Self-healing Capacity Research Articles

Mechanical activation assisted of biobased encapsulated rejuvenators to promote asphalt self-healing

This research aimed to evaluate the effect of the addition of biobased encapsulated rejuvenators on the self-healing properties of asphalt mixtures. With this objective, polynuclear capsules were synthesised using alginate biopolymer as encapsulating material and sunflower oil as rejuvenator. The capsules were physically and mechanically characterised by optic and scanning electron microscopy techniques as well compressive tests. Four types of semi-dense asphalt mixtures were manufactured, varying in capsule content: 0.0%, 0.125%, 0.25%, and 0.5%wt. The self-healing properties of each mixture were evaluated based on mechanical cracking, capsule activation, and healing level quantification processes. A new confined uniaxial compression test was developed for capsule activation. The self-healing capacity of the asphalt mixtures was determined under force and fracture energy criteria. Statistically significant differences in the healing variables were analysed through one-way ANOVA and Tukey post-hoc tests. The main results showed that the capsules presented regular spherical morphology and high mechanical stability to resist the mixing process at high temperature. The new activation approach effectively activated the alginate-based capsules inside the asphalt mixtures promoting their self-healing. Force and energy crack-healing criteria improved with the addition of capsules in the asphalt matrix, with healing values being higher for the force criterion than those for the energy one. Finally, the addition of capsules in a content equal or greater than 0.25%wt. significantly improved the self-healing properties of the asphalt mixtures.

Spider-Silk-Inspired Tough, Self-Healing, and Melt-Spinnable Ionogels.

As stretchable conductive materials, ionogels have gained increasing attention. However, it still remains crucial to integrate multiple functions including mechanically robust, room temperature self-healing capacity, facile processing, and recyclability into an ionogel-based device with high potential for applications such as soft robots, electronic skins, and wearable electronics. Herein, inspired by the structure of spider silk, a multilevel hydrogen bonding strategy to effectively produce multi-functional ionogels is proposed with a combination of the desirable properties. The ionogels are synthesized based on N-isopropylacrylamide (NIPAM), N, N-dimethylacrylamide (DMA), and ionic liquids (ILs) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]). The synergistic hydrogen bonding interactions between PNIPAM chains, PDMA chains, and ILs endow the ionogels with improved mechanical strength along with fast self-healing ability at ambient conditions. Furthermore, the synthesized ionogels show great capability for the continuous fabrication of the ionogel-based fibers using the melt-spinning process. The ionogel fibers exhibit spider-silk-like features with hysteresis behavior, indicating their excellent energy dissipation performance. Moreover, an interwoven network of ionogel fibers with strain and thermal sensing performance can accurately sense the location of objects. In addition, the ionogels show great recyclability and processability into different shapes using 3D printing. This work provides a new strategy to design superior ionogels for diverse applications.

Healing capacity of Ultra High Performance Concrete under sustained through crack tensile stresses and aggressive environments

This study investigates the self-healing capabilities of Ultra-High Performance Concrete (UHPC) under the combined influence of mechanical and environmental factors. Specifically, it delves into the long-term self-healing process in pre-cracked UHPC samples that endure continuous sustained tensile stresses across the cracks and are exposed to aggressive environmental conditions for one year. The results reveal that UHPC with narrow cracks exhibits a higher degree of self-healing, especially when exposed to tap water, where its self-healing capacity is most pronounced and improves with extended exposure. Furthermore, these self-healing mechanisms contribute to the restoration of mechanical properties and prevent chloride ion penetration by sealing the cracks. While a reduced level of self-healing is observed in saltwater and geothermal water exposure, prolonged exposure mitigates the inhibitory effect of aggressive ions on self-healing. SEM and EDS results provide evidence that samples subjected to extended exposure to salt and geothermal water exhibit a substantial presence of self-healing product-CaCO3. This study not only emphasizes that pre-cracked UHPC, when exposed to both mechanical stresses and aggressive environments, can maintain excellent durability and mechanical strength due to its self-healing effect but also lays the foundation for evaluating the self-healing potential of cement-based materials under conditions representative of real-world structural scenarios. This is essential for advancing the integration of self-healing advantages into design concepts and performance-based verification approaches.

