In vivo adipose tissue regeneration by preadipocytes was evaluated by combining them with collagen sponges with different biodegradabilities and gelatin microspheres incorporating basic fibroblast growth factor (bFGF) for the controlled release. The collagen sponge biodegradability was regulated from 1-4 weeks by changing the cross-linking conditions in collagen sponge preparation. The time profile of bFGF release was controlled from 1-5 weeks by the biodegradability of gelatin microspheres used. The collagen sponges combined with human preadipocytes and gelatin microspheres incorporating bFGF were implanted into the back subcutis of nude mice to evaluate the adipose tissue regeneration. The regeneration of adipose tissue was observed in every collagen sponge. The area of regenerated adipose tissue was maximal in the collagen sponge with a degradation time of 2 weeks. No influence of the time profile of bFGF release on the area of regenerated adipose tissue was detected. (C) Koninklijke Brill NV, Leiden, 2010