance the healing of bone tunnel tissue in animal studies. Mechanical testing shows fixation strengths to be improved, particularly by the application of CaP-based cement in the bone tunnel. Significantly, CaP-based cements have been shown to produce improvements comparable to those induced by potentially more complex treatments such as biologics (including fibronectin and chitin) and cultured cells. Further investigation of CaP-based treatment in the bone tunnels during ACL replacement is therefore warranted in order to establish what improvements in healing and resulting clinical benefits may be achieved through its application

Optimal bone structure is dependent on the interplay between mechanics and cellular activities

Bone is a tissue with the remarkable capacity to adapt its structure to an optimized microstructural form depending on variations in the loading conditions. The remodeling process in bone produces distinct tissue distributions such as cortical and trabecular bone but also fibrous and cartilage tissues. Although it has been demonstrated that mechanical factors play a decisive role in the architectural optimization, it may also follow that biological factors have an influence. This interplay between loading and physiology has not been previously reported but is paramount for a proper assessment of bone remodeling outcomes. In this work we present a mechanostat model for bone remodeling which is shown to predict the mechanically driven homeostasis. It is further demonstrated that the steady-state reached is innately dependent upon the loading magnitudes and directions. The model was then adjusted to demonstrate the influence of specific biological factors such as cell proliferation, migration and resorption. Furthermore, two scenarios were created to replicate the physiological conditions of two bone disorders – osteoporosis and osteopetrosis – where the results show that there is a significant distinction between the homeostatic structures reached in each case and that the tissue adaptations follow similar trends to those observed in clinical studies