Study Guide MEE 0844 - 001
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This 7 page Study Guide was uploaded by Lillian Rowell on Saturday March 26, 2016. The Study Guide belongs to MEE 0844 - 001 at Temple University taught by George Baran in Spring 2016. Since its upload, it has received 15 views. For similar materials see THE BIONIC HUMAN in Mechanical Engineering at Temple University.
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Date Created: 03/26/16
Study Guide for Exam 2 Chapter 7 Different classes of biomaterials used to manufacture medical devices Metals (stainless steel, cobaltbased alloys, titaniumbased alloys, noble metals, and mercury) Ceramics (glasses, carbon, inert ceramics, pyrolytic carbon ceramic) Polymers (thermosets vs. thermoplastics, elastomers, hydrogels, polyelectrolytes, biodegradable) Common metals (e.g. titanium, stainless steel) used to manufacture medical devices. Titanium known for strength and lightness Alloys and amalgams and where they are used in medicine Alloy is a metal composed of more than one element. Alloys are used because pure metal are rarely used as implants Example brass is an alloy of copper and zinc Amalgam is a mercury alloy and in dentistry it is a material of “silver” tooth filling What ceramics are used to manufacture hip or knee joint implants? Inert Ceramics which are Alumina and Zirconia (strong, stable, wettable) Hard and scratch resistant Extremely biocompatible Low friction and wear properties Different types of polymers (e.g. synthetic versus natural) used in medicine and provide some examples of each Natural polymers (plant or animal derived) Source of natural polymers proteins, cellulose, silk Synthetic polymers (petroleum, crude oil or natural gas byproduct) Source of synthetic polymers Rayon, Teflon, polycarbonate How polymers are made. What is the difference between thermosetting polymers and thermoplastics? Thermoset once these polymers have cured, the application of heat will not soften them; they have been crosslinked Thermoplastic once these polymers have cured, they may be softened by heating Hydrogels and examples of where they are commonly used in medicine Network of hydrophilic polymers dispersed in up to 99.9% water Very flexible due to their significant water content Example contact lenses Polymer composites and why we need them Polymer monomers (acrytates) + inorganic material (glass powder/Silica) We need them because the polymer provides the toughness and the glass provides the hardness strength and wear resistance Contact angles the angle, conventionally measured through the liquid, where a liquid–vapor interface meets a solid surface Quantifies the wettability of a solid surface by a liquid Mechanical testing, stressstrain curve Tensile testing is done in order to get a stress vs. strain curve Stress = force/cross sectional area (example: tensile or compressive load) Strain = change in length/original length (example: deformation) Mechanical properties such as stress, strain, stiffness, hardness, viscoelastic behavior Fracture toughness: (Kc) the resistance of a material to fracture from a preexisting crack. A crack will grow under the influence of static. Hardness: the resistance of a material to penetration by a sharp instrument called an indenter (Brinell hardness test with sphere) Viscoelastic: exhibit elastic (springlike behavior) and viscous (resistance to flow in liquids) properties. Example: foams and gels, silly putty Fatigue. Fatigue is stress or strain applied in a cyclic manner (for example your shoes, leg bones, and spine all undergo fatigue when you walk or run) Fatigue is important because materials loaded in a cyclic manner decrease in strength over time and break/fail. Corrosion and polymer biodegradation defined as a deterioration of a metal due to its interaction (reaction) with the surrounding aqueous environment facilitates crack initiation and thereby weaken a medical device Polymer biodegradation is a change in properties under the influence of environmental factors Hydrolysis water mediated degradation (absorption of fluid/water) Leaching unreacted monomers is the result from incomplete polymerization Chapter 8 Types of metals used in medicine (e.g. stainless steel, titanium, etc.) and where they are applied Stainless steels: 316L alloy is mainly used in implants Titaniumbased alloys: commercially pure titanium (implants where high strength is not required, examplefiber glass) and Ti 6AI4V ELI (6% Aluminium and 4% Vanadium