# Development of a Natural Matrix Hybrid Hydrogel Patch and Evaluation of Its Efficacy against
## 3 Results and Discussion  
### Physical and Chemical Evaluation  
BDDE binding of Dex, HA, and HA-Dex hybrids was analyzed using FT-IR spectra. The Dex -OH group was observed at 3200-3300 cm\({}^{-1}\). Moreover, at 1010 cm\({}^{-1}\), the COOH bond vibration intensity decreased as the HA concentration increased and the absorption peak decreased due to C-O-C contraction. This may be because -COOH (carboxyl group) underwent esterification to produce -COO through bonding, which resulted in an increased \(-\)C = 0 bond strength. The ester bond band was observed at 1709 cm\({}^{-1}\), confirming that the bond was formed by the crosslinking agent (Figure 3).  
FE-SEM analysis of the surface and a cross-section of the CAE-loaded HA-Dex hybrid hydrogel patches showed that the pore size decreased as the CAE content increased, and irregular pore shapes and surface distortions were observed (Figure 4).  
Figure 3: Fourier transform infrared spectra of hyaluronic acid-dextran (HA-Dex) hybrid hydrogel patches; (a) Dex, (b) HA, (c) Dex-HA (9.5:1.0), (d) Dex-HA (9.5:0.5).  
The porosity decreased slightly as the CAE concentration increased (Table 2).  
UTM measurements showed that the tensile strength increased as the CAE content increased, then decreased when CAE was added over 0.8 wt%. In addition, hydrated state hydrogels presented similar tensile properties when compared the different conditions. The dry state is the one where the CAE concentrations more affect the tensile properties of the hydrogels probably affected by the porosity. But nor in the hydrated state (Figure 5). Because, it may be that a greater number of holes on the surface and greater porosity led to decreased bonding strength due to pore-pore interaction, resulting in decreased tensile strength. In that case, decreased porosity would result in greater bonding strength, leading to increased tensile strength.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Patch Type**} & **Total Intrusion** & **Total Pore** & **Median Pore** & **Median Pore** & **Average Pore** & **Porosity(\%)** \\  & **Volume** & **Area** & **Diameter** & **Diameter** & **Diameter** & **Diameter \\  & **(M/G)** & **(M/G)** & **(Volume/Nm)** & **(Area/Nm)** & **(A/N)** & **(A/N)** & **(A/N)** \\ \hline a & 1.6388 & 4.930 & 85,324.9 & 14.0 & 1329.6 & 68.2117 \\ b & 0.4233 & 0.943 & 16,078.3 & _77.7_ & 1795.0 & 42.5677 \\ c & 0.4328 & 0.156 & 12,349.2 & 10,966.7 & 11,109.2 & 41.5143 \\ d & 0.3350 & 5.695 & 132,087.9 & 6.6 & 235.3 & 32.2406 \\ e & 0.2199 & 0.861 & 12,196.2 & 90.2 & 1021.8 & 26.5290 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Porosity of _Centella asiatica_ extract (CAE)-loaded hyaluronic acid-dextran (HA-Dex) hybrid hydrogel patches.  
Figure 4: Morphologies of _Centella asiatica_ extract-loaded hyaluronic acid-dextran hybrid patches by field emission scanning electron microscope analysis. Control: HA-Dex hybrid hydrogel patches with no CAE; **(a)** 9.8:0.2, **(b)** 9.6:0.4, **(c)** 9.4:0.6, **(d)** 9.2:0.8, and **(e)** 9:1 wt% HA-Dex: CAE (scale bars 5.0 kV \(\times\) 5.0 K).  
Figure 5: Tensile strength of _Centella asiatica_ extract-loaded hyaluronic acid-dextran (HA-Dex) hybrid hydrogel patches (\(n=3\), mean \(\pm\) SD). Control: HA-Dex hybrid hydrogel patches with no CAE; (a) 9.8:0.2, (b) 9.6:0.4, (c) 9.4:0.6, (d) 9.2:0.8, and (e) 9:1 wt% HA-Dex: CAE.