Polyacrylamide Hydrogel Differences: Getting Rid of the Confusion

Polyacrylamide hydrogels (PAAH) have been used for many years in European and Asian countries, and they have been and some still are produced by a number of different manufacturers (Table 1). None of the products are currently marketed in the U.S., but a pivotal clinical study of Aquamid (Contura International A/S, Denmark) has recently been completed in the U.S.

The PAAH products are often considered to be the same material in different packaging, but this is not the case. There are important differences in the composition of the hydrogels, their manufacturing and control, injection technique used to implant the gels, and their ability to interact with the tissue into which they are injected. All these factors are likely to impact the performance and/or safety profile of the PAAH product.

Different polymer hydrogels have different chemical and physical structures: Bio-Alcamid (Polymekon, Italy), for example, is reported to be composed of polymers of alkylimide units;¹ Evolution (ProCytech, France) is composed of positively charged polyvinyl microspheres suspended in an acrylamide polymer;² Aquamid is composed solely of a cross-linked polyacrylamide.³ Moreover, there are different cross-linking techniques applied for the various hydrogels, which have a significant impact on the physical and chemical product characteristics and thereby on the tissue interaction and longevity. Information on details regarding stability, visco-elastic properties, pH, and dry matter content of different PAAH products is sparse and stems mainly from the manufacturers. Among the PAAH products, Interfall, appeared at the market in the early 90s and was invented and patented in Ukraine. The first world conference on its application was held in Kiev in November 2000. Subsequently a number of similar preparations emerged: Formacryl, Bioformacryl, Cosmogel, Argiform (from Russia), and Amazingel (from China).

In the following, three of the best known and most widely used hydrogels will be more thoroughly described with respect to these characteristics, and their differences will be highlighted in Tables 1 and 2. Unless otherwise indicated, all analyzes have been carried-out by Chempilots A/S, Farum, Denmark.

History
The gel started out as Formacryl, a product manufactured by the Russian company, Bioform, but in 2000, the product was manufactured by the Italian company, B&B Dental SRL (Progen, now Polymekon) and the name changed to BioFormacryl-the forerunner of Bio-Alcamid.