Exam 1

Question 1

Mn, Mw, and PDI, what is PDI=1 mean

Answer 1

Mw = Weight Average molecular weight
Mn = Number average molecular weight
PDI = Mw/Mn
If PDI = 1 –> Similar length chains

Question 2

Atactic vs. Isotactic vs. Syndiotactic

Answer 2

Atactic = no order = Amorphous
Isotactic = one side = partial crystalline
Syndiotactic = alternating = partial crystalline

Question 3

Addition polymerization

Answer 3

Addition of mer (repeated units)

Initiation with radical species, elongation/propagation, and termination

Question 4

Condensation polymerization involves:

Answer 4

Elimination of certain byproducts (usually water) as a part of the synthesis reaction

Question 5

Yield Stress vs. Fracture Stress vs. Ultimate Stress

Answer 5

Yield stress = max stress in the ELASTIC region
Fracture stress = Max load at failure
Ultimate stress = max load before necking occurs (absolute max)

Question 6

PXRD peak sizes narrow vs wide

Answer 6

Amorphous = Wide smooth peaks, smaller crystal size, more noise

Crystalline = narrow peaks, larger crystal size, less noise

Question 7

Ceramics have what qualities

Answer 7

High compression modulus, low ductility

Question 8

Calcium Phosphate and HA make up _____ in body

Answer 8

Inorganic bone – (not ligaments)

Question 9

HA in human body is (high/low) crystallinity

(high/low) crystallinity is more easily absorbed

Answer 9

Low, Low

Low Crystallinity HA is more easily absorbed

Question 10

Galvanic Corrosion can occur (not exclusively) when:

Answer 10

Two different metals of DIFFERING potential are placed near each other

Question 11

Pitting

Answer 11

Passivation layer is removed, leads to ion loss at the site of pitting

Question 12

Fretting corrosion

Answer 12

Occurs in metallic devices due to CYCLIC LOADING over time

Question 13

Passivation on metallic surface (increases/reduces) rate of corrosion

Answer 13

Reduces rate of corrosion

Question 14

PLGA degrades to:

Answer 14

Acidic degradation products

Question 15

PLGA/PPHOS composite degrades to:

Answer 15

Neutral byproduct, since PPHOS neutralizes the acidic byproduct of PLGA

Question 16

Calcium Sulfate used for:

Answer 16

Non-load-bearing injectable bone void filler

Question 17

Molybdenum added to stainless steel to:

Answer 17

Increase corrosion resistance AND Hardness

Question 18

Contact angle goniometry measures:

Answer 18

Strength of adhesion and hydrophilicity

Low contact angle = higher adhesiveness

Question 19

Is Scanning Electron Microscopy suitable for live cell analysis?

Answer 19

No, it kills cells – Specimen must be conductive and in a vacuum

Question 20

Secondary Ion Mass Spectroscopy:

Answer 20

Analysis of surface based on MASS AND FORCE

Question 21

FTIR measures:

Answer 21

Absorbance/transmittance of IR light energy reflected back from a material’s surface

Question 22

Tg associated with: ____

Tm associated with: ____

Answer 22

Amorphous polymers = Tg

Crystalline polymers = Tm

Question 23

Sterilization of UHMWPE in ABSENCE of O2 does what?

Answer 23

Increases resistance to wear

Question 24

Change in pH and/or Temp are both methods for:

Answer 24

Desorbing proteins from a surface

Question 25

Bulk degrading polymers, what happens:

Answer 25

Molecular weight is reduced, rate of water penetration exceeds rate of material breakdown - hydrophilic

Question 26

Surface eroding polymers, what happens?

Answer 26

Outside of material peels away like an onion, steady degradation - hydrophobic process

Question 27

Degradation of Poly(lactide-co-glycolide) :

Answer 27

Affects surrounding environment Undergoes BULK DEGRADATION Hydrolysis, turns to Lactic acid + Glycolic acid Degrades a different rates depending on Polylactide:polyglycolide ratio

Question 28

Tissue sterilization of bone allografts (Increases/reduces/eliminates) risk of disease transmission between donor and recipient:

Answer 28

Reduces risk, not eliminate

Question 29

Thermoplasts vs. Elastomers vs. Thermosets, which can be recycled:

Answer 29

Thermoplasts and Elastomers can be recycled | ThermoSET state is SET so they can't be recycled

Question 30

Process of killing organisms causing infection known as:

Answer 30

Sterilization

Question 31

EPOCH hip components

Answer 31

75% less stiff than similar Co-Cr implant (less stress shielding) Exterior is composed of Titanium Fiber mesh Core composed of metal - surrounding polymer Composed of: PAEK, Ti, Co-Cr

Question 32

Nitinol

Answer 32

The nickel-titanium material which goes back to its shape when placed in water

Question 33

Which surface characterization method involves the creation of secondary electrons as part of analysis:

Answer 33

SEM - Scanning electron microscopy NOT FTIR or Energy dispersive spectroscopy

Question 34

Which methods of analysis provide a "fingerprint"

Answer 34

X-Ray diffraction (bulk analysis) | FTIR (surface analysis)

Question 35

Most common mechanism for degradation in biomedical polymers?

