Surface Properties of Biomaterials

Question 1

What is surface tension?

Answer 1

excess energy caused by regions or atoms on the surface not bonded; unfilled valence shells

Question 2

What interactions occur on the surface of the material? (3)

Answer 2

1. surface tension
2. adsorption
3. absorption
4. biocompatibility

Question 3

What is adsorption?

Answer 3

adhesion of molecules to a solid surface

Question 4

What is absorption?

Answer 4

penetration of molecules into the bulk of another material

Question 5

What is biocompatibility at the surface of a material?

Answer 5

controlling protein adsorption to the surface

Question 6

Protein adsorption can cause: (4)

Answer 6

1. more proteins to attach
2. inflammatory response
3. cellular interaction inhibiting proliferation
4. biofilm formation

Question 7

What are 2 properties that impact adsorption?

Answer 7

1. surface hydrophobicity
2. surface charge

Question 8

Protein adsorption increases with increased _________________

Answer 8

hydrophobicity

Question 9

Surface charge occurs by:

Answer 9

dissociation of ionizable surface groups or through adsorption of ions from a solution

Question 10

Steric hinderance

Answer 10

presence of chemical groups prevents or slows down adsorption

Question 11

Surface roughness can _______ proteins

Answer 11

trap

Question 12

Contact Angle analysis determines

Answer 12

the hydrophobicity of the surface

Question 13

Advancing contact angle measured by

Answer 13

adding water slowly to surface with syringe

Question 14

Receding contact angle is measured by

Answer 14

removing water from surface with syringe

Question 15

Contact Angle Hysteresis is measured by

Answer 15

subtracting the advancing by receding values

Question 16

Contact Angle Hysteresis describes

Answer 16

how the surface tension of the material changes before and after it is exposed to an aqueous environment.

Question 17

The lowest critical surface tension value means

Answer 17

the most hydrophobic surface

Question 18

What are the two types of surface treatments? And what do they include?

Answer 18

1. chemical - covalent and non-covalent bonding to surface
2. biological - covalent and non-covalent bonding to surface

Question 19

What is Plasma treatment? What surface is to be treated? What happens to the electrodes in the chamber? Do they interact with the cathode surface?

Answer 19

chemical surface treatment & covalent bonding

plasma environment created by applying an electric potential across a gas.

cathode = surface to be treated = negative potential relative to anode

Electrons move around chamber from cathode to anode and collide with molecules to form gaseous ions and radicals = interact with cathode surface and cause reactions

Question 20

What is Chemical Vapor Deposition (CVD)? What does it cause to happen? What is it used for?

Answer 20

chemical surface treatment & covalent bonding

a mix of gases exposed to a material at a high temperature.

causes decomposition of one or more components of the gas mixture and subsequent deposition.

used for pyrolytic carbon coatings and Tantalum

Question 21

What is Physical Vapor Deposition (PVD)? What do the ions/atoms do to the surface? What does it increase? What devices is it used for?

Answer 21

chemical surface treatment & covalent bonding

Deposition of atoms generated through physical processes.
- ions or atoms strike surface and condense it to form a thin film

increases water resistance of metal implants
for orthopedics or surgical tools.

Question 22

What is radiation grafting/photografting? What is it typically used for?

Answer 22

chemical surface treatment & covalent bonding

material is exposed to source of high energy, ionizing radiation, electron beam or UV light which forms the reaction at the surface.

used for hydrogels to bind to hydrophobic substrates

Question 23

In Self-Assembled Monolayers (SAM) what is amphiphilic? What are the three key regions?

Answer 23

chemical surface treatment & covalent bonding

amphiphilic = hydrophilic (polar) and hydrophobic (non-polar) areas

1. attachment group
2. long hydrocarbon (alkyl) chain
3. functional polar head group

Question 24

What are Langmuir-Blodgett Films similar to? What is the Langmuir trough used for?

Answer 24

chemical surface treatment & non-covalent bonding

similar to SAMs with hydrophilic head and hydrophobic tail

Langmuir trough used for molecules transferred to the surface of the biomaterial - reaches critical area = function of size and type of hydrophobic tail on molecule.

Question 25

What happens in Layer-by-layer Coatings?

Answer 25

chemical surface treatment & non-covalent bonding

+ charge substrate put in anionic solution, surface becomes - charge, rinsed, substrate put in cationic solution, adsorption of + charge occurs, surface becomes + charge, rinsed

cycle repeats until coating of desired thickness is reached

Question 26

What happens with Covalent Biological Coatings? What are the two methods?

Answer 26

attaching biologically active molecules to substrates through covalent bonds.

post-fabrication methods or attachment during synthesis

Question 27

What happens with Non-Covalent Biological Coatings? What is used to prevent formation of clots? What region is added to the heparin?

Answer 27

involves adsorption of biomolecule into the biomaterial, then cross-linking to improve the coating stability

heparin = complex carbohydrate -> prevents clots
hydrophobic region added = negative charge so no modification of biomolecule = allows for adsorption of heparin to + charged surfaces