https://en.wikipedia.org/wiki/Copper_peptide_GHK-Cu https://www.tandfonline.com/doi/abs/10.1163/156856208784909435 https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-3164.2007.00647.x https://www.ncbi.nlm.nih.gov/pubmed/23285694 https://jamanetwork.com/journals/jamafacialplasticsurgery/fullarticle/480344 https://www.ncbi.nlm.nih.gov/pubmed/27517151 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3359723/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4508379/ https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-3164.2006.00551.x https://www.hindawi.com/journals/bmri/2014/151479/ https://onlinelibrary.wiley.com/doi/full/10.1111/j.1468-2494.2009.00490.x https://www.infona.pl/resource/bwmeta1.element.elsevier-f015a350-2cce3361-99cf-79290da3bb45 https://www.ncbi.nlm.nih.gov/pubmed/8326148 https://www.taylorfrancis.com/books/9780429192258/chapters/10.1201/NOE0824759438-38