siRNA treatment has great,promise to specifically control gene expression and select cell behaviors but has delivery challenges limiting its use Particularly for applications in regenerative,medicine, uniform and consistent delivery of siRNA to control gene expression and subsequent stem cell functions, such as differentiation, is paramount. Therefore, a diblock copolymer was examined for its ability to effectively deliver siRNA to mesenchymal stem cells (MSCs). The diblock copolymers, which are composed, of cationic blocks for siRNA complexation, protection, and uptake and pH-responsive blocks for endosomal escape, were shown to facilitate nearly 100% MSC uptake of siRNA. This is vastly superior to a commercially available control, Dharma FECT, which resulted in only similar to 60% siRNA positive MSCs. Moreover, the diblock copolymer, at conditions that result in excellent knockdown (down to similar to 10% of control gene expression); was cytocompatible, causing no negative effects on MSC survivability. In contrast, Dharma FECT/siRNA treatment resulted in only, similar to 60% survivability of MSCs. Longitudinal knockdown. after siRNA treatment was examined and protein knockdown persists for similar to 6 days regardless, of delivery system (diblock copolymer.,or Dharma FECT). Finally, MSC. phenotype and differentiation. capacity was examined after treatment with control siRNA. There was no statistically significant differences on cell surface Markers of diblock copolymer/siRNA or DharmaFECT/siRNA-treated; Or cells measured 2 weeks after siRNA delivery compared to untreated " cells., Upon differentiation with :typical media/culture conditions to adipogenic, chondrogenic, and osteogenic lineages and examination of histological staining markers, there was no discernible differences between. treated and untreated cells, regardless of delivery mechanism. Thus, diblock copolymers examined herein facilitated uniform siRNA treatment of MSCs, inducing siRNA-specific gene and Protein knockdown without adversely affecting MSC survival or differentiation Capacity and therefore show, great promise for use within regenerative medicine applications.