Self-healing Mechanism Research Articles

Self-healing mechanisms for Ge–Sb–S chalcogenide glasses upon gamma irradiation

Self-healing mechanisms for Ge–Sb–S chalcogenide glasses upon gamma irradiation

Enhancing durability and sustainability in concrete with fibre-reinforced composites

This paper presents a study focused on two pivotal innovations in the field of fibre-reinforced concrete (FRC) to significantly enhance its durability and sustainability in construction. First, our research investigates the application of advanced self-healing mechanisms in FRC. By embedding microcapsules containing healing agents within the concrete matrix, we achieved a remarkable reduction in crack propagation and improved structural integrity. Our results demonstrate that the self-healing FRC exhibited a 30% increase in compressive strength and a 40% reduction in crack width, leading to a longer service life for concrete structures. Second, we explore the integration of sustainable materials in FRC production. By incorporating locally sourced and recycled materials, we successfully reduced the environmental impact associated with FRC manufacturing. Our findings reveal a substantial reduction in carbon emissions, with a 25% decrease in the overall carbon footprint of FRC production. This innovation not only contributes to a greener construction industry but also aligns with sustainability goals and regulations. This research underscores the transformative potential of self-healing mechanisms and sustainable material integration in FRC, offering tangible results in terms of increased durability and reduced environmental impact. These innovations promise to reshape the construction landscape, aligning it with the principles of sustainability and long-term structural resilience.

Robust superhydrophobic cotton fabric based on dual-sized silica particles with self-healing nature

Improving the durability of wear-resistant superhydrophobic surfaces is crucial for their practical use. To tackle this, research is now delving into self-healing superhydrophobic surfaces. In our study, we developed superhydrophobic cotton fabrics by embedding nano-silica particles, micro-silica powder, and polydimethylsiloxane (PDMS) using a dipping method. This innovative design grants the SiO2/PDMS cotton fabric remarkable superhydrophobicity, reflected by a water contact angle of 155°. Moreover, the PDMS was stored in the amorphous areas of cellulose of cotton fabrics, attaching to the fiber surface and playing a role in connecting micro-blocks and nano-particles. This causes a self-diffusion of PDMS molecules in these fabrics, allowing the surface to regain its superhydrophobicity even after abrasion damage. Impressively, this self-healing property can be renewed at least 8 times, showcasing the fabric's resilience. Moreover, these superhydrophobic cotton fabrics exhibit outstanding self-cleaning abilities and repel various substances such as blood, milk, cola, and tea. This resilience, coupled with its simplicity, low cost-effectiveness, and eco-friendliness, makes this coating highly promising for applications across construction, chemical, and medical fields. Our study also delves into understanding the self-healing mechanism of the SiO2/PDMS cotton fabric, offering insights into their long-term performance and potential advancements in this field.

Synergistic self-healing effect and mechanism of fiber and biological capsule on mortar cracks

In this paper, biological capsules were prepared with volcanic rock particles as bacterial carriers, while water glass and low alkaline sulphoaluminate cement were used as shell materials. The self-healing effect and mechanism of mortar samples prepared with Polyvinyl alcohol (PVA) fibers and biological capsules were studied. The results showed that the samples had the best crack-healing effect after adding PVA fibers and biological capsules. The cracks (<400 μm width) were completely healed. Calcite-type CaCO3 was identified as the primary healing product with irregular and square crystals. In addition, the formation rate of healing products was analyzed by measuring the changes in Ca2+ concentration and pH value in the curing solution. The three-dimensional morphology of healing products attached to the PVA fibers was obtained by laser scanning confocal microscope. Finally, the cementation mechanism between calcite and C-S-H was studied by molecular dynamics simulation. Highlights: The crack healing mechanism of fibers and biological healing agents was studied. The relationship between ion concentration, pH and crack healing was clarified. The cementation mechanism between cracks and mineralized products was revealed.

