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Physical Properties of Acidic Calcium Phosphate Cements
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Materials in Medicine)
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The gold standard for bone replacement today, autologous bone, suffers from several disadvantages, such as the increased risk of infection due to the need for two surgeries. Degradable synthetic materials with properties similar to bone, such as calcium phosphate cements, are a promising alternative. Calcium phosphate cements are suited for a limited amount of applications and improving their physical properties could extend their use into areas previously not considered possible. For example, cement with increased strength could be used as load bearing support in selected applications. The focus of this thesis is, therefore, on how the physical properties of acidic calcium phosphate cements (brushite cements) are affected by compositional variations, with the ultimate aim of making it possible to formulate brushite cements with desired properties.

In this thesis a method to measure the porosity of a cement was developed. This method is advantageous over existing methods as it is easy to use, requiring no advanced equipment. A model estimating the porosity of the hardened cement from the initial chemical composition was further formulated and the accuracy affirmed. Utilization of this model allows the porosity to be optimized by calculations rather than extensive laboratory work. The effect on strength and porosity of several compositional variations were also assessed and it was found that the optimal composition to achieve a high strength was: monocalcium phosphate particles in sizes <75µm, 10 mol% excess of beta-tricalcium phosphate, 1 wt% disodium dihydrogen pyrophosphate, and 0.5 M citric acid in a liquid-to-powder ratio of 0.22 ml/g. This composition gave the highest compressive strength historically measured for this type of cement, i.e., 74.4 (±10.7) MPa. Although such a high strength may not be necessary for all applications, it allows for the use of brushite cements in new applications. Furthermore, a high strength of the bulk allows for alterations to the cement that cause a decrease in strength. One application is fast degrading materials, allowing rapid bone ingrowth. A fast degradation is obtained with a high macroporosity, which would reduce strength. The high strength composition was therefore utilized to achieve brushite cement with a high macroporosity.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. , 73 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1195
National Category
Biomaterials Science Ceramics Medical Materials
Identifiers
URN: urn:nbn:se:uu:diva-233637ISBN: 978-91-554-9081-2 (print)OAI: oai:DiVA.org:uu-233637DiVA: diva2:756900
Public defence
2014-12-05, Polhemsalen, Ångströmlaboratoriet, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework ProgrammeSwedish Research Council
Available from: 2014-11-14 Created: 2014-10-07 Last updated: 2015-02-03
List of papers
1. Porosity prediction of calcium phosphate cements based on chemical composition
Open this publication in new window or tab >>Porosity prediction of calcium phosphate cements based on chemical composition
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2015 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 26, no 7, 210Article in journal (Refereed) Published
Abstract [en]

The porosity of calcium phosphate cements has an impact on several important parameters, such as strength, resorbability and bioactivity. A model to predict the porosity for biomedical cements would hence be a useful tool. At the moment such a model only exists for Portland cements. The aim of this study was to develop and validate a first porosity prediction model for calcium phosphate cements. On the basis of chemical reaction, molar weight and density of components, a volume-based model was developed and validated using calcium phosphate cement as model material. 60 mol% beta-tricalcium phosphate and 40 mol% monocalcium phosphate monohydrate were mixed with deionized water, at different liquid-to-powder ratios. Samples were set for 24 h at 37 degrees C and 100 % relative humidity. Thereafter, samples were dried either under vacuum at room temperature for 24 h or in air at 37 degrees C for 7 days. Porosity and phase composition were determined. It was found that the two drying protocols led to the formation of brushite and monetite, respectively. The model was found to predict well the experimental values and also data reported in the literature for apatite cements, as deduced from the small absolute average residual errors (<2.0 %). In conclusion, a theoretical model for porosity prediction was developed and validated for brushite, monetite and apatite cements. The model gives a good estimate of the final porosity and has the potential to be used as a porosity prediction tool in the biomedical cement field.

