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Coatings (Function (Modulation of interaction w the environment, Hide…
Coatings
Function
Modulation of interaction w the environment
Hide material from immune system
Prevention of bacterial attachment
Protection from deterioration
Provide stimulus responsive mechanisms
Types
Passive
stable as environment changes
Low cost
Simple
Existing products, well researched
Stable
Can use harsh conditions
Protects mechanical properties
Protect against degredation
Active
properties can be
tuned with stimuli
pH
electrical field
light
High cost
Complex
New
(no existing commercial applications)
Requires mild conditions
Control biological interactions
Polymers & biomolecules
Passive Applications
Titanium orthopedic implants
Why is titanium used?
Low stiffness (for metal)
High corrosion resistance
High biocompatibility
Problems
Low wear resistance
Much stiffer than bone
Less force on bone
Wolf's Law: bone adapts to load applied
Bone weakens
Solution: Porus implant
Closer match to bone stiffness
Better bone integration
More prone to corrosion and wear
Diamond-like coating (DLC)
Thin film of tetrahedrically coordinated carbon
Corrosion resistance
Hardness
Better tribological properties
graphite sheets form under shear
Nanoparticles
Problems
Covered by opsonins
Immune system recognition
Phagocytosis
Removal of particles
Anaphylactic shock
Polyethylene Glycol (PEG) chains
Cover surface
Shields from opsonins
Protein > gap between chains = repelled
Protein < gap between chains = penetration
Effective protection if:
Highly biocompatible
Problems
Body may develop antibodies
Coating must be dense and homogenous
Short-term protection
Not useful for macroscopic implants
Active Applications
Dynamically controlled adhesion
Charged polymer chain (or head)
Surface changes from +ve to -ve charge
Polymer flattens or extends depending on the electric potential
Must be surrounded by short polymers
e.g. RGD peptides (cells)
Testing male infertility
'obstacle course'
Assess mobility
Controlled drug release
e.g. implants
Anti-inflammatory
Anti-proliferative
PNIPAM
Volume transition at body temp
Swollen T<Tc
Collapses T>Tc
Releasing fluid and any suspended drugs
Tc affected by low pH, salinity
Gel matrix
