@marilyncarkner I have not heard of this either but will definitely check it out if I have another knee replacement. Thanks @rainerhans for sharing this information!

Although not specifically about a total knee replacement, here are a couple of articles on the topic.
--- Mesenchymal stem cell therapy combined with arthroscopic abrasion arthroplasty regenerates cartilage in patients with severe knee osteoarthritis: a case series: https://www.futuremedicine.com/doi/full/10.2217/rme-2020-0128
--- Recent Development of Biomaterials Combined with Mesenchymal Stem Cells as a Strategy in Cartilage Regeneration: https://www.mdpi.com/2673-8937/2/3/35