Injectable gels for tissue engineering

Recently, tissue engineering approaches using injectable, in situ gel formi ng systems have been reported. In this review, the gelation processes and s everal injectable systems that exhibit in situ gel formation at physiologic al conditions are discussed. Applications of selected injectable systems (a lginate, chitosan, hyaluronan, polyethylene oxide/polypropylene oxide) in t issue engineering are also described. Injectable polymer formulation can ge l in vivo in response to temperature change (thermal gelation), pH change, ionic cross-linking, or solvent exchange. Kinetics of gelation is directly affected by its mechanism. Injectable formulations offer specific advantage s over preformed scaffolds such as: possibility of a minimally invasive imp lantation, an ability to fill a desired shape, and easy incorporation of va rious therapeutic agents. Several factors need to be considered before an i njectable gel can be selected as a candidate for tissue engineering applica tions. Apart from tissue-specific cell-matrix interactions, the following g el properties need to be considered: gelation kinetics, matrix resorption r ate, possible toxicity of degradation products and their elimination routes , and finally possible interference of the gel matrix with histogenesis. An at Rec 263:342-349, 2001. (C) 2001 Wiley-Liss, Inc.