BENG 375 Exam 1 Study Guide PDF

Study Guide: Steps in asceptic loosening: Caused by wearing damage Occurs when a large amount of tiny micro-scale particles are generated around a joint replacement Without infection 1. Debris production: The initial stage of aseptic loosening is the production of debris, such...

Study Guide: Steps in asceptic loosening: Caused by wearing damage Occurs when a large amount of tiny micro-scale particles are generated around a joint replacement Without infection 1. Debris production: The initial stage of aseptic loosening is the production of debris, such as metal or particulate debris. 2. Macrophage activated osteolysis: The body's macrophages respond to the debris, which triggers an inflammatory response. 3. Prosthesis micromotion: The implant moves slightly, which increases the amount of wear particles. 4. Particulate debris dissemination: The wear particles spread throughout the body. Steps in the foreign body response: A complex process that occurs when a biomaterial is implanted in the body. Bodies immune system views the implant as a foreign entity and attacks it. 1. Protein adsorption: Proteins from the body's plasma and interstitial fluids rapidly adhere to the surface of the implant. The surface properties of the implant determine the type, amount, and composition of the adsorbed proteins. 2. Exudation: Blood cells, proteins, and fluid escape from the vascular system into the injured tissue. 3. Cell adhesion: Cells adhere to the implant, which is the first step in determining how the cells will respond to the implant. 4. Macrophage fusion: Macrophages can phagocytose biomaterials up to 5 μm in size. If the biomaterial is larger, macrophages often fuse to form foreign body giant cells (FBGCs). 5. Fibrous capsule formation: The final stage of the foreign body response, in which fibroblasts differentiate into myofibroblasts and synthesize and secrete collagen. This results in a collagenous capsule around the biomaterial. Steps that a material goes through to fatigue failure: Defect, internal stress concentrations, permanent defects accumulation, catastrophic failure How to resist cracking under fatigue: High elastic modulus, high yield strength, high fracture toughness, resistance to deformation How to strengthen/harden polymers: Hinder chain motion, increase molecular weight, add hard particles or fibers, increase crosslinking, increase crystallinity Biodegradation mechanism – for polymers:  Cleaved to low molecular weight, taken up and metabolized by the cell, excreted by the body Tuning biodegradation kinetics: Chemical bonds in polymer chains (weak ester bonds), steric interference, crosslink density, crystallinity Pros and cons of Ti alloys: HCP structure has poor bending ductility. Ti alloys have a poor wear resistance Where are they used ○ Used at highly (compressive or tensile) stressed regions especially for Cr/Ni-allergic patients (High strength) ○ Used as permanent implants (bone-bonding ability) or short-term temporary device. ○ Avoid use at shear stressed regions (due to poor bending strength) ○ Avoid use at wearing sites (due to poor wear resistance) ○ Poor tribological properties ○ Avoid use as long-term temporary device (due to bone-bonding tendency) PU polyurethane: Thermoplastic elastomer: Physical cross-links (Reversible) Thermoset elastomer: Chemically (covalent) cross-links (Irreversible) How to change properties: use a chain extender ○ Usually a diol (HO-R-OH) or a diamine (H2N-R-NH2) Properties of the final polyurethane produced are primarily dependent on? ○ The chemical nature of the types of (diol, diamine, isocyanine) the three building blocks ○ And the relative proportions used during synthesis Design principles of Co-alloys Pros and cons: Pros: ○ FCC-HCP Co forms the foundation of high-strength properties of this alloy system, thus ensuring super fatigue resistance. ○ Cr, Mo and Ni together provide excellent corrosion resistance. ○ The high strength and excellent corrosion resistance offers good SCC and fatigue resistance. Cons: ○ Wrought CoCrMo alloys are expensive. ○ Stress shielding effects. Cobalt alloys have a high Young’s modulus (220-230 GPa), which is much higher than that of cortical bone (10-30 Gpa). ○ Metal toxicity.  