protein interactions with biomaterials
DESCRIPTION
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 beTRANSCRIPT
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Protein Interactions with Biomaterials
Topics:
•Thermodynamics of Protein Adsorption
•Protein Structure
•Protein Transport and Adsorption Kinetics
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ThermodynamicsFor a reaction to spontaneously occur, the change
in Gibbs free energy, G, must be <0:
Surfsolprotads GGGG
STHG
G = Gibbs free energy
H = enthalpy (energy available to do work)
S = entropy (disorder)
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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
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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
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Protein StructureProteins 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 (NH2)
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
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The pK value is related to the pH of the amino acid. Higher values are more
acidic (lower pH)
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Proteins (polypeptides) are
formed from condensation
reactions between amino acids
(peptide bonds).
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Tertiary and Quaternary StructuresInteractions between side chains control how the protein folds in three and four dimensions. These interactions include:
•Covalent bonding
•Ionic interactions
•Hydrogen bonding
•Hydrophobic interactions
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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
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2
21
2
R
r
R
QV
The velocity profile is given by:
Diffusion is Fick’s 2nd law, with the addition of a contribution from flow:
r
Cr
rrD
dz
dCV
dt
dC 1
Here in cylindrical coordinates
V = velocity = viscosity
Q = volumetric flow rate
C = concentration
D = diffusivity
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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