Development of an innovative urease-aided self-healing dental composite

Dental restorative materials suffer from major drawbacks, namely fracture and shrinkage, which result in failure and require restoration and replacement. There are different methods to address these issues, such as increasing the filler load or changing the resin matrix of the composite. In the present work, we introduce a new viable process to heal the generated cracks with the aid of urease enzyme. In this system, urease breaks down the salivary urea which later binds with calcium to form calcium carbonate (CaCO₃). The formation of insoluble CaCO₃ fills any resultant fracture or shrinkage from the dental composure hardening step. The healing process and the formation of CaCO₃ within dental composites were successfully confirmed by optical microscope, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDS) methods. This research demonstrates a new protocol to increase the service life of dental restoration composites in the near future

Bioconcrete: next generation of self-healing concrete

Concrete is one of the most widely used construction materials and has a high tendency to form cracks. These cracks lead to significant reduction in concrete service life and high replacement costs. Although it is not possible to prevent crack formation, various types of techniques are in place to heal the cracks. It has been shown that some of the current concrete treatment methods such as the application of chemicals and polymers are a source of health and environmental risks, and more importantly, they are effective only in the short term. Thus, treatment methods that are environmentally friendly and long-lasting are in high demand. A microbial self-healing approach is distinguished by its potential for long-lasting, rapid and active crack repair, while also being environmentally friendly. Furthermore, the microbial self-healing approach prevails the other treatment techniques due to the efficient bonding capacity and compatibility with concrete compositions. This study provides an overview of the microbial approaches to produce calcium carbonate (CaCO₃). Prospective challenges in microbial crack treatment are discussed, and recommendations are also given for areas of future research

Induced calcium carbonate precipitation using Bacillus species

Microbially induced calcium carbonate precipitation is an emerging process for the production of self-healing concrete. This study was aimed to investigate the effects and optimum conditions on calcium carbonate biosynthesis. Bacilluslicheniformis, Bacillus sphaericus, yeast extract, urea, calcium chloride and aeration were found to be the most significant factors affecting the biomineralization of calcium carbonate. It was noticed that the morphology of microbial calcium carbonate was mainly affected by the genera of bacteria (cell surface properties), the viscosity of the media and the type of electron acceptors (Ca²⁺). The maximum calcium carbonate concentration of 33.78 g/L was achieved at the optimum conditions This value is the highest concentration reported in the literature

THE INFLUENCE OF GEOMETRIC PARAMETERS AND MECHANICAL PROPERTIES OF ADHESIVE ON STRESS ANALYSIS IN ADHESIVELY BONDED ALUMINUM SINGLE LAP JOINT

The aim of this study was to investigate adhesively bonded joints, and the influence of geometric parameters and mechanical properties of the adhesive in single lap aluminum structures under tensile load. A finite element model has been constructed in the ANSYS FE package and the effects of adhesive thickness, rigidity, strength and geometry have been studied in order to adjust peel stress. Various paths have been defined and obtained along the length of the adhesive and aluminum joint overlap. The results indicate that by increasing the adhesive thickness, the stress concentration decreases in the areas prone to yielding if a flexible adhesive is used instead of a rigid one, and effective stresses along the overlap length are also reduced. In addition, for a given tensile force, three different adhesive area geometries are defined. Considering the variation of peel and shear stress along the corners, the amount of adhesive used according to the introduced geometries is saved without sacrificing joint strength

The Effect of Cell Immobilization by Calcium Alginate on Bacterially Induced Calcium Carbonate Precipitation

Microbially induced mineral precipitation is recognized as a widespread phenomenon in nature. A diverse range of minerals including carbonate, sulphides, silicates, and phosphates can be produced through biomineralization. Calcium carbonate (CaCO₃) is one of the most common substances used in various industries and is mostly extracted by mining. In recent years, production of CaCO₃ by bacteria has drawn much attention because it is an environmentally- and health-friendly pathway. Although CaCO₃ can be produced by some genera of bacteria through autotrophic and heterotrophic pathways, the possibility of producing CaCO₃ in different environmental conditions has remained a challenge to determine. In this study, calcium alginate was proposed as a protective carrier to increase the bacterial tolerance to extreme environmental conditions. The model showed that the highest concentration of CaCO₃ is achieved when the bacterial cells are immobilized in the calcium alginate beads fabricated using 1.38% w/v Na-alginate and 0.13 M CaCl₂

Recycling of waste glass as aggregate in cement-based materials

Glass is a common material made from natural resources such as sand. Although much of the waste glass is recycled to make new glass products, a large proportion is still being sent to landfill. Glass is a useful resource that is non-biodegradable, occupying valuable landfill space. To combat the waste glass that is heading to landfill, alternative recycling forms need to be investigated. The construction industry is one of the largest CO₂ emitters in the world, producing up to 8% of the global CO₂ to produce cement. The use of sand largely depletes natural resources for the creation of mortars or concretes. This review explores the possibilities of incorporating waste glass into cement-based materials. It was found waste glass is unsuitable as a raw material replacement to produce clinker and as a coarse aggregate, due to a liquid state being produced in the kiln and the smooth surface area, respectively. Promising results were found when incorporating fine particles of glass in cement-based materials due to the favourable pozzolanic reaction which benefits the mechanical properties. It was found that 20% of cement can be replaced with waste glass of 20 μm without detrimental effects on the mechanical properties. Replacements higher than 30% can cause negative impacts as insufficient amounts of CaCO₃ remain to react with the silica from the glass, known as the dilution effect. As the fine aggregate replacement for waste glass increases over 20%, the mechanical properties decrease proportionally; however, up to 20% has similar results to traditionally mixes

Mechanical and rheological properties of 3D printable cement composites

Additive manufacturing is a recent revolution in the construction field since cementitious materials became printable. This extrusion technique has enabled the construction of very complex geometry with a reduction in costs, time and labour interventions. This study aims to evaluate the possibility of reinforcing 3D printable cementitious composites with the use of nano and micro materials, particularly nano silica, micro silica and microfibrillated cellulose (MFC) which are known for their ability to enhance the fresh and hardened properties of cement-based composites. Rheology property test, flowability and mechanical properties are the types of tests performed to evaluate the fresh and hardened properties of mortar modified with the rested additives. The results show the addition of MFC of 0.4% (of total solid matter) can significantly enhance the mechanical property. In addition, the presence of MFC (at 0.4% of total solid matter) can reduce the pressure required to extrude the mortar, enabling a steady state extrusion. It was also found that 1% nano silica addition significantly improves the mechanical properties and minimizes segregation in the failure surface