Nanocarriers

Introduction to nanocarriers:

Nanocarriers are colloidal drug delivery systems with submicron particles, usually 500 nm or smaller 1. Over the past few decades, there has been a lot of research done on nanocarriers since they have shown great promise for medication delivery. Due to their high surface area to volume ratio, nanocarriers can change the fundamental characteristics and bioactivity of medicines. Some of the characteristics that nanocarriers can include in drug delivery systems include enhanced pharmacokinetics and biodistribution, lower toxicities, improved solubility and stability, controlled release, and site-specific delivery of therapeutic agents.

Biological nanocarriers

Solid lipid nanoparticles (SLNs), which were created in the early 1990s, are colloidal drug delivery systems with sizes ranging from 50 to 1,000 nm. Emulsifier(s) are utilized to stabilize the dispersion while emulsifier(s) are used to prepare SLNs by dispersing melted solid lipid(s) in water. High pressure homogenization and microemulsification are the two approaches that are most frequently utilized to create SLNs. SLNs offer a highly lipophilic lipid matrix for the dispersion or dissolution of medicines.8 For the creation of SLNs, a wide range of solid lipids, such as mono-, di-, and triglycerides; free fatty acids; free fatty alcohols; waxes; and steroids, have been used. Except for the fact that different types of lipids are employed in both formulations, SLNs and nanoemulsions are relatively comparable.

Figure 1

Schematics of SLN.

Abbreviation: SLN, solid lipid nanoparticle.

Liposomes

Over the past few decades, liposomes have drawn significant attention in biomedicine, particularly as a method of delivering anticancer medications.18 They demonstrated a number of advantages over conventional systems, including improved drug delivery, protection of the active ingredient from environmental factors, enhanced product performance features, preventing early encapsulated drug degradation, cost-effective formulations of pricey medications, and effective treatment with lower systemic toxicity.19 In addition, when compared to free pharmaceuticals in solution, the pharmacokinetic characteristics of medications coupled with liposomes are significantly altered.8 To demonstrate a prolonged half-life in blood circulation, they can be coated with polymers such as polyethylene glycol (PEG; PEGylated or stealth liposomes). The aqueous core of liposomes, which are spherical vesicles, is encased in lipid bilayers.

Figure 2

Diagrammatic representation of liposome structure

Drug-loaded liposome formulations improve drug biodistribution and pharmacokinetics by controlling drug distribution within plasma. When compared to free medicines in solution, doxorubicin-loaded PEGylated liposomes reduce the volume of doxorubicin dispersion in plasma from 1,000 to 2.8 L/m2.6 Additionally, it results in a lower medication concentration in healthy tissues while increasing drug concentration inside tumours. To increase target selectivity, liposomes can also be coupled to ligands or antibodies.

Dendrimers

Often branching macromolecules, dendrimers have several arms that branch out of a central core. They are often made utilizing natural or synthetic ingredients such sugars, nucleotides, and amino acids.

Due to their peculiar molecular weight, increased number of branching, multivalency, spherical morphologies, and monodispersed macromolecules with an average diameter of 1.5–14.5 nm, dendrimers are the most plausible drug delivery vehicles.

Creating dendrimer-drug conjugates has been a major focus of dendrimer preclinical development. Dendrimers have recently been widely used in biomedical domains, such as gene transfer, immunology, magnetic resonance imaging, vaccinations, and the delivery of antiviral, antibacterial, and anticancer drugs.

Polymeric nanoparticle:

PNPs are solid, colloidal nanoparticles (10–1,000 nm), composed of biodegradable polymers.30,31 PNPs can be classified as either nanospheres (matrix type) or nanocapsules (reservoir type) depending on how their structural organisation. In contrast to nanocapsules, which dissolve/disperse the drug in a liquid core of oil or water enclosed by a solid polymeric membrane, nanospheres type PNPs entrap the drug in the polymer matrix. Both PNP kinds allow for the chemical conjugation or adsorption of the medication on the surface (of the matrix or capsule). These techniques can easily be divided into two groups: direct monomer polymerization and dispersion of premade polymers. Solvent evaporation and salting out are two techniques used to disperse premade polymers.

Figure 4

Schematics of PNPs.

Abbreviation: PNP, polymeric nanoparticle.