Answer 35

Hydrolytic degradation

Question 36

Advantages of bone autografts:

Answer 36

No recipient immune response Graft is osteoinductive - with all the growth factors No disease transfer

Question 37

Osteoinductive vs. Osteoconductive

Answer 37

``` Osteoinductive = growth factors, osteoblasts stimulated Osteoconductive = will bone grow on the surface ```

Question 38

What influences Ca3(PO4)2 deposition

Answer 38

LOW crystallinity HA easily resorbed - more deposition NaOH and HA can increase deposition High crystallinity HA is NOT easily resorbed by the body

Question 39

BAK/C implants made from

Answer 39

Titanium Alloy BAK/C implants are for intervertebral discs

Question 40

Particulate debris from metallic implants results from:

Answer 40

Wear, Fretting, Fragmentation

Question 41

Which metals suitable for hip replacement?

Answer 41

Titanium Tantalum Cobalt Chromium NOT Stainless Steel

Question 42

Hydrogels have what properties

Answer 42

Good stability, refractive index, high oxygen permeability Degree of cross-linking influences: Degradation, diffusion, mesh size, mech. properties

Question 43

Hydrogels have what functions?

Answer 43

Prevent fluid loss, microorganism entry Transparency Injectable for filling in complex shapes

Question 44

Bulk degradation vs. Surface erosion - which for drug delivery

Answer 44

Surface erosion for drug delivery -- Degrades over time = controlled release Bulk degradation - Mw decreased until material experiences catastrophic failure

Question 45

Benefits of forming polymer/ceramic composite scaffold for bone tissue vs. polymer/ceramics alone

Answer 45

Offset drawbacks of each when used together vs. alone Polymer offers greater biocompatibility, degradability, and TENSILE strength, and has Greater WORKABILITY. Ceramic offers greater biocompatibility from ion exchange interactions with bone. It also offers greater COMPRESSIVE strength, but has low ductility. When making degradable materials, a composite can be controlled better than a pure substance.

Question 46

Describe corrosion and passivation -- How does corrosion occur? What is the effect of passivation and how does it perform this effect?

Answer 46

Corrosion = loss of ions = loss of mass over time 2 different metals placed in an environment with conditions that allow for ion exchange --> Formation of anode/cathode. The reduction potential difference determines rate of corrosion. Passivation - formation of thin protective layer on the surface of the metal that protects substance from corrosion by shielding the material from changes in electrical potential

Question 47

Advantage of low crystalline HA over highly crystalline HA:

Answer 47

Natural bone in body is made of low crystallinity HA, which is more easily resorbed by osteoclasts and osteoinductive. High Crystal HA not as osteoinductive - not easily resorbed.

Question 48

Trabecular metal tech - unique features

Answer 48

Made of tantalum metal - mimics trabecular structure of bone - consists of porous, honeycomb-like structures Tantalum's porosity allows for much greater biocompatibility with trabecular bone - organic bone can grow on and inside implant, VASCULARIZATION can occur.

Question 49

Design question: New Hip - What materials?

Answer 49

Use Co-Cr alloy, Titanium, PEEK polymer, and Low Crystallinity HA

Question 50

Design new hip - WHY materials

Answer 50

Co-Cr for core - high ultimate stress and fracture stress PEEK for surrounding the core - for elastic modulus similar to bone - LESS STRESS SHIELDING Ti alloy mesh for a HA framework on surface - low crystal = more mineral deposition on implant = more osteoinductivity = more biocompatible

Question 51

Design new hip - how to sterilize and why?

Answer 51

Gamma ray radiation, since it penetrates the entire implant and leaves no leftover debris or residue

Question 52

Design new hip - 3 methods of characterization and why

Answer 52

Contact angle goniometer - determine hydrophilicity - know if material will swell in aq. environment ESCA (Electron spectroscopy for chem. analysis) - determination of groups present on surface - compare to groups present on desired materials (Low Crys. HA and Ti alloy) FTIR to make unique fingerprint of surface material - in conjunction with ESCA can determine surface materials. Any impurities can be detected and fixed before further development to mitigate risks of inflammation or recipient rejection of implant.

Question 53

STM vs. AFM

Answer 53

Scanning Tunneling microscopy - Current, and probe with electron cloud detects surface molecules Atomic Force Microscopy - Probe actually touches surface and detects surface topography Both very prone to vibrations, and good really only for conductive surfaces.