Publications by authors named "Taeyong Lee"

45 Publications

Relationship between ankle varus moment during gait and radiographic measurements in patients with medial ankle osteoarthritis.

PLoS One 2021 24;16(6):e0253570. Epub 2021 Jun 24.

Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Seongnam-si, South Korea.

Background: Kinetic data obtained during gait can be used to clarify the biomechanical pathogenesis of osteoarthritis of the lower extremity. This study aimed to investigate the difference in ankle varus moment between the varus angulation and medial translation types of medial ankle osteoarthritis, and to identify the radiographic measurements associated with ankle varus moment.

Methods: Twenty-four consecutive patients [mean age 65.8 (SD) 8.0 years; 9 men and 15 women] with medial ankle osteoarthritis were included. Fourteen and 10 patients had the varus angulation (tibiotalar tilt angle≥3 degrees) and medial translation (tibiotalar tilt angle<3 degrees) types, respectively. All patients underwent three-dimensional gait analysis, and the maximum varus moment of the ankle was recorded. Radiographic measurement included tibial plafond inclination, tibiotalar tilt angle, talar dome inclination, and lateral talo-first metatarsal angle. Comparison between the two types of medial ankle osteoarthritis and the relationship between the maximum ankle varus moment and radiographic measurements were analyzed.

Results: The mean tibial plafond inclination, tibiotalar tilt angle, talar dome inclination, lateral talo-first metatarsal angle, and maximum ankle varus moment were 6.4 degrees (SD 3.3 degrees), 5.0 degrees (SD 4.6 degrees), 11.4 degrees (SD 5.2 degrees), -6.5 degrees (SD 11.7 degrees), and 0.185 (SD 0.082) Nm/kg, respectively. The varus angulation type showed a greater maximum ankle varus moment than the medial translation type (p = .005). The lateral talo-first metatarsal angle was significantly associated with the maximum ankle varus moment (p = .041) in the multiple regression analysis.

Conclusion: The varus angulation type of medial ankle osteoarthritis is considered to be more imbalanced biomechanically than the medial displacement type. The lateral talo-first metatarsal angle, being significantly associated with the ankle varus moment, should be considered for correction during motion-preserving surgeries for medial ankle osteoarthritis to restore the biomechanical balance of the ankle.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0253570PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8224910PMC
June 2021

Estimating the basic reproductive number of varicella in South Korea incorporating social contact patterns and seroprevalence.

Hum Vaccin Immunother 2021 Apr 8:1-6. Epub 2021 Apr 8.

Division of Infectious Diseases, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.

Varicella, which is caused by the varicella zoster virus (VZV), is a common infectious disease affecting children. Varicella vaccines have been used for decades; however, vaccination policies vary across countries because of differences in VZV epidemiology. The basic reproductive number transmissibility measure parameter, also differs from country to country. In this study for varicella was estimated in South Korea using the contact rate matrix derived from averaged POLYMOD contact data, the Korean population, and proportionality factor fitted to the Korean VZV seroprevalence for varicella in South Korea was estimated to be 5.67 (95% CI: 5.33, 6.33). Therefore, to reach the herd immunity threshold, the critical vaccine coverage should be greater than 82.4% with a perfect vaccine, or the primary vaccine failure proportion should be less than 17.6% with 100% coverage. Because of the relatively low seroconversion rate and rapidly waning immunity after one-dose vaccination in South Korea, the herd immunity threshold is difficult to attain with only a one-dose vaccine. Two doses of vaccination may be necessary to effectively interrupt varicella transmission and maintain herd immunity in South Korea. The study results can help guide the decision-making on an effective varicella vaccination policy in South Korea.
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http://dx.doi.org/10.1080/21645515.2021.1898917DOI Listing
April 2021

The impact of two-dose varicella vaccination on varicella and herpes zoster incidence in South Korea using a mathematical model with changing population demographics.

Vaccine 2021 04 1;39(18):2575-2583. Epub 2021 Apr 1.

Division of Infectious Diseases, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea. Electronic address:

Background: In South Korea, one-dose varicella vaccination was introduced to the National Immunization Program in 2005, but varicella outbreaks have continued to occur. Therefore, a two-dose vaccination strategy is considered.

Methods: We developed an age-structured deterministic compartment model using Korean population projection data. The impact of adding a second dose of varicella vaccine on varicella and herpes zoster (HZ) epidemiology was assessed under four different vaccine effectiveness (VE) scenarios (base, moderate, lowest, highest) and the optimal timing of the second vaccine dose (18 months, 4, 5, or 6 years of age) was examined over the period 2020-2065.

Results: A two-dose vaccination schedule reduced the cumulative varicella incidence by > 90% compared to no vaccination, regardless of the VE. The additional reduction attributable to a second dose compared to a single dose was greatest (82%) with the lowest VE scenario. A second dose at 6 years of age reduced the varicella incidence at a population level, whereas a second dose at 18 months of age reduced the varicella incidence primarily in the target birth cohorts. Routine vaccination at the age of 18 months with a catch-up vaccination of 6-year-olds was the optimal strategy for birth cohort and population-level control. HZ incidence continued to increase under no vaccination scenario, which represents the effect of aging population. Under a two-dose scenario, the additional increase in HZ incidence attributable to the reduced exogenous boosting was small relative to a one-dose scenario and a further reduction in HZ cases was observed.

Conclusion: A two-dose varicella vaccination schedule would significantly reduce varicella and HZ incidence in the long term. A second dose at the age of 18 months with a catch-up vaccination of 6-year-olds would be optimal for controlling varicella in South Korea.
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http://dx.doi.org/10.1016/j.vaccine.2021.03.056DOI Listing
April 2021

The effect of control measures on COVID-19 transmission in South Korea.

PLoS One 2021 29;16(3):e0249262. Epub 2021 Mar 29.

School of Mathematics and Computing (Mathematics), Yonsei University, Seoul, Korea.

