Chengyun Ning

Polymeric Nanoarchitectures on Ti-Based Implants for Antibacterial Applications

Because of the excellent mechanical properties and good biocompatibility, titanium-based metals are widely used in hard tissue repair, especially load-bearing orthopedic applications. However, bacterial infection and complication during and after surgery often causes failure of the metallic implants. To endow titanium-based implants with antibacterial properties, surface modification is one of the effective strategies. Possessing the unique organic structure composed of molecular and functional groups resembling those of natural organisms, functionalized polymeric nanoarchitectures enhance not only the antibacterial performance but also other biological functions that are difficult to accomplish on many conventional bioinert metallic implants. In this review, recent advance in functionalized polymeric nanoarchitectures and the associated antimicrobial mechanisms are reviewed.

Concentration ranges of antibacterial cations for showing the highest antibacterial efficacy but the least cytotoxicity against mammalian cells: implications for a new antibacterial mechanism.

Antibacterial metal ions, such as Ag(+), Zn(2+) and Cu(2+), have been extensively used in medical implants and devices due to their strong broad spectrum of antibacterial activity. However, it is still a controversial issue as to whether they can show the desired antibacterial activity while being toxic to mammalian cells. It is very important to balance their antibacterial effectiveness with minimal damage to mammalian cells. Toward this end, this study is to identify the suitable concentrations of these three ions at which they can effectively kill two types of clinically relevant bacteria (Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)) but show no obvious cytotoxicity on fibroblasts. Such concentration ranges are found to be 2.5 × 10(-7) M-10(-6) M, 10(-5) M-10(-4) M, and 10(-5) M-10(-4) M for Ag(+), Zn(2+), and Cu(2+), respectively. Investigation of their antibacterial mechanism shows that these three metal ions all show antibacterial property through a mechanism of damaging bacterial cell membranes by the generation of reactive oxygen species but surprisingly preserving the integrity of bacterial genomic DNA. The encouraging results indicate that antibacterial metal ions with controlled concentrations can bring considerable benefits to biomedical applications.

Reversibly Controlling Preferential Protein Adsorption on Bone Implants by Using an Applied Weak Potential as a Switch

A facile method is needed to control the protein adsorption onto biomaterials, such as, bone implants. Herein we doped taurocholic acid (TCA), an amphiphilic biomolecule, into an array of 1D nano-architectured polypyrrole (NAPPy) on the implants. Doping TCA enabled the implant surface to show reversible wettability between 152° (superhydrophobic, switch-on state) and 55° (hydrophilic, switch-off state) in response to periodically switching two weak electrical potentials (+0.50 and -0.80 V as a switch-on and switch-off potential, respectively). The potential-switchable reversible wettability, arising from the potential-tunable orientation of the hydrophobic and hydrophilic face of TCA, led to potential-switchable preferential adsorption of proteins as well as cell adhesion and spreading. This potential-switchable strategy may open up a new avenue to control the biological activities on the implant surface.

Silicon nitride films for the protective functional coating: blood compatibility and biomechanical property study.

Behaviors of silicon nitride films and their relation to blood compatibility and biomechanical have been interesting subjects to researchers. A systematic blood compatibility and biomechanical property investigation on the deposition of silicon-nitride films under varying N₂ and CF₄ flows was carried out by direct current unbalanced magnetron sputtering techniques. Significant role of surface property, chemical bonding state of silicon nitride film and blood compatibility, mechanical properties for the films were observed. The chemical bonding configurations, surface topography, contact angle and mechanical properties were characterized by means of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and nano-indentation technique and CSEM pin-on-disk tribometer. Blood compatibility of the films was evaluated by platelet adhesion investigation. The results of the platelet adhesion tests shown that the effect of fluorine and nitrogen-doped revealed an intimate relationship between the ratio of polar component and dispersion component of the surface energy and its hemocompatibility. Si-N-O coating can be a great candidate for developing antithrombogenic surfaces in blood contacting materials. The chemical bonding state made an adjustment in microstructured surfaces, once in the totally wettable configuration, may improve the initial contact between platelet and biomedical materials, due to the appropriate ratio of dispersion component and polar component. To resist wear, biomedical components require coatings that are tough and hard, have low friction, and are bio-inert. The study suggests that by Si-N coating the metal surfaces could be a choice to prolong the life of the sliding pair Co-Cr-Mo alloy/UHMWPE implants.

Biomimetic mineralization of anionic gelatin hydrogels: effect of degree of methacrylation

Mineral–polymer composite materials have been used as artificial bone grafts and scaffolds in bone tissue engineering. Polymer-controlled mineralization is effective for fabricating such composites. In this study, we synthesized organic–inorganic composites using anionic gelatin methacrylate (GelMA) hydrogels containing a high percentage of Ca2+ binding-carboxyl groups as a template for mineralization. A homogeneous surface and interior carbonated hydroxyapatite were achieved on the resulting mineralized porous hydrogel composites, and they were confirmed to resemble apatite-like structures. The effect of crosslinker content on mineralization was examined using GelMA hydrogels with different degrees of methylacrylation (DM). It was found that increasing the DM of the hydrogel suppressed the growth of carbonated hydroxyapatite layers, as was evident from the extent of calcification and the morphology of the minerals. The dependency of the mineralization on hydrogel variables was related to the changes in physicochemical properties of gel, including charge density and swelling. Compressive mechanical testing demonstrated that the compressive modulus and strength of the hydrogels increased with increasing DM and mineralization extent. Overall, mineralization of GelMA hydrogels with controllable mineral content and good mechanical properties provides a biomimetic route toward the development of bone substitutes for the next generation of biomaterials. The results of this study also provide insight into better understanding the role of the hydrogel matrix in biomineralization.

