Solid Lipid Nanoparticles (SLNs)
Solid lipid nanoparticles (SLN) are lipid bilayers; they can encapsulate the drug. This bilayer can be attached to the bilayer of cell membranes to deliver the drug. Mishra et al. have reported that SLNs are emerging as one of the colloidal nanodrug delivery systems Figure 13.8 (a) explains the synthesis procedure of SLNs. Figure 13.8 (b) illustrates the various applications of SLNs in drug delivery systems .
SLNs consist of glycerides, fatty acids, and hydrophilic drugs along with an emulsifier . Even though more SLN products are patented, marketed products are still few. Regulatory restrictions and economic issues are the major reasons for the low number of marketed products. Muller and Lucks have filed a patent application for an SLN product (nanoemulsion) during 1996. It is the first patented SLN product that describes nanoemulsion preparation using a high-pressure homogenization process .
Proteins are used as drugs which are easily digested in the stomach before they reach the target. Hence, proteins are coated with polymers to release in a controlled way. This controlled release technique is known as polymer therapeutics. Dendrimers are branched polymers and are used as drug carriers. Cancer medicine like methotrexate is attached to dendrimers for drug delivery.
Polymer therapeutics can improve the pharmacokinetic properties of the drug . Anticancer drugs, therapeutic DNAs, and Small interfering RNA (Ribonucleic Acid) (siRNAs) are attached on the surface of dendrimers due to the presence of more functional groups on the surface . Many dendrimers like polyamidoamine (РАМАМ) have been patented for various applications related to drug delivery, imaging, and diagnosis . Polymer NPs like polyhydroxyalkanoate are
FIGURE 13.7 Schematic diagram shows the particle therapy and nanomedicine, (a) Highly penetrating X-ray radiation damaging the healthy tissues, (b) Ballistic effects of ions: negligible radiation effects around the tumor or healthy cells and considerable effects at the entrance of the tumor, (c) Improvement of ion radiation effects by nanoparticles without affecting the healthy cells (nanoparticles are present inside the tumor or target). (From Lacombe Sandrine et al. 2017.) used as drug carriers. They are also utilized in protein purification and immobilization of matrices. These polymer NPs have biodegradable and good mechanical flexibility properties . Polymeric micelles are one kind of drug delivery carrier formed by block co-polymers with an inner hydro- phobic core and outer hydrophilic nature. The stability of polymeric micelles is affected by polymer composition, drug encapsulation, and environmental conditions .
FIGURE 13.8 Schematic illustration of solid lipid nanoparticles (SLNs). (a) Step by step preparation of SLNs in the hot homogenization method, (b) Various applications of SLNs in medicine. (From Mishra Vijay 2018.)
Polymers with more water content are known as hydrogels. These hydrogel NPs are used as dru carriers. Biopolymers like chitosan and alginate are utilized to prepare hydrogel NPs for the loadin of drugs. Some synthetic polymers like polyvinyl alcohol, polyethyleneimine, and polyN-isopro- pylacrylamide are also utilized to prepare hydrogel NPs. Patra et al. have reported on the applications of natural compounds in nanomedicines and sources of natural compounds. Figure 13.9 (a) exhibits sources of biopolymers. Figure 13.9 (b) enumerates the natural compounds obtained from higher plants as well as their applications related to nanomedicines .
Anticancer drugs like paclitaxel, doxorubicin, 5- fluorouracil, and dexamethasone are prepared using nanomaterials. For example, doxorubicin is loaded inside liposomes and then coated with the polymer polyethyleneglycol (PEG). The PEG coating process is knowm as PEGylation. Paclitaxel is attached with albumin NPs and it is currently available on the market with the trade name Abraxane.
FIGURE 13.9 Schematic diagram shows the natural materials utilized in nanomedicine, (a) Various sources of natural biopolymers, i.e. higher plants, animals, microorganisms and algae (b) Some of the natural compounds obtained from higher plants for nanomedicine applications. Among these natural compounds, some are already available on the market, others are in clinical trials and others are undergoing research. (From Patra et al. 2018.)
Pillai et al. reported that the cancer nanomedicines like Abraxane, Doxil, DaunoXome, Oncaspar, and DepoCyt are in the advanced stage of clinical development. The FDA has given approval for these nanomedicines due to their advanced stage in clinical development. .
Paclitaxel and doxorubicin are the well-known cancer drugs formulated with liposomes and albumin nanoparticles. Dexamethasone and 5-fluorouracil are some other cancer drugs designed with nanoparticles. Quantum dots, chitosan nanoparticles, and polylacticglycolic acid (PLGA) NPs are some of the drug carriers used to encapsulate iRNA for in vitro delivery .
Polymers are also used to mask the taste of drugs. As an example, Eudragit El00 is employed for the coating of potassium chloride (KC1). This drug is utilized for the treatment of hypokalemia. Eudragit E100 is a water-insoluble polymer that effectively (2 times) masks the unpleasant taste and improves the palatability of the KCl. After administration of this drug, i.e. within 30 minutes, it releases the entire (100%) KCl. The graph (Figure 13.10) compares the in vitro analysis result related to the KCl releasing time of marketed KCl syrup formulation and Eudragit E100 coated KCl syrup formulation .