Developments in bacteria-based self-healing of cementitious composites

The paper reports on work being carried out on bacteria-based self-healing of cementitious composites as part of the UK’s Resilient Materials for Life (RM4L) programme grant. RM4L is a follow-up to a previous project that developed bacteria- based self-healing using non-ureolytic bacteria encapsulated in lightweight aggregates and microcapsules. This led to the UK’s first full-scale trial of bacteria-based self- healing concrete. In RM4L, research has been undertaken to overcome a number of application issues with use of bacteria-based self-healing in practice. In particular, a large number of environmental bacteria have been screened that are potentially capable of working in cold and saline conditions. It has been shown that different microbial metabolisms can result in different mechanisms of precipitation, possibly impacting on performance in application. Further work has shown that it is possible to get healing to occur in aged concretes provided the healing agents are included appropriately. Work has also demonstrated to what extent wet/dry conditions are necessary for healing. Finally, the paper reports on work to genetically engineer bacteria to obtain more effective healing

Incorporation of bacteria in concrete: the case against MICP as a means for strength improvement

Strength improvement of cement-based materials by the addition of bacteria has been reported over the past decade and has been mainly attributed to microbially induced calcite precipitation (MICP 1). However, the ability of bacteria to survive, grow and retain their metabolic activity in concrete is questionable. This research sheds light on the mechanisms involved in the strength enhancement of cementitious materials that contain bacteria. The addition of different concentrations of live and dead cells of Bacillus cohnii in cement mortars led to an increase in flexural and compressive strength for the mortars containing both types of bacteria. Findings of the present study led to exclusion of MICP as the main cause of strength enhancement, disproving earlier theories. Other known hypotheses including the behaviour of bacteria as organic fibres or as nucleation sites are thoroughly discussed, and a new approach is proposed.</p

Metabolomic analyses of the malaria parasite after inhibition of polyamine biosynthesis

Malaria, a disease transmitted by female mosquitoes, has plagued the world for many centuries. The disease is associated with high mortality rates, severe poverty, and economic burden. These are factors which hamper effective eradication of the disease. Drug resistant forms of the parasite have caused increasing concerns and questioned the longevity of current effective antimalarials. Efforts are therefore aimed at the identification and exploitation of essential parasite proteins as potential drug targets. The polyamine pathway of Plasmodium falciparum is an exploitable pathway which contains two distinct, chemically validated drug targets; a bifunctional PfAdoMetDC-ODC protein and PfSpdSyn. These enzymes ensure intricate regulation of polyamine production and the pathway contains various distinctive features which could be selectively targetable from the mammalian counterpart pathways. However, inhibition of polyamine production through the use of specific enzyme inhibitors has revealed various compensatory responses that negate the efficacy of these inhibitors. An account is given of the metabolomic fluctuations in the parasite during inhibition of polyamine biosynthesis. From co-inhibited P. falciparum extracts, it could be demonstrated that the characteristic growth-arrest coincided with the depletion in spermidine, the metabolic product of PfSpdSyn. The co-inhibition strategy therefore emphasised the importance of spermidine biosynthesis by PfSpdSyn. Moreover, adenosyl-related metabolite levels were not disrupted during polyamine depletion, supporting the notion that these metabolites are intricately recycled within the parasites. The identified metabolic compensatory mechanisms have further potential for exploitation, and can strategically be combined with polyamine biosynthesis inhibition to ensure parasitic attenuation. In addition, several novel inhibitors were previously computationally identified, based on a dynamic receptor-based pharmacophore model of PfSpdSyn. The in vitro inhibiting activity of these compounds was determined against PfSpdSyn. Results from the in vitro experiments supported the in silico predictions, and emphasized the supportive role of pharmacophore modelling has for the identification of novel inhibitors. The research contributed in understanding parasitic polyamine metabolite regulation, and will aid in the future optimization of therapeutic strategies, aimed at exploitation of the polyamine pathway as a potential antimalarial drug target. CopyrightDissertation (MSc)--University of Pretoria, 2009.Biochemistryunrestricte