National Category
Ceramics Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-233632 (URN)10.1007/s10856-015-5497-0 (DOI)000358671200009 ()
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), GA IG2011-2047EU, FP7, Seventh Framework Programme, GA 262948Swedish Research Council, 621-2011-6258Swedish Research Council, 2011-3399
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
2. An evaluation of methods to determine the porosity of calcium phosphate cements
Open this publication in new window or tab >>An evaluation of methods to determine the porosity of calcium phosphate cements
2015 (English)In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 103, no 1, 62-71 p.Article in journal (Refereed) Published
Abstract [en]

The porosity of a material can be determined using a diversity of methods; however, the results from these methods have so far not been compared and analyzed for calcium phosphate cements (CPCs). The aim of this study was to compare a fast and easy method for porosity measurements with some commonly used porosity methods for CPCs. The investigated method is based on the assumption that when a wet cement sample is dried, the volume of the evaporated water is equal to the volume of pores within the cement. Moreover, different methods of drying the cements were evaluated for acidic CPCs. The results showed that drying at room temperature (22°C ±1°C) is preferable, since a phase transformation was observed at higher temperatures. The results also showed that drying for 24 hours in vacuum was sufficient to achieve water free cements. The porosity measured was found to vary between the porosity methods evaluated herein, and to get a complete picture of a cement’s porosity more than one method is recommended. Water evaporation, is, however, a fast and easy method to estimate the porosity of CPCs and could simplify porosity measurements in the future.

Keyword
porosity, calcium phosphate, ceramic
National Category
Ceramics Medical Materials
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-233543 (URN)10.1002/jbm.b.33173 (DOI)000346191600008 ()
Funder
EU, FP7, Seventh Framework ProgrammeSwedish Research Council
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
3. The effect of composition on mechanical properties of brushite cements
Open this publication in new window or tab >>The effect of composition on mechanical properties of brushite cements
2014 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 29, 81-90 p.Article in journal (Refereed) Published
Abstract [en]

Due to a fast setting reaction, good biological properties, and easily available starting materials, there has been extensive research within the field of brushite cements as bone replacing material. However, the fast setting of brushite cement gives them intrinsically low mechanical properties due to the poor crystal compaction during setting. To improve this, many additives such as citric acid, pyrophosphates, and glycolic acid have been added to the cement paste to retard the crystal growth. Furthermore, the incorporation of a filler material could improve the mechanical properties when used in the correct amounts. In this study, the effect of the addition of the two retardants, disodium dihydrogen pyrophosphate and citric acid, together with the addition of β-TCP filler particles, on the mechanical properties of a brushite cement was investigated. The results showed that the addition of low amounts of a filler (up to 10%) can have large effects on the mechanical properties. Furthermore, the addition of citric acid to the liquid phase makes it possible to use lower liquid-to-powder ratios (L/P), which strongly affects the strength of the cements. The maximal compressive strength (41.8 MPa) was found for a composition with a molar ratio of 45:55 between monocalcium phosphate monohydrate and beta-tricalcium phosphate, an L/P of 0.25 ml/g and a citric acid concentration of 0.5 M in the liquid phase.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Brushite, Calcium phosphate cement, Compressive strength, Porosity, X-ray diffraction, Rietveld analysis
National Category
Biomaterials Science Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-208134 (URN)10.1016/j.jmbbm.2013.08.024 (DOI)000330085700008 ()
Funder
Swedish Research Council
Available from: 2013-09-24 Created: 2013-09-24 Last updated: 2017-12-06Bibliographically approved
4. Development of a Resorbable Calcium Phosphate Cement with Load Bearing Capacity
Open this publication in new window or tab >>Development of a Resorbable Calcium Phosphate Cement with Load Bearing Capacity
2014 (English)In: Bioceramics Development and Applications, ISSN 2090-5017, E-ISSN 2090-5025, Vol. 4, no 1, 1000074- p.Article in journal (Refereed) Published
Abstract [en]