3D printing viscoelastic hydrogel-based scaffolds with a swelling-dependent gate for cartilage injury regeneration

Regeneration of articular cartilage remains a great challenge due to its poor self-healing capacity and weak stability. The microfracture surgery (MF) can provide bone marrow mesenchymal stem cells (BMSCs) and is commonly used in clinical practice, but its therapeutic effect is still limited by the lack of effective adhesion matrix and the uncontrollable tendency to develop fibrosis and even mineralization. In this study, a small molecular drug-loaded viscoelastic hydrogel-based 3D printing bilayer scaffold with a swelling-dependent gate was successfully developed to address these limitations. The scaffold consisted of a lower layer with a smaller pore size and an upper matrix with larger pore size. The former acted as a swelling-dependent gate to switch pore size, which initially was on-state allowing the infiltration of BMSCs, and eventually transformed into off-state serving as a barrier blocking excessive blood support from the bone marrow after swelling-induced closure of pores. This barrier structure cooperated with fatty acid inhibitor-suppressed hypertrophy of neo-cartilage matrix. The latter provided a biocompatible and viscoelastic matrix to guide MSCs toward stable chondrogenic commitment. By integrating structural design with the inhibitor, the bilayer scaffold provides a promising platform for future clinical applications of MF surgery in cartilage regeneration.

Self-Configuration and Self-Healing Framework Using Extreme Gradient Boosting (XGBoost) Classifier for IoT-WSN

In most Internet of Things (IoT) systems, Quality of service (QoS) must be confirmed with respect to the requirement of implementation domain. The dynamic nature of the IoT surroundings shapes it to complicate the fulfilment of these commitments. A wide range of unpredictable events endanger the quality of service. While execution the self-adaptive schemes handle with system’s unpredictable. In IoT-based Wireless Sensor Networks (WSNs), the significant self-management objectives are self-configuration (SC) and self-healing (SH). In this paper, Self-Configuration and Self-healing Framework using an extreme gradient boosting (XGBoost) Classifier are proposed. In this framework, the IoT traffic classes are categorized as several types under XGBoost classifier. In SC phase, the IoT devices are self-configured by allocating various transmission slots, contention access period (CAPs) on the basis of its categories with priorities. In SH phase, the source node cardinally establishes a confined route retrieval method if the residual power in-between node is truncated or the node has displaced far away. The proposed framework is executed in NS-2 and the results exhibit that the proposed framework has higher packet delivery ratio with reduced packet drops and computational cost. Therefore, the proposed approach has attained 24.7%, 28.9%, 12.75% higher PDR, and 16.8%, 19.87%, and 13.7% higher residual energy than the existing methods like Self-Healing and Seamless Connectivity using Kalman Filter among IoT Networks (SH-SC-KF-IoT), Provenance aware run-time verification mechanism for self-healing IoT (PA-RVM-SH-IoT), and Fully Anonymous Routing Protocol and Self-healing Capacity in Unbalanced Sensor Networks (FARP-SC-USN) methods, respectively.

Full-thickness osteochondral defect repair using a biodegradable bilayered scaffold of porous zinc and chondroitin sulfate hydrogel

The regeneration of osteochondral tissue necessitates the re-establishment of a gradient owing to the unique characteristics and healing potential of the chondral and osseous phases. As the self-healing capacity of hyaline cartilage is limited, timely mechanical support during neo-cartilage formation is crucial to achieving optimal repair efficacy. In this study, we devised a biodegradable bilayered scaffold, comprising chondroitin sulfate (CS) hydrogel to regenerate chondral tissue and a porous pure zinc (Zn) scaffold for regeneration of the underlying bone as mechanical support for the cartilage layer. The photocured CS hydrogel possessed a compressive strength of 82 kPa, while the porous pure Zn scaffold exhibited a yield strength of 11 MPa and a stiffness of 0.8 GPa. Such mechanical properties are similar to values reported for cancellous bone. In vitro biological experiments demonstrated that the bilayered scaffold displayed favorable cytocompatibility and promoted chondrogenic and osteogenic differentiation of bone marrow stem cells. Upon implantation, the scaffold facilitated the simultaneous regeneration of bone and cartilage tissue in a porcine model, resulting in (i) a smoother cartilage surface, (ii) more hyaline-like cartilage, and (iii) a superior integration into the adjacent host tissue. Our bilayered scaffold exhibits significant potential for clinical application in osteochondral regeneration.

