Engineering nature-inspired damage-responsive polymeric fibers (bioFibers) for advanced delivery of microbial-based self-healing agents into cementitious composites
Authors:   , Houshmand Khaneghahi Mohammad , Farnam Amir 
Published: February 2025

Waste The primary goal of this research is to develop an innovative delivery and activation system to establish a robust autonomous self-healing framework in cementitious composites using a multifunctional polymeric-based biotic self-healing fiber, hereafter referred to as bioFiber. The engineered bioFiber possesses three key functionalities: first, it acts as a macro reinforcement to control crack propagation; second, it facilitates damage-induced activation of healing processes within localized damaged zones; and third, it enables bacterial-based healing through the precipitation of calcium carbonate minerals to enable concrete self-repairing. The engineering of bioFiber was structured into three key stages: the feasibility and development phase, the evaluation of self-healing kinetics and capacity through characterization of the healing end-products, and the mechanical performance of bioFiber/matrix composite. A three-component fiber system was engineered, consisting of a load-bearing core fiber with energy-absorbing properties, a hydrogel sheath infused with bio-agents, and a strain-responsive outer shell. The hydrogel was designed to serve as a carrier for encapsulating bio-agents, enhancing the viability of bacterial species, and providing swelling capacity to supply the necessary aqueous solution for the bio-healing process. The outer shell was designed to prevent the premature release of bio-agents from the hydrogel before crack initiation and to facilitate controlled breakage upon concrete cracking, thereby triggering the self-healing and sealing process. Various polymeric materials were investigated to tailor the processing, composition, and structural properties of bioFiber. bioFibers were produced using the Instant Immersion Deposition process, which involved soaking in subsequent alginate-based hydrogel and copolymer shell solutions. The research concluded that a Polyvinyl Alcohol (PVA) core fiber, a calcium alginate hydrogel (crosslinked using a 0.39 M sodium alginate solution and 0.259 M calcium acetate), and a shell composed of a 1:1 wt.% polymer blend of polystyrene and polylactic acid with an 18% w/v polymer/solvent ratio applied as a single-layer coating successfully passed the survivability tests. These tests included (i) bacterial survivability, (ii) fluid ingress survivability, and (iii) abrasion resistance performance. The tests were designed to simulate the effective integration and durability of BioFiber throughout the manufacturing process, concrete casting, and post-hardening phases. To evaluate the mineral-forming capacity of BioFibers, qualitative and quantitative experiments were conducted on self-healing kinetics, microstructural, and crystal structure analyses of the precipitated materials. The findings underscored the potential of BioFibers to produce crystalline calcium carbonate as a self-healing product, with the formation of polymorphs influenced by reaction kinetics and environmental conditions. In the final stage of this study, the self-healing mechanism and the surface/deep crack-filling performance of bioFiber within the cementitious matrix were evaluated. Further, the mechanical performance of bioFiber-reinforced cementitious composites was assessed, including the bridging effect of bioFiber--controlling crack opening width--based on the interfacial bonding properties of bioFiber/matrix. The results demonstrated that even with a limited number of bioFibers, they can effectively restrain surface microcracks. The bioFibers crack-filling performance for in-depth cracks varied depending on the crack morphology and accessibility to water/air. The bioFibers effectively bridged the matrix and exhibited competitive interfacial bonding properties compared to commercial polymeric fibers.