Silica-Based Nanomaterials for Diabetes Mellitus Treatment

Diabetes mellitus, a chronic metabolic disease with an alarming global prevalence, is associated with several serious health threats, including cardiovascular diseases. Current diabetes treatments have several limitations and disadvantages, creating the need for new effective formulations to combat this disease and its associated complications. This motivated the development of therapeutic strategies to overcome some of these limitations, such as low therapeutic drug bioavailability or poor compliance of patients with current therapeutic methodologies. Taking advantage of silica nanoparticle characteristics such as tuneable particle and pore size, surface chemistry and biocompatibility, silica-based nanocarriers have been developed with the potential to treat diabetes and regulate blood glucose concentration. This review discusses the main topics in the field, such as oral administration of insulin, glucose-responsive devices and innovative administration routes.

Comprehensive understanding of the synthesis and formation mechanism of dendritic mesoporous silica nanospheres

The interest in the design and controlled fabrication of dendritic mesoporous silica nanospheres (DMSNs) emanates from their widespread application in drug-delivery carriers, catalysis and nanodevices owing to their unique open three-dimensional dendritic superstructures with large pore channels and highly accessible internal surface areas. A variety of synthesis strategies have been reported, but there is no basic consensus on the elucidation of the pore structure and the underlying formation mechanism of DMSNs. Although all the DMSNs show a certain degree of similarity in structure, do they follow the same synthesis mechanism? What are the exact pore structures of DMSNs? How did the bimodal pore size distributions kinetically evolve in the self-assembly? Can the relative fractions of small mesopores and dendritic large pores be precisely adjusted? In this review, by carefully analysing the structures and deeply understanding the formation mechanism of each reported DMSN and coupling this with our research results on this topic, we conclude that all the DMSNs indeed have the same mesostructures and follow the same dynamic self-assembly mechanism using microemulsion droplets as super templates in the early reaction stage, even without the oil phase.

Design of Dendritic Large-Pore Mesoporous Silica Nanoparticles with Controlled Structure and Formation Mechanism in Dual-Templating Strategy

Dendritic large-pore mesoporous silica nanoparticles (DLMSN) is an important biodegradable drug carrier due to its high porosity, which can be prepared by coassembly of a major template and an auxiliary template in aqueous solution, followed by hydrolysis of tetraethyl orthosilicate (TEOS). The auxiliary template is key to obtaining dendritic large-pore structures; however, how to choose the auxiliary template to obtain the desired pore structure is largely unknown. This is because the formation mechanism of DLMSN is still not clear. In this study, a series of therapeutic agent molecules were used as the auxiliary templates to study the control of the pore morphology of DLMSN. Transmission electron microscopy observation and theoretical modeling were used to study the micelle formation, and early stage silica formation was also observed. It is proposed that the silica branches and sheets formed by hydrolysis of TEOS on single micelle and micelle bundles, which formed the initial nanoparticles with spherical structures and new silica species growing on the early formed particles to form DLMSN. The fine control of pore morphology was demonstrated by using auxiliary templates with different structural characteristics, which were used for selective drug loading. This work provides a design strategy of how to choose suitable auxiliary templates for preparing DLMSN with desired pore structure for biomedical applications.

A non-surfactant self-templating strategy for mesoporous silica nanospheres: beyond the Stöber method

The well-known Stöber method has been widely used to synthesize nonporous silica nanospheres (NPs), however, in the absence of surfactant templates, the synthesis of mesoporous silica nanospheres (MSNs) has not been achieved. Herein, in the absence of organic surfactant templates, by a simple premixing of three components tetraethoxysilane-water-ethanol (TEOS-H₂O-EtOH) with a precise molar ratio, the parent silica nanoparticles with a low condensation degree and controlled particle size can be readily obtained. Subsequently, via a simple two-step post-treatment, the obtained MSNs exhibited a high surface area (ca. 500 m² g^-1), accessible mesopores (3.0 nm), and a large pore volume (0.87 mL g^-1), similar to those of MCM-41 and SBA-15 silicas. The unique self-templating role of the 'pre-Ouzo' effect of ternary surfactant-free TEOS-H₂O-EtOH systems was proposed to understand the formation of mesoporosity.

Origin of the Photoluminescence of Metal Nanoclusters: From Metal-Centered Emission to Ligand-Centered Emission

Recently, metal nanoclusters (MNCs) emerged as a new class of luminescent materials and have attracted tremendous interest in the area of luminescence-related applications due to their excellent luminous properties (good photostability, large Stokes shift) and inherent good biocompatibility. However, the origin of photoluminescence (PL) of MNCs is still not fully understood, which has limited their practical application. In this mini-review, focusing on the origin of the photoemission emission of MNCs, we simply review the evolution of luminescent mechanism models of MNCs, from the pure metal-centered quantum confinement mechanics to ligand-centered p band intermediate state (PBIS) model via a transitional ligand-to-metal charge transfer (LMCT or LMMCT) mechanism as a compromise model.