A biofunctionalization scheme for neural interfaces using polydopamine polymer

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.

Polydopamine-enabled surface functionalization of gold nanorods for cancer cell-targeted imaging and photothermal therapy

AIM

A novel biomimetic strategy was employed for presenting antibodies on gold nanorods (NRs) to target growth factor receptors on cancer cells for use in photothermal therapy.

MATERIALS & METHODS

Polydopamine (PD) was polymerized onto gold NRs, and EGF receptor antibodies (anti-EGFR) were immobilized onto the layer. Cell-binding affinity and light-activated cell death of cancer cells incubated with anti-EGFR-PD-NRs were quantified by optical imaging.

RESULTS

PD was deposited onto gold NRs, and antibodies were bound to PD-coated NRs. Anti-EGFR-PD-NRs were stable in media, and were specifically bound to EGFR-overexpressing cells. Illumination of cells targeted with anti-EGFR-PD-NRs enhanced cell death compared with nonirradiated controls and cells treated with antibody-free NRs.

CONCLUSION

PD facilitates the surface functionalization of gold NRs with biomolecules, allowing cell targeting and photothermal killing of cancer cells. PD can potentially coat a large variety of nanoparticles with targeting ligands as a strategy for biofunctionalization of diagnostic and therapeutic nanoparticles.

Mussel-inspired immobilization of vascular endothelial growth factor (VEGF) for enhanced endothelialization of vascular grafts

Most polymeric vascular prosthetic materials have low patency rate for replacement of small diameter vessels (<5 mm), mainly due to failure to generate healthy endothelium. In this study, we present polydopamine-mediated immobilization of growth factors on the surface of polymeric materials as a versatile tool to modify surface characteristics of vascular grafts potentially for accelerated endothelialization. Polydopamine was deposited on the surface of biocompatible poly(L-lactide-co-ε-caprolactone) (PLCL) elastomer, on which vascular endothelial growth factor (VEGF) was subsequently immobilized by simple dipping. Surface characteristics and composition were investigated by using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Immobilization of VEGF on the polydopamine-deposited PLCL films was effective (19.8 ± 0.4 and 197.4 ± 19.7 ng/cm(2) for DPv20 and DPv200 films, respectively), and biotin-mediated labeling of immobilized VEGF revealed that the fluorescence intensity increased as a function of the concentration of VEGF solution. The effect of VEGF on adhesion of HUVECs was marginal, which may have been masked by polydopamine layer that also enhanced cell adhesion. However, VEGF-immobilized substrate significantly enhanced proliferation of HUVECs for over 7 days of in vitro culture and also improved their migration. In addition, immobilized VEGF supported robust cell to cell interactions with strong expression of CD 31 marker. The same process was effective for immobilization of basic fibroblast growth factor, demonstrating the robustness of polydopamine layer for secondary ligation of growth factors as a simple and novel surface modification strategy for vascular graft materials.

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.

The present and future of biologically inspired adhesive interfaces and materials

The natural world provides many examples of robust, permanent adhesive platforms. Synthetic adhesive interfaces and materials inspired by mussels of genus Mytulis have been extensively applied, and it is expected that characterization and adaptation of several other biological adhesive strategies will follow the Mytilus edulis model. These candidate species will be introduced, along with a discussion of the adhesive behaviors that make them attractive for synthetic adaptation. While significant progress has been made in the development of biologically inspired adhesive interfaces and materials, persistent questions, current challenges, and emergent areas of research will be also be discussed.

Electrochemical release of amine molecules from carbamate-based, electroactive self-assembled monolayers

In this paper, carbamate-based self-assembled monolayers (SAMs) of alkanethiolates on gold were suggested as a versatile platform for release of amine-bearing molecules in response to the electrical signal. The designed SAMs underwent the electrochemical oxidation on the gold surface with simultaneous release of the amine molecules. The synthesis of the thiol compounds was achieved by coupling isocyanate-containing compounds with hydroquinone. The electroactive thiol was mixed with 11-mercaptoundecanol [HS(CH(2))(11)OH] to form a mixed monolayer, and cyclic votammetry was used for the characterization of the release behaviors. The mixed SAMs showed a first oxidation peak at +540 mV (versus Ag/AgCl reference electrode), indicating the irreversible conversion from carbamate to hydroquinone groups with simultaneous release of the amine molecules. The analysis of ToF-SIMS further indicated that the electrochemical reaction on the gold surface successfully released amine molecules.

Polydopamine--a nature-inspired polymer coating for biomedical science

Polymer coatings are of central importance for many biomedical applications. In the past few years, poly(dopamine) (PDA) has attracted considerable interest for various types of biomedical applications. This feature article outlines the basic chemistry and material science regarding PDA and discusses its successful application from coatings for interfacing with cells, to drug delivery and biosensing. Although many questions remain open, the primary aim of this feature article is to illustrate the advent of PDA on its way to become a popular polymer for bioengineering purposes.