An autonomous self-healing mechanism to improve the chemical durability vs. moisture of PVDF-based gel electrolytes for lithium-ion batteries

Lithium-ion batteries (LIBs) are at the forefront of electrochemical energy storage both for consumer electronics, and for power/energy more demanding applications, such as in automotive and grid levelling. However, their chemical and electrochemical stability must be further improved. Among the instability causes, a major role is played by residual moisture. As a matter of fact, hydrofluoric acid generated by hydrolysis of LiPF6, the most common lithium salt in LIBs, causes safety issues and performance losses. Here we demonstrate the scavenging properties vs. HF of a barium silicate glass used as a filler in a PVDF-HFP based gel polymer electrolyte. A full LiTi2(PO4)3|electrolyte|LiMn2O4 cell is stable for 200 cycles at 0.1C.

Reversible Photoinduced Ligand Substitution in a Luminescent Chromium(0) Complex.

Light-triggered dissociation of ligands forms the basis for many compounds of interest for photoactivated chemotherapy (PACT), in which medicinally active substances are released or "uncaged" from metal complexes upon illumination. Photoinduced ligand dissociation is usually irreversible, and many recent studies performed in the context of PACT focused on ruthenium(II) polypyridines and related heavy metal complexes. Herein, we report a first-row transition metal complex, in which photoinduced dissociation and spontaneous recoordination of a ligand unit occurs. Two scorpionate-type tridentate chelates provide an overall six-coordinate arylisocyanide environment for chromium(0). Photoexcitation causes decoordination of one of these six ligating units and coordination of a solvent molecule, at least in tetrahydrofuran and 1,4-dioxane solvents, but far less in toluene, and below detection limit in cyclohexane. Transient UV-vis absorption spectroscopy and quantum chemical simulations point to photoinduced ligand dissociation directly from an excited metal-to-ligand charge-transfer state. Owing to the tridentate chelate design and the substitution lability of the first-row transition metal, recoordination of the photodissociated arylisocyanide ligand unit can occur spontaneously on a millisecond time scale. This work provides insight into possible self-healing mechanisms counteracting unwanted photodegradation processes and seems furthermore relevant in the contexts of photoswitching and (photo)chemical information storage.

Structural behaviour of reinforced concrete beams with self-healing cover zone as lost formwork

This study investigates the structural behaviour and self-healing performance of hybrid reinforced concrete (RC) beams, enhanced with a 1.5-cm-thick self-healing cover composed of bacteria-embedded strain hardening cementitious composite (SHCC), for its potential in crack width control and crack healing. The research focuses on the performance under both flexural and shear loading, examining aspects such as load-bearing capacity, surface crack pattern, crack propagation between layers, and healing effectiveness. Results demonstrate the successful activation of the healing function, alongside improvements in structural performance. Under flexural loading, hybrid beams exhibited greater load-bearing capacity and significantly improved crack control ability. The maximum crack width of the hybrid beams exceeded 0.3 mm at 124.7 kN load, whereas in the control beam the largest crack exceeded 0.3 mm at only 59.8 kN load. Under shear loading, while the influence of the cover on structural capacity was minimal, it notably improved post-peak ductility and energy dissipation. Interface delamination was not observed in both cases. The results of the current study demonstrate the potential of delivering the self-healing mechanism precisely where it is most needed, which presents a scalable and economically viable strategy for integrating self-healing technology into standard construction practices.

Microscopic Mechanisms of Self-Healing in Polymers Revealed by Molecular Simulations and Machine Learning

Microscopic Mechanisms of Self-Healing in Polymers Revealed by Molecular Simulations and Machine Learning

The synergistic effect of microorganisms and multiple admixtures on improving the self-healing of cracks in biogenic mortar exposed to different marine environments

