Girsang, Lora Coarnita, Edy Fachrial, and I Nyoman Ehrich Lister. 2020. “Effectiveness Test of Robusta Coffee (Coffea Cenephora) Extract from North Sumatra in Collagen and Hydration Skin Level of Female Wistar Rattus Norvegicus”. American Scientific Research Journal for Engineering, Technology, and Sciences 65 (1):108-15. https://asrjetsjournal.org/index.php/American_Scientific_Journal/article/view/5661.