Mechanical behavior of surgical meshes for abdominal wall repair: In vivo versus biaxial characterization

Despite the widespread use of synthetic meshes in the surgical treatment of the hernia pathology, the election criteria of a suitable mesh for specific patient continues to be uncertain. Thus, in this work, we propose a methodology to determine in advance potential disadvantages on the use of certain meshes based on the patient-specific abdominal geometry and the mechanical features of the certain meshes. To that purpose, we have first characterized the mechanical behavior of four synthetic meshes through biaxial tests. Secondly, two of these meshes were implanted in several New Zealand rabbits with a total defect previously created on the center of the abdominal wall. After the surgical procedure, specimen were subjected to in vivo pneumoperitoneum tests to determine the immediate post-surgical response of those meshes after implanted in a healthy specimen. Experimental performance was recorded by a stereo rig with the aim of obtaining quantitative information about the pressure-displacement relation of the abdominal wall. Finally, following the procedure presented in prior works (Simón-Allué et al., 2015, 2017), a finite element model was reconstructed from the experimental measurements and tests were computationally reproduced for the healthy and herniated cases. Simulations were compared and validated with the in vivo behavior and results were given along the abdominal wall in terms of displacements, stresses and strain. Mechanical characterization of the meshes revealed Surgipro TM as the most rigid implant and Neomesh SuperSoft® as the softer, while other two meshes (Neomesh Soft® Neopore®) remained in between. These two meshes were employed in the experimental study and resulted in similar effect in the abdominal wall cavity and both were close to the healthy case. Simulations confirmed this result while showed potential objections in the case of the other two meshes, due to high values in stresses or elongation that may led to discomfort in real tissue. The use of this methodology on human surgery may provide the surgeons with reliable and useful information to avoid certain meshes on specific-patient treatment

Using Inverse Finite Element Analysis to Obtain Passive Mechanical Behavior of Abdominal Wall

In this work we develop a methodology to characterize in vivo the passive mechanical behavior of abdominal muscle, using for that finite element simulations combined with inverse analysis and optimization algorithms. The knowledge of the mechanical response of the muscle is needed to determine the features of the mesh in cases of hernia surgery

Developing a new methodology to characterize in vivo the passive mechanical behavior of abdominal wall on an animal model

The most common surgical repair of abdominal wall hernia goes through implanting a mesh that substitutes the abdominal muscle/fascia while it is healing. To reduce the risk of relapse or possible complications, this mesh needs to mimic the mechanical behavior of the muscle/fascia, which nowadays is not fully determined. The aim of this work is to develop a methodology to characterize in vivo the passive mechanical behavior of the abdominal wall. For that, New Zealand rabbits were subjected to pneumoperitoneum tests, taking the inner pressure from 0 mmHg to 12 mmHg, values similar to those used in human laparoscopies. Animals treated were divided into two groups: healthy and herniated animals with a surgical mesh (polypropylene SurgiproTM Covidien) previously implanted. All experiments were recorded by a stereo rig composed of two synchronized cameras. During the postprocessing of the images, several points over the abdominal surface were tracked and their coordinates extracted for different levels of internal pressure. Starting from that, a three dimensional model of the abdominal wall was reconstructed. Pressure–displacement curves, radii of curvature and strain fields were also analysed. During the experiments, animals tissue mostly deformed during the first levels of pressure, showing the noticeable hyperelastic passive behavior of abdominal muscles. Comparison between healthy and herniated specimen displayed a strong stiffening for herniated animals in the zone where the high density mesh was situated. Cameras were able to discern this change, so this method can be used to measure the possible effect of other meshes

Towards the in vivo mechanical characterization of abdominal wall in animal model: application to hernia repair