Effect of carbonation on bacteria-based self-healing of cementitious composites

Self-healing cementitious composites are being developed to respond to the high cost of repair and maintenance of infrastructure. A promising solution is the use of bacteria to induce calcium carbonate precipitation within cracks when they occur and prevent further deterioration. Previous work has shown successful bacteria-mediated self-healing of cementitious composites at early-ages, in conditions where the material was uncarbonated prior to cracking. However, as cementitious composites often crack when they have reached a more aged state and are likely carbonated at the time of crack formation, these previous experiments did not fully reflect the real-world situation. In the present study, we show that for cementitious composites that do not carbonate prior to cracking the calcium hydroxide created as a hydration product is a sufficient source of Ca2+ ions to provide effective bacteria-induced healing. We note that supplying an extra source of Ca2+ ions at the moment of cracking, delivered via encapsulation, further enhances the degree of healing. Importantly however, in carbonated mortars calcium hydroxide is not available as a source of Ca2+ ions. Consequently, we show for the first time that bacteria-based self-healing in mortars that have carbonated prior to cracking is almost totally dependent on the availability of Ca2+ ions released from an encapsulated source. Our study therefore provides important insights for the rational design of self-healing concrete, where the conditions of the concrete during service life need to be taken into consideration when choosing between direct addition or encapsulation of calcium sources to ensure optimal performance.<br/

Effect of carbonation on bacteria-based self-healing of cementitious composites

Self-healing cementitious composites are being developed to respond to the high cost of repair and maintenance of infrastructure. A promising solution is the use of bacteria to induce calcium carbonate precipitation within cracks when they occur and prevent further deterioration. Previous work has shown successful bacteria-mediated self-healing of cementitious composites at early-ages, in conditions where the material was uncarbonated prior to cracking. However, as cementitious composites often crack when they have reached a more aged state and are likely carbonated at the time of crack formation, these previous experiments did not fully reflect the real-world situation. In the present study, we show that for cementitious composites that do not carbonate prior to cracking the calcium hydroxide created as a hydration product is a sufficient source of Ca2+ ions to provide effective bacteria-induced healing. We note that supplying an extra source of Ca2+ ions at the moment of cracking, delivered via encapsulation, further enhances the degree of healing. Importantly however, in carbonated mortars calcium hydroxide is not available as a source of Ca2+ ions. Consequently, we show for the first time that bacteria-based self-healing in mortars that have carbonated prior to cracking is almost totally dependent on the availability of Ca2+ ions released from an encapsulated source. Our study therefore provides important insights for the rational design of self-healing concrete, where the conditions of the concrete during service life need to be taken into consideration when choosing between direct addition or encapsulation of calcium sources to ensure optimal performance.<br/

A rapid and quantitative technique for assessing IgG monomeric purity, calibrated with the NISTmAb reference material

This is the final version. Available from Springer via the DOI in this record.The fraction of intact monomer in a sample (moles/moles), the monomeric purity, is measured as a quality control in therapeutic monoclonal antibodies but is often unknown in research samples and remains a major source of variation in quantitative antibody-based techniques such as immunoassay development. Here, we describe a novel multiplex technique for estimating the monomeric purity and antigen affinity of research grade antibody samples. Light scattering was used to simultaneously observe the mass of antibody binding to biosensor surfaces functionalised with antigen (revealing Fab binding kinetics) or protein A/G (PAG). Initial estimates of monomeric purity in 7 antibody samples including a therapeutic infliximab biosimilar were estimated by observing a mass deficit on the PAG surface compared to the NISTmAb standard of high monomeric purity. Monomeric purity estimates were improved in a second step by observing the mass of antigen binding to the mass of antibody on the PAG surface. The NISTmAb and infliximab biosimilar displayed tightly controlled stoichiometries for antigen binding of 1.31 ± 0.57 and 1.71 ± 0.16 (95% confidence interval)—within the theoretical limit of 1–2 antigens per antibody depending on avidity. The other antibodies in the panel displayed antigen binding stoichiometries in the range 0.06–1.15, attributed to lower monomeric purity. The monomeric purity estimates were verified by electrospray ionization mass spectrometry (ESI), the gold standard technique for structural characterization of antibodies. ESI data indicated that the NISTmAb and infliximab biosimilar samples had monomeric purity values of 93.5% and 94.7%, respectively, whilst the research grade samples were significantly lower (54–89%). Our results demonstrate rapid quality control testing for monomeric purity of antibody samples (< 15 min) which could improve the reproducibility of antibody-based experiments.EPSR

Catechin or quercetin guests in an intrinsically microporous polyamine (PIM-EA-TB) host: accumulation, reactivity, and release

