Midfacial rejuvenation by hyaluronic acid fillers and subcutaneous adipose tissue--a new concept.

In midface rejuvenation, hyaluronic acid (HA) fillers are commonly used as a versatile tool to improve appearance and to correct V-deformities and loss of volume. The induction of collagen as a major constituent of extracellular matrix (ECM) has been considered to be a basic effect of the rejuvenation procedure. Although commonly described as "dermal" soft fillers, histologic studies localized HA filler in the subcutaneous adipose tissue. Deep injection whenever possible lead to prolonged efficacy. Since volumizing HA filler induce mechanical stress not only to fibroblasts but adipocytes and deep injection itself causes minor trauma in the subcutaneous adipose tissue we suggest that the activation of adipose tissue-derived mesenchymal stem cells (ADMSC) is responsible for the observed clinical effects. We present a concept of filler action that discusses interactions of HA with adipocytes, ECM fiber network and ADMSC. Such a concept can explain the prolonged efficacy of deep midfacial filler placement and offers a new understanding to tailor HA fillers in the future.