Protein Interactions with Biomaterials

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Protein Interactions with Biomaterials

• Topics
• Thermodynamics of Protein Adsorption
• Protein Structure
• Protein Transport and Adsorption Kinetics

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Thermodynamics

• For a reaction to spontaneously occur, the change
  in Gibbs free energy, DG, must be lt0

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 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)
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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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(No Transcript)
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Proteins (polypeptides) are formed from
condensation reactions between amino acids
(peptide bonds).
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Secondary Structures
a-helix
b pleated structure
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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

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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
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Diffusion is Ficks 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
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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
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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