Methods for medical applications

Scaffolds have been produced by supercritical CO<inf>2</inf> drying of Poly-L-Lactid Acid (PLLA) gels loaded with micrometric fructose particles used as porogens. These structures show a microporous architecture generated by the voids left in the solid material by porogen leaching, while they maintain the nanostructure of the gel, consisting of a network of nanofilaments. These scaffolds have also been loaded with Hydroxyapatite (HA) nanoparticles, from 10 to 50% w/w with respect to the polymer, to improve the mechanical properties of the PLLA structure.Based on miscroscopic and mechanical considerations, we propose a parametric Finite Element Method (FEM) model of PLLA-HA composites that describes the microporous structure as a close-packing of equal spheres and the nanoscale structure as a space frame of isotropic curved fibers. The effect of HA on the mechanical properties of the scaffolds has been modeled on the basis of SEM images and by taking into consideration the formation of concentric cylinders of HA nanoparticles around PLLA nanofibers. Modeling analysis confirms that mechanical properties of these scaffolds depend on nanofibrous network connections and that bending is the major factor causing deformation of the network. The FEM model also takes into account the formation of HA multi-layer coating on some areas in the nanofiber network and its increase in thickness with HA percentage. The Young modulus tends to a plateau for HA percentages larger than 30% w/w and when the coverage of the nanofibers produced by HA nanoparticles reaches a loaded surface index of 0.14 in the FEM model.

Keywords: FEM modeling , Hydroxyapatite nanoparticles , Poly(L-Lactic Acid) nanofibers , Scaffold , Supercritical fluids

In a web-based learning environment, interactivity has been referred to as the most important element for successful e-learning. This article presents the production cycle of an interactive medical device, namely a virtual 3D electroencephalogram, and the study conducted to measure the students' satisfaction of the learning application based on Kano's quality model. The web-based interactive learning application introduces unique elements of interactivity with the learning content, specifically designed to train biomedical engineering students at the use of the medical device. The results of a post-deployment student survey suggest that the visual and interactive features embedded in the application have the potential to induce positive satisfaction of users. The proposed approach may serve as reference for the correct design of similar learning applications not only in the biomedical engineering context but also outside the realms of engineering sciences.

Keywords: E-learning , Electroencephalogram , Kano's model , Learner satisfaction , Web-based interactive application

This paper presents a novel method for measuring with great precision the stereoacuity, that is the smallest depth difference that can be detected in binocular vision. The proposed technique is implemented by a software program that runs on a PC with 3D capabilities. The 3D technology is exploited to provide two different images to the two eyes. The measurement is performed by a classical random dot test, but differently to other tests printed on paper or plastic, the images shown to the patient can vary and the disparity between the two images can be set in order to exactly measure the stereoacuity. Moreover, thanks to the exploited 3D technology, the test does not present any monocular clue. These features allow delivering the test also in groups (instead of individuals) like school classes, and to reduce the risk of undetected amlyopia. The system can be easily operated also by not specialized personnel and this may further increase the cost efficiency of the test. We present the experiments carried on with a large set of children of age between five and seven years. We discuss the results and compare our technique with some traditional approaches.

Keywords: 3D , Amblyiopia , Randomdot test , Stereopsis

The research paper concerns the development of a new mobile application emulating measurements of stereoacuity using Google Cardboard. Stereoacuity test is based on binocular vision that is the skill of human beings and most animals to recreate depth sense in visual scene. Google Cardboard is a very low cost device permitting to recreate depth sense of images showed on the screen of a smartphone. Proposed solution exploits Google Cardboard to recreate and manage depth sense through our mobile application that has been developed for Android devices. First, we describe the research context as well as the aim of our research project. Then, we introduce the concept of stereopsis and technology used for emulating stereoacuity test. Finally, we portray preliminary tests made so far and achieved results are discussed.

