Self-Healing Materials

Principles and Technology

George Wypych

• Publisher: ChemTec Publishing
• Year: 2017
• eBook ISBN: 9781927885246
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Self-Healing Materials: Principles and Technology is a practical book aimed at giving engineers and researchers in both industry and academia the information they need to deploy self-healing technology in a wide range of potential applications—from adhesives to the automotive industry, and from electronics to biomedical implants. Developments are increasingly seeing real-world application, and this book enables practitioners to use this technology in their own work. The book first discusses the principal mechanisms of self-healing and how these are applied to the development of materials which have the ability to repair themselves—either with minimal human intervention or without human intervention at all. The book provides a theoretical background and a review of the major research undertaken to date, to give a thorough grounding in this concept and related technology. The book specifically covers fault detection mechanisms in materials, and experimental methods to enable engineers to assess the efficiency of the self-healing process. It then discusses typical aids and additives in self-healing materials, including plasticizers, catalysts, shape-memory components, and more. Finally, the book contains real world examples of self-healing materials and how these have been applied to around 40 groups of products and industries, including materials used in the automotive industry, construction, composite materials for aerospace, biomaterials and materials used in medical devices, and adhesives and sealants. - Helps materials scientists and engineers to reduce risk of degradation and materials failure by using self-healing materials in a range of applications - Provides real world application examples, so practitioners can assess the applicability and usefulness of self-healing materials in their work - Includes guidance on the efficiency and efficacy of self-healing mechanisms, with coverage of the different parameters to be considered, and methodologies to use - Discusses typical aids and additives in self-healing materials, including plasticizers, catalysts, shape-memory components, and more

1

INTRODUCTION

LESSONS FROM LIVING THINGS

In the present environment of conservation of both natural resources and human efforts, preventive measures of materials damage and its repair, if the prevention fails, are topics of primary interest. Although the most important reason for material disposal is its out-of-fashion appearance rather than the mechanical or chemical failure, many materials prematurely fail, and a large number of these products could still be useful if proper methods are available to heal the damage.

Biological tissues are known for their abilities to heal, even when the material is critically damaged.¹ This process is initiated by chemical signals (e.g., inflammation).¹ The signals lead to wound closure and matrix remodeling.¹ In the leaving things, the healing process takes place at the molecular level, followed by the processes at the tissue level. Many elements of these processes are considered by the branches of polymer chemistry developing effective repair mechanisms. We will briefly evaluate some findings of the studies in medicine and biology.

Wound healing requires a coordinated response from various cell types within an injured tissue.² Cells have to first detect the existence of wound.² Cells are able to detect wounds from over hundreds of micrometers within seconds-to-minutes.² Wound detection involves the conversion of an injury-induced steady perturbation into a chemical or physical signal.² The signal is then propagated through the tissue to synchronize protective responses of cells near the wound site and at a distance.²

Figure 1.1 shows the sequence of events from injury to repair based on the studies of the larval zebrafish.² The events include: wound detection, stress signaling, protective response, regenerative events, and completion of tissue healing.² Figure 1.2 shows the complex mechanisms of cell lysis- and stress-mediated damage detection.² They include²

Figure 1.1 Phases of wound detection and repair in the larval zebrafish. Wound detection is triggered by tissue intrinsic cues. Injury induces stress signaling. In minutes following injury, these signals trigger protective responses, such as epithelial closure and leukocyte recruitment. The initial ‘detection phase’ is followed by the amplification and resolution of the inflammatory response, cell proliferation, and regenerative events. Completion of tissue healing can take anywhere from hours to days. [Adapted, by permission, from Enyedi, B; Niethammer P, Trends Cell Biol., 25, 7, 398-407, 2015.]

Figure 1.2 Molecular mechanism of cell lysis- and stress-mediated damage detection. (explanation in the text). [Adapted, by permission, from Enyedi, B; Niethammer P, Trends Cell Biol., 25, 7, 398-407, 2015.]

