Time filter

Source Type

Song Y.,Institute for Biomedical Technology and Technical Medicine MIRA | Song Y.,University of Twente | Wennink J.W.H.,Institute for Biomedical Technology and Technical Medicine MIRA | Wennink J.W.H.,University of Twente | And 14 more authors.
Tissue Engineering - Part A | Year: 2011

Porous, tubular, flexible, and elastic poly(trimethylene carbonate) (PTMC) scaffolds (length 8cm and inner diameter 3mm) for vascular tissue engineering were prepared by means of a dip-coating and particulate leaching procedure. Using NaCl as porogen, scaffolds with an average pore size of 110μm and a porosity of 85% were obtained. Before leaching the salt, the structures were made creep-resistant by means of crosslinking at 25kGy gamma irradiation. To increase the efficiency of cell seeding, the scaffolds were provided with a microporous outer layer of 0.2mm with an average pore size of 28μm and a porosity of 65% (total wall thickness 1mm). Human smooth muscle cells (SMCs) were seeded in these scaffolds with an efficiency of 43%, as determined after 24h cell adhesion. SMCs were cultured in the scaffolds up to 14 days under stationary conditions or under pulsatile flow conditions in a bioreactor (pressure 70-130mmHg, 69 pulsations/min, and average wall shear rate 320s -1). Although SMCs proliferated under both conditions, cell numbers were three to five times higher in case of dynamic culturing. This was qualitatively confirmed by means of histology. Also, in terms of mechanical properties, the dynamically cultured constructs performed better than the statically cultured constructs. After culturing for 14 days, the maximum tensile strengths of the constructs, determined in the radial direction, had increased from 0.16MPa (unseeded scaffold) to 0.48MPa (dynamic culturing) and 0.38MPa (static culturing). The results of this study indicate that a potentially useful medial layer for tissue-engineered vascular grafts can be prepared by dynamic culturing of human SMCs seeded in porous tubular poly(trimethylene carbonate) scaffolds. © 2011 Mary Ann Liebert, Inc.

Faber G.S.,Harvard University | Faber G.S.,Liberty Mutual Research Institute for Safety | Chang C.-C.,Liberty Mutual Research Institute for Safety | Kingma I.,VU University Amsterdam | And 4 more authors.
Journal of Biomechanics | Year: 2012

This study describes a novel calibration method for six-degrees-of-freedom force/torque sensors (FTsensors) using a pre-calibrated force plate (FP) as a reference measuring device. In this calibration method, the FTsensor is rigidly connected to a FP and force/torque data are synchronously recorded while a dynamic functional loading procedure is applied by the researcher. Based on these data an accurate calibration matrix for the FTsensor can easily be obtained via least-squares optimization.Using this calibration method, this study further investigated what loading methods are appropriate for the calibration of FTsensors intended for ambulatory measurement of ground reaction forces (GRFs). Seven different loading methods were compared (e.g., walking, pushing while standing on the FTsensor). Calibration matrices were calculated based on the raw data from the seven loading methods individually and all loading methods combined. Performance of these calibration matrices was subsequently compared in an . in situ trial. During the . in situ trial, five common work tasks (e.g., walking, manual lifting, pushing) were performed by an experimenter, while standing on the FP wearing a "ForceShoe" with two calibrated FTsensors attached to its sole. Root-mean-square differences (RMSDs) between the FTsensor and FP outcomes were calculated over all tasks. Using the calibration matrices based on all loading methods combined resulted in small RMSDs (GRF: <8. N, center of pressure: <2. mm). Using the calibration matrices based on "pushing against manual resistance" resulted in similar RMSDs, proving it to be the best single loading method. © 2012 Elsevier Ltd.

Franken M.,University of Twente | Franken M.,Institute for Biomedical Technology and Technical Medicine MIRA | Reilink R.,University of Twente | Reilink R.,Institute of Mechanics Processes and Control Twente IMPACT | And 4 more authors.
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2010

Passivity of virtual environments running in discrete time is a sufficient condition for stability of the system. The framework for passive sampled Port-Hamiltonian systems allows multi-dimensional virtual environments exhibiting internal dynamic behavior to be computed on a discrete medium in a passive manner. It is shown that a causality analysis is required in the framework to detect if any of the model elements have, a time dependent change of energy function in the energy balance of the system. The Standard Linear Solid model, which is often used to simulate the visco-elastic interaction with soft biological tissue is used as an example. Simulated and experimental results are provided to demonstrate the benefit of the described framework. It is shown that using this approach a multidimensional model which is passive in the continuous domain remains passive in the discrete domain, whereas a standard discretization approach can become non-passive. ©2010 IEEE.

Faber G.S.,VU University Amsterdam | Kingma I.,VU University Amsterdam | Martin Schepers H.,Institute for Biomedical Technology and Technical Medicine MIRA | Veltink P.H.,Institute for Biomedical Technology and Technical Medicine MIRA | van Dieen J.H.,VU University Amsterdam
Journal of Biomechanics | Year: 2010

Ground reaction forces (GRFs) are often used in inverse dynamics analyses to determine joint loading. These GRFs are usually measured using force plates (FPs). As an alternative, instrumented force shoes (FSs) can be used, which have the advantage over FPs that they do not constrain foot placement. This study tested the FS system in one normal weight subject (77. kg) performing 19 different lifting, pushing and pulling and walking tasks. Kinematics were measured with an optoelectronic system and the GRFs and the positions of the centre of pressure (CoP) were synchronously measured with FPs and FSs. Differences between the outcomes of the two measurement systems (i.e. CoP and GRFs) and the resulting ankle and L5/S1 joint moments were determined at the instant of the peak GRF (DaPF). For most lifting and pushing and pulling tasks, the difference between the FP and FS measurements remained small: GRF DaPF remained below 3% body weight, CoP DaPF remained below 10. mm, ankle moment DaPF remained below 7% of the peak total ankle moment that occurred during normal walking and L5/S1 moment DaPF remained below 7% of the peak total L5/S1 moment that occurred during normal symmetric lifting. More substantial differences were only found in the maximal pushing tasks. For the walking tasks, peak vertical GRFs were somewhat underestimated. However, differences in ankle and L5/S1 moments remained small, i.e. DaPF below 7% of the peak total moment that occurred during normal walking. © 2010 Elsevier Ltd.

Franken M.,University of Twente | Franken M.,Institute for Biomedical Technology and Technical Medicine MIRA | Misra S.,University of Twente | Misra S.,Institute for Biomedical Technology and Technical Medicine MIRA | And 2 more authors.
IEEE/RSJ 2010 International Conference on Intelligent Robots and Systems, IROS 2010 - Conference Proceedings | Year: 2010

In bilateral telemanipulation algorithms based on time-domain passivity, internal friction in the devices poses an additional energy drain. Based on a model of the friction, the dissipated energy can be estimated and reclaimed inside the energy balance of the control algorithm. As long as the estimate is conservative, passivity of the entire system is maintained. In this paper we consider two types of friction and discuss the influence of two types of measurement noise. Without noise compensation the dissipated energy is largely overestimated. A compensation method based on the probability density of the noise is proposed. This leads to an energy estimate which is always conservative even in the presence of measurement noise and does not require additional filtering. Simulation results are provided that show the increase in obtained transparency when this energy compensation technique is applied. ©2010 IEEE.

Loading Institute for Biomedical Technology and Technical Medicine MIRA collaborators
Loading Institute for Biomedical Technology and Technical Medicine MIRA collaborators