Printable Alginate Hydrogels with Embedded Network of Halloysite Nanotubes: Effect of Polymer Cross-Linking on Rheological Properties and Microstructure

Abstract

Rapidly growing 3D printing of hydrogels requires network materials which combine enhanced mechanical properties and printability. One of the most promising approaches to strengthen the hydrogels consists of the incorporation of inorganic fillers. In this paper, the rheological properties important for 3D printability were studied for nanocomposite hydrogels based on a rigid network of percolating halloysite nanotubes embedded in a soft alginate network cross-linked by calcium ions. Particular attention was paid to the effect of polymer cross-linking on these properties. It was revealed that the system possessed a pronounced shear-thinning behavior accompanied by a viscosity drop of 4–5 orders of magnitude. The polymer cross-links enhanced the shear-thinning properties and accelerated the viscosity recovery at rest so that the system could regain 96% of viscosity in only 18 s. Increasing the cross-linking of the soft network also enhanced the storage modulus of the nanocomposite system by up to 2 kPa. Through SAXS data, it was shown that at cross-linking, the junction zones consisting of fragments of two laterally aligned polymer chains were formed, which should have provided additional strength to the hydrogel. At the same time, the cross-linking of the soft network only slightly affected the yield stress, which seemed to be mainly determined by the rigid percolation network of nanotubes and reached 327 Pa. These properties make the alginate/halloysite hydrogels very promising for 3D printing, in particular, for biomedical purposes taking into account the natural origin, low toxicity, and good biocompatibility of both components.

An Electroconductive, Thermosensitive, and Injectable Chitosan/Pluronic/Gold-Decorated Cellulose Nanofiber Hydrogel as an Efficient Carrier for Regeneration of Cardiac Tissue

“…This observation indicates that the networks of Au@OBC nanofibers produced by physical interactions are quickly disrupted by the shear rate. Such behavior, which has also been reported in other hydrogels (for example, alginate/halloysite nanotubes [ 58 ]), may be attributed to (i) the breaking of physical crosslinks in the polymer network, (ii) interactions between fillers and filler/matrix interaction, and (iii) the alignment of polymer chains along the direction of flow [ 59 ]. However, at the higher gold concentration (75 mM), the shear-thinning index falls in the range of most thermosensitive chitosan-based hydrogels [ 60 ].…”

Anionic exopolysaccharide from Cryptococcus laurentii 70766 as an alternative for alginate for biomedical hydrogels

“…1 c&d). Both hydrogels exhibited a frequency-independent G' in the range of frequency of 1 to 10 Hz, and a higher value of G' compared to G", indicating the elastic and rigid structure of the hydrogels due to the presence of only covalent bonding [81][82][83].…”

Modulation of Molecular Structure and Mechanical Properties of κ-Carrageenan-Gelatin Hydrogel with Multi-Walled Carbon Nanotubes

“…So, experimental data show that nanotube additivity affects the gel's elastic characteristics, increasing the storage modulus. Obviously, this is a consequence of formation of a more "rigid" structure in the CNT-modified system [58,59].…”

“…So, experimental data show that nanotube additivity affects the gel's teristics, increasing the storage modulus. Obviously, this is a consequence o a more "rigid" structure in the CNT-modified system [58,59]. The linear and non-linear behavior of the studied systems in the gel a states was studied by the method of large amplitude oscillatory shear (strai urements).…”