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SCIENCE CHINA Materials, Volume 62, Issue 4: 586-596(2019) https://doi.org/10.1007/s40843-018-9347-5

Self-recoverable semi-crystalline hydrogels with thermomechanics and shape memory performance

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  • ReceivedJul 18, 2018
  • AcceptedAug 31, 2018
  • PublishedSep 21, 2018

Abstract

Stimuli-responsive hydrogels have become one of the most popular artificial soft materials due to their excellent adaption to complex environments. Thermoresponsive hydrogels triggered by temperature change can be efficiently utilized in many applications. However, these thermoresponsive hydrogels mostly cannot recover their mechanical states under large strain during the process. Herein, we utilize the heterogeneous comb-type polymer network with semi-crystalline hydrophobic side chains to design self-recovery semi-crystalline hydrogels. Based on hydrophilic/hydrophobic cooperative complementary interaction and heterogeneous polymer network, hydrogels can be endowed with excellent thermosensitive properties and mechanical performance. The hydrogels exhibit high compressive strength (7.57 MPa) and compressive modulus (1.76 MPa) due to the semi-crystalline domains formed by association of the hydrophobic poly(ε-caprolactone) PCL. The melting-crystalline transition of PCL and elastic polymer network provide the hydrogels excellent thermomechanical performance and self-recovery property. Furthermore, the hydrogels exhibit shape memory behavior, which can be realized by simple process and smart surface patterning. With these excellent properties, our hydrogels can be applied in sensors, flexible devices and scaffolds for tissue engineering.


Funded by

the National Natural Science Foundation of China(21574004)

the National Natural Science Funds for Distinguished Young Scholar(21725401)

the Fundamental Research Funds for the Central Universities

the National ‘Young Thousand Talents Program’

and the China Postdoctoral Science Foundation(2017M620012)


Acknowledgment

This work was financially supported by the National Natural Science Foundation of China (21574004), the National Natural Science Funds for Distinguished Young Scholar (21725401), the Fundamental Research Funds for the Central Universities, the National ‘Young Thousand Talents Program’, and the China Postdoctoral Science Foundation (2017M620012).


Interest statement

The authors declare that they have no conflict of interest.


Contributions statement

Zhang K, Zhao Z and Liu M designed the project. Zhang K and Huang J preformed the experiments. Zhang K, Zhao Z, Zhao T and Fang R analyzed the results. Zhang K, Fang R and Liu M wrote the paper. All authors contributed to general discussion of the article


Author information

Kangjun Zhang received his BSc degree from Beihang University in 2016. He is now a master candidate under the supervision of Prof. Mingjie Liu at Beihang University. His research focuses on the fabrication of smart hydrogels based on cooperative complementary interaction.


Ruochen Fang is a post-doctor in Beihang University. In 2011, He received his BSc degree in polymer materials and engineering in the Department of Chemistry from Jilin University. Then he joined Prof. Xi Zhang’s group and received his PhD degree from Tsinghua University in 2016. His current research interest focuses on binary cooperative complementary nanomaterials and bioinspired material science.


Mingjie Liu is currently a full-time professor at Beihang University. In 2005, he joined Prof. Lei Jiang’s group and received his PhD degree from the National Center for Nanoscience and Technology, Chinese Academy of Sciences (2010). He then worked as a postdoc in Prof. Takuzo Aida’s group in Riken in Japan from 2010 to 2015. In 2015, he was awarded the “1000 Youth Plan program” and joined Beihang University. In 2017, he was awarded the National Science Fund for Distinguished Young Scholars. His current research interest focuses on anisotropic soft matter with ordered structures, bioinspired design, and application of gel materials.


Supplement

Supplementary information

Experimental details and supporting data are available in the online version of the paper.


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  • Figure 1

    Preparation of SCHs. (a) Molecular structure of DMA, MEA and PCL-MA. (b) Schematic illustration of SCHs prepared by UV light polymerization and subsequently swelling. (c) The photos of precursor solution, polymer networks and SCHs. (d) The fitting of SAXS data of SCH2.5-6000 by T-S model. (e) SAXS profiles of SCHs with different PCL contents.

  • Figure 2

    Mechanical properties of SCHs. (a) Compressive strain-stress curves of hydrogel and SCHs with different PCL molecular weights. (b) Compressive strain-stress curves of hydrogel and SCHs with different PCL contents. (c, d) Compressive modulus of hydrogel, SCHs with different molecular weights and SCHs with different PCL contents, respectively.

  • Figure 3

    Thermomechanical properties of SCHs. (a) Compressive strain-stress curves of SCH2.5-6000 at different temperature. (b) Compressive modulus of SCHs with different molecular weights. (c) Compressive modulus of SCHs with different PCL contents. (d, e) The storage moduli (Gʹ) of the SCHs with different PCL molecular weights and contents at a frequency (ω) sweep of 15.8 rad s−1 and a constant shear strain (γ) of 0.5% by increasing temperature. (f) The storage moduli (Gʹ) of the SCH2.5-6000 in a temperature circulating test.

  • Figure 4

    Self-recovery performance of SCHs. (a) The loading-unloading curves of the SCH2.5-4000 with different compressive strains at 20°C. (b) The cyclic loading-unloading compressive tests of SCH2.5-4000 at 20°C. (c) The loading-unloading compressive tests of SCH2.5-4000 at 20 and 70°C. (d) The cyclic loading-unloading compressive tests of SCH2.5-4000 at 20°C with recovered by heat.

  • Figure 5

    Shape memory behaviors of SCHs. (a) Schematic illustration of the shape memory behavior of SCHs in the process of deforming, fixing and recovering. (b) Schematic illustration of internal structure of the PCL domains in the shape memory process. (c) Images showing the shape memory effects of SCHs. (d) The surface microstructure embossing and erasing during the shape memory process. The scale bar is 1 mm. (e) DSC thermograms exhibiting the melting (Tm=58.9°C) and crystallization temperature (Tc=21.5°C) of SCHs samples. (f) Shape memory behavior of compression and recovery. The black arrows indicate the four stages: (1) compressing at 70°C; (2) cooling to 20°C; (3) uploaded; and (4) heating to 70°C. (g) The fixed ratios and recovery ratios of SCHs with different molecular weights. (h) The fixed ratios and recovery ratios of SCHs with different PCL contents.

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