Jiahua Ni

In vitro and in vivo studies on the degradation of high-purity Mg (99.99wt.%) screw with femoral intracondylar fractured rabbit model

High-purity magnesium (HP Mg) takes advantage in no alloying toxic elements and slower degradation rate in lack of second phases and micro-galvanic corrosion. In this study, as rolled HP Mg was fabricated into screws and went through in vitro immersion tests, cytotoxicity test and bioactive analysis. The HP Mg screws performed uniform corrosion behavior in vitro, and its extraction promoted cell viability, bone alkaline phosphatase (ALP) activity, and mRNA expression of osteogenic differentiation related gene, i.e. ALP, osteopontin (OPN) and RUNX2 of human bone marrow mesenchymal stem cells (hBMSCs). Then HP Mg screws were implanted in vivo as load-bearing implant to fix bone fracture and subsequently gross observation, range of motion (ROM), X-ray scanning, qualitative micro-computed tomography (μCT) analysis, histological analysis, bending-force test and SEM morphology of retrieved screws were performed respectively at 4, 8, 16 and 24 weeks. As a result, the retrieved HP Mg screws in fixation of rabbit femoral intracondylar fracture showed uniform degradation morphology and enough bending force. However, part of PLLA screws was broken in bolt, although its screw thread was still intact. Good osseointegration was revealed surrounding HP Mg screws and increased bone volume and bone mineral density were detected at fracture gap, indicating the rigid fixation and enhanced fracture healing process provided by HP Mg screws. Consequently, the HP Mg showed great potential as internal fixation devices in intra-articular fracture operation.

Preparation of near micrometer-sized TiO2 nanotube arrays by high voltage anodization.

Highly ordered TiO2 nanotube arrays with large diameter of 680-750 nm have been prepared by high voltage anodization in an electrolyte containing ethylene glycol at room temperature. To effectively suppress dielectric breakdown due to high voltage, pre-anodized TiO2 film was formed prior to the main anodizing process. Vertically aligned, large sized TiO2 nanotubes with double-wall structure have been demonstrated by SEM in detail under various anodizing voltages up to 225 V. The interface between the inner and outer walls in the double-wall configuration is porous. Surface topography of the large diameter TiO2 nanotube array is substantially improved and effective control of the growth of large diameter TiO2 nanotube array is achieved. Interestingly, the hemispherical barrier layer located at the bottom of TiO2 nanotubes formed in this work has crinkles analogous to the morphology of the brain cortex. These structures are potentially useful for orthopedic implants, storage of biological agents for controlled release, and solar cell applications.

Dual effects and mechanism of TiO2 nanotube arrays in reducing bacterial colonization and enhancing C3H10T1/2 cell adhesion

Competition occurs between the osteoblasts in regional microenvironments and pathogens introduced during surgery, on the surface of bone implants, such as joint prostheses. The aim of this study was to modulate bacterial and osteoblast adhesion on implant surfaces by using a nanotube array. Titanium oxide (TiO2) nanotube arrays, 30 nm or 80 nm in diameter, were prepared by a two-step anodization on titanium substrates. Mechanically polished and acid-etched titanium samples were also prepared to serve as control groups. The standard strains of Staphylococcus epidermidis (S. epidermidis, American Type Culture Collection [ATCC]35984) and mouse C3H10T1/2 cell lines with osteogenic potential were used to evaluate the different responses to the nanotube arrays, in bacteria and eukaryotic cells. We found that the initial adhesion and colonization of S. epidermidis on the surface of the TiO2 nanotube arrays were significantly reduced and that the adhesion of C3H10T1/2 cells on the surface of the TiO2 nanotube arrays was significantly enhanced when compared with the control samples. Based on a surface analysis of all four groups, we observed increased surface roughness, decreased water contact angles, and an enhanced concentration of oxygen and fluorine atoms on the TiO2 nanotube surface. We conclude that the TiO2 nanotube surface can reduce bacterial colonization and enhance C3H10T1/2 cell adhesion; multiple physical and chemical properties of the TiO2 nanotube surface may contribute to these dual effects.

Ag-Incorporated FHA Coating on Pure Mg: Degradation and in Vitro Antibacterial Properties.

Fluoridated hydroxyapatite (FHA) coating can help retard the degradation of magnesium, and possess good biocompatibility. However, the antibacterial property of FHA is very limited. In this work, we aimed to incorporate silver into FHA structure to fabricate biocompatible and antibacterial coatings with enhanced anticorrosion property. The results showed that the Ag-FHA coating prepared by electrochemical deposition and subsequent immersion in AgNO3 solution was superior to the Ag-FHA coating prepared by coelectrodeposition in terms of crystal structure, surface morphology and corrosion resistance. The release of Ag(+) ion causing high antiplanktonic bacterial rate and excellent antiadherence property to MRSA. Meanwhile, good cell compatibility of MC3T3-E1 including cell viability, cell adhesion, and cell morphology was achieved under the controlled degradation. The balance of degradation and antimicrobial property of Ag-incorporated FHA coating made it an alternative in the application of surface modification for biodegradable Mg.

Guided proliferation and bone-forming functionality on highly ordered large diameter TiO2 nanotube arrays.

