Keywords: Hydrogels, Pluronic F127, drug release, florescence TR-BSA

Problem: Many of currently available methods of delivering a single factor have demonstrated a limited efficacy in stimulating tissue repair. This has been associated with the complexity of tissue healing process. Therefore, it is critical that multiple therapeutic factors should be delivered to act in concert with the normal process of tissue healing, which may provide physiologically relevant release profiles that mimic the natural healing response. The purpose of this study is to demonstrate a proof-of-concept of achieving the controlled release of drugs in a sequential fashion by developing composite of biodegradable hydrogels consisting of F-127 hydrogel and gelatin microspheres.

Methods: Two forms of hydrogels, Pluronic F127 and gelatin microspheres, were prepared separately by mixing them with a model drug (Texas Red bovine serum albumin, TR-BSA) and the prepared hydrogels were incubated at 37^oC over days. At selected time points, supernatants were collected to quantify the extent of drug release from the gels based on the intensity of the florescence from TR-BSA.

Results and Conclusion: Our data supports that the sequential delivery system can enable the release of TR-BSA loaded with F-127 gel over ~8hr and gradual release of TR-BSA loaded within gelatin microsphere over duration of days. This study implicates that a sequential release of two different drugs can be achieved by triggering an initial release of one drug from F-127 gel followed by slow release of another drug from gelatin microspheres.