1. 3 Physical Properties of Biomaterials CHAPTER
3.1 Introduction: From Atomic Groupings to Bulk Materials
Metals and Ceramics: Polycrystalline materials (interactions of multiple crystals)
Amount and type of dislocations
Polymers: Crystalline and amorphous regions (% Crystallinity)
Thermal transition of physical properties

2. 3.2 Crystallinity and Linear Defects
point defects, linear defects, planar defects
Dislocations
Edge dislocations
half-plane
dislocation line
magnitude and direction of
atomic displacement
atomic circuit drawing
Burger’s vector

3. (2) Screw and mixed dislocations
Screw dislocation: shear force ---- helical pattern
Mixed dislocation: Edge + Screw
(3) Characteristics of dislocations
a) localized lattice strains
b) relationship between the Burger’s vector and the dislocation line
c) invariant Burger’s vector
d) termination of dislocation
e) slipping of dislocations (slip planes)

4. Deformation
plastic (permanent) deformation [dislocation glide]
dislocation glide: planes with higher atomic density
slip and slip plane
dislocation’s geometry plane = crystallographic slip plane
slip system: crystallographic planes x # of slip directions
high --- more deformable (ductile), low --- little deformation (brittle)

5. Ceramics
limited movement
electroneutrality requirement
longer Burger’s vector
less slip --- brittle ceramics
3.3. Crystallinity and Planar Defects
planar defects: surface and grain boundaries
External surface
atoms at the surface --- no maximum coordination --- higher energy [surface tension]
---- thermodynamic instability ---- chemical reaction at the surface
Grain boundaries
metals and ceramics: polycrystalline
atoms at grain boundary --- no optimal coordination
---- higher energy ---- higher chemical reactivity
total interfacial energy: low in materials with larger grains

6. Two types of grain boundaries
(1) small-angle grain boundary
tilt boundary (edge dislocations), twist boundary (screw dislocations)
(2) high-angle grain boundary
severe misalignment [atomic mismatch ---- energy increase]
cf) twin boundary

7. 3.4 Crystallinity and Volume Defects
volume defects: precipitates and voids
voids (pores): 1) accidental formation, 2) creation with porogens and fibers
porogens:
1) solid porogens [salts, gelatin (collagen), waxy materials (lipids or paraffin)]
---- extraction --- pore formation
extraction methods
amount and shape --- porosity and pore geometry
2) gaseous porogens
N2, CO2 / liberation and bubbling
amount, rate, timing of gas introduction --- porosity and pore geometries
fibers:
fiber size and packing density --- porosity and pore geometry
advantages: 1) exchange of fluids and gases, 2) tissue ingrowth & implant anchoring
3) tissue engineering applications
disadvantages: 1) decrease in mechanical strength,
2) altering biodegradation and corrosive properties
% porosity must be optimized

8. 3.5 Crystallinity and Polymeric Materials
physical property of polymer ---- % crystallinity
% Crystallinity
chemical structure of mer and polymer’s configuration
factors:
1) mer side groups
2) chain branching
3) tacticity
4) regularity of mer placement
in copolymer
side groups:
large and bulky
branched vs. linear
location of side groups
tacticity
block copolymer
% crystallinity : density 비교

9. 3.5.2. Chain-folded model of crystallinity
Basic unit of polymer crystalline structure: Lamella structure
cf.) polymeric crystal’s unit cell
Real situation
1) several polymer chains per each lamella
2) single chain between lamella structure and interface
3) amorphous regions separating lamellae
4) intermingled chains
Spherulite formation
three dim. radial arrangement of lamellae
impingement upon growth

10. 3.5.3. Defects in Polymer Crystals
Linear defects
(2) Planar and Volume defects
planar defects: boundaries between spherulites
volume defects: void formation
3.6 Thermal Transition of Crystalline and Non-crystalline Materials
thermal transition of biomaterials ---- viscosity and material deformation
Viscous flow
crystalline materials --- plastic deformation
non-crystalline materials --- viscous flow
rate of deformation & applied stress
viscosity: material’s ability to resist deformation (handle-ability)
water; caramel; glass

11. Thermal transition
(1) Metals and crystalline ceramics
T > Tm: liquid and viscous flow
T < Tm: solid --- crystal structure and grain boundaries 유지
(2) Amorphous ceramics (Glasses)
T>Tm: liquid state
Tm: temp with viscosity of 100 P
Tw: temp with glass viscosity of 104 P
T<Tg: solid state (glass)
(3) Polymers
liquid (rubbery solid) & glass
Tm and Tg

12. Crystalline polymers
T>Tm: random ordering of chains with no repeating structure
[translational motions]
Tm>T: highly ordered crystals
secondary bonds and Tm
1) degree of branching --- Tm 감소
2) molecular weight --- Tm 증가
Amorphous polymers
T>Tg: rubbery elastic materials
T<Tg: glassy and brittle polymer
[Tg<Tm] < Tm/Tg < 2.0 for polymer
chain vibration and rotation
1) chain flexibility
2) chemical constituents
[bulky side groups, polar groups, high mol. wt., X-linking]

13. Polymers to be crystallizable
Tg< Tc <Tm
temp increase --- polymer chains with energy
--- highly ordered crystalline state [exothermic process]
--- disruption of the crystal structure
polymer annealing
degree of crystallinity
3.7 Techniques: Introduction to Thermal Analysis
Temp analysis; measurement of the physical properties of a material as a function
of temperature
TGA (thermogravimetric analysis)
DMA (dynamic mechanical analysis)
DSC (differential scanning calorimetry)

14. 3.7.1. Differential Scanning Calorimetry
(1) Basic principles
power-compensated DSC
heat-flux DSC
(2) Instrumentation
furnace/DSC sensors/ processor

15. (3) Information provided
Tg: heat capacity
Tm: peak temp
% crystallinity