Lamellae-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films, with bulk period L 0, were directed to assemble on lithographically nanopatterned surfaces. The chemical pattern was comprised of “guiding” stripes of cross-linked polystyrene (X-PS) or poly(methyl methacrylate) (X-PMMA) mats, with width W, and interspatial “background” regions of a random copolymer brush of styrene and methyl methacrylate (P(S-r-MMA)). The fraction of styrene (f) in the brush was varied to control the chemistry of the background regions. The period of the pattern was L s. After assembly, the density of the features (domains) in the block copolymer film was an integer multiple (n) of the density of features of the chemical pattern, where n = L s/L 0. The quality of the assembled PS-b-PMMA films into patterns of dense lines as a function of n, W/L 0, and f was analyzed with top-down scanning electron microscopy. The most effective background chemistry for directed assembly with density multiplication corresponded to a brush chemistry (f) that minimized the interfacial energy between the background regions and the composition of the film overlying the background regions. The three-dimensional structure of the domains within the film was investigated using cross-sectional SEM and Monte Carlo simulations of a coarse-grained model and was found most closely to resemble perpendicularly oriented lamellae when W/L 0 ∼ 0.5–0.6. Directed self-assembly with density multiplication (n = 4) and W/L 0 = 1 or 1.5 yields pattern of high quality, parallel linear structures on the top surface of the assembled films, but complex, three-dimensional structures within the film.
Nanomedicine to overcome both systemic and tumor tissue barriers ideally should have a transformable size and surface, maintaining a certain size and negative surface charge for prolonged circulation, while reducing to a smaller size and switching to a positive surface charge for efficient penetration to and retention in the interstitial space throughout the tumor tissue. However, the design of such size and charge dual-transformable nanomedicine is rarely reported. Here, the design of a shell-stacked nanoparticle (SNP) is reported, which can undergo remarkable size reduction from about 145 to 40 nm, and surface charge reversal from -7.4 to 8.2 mV at acidic tumor tissue, for enhanced tumor penetration and uptake by cells in deep tumor tissue. The disulfide-cross-linked core maintains the stability of the particle and prevents undesired premature drug release until the shedding of the shell, which accelerates the cleavage of more exposed disulfide bond sand intracellular drug release. SNP penetrates about 1 mm into xenografted A549 lung carcinoma, which is about four times penetration depth of the nontransformable one. The doxorubicin (DOX)-loaded SNP (SNP/DOX) shows significant antitumor efficacy and nearly eradicates the tumor, substantiating the importance of the design of size and charge dual-transformable nanomedicine.
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