Table 3.

Some surface modifications to NPs for targeting the brain and increasing adsorption.

Ligand	Favorable Properties	Ref.
Transferrin	Transferrin receptors (TfR) are highly expressed in the BCECs and are thus commonly used targeting ligands. They promote efficient accumulation of therapeutics in the brain.	[71]
Lactoferrin	Lactoferrin, a glycoprotein present in the brain, acts as a receptor at the BBB. This approach has been identified to enhance the pharmacological properties of drugs. Furthermore, a positively charged group is exhibited upon binding, creating greater potential for NP entry.	[72,73]
Glucose	The BBB possesses glucose transporters (GLUTs) for active delivery of glucose into the brain to meet the high energy demand. NPs coated with glucose may be able to efficiently overcome the BBB via this transport system.	[74,75]
Glutathione PEGylation	PEGylated lipids with glutathione conjugates (G-Technology®) can pass through the BBB via the sodium-dependent transporter.	[76]
Angiopep-2	Has good transcytosis ability across the BBB. Can be conjugated to LNPs.	[8,77,78,79]

BCECs = brain capillary endothelial cells.