Injectable fillers are commonly used in Plastic and Reconstructive Surgery to correct serious and slight aesthetic defects due to their low invasiveness and an easy implant technique procedure. Synthetic hydrogels are proposed as filler materials for their similarity with soft tissue and to avoid many disadvantages of naturally derived materials such as short persistence, allergenicity, and immunogenicity. Our studies are focused on the biocompatibility evaluation of a polyacrylic hydrogel containing alkylimide-amide groups and pyrogen free water (96%) (Bio-Alcamid by means of the in vitro cytotoxicity and mutagenicity assays and the in vivo skin irritation, sensitization test, and subcutaneous implant. All tests conducted on Bio-Alcamid showed no toxicity. It is a substance easy to inject and remove; it does not migrate, and its safety allows it to be a suitable filler for the correction of slight and also very serious aesthetic defects.

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The in vitro effects of polyalkyl-imide hydrogel (PAI) containing 96% pyrogen-free water on the viability, apoptosis, cell shape and metabolic activities of murine 3T3 and human Detroit 555 fibroblasts were investigated. Analysis of the viscous-elastic properties and the ultrastructure of PAI, performed by rheometer and AFM respectively, showed that the material has the typical characteristics of hydrogel, including a three-dimensional configuration of molecules arranged in a regular network with many discrete caveolae where most of the water is captured. Hydrogel biocompatibility was found to be high for both cell lines, with some differences. Cell viability decreased more in 3T3 cells than Detroit 550 fibroblasts when cultured in the presence of 100 mg/ml hydrogel but not at concentrations of 25 and 50 mg/ml hydrogel. The period of incubation with PAI (24 and 48 h) only partially affected cell viability. Apoptosis, most likely due to cells' inability to adhere to the polymer, was the only type of cell death observed. Fibroblasts grown in the presence of polymer were always metabolically active since they continued to synthesize collagen. In conclusion, PAI hydrogel, even at high concentrations, was biocompatible for both fibroblasts, but in particular for human cells, thus encouraging its use as a dermal filler.