Biomimetics

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13 pages, 1681 KiB

Open AccessArticle

A Highly Stretchable, Tough, Fast Self-Healing Hydrogel Based on Peptide–Metal Ion Coordination

by Liang Zeng, Mingming Song, Jie Gu, Zhengyu Xu, Bin Xue, Ying Li and Yi Cao

Biomimetics 2019, 4(2), 36; https://doi.org/10.3390/biomimetics4020036 - 10 May 2019

Cited by 56 | Viewed by 8051

Abstract

Metal coordination bonds are widely used as the dynamic cross-linkers to construct self-healing hydrogels. However, it remains challenging to independently improve the toughness of metal coordinated hydrogels without affecting the stretchability and self-healing properties, as all these features are directly correlated with the [...] Read more.

Metal coordination bonds are widely used as the dynamic cross-linkers to construct self-healing hydrogels. However, it remains challenging to independently improve the toughness of metal coordinated hydrogels without affecting the stretchability and self-healing properties, as all these features are directly correlated with the dynamic properties of the same metal coordination bonds. In this work, using histidine–Zn²⁺ binding as an example, we show that the coordination number (the number of binding sites in each cross-linking ligand) is an important parameter for the mechanical strength of the hydrogels. By increasing the coordination number of the binding site, the mechanical strength of the hydrogels can be greatly improved without sacrificing the stretchability and self-healing properties. By adjusting the peptide and Zn²⁺ concentrations, the hydrogels can achieve a set of demanding mechanical features, including the Young’s modulus of 7–123 kPa, fracture strain of 434–781%, toughness of 630–1350 kJ m⁻³, and self-healing time of ~1 h. We anticipate the engineered hydrogels can find broad applications in a variety of biomedical fields. Moreover, the concept of improving the mechanical strength of metal coordinated hydrogels by tuning the coordination number may inspire the design of other dynamically cross-linked hydrogels with further improved mechanical performance. Full article

(This article belongs to the Special Issue Biogenic and Bioinspired Self-Healing Materials)

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17 pages, 2528 KiB

Open AccessArticle

Bioinspired Histidine–Zn²⁺ Coordination for Tuning the Mechanical Properties of Self-Healing Coiled Coil Cross-Linked Hydrogels

by Isabell Tunn, Matthew J. Harrington and Kerstin G. Blank

Biomimetics 2019, 4(1), 25; https://doi.org/10.3390/biomimetics4010025 - 18 Mar 2019

Cited by 42 | Viewed by 6863

Abstract

Natural biopolymeric materials often possess properties superior to their individual components. In mussel byssus, reversible histidine (His)–metal coordination is a key feature, which mediates higher-order self-assembly as well as self-healing. The byssus structure, thus, serves as an excellent natural blueprint for the development [...] Read more.

Natural biopolymeric materials often possess properties superior to their individual components. In mussel byssus, reversible histidine (His)–metal coordination is a key feature, which mediates higher-order self-assembly as well as self-healing. The byssus structure, thus, serves as an excellent natural blueprint for the development of self-healing biomimetic materials with reversibly tunable mechanical properties. Inspired by byssal threads, we bioengineered His–metal coordination sites into a heterodimeric coiled coil (CC). These CC-forming peptides serve as a noncovalent cross-link for poly(ethylene glycol)-based hydrogels and participate in the formation of higher-order assemblies via intermolecular His–metal coordination as a second cross-linking mode. Raman and circular dichroism spectroscopy revealed the presence of α-helical, Zn²⁺ cross-linked aggregates. Using rheology, we demonstrate that the hydrogel is self-healing and that the addition of Zn²⁺ reversibly switches the hydrogel properties from viscoelastic to elastic. Importantly, using different Zn²⁺:His ratios allows for tuning the hydrogel relaxation time over nearly three orders of magnitude. This tunability is attributed to the progressive transformation of single CC cross-links into Zn²⁺ cross-linked aggregates; a process that is fully reversible upon addition of the metal chelator ethylenediaminetetraacetic acid. These findings reveal that His–metal coordination can be used as a versatile cross-linking mechanism for tuning the viscoelastic properties of biomimetic hydrogels. Full article

(This article belongs to the Special Issue Biogenic and Bioinspired Self-Healing Materials)

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18 pages, 2338 KiB

Open AccessArticle

Synthesis and Mechanochemical Activity of Peptide-Based Cu(I) Bis(N-heterocyclic carbene) Complexes

by Sebastian Funtan, Philipp Michael and Wolfgang H. Binder

Biomimetics 2019, 4(1), 24; https://doi.org/10.3390/biomimetics4010024 - 14 Mar 2019

Cited by 20 | Viewed by 5375

Abstract

With the class of shock-absorbing proteins, nature created some of the most robust materials combining both mechanical strength and elasticity. Their excellent ability to dissipate energy to prevent surrounding cells from damage is an interesting property that regularly is exploited for applications in [...] Read more.

