Ke-feng Ren

Mussel-Inspired Polydopamine: A Biocompatible and Ultrastable Coating for Nanoparticles in Vivo

Bioinspired polydopamine (PDA) has served as a universal coating to nanoparticles (NPs) for various biomedical applications. However, one remaining critical question is whether the PDA shell on NPs is stable in vivo. In this study, we modified gold nanoparticles (GNPs) with finely controlled PDA nanolayers to form uniform core/shell nanostructures (GNP@PDA). In vitro study showed that the PDA-coated GNPs had low cytotoxicity and could smoothly translocate to cancer cells. Transmission electron microscopy (TEM) analysis demonstrated that the PDA nanoshells were intact within cells after 24 h incubation. Notably, we found the GNP@PDA could partially escape from the endosomes/lysosomes to cytosol and locate close to the nucleus. Furthermore, we observed that the PDA-coated NPs have very different uptake behavior in two important organs of the liver and spleen: GNP@PDA in the liver were mainly uptaken by the Kupffer cells, while the GNP@PDA in the spleen were uptaken by a variety of cells. Importantly, we proved the PDA nanoshells were stable within cells of the liver and spleen for at least six weeks, and GNP@PDA did not show notable histological toxicity to main organs of mice in a long time. These results provided the direct evidence to support that the PDA surface modification can serve as an effective strategy to form ultrastable coatings on NPs in vivo, which can improve the intracellular delivery capacity and biocompatibility of NPs for biomedical application.

Surface engineering of cardiovascular stent with endothelial cell selectivity for in vivo re-endothelialisation.

The in vivo endothelialisation of materials provides a promising strategy for the rapid re-endothelialisation of a cardiovascular implantation. Although many studies have focused on improving the rapid endothelialisation through the immobilisation of bioactive molecules, it should be noted that the endothelial cells (ECs) will compete with other cell types in vivo. Thus, the efforts to partially enhance the EC growth without considering the cell competition might be misleading and meaningless in vivo. In this study, we demonstrated that the competitive growth of human umbilical vein endothelial cells (HUVECs) over human aortic smooth muscle cells (HASMCs) could be increased through the synergic action of the nonspecific resistance to phosphorylcholine and the specific recognition of the REDV peptide. Further in vivo data indicate that the competitive ability of ECs over SMCs, instead of the number of ECs, is a significantly more important criterion for the development of a pure endothelial layer in vivo and thus the attainment of a better anti-restenosis effect. Consequently, the surface tailoring of a stent to obtain high endothelial cell selectivity is likely an effective design criterion for in situ endothelialisation and a possible future solution for the problem of in-stent restenosis.

Fast and long-acting antibacterial properties of chitosan-Ag/polyvinylpyrrolidone nanocomposite films.

Infection associated with medical devices is one of the most frequent complications of modern medical biomaterials. Preparation of antibacterial films on the medical devices is a great challenge owing to bactericidal efficiency, long acting and biocompatibility. In this study, silver nanoparticles (Ag NPs) doped chitosan/polyvinylpyrrolidone (PVP) films were successfully prepared by dip coating method. The nanocomposite films with spherical Ag NPs (diameters in 10-50 nm) were stable after being immersed in PBS for 35 days. Through regulating the concentration of AgNO3, the nanocomposite films showed good cell compatibility. The nanocomposite films could eliminate 100% Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 8739) in 5 min and had favorable long-acting antibacterial property. The increase of PVP amount obviously enhanced anti-adhesion activity of the nanocomposite film. Such nanocomposite films can be expected to have good potential in biomaterials applications.

Layer-by-Layer-Assembled Healable Antifouling Films

Healable antifouling films are fabricated by the exponential layer-by-layer assembly of PEGylated branched poly(ethylenimine) and hyaluronic acid followed by post-crosslinking. The antifouling function originates from the grafted PEG and the extremely soft nature of the films. The rapid and multiple healing of damaged antifouling functions caused by cuts and scratches can be readily achieved by immersing the films in normal saline solution.

Zwitterionic polycarboxybetaine coating functionalized with REDV peptide to improve selectivity for endothelial cells.

Surface immobilization of bioactive molecules has been a promising strategy to develop in situ endothelialization for cardiovascular implants. With the aim to construct endothelial cell specific coating with low fouling property, zwitterionic carboxybetaine methacrylate and butyl methacrylate were copolymerized as coating materials, spin-coated onto substrates, and immobilized with endothelial cell selective peptide Arg-Glu-Asp-Val (REDV) through functionalization of carboxy groups in carboxybetaine by NHS/EDC chemistry. Experimental results proved that carboxybetaine-REDV coating maintained desirable antifouling ability and fine hemocompatibility. Separate culture and coculture of HUVECs (human umbilical vein endothelial cells) with HUASMCs (human umbilical artery smooth muscle cells) showed that the coating was able to enhance the competitive growth of endothelial cells while limiting the adhesion, proliferation, and migration of smooth muscle cells. The existence of zwitterionic carboxybetaine helps to screen undesirable adsorption of platelets, and its nonspecific resistance to smooth muscle cells contributes to the realization of endothelial cell selectivity.

Hyaluronic acid and chitosan-DNA complex multilayered thin film as surface-mediated nonviral gene delivery system.

