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Can Bone Void Fillers Carry Load?: Behaviour of Calcium Phosphate Cements Under Different Loading Scenarios
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Materials in Medicine)ORCID iD: 0000-0002-1524-2059
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

Calcium phosphate cements (CPCs) are used as bone void fillers and as complements to hardware in fracture fixation. The aim of this thesis was to investigate the possibilities and limitations of the CPCs’ mechanical properties, and find out if these ceramic bone cements can carry application-specific loads, alone or as part of a construct. Recently developed experimental brushite and apatite cements were found to have a significantly higher strength in compression, tension and flexion compared to the commercially available CPCs chronOS™ Inject and Norian® SRS®. By using a high-resolution measurement technique the elastic moduli of the CPCs were determined and found to be at least twice as high compared to earlier measurements, and closer to cortical bone than trabecular bone. Using the same method, Poisson's ratio for pure CPCs was determined for the first time. A non-destructive porosity measurement method for wet brushite cements was developed, and subsequently used to study the porosity increase during in vitro degradation. The compressive strength of the experimental brushite cement was still higher than that of trabecular bone after 25 weeks of degradation, showing that the cement can carry high loads over a time span sufficiently long for a fracture to heal. This thesis also presents the first ever fatigue results for acidic CPCs, and confirms the importance of testing the materials under cyclic loading as the cements may fail at stress levels much lower than the material’s quasi-static compressive strength. A decrease in fatigue life was found for brushite cements containing higher amounts of monetite. Increasing porosity and testing in a physiological buffer solution (PBS), rather than air, also decreased the fatigue life. However, the experimental brushite cement had a high probability of surviving loads found in the spine when tested in PBS, which has previously never been accomplished for acidic CPCs. In conclusion, available brushite cements may be able to carry the load alone in scenarios where the cortical shell is intact, the loading is mainly compressive, and the expected maximum stress is below 10 MPa. Under such circumstances this CPC may be the preferred choice over less biocompatible and non-degradable materials.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1492
Keyword [en]
Calcium phosphate, bone cement, brushite, apatite, monetite, porosity, solvent exchange, degradation, compressive strength, diametral tensile strength, flexural strength, elastic modulus, Poisson’s ratio, fatigue
National Category
Ceramics Medical Materials Biomaterials Science
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-316656ISBN: 978-91-554-9865-8 (print)OAI: oai:DiVA.org:uu-316656DiVA: diva2:1083749
Public defence
2017-05-12, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-04-19 Created: 2017-03-22 Last updated: 2017-04-19
List of papers
1. Mechanical Properties of Brushite Calcium Phosphate Cements
Open this publication in new window or tab >>Mechanical Properties of Brushite Calcium Phosphate Cements
2017 (English)In: The World Scientific Encyclopedia of Nanomedicine and Bioengineering II: Bioimplants, Regenerative Medicine, and Nano-Cancer Diagnosis and Phototherapy: Volume 3: Design of Bioactive Materials for Bone Repair and Regeneration / [ed] Shi, D., Singapore: World Scientific Pte Ltd. , 2017Chapter in book (Refereed)
Place, publisher, year, edition, pages
Singapore: World Scientific Pte Ltd., 2017
National Category
Biomaterials Science Ceramics Medical Materials
Identifiers
urn:nbn:se:uu:diva-316712 (URN)978-981-4667-58-6 (ISBN)
Funder
Swedish Research Council, GA 621-2011-6258
Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2017-03-22
2. Compressive, diametral tensile and biaxial flexural strength of cutting-edge calcium phosphate cements
Open this publication in new window or tab >>Compressive, diametral tensile and biaxial flexural strength of cutting-edge calcium phosphate cements
Show others...
2016 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 60, 617-627 p.Article in journal (Refereed) Published
Abstract [en]

Calcium phosphate cements (CPCs) are widely used in bone repair. Currently there are two main types of CPCs, brushite and apatite. The aim of this project was to evaluate the mechanical properties of particularly promising experimental brushite and apatite formulations in comparison to commercially available brushite- and apatite-based cements (chronOS Inject and Norian® SRS®, respectively), and in particular evaluate the diametral tensile strength and biaxial flexural strength of these cements in both wet and dry conditions for the first time. The cements׳ porosity and their compressive, diametral tensile and biaxial flexural strength were tested in wet (or moist) and dry conditions. The surface morphology was characterized by scanning electron microscopy. Phase composition was assessed with X-ray diffraction. It was found that the novel experimental cements showed better mechanical properties than the commercially available cements, in all loading scenarios. The highest compressive strength (57.2±6.5 MPa before drying and 69.5±6.0 MPa after drying) was found for the experimental brushite cement. This cement also showed the highest wet diametral tensile strength (10.0±0.8 MPa) and wet biaxial flexural strength (30.7±1.8 MPa). It was also the cement that presented the lowest porosity (approx. 12%). The influence of water content was found to depend on cement type, with some cements showing higher mechanical properties after drying and some no difference after drying.

