Autonomous Healing Research Articles

A Versatile Microporous Design toward Toughened yet Softened Self-Healing Materials.

Realizing the full potential of self-healing materials in stretchable electronics necessitates not only low modulus to enable high adaptivity, but also high toughness to resist crack propagation. However, existing toughening strategies for soft self-healing materials have only modestly improves mechanical dissipation near the crack tip (ГD), and invariably compromise the material's inherent softness and autonomous healing capabilities. Here, a synthetic microporous architecture is demonstrated that unprecedently toughens and softens self-healing materials without impacting their intrinsic self-healing kinetics. This microporous structure spreads energy dissipation across the entire material through a bran-new dissipative mode of adaptable crack movement (ГA), which substantially increases the fracture toughness by 31.6 times, from 3.19 to 100.86 kJ m-2, and the fractocohesive length by 20.7 times, from 0.59 mm to 12.24 mm. This combination of unprecedented fracture toughness (100.86 kJ m-2) and centimeter-scale fractocohesive length (1.23 cm) surpasses all previous records for synthetic soft self-healing materials and even exceeds those of light alloys. Coupled with significantly enhanced softness (0.43 MPa) and nearly perfect autonomous self-healing efficiency (≈100%), this robust material is ideal for constructing durable kirigami electronics for wearable devices.

Polyetherimide copolymer film with room-temperature self-healing properties and high breakdown field strength

With the waste of resources caused by human activities, it has gradually become an increasingly prominent social problem. The development of self-healing polymers in the field of insulation has attracted widespread attention. Develop polymer matrices with efficient healing efficiency and sound insulation properties to achieve green and sustainable resource conservation. In addition, improving the dielectric properties of intrinsic self-healing matrices has been a hot topic. In this work, we developed a new PEI matrix-modified self-healing polymer substrate that provides a breakdown field strength of 240 kV/mm and self-healing properties at room temperature, this has significantly improved the dielectric properties over other previously reported self-healing polymers. In addition to the abovementioned performance, we found significant differences in thermodynamic behavior in the synthesized end-modified polymers. By dielectric characterization (LCR), the breakdown composite can be left at room temperature for 60 min, and the material can recover 80 % of the initial properties without external intervention(This is demonstrated by the fact that its DC conductivity at 60 min of autonomous healing was significantly changed from that of the freshly electrically pierced DC conductivity and remained around 5.38 × 10−11 S/cm for a longer period of time thereafter). The microscopic morphology of the modified PEI matrix was observed by scanning electron microscopy (SEM) and EDS surface elemental analysis, which further supports the existence of metal coordination structures. These findings can further deepen the thinking of self-healing dielectric composites. The work inspired by this may break the limits and take self-healing composite dielectric materials to a new height.

Tailoring of Self-Healable Polydimethylsiloxane Films for Mechanical Energy Harvesting.

Triboelectric nanogenerators (TENGs) have emerged as potential energy sources, as they are capable of harvesting energy from low-frequency mechanical actions such as biological movements, moving parts of machines, mild wind, rain droplets, and others. However, periodic mechanical motion can have a detrimental effect on the triboelectric materials that constitute a TENG device. This study introduces a self-healable triboelectric layer consisting of an Ecoflex-coated self-healable polydimethylsiloxane (SH-PDMS) polymer that can autonomously repair mechanical injury at room temperature and regain its functionality. Different compositions of bis(3-aminopropyl)-terminated PDMS and 1,3,5-triformylbenzene were used to synthesize SH-PDMS films to determine the optimum healing time. The SH-PDMS films contain reversible imine bonds that break when the material is damaged and are subsequently restored by an autonomous healing process. However, the inherent stickiness of the SH-PDMS surface itself renders the material unsuitable for application in TENGs despite its attractive self-healing capability. We show that spin-coating a thin layer (≈32 μm) of Ecoflex on top of the SH-PDMS eliminates the stickiness issue while retaining the functionality of a triboelectric material. TENGs based on Ecoflex/SH-PDMS and nylon 6 films show excellent output and fatigue performance. Even after incisions were introduced at several locations in the Ecoflex/SH-PDMS film, the TENG spontaneously attained its original output performance after a period of 24 h of healing. This study presents a viable approach to enhancing the longevity of TENGs to harvest energy from continuous mechanical actions, paving the way for durable, self-healable mechanical energy harvesters.