A procedure for the constitutive analysis of bladder tissues mechanical behavior is provided, by using a coupled experimental and computational approach. The first step pertains to the design and development of mechanical tests on specimens from porcine bladders. The bladders have been harvested, and the specimens have been subjected to uniaxial cyclic tests at different strain rates along preferential directions, considering the distribution of tissue fibrous components. Experimental results showed the anisotropic, non-linear and time-dependent stress-strain behavior, due to tissue conformation with fibers distributed along preferential directions and their interaction phenomena with ground substance. In detail, experimental data showed a greater tissue stiffness along transversal direction. Viscous behavior was assessed by strain rate dependence of stress-strain curves and hysteretic phenomena. The second step pertains the development of a specific fiber-reinforced visco-hyperelastic constitutive model, in the light of bladder tissues structural conformation and experimental results. Constitutive parameters have been identified by minimizing the discrepancy between model and experimental data. The agreement between experimental and model results represent a term for evaluating the reliability of the constitutive models by means of the proposed operational procedure.

Keywords: Bladder , Computational approach , Experimental test , Non-linear mechanics , Soft tissue mechanics

Aim Today Cone Beam Computed Tomography (CBCT) has become an important image technique for dento-maxilla facial applications. In the paper a new method to assess the geometric accuracy of these systems was proposed. It uses a free form benchmark model and a non-contact Reverse Engineering (RE) system. Method The test geometry chosen for this study was designed in such a way that it simulated human spongy bone, cortical bone, gingiva and teeth and it composed of removable free form parts. It was acquired with a high-resolution laser scanner (D700 Scanner - 3Shape, Denmark). The reference 3D surface models obtained with the laser scanner was compared with the 3D models that were created from a CBCT system (Scanora 3D - Soderex, Finland) and from a traditional Multi-Slice Computed Tomography (MSCT) scanner (LightSpeed VCT 64 Slice - General Electric, USA) at different reconstruction settings, using an iterative closest point algorithm (ICP) in Geomagic® software. Results The comparison between the different pairs of CAD models clearly shows that there is a good overlap between the models. Conclusions Although the results obtained in this study could lead to increase the use of CBCT for an increasing number of dental procedures, the publication of the European Commission guidelines represents a baseline on which the clinicians should rely heavily when considering the use of CBCT in their practice. Clinical Significance The results of this research show that the accuracy of CBCT 3D models is comparable to MSCT 3D models. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Benchmark free form model , Cone Beam Computed Tomography (CBCT) , Laser scan , Multi-Slice Computed Tomography (MSCT) , Virtual modelling

Purpose: A suture passed along the part of the graft that will be inserted into the femoral tunnel is widely used by surgeons, because it could prevent the graft sliding on the femoral fixation device during pulling from the tibial side. The aim of this study was to evaluate the biomechanical effects of suturing the intratunnel femoral part of the graft during an anterior cruciate ligament (ACL) reconstruction. Methods: Bovine digital extensor tendons and tibias were harvested from 20 fresh-frozen mature bovine knees ranging in age from 18 to 24 months. Quadruple-strand bovine tendons were passed through the tibial tunnel and secured distally with a bioabsorbable interference screw. In one half of all grafts (N = 10), the looped-over part of the graft was sutured in a whipstitch technique over a distance of 30 mm (Group 1). In one half of all grafts (N = 10), the looped-over part was left free from any suture (Group 2). The grafts were preconditioned at 50 N for 10 min, followed by cyclic loading at 1 Hz between 50 N and 250 N for 1,000 cycles. Load-to-failure test was then carried out at a rate of 1 mm/s. Results: There was no statistically significant difference between mean stiffness at pullout and yield load between the two groups. In all specimens on Group 1, failure occurred following to partial breaking and then slipping of the tendons between the screw and the tunnel. Concerning Group 2, in six cases failure occurred as described for Group 1 specimens. In the remaining four cases, failure occurred entirely through the ligament mid-substance. Conclusions: Suturing in a whipstitch fashion the femoral portion of the graft doesn't affect the mechanical proprieties of the ACL graft. When suspension fixation device is used, suturing the looped-over part of the graft could be helpful in order to provide equal tension in all of the strands of the graft at time of tibial fixation. © 2013 Springer-Verlag Berlin Heidelberg.