Countries around the world have taken control measures to mitigate the spread of COVID-19, including Korea. Social distancing is considered an essential strategy to reduce transmission in the absence of vaccination or treatment. While interventions have been successful in controlling COVID-19 in Korea, maintaining the current restrictions incurs great social costs. Thus, it is important to analyze the impact of different polices on the spread of the epidemic. To model the COVID-19 outbreak, we use an extended age-structured SEIR model with quarantine and isolation compartments. The model is calibrated to age-specific cumulative confirmed cases provided by the Korea Disease Control and Prevention Agency (KDCA). Four control measures-school closure, social distancing, quarantine, and isolation-are investigated. Because the infectiousness of the exposed has been controversial, we study two major scenarios, considering contributions to infection of the exposed, the quarantined, and the isolated. Assuming the transmission rate would increase more than 1.7 times after the end of social distancing, a second outbreak is expected in the first scenario. The epidemic threshold for increase of contacts between teenagers after school reopening is 3.3 times, which brings the net reproduction number to 1. The threshold values are higher in the second scenario. If the average time taken until isolation and quarantine reduces from three days to two, cumulative cases are reduced by 60% and 47% in the first scenario, respectively. Meanwhile, the reduction is 33% and 41%, respectively, for rapid isolation and quarantine in the second scenario. Without social distancing, a second wave is possible, irrespective of whether we assume risk of infection by the exposed. In the non-infectivity of the exposed scenario, early detection and isolation are significantly more effective than quarantine. Furthermore, quarantining the exposed is as important as isolating the infectious when we assume that the exposed also contribute to infection.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0249262PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8006988PMC
April 2021

A mathematical model of COVID-19 transmission in a tertiary hospital and assessment of the effects of different intervention strategies.

PLoS One 2020 26;15(10):e0241169. Epub 2020 Oct 26.

Department of Internal Medicine, Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.

Novel coronavirus (named SARS-CoV-2) can spread widely in confined settings including hospitals, cruise ships, prisons, and places of worship. In particular, a healthcare-associated outbreak could become the epicenter of coronavirus disease (COVID-19). This study aimed to evaluate the effects of different intervention strategies on the hospital outbreak within a tertiary hospital. A mathematical model was developed for the COVID-19 transmission within a 2500-bed tertiary hospital of South Korea. The SEIR (susceptible-exposed-infectious-recovered) model with a compartment of doctor, nurse, patient, and caregiver was constructed. The effects of different intervention strategies such as front door screening, quarantine unit for newly admitted patients, early testing of suspected infected people, and personal protective equipment for both medical staff and visitors were evaluated. The model suggested that the early testing (within eight hours) of infected cases and monitoring the quarantine ward for newly hospitalized patients are effective measures for decreasing the incidence of COVID-19 within a hospital (81.3% and 70% decrease of number of incident cases, respectively, during 60 days). Front door screening for detecting suspected cases had only 42% effectiveness. Screening for prohibiting the admission of COVID-19 patients was more effective than the measures for patients before emergency room or outpatient clinic. This model suggests that under the assumed conditions, some effective measures have a great influence on the incidence of COVID-19 within a hospital. The implementation of the preventive measures could reduce the size of a hospital outbreak.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0241169PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7588052PMC
November 2020

Scalable Synthesis of Hollow β-SiC/Si Anodes Selective Thermal Oxidation for Lithium-Ion Batteries.

ACS Nano 2020 Sep 21;14(9):11548-11557. Epub 2020 Aug 21.

Department of Energy Engineering and School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea.

Silicon for anodes in lithium-ion batteries has received much attention owing to its superior specific capacity. There has been a rapid increase of research related to void engineering to address the silicon failure mechanism stemming from the massive volume change during (dis)charging in the past decade. Nevertheless, conventional synthetic methods require complex synthetic procedures and toxic reagents to form a void space, so they have an obvious limitation to reach practical application. Here, we introduce SiC consisting of nanocrystallite Si embedded in the inactive matrix of β-SiC to fabricate various types of void structures using thermal etching with a scalable one-pot CVD method. The structural features of SiC make the carbonaceous template possible to be etched selectively without Si oxidation at high temperature with an air atmosphere. Furthermore, bottom-up gas phase synthesis of SiC ensures atomically identical structural features (.., homogeneously distributed Si and β-SiC) regardless of different types of sacrificial templates. For these reasons, various types of SiC hollow structures having shells, tubes, and sheets can be synthesized by simply employing different morphologies of the carbon template. As a result, the morphological effect of different hollow structures can be deeply investigated as well as the free volume effect originating from void engineering from both a electrochemical and computational point of view. In terms of selective thermal oxidation, the SiC hollow shell achieves a much higher initial Coulombic efficiency (>89%) than that of the Si hollow shell (65%) because of its nonoxidative property originating from structural characteristics of SiC during thermal etching. Moreover, the findings based on the clearly observed different electrochemical features between half-cell and full-cell configuration give insight into further Si anode research.
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http://dx.doi.org/10.1021/acsnano.0c04013DOI Listing
September 2020

Calendering-Compatible Macroporous Architecture for Silicon-Graphite Composite toward High-Energy Lithium-Ion Batteries.

Adv Mater 2020 Sep 2;32(37):e2003286. Epub 2020 Aug 2.

Department of Energy Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, South Korea.