Keyword
Calcium phosphate cement; Brushite; Apatite; Compressive strength; Tensile strength; Flexural strength
National Category
Ceramics
Identifiers
urn:nbn:se:uu:diva-284218 (URN)10.1016/j.jmbbm.2016.03.028 (DOI)000378969100055 ()27082025 (PubMedID)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2011-2047Swedish Research Council, 621-2011-6258
Available from: 2016-04-15 Created: 2016-04-15 Last updated: 2017-03-22Bibliographically approved
3. Elastic properties and strain-to-crack-initation of calcium phosphate bone cements: revelations of a high-resolution measurement technique
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
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Ceramics Medical Materials Biomaterials Science
Identifiers
urn:nbn:se:uu:diva-316718 (URN)
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: 2017-03-22
4. Evaluation of a porosity measurement method for wet calcium phosphate cements
Open this publication in new window or tab >>Evaluation of a porosity measurement method for wet calcium phosphate cements
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2015 (English)In: Journal of biomaterials applications, ISSN 0885-3282, E-ISSN 1530-8022, Vol. 30, no 5, 526-536 p.Article in journal (Refereed) Published
Abstract [en]

The porosity of a calcium phosphate cement is a key parameter as it affects several important properties of the cement. However, a successful, non-destructive porosity measurement method that does not include drying has not yet been reported for calcium phosphate cements. The aim of this study was to evaluate isopropanol solvent exchange as such a method. Two different types of calcium phosphate cements were used, one basic (hydroxyapatite) and one acidic (brushite). The cements were allowed to set in an aqueous environment and then immersed in isopropanol and stored under three different conditions: at room temperature, at room temperature under vacuum (300 mbar) or at 37􏰀C. The specimen mass was monitored regularly. Solvent exchange took much longer time to reach steady state in hydroxyapatite cements compared to brushite cements, 350 and 18 h, respectively. Furthermore, the immersion affected the quasi-static compressive strength of the hydroxyapatite cements. However, the strength and phase composition of the brushite cements were not affected by isopropanol immersion, suggesting that isopropanol solvent exchange can be used for brushite calcium phosphate cements. The main advantages with this method are that it is non-destructive, fast, easy and the porosity can be evaluated while the cements remain wet, allowing for further analysis on the same specimen. 

Place, publisher, year, edition, pages
Sage Publications, 2015
Keyword
Calcium phosphate, bone cement, porosity, solvent exchange, brushite, hydroxyapatite
National Category
Ceramics Biomaterials Science Medical Materials
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-258636 (URN)10.1177/0885328215594293 (DOI)000367743900003 ()26163278 (PubMedID)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2011-2047Swedish Research Council, 621-2011-6258
Available from: 2015-07-17 Created: 2015-07-17 Last updated: 2017-03-22Bibliographically approved
5. Long-term in vitro degradation of a high-strength brushite cement in water, PBS, and serum solution
Open this publication in new window or tab >>Long-term in vitro degradation of a high-strength brushite cement in water, PBS, and serum solution
2015 (English)In: BioMed Research International, ISSN 2314-6133, E-ISSN 2314-6141, 575079Article in journal (Refereed) Published
Abstract [en]

Bone loss and fractures may call for the use of bone substituting materials, such as calcium phosphate cements (CPCs). CPCs can be degradable, and, to determine their limitations in terms of applications, their mechanical as well as chemical properties need to be evaluated over longer periods of time, under physiological conditions. However, there is lack of data on how the in vitro degradation affects high-strength brushite CPCs over longer periods of time, that is, longer than it takes for a bone fracture to heal. This study aimed at evaluating the long-term in vitro degradation properties of a high-strength brushite CPC in three different solutions: water, phosphate buffered saline, and a serum solution. Microcomputed tomography was used to evaluate the degradation nondestructively, complemented with gravimetric analysis. The compressive strength, chemical composition, and microstructure were also evaluated. Major changes from 10 weeks onwards were seen, in terms of formation of a porous outer layer of octacalcium phosphate on the specimens with a concomitant change in phase composition, increased porosity, decrease in object volume, and mechanical properties. This study illustrates the importance of long-term evaluation of similar cement compositions to be able to predict the material’s physical changes over a relevant time frame. 

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2015
Keyword
Calcium phosphate, brushite, bone cement, degradation, in vitro, solvent exchange, compressive strength, micro-CT, porosity
National Category
Ceramics Bio Materials Biomaterials Science Medical Materials
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-265319 (URN)10.1155/2015/575079 (DOI)000364660000001 ()
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2011-207Swedish Research Council, 621-2011-6258
Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2017-03-22Bibliographically approved
6. Compressive fatigue properties of an acidic calcium phosphate cement—effect of phase composition
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, 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. 

Keyword
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: 2017-04-03Bibliographically approved
7. Compressive fatigue properties of a high-strength, degradable calcium phosphate bone cement – influence of porosity and environment
Open this publication in new window or tab >>Compressive fatigue properties of a high-strength, degradable calcium phosphate bone cement – influence of porosity and environment
(English)Manuscript (preprint) (Other academic)
National Category
Ceramics Medical Materials Biomaterials Science
Identifiers
urn:nbn:se:uu:diva-316717 (URN)
Funder
Swedish Research Council, 621-2011-6258
Available from: 2017-03-22 Created: 2017-03-22 Last updated: 2017-03-22

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  • modern-language-association-8th-edition
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Output format
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