Background: Hyaluronic acid (HA) formulations are used for aesthetic applications. Different cross-linking technologies result in HA dermal fillers with specific characteristic visco-elastic properties. Objective: Bio-integration of three CE-marked HA dermal fillers, a cohesive (monophasic) polydensified, a cohesive (monophasic) monodensified and a non-cohesive (biphasic) filler, was analysed with a follow-up of 114 days after injection. Our aim was to study the tolerability and inflammatory response of these fillers, their patterns of distribution in the dermis, and influence on tissue integrity. Methods: Three HA formulations were injected intradermally into the iliac crest region in 15 subjects. Tissue samples were analysed after 8 and 114 days by histology and immunohistochemistry, and visualized using optical and transmission electron microscopy. Results: Histological results demonstrated that the tested HA fillers showed specific characteristic bio-integration patterns in the reticular dermis. Observations under the optical and electron microscopes revealed morphological conservation of cutaneous structures. Immunohistochemical results confirmed absence of inflammation, immune response and granuloma. Conclusion: The three tested dermal fillers show an excellent tolerability and preservation of the dermal cells and matrix components. Their tissue integration was dependent on their visco-elastic properties. The cohesive polydensified filler showed the most homogeneous integration with an optimal spreading within the reticular dermis, which is achieved by filling even the smallest spaces between collagen bundles and elastin fibrils, while preserving the structural integrity of the latter. Absence of adverse reactions confirms safety of the tested HA dermal fillers.

The different types of cross-linked HA have different behaviors in the dermis immediately after their injection. The patterns are consistent between patients and are predictable. These histologic patterns do not change when biopsies are examined at 2 weeks.

Since 1995, I have 8 patients with adverse reactions to injectable hyaluronic acid, which after several tests, may be allergic to those products. Isn't it time to introduce intradermal tests before any injection of this type, as done with injectable bovine collagen?

Aim: Over the last 15 years, hyaluronic acid (HA) fillers have become the most popular injectable biomaterial for soft tissue correction. With the increasing number of available HA fillers and the multiplication of facial treatments all over the world, there has been a need from physicians to better understand the HA fillers science. There is especially a growing interest in the science-based evaluation of rheological characteristics which represents an essential tool to guide physicians in the selection of the most appropriate HA fillers, administration techniques and depths of injection for their clinical applications. Methods: Four key rheological parameters (viscosity η, elasticity G', normal force F N and elasticity E') are measured and discussed on five HA fillers. Results: These four key rheological parameters are demonstrated to play a pivotal role, in combination with the cohesivity, for better predicting the clinical behavior of HA fillers at different stages of their lifetime. Conclusion: This article discusses the importance of four key rheological parameters during the main steps of the clinical HA fillers' lifetime, from the product injection to the loss of clinical effects. A better knowledge of these HA fillers' rheological parameters can help the physicians to optimize their aesthetic outcomes, safety and patient satisfaction.

With the proliferation of dermal fillers in the aesthetic workplace have come instructions from various manufacturers regarding dermal placement. Determination of injection needle location in the dermis has in large part been based on physician expertise, product and needle familiarity, and patient-specific skin characteristics. An understanding of the precise depth of dermal structures may help practitioners improve injection specificity. Unlike other dermal fillers that suggest intradermal and deep dermal injection planes, a new hyaluronic acid with a cohesive polydensified matrix may be more appropriate for the superficial dermis because of its structure and its high degree of integration into the dermis. To that end, the authors designed a small study to quantify the depth of the superficial dermis by means of ultrasound and histology. Using ultrasound resources, the authors determined the depths of the epidermis, the dermis, and the reticular dermis in the buttocks of six patients; the authors then extrapolated the depth of the superficial reticular dermis. Histologic studies of two of the patients showed full integration of the product in the reticular dermis. Following determination of injection depths and filler integration, the authors describe a technique ("blanching") for injection of the cohesive polydensified matrix hyaluronic acid into the superficial dermis. At this time, blanching is appropriate only for injection of the cohesive polydensified matrix hyaluronic acid known as Belotero Balance in the United States, although it may have applications for other hyaluronic acid products outside of the United States.