Synthetic nanoscale electrostatic particles as growth factor carriers for cartilage repair

The efficient transport of biological therapeutic materials to target tissues within the body is critical to their efficacy. In cartilage tissue, the lack of blood vessels prevents the entry of systemically administered drugs at therapeutic levels. Within the articulating joint complex, the dense and highly charged extracellular matrix (ECM) hinders the transport of locally administered therapeutic molecules. Consequently, cartilage injury is difficult to treat and frequently results in debilitating osteoarthritis. Here we show a generalizable approach in which the electrostatic assembly of synthetic polypeptides and a protein, insulin‐like growth factor‐1 (IGF‐1), can be used as an early interventional therapy to treat injury to the cartilage. We demonstrated that poly(glutamic acid) and poly(arginine) associated with the IGF‐1 via electrostatic interactions, forming a net charged nanoscale polyelectrolyte complex (nanoplex). We observed that the nanoplex diffused into cartilage plugs in vitro and stimulated ECM production. In vivo, we monitored the transport, retention and therapeutic efficacy of the nanoplex in an established rat model of cartilage injury. A single therapeutic dose, when administered within 48 hr of the injury, conferred protection against cartilage degradation and controlled interleukin‐1 mediated inflammation. IGF‐1 contained in the nanoplex was detected in the joint space for up to 4 weeks following administration and retained bioactivity. The results indicate the potential of this approach as an early intervention therapy following joint injury to delay or even entirely prevent the onset of osteoarthritis.

Carbon nanotube–polyaniline core–shell nanostructured hydrogel for electrochemical energy storage

Highly porous three-dimensional core (carbon nanotube)–shell (polyaniline) conductive hydrogels synergize the advantageous features of hydrogels and conductive materials, showing enhanced electrical conductivity and electrochemical activity.

Assembly of viral hydrogels for three-dimensional conducting nanocomposites

M13 bacteriophages act as versatile scaffolds capable of organizing single-walled carbon nanotubes and fabricating three-dimensional conducting nanocomposites. The morphological, electrical, and electrochemical properties of the nanocomposites are presented, as well as its ability to disperse and utilize single-walled carbon nanotubes effectively.

Separating oil-water nanoemulsions using flux-enhanced hierarchical membranes

Membranes that separate oil-water mixtures based on contrasting wetting properties have recently received significant attention. Separation of nanoemulsions, i.e. oil-water mixtures containing sub-micron droplets, still remains a key challenge. Tradeoffs between geometric constraints, high breakthrough pressure for selectivity, high flux, and mechanical durability make it challenging to design effective membranes. In this paper, we fabricate a hierarchical membrane by the phase inversion process that consists of a nanoporous separation skin layer supported by an integrated microporous layer. We demonstrate the separation of water-in-oil emulsions well below 1 μm in size. In addition, we tune the parameters of the hierarchical membrane fabrication to control the skin layer thickness and increase the total flux by a factor of four. These simple yet robust hierarchical membranes with engineered wetting characteristics show promise for large-scale, efficient separation systems.

Surface-mediated bone tissue morphogenesis from tunable nanolayered implant coatings

The functional success of a biomedical implant critically depends on its stable bonding with the host tissue. Aseptic implant loosening accounts for more than half of all joint replacement failures. Various materials, including metals and plastic, confer mechanical integrity to the device, but often these materials are not suitable for direct integration with the host tissue, which leads to implant loosening and patient morbidity. We describe a self-assembled, osteogenic, polymer-based conformal coating that promotes stable mechanical fixation of an implant in a surrogate rodent model. A single modular, polymer-based multilayered coating was deposited using a water-based layer-by-layer approach, by which each element was introduced on the surface in nanoscale layers. Osteoconductive hydroxyapatite (HAP) and osteoinductive bone morphogenetic protein-2 (BMP-2) contained within the nanostructured coating acted synergistically to induce osteoblastic differentiation of endogenous progenitor cells within the bone marrow, without indications of a foreign body response. The tuned release of BMP-2, controlled by a hydrolytically degradable poly(β-amino ester), was essential for tissue regeneration, and in the presence of HAP, the modular coating encouraged the direct deposition of highly cohesive trabecular bone on the implant surface. In vivo, the bone-implant interfacial tensile strength was significantly higher than standard bioactive bone cement, did not fracture at the interface, and had long-term stability. Collectively, these results suggest that the multilayered coating system promotes biological fixation of orthopedic and dental implants to improve surgical outcomes by preventing loosening and premature failure.

Synthesis of highly stable sub-8 nm TiO2 nanoparticles and their multilayer electrodes of TiO2/MWNT for electrochemical applications

Next-generation electrochemical energy storage for integrated microsystems and consumer electronic devices requires novel electrode materials with engineered architectures to meet the requirements of high performance, low cost, and robustness. However, conventional electrode fabrication processes such as doctor blading afford limited control over the electrode thickness and structure at the nanoscale and require the incorporation of insulating binder and other additives, which can promote agglomeration and reduce active surface area, limiting the inherent advantages attainable from nanoscale materials. We have engineered a route for the synthesis of highly stable, sub-8 nm TiO2 nanoparticles and their subsequent incorporation with acid-functionalized multiwalled carbon nanotubes (MWNTs) into nanostructured electrodes using aqueous-based layer-by-layer electrostatic self-assembly. Using this approach, binder-free thin film electrodes with highly controllable thicknesses up to the micrometer scale were developed with well-dispersed, nonagglomerated TiO2 nanoparticles on MWNTs. Upon testing in an Li electrochemical half-cell, these electrodes demonstrate high capacity (>150 mAh/gel(ectrode) at 0.1 A/gel(ectrode)), good rate capability (>100 mAh/gel(ectrode) up to 1 A/g(electrode)) and nearly no capacity loss up to 200 cycles for electrodes with thicknesses up to 1480 nm, indicating their promise as thin-film negative electrodes for future Li storage applications.

Drastically lowered protein adsorption on microbicidal hydrophobic/hydrophilic polyelectrolyte multilayers

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.

Layer-by-layer assembled polyaniline nanofiber/multiwall carbon nanotube thin film electrodes for high-power and high-energy storage applications

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.

Thermodynamic modeling of contact angles on rough, heterogeneous surfaces

Theoretical modelling for contact angle hysteresis carried out to date has been mostly limited to several idealized surface configurations, either rough or heterogeneous surfaces. This paper presents a preliminary study on the thermodynamics of contact angles on rough and heterogeneous surfaces by employing the principle of minimum free energy and the concept of liquid front. Based on a two-dimensional regular model surface, a set of relations were obtained, which correlate advancing, receding and system equilibrium contact angles to surface topography, roughness and heterogeneity. It was found that system equilibrium contact angles (theta(ES)) can be expressed as a function of surface roughness factor (delta) and the Cassie contact angle (theta(C)): costheta(ES) = deltacostheta(C). This expression can be reduced to the classical Wenzel equation.: theta(ES) = theta(W) for rough but homogeneous surfaces, and the classical Cassie equation theta(ES) = theta(C) for heterogeneous but smooth surfaces. A non-dimensional parameter called surface feature factor (omega) was proposed to classify surfaces into three categories (types): roughness-dominated, heterogeneity-dominated and mixed-rough-heterogeneous. The prediction of advancing and receding contact angles of a surface is dependent on which category the surface belongs to. The thermodynamic analysis of contact angle hysteresis was further extended from the regular model surface to irregular surfaces; consistent results were obtained. The current model not only agrees well with the models previously studied by other researchers for idealized surfaces, but also explores more possibilities to explain the reported experimental results/observations that most existing theories could not explain.