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Class 1: Classes of materials used in medicine (Polymers)Biomaterial: a nonviable material used in a medical device, intended to interact with biological
systems. This material can be any matter, surface, or constructs that interacts with biological systems.
This material has to be biocompatible, non-toxic.
Biocompatibility: the ability of a material to perform within an appropriate host-response in a
specific application.
21st century: focus on regeneration instead of repair!
Collagen, aliginate (carbohydrate) vs silk, cotton (protein)
Natural vs synthetic: natural polymers (silk, gelatin) have a much more complex structure than
synthetic polymers (nylon, PET)
Tacticity
Common polymers in Biomaterials
PTFE: fluor (-F) make the polymer hydrophobic, and is therefore good for vesicular grafts (blood
flow)
PHEM: hydrophilic groups (-OH) can cause the polymer to form a hydrogel
,Common bonds in polymers
Fact: The more hydrophobic the polymer, the less degradable.
Molecular weight distribution measurements (Mn Mw Ð Xn)
- GPC
- Mass spectroscopy
- NMR
Low MW: more brittle, less stiff
High MW: less brittle, more stiff
Stress-strain curve
Reversibility of stress-strain curve
A: complete (elastic)
B: partly (elastic-plastic
C: not (plastic)
D: hysteresis (time-dependent: visco-elastic)
Amorphous vs semi-crystalline
- Polymers are never 100% crystalline
- Polymers have never achieved their theoretical stiffness
- Crystalline part is hard
- Amorphous part is soft (elastic)
Thermal properties: The three fundamental molecular properties of polymer molecules are chain
stiffness, chain polarity, and chain architecture. They determine two important temperatures that
characterize polymer molecules: T g (glass transition temperature) and T m (crystalline melting
temperature).
Mechanical properties via tensile testing
Thermal properties via Differential Scanning Calorimetry (DSC)
, Class 2: Classes of materials used in medicine (Polymers, DSC)
DSC graph
Three heating runs (semi-crystalline polymer)
2nd and 3rd heating run: These two heating runs give the intrinsic properties of the polymer, and should
be the same in case the heating rate is the same.
Heating rate: normally 10-20 oC per minute (you should always report this!)
Why is the 1st heating run different?
The 1st heating run does delete the history of the polymer crystals (T m). The crystals are formed
differently during different conditions during cooling down.
What if the 2nd and 3rd heating runs are different?
Could be a too high temperature during the 2nd heating run, which causes degradation of the polymer
crystals change structure as well and cause different T m
Aging of polymers: the structure of the polymers changes over time.
Tc (crystallization temperature): some polymers crystallize during heating (exothermic process)
Melting trajectory: Some polymers can not pack in perfect crystals like salts, therefore there is a
melting trajectory instead of a perfect melting peak.
The integral of the following peaks results in …
Tg heat capacity (J/oC) ΔC p
Tm melting enthalpy (J) ΔHm
Tc crystallization enthalpy (J) ΔHc
Well-mixed polymer materials: The Tm peaks are different and therefore the crystals are formed at
different spots. This indicates that the mixture is mixed well
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