Riboflavin mediated UV crosslinking of chitosan-gelatin cryogels for loading of hydrophobic bioactive compounds

Chitosan-gelatin cryogels with good loading capacity of hydrophobic compounds were successfully obtained by UV-induced crosslinking. Using riboflavin as photoinitiator was a suitable alternative to classical carbodiimide crosslinking in obtaining carrier matrices for bioactive hydrophobic compounds. Chitosan had a double role, acting both as a base polymer for the hydrogel network and as co-initiator in riboflavin photo-crosslinking. This co-initiator role of chitosan is due to its electron donor capacity, being well known as a Lewis base type macromolecule. The rheological behaviour of the chitosan-gelatin hydrogel precursor solutions was greatly influenced by riboflavin addition as well as by UV irradiation. As a consequence, the temperature of the sol-gel transition during cooling decreased to 25.5 °C. Compared with classical carbodiimide crosslinking, UV irradiation lead to gels with increased network stability, enhanced elastic behaviour, higher structural strength and almost total stress recovery yield (99 %), the latter indicating self-healing capacity. The cryogels manifested pH responsive swelling, this being highest at close to neutral pH of 7.4. Although hydrophilic in nature, the chitosan-gelatin cryogels crosslinked under the combined effect of riboflavin and UV exposure possess the necessary chemical functionality and morphology that allowed successful embedding of hydrophobic clove essential oil. This was loaded by immersion or fumigation and imparted antioxidant activity to the polymeric matrix.

Prim-O-glucosylcimifugin ameliorates aging-impaired endogenous tendon regeneration by rejuvenating senescent tendon stem/progenitor cells

Adult tendon stem/progenitor cells (TSPCs) are essential for tendon maintenance, regeneration, and repair, yet they become susceptible to senescence with age, impairing the self-healing capacity of tendons. In this study, we employ a recently developed deep-learning-based efficacy prediction system to screen potential stemness-promoting and senescence-inhibiting drugs from natural products using the transcriptional signatures of stemness. The top-ranked candidate, prim-O-glucosylcimifugin (POG), a saposhnikovia root extract, could ameliorate TPSC senescent phenotypes caused by long-term passage and natural aging in rats and humans, as well as restore the self-renewal and proliferative capacities and tenogenic potential of aged TSPCs. In vivo, the systematic administration of POG or the local delivery of POG nanoparticles functionally rescued endogenous tendon regeneration and repair in aged rats to levels similar to those of normal animals. Mechanistically, POG protects TSPCs against functional impairment during both passage-induced and natural aging by simultaneously suppressing nuclear factor-κB and decreasing mTOR signaling with the induction of autophagy. Thus, the strategy of pharmacological intervention with the deep learning-predicted compound POG could rejuvenate aged TSPCs and improve the regenerative capacity of aged tendons.

A Dual Reversible Cross-Linked Hydrogel with Enhanced Mechanical Property and Capable of Proangiogenic and Osteogenic Activities for Bone Defect Repair.

