Shared Flashcard Set

Details

Exam 2 - Ch. 7 (Surface Properties of Biomaterials)
BME 103 Ch. 7 Study Material
24
Engineering
Undergraduate 2
03/15/2011

Additional Engineering Flashcards

 


 

Cards

Term
Surface tension
Definition
Extra energy associated with atoms at the matl's surface due to unfilled valance shells
Term
Adsorption
Definition

The adhesion of molecules to a solid surface

 

Affected by surface hydrophobicity (directly proportional) and surface charge (if opposite, adsorption but repulsion if same), roughness (increases protein adsorption by physically trapping proteins on surface 'valleys')

 

Ex: PEG repels proteins due to large amount of surface-absorbed water by PEG chains; PEG chains are in constant motion, moving too quickly for proteins to adsorb to chains; chains form a barrier-like wall that prevents protein adsorption (steric repulsion); proteins compete w/ water for adsorption

 

 

 

 

 

Term
Absorption
Definition
Penetration of molecules into the bulk of another matl
Term
Physiochemical modifications
Definition

Covalent (grafting) and non-covalent surface coating

 

Modification of the original surface

 

Laser methods for surface modification (patterning)

Term
Biological Modifications
Definition

Covalent (grafting) and non-covalent biological coating

 

Immobilized enzymes

Term
Sputter Coating
Definition
Ejecting material from a source/target which is deposited onto a substrate (SAM or SEM samples)
Term
Surface modification with lasers
Definition
Increasing laser intensity increases surface roughness
Term
Properties of plasma treatment
Definition

Surface cleaning

 

Adhesion promotion (creates chemically active functional groups)

 

Controlling of surface energy (adjusting hydrophobicity)

 

Improving biocompatibility (grafting molecules to surfaces

 

Performance enhancing

Term
Self-assembled M monolayers (SAMs)
Definition

Amphiphilic

 

Thermodynamically favorable; exothermic bonding between head group and matl surface

 

Van der waals and electrostatic forces among alkyl chains

 

Easy to make (no specialized equipment, room temp., normal atmospheric pressure); very stable

Term
Solution coating
Definition
Dipping biomaterials in a solution containing the dissolved coating materials (LB film, SMAs)
Term
LB Film
Definition

Amphiphilic molecules: hydrophilic head + hydrophobic tail

 

Advantage: altering surface chemistry similar to SAMs

 

Disadvantage: instability of coating

Term
SMAs
Definition

Incorporated during matl fabrication

 

Additives that rise spontaneously to the matl surface, driven by reductions in surface energy

 

Easily done w/ polymers

 

Incompatible bulk is outside the matl; compatible bulk is inside

 

Ex: Chromium added to steel--prevents corrosion

Term

Biolgical surface modifications

Definition

 

RGD (Arginine-Glycine-Aspartic Acid) - Cell recognition site for numerous adhesive proteins in the ECM

 

Can be introduced covalently or non-covalently

 

Spacer: greater rotational freedom (improves bioactivity) and release of biological molecules

 

*Modulus does not change despite surface modifications

Term
Process for Optical Lithography
Definition

1) Starting water w/ layer to be patterned

2) Coat w/ photoresist

3) Bake the photoresist to set its dissolution properties

4) Expose photoresist by shining light through a photomask

5) Immerse exposed wafer in developer solution

6) Etch underlying layer

7) Strip photoresist

Term
Microcontact Printing
Definition

A mold of the desired pattern is created using photolithography on a silicon wafer

 

A silicone rubber material (PDMS) is polymerized in the mold to make a positive stamp

 

The stamp is inked with the surface-modifying substance by interaction w/ the molecule of interest; the inked stamp is then pressed onto the substrate

Term
Microfluidics
Definition

Mold is fabricated as in microcontact printing, but is a positive instead of a negative

 

PDMS is polyermized in the mold to make channels where required; formed PDMS is pressed against a glass slide and plasma-treated to increase inner area hydrophobicity

 

PDMS form is pressed against the substrate and a small amount of solution containging the molecule of interest is injected or placed near a channel opening; molecule is pulled through by capillary action

Term
Contact Angle Analysis
Definition

Used to provide overall info about surface hydrophobicity; defines surface tension thermodynamically as the work of making a unit area of new surface

 

Surface tension is measured across 3 interfaces: solid-liquid, solid-vapor, vapor-liquid (summed in +x)

 

Young's Equation: S-L = S-V + V-L cos (angle between L and V)

 

Angle = 180- Max S-L (most hydrophobic), 0- min S-L (most hydrophilic), complete surface wetting; L-V = critical surface tension (complete spreading)

Term
Zisman Method
Definition

Measure how the angle between L-V and S-L determines critical surface tension

 

Drops of liquid w/ known surface tension are placed onto solids, and the contact angle is measured. Unknown is compared to known values; extrapolated to 0, angle determined to estimate critical surface tension

Term
Optical Microscopy
Definition
Limited by wavelength of white light; examines fracture mechanics
Term
ESCA/XPS
Definition

Binding energy of an electron ejected from the innermost atomic orbital of a surface is measured

 

Larger binding energy = tighter electron bonding to nucleus

 

Used to identify elements present at a matl's surface, neighboring atoms

Term
TEM/SEM
Definition

TEM: greater resolving power than optical microscopy (electron wavelength is shorter than white light) but requires thinner images and is used less than SEM

 

SEM: sample surface is scanned with an electron beam; electrons undergo elastic and inelastic scattering

 

Atom emits secondary electrons to release excess energy

Term
SIMS
Definition

Primary ions are ejected from an ion gun and strike the sample surface; surface layer is stripped off

 

Emitted (secondary) ions are analyzed similar to bulk mass spectroscopy

 

Static SIMS: Uses a low ion dose, inducing minimal surface damage

 

Dynamic SIMS: Larger ion dose, increase sputtering causes the surface to erode; allows depth profiling of specimens

Term
SPM/ AFM
Definition

A small tip is attached to a cantilever; when the tip encounters the matle surface, Vdw and electrostatic interactions create a force profile that attracts the tip to the surface

 

Used to visualize surface topography; number of interacting atoms increases with tip width, decreasing resolution

Supporting users have an ad free experience!