| Background and Purpose:Biomaterials not only have important social effect in bettering the living quality of human beings, improving their health and saving their lives, but also become a new growth point in economic and scientific-technological areas. Magnesium alloys provide potential advantages for patients with bone fractures or defects due to their good biocompatibility, biodegradability, high specific strength and specific rigidity and elastic modulus approximating human bone, which could effectively reduce stress shield effect. As a degradable biomaterial for osteosynthesis, magnesium alloys provide potential advantages for patients,they need not the second operation to take out, which not only decreases the cost, but also avoids unwanted sufferings to patients. Therefore, the degradable metallic biomaterials are much desirable.Because of the advantages of excellent biocompatiblity and similar mechnical properties to bone, the magnesium alloys in biomaterials field have caused great interests of research in the world.However, the major drawbacks of magnesium and magnesium alloys in many applications are low corrosion resistance. So some surface treatments should be applied to meet the use of long-term implantation. In this experiment we design a novel degradable magnesium alloy and the pulse electrodeposition technology will be used to magnesium alloy surface modification. Through the experiment we can investigate the biocompatibility in vivo and in vitro. This research will introduce the magnesium alloy into the field of biomaterials. Through the experiment we can investigate the cytotoxicity and hemolytic properties in vitro of Bio-magnesium alloys and the biocompatibility degradation and bone formation in vivo to implant the bio-magnesium alloys in rabbit. Materials and Methods:1. Experiment in vitro:The L-929 mouce fibroblast cells were incubated in the 96-well tissue-culture plates and the cells were incubated for 24 hours to allow attachment. The medium was then replaced with the extraction medium of 100%, 50% and 10% concentration in the test groups. Simple culture solution in the negative control groups and 0.64% phenol culture solution in the positive control groups. The cytotoxicity of the magnesium alloys was evaluated by cell morphological observation and MTT assay at 2,4 and 7 days. The hemolysis in vitro was evaluated through indirect contact methods.2. Experiment in. vivo:A total of 40 China rabbits (offered by the experimental animal center of Henan province) were randomly divided into magnesium alloys without hydroxyapatite (HA) coatings group(Group A) and magnesium alloys with hydroxyapatite (HA) coatings group(Group B). The left condyles of femur were drilled (φ3.5mm×9mm) and separately implanted with different magnesium alloys.The concentrations of magnesium ion in blood and urine, the levels of serum glutamic-oxalacetic transaminase, albumin, urea nitrogen and urine creatinine were measured at 1 day pre-operatively,8,12,16,and 24 weeks post-operatively. The magnesium alloys samples were photographed by X-ray at 1,4,8,12,16and 24 weeks post-implantations, and then the condyles of femur were obtained and analyzed using.Micro-CT. After that the magnesium alloys were taken out and analyzed using SEM (scanning electron microscopy). The tissue of heart, liver, spleen, kidney and the condyles of femur were used for pathological analysis.Results:1. Experiment in vitro:The cells in the positive control groups fell off and died, While the cells in different test groups and negative groups almost attached well on the bottom of the culture plate and the morphology was not changed. The cytotoxicity of the magnesium alloys was in grade 0-1 and the hemo lysis index was 3.4% which was less than the national standard (5%) about biomaterials.2. Experiment in vivo:There were no significant variations in the concentrations of magnesium ion in blood and urine, and the concentrations were in normal range.The pathology of all the organs were normal, and there were no significant difference of bio-chemical indicator between the two groups. There were no significant abnormalities in the pathological analysis of heart, liver, spleen and kidney in the two groups. New bones in Group A were more and had tighter binding with the magnesium alloys, compared with the Group B.In addition, the magnesium alloys in Group A had a slower degradation rate.Conclusions:1. The cytotoxicity and hemolytic properties of the magnesium alloys reach the requirement of the biomaterials.2. HA-coated magnesium alloys which have good biocompatibility can slow down the degradation rate and stimulate the formation of new bone tissue.
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