Statement of Purpose: Macrophages are key mediators in the inflammatory response to implanted biomaterials and their behavior ultimately determines the function and longevity of implants. Therefore, there is a need to modulate macrophage behavior in response to implanted biomaterials to promote healthy biomaterial-tissue integration. Here, we propose to use the biotin-streptavidin affinity system to modify scaffolds with immunomodulatory cytokines to promote the desired macrophage phenotype, which varies depending on the application. The bond between biotin and streptavidin has been assumed to be essentially covalent, however, biotinylated proteins exhibit reduced bond strength with streptavidin, leading to release of the biotinylated proteins. Additionally, in the presence of excess biotin, biotinylated proteins are displaced by free biotin due to the higher affinity between free biotin and streptavidin. Therefore, the biotin-streptavidin system holds potential to be used to impart controlled release functionality to any biomaterial that is amenable to biotinylation. The objective of this study was to investigate how conjugation parameters affect release of biotinylated macrophage-modulating proteins from biotinylated scaffolds. Gelatin sponges, a model biomaterial, were biotinylated with varying degrees of biotin, followed by attachment to biotinylated interleukin-4 (IL4) via streptavidin in order to promote the pro-healing "M2" macrophage phenotype. Additionally, two variants of avidin, streptavidin and captavidin, which have different affinities for biotin, were used to modulate the rate of release of protein over time.