In vitro measurement of the chemical changes occurring within β-tricalcium phosphate bone graft substitutes

• Published in: Acta biomaterialia 2020-01, Vol.102, p.440-457
• Main Authors: Maazouz, Yassine, Rentsch, Iris, Lu, Bin, Santoni, Bastien Le Gars, Doebelin, Nicola, Bohner, Marc
• Format: Article
• Language: English
• Subjects: Beta-tricalcium phosphate; Bioactivity; Biological activity; Biomedical materials; Body fluids; Bone graft substitute; Bone grafts; Bone Substitutes - chemistry; Calcium; Calcium phosphate; Calcium phosphates; Calcium Phosphates - chemistry; Computer simulation; Concentration gradient; Design of experiments; Ectopic bone formation; Factorial design; Grafting; Grafts; Granular materials; Heterotopic bone formation; In vitro methods and tests; Kinetics; Local pH; Microporosity; Mineralization; Organic chemistry; Osteogenesis; Osteoinductivity; Particle Size; pH effects; Phosphate; Phosphates; Pores; Porosity; Process parameters; Prostheses and Implants; Skin & tissue grafts; Solubility; Substitute bone; Surgical implants; Tricalcium phosphate
• ISSN: 1742-7061; 1878-7568
• DOI: 10.1016/j.actbio.2019.11.035

Several mechanisms proposed to explain the osteoinductive potential of calcium phosphates involve surface mineralization (“bioactivity”) and mention the occurrence of concentration gradients between the inner and the outer part of the implanted material. Determining the evolution of the local chemical environment occurring inside the pores of an implanted bone graft substitute (BGS) is therefore highly relevant. A quantitative and fast method was developed to measure the chemical changes occurring within the pores of β-Tricalcium Phosphate (β-TCP) granules incubated in a simulated body fluid. A factorial design of experiment was used to test the effect of particle size, specific surface area, microporosity, and purity of the β-TCP granules. Large pH, calcium and phosphate concentration changes were observed inside the BGS and lasted for several days. The kinetics and magnitude of these changes (up to 2 pH units) largely depended on the processing and properties of the granules. Interestingly, processing parameters that increased the kinetics and magnitude of the local chemical changes are parameters considered to favor calcium phosphate osteoinduction, suggesting that the model might be useful to predict the osteoinductive potential of BGSs. Recent results suggest that in situ mineralization of biomaterials (polymers, ceramics, metals) might be key in their ability to trigger ectopic bone formation. This is the reason why the effect on in situ mineralization of various synthesis parameters of β-tricalcium phosphate granules was studied (size, microporosity, specific surface area, and Ca/P molar ratio). To the best of our knowledge, this is the first article devoted to the chemical changes occurring within the pores of a bone graft substitute. We believe that the manuscript will prove to be highly important in the design and mechanistic understanding of drug-free osteoinductive biomaterials. [Display omitted]