Characterization and multiscale modeling of novel calcium phosphate composites containing hydroxyapatite whiskers and gelatin microspheres

Abstract

In this study, novel calcium phosphate cement (CPC) composites were prepared by simultaneous incorporation of porogenic crosslinked gelatin microspheres (GMs) and reinforcing hydroxyapatite whiskers (HAWs) into the CPC matrix and the effects of the mentioned additives on the compositional characteristics, phase evolution, setting time, microstructure and mechanical properties of the CPC matrix, were thoroughly investigated. Simulation techniques and multiscale modeling were also employed to predict and compare mechanical properties of the composite formulations with those of real mechanical tests. For this purpose, composite CPCs of varying compositions were prepared by concurrent addition of GMs (5, 10 wt %) and HAWs (5–30 wt %) to the typical apatitic CPC composed of equimolar mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA). Morphological observations by SEM confirmed proper dispersion of the additive materials in the CPC matrix. The results of the compositional evaluation of the composites by FTIR and XRD also revealed that the additives preferably didn’t exhibit a considerable inhibitive effect on the HA conversion during the composite CPC setting process. Porosity measurements approved that GMs could act as porogenic materials which introduced an increased total porosity of up to ∼69% to the structure of composites. The CPC sample and the composite cements also exhibited considerable specific surface area of 12.99 and 4.32–8.20 m 2 /g, respectively. Moreover, the results of compressive mechanical testing showed that the CPC control and the composites had a compressive strength of 28.1, 9.5–29.4 MPa and Young modulus of 3860 and 515–2630 MPa, respectively. However, in terms of mechanical and microstructural features, the composites containing 10 wt % of HAWs exhibited the most preferable characteristics. The mechanical results of the multiscale modeling method were also in the same range of those obtained by experimental compressive tests. Such finding was more notable for the composites with lower content of HAWs (5 and 10 wt %), when the predicted mechanical values for such samples were more than 80% accurate. In-vitro cellular tests also showed that the additives (GMs and HAWs) improved biological response of the composites, with 10 wt % of GMs and HAWs as the optimal amount. Nevertheless, depending on the bone graft requirements and the needed compromise between porosity and mechanical properties; the optimum composite can be chosen. • Successful synthesis of Gelatin Microspheres (GMs) and Hydroxyapatite whiskers (HAWs). • Incorporation of GMs and HAWs into the calcium phosphate cement (CPCs). • Designing novel composite CPC formulations with different amounts of GMs and HAWs. • Thorough characterization of CPC composites to determine optimum formulations. • Observation of reinforcing and porogenic roles by HAWs and GMs, respectively.