Compared to cortical bone and polymeric bone cements, the mechanical properties of calcium phosphate cements are generally poor. This has resulted in them being used in non-load bearing clinical applications. The aim of this study was to investigate the possibility of producing a brushite cement with mechanical properties closer to those of cortical bone (i.e., >100 MPa in compression), i.e. with a potential to be used in load bearing applications. With a compressive strength of 74.4 (± 10.7) MPa, maximum at 91.8 MPa, the cement presented herein is comparable with the non degradable polymeric counterparts and the strongest hydroxyapatite cements, and is close in strength of cortical bone. Furthermore, it has a high injectability (>90%) and a setting time of approximately 17 minutes. A cement comprising these properties has great potential of changing the future clinical indications for calcium phosphate cements, and could potentially reduce the use of non-degradable polymeric cements.

Keyword
Brushite, Cement, Calcium phosphate, Strongest
National Category
Ceramics Medical Materials
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-233540 (URN)10.4172/2090-5025.1000074 (DOI)
Funder
EU, FP7, Seventh Framework ProgrammeSwedish Research Council
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
5. Brushite foams - the effect of Tween® 80 and Pluronic® F-127 on foam porosity and mechanical properties
Open this publication in new window or tab >>Brushite foams - the effect of Tween® 80 and Pluronic® F-127 on foam porosity and mechanical properties
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(English)In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981Article in journal (Other academic) Submitted
Abstract [en]

Resorbable calcium phosphate  based bone void  fillers  should work as  temporary  templates  for new bone formation. The incorporation of macropores with sizes of 100 -300 µm has been shown to  increase the resorption rate of the implant and speed up bone ingrowth. In this work, macroporous brushite cements were fabricated through foaming of the cement paste, utilizing two different synthetic surfactants,  Tween® 80 and Pluronic® F-127.  The macropores formed in the Pluronic  samples  were  both smaller and less  homogeneously  distributed  compared with  the pores formed in the Tween samples. The porosity and compressive strength were comparable to previously developed hydroxyapatite foams. The cement foam containing Tween, 0.5 M citric acid in the liquid, 1 mass% of disodium dihydrogen pyrophosphate mixed in the powder and a liquid to powder ratio  of 0.43  mL/g,  showed  the highest  porosity values  (76  %  total and  56  % macroporosity), while the compressive strength was higher than 1 MPa, i.e. the hardened cement could be handled without rupture of the foamed structure. The investigated brushite foams show potential for future clinical use, both as bone void fillers and as scaffolds for in vitro bone regeneration.

Keyword
Brushite, foam, Tween® 80, Pluronic® F-127, porosity, strength, setting time
National Category
Medical Materials Ceramics
Identifiers
urn:nbn:se:uu:diva-233630 (URN)
Funder
EU, FP7, Seventh Framework ProgrammeThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT), GA IG2011-2047Swedish Research Council, GA 621- 2011-6258Swedish Research Council, GA 621-2011-3399
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05
6. Influence of water content on hardening and handling of a premixed calcium phosphate cement
Open this publication in new window or tab >>Influence of water content on hardening and handling of a premixed calcium phosphate cement
2013 (English)In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 33, no 1, 527-531 p.Article in journal (Refereed) Published
Abstract [en]

Handling of calcium phosphate cements is difficult, where problems often arise during mixing, transferring tosyringes, and subsequent injection. Via the use of premixed cements the risk of handling complications is reduced. However, for premixed cements to work in a clinical situation the setting time needs to be improved. The objective of this study is to investigate the influence of the addition of water on the properties of premixed cement. Monetite-forming premixed cements with small amounts of added water (less than 6.8 wt.%) were prepared and the influence on injectability, working time, setting time and mechanical strength was evaluated. The results showed that the addition of small amounts of water had significant influence on the properties of the premixed cement. With the addition of just 1.7 wt.% water, the force needed to extrude the cement from a syringe was reduced from 107 (±15)N to 39 (±9)N, the compression strength was almost doubled, and the setting time decreased from 29 (±4)min to 19 (±2)min, while the working time remained 5 to 6 h. This study demonstrates the importance of controlling the water content in premixed cement pastes and how water can be used to improve the properties of premixed cements.

