optimisation and development of the peel-off gel...
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Optimisation and Development of the Peel-off Gel Formulation for
the Decontamination of Radiological Contaminants from Skin
CHAPTER 5
164
5.1 Background
In the present work, an effective and systematic modelling technique is devised to
generate optimal formulations for explicit polymer film applications. These methods aim
at developing quantitative values for not only intrinsic properties, but qualitative
characteristics are developed in order to simultaneously optimise the formulation subject
to the specific radio-contaminants decontamination. The predictive modelling framework
developed is comprised of a) polymer optimisation, b) film forming property, c) peel-off
the film, d) constraint parameters, e) constitutive equations design/optimisation variables
and f) development the peel-off gel formulation (El‐Halwagi et al., 2004; Eden et al.,
2004; Ponce-Ortega et al., 2010). A set of user defined design constraints produces a
subset of different optimisation formulations comprised of different polymer blends,
molecular weights, hydrolysation extents, solvents, and additives. This contribution
illustrates a novel way to evaluate a wide range of polymeric film compounds and
mixtures with fewer testing interactions. Peel-off gel formulation developed is suited for
the application over the open and exposed parts of the body. Gels due to vast network
have comparatively better loading capacity with least leakage problem. It also has the
good stability comparatively with other drug dosages form and does not associated with
breaking and rancidity problems. Hence formulation was developed for the skin
decontamination for localised radiological decontaminants.
5.2 Experimental
The optimisation variables are most often determined by qualitative attributes,
stochastic variables, visual observations and/or design experience. Identification of
an optimal formulation that is suitable for the desired system requires integration
of all the interlacing behaviours of the formulation ingredients. The conventional
approach for the formulation development was selecting constituents that exhibit
desired produced properties and optimising the mixing ratios (El-Halwagi et al.,
2004; Grooms et al., 2005).
Formula constraint equations The formula balance equations are separated into a
reverse simulation problem that includes active pharmaceutical ingredients,
polymer, additive and solvent choices. This assortment of compounds contains
wetting agents, surface tension reducers, and biocides, cross-linking agents,
elastomers, resin hardeners, dyes, pigments and dispersants. The choice of
Optimisation and Development of the Peel-off Gel Formulation for
the Decontamination of Radiological Contaminants from Skin
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solvents is limited not only by the polymer selection, but also by the application.
The initial concentration of solvent present in the coating is the primary driving
force involved with drying time. It is imperative for this part of the overall model
to simultaneously optimise the formulation so that target properties are exhibited
and the overall film behaviour was obtained (Qin et al., 2004).
Design parameters: The primary design parameters are the decontamination
ability, drying time and re-dissolvability. The ability for the film to remove
contaminates is measured by the ratio of radiation detected after decontamination
divided by the radiation present before the film removal. This numeric value is
known as the decontamination factor and is a major point that must be equivalent
or better than other possible decontamination products and processes. Another
parameter where the new formulation must outperform the competing processes is
drying time. It is desired that the film can be disposed of by utilising these same
processing procedures. Other constraints include a simple and effective means to
apply the coating to the personnel’s face and other open body surfaces as well as
removal techniques (Eljack et al., 2005).
Target property variables: The development of a set of target properties allows
this model to utilize reverse property prediction to identify the design alternatives.
This is accomplished through experimentation to determine what property ranges
equate to final film behaviour. This value becomes the viscosity design target of
the qualitative prediction model. By implementing the reverse simulation of
mixing rules and formula concentration models, a set of viable product
formulations that meet the 4000cps design target are determined. These techniques
seem unnecessary when considering only one target property, but when numerous
targets are set, these simplification processes are extremely advantageous
(Kazantzi et al., 2004; Ng et al., 2010).