Existing research has inadequately addressed the synergistic effects of microorganisms and admixtures in promoting self-healing behavior and mechanisms of cracks in marine environments, including the atmospheric zone, tidal-splash zone, and submerged zone. This study primarily involved the incorporation of multiple admixtures and microorganisms into cement to prepare two types of biogenic mortars: Bacillus pasteurii-based mortar (BPM) and Bacillus subtilis-based mortar (BSM), with ordinary mortar (OM) serving as the control group. The mechanical properties, electrical flux, and pore structure of the mortars were investigated. Additionally, the self-healing behavior and mechanisms of cracks were studied under atmospheric, tidal-splash, and submerged conditions. The results indicate that with increasing curing age, the synergistic effect of admixtures and microorganisms continuously refined the pore structure of the specimens and enhanced their flexural strength, compressive strength, and resistance to chloride ion penetration. The atmospheric environment was found to be unfavorable for the self-healing of cracks in the specimens. However, in the submerged and tidal-splash zones, the combined action of microorganisms and admixtures led to more pronounced self-healing phenomena in the biogenic mortars compared to OM. Particularly, the self-healing effect of BSM cracks was more pronounced in the tidal-splash zone, with a 100% self-healing efficiency observed after 53 days. This was attributed to the ability of microorganisms in the tidal-splash zone to induce calcium carbonate precipitation on the surface of cracks in admixture-modified cementitious materials, thereby reducing the penetration of seawater, CO2, and O2 into the cracks, lowering the carbonation reaction of Ca(OH)2 crystals, and reducing the formation of brucite crystals inside the cracks, consequently enhancing the water permeability resistance of the specimens. These research findings hold significant engineering implications for improving the durability and service life of coastal self-healing concrete structures.

Cross-scale modeling of microencapsulated self-healing composite with multiphase medium and their damage competition behavior

Constructing a high-fidelity cross-scale numerical model is the primary challenge in the multiscale analysis of multiphase medium composites.The Discrete Element Method is used in this study to build a three-medium multiscale numerical model. Further, the dynamic damage problem of microcapsules and the damage competition issues are investigated. The results indicate that (1) The damage evolution process, the location of maximum damage, and the final damage pattern of microcapsule embedded in the matrix and exposed to the ideal environment differed considerably. (2) The effect of microcapsule volume fraction on the mechanical strength of the matrix in self-healing composites is not linearly negatively correlated, but instead, there is a non-linear relationship, which is highly dependent on the strength ratio of the microcapsule to the matrix. (3) In self-healing composites, damage competition between the microcapsules and the matrix has a decisive influence on triggering the self-healing mechanism. (4) To obtain a better self-healing effect, the microcapsule volume fraction should not exceed 1.5 %, and the mechanical strength pre-maintenance should not be more than 95 % of the failure strength. The multiphase medium & multiscale analysis method proposed in this study also provides a new approach for visualizing the progressive dynamic damage problem in self-healing composites.

Evolution of self-healing performance of UHPC exposed to aggressive environments and cracking/healing cycles

This paper investigates the resilience of UHPC's self-healing capabilities under aggressive environmental conditions and cracking/healing cycles. UHPC specimens ‘with a double-edged wedge splitting geometry were made, incorporating a commercial crystalline admixture (Penetron Admix®). The evaluation of UHPC's healing capacity involved subjecting pre-cracked samples to three different water immersion conditions: tap water, saltwater, and geothermal water. The closure of cracks during different curing periods was meticulously recorded using optical microscopy. Furthermore, specialized tests, including ultrasonic pulse velocity (UPV) measurements and splitting tensile tests, were conducted to quantify the recovery of mechanical properties. The results reveal that extended exposure results in a gradual closure of cracks, where salt water and geothermal water exhibit lower self-healing capabilities. Self-healing improves after the 1st crack/self-healing cycle but decline rapidly after the 2nd cycle. Mechanical property is strongly correlated with the extent of self-healing, and all samples display varying degrees of stiffness recovery, with the most pronounced recovery occurring after the 1st cycle. However, following the 2nd cycle, the stiffness recovery values decrease due to repeated loading, resulting in increased damage and a reduced number of reactive particles, thereby compromising self-healing and stiffness recovery. Despite enduring multiple instances of crack damage, UHPC samples still exhibit notable toughness recovery, underscoring the enduring efficacy of the self-healing mechanism even in challenging conditions.