The clinical treatment of bone defects presents ongoing challenges. One promising approach is bone tissue engineering (BTE), wherein hydrogels have garnered significant attention. However, the application of hydrogels in BTE is severely limited due to their poor mechanical properties, as well as their inferior proangiogenic and osteogenic activities. To address these limitations, our develop a dual cross-linked alendronate (ALN)-Ca2+ /Mg2+ -doped sulfated hyaluronic acid (SHA@CM) hydrogel, using a one-step mixing injection molding method known as "three-in-one" approach. This approach enabled the simultaneous formation of Schiff-Base crosslinking and electric attraction-based crosslinking within the hydrogel. The Schiff-Base crosslinking contributed to the majority of the hydrogel's mechanical strength, while the electric attraction-based crosslinking served as a release reservoir for Ca2+ /Mg2+ and ALN, promoting enhanced osteogenic activities and providing additional mechanical reinforcement to the hydrogel. These experimental data demonstrates several favorable properties of the SHA@CM hydrogel, including satisfactory injectability, rapid gelation, self-healing capacity, and excellent cytocompatibility. Moreover, the presence of sulfated groups and Mg2+ within the SHA@CM hydrogel exhibited pro-angiogenic effects, while the controlled release of nanoparticles formed by Ca2+ /Mg2+ and ALN further enhanced the osteogenesis of the hydrogel. Overall, these results indicate that the SHA@CM hydrogel holds significant potential for the clinical translation of BTE.

New recyclable and self-healing elastomer composites using waste from toner cartridges

Product recycling reintroduces what is discarded as waste and minimizes the environmental impact on our society. Among the different types of waste from electrical and electronic equipment, toner recycling often falls short, downcycling plastic components. This study introduces an innovative approach in which waste parts from toner cartridges are valorized to develop (recyclable and) self-healing elastomeric composite materials. The synergy between carboxylated nitrile rubber (XNBR) as the elastomeric phase and high-impact poly (styrene) (HIPS) as the thermoplastic phase derived from toner cartridge waste was explored and optimized. This combination resulted in the creation of a thermoplastic elastomer exhibiting robust mechanical properties and self-healing capabilities with a tensile strength of 6.6 ± 0.2 MPa and a temperature-driven mechanical recovery of 100%. Furthermore, the capacity of toner powder, an integral component of waste, to act as a reinforcing filler was confirmed, with a 50% increase in mechanical strength compared with the unfilled composite. Moreover, an increase in toner content (up to 20 phr) resulted in an optimal balance between tensile strength and self-healing capacity, surpassing the traditional antagonism between these properties. As a result, this research opens a new pathway in the field of self-healing composites and suggests a practical and environmentally friendly approach for managing electronic waste, effectively supporting the principles of Circular Economy.

Electrical impedance-based evaluation of self-healing degree in cement composites with biological admixtures

The present study aims to explore the potential of using electrical impedance measurements for evaluating the self-healing degree in cement composites incorporating biological admixtures. Four different carbon-based conductive fillers such as carbon black, carbon nanotube, carbon fiber, and graphene were employed in the cementitious composites to ensure the electrical conductivity in the composite samples. The applicability of carbon-based fillers for evaluating self-healing degree was assessed by comparing the present electrical impedance-based evaluation with the self-healing degree quantitatively obtained from microscopic images and the regain in compressive strength. The samples containing carbon nanotube or graphene were shown to have satisfactory self-healing capacities, as evidenced by the restoration of electrical conductivity and the regain in compressive strength.

Preparation and characterization of polyurethane-modified asphalt containing dynamic covalent bonds

