Solid Lipid Nanoparticles (SLNs)
A globular structure containing a monolayer of phospholipid surrounds the dissolved or dispersed drug in the solid core. The employment of Solid Lipid Nanoparticles (SLN) as a drug delivery vehicle is being increasing day by day because it paves the way to an alternative suitable approach to the available traditional colloidal carrier mediated systems such as liposomes, polymer-based nanocarriers, and emulsions (Figure 3.4). Generally, SLN ranges from 50 to 1000 nm in size. They are constructed using a highly melting fatty matrix (solid lipid ingredients) to mask the challenges and limitations such as cytotoxicity, lipid and polymer degradation, drug leakage, nanoparticles agglomeration, high production cost, lack of large-scale manufacturing, and stability issues. SLN aims to formulate a biologically bio-compatible and protect the drug degradation and prolong the storage stability. Commonly they are formulated as a vehicle for delivering the therapeutic agent to the brain, cancerous tissues, for tubercular therapy, carriers for vaccines, topical application, and cosmetics [34].
Figure 3.4 Solid lipid nanoparticles (SLNs).
3.3.3 Nanocarbon Tubes
These are cylindrical structured molecules having a diameter of 0.3 to 3 nm and length of 20 to 1000 nm (Figure 3.5). Crystalline allotropic carbon sheets form mono- or multilayers of nanotubes. They take advantage by increasing the solubility and enhancing the cellular cytoplasmic and nuclei permeation, and they serve as a carrier for gene-based and protein-based drug delivery, while striking the thermal, electrical, and mechanical properties for the early-stage diagnosis of cancer in patients [35].
3.3.4 Polymer-Based Nanoparticles
Polymeric nanoparticles are synthesized by the spontaneous aggregation of copolymers with unlikely hydrophobicity in the micelles forming core shell in the aqueous medium (Figure 3.6). They facilitate the encapsulation of lipophilic or hydrophilic drug molecules, nucleic acids, peptides, and smaller molecules to completely strengthen the drug protection in the systemic circulation. Usually they are biocompatible and systemic degradable particle of 10 to 1000 nm in size. They are used as carriers for sustained and controlled drug delivery by modifying the surface of the nanoparticle for passive and active target delivery [36].
3.3.5 Polymer-Based Micelles
Amphiphilic blockage of copolymers is structurally arranged in a nanosized core (Figure 3.7) ranging from 10 to 100 nm. They have a unique microscopic architecture enhancing their property such as increasing the solubility of poorly solubilizing agents, higher entrapment efficiency, nanosize, and biologically stable. They have the ability to tailor micelles for higher degree of desire drug compatibility for the delivery system [37].
Figure 3.5 Carbon nanotubes.
Figure 3.6 Polymer-based nanoparticles.
Figure 3.7 Polymer-based micelle formation.
3.3.6 Dendrimers
They are macromolecules that are naturally or synthetically branched compositions of amino acids, nucleotides, and saccharides (Figure 3.8). They are structured with an exterior outer surface, following the inner branched layers and centrally contain the core. They are synthesized by controlled polymerization to produce monodispersed highly branched polymer system. The cavities of the branched polymers in the core are loaded with small molecules by chemical bondage or hydrophobic linkage or by simple hydrogen bonding. They vary in size NMT 10 nm. They serve the positivity of their controlled delivery of biologically active agents targeting the macrophages and hepatic tissues [38].
Figure 3.8 Dendrimers.
3.3.7 Metallic Nanoparticles
Particles smaller than 100 nm using metals such as gold, silver, and iron oxides to formulate nanoparticles, nanocages, and nanoshells are utilized to enable and modify their advantages in therapy and diagnosis of diseases [39].
3.3.7.1 Gold Nanoparticles
Colloidal or suspension of gold in the nanometer scale offers different shapes and sides based on the optical property, chemical characteristics, surface modification, and biologically stable and compatible delivery of agents (Figure 3.9). They strongly process the optical properties like photo absorption, light scattering, modified SERS (Surface Enhanced Raman Scattering), and fluorescence because of their unparalleled free electron interaction in the nanoparticulate with light. Their investigation and estimations are used in determination of biomarkers in cancer and cardiac diseases; they also have several biomedical therapeutic applications. In a recent research, PEGylation of AuNPs that are conjugated with drugs helps to bypass the RES (reticular endothelial system) clearance. The antibodies can be conjugated to the surface of the gold nanocages and targeted to the cancerous cell receptors. FDA-approved drugs Verigene and Aurimmune in clinical trials (Phase II) are some of the AuNP for particular therapeutic areas. AuNP utilizes the principle of receptor site-specific targeted drug delivery strategy for the development and advances in the application of photothermal medical care, genomic regulations, and choice of drug for treatment for the disease. Hence, the solid spherical colloidal gold nanoparticles of 50 nm and above report of plasmonic photo thermal therapy (PPTT) due to its stronger NIR absorption (near-infrared). The Ab conjugated with AuNPs can be applicable for both PPTT and diagnosis [40].
Figure 3.9 PEG coated gold nanospheres.
3.3.7.2 Iron Oxide Nanoparticles
Ferric oxide is a paramagnetic inorganic compound. It is one of the three iron oxides. Fe2O3 NPs are magnetic nanosized particles present in reddish brown color. They are widely used in biological