Porous strategies based on nanoengineering successfully mitigate several problems related to volume expansion of alloying anodes. However, practical application of porous alloying anodes is challenging because of limitations such as calendering incompatibility, low mass loading, and excessive usage of nonactive materials, all of which cause a lower volumetric energy density in comparison with conventional graphite anodes. In particular, during calendering, porous structures in alloying-based composites easily collapse under high pressure, attenuating the porous characteristics. Herein, this work proposes a calendering-compatible macroporous architecture for a Si-graphite anode to maximize the volumetric energy density. The anode is composed of an elastic outermost carbon covering, a nonfilling porous structure, and a graphite core. Owing to the lubricative properties of the elastic carbon covering, the macroporous structure coated by the brittle Si nanolayer can withstand high pressure and maintain its porous architecture during electrode calendering. Scalable methods using mechanical agitation and chemical vapor deposition are adopted. The as-prepared composite exhibits excellent electrochemical stability of >3.6 mAh cm , with mitigated electrode expansion. Furthermore, full-cell evaluation shows that the composite achieves higher energy density (932 Wh L ) and higher specific energy (333 Wh kg ) with stable cycling than has been reported in previous studies.
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http://dx.doi.org/10.1002/adma.202003286DOI Listing
September 2020

Application of control theory in a delayed-infection and immune-evading oncolytic virotherapy.

Math Biosci Eng 2020 02;17(3):2361-2383

Department of Mathematics, College of Science, Yonsei University, Seoul, Korea.

Oncolytic virotherapy is a promising cancer treatment that harnesses the power of viruses. Through genetic engineering, these viruses are cultivated to infect and destroy cancer cells. While this therapy has shown success in a range of clinical trials, an open problem in the field is to determine more effective perturbations of these viruses. In this work, we use a controlled therapy approach to determine the optimal treatment protocol for a delayed infection from an immune-evading, coated virus. We derive a system of partial differential equations to model the interaction between a growing tumour and this coated oncolytic virus. Using this system, we show that viruses with inhibited viral clearance and infectivity are more effective than uncoated viruses. We then consider a hierarchical level of coating that degrades over time and determine a nontrivial initial distribution of coating levels needed to produce the lowest tumour volume. Interestingly, we find that a bimodal mixture of thickly coated and thinly coated virus is necessary to achieve a minimum tumour size. Throughout this article we also consider the effects of immune clearance of the virus. We show how different immune responses instigate significantly different treatment outcomes.
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http://dx.doi.org/10.3934/mbe.2020126DOI Listing
February 2020

Identification of potential plantar ulceration among diabetes patients using plantar soft tissue stiffness.

J Mech Behav Biomed Mater 2020 03 30;103:103567. Epub 2019 Nov 30.

Division of Mechanical and Biomedical Engineering, Faculty of Engineering, EwhaWomans University, South Korea. Electronic address:

This study investigates the relationship between plantar tissue stiffness and selected parameters, including age, diabetes mellitus (DM) duration, body mass index (BMI), and HbA level. 70 diabetes patients with no foot problems were recruited. The plantar soft tissue at the 2nd sub-metatarsal head (MTH) pad was examined using the novel indentation system developed. The stiffness constant, K, was used to describe the tissue stiffness. The four factors (age, DM duration, BMI, and HbA level) were plotted against the plantar tissue stiffness. The scatter plots revealed that a higher plantar tissue stiffness was usually associated with (1) BMI>25  kgm, (2) HbA score >10% (86 mmol/mol), and (3) DM duration >10 years. The three risk criteria were further evaluated using the binary classification test. The predictions were reported to be fairly accurate and reliable in detecting stiffened tissues. The study has successfully identified the strong association of BMI, HbA, and DM duration with the plantar tissue properties. Special attention should be given to the high risk group with BMI>25 kgm, HbA score >10% (86 mmol/mol), and DM duration >10 years. The high diagnostic odds ratio attained suggests its potential usefulness in helping clinicians to diagnose diabetic foot more efficiently.
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http://dx.doi.org/10.1016/j.jmbbm.2019.103567DOI Listing
March 2020

Strain-rate dependence of viscous properties of the plantar soft tissue identified by a spherical indentation test.

J Mech Behav Biomed Mater 2020 02 3;102:103470. Epub 2019 Oct 3.

Department of Mechanical Engineering, Keio University, Yokohama, Japan; Department of Biological Science, Graduate School of Science, The University of Tokyo, Tokyo, Japan. Electronic address:

The mechanical properties of the plantar soft tissue are known to vary in diabetic patients, indicating that parameter identification of the mechanical properties of the foot tissue using an indentation test is clinically important for possible early diagnosis and interventions of diabetic foot. However, accurate mechanical characterization of the viscous properties of the plantar soft tissue has been difficult, as measured force-relaxation curves of the same soft tissue differ depending on how the material is loaded. In the present study, we attempted to clarify how the indentation rate of the plantar soft tissue affects the measured force-relaxation curves, which is necessary in order to identify the viscoelastic properties. The force-relaxation curves of the heel pads were obtained from the indentation experiment in vivo at indentation rates of 15, 25, 50, 75, and 100 mm/s. The curves were fit to an analytical contact model of spherical indentation incorporating a five-element Maxwell model. The results of the present study demonstrated that, although experimentally obtained force-relaxation curves were actually variable depending on the indentation rate, similar viscous parameters could be identified for the same heel if the effects of (1) the underestimation of the peak force due to the energy dissipation occurring during indentation and (2) the deceleration of the indenter at the target position were incorporated in the parameter identification process. The indentation-rate-independent viscous properties could therefore be estimated using the proposed method.
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http://dx.doi.org/10.1016/j.jmbbm.2019.103470DOI Listing
February 2020

Mechanical and Mechanosensing Properties of Tumor Affected Bone Cells Were Inhibited via PI3K/Akt Pathway.

Authors:
Taeyong Lee

J Bone Metab 2019 Aug 31;26(3):179-191. Epub 2019 Aug 31.

Division of Mechanical and Biomedical Engineering, Ewha Womans University, Seoul, Korea.

Background: Osteolytic metastasis is a common destructive form of metastasis, in which there is an increased bone resorption but impaired bone formation. It is hypothesized that the changed mechanical properties of tumor affected bone cells could inhibit its mechanosensing, thus contributing to differences in bone remodeling.