Self-healing behavior of binder has important potential for promoting low-carbon service and extending service life of asphalt pavement. A novel self-healing polyurethane modified asphalt with dynamic covalent bonds was prepared in this work. The chemical structure, thermal-oxygen stability, rheological properties, fatigue properties and self-healing capability of polyurethane modified asphalt with dynamic covalent bonds were systemically investigated through Fourier infrared spectrum test, thermal gravimetric test, dynamic shear rheology test, linear amplitude sweep(LAS) test and multiple fatigue-healing-fatigue test. The result indicates disulfide dynamic covalent bond and oxime urethane dynamic covalent bond were successfully introduced into polyurethane cross-linking structure in asphalt, and the thermal-oxygen stability of asphalt has a significant increase after modification under the environmental conditions of construction and service. Rheological properties analysis suggests the introduction of dynamic covalent bonds is beneficial to improve the low-temperature toughness of polyurethane modified asphalt, and enhances its low-temperature cracking resistance. LAS analysis indicates the fatigue life of polyurethane modified asphalt can also be lengthened by over 70% at different strain levels(1.5%, 2.5% and 5%) with the introduction of dynamic covalent bonds, which is attributed to the excellent conformation adjustment ability and stress dissipation ability of dynamic cross-linking structure in asphalt. The multiple fatigue-healing-fatigue test shows the self-healing capability of polyurethane modified asphalt has an improvement with the introduction of dynamic covalent bonds, especially at the later stage with serious fatigue damage, and oxime urethane dynamic covalent bond shows the better contribution effect as compared with disulfide bond. This is due to the reversible fracture-rearrangement characteristics of dynamic covalent bonds. This work provides a new idea for improving the self-healing capacity and rheological properties of binder, reducing the frequency of pavement maintenance and extending the pavement service life.

Non-destructive tests to evaluate the self-healing capacity for a 3D printing ECC material

The conventional construction sector is the one that generates CO2 emissions, as well as waste generation. Faced with this problem, 3D printing has positioned itself as an alternative. Therefore, in recent years, interest in cement-based material for 3D printing has increased in the construction sector as a partial or total replacement for conventional construction methods. However, 3D printing, despite being a novel technique, has some drawbacks, one of the biggest threats being the generation of cracks or microcraks that appears by the transport or the design of the 3D printed figures. These cracks can cause major structural and durability problems in the final application. Numerous materials have been developed to meet the requirements of 3D printing. Nevertheless, there are few publications on materials that are able to be printed in 3D and have an autogenous self-healing capacity. Therefore, in this study, we are working on the development of an Engineered Cementitious Composites (ECC) material, also known as Strain Hardening Cementitious Composites (SHCC) that has the characteristics to achieve structural integrity, durability, reliability, and robustness of 3D printing (ECC-A3D).This paper describes the experimental procedure of an ECC material in two different environments (at room temperature, 34 ± 2% RH and 20 ± 2 °C, and curing chamber 98 ± 2% RH and 20 ± 2 °C). The characterization of the ECC-A3D material is studied by fresh properties, consistency, open time, extrudability and buildability and hardened properties, compressive and flexural strength up to 90 days. A 3D printing material has been achieved that reaches a value of 16.54 MPa and 50.82 MPa in flexural and compression at the hydration age of 28 days at room temperature, and 17.13 MPa and 58.26 MPa in curing chamber. The self-healing behavior of ECC is evaluated by three non-destructive methods: absorption and sorptivity tests, optical microscopy, and micro-computed tomography, confirming a reduction in absorption and crack healing during hydration time.

Characterization and role analysis of bacteria types in self-healing behaviour of cemented paste backfill

A common approach to enhance the self-healing behaviour of cracked backfill is through the addition of carriers, but this practice can potentially disrupt the overall performance of the backfill and pose environmental concerns. Overcoming the limitations of traditional carrier-based methods to improve self-healing efficiency has been a challenging task. This study proposed an environmentally friendly approach to enhance the healing ratio of cracked backfill without the need for additional carriers. Specifically, a mixture of aerobic and anaerobic bacteria was pre-embedded in polypropylene-fiber reinforced backfill. The self-healing capacity of the cracked backfill was systematically evaluated in terms of crack width and area healing efficiency, strength recovery ratio, permeability coefficient, and water absorption. The results showed that the incorporation of mixed bacteria in the backfill resulted in an area healing ratio of 44.71% and a strength recovery ratio of 30.88%. The mixed bacteria had a higher biomineralization ratio compared to the noted single strain, suggesting its enhanced capacity in self-healing. Also, the mixed bacteria exhibited higher sustainability in self-healing. These findings provide compelling evidence that the self-healing ratio of cracked backfill can be improved through a benign approach that only involves pre-embedding mixed bacteria without the use of additional carriers.

