The experiments were repeated three times, under the same conditions, to ensure accuracy.

Quantification of secreted type I collagen by fibroblast cultures on to the different surfaces was evaluated by enzyme-linked immunosorbent assay (ELISA). The supernatant was collected and centrifuged at 336g for 10 min. Type I collagen quantification was carried out using the Human Type I Collagen kit (R&D Systems, Minneapolis, USA) according to the manufacturer’s instructions. The values were expressed as picogram per milliliter. All the experiments were carried out in triplicate.

To investigate whether acid treatment time had an influence on cell proliferation and viability and type I collagen expression after 24 h, 48 h, and 72 h of culture, one-way ANOVA analysis was applied. Fisher’s LSD test was used for multiple comparisons. Statistical calculations were conducted in the SPSS 23 program (SPSS INC., Chicago, IL, USA), adopting a significance level of 5%.