Preparation and characterisation of bioactive anion-modified hydroxyapatite particles: Protein adsorption mechanism on biomaterials
Final Report Abstract
It is well accepted that ion-substituted hydroxyapatite (HAp) particles can be used as carriers of proteins and their controlled release for bone regeneration. Very little is known concerning surface sites (molecular groups) of the inorganic carrier nanoparticles and, most importantly, with respect to the protein binding mechanism to these surface units. The requested research proposal aimed to investigate (i) the structure, particularly of the surface sites of borate substituted HAp and (ii) the mechanism of the protein release from such modified HAp particles by combining the expertise of the two research teams at the BAM and in Okayama. The Japanese site focused on the preparation of the materials and the protein adsorption measurements whereas the Berlin term was responsible for all structural characterisations, preferably using solid state NMR, including first efforts to explore the possibilities for monitoring the protein adsorption/binding using unlabelled samples. Part (i) of these goals was pursued in the first (and only) research grant period. A project renewal (focus on the protein binding mechanisms) was not handed in to the DFG. Main results can be summarized as follows: a) Advanced NMR experiments were carried out on various borate containing apatites prepared by wet chemical process and high temperature solid-state reactions to investigate the structure and specifically the borate incorporation in apatitic biomaterials. Focussing on a specific sample (10CaO•5.5PO2.5•0.5BO1.5)) the NMR data show that the only about 30% of the entire phosphate content is existent as crystalline hydroxyapatite (HAp) as seen be XRD. The verified borate units (BO33- and BO2-) are accommodated in the disordered calcium phosphate phase forming the main phosphate content (ca. 70%). In addition, a structure model is proposed, where HAp forms the crystalline core covered by an interface and the disordered BCaP phase. b) A second research topic focussed on the comparison of XRD and NMR phase characterizations of nanoscopic boron containing HAp (BHap). The main problem was and is (and is still not understood) that – although significant borate amount are present in apatite particles - that XRD solely shows pure HAp as crystal phase, whereas NMR tells, the only a fraction of the phosphate content in fact forms crystalline HAp; but the major part is amorphous and contains the borates. Therefore, various samples were prepared with different borate contents and their structures and properties were investigated in details. This study proposed a new guideline for designing biodegradable apatite ceramics. Boron-containing hydroxyapatite (BHAp) particles were prepared by a high-temperature solid-state reaction processing method and were characterized in terms of their chemical composition, apatite lattice defects and in vitro biodegradability. Solid-state nuclear magnetic resonance analysis showed that boronincorporation into hydroxyapatite (HAp) derived by thermo-chemical reactions between borate and calcium phosphate phases led to disordered phases (BCaP) of a CaO–P2O5– B2O3–OH system covering the crystalline HAp core. X-ray diffraction analysis indicated that the BCaP phase must consist mainly of a crystalline oxyboroapatite (OBAp) phase. An in vitro biodegradability test showed that BHAp degraded quicker than HAp or btricalcium phosphate. The biodegradability of BHAp particles can be controlled by boron incorporation into a HAp lattice leading to the formation of a disordered OBAp phase.
Publications
- A NMR Investigation of Borate Incorporation in Apatitic Biomaterials. GDCh-Fachgruppentagung, Magnetic Resonance Division, Regensburg 2008
S. Barheine, S. Hayakawa, A. Osaka, C. Jäger
- A NMR Investigation of Borate Incorporation in Apatitic Biomaterials., Bioceramics21, Búzios, Brazil, October 2008
C. Jäger, S. Barheine, S. Hayakawa, A. Osaka
- A Solid-State NMR Investigation of Borate Containing Hydroxyapatite. Beiratstagung BAM, 2008
S. Barheine, C. Jäger
- Bulk and surfaces of nanosized calcium phosphates and their interaction with organic molecules in bone and synthetic biomaterials. ISIPM, La Rochelle, France, August 2008
C. Jäger, S. Barheine, S. Maltsev
- Mission Impossible? Surfaces of phosphate nanoparticles and the mineral-organic interface in biomaterials. Seminar “Festkörper-NMR-Methoden und Anwendungen in der Materialforschung”, Oberjoch, July 2008
C. Jäger, S. Barheine
- Preparation and characterization of boron-containing hydroxyapatite. Trans Tech Publications: Key Engineering Materials vol. 361-363, pp. 191-194 (2008)
Satoshi Hayakawa, Akihito Sakai, Kanji Tsuru, Akiyoshi Osaka, Eiji Fujii, Koji Kawabata, Christian Jäger
- A NMR Investigation of Borate Incorporation in Apatitic Biomaterials. Trans Tech Publications: Key Engineering Materials vol. 396-398, pp. 205-208 (2009)
Sabrina Barheine, Satoshi Hayakawa, Akiyoshi Osaka, Christian Jäger
- NMR studies of short and medium range order in glasses and disordered surfaces of biomaterials. MPG Summer School on Amorphous Solids in Physics and Biology, Neuhardenberg, June 2009
C. Jäger
- Surface, Interface, and Bulk Structure of Borate Containing Apatitic Biomaterials. 6th Alpine Conference on Solid-State NMR, Chamonix-Mont Blanc, France, September 2009
S. Barheine, S. Hayakawa, A. Osaka, C. Jäger
- Surface, Interface, and Bulk Structure of Borate Containing Apatitic Biomaterials. Chem. Mater. vol. 21, pp. 3102-3109 (2009)
Sabrina Barheine, Satoshi Hayakawa, Akiyoshi Osaka, Christian Jäger
- Surface, Interface, and Bulk Structure of Borate Containing Apatitic Biomaterials. GDCh-Fachgruppentagung, Magnetic Resonance Division, Dresden, September 2009
S. Barheine, S. Hayakawa, A. Osaka, C. Jäger
- Effect of Disordered Structures of Boron-Containing Calcium Phosphates on their In Vitro Biodegrability. J. Am. Ceram. Soc. Vol. 94, pp. 2656-2662 (2011)
Sabrina Barheine, Satoshi Hayakawa, Christian Jäger, Yuki Shirosaki, Akiyoshi Osaka
