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Showing 1401 - 1600 of 1720 Journals sorted alphabetically
Virology Journal     Open Access   (Followers: 6)
Virulence     Full-text available via subscription   (Followers: 1)
Virus Evolution     Open Access   (Followers: 1)
Virus Genes     Hybrid Journal   (Followers: 1)
Virus Research     Hybrid Journal   (Followers: 1)
Visnyk of Dnipropetrovsk University. Biology, ecology     Open Access   (Followers: 2)
Visnyk of Dnipropetrovsk University. Biology, medicine     Open Access  
Walailak Journal of Science and Technology     Open Access  
Web Ecology     Open Access   (Followers: 5)
Weed Science     Full-text available via subscription   (Followers: 6)
Weed Technology     Full-text available via subscription   (Followers: 2)
West African Journal of Applied Ecology     Open Access  
Western Undergraduate Research Journal : Health and Natural Sciences     Open Access  
Wetlands     Hybrid Journal   (Followers: 24)
Wildlife Biology     Open Access   (Followers: 14)
Wildlife Research     Hybrid Journal   (Followers: 15)
Wiley Interdisciplinary Reviews - System Biology and Medicine     Hybrid Journal   (Followers: 5)
Wiley Interdisciplinary Reviews : Developmental Biology     Hybrid Journal   (Followers: 3)
Wiley Interdisciplinary Reviews : Membrane Transport and Signaling     Hybrid Journal  
Wiley Interdisciplinary Reviews : RNA     Hybrid Journal   (Followers: 3)
World Crop Pests     Full-text available via subscription   (Followers: 1)
World Mycotoxin Journal     Full-text available via subscription   (Followers: 6)
Xenobiotica     Hybrid Journal   (Followers: 8)
Yeast     Hybrid Journal   (Followers: 9)
Zebrafish     Hybrid Journal   (Followers: 1)
Zeitschrift für Evidenz, Fortbildung und Qualität im Gesundheitswesen     Full-text available via subscription   (Followers: 5)
Zeitschrift für Naturforschung C : A Journal of Biosciences     Open Access   (Followers: 2)

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Journal Cover Medical Engineering & Physics
  [SJR: 0.784]   [H-I: 76]   [9 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1350-4533
   Published by Elsevier Homepage  [3043 journals]
  • Special Issue “Micro and Nano Flows 2016 (MNF2016) –
           Biomedical Stream”
    • Authors: Gabriele Dubini; Carola S. König; Alberto Redaelli
      Pages: 1 - 2
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Gabriele Dubini, Carola S. König, Alberto Redaelli


      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.09.001
      Issue No: Vol. 48 (2017)
       
  • Engineering human renal epithelial cells for transplantation in
           regenerative medicine
    • Authors: Vita Manzoli; David C. Colter; Sridevi Dhanaraj; Alessia Fornoni; Camillo Ricordi; Antonello Pileggi; Alice A. Tomei
      Pages: 3 - 13
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Vita Manzoli, David C. Colter, Sridevi Dhanaraj, Alessia Fornoni, Camillo Ricordi, Antonello Pileggi, Alice A. Tomei
      Cellular transplantation may treat several human diseases by replacing damaged cells and/or providing a local source of trophic factors promoting regeneration. We utilized human renal epithelial cells (hRECs) isolated from cadaveric donors as a cell model. For efficacious implementation of hRECs for treatment of kidney diseases, we evaluated a novel encapsulation strategy for immunoisolation of hRECs and lentiviral transduction of the Green Fluorescent Protein (GFP) as model gene for genetic engineering of hRECs to secrete desired trophic factors. In specific, we determined whether encapsulation through conformal coating and/or GFP transduction of hRECs allowed preservation of cell viability and of their trophic factor secretion. To that end, we optimized cultures of hRECs and showed that aggregation in three-dimensional spheroids significantly preserved cell viability, proliferation, and trophic factor secretion. We also showed that both wild type and GFP-engineered hRECs could be efficiently encapsulated within conformal hydrogel coatings through our fluid dynamic platform and that this resulted in further improvement of cell viability and trophic factors secretion. Our findings may lay the groundwork for future therapeutics based on transplantation of genetically engineered human primary cells for treatment of diseases affecting kidneys and potentially other tissues.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.03.009
      Issue No: Vol. 48 (2017)
       
  • Modeling the cleavage of von Willebrand factor by ADAMTS13 protease in
           shear flow
    • Authors: Brooke Huisman; Masoud Hoore; Gerhard Gompper; Dmitry A. Fedosov
      Pages: 14 - 22
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Brooke Huisman, Masoud Hoore, Gerhard Gompper, Dmitry A. Fedosov
      Von Willebrand factor (VWF) is a key protein in hemostasis as it mediates adhesion of blood platelets to a site of vascular injury. A proper distribution of VWF lengths is important for normal functioning of hemostatic processes, because a diminished number of long VWF chains may significantly limit blood clotting and lead to bleeding, while an abundant number of long VWFs may result in undesired thrombotic events. VWF size distribution is controlled by ADAMTS13 protease, which can cleave VWF chains beyond a critical shear rate when the chains are stretched enough such that cleavage sites become accessible. To better understand the cleavage process, we model VWF cleavage in shear flow using mesoscopic hydrodynamic simulations. Two cleavage models are proposed, a geometrical model based on the degree of local stretching of VWF, and a tension-force model based on instantaneous tension force within VWF bonds. Both models capture the susceptibility of VWF to cleavage at high shear rates; however, the geometrical model appears to be much more robust than the force model. Our simulations show that VWF susceptibility to cleavage in shear flow becomes a universal function of shear rate, independent of VWF length for long enough chains. Furthermore, VWF is cleaved with a higher probability close to its ends in comparison to cleaving in the middle, which results into longer circulation lifetimes of VWF multimers. Simulations of dynamic cleavage of VWF show an exponential distribution of chain lengths, consistently with available in vitro experiments. The proposed cleavage models can be used in realistic simulations of hemostatic processes in blood flow.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.044
      Issue No: Vol. 48 (2017)
       
  • Red blood cell aggregate flux in a bifurcating microchannel
    • Authors: E Kaliviotis; D. Pasias; J.M. Sherwood; S. Balabani
      Pages: 23 - 30
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): E Kaliviotis, D. Pasias, J.M. Sherwood, S. Balabani
      Red blood cell aggregation plays a key role in microcirculatory flows, however, little is known about the transport characteristics of red blood cell aggregates in branching geometries. This work reports on the fluxes of red blood cell aggregates of various sizes in a T-shaped microchannel, aiming to clarify the effects of different flow conditions in the outlet branches of the channel. Image analysis techniques, were utilised, and moderately aggregating human red blood cell suspensions were tested in symmetric (∼50–50%) and asymmetric flow splits through the two outlet (daughter) branches. The results revealed that the flux decreases with aggregate size in the inlet (parent) and daughter branches, mainly due to the fact that the number of larger structures is significantly smaller than that of smaller structures. However, when the flux in the daughter branches is examined relative to the aggregate size flux in the parent branch an increase with aggregate size is observed for a range of asymmetric flow splits. This increase is attributed to size distribution and local concentration changes in the daughter branches. The results show that the flow of larger aggregates is not suppressed downstream of a bifurcation, and that blood flow is maintained, for physiological levels of red blood cell aggregation.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.04.007
      Issue No: Vol. 48 (2017)
       
  • Characterisation of medical microfluidic systems regarding fast changing
           flow rates using optical front tracking methods
    • Authors: Joerg Schroeter; Lino del Bianco; Christian Damiani; Stephan Klein; Bodo Nestler
      Pages: 39 - 48
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Joerg Schroeter, Lino del Bianco, Christian Damiani, Stephan Klein, Bodo Nestler
      The presented optical flow metering methods are appropriate to characterise the dynamic properties of microfluidic systems. The dynamic behaviour of clinical or medical devices, micro pumps and flow sensors based on thermal methods were investigated. The Camera-System covers a flow range from 50nl/min to 500µl/min. The uncertainty is less than 4%, sample rates up to 5kS/s. The Displacement-Sensor-System covers a flow range between 100µl/min and 50ml/min. The uncertainty is less than 3% at sample rates up to 49kS/s. It was shown that measuring pulsating flow rates with thermal flow sensors is possible, but the signal is low pass filtered. The low pass behaviour is determined by the thermal properties, thermal resistance and heat capacity, of the flow channel. But the mean flow rate was always measured properly. The fluidic properties of two different types of micro pumps were examined and characterised exemplary.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.05.001
      Issue No: Vol. 48 (2017)
       
