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Influence of calcium hydroxylapatite on the soft tissues– a critical viewpoint

Augmentation of the face tissues with different products has been practiced in aesthetic medicine for the last decades. During the last 15 years, a lot of different commercial forms of calcium hydroxylapatite (CaHA) for soft-tissue augmentation appeared on the market. Most of them use the similar concentrations of a synthetic form of CaHA with the same size of CaHA particles of 25-45 μm and the carboxymethyl cellulose gel as a carrier. To explain the observed effect of CaHA on the skin, some authors supposed that it induces neocollagenogenesis; however, temporary increase of collagens I and III caused by CaHA cannot explain the long-term improvement of the skin quality. Also, whereas CaHA is mainly injected subcutaneously, there were no reliable investigations of the influence of CaHA on the structure and physiology of subcutaneous white adipose tissue (sWAT). In our opinion, all the main conclusions concerning the collagen-stimulating properties of 30% CaHA (particle size >25 μm) are at least doubtful and based on misunderstanding, which provides a potential for erroneous interpretation in the future. Additionally, there is no clear understanding of the mechanism of elimination of CaHA with large (25-45 μm) particle sizes from the soft tissues. We believe that this mechanism should be the non-fermented hydrolysis and that the speed of such elimination is dependent on the form of particles, the quality of their surface, and on the level of particle conglomeration. Skin aging leads to various microscopic and mesoscopic structural changes within single skin layers as well as in the interactions between these layers. These skin modifications also affect the interactions between the cells and extracellular matrix (ECM). We propose that CaHA may affect formation and secretion of exosomes producing a long-ranged effect on the skin, but it’s strongly related with concentration and size of the CaHA particles.

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