Keywords: ACL graft , ACL reconstruction , Anterior cruciate ligament , Biomechanics , Graft properties

This paper presents a new mirroring-and-registration method for the automatic symmetry plane detection of 3D asymmetrically scanned human faces. Once the mirroring of the original data is carried out with respect to the first-attempt symmetry plane, which is estimated by the PCA method, the source point cloud and the mirrored data are registered by the ICP algorithm that minimises a new weighted function. The final symmetry plane obtained approximates in the least-squares sense the midpoints of the lines connecting homologous points randomly chosen. This method is validated by analysing some specifically-designed test cases. The obtained results show that the method is quite insensitive to asymmetries of data resulting from the acquisition process. © 2013 © 2013 CAD Solutions, LLC.

Keywords: iterative closest points , mirroring , rasterstereography , registration , symmetry plane

In this work a commercial reverse shoulder prosthesis has been redesigned to improve performances in terms of range of movements of the implant and stability to dislocation. A kinematic and mechanic study has been performed using a realistic solid model of the prothesised shoulder: in particular, all the components of the prosthesis have been acquired via a 3D laser scanner and inserted in a virtual humerus-glenoid system by reproducing the common surgical procedure. The final model has been used to measure the maximum angles of abduction and rotation of the arm and the shear forces that cause dislocation. Modifications proposed to the commercial prosthesis are: a different orientation of the cutting plane of the glenoid component and the interposition of a spacer to move the center of rotation of the arm.

Keywords: CAD modelling , Digital shape acquisition , Reverse shoulder prosthesis

Aim of this paper is to setup a novel procedure able to analyze performances of a reverse shoulder prosthesis when different geometrical configurations are assumed. Nowadays, such a prosthesis is widely used but, because of its novelty, data in literature give poor information about performances and limits to its applicability. The activity has been divided into the following steps. At the beginning the shape of the prosthesis has been digitally acquired via a 3D scanner. Then, CAD models of all prosthetic components have been geometrically optimized in a way to obtain final entities suitable for numerical simulations. After that, CAD assemblies have been created between prosthetic components and bones (humerus and scapula) involved in the shoulder joint. Following step has been the setup of numerical finite element method models to simulate use conditions. To this scope, analyses have been performed in accordance with experimental conditions found in literature. Stability conditions have been verified under the action of horizontal and vertical instability loads with different version angles between humerus and the humeral implant. In particular, the stability ratios of the prosthesis have been calculated for the analysed loading conditions. Obtained results show how the positioning has a great influence on the shoulder stability and allow the definition of guidelines for the application of this prosthesis. © 2014 Springer-Verlag France.

Keywords: 3D scanner acquisition , Non linear FEM analyses , Reversed shoulder prosthesis , Shoulder stability ratio

Total reverse shoulder arthroplasty is becoming more and more the standard therapeutic practice for glenohumeral arthropathy with massive lesions of the rotator cuff. The biomechanical principle of this prosthesis is represented by the reversion of the normal anatomy of the shoulder joint. This non-anatomical prosthesis leads to a medialization of the rotation centre of the glenohumeral joint and also to a distalization of the humeral head. All that causes a deltoid tension increasing so allowing a larger abduction of the arm. Main complications of the reverse shoulder prosthesis are due to the joint instability, the scapular notching and the wear of the polyethylene insert. Purpose: The main goal of the present work is to study the effect of the positioning of the humeral component on the intrinsic stability of the reverse shoulder prosthesis. In particular, through finite element method simulations, the variation of the stability ratio of the shoulder joint has been calculated for both vertical and horizontal dislocating loads depending on the humeral stem version angle. Moreover, in order to estimate the wear of the polyethylene cup, some analyses have been developed to calculate the pressures on the polyethylene insert. Results: The obtained results demonstrate the dislocation of a shoulder prosthesis and the wear of the polyethylene insert can be prevented or limited by conveniently varying the version angle of the humeral component. © 2013 Istituto Ortopedico Rizzoli.