El trabajo presentado en esta tesis se centra en el diseño e implementación de una metodología que permita caracterizar in vivo el comportamiento mecánico pasivo de la pared abdominal. Esta metodología permitiría a los cirujanos disponer de información mecánica relevante sobre un paciente especí co, lo que podría contribuir a mejorar el tratamiento quirúrgico de hernias mediante malla protésica. El tratamiento quirúrgico de hernias consiste en cerrar la debilidad creada en el músculo, ya sea directamente con puntos de sutura o mediante la implantación de una malla protésica. En el caso de la malla, ésta es la responsable de absorber las tensiones a las que el músculo se ve sometido durante el tiempo en el que se produce la regeneración de tejido. Para reducir el riego de aparición de dolor postoperatorio, rotura o rasgadura de tejido o incluso una recidiva, la malla debe mimetizar la respuesta mecánica de la zona de la pared donde vaya a ser colocada, que a su vez puede variar de un paciente a otro en función de su edad, género, índice de masa corporal u otras características físicas. Un mejor conocimiento de las propiedades mecánicas del abdomen en paciente especí co ayudaría al cirujano a determinar qué malla protésica se puede considerar la ideal, mecánicamente hablando. Por todo ello, el trabajo que aquí se presenta plantea una aproximación in vivo para caracterizar la pared abdominal sobre un modelo animal y su posterior implementación en casos de patologías herniarias. En un primer paso, se ha realizado un estudio biomecánico del cierre en línea alba, que ayudase a entender los aspectos mecánicos y biológicos que tienen lugar durante la curación de la herida a corto y largo plazo. A continuación, se han llevado a cabo ensayos mecánicos de in ado sobre la pared, que combinados con el uso de cámaras y técnicas de adquisición de imagen han permitido extraer la respuesta del tejido de una manera no invasiva. Este estudio experimental, se ha llevado a cabo sobre especímenes sanos y otro herniados y reparados con distintas mallas quirúrgicas, lo que ha permitido extrapolar el efecto in vivo que provocan estas mallas. A partir de los datos experimentales también se ha desarrollado un análisis numérico que permitiese caracterizar la respuesta mecánica especí ca de cada espécimen. A este efecto, dicha caracterización se ha tratado como un problema inverso y resuelto primeramente mediante un análisis de super cies de respuesta y después con un algoritmo propio aplicado a modelos hiperelásticos. Finalmente, también se ha reconstruido un modelo de elementos nitos de la cavidad abdominal que permite simular el efecto producido por distintas mallas protésicas así como su alteración respecto al tejido sano

Towards the mechanical characterization of abdominal wall by inverse analysis

The aim of this study is to characterize the passive mechanical behaviour of abdominal wall in vivo in an animal model using only external cameras and numerical analysis. The main objective lies in defining a methodology that provides in vivo information of a specific patient without altering mechanical properties. It is demonstrated in the mechanical study of abdomen for hernia purposes. Mechanical tests consisted on pneumoperitoneum tests performed on New Zealand rabbits, where inner pressure was varied from 0 mmHg to 12 mmHg. Changes in the external abdominal surface were recorded and several points were tracked. Based on their coordinates we reconstructed a 3D finite element model of the abdominal wall, considering an incompressible hyperelastic material model defined by two parameters. The spatial distributions of these parameters (shear modulus and non linear parameter) were calculated by inverse analysis, using two different types of regularization: Total Variation Diminishing (TVD) and Tikhonov (H1). After solving the inverse problem, the distribution of the material parameters were obtained along the abdominal surface. Accuracy of the results was evaluated for the last level of pressure. Results revealed a higher value of the shear modulus in a wide stripe along the craneo-caudal direction, associated with the presence of linea alba in conjunction with fascias and rectus abdominis. Non linear parameter distribution was smoother and the location of higher values varied with the regularization type. Both regularizations proved to yield in an accurate predicted displacement field, but H1 obtained a smoother material parameter distribution while TVD included some discontinuities. The methodology here presented was able to characterize in vivo the passive non linear mechanical response of the abdominal wall

Numerical analysis of the fluid flow and heat transfer of a hybrid PV-thermal collector and performance assessment

In recent years, new materials and absorber configurations have been proposed to improve the performance of hybrid photovoltaic-thermal (PV-T) collectors. This work analyses the fluid flow and the energy performance of an uncovered water-based PV-T collector with a roll-bond thermal absorber. A detailed CFD model was developed and the results were compared with the experimental performance features provided by the PV-T manufacturer. The fluid flow results show uneven flow distribution among the roll-bond microchannels which leads to areas with larger PV cell temperatures and thus a lower electricity generation. The PV-T collector layers were also modelled using the energy transfer equations layer-by-layer. The model was run for several water inlet temperatures and water flow-rates to obtain the thermal performance curve. The results show that the electrical efficiency of the PV-T collector is 14.5–10.3% larger than for a PV-only system for water inlet temperatures of 20–30 °C, respectively. The developed CFD model reproduces accurately the thermal performance of the PV-T collector, with a maximum error of 6.5% for inlet water temperatures of 20–60 °C. Therefore, this model can be used with confidence to propose alternative designs that achieve a homogeneous temperature distribution in the PV layer and improve the overall PV-T collector performance

In-situ Mechanical Characterization of Abdominal Muscle Using Stereo Imaging

We present a method to characterize in vivo the mechanical behavior of abdominal muscle, using inverse finite element analysis and image processing algorithms to estimate the properties. The aim of this technique is to help surgeon to choose the hernia mesh that better reproduces the mechanical behavior of the healthy muscle

