Week 13 Flashcards
What does the bulk of biomaterial govern?
mechanical integrity or “failure”
What does the surface of biomaterials govern?
cell-biomaterial interactions within a depth of < 1 nm
What is the purpose of surface modification?
to alter surface properties to enhance performance in biological environment while retaining bulk properties of biomaterial/device
What are the 6 biomaterial surface interactions?
What are the 6 objectives of surface functionalization?
- clean a surface
- reduce/eliminate protein adsorption
- reduce/eliminate cell adhesion (pathogens)
- promote cell attachment/adhesion
- increase hardness (stiffness)
- enhance corrosion/degradation resistance
What are the two types of surface modification approaches?
- subtractive modification (physical method)
- additive modification (chemical method)
What is subtractive modification?
removal of surface layer via
- abrasive blasting
- plasma treatments
What is additive modification?
depositing films or biological factors via
- physical and chemical vapor deposition
- grafting
- attachment of self-assembly molecules
- layer-by-layer deposition
preparing biomaterial surfaces for further treatment, cleaning or finishing
abrasive blasting
Abrasive blasting is performed to do what 3 things?
- remove surface contaminants
- roughen implant surfaces to increase surface area
- improve the adhesion of coatings on implant surfaces
Is high roughness good or bad for bacteria and infection?
good for bacteria
bad for infection
Describe the stent surface before and after abrasive blasting
after fabrication
- surface quality has lots of scratches and inconsistencies
after sand blasting
- roughness is even
What 4 things is surface roughness influenced by?
- type of abrasive media (“powder”)
- sodium bicarbonate
- glass (SiO2)
- alumina
- CaP - size/shape of abrasive media
- gas or air pressure
- nozzle to substrate distance
How does abrasive blasting affect the wettability of a surface?
adding surface roughness makes a surface go from hydrophilic –> superhydrophilic
What are the 3 advantages of increased surface roughness?
bone-implant interaction:
- increase surface area of the biomaterial adjacent to tissue
- improved bone-type cell attachment
- increased bone present at the implant surface
What are the disadvantages of increased surface roughness?
bacteria/pathogen –> if you have rough surfaces its going to be hard to remove the bacteria/pathogen
What two types of surface alteration is plasma glow discharge used for?
- chemical
- physical
What is plasma glow discharge strongly dependent on?
process parameters
What is plasma glow discharge frequently used for?
- cleaning
- preparation
- modification
an atom/molecule acquires a negative or positive charge by gaining or losing electons
ionization
Describe direct current glow discharge
Describe what happens during surface modification from direct current glow discharge
by forcing the electrons to come out, and go towards the material surface, you can create a specific plasma that can:
- etch surface
- add functional groups
- change chemistry of the material
**utilizing electrical field –> create ions –> forced to heat and strike the material –> change material properties
What is the plasma outcome?
before plasma, contact angle is larger
after plasma, contact angle is smaller
What is the plasma outcome for chemical modification?
change the chemistry of the surface
What is the plasma outcome for antibacterial?
This method involves depositing hydroxyapatite on implants and is the common commercial and accepted method for dental implants
thermal spraying
Describe the thermal spray process
- Processes in which melted (or heated) materials aresprayed onto a surface
- the “feedstock” (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame)
- can provide coatings of 30-150 μm thick
- powder is fed into the plasma flame through a feed and is propelled to the implant surface as semi-molten particles
Describe the plasma spray diagram
plasma spray particles are on top of the material (black surface) which can change the properties of a material (i.e., make the surface more rough)
What 7 things determine coating properties?
a deposition method to produce solid materials under vacuum
chemical vapor deposition (CVD)
CVD is a chemical process using temperature to _____ and drive the _____
heat up the gases
deposition raction
What happens to the gas reactants during chemical vapor deposition?
they absorb and react with substrate surface
What is the result of chemical vapor deposition?
film on the surface
This method deposits thin films on substrates
physical vapor deposition (PVD)
What are the 4 steps involved in physical vapor deposition (PVD)?
- evaporation
- transportation
- reaction
- deposition
What are the 3 different types of CVD?
What are the two most common PVD processes?
- sputtering
- evaporation
What happens during PVD?
heat the metal –> release metal molecules –> metal molecules strike the item to be plated (biomaterial)
Describe evaporation deposition
relates to the tendency of particles to escape from the liquid (or a solid)
vapor pressure
Describe sputtering deposition
What is electrophoretic deposition?
