biointerfacial characterization rci.rutgers/~moghe/583.html
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Biointerfacial Characterization www.rci.rutgers.edu/~moghe/583.html. BME 125:583. Lecture 1 Sep. 7, 2006 Prof. Prabhas Moghe. PROPERTIES OF MATERIALS. P. Moghe. • Bulk and Surface Properties Can Control Tissue Interface Dynamics After In Vivo Implantation of Biomaterials. - PowerPoint PPT PresentationTRANSCRIPT
Biointerfacial Characterizationwww.rci.rutgers.edu/~moghe/583.html
Lecture 1Sep. 7, 2006
Prof. Prabhas Moghe
BME 125:583
PROPERTIES OF MATERIALS
• Bulk and Surface Properties Can Control Tissue InterfaceDynamics After In Vivo Implantation of Biomaterials
• Bulk and Surface Material Characteristics are Property Dependent - These Features must be known prior to anyMedical Application!
P. Moghe
e.g. does the application require load-bearing materials? does the application require a soft, resorbable material?
- Interatomic forces
- Atomic structure based material classes- Metals, Ceramics, Glasses, Polymers
-Microstructure-Interatomic bonds-3-D atomic clusters-Crystallite structure-Grain size and phase changes
-Mechanical Properties of Materials
BULK PROPERTIES - MATERIAL DISTINCTIONS
SURFACE PROPERTIES OF MATERIALS
celltissue fluidand proteins
BIOMATERIAL
• Surface properties determine biomaterial-tissue interface.
• Properties: BiocompatibilityTopography/RoughnessWettabilitySurface MobilityCrystallinityChemical Composition
Method Principle Depth analyzed Resolution CostContactangles
Liquid wetting of materialestimates surface energy
3 – 20 Ao 1 mm Moderate
ESCA /XPS
X rays causeElectron emission
10 –250 A 10 –1 50um
V.Expensive
AES Electron beam causesAuger e. emission
50 – 100 A 100 A V.Expensive
SIMS Bombarded ions cause surfacesecondary ion emission
10 A – 1 um 100 A V.Expensive
FTIR-ATR
IR radiation causes excitation 1-5 um 10 um Expensive
STM Quantum tunneling current betnprobe & conducting material
5 A 1 A Expensive
SEM Electron beam causes secondaryelectron emission
5 A 40 A Expensive
CLSM Reflected /fluorescent imagesspatially determined
10 um – 2000um
0.5 um Expensive
Methods to Characterize Biomaterial Surfaces
http://www.rci.rutgers.edu/~moghe/Bioprop.html
Surface Contact Energetics
-Molecules exterior to materials are most accessible to adjacent phases as well as incoming cells (Surface Reaction)
-There is always a positive energy necessary to create a unit area of surface. Systems reach equilibrium by minimizing this surface area/energy. In solids, this happens by changing the nature of interface to one with lower (lowest) energy.
-Energy minimization occurs when groups/chains in polymer rearrange to yield lowest interfacial energy.e.g. hydrogel migrates to/from surface of a graft copolymerexposed to water/dry air.
Determination of Surface Energetics
• Excess free energy per unit surface area is surface tension
• Young’s Theory of the Spreading of Liquid Droplet:
svsl
lv
At equilibrium, surface energy sv sl lv cos = +
Techniques to measure contact angles
air
Static Drop
Capillary air-bubble
DuNouy Ring orWilhelmy plate
Electrobalance Recorder
Lid
MeasuringCell
liquid
MotorizedPlatform Clamp support
Measuring Plate/Rod
Wilhelmy Technique for Contact Angle Analysis
Wilhelmy Plate Method for Contact Angle Measurement
F FF
mg
mgmg Fb
LL
LL
F = mg + p L Cos - Fb where Fb = L Vimm g
1 23
Both liquid surface tension & L/S/V contact angle can be computedFirst do experiment with fully wetting plate and find L. Then mountbiomaterial on the recording balance and find cos.
P, perimeter,=2(t+w)
Ramé-Hart Goniometer
Drop-Image Program: http://www.ramehart.com/goniometers/dropimagefinn.htm
Dynamic Contact Angle Measurements
ra
ADVANCING CONTACT ANGLE
RECEDING CONTACT ANGLE
Dynamic contact analysis is done by increasing ordecreasing the drop volume until the three-phaseboundary moves over the surface.
Contact Angle Hysteresis
Difference between advancing and receding contact angle is called contact angle hysteresis.
Force
Immersion Depth
Buoyancy Slope
in
out
advancement
recession
zerodepth
Low hysteresisis obtained onwell cleaned,non-interactingsurfaces.
Force
Immersion Depth
zerodepth
in
out
second cycle(red)
2
1 21
Buoyancy Slope
receding
advancing
A
B
HYSTERESIS LOOP FOR POLYMERIC BIOMATERIAL
A=>receding contact angleB=>advancing contact angle
Zisman Method Critical Surface Tension
Various liquids
10 20 30 40 50 60
lv Dynes/cm
0
90
Critical surface tension, c
Cos=1.0
Cos=0
Smaller ContactAngles
Completespreading
StableSessileDrop
poly(ethylene):31 dyn/cmPTFE : 19 dyn/cmPVC : 41 dyn.cm
Thermodynamics of Spreading/Adhesion on Materials
Fadh = cs - cl - sl
Interfacial free energy of adhesion = Cell-solid interfacial freeenergy - Cell-liquid interfacial free energy - Solid-liquid interfacial free energy.
If Fadh < 0, adhesion and spreading are energetically favorable
50 100
s [erg. cm-2]
Fadh
and Substratum free energy (wettability)Fadh
Very hydrophobicsubstrates
Biological Interactiveness & Biomaterial Critical Surface Tension
Critical Surface Tension (dynes/cm)Rela
tive b
iolo
gic
al in
tera
ctio
n
Non-adhesive zoneBiomaterials with good adhesion
40 803020
Baier, Adv. Chem. Ser. 145:1, 1975
Industrial Products for Contact Angle Measurement
• Advanced Surface Technology Products, Inc.Computer-interfaced contact angle analysis
• Cahn, Inc.Dynamic Contact Angle Analysis Zisman MethodWilhelmy and DuNuoy Rings
• KSV Limited, FinlandDigital Tensiometer (DR/W)
Concerns in Contact Angle Measurements
•The measurement is subjective
•Surface roughness influences the contact analysis
•Surface unevenness influences the results
•The liquids used can be contaminated (reducing lv)
•Liquids can reorient the surface structure
•Liquids can absorb, swelling the surface
•Liquids can dissolve the surface
•Environment needs to be controlled carefully
•Dynamic measurements have hysteresis
Research Paper Discussion
Relationship between substrate PEG content and surface hydrophobicity
Tziampazis, Kohn, and Moghe, Biomaterials 21:511, 2000
Discussion