Investigation of the inner microstructure of composite materials during their densification by scanning electron microscopy – LSM:YSZ electrode case study

An understanding of the high-temperature processes, such as sintering, remains a challenge despite its paramount importance, and has yet to be achieved by the scientific community. Scanning electron microscopy is a valuable technique for investigating morphological changes, including elemental composition, by means of an energy-dispersive X-ray detector associated with these processes, with high resolution in-situ. Historically, this technique has been limited to experiments conducted at ambient temperature. However, by integrating scanning electron microscopy with a MEMS® heating chip, this limitation can be overcome, enabling the study of solid-state processes at temperatures of up to 1 200 °C. This study demonstrates one potential application of in-situ scanning electron microscopy – the densification of La1-xSrxMnO3-δ : (ZrO2:Y2O3) composite. This material, employed as an oxygen electrode in solid oxide cells, exhibits a complex microstructure. Achieving a balance between effective particle interconnection, ensuring high electric conductivity, and efficient mass transport through its porous structure is crucial. A comprehensive understanding of microstructure and surface composition evolution during the sintering process is vital to addressing trade off when optimizing densification conditions. It was shown that the densification of La1-xSrxMnO3-δ : (ZrO2:Y2O3) composite occurs in two steps. At 900 °C a significant additional porosity emerged due to the La1-xSrxMnO3-δ phase shrinkage (densification). The main densification process at 1 150 °C then acts as a self-healing mechanism, leading to the formation of a well-interconnected microstructure. Interparticle ligament formation is exclusively induced by the La1-xSrxMnO3-δ phase. Notably, no common degradation processes, such as La2Zr2O7 formation, were observed under the experimental conditions employed. This study underscores the promise of scanning electron microscopy with a heating chip extension for in-situ investigations pertinent to various high-temperature technologies.

Self-Healing Hydrogel Bioelectronics.

Hydrogels have emerged as powerful building blocks to develop various soft bioelectronics because of their tissue-like mechanical properties, superior bio-compatibility, the ability to conduct both electrons and ions, and multiple stimuli-responsiveness. However, hydrogels are vulnerable to mechanical damage, which limits their usage in developing durable hydrogel-based bioelectronics. Self-healing hydrogels aim to endow bioelectronics with the property of repairing specific functions after mechanical failure, thus improving their durability, reliability, and longevity. This review discusses recent advances in self-healing hydrogels, from the self-healing mechanisms, material chemistry, and strategies for multiple properties improvement of hydrogel materials, to the design, fabrication, and applications of various hydrogel-based bioelectronics, including wearable physical and biochemical sensors, supercapacitors, flexible display devices, triboelectric nanogenerators (TENGs), implantable bioelectronics, etc. Furthermore, the persisting challenges hampering the development of self-healing hydrogel bioelectronics and their prospects are proposed. This review is expected to expedite the research and applications of self-healing hydrogels for various self-healing bioelectronics.

Synergistic Self-Healing Enhancement in Multifunctional Silicone Elastomers and Their Application in Smart Materials.

Organosilicon polymers (silicones) are of enduring interest both as an established branch of polymer chemistry and as a segment of commercial products. Their unique properties were exploited in a wide range of everyday applications. However, current silicone trends in chemistry and materials engineering are focused on new smart applications, including stretchable electronics, wearable stress sensors, protective coatings, and soft robotics. Such applications require a fresh approach to methods for increasing the durability and mechanical strength of polysiloxanes, including crosslinked systems. The introduction of self-healing options to silicones has been recognized as a promising alternative in this field, but only carefully designed multifunctional systems operating with several different self-healing mechanisms can truly address the demands placed on such valuable materials. In this review, we summarized the progress of research efforts dedicated to the synthesis and applications of self-healing hybrid materials through multi-component systems that enable the design of functional silicon-based polymers for smart applications.

