50 mol% C18A after heating-induced healing exhibit a compressive strength of
138 Æ 10 MPa, which is around 87% of the virgin ones. Semicrystalline hydrogels
can also be made highly stretchability when a small amount of non-crystallizable
units are incorporated in the gel network to create mobility.
Research directed toward synthesis of self-healing hydrogels provided several
important findings not only in the field of self-healing but also in other hydrogel
applications. For instance, the presence of surfactants in hydrophobically modified
hydrogels significantly changes their viscoelastic and mechanical properties. Surfactant micelles solubilize hydrophobic associations and alkyl crystals and hence
facilitate the diffusion of polymer chains, thereby inducing self-healing. They are
also able to solubilize semicrystalline hydrogels of high mechanical strength opening
up their applications as injectable gels and as smart inks for 3D or 4D printing.
Similarly, H-bonded self-healing hydrogels dissolve in aqueous urea solutions,
while the injectable solution thus formed turns into a gel when the urea is forced
to diffuse out of the solution. The viscoelastic and mechanical properties of
H-bonded and hydrophobically modified hydrogels can be tailored by aqueous
urea solutions or surfactant micelles, respectively, to fit a variety of needs. Thus,
urea- or surfactant-induced processability may provide several future applications of
high-strength H-bonded and hydrophobically modified physical hydrogels.
Acknowledgment Work was partially supported by the Turkish Academy of Sciences (TUBA).
The author would like to thank all collaborators and graduate students for their contributions in the
development of hydrophobically modified and H-bonded physical hydrogels.
References
1. Calvert P (2009) Hydrogels for soft machines. Adv Mater 21:743–756
2. Means AK, Grunlan MA (2019) Modern strategies to achieve tissue-mimetic, mechanically
robust hydrogels. ACS Macro Lett 8:705–713
3. Chai Q, Jiao Y, Yu X (2017) Hydrogels for biomedical applications: their characteristics and
the mechanisms behind them. Gels 3(1). pii: E6
4. Hoare TR, Kohane DS (2008) Hydrogels in drug delivery: progress and challenges. Polymer
49:1993–2007
5. Brown HR (2007) A model of the fracture of double network gels. Macromolecules
40:3815–3818
6. Gong JP (2010) Why are double network hydrogels so tough? Soft Matter 6:2583–2590
7. Zhao X (2014) Multi-scale multi-mechanism design of tough hydrogels: building dissipation
into stretchy networks. Soft Matter 10:672–687
8. Creton C, Ciccotti M (2016) Fracture and adhesion of soft materials: a review. Rep Prog Phys
79:056601
9. Creton C (2017) 50th anniversary perspective: networks and gels: soft but dynamic and tough.
Macromolecules 50:8297–8316
10. Fu J (2018) Strong and tough hydrogels crosslinked by multi-functional polymer colloids.
J Polym Sci Part B Polym Phys 56:1336–1350
11. Fu J, in het Panhuis M (2019) Hydrogel properties and applications. J Mater Chem B
7:1523–1525
How to Design Both Mechanically Strong and Self-Healable Hydrogels?
55
138 Æ 10 MPa, which is around 87% of the virgin ones. Semicrystalline hydrogels
can also be made highly stretchability when a small amount of non-crystallizable
units are incorporated in the gel network to create mobility.
Research directed toward synthesis of self-healing hydrogels provided several
important findings not only in the field of self-healing but also in other hydrogel
applications. For instance, the presence of surfactants in hydrophobically modified
hydrogels significantly changes their viscoelastic and mechanical properties. Surfactant micelles solubilize hydrophobic associations and alkyl crystals and hence
facilitate the diffusion of polymer chains, thereby inducing self-healing. They are
also able to solubilize semicrystalline hydrogels of high mechanical strength opening
up their applications as injectable gels and as smart inks for 3D or 4D printing.
Similarly, H-bonded self-healing hydrogels dissolve in aqueous urea solutions,
while the injectable solution thus formed turns into a gel when the urea is forced
to diffuse out of the solution. The viscoelastic and mechanical properties of
H-bonded and hydrophobically modified hydrogels can be tailored by aqueous
urea solutions or surfactant micelles, respectively, to fit a variety of needs. Thus,
urea- or surfactant-induced processability may provide several future applications of
high-strength H-bonded and hydrophobically modified physical hydrogels.
Acknowledgment Work was partially supported by the Turkish Academy of Sciences (TUBA).
The author would like to thank all collaborators and graduate students for their contributions in the
development of hydrophobically modified and H-bonded physical hydrogels.
References
1. Calvert P (2009) Hydrogels for soft machines. Adv Mater 21:743–756
2. Means AK, Grunlan MA (2019) Modern strategies to achieve tissue-mimetic, mechanically
robust hydrogels. ACS Macro Lett 8:705–713
3. Chai Q, Jiao Y, Yu X (2017) Hydrogels for biomedical applications: their characteristics and
the mechanisms behind them. Gels 3(1). pii: E6
4. Hoare TR, Kohane DS (2008) Hydrogels in drug delivery: progress and challenges. Polymer
49:1993–2007
5. Brown HR (2007) A model of the fracture of double network gels. Macromolecules
40:3815–3818
6. Gong JP (2010) Why are double network hydrogels so tough? Soft Matter 6:2583–2590
7. Zhao X (2014) Multi-scale multi-mechanism design of tough hydrogels: building dissipation
into stretchy networks. Soft Matter 10:672–687
8. Creton C, Ciccotti M (2016) Fracture and adhesion of soft materials: a review. Rep Prog Phys
79:056601
9. Creton C (2017) 50th anniversary perspective: networks and gels: soft but dynamic and tough.
Macromolecules 50:8297–8316
10. Fu J (2018) Strong and tough hydrogels crosslinked by multi-functional polymer colloids.
J Polym Sci Part B Polym Phys 56:1336–1350
11. Fu J, in het Panhuis M (2019) Hydrogel properties and applications. J Mater Chem B
7:1523–1525
How to Design Both Mechanically Strong and Self-Healable Hydrogels?
55