Thin film electrodes of polyaniline (PANi) nanofibers and functionalized multiwall carbon nanotubes (MWNTs) are created by layer-by-layer (LbL) assembly for microbatteries or -electrochemical capacitors. Highly stable cationic PANi nanofibers, synthesized from the rapid aqueous phase polymerization of aniline, are assembled with carboxylic acid functionalized MWNT into LbL films. The pH-dependent surface charge of PANi nanofibers and MWNTs allows the system to behave like weak polyelectrolytes with controllable LbL film thickness and morphology by varying the number of bilayers. The LbL-PANi/MWNT films consist of a nanoscale interpenetrating network structure with well developed nanopores that yield excellent electrochemical performance for energy storage applications. These LbL-PANi/MWNT films in lithium cell can store high volumetric capacitance (~238 ± 32 F/cm(3)) and high volumetric capacity (~210 mAh/cm(3)). In addition, rate-dependent galvanostatic tests show LbL-PANi/MWNT films can deliver both high power and high energy density (~220 Wh/L(electrode) at ~100 kW/L(electrode)) and could be promising positive electrode materials for thin film microbatteries or electrochemical capacitors.

Retention of agricultural sprays on plant surfaces is an important challenge. Bouncing of sprayed pesticide droplets from leaves is a major source of soil and groundwater pollution and pesticide overuse. Here we report a method to increase droplet deposition through in-situ formation of hydrophilic surface defects that can arrest droplets during impact. Defects are created by simultaneously spraying oppositely charged polyelectrolytes that induce surface precipitation when two droplets come into contact. Using high-speed imaging, we study the coupled dynamics of drop impact and surface precipitate formation. We develop a physical model to estimate the energy dissipation by the defects and predict the transition from bouncing to sticking. We demonstrate macroscopic enhancements in spray retention and surface coverage for natural and synthetic non-wetting surfaces and provide insights into designing effective agricultural sprays.

Traumatic wounds and congenital defects that require large-scale bone tissue repair have few successful clinical therapies, particularly for craniomaxillofacial defects. Although bioactive materials have demonstrated alternative approaches to tissue repair, an optimized materials system for reproducible, safe, and targeted repair remains elusive. We hypothesized that controlled, rapid bone formation in large, critical-size defects could be induced by simultaneously delivering multiple biological growth factors to the site of the wound. Here, we report an approach for bone repair using a polyelectrolye multilayer coating carrying as little as 200 ng of bone morphogenetic protein-2 and platelet-derived growth factor-BB that were eluted over readily adapted time scales to induce rapid bone repair. Based on electrostatic interactions between the polymer multilayers and growth factors alone, we sustained mitogenic and osteogenic signals with these growth factors in an easily tunable and controlled manner to direct endogenous cell function. To prove the role of this adaptive release system, we applied the polyelectrolyte coating on a well-studied biodegradable poly(lactic-co-glycolic acid) support membrane. The released growth factors directed cellular processes to induce bone repair in a critical-size rat calvaria model. The released growth factors promoted local bone formation that bridged a critical-size defect in the calvaria as early as 2 wk after implantation. Mature, mechanically competent bone regenerated the native calvaria form. Such an approach could be clinically useful and has significant benefits as a synthetic, off-the-shelf, cell-free option for bone tissue repair and restoration.regenerative medicine | layer-by-layer | biomaterial | controlled drug release | wound healing

Rapid fabrication of layer-by-layer (LbL) electrodes is essential to expand their utility in energy storage applications. Herein, we address challenges in developing thick LbL electrodes of multi-wall carbon nanotubes (MWNTs) using conventional dip-and spray-LbL processes, and present a solution to overcome these challenges. The vacuum-assisted spray-LbL process using porous carbon substrates enabled a linear growth of LbL-MWNT electrodes with a 600 time decrease in their fabrication time.This result was attributed to the enhanced surface interactions between MWNTs and substrate via increased surface areas, enhanced capillary forces, physical entrapment in pores, and changes in hydrodynamic drag forces. Scanning electron microscopy (SEM) revealed high surface area carbon nanotube networks comprised of individual MWNT's. The spray MWNT electrodes delivered a high gravimetric energy of 100 W h kg À1 at high gravimetric power of 50 kW kg À1 , which is higher than those of most carbon nanotube electrodes reported. Moreover, the spray MWNT electrodes delivered the highest energy capacity per unit area (up to 300 mW h cm À2 at 0.4 mW cm À2 among the LbL electrodes reported, and showed excellent retention of energy capacity up to 100 mW h cm À2 at high power capacity of 200 mW cm À2 . These performance values are higher or comparable to the most advanced battery electrodes for high energy capacity per unit area. Broader contextWith emerging applications of Li-ion batteries such as electrical vehicles, load-leveling, and new electronic devices, the demand for improving both the gravimetric and areal energy and power output of battery electrodes is ever increasing. Although the previously reported battery electrodes assembled via layerby-layer (LbL) assembly have been shown to provide high gravimetric energy and power densities, the LbL electrodes deliver only limited total energy (per area) because of the long fabrication time required by traditional LbL processes. In this work, we demonstrate a rapid fabrication of thick LbL electrodes of multi-wall carbon nanotubes (MWNTs) via the modied spray-LbL method; the fabrication time decreased 600 times compared with traditional processes. The spray LbL-MWNT electrode showed both high gravimetric energy (100 W h kg electrode À1 ) and areal energy (100 mW h cm À2 ) without the expense of gravimetric or areal power density (50 kW kg electrode À1 or 200 mW cm À2 ). Our method can be easily expanded to different combinations of energy storage materials, substrates with different structures, and spray conditions, allowing us to efficiently fabricate novel energy storage electrodes via LbL assembly.

Polyelectrolyte multilayer films assembled from a hydrophobic N-alkylated polyethylenimine and a hydrophilic polyacrylate were discovered to exhibit strong antifouling, as well as antimicrobial, activities. Surfaces coated with these layer-by-layer (LbL) films, which range from 6 to 10 bilayers (up to 45 nm in thickness), adsorbed up to 20 times less protein from blood plasma than the uncoated controls. The dependence of the antifouling activity on the nature of the polycation, as well as on assembly conditions and the number of layers in the LbL films, was investigated. Changing the hydrophobicity of the polycation altered the surface composition and the resistance to protein adsorption of the LbL films. Importantly, this resistance was greater for coated surfaces with the polyanion on top; for these films, the average zeta potential pointed to a near neutral surface charge, thus, presumably minimizing their electrostatic interactions with the protein. The film surface exhibited a large contact angle hysteresis, indicating a heterogeneous topology likely due to the existence of hydrophobic-hydrophilic regions on the surface. Scanning electron micrographs of the film surface revealed the existence of nanoscale domains. We hypothesize that the existence of hydrophobic/hydrophilic nanodomains, as well as surface charge neutrality, contributes to the LbL film's resistance to protein adsorption.