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Protein Interactions with Biomaterials

Protein Interactions with Biomaterials. Topics: Thermodynamics of Protein Adsorption Protein Structure Protein Transport and Adsorption Kinetics. Thermodynamics. For a reaction to spontaneously occur, the change in Gibbs free energy , D G, must be <0:. G = Gibbs free energy

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Protein Interactions with Biomaterials

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  1. Protein Interactions with Biomaterials • Topics: • Thermodynamics of Protein Adsorption • Protein Structure • Protein Transport and Adsorption Kinetics

  2. Thermodynamics For a reaction to spontaneously occur, the change in Gibbs free energy, DG, must be <0: G = Gibbs free energy H = enthalpy (energy available to do work) S = entropy (disorder)

  3. Thermodynamics of Protein Adsorption Hydrophobicity: Hydrophobic areas attract hydrophobic areas Charge: Opposite charges attract Size: Larger molecules have more active sites Structure: the stability (strength of intramolecular bonds) and molecule unfolding rate

  4. Surface features and their interactions with proteins: • Topography: greater texture means greater interaction • Composition: Chemistry governs types of interactions • Hydrophobicity: hydrophobic surfaces bind more protein • Heterogeneity: non-uniform surfaces have many different types of domains to interact with proteins • Potential: surface charge affects charge distributions of ions in solution and proteins

  5. Protein Structure Proteins are polymeric chains of amino acids. Each of the 20 standard amino acids have a one-letter symbol. A sequence of three symbols, as shown for RNA (right) is called a codon Amino acids have a central carbon atom attached to a hydrogen, a carboxyl group (COOH) and an amine group (NH2)

  6. The pK value is related to the pH of the amino acid. Higher values are more acidic (lower pH)

  7. Proteins (polypeptides) are formed from condensation reactions between amino acids (peptide bonds).

  8. Secondary Structures a-helix b pleated structure

  9. Tertiary and Quaternary Structures • Interactions between side chains control how the protein folds in three and four dimensions. These interactions include: • Covalent bonding • Ionic interactions • Hydrogen bonding • Hydrophobic interactions

  10. Protein Transport and Adsorption Kinetics • Four main types of protein transport: • Diffusion • Thermal convection • Flow (convective transport) • Coupled transport (combinations of 1-3) A concentration gradient drives diffusion, while a temperature gradient creates thermal convection

  11. Diffusion is Fick’s 2nd law, with the addition of a contribution from flow: The velocity profile is given by: Here in cylindrical coordinates C = concentration D = diffusivity V = velocity m = viscosity Q = volumetric flow rate

  12. Initial absorption rate is high on a clean surface Rate slows as surface becomes covered Further absorption occurs as molecules rearrange to create new free surface

  13. Protein exchange on a material surface. The initial protein (light gray) is wedged out of the way by the newer proteins (dark gray), which have a greater affinity for the material

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