Microporous polymer materials based on molecularly "stiff"structures provide intrinsic microporosity, typical micropore sizes of 0.5 nm to 1.5 nm, and the ability to bind guest species. The polyamine PIM-EA-TB contains abundant tertiary amine sites to interact via hydrogen bonding to guest species in micropores. Here, quercetin and catechin are demonstrated to bind and accumulate into PIM-EA-TB. Voltammetric data suggest apparent Langmuirian binding constants for catechin of 550 (±50) × 103 M-1 in acidic solution at pH 2 (PIM-EA-TB is protonated) and 130 (±13) × 103 M-1 in neutral solution at pH 6 (PIM-EA-TB is not protonated). The binding capacity is typically 1 : 1 (guest : host polymer repeat unit), but higher loadings are readily achieved by host/guest co-deposition from tetrahydrofuran solution. In the rigid polymer environment, bound ortho-quinol guest species exhibit 2-electron 2-proton redox transformation to the corresponding quinones, but only in a thin mono-layer film close to the electrode surface. Release of guest molecules occurs depending on the level of loading and on the type of guest either spontaneously or with electrochemical stimuli

Air-entraining admixtures as a protection method for bacterial spores in self-healing cementitious composites:Healing evaluation of early and later-age cracks

Costs associated with the encapsulation process of bacterial spores continue to be a limiting factor for the commercialisation of self-healing cementitious materials. The feasibility of using air-entraining admixtures (AEAs) as an economical and straightforward encapsulation method for bacterial spores was evaluated to heal cracks (∼0.50 mm) that were formed at an early (28 days) or later age (9 months). Three AEAs, commonly used in concrete industry, were compared to a successfully proven protection method (i.e., via aerated concrete granules (ACGs)). In this regard, only one of the three AEAs investigated improved the healing performance when compared to an equivalent mix using bacterial spores encapsulated in ACGs. Healing ratios obtained with this successful AEA were 59.6% and 46.2% higher than the results observed for the ACGs-containing mix when the cracking age was 28 days and 9 months, respectively. Moreover, water penetration resistance was increased by 18.1% or presented very similar values (∼84%) after 56 days of healing for early or later-formed cracks, respectively. Moreover, a simple cost analysis was conducted to confirm the significant economic benefits of using AEAs to protect directly added bacterial spores. In this regard, the cost of using AEAs is about 13 times lower than for ACGs. Therefore, this study provides for the first time, evidence of the feasibility of using AEAs to protect bacterial spores, opening the doors to the development of bespoke AEAs to design cost-efficient self-healing cementitious materials.</p

Integrating Self-Sensing in Self-Healing Concrete: Towards a Biomimetic Approach to Repair

Material degradation of our civil infrastructure is inevitable, and regular maintenance is required to mitigate against failure during the service-life. However, understanding and knowledge of composites is now leading to the creation of concretes with autonomic self-healing capabilities. This development will transform our infrastructure by embedding self-immunity and resilience so that structures evolve over their lifespan enhancing durability and serviceability, improving safety and reducing maintenance costs. Research in the UK under the auspices of Resilient Materials for Life (RM4L) has developed a suite of multiple-scale biomimetic self-healing concretes that can adapt and respond to damage without external intervention. This paper discusses the development of bacteria to precipitate calcite in cracks in concrete. Whilst bacteria-based healing is possible through several pathways, it is only now that a better understanding is permitting the optimization of the process. There are two key technologies for including bacteria healing in concrete: (i) encapsulation and (ii) vascular flow networks. Vascular flow networks permit continuous unlimited delivery of healing agents to internal areas of damage, facilitating repair on a reoccurring basis. However, in order to use them effectively human intervention is required to identify cracking and trigger healing processes. A more biomimetic approach is to provide the concrete with a form of self-sensing capability to enable it to initiate crack healing itself. Research using PZT sensors to detect cracking is described

Flooding and Phytophthora cinnamomi : effects on photosynthesis and chlorophyll fluorescence in shoots of non-grafted Persea americana (Mill.) rootstocks differing in tolerance to Phytophthora root rot

Please read abstract in the article.The Hans-Merensky Foundation and the National Research Fund (NRF) through the THRIP programme (Department of Science and Technology, South Africa).http://www.elsevier.com/locate/sajbhj201