Multifunctional Janus-type self-healing MXene/polyionic liquid flexible sensor

Integration of electronic sensors with signal processing systems is important for artificial intelligence and intelligent robots. It requires mechanically robust, highly sensitive, and self-healing sensing materials that produce recognizable electrical changes in response to external stimuli. Here, we report a multifunctional Janus-type self-healing MXene/polyionic liquid-based flexible membrane for smart sensing. Flexible MXene-NH2@PIL material with self-healing capacity and high tensile properties was constructed by compounding functionalized MXene with polyionic liquid (PIL) with self-healing ability. Deposition of MXene-NH2 resulted in MXene-NH2@PIL with a unique Janus structure that exhibits a variation in the degree of hydrophilicity on both sides and a certain pH response. The material, which can be warmed to over 70 °C in 8 s, also has excellent photothermal conversion. The internal ionic and hydrogen bonding interactions ensure that it can repair damage at 60 °C. The flexible MXene-NH2@PIL sensor prepared from this material can produce significant signal changes in response to small deformations, such as knocks. The flexible MXene-NH2@PIL sensor can also be worn on the finger to detect the bending motion of the finger. This provides an idea for the preparation of self-healing flexible wearable sensors. This study explores the preparation of flexible self-healing sensors by combining the electron-conducting MXene material and ion-conducting PIL.

Assessing the potential application of bacteria-based self-healing cementitious materials for enhancing durability of wastewater treatment infrastructure

Wastewater treatment plants (WWTPs) around the world are mainly built using concrete. The continuous exposure to wastewater affects the durability of concrete structures and requires costly maintenance or replacement. Concrete production and repair represents ∼8% of the global anthropogenic CO2 emissions due to the use of cement, thus contributing to climate change. Developing a more sustainable cementitious material is therefore required for this vital health infrastructure. In this study, the feasibility of using bacteria-based self-healing (BBSH) cementitious materials for WWTPs is assessed by exposing BBSH mortar prisms to a continuous municipal wastewater flow and comparing their self-healing capacity to equivalent mortar prisms exposed to tap water. Microscopy imaging, water-flow tests and micro-CT analyses were performed to evaluate the self-healing efficiency of the mortar prisms, while SEM-EDX and Raman spectroscopy were used to characterise the healing products. Our work represents the first systematic study of the healing potential of BBSH in mortar exposed to wastewater. The results indicate that the purposely added bacteria are able to induce calcium carbonate precipitation when exposed to wastewater conditions. Moreover, if additional sources of calcium and carbon are embedded within the cement matrix, the rich bacterial community inherently present in the wastewater is capable of inducing calcium carbonate precipitation, even if no bacteria are purposely added to the mortar. The results of this study offer promising avenues for the construction of more sustainable wastewater infrastructure, with the potential of significantly reducing costs and simplifying the production process of BBSH concretes for this specific application.

On the use of non-destructive testing for the measurement of self-healing in lime-based mortars

The study of self-healing construction materials has increased in popularity over the last couple of decades. Nevertheless, most research has predominantly focused on cement-based materials and work on other type of binders such as lime-based mortars remains rather limited. Despite the multiple testing methods available to assess the efficacy of self-healing, these techniques are not always suitable for materials of different mechanical strengths and behavior. In order to further expand the knowledge on self-healing beyond the high-strength cement-based materials, self-healing has been studied on low-strength binders. Here it is shown how the use of non-destructive testing with ultrasonic pulse velocity (UPV) can help determine the self-healing capacity of low-strength mortars. A hydrated-lime:metakaolin mortar mix and cement mix were cast and damaged after 7 days of curing. The samples were damaged under compression using 70 % of the average compressive strength. Before and after damaging, the samples were tested by UPV and superficial cracks were studied by microscopy. The samples were then placed under wet-dry cycles of 1 h wet/23 h dry or submersion for 28 days and tested again. As healing proceeded, an increase in the UPV was observed. Microscopy measurements confirmed visually the self-healing of cracks in all samples. The mechanical strength of both formulations was similar after healing when compared to a non-damaged and non-healed sample. These results show the necessity for techniques that are tailored to the mechanical nature of the different studied materials and opens up the possibility of further investigating self-healing in a wider variety of construction materials.

