Immobilization of bacterial spores using eggshells nanoparticles and their effective role in concrete bio-healing process: novel approach

Microbially induced calcium carbonate precipitation (MICP) has gained increasing attention as a sustainable bioengineering strategy for improving the strength and bio-healing capacity of concrete. Through biologically mediated CaCO₃ formation, microorganisms can bridge cracks and enhance material cohesion. A persistent challenge, however, lies in maintaining bacterial viability under the mechanically harsh conditions of cementitious systems. To overcome this issue, the present study introduces eggshell-derived nanoparticles (EShN) as an innovative, low-cost carrier for bacterial spores, aiming to improve their protection. The size, chemical composition of the EShN, and the spores’ immobilization process were examined using methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX), and transmission electron microscopy (TEM). The biohealing of concrete and its strengths were investigated. SEM imaging revealed efficient immobilization of Bacillus spores onto the nanoparticle surfaces, while EDX analysis verified calcium carbonate as the main mineral formed within healed cracks. Concrete samples incorporating immobilized bacterial spores exhibited remarkable enhancements in mechanical performance, showing increases of approximately 45, 49.5, and 47.5% in compressive, tensile, and flexural strengths, respectively, compared with negative control. This research demonstrates that eggshell nanoparticles serve as an effective and sustainable medium for bacterial immobilization, significantly improving both the healing efficiency and mechanical properties of bio-concrete. Overall, this approach provides a promising pathway toward the development of resilient, eco-friendly, and biorepairing construction materials.