1. MSE-536 Protein Interactions with Biomaterials Topics: Thermodynamics of Protein Adsorption Protein Structure Protein Transport and Adsorption Kinetics

2. MSE-536 Thermodynamics For a reaction to spontaneously occur, the change in Gibbs free energy,  G, must be <0: G = Gibbs free energy H = enthalpy (energy available to do work) S = entropy (disorder)

3. MSE-536 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. MSE-536 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. MSE-536 Protein Structure Proteins are polymeric chains of amino acids. Amino acids have a central carbon atom attached to a hydrogen, a carboxyl group (COOH) and an amine group (NH 2 ) 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

6. MSE-536 The pK value is related to the pH of the amino acid. Higher values are more acidic (lower pH)

7. MSE-536

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

9. MSE-536 Secondary Structures  -helix  pleated structure

10. MSE-536 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

11. MSE-536 Protein Transport and Adsorption Kinetics Four main types of protein transport: 1.Diffusion 2.Thermal convection 3.Flow (convective transport) 4.Coupled transport (combinations of 1-3) A concentration gradient drives diffusion, while a temperature gradient creates thermal convection

12. MSE-536 The velocity profile is given by: Diffusion is Fick’s 2 nd law, with the addition of a contribution from flow: Here in cylindrical coordinates V = velocity  = viscosity Q = volumetric flow rate C = concentration D = diffusivity

13. MSE-536 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

14. MSE-536 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