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Biomimetic Deposition of Hydroxyapatite on Titanium Implant Materials
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Materials in Medicine)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The clinical success of a bone-anchored implant is controlled by many factors such as implant shape, chemical composition, mechanical and surface properties. The surface properties (e.g. charge, wettability and roughness) are considered to be important parameters for the biological acceptance of the biomaterial, whereas the bulk properties control the biomechanical behaviour. For implants designed to be used in load-bearing applications in the skeletal system, the biomaterial should preferably integrate into bone tissue for a long lasting function. Lack of integration between the implant and bone increases the risk of micromotions, infections, soft tissue encapsulation, which all reduces the survival rate of the implant and makes revision surgery necessary. Coatings and surface modifications can be used to tailor properties of implant surfaces, and further improve the potential bone bonding and bone in-growth, compared to unmodified surfaces. A biomimetic method, developed by Kokubo, can be used to prepare a hydroxyapatite coating on to titanium substrates. The method is based on a solution based process where the compositions of the soaking medium and thus the formed coatings can be controlled. In this thesis, titanium (oxide) surfaces have been tailored via deposition of ion substituted hydroxyapatite coatings. Biologically relevant ions like strontium, silicon and fluoride were incorporated into apatite coatings. The substrates included well-defined rutile single crystals, as well as poly-crystalline titanium oxide surfaces and experimental Ti implants. The results showed that incorporation of substitute ions alters the morphology, crystallinity, composition and dissolution rates of apatite coatings. The in vivo effects of the ion substituted apatite coatings were also studied. The results showed that the ion substituted apatite coatings have good biocompatibility and can promote early bone formation.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , p. 57
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 986
National Category
Bio Materials
Research subject
Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-183345ISBN: 978-91-554-8510-8 (print)OAI: oai:DiVA.org:uu-183345DiVA, id: diva2:562491
Public defence
2012-12-06, Polacksbacken 2146, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2012-11-16 Created: 2012-10-24 Last updated: 2018-02-08Bibliographically approved
List of papers
1. Studies of early growth mechanisms of hydroxyapatite on single crystalline rutile: a model system for bioactive surfaces
Open this publication in new window or tab >>Studies of early growth mechanisms of hydroxyapatite on single crystalline rutile: a model system for bioactive surfaces
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2010 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 21, no 10, p. 2743-2749Article in journal (Refereed) Published
Abstract [en]

Previous studies have shown that crystalline titanium oxide is in vitro bioactive and that there are differences in the HA formation mechanism depending on the crystalline direction of the titanium oxide surface. In the present study, the early adsorption of calcium and phosphate ions on three different surface directions of the single-crystal rutile TiO2 substrate has been investigated. A crucial step in the nucleation of HA is believed to be the adsorption of Ca2+ and PO4 3− from phosphate buffer solutions. The (001), (100) and (110) single crystalline rutile surfaces were soaked in phosphate buffer saline solution for 10 min, 1 h and 24 h at 37°C. The surfaces were then analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS). The results show that the adsorption of Ca2+ and PO4 3− is faster on the (001) and (100) surfaces than on the (110) surface. This study also shows that TOF-SIMS can be used as a tool to better understand the adsorption of calcium and phosphate ions and the growth mechanism of HA. This knowledge could be used to tailor new bioactive surfaces for better biological reaction.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-133419 (URN)10.1007/s10856-010-4137-y (DOI)000283371200004 ()
Available from: 2010-11-10 Created: 2010-11-10 Last updated: 2018-02-08Bibliographically approved
2. Influence of surface treatments on the bioactivity of Ti
Open this publication in new window or tab >>Influence of surface treatments on the bioactivity of Ti
2013 (English)In: Biomaterials, ISSN 0142-9612, E-ISSN 1878-5905, Vol. 2013, p. 205601-Article in journal (Refereed) Published
Abstract [en]

Several techniques have been described to modify the surface of titanium to make it more bioactive. Heat treatment (HT) and sodium hydroxide treatment (NaOH) have been used and can change the crystallinity and surface chemistry of titanium implants. However, no studies have systemically focused on comparing these different methods and their effect on the bioactivity of Ti. Therefore, in this study, Ti substrates were systematically treated using HT, NaOH, and a combination of HT and NaOH. The Ti plates were heat treated at various temperatures, and the plates were subjected to HT followed by soaking in NaOH or first soaked in NaOH and then heat treated. The morphology, crystallinity, hardness, water contact angle, and surface energy of the samples were analyzed as well as the bioactivity after immersion in PBS. Morphology and crystallinity changed with increasing temperature. The difference was most pronounced for the 800°C treated samples. The water contact angle decreased, and the surface energy increased with increasing temperature and was highest for 800°C. The rutile surface showed faster hydroxyapatite formation. NaOH treatment of the HT Ti samples increased the surface energy and improved its bioactivity further. Also, HT of NaOH samples improved the bioactivity compared to only HT.

