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Synthesis

   The aim of research on the synthesis stage is to study the effect of the operating parameters on the particle size, purity, shape (individual particles and magnetic beads, i.e. random dispersion of iron oxide nanoparticles in polymeric beads and magnetite colloidal nanocrystal clusters) and magnetic saturation for targeting drug delivery, hyperthermia and/or imaging. In this work, magnetite nanoparticles with specific size and saturation magnetization are synthesized. Since blood flow is different in various capillaries, specific sizes and saturation magnetizations are needed to prevent particle agglomeration as well as particles withstanding the drag of blood flow. The nanoparticles were coated by polyvinyl alcohol (PVA) to prevent coagulation of particles during bio-applications.

Design of Experiments (DOE) Approach:

   To reduce the large number of experiments due to a number of operating parameters, or factors, a design of experiments (DOE) approach is used here. The application of DOE methods in optimization of nanomaterials processing is beneficial, particularly given the high cost of experimentation and complex random error structures.
Different types of problems can be realized during DOE practice. For the first type, one may be interested in a screening procedure in which a small number of factors (called ‘main effects’) are extracted from a larger pool of factors. For the second type, one may aim at finding a description of how factors affect the response (the input-output relation). Eventually, using such a relation the goal can be to optimize the response surface function. The third type is when the experiments are tuned to give an estimation of testing errors (i.e., the robustness of the solution is of interest rather than its optimality). The fourth type relies on obtaining a mathematical model for the input-output relation and also to estimate the typical size and structure of errors. Specifically, a uniform design (UD) of experiments, with a type-II objective (i.e., finding a description of how the input factors affect the output response and optimizing the response) is adapted to study the effects of stirring rate and chemical composition of the synthesis media on particle size and distribution, the magnetic properties as well as the morphology of the synthesized particles.

   According to our results, both uniform-spherical magnetite nanoparticles, nanorods and cubic polymeric nanocomposite/magnetic beads were synthesized by an aqueous co-precipitation process. A rich behavior in particle size, particle type formation and superparamagnetic properties was observed as a function of molarity and stirring conditions. From the size, shape and magnetic measurements, it was shown that nanoparticles, magnetic beads, and the CNCs, exhibit well-defined superparamagnetic behavior with different magnetic saturations. The XRD patterns show that the purity and the size of prepared magnetite needs be considered as a function of the synthesis parameters. Using a uniform DOE approach with 3-D response surfaces, it is found that desirable size and/or magnetic saturation can be achieved by choosing appropriate parameters for targeting delivery or imaging applications. From the investigations on particle size and magnetization responses, one can conclude that for a bi-objective optimization of these two functions, a solution in the neighborhood of 7,200-9,000 RPM and 1.1 M may be considered as a possible robust solution. Magnetic beads consisting of larger primary particles showed significant decrease in saturation magnetization in comparison with individual smaller nanoparticles. The CNCs, composed of smaller primary particles, showed a considerable saturation magnetization with respect to larger individual nanoparticles.