Reaction that generates electrons from the reactant(s)

Takes place at the anode in a galvanic cell

Oxidation

Example: Zn(s) -> Zn²⁺ +2e^-

Reaction that adds electrons to the reactant(s)

Takes place at the cathode in a galvanic cell

Reduction

Ex: Cu²⁺ + 2e^-  -> Cu(s)

a: cathodes

b: anodes

Plots V vs. pH to determine areas of corrosion

Corrosion = area between 2 dashed lines that is not within the passivation area (all other regions = corrosive immunity/ cathodic protection)

Occurs in areas with a deep, narrow crack

Oxygen depletion w/in the material prevents reduction from occuring; metal oxidation occurs within the crevice (remaining metal becomes the cathode)

Oxygen reduction outside the material increases pH

Processing or handling leads to a small flaw or area where the passivation layer is disrupted (leads to a small anode and large cathode)

Causes significant anodic dissolution (rxn rates must be equal); often goes undetected until matl failure

Occurs in a metal under stress in a corrosive environment

Small cracks form perpendicular to direction of stress (occurs at low loads below UTS); cracks lead to brittle fracture

Continued bending, loading, or motion around the implant disrupts the passivation layer, leading to corrosion of the layer underneath

Maximum stress at failure decreases as # of loading cycles increases

Form of chain scission

Free radicals attack polymer covalent bonds

Initiation, propagation, termination steps

2 different initiation steps: homolysis (R-R ->2R⁺) and heterolysis (R-R -> R⁺ + R^-)

Affected by number of susceptible domains, molecular weight, crosslinking

Form of chain scission; water is used to cleave certain macromolecular bonds

Affected by backbone group reactivity, extent of interchain bonding, amount of water/media available to the polymer, secondary bonding, crystallinity

1. Molecular Weight

2. Strength

3. Mass

Primary form of polymer degradation

Hydrophillic domains absorb water, which causes the matl to swell, disrupting secondary bonds

Polymer becomes more ductile, and may dissolve completely if the matl is soluble enough

Influences thermomechanical properties (obviously)

Changes in matl shape and size that may or may not be caused by degradation (also includes physical dissolution/disentigration)

Rate of degradation is affected by matl's chemical susceptibility, crystallinity, amount of available media, matl surface area:volume ratio

Breaking of chemical bonds by biological factors

Products shold have low MW, be water-soluble, and be bioresorbable (able to be reabsorbed by the body)

The rate of water penetration into the polymer < the rate of polymer hydrolysis

While thickness decreases, mechanical properties are maintained

Highly hydrolytically labile + high hydrophobic content

Continuing surface turnover = poor tissue integration

Breaking of bonds in polymer crosslinks

Hydrophobic side chains may be cleaved to reveal hydrophillic groups, making the polymer more soluble

Attack on the polymer backbone, degrading it into water-soluble monomers

In vitro: Matl is cut to standard dimensions and placed in vials containing a fluid w/ pH and ion content similar to in vivo conditions

In vivo: choose animals, impant site similar to human conditions