# Formulation of Boron Encapsulated Smart Nanocapsules for Targeted Drug Delivery to the Brain
## 3 Results
### Preliminary Cell Studies
#### 3.3.3 Permeation Studies
The zeta surface charge is an important parameter for nanoparticle delivery through the BBB, as a study showed that highly positive surface charged nanovolhetics might cause toxicity to the BBB [44]. [PERSON] et al. [45] and [PERSON] et al. [46] showed efficient drug delivery of positively surface charged (above 15 mV) vehicles across the BBB. These results are significant, as brain drug delivery is regulated by multiple factors, including size, shape, hydrophobicity, and surface charge. Having control over these features can help permeate through the BBB and help improve the therapeutic agent's stability when in circulation [47; 48; 49]. In addition, the alteration of the size of the nanoparticles is essential in order to infiltrate the blood-brain barrier; this can be achieved through the potential modification of chitosan or polypyrrole. Several studies have shown an inverse correlation between the nanoparticle size and the BBB penetration [50; 51; 52]. The smaller the nanoparticles, the higher the penetration of the nanovehicle through the BBB. Furthermore, the shape of the nanovehicles influences the body distribution and cellular uptake [53]. Over the years, DLCs have been known to accumulate selectively at a higher rate in tumour cells [15] because mitochondria of tumour cells present a higher transmembrane potential than healthy ones. The positive surface charge of DLCs in combination with their lipophilicity allows for diffusion of DLCs at a higher rate into cancer cells. This can be favourably used to promote the selective accumulation of therapeutic amounts of boron into cancer cells [22]. In this study, three carbonyl DLCs: (3-carboranylpropyl) (triphenyl phosphonium) bromide (2), (3-carboranylpropyl) (N9,N9-diethyl-9H-benzo[\(a\)]phenyloxazine-5,9-diamine) bromide (4), and (3-carboranylpropyl) (3,7-diamino-5-phenylphenazin-5-ium) bromide (6) were successfully synthesized and characterized. Results indicated promising signs of the accumulation of these compounds towards both CaCo2 and U-87 MG cell lines. When performing release studies, three pH environments are used to assess the validity and suitability of these nanovehicles to selectively target tumour cells. The chosen pH values are pH 7.4 (mimicking the pH of the blood), pH 6.5 (pH of normal cells), and pH 5.5 (mimicking a tumour microenvironment). In addition, we compared the formulation of chitosan NP vs. PPy-CHIT NC. Results from Figure 12 show a clear difference in release profiles and indicate that the addition of polypyrrole has had a significant effect on the release profiles of the pharmacophore entrapped within the nanovehicle. Other pharmacophore-loaded NC show a similar trend in terms of release, with delayed release of entrapped drug at pH 6.5 and to a longer extent at pH 7.4. In most cases, it took between three to four hours for the drug to release in the higher pH values, compared to the immediate release shown via the IG formulation that is significantly better. Furthermore, the release at 5.5 was immediate in the PPy-CHIT formulation due to two factors. First, the protonation that may have occurred at the amine terminal of the pyrrole may have allowed the vehicle to expand and hence allow for drug release through the pyrrole layers. Secondly, complete disintegration of NC may have occurred over time, causing the release of drug entrapped. The delay in release allowed for around 20-30% of the drug to be released after 24 h at pH 6.5 and 7.4 for all PPy-CHIT formulations. This is significantly lower than IG, whereby almost all drug within the nanoparticle is released. Finally, statistical analysis was performed on the release profile to compare the rates at which the drug was released from the second formulation as opposed to formulation via IG and values <0.01 were obtained consistently, showing that there is a significant difference between the two formulations in release time of the encapsulated compounds. Regarding their synthesis, the three new boronated DLCs produced high yields, averaging between 73% and 78%.