The significantly enhanced osteoblast adhesion, proliferation and alkaline phosphatase (ALP) activity were observed on TiO2 nanotube surface in recent studies in which the scale of nanotube diameter was restricted under 100 nm. In this paper, a series of highly ordered TiO2 nanotube arrays with larger diameters ranging from 150 nm to 470 nm were fabricated via high voltage anodization. The behaviors of MC3T3-E1 cells in response to the diameter-controlled TiO2 nanotubes were investigated. A contrast between the trend of proliferation and the trend of cell elongation was observed. The highest cell elongation (nearly 10:1) and the lowest cell number were observed on the TiO2 nanotube arrays with 150 nm diameter. While, the lowest cell elongation and highest cell number were achieved on the TiO2 nanotube arrays with 470 nm diameter. Furthermore, the ALP activity peaked on the 150 nm diameter TiO2 nanotube arrays and decreased dramatically with the increase of nanotube diameter. Thus a narrow range of diameter (100-200 nm) that could induce the greatest bone-forming activity is determined. It is expected that more delicate design of orthopedic implant with regional abduction of cell proliferation or bone forming could be achieved by controlling the diameter of TiO2 nanotubes.

Fabrication of thin film TiO2 nanotube arrays on Co-28Cr-6Mo alloy by anodization.

Titanium oxide (TiO2) nanotube arrays were prepared by anodization of Ti/Au/Ti trilayer thin film DC sputtered onto forged and cast Co-28Cr-6Mo alloy substrate at 400 °C. Two different types of deposited film structures (Ti/Au/Ti trilayer and Ti monolayer), and two deposition temperatures (room temperature and 400 °C) were compared in this work. The concentrations of ammonium fluoride (NH4F) and H2O in glycerol electrolyte were varied to study their effect on the formation of TiO2 nanotube arrays on a forged and cast Co-28Cr-6Mo alloy. The results show that Ti/Au/Ti trilayer thin film and elevated temperature sputtered films are favorable for the formation of well-ordered nanotube arrays. The optimized electrolyte concentration for the growth of TiO2 nanotube arrays on forged and cast Co-28Cr-6Mo alloy was obtained. This work contains meaningful results for the application of a TiO2 nanotube coating to a CoCr alloy implant for potential next-generation orthopedic implant surface coatings with improved osseointegrative capabilities.

Reduced antibacterial property of metallic magnesium in vivo.

Magnesium and its alloys have drawn interest as antibacterial biomaterials, owing to their ability to alkalize the surrounding medium during degradation. The antibacterial effect of pure Mg and Mg alloys in vitro has previously been reported. However, the antibacterial property of Mg in vivo might be different because of the apparently dissimilar corrosion characteristics. In this study, pure Mg rods were implanted and bacterial suspension were injected into rat femurs to investigate the antibacterial property of Mg in vivo. The results showed that contrary to the high antibacterial rate in vitro, Mg exhibited a dramatic drop in antibacterial effect in vivo. Bacteria proliferated on the surface of the Mg rods as well as in the femur. Inflammatory cells filled cavities in the cortical bone of the femur, which was demonstrated by histological and micro-CT examination after 2 and 4 weeks of implantation. It is suggested that a reduced corrosion rate in vivo would result in insufficient pH value. In addition, the deposition layer would prevent further corrosion of Mg and provide a favorite site for bacteria adhesion. Hence, the dramatically reduced antibacterial property of Mg needs to be noticed when it is used as a biomaterial.

Research of a novel biodegradable surgical staple made of high purity magnesium.

Surgical staples made of pure titanium and titanium alloys are widely used in gastrointestinal anastomosis. However the Ti staple cannot be absorbed in human body and produce artifacts on computed tomography (CT) and other imaging examination, and cause the risk of incorrect diagnosis. The bioabsorbable staple made from polymers that can degrade in human body environment, is an alternative. In the present study, biodegradable high purity magnesium staples were developed for gastric anastomosis. U-shape staples with two different interior angles, namely original 90° and modified 100°, were designed. Finite element analysis (FEA) showed that the residual stress concentrated on the arc part when the original staple was closed to B-shape, while it concentrated on the feet for the modified staple after closure. The in vitro tests indicated that the arc part of the original staple ruptured firstly after 7 days immersion, whereas the modified one kept intact, demonstrating residual stress greatly affected the corrosion behavior of the HP-Mg staples. The in vivo implantation showed good biocompatibility of the modified Mg staples, without inflammatory reaction 9 weeks post-operation. The Mg staples kept good closure to the Anastomosis, no leaking and bleeding were found, and the staples exhibited no fracture or severe corrosion cracks during the degradation.

Accelerating Corrosion of Pure Magnesium Co-implanted with Titanium in Vivo.

Magnesium is a type of reactive metal, and is susceptible to galvanic corrosion. In the present study, the impact of coexistence of Ti on the corrosion behavior of high purity Mg (HP Mg) was investigated both in vitro and in vivo. Increased corrosion rate of HP Mg was demonstrated when Mg and Ti discs were not in contact. The in vivo experiments further confirmed accelerating corrosion of HP Mg screws when they were co-implanted with Ti screws into Sprague-Dawley rats’ femur, spacing 5 and 10 mm. Micro CT scan and 3D reconstruction revealed severe corrosion morphology of HP Mg screws. The calculated volume loss was much higher for the HP Mg screw co-implanted with Ti screw as compared to that co-implanted with another Mg screw. Consequently, less new bone tissue ingrowth and lower pullout force were found in the former group. It is hypothesized that the abundant blood vessels on the periosteum act as wires to connect the Mg and Ti screws and form a galvanic-like cell, accelerating the corrosion of Mg. Therefore, a certain distance is critical to maintain the mechanical and biological property of Mg when it is co-implanted with Ti.