Tissue integration of polyacrylamide hydrogel: an experimental study of periurethral, perivesical, and mammary gland tissue in the pig.

BACKGROUND Polyacrylamide hydrogel (PAAG) is a nondegradable water-based polymer with high viscoelasticity. The gel is used as a tissue filler, the only risk being prolonged infection with anaerobic, contaminating microorganisms if not treated early with broad-spectrum antibiotics. OBJECTIVE With silicone gel as reference, PAAG tissue integration and migration was studied in a longitudinal study of the pig. MATERIALS AND METHODS Forty-one pigs were used. PAAG and silicone gel were injected into mammary tissue, and PAAG was injected into urethral or bladder wall or the anal canal. Tissues and regional lymph nodes were examined at 1, 1(1/2), 3, 3(1/2), 6, 12, and 14 months, and other lymph nodes and organs were examined at 1, 6, 12, and 14 months. RESULTS PAAG was invaded by macrophages and giant cells that were gradually replaced by a network of fibrous tissue. Silicone gel was seen inside these cells or as large vacuoles, surrounded by a fibrous capsule. Regional lymph nodes contained PAAG only at 1 1/2 months and silicone gel at 12 months. CONCLUSION PAAG is a stable, viscoelastic bulking agent, which unlike silicone gel is slowly integrated within its host tissue via a thin fibrous network. Long-term risk of fibrosis and migration is minimal.