# Self-healing material
A **self-healing material** is a material that repairs damage, such as a crack, either autonomously or with an external input of energy or pressure[1](https://www.annualreviews.org/content/journals/10.1146/annurev-matsci-070909-104532). Healing can be autonomic, requiring no human intervention, or it may require some external energy or pressure; all classes of polymers, from thermosets to thermoplastics to elastomers, have shown potential for self-healing[1](https://www.annualreviews.org/content/journals/10.1146/annurev-matsci-070909-104532). The field spans polymers, cementitious materials, ceramics, and fiber-reinforced composites, with target industries including coatings, electronics, transportation, and energy[1](https://www.annualreviews.org/content/journals/10.1146/annurev-matsci-070909-104532).
| Key fact | Detail |
|---|---|
| Three approaches | Capsule-based healing systems, vascular healing systems, and intrinsic healing polymers[1](https://www.annualreviews.org/content/journals/10.1146/annurev-matsci-070909-104532) |
| Typical efficiency | Reported healing efficiencies range from about 50% to near-complete (~100%) recovery, depending on system and test conditions[2](https://www.mdpi.com/2227-9717/14/9/1436) |
| Repair count | Capsule systems heal a given location once; vascular systems have reached 10 to 1,000 cycles; intrinsic systems heal repeatedly but mainly at microdamage scale[3](https://www.nature.com/articles/nmat1934) • [4](https://www.pnas.org/doi/10.1073/pnas.2523447123) • [5](https://iopscience.iop.org/article/10.1088/1361-665X/ae21ac/meta) |
| Concrete crack widths | Autogenous healing handles roughly 50–300 µm; bacterial MICP up to ~970 µm; microencapsulation 100–800 µm; vascular networks 200–3000 µm[6](https://jmce.a2zjournals.com/index.php/mce/article/download/96/75/437) |
| Fatigue result | A self-healing epoxy showed essentially no crack growth where a standard epoxy failed after about 62,000 load cycles (~2.7 µm per cycle)[2](https://www.mdpi.com/2227-9717/14/9/1436) |
| Cost barrier | A bacterial concrete healing agent (CERUP) still cost about €30.7 (~$35.5) per kilogram after process optimization[2](https://www.mdpi.com/2227-9717/14/9/1436) |
| Market outlook | Expected compound annual growth of 56.5% from 2021 to 2029; construction is projected to account for about 55.5% of the market[7](https://www.mdpi.com/1996-1944/17/19/4681) |
## Classification and mechanisms
Self-healing has been demonstrated by three conceptual approaches: capsule-based healing systems, vascular healing systems, and intrinsic healing polymers[1](https://www.annualreviews.org/content/journals/10.1146/annurev-matsci-070909-104532).
**Capsule-based (extrinsic) systems** embed microcapsules of liquid healing agent in the matrix. A crack ruptures the capsules, the agent flows into the crack plane, and it cures there, bonding the faces closed. Because crack-induced rupture depletes the local healing agent, microencapsulated systems are limited to autonomic repair of a single damage event in a given location[3](https://www.nature.com/articles/nmat1934). Once the released agent cures into a permanent, irreversible network, subsequent microcracks in the same region cannot be healed again[8](https://www.sciencedirect.com/science/article/abs/pii/S138589472603634X). Because the agent is physically isolated from the matrix, however, capsule systems preserve the base resin's crosslink density and mechanical properties[8](https://www.sciencedirect.com/science/article/abs/pii/S138589472603634X).
**Vascular systems** replace discrete capsules with interconnected channels, inspired by leaf venation and blood vascular systems, that deliver healing agent from a reservoir to the damage site; this lets one network address varying magnitudes of damage[9](https://iopscience.iop.org/article/10.1088/1361-665X/abf41d). Because the channels can be refilled, vascular systems offer repeated healing and cover larger damage zones than single-use capsules, at the cost of manufacturing complexity and the risk of channels blocked by cured resin[2](https://www.mdpi.com/2227-9717/14/9/1436).
