Healing Behavior Research Articles

Effect of grain size on self -healing behaviour of sensitized S304HCu stainless steel

S304HCu stainless steel is extensively used for superheater and reheater applications in power plants due to its superior creep strength and oxidation resistance which are derived from the coherently dispersed precipitates formed in austenite matrix. In addition to the beneficial precipitates, chromium carbide precipitates can also form. Formation of chromium carbide precipitates during service will lead to sensitization. In this investigation, S304HCu samples were solutionized at 1100 °C and 1200 °C for 1 h, and further aged at 750 °C for upto 400 h to introduce sensitization and subsequent healing. The influence of ageing time and grain size on the degree of sensitization (DOS) was evaluated by using oxalic acid and double loop electrochemical potentiodynamic reactivation (DLEPR) tests. DOS initially increased up to 10 h of ageing and subsequently was reduced due to healing and attained a steady value at 50 h. Faster and higher DOS was observed in coarse grain structure than in the fine grain structure. However, healing was largely delayed in coarse grained structure. The difference in solute and excess vacancy concentration and shifting of the nose in TTP curve were attributed to the difference in the kinetics of sensitization and healing. The extent of the attack on the grain boundary was analyzed using AFM.

Description of the Damage and Healing Behavior of an Extrinsic and Autonomous Self‐Healing Anisotropic Material

AbstractIn this contribution, the damage and healing behavior of a fiber reinforced polymeric composite will be investigated. Therefore, the considered Helmholtz free energy function for the polymeric matrix material consists of two parts, an isotropic part for the description of the isotropic polymer and an anisotropic part for the reinforcement. As theoretical framework, the Theory of Porous Media is used, where internal interactions (phase transitions, temperature exchange, ...) can be described by so‐called production terms. At the end a numerical example of an anisotropic self‐healing polymer is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Self-Healing Behavior of Sodium Polyacrylate-Hydroxyapatite Coatings on Biodegradable Magnesium Alloy

The effect of the anionic polymer sodium polyacrylate (SPA) on the healing behavior of a hydroxyapatite (HAp) coating formed on Mg-3 mass% Al-1 mass% Zn (AZ31) alloy was examined. Static immersion ...

Elastic evolution of a self-healing ionomer observed via acoustic and ultrasonic resonant spectroscopy

Self-healing poly (ethylene co-methacrylic acid) ionomers (EMAA) are thermoplastic materials that when punctured, cut, shot or damaged in a variety of ways, are capable of autonomously reorganizing their physical structure to heal and, in many instances, permanently seal the damaged location. However, a complete picture of the mechanisms responsible for their unusual behavior is not well understood. In this article we report the observation of time dependent acoustic and ultrasonic spectral evolution, measured using resonant acoustic and ultrasonic spectroscopy, for both pre and post-damage EMAA samples. The results provide a means to differentiate healing phases, quantify healing timescales, and potentially elucidate the composition parameters that most significantly impact healing behavior.

Crack-healing behavior of Al2O3-TiB2-TiSi2 ceramic material

Al2O3-TiB2-TiSi2 ceramic material was fabricated by vacuum hot pressing technique and the crack healing behavior was investigated by means of high-temperature oxidation. The Vickers hardness indenter was used to precrack with a standard crack length of 300µm. According to the recovery of flexural strength and the microstructure of crack appearance, the effects of crack healing temperature, healing time and crack length on crack-healing were studied. At the healing temperature of 800°C for 90min, the strength of crack-healing specimen was recovered completely and the recovery percentage of flexural strength reached up to 107.25%, compared with the flexural strength of the smooth specimen. The strength of crack-healing specimens with a crack length of 150µm and 300µm were fully recovered, but incomplete recovery appeared at the crack length of 500µm. The crack-healing mechanism was attributed to the crack-filling with liquid phases of SiO2 and TiO2 obtained by X-ray diffraction. The crack surface of Al2O3-TiB2-TiSi2 ceramic material was observed by Scanning Electron Microscopy and Energy-dispersive Spectrometry.