Cobaltbased alloys: two types of alloy used in implant fabrications (1) Castable CoCrMo – F75 (joints) – by casting & Wrought CoNiCrMo – F562 (hip stems) – by forging Composition of stainless steel and how certain components improve corrosion resistance (or resistance to rusting) Chromium oxide is responsible for corrosion resistance Iron Chromium gives the steel its scratch and corrosion resistance Nickel smooth and polished finish Molybdenum gives greater hardness Low carbon desirable for corrosion resistance Properties of titanium Nonmagnetic and osseointegration properties (a strong bond of implant to bone achieved with titanium implants; mechanical fixation not needed) Light weight, high strength Good corrosion resistance due to solid oxide layer Shape memory alloys Nickeltitanium alloys after the alloy is deformed, they snap back to their previous shape when heated. The phenomenon is called shape memory effect NiTi (NiTinol) recovers virtually to any shape as long as the deformation is within 10% Advantages: biocompatible, does not calcify Disadvantages: “expensive”, potential risk of fracture Used in: blood vessel stents, aneurysm clips, orthopedics Metals used as antimicrobials Example: Copper, silver Interferes with bacterial enzymes, and used in wound dressings Alfred Barnes developed a mild silver nitrate antiseptic solution and marketed the drug as Argyrol, a treatment for gonorrhea Types of ceramics used in medicine and where are they applied? Ceramics used to manufacture hip or knee joint implants Nonporous, nearly inert – structural components (joints) Porous, inert – nonload bearing, coatings, fillers Bioactive – coatings, dental applications, strong attachment to bone (Calcium Phosphate Cement, Bioglass, Pyrolytic carbon, Resorbable – fillers, spinal/defect repair, drug delivery Pyrolytic carbon (ceramic) and where is it used? Often used as a coating material for heart valve components and stents Preforms are coated, then machined and polished before assembly Very hard and finish can be made very smooth Very good bloodcontacting properties Types of polymers Natural Polymers plant derived (cellulose, latex) and animal derived (silk, keratin, hyalouronic acid, collagen, all proteins Synthetic polymers dentures for example Applications of polymers in medicine Polylactic acid or polyglycolic acid is used to manufacture sutures, drug delivery devices, and scaffolds for tissue engineering. Role of wear in implant failure Purpose of using degradable polymers, and give examples of their application in medicine. Poly(lactic), (glycolic) acid, poly(caprolactone), used for sutures, drug delivery devices, and scaffolds for tissue engineering. Bioactive ceramics contribute to patient recovery and health Mixture of tetracalcium phosphate and dicalcium phosphate anhydrous When mixed with water forms hydroxyapatite – the mineral that is present in bone and teeth. Calcium phosphate cements are osteoconductive, bioresorbable, and do not produce any heat during hardening Chapter 9 Understanding of the biology and physiology of the heart. How is cardiac muscle different from skeletal muscle? Skeletal muscles are voluntary striated muscles attached to bones via tendons or each other via aponeurosis. They provide body movement. Cardiac muscles are involuntary muscles found along the heart wall. They are responsible for pumping blood away from the heart towards the lungs and throughout the body. (stimulated by nerves, selfexcitable (automaticity) and contracts as a unit) Risk factors for heart disease Age Gender Heredity (including race) Tobacco smoke High blood cholesterol High blood pressure Physical inactivity Obesity and overweight Diabetes mellitus Alcohol (efficacy vs. toxicity)! Mechanisms for cardiac pacing and Arrhythmia Electrical cardiac pacing for the management of bradyarrhythmias (first described in 1952) They directly control the heart rate by setting the pace. Sinoatrial (SA) node generates impulses about 75 times/minute, but this is damaged we need artificial pacemakers Arrhythmia is an abnormal heart rhythm Artificial pacemakers used, how are they implanted, potential complications Stimulate cardiac depolarization, sense intrinsic cardiac function, respond to increased metabolic demand by providing rate responsive pacing, provide diagnostic information stored by the pacemaker Pulse generator has electrical wire (pacing leads) in contact with the heart muscle inside the right atrium and ventricle Complications: fixations of leads to