2.5 Solid lipid nanoparticles and drug targeting

In the emerging field of nanomedicine, SLNs is at the forefront. It is made up from biocompatible/physiological lipids (e.g. partial glycerides, triglycerides, fatty acids, wax, and steroids) that remain in solid form at room temperature. Numerous techniques are being developed for the fabrication of SLNs using the biocompatible/ physiological lipid which has records of innocuous use in medicine [8]. Apart from drugs, the essential materials for fabricating SLNs are solid lipids as matrix materials, emulsifiers, stabilizers, and water. The nanometric size and larger surface area of SLNs is suitable to be embedded with some potential functionalized ligands, antibodies, moieties, and other functional groups that help in drug targeting [5].

The real success of lipid nanoparticles relies on the development of dosage forms that are able to improve the therapeutic index of the drugs by mounting their concentration specifically at the targeted site or organs. Drugs can be incorporated in SLNs which lead to offer a new model in drug delivery that could be applied for drug targeting. The therapeutic payload of various categories of drugs (such as antiinfective, anticancer drugs, anti-inflammatory, etc.), antigens, proteins, and nucleotides can be enhanced in specific site and organs by associating with SLNs. On another side, SLNs face numerous challenges which include rapid clearance, serum instability (dependent on the specific formulation) and nonspecific uptake by the mononuclear phagocytic system (play a major role for opsonizing the foreign particles and remove SLNs from the circulation) [9]. The above mentioned limitations can be nullified by conjugating different ligands to the surface of SLNs which could help to increase the circulation time and targeted delivery of the drug to the specific site. The targeting properties to a specific site can be further enhanced by selecting surface markers [10]. Thus, in this article, we focused on SLNs and various ligand conjugated SLNs which act as suitable carriers for targeting to different sites such as lungs, brain, liver, breast, eyes, colon, kidney, etc.