**Intrinsic systems** build reversibility into the material itself. The mechanisms used to construct self-healing polymers include diffusion and flow, shape-memory effects, heterogeneous self-healing systems, covalent-bond reformation and reshuffling, and the dynamics of supramolecular chemistry, or combinations of these[10](https://www.nature.com/articles/s41578-020-0202-4). In a coating, two conditions must be met: elastic recovery must bring the two crack planes into contact, and local viscous flow must then allow interface diffusion and reaction to restore the barrier. Shape-memory effects that store energy during damage have been produced through main-chain entanglements, permanent cross-linking, polymer blending, and microphase separation[11](https://pubs.acs.org/doi/10.1021/acsapm.1c00323).
The two families trade different strengths. Extrinsic self-healing offers high healing efficiency, low cost, and applicability to a wider range of materials, while intrinsic self-healing is limited to materials with inherent reversible molecular interactions, often needs external stimuli such as temperature or UV light, and handles smaller damage volumes; its advantages are repeatability and ease of application[7](https://www.mdpi.com/1996-1944/17/19/4681). Intrinsic non-autonomous systems require external stimuli such as temperature, UV, visible light, or an electric field[5](https://iopscience.iop.org/article/10.1088/1361-665X/ae21ac/meta).
## Material classes
**Polymers** span thermosets, thermoplastics, and elastomers, and all classes have shown potential for self-healing[1](https://www.annualreviews.org/content/journals/10.1146/annurev-matsci-070909-104532). Reversible covalent chemistry is a mainstay: a Diels–Alder network healed with about 96% efficiency in the first cycle but dropped to about 73% after 10 cycles, a 23-percentage-point decrease[2](https://www.mdpi.com/2227-9717/14/9/1436).
**Concrete** heals by several routes with different crack-width capacities and mechanical recovery: autogenous healing handles roughly 50–300 µm cracks with 10–40% recovery; bacterial microbially induced calcite precipitation (MICP) reaches up to about 970 µm with 14–100% recovery; microencapsulation handles 100–800 µm with 14–80% recovery in a single use; and vascular networks address 200–3000 µm with 40–90% recovery and refillability[6](https://jmce.a2zjournals.com/index.php/mce/article/download/96/75/437). Microcapsule-based [self-healing concrete](https://www.edgepedia.org/self-healing-concrete) has been scaled up for field trials, where the capsules reduce permeability, enhance durability, and aid some recovery of structural strength[12](https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2018.00051/full), and the first UK field application demonstrated agents that react with the cementitious matrix, including hydration and carbonation products such as lime, or with the environment, such as moisture-activated cyanoacrylates, to fill and seal cracks[13](https://www.sciencedirect.com/science/article/abs/pii/S0950061819304714).
**Ceramics** heal by high-temperature oxidation and diffusion: magnesium aluminate spinel (MgAl2O4) nanopowder recovered about 91% of its tensile strength after crack healing at 1600 °C for 100 h[2](https://www.mdpi.com/2227-9717/14/9/1436).
**Structural composites** heal delamination and fracture through embedded vasculature. Vascular fiber-reinforced composites with embedded microvascular channels achieved ten cycles of fracture and healing with, on average, 55% and as much as 95% recovery of the virgin critical strain energy release rate, with epoxy and amine agents pumped to the fracture plane[14](http://whitegroup.beckman.illinois.edu/journal%20articles/CST_Pety2017.pdf). An interpenetrating vasculature showed improved in situ fluid mixing over segregated microchannels, giving full recovery of more than 100% of mode-I fracture toughness after interlaminar delamination[15](https://onlinelibrary.wiley.com/doi/10.1002/adma.201400248).
