['The aim of the study is to determine whether a biodegradable elastomeric device that uses an osmotic pressure delivery mechanism can release different therapeutic proteins at a nearly constant rate in nanomolar concentrations with high bioactivity, given the same formulation conditions. Vascular endothelial growth factor (VEGF) and interleukin-2 (IL-2) were embedded in the device as sample therapeutic proteins, and their release and bioactivity were compared to that achieved previously with interferon-gamma (IFN-gamma).', 'A photo-cross-linkable biodegradable macromer consisting of acrylated star(epsilon-caprolactone-co-D,L-lactide) was prepared. VEGF, IL-2, and IFN-gamma were co-lyophilized with serum albumin and trehalose at different ratios and were then embedded into the elastomer by photo-cross-linking the lyophilized particles in a macromer solution. The protein mass and the bioactivity in the release supernatant were measured by enzyme-linked immunosorbent and cell-based assays.', 'VEGF, IL-2, and IFN-gamma were released at the same, nearly constant rate of 25.4 ng/day for over 18 days. Using the optimum elastomer formulation, the release profiles of the proteins were essentially identical, and their rates were linear and constant. Cell-based bioactivity assays showed that 70 and 88% of the released VEGF and IL-2, respectively, were bioactive. The rate of protein release can be adjusted by changing the trehalose loading concentration in the elastomer matrix without altering the linear nature of the protein release kinetics. The elastomeric device degraded in PBS buffer within 85 days.'] Are osmotic-driven release kinetics of bioactive therapeutic proteins from a biodegradable elastomer linear , constant , similar , and adjustable?