## 3 Results and Discussion
Thus, it can be suggested that the bioadhesive property of the gel formulation coded with G-NR seems to be the highest one among the gel formulations studied, whereas G-EU is expected to show the weakest bioadhesive characteristics [37]. The compressibility defines the work required for the compaction of the gel along a definite distance [36, 38]. According to our data, it can be assumed that the spreadability of G-LM and G-NR can be better than that of G-EU and G-TP because of their low compressibility value. It was evident from the TPA data that all of the sodium alginate based gel formulations showed suitable mechanical characteristics and they could be used to prepare the transdermal films of MTC. All transdermal films (TF-NR, TF-EU, TF-TP, and TF-LM) of MTC prepared using sodium alginate as matrix agent in this study were thin, flexible and smooth. The thickness, weight and drug content of the film formulations are represented in Table 3.  
The thickness of MTC transdermal films was found between \(0.47\pm 0.03\) and \(0.67\pm 0.04\) mm and the standard deviation of weight was less than 2%, indicating homogenously spreadability of gels while preparing transdermal films. The MTC content of the transdermal films (TF-NR, TF-EU, TF-TP and TF-LM) varied between \(92.70\%\pm 0.74\%\) and \(102.48\%\pm 0.73\%\), confirming the reproducibility of the manufacturing process [11]. The content uniformity of all formulations satisfied pharmacopeia requirements for transdermal drug delivery systems evidenced by the low standard deviation values [39]. This implies also that the mechanical properties of the sodium alginate gel formulations were convenient to provide homogeneous drug distribution throughout the film casting and drying process. The adhesion of transdermal drug delivery systems is one of the most critical parameters for product safety, efficiency and quality [11, 40]. In matrix type transdermal systems, where the drug is \begin{table}
\begin{tabular}{c c c c} \hline
**Transdermal Film** & **Thickness (mm)** & **Weight (mg:cm\({}^{-2}\))** & **MTC Content (\%)** \\ \hline TF-NR & \(0.55\pm 0.05\) & \(60.12\pm 1.46\) & \(102.48\pm 0.73\) \\ TF-EU & \(0.67\pm 0.04\) & \(58.60\pm 1.51\) & \(101.56\pm 1.43\) \\ TF-TP & \(0.51\pm 0.02\) & \(63.59\pm 1.77\) & \(98.29\pm 1.76\) \\ TF-LM & \(0.47\pm 0.03\) & \(51.18\pm 1.16\) & \(92.70\pm 0.74\) \\ \hline \end{tabular}
\end{table} 
Table 3: Thickness, weight and drug content uniformity of the MTC transdermal films (mean \(\pm\) SD, \(n=3\)–\(6\)). dispersed or solubilized in a polymer matrix, the quality of contact between the film and the membrane (skin) determines the consistency of drug delivery [41]. The _in vitro_ adhesion results of sodium alginate based transdermal films of MTC showed that the highest adhesion force values were obtained with the film formulations TF-TP (36.10 \(\pm\) 1.20) and TF-NR (35.23 \(\pm\) 1.59), containing terpionlene and nerolidol as penetration enhancer, respectively (Figure 4). These values are significantly higher than those of obtained with the other two film formulations TF-EU (26.57 \(\pm\) 1.80) and TF-LM (23.17 \(\pm\) 1.06) (\(p<0.05\)). A plasticizer is added to a polymer formulation to enhance its flexibility and to help its processing [42]. The addition of a plasticizer to a polymer results an increase in molecular motion so that drug molecules can diffuse through the plasticized polymer matrix at a higher rate [7, 42]. In pre-formulation studies we observed that the unplasticized sodium alginate films were non-flexible (data not given). Correspondingly, the use of propylene glycol (7.5%) as plasticizer improved the mechanical properties of the developed films in terms of flexibility and elasticity. During the _in vitro_ adhesion test, the films were stripped cleanly from the plate and left no visually residue.