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Parametric elastic analysis of coupled helical coils for tubular implant applications: Experimental characterization and numerical analysis
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
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2014 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 29, 462-469 p.Article in journal (Refereed) Published
Abstract [en]

Coupled helical coils show promising mechanical behavior to be used as tubular organ constructs, e.g., in trachea or urethra. They are potentially easy to manufacture by filament winding of biocompatible and resorbable polymers, and could be tailored for suitable mechanical properties. In this study, coupled helical coils were manufactured by filament winding of melt-extruded polycaprolactone, which was reported to demonstrate desired in vivo degradation speed matching tissue regeneration rate. The tensile and bending stiffness was characterized for a set of couple helical coils with different geometric designs, with right-handed and left-handed polymer helices fused together in joints where the filaments cross. The Young's modulus of unidirectional polycaprolactone filaments was characterized, and used as input together with the structural parameters of the coupled coils in finite element simulations of tensile loading and three-point bending of the coils. A favorable comparison of the numerical and experimental results was found, which paves way for use of the proposed numerical approach in stiffness design under reversible elastic conditions of filament wound tubular constructs.

Place, publisher, year, edition, pages
2014. Vol. 29, 462-469 p.
Keyword [en]
Coupled helical coils, Finite element simulation, Structural stiffness, Tubular implants
National Category
Natural Sciences Engineering and Technology
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
URN: urn:nbn:se:uu:diva-218968DOI: 10.1016/j.jmbbm.2013.09.026ISI: 000330085700042OAI: oai:DiVA.org:uu-218968DiVA: diva2:698144
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Biomechanical Analysis of Stress and Stiffness of New Load-Bearing Implants
Open this publication in new window or tab >>Biomechanical Analysis of Stress and Stiffness of New Load-Bearing Implants
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Medical implants are essential products for saving lives and improving life quality. Nowadays, the demand for implants, especially biocompatible and personalized ones, is increasing rapidly to deal with factors like congenital malformations, aging, and increasing prevalence of cancer. To facilitate their clinical applications, better understanding of their biomechanical properties is important. This thesis focuses on tubular and mandibular implants, and aims at studying stiffness properties and assessing stress distributions.

Tubular implants with coupled helical-coil structure, which can be potentially used as tubular organ constructs, were manufactured by winding polycaprolactone filaments. Tensile and bending stiffnesses were evaluated through mechanical testing and finite element simulations. By increasing the number of helical coils, we could realize a new type of tubular implants which could be used in applications like trachea and urethra stents. Stiffness properties of such implants were investigated analytically, due to the geometrical periodicity. Through computational homogenization, the discrete mesh structures were converted to equivalent continua, whose structural properties were studied using composite beam theories. The numerical and analytical models developed can serve as tools for the mechanical design of implants.

A patient-specific mandibular implant, additively manufactured of titanium alloys, failed shortly after surgery. The failure was studied using a numerical approach. Finite element models were generated from the 3D bone reconstructed from computed tomography data and implants processed by computational homogenization. The failure location and that of the numerically predicted largest von Mises stress agree well, which confirms the feasibility of using finite element simulations to quantitatively analyze implant failures and assist in implants design.

For implant failures caused by local bone loss, analytical studies were also carried out to assess the stress distribution around screw-loaded holes in bones. The mandibular bone was treated as a laminate of which elastic properties were obtained by classical laminate theory. The stress profiles were predicted using a complex stress function method. The loading direction was found to have a minor influence on the stress distributions, while the friction coefficient has non-negligible influence. The stress state can serve as starting point to predict bone remodeling and be compared with criteria for bone strength.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 61 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1290
National Category
Applied Mechanics
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-262688 (URN)978-91-554-9342-4 (ISBN)
Public defence
2015-11-06, Sal 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2015-10-15 Created: 2015-09-18 Last updated: 2015-10-27

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Huo, JinxingRojas, RamiroBohlin, JanHilborn, JönsGamstedt, E Kristofer

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