A Strong Bio‐Inspired Layered PNIPAM–Clay Nanocomposite Hydrogel

Abstract

The demand for robust hydrogels in pharmaceutical, biomedical, and industrial applications has motivated intense research efforts in these wet polymeric materials. [1] Recent advances have resulted in different strategies for creating highly stretchable polymeric hydrogels, including sliding-ring gels (SR gels), [2] nanocomposite gels (NC gels), [3] doublenetwork gels (DN gels), [4] macromolecular microsphere composite gels, [5] and tetra-poly(ethylene glycol) gels. [6] Among them, NC gels have attracted significant interest because of the simplicity of synthesis, high transparency, impressive mechanical properties, large reversible deformation, and excellent swelling and stimuli sensitivities. [7] The high mechanical properties of NC gels are desirable for practical application in many fields. However, it remains a great technical challenge to improve mechanical properties by enhancing the content of inorganic composition. Only a few percent of inorganic clay can be incorporated into NC gels (< 12 wt % at most), even though special mixing or modification of clay are adopted. [8] Further incorporation of clay leads to opacity and lower mechanical properties than the expected theoretical values resulting from the insufficiency of the nanoplatelet dispersion at high viscosity.As natural inorganic-organic nanocomposites, nacre finds its way around this problem by developing a well-ordered brick-and-mortar microstructure and robust interface. [9] Although mostly made of mineral platelets, nacre possesses an excellent combination of elastic modulus, strength, and toughness [10] and it provides a prime microstructural design model for the development of new materials. Recently, the layered microstructure of nacre has been successfully mim-icked and nacrelike hard structure materials with high mechanical performance were fabricated. [11] As for soft, wet inorganic-organic composites, NC gels can also benefit from duplication of the micro-/nanoscale structures of nacre. Herein, inspired by the ordered brick-and-mortar arrangement of inorganic and organic layers in nacre, we first demonstrate layered nanocomposite hydrogel (L-NC gel) films with a high clay content. The perfect micro-/nanoscale layered structure results in excellent mechanical properties higher than that of other reported NC hydrogels. We believe that it could offer innovative insights into the design of robust polymeric hydrogels for practical application.In our experiment, we prepared layered poly(N-isopropylacrylamide)-nanoclay (i.e. PNIPAM-nanoclay) hydrogel films with a nacrelike structure (Scheme 1). In a first step, clay platelets with a diameter of 28.4 nm and a thickness of 1.11 nm, the NIPAM monomer and the initiator were assembled into a lamellar structure by vacuum filtration (Scheme 1 b). [12] Then, L-NC gels were synthesized easily by in situ radical polymerization of NIPAM initiated through UV light. After polymerization, none of the hydrogel films dissolved when kept in water for a long time or sonicated, implying that PNIPAM and clay s...

Bioinspired Nanocomposite Hydrogels with Highly Ordered Structures

“…Moreover, some research groups have developed nanocomposite hydrogels with ordered structures using techniques for assembling 2D nanosheets such as GO nanosheets, nanoclay, and some liquid-crystalline inorganic nanosheets. [133][134][135][136][137] These reported ordered structured nanocomposite hydrogels can serve as high-performance bioengineering materials for tissue engineering. Figure 7.…”

Ternary Artificial Nacre Reinforced by Ultrathin Amorphous Alumina with Exceptional Mechanical Properties

“…When the content of Al was lower than that of GO (GO/AA = 6.5:3.5), the "pull-out" mode was the main toughening mechanism according to previous reports on binary artifi cial nacre. [ 45,51 ] With increasing Al content, the "pull-out" mechanism was partly weakened and the crack-defl ection mechanism was still not thoroughly formed, so that the failure strain decreased (ca. 3%).…”

Recent advances in clay mineral-containing nanocomposite hydrogels

“…hydrogels have been reported. These studies indicated that when such 2D CNPs are added to a polymeric hydrogel matrix, additional interactions take place between CNPs and polymers, resulting in the creation of nanocomposite hydrogels with improved mechanical properties, [33][34][35] stimuli-responsiveness, 36,37 swellability, 38 and self-healing abilities, 39 compared to hydrogels consisting of single hydrophilic polymers. This paper intends to review and analyze recent advances in clay mineral-containing nanocomposite hydrogels with an objective to highlight the state-of-the-art technologies used in the preparation of clay mineral-containing nanocomposite hydrogels.…”