Establishment of a cell-based wound healing assay for bio-relevant testing of wound therapeutics

IntroductionPredictive in vitro testing of novel wound therapeutics requires adequate cell-based bio-assays. Such assays represent an integral part during preclinical development as pre-step before entering in vivo studies. Simple “scratch tests” based on defected skin cell monolayers exist, however these can solely be used for testing liquids, as cell monolayer destruction and excessive hydration limit their applicability for (semi-)solid systems like wound dressings. In this context, a cell-based wound healing assay is introduced for rapid and predictive testing of wound therapeutics independent of their physical state in a bio-relevant environment. MethodsA novel wound healing assay was established for bio-relevant and predictive testing of (semi-) solid wound therapeutics. ResultsThe assay allows for physiologically relevant hydration of the tested wound therapeutics at the air-liquid interface and their removal without cell monolayer disruption. In a proof-of-concept study, the applicability and discriminative power could be demonstrated by examining unloaded and drug-loaded wound dressings with two different established wound healing actives (dexpanthenol and metyrapone) and their effect on skin cell behavior. The influence of the released drug on the cells´ healing behavior could successfully be monitored over time. Wound size assessment after 96h resulted in an eight fold smaller wound area for drug treated models compared to the ones treated with unloaded fibers and non-treated wounds. DiscussionThis assay provides valuable first insights towards the establishment of a valid screening and evaluation tool for preclinical wound therapeutic development from liquid to (semi-)solid systems to improve predictability in a simple, yet standardized way.

Effect of the polymer structure on the viscoelastic and interfacial healing behaviour of poly(urea-urethane) networks containing aromatic disulphides

The macroscopic interfacial healing behaviour in a series of urea-urethane networks as function of the hydrogen bonds and disulphides content is presented. The polymers were prepared with different crosslinking densities but with the same amount of dynamic covalent bonds (disulphide linkages). Tensile and fracture measurements were adopted to evaluate the degree of recovery of the mechanical properties after damage. Healing kinetics and healing efficiencies were quantitatively determined as a function of network composition, healing temperature and contact time. Finally, the recovery of mechanical properties was correlated with the viscoelastic response of the networks through rheological measurements and time-temperature superposition principle (TTS). The application of the TTS approach on both fracture healing and DMTA and subsequent mathematical descriptive model led to a better understanding of the influence of polymer architecture and that of the amount of reversible groups on the healing process.

Multiscale Models of Degradation and Healing of Bone Tissue Engineering Nanocomposite Scaffolds

Biomaterials selection and design, and mechanical properties evolution during degradation and tissue regeneration play a critical role in the successful design of nanocomposite scaffolds for bone tissue regeneration. A new multiscale mechanics-based in silico approach is developed to provide a robust predictive methodology for nanocomposite scaffolds. Scaffolds are fabricated using amino acid–modified nanoclay with biomineralized hydroxyapatite (in situ HAPclay) and polycaprolactone (PCL). Steered molecular dynamics (SMD) simulations of the molecular models of HAPclay and the PCL composite provide a mechanical response of the material and the nature of the molecular interactions among constituents. The mechanical responses obtained from SMD are incorporated into a finite element (FE) model of a PCL/in situ HAPclay scaffold with its microstructure obtained from microcomputed tomography images. The model is validated using experimental results. The stress–strain response from multiscale models and experiments shows good agreement with the consideration of wall porosity correction. The multiscale models incorporate damage mechanics–based degradation and healing behavior to capture the evolution of the mechanical properties as the scaffolds degrade and human osteoblasts grow and proliferate inside the scaffolds. The novel multiscale models provide a robust prediction of the mechanical properties evolution in the scaffolds over the time evolution of cell growth proliferation and tissue formation.

Application of Elastic-Damage-Heal Model for Self-Healing Concrete Thick-Walled Cylinders Through Thermodynamics of Irreversible Processes

Elastic-damage-heal models are used for a phenomenological study of self-healing materials. Self-healing materials are a class of smart materials that have a structural capability to recover damage caused by environmental stimuli over time. In this paper, a semi-analytic modeling for self-healing concrete thick-walled cylinders is presented. For this purpose, an elastic-damage-heal model through thermodynamics of irreversible processes, in the framework of continuum damage-healing mechanic is used. This model uses stress spectral decomposition method to model the different behavior of concrete in tensile and compressive loadings. Gibbs potential energy is divided into three parts: elastic energy, damage energy and healing energy. In this regard, the model introduces damage and healing surfaces to detect damage and healing behaviors from the elastic one. We derive an analytical closed-form solution for a self-healing concrete thick-walled cylinder. The verification of the model is shown by solving an example. Finally, a parametric study on the healing parameters of the self-healing concrete thick-walled cylinder is performed to demonstrate the capability of the model. It is noted that for a case with the specified values of healing parameters, the tangential stress level in an internal radius of thick-walled self-healing cylinder is more than tripled off a thick-walled nonself-healing cylinder.

