I am using PDGF (https://www.fishersci.com/shop/products/thermo-scientific-pierce-pdgf-bb-human-recombinant-protein/pirp8657) for a chemotaxis assay. I would like to know how long I can use the product for before it expires. On the website it says that the "shelf life" is 12 months. However, many similar drugs have a significantly expanded shelf life once aliquots are made and stored at -20 deg C (which I have done with the PDGF). Does anyone have any experience working with this product?