Keywords: FEM analyses , Intrinsic stability , Polyethylene wear , Stability ratio , Total reverse shoulder arthroplasty

This paper refers to the design of prosthetic socket adopting a computer-aided approach. The main goal is to make available a modeling tool, named SMA-Socket Modeling Assistant, which permits to replicate/emulate manual operations usually performed by the prosthetist. Typically, s/he also relies on the sense of touch; therefore the underlying idea has been to develop and experiment haptic devices. The paper presents a haptic mouse at low-cost to make it affordable also by small orthopedic labs. It is essentially a traditional mouse device enhanced with a servomotor and a pressure sensor pad integrated with Arduino board and SMA. The application within SMA is described as well as the haptic interaction with physically-based model of the residual limb. Finally preliminary tests are illustrated. © 2014 Springer International Publishing Switzerland.

Keywords: Arduino , haptic devices , low cost haptic mouse , prosthesis socket modelling

This paper presents an automatic simulation procedure to study the stump-socket interaction that has been embedded within a software platform specifically developed to design lower limb prosthesis. In particular, it investigates and compares the results obtained by means of FE tools with the experimental data acquired with pressure transducers. A transfemoral (amputation above knee) male amputee has been considered as case study. Numerical simulations have been carried out considering different techniques to acquire the residuum geometry and different socket models. In details, two residuum geometric models were reconstructed starting from MRI images and from 3D scanning to investigate how acquisition techniques influence the final results. Two socket geometric models were taken into account. The first was the patient's real socket, acquired by 3D scanning; the second one has been modeled using a dedicated CAD system, named Socket Modeling Assistant. The patient's real socket has been also used to perform the experimental pressure measurements. The experimental data have been acquired by means of the Tekscan F-socket system. Results reached so far allowed identifying main criticalities and future developments to improve the accuracy of the numerical results and make available a full-automated simulation procedure.

This paper presents a research work on the augmented interaction applied to an innovative platform to design lower limb prosthesis, in particular the prosthetic socket. The underlining idea is to experiment low-cost hand-tracking devices, to manipulate the 3D virtual model of the socket using hands as traditional done by the prosthetist. The goal is to make available a modeling tool, named Socket Modeling Assistant-SMA that permits to replicate/emulate manual operations usually performed by the prosthetist during the traditional development process. Two devices have been considered and compared: the Leap Motion device and the Intel Gestures Camera. To this end a set of gestures has been identified to make more natural the interaction with SMA. Preliminary tests and results reached so are described and discussed.

This paper refers to the integration of simulations tools to assess the design of prosthetic devices. We address issues arising when the prosthesis needs to be virtually tested, i.e., the gait of the virtual patient wearing the prosthesis. Therefore, we integrate two different simulation tools: the first one to study the interaction between socket and residual limb during the gait and the second one to analyze the patient's gait deviations. Combining these numerical analyses, it is possible to investigate the causes of gait deviations and suggest remedies, both related to the prosthesis setup and the socket modeling. To prove the validity of the approach, we implemented a Finite Element Analysis model to analysis the stump-socket contact and we assembled a low cost Motion Capture system to acquire and elaborate patient gait. Preliminary results and remarks conclude the paper.

The contact pressure at the socket-residual limb interface is the most important parameter to evaluate comfort of leg prosthesis. Experimental works analyzed this parameter for typical postures and during walking of an amputee; but experimental tests require a real prototype of the socket equipped with transducers. To optimize socket design, this work presents a virtual approach based on a digital avatar of the patient wearing lower limb prosthesis. Our approach considers the integration of two different types of simulation: the first one concerns the multi-body gait analysis, the second one the pressure evaluation at the socket-residual limb interface with FE analyses. The paper describes the model used, the simulation tools adopted and their integration. Finally the case study related to patient walking on flat floor is described. © 2014 CAD Solutions, LLC.