A Nano-Scale Approach to Study the Healing Phenomenon in Warm Mix Asphalt

Abstract During the past decade, new technologies such as warm mix asphalt (WMA) technology have been used to help in reducing the carbon footprint of asphalt pavements. However, there are still unanswered questions and concerns regarding the long-term performance of asphalt material produced using these technologies. One of these questions is the influence of using these technologies on the healing behavior of asphalt binders, which might have a significant impact on their performance. In this paper, a nano-scale approach that uses atomic force microscopy (AFM) was developed and employed to evaluate the effect of different WMA technologies on the healing characteristics of commonly used asphalt binders, namely, PG 64-22, and PG 70-22M. The considered WMA technologies included: Advera®, Evotherm® M1, Sasobit®, and foamed WMA. The results of this paper indicated that Advera®, Evotherm® M1, and foamed WMA technologies improved the micro-crack closure rate in the considered asphalt binders. Furthermore, only the Sasobit significantly decreased the cohesive bonding energy in the asphalt binders, which may suggest that it may adversely affect their intrinsic healing. The other WMA technologies improved the hydroxyl cohesive bonding energy with an asphalt binder but did not significantly influence the carboxyl cohesive bonding energy.

A framework to characterize the healing potential of asphalt binder using the linear amplitude sweep test

The healing characteristics of asphalt binders affect the fatigue performance of asphalt mixtures and field pavements. The objective of this paper is to quantify the healing potential of asphalt binders using the linear amplitude sweep (LAS) test under various damage level and rest period durations. A healing protocol based on the LAS test is successfully established to measure the healing behaviour of asphalt binder by applying the rest periods before and after cohesive failure. Based on the simplified-viscoelastic continuum damage (S-VECD) model, the percent healing (%HS) is quantified from the healing recovery of the accumulated damage growths. The neat asphalt binder exhibits better %HS results than the SBS modified binder in the pre-failure conditions. However, the SBS modified binder exhibits a higher healing potential in the post-failure case. The rest-damage superposition principle (RDSP) is further investigated in the pre-failure cases to remove and unify the effects of damage level and rest period by constructing a %HS mastercurve at a given reference damage level. The developed healing mastercurve and related damage shift factor can be used to represent the intrinsic healing potential of a given asphalt binder. A series of healing indices are proposed and discussed based on the healing mastercurve to numerically compare the healing performance of asphalt binders.

Natural healing behavior of gamma radiation induced defects in multicomponent phosphate glasses used for high energy UV lasers

Obvious healing behavior of gamma radiation induced defects in multicomponent phosphate glass was observed at room temperature. The recovery of the defects depends on the ratio of H3BO3/SiO2 in the investigated glasses, the total gamma radiation dose, and the time of ageing at room temperature. Meanwhile, the synchronous decreases of PO3-EC and POHC defects contribute to the corresponding recovery of the transmittance change at 385 nm and 525 nm, which could be described by the charge transfer. Besides, a general model of the healing mechanism associated with the release and capture of the electrons between PO3-EC and POHC defects in these phosphate glass was proposed.

Oxytocin effects on experimental skin wound healing.

Objective:Oxytocin (OXY) has significant effects on mammalian behavior. Next to its role in lactation and social interactions, it is described to support better wound healing as well. However, direct OXY effects on wound healing and the regeneration of the microvascular network are still not clarified. We therefore examined the effects of OXY and an OXY receptor antagonist [atosiban (ATO)] on skin wound healing, focusing on epithelialization and neovascularization.Methods:Skin wound healing has been assessed using intravital fluorescence microscopy in a model of full dermal thickness wounds in the dorsal skin fold chamber of hairless mice. Animals received repetitive low or high doses of OXY or ATO. Morphological and cellular characterization of skin tissue repair was performed by histology and in vitro cell assays.Results:The assessment of skin tissue repair using this therapy regimen showed that OXY and ATO had no major influence on epithelialization, neovascularization, wound cellularity, or inflammation. Moreover, OXY and ATO did neither stimulate nor deteriorate keratinocyte or fibroblast migration and proliferation.Conclusion:In summary, this study is the first to demonstrate that OXY application does not impair skin wound healing or cell behavior. However, until now, the used transmitter system seems not to be clarified in detail, and it might be proposed that it is associated with the stress response of the organism to various stimuli.

