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BackgroundHyaluronic acid (HA), a naturally occurring polysaccharide, is used in the production of dermal fillers for esthetic purposes. As it has a few days of half-life in human tissues, HA-based dermal filler is chemically modified to increase its lifetime in the body. The most common modification used in commercial HA-based filler is the cross-linking of HA chains using 1,4-butanediol diglycidyl ether (BDDE) as cross-linking agent. Residual, or unreacted, BDDE is considered nontoxic when it is <2 parts per million (ppm); therefore, the quantification of residual BDDE in the final dermal filler is mandatory to ensure the safety of the patients.Materials and methodsThe present study describes the detection and characterization of one by-product of the cross-linking reaction between BDDE and HA in alkaline conditions by combining both liquid chromatography and mass spectroscopy (LC–MS).ResultsAfter different analyses, it was found that the alkaline conditions and the high temperatures employed to sterilize the HA–BDDE hydrogel promote the formation of this new by-product, a “propene glicol-like” compound. LC–MS analysis confirmed that this by-product have the same monoisotopic mass as that of BDDE, a different retention time (tR), and also a different UV absorbance (λ=200 nm) pattern. Unlike BDDE, it was observed in the LC–MS analysis that this by-product had a higher detection at 200 nm in the same assay conditions.ConclusionThese results suggest that this new compound does not have an epoxide on its structure. The discussion is open to assess the risk of this new by-product found in the production of HA–BDDE hydrogels (HA dermal fillers) for commercial purposes.

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