BME 314 Lecture 4 2010 - PolymericBiomaterialsand...

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Polymeric Biomaterials and  Tissue Engineering Krish Roy, Ph.D. Associate Professor Dept. of Biomedical Engineering
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Learning Objectives By the end of this lecture, you should be able to: Describe the use of polymers as biomaterials in various applications Define crystallinity, amorphousness, Tg, Tm and their affects on polymer properties Discuss how to choose a biomedical polymer for particular applications Name a biodegradable polymer and describe its use Define tissue engineering and describe the different approaches used (be able to compare and contrast and provide an example for different approaches) List and discuss the key challenges of tissue engineering
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Morphological properties:  Crystallinity Polymers melt at high temperatures (characteristic properties of each polymer). When a polymer is slowly cooled from the melt state, it can form ordered structures (similar to crystals ). Such polymers are called crystalline (semi-crystalline) Polymers with regular, compact structures and strong intermolecular forces, such as hydrogen bonds have high degrees of crystallinity as crystallinity increases, the polymer becomes more opaque due to scattering of light by the crystalline regions…for example, Teflon -(CF 2 =CF 2 )- “looks” white Melt transition temperature, T m (or Crystalline melting point): The temperature at which all crystalline regions melt i.e. crystallinity disappears as the degree of crystallinity increases, T m increases
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Morphological properties: Crystallinity Crystallinity has major effects on a. Mechanical properties Increased stiffness Less flexible a. Diffusion rates Less permeable to diffusing molecules a. Rates of hydrolysis Low penetration of water and hence slow hydrolysis Diffusion constants of gases through high and low density polyethylene Gas High density Low density CO 2 1.55 4.60 CH 4 0.76 2.60 C 2 H 6 0.16 0.82
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Morphological properties:  Amorphousness Polymers that doesn’t form an ordered structure when cooled from a melt are called amorphous polymers Amorphous polymers are also referred to as glassy polymers They lack crystalline domains that scatter light and are transparent…. Poly(methyl methacrylate) On heating, amorphous polymers are transformed from a hard glass (stiff, brittle) to a soft, flexible, rubbery state Glass transition temperature, Tg : The temperature at which a polymer undergoes a transition from a hard glassy state (amorphous solid) to a rubbery state (ca. 100 degrees for high molecular weight polystyrene)
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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 at Austin.

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BME 314 Lecture 4 2010 - PolymericBiomaterialsand...

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