Several biomaterials are currently available for soft-tissue augmentation. Biocompatibility is an indispensable condition for any such product. Appropriate histologic evaluation is a prerequisite for understanding the responses of tissues to implant materials. Recently, hyaluronic acid and polyacrylamide gel products have been introduced as dermal fillers. Both types of product are widely considered to be biocompatible.
The present study compared tissue responses in a rat in vivo model (n = 80) to a hyaluronic acid filler (Restylane Perlane; Q-Med AB, Uppsala, Sweden) and a polyacrylamide gel filler (Aquamid; Contura SA, Montreux, Switzerland). Four groups were evaluated: group 1 (n = 20) received the Restylane Perlane implant, group 2 received the Aquamid implant (n = 20), group 3 comprised a placebo group (n = 20), group 4 was the control group (n = 20). Responses and biocompatibility were assessed by histopathologic and histomorphometric evaluations between 1 week and 8 months after implantation.
The two products induced very different tissue responses. The polyacrylamide gel filler was highly bioactive, undergoing cell infiltration and integration into tissues. The hyaluronic acid filler underwent minimal cell infiltration, and the product remained surrounded by a uniformly thin capsule.
This study reveals that two soft-tissue fillers considered to be biocompatible induce very different tissue reactions. This indicates that their behavior in clinical practice is likely to be different.