Epithelial-to-Mesenchymal Transition in the Pathogenesis and Therapy of Head and Neck Cancer.

Head and neck cancer (HNC) is one of the most prevalent human malignancies worldwide, with a high morbidity and mortality. Implementation of interdisciplinary treatment modalities has improved the quality of life, but only minor changes in overall survival have been achieved over the past decades. Main causes for treatment failure are an aggressive and invasive tumor growth in combination with a high degree of intrinsic or acquired treatment resistance. A subset of tumor cells gain these properties during malignant progression by reactivating a complex program of epithelia-to-mesenchymal transition (EMT), which is integral in embryonic development, wound healing, and stem cell behavior. EMT is mediated by a core set of key transcription factors, which are under the control of a large range of developmental signals and extracellular cues. Unraveling molecular principles that drive EMT provides new concepts to better understand tumor cell plasticity and response to established as well as new treatment modalities, and has the potential to identify new drug targets for a more effective, less toxic, and individualized therapy of HNC patients. Here, we review the most recent findings on the clinical relevance of a mesenchymal-like phenotype for HNC patients, including more rare cases of mucosal melanoma and adenoid cystic carcinoma.

Contributions of hard and soft blocks in the self-healing of metal-ligand-containing block copolymers

The main aim of this work is to study the respective contribution of the hard and soft blocks of a metal-ligand containing block copolymer to the self-healing behavior. To this aim, different block copolymers containing terpyridine were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. These block copolymers consisted of polystyrene as the hard block, n-butyl acrylate (BA) as soft block and terpyridine units as the ligand moiety placed at different locations in the soft block. These block copolymers were complexed with manganese(II) chloride to introduce transient crosslinks and, thus, self-healing behavior. Homopolymers with the hard and soft block only were also synthesized and tested. A quasi-irreversible crosslinking, i.e. by using nickel(II) nitrate, was performed in order to study the dynamics of the permanently (strongly) crosslinked network. Rheological master curves were generated enabling the determination of the terminal flow in these networks and the reversibility of the supramolecular interactions. Additionally, the macroscopic scratch healing behavior and the molecular mobility of the polymer chains in these supramolecular networks were investigated. A kinetic study of the scratch healing was performed to determine the similarities in temperature dependence for rheological relaxations and macroscopic scratch healing. In our previous work, we have explored the effect of strength of the reversible metal-ligand interaction and the effect of changing the ratio of hard to soft block. This work goes further in separating the individual contributions of the hard and soft blocks as well as the reversible interactions and to reveal their relative importance in the complex phenomenon of scratch healing.

A comprehensive sintering mechanism for TBCs‐Part II: Multiscale multipoint interconnection‐enhanced initial kinetics

AbstractDuring thermal exposure, the sintering process of the plasma‐sprayed thermal barrier coatings (PS‐TBCs) presents significant two‐stage kinetics, as reported in the Part I. As a companion study, this part aims to reveal the mechanism responsible for the ultrafast sintering kinetics when initially exposed, since the initial short stage (stage‐I) often finishes most increment of the mechanical and thermal properties. A detailed examination of the pore healing behavior was carried out, based on the experimental result in Part I that the dominant structural change at the stage‐I is the significant healing at intersplat pore tips. Results show that the smooth splat surface, which made up the wedge‐shaped intersplat pores, changed to a rough surface with multiscale convexs after high‐temperature thermal exposure. Moreover, the multiscale roughening is highly sensitive to various orientations of the columnar grains inside the splats. Subsequently, multipoint connection between the counter‐surfaces of the intersplat pores was formed by the bridging of multiscale convexs. This multiscale multipoint connection between pore surfaces significantly accelerated the healing of intersplat pores, which can be dominantly responsible for the ultrafast sintering kinetics at the stage‐I. This comprehensive sintering mechanism could offer some positive suggestions toward prolonging the thermal‐insulating effect of TBCs.