• (A) Wound detection triggered when damaged cells release cytoplasmic factors into the extracellular space, such as high-mobility group protein (HMGB1), formal peptides, or adenosine triphosphate (ATP).²

• (B) Perturbations resulting in the cell stress induce cytoplasmic Ca²⁺ signals by opening mechanosensitive, cation-permeable channels (transient receptor potential channels (TRPs), Piezo channels) or by releasing Ca²⁺ from intracellular stores.² Calcium signals initiate production of reactive oxygen species (ROS), either by activating the epithelial NADPH-oxidase DUOX (dual oxidase) or by triggering mitochondrial permeability transition.² Calcium signals also initiate the production and enzymatic oxidation of arachidonic acid into eicosanoids.² This leads to the production of proinflammatory eicosanoids.² Ca²⁺ also governs the secretion of paracrine mediators into the extracellular space (e.g., ATP).²

• (C) Most DAMPs (damage associated molecular patterns) act through transcriptional relay mechanisms in ‘sentinel’ cells such as tissue-resident macrophages dispersed throughout the tissue. DAMPs are recognized by pattern recognition receptors (PRRs) such as toll-like receptors (TLRs) or receptors for advanced glycation end-products (RAGE).² PRR and inflammasome signaling lead to processing and release of interleukin 1 (IL-1), which in turn stimulates chemokine secretion in target cells.² Signals from lysed and stressed cells along with these chemokines trigger neutrophil recruitment and epithelial migration.²

• (D) Rapid leukocyte migration to injury sites is mediated by G-protein coupled receptors, such as the N-formyl peptide receptor FPR1 and the 5-oxo-ETE and LTB4 eicosanoid receptors.² Leukocyte recruitment also depends on the H₂O₂-mediated oxidation of Src family kinases (SFK), such as the lck/yes-related novel protein tyrosine kinase (LYN).²

• (E) Extracellular ATP regulates wound closure by acting either as a DAMP or a stress signal through purinergic P2X channels or G-protein coupled P2Y receptors, which cause cytosolic [Ca²⁺]-elevation and IP3 production.² Alternatively, ATP may initiate wound responses through yet unknown mechanisms.²

Recent studies also show the existence of extrinsic detection mechanisms.² Wounds are detected by changes in epithelial permeability: namely, breach-induced osmotic stress on cells near wounds in larval zebrafish epidermis triggers wound signal release.²

Figure 1.3 shows evidence that self-healing behavior of mussels is based on reversible bonds dependent on the presence of intermolecular interactions and on their spatial distribution.⁴ In order to understand the function of self-healing materials and to optimize their functions, the morphochemistry and hierarchical structure of such systems need to be considered.⁴

Figure 1.3 Raman evidence of metal coordination in the mussel byssus. (a) Mussels attach to hard surface...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Chapter 1: INTRODUCTION: LESSONS FROM LIVING THINGS
• Chapter 2: MECHANISMS OF SELF-HEALING
• Chapter 3: CHEMICAL AND PHYSICAL PROCESSES OCCURRING DURING SELF-HEALING OF POLYMERS
• Chapter 4: FAULT DETECTION MECHANISMS
• Chapter 5: TRIGGERING AND TUNING THE HEALING PROCESSES
• Chapter 6: ACTIVATION ENERGY OF SELF-HEALING
• Chapter 7: MEANS OF DELIVERY OF HEALANT TO THE DEFECT LOCATION
• Chapter 8: SELF-HEALING TIMESCALE
• Chapter 9: SELF-HEALING EXTENT
• Chapter 10: MOLECULAR DYNAMICS SIMULATION
• Chapter 11: MORPHOLOGY OF HEALING
• Chapter 12: SELECTED EXPERIMENTAL METHODS IN EVALUATION OF SELF-HEALING EFFICIENCY
• Chapter 13: ADDITIVES AND CHEMICAL STRUCTURES USED IN SELF-HEALING TECHNOLOGY
• Chapter 14: SELF-HEALING OF DIFFERENT POLYMERS
• Chapter 15: SELF-HEALING IN DIFFERENT PRODUCTS
• INDEX