Titanium Carbide MXene Quantum Dots-Modified Hydroxyapatite Hollow Microspheres as pH/Near-Infrared Dual-Response Drug Carriers.

Titanium carbide MXene quantum dots (MQDs) possess intrinsic regulatory properties and selective toxicity to cancer cells. Here, MDQs were selected for the modification of hydroxyapatite (HA) microspheres, and MXene quantum dots-modified hydroxyapatite (MQDs-HA) hollow microspheres with controllable shapes and sizes were prepared as bone drug carriers. The results show that the prepared MQDs-HA hollow microspheres had a large BET surface area (231.2 m2/g), good fluorescence, and low toxicity. In addition, MQDs-HA showed a mild storage-release behavior and good responsiveness of pH and near-infrared (NIR). Thus, the MQDs-HA hollow microspheres have broad application prospects in the field of drug delivery and photothermal therapy.

CaCO3 Crystals with Unique Morphologies Controlled by the Hydrogen-Bonded Supramolecular Assemblies of Ureido-Pyrimidinone-Amino Acid Derivatives.

Biomineral materials such as nacre of shells exhibit high mechanical strength and toughness on account of their unique "brick-mortar" multilayer structure. 2-Ureido-4[1H]-pyrimidinone (UPy) derivatives with different types of end groups, due to the self-complementary quadruple hydrogen bonds and abundant Ca2+ binding sites, can easily self-assemble into supramolecular aggregates and act as templates and skeleton in the process of inducing mineral crystallization. In this work, UPy derivatives were used as templates to induce the mineralization and growth of CaCO3 through a CO2 diffusion method. The morphology of CaCO3 crystals was modulated and analyzed by adjusting the synthesizing parameters including Ca2+ concentration, pH, and end groups. The results showed that, by the regulatory role of the mineralization template, it was easier to realize the multilayer crystal structure at a lower concentration of Ca2+ (less than 0.01 mol L-1). Under alkaline regulation, the quadruple hydrogen bonds would be destroyed, and the template's regulation effect on the morphology of CaCO3 crystals would be weakened. Moreover, by comparing different types of end groups, it was proven that the UPy derivatives with carboxylic acid groups (-COOH) played a crucial role in the process of CaCO3 crystallization with unique morphologies.

Urchin-like Hydroxyapatite/Graphene Hollow Microspheres as pH-Responsive Bone Drug Carriers.

Hydroxyapatite (HA) is the main inorganic component of human bones and teeth. It has good biocompatibility and bioactivity, which promotes its good application prospects in the field of bone drug carriers. In this study, tetraethylenepentamine-graphene (rGO-TEPA)/CaCO3:HA composite microspheres were prepared via microwave hydrothermal synthesis using rGO-TEPA/CaCO3 solid microspheres as intermediates. Furthermore, the incompletely transformed CaCO3 was removed by soaking in a citric acid buffer to obtain rGO-TEPA/HA hollow composite microspheres. The two types of as-prepared composite microspheres exhibited sea urchin-like structures, large BET surface areas, and good dispersibility. Mouse preosteoblast cells (MC3T3-E1) were used for in vitro cytotoxicity experiments. The in vitro cell viability test showed that the two composite drug carriers exhibited noncytotoxicity. Moreover, the doxorubicin (DOX) loading and releasing investigations revealed that the two types of prepared carriers had mild storage-release behaviors and good pH responsiveness. Hence, these rGO-TEPA/HA hollow microspheres have promising applications as bone drug carriers.