Keywords: gait simulation , human modeling , prosthesis design , socket-residual limb contact

The accurate reconstruction of a human digital dental model represents a wide research area within the orthodontic field due to its importance for the customization of patient treatments. Usually, 3-D dental root geometries are obtained by segmenting tomographic data. However, concerns about radiation doses may be raised since tomographic scans produce a greater X-ray dose than conventional 2-D panoramic radiographs (PAN). The present work is aimed at investigating the possibility to retrieve 3-D shape of individual teeth by exposing the patient to the minimum radiation dose. The proposed methodology is based on adapting general CAD templates over patient-specific dental anatomy, which is reconstructed by integrating the optical digitization of dental plaster models with a PAN image. The radiographic capturing process is simulated through the Discrete Radon Transform (DRT) and performed onto the patient crowns geometry obtained by segmenting the digital plaster model. A synthetic PAN image is then reconstructed and used to integrate the radiographic data within the digitized plaster model, thus allowing to retrieve roots information which guide the CAD templates adapting over the patient anatomy.

In the last decades, research in the orthodontic field has focused on the development of more comfortable and aesthetic appliances such as thermoformed aligners. Aligners have been used in orthodontics since the mid 20-century. Nonetheless, there is still not enough knowledge about how they interact with teeth. This paper is focused on the development of a Finite Element Method (FEM) model to be used in the optimization process of geometrical attributes of removable aligners. The presented method integrates Cone Beam Computed Tomography (CBCT) data and optical data in order to obtain a customized model of the dental structures, which include both crown and root shapes. The digital simulation has been focused on analyzing the behavior of three upper frontal teeth. Moreover, the analyses have been carried out by using different aligners' thicknesses with the support of composite structures polymerized on teeth surfaces while simulating a 2 degrees rotation of an upper central incisor.

Dental panoramic tomography represents a standard imaging modality in dentistry since it provides a convenient and inexpensive method to visualize anatomic structures and pathologic conditions with low radiation doses. However, this technique does not provide comprehensive 3D geometries of dental shapes which are conventionally demanded to computerised tomography (CT) techniques. In this paper, a tooth reconstruction process is presented by integrating patient-specific information with general dental templates. A 2D panoramic radiograph and the digitised patient plaster cast are used to customise both shape and orientation of teeth templates thus allowing a consistent 3D tooth reconstruction with minimally invasive imaging modalities. The proposed methodology does not make any assumption about the tomographic device used to collect the panoramic radiograph. Copyright © 2014 SCITEPRESS - Science and Technology Publications. All rights reserved.

Keywords: Customised Tooth Reconstruction , Digital Cast , Discrete Radon Transform , Panoramic Radiograph

Monitoring the internal loads acting in a total knee prosthesis (TKP) is fundamental aspect to improve their design. One of the main benefits of this improvement is the longer duration of the tibial inserts. In this work, an electromagnetic energy harvesting system, which is implantable in a TKP, is presented. This is conceived for powering a future implantable system that is able to monitor the loads (and, possibly, other parameters) that could influence the working conditions of a TKP in real-time. The energy harvesting system (EHS) is composed of two series of NdFeB magnets, positioned into each condyle, and a coil that is placed in a pin of the tibial insert and connected to an implantable power management circuit. The magnetic flux variation and the induced voltage are generated by the knee's motion. A TKP prototype has been realized in order to reproduce the knee mechanics and to test the EHS performance. In the present work, the experimental results are obtained by adopting a resistive load of 2.2 kω, in order to simulate a real implanted autonomous system with a current consumption of 850 μA and voltage of 2 V. The tests showed that, after 7 to 30 s of walking with a gait cycle frequency of about 1.0 Hz, the EHS can generate an energy of about 70 μJ, guaranteeing a voltage between 2 and 1.4 V every 7.6 s. With this prototype we can verify that it is possible to power for 16 ms a circuit having a power consumption of 1.7 mW every 7.6 s. The proposed generator is a viable solution to power an implanted electronic system that is conceived for measuring and transmitting the TKP load parameters. © 2014 IOP Publishing Ltd.

Keywords: autonomous device , electromagnetic generator , energy harvesting , implantable sensor , knee prosthesis