Nonlinear effects in finite elements analysis of colorectal surgical clamping

Minimal Invasive Surgery (MIS) is a procedure that has increased its applications in past few years in different types of surgeries. As number of application fields are increasing day by day, new issues have been arising. In particular, instruments must be inserted through a trocar to access the abdominal cavity without capability of direct manipulation of tissues, so a loss of sensitivity occurs. Generally speaking, the student of medicine or junior surgeons need a lot of practice hours before starting any surgical procedure, since they have to difficulty in acquiring specific skills (hand–eye coordination among others) for this type of surgery. Here is what the surgical simulator present a promising training method using an approach based on Finite Element Method (FEM). The use of continuum mechanics, especially Finite Element Analysis (FEA) has gained an extensive application in medical field in order to simulate soft tissues. In particular, colorectal simulations can be used to understand the interaction between colon and the surrounding tissues and also between colon and instruments. Although several works have been introduced considering small displacements, FEA applied to colorectal surgical procedures with large displacements is a topic that asks for more investigations. This work aims to investigate how FEA can describe non-linear effects induced by material properties and different approximating geometries, focusing as test-case application colorectal surgery. More in detail, it shows a comparison between simulations that are performed using both linear and hyperelastic models. These different mechanical behaviours are applied on different geometrical models (planar, cylindrical, 3D-SS and a real model from digital acquisitions 3D-S) with the aim of evaluating the effects of geometric non-linearity. Final aim of the research is to provide a preliminary contribution to the simulation of the interaction between surgical instrument and colon tissues with multi-purpose FEA in order to help the preliminary set-up of different bioengineering tasks like force-contact evaluation or approximated modelling for virtual reality (surgical simulations). In particular, the contribution of this work is focused on the sensitivity analysis of the nonlinearities by FEA in the tissue-tool interaction through an explicit FEA solver. By doing in this way, we aim to demonstrate that the set-up of FEA computational surgical tools may be simplified in order to provide assistance to non-expert FEA engineers or medicians in more precise way of using FEA tools

Finite element model set-up of colorectal tissue for analyzing surgical scenarios

Finite Element Analysis (FEA) has gained an extensive application in the medical field, such as soft tissues simulations. In particular, colorectal simulations can be used to understand the interaction with the surrounding tissues, or with instruments used in surgical procedures. Although several works have been introduced considering small displacements, as a result of the forces exerted on adjacent tissues, FEA applied to colorectal surgical scenarios is still a challenge. Therefore, this work aims to provide a sensitivity analysis on three geometric models, taking in mind different bioengineering tasks. In this way, a set of simulations has been performed using three mechanical models named Linear Elastic, Hyper-Elastic with a Mooney-Rivlin material model, and Hyper-Elastic with a YEOH material model

Digital design of medical replicas via desktop systems: shape evaluation of colon parts

In this paper, we aim at providing results concerning the application of desktop systems for rapid prototyping of medical replicas that involve complex shapes, as, for example, folds of a colon. Medical replicas may assist preoperative planning or tutoring in surgery to better understand the interaction among pathology and organs. Major goals of the paper concern with guiding the digital design workflow of the replicas and understanding their final performance, according to the requirements asked by the medics (shape accuracy, capability of seeing both inner and outer details, and support and possible interfacing with other organs). In particular, after the analysis of these requirements, we apply digital design for colon replicas, adopting two desktop systems. ,e experimental results confirm that the proposed preprocessing strategy is able to conduct to the manufacturing of colon replicas divided in self-supporting segments, minimizing the supports during printing. ,is allows also to reach an acceptable level of final quality, according to the request of having a 3D presurgery overview of the problems. ,ese replicas are compared through reverse engineering acquisitions made by a structured-light system, to assess the achieved shape and dimensional accuracy. Final results demonstrate that low-cost desktop systems, coupled with proper strategy of preprocessing, may have shape deviation in the range of ±1 mm, good for physical manipulations during medical diagnosis and explanation

Diseño y Construcción de una Máquina Automática para llenado de Material Pirotécnico en Tubos de Cartón.

En el presente trabajo se ha diseñado, construido y probado una máquina dosificadora y compactadora de pólvora negra en tubos de cartón; utilizados en la fabricación de cohetes pirotécnicos. En base a una metodología de diseño se ha logrado elegir la alternativa más apropiada para el diseño y construcción de la máquina, considerando para esto los requerimientos tecnológicos y económicos. La compactación uniforme determina la calidad del producto, el diseño de la máquina se realizó en base al requerimiento principal, la fuerza de compactado de la pólvora, esta fue determinada en base a pruebas experimentales y el resultado corresponde a 80kg. La máquina ha sido desarrollada con la finalidad de reducir la mano de obra, el tiempo de producción y mejorar la calidad del producto respecto al que se obtiene manualmente. Además servirá como un aporte a la innovación tecnológica. Con estos resultados, la máquina se ha diseñado en cinco módulos correspondientes a cada etapa del proceso. El funcionamiento es automático y para el control y ejecución de sus fases se ha utilizado un PLC Siemens S-7200CPU 224. Para la simulación del proceso se utilizó el programa Automation Studio, con el cual se simuló la secuencia, obteniéndose un resultado satisfactorio. Con este tipo de dosificación y compactación se ha logrado incrementar la producción, mejorar la calidad del producto y reducir los productos defectuosos casi en su totalidad. Se recomienda analizar la opción de la mesa revolver, para tratar de reducir el espacio utilizado y el peso de la máquina

Geometrical Modelling Effects on FEA of Colorectal Surgery

The research reported in this paper applies an explicit non-linear FEA solver to simulate the interaction between a clamp and a hyper-elastic material that aims to mimic the biological tissue of the colon. More in detail, the paper provides new results as a continuation of a previous works aimed at the evaluation of this solver to manage contact and dynamic loading on complex, multiple shapes. Results concern with the evaluation of the contact force during clamping, thus to the assessment of the forcefeedback. The analysis is carried out on two geometries, using the hyper-elastic Mooney-Rivlin model for the mechanical behavior of the soft tissues. A pressure is applied on the colon to simulate the surgical clamp, which goes progressively in contact with tissue surface. To assess FEA criticality, and, then, its feasibility, the stress-strain and the contact force are analysed according to geometrical model and thickness variation, leaving the pressure constant. Doing so, their effect on the force-feedback can be foreseen, understanding their role on the accuracy of the final result

APPARATUS FOR THE AUTOMATED PIPETTING AND RELATED PROCESS

It is herein described an apparatus for the automated pipetting arranged to automatically aspirate, transfer and dispense a liquid, such as a biological sample or a reagent, comprising: - an air displacement system to aspirate and dispense a determined volume of liquid, including a pneumatic circuit and a pressure and vacuum source (3), - pipetting means (2) comprising at least one pipetting head (6) connected to said source (3) by means of said pneumatic circuit, - a pipetting tip (21 ) arranged to contain the aspirated liquid, following the activation of the air displacement system to aspirate and dispense a determined volume of liquid, - an internal duct (9) arranged to convey the air displacement generated by said pressure and vacuum source (3), up to the end of the pipetting tip (21 ), so as to perform the operations of aspiration and dispensing of liquid, - a first solenoid valve (4) in communication with the internal duct (9), arranged to control the leakage or retention of the air flow introduced by the source (3), said first solenoid valve (4) being in a normally closed position, - a flow sensor (8) arranged to detect the volume of aspirated/dispensed liquid, wherein said flow sensor (8) is a MEMS thermal sensor