## Measuring healing efficiency
Healing efficiency is typically the ratio of a mechanical property, such as fracture resistance, fracture stress, strength, or [Young's modulus](https://www.edgepedia.org/youngs-modulus), measured before and after repair; a perfectly healed material has an efficiency of 1 (η = 1)[7](https://www.mdpi.com/1996-1944/17/19/4681). Studies do not use a standardized definition, which makes cross-study comparison non-linear[7](https://www.mdpi.com/1996-1944/17/19/4681). Different groups use different metrics, including tensile strength, conductivity, crack closure, water permeability, stiffness recovery, and visual crack closure, and healing conditions such as temperature and waiting time vary[2](https://www.mdpi.com/2227-9717/14/9/1436). Reported efficiencies in concrete are not directly comparable across studies because laboratories use different specimen sizes, pre-cracking methods, healing durations, and exposure conditions[6](https://jmce.a2zjournals.com/index.php/mce/article/download/96/75/437).
To address this, the EU COST action SARCOS included six inter-laboratory testing programs, each focused on test methods for a specific self-healing technique, because the lack of standardized test methods hampers commercialization of self-healing concrete[16](https://www.tandfonline.com/doi/full/10.1080/14686996.2020.1814117). Its pre-standard procedure uses three-point bending pre-cracking with active crack width control followed by a water permeability test[17](https://link.springer.com/article/10.1617/s11527-021-01818-3). In the macrocapsule round-robin, mortar specimens with polyurethane in cementitious macro-capsules gave average sealing efficiencies of 54 to 74%, versus 56% for glass macro-capsules, and repeated tests gave the same results[17](https://link.springer.com/article/10.1617/s11527-021-01818-3). For the permeability test, 4 of 6 labs obtained a comparable flow rate for reference specimens, yet all 6 labs obtained comparable sealing efficiencies[16](https://www.tandfonline.com/doi/full/10.1080/14686996.2020.1814117).
## By the numbers
Reported healing efficiencies typically fall between about 50% and near-complete (~100%) recovery[2](https://www.mdpi.com/2227-9717/14/9/1436). Cycle counts separate the approaches: capsules heal once per location[3](https://www.nature.com/articles/nmat1934); microvascular delivery of two-part chemistry achieved healing efficiencies over 60% for up to 16 cycles, with both components wicked into the crack plane by capillary forces[18](https://onlinelibrary.wiley.com/doi/10.1002/adfm.200801824); interpenetrating microvascular networks reached healing efficiency approaching 100% in some cases and retained 50% after 30 cycles[19](http://autonomic.beckman.illinois.edu/nrs086.pdf); and in situ thermo-mechanical experiments on composites reached 1,000 cycles, an order-of-magnitude improvement over prior work, with healing beginning at 175% of the mode-I fracture resistance of a plain composite and declining to 60% over repeated cycles[4](https://www.pnas.org/doi/10.1073/pnas.2523447123).
Healing times vary widely. A recent cement composite sealed a fracture about 2 mm deep within about 4 hours, a healing rate of about 10 mm per day, with bi-exponential kinetics of characteristic times of about 10 minutes and about 9 hours[20](https://www.nature.com/articles/s41467-026-76061-x). A supramolecular epoxy coating healed over 24 hours at 80 °C, or in 5 minutes with a household hair dryer[8](https://www.sciencedirect.com/science/article/abs/pii/S138589472603634X). Cost remains a concrete-specific barrier: the CERUP bacterial agent cost about €30.7 (~$35.5) per kilogram even after process optimization, an impractically high cost to add to common concrete in large volumes[2](https://www.mdpi.com/2227-9717/14/9/1436).
## Trade-offs and comparison with conventional damage tolerance
There is a clear trade-off relationship between the rate of self-healing and the mechanical modulus of the material, and design principles have been proposed for polymers that surpass this trade-off[21](https://pubs.acs.org/chreay/article/123/2/701/317204/Intrinsically-Self-Healing-Polymers-From). Across the field, all self-healing methods tend to jeopardize base mechanical properties, requiring a balance between strength loss and healing ability[7](https://www.mdpi.com/1996-1944/17/19/4681).