Methods: Here, atomic force microscopy indentation on primary bone cells exposed to 50% conditioned medium from Walker 256 (W) carcinoma cell line or its adaptive tumor (T) cells was carried out. Nitric oxide levels of bone cells were monitored in response to low-magnitude, high-frequency (LMHF) vibrations.

Results: A stronger sustained inhibitive effect on bone cell viability and differentiation by T cells as compared to that of its cell line was demonstrated. This could be attributed to the higher levels of transforming growth factor-β1 (TGF-β1) in the T-conditioned medium as compared to W-conditioned medium. Bone cell elastic moduli in W and T-groups were found to decrease significantly by 61.0% and 69.6%, respectively compared to control and corresponded to filamentous actin changes. Nitric oxide responses were significantly inhibited in T-conditioned group but not in W-conditioned group.

Conclusions: It implied that a change in cell mechanical properties is not sufficient as an indicator of change in mechanosensing ability. Moreover, inhibition of phosphoinositide 3-kinase/Akt downstream signaling pathway of TGF-β1 alleviated the inhibition effects on mechanosensing in T-conditioned cells, further suggesting that growth factors such as TGF-β could be good therapeutic targets for osteoblast treatment.
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http://dx.doi.org/10.11005/jbm.2019.26.3.179DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6746668PMC
August 2019

Investigation of the relationship between localized cumulative stress and plantar tissue stiffness in healthy individuals using the in-vivo indentation technique.

J Mech Behav Biomed Mater 2019 10 20;98:157-162. Epub 2019 Jun 20.

Division of Mechanical and Biomedical Engineering, Ewha Womans University, Republic of Korea. Electronic address:

This study was conducted to determine whether prolonged and repetitive exercise stiffens the plantar soft tissue. Healthy female subjects in their early 20s with a similar body mass index but different majors (13 engineers (controls) and 13 ballet dancers) were recruited. Tissue thickness was measured using ultrasound, while peak stress, stress distribution, and center of pressure were obtained Zebris pressure mat. Stiffness was evaluated using a custom-made tissue indentation system. F-test and independent sample T-test were used to determine significant differences between the two groups. No significance was found in the thickness of the second sub-metatarsal head (MTH) and heel between the two groups. In the second sub-MTH, the ballet group showed higher peak stress, loading rate, and stiffness than the control group. Conversely, in the heel region, all the results were higher for the control group. The results of this study quantify the impact of exercise on the stiffness of plantar soft tissue and confirm that even healthy individuals who do prolonged and repetitive exercise have stiffer plantar soft tissue.
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http://dx.doi.org/10.1016/j.jmbbm.2019.06.020DOI Listing
October 2019

Assessment of finite element models for prediction of osteoporotic fracture.

J Mech Behav Biomed Mater 2019 09 11;97:312-320. Epub 2019 May 11.

Division of Mechanical and Biomedical Engineering, Ewha Womans University, Republic of Korea. Electronic address:

With increasing life expectancy and mortality rates, the burden of osteoporotic hip fractures is continually on an upward trend. In terms of prevention, there are several osteoporosis treatment strategies such as anti-resorptive drug treatments, which attempt to retard the rate of bone resorption, while promoting the rate of formation. With respect to prediction, several studies have provided insights into obtaining bone strength by non-invasive means through the application of FE analysis. However, what valuable information can we obtain from FE studies that have focused on osteoporosis research, with respect to the prediction of osteoporotic fractures? This paper aims to fine studies that have used FE analysis to predict fractures in the proximal femur through a systematic search of literature using PUBMED, with the main objective of supporting the diagnosis of osteoporosis. The focus of these FE studies is first discussed, and the methodological aspects are summarized, by mainly comparing and contrasting their meshing properties, material properties, and boundary conditions. The implications of these methodological differences in FE modelling processes and propositions with the aim of consolidating or minimalizing these differences are further discussed. We proved that studies need to start converging in terms of their input parameters to make the FE method applicable to clinical settings. This, in turn, will decrease the time needed for in vitro tests. Current advancements in FE analysis need to be consolidated before any further steps can be taken to implement engineering analysis into the clinical scenario.
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http://dx.doi.org/10.1016/j.jmbbm.2019.05.018DOI Listing
September 2019

In-vivo viscous properties of the heel pad by stress-relaxation experiment based on a spherical indentation.

Med Eng Phys 2017 12 2;50:83-88. Epub 2017 Nov 2.

Department of Mechanical Engineering, Keio University, Yokohama, Japan. Electronic address:

Identifying the viscous properties of the plantar soft tissue is crucial not only for understanding the dynamic interaction of the foot with the ground during locomotion, but also for development of improved footwear products and therapeutic footwear interventions. In the present study, the viscous and hyperelastic material properties of the plantar soft tissue were experimentally identified using a spherical indentation test and an analytical contact model of the spherical indentation test. Force-relaxation curves of the heel pads were obtained from the indentation experiment. The curves were fit to the contact model incorporating a five-element Maxwell model to identify the viscous material parameters. The finite element method with the experimentally identified viscoelastic parameters could successfully reproduce the measured force-relaxation curves, indicating the material parameters were correctly estimated using the proposed method. Although there are some methodological limitations, the proposed framework to identify the viscous material properties may facilitate the development of subject-specific finite element modeling of the foot and other biological materials.
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http://dx.doi.org/10.1016/j.medengphy.2017.10.010DOI Listing
December 2017

The use of shear thickening polymer as a hip protecter.

