Host Tissue Interaction, Fate, and Risks of Degradable and Nondegradable Gel Fillers

BACKGROUND: A constantly increasing number of gel fillers for aesthetic and reconstructive purposes have been introduced during the last 20 years. Most of the new ones are modified versions of the original collagen and hyaluronic acid gels. They have been reconstructed, often by adding cross-bindings to the polymer in order to obtain a more dense molecular structure, which will prolong degradation and filling effect of the gel. Other gel fillers contain particles of organic (poly-lactic acid) or inorganic (calcium hydroxylapatite) material, which have been used in human tissue for other purposes (degradable suture material and bone cement, respectively). The permanent fillers (silicone oil and polyacrylamide gel) have been used for many years, silicone mainly in the US and polyacrylamide gel in most countries outside the US and Canada. OBJECTIVE: Complications occur, and they appear to be more frequent with particulated fillers, polyacrylamide gel and silicone oil. However, these complications differ in nature and depend on the filler type used. METHODS AND MATERIALS: This overview presents the different gel filler types, how they interact with host tissue, and what can go wrong. The results and conclusion are based on experimental and clinical observations coupled with a search of the literature. RESULTS AND CONCLUSION: Complications following homogenous hydrogels are caused by infection with bacteria, which have been inserted into the gel during injection. If not treated with relevant antibiotics (but instead steroids or large doses of NSAIDs) the bacteria form a biofilm, which gives rise to a low-grade chronic infection that is resistant to antibiotics. Complications following particulated gels and silicone oil are not known, but bacteria in a biofilm and/or endotoxins released by these is a possibility which deserves further investigations, primarily by using the fluorescence in situ hybridization (FISH) technique.