Exploring cement content's impact on self-healing in super absorbent polymer-modified concrete

This study shows the impact of varying cement content while maintaining a constant water-to-cement (w/c) ratio on the performance of self-healing concrete. It also explores the effect of F-type fly ash on the self-healing mechanism of concrete. Self-healing concrete, incorporating super absorbent polymers, offers a viable remedy to diminish the detrimental effects of cracks, enhancing the durability and lifespan of concrete structures. While the w/c ratio is a crucial factor influencing concrete properties, the impact of varying cement content under a constant w/c ratio in self-healing concrete remains understudied. Therefore, this experiment involved preparing 18 different concrete mixtures using three distinct cement contents under three specific w/c ratios. Fly ash was mixed in half of the specimens. Super absorbent polymers are incorporated into all mixtures to facilitate autonomous healing by absorbing and retaining water, which is released upon crack formation. Specimens were pre-cacked using a stress-controlled UTM machine. To evaluate the self-healing mechanism, low water pressure permeability test, water absorption test, and image analysis were conducted at 7, 14, 28, and 56 days. The findings of this study show that a w/c ratio of 0.35 yielded the best performance which indicates a lower w/c shows a higher self-healing performance. Additionally, the specimen containing a higher cement content exhibited enhanced healing capacity compared to other specimens. However, the specimens with fly ash failed to show a satisfactory result on self-healing capacity because the addition of silicon-based fly ash (F type) created an adverse effect on the self-healing mechanism.

Bio-based polyurethane triboelectric nanogenerator with superior low-temperature self-healing performance for unmanned surveillance

Damaged flexible triboelectric nanogenerators face difficulties in autonomous healing at low temperatures, limiting their application range. Impeded dynamic network reconstruction presents a challenge in developing materials for autonomous low-temperature healing. This study constructed a multi-dynamic network utilizing both strong and weak hydrogen and disulfide bonds to develop a biobased polyurethane elastomer (PBES-U, prepared from biobased monomers such as itaconic acid, sebacic acid, etc.), featuring a cross-linked network capable of cryogenic self-healing, superior toughness, and reprocessability. This elastomer extends to 1100 % of its original length, achieving 90 % self-healing efficiency at temperatures down to −10 °C due to the low glass transition temperature (Tg, −30 ℃) achieved by modulating the flexibility of chain segments. Consequently, a bio-based TENG (LS-TENG) was produced using this elastomer as a positive friction layer through a dynamic interfacial interlocking method. The results reveal that LS-TENG achieves a notable power density of 12.2 mW/m2, an output voltage reaching 160 V, and a 98 % output voltage recovery post-low-temperature self-healing. Furthermore, a non-contact LS-TENG-based monitoring system was developed with significant potential for applications in battlefield sensing, wildlife monitoring, and intelligent driving.

Natural light‐triggered microcapsules for non‐contact and autonomous healing of surface damages on insulating materials

AbstractIn the process of curing or service, epoxy resin is prone to crack damage due to complex stress, resulting in material performance degradation and other catastrophic accidents. Self‐healing microcapsules offer an effective strategy to address the aforementioned issues and enhance the long‐term durability of materials. However, traditional microcapsules face challenges in achieving non‐contact repair, as the healing agent requires high temperature or other extreme conditions to achieve curing, which necessitates the artificial provision of these conditions. Moreover, such extreme conditions may accelerate equipment aging or negatively impact the matrix material. To address these issues, this paper reports a photosensitive microcapsule that can achieve healing by natural light for non‐contact self‐healing of insulating composites. In particular, SiO2 nanoparticles are incorporated into the shell of the microcapsules to construct a UV shielding layer, effectively preventing premature curing and failure of the untriggered microcapsules. Experimental results indicate that the proposed photosensitive microcapsule@SiO2 exhibits excellent thermal stability, remaining intact at temperatures up to 200°C. With a healing agent content of approximately 77.5%, the photosensitive microcapsule@SiO2 ensures effective repair. Furthermore, when cross‐linked with epoxy resin, it has minimal negative impact on the epoxy matrix, with a slight improvement in mechanical properties. The composites demonstrate outstanding self‐healing performance in response to mechanical scratch damage. Without the need for any artificial stimuli, the healing process can be easily activated by natural light, facilitating intelligent, contactless, and autonomous self‐healing.

