Adv Polym Sci (2020) 285: 21–62
https://doi.org/10.1007/12_2019_53
© Springer Nature Switzerland AG 2020
Published online: 10 April 2020
How to Design Both Mechanically Strong
and Self-Healable Hydrogels?
Oguz Okay
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2 H-Bonding Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3 Hydrophobic Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.1 Hydrophobically Modified Associative Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Mechanically Strong Hydrophobically Modified Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4 Conclusions and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Abstract Several strategies have been developed in the past decade for the fabrication of self-healing or self-recovery hydrogels. Because self-healing and mechanical strength are two antagonistic features, this chapter tries to answer the question
“How to design both mechanically strong and self-healable hydrogels?”. Here, I
show that although autonomic self-healing could not be achieved in high-strength
hydrogels, a significant reversible hard-to-soft or first-order transition in cross-link
domains induced by an external trigger creates self-healing function in such
hydrogels. I mainly focus on the physical hydrogels prepared via hydrogen-bonding
and hydrophobic interactions. High-strength H-bonded hydrogels prepared via selfcomplementary dual or multiple H-binding interactions between hydrophilic polymer chains having hydrophobic moieties exhibit self-healing capability at elevated
temperatures. Hydrophobic interactions between hydrophobically modified hydrophilic polymers lead to physical hydrogels containing hydrophobic associations and
crystalline domains acting as weak and strong cross-links, respectively. Semicrystalline self-healing hydrogels exhibit the highest mechanical strength reported so far
and a high self-healing efficiency induced by heating above the melting temperature
of the alkyl crystals. Research in the field of self-healing hydrogels provided several
O. Okay (*)
Department of Chemistry, Istanbul Technical University, Istanbul, Turkey
e-mail: okayo@itu.edu.tr
https://doi.org/10.1007/12_2019_53
© Springer Nature Switzerland AG 2020
Published online: 10 April 2020
How to Design Both Mechanically Strong
and Self-Healable Hydrogels?
Oguz Okay
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2 H-Bonding Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3 Hydrophobic Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.1 Hydrophobically Modified Associative Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Mechanically Strong Hydrophobically Modified Hydrogels . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4 Conclusions and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Abstract Several strategies have been developed in the past decade for the fabrication of self-healing or self-recovery hydrogels. Because self-healing and mechanical strength are two antagonistic features, this chapter tries to answer the question
“How to design both mechanically strong and self-healable hydrogels?”. Here, I
show that although autonomic self-healing could not be achieved in high-strength
hydrogels, a significant reversible hard-to-soft or first-order transition in cross-link
domains induced by an external trigger creates self-healing function in such
hydrogels. I mainly focus on the physical hydrogels prepared via hydrogen-bonding
and hydrophobic interactions. High-strength H-bonded hydrogels prepared via selfcomplementary dual or multiple H-binding interactions between hydrophilic polymer chains having hydrophobic moieties exhibit self-healing capability at elevated
temperatures. Hydrophobic interactions between hydrophobically modified hydrophilic polymers lead to physical hydrogels containing hydrophobic associations and
crystalline domains acting as weak and strong cross-links, respectively. Semicrystalline self-healing hydrogels exhibit the highest mechanical strength reported so far
and a high self-healing efficiency induced by heating above the melting temperature
of the alkyl crystals. Research in the field of self-healing hydrogels provided several
O. Okay (*)
Department of Chemistry, Istanbul Technical University, Istanbul, Turkey
e-mail: okayo@itu.edu.tr