br Characteristics of NLCs br Biotin SUN NLCs
3.2. Characteristics of NLCs
Biotin-SUN-NLCs were prepared using the emulsion-solvent
Fig. 1. 1H NMR spectra of (A) Biotin (B), stearylamine and (C) Biotin-stearylamine conjugate.
diffusion and U 0126 method. Irregular factorial design was em-ployed to evaluate the effect of several formulation parameters and their interactions on properties of biotin-SUN-NLCs. A number of NP formulations were prepared and the basic characteristics of the pro-ducts such as particle size, PdI, zeta potential, EE, and RE8% were
determined (Table 3). Percent contribution of each variable on SUN EE, particle size, zeta potential and RE8% in biotin-SUN-NLCs is also de-picted in Fig. 3. The one factor graphs plotted by Design-Expert soft-ware are shown in Figs. 4–8. In each graph, the effect of one variable was investigated while other factors were in its middle level value.
Fig. 2. FTIR of (A) Biotin (B), stearylamine and (C) Biotin-stearylamine conjugate.
Physical properties of different SUN loaded biotin modified NLCs.
D: Lipid/Drug ratio O: Aqueous/organic phase ratio L: Labrafac/lipid ratio S: Pluronic F127(%).
Particle size is the most important characteristic of NPs determining the amount of drug delivered to the tumor tissue through EPR effect. The size of pores in tumor vasculature endothelium is tumor-dependent ranging between 0.2 and 2 μm, but in the majority of tumors, pore cut-off sizes is about 380–780 nm. Based on the literature review, NPs with a size less than 400 nm are ideal from the perspective of EPR. However, particles smaller than 200 nm are required to get long circulation time and prevent the removal of NPs from blood circulation by
reticuloendothelial system (RES) . As depicted in Table 3, the mean values of particle size of biotin-SUN-NLCs were in range of 125.5–410.63 nm. Design of experiment (DOE) result indicates surfac-tant concentration (%), lipid/drug weight ratio, liquid lipid to total lipid ratio and interaction between of each two pairs of factors have significant effect on the particle size of NPs. The effect of each para-meter on resulted particle size is given below:
S. Taymouri et al.
Fig. 3. Contribution of different studied parameters on particle size, zeta po-tential, encapsulation efficiency and release efficiency of biotin-SUN-NLCs.
Where A, B, C and D are surfactant concentration (%), liquid lipid to total lipid ratio (w/w), lipid/drug ratio (w/w), aqueous/organic phase volume ratio, respectively.
Statistical analysis using Design Expert Software showed the most effective factor on the particle size is surfactant concentration (Fig. 3). According to Fig. 4a, by increasing PF127 concentration from 0.5% to 1%, particle size increased. This could be due to particle aggregation induced by increasing the medium viscosity which accompanies in-creasing PF127 concentrations. Furthermore, employing higher con-centration of PF127 reduced the mixing speed during preparation which in turn caused formation of larger NPs . Emami et al.  also observed that increasing emulsifier concentration from 0.25 to 0.5% decreased particle size, However, increasing emulsifier
concentration more than 0.5% in the formulation resulted in a sig-nificant increase in particle size. As it can be seen in Fig. 4b, increasing lipid/drug weight ratio from level 1 to level 2 (decreasing drug content) significantly decreased particle size. This finding is in accordance with other investigations such as those conducted by Fathi and coworkers  who reported increasing in size with incorporating higher amount of hesperetin. This was explained with massive physical structure of hesperetin which occupied a huge volume of NPs. The ratio of liquid lipid to total lipid also significantly contributed on particle size. In-crement of labrafac content increased mobility of the internal lipids and fluidity of the surfactant layer which in turn increased particle size (Fig. 4c). This observation is well correlated to Das et al.  study, who demonstrated that enhancing percentage of liquid lipid increased the particle size of clotrimazole loaded NLCs. PdI is the parameter that gave us information about homogeneity of nanosuspension. The PdI is dimensionless number ranged from 0 to 1. A small value of PdI, usually less than 0.3, indicates that dispersion is monodisperse . As de-picted in Table 3, PdI was fluctuating between 0.12 and 0.64. Statistical analysis using Design Expert Software showed that none of studied factors significantly contributed on the PdI of biotin-SUN-NLCs.
3.4. Encapsulation efficiency
(5) can be used to accurately predict EE of particles: