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Localized delivery of small interfering RNA (siRNA) is a promising approach for spatial control of cell responses at biomaterial interfaces. Layer-by-layer (LbL) assembly of siRNA with cationic polyelectrolytes has been used in film and nanoparticle vectors for transfection. Herein, we combine the ability of particles to efficiently deliver siRNA with the ability of film polyelectrolyte multilayers to act locally. LbL particles were prepared with alternating layers of poly(l-arginine) and siRNA and capped with hyaluronic acid. Negatively charged LbL particles were subsequently assembled on the poly(l-lysine)-functionalized substrate to form a LbL particle-decorated surface. Cells grown in contact with the particle-decorated surface were able to survive, internalize particles, and undergo gene silencing. This work shows that particle-decorated surfaces can be engineered by using electrostatic interactions and used to deliver therapeutic payloads for cell-instructive biointerfaces.

Purified collagen possesses weak mechanical properties, hindering its broad application in tissue engineering. Strategies based on manipulating the hydrogel to induce fiber formation or incorporate nanomaterials have been proposed to overcome this issue. Herein, we use a microfluidic device to fabricate, for the first time, collagen hydrogels with aligned and oriented fibers doped with gold nanoparticles and carbon nanotubes. Results based on rheology, atomic force microscopy, and scanning electron microscopy reveal the formation of aligned and oriented collagen fibers possessing greater rigidity and stiffness on the doped hydrogels in comparison with native collagen. The mechanical properties of the hydrogels increased with the nanomaterial loading percentage and the stiffest formulations were those prepared in the presence of carbon nanotubes. We further evaluate the in vitro response of NIH-3T3 fibroblasts to the change in stiffness. The cells were found to be viable on all substrates with directional cell growth observed for the carbon nanotube-doped collagen fibers. No significant differences in the cell area, aspect ratio, and intensification of focal adhesions driven by the increase in stiffness were noted. Nonetheless, fibroblast proliferation and secretion of TGF-β1 were greater on the hydrogels doped with carbon nanotubes. This nanomaterial-collagen composite provides unique features for cell and tissue substrate applications.