Annu Int Conf IEEE Eng Med Biol Soc 2017 Jul;2017:1633-1635

External hip protectors are used by the elderly in preventing hip fracture due to sideway falls. There are some commercial hip protectors which has both energy absorbing and energy shunting properties. In this study, a novel hip protector using shear thickening polymer (STP) is studied. The purpose of this work is to determine the optimal thickness of STP needed for maximum force attenuation. A mechanical test rig to simulate a person falling with sufficient impact energy to fracture the greater trochanter if unprotected was used together with biofidelic femur model which simulates the layer of flesh with skin. 8mm of STP together with 5mm foam gives the best force attenuation. When comparing the overall thickness with commercial hip protectors, STP hip protectors tested have much less thickness. Reduced thickness increases the compliance and comfort of STP hip protectors.
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http://dx.doi.org/10.1109/EMBC.2017.8037152DOI Listing
July 2017

The correlation between bone mineral density/trabecular bone score and body mass index, height, and weight.

Osteoporos Sarcopenia 2017 Jun 14;3(2):98-103. Epub 2017 Mar 14.

Division of Mechanical and Biomedical Engineering, College of Engineering, Ewha Womans University, Seoul, South Korea.

Objectives: This study investigated the correlation between bone mineral density (BMD)/trabecular bone score (TBS) and body mass index (BMI), height and weight in Korean adults.

Methods: We enrolled 2555 female participants in their 20s-80s and 1631 male participants in their 20s-70s. Participants with history of previous vertebral surgeries or current vertebral diseases were excluded. Female and male participants were divided into osteoporosis group (n = 136 and n = 31, respectively), osteopenia group (n = 822 and n = 460, respectively), and normal group (n = 1596 and n = 1140, respectively) based on their BMD T-score. Dual-energy X-ray absorptiometry image analysis and linear regression analysis were conducted on each participant in each group to determine the P-value and the correlation between BMD T-score/TBS T-score and BMI, weight, and height.

Results: We found a significant correlation between BMI and TBS in both male and female participants. In the male participants, the correlation coefficient increased progressively from the normal group to the osteoporosis group. In the female group, we observed a significant positive correlation between height and TBS, and in the male group a significant negative correlation between weight and TBS was observed.

Conclusions: BMI and weight are closely correlated to body fat content. BMD was positively correlated to BMI and weight, while TBS was negatively correlated to BMI and weight. Therefore, although BMI causes an increase in BMD, it appears to be negatively affecting bone quality.
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http://dx.doi.org/10.1016/j.afos.2017.02.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6372832PMC
June 2017

Dynamic measurement of surface strain distribution on the foot during walking.

J Mech Behav Biomed Mater 2017 05 18;69:249-256. Epub 2016 Dec 18.

Department of Mechanical Engineering, Faculty of Science and Technology, Keio University, Yokohama, Japan. Electronic address:

To clarify the mechanism underlying the development of foot disorders such as diabetic ulcers and deformities, it is important to understand how the foot surface elongates and contracts during gait. Such information is also helpful for improving the prevention and treatment of foot disorders. We therefore measured temporal changes in the strain distribution on the foot surface during human walking. Five adult male participants walked across a glass platform placed over an angled mirror set in a wooden walkway at a self-selected speed and the dorsolateral and plantar surfaces of the foot were filmed using two pairs of synchronized high-speed cameras. Three-dimensional (3D) digital image correlation was used to quantify the spatial strain distribution on the foot surface with respect to that during quiet standing. Using the proposed method, we observed the 3D patterns of foot surface strain distribution during walking. Large strain was generated around the ball on the plantar surface of the foot throughout the entire stance phase, due to the windlass mechanism. The dorsal surface around the cuboid was stretched in the late stance phase, possibly due to lateral protruding movement of the cuboid. It may be possible to use this technique to non-invasively estimate movements of the foot bones under the skin using the surface strain distribution. The proposed technique may be an effective tool with which to analyze foot deformation in the fields of diabetology, clinical orthopedics, and ergonomics.
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http://dx.doi.org/10.1016/j.jmbbm.2016.12.009DOI Listing
May 2017

Parameter identification of hyperelastic material properties of the heel pad based on an analytical contact mechanics model of a spherical indentation.

J Mech Behav Biomed Mater 2017 01 22;65:753-760. Epub 2016 Sep 22.

Department of Mechanical Engineering, Keio University, Yokohama, Japan. Electronic address:

Accurate identification of the material properties of the plantar soft tissue is important for computer-aided analysis of foot pathologies and design of therapeutic footwear interventions based on subject-specific models of the foot. However, parameter identification of the hyperelastic material properties of plantar soft tissues usually requires an inverse finite element analysis due to the lack of a practical contact model of the indentation test. In the present study, we derive an analytical contact model of a spherical indentation test in order to directly estimate the material properties of the plantar soft tissue. Force-displacement curves of the heel pads are obtained through an indentation experiment. The experimental data are fit to the analytical stress-strain solution of the spherical indentation in order to obtain the parameters. A spherical indentation approach successfully predicted the non-linear material properties of the heel pad without iterative finite element calculation. The force-displacement curve obtained in the present study was found to be situated lower than those identified in previous studies. The proposed framework for identifying the hyperelastic material parameters may facilitate the development of subject-specific FE modeling of the foot for possible clinical and ergonomic applications.
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http://dx.doi.org/10.1016/j.jmbbm.2016.09.027DOI Listing
January 2017

The influence of sex, body mass and body mass index on plantar soft-tissue stiffness in healthy people in their 60s.

J Biomech 2016 09 17;49(13):3022-3025. Epub 2016 Jun 17.