National Category
Engineering and Technology Bio Materials
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-183342 (URN)10.5402/2013/205601 (DOI)
Available from: 2012-10-24 Created: 2012-10-24 Last updated: 2018-02-08Bibliographically approved
3. Biomineralized strontium-substituted apatite/titanium dioxide coating on titanium surfaces
Open this publication in new window or tab >>Biomineralized strontium-substituted apatite/titanium dioxide coating on titanium surfaces
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2010 (English)In: Acta Biomaterialia, ISSN 1742-7061, Vol. 6, no 4, p. 1591-1600Article in journal (Refereed) Published
Abstract [en]

Bone mineral is a multi-substituted calcium phosphate. One of these ion substitutions, strontium, has been proven to increase bone strength and decrease bone resorption. Biomimetics is a potential way to prepare surfaces that provide a favorable bone tissue response, thus enhancing the fixation between bone and implants. Here we prepared double-layered strontium-substituted apatite and titanium dioxide coatings on titanium substrates via mimicking bone mineralization. Morphology, crystallinity, surface chemistry and composition of Sr-substituted coatings formed via biomimetic coating deposition on crystalline titanium oxide substrates were studied as functions of soaking temperature and time in phosphate buffer solutions with different Sr ion concentration. The morphology of the biomimetic apatite changed from plate-like for the pure HA to sphere-like for the Sr ion substituted. Surface analysis results showed that 10-33% of Ca ions in the apatite have been substituted by Sr ions, and that the Sr ions were chemically bonded with apatite and successfully incorporated into the structure of apatite.

Keyword
Biomineralization, Hydroxyapatite, Coating, Substitution, Strontium
National Category
Medical and Health Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-136686 (URN)10.1016/j.actbio.2009.10.030 (DOI)000276013500045 ()19861177 (PubMedID)
Available from: 2010-12-14 Created: 2010-12-14 Last updated: 2018-02-08Bibliographically approved
4. Changes of Surface Composition and Morphology after Incorporation of Ions into Biomimetic Apatite Coating
Open this publication in new window or tab >>Changes of Surface Composition and Morphology after Incorporation of Ions into Biomimetic Apatite Coating
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2010 (English)In: Journal of Biomaterials and Nanobiotechnology, ISSN 2158-7027, E-ISSN 2158-7043, Vol. 1, no 1, p. 7-16Article in journal (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-134454 (URN)10.4236/jbnb.2010.11002 (DOI)
Available from: 2010-11-26 Created: 2010-11-26 Last updated: 2018-02-08Bibliographically approved
5. Incorporation of active ions into calcium phosphate coatings, their release behavior and mechanism
Open this publication in new window or tab >>Incorporation of active ions into calcium phosphate coatings, their release behavior and mechanism
2012 (English)In: Biomedical Materials, ISSN 1748-6041, E-ISSN 1748-605X, Vol. 7, no 4, p. 045018-Article in journal (Refereed) Published
Abstract [en]

The dissolution and release of active ions from ion-doped apatites is currently gaining interest due to indications of a beneficial biologic response. The release of ions from apatite coatings is important because it influences the biological effect of these types of materials. In this study the ion release from three different ion-doped apatite coatings (iHA coatings), SrCaP, SiHA and FHA, has been studied. The coatings were prepared by a mineralization method based on immersion in modified PBS solutions containing additions of Sr, Si or F. The kinetics of ion release from the iHA coatings were studied in two different media with and without calcium and phosphate ions (phosphate buffer saline solution (PBS) and Tris-HCl). The amount of cumulative release of Sr, Si and F ions from the iHA coatings was SrCaP > SiHA > FHA in Tris-HCl, which could be also be related to the solubility for these iHA coatings. According to analysis using the Korsmeyer-Peppas model, the release of ions from the coatings was in most cases controlled by a combination of Fickian diffusion and dissolution of the coatings. The morphologies of the iHA coatings were not markedly changed after immersion in Tris-HCl. In the phosphate buffer solution, there was a concurrent redeposition of new apatite crystals on the surface of all of the iHA coatings, which means there were both a dissolution and a remineralization process acting, ultimately controlling the ion release rate.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-179905 (URN)10.1088/1748-6041/7/4/045018 (DOI)000306712900018 ()
Available from: 2012-08-28 Created: 2012-08-27 Last updated: 2018-02-08Bibliographically approved
6. Bone tissue reactions to biomimetic ion-substituted apatite surfaces on titanium implants
Open this publication in new window or tab >>Bone tissue reactions to biomimetic ion-substituted apatite surfaces on titanium implants
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2012 (English)In: Journal of the Royal Society Interface, ISSN 1742-5689, E-ISSN 1742-5662, Vol. 9, no 72, p. 1615-1624Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to evaluate the bone tissue response to strontium-and silicon-substituted apatite (Sr-HA and Si-HA) modified titanium (Ti) implants. Sr-HA, Si-HA and HA were grown on thermally oxidized Ti implants by a biomimetic process. Oxidized implants were used as controls. Surface properties, i.e. chemical composition, surface thickness, morphology/pore characteristics, crystal structure and roughness, were characterized with various analytical techniques. The implants were inserted in rat tibiae and block biopsies were prepared for histology, histomorphometry and scanning electron microscopy analysis. Histologically, new bone formed on all implant surfaces. The bone was deposited directly onto the Sr-HA and Si-HA implants without any intervening soft tissue. The statistical analysis showed significant higher amount of bone-implant contact (BIC) for the Si-doped HA modification (P = 0.030), whereas significant higher bone area (BA) for the Sr-doped HA modification (P = 0.034), when compared with the non-doped HA modification. The differences were most pronounced at the early time point. The healing time had a significant impact for both BA and BIC (P < 0.001). The present results show that biomimetically prepared Si-HA and Sr-HA on Ti implants provided bioactivity and promoted early bone formation.

Keyword
bioactivity, biomimetic, hydroxyapatite, osseointegration, implant, in vivo
National Category
Medical and Health Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-178482 (URN)10.1098/rsif.2011.0808 (DOI)000304437400018 ()
Available from: 2012-08-01 Created: 2012-07-31 Last updated: 2018-02-08Bibliographically approved

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