Please enable JavaScript.
Coggle requires JavaScript to display documents.
Bioinert Polymers (General (High MW polymers, Do not degrade in the body,…
Bioinert Polymers
General
High MW polymers
Do not degrade in the body
Toxicity generally due to plasticisers and additives
Vary in purity over manufactures
Undergo fibrous encapsulation in the body
Polyethylene (PE)
Chemical Structure
Types
LDPE
Low degree of crystallinity
Non-linear
Cannot be sterilised
LLDPE
Short, linear chains
Can be sterilised
Better properties than LDPE
HDPE
Higher degree of crystallinity
Linear chains
UHMWPE
Molecular mass > 10^6
Properties
+
Chemically resistant
Low cost
Tough
-
Low yield strength
Hydrophobic
UHMWPE particles are toxic
Manufacture
of UHMWPE
Gamma-radiation cross-linking
Synthesise polymer
Thermal treatment
Remelt to eliminate free radicals
Promotes molecular recombination
Eliminates oxidative potential
Quality testing
Sintering
Machine to correct measurements
Sterilisation (gas plasma)
Applications
HDPE
Catheters
Drains
Bottles
LLDPE
Pouches and bags
UHMWPE
Acetabular cups
Meniscus replacement
Polyurethanes (PU)
Structure
Contain:
Properties
Heterogeneous elastomers
Good blood compatibility
Good fatigue resistance
Applications
Cardiac catheters
Pacemaker lead insulation
Vascular prostheses
Non-adsorbent wound dressings
Heart valves?
Issues
Prone to stress-corrosion cracking
Urethane linkage can be degraded
to reduce
Segmental Polyurethanes
Formed of hard and soft segments
PEG
Aromatic diisocyantes
Greater stability
Good haemocompatibility
Polypropylene (PP)
Properties
Lower density than PE
Higher Tg
Sterilisable
Applications
Finger joint hinges
Sutures
Hernia repair mesh
Chemical Structure
Polymethylmethacrylate (PMMA)
Chemical Structure
Properties
Hard
Rigid
Glassy (Tg = 105)
Stiff
Bulky side chains
Shrinks upon polymerisation
Offet by water absorption
Exothermic polymerisation
Necrosis
Optical
Atactic PMMA is amorphous
Excellent light transmission
High refractive index
Applications
Intra-ocular lenses
Membrane for blood dialysis
Cranioplasty
Maxillofacial implants
Dentures
Bone cement
Polysiloxanes (silicones)
Structure
Based on:
Properties
Widely used
Can form
Elastomers
Gels
Low molar mass
Lightly cross-linked
Unlinked oligomers may permeate envelope
Must be used in impervious envelope
Lubricant
Foam
Adhesive
Chemically stable - unreactive
Very hydrophobic
Highly flexible
High oxygen permeability
Poor tear resistance
Applications
Catheters
Heart valves
Facial implants
Drainage tubing
Soft contace lenses
Increased hydrophillicity required
Increased chain length
Decrease cross linking
Intraocular lenses
Allows varifocals
Silicone hinges use eye muscles to flex and focus lens
Polytetrafluoroethylene (PTFE/Teflon)
Structure
Properties
Highly crystalline
Diffucult to process
High melting point
Extremely low friction coefficient
Not wear resistance
Low E and tensile strength
No water absorption
Applications
GoreTex
Coatings of vascular prostheses
Polyethylene terephthalate (PET)
Structure
Aromatic ester
Properties
Hydrophillic protein adsorption
Thrombogenicity
Increases with hydrophobicity
Applications
Vascular graft
Amorphous PET fibres
Melt-spun
High strength
Crease-resistant
Must be pre-clotted to prevent leakage
Polyetheretherketone (PEEK)
Properties
Radiolucent
Carbon fibre reinforcement gives high E
Structure
Applications
Shielding stress from grafts
Spinal fusion cages
