## 5 Strategies to Improve the Performance of SLNs and NLCs as Nanovehicles for Nutraceuticals  
Despite the well-recognized consensus that SLNs (and NLCs) exhibit great potential as effective nanovechlies for improving the oral bioavailability of many drugs and nutraceuticals [16, 18, 56, 170], the effectiveness of such nanoparticles is determined by the nature and biocompatibility (with lipid matrix) of nutraceuticals, the stability of global stability during the digestion, the targeted site where the encapsulated bioactive is expected to be released and absorbed, and the in vivo stability of absorbed nutraceuticals in the circulation system. For poorly soluble and highly susceptible nutraceuticals, e.g., curcumin, the loading capacity of such delivery systems is also an important parameter impacting their effectiveness when formulated in foods. To date, many strategies have been proposed to improve the effectiveness of SLNs (or NLCs) as nanovehicles for nutraceuticals. Such improvements include increased encapsulation performance (e.g., bioactive loading), enhanced oral bioavailability of nutraceuticals, improved stability of nutraceuticals during digestion and circulation, and improved targeted delivery. The bioactive encapsulation performance of such lipid nanoparticles can be improved by selecting an appropriate lipid matrix (solid and/or liquid lipids) in which the to-be-loaded bioactive can be well solubilized, even when the matrix has solidified upon cooling. The composition and nature of the lipid matrix is also important for the stability, release behavior, and bioaccessibility of encapsulated nutraceuticals in such nanoparticles. For example, MCT tends to be digested more rapidly than long-chain triglycerides, but the mixed micelles formed by the digestion products of long-chain triglycerides tend to have higher solubility than those of MCT [24, 25]. In this section, we only presented strategies to improve the oral bioavailability of nutraceuticals loaded in such lipid nanoparticles by surface coating or modification techniques, as well as their targeted delivery in vivo. Improving Oral Bioavailability of Loaded Nutraceuticals in SLNs (or NLCs) by Coating with Chitosan or Its Derivatives  
The interfacial structure and surface properties of SLNs and NLCs are of crucial importance for their stability and in vivo oral bioavailability and/or bioactivities. Appropriate surface modification is considered an effective strategy to improve the delivery and bioavailability of drugs or nutraceuticals loaded in the SLNs or NLCs [171]. Surface coating with polymers is frequently used to overcome the defects, e.g., burst release and chemical degradation of encapsulated molecules, occurring in the highly acidic environment of the stomach during oral administration, for SLNs or NLCs, as small intestine-targeted nanovuehicles of nutraceuticals. The potential effectiveness of many natural and synthetic polymers to modify the surface properties of such delivery systems has been well investigated, including chitosan or its derivatives, thiomers, polyethylene glycol (PEG), ligands, and cell-penetrating peptides (Figure 8). Chitosan is a cationic polysaccharide, and as a non-cytotoxic polymer, it is well known for its good mucoadhesive properties and penetration-enhancing properties across mucus epithelia in the digestive tract [172, 173]. It can readily adsorb to the negatively-charged surface of common anionic surfactant-stabilized lipid nanoparticles (SLNs or NLCs) through electrostatic interactions [103] and, as a result, a viscoelastic interfacial film coating these nanoparticles is formed, resulting in surface modification. Due to the cationic charge of chitosan, the internal structure stability of chitosan-coated SLNs or NLCs in the gastric environment is enhanced, and the action of lipases on these nanoparticles is, to a certain extent, inhibited.