With the class of shock-absorbing proteins, nature created some of the most robust materials combining both mechanical strength and elasticity. Their excellent ability to dissipate energy to prevent surrounding cells from damage is an interesting property that regularly is exploited for applications in biomimetic materials. Similar to biomaterials, where mechanical stimuli are transmitted into a (bio)chemical response, mechanophoric catalysts transform mechanical energy into a chemical reaction. Force transmission is realized commonly by polymeric handles directing the applied force to the mechanophoric bond, which in turn leads to stress-induced activation of the catalyst. Therefore, shock-absorbing proteins able to take up and store mechanical energy elastically for subsequent force transduction to the labile bond seem to be perfect candidates to fulfill this task. Here, we report on the synthesis of two different latent mechanophoric copper(I) bis(N-heterocyclic carbene) complexes bearing either two carboxyl groups or two amino groups which allow conjugation reactions with either the N- or the C-terminus of amino acids or peptides. The chosen catalysts can be activated, for instance, by applying external mechanical force via ultrasound, removing one N-heterocyclic carbene (NHC) ligand. Post-modification of the mechanophoric catalysts via peptide coupling (Gly, Val) and first reactions showed that the mechanoresponsive behavior was still present after the coupling. Subsequent polycondensation of both catalysts lead to a polyamide including the Cu(I) moiety. Mechanochemical activation by ultrasound showed conversions in the copper(I)-catalyzed alkyne-azide “click” reaction (CuAAC) up to 9.9% proving the potential application for the time and spatial controlled CuAAC. Full article

(This article belongs to the Special Issue Biogenic and Bioinspired Self-Healing Materials)

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20 pages, 6068 KiB

Open AccessArticle

A High Coordination of Cross-Links Is Beneficial for the Strength of Cross-Linked Fibers

by Huzaifa Shabbir, Christoph Dellago and Markus A. Hartmann

Biomimetics 2019, 4(1), 12; https://doi.org/10.3390/biomimetics4010012 - 4 Feb 2019

Cited by 14 | Viewed by 4469

Abstract

The influence of the coordination of (reversible) cross-links on the mechanical properties of aligned fiber bundles is investigated. Two polymeric systems containing cross-links of different coordination (two- and three-fold coordination) but having the same binding energy are investigated. In particular, the response to [...] Read more.

The influence of the coordination of (reversible) cross-links on the mechanical properties of aligned fiber bundles is investigated. Two polymeric systems containing cross-links of different coordination (two- and three-fold coordination) but having the same binding energy are investigated. In particular, the response to loading of these systems is compared. Mechanical parameters (strength, stiffness and work-to-fracture) are obtained by computational loading tests. The influence of coordination is studied for simple test systems with pre-defined topologies that maximize strength as well as for more realistic fiber bundles containing nine chains. The results show that a higher coordination of cross-links has a beneficial effect on the strength and the stiffness of the systems, while the work-to-fracture was found larger for the system having a smaller coordination of cross-links. It can be concluded that controlling the coordination of cross-links is a versatile tool to specifically tailor the mechanical properties of polymeric structures. Full article

(This article belongs to the Special Issue Biogenic and Bioinspired Self-Healing Materials)

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Review

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19 pages, 4672 KiB

Open AccessReview

Bioinspired Metal–Polyphenol Materials: Self-Healing and Beyond

by Amanda Andersen, Yaqing Chen and Henrik Birkedal

Biomimetics 2019, 4(2), 30; https://doi.org/10.3390/biomimetics4020030 - 4 Apr 2019

Cited by 42 | Viewed by 9653

Abstract

The blue mussel incorporates the polyphenolic amino acid l-3,4-dihydroxyphenylalanine (DOPA) to achieve self-healing, pH-responsiveness, and impressive underwater adhesion in the byssus threads that ensure the survival of the animal. This is achieved by a pH-dependent and versatile reaction chemistry of polyphenols, including [...] Read more.

The blue mussel incorporates the polyphenolic amino acid l-3,4-dihydroxyphenylalanine (DOPA) to achieve self-healing, pH-responsiveness, and impressive underwater adhesion in the byssus threads that ensure the survival of the animal. This is achieved by a pH-dependent and versatile reaction chemistry of polyphenols, including both physical interactions as well as reversible and irreversible chemical bonding. With a short introduction to the biological background, we here review the latest advances in the development of smart materials based on the metal-chelating capabilities of polyphenols. We focus on new ways of utilizing the polyphenolic properties, including studies on the modifications of the nearby chemical environment (on and near the polyphenolic moiety) and on the incorporation of polyphenols into untraditional materials. Full article

(This article belongs to the Special Issue Biogenic and Bioinspired Self-Healing Materials)

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34 pages, 8762 KiB

Open AccessReview

An Overview of Bioinspired and Biomimetic Self-Repairing Materials

by Olga Speck and Thomas Speck

Biomimetics 2019, 4(1), 26; https://doi.org/10.3390/biomimetics4010026 - 20 Mar 2019

Cited by 97 | Viewed by 15642

Abstract

During the 3.8 billion years of biological evolution, a multitude of functional principles has been developed in all kingdoms of life enabling the sealing and healing of diverse types of damage. Inspired by this treasure trove, biologists and engineers have become increasingly interested [...] Read more.

