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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.

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slide1

Biointerfacial Characterization

www.rci.rutgers.edu/~moghe/583.html

BME 125:583

Lecture 1

Sep. 7, 2006

Prof. Prabhas Moghe

slide2

PROPERTIES OF MATERIALS

P. Moghe

•  Bulk and Surface Properties Can Control Tissue Interface

Dynamics After In Vivo Implantation of Biomaterials

• Bulk and Surface Material Characteristics are Property

Dependent - These Features must be known prior to any

Medical Application!

e.g. does the application require load-bearing materials?

does the application require a soft, resorbable material?

slide3

BULK PROPERTIES - MATERIAL DISTINCTIONS

- 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

slide4

SURFACE PROPERTIES OF MATERIALS

tissue fluid

and proteins

cell

BIOMATERIAL

• Surface properties determine biomaterial-tissue interface.

• Properties: Biocompatibility

Topography/Roughness

Wettability

Surface Mobility

Crystallinity

Chemical Composition

slide5

Methods to Characterize Biomaterial Surfaces

http://www.rci.rutgers.edu/~moghe/Bioprop.html

surface contact energetics
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 copolymer

exposed to water/dry air.

slide7

lv

sl

sv

Determination of Surface Energetics

  • Excess free energy per unit surface area is surface tension
  • Young’s Theory of the Spreading of Liquid Droplet:

sv

sl

lv

cos 

At equilibrium, surface energy

=

+

slide8

Techniques to measure contact angles

air

Static Drop

Capillary air-bubble

DuNouy Ring or

Wilhelmy plate

slide9

Wilhelmy Technique for Contact Angle Analysis

Electrobalance

Recorder

Lid

Measuring

Plate/Rod

Measuring

Cell

liquid

Motorized

Platform

Clamp support

slide10

q

q

Wilhelmy Plate Method for

Contact Angle Measurement

F

1

2

F

3

F

P,

perimeter,

=2(t+w)

mg

gL

gL

gL

gL

mg

mg

Fb

gL

where Fb = rL Vimm g

Cos q - Fb

F = mg + p

Both liquid surface tension & L/S/V contact angle can be computed

First do experiment with fully wetting plate and find gL. Then mount

biomaterial on the recording balance and find cosq.

ram hart goniometer
Ramé-Hart Goniometer

Drop-Image Program: http://www.ramehart.com/goniometers/dropimagefinn.htm

slide12

Dynamic Contact Angle Measurements

Dynamic contact analysis is done by increasing or

decreasing the drop volume until the three-phase

boundary moves over the surface.

ADVANCING

CONTACT ANGLE

RECEDING

CONTACT ANGLE

r

a

slide13

Contact Angle Hysteresis

Difference between advancing and receding contact angle is

called contact angle hysteresis.

recession

Buoyancy Slope

Low hysteresis

is obtained on

well cleaned,

non-interacting

surfaces.

advancement

Force

in

out

zero

depth

Immersion Depth

slide14

HYSTERESIS LOOP FOR POLYMERIC BIOMATERIAL

Buoyancy Slope

A=>receding

contact angle

B=>advancing

contact angle

q receding

A

out

2

Force

second cycle

(red)

1

2

in

1

B

zero

depth

q advancing

Immersion Depth

zisman method critical surface tension
Zisman Method Critical Surface Tension

Critical surface tension, c

Complete

spreading

Cosq=1.0

Various liquids

0

Smaller

Contact

Angles

poly(ethylene):31 dyn/cm

PTFE : 19 dyn/cm

PVC : 41 dyn.cm

Cosq=0

90

Stable

Sessile

Drop

10

20

30

40

50

60

lv

Dynes/cm

slide16

Thermodynamics of Spreading/Adhesion on Materials

Interfacial free energy of adhesion = Cell-solid interfacial free

energy - Cell-liquid interfacial free energy - Solid-liquid

interfacial free energy.

Fadh = cs - cl - sl

If Fadh < 0, adhesion and spreading are energetically favorable

Fadh

and Substratum free energy (wettability)

Fadh

50

100

s [erg. cm-2]

Very hydrophobic

substrates

slide17

Biological Interactiveness &

Biomaterial Critical Surface Tension

Non-adhesive zone

Biomaterials with good adhesion

Relative biological interaction

20

30

40

80

Critical Surface Tension (dynes/cm)

Baier, Adv. Chem. Ser. 145:1, 1975

slide18

Industrial Products for Contact Angle Measurement

  • Advanced Surface Technology Products, Inc.
  • Computer-interfaced contact angle analysis
  • Cahn, Inc.
  • Dynamic Contact Angle Analysis
  • Zisman Method
  • Wilhelmy and DuNuoy Rings
  • KSV Limited, Finland
      • Digital Tensiometer (DR/W)
slide19

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
slide21
Relationship between substrate PEG content and surface hydrophobicityTziampazis, Kohn, and Moghe, Biomaterials 21:511, 2000