  • Deformability- and size-based microcapsule sorting
    • Authors: Doriane Vesperini; Oriane Chaput; Nadège Munier; Pauline Maire; Florence Edwards-Lévy; Anne-Virginie Salsac; Anne Le Goff
      Pages: 68 - 74
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Doriane Vesperini, Oriane Chaput, Nadège Munier, Pauline Maire, Florence Edwards-Lévy, Anne-Virginie Salsac, Anne Le Goff
      Biomedical applications often require to sort cells according to their physical properties, such as size, density or deformability. In recent years, microfluidics has provided a variety of tools to sort micro-objects. We present here a simple microfluidic device consisting of a channel containing a semi-cylindrical obstacle against which capsules are squeezed by the flow, followed by a diverging chamber where streamlines separate. We demonstrate that this basic system is capable of sorting elastic microcapsules according to their size at low flow strength, and according to the stiffness of their membrane at high flow strength. Contrary to most existing sorting devices, we show that the present one is very sensitive and capable of discriminating between capsules with differences in membrane elasticity of order unity.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.040
      Issue No: Vol. 48 (2017)
       
  • On the halt of spontaneous capillary flows in diverging open channels
    • Authors: J. Berthier; K.A. Brakke; D. Gosselin; F. Navarro; N. Belgacem; D. Chaussy; E. Berthier
      Pages: 75 - 80
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): J. Berthier, K.A. Brakke, D. Gosselin, F. Navarro, N. Belgacem, D. Chaussy, E. Berthier
      Due to their compactness and independence of exterior energy sources, capillary microsystems are increasingly used in many different scientific domains, from biotechnology to medicine and biology, chemistry, energy and space. Obtaining a capillary flow depends on channel geometry and contact angle. A general condition for the establishment of a spontaneous capillary flow in a uniform cross section channel has already been derived from Gibbs free energy. In this work, we consider spontaneous capillary flows (SCF) in diverging open rectangular channels and suspended channels, and we show that they do not flow indefinitely but stop at some location in the channel. In the case of linearly diverging open channels, we derive the expression that determines the location where the flow stops. The theoretical approach is verified by using the Surface Evolver numerical program and is checked by experiments. The approach is extended to sudden enlargements, and it is shown that the enlargements can act as stop and trigger valves.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.05.005
      Issue No: Vol. 48 (2017)
       
  • Simulation and performance analysis of a novel high-accuracy sheathless
           microfluidic impedance cytometer with coplanar electrode layout
    • Authors: Federica Caselli; Paolo Bisegna
      Pages: 81 - 89
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Federica Caselli, Paolo Bisegna
      The performance of a novel microfluidic impedance cytometer (MIC) with coplanar configuration is investigated in silico. The main feature of the device is the ability to provide accurate particle-sizing despite the well-known measurement sensitivity to particle trajectory. The working principle of the device is presented and validated by means of an original virtual laboratory providing close-to-experimental synthetic data streams. It is shown that a metric correlating with particle trajectory can be extracted from the signal traces and used to compensate the trajectory-induced error in the estimated particle size, thus reaching high-accuracy. An analysis of relevant parameters of the experimental setup is also presented.
      Graphical abstract image

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.04.005
      Issue No: Vol. 48 (2017)
       
  • A review of bioregulatory and coupled mechanobioregulatory mathematical
           models for secondary fracture healing
    • Authors: Monan Wang; Ning Yang
      Pages: 90 - 102
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Monan Wang, Ning Yang
      Fracture healing is a complex biological process involving many cellular and molecular events. During fracture healing, biochemical signals play a regulatory role in promoting the healing process. Although many experiments have been conducted to study fracture healing, not all of the mechanisms are clearly understood. Over the past years, a lot of mathematical models and computational simulations have been established to investigate the fracture healing process. These models offer a powerful tool to study the interplay between cell behaviour, mechanical stimuli and biochemical signals and help design new treatment strategies. However, most of the mathematical models focus on the effect of mechanical stimuli and few models consider the important role of biochemical signals during fracture healing. In this review, we first emphasize the importance of biochemical signals during fracture healing. Then, existing bioregulatory and coupled mechanobioregulatory models are presented. Finally, some limitations and possible solutions are discussed.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.031
      Issue No: Vol. 48 (2017)
       
  • Influence of design features of tibial stems in total knee arthroplasty on
           tibial bone remodeling behaviors
    • Authors: Zhengbin Jia; He Gong; Shimin Hu; Juan Fang; Ruoxun Fan
      Pages: 103 - 113
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Zhengbin Jia, He Gong, Shimin Hu, Juan Fang, Ruoxun Fan
      In total knee arthroplasty, the optimal length and material of tibial stem remain controversial. This study aimed to evaluate influences of lengths and materials of cementless stems on tibial remodeling behaviors. Three groups of lengths were investigated (i.e., 110, 60, and 30 mm), and four materials (i.e., titanium, flexible ‘iso-elastic’ material, and two functionally graded materials [FGMs]) were selected for each group. FGM is a kind of material whose composition gradually varies in space. In this study, the compositions of two FGMs were Ti and hydroxyapatite (FGM I), and Ti and bioglass (FGM II), respectively. Tibial models were incorporated with finite element analysis to simulate bone remodeling. Distributions of bone mineral density, von Mises stress, and interface shear stress were obtained. For the length, the long stem produced more serious stress shielding and stress concentration than the short stem, but it could provide better mechanical stability. For the material, FGM I could reduce stress shielding and stress concentration and reduce the risk of loosening. Compared with the length, the material had a pronounced effect on remodeling. This study provided theoretical basis for optimal design of stem to improve service life of tibial components and to reduce pain of patients.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.046
      Issue No: Vol. 48 (2017)
       
  • What are the six degree-of-freedom errors of a robotically-machined
           femoral cavity in total hip arthroplasty and are they clinically
           important' An in-vitro study
    • Authors: Chih Ming Hsieh; Stephen M. Howell; Maury L. Hull
      Pages: 120 - 130
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Chih Ming Hsieh, Stephen M. Howell, Maury L. Hull
      Errors during a robot-assisted THA may result in a femoral cavity with position and orientation different than planned. This can lead to a femoral component placement that inaccurately sets a patient's femoral anteversion (FA), femoral offset (FO), and vertical offset (VO). The objectives of this study were to determine the position and orientation errors of robotically-machined femoral cavities in six degrees of freedom and to determine how position and orientation errors translate into errors in the setting of FA, FO, and VO. After creating preoperative plans, robot-assisted THAs were performed on twelve cadaveric specimens. The position and orientation of the machined cavities were compared to those of the planned cavities to determine the errors in six degrees of freedom. Placement of femoral components into the machined cavities was simulated, and the differences in FA, FO, and VO between the simulated and planned component placement were computed. While bias (i.e. mean error) occurred for three of six degrees of freedom in femoral cavities machined by a robotic system, the root mean squared errors (RMSEs) when the placement of femoral component was simulated were limited to 1.9° for FA, 1.0mm for FO, and 2.1mm for VO and were clinically unimportant.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.016
      Issue No: Vol. 48 (2017)
       
  • Development of a multi-DoF transhumeral robotic arm prosthesis
    • Authors: D.S.V. Bandara; R.A.R.C. Gopura; K.T.M.U. Hemapala; Kazuo Kiguchi
      Pages: 131 - 141
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): D.S.V. Bandara, R.A.R.C. Gopura, K.T.M.U. Hemapala, Kazuo Kiguchi
      An anthropomorphic transhumeral robotic arm prosthesis is proposed in this study. It is capable of generating fifteen degrees-of-freedom, seven active and eight passive. In order to realize wrist motions, a parallel manipulator-based mechanism is proposed. It simulates the human anatomical structure and generates motions in two axes. The hand-of-arm prosthesis consists of under-actuated fingers with intrinsic actuation. The finger mechanism is capable of generating three degrees of freedom, and it exhibits the capability of adjusting the joint angles passively according to the geometry of the grasping object. Additionally, a parameter to evaluate finger mechanisms is introduced, and it measures the adoptability of a finger mechanism. In order to verify the mechanism's efficacy in terms of motion generation, motion simulation and kinematic analysis were carried out. Results demonstrated that the mechanisms are capable of generating the required motions.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.034
      Issue No: Vol. 48 (2017)
       
  • A new mathematical model of wrist pulse waveforms characterizes patients
           with cardiovascular disease – A pilot study
    • Authors: Dianning He; Lu Wang; Xiaobing Fan; Yang Yao; Ning Geng; Yingxian Sun; Lisheng Xu; Wei Qian
      Pages: 142 - 149
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Dianning He, Lu Wang, Xiaobing Fan, Yang Yao, Ning Geng, Yingxian Sun, Lisheng Xu, Wei Qian
      The purpose of this study was to analyze and compare a series of measured radial pulse waves as a function of contact pressure for young and old healthy volunteers, and old patients with cardiovascular disease. The radial pulse waves were detected with a pressure sensor and the contact pressure of the sensor was incremented by 20gf during the signal acquisition. A mathematical model of radial pulse waveform was developed by using two Gaussian functions modulated by radical functions and used to fit the pulse waveforms. Then, a ratio of area (rA ) and a ratio of peak height (rPH ) between percussion wave and dicrotic wave as a function of contact pressure were calculated based on fitted parameters. The results demonstrated that there was a maximum for waveform peak height, a minimum for rA ( r A m i n ) and a minimum for rPH ( r P H m i n ) appeared as contact pressure varied. On average, older patients had higher peak amplitude and a significantly smaller r A m i n (p <0.001) and r P H m i n (p <0.02) than the young and old volunteers. The r A m i n and r P H m i n calculated with the mathematical model had moderate to strong positive linear correlations (r =0.66 to 0.84, p <0.006) with those directly calculated without the model. The receiver operating characteristic (ROC) analysis showed that the r A m i n calculated with the model and the contact pressure measured at the r A m i n had good diagnostic accuracy to distinguish healthy volunteers vs. diseased patients. Therefore, using the mathematical model to quantitatively analyze the radial pulse waveforms as a function of contact pressure could be useful in the diagnosis of cardiovascular diseases.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.022
      Issue No: Vol. 48 (2017)
       