College of Science & Industry Convergence, Ewha Womans University, Seoul, South Korea. Electronic address:

Foot abnormality has become a public health concern. Early detection of pathological soft tissue is therefore an important preventive measure, especially in older people who generally have a higher risk of foot pathology. However, the interpretation of plantar tissue stiffness data - whether to normalize the data or to separate the data on the basis of sex- remains questionable. The objective of this study was to assess the influence of sex and physical attributes such as body mass (BM) and body mass index (BMI) on plantar soft-tissue stiffness, and to evaluate whether it is necessary to isolate the differences in sex, BM and BMI in the data analysis. One hundred healthy subjects in their 60s were recruited for the experiment. Localized force response was obtained underneath the second metatarsal head (MTH) pad at three different dorsiflexion angles of 0°, 20°, 40° and the hallux and heel at 0°. No significant relationship was found between the independent variables and plantar stiffness. From the experimental results, it can be deduced that BM and BMI are weakly associated with plantar tissue stiffness, and that there is no significant difference in stiffness between male and female participants. No difference was found between left and right foot measurements. This suggests that normalizing of plantar tissue stiffness by BM and BMI is not necessary in healthy people in their 60s. The data can be pooled and treated equally regardless of sex.
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http://dx.doi.org/10.1016/j.jbiomech.2016.05.032DOI Listing
September 2016

Analysis of compressive load on intervertebral joint in standing and sitting postures.

Technol Health Care 2016 ;24(2):215-23

Department of Medical Biotechnology, Dongguk University, Seoul, Korea.

Background: There have been some disagreements on the comparison of disc pressures in the standing and sitting postures in literature. Most research on in vivo pressure needle measurement found higher disc pressure in sitting than in standing. The disc pressure data can help to advocate better postures for clinical advice.

Objective: The aim of this paper is to develop a procedure to study the compressive load on intervertebral joint in the standing and sitting postures through the approach of motion capture and musculoskeletal modeling.

Methods: The marker data of six subjects performing various standing and sitting postures was obtained during the motion capture experiment and used to train the musculoskeletal model with an enhanced discretized spine developed for subject in the inverse and forward simulations.

Results: Compressive loads on L3-L4 and L4-L5 joints are found higher in upright sitting than in upright standing. Slumped sitting, cross-legged sitting and flexion sitting can introduce higher compressive loads on intervertebral joints compared with upright sitting.

Conclusions: These findings indicate the effects of standing and sitting postures on the spinal joint loads. The results can provide doctors and therapists with more information on clinical advice on better postures for people with spinal problems.
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http://dx.doi.org/10.3233/THC-151100DOI Listing
January 2017

Prediction of plantar soft tissue stiffness based on sex, age, bodyweight, height and body mass index.

J Mech Behav Biomed Mater 2016 Feb 1;54:219-22. Epub 2015 Oct 1.

Department of Medical Biotechnology Dongguk University, 30, Pildong-ro 1-gil, Jung-gu Seoul, 100-705 Seoul, Korea. Electronic address:

15% of Diabetes Mellitus (DM) patients suffer high risk of ulceration and 85% of the amputation involving DM population is caused by non-healing ulcers. These findings elucidate the fact that foot ulcer can result in major amputation especially to the DM and elderly population. Therefore, early diagnosis of abnormally stiffened plantar soft tissue is needed to prevent the catastrophic tissue damage. In order to differentiate between normal and pathological tissues, a threshold reference value that defines healthy tissue is required. The objective of this study is to perform a multivariate analysis to estimate the healthy plantar tissue stiffness values based on the individuals physical attributes such as bodyweight (BW), height and body mass index (BMI) as well as their age and sex. 100 healthy subjects were recruited. Indentation was performed on 2nd metatarsal head pad at 3 different dorsiflexion angles of 0°, 20°, 40° and the hallux and heel at 0°. The results showed the important influences of BW, height and BMI in determining the plantar tissue stiffness. On the other hand, age and sex only play minimal roles. The study can be further extended to increase the reliability and accuracy of the proposed predictive model by evaluating several other related parameters such as body fat content, footwear usage, frequency of sports participation, etc.
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http://dx.doi.org/10.1016/j.jmbbm.2015.09.015DOI Listing
February 2016

Comparative Effects of Ibandronate and Paclitaxel on Immunocompetent Bone Metastasis Model.

Yonsei Med J 2015 Nov;56(6):1643-50

Department of Medical Biotechnology, Dongguk University, Seoul, Korea.

Purpose: Bone metastasis invariably increases morbidity and mortality. This study compares the effects of ibandronate and paclitaxel on bone structure and its mechanical properties and biochemical turnover in resorption markers using an immunocompetent Walker 256-Sprague-Dawley model, which was subjected to tumor-induced osteolysis.

Materials And Methods: Seventy rats were divided equally into 4 groups: 1) sham group (SHAM), 2) tumor group (CANC), 3) ibandronate treated group (IBAN), and 4) paclitaxel treated group (PAC). Morphological indices [bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp)] and mechanical properties (failure load, stiffness) were evaluated after thirty days of treatment period. Bone resorption rate was analysed using serum deoxypyridinoline (Dpd) concentrations.

Results: Morphological indices showed that ibandronate (anti-resorptive drug) had a better effect in treating tumor-induced architectural changes in bone than paclitaxel (chemotherapeutic drug). The deterioration in bone architecture was reflected in the biomechanical properties of bone as studied with decreased failure load (F(x)) and stiffness (S) of the bone on the 30th day postsurgery. Dpd concentrations were significantly lower in the IBAN group, indicating successful inhibition of bone resorption and destruction.

Conclusion: Ibandronate was found to be as effective as higher doses of paclitaxel in maintaining stiffness of bone. Paclitaxel treatment did not appear to inhibit osteoclast resorption, which is contrary to earlier in-vitro literature. Emphasis should be placed on the use of immunocompetent models for examining drug efficacy since it adequately reflects bone metastasis in clinical scenarios.
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http://dx.doi.org/10.3349/ymj.2015.56.6.1643DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4630055PMC
November 2015

Minimum indentation depth for characterization of 2nd sub-metatarsal head and heel pad tissue properties.

J Biomech 2015 Jul 20;48(10):2096-101. Epub 2015 Mar 20.

