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Testing is done mainly
to verify the claims or to validate the system to meet product
specifications.
Test results are
functions of operating environment and procedure adopted and the data
generated should be interpreted in these contexts.
Tests may be
categorized as:
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Time testing to determine long-time reliability
by estimating failure rate and mean time between failures and can
show which part or component cause failure and also, mechanism of
failure.
-
Event Testing is repeated testing, till
failure.
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Stress Test done by applying limiting stress
that may be encountered in normal usage as well as possible
(usual) mishandling. Cause of failure may be investigated by step
by step evaluation.
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Environmental Testing is done by exposing the
device to environmental and transport conditions (temperature, humidity,
vibration, electromagnetic radiation etc.), that are normally
encountered.
Time related: Test
conditions are applied for certain period of time.
Failure related: Tests
conducted till one or more devices fail.
Purpose of Test
determines the choice and methods of test.
Design verification
requires most extensive testing of every minute stage or component to
verify the output conforms to the input and the parameters selected
would be determined by the expected output.
Tests during
manufacture are so selected as to ensure consistency of the component
and the system to predetermined specifications likely to be crossed
due to random variations.
Tests for acceptance
are usually limited to parameters most likely to affect functioning of
the device.
Investigation of
failure in the field will be determined by the type of failure.
Another important area
of Evaluation is Biocompatibility. Devices which directly or
indirectly came into contact with body of the consumer would have to
be tested. These are designed to assess potential adverse effects in
conditions of actual use or close to them.
Types of Tests and
parameters of study depend on the tissue and duration of contact.
The tests take into
consideration and effect of device or its materials on the body or
tissues and effect of body or tissues on the device.
While it is possible to
correlate local reactions elicited by implant materials in animals and
humans, the same can not be said of systemic effects or correlation
with in vitro findings.
Metal alloys and
coatings used for implantation rarely cause biocompatibility problem.
Polymers which are
widely used in devices themselves are usually biocompatible but the
additives, residual monomer contaminants may cause local or systemic
reaction.
Biological tests
usually performed on starting materials and some times on components
are :
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Sensitizing assay
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Irritation tests
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Cytotoxicity
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Acute systemic toxicity
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Haematocompatibility
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Pyrogenicity
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Implantation tests
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Mutagenicity
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Subchronic toxicity
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Chronic toxicity
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Carcinogenesis bioassay
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Pharmacokinetics
Selection of biological
tests depends on the nature and duration of contact. Additionally a
device which comes into contact with broken skin or inserted into body
cavity or implanted in the body needs to be sterile.
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