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Robo, C., Öhman, C. & Persson, C. (2018). Compressive fatigue properties of commercially available standard and low-modulus acrylic bone cements intended for vertebroplasty. Journal of The Mechanical Behavior of Biomedical Materials, 82, 70-76
Open this publication in new window or tab >>Compressive fatigue properties of commercially available standard and low-modulus acrylic bone cements intended for vertebroplasty
2018 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 82, p. 70-76Article in journal (Refereed) Published
Abstract [en]

Vertebroplasty (VP) is a minimally invasive surgical procedure commonly used to relieve severe back pain associated with vertebral compression fractures. The poly(methyl methacrylate) bone cement used during this procedure is however presumed to facilitate the occurrence of additional fractures next to the treated vertebrae. A reason for this is believed to be the difference in stiffness between the bone cement and the surrounding trabecular bone. The use of bone cements with lower mechanical properties could therefore reduce the risk of complications post-surgery. While intensive research has been performed on the quasi-static mechanical properties of these cements, there is no data on their long-term mechanical properties. In the present study, the in vitrocompressive fatigue performance as well as quasi-static mechanical properties of two commercially available acrylic bone cements - a low-modulus cement (Resilience®) and a standard cement (F20) from the same manufacturer - were determined. The quasi-static mechanical properties of the low-modulus and standard cements after 24h of setting were in the range of other vertebroplastic cements (σ=70-75 MPa; E=1600-1900 MPa). F20 displayed similar mechanical properties over time in 37˚C phosphate buffered saline solution, while the mechanical properties of the Resilience®cement decreased gradually due to an increased porosity in the polymeric matrix. The standard cement exhibited a fatigue limit of approx. 47 MPa, whereas the low-modulus cement showed a fatigue limit of approx. 31 MPa. 

In summary, the low-modulus bone cement had a lower fatigue limit than the standard cement, as expected. However, this fatigue limit is still substantially higher than the stresses experienced by vertebral trabecular bone.  

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Acrylic bone cement, low-modulus, elastic modulus, compression, fatigue, vertebroplasty
National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-349032 (URN)10.1016/j.jmbbm.2018.03.001 (DOI)000432508800009 ()
Funder
The Royal Swedish Academy of Sciences, FOA13H-141
Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2018-08-02Bibliographically approved
Ajaxon, I., Holmberg, A., Öhman, C. & Persson, C. (2018). Fatigue performance of a high-strength, degradable calcium phosphate bone cement. Journal of The Mechanical Behavior of Biomedical Materials, 79, 46-52
Open this publication in new window or tab >>Fatigue performance of a high-strength, degradable calcium phosphate bone cement
2018 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 79, p. 46-52Article in journal (Refereed) Published
Abstract [en]

Calcium phosphate cements (CPCs) are clinically used as injectable materials to fill bone voids and to improve hardware fixation in fracture surgery. In vivo they are dynamically loaded; nonetheless little is known about their fatigue properties. The aim of this study was to, for the first time, investigate the fatigue performance of a high strength, degradable (brushitic) CPC, and also evaluate the effect of cement porosity (by varying the liquid to powder ratio, L/P) and the environment (air at room temperature or in a phosphate buffered saline solution, PBS, at 37 degrees C) on the fatigue life. At a maximum compressive stress level of 15 MPa, the cements prepared with an L/P-ratio of 0.22 and 0.28 ml/g, corresponding to porosities of approximately 12% and 20%, had a 100% probability of survival until run-out of 5 million cycles, in air. When the maximum stress level, or the L/P-ratio, was increased, the probability of survival decreased. Testing in PBS at 37 degrees C led to more rapid failure of the specimens. However, the high-strength cement had a 100% probability of survival up to approximately 2.5 million cycles at a maximum compressive stress level of 10 MPa in PBS, which is substantially higher than some in vivo stress levels, e.g., those found in the spine. At 5 MPa in PBS, all specimens survived to run-out. The results found herein are important if clinical use of the material is to increase, as characterisation of the fatigue performance of CPCs is largely lacking from the literature.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Bone cement, Calcium phosphate, Brushite, Fatigue, Compression, Porosity, Mechanical properties
National Category
Medical Materials
Identifiers
urn:nbn:se:uu:diva-347539 (URN)10.1016/j.jmbbm.2017.12.005 (DOI)000425072300006 ()29272812 (PubMedID)
Funder
Swedish Research Council, 621-2011-6258
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-04-09Bibliographically approved
Díez-Escudero, A., Montserrat, E., Bonany, M., Lu, X., Persson, C. & Ginebra, M.-P. (2018). Heparinization of Beta Tricalcium Phosphate: Osteo-immunomodulatory Effects. Advanced Healthcare Materials, 7(5), Article ID 1700867.
Open this publication in new window or tab >>Heparinization of Beta Tricalcium Phosphate: Osteo-immunomodulatory Effects
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2018 (English)In: Advanced Healthcare Materials, ISSN 2192-2640, E-ISSN 2192-2659, Vol. 7, no 5, article id 1700867Article in journal (Refereed) Published
Abstract [en]