Department of Medical Biotechnology, Dongguk University-Seoul, 30, Pildong-ro 1-gil, Jung-gu, Seoul 100-705, Republic of Korea. Electronic address:

Most in-vivo indentation techniques are limited by the lack of adequate indentation into the plantar soft tissue. The purpose of this study is therefore to assess the effect of deformation depth on plantar soft tissue behavior and to establish a guideline for the minimum indentation depth that is sufficient to quantify critical plantar soft tissue behavior. Twenty young subjects (20-25 years) participated in this study. The test was conducted with equal weight borne on each of the participants׳ feet to mimic the static stance of the gait cycle. During the experiment, the indenter probed the 2nd sub-metatarsal head (MTH) and heel pad tissue at a constant rate of 12.3 mm/s. The maximum tissue deformation induced was varied from 1.2 mm to 6.0 mm, in steps of 1.2 mm. The tissue stiffness obtained from the tissue response curves was compared and fitted to the proposed viscoelastic model. As the probe tip indents deeper into the plantar soft tissue beyond a threshold depth, Xs, the force gradient increases notably. The absolute value of Xs was approximately 2.23 mm and 2.14 mm at the heel and 2nd sub-MTH respectively. Indentation depths which were less than this threshold depth might not be representative of the nature of plantar soft tissue nor reflect the critical deformation it experiences during physical activities that expose the tissue to risk of ulceration. Our study indicated the necessity to induce a minimum tissue indentation depth in order to describe its actual characteristics. By doing so, additional useful parameters can be obtained to identify potentially abnormal soft tissue.
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http://dx.doi.org/10.1016/j.jbiomech.2015.03.008DOI Listing
July 2015

Assessing bone quality in terms of bone mineral density, buckling ratio and critical fracture load.

J Bone Metab 2014 Nov 30;21(4):243-7. Epub 2014 Nov 30.

Department of Medical Biotechnology, Dongguk University, Seoul, Korea.

Background: Bone mineral density (BMD) is used as a sole parameter in the diagnosis of osteoporosis. Due to the ease of acquirement of BMD, clinical diagnosis still involves its usage although the limitations of BMD are quite well-established. Therefore, this preliminary study hoped to reduce the errors introduced by BMD alone by incorporating geometric and structural predictors simultaneously to observe if strength was implicitly dependent on the geometry and BMD. Hence, we illustrated the triadic relationship between BMD, buckling ratio (BR) and critical fracture load (Fcr).

Methods: The geometric predictor was the BR as it involves both the changes in the periosteum and the cortical thickness. Also, structural changes were monitored by finite element (FE) analysis-predicted Fcr. These BR and Fcr measurements were plotted with their respective femoral neck BMD values in elderly female patients (n=6) in a 3-year follow-up study, treated with ibandronate.

Results: In all the three-dimensional plots (baseline, mid and final year), high Fcr values were found at regions containing high BMD and low BR values. Quantitatively, this was also proven where an averaged highest Fcr across the three years had a relatively higher BMD (46%) and lower BR (19%) than that of the averaged lowest Fcr. The dependence of FE predicted strength on both the geometry and bone density was illustrated.

Conclusions: We conclude that use of triadic relationships for the evaluation of osteoporosis and hip fractures with the combination of strength, radiology-derived BR and bone density will lay the foundation for more accurate predictions in the future.
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http://dx.doi.org/10.11005/jbm.2014.21.4.243DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4255044PMC
November 2014

Comparison of Buckling Ratio and Finite Element Analysis of Femoral Necks in Post-menopausal Women.

J Menopausal Med 2014 Aug 27;20(2):52-6. Epub 2014 Aug 27.

Department of Medical Biotechnology, Dongguk University, Seoul, Korea.

Objectives: Osteoporosis is a prevalent problem amongst the elderly. Bone mineral density (BMD) obtained from dual X-ray absorptiometry (DXA) is the gold standard in diagnosing osteopenia (-1.0 < t < -2.5) and osteoporosis (t > -2.5). However, following osteoporosis therapy, increases in BMD may be unreliable. Although hip fracture risk can be reduced with the aid of drugs, treated patients still face considerable risk as most people who sustain hip fracture do not have generalized osteoporosis. A study of the local distribution of bone mass was necessary as they contribute to the geometry and consequently the bone strength.

Methods: By identifying the respective regions in the femoral neck, the geometric changes were localized and differed between each patient, proving that drug treatment elicits local changes in mean outer radius and mean cortical thickness. Numerical analysis also validated the above findings, where critical strain regions were predicted at similar zones and this is coherent with the fact that reduced thickness of the cortical bone has been related to increased risk of fracture initiation.

Results: Hence, from individual radar plots, we can determine if the effect of drugs had outweighed the effect of aging. We can then propose a course of treatment drug better suited for the patient in the clinical scenario.

Conclusion: Clinically, little conclusion can be drawn from just the BMD in osteopenic / osteoporotic patients. This emphasizes the necessity of using geometry and structure to predict fracture risk. Focusing on a patient specific analysis at a local level will improve diagnosis of osteoporosis and ultimately fracture prediction.
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http://dx.doi.org/10.6118/jmm.2014.20.2.52DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4207002PMC
August 2014

Quantification of plantar soft tissue changes due to aging in various metatarsophalangeal joint angles with realistic tissue deformation.

J Biomech 2014 Sep 5;47(12):3043-9. Epub 2014 Jul 5.

