Solid Lipid Nanoparticles vs. Nanostructured Lipid Carriers: A Comparative Review

Abstract

Solid-lipid nanoparticles and nanostructured lipid carriers are delivery systems for the delivery of drugs and other bioactives used in diagnosis, therapy, and treatment procedures. These nanocarriers may enhance the solubility and permeability of drugs, increase their bioavailability, and extend the residence time in the body, combining low toxicity with a targeted delivery. Nanostructured lipid carriers are the second generation of lipid nanoparticles differing from solid lipid nanoparticles in their composition matrix. The use of a liquid lipid together with a solid lipid in nanostructured lipid carrier allows it to load a higher amount of drug, enhance drug release properties, and increase its stability. Therefore, a direct comparison between solid lipid nanoparticles and nanostructured lipid carriers is needed. This review aims to describe solid lipid nanoparticles and nanostructured lipid carriers as drug delivery systems, comparing both, while systematically elucidating their production methodologies, physicochemical characterization, and in vitro and in vivo performance. In addition, the toxicity concerns of these systems are focused on.

Keywords: NLC; SLN; lipid nanoparticle; nanocarrier; nanoparticle characterization; nanoparticle production.

Figure 1

Structural matrix of SLN and NLC. Adapted with permission from [25].

Figure 2

Structure of the 3 different types of SLN: homogenous matrix model (Type I), drug-enriched shell model (Type II), and drug-enriched core model (Type III). The drug is represented in white color. Reprinted with permission from [35].

Figure 3

Structures of different types of NLC: imperfect crystal (Type I), amorphous (Type II), and multiple type (Type III). The drug is represented in white. Reprinted with permission from [35].

Figure 4

Production methods to obtain SLNs and NLCs. Adapted from [35].

Figure 5

Spray drying (A) and microfluidics (B) methods to obtain SLN and NLC.

Figure 6

SEM microphotographs of insulin-loaded SLNs (Ins-SLN) stored at 4 °C/60% RH and 40 °C/75% RH after 6 months (t6). Scale bar: (a,b,d) 1 μm; (c) 5 μm. Reprinted with permission from [88].

Figure 7

Cumulative permeation of insulin through Caco-2/HT29 co-culture monolayer loaded into SLN (filled diamonds), and into chitosan-coated SLN (filled squares), compared to insulin solution (circles). n = 3; mean ± SD; (*) p < 0.05, chitosan-coated SLN presented a significant difference from insulin solution. Reprinted with permission from [115].

Figure 8

Decrease of plasma glucose concentration (%) in diabetic rats upon administration of subcutaneous insulin, 2.5 UI/kg (empty squares); oral insulin solution, 25 IU/kg (empty triangles); insulin-loaded SLNs, 25 IU/kg (filled squares); and insulin-loaded chitosan-coated SLN, 25 IU/Kg (filled circles). N = 6; mean ± SEM. Reprinted with permission from [115].