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Abstract:
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The aim of this study was to develop a bioactive and resorbable composite material that can be used in spinal surgery. The focus here is on the development of medical implants called fusion cages, which serve in situ as devices that help adjacent vertebrae to ossify together. To function properly fusion cages must be made of a material that can withstand sresses focused onto instrumentation site between vertebrae. As the fusion operation removes the motion segment between vertebrae, the compression strength of an implant material is a crucial mechanical property in determining whether or not an implant in situ. Fusion cages with four different structures were made. The raw materials used were PLA70 granules, b-TCP powder and prefabricated PLA96 fibers. PLA70 was a matrix material and the reason for adding b-TCP was to increase the bioactivity of the composite. The function of PLA96 fibers is to reinforce the composite. PLA70 and b-TCP were mixed using a twin screw extruder. Different degrees of admission were tested. The final shape of the implant was made by means of compression moulding. A 24 week in vitro follow-up was carried out in simulated body fluid (SBF K9) and compression properties as a function of time in vitro were measured. The pH of the solution and masses in vitro specimens were measured every second week. The stiffness of material combinations was studied using the charpy impact strenght method. Changes in surface morphology were examined using scanning electron microscopy (SEM). Thermal properties were studied using differential scanning calorimetry (DSC) and molecular weights were measured using gel permeation chromatography (GPC). All structured demonstrated bioactivity in vitro and there were no significant differences in bioactivity between samples containing 25 and 50 wt-% (12 and 30V- %) of b-TCP. Reinforcing PLA96 braids in structures had no effect on bioactivity between samples containing 25 and 50 wt-% (12 and 30 V-%) of b-TCP. Reinforcing PLA96 braids in structures had no effect on bioactivity. However, the presence of PLA96 braids enhanced strength retention of the composites and the amount of b-TCP in composite structures had an effect on the strength retention properties of in vitro specimens. At 24 weeks, in vitro specimens of 25/75 (25 wt-% b-TCP/ 75 wt-% PLA70) lost, on average,7 % of their initial compression strength, whereas braid reinforced specimens (25/75 + braids) lost on average 18.7-% of their initial strength. For specimens containing 50 wt-% b-TCP, the decrease was greater; on average of 42.3% for 50/50 and an average of 42.5% for 50/50 +braids. Thought strength retention was significant, even the weakest in vitro specimens demonstrated adequate strength properties after hydrolysis. /Kir10 |