Interface versus bulk gelation and UCST in hydrophobically assembled TX-100 molecular gels

A high-performance GelMA-GelMA homogeneous double-network hydrogel assisted by 3D printing

Gelatin methacryloyl (GelMA) is a popular photocrosslinkable hydrogel that has been widely utilized in tissue engineering and regenerative medicine fields due to its excellent biocompatibility, biodegradability and cell response. However, the lack of mechanical properties limits its application. In the present study, a method for the preparation of a GelMA-GelMA (G-G) homogeneous double-network (DN) hydrogel to improve mechanical strength based on DLP 3D printing is proposed. The G-G DN hydrogel was fabricated and characterized in terms of microstructure, mechanical properties and rheological behavior. By modifying the degree of substitution (DS), the polymer concentration of double network crosslinking and the soak time, the novel G-G DN hydrogel could significantly improve the properties of strength, self-recovery and fatigue resistance. After all, the novel porous composite hydrogel (G-G DN hydrogel) could achieve more than twice that of the pure GelMA hydrogel, better fatigue resistance and printable ability. Therefore, it can be a potential choice of applications attracting great attention for its mechanical properties, great transmittance and biocompatibility.

Fabrication, Structure and Functional Characterizations of pH-Responsive Hydrogels Derived from Phytoglycogen

The pH-responsive hydrogels were obtained through successive carboxymethylation and phosphorylase elongatation of phytoglycogen and their structure and functional characterizations were investigated. Phytoglycogen (PG) was first carboxymethylated to obtain carboxymethyl phytoglycogen (CM-PG) with degree of substitution (DS) at 0.15, 0.25, 0.30, and 0.40, respectively. Iodine staining and X-ray diffraction analysis suggested that the linear glucan chains were successfully phosphorylase-elongated from the non-reducing ends at the CM-PG surface and assembled into the double helical segments, leading to formation of the hydrogel. The DS of CM-PG significantly influenced elongation of glucan chains. Specifically, fewer glucan chains were elongated for CM-PG with higher DS and the final glucan chains were shorter, resulting in lower gelation rate of chain-elongated CM-PG and lower firmness of the corresponding hydrogels. Scanning electron microscope observed that the hydrogels exhibited a porous and interconnected morphology. The swelling ratio and volume of hydrogels was low at pH 3–5 and then became larger at pH 6–8 due to electrostatic repulsion resulting from deprotonated carboxymethyl groups. Particularly, the hydrogel prepared from chain-elongated CM-PG (DS = 0.25) showed the highest sensitivity to pH. These results suggested that phosphorylase-treated CM-PG formed the pH-responsive hydrogel and that the elongation degree and the properties of hydrogels depended on the carboxymethylation degree. Thus, it was inferred that these hydrogels was a potential carrier system of bioactive substances for their targeted releasing in small intestine.

Universal Validity of Einstein Relation and Size-Dependent Viscosity and Surface-Active Characteristics of Nanofluids

In this report, the general validity of the Einstein viscosity relation, [Formula: see text], [Formula: see text], ratio of solution to solvent viscosity), is examined in nanofluids where monodisperse spherical nanoparticles (polystyrene latex spheres) of size 50–400[Formula: see text]nm were dispersed in water at room temperature, 25[Formula: see text]C. In addition to viscosity, we also measured contact angle, [Formula: see text], and surface free-energy, [Formula: see text], as function of particle concentration and observed that the universal relation [Formula: see text], [Formula: see text], remained valid, where [Formula: see text] may be relative viscosity, contact angle or surface free-energy and [Formula: see text] is a shape-dependent constant and is 2.5 in the Einstein limit. Thus, the Einstein relation has a wider validity than is generally thought encompassing both bulk and surface properties of nanofluids. Furthermore, we extend the study to establish an empirical relation between intrinsic viscosity [[Formula: see text]] and Huggins interaction parameter [Formula: see text], with particle size [Formula: see text], which obeyed: [Formula: see text] or [Formula: see text], where [Formula: see text] is in nm, [[Formula: see text]] is in cc/g, [Formula: see text] is in (g/cc)2 and [Formula: see text], [Formula: see text] and [Formula: see text] are constants of particle size. Identical expressions could be established for contact angle and surface free energy. These remarkable observations have not been reported hitherto.

Thermoresponsive Gels

Thermoresponsive gelling materials constructed from natural and synthetic polymers can be used to provide triggered action and therefore customised products such as drug delivery and regenerative medicine types as well as for other industries. Some materials give Arrhenius-type viscosity changes based on coil to globule transitions. Others produce more counterintuitive responses to temperature change because of agglomeration induced by enthalpic or entropic drivers. Extensive covalent crosslinking superimposes complexity of response and the upper and lower critical solution temperatures can translate to critical volume temperatures for these swellable but insoluble gels. Their structure and volume response confer advantages for actuation though they lack robustness. Dynamic covalent bonding has created an intermediate category where shape moulding and self-healing variants are useful for several platforms. Developing synthesis methodology-for example, Reversible Addition Fragmentation chain Transfer (RAFT) and Atomic Transfer Radical Polymerisation (ATRP)-provides an almost infinite range of materials that can be used for many of these gelling systems. For those that self-assemble into micelle systems that can gel, the upper and lower critical solution temperatures (UCST and LCST) are analogous to those for simpler dispersible polymers. However, the tuned hydrophobic-hydrophilic balance plus the introduction of additional pH-sensitivity and, for instance, thermochromic response, open the potential for coupled mechanisms to create complex drug targeting effects at the cellular level.