Immune cells play a vital role in regulating bone dynamics. This has boosted the interest in developing biomaterials that can modulate both the immune and skeletal systems. In this study, calcium phosphates discs (i.e., beta-tricalcium phosphate, β-TCP) are functionalized with heparin to investigate the effects on immune and stem cell responses. The results show that the functionalized surfaces downregulate the release of hydrogen peroxide and proinflammatory cytokines (tumor necrosis factor alpha and interleukin 1 beta) from human monocytes and neutrophils, compared to nonfunctionalized discs. The macrophages show both elongated and round shapes on the two ceramic substrates, but the morphology of cells on heparinized β-TCP tends toward a higher elongation after 72 h. The heparinized substrates support rat mesenchymal stem cell (MSC) adhesion and proliferation, and anticipate the differentiation toward the osteoblastic lineage as compared to β-TCP and control. The coupling between the inflammatory response and osteogenesis is assessed by culturing MSCs with the macrophage supernatants. The downregulation of inflammation in contact with the heparinized substrates induces higher expression of bone-related markers by MSCs.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2018
Keywords
calcium phosphates; heparinization; inflammation; osteogenesis
National Category
Medical Materials Biomaterials Science
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-340741 (URN)10.1002/adhm.201700867 (DOI)000426758500005 ()
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), STINT-IG2011-2047
Available from: 2018-02-02 Created: 2018-02-02 Last updated: 2018-08-09Bibliographically approved
Robo, C., Hulsart Billström, G., Nilsson, M. & Persson, C. (2018). In vivo response to a low-modulus PMMA bone cement in an ovine model. Acta Biomaterialia, 72, 362-370
Open this publication in new window or tab >>In vivo response to a low-modulus PMMA bone cement in an ovine model
2018 (English)In: Acta Biomaterialia, ISSN 1742-7061, E-ISSN 1878-7568, Vol. 72, p. 362-370Article in journal (Refereed) Published
Abstract [en]

Poly(methyl methacrylate) (PMMA) is the most commonly used material for the treatment of osteoporosis-induced vertebral compression fractures. However, its high stiffness may introduce an increased risk of adjacent vertebral fractures post-surgery. One alternative in overcoming this concern is the use of additives. This presents its own challenge in maintaining an adequate biocompatibility when modifying the base cement. The aim of this study was to evaluate the in vivobiocompatibility of linoleic acid (LA)-modified acrylic bone cement using a large animal model for the first time, in order to further advance towards clinical use. A worst-case approach was used, choosing a slow-setting base cement. The in vitro monomer release from the cements was also assessed. Additional material characterization, including mechanical tests, are summarized in Appendix A. Unmodified and LA-modified cements were injected into a total of 56 bone defects created in the femur and humerus of sheep. Histopathologic and histomorphometric analysis indicated that LA-modified cement showed a harmless tissue response similar to that of the unmodified cement. Adjacent bone remodeling was observed microscopically 4 weeks after implantation, suggesting a normal healing process of the bone tissues surrounding the implant. LA-modified cement exhibited lower mechanical properties, with a reduction in the elastic modulus of up to 65%. The handling properties were slightly modified without negatively affecting the injectability of the base cement. LA-modified bone cement showed good biocompatibility as well as bone compliant mechanical properties and may therefore be a promising material for the treatment of osteoporotic vertebral fractures. 