Paneles solares híbridos: electricidad y calor en un solo panel

Las nuevas directivas europeas en materia de construcción están orientadas a la obtención de edificios de consumo energético casi nulo. Para ello, el desarrollo e implantación de energías renovables que sean capaces de satisfacer necesidades energéticas mediante una producción limpia, asequible e in-situ, se erige como una estrategia fundamental. Es por ello que presentamos en este trabajo la aplicación de una tecnología emergente, los paneles solares híbridos, capaces de proporcionar energía térmica y eléctrica en un mismo panel. Gracias a esta producción dual, este tipo de paneles aumenta la cantidad total de energía producida por m2 en un 40% respecto a las soluciones tradicionales de colector térmico y panel fotovoltaico, lo que hace de su implantación una opción muy interesante en edificaciones con limitación de espacio en cubierta, como ocurre frecuentemente en centros urbanos. En este trabajo se estudia su aplicación a tres tipologías de edificios con consumos energéticos tipo asociados a sector residencial y terciario (hotel, polideportivo), para lo cual se han considerado a su vez diferentes tipos de paneles solares híbridos, asignados según su temperatura de abastecimiento. El análisis final abarca desde la producción eléctrica y térmica de cada instalación a los ahorros obtenidos tanto en términos económicos como en disminución de emisiones de CO2.Consejo General de la Arquitectura Técnica de Españ

Biomechanical and morphological study of a new elastic mesh (Ciberlastic) to repair abdominal wall defects

The aim of this study was to conduct a preclinical evaluation of the behaviour of a new type of abdominal LW prosthesis (Ciberlastic), which was designed with a non-absorbable elastic polyurethane monofilament (Assuplus, Assut Europe, Italy) to allow greater adaptability to mechanical area requirements and higher bio-mimicking with the newly formed surrounding tissues. Our hypothesis was that an increase in the elasticity of the mesh filament could improve the benefits of LW prostheses. To verify our hypothesis, we compared the short- and long-term behaviour of Ciberlastic and Optilene® elastic commercial meshes by repairing the partially herniated abdomen in New Zealand White rabbits. The implanted meshes were mechanically and histologically assessed at 14 and 180 days post-implant. We mechanically characterized the partially herniated repaired muscle tissue and also determined mesh shrinkage at different post-implant times. This was followed by a histological study in which the tissue incorporation process was analysed over time. The new prosthesis designed by our group achieved good behaviour that was similar to that of Optilene®, one of the most popular LW prostheses on the market, with the added advantage of its elastic property. The mechanical properties are significantly lower than those of the polypropylene Optilene® mesh, and the new elastic mesh meets the basic mechanical requirements for positioning in the abdominal wall, which was also demonstrated by the absence of recurrences after implantation in the experimental model. We found that the growth of a connective tissue rich in collagen over the hernial defect and the proper deposit of the collagen fibres in the regenerated tissue substantially modified the original properties of the mesh, thereby increasing its biomechanical strength and making the whole tissue/mesh stiffer

The challenges of solar hybrid PVT systems in the food processing industry

14 figures, 3 tables.This paper assesses the challenges of alternative solar systems based on hybrid PVT collectors coupled with an absorption chiller (AbCH, single-stage NH3-H2O) in the food-processing industry, from the technical, economic and environmental points of view. This type of industry is usually characterised by a constant cooling demand throughout the year, hot water demand for production processes and electricity consumption for factory equipment and lighting. To the authors¿ knowledge, this work constitutes one of the first studies to address the integration of PVT-water collectors with a single-stage NH3-H2O AbCH for industrial applications. Two alternative PVT-water collectors are analysed, covered and uncovered. A biomass boiler is proposed as an auxiliary heater. To compare the proposed solar solutions, a vegetable and fruit processing and canning factory is considered as a representative case study. Hourly transient simulations considering the real factory demands and real weather data are performed over a year. Two main challenges are found for the solar systems based on the covered PVT collectors, an AbCH and a biomass boiler: the overlapping of the cooling and hot water demands of the food-processing industry, and the high hot water temperatures required. If, alternatively, the current electrical chillers are retained, the system based on uncovered PVT collectors has a reasonable-to-attractive payback time (14.3 years). When the potential environmental benefit is quantified (through carbon pricing), all the proposed solar systems become economically attractive, i.e., with positive total cost savings at the end of the system lifetime. Still, the high cost of PVT collectors, along with the considerably lower price of fuels compared to electricity, hinder the potential of systems that displace fossil fuels.This work was undertaken in the framework of 3GSol, a project funded under the Retos-Colaboración 2017 Programme, National R&D and Innovation Plan, by the Spanish Government, Ministry of Science, Innovation and Universities and co-funded by the EU, through the European Regional Development Fund (ERDF) [grant number RTC-2017-6026-3].Peer reviewe