Hamada Elsayed1,2, Michele Secco3, Federico Zorzi4
1Department of Industrial Engineering, Universita degli Studi di Padova, 35131 Padova, Italy.
Porosity in Cement Paste
Hydration of Cement
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This study developed a new type of highly porous bioceramic material using a complex hardystonite solid solution. The material was made from silicone resins and oxide fillers, with calcium borate playing a key role in forming the ceramic structure during high-temperature processing. The researchers tested two shaping methods: direct ink writing and foaming. Foaming was improved by using hydrated calcium borate, which released water at a lower temperature. The resulting scaffolds and foams had high strength-to-density ratios and showed no cytotoxicity in cell tests. The findings suggest that this approach could lead to the development of biocompatible, high-performance materials for tissue engineering applications.
Area of Science:
Background:
Current research in biomedical materials seeks to develop porous scaffolds with controlled mechanical and biological properties. While traditional bioceramics have been used in bone regeneration, their performance is often limited by poor mechanical strength or inadequate porosity. Prior studies have demonstrated that incorporating oxide fillers and polymer templates can improve scaffold architecture. However, the formation of complex solid solutions during high-temperature processing remains poorly understood. This gap motivated the investigation of how specific oxide precursors influence phase development in polymer-derived bioceramics. No prior work had resolved how calcium borate affects the formation of hardystonite-based solid solutions. The role of liquid-phase sintering in shaping ceramic microstructures is still debated. This study aimed to clarify how precursor selection impacts the final ceramic phase and scaffold performance.
Purpose Of The Study:
The study confirmed the formation of a novel hardystonite solid solution with the formula (Ca<sub>0.70</sub>Sr<sub>0.30</sub>)<sub>2</sub>(Zn<sub>0.72</sub>Mg<sub>0.15</sub>Si<sub>0.13</sub>)(Si<sub>0.85</sub>B<sub>0.15</sub>)<sub>2</sub>O<sub>7</sub>.
Calcium borate acts as a liquid-phase sintering aid, promoting the formation of the hardystonite solid solution during firing at 950 °C.
Hydrated calcium borate was used to enable water vapour release at 420 °C, which improved foaming and scaffold morphology.
Cell culture experiments were conducted to evaluate cytotoxicity associated with the ceramic phase assemblage.
The research aimed to develop a novel class of highly porous bioceramics by using a complex hardystonite solid solution. The goal was to evaluate how different oxide precursors and processing conditions affect ceramic phase formation and scaffold properties. The authors sought to determine whether calcium borate could act as a liquid-phase sintering aid in this system. They also aimed to test the feasibility of using thick silicone-filler pastes for direct ink writing or foaming. A specific focus was placed on how hydrated calcium borate influences the foaming process through water vapour release. The study also aimed to assess the mechanical performance of the resulting scaffolds and foams. Another objective was to investigate whether the formation of a borosilicate glassy phase could lead to cytotoxic effects. The ultimate purpose was to provide a scalable method for fabricating biocompatible, high-strength scaffolds.
Main Methods:
The researchers prepared bioceramic precursors by mixing silicone resins with micro-sized oxide fillers. They used CaO, SrO, MgO, and ZnO as primary precursors and added calcium borate as a liquid-phase sintering aid. The mixtures were processed into thick pastes suitable for direct ink writing or foaming. For foaming, hydrated calcium borate was included to enable water vapour release at 420 °C. The samples were fired at 950 °C in air to produce the final ceramic structures. Phase analysis was conducted using X-ray diffraction to confirm the formation of the hardystonite solid solution. Mechanical testing was performed to evaluate strength-to-density ratios. Cell culture experiments were used to assess cytotoxicity associated with the ceramic phase assemblage.
Main Results:
The study confirmed the formation of a novel hardystonite solid solution with the formula (Ca0.70Sr0.30)2(Zn0.72Mg0.15Si0.13)(Si0.85B0.15)2O7. Calcium borate was essential in promoting the liquid phase during firing and facilitating solid solution formation. Both scaffolds and foams retained the desired phase assemblage after firing. The scaffolds exhibited high strength-to-density ratios, indicating good mechanical performance. Foaming was enhanced by the use of hydrated calcium borate, which released water vapour at 420 °C. The resulting structures showed a reticulated morphology suitable for tissue engineering applications. Cell tests confirmed the absence of cytotoxicity from the ceramic phase. The study demonstrated that the combination of oxide precursors and calcium borate enabled the production of biocompatible, high-performance bioceramics.
Conclusions:
The authors concluded that calcium borate played a crucial role in forming the hardystonite solid solution during firing. The use of hydrated calcium borate allowed for low-temperature dehydration, which improved foaming and scaffold morphology. The resulting bioceramics exhibited high strength-to-density ratios, making them suitable for biomedical applications. The study demonstrated that the combination of specific oxide precursors and sintering aids could produce novel ceramic phases. The phase assemblage remained stable after firing, confirming the effectiveness of the processing method. Cell tests showed no cytotoxicity from the ceramic phase, supporting its biocompatibility. The findings suggest that this approach could be used to fabricate scaffolds with tailored mechanical and biological properties. The study provides a scalable method for producing high-performance bioceramics for tissue engineering.
The strength-to-density ratios of the scaffolds and foams were evaluated to assess mechanical performance.
The authors proposed that the method could be used to fabricate scaffolds with tailored mechanical and biological properties for tissue engineering.