Carbonate biomineralization potential of endospore-laden polymeric fibers (BioFibers) for bio-self-healing applications

This study explores the capacity and kinetics of microbially-induced calcium carbonate precipitation (MICCP) using BioFibers-endospore-laden polymeric fibers. Innovatively developed as a delivery system, BioFibers incorporate a bio-self-healing feature into quasi-brittle composites like concrete. Constructed with a load-bearing core fiber, a bio-compatible hydrogel sheath, and an outer protective shell layer, BioFibers represent a novel approach to enhancing material healing properties. BioFibers have been engineered to provide the matrix with three functionalities: autonomous self-healing, crack growth control, and damage-induced activation. The primary goal of this study was to focus on the self-healing functionality of BioFibers and evaluate the biomineralization performance through advanced material characterization techniques. In this context, we conducted quantitative and qualitative experiments to study bio-self-healing kinetics and precipitates material characterizations using thermogravimetric analysis (TGA), scanning electron microscopy equipped with energy-dispersive spectroscopy (SEM-EDS) and X-ray powder diffraction (XRD). TGA results revealed that the self-healing kinetics based on calcium carbonate precipitation were mainly exhibited by three stages: (i) endospore germination lag phase, (ii) ureolytic activity, and (iii) saturation degree of carbonate, resulting in precipitations of calcium carbonate per one activated BioFiber (with an average mass of 56.9 +/- 1.4 mg) equal to: (i) 3.35-30.30 mg, (ii) 31.08-140.91 mg, and (iii) 381.39-620.08 mg, respectively. SEM imaging revealed growing calcium carbonate crystal formation, primarily vaterite, during the progression of MICCP. EDS data in the initial stage indicated traces of phosphorus, potassium, nitrogen, sodium, and sulfur, signaling the endospore germination phase. In subsequent stages, carbon, calcium, and oxygen elements dominated, confirming calcium carbonate precipitation. XRD phase analysis showed that amorphous content was the primary residue in the first stage, with 85.5% associated with organic matter and 5.6 wt% due to amorphous calcium carbonate. As the MICCP process continued, the amorphous content, mainly organic matter, decreased, reaching 23.5 wt% in the last stage. Conversely, the crystalline phase increased, with calcite accounting for 21.4 wt% and vaterite accounting for 51.7 wt% in the final stage.