UBT Biomaterials Magnetic Nanoparticles Sintering & Phase Diagrams Discussion
Question Description
True or False
Please carefully read the following statements and determine if the statement is true as a whole or if there are any errors in the statement. If it is wholly true, mark the statement as True. If there are any false portions of the statement, then underline the false portions and correct them by replacing the false information with true information. You must show your work for any calculations.
1) Magnetic nanoparticles (mnps) are a class of biomaterials that have many applications in therapies including cell separations, gene therapy, and magnetic nanoparticle hypothermia. Polymers, ceramics, and metals can be used to make mnps due to the ability to have paired electrons that rotate. This mechanism is similar to superconductivity where electrons pair up and move through a metal like Soul Train Dancers with lots of resistance. The mechanism for magnetic nanoparticle hypothermia involves using mnps to cool cancer cells to the point that they become unhealthy. The mnps can pass through the cell membrane due to their small size and very low surface area. A typical surface area for mnps with a diameter of 10 nm would range from 5-15 m2/kg and this data can be collected using BET N2 adsorption. An analogy for how mnps work with cancer cells can be developed based on how Japanese HoneyBees protect their hive from Japanese Murder Hornets.
2) Sintering
Sintering is a phenomenon that is used to densify materials by converting a liquid metal, ceramic, or polymer into a solid structure. The benefit of sintering as a processing technique relates to the ability to make dense materials at a lower temperature that is around 1-2% of the melting temperature.
3) Phase diagrams are another tool that can help us to understand how to process biomaterials to control the microstructure and properties. Phase Diagrams can be used for metals but not ceramics. The eutectic point on a phase diagram can occur for two metals that have complete solubility like Ni and Cu and represents the lowest melting composition for the two metals. The eutectic microstructure displays a criss-cross or plaid pattern of and it forms due to the long time that atoms have to diffuse over long distances during direct cooling from a solid to a liquid through the eutectic temperature.
4) A stress vs strain curve can be used to compare the Mechanical Properties of engineered materials (ceramics, metals, and polymers) and biological tissues. The slope of the stress vs strain curve is called the elastic modulus and lower slopes indicate stronger atomic bonds and stronger materials. Atomic defects are responsible for the properties of biomaterials. Slip planes are also called dislocations (missing planes of atoms) and they can be manipulated to control the strength and level of malleability of ceramics and polymers. Stress shielding occurs when bone is fully loaded and the implant and bone share the load equally. Stress concentration occurs when the stress on a system is amplified due to a geometric effect. This is beneficial for preparing and testing accurate samples to measure the mechanical strength of materials.
5) Bioactivity is a very important consideration when designing Biomaterials that are implanted within the body. Bioglass is a great example of bioactivity. Bioglass is a metallic polymer that can bond with bone and soft tissue. Its main component is C. Hapex is another bioactive material that contains Si. It is a composite that contains polyethylene and hydroxyapatite. Polyethylene by itself is bioactive and when 20 vol% hydroxyapatite is added to polyethylene, it is transformed to a bioinert material. Polyethylene can be made as low density, high density, and ultralow density polyethylene for use with hip implants. One way to improve the mechanical properties of Hapex is to increase the size of the hydroxyapatite particles. Larger hydroxyapatite particles can result in stronger interfacial bonds due to the extremely large surface area for larger particles. The specific surface area, packing factor, and density for Hydroxyapatite [Ca10(PO4)6(OH)2] nanoparticles that are hexagonal plates (a = b = 0.94 nm, c = 0.68 nm) cannot be calculated accurately.
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