Ultratough and self‐healable electromagnetic interference shielding materials with sandwiched silver nanowires in polyurethane composite films

AbstractThis study presents a facile self‐healing electromagnetic interference (EMI) shielding composite by sandwiching a layer of silver nanowires (AgNWs) between two layers of self‐healing polyurethane (SPU). The AgNWs layer forms an interconnected conductive network that effectively reflects and absorbs electromagnetic radiation, providing efficient EMI shielding. The SPU layers contribute autonomous healing of mechanical damages and restoring structural integrity and conductive pathways. The composite films exhibit remarkable EMI shielding effectiveness (SE) (up to 64.6 dB), exceptional mechanical toughness (106.4 MJ/m3), and self‐healing capabilities, outperforming conventional shielding materials. The synergy between AgNWs and SPU layers offers lightweight, flexible, tough, and self‐healing properties, making this material highly promising for applications in wearable electronics, aerospace, and automotive industries where durability and long‐term reliability are critical.Highlights Facile fabrication of sandwiched AgNWs layer between SPU films. Sandwiched AgNWs/SPU films with exceptional EMI shielding. AgNWs form conductive networks for efficient EMI shielding. Remarkable mechanical toughness of 106.4 MJ/m3 and self‐healing capability. Potential shielding materials for lightweight, wearable electronics, aerospace.

Autonomous Self-Healing Agents in Cementitious Materials: Parameters and Impacts on Mortar Properties

The concept of self-healing materials and the development of encapsulated curing agents represent a cutting-edge approach to enhancing the longevity and reducing the maintenance costs of cementitious structures. This systematic literature review aims to shed light on the parameters involved in the autonomous self-healing of cementitious materials, utilizing various encapsulated healing agents such as pellets, granules, and capsules. This review also identifies and selects studies that offer additional insights into the efficacy of the self-healing process in cementitious materials and the influence of these specific encapsulated healing agents on the physical mechanical properties of mortars. This comprehensive approach provides a deep understanding of the interplay between self-healing and the physical–mechanical properties of mortars containing these encapsulated healing agents. The main findings indicate that the cement-to-sand ratio, characteristics of fine aggregates, and encapsulation methods significantly impact crack control, self-healing efficiency, and properties of mortar in both fresh and hardened states. The content of encapsulated healing agents within the cementitious matrix affects both the initial workability or flow and subsequent mechanical properties. While pellets coated with PVA film typically reduce workability in the fresh state and compressive strength, capsules coated with Portland cement and sodium silicate mitigate these effects and improve crack sealing in fresh and hardened states without compromising the self-healing capacity of cracks. The three-point flexural test has emerged as the preferred method for a pre-crack assessment over 28 days, with variations depending on the type of healing agent used. As noted in the literature, water has been identified as the optimal environment for autonomous healing. These findings underscore the potential of encapsulation techniques to enhance self-healing capabilities through the controlled release of agents within the cementitious matrix, thereby advancing the research on and development of intelligent construction materials and increasing the durability of cement-based structures.

Unveiling the impact of graphene oxide on bacteria-based autonomous healing of cracks in cementitious composites

High pH in cracks depresses activities of bacteria even after they are protected well in cement-based materials, thereby restricting bacteria-based autonomous healing. To resolve this problem, graphene oxide was added to hydrogels encapsulating endospores for self-healing cementitious composites. Due to the graphene oxide incorporation, breakage ratios of hydrogels upon cracking were increased thus graphene oxide could be released to cracks. Thereafter, pH was declined to around 9 at crack mouths, where metabolic activities of bacteria were improved. Owing to the improved activities, bacteria-mediated calcium carbonate in cracks was expedited, thereby accelerating crack closure and water permeability reduction. Furthermore, flexural strength was completely restored in the presence of graphene oxide, which could be associated with needle-like morphology of generated calcium carbonate in cracks. With the outstanding self-healing performance, carbon emissions of the cementitious composites experiencing 150–400 μm wide cracks were reduced at a cradle-to-grave boundary, due to their extended service life.

Photopolymerizable and Antibacterial Hydrogels Loaded with Metabolites from Lacticaseibacillus rhamnosus GG for Infected Wound Healing.