Synthesis of radial mesoporous bioactive glass particles to deliver osteoactivin gene

Mesoporous bioactive glasses (MBGs) can be used as carriers for biomolecule delivery with improved functions. Although there are a great number of studies on drug delivery by MBGs, until now little work has been done to investigate the DNA gene transfection effect of MBGs. In this study, radial mesoporous bioactive glasses (rMBGs) were prepared by sol-gel process combined with a micro-emulsion method. The surface was further modified by amino groups in order to improve its affinity for DNA. Our study showed that rMBGs have good apatite-forming ability and cellular biocompatibility. In addition, rMBGs can enter cells in a time- and dose-dependent manner, and mainly localize in the cytoplasm. Agarose gel electrophoresis demonstrated that pOA-EGFP (containing the osteoactivin and the green fluorescent protein fusion gene) can be completely absorbed and protected from DNase I degradation by the aminated rMBGs. Additionally, the plasmid can be successfully expressed in cells transfected by rMBGs.

Directing Stem Cell Differentiation via Electrochemical Reversible Switching between Nanotubes and Nanotips of Polypyrrole Array

Control of stem cell behaviors at solid biointerfaces is critical for stem-cell-based regeneration and generally achieved by engineering chemical composition, topography, and stiffness. However, the influence of dynamic stimuli at the nanoscale from solid biointerfaces on stem cell fate remains unclear. Herein, we show that electrochemical switching of a polypyrrole (Ppy) array between nanotubes and nanotips can alter surface adhesion, which can strongly influence mechanotransduction activation and guide differentiation of mesenchymal stem cells (MSCs). The Ppy array, prepared via template-free electrochemical polymerization, can be reversibly switched between highly adhesive hydrophobic nanotubes and poorly adhesive hydrophilic nanotips through an electrochemical oxidation/reduction process, resulting in dynamic attachment and detachment to MSCs at the nanoscale. Multicyclic attachment/detachment of the Ppy array to MSCs can activate intracellular mechanotransduction and osteogenic differentiation independent of surface stiffness and chemical induction. This smart surface, permitting transduction of nanoscaled dynamic physical inputs into biological outputs, provides an alternative to classical cell culture substrates for regulating stem cell fate commitment. This study represents a general strategy to explore nanoscaled interactions between stem cells and stimuli-responsive surfaces.

Surface-Dependent Self-Assembly of Conducting Polypyrrole Nanotube Arrays in Template-Free Electrochemical Polymerization

One-dimensional conducting polymer nanostructure arrays could provide short ion transport paths, thus delivering superior chemical/physical performance and having large potential as intelligent switching materials. In this work, in situ electrochemical atomic force microscopy is employed to monitor the self-assembly of conducting polypyrrole nanotube arrays in template-free electrochemical polymerization. The specific spreading behavior of pyrrole micelles on the conductive substrate is important to large-area self-assembly of conducting polypyrrole nanotube arrays and the insight into self-assembly of conducting polypyrrole nanotube arrays is discussed. Moreover, compared with unoriented nanostructured polypyrrole, the conducting polypyrrole nanotube arrays possess enhanced electrical and electrochemical performances.

Nanostructured Conducting Polymers as Intelligent Implant Surface: Fabricated on Biomedical Titanium with a Potential-Induced Reversible Switch in Wettability

Conducting polypyrrole (PPy) nanotube arrays, nanotube networks and irregular films are deposited on biomedical titanium. By in situ application of weak periodic potentials, the nanostructured conducting polymers undergo a reversible switch in wettability, which is a redox process of dopant molecules (as hydrophilic groups) immobilized and de-immobilized on the surface of the conducting polymers.

Taurine-induced fabrication of nano-architectured conducting polypyrrole on biomedical titanium.

In this article, taurine, one of the small biomolecules associated with bone metabolism, is firstly utilized to induce the fabrication of nano-architectured conducting polypyrrole (NCPPy) on biomedical titanium in diverse pH values of phosphate buffer solution (PBS). Accordingly, the possible mechanism for the fabrication of NCPPy is proposed, which is dependent on the states of polytaurine from the polymerization of taurine, i.e., the inability of forming polytaurine and unordered restricted space results in taurine-incorporated and polytaurine-incorporated tightly packed nanoparticles (pH 6.2 and 8.0), respectively, and however, ordered restricted space constructed by polytaurine chains induces the fabrication of polytaurine-incorporated nanopillars (pH 6.8) and polytaurine-incorporated nanowire networks (pH 7.4).