## 3 Results and Discussion  
### Purity and In Vitro Cell Viability of SK  
The SK component can be characterized with three ultraviolet-visible absorption peaks, which are approximately at 485, 518 and 574 nm [17,18]. In this study, the absorbance at 518 nm and the corresponding calibration curve were used to measure the content of SK. Table 1 shows the LE extraction results as related to the extraction temperature and extraction time. When the extraction temperature was 60, 50 and 25 \({}^{\circ}\)C and the extraction time was 24 h, the extraction concentration was 6.24, 3.30 and 1.93 mg/mL, and the SK content was 2.17, 1.15 and 0.78 mg/mL, respectively. The content of SK increased as a result of increasing the extraction temperature, but the opposite was true for the purity of the extract. Based on our previous study, in order to avoid damaging the activity of SK within a safe extraction temperature, the extraction percentage should be proportional to the extraction temperature. Moreover, this shortens the time it takes for the solvent to reach a saturation concentration [2]. However, a high extraction temperature increases the presence of impurities, decreasing the purity of the extraction. Therefore, in order to prove that a low extraction temperature can decrease the content of impurities to obtain a greater extraction purity, and in order to overcome the fact that the solvent cannot reach to a saturation concentration in a short extraction time, the other batch in the experiment was prepared using the extraction time of seven days and extraction temperatures of 10 \({}^{\circ}\)C and \(-\)10 \({}^{\circ}\)C.  
Table 1 shows the test results for a low-temperature extraction. Compared to the results of an extraction temperature of 25 \({}^{\circ}\)C, the SK content increases by 33.8% for 10 \({}^{\circ}\)C and 37.9% for \(-\)10\({}^{\circ}\)C. In particular, the optimal purity of extraction is 53.8%, and the optimal SK content is 1.07 mg/mL (\(p<\) 0.01) when the extraction temperature is \(-\)10 \({}^{\circ}\)C. LE is composed of shikonin and its derivatives, the former being the primary effective component. Therefore, a low extraction temperature is proven to effectively increase the SK content. Figure 1 shows the effect of SK concentration on the cell viability of fibroblasts. The test results show that SK with a concentration that is lower than 1.4 \(\upmu\)M does not have a negative influence on the cell viability of fibroblasts. Comparing to the control group, SK with a concentration between 1.4 and 0.7 \(\upmu\)M significantly facilitates the cell viablity by 134.2 and 136.8% (\(p<\) 0.01), while SK with a concentration between 2.1 and 3.5 \(\upmu\)M significantly suppresses the cell viablity by 66.3%, 60.1% and 47.1% (\(p<\) 0.01). Previous studies also showed that SK with a concentration of 1-10 \(\upmu\)M facilitated cell proliferation. [PERSON] et al. found that 1 \(\upmu\)M of SK accelerated the growth of human dermal fibroblasts, and 10 \(\upmu\)M of SK stimulated human keratinocyte growth [19]. [PERSON] et al. found that 1 \(\upmu\)M of SK significantly improved intestinal wound healing without preventing the growth of intestinal epithelial cells (IEC-18) [20]. Low-dose water extracts of gromwell (1 \(\upmu\)g/mL) enhanced the migration of both cultured human keratinocytes and fibroblasts with increased lipid synthesis in an in vitro wound scratch model [21]. Therefore, a maximum concentration of 1.4 \(\upmu\)M of SK was used for following evaluations and discussions.