Main Factors For Nano Based Delivery Systems
There are two main governing factors for the nanoparticle based delivery systems: particle size and surface charge.
4. 1. Particle size
Drug loading and its release is affected by particle size distribution (112). Higher intracellular uptake of nanoparticles has been recorded compared to micron sized particles. Nanoparticles can access wide collection of biological targets because of their tiny size and mobility (113). Delivery and distribution experiments have suggested that nanoparticles greater than 230 nm size can congregate in the organ especially in spleen due to the capillary size of this organ (113). Several in vitro studies have pointed out that particle size can also control the cellular uptake of nanoparticles (114, 115). Further, it has been found that particle size is significant for oral drug delivery (113,116). Topical application to the eye is the well established route (113,256). However, it has been found that small size differences may be of influence for the actual distribution and bioavailability (113,225).
Smaller nonoparticle has more surface area. So, the majority of the drug associated would close to the exterior part leading to rapid drug release (117). The large surface area causes the active ingredient to be coupled with in or near the particle exterior part, and this result in faster active ingredient release (117).
4. 2. Surface charge
Surface charge is another important nanoparticle drug delivery system property that can affect the outcome of particles. Surface charge of gold nanoparticles with PEG caused efficient internalization in endosomes and cytosol (118). Poly (DL-lactide-co-glyc0l1de) nanoparticles were found to be ingested by cells by endocytosis (119, 120). It is found that after entering, the nanoparticles get away from these endosomes into the cellular cytoplasm. This depends upon the change in surface charge especially from negative to positive (eg. the PLGA NP resulting in cytoplasmic delivery). It is hypothesized that the positive surface charge influences the escape of these nanoparticles from endosomes (119).
The blood-brain barrier (BBB) is an electrostatic barrier to boundary brain penetration of therapeutics. It has been reported that nanoparticle surface charge can alter blood-brain barrier permeability (121). When the particles are absorbed in the blood, their surface hydrophobicity is related with the amount of adsorbed blood components (122).
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