Keyword
monetite, brushite, injectability, handling, bone void filler
National Category
Ceramics Biomaterials Science
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-168648 (URN)10.1016/j.msec.2012.09.026 (DOI)000313155500072 ()
Funder
Swedish Research CouncilEU, FP7, Seventh Framework Programme
Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2017-12-07
7. Influence of particle size on hardening and handling of a premixed calcium phosphate cement
Open this publication in new window or tab >>Influence of particle size on hardening and handling of a premixed calcium phosphate cement
2013 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 24, no 4, 829-835 p.Article in journal (Refereed) Published
Abstract [en]

Premixed calcium phosphate cements (pCPC) have been developed to circumvent problems related to mixing and transfer of cements in the operating room. In addition, by using pCPC the short working times generally associated with conventional water-mixed cements are avoided. In this work, the influence of particle size on handlingand hardening characteristics of a premixed monetite cement has been assessed. The cements were evaluated with respect to their injectability, setting time and compressive strength. It was found that cements with smaller particle sizes were more difficult to inject and had higher compressive strength. Regarding setting time, no clear trend could be discerned. The addition of granules made the cements easier to inject, but setting time was prolonged and lower strengths were obtained. The main findings of this work demonstrate that particle size can be used to control handling and physical properties ofpremixed cements and that previous knowledge from water-based CPC, regarding effects of particle size, is not directly applicable to premixed CPC.

Keyword
monetite, brushite, injectability
National Category
Ceramics Biomaterials Science
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-168646 (URN)10.1007/s10856-013-4855-z (DOI)000318509100001 ()
Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2017-12-07
8. Setting mechanisms of an acidic premixed calcium phosphate cement
Open this publication in new window or tab >>Setting mechanisms of an acidic premixed calcium phosphate cement
2013 (English)In: Bioceramics Development and Applications, ISSN 2090-5017, E-ISSN 2090-5025, Vol. 3, no 1, 1000070- p.Article in journal (Refereed) Published
Abstract [en]

Premixed calcium phosphate cements (pCPC), where glycerol is used instead of water as mixing liquid, present better handling characteristics than water-based cements. However, the setting mechanisms of pCPC have not been described thoroughly. The aim of this paper is to increase the understanding of the setting mechanism of pCPC. The investigated cement starts to set when glycerol is exchanged with water via diffusion of glycerol out to the surrounding body fluid and water into the material. To better understand the water-glycerol exchange a method was developed where the setting depth of the cement was measured over time. Thermo gravimetric analysis (TGA) was used to determine the liquid exchange rate during setting. To study the influence of temperature on the crystalline end product, pCPC and water-mixed calcium phosphate cement (wCPC) were set at different temperatures and analyzed with X-ray diffraction (XRD). The setting depth measurements showed that the set layer of the pCPC grew with a speed proportional to t0.51 at 37°C. TGA results furthermore showed that less than 10% of the glycerol remained after 16 hours. Setting of pCPC at different temperatures showed that mainly brushite was formed at 5°C, a mixture of brushite and monetite at 21°C and mainly monetite at 37°C. It furthermore showed that brushite was the main phase after setting of wCPC, but some monetite was present in these cements. The study presents a new method for evaluation of pCPC that increases the understanding of their setting mechanism. Furthermore, the XRD results indicate that storage at 5°C could improve the shelf life of acidic pCPC.

Keyword
Premixed, Calcium phosphate, Cements, Setting, Monetite, Brushite
National Category
Ceramics Biomaterials Science
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-168645 (URN)10.4172/2090-5025.1000070 (DOI)
Note

Detta är den omarbetad versionen av artikeln ursprungligen inskickad till "Journal of Biomedical Materials Research. Part B - Applied biomaterials".

Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2017-12-07Bibliographically approved

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