  • Geometry of an inflated membrane in elliptic bulge tests: Evaluation of an
           ellipsoidal shape approximation by stereoscopic digital image correlation
           measurements
    • Authors: C. Jayyosi; K. Bruyère-Garnier; M. Coret
      Pages: 150 - 157
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): C. Jayyosi, K. Bruyère-Garnier, M. Coret
      Elliptic bulge tests are conducted on liver capsule, a fibrous connective membrane, associated with a field measurement method to assess the global geometry of the samples during the tests. The experimental set up is derived from a previous experimental campaign of bulge tests under microscope. Here, a stereoscopic Digital Image Correlation (DIC) system is used to measure global parameters on the test and investigate some assumptions made on the testing conditions which could not been assessed with microscopic measurements. In particular, the assumption of an ellipsoidal shape of the inflated membrane is tested by comparing the actual sample shape measured by stereoscopic DIC with an idealized ellipsoidal shape. Results indicate that a rather constant gap exists between the idealized and actual position. The approximation in the calculation of a macroscopic strain through analytical modeling of the test is estimated here. The study of the liver capsule case shows that important differences can be observed in strain calculation depending on the method and assumptions taken. Therefore, analytical modeling of mechanical tests through ellipsoidal approximation needs to be carefully evaluated in every application. Here the field measurement allows assessing the validity of these modeling assumptions. Moreover, it gives precious details about the boundary conditions of the bulge test and revealed the heterogeneous clamping, highlighted by strain concentrations.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.020
      Issue No: Vol. 48 (2017)
       
  • The impact of subchondral bone cysts on local bone stresses in the medial
           femoral condyle of the equine stifle joint
    • Authors: Lance L. Frazer; Elizabeth M. Santschi; Kenneth J. Fischer
      Pages: 158 - 167
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Lance L. Frazer, Elizabeth M. Santschi, Kenneth J. Fischer
      Subchondral lucency (SCL), also referred to as subchondral bone cysts, can cause clinical problems in horses and humans. In humans, SCLs occur in youths and adolescents [1] due to mechanical factors (often related to athletics) and in skeletally mature individuals secondary to osteoarthritis (OA). In horses, SCL most commonly occurs in the medial femoral condyle (MFC) of growing horses (without OA), and causes lameness. The cause of equine SCL is debated, but bone trauma due to overload is the likely mechanism. Investigating the biomechanics of the healthy and cystic MFC is important to understand cyst growth and to provide a foundation for new treatment strategies. We hypothesize that SCL alters the mechanical environment of surrounding bone, which in the presence of continued loading, may lead to enlargement of the SCL. In this study, we developed and validated a finite element model of an equine stifle joint and investigated the stresses associated with varying sizes of SCL. We found substantial differences in tensile and shear stress at various stages of SCL development that suggest further bone damage leading to SCL enlargement. These data provide a first step in understanding of the altered mechanics of subchondral bone surrounding a SCL. Additional studies may provide the basis for improved treatment strategies for SCL in young horses, and may improve the understanding of SCL in humans.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.019
      Issue No: Vol. 48 (2017)
       
  • Kinematic behavior of a customized surface-guided knee implant during
           simulated knee-bending
    • Authors: Shabnam Pejhan; Eric Bohm; Jan-Mels Brandt; Trevor Gascoyne; Urs Wyss
      Pages: 168 - 175
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Shabnam Pejhan, Eric Bohm, Jan-Mels Brandt, Trevor Gascoyne, Urs Wyss
      Different designs of total knee replacements (TKRs) aim to enhance the satisfaction of the patients by providing close to normal kinematics. In the surface-guided TKRs, the guidance of the motion in a normal pattern should be achieved through specially shaped articulating geometries. This study used virtual simulation along with a load-controlled knee wear simulator to evaluate the kinematic performance of a customized surface-guided TKR under weight-bearing conditions of lunging and squatting activities. The outcome pattern of TKR motion almost agreed with the predefined design target. The tibial insert rotated internally through a maximum angle of 10.6° and 19.94° for the experimentally simulated lunging and squatting cycles, respectively. This rotation occurred around a medial center, as indicated by a small amount of posterior translation of the medial condyle (maximum of 2.5mm and 6.4mm for lunging and squatting) versus the posterior translation of the lateral condyle (maximum of 12mm and 24.2mm for lunging and squatting). The contact forces mainly provided the guidance of the motion at the tibiofemoral articulating surfaces.The normalized root mean square error between outcomes of the virtual simulations and tests for the angle of internal-external rotation of the tibial insert was less than 8% for one cycle of lunging and squatting. These measures confirm the validity of the virtual simulation for future evaluations of the customized surface-guided TKRs.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.018
      Issue No: Vol. 48 (2017)
       
  • Improving the detection of evoked responses to periodic stimulation by
           using bivariate local spectral F-test – Application to EEG during photic
           stimulation
    • Authors: Leonardo Bonato Felix; Paulo Fábio Rocha; Eduardo Mazoni Andrade Marçal Mendes; Antonio Mauricio Ferreira Leite Miranda de Sá
      Pages: 176 - 180
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Leonardo Bonato Felix, Paulo Fábio Rocha, Eduardo Mazoni Andrade Marçal Mendes, Antonio Mauricio Ferreira Leite Miranda de Sá
      The spectral local F-test has been applied for detecting evoked responses to rhythmic stimulation that are embedded in the ongoing electroencephalogram (EEG). Based on the sampling distribution of a flat spectrum at the neighbourhood of the stimulation frequency, spectral peaks in an EEG signal that are due to the stimulation may be readily assessed. Nevertheless, the performance of the technique is strongly affected by both the signal-to-noise ratio (SNR) of the responses and the number of data segments used in the estimation. The present work aims at both deriving and evaluating a multivariate extension of local F-test by including the EEG collected at a second distinct derivation. The detection rate with this multivariate detector was found to be greater than that using a single channel in case of equal SNR in both signals. Monte Carlo simulation results showed that the probability of detection with this new detector saturates for signal-to-noise ratios above 12 dB and indicated a greater detection rate in practical situations, even when smaller SNR-values are found in the added signal (e.g. 5 dB for 16 neighbouring frequencies used in the estimation). The technique was next applied to the EEG from 12 subjects during intermittent, photic stimulation leading to superior performance in comparison with the univariate local F-test. Since a higher detection rate with the proposed technique is achieved without the need of increasing the number of data segments, it allows evoked responses to be detected faster, once the same detection rate may be accomplished with less segments. This might be useful in clinical practice.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.032
      Issue No: Vol. 48 (2017)
       
  • Investigation of the feasibility of non-invasive optical sensors for the
           quantitative assessment of dehydration
    • Authors: Cobus Visser; Eduard Kieser; Kiran Dellimore; Dawie van den Heever; Johan Smith
      Pages: 181 - 187
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Cobus Visser, Eduard Kieser, Kiran Dellimore, Dawie van den Heever, Johan Smith
      This study explores the feasibility of prospectively assessing infant dehydration using four non-invasive, optical sensors based on the quantitative and objective measurement of various clinical markers of dehydration. The sensors were investigated to objectively and unobtrusively assess the hydration state of an infant based on the quantification of capillary refill time (CRT), skin recoil time (SRT), skin temperature profile (STP) and skin tissue hydration by means of infrared spectrometry (ISP). To evaluate the performance of the sensors a clinical study was conducted on a cohort of 10 infants (aged 6–36 months) with acute gastroenteritis. High sensitivity and specificity were exhibited by the sensors, in particular the STP and SRT sensors, when combined into a fusion regression model (sensitivity: 0.90, specificity: 0.78). The SRT and STP sensors and the fusion model all outperformed the commonly used “gold standard” clinical dehydration scales including the Gorelick scale (sensitivity: 0.56, specificity: 0.56), CDS scale (sensitivity: 1.0, specificity: 0.2) and WHO scale (sensitivity: 0.13, specificity: 0.79). These results suggest that objective and quantitative assessment of infant dehydration may be possible using the sensors investigated. However, further evaluation of the sensors on a larger sample population is needed before deploying them in a clinical setting.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.036
      Issue No: Vol. 48 (2017)
       
