LAUSR

Since the popularization of fat grafting by Syd Coleman1 in the last decade of the last century, a variety of techniques for fat harvesting, preparation, and injection have been proposed. As the authors correctly state, these multiple processing and handling methods lead to variations in graft retention and viability, resulting in unpredictable clinical outcomes.2 They also argue that the underlying molecular mechanisms belying the varying fat grafting processes are not well understood.2 Since the discovery by Zuk3 in 2002 that human adipose tissue is a rich source of multipotent stem cells, the adipose derived stem cell (ADSC) became so hyped that some surgeons now even talk about “stemcell facelifts”—all this without much evidence. The authors must be congratulated with their simple but very clever experimental setup. They processed lipoaspirates into emulsified fat and isolated stromal vascular fraction (SVF) and free lipids (adipocyte fractions) by centrifugation. They enriched the SVF with 0%, 5%, 10%, and 15% free lipid and injected these under the panniculus carnosus along the dorsum of athymic rats. Forty-five days later, they saw that SVF with 10% free lipid showed the best adipocyte architecture with rich collagen and elastin network. Also, the CD44 staining demonstrated a higher inflammatory response in the 10% free-lipid group. Their study suggests that free lipids provide a milieu for enhancing cell viability and stem cell differentiation into adipocytes and other cells. On top of that, their study also implies that the free lipids stimulate inflammation of the fat graft and increase collagen and elastin production. To our knowledge, this is the first time that the importance of the oily fraction of the fat grafting specimen has been so clearly and simply demonstrated. The article also reminds us how little we know about the fundamental mechanisms of fat grafting, and the effects of SVF grafting on skin rejuvenation. A lot of unanswered questions still remain: what is the role of inflammation in the fat grafting process? What is the role of the extracellular matrix (ECM) in the fat grafting process? Is fat grafting with the purpose of volume augmentation, such as breast or buttocks augmentation, the same as fat grafting with the purpose of skin rejuvenation, such as in the face, neck, décolleté, and hands? Does injected fat behave the same in the subcutaneous level as in the intradermal level? What is the role of ADSC in the fat grafting process? What is the role of signaling factors between mechanically traumatized adipocytes by, for instance, exosomes in the fat grafting and/ or regeneration process? Isolation of the stromal vascular fraction is typically done by enzymatic digestion of the collagen matrix and has been proven to be time consuming, complicated, and nowadays virtually impossible in most countries, due to regulation issues of bioactive medication. In 2013, we described a technique to concentrate the SVF trough mechanical dissociation of the microfat lipoaspirate tissue by means of a simple emulsification process.3 This product