(A) In a controlled cortical impact (CCI) mouse model, propidium iodide (PI)-encapsulated silk films were placed onto the exposed cortical surface immediately after CCI, and the brains were harvested at 5hr post-injury. (B) (a) No PI-positive cells were found in uninjured brains (sham) with PI films. (b) PI+ cells (red) were found in TBI brains with PI films. (c) Co-staining of PI (red) and Hoechst 33258 (blue) showed selectively injured cells (pink) in TBI brains with PI+Hoechst 33258 combined films. Scale bar, 100 μm. (C) Quantification of PI+ cells in contused cortex in mice after CCI. Animals were either pre-treated with PI-films for 24hr (pre-treat, n=4) or resided in the brain for 5hr after placement on top of the contusion site immediately after CCI (post-treat, n=8), and compared with those with conventional systemic PI injection (tail IV inj., n=8).