Sustained release of DNA from the surface of materials represents a promising approach to combine the gene therapy and implantable biomaterials. The nonviral chitosan-DNA complexes were incorporated into the multilayer via layer-by-layer deposition with hyaluronic acid (HA). The UV-vis spectroscopy and atomic force microscopy (AFM) results showed the successful construction of the nonviral complex contained multilayers. The complexes were releasable in physiological condition and a sustained release manner was gained when the multilayer was crosslinked. The cell viability test and the gene transfection assay showed that the natural polyelectrolyte-based nonviral complex incorporated multilayer not only had good cytocompatibility, but also possessed the in vitro gene transfection ability. This kind of surface-mediated nonviral complex incorporated multilayer may have great potential in the localized and controlled delivery of DNA in biomedical implants and tissue engineering application.

Direct Adhesion of Endothelial Cells to Bioinspired Poly(dopamine) Coating Through Endogenous Fibronectin and Integrin α5β1

Mussel-inspired poly(dopamine) (PDA) coating is proven to be a simple, versatile, and effective strategy to promote cell adhesion onto various substrates. In this study, the initial adhesive behavior of human umbilical vein endothelial cells (HUVECs) is evaluated on a PDA coating under serum-free conditions. It is found that HUVECs can attach directly to and spread with well-organized cytoskeleton and fibrillar adhesions on the PDA surface, whereas cells adhere poorly to and barely spread on the control polycaprolactone surface. Endogenous fibronectin and α5 β1 integrin are found to be involved in the cell adhesion process. These findings will lead to a better understanding of interactions between cells and PDA coating, paving the way for the further development of PDA.

Facile fabrication of robust superhydrophobic multilayered film based on bioinspired poly(dopamine)-modified carbon nanotubes

Thin organic films containing carbon nanotubes (CNTs) have received increasing attention in many fields. In this study, a robust thin superhydrophobic film has been created by using layer-by-layer assembly of the carbon nanotubes wrapped by poly(dopamine) (CNT@PDA) and poly(ethyleneimine) (PEI). UV-vis spectroscopy, ellipsometry, and quartz crystal microbalance with dissipation (QCM-D) measurements confirmed that the sequential deposition of PEI and CNT@PDA resulted in a linear growth of the (PEI-CNT@PDA) film. This thin film contained as much as 77 wt% CNTs. Moreover, a very stable and flexible free-standing (PEI-CNT@PDA) film could be obtained by employing cellulose acetate (CA) as a sacrificial layer. The film could even withstand ultrasonication in saturated SDS aqueous solution for 30 min. SEM observations indicated that the ultrathin film consisted of nanoscale interpenetrating networks of entangled CNTs and exhibited a very rough surface morphology. The (PEI-CNT@PDA) film turned superhydrophobic after being coated with a low-surface-energy compound. The superhydrophobic films showed excellent resistance against the adhesion of both platelets and Escherichia coli (E. coli). The (PEI-CNT@PDA) films and the proposed methodology may find applications in the area of medical devices to reduce device-associated thrombosis and infection.

Mixed-charge nanoparticles for long circulation, low reticuloendothelial system clearance, and high tumor accumulation.

Mixed-charge zwitterionic surface modification shows great potential as a simple strategy to fabricate nanoparticle (NP) surfaces that are nonfouling. Here, the in vivo fate of 16 nm mixed-charge gold nanoparticles (AuNPs) is investigated, coated with mixed quaternary ammonium and sulfonic groups. The results show that mixed-charge AuNPs have a much longer blood half-life (≈30.6 h) than do poly(ethylene glycol) (PEG, M¯w = 2000) -coated AuNPs (≈6.65 h) and they accumulate in the liver and spleen far less than do the PEGylated AuNPs. Using transmission electron microscopy, it is further confirmed that the mixed-charge AuNPs have much lower uptake and different existing states in liver Kupffer cells and spleen macrophages one month after injection compared with the PEGylated AuNPs. Moreover, these mixed-charge AuNPs do not cause appreciable toxicity at this tested dose to mice in a period of 1 month as evidenced by histological examinations. Importantly, the mixed-charge AuNPs have higher accumulation and slower clearance in tumors than do PEGylated AuNPs for times of 24-72 h. Results from this work show promise for effectively designing tumor-targeting NPs that can minimize reticuloendothelial system clearance and circulate for long periods by using a simple mixed-charge strategy.

Surface-mediated functional gene delivery: an effective strategy for enhancing competitiveness of endothelial cells over smooth muscle cells.

The non-biorecognition of general biomaterials and inherent biospecificity of biological systems pose key challenges to the optimal functions of medical devices. In this study, we constructed the surface-mediated functional gene delivery through layer-by-layer self-assembly of protamine sulfate (PrS) and plasmid DNA encoding hepatocyte growth factor (HGF), aiming at specific enhancing endothelial cells (EC) compeititiveness over smooth muscle cells (SMC). Characterizations of the (PrS/HGF-pDNA) multilayered films present the linear buildup with homogeneous and flat topographical feature. The amount of DNA can be easily controlled. By using these multilayered films, both human umbilical vein endothelial cells (HUVEC) and human umbilical artery smooth muscle cells (HUASMC) can be directly transfected when they contact with the multilayered films. On transfection, increasing secretion of HGF has been detected in both HUVEC and HUASMC culture, which leads to selective promotion of HUVEC proliferation. In the co-culture experiment, we also exhibit the promoted and hindered growth of HUVEC and HUASMC, respectively, which could be attributed to the inverse influence of HUVEC on HUASMC. These results collectively demonstrate that our system can be served as a powerful tool for enhancing competitiveness of EC over SMC, which opens perspectives for the regulation of intercellular competitiveness in the field of interventional therapy.