A comparative study of the induction healing behaviors of hot and warm mix asphalt

In this paper, the induction healing behaviors of both warm mix asphalt and hot mix asphalt were investigated and compared through damage-healing-damage test. The steel fibers used for making asphalt mixture conductive were first optimized according to the thermal conductivity and induction heating speed of the mixture. Then, the gradient induction heating characteristics, cracking and fatigue resistance, and self-healing ratios of both warm mix asphalt and hot mix asphalt were studied. It is found that warm mix asphalt and hot mix asphalt have similar induction heating speed. The Aspha-Min based warm mix asphalt shows slightly higher fatigue resistance but slightly lower self-healing ratios than hot mix asphalt mixture. Both warm and hot mix asphalt mixtures have very high fatigue life ratios with induction heating, which means that induction heating can improve the durability of WMA. The optimal induction heating temperature of warm mix asphalt is slight lower than that of hot mix asphalt due to the remaining active ingredient, which also deceases the healing ratio slightly. It is also found that the healing ratios of both warm and hot mix asphalt mixtures are highly strain-dependent and the mixtures obtained best healing behaviors at medium microstrain amplitudes.

A comprehensive sintering mechanism for TBCs‐Part I: An overall evolution with two‐stage kinetics

AbstractA comprehensive sintering mechanism for lamellar thermal barrier coatings was reported experimentally and theoretically in this study. To begin with, an overall property evolution with two‐stage kinetics was presented during thermal exposure. The increase in mechanical property at initial thermal exposure duration (stage‐I) was much faster with respect to that in the following longer duration (stage‐II). At the stage‐I, the in situ pore healing behavior revealed that the significant faster sintering kinetics was attributed to the rapid healing induced by multipoint connection at the intersplat pore tips, as well as a small quantity of the narrow intrasplat cracks. At the following stage‐II, the residual wide intersplat pore parts and the wide intrasplat cracks decreased the possibility of multiconnection at their counter‐surfaces, resulting in a much lower sintering kinetic. Moreover, a structural model based on the microstructure of plasma sprayed YSZ coatings was developed to correlate the microstructural evolution with mechanical property. Consequently, the model predicted a two‐stage evolutionary trend of mechanical property, which is well consistent with experiments. In brief, by revealing the pore healing behavior, this comprehensive sintering mechanism shed light to the structure tailoring toward the advanced TBCs with both higher thermal‐insulating effect and longer life time.

Precipitation induced crack healing in a Ti2SnC ceramic in vacuum

Self-healing ceramics are able to heal cracks through an oxidative healing mechanism at high temperature in oxidizing environments with the recovery of original performance and functionality. However, the oxidation induced repair may be impossible when the ceramics are used in vacuum or inert atmospheres with low oxygen partial pressures. So far little work has been done on crack healing in vacuum or inert atmospheres. Here we report on the crack healing of a Ti2SnC ceramic in vacuum by a precipitation induced repair mechanism. Cracks induced by thermal shock in Ti2SnC are completely filled by only metallic Sn at temperatures above 800°C for only 1h in vacuum. The electrical conductivity of healed materials is fully recovered, and it even exceeds the initial conductivity. This work might bring a new wave of research on crack healing behavior of ceramics in low oxygen partial pressure environments.

Aqueous-Only, Green Route to Self-Healable, UV-Resistant, and Electrically Conductive Polyurethane/Graphene/Lignin Nanocomposite Coatings

Lignin is an undervalued sustainable commodity with many potential applications. In this work, we used lignin to produce noncovalently modified graphene from pristine graphite. Lignin-modified graphene (LMG) was added to waterborne polyurethane (WPU) to produce nanocomposites through a facile, aqueous-only route. Dynamic mechanical analysis shows increased storage modulus, i.e., as high as 171%, for WPU/LMG nanocomposites. Unlike unloaded WPU, WPU/LMG nanocomposite coatings show complete self-healing after only 150 s of infrared (IR) irradiation because of entropic and enthalpic contributions of LMG to self-healing. Moreover, it is revealed for the first time that although the nanocomposite coatings display two-dimensional healing behavior, at each phase the healing progresses uniaxially, which can be attributed to the interplay among viscoelastic recovery response, surface-tension-driven viscoelastic restoration, and polymer diffusion. Furthermore, WPU/LMG nanocomposites exhibit substantial improvement i...