During the 3.8 billion years of biological evolution, a multitude of functional principles has been developed in all kingdoms of life enabling the sealing and healing of diverse types of damage. Inspired by this treasure trove, biologists and engineers have become increasingly interested in learning from biological insights for the development of self-repairing materials. In this review, particular attention is paid to the systematic transfer of knowledge from wound reactions in biological role models to technical applications with self-repair function. This knowledge transfer includes bioinspiration in terms of the conscious implementation of an idea from nature or biomimetics in the form of a systematic transfer of underlying functional principles found in selected biological role models. The current overview presents a selection of breakthroughs regarding bioinspired or biomimetic self-repairing materials, including the initial basic publications and the recent publications of the last eight years. Each reviewed publication is presented with reference to three key criteria: (i) self-repair mechanisms in plants or animals as role models; (ii) knowledge transfer from living nature to technology; and (iii) bioinspired or biomimetic materials with self-repair function. Finally, damage control is discussed with a focus on damage prevention and damage management. Full article

(This article belongs to the Special Issue Biogenic and Bioinspired Self-Healing Materials)

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21 pages, 7110 KiB

Open AccessReview

Healing through Histidine: Bioinspired Pathways to Self-Healing Polymers via Imidazole–Metal Coordination

by Stefan Zechel, Martin D. Hager, Tobias Priemel and Matthew J. Harrington

Biomimetics 2019, 4(1), 20; https://doi.org/10.3390/biomimetics4010020 - 27 Feb 2019

Cited by 69 | Viewed by 16528

Abstract

Biology offers a valuable inspiration toward the development of self-healing engineering composites and polymers. In particular, chemical level design principles extracted from proteinaceous biopolymers, especially the mussel byssus, provide inspiration for design of autonomous and intrinsic healing in synthetic polymers. The mussel byssus [...] Read more.

Biology offers a valuable inspiration toward the development of self-healing engineering composites and polymers. In particular, chemical level design principles extracted from proteinaceous biopolymers, especially the mussel byssus, provide inspiration for design of autonomous and intrinsic healing in synthetic polymers. The mussel byssus is an acellular tissue comprised of extremely tough protein-based fibers, produced by mussels to secure attachment on rocky surfaces. Threads exhibit self-healing response following an apparent plastic yield event, recovering initial material properties in a time-dependent fashion. Recent biochemical analysis of the structure–function relationships defining this response reveal a key role of sacrificial cross-links based on metal coordination bonds between Zn²⁺ ions and histidine amino acid residues. Inspired by this example, many research groups have developed self-healing polymeric materials based on histidine (imidazole)–metal chemistry. In this review, we provide a detailed overview of the current understanding of the self-healing mechanism in byssal threads, and an overview of the current state of the art in histidine- and imidazole-based synthetic polymers. Full article

(This article belongs to the Special Issue Biogenic and Bioinspired Self-Healing Materials)

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Other

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16 pages, 2087 KiB

Open AccessPerspective

Mechanoregulation of Bone Remodeling and Healing as Inspiration for Self-Repair in Materials

by Richard Weinkamer, Christoph Eberl and Peter Fratzl

Biomimetics 2019, 4(3), 46; https://doi.org/10.3390/biomimetics4030046 - 9 Jul 2019

Cited by 19 | Viewed by 8036

Abstract

The material bone has attracted the attention of material scientists due to its fracture resistance and ability to self-repair. A mechanoregulated exchange of damaged bone using newly synthesized material avoids the accumulation of fatigue damage. This remodeling process is also the basis for [...] Read more.

The material bone has attracted the attention of material scientists due to its fracture resistance and ability to self-repair. A mechanoregulated exchange of damaged bone using newly synthesized material avoids the accumulation of fatigue damage. This remodeling process is also the basis for structural adaptation to common loading conditions, thereby reducing the probability of material failure. In the case of fracture, an initial step of tissue formation is followed by a mechanobiological controlled restoration of the pre-fracture state. The present perspective focuses on these mechanobiological aspects of bone remodeling and healing. Specifically, the role of the control function is considered, which describes mechanoregulation as a link between mechanical stimulation and the local response of the material through changes in structure or material properties. Mechanical forces propagate over large distances leading to a complex non-local feedback between mechanical stimulation and material response. To better understand such phenomena, computer models are often employed. As expected from control theory, negative and positive feedback loops lead to entirely different time evolutions, corresponding to stable and unstable states of the material system. After some background information about bone remodeling and healing, we describe a few representative models, the corresponding control functions, and their consequences. The results are then discussed with respect to the potential design of synthetic materials with specific self-repair properties. Full article

(This article belongs to the Special Issue Biogenic and Bioinspired Self-Healing Materials)

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