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Quality Requirements For
Medical Textiles, PPES / Face Masks
Cytotoxicity Test
Biological Evaluation of Medical Devices -
Part 5, Tests for in vitro Cytotoxicity, ISO 10993-5:2009(E).
In vitro cytotoxicity testing is a rapid,
standardized, sensitive, reliable, and cost-effective means to
determine whether a material contains significant quantities
of biologically harmful extractables.
Qualitative cytotoxicity evaluation is
appropriate for screening purposes, where the cells are
examined microscopically using cytochemical staining if
desired and changes are assessed: for example, general
morphology, vacuolization, detachment, cell lysis and membrane
integrity.
Whereas, quantitative cytotoxicity
evaluation involves MTT assay/ NRU assay/ CFU assay which
measure cell death, inhibition of cell growth, cell
proliferation or colony formation. The number of cells, amount
of protein, release of enzymes, release of vital dye,
reduction of vital dye or any other measurable parameter may
be quantified by objective means.
Any cytotoxic effect can be of concern. It
is primarily an indication of potential for in vivo toxicity
and the device cannot necessarily be determined to be
unsuitable for a given clinical application based solely on
cytotoxicity data. Given the extreme sensitivity of this test,
medical devices demonstrated to be cytotoxic must be assessed
along with in vivo studies to evaluate the risk to human life.
Sensitization
Test
Sensitization (e.g. delayed-type
hypersensitivity) tests are used to estimate the potential for
contact sensitization by PPE, materials and/or their extracts,
using an appropriate model. These tests are important because
repeat exposure or contact to even small amounts of potential
leachable can result in sensitization, which can lead to
allergic reactions.
Skin sensitizers are substances that elicit
an allergic response following contact with the skin, termed
allergic contact dermatitis (ACD) in humans.
Sensitization involves two phases:
-
The first phase is the induction of
specialized immunological memory in an individual following
exposure to an allergen.
-
The second phase is elicitation, i.e. the
production of a cell
mediated allergic response by exposure of a
sensitized individual to the same allergen.
Prolonged use of PPE may cause allergic contact dermatitis and
are may be due to allergen. Allergens causing allergic contact
dermatitis include:
-
Rubber accelerators commonly used in latex and non-latex
gloves
- Zinc Diethyl Dithiocarbamate (ZDEC)
- Thiurams
- Thiazoles and
- Diphenylguanidines
-
Textile dyes in clothing
- Azo dyes
-
Metals in masks and boots
-
Formaldehyde and other preservatives found in
N95 respirators and other surgical masks
The Guinea Pig Maximization Test (GPMT) is preferred test
method for studying sensitization (ISO 10993-10:2010).
Skin Irritation Test
Irritation test is recommended for most PPE.
Skin irritation is to determine irritant effects of PPE and
its extracts on skin tissues. Skin irritation test evaluate
local tissue response characterized by the usual signs of
inflammation—redness and swelling—and sometimes accompanied by
heat and pain. It is reported that residual concentrations of
ethylene oxide present in gas-sterilized devices can produce
an irritant response if they are not reduced to acceptable
levels before the device is used; and residues of such
contaminants as chemical detergents in a particular batch of
materials or devices can cause unexpected irritation responses
in users or patients.
Skin irritation test (Dermal irritation)
-
Topical application for at least 4 hours
-
Erythema & oedema formation
-
Primary or cumulative (for repeated dose)
irritation index
The biocompatibility assessment is a part of the overall
safety assessment of a device. Of course, the primary purpose
of a device biocompatibility assessment is to protect patient
safety. Ultimately, evaluating the biocompatibility of a
device is a risk assessment exercise. There is no risk-free
device or device material. Biocompatibility plays major role
to minimize risk while maximizing benefit to patients while
using PPE/ Medical Textiles. If a device is cytotoxic in vitro
but does not produce any irritation or sensitization responses
in animals, a biological safety evaluation can be performed to
support and document the safety of the device. A Biological
Safety Evaluation Report from an expert toxicologist can be a
strong supporting document for regulatory submissions.
Therefore, it is important that the biological safety of all
PPEs is thoroughly evaluated through adequate testing for
biocompatibility and risk assessment, to ensure their quality
and safety.
References
Biological Evaluation of Medical Devices -
Part 1, Evaluation and Testing within a Risk Management
Process, ISO 10993-1:2018(E).
Biological Evaluation of Medical Devices - Part 5, Tests for
in vitro Cytotoxicity, ISO 10993-5:2009(E).
Biological Evaluation of Medical Devices - Part 10, Tests for
Irritation and Skin Sensitization, ISO 10993-10:2010(E).
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