Mechanical Properties of a Supramolecular Nanocomposite Hydrogel Containing Hydroxyl Groups Enriched Hyper-Branched Polymers.

Wenjin Xing,Amin Jamshidi Ghahfarokhi,Youhong Tang,Chaoming Xie,Jonathan A Campbell,Sanaz Naghibi

doi:10.3390/polym13050805

Wenjin Xing, Amin Jamshidi Ghahfarokhi + Show 4 more

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https://doi.org/10.3390/polym13050805

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Journal: Polymers	Publication Date: Mar 6, 2021
Citations: 8	License type: CC BY 4.0

Affiliation: Flinders University, Southwest Jiaotong University

Abstract

Owing to highly tunable topology and functional groups, hyper-branched polymers are a potential candidate for toughening agents, for achieving supramolecular interactions with hydrogel networks. However, their toughening effects and mechanisms are not well understood. Here, by means of tensile and pure shear testings, we characterise the mechanics of a nanoparticle–hydrogel hybrid system that incorporates a hyper-branched polymer (HBP) with abundant hydroxyl end groups into the matrix of the polyacrylic acid (PAA) hydrogel. We found that the third and fourth generations of HBP are more effective than the second one in terms of strengthening and toughening effects. At a HBP content of 14 wt%, compared to that of the pure PAA hydrogel, strengths of the hybrid hydrogels with the third and fourth HBPs are 2.3 and 2.5 times; toughnesses are increased by 525% and 820%. However, for the second generation, strength is little improved, and toughness is increased by 225%. It was found that the stiffness of the hybrid hydrogel is almost unchanged relative to that of the PAA hydrogel, evidencing the weak characteristic of hydrogen bonds in this system. In addition, an outstanding self-healing feature was observed, confirming the fast reforming nature of broken hydrogen bonds. For the hybrid hydrogel, the critical size of failure zone around the crack tip, where serious viscous dissipation occurs, is related to a fractocohesive length, being about 0.62 mm, one order of magnitude less than that of other tough double-network hydrogels. This study can promote the application of hyper-branched polymers in the rapid evolving field of hydrogels for improved performance.

Highlights

Due to a large volume fraction of water in the polymer network, most conventional hydrogels exhibit poor mechanical performance, greatly confining their application scope
Results are presented in sequence, regarding the characterisations with instruments (Section 3.1), the comparison of mechanical properties (Section 3.2) and fracture toughness (Section 3.3) among the hybrid hydrogels of three-generation hyper-branched polymer (HBP), and the hysteresis and self-healing properties (Section 3.4)
A dense and smooth surface was observed for polyacrylic acid (PAA) hydrogel (Figure 3a), whereas the hybrid hydrogel of PAA and HBP displayed a relatively rough and wavy surface (Figure 3b), indicating potential physical interactions

Summary

Introduction

Due to a large volume fraction of water in the polymer network, most conventional hydrogels exhibit poor mechanical performance, greatly confining their application scope These compliant, weak, low-toughness, and notch-sensitive hydrogels cannot be used as supporting base materials for flexible bioelectronics [1,2,3], functional materials for externally controlled soft actuators [4,5], repeatedly loaded artificial muscles [6,7], and heavy load-bearing tissue scaffolds and replacements in tissue engineering [8,9]. The first network, either covalently or noncovalently cross-linked, serves as a sacrificial network, whose breakage into fragments can consume elastic energy; the second network maintains the basic shape under large deformation, even in the presence of macroscopic cracks In this way, the alginate/polyacrylamide (PAAm) DN hydrogels could achieve exceptional mechanical behaviours with tensile strength of 160 kPa and fracture toughness of 9000 J/m2 [14]

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Conclusion