  • Non-invasive vibrometry-based diagnostic detection of acetabular cup
           loosening in total hip replacement (THR)
    • Authors: Abdullah A. Alshuhri; Timothy P. Holsgrove; Anthony W. Miles; James L. Cunningham
      Pages: 188 - 195
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Abdullah A. Alshuhri, Timothy P. Holsgrove, Anthony W. Miles, James L. Cunningham
      Total hip replacement is aimed at relieving pain and restoring function. Currently, imaging techniques are primarily used as a clinical diagnosis and follow-up method. However, these are unreliable for detecting early loosening, and this has led to the proposal of novel techniques such as vibrometry. The present study had two aims, namely, the validation of the outcomes of a previous work related to loosening detection, and the provision of a more realistic anatomical representation of the clinical scenario. The acetabular cup loosening conditions (secure, and 1 and 2 mm spherical loosening) considered were simulated using Sawbones composite bones. The excitation signal was introduced in the femoral lateral condyle region using a frequency range of 100–1500 Hz. Both the 1 and 2 mm spherical loosening conditions were successfully distinguished from the secure condition, with a favourable frequency range of 500–1500 Hz. The results of this study represent a key advance on previous research into vibrometric detection of acetabular loosening using geometrically realistic model, and demonstrate the clinical potential of this technique.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.037
      Issue No: Vol. 48 (2017)
       
  • Dynamic simulation of knee-joint loading during gait using force-feedback
           control and surrogate contact modelling
    • Authors: Jonathan P. Walter; Marcus G. Pandy
      Pages: 196 - 205
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Jonathan P. Walter, Marcus G. Pandy
      The aim of this study was to perform multi-body, muscle-driven, forward-dynamics simulations of human gait using a 6-degree-of-freedom (6-DOF) model of the knee in tandem with a surrogate model of articular contact and force control. A forward-dynamics simulation incorporating position, velocity and contact force-feedback control (FFC) was used to track full-body motion capture data recorded for multiple trials of level walking and stair descent performed by two individuals with instrumented knee implants. Tibiofemoral contact force errors for FFC were compared against those obtained from a standard computed muscle control algorithm (CMC) with a 6-DOF knee contact model (CMC6); CMC with a 1-DOF translating hinge-knee model (CMC1); and static optimization with a 1-DOF translating hinge-knee model (SO). Tibiofemoral joint loads predicted by FFC and CMC6 were comparable for level walking, however FFC produced more accurate results for stair descent. SO yielded reasonable predictions of joint contact loading for level walking but significant differences between model and experiment were observed for stair descent. CMC1 produced the least accurate predictions of tibiofemoral contact loads for both tasks. Our findings suggest that reliable estimates of knee-joint loading may be obtained by incorporating position, velocity and force-feedback control with a multi-DOF model of joint contact in a forward-dynamics simulation of gait.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.043
      Issue No: Vol. 48 (2017)
       
  • Evaluating and improving the performance of thin film force sensors within
           body and device interfaces
    • Authors: Jirapat Likitlersuang; Matthew J. Leineweber; Jan Andrysek
      Pages: 206 - 211
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Jirapat Likitlersuang, Matthew J. Leineweber, Jan Andrysek
      Thin film force sensors are commonly used within biomechanical systems, and at the interface of the human body and medical and non-medical devices. However, limited information is available about their performance in such applications. The aims of this study were to evaluate and determine ways to improve the performance of thin film (FlexiForce) sensors at the body/device interface. Using a custom apparatus designed to load the sensors under simulated body/device conditions, two aspects were explored relating to sensor calibration and application. The findings revealed accuracy errors of 23.3±17.6% for force measurements at the body/device interface with conventional techniques of sensor calibration and application. Applying a thin rigid disc between the sensor and human body and calibrating the sensor using compliant surfaces was found to substantially reduce measurement errors to 2.9±2.0%. The use of alternative calibration and application procedures is recommended to gain acceptable measurement performance from thin film force sensors in body/device applications.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.06.017
      Issue No: Vol. 48 (2017)
       
  • Special Issue on “Frontier Biomechanical Challenges in
           Cardiovascular Physiopathology”
    • Authors: Salvatore Pasta; Massimiliano Zingales
      First page: 1
      Abstract: Publication date: September 2017
      Source:Medical Engineering & Physics, Volume 47
      Author(s): Salvatore Pasta, Massimiliano Zingales


      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.001
      Issue No: Vol. 47 (2017)
       
  • Force estimation in fatigue condition using a muscle-twitch model during
           isometric finger contraction
    • Authors: Youngjin Na; Sangjoon J. Kim; Jung Kim
      Abstract: Publication date: Available online 18 October 2017
      Source:Medical Engineering & Physics
      Author(s): Youngjin Na, Sangjoon J. Kim, Jung Kim
      We propose a force estimation method in fatigue condition using a muscle-twitch model and surface electromyography (sEMG). The twitch model, which is an estimate of force by a single spike, was obtained from sEMG features and measured forces. Nine healthy subjects performed isometric index finger abduction until exhaustion for a series of dynamic contractions (0–20% MVC) to characterize the twitch model and static contractions (50% MVC) to induce muscle fatigue. Muscle fatigue was identified based on the changes of twitch model; the twitch peak decreased and the contraction time increased as muscle fatigue developed. Force estimation performance in non-fatigue and fatigue conditions was evaluated and its results were compared with that of a conventional method using the mean absolute value (MAV). In non-fatigue conditions, the performance of the proposed method (0.90 ± 0.05) and the MAV method (0.88 ± 0.06) were comparable. In fatigue conditions, the performance was significantly improved for the proposed method (0.87 ± 0.05) compared with the MAV (0.78 ± 0.09).

      PubDate: 2017-10-19T16:18:08Z
      DOI: 10.1016/j.medengphy.2017.10.002
       
  • Non-contact and through-clothing measurement of the heart rate using
           ultrasound vibrocardiography
    • Authors: Nathan Jeger-Madiot; Jérôme Gateau; Mathias Fink; Ros-Kiri Ing
      Abstract: Publication date: Available online 17 October 2017
      Source:Medical Engineering & Physics
      Author(s): Nathan Jeger-Madiot, Jérôme Gateau, Mathias Fink, Ros-Kiri Ing
      We present a novel non-contact system for monitoring the heart rate on human subjects with clothes. Our approach is based on vibrocardiography, and measures locally skin displacements. Vibrocardiography with a laser Doppler vibrometer already allows monitoring of this vital sign, but can only be used on bare skin and requires an expensive piece of equipment. We propose here to use an airborne pulse-Doppler ultrasound system operating in the 20–60 kHz range, and comprised of an emitter focusing the ultrasound pulses on skin and a microphone recording the reflected waves. Our implementation was validated in vitro and on two healthy human subjects, using simultaneously laser vibrocardiography and electrocardiography as references. Accurate measurements of the heart rate on clothed skin suggest that our non-contact ultrasonic method could be implemented both inside and outside the clinical environment, and therefore benefit both medical and safety applications.

      PubDate: 2017-10-19T16:18:08Z
      DOI: 10.1016/j.medengphy.2017.09.003
       
  • Modelling of thrombin generation under flow in realistic left anterior
           descending geometries
    • Authors: Konstantinos P. Papadopoulos; Grigoris T. Gerotziafas; Manolis Gavaises
      Abstract: Publication date: Available online 16 October 2017
      Source:Medical Engineering & Physics
      Author(s): Konstantinos P. Papadopoulos, Grigoris T. Gerotziafas, Manolis Gavaises
      Currently there are no available methods for prediction of thrombotic complications in Coronary Artery disease. Additionally, blood coagulation tests are mainly performed in a steady system while coagulation in vivo occurs under flow conditions. In this work, a phenomenological model for coagulation up-to thrombin generation is proposed; the model is mainly based on the results of thrombin generation assays and therefore it can account for the variation of the coagulability that is observed in different individuals. The model is applied on 3 cases of left anterior descending arteries (LAD) with 50% maximum stenosis placed at a different location and have been statistically assessed as of different complication risk. The simulations showed that parameters of thrombin generation assays obtain different values when they refer to thrombin generation under realistic coronary flow conditions. The flow conditions prevailing locally because of the geometric differences among the arterial trees can lead to different initiation times and thrombin production rates and it also alters the spatial distribution of the coagulation products. Similarly, small changes of the coagulation characteristics of blood under identical flow conditions can allow or prevent the initiation of coagulation. The results indicate that combined consideration of geometry and coagulation characteristics of blood can lead to entirely different conclusions compared to independent assessment of each factor.