Against conventional damage tolerance, the clearest quantified comparison is in fatigue: where a standard non-healing epoxy failed after about 62,000 load cycles with crack growth of about 2.7 µm per cycle, a self-healing epoxy showed essentially no crack growth in the same test, after recovering about 56% of original fracture toughness in 24 h at room temperature[2](https://www.mdpi.com/2227-9717/14/9/1436). Healing has also been demonstrated for fatigue, impact damage, puncture, and corrosion, though most research targets recovery of mechanical integrity after quasi-static fracture[1](https://www.annualreviews.org/content/journals/10.1146/annurev-matsci-070909-104532).
## Applications, commercialization, and scale-up barriers
Microcapsule systems are applied in cement, concrete, asphalt, biomaterials, epoxy resins, and polymer coatings, while vascular networks target aerospace and large-scale structures[5](https://iopscience.iop.org/article/10.1088/1361-665X/ae21ac/meta). In coatings, a TFAT-based coating regained essentially 100% of its corrosion protection ability after a two-step thermal healing process[2](https://www.mdpi.com/2227-9717/14/9/1436). The market is expected to grow at a compound annual rate of 56.5% from 2021 to 2029, with construction projected to be the largest consumer, at approximately 55.5% of the market[7](https://www.mdpi.com/1996-1944/17/19/4681).
**Barriers.** The lack of standardized test methods hinders comparison between studies and hampers commercialization, since the construction sector is used to strictly regulated concrete production[17](https://link.springer.com/article/10.1617/s11527-021-01818-3); comparable harmonization has not been achieved for bacterial, vascular, or crystalline-admixture systems, and an internationally recognized test standard is identified as a priority research need[6](https://jmce.a2zjournals.com/index.php/mce/article/download/96/75/437). Composites are yet to be scaled up for practical applications because repair efficiency varies significantly with damage size and environmental conditions such as pressure and temperature[7](https://www.mdpi.com/1996-1944/17/19/4681). Extrinsic approaches that sequester an external agent, such as microcapsules or hollow fibers, face limits in repeatability due to the finite supply of healing agents[4](https://www.pnas.org/doi/10.1073/pnas.2523447123).
## Recent developments
**Capsule-free concrete.** A cement composite incorporating an ultra-low polymer concentration, under 0.15 wt%, achieves autonomous, multi-cycle crack healing without capsules or vascular networks and with minimal impact on hydration, setting, or workability, using a reversible poly(acrylic acid)/poly(ethylene oxide)/branched poly(ethylene imine) "molecular Velcro" network[20](https://www.nature.com/articles/s41467-026-76061-x). After severe post-peak loading with 20% strength loss beyond the maximum, strength recovery reached up to 62% in compression and 59% in direct tension, sustained across multiple damage–healing cycles[20](https://www.nature.com/articles/s41467-026-76061-x).
**Reversible extrinsic coatings.** A supramolecular poly(TA-DIB-Fe)/epoxy interpenetrating polymer network coating exhibited full morphological recovery and tensile-strength recovery efficiencies of 106%, 104.7%, and 106.5% over three successive 24-hour healing cycles at 80 °C, and a 5-minute treatment with a household hair dryer achieved comparable healing[8](https://www.sciencedirect.com/science/article/abs/pii/S138589472603634X). This bears on a point of disagreement in the literature: microcapsule systems are widely described as one-time repairs because the capsule core is depleted[5](https://iopscience.iop.org/article/10.1088/1361-665X/ae21ac/meta), yet this extrinsic reversible design healed the same location repeatedly, showing that extrinsic systems need not be single-use.
**Cycle life and capsule architecture.** [The 1](https://www.edgepedia.org/the-1),000-cycle composite result[4](https://www.pnas.org/doi/10.1073/pnas.2523447123) extends a lineage that ran from 16 cycles with two-part microvascular delivery[18](https://onlinelibrary.wiley.com/doi/10.1002/adfm.200801824) through 30 cycles at 50% efficiency[19](http://autonomic.beckman.illinois.edu/nrs086.pdf). On the capsule side, current architectures include single-core, dual-core, and multi-walled types, enabling localized repair of microcracks beyond conventional groove filling, grouting, and coating methods[22](https://pubs.rsc.org/en/content/articlelanding/2026/lp/d5lp00210a).
