Guoxin Tan

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.

Cell-laden photocrosslinked GelMA–DexMA copolymer hydrogels with tunable mechanical properties for tissue engineering

To effectively repair or replace damaged tissues, it is necessary to design three dimensional (3D) extracellular matrix (ECM) mimicking scaffolds with tunable biomechanical properties close to the desired tissue application. In the present work, gelatin methacrylate (GelMA) and dextran glycidyl methacrylate (DexMA) with tunable mechanical and biological properties were utilized to prepared novel bicomponent polymeric hydrogels by cross-linking polymerization using photoinitiation. We controlled the degree of substitution (DS) of glycidyl methacrylate in DexMA so that they could obtain relevant mechanical properties. The results indicated that copolymer hydrogels demonstrated a lower swelling ratio and higher compressive modulus as compared to the GelMA. Moreover, all of the hydrogels exhibited a honeycomb-like architecture, the pore sizes decreased as DS increased, and NIH-3T3 fibroblasts encapsulated in these hydrogels all exhibited excellent viability. These characteristics suggest a class of photocrosslinkable, tunable mechanically copolymer hydrogels that may find potential application in tissue engineering and regenerative medicine 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.

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.

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).

Polydopamine assisted immobilisation of copper(II) on titanium for antibacterial applications

Abstract Copper(II) were immobilised onto medical titanium surface by polydopamine (PDA) chelating, to build intrinsic antibacterial implant materials for inhibition of implant infection. A scanning electrical microscope showed that the modified titanium surface morphology was a porous nanostructure. An energy dispersive spectrometer showed the existence of Cu, and X-ray photoelectron spectroscopy results further confirmed that the immobilised copper element was in the form of Cu(II). Bacteria plate colony counting results showed that modified titanium surface had decent antibacterial property, matching the ion release outcomes. It could be conclude that the PDA assisted Cu(II) immobilisation was an efficient and effective method for antibacterial modification of titanium.

Controlled oxidative nanopatterning of microrough titanium surfaces for improving osteogenic activity

To further enhance the biological properties of acid-etched microrough titanium surfaces, titania nanotextured thin films were produced by simple chemical oxidation, without significantly altering the existing topographical and roughness features. The nanotextured layers on titanium surfaces can be controllably varied by tuning the oxidation duration time. The oxidation treatment significantly reduced water contact angles and increased the surface energy compared to the surfaces prior to oxidation. The murine bone marrow stromal cells (BMSCs) were used to evaluate the bioactivity. In comparison, oxidative nanopatterning of microrough titanium surfaces led to improved attachment and proliferation of BMSCs. The rate of osteoblastic differentiation was also represented by the increased levels of alkaline phosphatase activity and mineral deposition. These data indicated that oxidative nanopatterning enhanced the biological properties of the microrough titanium surfaces by modulating their surface chemistry and nanotopography. Based on the proven mechanical interlocking ability of microtopographies, enhancement of multiple osteoblast functions attained by this oxidative nanopatterning is expected to lead to better implant osseointegration in vivo.

Potential-induced reversible switching in the tubular structure of conducting polypyrrole nanotube arrays

In this article, we report a novel switch property of conducting polypyrrole nanotube arrays (CPNAs) on biomedical titanium, in which the nanotubular structure can be reversibly switched between open and closed states by applying switch-open/close potentials in situ. We propose a new insight into the study of reversible tubular switches in CPNAs.