      PubDate: 2017-10-19T16:18:08Z
      DOI: 10.1016/j.medengphy.2017.10.001
       
  • A comparative surface topographical analysis of explanted total knee
           replacement prostheses: Oxidised zirconium vs cobalt chromium femoral
           components
    • Authors: Emma Kennard; Susan C. Scholes; Raghavendra Sidaginamale; Rajkumar Gangadharan; David J. Weir; James Holland; David Deehan; Thomas J. Joyce
      Abstract: Publication date: Available online 15 October 2017
      Source:Medical Engineering & Physics
      Author(s): Emma Kennard, Susan C. Scholes, Raghavendra Sidaginamale, Rajkumar Gangadharan, David J. Weir, James Holland, David Deehan, Thomas J. Joyce
      It has been proposed that an increased surface roughness of the femoral components of Total Knee Replacements (TKRs) may be a contributing factor to the accelerated wear of the polyethylene (PE) bearing and ultimately prosthesis failure. Oxidised Zirconium was introduced to the orthopaedic market in an attempt to reduce PE wear associated failures and increase the longevity of the prosthesis. In this study, non-contacting profilometry was used to measure the surface roughness of the femoral components of 6 retrieved TKRs (3 Oxidised Zirconium (OxZr) and 3 Cobalt Chromium alloy (CoCr) femoral components) and 2 as-manufactured femoral components (1 OxZr and 1 CoCr). A semi-quantitative method was used to analyse the damage on the retrieved PE components. The S a values for the retrieved OxZr femoral components (Sa = 0.093 µm ± 0.014) and for the retrieved CoCr femoral components (Sa = 0.065 µm ± 0.005) were significantly greater (p < .05) than the roughness values for the as-manufactured femoral components (OxZr Sa = 0.061 µm ± 0.004 and CoCr Sa = 0.042 µm ± 0.003). No significant difference was seen between the surface roughness parameters of the retrieved OxZr and retrieved CoCr femoral components. There was no difference between the PE component damage scores for the retrieved OxZr TKRs compared to the retrieved CoCr TKRs. These results agree with other studies that both OxZr and CoCr femoral components roughen during time in vivo but the lack of difference between the surface roughness measurements of the two materials is in contrast to previous topographical reports. Further analysis of retrieved OxZr TKRs is recommended so that a fuller appreciation of their benefits and limitations be obtained.

      PubDate: 2017-10-19T16:18:08Z
      DOI: 10.1016/j.medengphy.2017.10.003
       
  • Development of an instrumented spinal cord surrogate using optical fibers:
           A feasibility study
    • Authors: Yann Facchinello; Wagnac Bora Ung Yvan Petit Prabin Pradhan Louis-Marie
      Abstract: Publication date: October 2017
      Source:Medical Engineering & Physics, Volume 48
      Author(s): Yann Facchinello, Éric Wagnac, Bora Ung, Yvan Petit, Prabin Pradhan, Louis-Marie Peyrache, Jean-Marc Mac-Thiong
      In vitro replication of traumatic spinal cord injury is necessary to understand its biomechanics and to improve animal models. During a traumatic spinal cord injury, the spinal cord withstands an impaction at high velocity. In order to fully assess the impaction, the use of spinal canal occlusion sensor is necessary. A physical spinal cord surrogate is also often used to simulate the presence of the spinal cord and its surrounding structures. In this study, an instrumented physical spinal cord surrogate is presented and validated. The sensing is based on light transmission loss observed in embedded bare optical fibers subjected to bending. The instrumented surrogate exhibits similar mechanical properties under static compression compared to fresh porcine spinal cords. The instrumented surrogate has a compression sensing threshold of 40% that matches the smallest compression values leading to neurological injuries. The signal obtained from the sensor allows calculating the compression of the spinal cord surrogate with a maximum of 5% deviation. Excellent repeatability was also observed under repetitive loading. The proposed instrumented spinal cord surrogate is promising with satisfying mechanical properties and good sensing capability. It is the first attempt at proposing a method to assess the internal loads sustained by the spinal cord during a traumatic injury.

      PubDate: 2017-09-21T13:32:43Z
       
  • Identification of the period of stability in a balance test after stepping
           up using a simplified cumulative sum
    • Authors: Doha Safieddine; Aly Chkeir; Cyrille Herlem; Delphine Bera; Michèle Collart; Jean-Luc Novella; Moustapha Dramé; David J. Hewson; Jacques Duchêne
      Abstract: Publication date: Available online 19 September 2017
      Source:Medical Engineering & Physics
      Author(s): Doha Safieddine, Aly Chkeir, Cyrille Herlem, Delphine Bera, Michèle Collart, Jean-Luc Novella, Moustapha Dramé, David J. Hewson, Jacques Duchêne
      Falls are a major cause of death in older people. One method used to predict falls is analysis of Centre of Pressure (CoP) displacement, which provides a measure of balance quality. The Balance Quality Tester (BQT) is a device based on a commercial bathroom scale that calculates instantaneous values of vertical ground reaction force (Fz) as well as the CoP in both anteroposterior (AP) and mediolateral (ML) directions. The entire testing process needs to take no longer than 12 s to ensure subject compliance, making it vital that calculations related to balance are only calculated for the period when the subject is static. In the present study, a method is presented to detect the stabilization period after a subject has stepped onto the BQT. Four different phases of the test are identified (stepping-on, stabilization, balancing, stepping-off), ensuring that subjects are static when parameters from the balancing phase are calculated. The method, based on a simplified cumulative sum (CUSUM) algorithm, could detect the change between unstable and stable stance. The time taken to stabilize significantly affected the static balance variables of surface area and trajectory velocity, and was also related to Timed-up-and-Go performance. Such a finding suggests that the time to stabilize could be a worthwhile parameter to explore as a potential indicator of balance problems and fall risk in older people.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.07.005
       
  • A combined kinematic and kinetic analysis at the residuum/socket interface
           of a knee-disarticulation amputee
    • Authors: Jinghua Tang; Michael McGrath; Nick Hale; Liudi Jiang; Dan Bader; Piotr Laszczak; David Moser; Saeed Zahedi
      Abstract: Publication date: Available online 15 September 2017
      Source:Medical Engineering & Physics
      Author(s): Jinghua Tang, Michael McGrath, Nick Hale, Liudi Jiang, Dan Bader, Piotr Laszczak, David Moser, Saeed Zahedi
      The bespoke interface between a lower limb residuum and a prosthetic socket is critical for an amputee's comfort and overall rehabilitation outcomes. Analysis of interface kinematics and kinetics is important to gain full understanding of the interface biomechanics, which could aid clinical socket fit, rehabilitation and amputee care. This pilot study aims to investigate the dynamic correlation between kinematic movement and kinetic stresses at the interface during walking tests on different terrains. One male, knee disarticulation amputee participated in the study. He was asked to walk on both a level surface and a 5° ramped surface. The movement between the residuum and the socket was evaluated by the angular and axial couplings, based on the outputs from a 3D motion capture system. The corresponding kinetic stresses at anterior-proximal (AP), posterior-proximal (PP) and anterior-distal (AD) locations of the residuum were measured, using individual stress sensors. Approximately 8° of angular coupling and up to 32 mm of axial coupling were measured when walking on different terrains. The direction of the angular coupling shows strong correlation with the pressure difference between the PP and AP sensors. Higher pressure was obtained at the PP location than the AP location during stance phase, associated with the direction of the angular coupling. A strong correlation between axial coupling length, L, and longitudinal shear was also evident at the PP and AD locations i.e. the shortening of L corresponds to the increase of shear in the proximal direction. Although different terrains did not affect these correlations in principle, interface kinematic and kinetic values suggested that gait changes can induce modifications to the interface biomechanics. It is envisaged that the reported techniques could be potentially used to provide combined kinematics and kinetics for the understanding of biomechanics at the residuum/socket interface, which may play an important role in the clinical assessment of prosthetic component settings, including socket fit quality.

      PubDate: 2017-09-16T13:05:59Z
      DOI: 10.1016/j.medengphy.2017.08.014
       
  • Iterative approach for 3D reconstruction of the femur from un-calibrated
           2D radiographic images
    • Authors: Kibeom Youn; Moon Soek Park; Jehee Lee
      Abstract: Publication date: Available online 15 September 2017
      Source:Medical Engineering & Physics
      Author(s): Kibeom Youn, Moon Soek Park, Jehee Lee
      Three-dimensional reconstruction of the femur is important for surgical planning in patients with cerebral palsy. This study aimed to reconstruct the three-dimensional femur shape from un-calibrated bi-planar radiographic images using self-calibration to allow for low-dose preoperative planning. The existing self-calibration techniques require anatomical landmarks that are clearly visible on bi-planar images, which are not available on the femur. In our newly developed method, the self-calibration is performed so that the contour of the statistical shape matches the image contour while the statistical shape is concomitantly optimized. The proposed approach uses conventional radiograph systems and can be easily incorporated into existing clinical protocols, as compared to other reconstruction methods.

