**3. Polymeric nanoparticle drug delivery systems**

Nanoparticles in drug delivery systems normally have sizes ranging from 1 to 1000 nm. In essence, nanoparticles with sizes in this range have a high surface

*Aliphatic Polyester Nanoparticles for Drug Delivery Systems DOI: http://dx.doi.org/10.5772/intechopen.100977*

area to volume ratio and their behavior in the body could cause increases in the absorption potential and cytotoxicity as the expanded surface is proportional to cytotoxicity [24]; thus, these nanoparticles could potentially lead to an increase in cytotoxicity. Nevertheless, nanoparticles prepared from aliphatic polyesters could possibly lead to a reduction in cytotoxicity, as they are highly biocompatible and biodegradable. Aliphatic polyester nanoparticles play key roles in improving the pharmacokinetics, drug bioavailability, specific delivery at the site of action, and stability in the bloodstream. Their high surface area can adsorb drug molecules and encapsulate a large number of drugs in their matrix, effectively carrying drugs, proteins, DNA, and organs. Therefore, the development of aliphatic polyester nanoparticles is one of the most successful ideas for drug delivery innovation.

#### **3.1 Polymeric nanoparticles**

Polymeric nanoparticle delivery systems refer to both nanospheres and nanocapsules. Their classification is based on the positional characteristics of the drugs and polymers, as shown schematically in **Figure 4a** and **b.** Nanospheres contain drug molecules within a uniformly dispersed polymeric matrix, while nanocapsules entrap the drug molecules inside their core, a cavity surrounded by a polymeric membrane that acts as a shell [25].

Regarding the molecular orientation surface, we propose a possible schematic of the polyester chain on the nanoparticle surface as shown in **Figure 4**. In the case of PLGA nanospheres, the polymeric chains ignore water molecules, which is consistent with computational simulation results that demonstrated that PLGA is strictly hydrophobic [26]. At both the surface and interface, the carbon backbones clump together rather than being distributed in the aqueous solution. This causes the hydrophobic molecules to have minimal contact with hydrophilic molecules. On the other hand, the oxygen atoms of the hydroxyl groups (▬OH), carboxylic acids (▬COOH), and ester groups (▬COO▬) interact with the water molecules residing near the water-PLGA interface, and the hydrogen atoms in the polymer chain resemble the oxygen atoms. Hydrophobic drugs display the tendency to accumulate

#### **Figure 4.**

*Schematic representation of the structures and molecular orientations of PLGA nanospheres (a), PLGA nanocapsules (b), and the packing of emulsifiers (Span 80 and Tween 80) at the interface of the dispersed polymer droplets (c).*

on the surface, with a few drug molecules migrating to the core, leading to the uniform distribution of drug molecules within the polymeric matrix, especially in the vicinity of the nanosphere surface (**Figure 4a**). The nanocapsules have contact with both the inner and outer aqueous solutions. Thus, the molecular orientation of aliphatic polyesters on the inner and outer membrane surfaces corresponded to nanospheres. Nevertheless, the hydrophilic drugs tend to be entrapped inside the core of a cavity surrounded by the polymeric membrane due to the insolubility between the drug and the polymer (**Figure 4b**).
