Investigation of biodegradability properties of polycaprolactone-chitosan nanofiber coated Ti-microalloyed AZ31 Mg alloy for orthopedic applications

In this thesis, improvement of controlled biodegradability of AZ31 Mg alloy by Ti microalloying (0.1 wt%Ti, AZ31Ti) for orthopedic implant applications was studied. Within the scope of this study, microstructure, hardness and tensile strength of AZ31, AZ31Ti alloys were compared. The biocompatibility and cell adhesion tests of both uncoated and nanofiber-coated alloys by using the electrospinning method, were investigated along with their in-vitro corrosion resistance in simulated body fluid (SBF). Polycaprolactone (PCL) was used as a synthetic polymer and chitosan (CS) as a natural polymer for fiber formation (PCL/CS). In addition, a separate coating mixture (PCL/CS-eAgNP) was prepared by adding clove extract encapsulated silver nanoparticles (eAgNP) to the PCL/CS mixture. The two different nanofiber coatings, PCL/CS and PCL/CS-eAgNP, were made on AZ31Ti surfaces by electrospinning method. MC3T3-E1 (CRL-2593) osteoblast cells were used as a model for cell proliferation and biocompatibility assessment. Material characterization analyses were conducted using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Field Emission Scanning Electron Microscopy (FE-SEM), X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and water contact angle measurements. Optical microscope images and SEM microstructure results showed that there was no considerable difference in the average grain size and grain shapes with Ti microalloying compared with AZ31 alloy. XRD analyses indicated that the diffraction patterns of AZ31 and AZ31Ti alloys were similar, showing that Ti micro-alloying did not alter the crystal structure of AZ31 alloy. Although it was observed that there was no significant change in the hardness values and mechanical properties of the rolled samples with Ti microalloying, SEM analysis confirmed the corrosion loss results and showed that the most corroded alloy was the AZ31 alloy. FE-SEM images showed that there was no significant difference between the average fiber diameters of PCL/CS and PCL/CS-eAgNP coatings and were ~55 nm for both coatings. The water contact angle was measured at 123° for the PCL/CS coated sample and 118° for the PCL/CS-eAgNP-coated sample, concluding that the wetting properties of the coating with eAgNP didn't change much, the corrosion loss of the PCL/CS nanofiber-coated AZ31Ti alloy was very close to the that of the uncoated AZ31Ti sample, so the nanofiber coating could not show the expected performance in corrosion control. The absorbance results obtained from the XTT cell proliferation test showed that PCL/CS coated samples had better biocompatibility compared to the uncoated alloy group, while PCL/CS-eAgNP coated samples had the poorest biocompatibility. SEM images of cell culture studies revealed poor cell adhesion on uncoated samples, while cells flattened and expanded on PCL/CS nanofiber-coated samples due to the characteristic coating morphology. Keywords: AZ31 Alloy, Biocompatibility, Biodegradation, Electrospinning Method, Ti MicroAlloying