      PubDate: 2017-09-16T13:05:59Z
      DOI: 10.1016/j.medengphy.2017.08.016
       
  • Shifts in the relationship between motor unit recruitment thresholds
           versus derecruitment thresholds during fatigue
    • Authors: Matt S. Stock; Jacob A. Mota
      Abstract: Publication date: Available online 14 September 2017
      Source:Medical Engineering & Physics
      Author(s): Matt S. Stock, Jacob A. Mota
      Muscle fatigue is associated with diminished twitch force amplitude. We examined changes in the motor unit recruitment versus derecruitment threshold relationship during fatigue. Nine men (mean age = 26 years) performed repeated isometric contractions at 50% maximal voluntary contraction (MVC) knee extensor force until exhaustion. Surface electromyographic signals were detected from the vastus lateralis, and were decomposed into their constituent motor unit action potential trains. Motor unit recruitment and derecruitment thresholds and firing rates at recruitment and derecruitment were evaluated at the beginning, middle, and end of the protocol. On average, 15 motor units were studied per contraction. For the initial contraction, three subjects showed greater recruitment thresholds than derecruitment thresholds for all motor units. Five subjects showed greater recruitment thresholds than derecruitment thresholds for only low-threshold motor units at the beginning, with a mean cross-over of 31.6% MVC. As the muscle fatigued, many motor units were derecruited at progressively higher forces. In turn, decreased slopes and increased y-intercepts were observed. These shifts were complemented by increased firing rates at derecruitment relative to recruitment. As the vastus lateralis fatigued, the central nervous system's compensatory adjustments resulted in a shift of the regression line of the recruitment versus derecruitment threshold relationship.

      PubDate: 2017-09-16T13:05:59Z
      DOI: 10.1016/j.medengphy.2017.08.015
       
  • A model of blood supply to the brain via the carotid arteries: Effects of
           obstructive vs. sclerotic changes
    • Authors: O. Onaizah; T.L. Poepping; M. Zamir
      Abstract: Publication date: Available online 13 September 2017
      Source:Medical Engineering & Physics
      Author(s): O. Onaizah, T.L. Poepping, M. Zamir
      The carotid artery is one of the major supply routes of blood to the brain and a common site of vascular disease. Obstructive and sclerotic disorders within the carotid artery impact local blood flow patterns as well as overall impedance and blood supply to the brain. A lumped parameter model and an experimental in-vitro flow loop were used to study the effects of local stenosis and stiffness in the carotid artery based on a family of phantoms with different degrees of stenosis and compliance. The model also allows independent examination of the effects of downstream resistance and compliance. Mild to moderate stenosis was found to lead to minimal (∼1%) reduction in blood supply to the brain. Reduction in mean internal carotid artery (ICA) flow was statistically significant (p< 0.01) only above 70% stenosis. On the other hand, a three-fold increase in stiffness of the carotid artery, as might occur in aging, was found to lead to a modest yet statistically significant reduction (p< 0.01) in mean ICA flow. Effects of changing downstream resistance and compliance were examined. For a given pressure waveform, reduction in downstream compliance led to altered waveform shape and reduction in peak systolic flow rates where the mean flow rates were not altered. Increased downstream resistance resulted in drastic reduction in mean flow rates.

      PubDate: 2017-09-16T13:05:59Z
      DOI: 10.1016/j.medengphy.2017.08.009
       
  • Intra- and inter-session reliability of traditional and entropy-based
           variables describing stance on a wobble board
    • Authors: Lucia Bizovska; Miroslav Janura; Zdenek Svoboda; Martin Cerny; Jana Krohova; Maros Smondrk
      Abstract: Publication date: Available online 12 September 2017
      Source:Medical Engineering & Physics
      Author(s): Lucia Bizovska, Miroslav Janura, Zdenek Svoboda, Martin Cerny, Jana Krohova, Maros Smondrk
      A wobble board (WB) is a balance rehabilitation tool that is used in physiotherapy to improve strength and stability. The WB tested in this study includes a sensory module for measuring patients’ tilt and rotation during stance. The aim of this study was to assess the reliability and validity of a balance measurement using a WB. Thirty healthy young adults participated in this study. The participants stood on the WB to simultaneously record the tilt of the WB and the center of pressure data using a force plate. The data were recorded during five measurement sessions on various days, with four trials each. Sways, velocities and indexes of complexity (CI) were computed. For reliability assessment, we used intra-class correlation coefficients within and between sessions; for validity, we computed Spearman correlation coefficients. The velocities and CI showed good intra-session reliability, and the sways showed mostly poor intra-session reliability. The results of inter-session reliability showed good to excellent reliability for CI, poor reliability for sways and poor to good reliability for velocities. The Spearman correlation coefficient showed excellent agreement between the mean velocities computed from the force plate and the WB. Our results confirm that the WB tested is suitable for stability assessment in young adults.

      PubDate: 2017-09-16T13:05:59Z
      DOI: 10.1016/j.medengphy.2017.08.017
       
  • A simulation framework for humeral head translations
    • Authors: Ehsan Sarshari; Alain Farron; Alexandre Terrier; Dominique Pioletti; Philippe Mullhaupt
      Abstract: Publication date: Available online 8 September 2017
      Source:Medical Engineering & Physics
      Author(s): Ehsan Sarshari, Alain Farron, Alexandre Terrier, Dominique Pioletti, Philippe Mullhaupt
      Humeral head translations (HHT) play a crucial role in the glenohumeral (GH) joint function. The available shoulder musculoskeletal models developed based on inverse dynamics however fall short of predicting the HHT. This study aims at developing a simulation framework that allows forward-dynamics simulation of a shoulder musculoskeletal model with a 6 degrees of freedom (DOF) GH joint. It provides a straightforward solution to the HHT prediction problem. We show that even within a forward-dynamics simulation addressing the HHT requires further information about the contact. To that end, a deformable articular contact is included in the framework defining the GH joint contact force in terms of the joint kinematics. An abduction motion in the scapula plane is simulated. The results are given in terms of HHT, GH joint contact force, contact areas, contact pressure, and cartilage strain. It predicts a superior-posterior translation of the humeral head followed by an inferior migration.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.013
       
  • Ulna-humerus contact mechanics: Finite element analysis and experimental
           measurements using a tactile pressure sensor
    • Authors: Mohsen Sharifi Renani; Munsur Rahman; Akin Cil; Antonis P. Stylianou
      Abstract: Publication date: Available online 8 September 2017
      Source:Medical Engineering & Physics
      Author(s): Mohsen Sharifi Renani, Munsur Rahman, Akin Cil, Antonis P. Stylianou
      Elbow articular cartilage withstands high compressive and shear forces while protecting the bone from excessive loading. Better understanding of elbow cartilage contact mechanics can provide insight into cartilage degeneration. In this study a tactile pressure sensor was used to measure the contact pressure distribution within the ulno-humeral joint of two cadaver specimens at 20° flexion angle across three different axial loads of 80 N, 110 N, and 140 N. Corresponding 3D finite element (FE) models were constructed from magnetic resonance imaging (MRI) and contact analysis was performed for each specimen with boundary and loading conditions identical to the experiment. Direct comparison between FE results and experimental measurements was conducted for the validation of the FE models and a sensitivity analysis was employed for assessing the effect of cartilage parameters on the model's outputs. The results showed a good agreement between the FE models and the experiments in terms of contact characteristics. The sensitivity analysis demonstrated that outcomes of the model, particularly peak contact pressure is more sensitive to the Poisson's ratio rather than to Young's modulus under static conditions. This result suggests that selection of Poisson's ratio is very critical for accurate prediction of contact mechanics within the ulno-humeral joint.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.010
       
  • Modal analysis for the assessment of cementless hip stem primary stability
           in preoperative THA planning
    • Authors: Andres Rondon; Elhadi Sariali; Quentin Vallet; Quentin Grimal
      Abstract: Publication date: Available online 7 September 2017
      Source:Medical Engineering & Physics
      Author(s): Andres Rondon, Elhadi Sariali, Quentin Vallet, Quentin Grimal
      This numerical vibration finite element (FE) study introduces resonance three-dimensional planning (RP3D) to assess preoperatively the primary stability of a cementless stem for total hip arthroplasty. Based on a patient’s CT-scan and a numerical model of a stem, RP3D aims at providing mechanical criteria indicative of the achievable primary stability. We investigate variations of the modal response of the stem to changes of area and apparent stiffness of the bone-implant interface. The model is computationally cheap as it does not include a mesh of the bone. The apparent stiffness of the bone is modeled by springs attached to the nodes of the stem’s mesh. We investigate an extended range of stiffness values while, in future works, patient’s specific Hounsfield values could be used to define stiffness. We report modal frequencies, shapes, and a ratio of elastic potential energies (rEPE) that quantifies the proximal motion that should be minimum for a stable stem. The modal response exhibits a clear transition between loose and tight contact as area and stiffness of the interface increase. rEPE thresholds that could potentially discriminate preoperatively between stable and unstable stems are given for a Symbios SPS® size C stem.
      Graphical abstract image

