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  1. Free, publicly-accessible full text available December 1, 2024
  2. Free, publicly-accessible full text available November 1, 2024
  3. Van Mullem, T. ; De Belie, N. ; Ferrara, L. ; Gruyaert, E. ; Van Tittelboom, K. (Ed.)

    The goal of this research is to develop innovative damage-responsive bacterial-based self-healing fibers (hereafter called BioFiber) that can be incorporated into concrete to enable two functionalities simultaneously: (1) crack bridging functionality to control crack growth and (2) crack healing functionality when a crack occurs. The BioFiber is comprised of a load-bearing core fiber, a sheath of bacteria-laden hydrogel, and an outer impermeable strain-responsive shell coating. An instant soaking manufacturing process was used with multiple reservoirs containing bacteria-laden, hydrophilic prepolymer and crosslinking reagents to develop BioFiber. Sodium-alginate was used as a prepolymer to produce calcium-alginate hydrogel via ionic crosslinking on the core fiber. The dormant bacteria (spore) ofLysinibacillus sphaericuswas incorporated in hydrogel as a self-healing agent. Then, an impermeable polymeric coating was applied to the hydrogel-coated core fibers. The impermeable strain-responsive shell coating material was manufactured using the polymer blend of polystyrene and polylactic acid. The high swelling capacity of calcium-alginate provides the water required for the microbially induced calcium carbonate precipitation (MICP) chemical pathway, i.e., ureolysis in this study. The strain-responsive impermeable coating provides adequate flexibility during concrete casting to protect the spores and alginate before cracking and sufficient stress-strain behavior to grant damage-responsiveness upon crack occurrence to activate MICP. To evaluate the behavior of developed BioFiber, the swelling capacity of the hydrogel, the impermeability of shell coating, the spore casting survivability, and MICP activities were investigated.

     
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  4. Van Mullem, T. ; De Belie, N. ; Ferrara, L. ; Gruyaert, E. ; Van Tittelboom, K. (Ed.)

    Vegetative cells used for the concrete bio self-healing process often face threatening environmental conditions such as extreme temperature, pH, salinity, shear stress, and starvation during the hardening process and the service life of the concrete. These conditions can eventually lead to cell death. Since endospores are likely to remain dormant for prolonged periods and can survive, germinate, and grow under inhospitable conditions, they are a suitable bacterial phenotype to introduce into concrete for microbial-inducing calcite precipitation. This study investigated how different endosporulation methods affect the endosporulation ratio (i.e., the fraction of vegetative cells that are converted to endospores during endosporulation), as well as the germination ratio (i.e., the fraction of endospores that are converted to vegetative cells following germination) and the microbial-induced calcite precipitation (MICP) performance of germinated endospores after facing harsh conditions of concrete, specifically, freeze and that cycling. Results from this study show that thermal shock followed by cell incubation in alkaline conditions leads to increased sporulation and germination ratios. It was also observed that freeze and thaw cycling had negligible effects on calcite production by endospores, while exposure of vegetative cells to these harsh conditions led to not only less biomass and calcite production but also to a lower mass of calcite produced per mass of cells, as determined by thermogravimetric analysis (TGA). The results from this study provide key insights into improving methods for endosporulation and germination to effectively use them for bio self-healing applications in concrete.

     
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  5. Abstract

    Electrospun biopolymer fibers are utilized in a wide variety of industries such as tissue engineering, sensors, drug delivery, membrane filtration, and protective membranes. The biopolymer chitosan, the partiallyN‐deacetylated derivative of chitin, which has been the focus of many studies, contains amine or hydroxyl functionalities that may be substituted with a number of chemistries such as carboxylate, benzene, or cyano groups. Modified chitosan solutions are often challenging to electrospin, as an entirely new set of solution and operating conditions must be developed for each modification. In this study, a facile post‐modification processing method for chitosan is introduced that circumvents the need to perform bulk modification prior to electrospinning, and therefore new spinning conditions. The chitosan mats were solution‐phase post‐processed by chemically functionalizing the mats with carboxylate, benzene and cyano groups. Scanning electron microscopy and Fourier‐transform infrared have been performed to determine fiber morphology retention and chemical interactions, respectively. Post‐modification retained the fibrous structure of the white‐colored, round and smooth mats with spectral changes indicating changes in the chitosan mat. Mean fiber diameters were 131 ± 75 nm (~31% smaller), 210 ± 81 nm (46% larger), and 85 ± 29 nm (~11% smaller) for carboxymethylchitosan, benzylidenechitosan, and cyanochitosan, respectively.

     
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