OSTEOINDUCTIVE INJECTABLE CALCIUM PHOSPHATE BIOACTIVATED BY PHOSPHOSERINE DENDRONS

Jun 29, 2022, 11:20 AM
20m
Room: S2

Room: S2

Speaker

Grazia Raucci, Maria (Institute of Polymers, Composites and Biomaterials – National Research Council (IPCB-CNR) )

Description

"Introduction
In recent years, the clinical application of injectable bone pastes has been increasing because of their benefits including ease to adaptation into irregular-structured defects and injectability suitable to minimally invasive surgery. These advantages are widely advocated to reduce patient complications and health care costs. Here, we successfully developed injectable bone pastes integrating biphasic calcium phosphate (BCP, HA:β-TCP=1:4) nanoparticles with poly(ɛ-lysine) dendron activated by phosphoserine at generation 3 (G3-K PS). Furthermore, the incorporation of strontium (Sr) element into the BCP nanocrystals was also considered to minimize bone resorption.

Methodology
The preparation of materials including G3-K PS semi-dendrimers, BCP, SrBCP (with 15 mol% Ca2+ replaced by Sr2+), BCPG3 (BCP in G3-K PS carrier) and SrBCPG3 (SrBCP in G3-K PS carrier) was adapted from previously protocols1. G3-K PS semi-dendrimer in ethanol solution was added at 1% (w/w) to BCP or SrBCP slurry under 200 rpm and 37 °C stirring until gelation occurred. In vitro cell tests to assess the osteogenic potential of the synthesized biomaterials were performed using bone marrow stromal cells (MSCs) isolated from ovariectomized rats and the expression of specific gene markers (Runx2, ALP, Cxcl9, RANKL) at 1, 3 and 7 days of cell culture were analyzed by RT-PCR. To confirm the role of Cxcl9 and Sr ions in material induced osteogenesis, additional Cxcl9 protein (250 ng mL-1) was introduced into the BCPG3 and SrBCP groups in culture medium, and Sr ions (3 mM) were introduced into the BCP and BCPG3 groups in cell culture medium. In vivo studies were performed using ovariectomized female Sprague Dawley rats. Several bone metabolic markers including P1NP, CTX-I and Cxcl9 were evaluated using ELISA assay at week 12. Immunohistochemistry analysis, micro-CT and scanning electron microscopy investigations were performed to evaluate the new bone tissue formation and osteointegration.

Results
Injectable bone paste material integrating BCP nanoparticles with G3-K PS carrier was successfully synthesized with or without the doping of Sr element into the BCP nanocrystals. Both in vitro and in vivo findings showed that the integration of G3-K PS would downregulate Cxcl9 gene and protein expressions to achieve an enhanced bone regeneration effect, with respect to a higher BMD and BV/TV. Immunohistological staining demonstrated lower expression of Cxcl9 in BCPG3 and SrBCPG3 groups, meanwhile Runx2 and RANKL positive expressions were more in BCPG3 group than others. The results were in accordance with in vitro gene and protein expression and in vivo serum biomarker analysis. This study demonstrated for the first time that G3-K PS carrier could down-regulate Cxcl9 expression and no additional benefit to osteoporotic bone regenerating ability of BCPG3 material was found with Sr incorporation.

Conclusion
The results indicated that the BCPG3 bone paste can become a high-performance bone filler in the treatment of osteoporotic bone defects.

References
1. Raucci, M. G. et al., Tissue Eng Part A 20, 474-85 (2014).
Acknowledgements: The authors would like to thank the Progetto MIUR PRIN2017 – ACTION Grant N. 2017SZ5WZB and H2020-MSCA-RISE-2016, SECOND.R.I., Grant Agreement No 734391 for financial support"

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