Temperature-dependent synergistic self-healing in thermoplastic-thermoset blends: Unraveling the role of thermoplastics and dynamic covalent networks

Two different self-healing approaches are studied in this work to analyze the possible contribution of each of the self-healing mechanisms at different temperatures and the possible synergetic effects between them. Thermal and mechanical properties were differently affected by the addition of each of the thermoplastic polymers. This was caused by different phase separations induced during the curing reaction in terms of size and number of the thermoplastic phase domains dispersed within the epoxy matrix and due to the different amounts of thermoplastic polymer that remain solved in the matrix. When using the vitrimeric matrix, phase separation only occurred at the nanometer scale when utilizing poly(bisphenol-A-co-epichlorohydrin) (PBAE) as a thermoplastic agent or higher contents of polycaprolactone (PCL).Self-healing capabilities showed a strong dependence on the temperature used and the type of crack. Low temperatures allowed the thermoplastic phase to flow and fill partially the cracks with moderate levels of self-healing which were only available when phases were separated. Higher temperatures allowed dynamic bonds to induce material healing reaching very high efficiencies but, more importantly, a synergic effect was observed when material was removed from the cracks. In these cases, the flow of the thermoplastic phase filled better the crack and there was an enhanced cooperation between the two healing mechanisms. At higher self-healing temperatures, materials with nanometric size phase separation enabled greater self-healing efficiencies (above 90 %) due to the vitrimeric self-healing capability while the thermoplastic phase helped fill the gaps due to material removal.

Depth-dependent self-healing capacity and mechanism of cracked fiber-reinforced concrete by bacterial community

The utilization of bacteria to facilitate the healing of engineered cementitious composites (ECC) has been an interesting approach. However, the commonly used microorganism has been the Bacillus strain, effective in forming bacterial calcium carbonate well at crack top surface but is less favorable for deep-crack healing due to its aerobic nature. In this study, a novel method was introduced that incorporated bacterial community to enhance the self-healing behavior along the depth, breaking away from the traditional single bacteria pattern. The depth-dependent healing ratio of for tire polymer (TP) fiber reinforced ECC using bacterial community (i.e., multiple strains mainly including 15 types of bacteria) was investigated. Healing behaviour was comprehensively evaluated in terms of crack-depth healing, water absorption ratio, and axial strength recovery. Micro-quantitative and macro-quantitative analysis of bacterial products at different depths and the entire crack were conducted through mapping and thermogravimetry. The results revealed the self-healing mechanisms and superiority of the TP-ECC with the bacterial community. Along the crack depth, the healing behaviour of TP-ECC incorporating bacterial community was superior to that of the traditional single bacteria approach. Bacterial communities had an advantage in axial tensile strength recovery compared to single bacteria. It was proved to be technically feasible to enhance self-healing capacity of the TP-ECC when incorporating a bacterial community.

Biomineralization in cement and concrete research

Biomineralization refers to the biological processes through which living organisms produce minerals. In recent years, biomineralizing microorganisms have been used to stabilize soil or to impart a self-healing or self-sealing mechanism to damaged cement and concrete materials. However, applications of biominerals in cement and concrete research can extend far beyond these applications. This article focuses on the biomineralization of calcium carbonate (CaCO3) and silicon dioxide (SiO2) and their past, present, and future potential applications in cement and concrete research. First, we review the mechanisms of CaCO3 and SiO2 biomineralization and the micro- and macroorganisms involved in their production. Second, we showcase the wide array of biomineral architectures, with an explicit focus on CaCO3 polymorphs and SiO2 morphologies found in nature. Third, we briefly summarize previous applications of CaCO3 and SiO2 biomineralization in cement and concrete research. Finally, we discuss emerging applications of biominerals in cement and concrete research, including mineral admixtures or raw meal for portland cement production, as well as other applications that extend beyond self-healing.