## References
1. [Self-Healing Polymers and Composites, Annual Review of Materials Research](https://www.annualreviews.org/content/journals/10.1146/annurev-matsci-070909-104532)
2. [Self-Healing Materials: Mechanisms, Properties, and Applications, Processes](https://www.mdpi.com/2227-9717/14/9/1436)
3. [Self-healing materials with microvascular networks, Nature Materials (2007)](https://www.nature.com/articles/nmat1934)
4. [Self-healing for the long haul: In situ automation delivers century-scale fracture recovery in structural composites, PNAS](https://www.pnas.org/doi/10.1073/pnas.2523447123)
5. [Microcapsules in self-healing materials: a review, Smart Materials and Structures](https://iopscience.iop.org/article/10.1088/1361-665X/ae21ac/meta)
6. [Concrete That Heals Itself: A Critical Review of Self-Healing Mechanisms, Performance](https://jmce.a2zjournals.com/index.php/mce/article/download/96/75/437)
7. [Self-Healing Composites: A Path to Redefining Material Resilience, Materials](https://www.mdpi.com/1996-1944/17/19/4681)
8. [Outstanding extrinsic reversible self-healing material for commercial epoxy coating, Chemical Engineering Journal](https://www.sciencedirect.com/science/article/abs/pii/S138589472603634X)
9. [A review of vascular networks for self-healing applications, Smart Materials and Structures](https://iopscience.iop.org/article/10.1088/1361-665X/abf41d)
10. [Self-healing polymers, Nature Reviews Materials](https://www.nature.com/articles/s41578-020-0202-4)
11. [From Scratch Closure to Electrolyte Barrier Restoration in Self-Healing Polyurethane Coatings, ACS Applied Polymer Materials](https://pubs.acs.org/doi/10.1021/acsapm.1c00323)
12. [Large Scale Application of Self-Healing Concrete: Design, Construction, and Testing, Frontiers in Materials](https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2018.00051/full)
13. [First UK field application and performance of microcapsule-based self-healing concrete, Construction and Building Materials](https://www.sciencedirect.com/science/article/abs/pii/S0950061819304714)
14. [Repeated healing of delamination damage in vascular composites by pressurized delivery of reactive agents, Composites Science and Technology (2017)](http://whitegroup.beckman.illinois.edu/journal%20articles/CST_Pety2017.pdf)
15. [Continuous Self-Healing Life Cycle in Vascularized Structural Composites, Advanced Materials](https://onlinelibrary.wiley.com/doi/10.1002/adma.201400248)
16. [Addressing the need for standardization of test methods for self-healing concrete: an inter-laboratory study on concrete with macrocapsules](https://www.tandfonline.com/doi/full/10.1080/14686996.2020.1814117)
17. [Durability of self-healing cementitious systems with encapsulated polyurethane evaluated with a new pre-standard test method, Materials and Structures](https://link.springer.com/article/10.1617/s11527-021-01818-3)
18. [Delivery of Two-Part Self-Healing Chemistry via Microvascular Networks, Advanced Functional Materials](https://onlinelibrary.wiley.com/doi/10.1002/adfm.200801824)
19. [Self-Healing Materials with Interpenetrating Microvascular Networks, Advanced Functional Materials](http://autonomic.beckman.illinois.edu/nrs086.pdf)
20. [A molecular velcro self-healing cement, Nature Communications](https://www.nature.com/articles/s41467-026-76061-x)
21. [Intrinsically Self-Healing Polymers: From Mechanistic Insight to Current Challenges, Chemical Reviews](https://pubs.acs.org/chreay/article/123/2/701/317204/Intrinsically-Self-Healing-Polymers-From)
22. [Future of concrete: autonomous self-healing with advanced microcapsule technology, RSC Applied Polymers](https://pubs.rsc.org/en/content/articlelanding/2026/lp/d5lp00210a)
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*Topic: Encyclopedia › Physical world and mathematics › Physics › Classical physics › Mechanics › Continuum, solid, and fluid mechanics › Solid mechanics › Fracture and failure › Failure by material class*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license