Department of Medical Biotechnology, Dongguk University, Seoul, Republic of Korea. Electronic address:

The nonlinearity of plantar soft tissue is seldom examined because of the small extent of deformation induced during indentation for measurement purposes. Furthermore, in most indentation experiments, the metatarsophalangeal joint (MTPJ) angle is not well controlled, although it has been proven to have a significant stiffening effect on sub-metatarsal head (MTH) pads. Hence, the study aims to quantify changes in the mechanical properties of plantar soft tissue due to aging under an experimental condition which is similar to walking. This is done by subjecting the tissue to an appropriate level of deformation at various MTPJ angles. A custom-made in vivo tissue indenter was used to measure directly the force-indentation response of the plantar tissue of two healthy groups: "Young" (n=25, mean age 22) and "Elderly" (n=25, mean age 67) subjects. Tests were performed on the 2nd sub-MTH pad at angles of 0°, 20°, 40° MTPJ dorsiflexion, as well as at the hallux and heel pad at 0° MTPJ angle. At all three plantar sites tested, elderly subjects showed significantly higher tissue stiffness than the young (p<0.05). However, the stiffening effect of MTPJ angle was not notably influenced by aging. In this work, tissue stiffness is quantified in stiffness constant (K) based on the proposed indentation technique. It is hypothesized that the increase in stiffness with age observed is probably due to compositional change in the plantar soft tissue.
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http://dx.doi.org/10.1016/j.jbiomech.2014.06.033DOI Listing
September 2014

Investigation of the biomechanical effect of variable stiffness shoe on external knee adduction moment in various dynamic exercises.

J Foot Ankle Res 2013 Sep 17;6(1):39. Epub 2013 Sep 17.

Department of Bioengineering, Faculty of Engineering, National University of Singapore, Block E3A #07-15, 7 Engineering Drive 1, Singapore 117574, Singapore.

Background: The growing ageing population and high prevalence of knee osteoarthritis (OA) in athletes across nations have created a strong demand for improved non-invasive therapeutic alternatives for knee OA. The aim of this study is to investigate the effect of the variable stiffness shoe (VSS), a new non-invasive therapeutic approach, on external knee adduction moment (EKAM) in various dynamic exercises. EKAM is believed to have positive correlation with the progression and development of knee OA.

Methods: Thirty young participants (16 male and 14 female; age 22.6 ± 1.9 years) from National University of Singapore were enrolled in this study. The tested activities were walking, running, drop-landing, and lateral hopping. All the dynamic exercises were recorded simultaneously by the 8-camera VICON Motion Systems (Oxford Metric, UK) with a sampling rate of 100 Hz.

Results: The results showed that the EKAM was reduced in all the dynamic exercises with the use of VSS. The VSS produced significant reductions in the peak EKAM during walking (4.97%, p = 0.039), running (11.15%, p = 0.011), drop-landing (11.18%, p = 0.038) and lateral hopping (17.34%, p = 0.023) as compared to the control shoe.

Conclusions: The reduction of EKAM with the use of VSS in various dynamic exercises demonstrates its potential in delaying the onset and the progression of knee OA in early stage of knee OA patients.
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http://dx.doi.org/10.1186/1757-1146-6-39DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3848782PMC
September 2013

Administration of PTH and ibandronate increases ovariectomized rat compact bone viscoelasticity.

J Mech Behav Biomed Mater 2013 Jun 30;22:51-8. Epub 2013 Mar 30.

Department of Bioengineering, Faculty of Engineering, National University of Singapore, Singapore.

In this study, the bone mineral density (BMD), geometry, macroscopic viscoelastic properties and mechanical strength in five different groups of Sprague-Dawley rats (sham operated, ovariectomized with vehicle, parathyroid hormone and/or ibandronate administration) were examined by peripheral quantitative computed tomography (pQCT), dynamic mechanical analysis (DMA) and three-point bending test. At the end of the study, storage modulus (E'), loss tangent (tanδ), ultimate force (Fu) and stiffness (S) had greatly decreased in vehicle-treated ovariectomized group as compared to sham group (p<0.05). The concurrent administration of parathyroid hormone and ibandronate group exhibited the largest cortical area (Ct.Ar) and thickness (Ct.Th), E', tanδ (0.3Hz) and subsequently highest Fu as compared to the mono-therapy groups (p<0.05). However, significant changes were not observed in the BMD values of different groups (p>0.05). The relationships between these potential predictors of bone strength (E', tanδ, BMD and Ct.Ar) and bone mechanical strength parameters (Fu, S and ultimate stress σu) were also examined. Interestingly, during normal daily activity frequency range (0.9-6Hz), tanδ and Fu were positively correlated. Taken together, these data suggest that DMA can serve as an effective tool to assess bone strength which would be ignored under the normal clinical screenings due to an unchanged BMD. DMA can therefore be used as a better tool to assess the osteoporotic drug efficacy.
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http://dx.doi.org/10.1016/j.jmbbm.2013.03.009DOI Listing
June 2013

Improving stability of locking compression plates through a design modification: a computational investigation.

Comput Methods Biomech Biomed Engin 2015 14;18(2):153-61. Epub 2013 Apr 14.

a Department of Bioengineering , National University of Singapore , Singapore.

Femoral shaft fractures are common in both the young and elderly due to high-impact trauma and low-impact trauma, respectively. Its treatment by indirect reduction through use of locking compression plates (LCPs) has been on the rise. The LCP possess several advantages in fracture fixation, combining angular stability through use of locking screws with misalignment correction and fracture reduction onto the plate through use of conventional screws. However, there have been cases of plate breakage and fracture non-unions to warrant a study to improve its stability. A design modification is suggested for mid-diaphyseal fractures, whereby unused screw holes are removed. The structural stability of the modified and commercially available LCP is computationally analyzed using finite element modelling and a comparison made in terms of mechanical performance across different fracture lengths. A critical fracture length for which the commercially available LCP is functional as a fixator for mid-diaphyseal fractures was established. The maximum von Mises' stress attained by the commercially available LCP rose to as high as 105 MPa, whereas for the modified LCP, it did not exceed 25 MPa. As expected, these stresses were also found at screw holes, nearest to the fracture site. Critical fracture length allows clinicians to quantitatively distinguish between mid-diaphyseal fractures that can or cannot be treated by the use of LCP fixation. It is also believed that the proposed design modification will substantially increase the fatigue life of the fixator, especially at screw holes nearest to the fracture region, where most fatigue fractures are known to occur and will consequently be functional for greater fracture lengths.
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http://dx.doi.org/10.1080/10255842.2013.785536DOI Listing
December 2015
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