Rheological properties of thermoresponsive nanocomposite hydrogels

Abstract

Highly elastic and robust nanocomposite hydrogels based on N-isopropylacrylamide (NIPAM) and cationic (3-acrylamidopropyl) trimethylammonium chloride (AMPTMA) were synthesized by photopolymerization. Nanoscopic clay, laponite XLS, was added in the gels during the synthesis. The effect of a hydrophobic salt, lithium bis(trifluoromethane) sulfonimide (LiNTf 2 ), and clay content on the viscoelastic properties, swelling ratio, and stiffness of the nanocomposite hydrogels were investigated as a function of temperature. Synthetic clay served as a multifunctional cross-linker, producing hydrogels with enhanced elastic properties. Anionic NTf 2 binds to the cationic comonomer units and significantly affected the viscoelasticity and thermal properties. DSC measurements showed that the volume phase transition temperature and its enthalpy changed with the clay content and with introducing the cationic comonomer (AMPTMA) in the PNIPAM network. With the addition of either laponite XLS or the comonomer and 5 mM solution of LiNTf 2 , a fourfold and fivefold increase in elastic modulus was obtained, respectively, compared to that of the homopolymer PNIPAM hydrogel. With increasing the temperature from 20 to 458C for the copolymer gel with 10% AMPTMA in 5 mM LiNTf 2 , the elastic modulus grew 15 times larger.

Self-Supporting Nanoclay as Internal Scaffold Material for Direct Printing of Soft Hydrogel Composite Structures in Air

“…It is noted that there is a need for and various applications of Laponite nanoclay based hydrogel composites. As an inorganic biomaterial, silicate-based nanoclay has already been mixed with various polymeric hydrogels, both synthetic − and natural. ,− The introduction of nanoclays into various polymeric hydrogels typically results in soft composites with higher mechanical strength, improved elasticity and rheological properties, and enhanced biological activities. ,,− ,− Relevant applications of such soft composites include medical diagnostic and therapeutic devices, controlled drug delivery devices, biomedical imaging, and regenerative medicine. ,− ,− ,− …”

Combining 3D Printing with Electrospinning for Rapid Response and Enhanced Designability of Hydrogel Actuators

“…Different well‐designed rigid PNIPAm/clay patterns are printed on PNIPAm membranes by a 3D printer. Although PNIPAm/clay composite exhibits less obvious responsiveness when compared with electrospun membranes, it holds particular relevance in guiding the formation of internal stresses, which govern the shape transitions of the substrates. Briefly, swelling mismatch between the substrates and the printed patterns will give rise to internal stresses in the thickness direction and in the plane simultaneously, resulting in complex shape transitions synergistically.…”

Functional Hydrogels and Their Application in Drug Delivery, Biosensors, and Tissue Engineering

“…Similarly, Devadhasan and Kim introduced a new method to quantify various pH solutions with a complementary metal oxide semiconductor image sensor, which produced high-accuracy analyses based on pH measurement [123]. In this approach, a thin film was fabricated by merging a pH indicator with the hydrogel matrix and the modified gel exhibited color change development across the full spectrum of pH (pH [1][2][3][4][5][6][7][8][9][10][11][12][13][14].The complementary metal oxide semiconductor image sensor then absorbed the color intensity of the hydrogel film, and the hue value was converted into digital data with the help of an analog-to-digital converter to determine the pH ranges of solutions [123]. This gel may be useful for in situ pH sensing in the presence of toxic chemicals and chemical vapors.…”

“…Hydrogels are a class of polymers having a three-dimensional network structure formed through physical and chemical cross-linking of monomers with a hydrophilic group [1]. Hydrogels swell when they absorb large volumes of water yet maintain their original structures without being dissolved [2,3] (Figure 1). In the biomedical field, hydrogels are a new class of functional polymer materials with enormous potential in biotechnology.…”

“…These hydrogels are mainly composed of two interpenetrating or semi-interpenetrating networks with different properties. Under stress, the first network absorbs energy to burst, endowing hydrogels with high strength and toughness, while the second network is loosely cross-linked and is more difficult to destroy, which maintains the integrity of hydrogels [3]. (iii) Nanoparticles as giant multifunctional crosslinking points, where polymer chains are cross-linked into a three-dimensional network by physical adsorption or chemical bonding [18].…”