Ni, Cr and Co each has toxic effects. They may cause systemic allergic reactions in the host body, which can increase inflammation. Abiotic vs biotic degradation mechanism: No cell vs with cells Typically, degradation is initiated by abiotic mechanisms, which do not involve living organisms (abiotic). These mechanisms are either hydrolysis or oxidation, and work by diffusion. The rate of abiotic degradation is determined by how easy it is for the water or oxygen molecules to diffuse into the polymer's structure. Biotic degradation is the metabolic breakdown by living organisms, such as oxidative enzymes. This type of degradation proceeds layer by layer because enzymes cannot diffuse into the dense polymer chains. Biotic degradation typically proceeds faster because the enzyme acts as a catalyst, but the chemical reactions for both mechanisms will still result in the same products. A quick double check to make sure the types of degradation are correct is by looking at the names. Abiotic means not derived from life, hence they do not involve living organisms, but biotic means it relates to life, which is why living organisms like cells or enzymes are involved. First requirement of a biomaterial: Biocompatible Define biocompatible: Do no harm Name the 4 types of biomaterials: Polymer Metal Ceramic Composite In polyester chain by what process are the weak ester bonds broken down: Hydrolysis What are the benefits and potential consequences of using PTFE in artificial blood vessels? Benefits: ○ PTFE is biocompatible, durable, flexible, and resistant to thrombosis. Potential consequences: ○ Thrombosis can occur when the PTFE blood vessel has a diameter of less than 6mm. This is correct because biocompatibility is the base criteria for all biomaterials, durability is important for permanent implants or artificial organ replacements, flexibility is needed  due to the twisting and motion of blood vessels in the body, and thrombosis can be a serious issue in cardiac health. Bone cement has to be fluid before implantation and be able to solidify (polymerize) in situ once implanted in the body. Shrinkage during polymerization is an issue, as it causes loosening of implants, which can be alleviated by using already polymerized---------(fill in blank): PMMA powder. The same strategy is also used for -------(fill in blank): Tooth fillings Describe bone bonding and how it occurs: Biological bonding The strong and tough bonding could be achieved only by a biological mechanism in the body. Why is the bonding site strong: Direct observation by transmission electron microscope has revealed that collagen can grow into the surface layer of HA, and that the tough collagen fibres and strong hydroxylapatite together form a strong and tough biological bonding layer. What does the Stability of HydroxyApitite depend on in physiological solutions? Composition of solution, pH, saturation limit, time in suspension, composition, crystallinity Fully crystallinity = degree of micro and macro porosities, defect microstructures, amount and type of other phases Design a knee replacement. What material properties would each component need to have What materials would suit each component How do their material properties overlap with the needs What would be potential drawbacks of your choices  Needs to be incongruent Design a shoulder joint replacement. What material properties would each component need to have What materials would suit each component How do their material properties overlap with the needs What would be potential drawbacks of your choices Needs to be congruent What are the goals for biomaterials? Phase out animal tissue Increase use of synthetic materials Lower cost of materials Support the patient Increase healing What makes a good biomaterial? Does what it is supposed to Low cost Non toxic What type of bonds form ceramics and what are their characteristics? Directional covalent/ionic bonds = non-conductive, super strong, chemically inert, brittle What are the typical properties of polymers and what is their typical structure? Long chain c-c structure Soft, flexible, ductile Plastic or elastic Light Oxidizable Draw a schematic for how step growth, chain growth, addition, and free radical: In a step-growth polymerization process, monomers react to first form many dimers, trimers, and even longer oligomers, which then connect with each other to eventually form long chain polymers. (the mers connect together to form small groups then form into a long chain) In a chain-growth polymerization process, monomers react to form first a limited number of oligomers with active sites at any moment during the polymerization, and then unsaturated monomer molecules add onto the active site on a growing polymer chain one at a time. (the mers connect to each other one at a time to from a long chain) Addition polymerisation: yields polymers with repeat units having identical molecular formulae to those of the monomers from which they are formed.  ○ All chain-growth polymers are addition polymers Free radical: successive addition of free radical (atoms/ions/molecules with unpaired electrons) building blocks ○ Is a chain-growth process First step in biodegradation mechanism and what hinders it: Diffusion of water Crosslink, crystallinity, steric hinderance Bone cement shrinkage calculation: PDMS properties: Stable and inert, flexible, oxygen permeable, non-wettable PGA, PLA, PLGA: PLA