Design and Prototyping of Miniaturized Straight Bevel Gears for Biomedical Applications

This paper presents a semi-automated design algorithm for computing straight bevel gear involute profiles. The proposed formulation is based on the Tredgold approximation method. It allows the design of a pair of bevel gears with any desired number of teeth and relative axes inclination angles by implementing additive manufacturing technology. A specific case study is discussed to calculate the profiles of two straight bevel gears of a biomedical application. Namely, this paper illustrates the design of the bevel gears for a new laparoscopic robotic system, EasyLap, under development with a grant from POR Calabria 2014–2020 Fesr-Fse. A meshing analysis is carried out to identify potential design errors. Moreover, finite element-based tooth contact analysis is fulfilled for determining the vibrational performances of the conjugate tooth profiles throughout a whole meshing cycle. Simulation results and a built prototype are reported to show the engineering feasibility and effectiveness of the proposed design approach

Computational fluid dynamics of a novel perfusion strategy using direct perfusion of a left carotid-subclavian bypass during hybrid thoracic aortic repair

To mitigate the risk of perioperative neurological complications during frozen elephant trunk procedures, we aimed to computationally evaluate the effects of direct cerebral perfusion strategy through a left carotid-subclavian bypass on hemodynamics in a patient-specific thoracic aorta model

Performances Analysis of Titanium Prostheses Manufactured by Superplastic Forming and Incremental Forming

Abstract Titanium and its alloys are widely used in cranioplasty because they are biocompatible with excellent mechanical properties and favor the osseointegration with the bone. However, when Titanium alloys have to be worked several problems occurred from a manufacturing point of view: the standard procedure for obtaining Titanium prostheses is represented by the machining processes, which result time and cost consuming. The aim of this research consist to introduce alternative flexible sheet forming processes, i.e. Super Plastic Forming (SPF) and Single Point Incremental Forming (SPIF), for the manufacturing of patient-oriented titanium prostheses. The research activities have already highlighted the potentiality of the investigated forming processes that can be alternatively used taking into account both the damage morphology and the need of urgency operation. In the present work, the way of manufacturing the Ti prostheses by SPF and SPIF is described. A comparative analysis has been performed, thus highlighting the peculiarities of the investigated processes and the prostheses feasibility

A Computational Fluid Dynamics Study to Compare Two Types of Arterial Cannulae for Cardiopulmonary Bypass

Thanks to recent technological and IT advances, there have been rapid developments in biomedical and health research applications of computational fluid dynamics. This is a methodology of computer-based simulation that uses numerical solutions of the governing equations to simulate real fluid flows. The aim of this study is to investigate, using a patient-specific computational fluid dynamics analysis, the hemodynamic behavior of two arterial cannulae, with two different geometries, used in clinical practice during cardiopulmonary bypass. A realistic 3D model of the aorta is extracted from a subject’s CT images using segmentation and reverse engineering techniques. The two cannulae, with similar geometry except for the distal end (straight or curved tip), are modeled and inserted at the specific position in the ascending aorta. The assumption of equal boundary conditions is adopted for the two simulations in order to analyze only the effects of a cannula’s geometry on hemodynamic behavior. Simulation results showed a greater percentage of the total output directed towards the supra-aortic vessels with the curved tip cannula (66% vs. 54%), demonstrating that the different cannula tips geometry produces specific advantages during cardiopulmonary bypass. Indeed, the straight one seems to generate a steadier flow pattern with good recirculation in the ascending aorta

Support Tool for Anchoring System Optimization of Titanium Craniofacial Prostheses

Titanium prostheses are artificial components used during cranioplasty, which can be made with the Incremental Sheet Forming (ISF). To repair the craniofacial defects, the implant must be fixed to the skull, so an adequate anchoring system is necessary. Because there are no specific guidelines regarding this system, the aim of this study was to present a methodology for the identification of the optimal screw shank diameter and the overlap length, considering different damage areas and accidental external loads. In this method, a numerical model for structural analysis, a statistical approach and a metamodeling technique were coupled. The results demonstrate that this methodology can be used as a decision support tool in the titanium prostheses design, ensuring the best anchorage

