Effect of minor amounts of β-calcium pyrophosphate and hydroxyapatite on the physico-chemical properties and osteoclastic resorption of β-tricalcium phosphate cylinders

B Le Gars Santoni; L Niggli; S Dolder; O Loeffel; G A Sblendorio; R Heuberger; Y Maazouz; C Stähli; N Döbelin; P Bowen; W Hofstetter; M Bohner

doi:10.1016/j.bioactmat.2021.09.003

Effect of minor amounts of β-calcium pyrophosphate and hydroxyapatite on the physico-chemical properties and osteoclastic resorption of β-tricalcium phosphate cylinders

Bioact Mater. 2021 Sep 23:10:222-235. doi: 10.1016/j.bioactmat.2021.09.003. eCollection 2022 Apr.

Authors

B Le Gars Santoni^{1

2}, L Niggli¹, S Dolder³, O Loeffel⁴, G A Sblendorio⁵, R Heuberger⁴, Y Maazouz¹, C Stähli¹, N Döbelin¹, P Bowen⁵, W Hofstetter³, M Bohner¹

Affiliations

¹ RMS Foundation, Bioceramics and Biocompatibility Group, Bischmattstrasse 12, CH-2544, Bettlach, Switzerland.
² University of Bern, Graduate School for Cellular and Biomedical Sciences, Mittelstrasse 43, CH-3012, Bern, Switzerland.
³ University of Bern, Department for BioMedical Research (DBMR), Murtenstrasse 35, CH-3008, Bern, Switzerland.
⁴ RMS Foundation, Materials Group, Bischmattstrasse 12, CH-2544, Bettlach, Switzerland.
⁵ EPFL, Ecole Polytechnique Fédérale de Lausanne, Construction Materials Laboratory, Station 12, CH-1015, Lausanne, Switzerland.

Abstract

β-Tricalcium Phosphate (β-TCP), one of the most used bone graft substitutes, may contain up to 5 wt% foreign phase according to standards. Typical foreign phases include β-calcium pyrophosphate (β-CPP) and hydroxyapatite (HA). Currently, the effect of small amounts of impurities on β-TCP resorption is unknown. This is surprising since pyrophosphate is a very potent osteoclast inhibitor. The main aim of this study was to assess the effect of small β-CPP fractions (<1 wt%) on the in vitro osteoclastic resorption of β-TCP. A minor aim was to examine the effect of β-CPP and HA impurities on the physico-chemical properties of β-TCP powders and sintered cylinders. Twenty-six batches of β-TCP powder were produced with a Ca/P molar ratio varying between 1.440 and 1.550. Fifteen were further processed to obtain dense and polished β-TCP cylinders. Finally, six of them, with a Ca/P molar ratio varying between 1.496 (1 wt% β-CPP) and 1.502 (1 wt% HA), were incubated in the presence of osteoclasts. Resorption was quantified by white-light interferometry. Osteoclastic resorption was significantly inhibited by β-CPP fraction in a linear manner. The presence of 1% β-CPP reduced β-TCP resorption by 40%, which underlines the importance of controlling β-CPP content when assessing β-TCP biological performance.

Keywords: Bioceramics; Calcium phosphate; Hydroxyapatite; Osteoclastic resorption; β‐Calcium pyrophosphate; β‐Tricalcium phosphate.