BME 314 Lecture 3 2010

BME 314 Lecture 3 2010 - BiomaterialsII Krish Roy, Ph.D....

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Biomaterials II Krish Roy, Ph.D. Associate Professor Biomedical Engineering
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Learning Objectives Specific Learning Objectives - At the end of the next two lectures students should be able to: Understand why surface properties of materials are important and how they can be modified Discuss the host response to implanted materials Explain what is a polymer Define monomers, polymers, oligomers, macromolecules etc. Describe how polymers are classified Calculate molecular weight of a polymer Explain various properties of polymeric materials Define the criteria to choose polymers for specific biomedical applications
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Mechanical properties of materials Fatigue: Process by which material structures fail/fracture as a result of cyclic stresses that may be much less than a single-cycle ultimate tensile stress Very important in implants and applications where the material is subjected to repetitive loading heart valves, prosthetic joints, bones (stress-fractures), cardiac pacemaker leads etc. Microscopic cracks in the materials can “propagate” over repetitive stress cycles and the local stress levels can exceed the ultimate stress stepwise propagation of cracks decrease in load-bearing cross-section failure
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Importance of mechanical  properties:  E.g. Vascular Grafts The physical properties essential for simple insertion and long- term success of a graft include Flexibility (stiffness) the ability to resist kinking and squashing the ability to stretch sufficient tensile and shear strength circumferential strength sufficient to withstand arterial pressures mechanical properties approximate to those of the native vessels to which they are attached. Things to remember: Anisotropy, Viscoelasticity, Non-linear stress strain relationship and Residual stress Complete characterization of the mechanical properties of the graft is required, especially under flow conditions
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Why surface properties are important? BIOMATERIAL SURFACES Direct interaction with the environment Proteins, Cells, Tissues Dictate host reaction Determines how the material behaves in in-vivo conditions FAILURE EARLY DAYS Most biomaterials selected based on their bulk properties consideration of surface properties only after trials revealed problems EXAMPLES: UHMWPE for joints Bulk: Highly crystalline, high elastic modulus, tough Surface: Long term surface wear due to friction , leaching debris or wear particles Failure of prosthetics, hip replacements PMMA for intraocular lens Bulk: Density (need lightweight), optical properties (refractive index) Surface: Possible inflammatory cells migration and adhesion formation between PMMA and iris IT’S ALL ABOUT BIOCOMPATIBILITY, OR IS IT?
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Important considerations Sample should resemble the device to be tested Remember FDA: Never approves a material, always approves a device. It is the device that needs to be biocompatible
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This note was uploaded on 11/29/2010 for the course BME 314 taught by Professor Frey during the Fall '08 term at University of Texas.

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BME 314 Lecture 3 2010 - BiomaterialsII Krish Roy, Ph.D....

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