In response to increasing antibiotic resistance and the pressing demand for safer infected wound care, probiotics have emerged as promising bioactive agents. To address the challenges associated with the safe and efficient application of probiotics, this study successfully loaded metabolites from Lacticaseibacillus rhamnosus GG (LGG) into a gelatin cross-linked macromolecular network by an in situ blending and photopolymerization method. The obtained LM-GelMA possesses injectability and autonomous healing capabilities. Importantly, the incorporation of LGG metabolites endows LM-GelMA with excellent antibacterial properties against Staphylococcus aureus and Escherichia coli, while maintaining good biocompatibility. In vivo assessments revealed that LM-GelMA can accelerate wound healing by mitigating infections induced by pathogenic bacteria. This is accompanied by a reduction in the expression of key proinflammatory cytokines such as TNF-α, IL-6, VEGFR2, and TGF-β, leading to increased re-epithelialization and collagen formation. Moreover, microbiological analysis confirmed that LM-GelMA can modulate the abundance of beneficial wound microbiota at family and genus levels. This study provides a facile strategy and insights into the functional design of hydrogels from the perspective of wound microenvironment regulation.

Endowing rubber with intrinsic self-healing properties using thiourea-based polymer.

Self-healing polymers are extensively researched for the sustainability of materials. The introduction of dynamic networks instead of traditional cross-linkers for an autonomous healing mechanism in elastomers is a promising strategy for improving rubber properties. However, exchangeable covalent bonds in a dynamic network generally rely on external stimulants and fillers, which can compromise the material's performance. Herein, we introduce a mechanically strong yet resilient and independent self-healing polymeric network by dual cross-linking of bonds based on covalent and non-covalent dual interaction. The thiourea-based polymer polyether thiourea ethylene glycol (PTUEG) was blended with natural rubber (NR) and epoxidized natural rubber (ENR) to strengthen the mechanical characteristics of the material NR-ENR-PTUEG3. In the material, the thermoplastic polymer PTUEG3 applied the thiourea linkage as a hydrogen bonding and dynamic covalent motif together to enhance mechanical adaptability in a self-healing polymer network exhibiting stiffness, toughness, and resilience, thereby extending its longevity. The resulting mechanical characteristics of the NR-ENR-PTUEG3 with 25 phr PTUEG3 exhibited tensile stress 4.8 ± 0.3 MPa and high elongation at break 833 ± 0.1%, demonstrating far better performance than that of pristine NR, and 85% recovery of its original strength at ambient temperature. The healing behaviour is strongly influenced by thiourea-based polymer contents, enabling autonomous self-healing at ambient temperature, exhibiting in situ load-bearing efficiency in the repaired material, and maintaining their mechanical characteristics.

Performance assessment of sustainable biocement mortar incorporated with bacteria-encapsulated cement-coated alginate beads

Despite the extensive research on bacteria that are directly added to concrete to promote self-healing, studies on encapsulated bacteria have not been sufficient to comprehend crack healing. By employing Bacillus megaterium enclosed in cement-coated alginate beads, this research helps to improve the understanding of crack closure and the strength of self-healing mortar, which may be applied to the concrete. Autogenous healing occurs naturally, which will only repair micro-cracks. Moreover, it is a time-consuming process. Therefore, autonomous healing can assist in repairing little wider cracks with the addition of healing agents. Bacillus megaterium MTCC 8510 was used as the healing agent in the current study due to its ability to induce calcite precipitation (MICP) microbially. This was enclosed with alginate beads, and then coated with cement to form cement-coated alginate beads (CCAB). When a crack propagates, these beads break and generate CaCO3, which clogs up the crack domain. Several tests, including compressive strength, water permeability, FESEM, surface healing and ultrasonic pulse velocity (UPV), have been carried out to understand the healing performance and other characteristics thoroughly. To determine the optimal amount of CCAB, these hardened cement-coated beads were mixed in mortar in different percentages of 10%, 15%, 20%, and 25% as a replacement for fine aggregate (FA). The reduced compressive strength, anticipated due to the addition of fragile beads, was compensated by adding nano-silica (NS) to maintain the minimum strength. The calcite precipitation was collected from the healed specimen and was observed under FESEM to analyse its microstructure. For 25% aggregate replacement, a healing percentage of 92.64% was attained in the internal domain of the crack with water permeability test, whereas 93.96% of the crack core was filled when checked using the UPV test each after 56 days. Specimens with 20% CCAB and 5% NS also satisfied the minimum criteria mentioned. Therefore, it is concluded that 20% sand replacement with CCAB containing 5% nano-silica is optimal for both strength and healing.

