ABSTRACT
Clinical applications of magnesium (Mg)-based screws have reported gas cavity formation in the surrounding tissue, which sometimes delays the fixation of the bone fracture. The gas cavity formation is considered to depend on the balance between hydrogen generation by Mg corrosion reacting with water in the body fluid and its diffusion into the surrounding tissue by capillary flow. In order to understand the gas cavity formation behavior by Mg-based material implantation, we developed a new in vitro model system to recreate this cavity formation phenomenon: the hydrogen generation by corrosion and its diffusion into the medium. A model tissue is prepared by gelation of the cell culture medium in a sterile condition. The immersion of Mg alloy samples was performed under 5% CO2 atmosphere with periodic observation by X-ray computed tomography, which enabled us to observe gas cavity growth up to 28 d. For demonstrating the usefulness of our model system, Mg alloy samples with different corrosion rates were prepared by a biodegradable polymer coating. AZ31 screws were spin-coated by poly-l-lactide (PLLA) and classified into three groups by their coating thickness as 1.0 ± 0.0, 1.6 ± 0.2, and 2.0 ± 0.1 µm (ave. ± s.d.). Upon their immersion into the model tissue, the gas cavity volumes formed were 1.57 ± 0.23, 1.06 ± 0.22, and 0.38 ± 0.09 mm3/mm2 for 1.0, 1.6, and 2.0 µm coating samples, having the weight loss of 20.2 ± 2.93, 18.5 ± 2.84, and 11.3 ± 3.54 µg/mm2, respectively (ave. ± s.d.). This result clearly indicates the dependence of gas cavity formation on the corrosion rate of the sample. The gas cavity volume was only 3.3â¼7.5% of the total hydrogen gas volume estimated based on the weight loss of the samples at 28 d, which is in the range of those calculated from the clinical report (3.2â¼9.4% at 4w). This system can be an effective tool to investigate the gas cavity formation behavior and contribute to understand the mechanisms and controlling factors of this phenomenon.
Subject(s)
Alloys , Magnesium , Coated Materials, Biocompatible , Humans , Hydrogen , Weight LossABSTRACT
BACKGROUND: Polymers are attractive materials for both biomedical engineering and cardiovascular applications. Although nano-topography has been found to influence cell behaviour, no established method exists to understand and evaluate the effects of nano-topography on polymer-blood interaction. RESULTS: We optimized a micro-fluidic set-up to study the interaction of whole blood with nano-structured polymer surfaces under flow conditions. Micro-fluidic chips were coated with polymethylmethacrylate films and structured by polymer demixing. Surface feature size varied from 40 nm to 400 nm and feature height from 5 nm to 50 nm. Whole blood flow rate through the micro-fluidic channels, platelet adhesion and von Willebrand factor and fibrinogen adsorption onto the structured polymer films were investigated. Whole blood flow rate through the micro-fluidic channels was found to decrease with increasing average surface feature size. Adhesion and spreading of platelets from whole blood and von Willebrand factor adsorption from platelet poor plasma were enhanced on the structured surfaces with larger feature, while fibrinogen adsorption followed the opposite trend. CONCLUSION: We investigated whole blood behaviour and plasma protein adsorption on nano-structured polymer materials under flow conditions using a micro-fluidic set-up. We speculate that surface nano-topography of polymer films influences primarily plasma protein adsorption, which results in the control of platelet adhesion and thrombus formation.
ABSTRACT
New short-term evaluation of material blood compatibility was attempted using a microchannel array with human blood under a flow condition. The microchannel array chips were made of silicon, having 8,736 microchannels of 10 microm-wide, 30 microm-long, and 4.5 microm-deep on the average, as the models of capillary blood vessels. Titanium, chromium, albumin and collagen were coated onto the chips to examine the difference of material blood compatibility and the effect of protein adsorption on it. The time for the first 100 microl portion of whole blood to pass through the channels (blood pass-through time, BPT) was measured under a pressure difference of 20 cmH2O. Simultaneously, the flow behavior of blood cells was observed by an optical microscope. The BPT tends to correlate well with the level of platelet adhesion. The highest BPT as well as platelet adhesion was observed on collagen, followed by titanium, chromium, silicon, and albumin. These results indicate that the BPT can detect the different levels of platelet adhesion and thrombus formation on microchannel surface and that the protein adsorption onto chip surface can influence BPT. We concluded that this method could be applied to evaluate initial blood compatibility of materials within several minutes in vitro.