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.07.013
       
  • Experimental and modelling characterisation of adjustable hollow
           Micro-needle delivery systems
    • Authors: Ting-Ting Liu; Kai Chen; Min Pan
      Abstract: Publication date: Available online 7 September 2017
      Source:Medical Engineering & Physics
      Author(s): Ting-Ting Liu, Kai Chen, Min Pan
      Background Hollow micro-needles have been used increasingly less in practice because the infusion into the skin is limited by the tissue resistance to flow. The relationship between the infusion flow rate and tissue resistance pressure is not clear. Methods A custom-made, hollow micro-needle system was used in this study. The driving force and infusion flow rate were measured using a force transducer attached to an infusion pump. Evans blue dye was injected into the air, polyacrylamide gel and in-vivo mouse skin at different flow rates. Two different micro-needle lengths were used for in-vivo infusion into the mouse. A model was derived to calculate the driving force of the micro-needle infusion into the air, and the results were compared to experimental data. Results The calculated driving forces match the experimental results with different infusion flow rates. The pressure loss throughout the micro-needle delivery system was found to be two orders smaller than the resistance pressure inside the gel and mouse skin, and the resistance pressure increased with increasing flow rate. A portion of liquid backflow was observed when the flow rate was relatively larger, and the backflow was associated with a sudden larger increase in resistance pressure at a higher flow rate. Conclusions The current micro-needle delivery system is capable of administering liquid into the mouse skin at a flow rate of up to 0.15 ml/min, without causing significant backflow on the surface. The resistance pressure increases with increasing flow rate, causing infusion restriction at higher flow rates.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.012
       
  • Hemodynamic parameters that may predict false-lumen growth in type-B
           aortic dissection after endovascular repair: A preliminary study on
           long-term multiple follow-ups
    • Authors: Huanming Xu; Zhenfeng Li; Huiwu Dong; Yilun Zhang; Jianyong Wei; Paul N. Watton; Wei Guo; Duanduan Chen; Jiang Xiong
      Abstract: Publication date: Available online 7 September 2017
      Source:Medical Engineering & Physics
      Author(s): Huanming Xu, Zhenfeng Li, Huiwu Dong, Yilun Zhang, Jianyong Wei, Paul N. Watton, Wei Guo, Duanduan Chen, Jiang Xiong
      Thoracic endovascular aortic repair (TEVAR) is commonly applied in type-B aortic dissection. For patients with dissection affects descending aorta and extends downward to involve abdominal aorta and possibly iliac arteries, false lumen (FL) expansion might occur post-TEVAR. Predictions of dissection development may assist in medical decision on re-intervention or surgery. In this study, two patients are selected with similar morphological features at initial presentation but with different long-term FL development post-TEVAR (stable and enlarged FL). Patient-specific models are established for each of the follow-ups. Flow boundaries and computational validations are obtained from Doppler ultrasound velocimetry. By analyzing the hemodynamic parameters, the false-to-true luminal pressure difference (PDiff) and particle relative residence time (RRT) are found related to FL remodeling. It is found that (i) the position of the first FL flow entry is the watershed of negative-and-positive PDiff and, in long-term follow-ups, and the position of largest PDiff is consistent with that of the greatest increase of FL width; (ii) high RRT occurs at the FL proximal tip and similar magnitude of RRT is found in both stable and enlarged cases; (iii) comparing to the RRT at 7days post-TEVAR, an increase of RRT afterwards in short-term is found in the stable case while a slight decrease of this parameter is found in the enlarged case, indicating that the variation of RRT in short-term post-TEVAR might be potential to predict long-term FL remodeling.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.011
       
  • Radiographic cup anteversion measurement corrected from pelvic tilt
    • Authors: Liao Wang; Andrew R. Thoreson; Robert T. Trousdale; Bernard F. Morrey; Kerong Dai; Kai-Nan An
      Abstract: Publication date: Available online 6 September 2017
      Source:Medical Engineering & Physics
      Author(s): Liao Wang, Andrew R. Thoreson, Robert T. Trousdale, Bernard F. Morrey, Kerong Dai, Kai-Nan An
      The purpose of this study was to develop a novel technique to improve the accuracy of radiographic cup anteversion measurement by correcting the influence of pelvic tilt. Ninety virtual total hip arthroplasties were simulated from computed tomography data of 6 patients with 15 predetermined cup orientations. For each simulated implantation, anteroposterior (AP) virtual pelvic radiographs were generated for 11 predetermined pelvic tilts. A linear regression model was created to capture the relationship between radiographic cup anteversion angle error measured on AP pelvic radiographs and pelvic tilt. Overall, nine hundred and ninety virtual AP pelvic radiographs were measured, and 90 linear regression models were created. Pearson's correlation analyses confirmed a strong correlation between the errors of conventional radiographic cup anteversion angle measured on AP pelvic radiographs and the magnitude of pelvic tilt (P < 0.001). The mean of 90 slopes and y-intercepts of the regression lines were −0.8 and −2.5°, which were applied as the general correction parameters for the proposed tool to correct conventional cup anteversion angle from the influence of pelvic tilt. The current method proposes to measure the pelvic tilt on a lateral radiograph, and to use it as a correction for the radiographic cup anteversion measurement on an AP pelvic radiograph. Thus, both AP and lateral pelvic radiographs are required for the measurement of pelvic posture-integrated cup anteversion. Compared with conventional radiographic cup anteversion, the errors of pelvic posture-integrated radiographic cup anteversion were reduced from 10.03 (SD = 5.13) degrees to 2.53 (SD = 1.33) degrees. Pelvic posture-integrated cup anteversion measurement improves the accuracy of radiographic cup anteversion measurement, which shows the potential of further clarifying the etiology of postoperative instability based on planar radiographs.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.008
       
  • Microfludic platforms for the evaluation of anti-platelet agent efficacy
           under hyper-shear conditions associated with ventricular assist devices
    • Authors: Annalisa Dimasi; Marco Rasponi; Filippo Consolo; Gianfranco B. Fiore; Danny Bluestein; Marvin J. Slepian; Alberto Redaelli
      Abstract: Publication date: Available online 30 August 2017
      Source:Medical Engineering & Physics
      Author(s): Annalisa Dimasi, Marco Rasponi, Filippo Consolo, Gianfranco B. Fiore, Danny Bluestein, Marvin J. Slepian, Alberto Redaelli
      Thrombus formation is a major adverse event affecting patients implanted with ventricular assist devices (VADs). Despite anti-thrombotic drug administration, thrombotic events remain frequent within the first year post-implantation. Platelet activation (PA) is an essential process underling thrombotic adverse events in VAD systems. Indeed, abnormal shear forces, correlating with specific flow trajectories of VADs, are strong agonists mediating PA. To date, the ability to determine efficacy of anti-platelet (AP) agents under shear stress conditions is limited. Here, we present a novel microfluidic platform designed to replicate shear stress patterns of a clinical VAD, and use it to compare the efficacy of two AP agents in vitro. Gel-filtered platelets were incubated with i) acetylsalicylic acid (ASA) and ii) ticagrelor, at two different concentrations (ASA: 125 and 250 µM; ticagrelor: 250 and 500 nM) and were circulated in the VAD-emulating microfluidic platform using a peristaltic pump. GFP was collected after 4 and 52 repetitions of exposure to the VAD shear pattern and tested for shear-mediated PA. ASA significantly inhibited PA only at 2-fold higher concentration (250 µM) than therapeutic dose (125 µM). The effect of ticagrelor was not dependent on drug concentration, and did not show significant inhibition with respect to untreated control. This study demonstrates the potential use of microfluidic platforms as means of testing platelet responsiveness and AP drug efficacy under complex and realistic VAD-like shear stress conditions.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.005
       
  • Thread-based microfluidics: Flow patterns in homogeneous and heterogeneous
           microfiber bundles
    • Authors: J. Berthier; K.A. Brakke; D. Gosselin; E. Berthier; F. Navarro
      Abstract: Publication date: Available online 23 August 2017
      Source:Medical Engineering & Physics
      Author(s): J. Berthier, K.A. Brakke, D. Gosselin, E. Berthier, F. Navarro
      Thread-based microfluidics has recently seen considerable developments in the domain of portable diagnostic systems, smart bandages and tissue engineering. Similarly to paper-based microfluidics, thread-based microfluidics uses the wicking of fibers to move fluids. It has the advantage of confining and guiding the fluid along the yarns in a one, two or three dimensional space. A global approach to the motion of fluids in yarns and fiber bundles has already been reported in the literature based on the Lucas–Washburn–Rideal law. However no detailed investigation of the flow pattern inside the bundle has been conducted, depending on the internal structure of the bundle. Especially when the bundle possesses heterogeneous wetting properties, such as two different wetting regions interior and exterior, different flow patterns may exist. In this work, we perform a theoretical and numerical analysis of the different flow regimes for homogenous and heterogeneous fiber bundles. It is demonstrated that a limited number of fibers is sufficient for thread-based capillary flows, and that a caging of the flow can be achieved by realizing a lyophobic envelope.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.004
       
