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In this study, three anhydrous forms of calcium carbonate, namely vaterite, aragonite and calcite, with distinct morphologies were incorporated inside silk-fibroin to fabricate composite scaffolds for tissue engineering applications. To assess calcium phosphate mineralization, composite scaffolds were treated with simulated body fluid up to one month. It was observed that composite scaffolds having different calcium carbonate polymorphs expressed different mineralization. Incorporating 25 wt. % of vaterite polymorph, which was the least stable form of calcium carbonate under aqueous conditions, induced the highest calcium phosphate mineralization in silk-fibroin while calcium carbonate-free silk-fibroin scaffolds expressed no calcium phosphate deposition. Results highlighted the importance of calcium carbonate particles in enhancing the bioactivity of silk-fibroin based composite scaffolds. [ABSTRACT FROM AUTHOR]

Abstract Calcium carbonate (CaCO 3) particles have been used in various applications, including medicine, drug delivery and orthopedics. Having three different polymorphs and exhibiting complex crystallization behavior, it is a challenging task to systematically control physical properties of CaCO 3 particles for desired applications. Herein, the influence of pH and [Ca2+]:[CO 3 2−] ratio on the morphology, size and polymorph of room temperature synthesized CaCO 3 particles were investigated. Although, in literature, ethylene glycol concentration of precursor solutions is considered as one of the most critical factors controlling polymorph and morphology of CaCO 3 particles, present work highlights precursor solution pH to be a stronger factor in controlling room temperature synthesized CaCO 3 particle properties. In fact, CaCO 3 particle size decreased from micron to sub-micron range and calcite polymorph transformed to vaterite upon decreasing pH of the precursors for all of the precursor solution [Ca2+]:[CO 3 2−] ratios investigated in this study. Importantly, CaCO 3 particles with different and distinct morphologies were obtained by altering pH and [Ca2+]:[CO 3 2−] ratios of the precursor solutions. Since requirements for the physical properties of CaCO 3 particles are diverse for industrial and medical applications, it is important to understand CaCO 3 crystallization behavior for tailored particle synthesis. Graphical abstract Unlabelled Image Highlights • Effects of pH and [Ca2+]:[CO 3 2−] ratio on CaCO 3 particles were investigated. • Vaterite and calcite particles having different sizes were synthesized. • Effects of pH and ethylene glycol concentration were compared. • pH was found to be the dominant factor on CaCO 3 particle properties. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAp, Ca 10 (PO 4) 6 (OH) 2) particles are widely used in orthopedic applications due to their chemical resemblance to the inorganic component of bone tissue. Since physical and chemical properties of HAp particles influence bone regeneration, various synthesis techniques were developed to precisely control the particle properties. However, most of these techniques required high reaction temperatures, which limited the spectrum of obtained HAp particle morphologies. In this study, ellipsoidal, bowknot-like and spherical calcium carbonate (CaCO 3) particles were utilized as solid templates to control the morphology of HAp particles (core@shell, CaCO 3 @HAp) under ambient conditions. Since CaCO 3 templates had different properties, i.e. morphology, polymorph and surface area, they induced HAp formation with different efficacies, where ellipsoidal vaterite and spherical calcite particles exhibited higher CaCO 3 -to-HAp conversion compared to bowknot-like aragonite particles. In vitro experiments showed that proliferation of human bone cells (hFOB) was higher upon their interaction with ellipsoidal and spherical CaCO 3 @HAp particles compared to bowknot-like CaCO 3 @HAp particles. These findings highlighted CaCO 3 particles as promising hard templates to control the morphology of CaCO 3 @HAp particles under ambient conditions for orthopedic applications. [ABSTRACT FROM AUTHOR]

Calcium carbonate (CaCO 3) microspheres consisting of vaterite polymorph have been widely used in biomedical applications. Specifically, vaterite microspheres having hollow cores showed significant potential in drug delivery, however the spontaneous transformation of vaterite to other polymorphs in aqueous environments reduced its controlled in vivo release capability. In this work, calcite and aragonite microspheres having hollow/porous inner cores were synthesized -for the first time-using sodium dodecyl sulfate (SDS) stabilized nitrogen (N 2) bubbles as CaCO 3 template in ethylene glycol (EG) solution and water as the precipitation medium. Results demonstrated that porous aragonite microspheres could be synthesized via N 2 gas incorporation, yet for the synthesis of hollow calcite microspheres, N 2 bubbles had be stabilized with SDS to be utilized as CaCO 3 templates. The synthesized aragonite and calcite microspheres were found to be stable up to 5 days in Dulbecco's Modified Eagle's Medium (DMEM), and thus would not allow polymorphic transformation in aqueous environments, while promoting proliferation of human bone cells (hFOB) up to 5 days of culture. These findings -for the first time-identified a viable synthesis route for hollow/porous calcite and aragonite microspheres and indicated their promising use in orthopedic applications. [ABSTRACT FROM AUTHOR]