Decellularized fetal collagen exhibits chondroinductive potential for bone marrow-derived mesenchymal stem cells by enhancing glycosaminoglycan production

Articular cartilage repair is challenging due to limited access to reparative cells and a lack of self-healing mechanisms. Bone marrow-derived mesenchymal stem cells (BM-MSCs) are a promising therapeutic option, but their tendency to form fibrocartilage during repair necessitates the optimization of culture conditions. To overcome this limitation, optimizing in-vitro culture conditions with biological coating using extracellular matrix-derived proteins has been efficient in mimicking in-vivo cellular behavior. Fetal cartilage, with abundant collagen, proteoglycans and glycosaminoglycans has emerged as a potential source for cartilage repair. No studies have so far evaluated the effect of fetal cartilage-derived collagen on BM-MSCs. This study aimed to evaluate the chondro-inductive potential of decellularized collagen derived from fetal cartilage, which was used as a coating material for expansion of BM-MSCs. The extraction of fetal collagen was performed from the tibiofemoral joint of a 36+4-week gestational age fetus. The freeze-dried collagen type II was reconstituted at a concentration of 10μg/ml and used to coat the culture flasks. Passage 3 BM-MSCs were divided into two groups: a) standard expansion medium (BM-MSCs) and b) collagen-coated plasticware (collagen-coated BM-MSCs). Growth kinetics, surface markers, gene expression, and differentiation potential were assessed. The decellularized collagen coating did not influence the growth kinetics, surface marker and gene expression of BM-MSCs. However, it positively influenced GAG accumulation and collagen type II deposition. Further studies utilizing in-vivo models are warranted to evaluate the potential of collagen-coated BM-MSCs and exploit their adjuvant effect on chondrogenesis.

Polymer Composites in 3D/4D Printing: Materials, Advances, and Prospects.

Additive manufacturing (AM), commonly referred to as 3D printing, has revolutionized the manufacturing landscape by enabling the intricate layer-by-layer construction of three-dimensional objects. In contrast to traditional methods relying on molds and tools, AM provides the flexibility to fabricate diverse components directly from digital models without the need for physical alterations to machinery. Four-dimensional printing is a revolutionary extension of 3D printing that introduces the dimension of time, enabling dynamic transformations in printed structures over predetermined periods. This comprehensive review focuses on polymeric materials in 3D printing, exploring their versatile processing capabilities, environmental adaptability, and applications across thermoplastics, thermosetting materials, elastomers, polymer composites, shape memory polymers (SMPs), including liquid crystal elastomer (LCE), and self-healing polymers for 4D printing. This review also examines recent advancements in microvascular and encapsulation self-healing mechanisms, explores the potential of supramolecular polymers, and highlights the latest progress in hybrid printing using polymer-metal and polymer-ceramic composites. Finally, this paper offers insights into potential challenges faced in the additive manufacturing of polymer composites and suggests avenues for future research in this dynamic and rapidly evolving field.

Nanoceramic-based coatings for corrosion protection: a review on synthesis, mechanisms, and applications.

Corrosion is a pervasive issue with significant economic and safety implications across various industries. Nanoceramic-based coatings have emerged as a promising solution for corrosion protection due to their unique properties and mechanisms. This review aims to comprehensively examine the synthesis, mechanisms, and applications of nanoceramic-based coatings for corrosion protection. The review begins by highlighting the importance of corrosion protection and its impact on different industries. It introduces nanoceramic-based coatings as a potential solution to address this challenge. The objective is to provide a thorough understanding of the synthesis methods, mechanisms, and applications of these coatings. The fundamental principles of corrosion and different corrosion mechanisms are discussed, along with the limitations of traditional corrosion protection methods. The review emphasizes how nanoceramic-based coatings can overcome these limitations and provide superior corrosion resistance. Various synthesis methods, including sol-gel, electrodeposition, and physical vapor deposition, are described in detail, along with the factors influencing the synthesis process. Recent advancements and innovations in nanoceramic coating synthesis techniques are also highlighted. This looks at how coatings made with tiny ceramic particles protect against corrosion. It examines the importance of small-scale details like particle size, shape, and what the particles are made of. The formation of passive layers, self-healing mechanisms, and barrier properties of nanoceramic coatings are explained. The diverse applications of nanoceramic coatings for corrosion protection in industries such as automotive, aerospace, and marine are comprehensively discussed. Case studies and examples demonstrating the significant corrosion resistance and improved performance achieved with nanoceramic coatings are presented.