  • Red blood cell (RBC) suspensions in confined microflows: Pressure-flow
           relationship
    • Authors: Hagit Stauber; Dan Waisman; Netanel Korin; Josué Sznitman
      Abstract: Publication date: Available online 23 August 2017
      Source:Medical Engineering & Physics
      Author(s): Hagit Stauber, Dan Waisman, Netanel Korin, Josué Sznitman
      Microfluidic-based assays have become increasingly popular to explore microcirculation in vitro. In these experiments, blood is resuspended to a desired haematocrit level in a buffer solution, where frequent choices for preparing RBC suspensions comprise notably Dextran and physiological buffer. Yet, the rational for selecting one buffer versus another is often ill-defined and lacks detailed quantification, including ensuing changes in RBC flow characteristics. Here, we revisit RBC suspensions in microflows and attempt to quantify systematically some of the differences emanating between buffers. We measure bulk flow rate (Q) of RBC suspensions, using PBS- and Dextran-40, as a function of the applied pressure drop (ΔP) for two hematocrits (∼0% and 23%). Two distinct microfluidic designs of varying dimensions are employed: a straight channel larger than and a network array similar to the size of individual RBCs. Using the resulting pressure-flow curves, we extract the equivalent hydrodynamic resistances and estimate the relative viscosities. These efforts are a first step in rigorously quantifying the influence of the ‘background’ buffer on RBC flows within microfluidic devices and thereby underline the importance of purposefully selecting buffer suspensions for microfluidic in vitro assays.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.006
       
  • Effect of longitudinal anatomical mismatch of stenting on the mechanical
           environment in human carotid artery with atherosclerotic plaques
    • Authors: Zhenmin Fan; Xiao Liu; Anqiang Sun; Nan Zhang; Zhanming Fan; Yubo Fan; Xiaoyan Deng
      Abstract: Publication date: Available online 18 August 2017
      Source:Medical Engineering & Physics
      Author(s): Zhenmin Fan, Xiao Liu, Anqiang Sun, Nan Zhang, Zhanming Fan, Yubo Fan, Xiaoyan Deng
      Longitudinal anatomic mismatch (LAM) of stenting (i.e., a stenotic artery segment is not fully covered by a deployed stent) worsens the mechanical environment in the treated artery, which most likely is the cause for the associated high risks of restenosis, myocardial infarction and stent thrombosis. To probe the possibility, we constructed a patient-specific carotid model with two components of plaques (lipid and calcified plaque) based on MRI images; we numerically compared three different stenting scenarios in terms of von Mises stress (VMS) distribution in the treated arteries, namely, the short stenting (LAM), the medium stenting and the long stenting. The results showed that the short stenting led to more areas with abnormally high VMS along the inner surface of the treated artery with a much higher surface-averaged VMS at the distal end of the stent than both the medium and long stenting. While the VMS distribution in the calcified plaques was similar for the three stenting models, it was quite different in the lipid plaques among the three stenting models. The lipid plaque of the short-stent model showed more volume of the lipid plaque subjected to high VMS than those of the other two models. Based on the obtained results, we may infer that the short stenting (i.e., LAM) may aggravate vascular injury due to high VMS on the artery-stent interaction surface and within the lipid plaque. Therefore, to obtain a better outcome, a longer stent, rather than a short one, might be needed for arterial stenting.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.06.010
       
  • Herringbone-like hydrodynamic structures in microchannels: A CFD model to
           evaluate the enhancement of surface binding
    • Authors: Elena Bianchi; Monica Piergiovanni; Chiara Arrigoni; Junji Fukuda; Alfonso Gautieri; Matteo Moretti; Gabriele Dubini
      Abstract: Publication date: Available online 9 August 2017
      Source:Medical Engineering & Physics
      Author(s): Elena Bianchi, Monica Piergiovanni, Chiara Arrigoni, Junji Fukuda, Alfonso Gautieri, Matteo Moretti, Gabriele Dubini
      Selected adsorption efficiency of a molecule in solution in a microchannel is strongly influenced by the convective/diffusive mass transport phenomena that supply the target molecule to the adsorption surface. In a standard microchannel with a rectangular cross section, laminar flow regime limits the fluid mixing, thus suggesting that mass transport conditions can be improved by the introduction of herringbone-like structures. Tuning of these geometrical patterns increases the concentration gradient of the target molecule at the adsorption surface. A computational fluid dynamic (CFD) study was performed to evaluate the relation between the geometrical herringbone patterns and the concentration gradient improvement in a 14 mm long microchannel. The results show that the inhomogeneity of the concentration gradient can provide an improved and localized adsorption under specific geometrical features, which can be tuned in order to adapt the adsorption pattern to the specific assay requirements.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.07.003
       
  • Finite element analysis of TAVI: Impact of native aortic root
           computational modeling strategies on simulation outcomes
    • Authors: Alice Finotello; Simone Morganti; Ferdinando Auricchio
      Abstract: Publication date: Available online 17 July 2017
      Source:Medical Engineering & Physics
      Author(s): Alice Finotello, Simone Morganti, Ferdinando Auricchio
      In the last few years, several studies, each with different aim and modeling detail, have been proposed to investigate transcatheter aortic valve implantation (TAVI) with finite elements. The present work focuses on the patient-specific finite element modeling of the aortic valve complex. In particular, we aim at investigating how different modeling strategies in terms of material models/properties and discretization procedures can impact analysis results. Four different choices both for the mesh size (from  20 k elements to  200 k elements) and for the material model (from rigid to hyperelastic anisotropic) are considered. Different approaches for modeling calcifications are also taken into account. Post-operative CT data of the real implant are used as reference solution with the aim of outlining a trade-off between computational model complexity and reliability of the results.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.045
       
  • Large eddy simulations of blood dynamics in abdominal aortic aneurysms
    • Authors: Christian Vergara; Davide Le Van; Maurizio Quadrio; Luca Formaggia; Maurizio Domanin
      Abstract: Publication date: Available online 12 July 2017
      Source:Medical Engineering & Physics
      Author(s): Christian Vergara, Davide Le Van, Maurizio Quadrio, Luca Formaggia, Maurizio Domanin
      We study the effects of transition to turbulence in abdominal aortic aneurysms (AAA). The presence of transitional effects in such districts is related to the heart pulsatility and the sudden change of diameter of the vessels, and has been recorded by means of clinical measures as well as of computational studies. Here we propose, for the first time, the use of a large eddy simulation (LES) model to accurately describe transition to turbulence in realistic scenarios of AAA obtained from radiological images. To this aim, we post-process the obtained numerical solutions to assess significant quantities, such as the ensemble-averaged velocity and wall shear stress, the standard deviation of the fluctuating velocity field, and vortical structures educed via the so-called Q-criterion. The results demonstrate the suitability of the considered LES model and show the presence of significant transitional effects around the impingement region during the mid-deceleration phase.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.030
       
  • Multi-objective optimization of nitinol stent design
    • Authors: G. Alaimo; F. Auricchio; M. Conti; M. Zingales
      Abstract: Publication date: Available online 10 July 2017
      Source:Medical Engineering & Physics
      Author(s): G. Alaimo, F. Auricchio, M. Conti, M. Zingales
      Nitinol stents continuously experience loadings due to pulsatile pressure, thus a given stent design should possess an adequate fatigue strength and, at the same time, it should guarantee a sufficient vessel scaffolding. The present study proposes an optimization framework aiming at increasing the fatigue life reducing the maximum strut strain along the structure through a local modification of the strut profile.The adopted computational framework relies on nonlinear structural finite element analysis combined with a Multi Objective Genetic Algorithm, based on Kriging response surfaces. In particular, such an approach is used to investigate the design optimization of planar stent cell.The results of the strut profile optimization confirm the key role of a tapered strut design to enhance the stent fatigue strength, suggesting that it is possible to achieve a marked improvement of both the fatigue safety factor and the scaffolding capability simultaneously. The present study underlines the value of advanced engineering tools to optimize the design of medical devices.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.026
       
  • A FSI computational framework for vascular physiopathology: A novel
           flow-tissue multiscale strategy
    • Authors: Daniele Bianchi; Elisabetta Monaldo; Alessio Gizzi; Michele Marino; Simonetta Filippi; Giuseppe Vairo
      Abstract: Publication date: Available online 6 July 2017
      Source:Medical Engineering & Physics
      Author(s): Daniele Bianchi, Elisabetta Monaldo, Alessio Gizzi, Michele Marino, Simonetta Filippi, Giuseppe Vairo
      A novel fluid-structure computational framework for vascular applications is herein presented. It is developed by combining the double multi-scale nature of vascular physiopathology in terms of both tissue properties and blood flow. Addressing arterial tissues, they are modelled via a nonlinear multiscale constitutive rationale, based only on parameters having a clear histological and biochemical meaning. Moreover, blood flow is described by coupling a three-dimensional fluid domain (undergoing physiological inflow conditions) with a zero-dimensional model, which allows to reproduce the influence of the downstream vasculature, furnishing a realistic description of the outflow proximal pressure. The fluid-structure interaction is managed through an explicit time-marching approach, able to accurately describe tissue nonlinearities within each computational step for the fluid problem. A case study associated to a patient-specific aortic abdominal aneurysmatic geometry is numerically investigated, highlighting advantages gained from the proposed multiscale strategy, as well as showing soundness and effectiveness of the established framework for assessing useful clinical quantities and risk indexes.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.028
       
 
 
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