Commentary on: The Effect of Different Diameters of Fat Converters on Adipose Tissue and Its Cellular Components: Selection for Preparation of Nanofat

One of the earliest reported cases of autologous fat grafting was to correct a depressed scar in the temporal fossa described by Neuber in 1893.¹ He astutely observed that pieces of larger pieces of graft would form cysts and advocated the utilization of smaller particles. That observation still holds true in modern grafting and has indirectly led to an evolution of graft preparation and processing to optimize our utility of fat.^2-4 In addition to the structural function of adipose tissue, there are a variety of immune cells, cytokines, and progenitor cells within the stromal vascular fraction (SVF) that have expanded the regenerative properties of fat as well.^5-7 Mechanical processing of the lipoaspirate or emulsification with filtration can remove cellular debris and produce a micronized graft product, so-called microfat or nanofat.^8-10

There are a number of steps in preparing the graft product that can impact our outcomes, and we know from traditional grafting for volume and structure that the mechanical force has an effect on the cells. Qiu and colleagues build on this concept through a series of in vitro experiments to determine the effect that the mechanical force of processing the lipoaspirate to a nanograft product has on both the content and viability of the graft as well as the functional outcome.¹¹ In their modeling, the authors demonstrate the differing stress values at distinct parts within the emulsification apparatus, that is, the piston, syringe, and converter. Collectively, these components produce higher stress on the tissue with smaller pore sizes or apertures.

The authors found that the oil ratio was comparable among the larger pore diameters, and as the pore diameter decreased the particle size was smaller and the oil ratio increased in vitro. The number of cells decreased with the aperture size, including SVF cells, but the overall viability was the same throughout; perhaps the mechanical damage that occurs with the emulsification process and smaller pore size is accounted for in the filtration step. I would be interested to see if there are changes in the fractions of cells from the SVF with the differing pore sizes, such as macrophages. Our group has recently presented a difference in SVF cell concentrations with comparable viability among different techniques to process standard grafts⁶ and would hypothesize that further processing may lead to a similar finding.

The most clinically relevant finding of the study is illustrated in Figure 3 with the macroscopic appearance of the adipose tissue after the shuffling process. The consistency of the product yielded from each pore size is well demonstrated, and the authors go on to show that as aperture size decreases, the oil ratio increases and the number of ASCs (ADSCs) and SVF cells decreases. However, the most interesting finding was the difference in differentiation capability observed with various aperture sizes, which should be explored further. The mechanical properties of ASCs account for an intrinsic resistance during the emulsification process, and we know that external mechanical force in the differentiation process can direct multiple lineages.¹² The observation here that adipogenesis was greater after emulsification through the 1.2- and 1.0-mm pore sizes while microtubule formation, as a means to detect angiogenesis, was less, hints at the effect of mechanical processing on the functional outcomes of nanofat.

In summary, the authors demonstrate that aperture size utilized in the emulsification process has an effect of the content and potential function of the resulting nanofat product. This may be an important factor in the clinical utility of processing as a means to further direct the function of the graft, as in larger aperture when the volume or structure of the graft is necessary vs smaller aperture when the regenerative properties of the graft are required and space is limited. As with most research, attempts to answer 1 question inevitably raise more, and further investigation into the impact of mechanical processing and stress on the differentiation abilities of ASCs is warranted. Overall, the study adds to the growing body of evidence that emulsified fat obtained through mechanical processing is a useful tool in fat grafting and regenerative medicine.

Disclosures

The author declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.

Funding

The author received no financial support for the research, authorship, and publication of this article.

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