**6. Conclusions**

In this chapter we demonstrate the most significant parameters in decreasing the nanoparticles size were the increase in stirring rate and PVA concentration. Other factors that also reduced the particles size were the increase in the ethanol percentage in the aqueous phase and in the organic phase, and the increase in the photosensitizer mass/polymer mass ratio. Nanoparticles prepared by the EDM showed smaller sizes than the nanoparticles prepared by the EEM but are less stable. The aqueous phase temperature showed double behavior in relation to the nanoparticles size, increasing or decreasing the size depending on the method used to prepare the nanoparticle. The other properties evaluated, such as zeta potential, entrapment and recovery efficiencies, residual PVA and residual chloroform, are dependent on

the size of the nanoparticle. Therefore, parameters that are significant in relation to size will also influence these properties. Properties as zeta potential, residual PVA and entrapment efficiency presented an inversely proportional relation with nanoparticle size while the recovery efficiency and residual chloroform were directly proportional. In most of the properties some significant binary effects were observed, but their influence was not predominant in the results.

Besides the parameters used in the nanoparticle preparation, the physicochemical properties of the photosensitizer can interfere on the entrapment efficiency, as well as the washing step of the nanoparticulate formulation can influence the residual PVA and the recovery efficiency. The short storage period of the nanoparticulate formulation can affect the characteristics of the particle, favoring the nanoparticle aggregation in different temperature.

We have shown that the encapsulation of photosensitizers reduces the photobleaching effect due to light scattering caused by the polymeric matrix, however more soluble photosensitizers even encapsulated can suffer photobleaching according to the laser power and irradiation dose used in the experiment, limiting their ability to be used in PDT. The aggregation of the photosensitizer also causes a reduction in its photodynamic efficiency because it reduces the singlet oxygen generation, but the encapsulation improves the photosensitizer efficiency since the entrapment can reduce the aggregation of the lipophilic compounds in aqueous medium.

The photocytotoxicity of encapsulated photosensitizers depends on the incubation time, the photosensitizer concentration and the laser power, as well as the uptake of photosensitizer into the cancer cells. Drug delivery systems have improving the efficiency of the phthalocyanines and porphyrins to reduce the cell viability. However, the generalization of the conclusions about preparation of nanoparticulate formulations and photooxidation conditions should be done carefully, each nanoparticulate formulation behaves in a characteristic way and should be treated singularly.
