Mussel-inspired anchoring for patterning cells using polydopamine

Microdevices for nanomedicine

This review surveys selected methods of manufacture and applications of microdevices-miniaturized functional devices capable of handling cell and tissue cultures or producing particles-and discusses their potential relevance to nanomedicine. Many characteristics of microdevices such as miniaturization, increased throughput, and the ability to mimic organ-specific microenvironments are promising for the rapid, low-cost evaluation of the efficacy and toxicity of nanomaterials. Their potential to accurately reproduce the physiological environments that occur in vivo could reduce dependence on animal models in pharmacological testing. Technologies in microfabrications and microfluidics are widely applicable for nanomaterial synthesis and for the development of diagnostic devices. Although the use of microdevices in nanomedicine is still in its infancy, these technologies show promise for enhancing fundamental and applied research in nanomedicine.

Sp2 C-dominant N-doped carbon sub-micrometer spheres with a tunable size: a versatile platform for highly efficient oxygen-reduction catalysts

A simple, yet versatile strategy to prepare size-controlled and monodisperse carbon sub-micrometer spheres is developed based on the biomolecule dopamine. Unlike traditional carbon materials, the resulting carbon sub-micrometer spheres contain much less sp(3) carbon with high-level electroactive nitrogen. Moreover, metal-carbon hybrid sub-micrometer spheres can be easily obtained, and show highly promising catalytic properties in the oxygen-reduction reaction.

Catechol-based biomimetic functional materials

Catechols are found in nature taking part in a remarkably broad scope of biochemical processes and functions. Though not exclusively, such versatility may be traced back to several properties uniquely found together in the o-dihydroxyaryl chemical function; namely, its ability to establish reversible equilibria at moderate redox potentials and pHs and to irreversibly cross-link through complex oxidation mechanisms; its excellent chelating properties, greatly exemplified by, but by no means exclusive, to the binding of Fe(3+); and the diverse modes of interaction of the vicinal hydroxyl groups with all kinds of surfaces of remarkably different chemical and physical nature. Thanks to this diversity, catechols can be found either as simple molecular systems, forming part of supramolacular structures, coordinated to different metal ions or as macromolecules mostly arising from polymerization mechanisms through covalent bonds. Such versatility has allowed catechols to participate in several natural processes and functions that range from the adhesive properties of marine organisms to the storage of some transition metal ions. As a result of such an astonishing range of functionalities, catechol-based systems have in recent years been subject to intense research, aimed at mimicking these natural systems in order to develop new functional materials and coatings. A comprehensive review of these studies is discussed in this paper.

Noncovalent microcontact printing for grafting patterned polymer brushes on graphene films

This article describes a simple and universal approach to prepare patterned polymer brushes on graphene-based substrate surfaces by microcontact printing (μCP) of initiator molecules and subsequent surface initiated atom transfer radical polymerization (SI-ATRP) method. Four different initiators are designed and have strong adhesion with graphene-based substrates through noncovalent interaction. Optical and fluorescence microscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the successful polymerization of vinyl monomers on substrate surfaces. To demonstrate the broad applicability of this strategy, polymer brushes with different functionalities including cationic and anionic polyelectrolyte, thermally and pH responsive polymers, as well as polymer patterns on different graphene-based surfaces are fabricated. Binary polymer brushes can also be easily prepared by further initiating the initiator backfilled in the bare areas.

Fabrication of tunable micropatterned substrates for cell patterning via microcontact printing of polydopamine with poly(ethylene imine)-grafted copolymers

Cell patterning is an important tool for biomedical research. In this work, we modified a technique combining mussel-inspired surface chemistry and microcontact printing (μCP) to modulate surface chemistry for cell patterning. Polymerized dopamine on poly(dimethylsiloxane) stamps was transferred to several cell-unfavorable substrates via μCP. Since cells only attached to the polydopamine (PDA)-imprinted areas, cell patterns were formed on a variety of cell-unfavorable surfaces. The stability of PDA imprints was proved under several harsh conditions. The cell affinity of PDA was modulated by co-deposition with several poly(ethylene imine) (PEI)-based copolymers, such as PEI, PEI-g-PEG (poly(ethylene glycol)) and PEI-g-galactose. The imprints of PDA/PEI-g-PEG provide the formation of cell patterns on cell-favorable substrates. Neuronal PC12 cells were patterned via imprinting of PDA/PEI, while HepG2/C3A cells were arranged on the imprint of PDA/PEI-g-galactose. Finally, co-culture of HepG2/C3A cells and L929 fibroblasts was accomplished by our micropatterning approach. This study demonstrated this simple and economic technique provides a powerful tool for development of functional patterned substrates for cell patterning. This technique should profit the preparation of cell patterns to study fundamental cell biology and to apply to biomedical engineering such as cell-based biosensors, diagnostic devices and tissue engineering.

"Contact" of nanoscale stiff films

We investigated the contact behaviors of a nanoscopic stiff thin film bonded to a compliant substrate and derived an analytical solution for determining the elastic modulus of thin films. Microscopic contact deformations of the gold and polydopamine thin films (<200 nm) coated on polydimethylsiloxane elastomers were measured by indenting a soft tip and analyzed in the framework of the classical plate theory and Johnson-Kendall-Roberts (JKR) contact mechanics. The analysis of this thin film contact mechanics focused on the bending and stretching resistance of thin films and is fundamentally different from conventional indentation measurements where the focus is on the fracture and compression of the films. The analytical solution of the elastic modulus of nanoscopic thin films was validated experimentally using 50 and 100 nm gold thin films coated on polydimethylsiloxane elastomers. The technical application of this analysis was further demonstrated by measuring the elastic modulus of thin films of polydopamine, a recently discovered biomimetic universal coating material. Furthermore, the method presented here is able to quantify the contact behaviors of nanoscopic thin films, effectively providing fundamental design parameters, the elastic modulus, and the work of adhesion, crucial for transferring them effectively into practical applications.

Tunable micropatterned substrates based on poly(dopamine) deposition via microcontact printing

A simple technique was developed to fabricate tunable micropatterned substrates based on mussel-inspired surface modification. Polydopamine (PDA) was developed on polydimethylsiloxane (PDMS) stamps and was easily imprinted to several substrates such as glass, silicon, gold, polystyrene, and poly(ethylene glycol) via microcontact printing. The imprinted PDA retained its unique reactivity and could modulate the chemical properties of micropatterns via secondary reactions, which was illustrated in this study. PDA patterns imprinted onto a cytophobic and nonfouling substrates were used to form patterns of cells or proteins. PDA imprints reacted with nucleophilic amines or thiols to conjugate molecules such as poly(ethylene glycol) for creating nonfouling area. Gold nanoparticles were immobilized onto PDA-stamped area. The reductive ability of PDA transformed silver ions to elemental metals as an electroless process of metallization. This facile and economic technique provides a powerful tool for development of a functional patterned substrate for various applications.