Mechanisms boosting material embodied intelligence to realize self-healing soft robots

The recent introduction of self-healing soft materials in robotics is a major step towards sustainable next generation robots. By manufacturing soft robots out of these smart materials, we integrate a self-healing ability and increase the physical intelligence of these systems. However, the embodied intelligence in the material level needs to be augmented by incorporating assistive mechanisms in the system level with minimized control, enabling healing of damage in different sizes and in diverse working conditions. These assistive mechanisms can provide damage detection, damage closure, healing stimuli providing, health monitoring, or a combination of the previous. In this paper, we present two different mechanisms for an autonomous healing of damages; (i) Embedding a healable heater in a self-healing soft actuator to increase the temperature required for an efficient healing, while it allows detecting the damage and monitoring the health of the system. (ii) Incorporating shape memory alloy wires in a self-heling soft bending actuator, with simultaneous sealing through contraction and heating abilities. Apart from assisting in the healing action, both mechanisms play a part in the actuation of the bending robots as strain limiting elements. These assistive mechanisms will overcome the limitation on the material level, leading to robots that can self-heal in applications outside of laboratories and factories.

An alkali-responsive mineral self-healing agent with mechanical property enhancement for cementitious composites

Self-healing cementitious materials are regarded as an effective choice to increase the sustainability of the resource and environment. In this study, an alkali-responsive mineral self-healing agent (AMS) was prepared inspired by bone repair. The healing component, phosphate, was loaded into the halloysite nanotubes (HNTs) and encapsulated by the layer-by-layer (LbL) self-assembly method. The structure and alkali-responsive behavior of AMS, the effect of AMS on the mechanical properties of cement pastes, the stability of AMS before cement cracking, and its effect on the self-healing efficiency of the cement pastes were investigated with a range of analytical techniques. Results showed that AMS was successfully encapsulated and endowed with excellent alkali responsiveness. The incorporation of AMS was effective in reinforcing the mechanical performances of cement pastes. XRD analysis showed that the phosphate encapsulated in AMS can be mostly retained until cracks appear. When cracks occurred, the B-type carbonated calcium-deficient hydroxyapatite was found as the main product in the crack environment. The surface crack around 130 μm in the damaged specimens containing 5% AMS was fully sealed and healed, and its damaged compressive strength was almost completely recovered after curing for 28 days. The synergistic effect of autonomous healing triggered by AMS and autogenous healing behavior promotes the self-healing process and improves the self-healing efficiency of the hardened cement pastes.

Cementitious materials with biological additive for enhanced durability in marine environment

AbstractConcrete structures suffer from cracking that leads to deterioration and shortening of service life. This is very critical for underwater structures, i.e., immersed bridge piles, immersed tunnel or submerged floating tunnels, which are consistently susceptible to ingress of harmful ions (chloride, sulphate and carbonate ions). Autonomous healing of concrete cracks can be beneficial to assure durability performance during the service life. In this context the paper presents a preliminary experimental activity carried out to study the self‐healing capacity of cementitious composites in marine environment. Four series of paste samples are prepared to evaluate the autonomous healing capabilities, achieved through biotic and abiotic additions. The experimental campaign is articulated in four phases, such as: specimen preparation; tests in compression; immersion in water; crack healing evaluation. The specimen performances are examined and compared in terms of mechanical strength and crack width healing over time. Results highlight the efficiency of the technology for crack healing.

Application of Shape Memory and Self-Healable Polymers/Composites in the Biomedical Field: A Review.

Shape memory-assisted self-healing polymers have drawn attention over the past few years owing to their interdisciplinary and wide range of applications. Self-healing and shape memory are two approaches used to improve the applicability of polymers in the biomedical field. Combining both these approaches in a polymer composite opens new possibilities for its use in biomedical applications, such as the "close then heal" concept, which uses the shape memory capabilities of polymers to bring injured sections together to promote autonomous healing. This review focuses on using shape memory-assisted self-healing approaches along with their respective affecting factors for biomedical applications such as tissue engineering, drug delivery, biomaterial-inks, and 4D printed scaffolds, soft actuators, wearable electronics, etc. In addition, quantification of self-healing and shape memory efficiency is also discussed. The challenges and prospects of these polymers for biomedical applications have been summarized.

Autonomous healing of fatigue cracks via cold welding.

