## 3 Results and Discussion
### Effect of Independent Variables on Viscosity and In Vitro Release Studies  
The percentages of insulin released across cellulose membranes from prepared gels are shown in Figure 4. It is evident from Figure 4 that about 96% of insulin was released after 1 h from solution form (control). On the other hand, 33.44%, 58.56%, 66.33%, 74.89% and 94.22% of the drug was released after 6 h from insulin niosome emulgel, insulin emulgel, insulin niosome gel, insulin niosome and insulin gel, respectively. The difference (\(p<0.05\)) in the drug release could be related to the viscosity for the four insulin preparations containing gelling agent. Gel consistency plays an important role as it ensures adequate retention and also releases the drug in controlled manner [35]. It is well known fact  
Figure 3: Representative scanning electron micrograph of insulin niosome emulgel. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Property** & **Insulin Gel** & \begin{tabular}{c} **Insulin** \\ **Niosome** \\ \end{tabular} & \begin{tabular}{c} **Insulin** \\ **Niosome Gel** \\ \end{tabular} & \
\begin{tabular}{c} **Insulin** \\ **Emulgel** \\ \end{tabular} &
\begin{tabular}{c} **Insulin Niosome** \\ **Emulgel** \\ \end{tabular} \\ \hline Viscosity (cP) & 6550 \(\pm\) 50 & 2150 \(\pm\) 75 & 8220 \(\pm\) 80 & 11,050 \(\pm\) 50 & 12,250 \(\pm\) 70 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Viscosity of the prepared formulations. that, the increase in viscosity can cause increase in resistance to drug diffusion, mobility and rate of dissolution [6]. Emulgel composed of paraffin oil, gelling agent (sodium carboxymethyl cellulose) and surfactant (Tween 80) which contribute to higher viscosities and hence showed lower percentage of drug release. The 3D response surface plot and contour plot (Figure 5) shows the effect of independent variables on viscosity of niosome emulgel. It is evident from the 3D response surface plot that as concentration of paraffin oil and sodium carboxymethyl cellulose increase, the viscosity of the formulation increase. There is no significant effect of Tween 80 observed on viscosity. It is also apparent from contour plot that sodium carboxymethyl cellulose and paraffin oil have significant effect (\(p<0.005\)) on the viscosity of formulations. The fitted polynomial equation for viscosity is given below:  
\[\text{Y}=9.74+0.0737\text{x}_{1}+0.0266\text{x}_{2}+0.2383\text{x}_{3}+0.004 4\text{x}_{1}\text{x}_{2}+0.0051\text{x}_{1}\text{x}_{3}+0.0061\text{x}_{2} \text{x}_{3}+0.0080 \tag{7}\]  
Therefore, minimum concentration of sodium carboxymethyl cellulose and paraffin oil compared to Tween 80 was found suitable for controlled in vitro release of drug. This was illustrated in the 3D response surface plot and contour plot (Figure 6). It was evident from the 3D response surface plot that as concentration of sodium carboxymethyl cellulose increased, in vitro release decreased. Sodium carboxymethyl cellulose concentration had a significant effect on in vitro drug release as discussed earlier. It was also apparent from contour plot that paraffin oil was having inverse effect on in vitro release. The fitted polynomial equation shown as:  
\[\text{Y}=3.26-0.0771\text{x}_{1}-0.0243\text{x}_{2}-0.1661\text{x}_{3}-0.0069 \text{x}_{1}\text{x}_{2}-0.0115\text{x}_{1}\text{x}_{3}-0.0021\text{x}_{2} \text{x}_{3}+0.0027 \tag{8}\]  
Figure 4: In vitro release profile of insulin from different formulations and control (insulin solution) across cellophane membrane into phosphate buffer (pH 7.4) at 37 \(\pm\) 0.5 \({}^{\circ}\)C. Data represented as mean \(\pm\) SD (n = 6). For the check point batches F9*, the predicted values were in good agreement with the observed values (Table 4). Thus, it could be concluded that the evolved equation could be used for prediction of responses using \(2^{3}\) full-factorial design.