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Poly (methyl methacrylate), bone cement, low-modulus, In vivo, linoleic acid
National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-349033 (URN)10.1016/j.actbio.2018.03.014 (DOI)000432766900031 ()29559365 (PubMedID)
Funder
VINNOVA, 2010-02073
Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2018-08-13Bibliographically approved
Pujari-Palmer, M., Robo, C., Persson, C., Procter, P. & Engqvist, H. (2018). Influence of cement compressive strength and porosity on augmentation performance in a model of orthopedic screw pull-out. Journal of The Mechanical Behavior of Biomedical Materials, 77, 624-633
Open this publication in new window or tab >>Influence of cement compressive strength and porosity on augmentation performance in a model of orthopedic screw pull-out
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2018 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 77, p. 624-633Article in journal (Refereed) Published
Abstract [en]

Disease and injuries that affect the skeletal system may require surgical intervention and internal fixation, i.e. orthopedic plate and screw insertion, to stabilize the injury and facilitate tissue repair. If the surrounding bone quality is poor the screws may migrate, or the bone may fail, resulting in screw pull-out. Though numerous studies have shown that cement augmentation of the interface between bone and implant can increase screw holding strength in bone, the physical properties of cement that influence pull-out force have not been investigated. The present study sought to determine how the physical properties of calcium phosphate cements (CPCs), and the strength of the biological or synthetic material surrounding the augmented screw, affected the corresponding orthopedic screw pull-out force in urethane foam models of healthy and osteoporotic bone (Sawbones). In the simplest model, where only the bond strength between screw thread and cement (without Sawbone) was tested, the correlation between pull-out force and cement compressive strength (R2 = 0.79) was weaker than correlation with total cement porosity (R2 = 0.89). In open pore Sawbone that mimics “healthy” cancellous bone density the stronger cements produced higher pull-out force (50-60% increase). Higher strength, lower porosity, cements also produced higher pull-out forces (50-190% increase) in Sawbones with cortical fixation if the failure strength of the cortical material was similar to (bovine tibial bone), or greater than (metal shell), actual cortical bone. This result is of particular clinical relevance where fixation with a metal plate implant is indicated, as the nearby metal can simulate a thicker cortical shell and, thereby, increase the pull-out force of screws augmented with stronger cements. The improvement in pull-out force was apparent even at low augmentation volumes of 0.5 ml (50% increase), which suggest that in clinical situations where augmentation volume is limited the stronger, lower porosity CPCs may still produce a significant improvement in screw holding strength. When correlations of all the tested models were compared both cement porosity and compressive strength accurately predicted pull-out force (R2=1.00, R2=0.808), though prediction accuracy depended upon the strength of the material surrounding the Sawbone. The correlations strength was low for bone with no, or weak, cortical fixation. Higher strength and lower porosity CPCs also produced greater pull-out force (1-1.5 kN) than commercial CPC (0.2-0.5kN), but lower pull-out force than PMMA (2-3 kN). The results of this study suggest that the likelihood of screw fixation failure may be reduced by selecting calcium phosphate cements with lower porosity and higher bulk strength, in patients with healthy bone mineral density and/or sufficient cortical thickness. This is of particular clinical relevance when fixation with metal plates is indicated, or where the augmentation volume is limited.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Screw pull-out, Orthopedic screw augmentation, Calcium phosphate cement, Bioceramic, Bone biomechanics, Sawbones, Cortical fixation
National Category
Medical Materials Ceramics Applied Mechanics Biomaterials Science
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-320157 (URN)10.1016/j.jmbbm.2017.10.016 (DOI)000418309500073 ()29100205 (PubMedID)
Funder
Swedish Research Council, 621–2011-3399EU, FP7, Seventh Framework Programme, 262948
Available from: 2017-04-16 Created: 2017-04-16 Last updated: 2018-02-16Bibliographically approved
Persson, J., Helgason, B., Engqvist, H., Ferguson, S. & Persson, C. (2018). Stiffness and strength of cranioplastic implant systems in comparison to cranial bone. Journal of Cranio-Maxillofacial Surgery, 46(3), 418-423
Open this publication in new window or tab >>Stiffness and strength of cranioplastic implant systems in comparison to cranial bone
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2018 (English)In: Journal of Cranio-Maxillofacial Surgery, ISSN 1010-5182, E-ISSN 1878-4119, Vol. 46, no 3, p. 418-423Article in journal (Refereed) Published
Abstract [en]

Purpose: The aim of this study was to evaluate skull replacement options after decompressive craniectomy by systematically investigating which combination of geometrical properties and material selection would result in a mechanical response comparable in stiffness to that of native skull bone and a strength as high or higher than the same. Materials and methods: The study was conducted using a Finite Element Model of the top part of a human skull. Native skull bone, autografts and commercial implants made of PEEK, solid titanium, two titanium meshes and a titanium-ceramic composite were modeled under a set load to evaluate deformation and maximum stress. Results: The computational result showed a large variation of the strength and effective stiffness of the autografts and implants. The stiffness of native bone varied by a factor of 20 and the strength by a factor of eight. The implants span the entire span of the native skull, both in stiffness and strength. Conclusion: All the investigated implant materials had a potential for having the same effective stiffness as the native skull bone. All the materials also had the potential to be as strong as the native bone. To match inherent properties, the best choice of material and thickness is thus patient specific, depending on the quality of the patient's native bone.

Keywords
Craniectomy, Cranioplasty, OSSDSIGN cranial, Craniocurve, KLS martin mesh system, Mechanical properties
National Category
Medical Materials Biomaterials Science
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-347586 (URN)10.1016/j.jcms.2017.11.025 (DOI)000425712500007 ()
Funder
EU, Horizon 2020, E!9741
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-04-26Bibliographically approved
Gallinetti, S., Mestres, G., Canal, C., Persson, C. & Ginebra, M.-P. (2017). A novel strategy to enhance interfacial adhesion in fiber-reinforced calcium phosphate cement. Journal of The Mechanical Behavior of Biomedical Materials, 75, 495-503
Open this publication in new window or tab >>A novel strategy to enhance interfacial adhesion in fiber-reinforced calcium phosphate cement
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2017 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 75, p. 495-503Article in journal (Refereed) Published
Abstract [en]

Calcium phosphate cements (CPCs) are extensively used as synthetic bone grafts, but their poor toughness limits their use to non-load-bearing applications. Reinforcement through introduction of fibers and yarns has been evaluated in various studies but always resulted in a decrease in elastic modulus or bending strength when compared to the CPC matrix. The aim of the present work was to improve the interfacial adhesion between fibers and matrix to obtain tougher biocompatible fiber-reinforced calcium phosphate cements (FRCPCs). This was done by adding a polymer solution to the matrix, with chemical affinity to the reinforcing chitosan fibers, namely trimethyl chitosan (TMC). The improved wettability and chemical affinity of the chitosan fibers with the TMC in the liquid phase led to an enhancement of the interfacial adhesion. This resulted in an increase of the work of fracture (several hundred-fold increase), while the elastic modulus and bending strength were maintained similar to the materials without additives. Additionally the TMC-modified CPCs showed suitable biocompatibility with an osteoblastic cell line.

Keywords
Calcium phosphate cement; Chitosan; Fiber reinforced; Interfacial adhesion; Toughness; Work of fracture
National Category
Biomaterials Science Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-328681 (URN)10.1016/j.jmbbm.2017.08.017 (DOI)000412959000055 ()28841545 (PubMedID)
Funder
EU, FP7, Seventh Framework Programme, 241879; IG2011-2047VINNOVA, 2013-01260Lars Hierta Memorial Foundation, FO2014-0334
Available from: 2017-08-29 Created: 2017-08-29 Last updated: 2018-02-19Bibliographically approved
Ajaxon, I., Öhman Mägi, C. & Persson, C. (2017). Compressive fatigue properties of an acidic calcium phosphate cement—effect of phase composition. Journal of materials science. Materials in medicine, 28(3), Article ID 41.
Open this publication in new window or tab >>Compressive fatigue properties of an acidic calcium phosphate cement—effect of phase composition
2017 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 28, no 3, article id 41Article in journal (Refereed) Published
Abstract [en]

Calcium phosphate cements (CPCs) are synthetic bone grafting materials that can be used in fracture stabilization and to fill bone voids after, e.g., bone tumour excision. Currently there are several calcium phosphate-based formulations available, but their use is partly limited by a lack of knowledge of their mechanical properties, in particular their resistance to mechanical loading over longer periods of time. Furthermore, depending on, e.g., setting conditions, the end product of acidic CPCs may be mainly brushite or monetite, which have been found to behave differently under quasi-static loading. The objectives of this study were to evaluate the compressive fatigue properties of acidic CPCs, as well as the effect of phase composition on these properties. Hence, brushite cements stored for different lengths of time and with different amounts of monetite were investigated under quasi-static and dynamic compression. Both storage and brushite-to-monetite phase transformation was found to have a pronounced effect both on quasi-static compressive strength and fatigue performance of the cements, whereby a substantial phase transformation gave rise to a lower mechanical resistance. The brushite cements investigated in this study had the potential to survive 5 million cycles at a maximum compressive stress of 13 MPa. Given the limited amount of published data on fatigue properties of CPCs, this study provides an important insight into the compressive fatigue behaviour of such materials. 

