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Global
Trends in Medical Plastics Technology and Applications
The ability of a
plastic material to withstand these ROIs is key to the
survival and functioning of the device. In addition to the
ROIs that induce oxidation response in the material, it is
also important that the material withstands the hydrolytic
action induced by the hydrophilic components in the body.
Therefore, it needs to be hydrolytically stable in
addition to being oxidatively stable to function as a
biostable material.
Hydrolytic stability is
often used in the opposite manner in the design of
biodegradable plastics. Certain chemical bonds such as
esters are very susceptible to hydrolytic action and thus
are attractive as plastics that degrade in the body. The
rate of degradation is dependent on the molecular weight
and the structure and alterations to these can tailor the
degradation rates. These biodegradable plastics are
especially useful for shorter term implant devices that
complete their function over a period of time and the
device forms a part of the regenerative medical treatment.
Processing: Processability is a big
advantage of plastics as their ability to the transformed
into a variety of complex shapes makes them very
attractive for existing and new medical device designs.
Thermal processing is the primary route for plastics,
however, other techniques involving solvents such as
dipping and spraying are also popular. Thermoplastics are,
with some exceptions, are preferred over thermosets.
Silicone polymers, one example of thermosets, are widely
used in the medical industry. Silicone polymers are chosen
mainly due to their chemical inertness, biocompatibility
and biostability.
Below are some examples of plastics and
their applications:
|
Polymer |
Medical Applications |
| Polytetrafluoroethylene (PTFE, Teflon,
Gore-Tex®) |
Vascular grafts, catheters,
introducers |
| Poly(ethylene terephalate) (PET,
polyester, Dacron®) |
Vascular grafts, drug delivery, non-resorbable
sutures |
| Poly(methyl methacrylate) (PMMA,
Perspex, acrylic) |
Bone cement, dental cement,
intraocular lens |
| Polyurethane (PU, TPU, Pellethane,
Bionate, Elast-Eon) |
Catheters, tubing, artificial heart,
pacing lead insulation |
| Silicone rubber (Polydimethylsiloxane,
PDMS) |
Catheters, feeding tubes, drainage
tubes, ventricular shunts,
introducer tips, adhesive systems |
| Polycarbonate (PC) |
Renal dialysis cartridge, trocar,
inter tubing connector |
| Polypropylene (PP) |
Non-resorbable sutures, hernia mesh |
Plastics in Medical Applications
Plastics form the main structure of
numerous medical devices. Some examples are listed below:
Cardio-vascular: Devices are used
directly inside the heart to correct the functioning of
the heart. In cardiac rhythm monitoring, devices capable
of delivering electrical pulses are used to slow down or
speed up heart rhythm. Plastics form the insulation of the
leads delivering the electrical pulses, the body of the
headers and connectors on the device. A device is
illustrated in the Figure 2.
Figure 2: Illustration of a cardiac
rhythm monitoring device
Stents are metallic
wire structures that are used to open up clogged arteries.
Stents are frequently coated with polymer solutions
incorporating drugs.
Vascular grafts are
used in bypass surgeries as conduits for blood flow. These
grafts, frequently greater in size than 6 mm, are made
from Teflon or polyester resins.
Neurological: Devices
are currently being tested and manufactured to treat
diseases such as Parkinson’s disease and dystonia. These
devices are similar in construction to cardiac pacemakers
in that they comprise a can delivering electrical impulses
through an insulated lead. Ventricular shunts are devices
used to treat hydrocephalus, wherein the cerebro-spinal
fluid pressure builds up in the brain and this is relieved
by use of a regulated flow device and usually into the
peritoneal cavity.
Figure 3: Illustration
of Neurological Devices, on the left, a Deep Brain
Stimulation (DBS) device for Parkinson’s disease and on
the right a ventricular shunt for hydrocephalus..
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