Lecture 4 Flashcards
(23 cards)
How do conductive polymers work?
they can be doped with ions or molecules to conduct electrical currents
What are some limitations with sterilising polymers?
Heat = melts the polymer
chemical = release toxic gas or reacts with it
radiation = breaking the polymer chain
Compare some features of PGA and PLA
PGA = hydrophilic (fast degradation)
e.g. resorbable sutures
metabolised by liver or discharged via urine
PLA = hydrophobic (slow degradation)
can be tailored by adjusting crystallinity
What are some polymers which break down over a short period of time?
PGA PLA and PLGA breakdown via hydrolysis
Do most polymers undergo mass loss?
no - often there is loss in strength and ductility but not mass loss
What is oxidation? Which materials are more susceptible to it?
Produced by hydrogen peroxide
Produced by FBGC
can lead to the breaking up of the chain
LDPE HDPE UHMWPE and PP
What is hydrolysis? Which materials are more susceptible to it?
breaking down by water
electrical attaction normally exists as it drags electrons from carbon to form 2 smaller molecules
PMMA PGA and PLA
What is the biodegradation of polymeric medical devices?
loss/change in material structure (breaking chain into smaller parts)
not necessary to have mass loss
chains break down into movable parts
mechanisms include hydrolysis, oxidation, enzymatic degradation, physical degradation
What is the FDA rule with breast implants, PE mesh, synthetic tendons/ligaments?
breast implants = safe
PE mesh = recall as was cutting muscle
tendons = class III
What are some polymers that are used for HARD STRUCTURES?
PEEK = bone like structures (expensive)
PMMA = bone implants (brittle), affected by hydrolysis
What are some polymers that are used for MESH AND FIBRES?
Nylon = non-resorbable sutures and fibres
PP = surgical mesh and non-resorbable stitches (cheap)
(affected by oxidative measures)
What are some polymers that are used for TUBING?
PTFE = grafts and artificial blood vessels
PDMS = breast implants and wound healing patches
PU = tubing
What are polyethylene polymers used for? Which is the most expensive?
LDPE = packaging
HDPE = non-load bearing implants
UHMWPE = articulating compoennts @ high load joints + resorbable sutures (most expensive)
ALL AFFECTED BY OXIDATIVE MEASURES
What are the 4 primary uses of polymers?
Structural implants, valves and vessels
Transparent biofluid interfacing catheters and containers
Flexible casings/coatings for metallic implants and electrodes
Flexible films/fibres/meshes for wound covering and sutures (e.g. bandaids)
What are the benefits of polymers over metals or ceramics?
Chemical inertness and resistance
transparency
softness
processability and tailorability
lightness
bioactive
What is the issue with Bisphenol A?
Acts like estrogen so it binds to the receptors however it does not perform the required acts
found in BPA
How do plasticisers, stabilisers and crosslinkers interact with organic molecules?
Plasticisers and stabilisers affect secondary bond between organic molecules
Crosslinkers create new bonds between organic molecules
Are there a limited number of polymers?
technically no - any new variation of weight or composition = new polymer
What are the 3 other components of polymeric devices?
Plasticisers = softness
Stabilisers = impact degradation
crosslinkers = increase strength but decrease toughness
What are polymers predominantly made from?
carbon –> monomers undergo polymerisation to form a polymer that is intrinsically safe
What is the main advantage of hydrogels?
permeability, retention and absorption of fluids
What is the mechanism in which polymers such as PEDOT conduct electricity?
Delocalised electrons in the conjugated pi-bonds flowing along the polymer with dopants providing gaps for electrons to move into
What leachant is known for protecting RBC from degradation but also causing liver toxicity?
Diethylhexyl phthalate
