The aggregation behavior of collagen in aqueous solution and its property of stabilizing liposomes in vitro

The aim of this study is to acquire the relationship between the aggregatio n behavior of collagen in aqueous solution and its property of stabilizing liposomes in vitro. Firstly, we used an intramolecular charge transfer comp ound 3-methoxy-4-N,N-dimethylamino flavone derivative (DMMF) as a fluoresce nce probe to detect collagen association in aqueous solution. Results showe d that, when collagen concentration was increased to 0.5 mg/ml or above, th e fluorescence intensity of DMMF at 465 nm increased dramatically. This ind icated that collagen could associate in aqueous solution. The subsequent fl uorescence polarization study on the same collagen solutions also proved th at the aggregation behavior existed in the aqueous solution of collagen. Se condly, to evaluate the in vitro stability of small unilamellar vesicles (S UV), made from soybean phosphatidylcholine (PC) and coated with collagen, 5 (6)-carboxyfluorescein was used as a fluorescence probe to determine the ch ange of their permeability. We found that the coating with a collagen PC we ight ratio of 2:1, significantly decreased the permeability of liposomal me mbranes. The likely weight ratio of collagen and PC was mainly dependent on the critical aggregation concentration of collagen in aqueous solution. In addition, the fluorescence polarization method was also used to study the influence of a coating with collagen at the above ratio on the fluidity of liposomal membranes, employing DMMF as a fluorescence probe. The fluidity o f liposomal membranes coated with collagen showed no obvious change, indica ting that SUV coated with collagen at an appropriate ratio, could significa ntly improve the in vitro stability of liposomal membranes without disturbi ng their fluidity. It is thus clear that collagen self-association behavior is closely correlated to its coating liposomes to improve their stability. (C) 2001 Elsevier Science Ltd. All rights reserved.