Using a New Photo Scale to Compare Product Integration of Different Hyaluronan-Based Fillers After Injection in Human Ex Vivo Skin

Background: The rheological properties of HA products have been investigated thoroughly, and these properties have been used to predict the clinical performance of HA fillers. It has been suggested that firm gels have a better ability to withstand deformation, and softer gels have been claimed to integrate and spread more into the tissue since they are perceived to deform more easily. However, the scientific published data regarding product integration of filler products with different physicochemical properties is limited. Thus, there is a need to improve the understanding regarding links between rheological properties of the gel material and the clinical performance. Objective: The objectives of this study were: to develop and validate a photo scale for assessment of product distribution after intradermal injection, and to evaluate if product differences, such as overall rheological properties, gel particle size, swelling factor, and cohesivity effect the product distribution into the tissue after intradermal injections. Material and Methods: Intradermal injections of HA fillers were performed in ex vivo human abdominal skin samples. The skin samples were processed for histological evaluation. In order to evaluate the product integration after intradermal injection and compare the results between different products a 5-grade product integration scale (from 0 to 4) was developed based on representative microphotographs. The scale was validated and used for the evaluation of integration of the different products used in the study. The results were correlated with the rheological properties of the different products. Results: G’, the elastic modulus, is one important rheological parameter. Strong and firm gels have higher G’ than weak and soft gels. When plotting the G’ to mean product integration score in human skin obtained in the study, there was a statistically significant correlation with products with lowest G’ having the highest integration score and products with high G’ having the lowest integration scores. No statistical correlation could be seen when analyzing the score versus particle size, swelling factor, and cohesivity. Conclusion: The degree of product integration can be assessed and scored according to a 5-grade visual scale based on representative microphotographs. Products with different rheological properties distribute differently when injected into the skin. Firmer gel texture resulted in more targeted product integration whiles softer gel texture resulted in distributed product integration. J Drugs Dermatol. 2018;17(9):982-986.