the heart (passive fixation tines get lodged in the trabeculae of the heart vs. direct fixation epicardial stable in, myocardial screwin, or sutureon) Fibrotic “capsule” develops around the electrode following lead implantation Sudden cardiac arrest and Types of defibrillators? Sudden cardiac arrest: the heart suddenly and unexpectedly stops beating. If this happens, blood stops flowing to the brain and other vital organs. SCA usually causes death if it's not treated within minutes Implantable defibrillator: Accurate sensing of heart electrical activity to determine if fibrillation has occurred and generation of a defibrillating pulse to restart the heart Atherosclerosis and Significance of Poiseuille’s law in cardiac disease. How are vulnerable plaques different from stable plaques? Disease in which plaque (fat, cholesterol, calcium, and other substances) builds up inside your arteries and is the usual cause of heart attacks, strokes, etc Poiseuille’s law: F = C * D^4 F: rate of blood flow D: vessel diameter C: vessel conductance (pressure difference across the vessel, vessel length, blood viscosity) Vulnerable Plaque Thin fibrous cap, Inflammatory cell infiltrates, Lipidrich plaque (more susceptible to rupture due to weak cap) Stable plaque Thick fibrous cap, Smooth muscle cells: more extracellular matrix, Lipid poor plaque (unlikely to rupture) Technologies used to diagnose and treat atherosclerosis and complications of each treatment Angioplasty (with stenting) shorter recovery, no openchest surgery, chest pain may persist, may require medication, and may need another angioplasty or bypass later Bypass surgery longer recovery, openchest surgery, chest pain unlikely, less likely to need medication, less likely to need another procedure Valve failure and how is it diagnosed? Heart valve disease occurs when the heart valves do not work the way they should. (don’t open and close how they are suppose too) Echocardiography, EKG, chest xray Advantages and Disadvantages of various synthetic and natural heart valves Bileaflet Design largest opening angle, lowest pressure gradients, and minimal turbulence and lower thrombogenicity Porcine Aortic Valve designed to be flexible at the opening Tilting Disc Design Complications: Material fatigue in mechanical valves, Thrombogenesis / haemocompatibility, Biocompatibility, Valvetissue interaction, Wear, Blockage, Getting stuck, Regurgitation Heart failure and how is it characterized/diagnosed? Risking factors that can cause heart failure: heart attack, high blood pressure, high cholesterol, damage to heart valves, diabetes, obesity and advancing age Symptoms: Fatigue, Activities limited, Chest congestion, Edema or ankle swelling, shortness of breath (FACES) Diagnoses: Echocardiogram, ejection fraction (healthy heart is 60% or more, and heart failure is 40% or less), Electrocardiogram, or chest xray Types and applications of left ventricular assist devices (LVAD) Used in patients with severe heart failure when the heart is no longer capable of pumping blood Inserted in the chest cavity Moves blood from the left ventricle to the aorta through a pump (continuous or pulsatile) Reduces the workload of the heart allowing the heart to recover its strength shortterm applications (“bridge to transplant“) Technologies for artificial hearts and potential complications ABIOCOR: first completely selfcontained total artificial heart (Hydraulic pump transports hydraulic fluid from side to side, blood is pumped to the lung and the rest of the body as fluid moves to right and left, Valve opens and closes to control fluid motion to the left and right) Uses a wireless transcutaneous energy transfer coil Has a rechargeable battery for 30 minutes of tetherfree operation A Battery pack can pump the AbioCor for 4 hours (external component) Complications: Device failure (up to 35% at 2 years), Infections, High cost (>$250,000), Power source, Thrombogenesis / haemocompatibility, Psychological (e.g. noise) How is blood pressure characterized and normal range of blood pressure for healthy subjects? Pressure of blood pushing against the walls of the arteries as the heart pumps blood Blood pressure numbers include systolic and diastolic pressures. – Systolic blood pressure is the pressure when the heart is pumping blood. – Diastolic blood pressure is the pressure when the heart is at rest between beats. Normal range: less than 120 mmHG (systolic) and less than 80 mmHG (diastolic)
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