الفهرس 
General Introduction, Experimental Techniques, Theoretical Consideration and MaterialsOnly 14 pages are availabe for public view
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Abstract
”The aim of this thesis is to characterize the optical, structural and mechanical properties and develop degradation rate of PGA/TMC copolymer surgical suture to be used in cardiac tissue engineering. Also, the thesis aims to synthesize a wet tissue adhesives inspired by mussel and based on dopamine, chitosan and iron oxide nanoparticles to be used as a tissue adhesive. The PGA/TMC copolymer surgical suture is considered one of the simplest bioabsorbable monofilament sutures commercialized to date and has a trade mark name of MaxonTM. Maxon is used in cardiac operations for reinforcing sternal closure to aid in preventing sternal dehiscence in high-risk patients. In addition, it can be used in types of cardiovascular surgery. A general introduction was given with a review of the previous work dedicated to the surgical suture material and tissue adhesives. The description of the experimental set-up and theoretical considerations of the experimental techniques used in this work was explained. The optical set up of interferometric techniques such as mach-Zehnder interferometer and multiple-beam Interferometer, which were used to measure the refractive indices and the birefringence of sutures, were mentioned in detail. The theoretical basic of some spectroscopic techniques such as X-ray diffraction and Fourier-transform infrared spectroscopy, which were used to measure the variations in the crystallinity percentage and to measure the variations of the structure, respectively, were also explain. The structure of Maxon suture was mentioned. The properties of chitosan, dopamine, and iron oxide nanoparticles, as building units of the synthesized tissue adhesive, were also mentioned. Multiple-beam Fizeau fringes in transmission was used to investigate the optical properties of Maxon surgical suture. The mechanical properties were measured by a suture-drawing apparatus attached to the multiple-beam interferometric system. The refractive indices, stress-strain curve, elastic shear modulus, Young’s modulus and crosslink density were investigated at various draw ratios. The biological activities were conducted by Quantitative Structure Activity Relationships (QSAR) descriptors. Molecular Electrostatic Potential (MESP) maps were used to describe the reactivity and functional active sites for the given molecule. The behavior of stress-strain curve confirms the compatibility of the suture with the sternum which proves that Maxon suture is a good candidate for cardiac operations. Mach-Zehnder interferometric technique equipped to a suture drawing device were used to determine the opto-mechanical properties of Maxon surgical suture. The degradation behavior of Maxon were examined through a period from 4 to 32 days. The crystallinity percent, swelling rates percent and weight retention of Maxon were measured in addition to pH level of buffer solution. The results indicate that, there was an overall decreasing for the mechanical properties with increasing the time of degradation. Maxon suture maintained approximately 55% from its original mechanical properties after 32 days of incubation in vitro. An empirical formula to simulate the degradation process and predict the value of Young’s modulus at any period during the hydrolysis process is given. It is found that, the incubated sutures will be completely absorbed after approximately 8 weeks. The effect of the annealing process on the Maxon suture at different temperatures was investigated. The variations in the degradation rate and mechanical properties of Maxon due to the thermal treatment were investigated. Maxon samples were subjected to a degradation process in phosphate buffer saline (PBS) for up to 32 days. Annealing temperatures used in this study were from 100 oC to 140 oC and the annealing time was 2 hrs. Birefringence was measured by using Mach-Zehnder interferometer. X-ray diffraction (XRD) was used to measure the variations in the crystallinity percentage and average crystal size at different annealing temperatures. Fourier-transform infrared spectroscopy (FTIR) was utilized to measure the variation of the structure, and the optical microscope was used to monitor the surface morphology variations. It is found that the annealing process results in an increase for both the mechanical properties and degradation time of Maxon suture samples. Therefore, by using simple and fast thermal treatment, the modified Maxon suture can be used as an alternative for both vicryl and Polydioxanone (PDS) surgical suture in a vascular surgery accompanying a coronary artery bypass graft procedure. Molecular modeling methods were used to mimic mussel adhesive protein (MAPs) by mussel-inspired metal-coordination chemistry at the polymer−particle interface using iron oxide nanoparticles (Fe3O4 NPs) and catechol−polymer as building blocks. Catechol group of dopamine conjugates with chitosan backbone and provides additional adhesion strength with tissue surfaces. Molecular modeling including two different methods, Quantitative structure-activity relationship (QSAR) and molecular electrostatic potential (MESP), were used to study the physical and structural properties of the suggested tissue adhesive. Four positions of Fe3O4 NPs to connect with chitosan-dopamine blend were proposed. The third sites was preferred by following the result of both band gap energy (ΔE) and total dipole moment (TDM). The suggested structural units of the tissue adhesive were synthesized. Iron oxide nanoparticles (Fe3O4 NPs) formed the catechol-Fe3+ complex with CS and DA. A loading process of DA on the nanocomposites was performed to produce dopamine-chitosan-iron oxide nanocomposite (DA-CS-Fe3O4 NCs). The CS-Fe3O4 NCs and DA-CS-Fe3O4 NCs were characterized with FTIR spectroscopy, X-Ray Diffraction, Vibrating Sample Magnetometer, and UV–VIS spectrophotometer. The cytotoxicity and wound healing assay were performed for the same two nanocomposites. The results of cytotoxicity test confirmed that the fibroblast cells of CS-Fe3O4 NCs and DA-CS-Fe3O4 NCs were healthy and did not show toxicity. The results of wound healing assay results suggested that the prepared CS-Fe3O4 NCs and DA-CS-Fe3O4 NCs facilitated cell migration. In addition, the prepared DA-CS-Fe3O4 NCs could attach to the tissue through two possible functional groups (catechol and amine groups), that make the prepared tissue adhesive is strongly recommended to use with wet and dry surface.