A multifunctional hydrogel based on nature polysaccharide fabricated by Schiff base reaction

A multifunctional hydrogel derived from carboxymethyl chitosan (CMCS) and oxidized hyaluronic acid (OHA), was fabricated by Schiff base reaction between the amino groups of CMCS and aldehyde groups in OHA. The aldehyde groups of OHA were prepared through the oxidation of hydroxy groups of hyaluronic acid (HA) by NaIO4, and the oxidation degree of OHA can be adjusted by varying amount of NaIO4. Furthermore, the gelation time, mechanical strength, swelling and deswelling properties of gels are different with varying the concentration of precursor solution. This hydrogel shows an excellent swelling capacity of 6000 % for the abounded hydroxyl groups in chains. For the dynamic action of Schiff base action, it also showed a good self-healing capacity to be healed in three minutes around 25 °C. In addition, OHA-CMCS gel had good water or heating induced shape memory property. Moreover, hydrogels with complex structures were fabricated by 3D printing. In a word, the versatility of OHA-CMCS gel makes it could have a widely application for biomedical and 4D printing applications.

Hydrogel-assisted self-healing of biomineralized living building materials

Living building materials (LBMs) are an emergent class of structural materials that leverage the biomineralization capability of microorganisms within sand-hydrogel scaffolds to produce living, load-bearing structures. In this study, we produced LBMs using a physically crosslinkable sand-hydrogel scaffold and two microorganisms with different biomineralization pathways—Synechococcus sp. PCC 7002 (photosynthetic) and S. pasteurii (ureolytic)—and investigated their self-healing capacity. Our results reveal that both Synechococcus sp. PCC 7002 and S. pasteurii demonstrated exceptional viability within all LBMs for more than 20 days. Damaged LBMs containing Synechococcus sp. PCC 7002 exhibited 103% and 112% of their original compressive and flexural strengths, respectively, after three days of healing at 50% relative humidity (RH) (i.e., ambient conditions). In contrast, LBMs containing S. pasteurii exhibited 71% and 66% of their original compressive and flexural strengths, respectively, after three days of healing at 50% RH. The compressive and flexural strengths of all LBMs rebounded to 93–100% after seven days of healing at 50% RH. Data substantiate that the self-healing ability of the hydrogel plays a critical role in facilitating healing of LBMs, as evidenced by the 82–118% rebounds in compressive and flexural strengths by the sand-hydrogel scaffold alone after three or seven days of healing at 50% RH. Healing was less effective at 100% RH for all LBMs investigated herein.

A Simple and Effective Physical Ball-Milling Strategy to Prepare Super-Tough and Stretchable PVA@MXene@PPy Hydrogel for Flexible Capacitive Electronics.

Biomimetic flexible electronics for E-skin have received increasing attention, due to their ability to sense various movements. However, the development of smart skin-mimic material remains a challenge. Here, a simple and effective approach is reported to fabricate super-tough, stretchable, and self-healing conductive hydrogel consisting of polyvinyl alcohol (PVA), Ti3 C2 Tx MXene nanosheets, and polypyrrole (PPy) (PMP hydrogel). The MXene nanosheets and Fe3+ serve as multifunctional cross-linkers and effective stress transfer centers, to facilitate a considerable high conductivity, super toughness, and ultra-high stretchability (elongation up to 4300%) for the PMP hydrogel with. The hydrogels also exhibit rapid self-healing and repeatable self-adhesive capacity because of the presence of dynamic borate ester bond. The flexible capacitive strain sensor made by PMP hydrogel shows a relatively broad range of strain sensing (up to 400%), with a self-healing feature. The sensor can precisely monitor various human physiological signals, including joint movements, facial expressions, and pulse waves. The PMP hydrogel-based supercapacitor is demonstrated with a high capacitance retention of ≈92.83% and a coulombic efficiency of ≈100%.