Nanoparticles

Nanoparticles are tiny materials with diameters between 1 and 100 nanometers (nm), which are the most common form of nanomaterial on the market. Due to their high surface area and nanoscale size, nanoparticles are suitable for catalysis, imaging, medical applications, energy research, and environmental applications.

In aqueous solutions, it was found that cyclodextrin (CD) can spontaneously aggregate to promote the spontaneous formation of nanoparticles ^[1]. Therefore, CD-based nanoparticles have received widespread attention. A variety of CD-based nanoparticle materials have been prepared, which can be divided into core-shell nanoparticles, inorganic nanoparticles and nanovesicles according to different structures.

Core-Shell Nanoparticles

Core-shell nanoparticles are biphasic materials with an inner core structure and an outer shell structure, which are promising in drug delivery as the shell material can effectively protect the core material from reacting with the bioactive substances contained. New CD-based nanoparticles with a core-shell structure were developed to reduce the possibility of initial drug release caused by core-shell nanoparticles. The nanoparticles with CD as a hydrophilic shell allow controlled release by including guest molecules and can modulate the release rate.

• Instance

Nanoparticles based on a hydrophobic poly (lactic acid) (PLA) core and a hydrophilic β-CD polymer (Poly-β-CD) shell were designed. The poly-β-CD chains have a branched structure and form a monolayer of coils on the PLA surface, as shown in Fig. 1. The novel nanoparticles with a hydrophilic shell containing CD cavities allow a controlled release by including guest molecules ^[2].

Fig. 1 Simplified schematic representation of the supposed structure of the PLA/Poly-β-CD nanoparticles showing: a monolayer of Poly-β-CD coils adsorbed on the surface of the PLA core ^[2].

Inorganic Nanoparticles

Hydroxyapatite (HA) is an inorganic compound similar to the main mineral constituent of bone tissue. It has excellent biological properties, such as non-toxicity, no inflammatory reaction and high bioabsorbability, so it is a key material in the biological field. There are potential uses for nanoparticles containing HA in the biological field, such as specific recognition of proteins, but it is important to note that blood compatibility determines whether HA nanoparticles are compatible with biological systems. By incorporating CD into inorganic nanoparticles, HA nanoparticles may be more blood compatible.

• Instance

A series of CD-HA composite inorganic nanoparticles with sizes of 150 to 350 nm were obtained by incorporating different contents of β-CD into HA using a co-precipitation method. As the concentration of β-CD increases, the nanoparticles show better hydrophobicity and the adsorption capacity for albumin also increases. PAGE electrophoresis and densitometric scanning of the CD-HA complexes are shown in Fig. 2. The results showed that CD-incorporated HA inorganic nanoparticles have better blood compatibility and are more suitable for in vivo applications ^[3].

Fig. 2 (a) PAGE electrophoresis of H, H1, H2 and H3 along with plasma (P); (b) densitometric scan P and samples H, H1, H2 and H3 to demonstrate preferential albumin adsorption ^[3].

Nanovesicles

In supramolecular self-assembly, covalent interactions and intermolecular interactions are dynamically combined to produce hollow vesicle-like particles. As their external dimensions are in the nanometer range, these vesicles are also called nanoparticle vesicles or nanovesicles. CD-modified nanoparticles can self-assemble with nanoparticles modified by other guest molecules to obtain nanovesicles. Storage and transfer of substances is made possible through the use of nanovesicle materials.

• Instance

Isenbugel ^[4] modified silica nanoparticles with CD and adamantyl groups respectively, and synthesized β-CD modified silica particles and adamantyl-functionalized nanoparticles. Due to the fact that adamantyl and CD can form inclusion structures under host-guest interactions, hollow nanoparticle vesicles are formed when the two nanoparticles are mixed in water. The assumed supramolecular structure is shown in Fig. 3. Even after the evaporation of water, the nanovesicle structures remain extremely stable, making them ideally suited to transporting and storing chemicals ^[4].

Fig. 3 Structures of CD-SiO₂ and adamantyl-SiO₂ and schematic representation of the assumed supramolecular structures ^[4].

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