Nanoparticles are materials with overall dimensions in the nanoscale, ie, under 200 nm. In recent years, these materials have emerged as important players in modern medicine, with clinical applications ranging from contrast agents in imaging to carriers for drug and gene delivery into tumors
[5]. Nanoparticles of PAA have been extensively studied in biomedical applications such as drug delivery due to the unique capability to deliver drugs, genes, and proteins via the peroral route. The thiolated PAA nanoparticles were developed by Greindl et al.
[6], whose architecture was covalently crosslinked via disulfide bonds. The cross-linkage of PAA with 2,2′-(ethylenedioxy)bis(ethylamine) (EDBEA) showed spherical morphology and 20–80 nm-sized nanoparticles
[7], while the PAA-PS-Ag composite nanoparticles revealed spherical morphology with 3 ± 1.2 nm sized particles
[8]. The exact morphology was obtained by Müller et al.
[9] with a mean diameter <200 nm. The human fibrinogen binding kinetics depended on the size of negatively charged PAA/Au nanoparticles. The larger nanoparticles revealed binding with fibrinogen with a slower dissociation rate and increasing affinity. When the size of nanoparticles was 7 nm, the two nanoparticles were accommodated by each fibrinogen molecule, but when the size increased up to 10 nm, only one was adapted. The size increments up to 10–12 nm changes from one site to the two-site binding. The bound nanoparticles felt more coulombic repulsion when the diameter was increased. Due to the flexibility of both binding sites, one nanoparticle with a sufficient diameter (15–17 nm) was also found enough for the interaction of fibrinogen. Hence, more than 12 nm, multiple protein molecules were found,
Figure 2i
[10]. PAA-coated iron oxide nanoparticles showed two types of molar mass (1800 and 5000) due to the different architecture of PAA chains, which influenced the molar mass. The magnetic diameter of these nanoparticles was found in between 7.3 to 11.9 nm
[11]. The architecture of nanoparticles of PAA-chitosan (CS) was dependent on the synthesis and pH of the synthetic medium. The nanoparticles at 4.5 pH (acetic buffer solution) revealed consistent and solid spherical particles unveiling PAA-CS nanoparticles’ matrix structure. PH 7.4 showed a dense core bounded by a fuzzy and diffuse coating 4 (ii). This architecture was due to ionic interaction between negatively charged PAA and positively charged CS. The different preparation processes of PAA-CS nanoparticles influenced the architecture of nanoparticles. When PAA was dropped into a solution of CS, the generation of PAA core occurred, and a membrane was formed on the PAA core surface resulting in a dark shell and soft-core spherical nanoparticles. On the other hand, When the CS solution was dropped in the PAA solution, the core of CS and membrane of PAA-CS were formed. There were no cavities formed in PAA-CS because of the not swelling of CS in acidic medium,
Figure 2iii. These all structures were created due to the construction of samples, conditions of staining, etc.
[12]. The PAA magnetic nanoparticles possessed uniform particles morphology with a 9.2 ± 2.6 nm average diameter while a hydrodynamic diameter of 246 ± 11 nm (
n = 3) was measured by the dynamic light scattering (DLS) measurements
[13]. The other magnetic nanoparticles of PAA had a 10 nm size and were semispherical in shape
[14]. PAA-coated iron oxide nanoparticles revealed a 10.1 ± 2.4 nm mean particle size. These were stable in water, and variation in pH or enhancement in ionic strength resulted in aggregation of these nanoparticles in water
[15].
Figure 2. Representation of (
i) binding of fibrinogen with PAA/Au nanoparticles (
a) Binding of 7 nm nanoparticle to fibrinogen revealing each protein molecule accommodated two nanoparticles (
b) 10–12 nm-sized nanoparticles prevent the binding of two particles to each fibrinogen due to the flexibility of fibrinogen at E domain of protein resulting the contact of second binding site with the nanoparticle (
c,
d) Larger nanoparticles (15–22 nm) can accommodate multiple fibrinogen molecules due to the larger surface area (
ii) TEM of PAA-CS nanoparticles at (
a) pH = 4.5 and (
b) at pH = 7.4. (
iii) Morphology of PAA-CS nanoparticles synthesized by the various processes at 4.5: (
a) CS dropping into PAA solution; (
b) PAA dropping into CS solution, (Reprinted from Refs.
[10][12] with permission).