Fatigue in metals involves gradual failure through incremental propagation of cracks under repetitive mechanical load. In structural applications, fatigue accounts for up to 90% of in-service failure1,2. Prevention of fatiguerelies on implementation of large safety factors and inefficient overdesign3. In traditional metallurgical design for fatigue resistance, microstructures are developed to either arrest or slow the progression of cracks. Crack growth is assumed to be irreversible. By contrast, in other material classes, there is a compelling alternative based on latent healing mechanisms and damage reversal4-9. Here, we report that fatigue cracks in pure metals can undergo intrinsic self-healing. We directly observe the early progression of nanoscale fatigue cracks, and as expected, the cracks advance, deflect and arrest at local microstructural barriers. However, unexpectedly, cracks were also observed to heal by a process that can be described as crack flank cold welding induced by a combination of local stress state and grain boundary migration. The premise that fatigue cracks can autonomously heal in metals through local interaction with microstructural features challenges the most fundamental theories on how engineers design and evaluate fatigue life in structural materials. We discuss the implications for fatigue in a variety of service environments.

Feasibility assessment of microwave-cured lightweight aggregate concrete by mineral encapsulated self-healing

A novel lightweight foam aggregate (FLWA) has been developed in this study through geopolymerization and microwave curing. Sodium silicate (Na2SiO3) is used as both an alkaline activator and a foaming agent. Afterwards, Na2SiO3 is impregnated into FLWA as a healing agent. The feasibility of FLWA for autonomous self-healing is evaluated using three scales: micro (optical microscopy, SEM-EDX, and sorptivity), molecular (FTIR), and macro (compression and flexural tests). To quantify the efficiency of healing at both autonomous and autogenous levels, two types of concrete specimens are cast: one using encapsulated self-healing FLWA and the other without any healing agent. The efficiency of crack healing is visualized using optical microscopy and SEM techniques. Then, the healing products are confirmed through EDX and FTIR analysis. As a result, the efficiency of autonomous crack healing is 100% after 90 d, compared to autogenous healing which is only 20.4%. Significant strength recovery is observed in compression and flexure. Therefore, developed FLWA with healing agent can be applicable for both autonomous and autogenous self-healing performance.

Self-healing efficiency of concrete containing engineered aggregates

This paper presents the results from a new approach for self-healing concrete. Conventional macro-capsules such as those made of glass cannot resist the harsh mixing process of concrete and require changes to conventional preparation methods. Here, a new encapsulation method; namely, engineered aggregates (EAs) were developed and tested, which do not require any changes to concrete preparation methods. EAs were shown to resist the conventional concrete mixing methods and effectively deliver healing agents when cracks appear in concrete. The mechanical properties of the produced self-healing concrete were examined by performing uniaxial compression, split tensile, and four-point bending tests. The self-healing efficiency of the concrete with EAs containing different healing agents (polyurethane, super glue, sodium silicate, magnesium oxidate) was determined based on split tensile, water absorption and water permeability tests. It was seen that more than 50% of the original strength and stiffness could be regained after self-healing. It was also found that the water permeability could be reduced by a factor 102 to 104 due to autonomous crack healing. Although some further research is still necessary concerning functional life of encapsulated healing agents and healing of cracks less than 50 μm, self-healing EA concrete was shown to be a novel approach that could lead to changes in the concrete industry.

Shape Memory Alloy Reinforced Self-Healing Metal Matrix Composites

This paper reviews the synthesis, characterization, healing assessment, and mechanics of NiTi and other shape memory alloy (SMA)-reinforced self-healing metal matrix composites (SHMMCs). Challenges to synthesizing and characterizing the SMA-reinforced SHMMCs and the strategies followed to overcome those challenges are discussed. To design the SMA-reinforced SHMMCs, it is necessary to understand their microstructural evolution during melting and solidification. This requires the knowledge of the thermodynamics of phase diagrams and nonequilibrium solidification, which are presented in this paper for a model self-healing composite system. Healing assessment provides information about the autonomous and multicycle healing capability of synthesized SHMMCs, which ultimately determines their success. Different techniques to assess the degree of healing of SHMMCs are discussed in this paper. Strategies are explored to find the optimum volume fraction of SMA wires needed to yield the matrix and prevent damage to the SMA wires for the most effective healing. Finally, major challenges, knowledge gaps, and future research directions, including the need for autonomous and multicycle healing capability in SMA-reinforced SHMMCs, are outlined.