Keywords
Bone cement, brushite, monetite, fatigue, mechanical properties
National Category
Ceramics Medical Materials Biomaterials Science
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-314237 (URN)10.1007/s10856-017-5851-5 (DOI)000394242700006 ()28144853 (PubMedID)
Funder
Swedish Research Council, 621-2011-6258
Available from: 2017-02-03 Created: 2017-01-31 Last updated: 2017-11-29Bibliographically approved
Wu, D., Joffre, T., Gallinetti, S., Öhman Mägi, C., Ferguson, S. J., Isaksson, P. & Persson, C. (2017). Elastic Modulus Of Human Single Trabeculae Estimated by Synchrotron CT Experiments And Numerical Models. In: : . Paper presented at 23rd Congress of the European Society of Biomechanics, Seville, 2-5 July,2017.
Open this publication in new window or tab >>Elastic Modulus Of Human Single Trabeculae Estimated by Synchrotron CT Experiments And Numerical Models
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2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Other Biological Topics Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-333080 (URN)
Conference
23rd Congress of the European Society of Biomechanics, Seville, 2-5 July,2017
Available from: 2017-11-06 Created: 2017-11-06 Last updated: 2017-12-29Bibliographically approved
Ajaxon, I., Acciaioli, A., Lionello, G., Ginebra, M.-P., Öhman, C., Baleani, M. & Persson, C. (2017). Elastic properties and strain-to-crack-initation of calcium phosphate bone cements: Revelations of a high-resolution measurement technique. Journal of The Mechanical Behavior of Biomedical Materials, 74, 428-437
Open this publication in new window or tab >>Elastic properties and strain-to-crack-initation of calcium phosphate bone cements: Revelations of a high-resolution measurement technique
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2017 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 74, p. 428-437Article in journal (Refereed) Published
Abstract [en]

Calcium phosphate cements (CPCs) should ideally have mechanical properties similar to those of the bone tissue the material is used to replace or repair. Usually, the compressive strength of the CPCs is reported and, more rarely, the elastic modulus. Conversely, scarce or no data are available on Poisson's ratio and strain-to-crack-initiation. This is unfortunate, as data on the elastic response is key to, e.g., numerical model accuracy. In this study, the compressive behaviour of brushite, monetite and apatite cements was fully characterised. Measurement of the surface strains was done using a digital image correlation (DIC) technique, and compared to results obtained with the commonly used built-in displacement measurement of the materials testers. The collected data showed that the use of fixed compression platens, as opposed to spherically seated ones, may in some cases underestimate the compressive strength by up to 40%. Also, the built-in measurements may underestimate the elastic modulus by up to 62% as compared to DIC measurements. Using DIC, the brushite cement was found to be much stiffer (24.3 ± 2.3 GPa) than the apatite (13.5 ± 1.6 GPa) and monetite (7.1 ± 1.0 GPa) cements, and elastic moduli were inversely related to the porosity of the materials. Poisson's ratio was determined to be 0.26 ± 0.02 for brushite, 0.21 ± 0.02 for apatite and 0.20 ± 0.03 for monetite. All investigated CPCs showed low strain-to-crack-initiation (0.17–0.19%). In summary, the elastic modulus of CPCs is substantially higher than previously reported and it is concluded that an accurate procedure is a prerequisite in order to properly compare the mechanical properties of different CPC formulations. It is recommended to use spherically seated platens and measuring the strain at a relevant resolution and on the specimen surface.

National Category
Ceramics Medical Materials Biomaterials Science
Identifiers
urn:nbn:se:uu:diva-316718 (URN)10.1016/j.jmbbm.2017.06.023 (DOI)000410253500046 ()28735216 (PubMedID)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2011-2047Swedish Research Council, 621-2011-6258
Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2017-12-04Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6663-6536

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