Support Tool for Anchoring System Optimization of Titanium Craniofacial Prostheses

Titanium prostheses are artificial components used during cranioplasty, which can be made with the Incremental Sheet Forming (ISF). To repair the craniofacial defects, the implant must be fixed to the skull, so an adequate anchoring system is necessary. Because there are no specific guidelines regarding this system, the aim of this study was to present a methodology for the identification of the optimal screw shank diameter and the overlap length, considering different damage areas and accidental external loads. In this method, a numerical model for structural analysis, a statistical approach and a metamodeling technique were coupled. The results demonstrate that this methodology can be used as a decision support tool in the titanium prostheses design, ensuring the best anchorage

A COUPLED EXPERIMENTAL AND NUMERICAL APPROACH TO CHARACTERIZE THE ANISOTROPIC MECHANICAL BEHAVIOR OF AORTIC TISSUES

Nowadays, the investigation of aortic wall biomechanics is a fundamental tool in clinicalresearch and vascular prosthesis design. This study aims at analyzing the biomechanicalbehavior of aortic tissues using a coupled experimental and computational approach. Con-sidering the typical fiber-reinforced configuration of aortic tissues, uni-axial tensile tests alongsix different loading directions were performed on specimens from pig aorta. Starting from theobtained experimental data, a suitable constitutive framework was defined and a methodologyfor the identification of the constitutive parameters was developed using the inverse analysis ofmechanical tests. Transversal stretch versus loading stretch and nominal stress versus loadingstretch curves were evaluated, showing the anisotropic and nonlinear mechanical behaviordetermined by tissue conformation with fibers distributed along preferential directions. Indetail, experimental data showed different mechanical responses between longitudinal andcircumferential directions, with a greater tissue stiffness along the longitudinal one. The reli-ability of the developed constitutive framework was evaluated by the comparison betweenexperimental data and model results. The mentioned analysis can be considered as a useful toolfor the development of reliable computational models, which allow a better understanding ofthe pathophysiology of cardiovascular diseases and can be applied for a proper planning ofsurgical procedures

Kinetic Analysis of Lidocaine Elimination by Pig Liver Cells Cultured in 3D Multi-Compartment Hollow Fiber Membrane Network Perfusion Bioreactors

Liver cells cultured in 3D bioreactors is an interesting option for temporary extracorporeal liver support in the treatment of acute liver failure and for animal models for preclinical drug screening. Bioreactor capacity to eliminate drugs is generally used for assessing cell metabolic competence in different bioreactors or to scale-up bioreactor design and performance for clinical or preclinical applications. However, drug adsorption and physical transport often disguise the intrinsic drug biotransformation kinetics and cell metabolic state. In this study, we characterized the intrinsic kinetics of lidocaine elimination and adsorption by porcine liver cells cultured in 3D four-compartment hollow fiber membrane network perfusion bioreactors. Models of lidocaine transport and biotransformation were used to extract intrinsic kinetic information from response to lidocaine bolus of bioreactor versus adhesion cultures. Different from 2D adhesion cultures, cells in the bioreactors are organized in liver-like aggregates. Adsorption on bioreactor constituents significantly affected lidocaine elimination and was effectively accounted for in kinetic analysis. Lidocaine elimination and cellular monoethylglicinexylidide biotransformation featured first-order kinetics with near-to-in vivo cell-specific capacity that was retained for times suitable for clinical assist and drug screening. Different from 2D cultures, cells in the 3D bioreactors challenged with lidocaine were exposed to close-to-physiological lidocaine and monoethylglicinexylidide concentration profiles. Kinetic analysis suggests bioreactor technology feasibility for preclinical drug screening and patient assist and that drug adsorption should be accounted for to assess cell state in different cultures and when laboratory bioreactor design and performance is scaled-up to clinical use or toxicological drug screening