Migration and 3D Traction Force Measurements inside Compliant Microchannels.

Cells migrate in vivo through channel-like tracks. While polydimethylsiloxane devices emulate such tracks in vitro, their channel walls are impermeable and have supraphysiological stiffness. Existing hydrogel-based platforms address these issues but cannot provide high-throughput analysis of cell motility in independently controllable stiffness and confinement. We herein develop polyacrylamide (PA)-based microchannels of physiological stiffness and prescribed dimensions for high-throughput analysis of cell migration and identify a biphasic dependence of speed upon confinement and stiffness. By utilizing novel four-walled microchannels with heterogeneous stiffness, we reveal the distinct contributions of apicolateral versus basal microchannel wall stiffness to confined versus unconfined migration. While the basal wall stiffness dictates unconfined migration, apicolateral stiffness controls confined migration. By tracking nanobeads embedded within channel walls, we innovate three-dimensional traction force measurements around spatially confining cells at subcellular resolution. Our unique and highly customizable device fabrication strategy provides a physiologically relevant in vitro platform to study confined cells.

Poly(ethylene glycol)-block-cationic polylactide nanocomplexes of differing charge density for gene delivery.

Representing a new type of biodegradable cationic block copolymer, well-defined poly(ethylene glycol)-block-cationic polylactides (PEG-b-CPLAs) with tertiary amine-based cationic groups were synthesized by thiol-ene functionalization of an allyl-functionalized diblock precursor. Subsequently the application of PEG-b-CPLAs as biodegradable vectors for the delivery of plasmid DNAs (pDNAs) was investigated. Via the formation of PEG-b-CPLA:pDNA nanocomplexes by spontaneous electrostatic interaction, pDNAs encoding luciferase or enhanced green fluorescent protein were successfully delivered to four physiologically distinct cell lines (including macrophage, fibroblast, epithelial, and stem cell). Formulated nanocomplexes demonstrated high levels of transfection with low levels of cytotoxicity and hemolysis when compared to a positive control. Biophysical characterization of charge densities of nanocomplexes at various polymer:pDNA weight ratios revealed a positive correlation between surface charge and gene delivery. Nanocomplexes with high surface charge densities were utilized in an in vitro serum gene delivery inhibition assay, and effective gene delivery was observed despite high levels of serum. Overall, these results help to elucidate the influence of charge, size, and PEGylation of nanocomplexes upon the delivery of nucleic acids in physiologically relevant conditions.