Decontamination efficacy evaluation: Human tissue equivalent and Sprague
Dawley rat model contaminated with medical-use radionuclides, allowed to air
dry, and then coated with the peelable polymer-based decontamination
formulation developed using wet film applicator. Once the decontamination agent
was peeled-off experimental models were measured for residual activity (Ct). A
plastic sheet was left on the detector which did not interfere with gamma counting
and protected the detector from contamination. A number of experiments were
Optimisation and Development of the Peel-off Gel Formulation for
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performed in the quantitative study of the efficacy of the developed
decontamination agents. Percent removal was calculated. DE of each of the
decontamination formulation was compared quantitatively and 95% confidence
interval. Single factor ANOVA calculations via Excel provided p-value and F-
value data to confirm any statistical differences.
5.3 Results
Formulation was successfully developed and prepared using different parameters of the
optimisation. Model of formula for the peel – off gel was designed according to the
conventional and decoupled model structure. In the conventional model structure different
mixing rules and concentrations of the polymer as well as APIs were extensively studied.
Qualitative parameters such as consistency, viscosity, dry off the film, thickness and ease
of removal were analysed. Design targets were radiological contaminants present over the
body surface and the designed parameters were behaviour and attributes of the friendly
use of the formulation as depicted in figure 5.1.
Fig. 5.1: Decoupling of constitutive equations for reverse problem formulation
Optimisation and Development of the Peel-off Gel Formulation for
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Fig. 5.2: Schematic representation of peel-off Gel formulation design and model decomposition
5.3.1 Optimisation of polymers
Formulation was prepared using three different polymers. Each of the polymers was
optimised individually according to the desired concentration as discussed below:
(i) Carbopol 934 grade
It is a gelling agent which provides appropriate thickness to the formulation.
Concentration of the carbopol was optimised on the basis of consistency of the dispersion
over the skin without breaking of the film. Optimised concentration and their observations
are presented in table 5.1.
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Table 5.1: Effect of concentration of Carbopol 934 polymer over the consistency of
the formulation
S. No. Water (ml) Carbopol (gm) Observation
1 50 0 Solution
2 50 1 Solidified within 24 hours
3 35 0.75 Viscous solution
4 30 0.5, 934 grade Semi solid
5 30 0.5, 934 grade Semi solid
6 30 0.5, 934 grade Semi solid
Inference: 0.5% carbopol 934 is best to prepare formulation
(ii) Optimisation of Polyvinyl alcohol (PVA)
PVA was dissolved in cold water gently with continuous mechanical stirring and allow
swelling for 2-3 hours. Its concentration was optimised based on its film forming nature
as given in Table 5.2.
Table 5.2: Effect of PVA over the consistency and peel off film forming ability
S. no. Water PVA (gm) Observation
1 30 0 Solution
2 30 2 Viscous solution
3 40 5 Sticky film
4 40 7 Thick solution
5 40 6 Peel off comes
6 40 6 Peel off with good film
Inference: 6% PVA (cold) was optimised to prepare peel off gel based on its consistency film forming and peel off property.
(ii) Optimisation of Sodium Carboxymethyl Cellulose (NaCMC)
Carboxymethyl cellulose (CMC) or cellulose gum is a cellulose derivative added as
viscosity modifier or thickener to stabilise emulsions. Polymer dispersed in cold water
and allows swelling on continuous magnetic stirrer. Observation of the polymer
optimisation is shown in Table 5.3.
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Table 5.3: Optimisation of NaCMC
S. No. Water (ml) NaCMC (%) Observation
1 30 0 Solution
2 30 4 Very thick gel
3 30 3 Thick gel
4 30 0.30 Peel gel observed
5 30 0.33 Peel gel observed
6 30 0.33 Peel off gel observed
Inference: 0.33% of the polymer was selected for the formulation development
Table 5.4: Optimised concentration of the ingredients for the Peel off gel formulation
S. No. Ingredients Category Optimised
concentration (%)
1
Disodium edetate /
DTPA
APIs 1.0
2 Polyvinyl Alcohol (PVA) Film former 6.0
3 Carbopol (934 grade) Gelling agent 0.5
4 Sodium-
carboxymethylcellulose
Thickening agent 0.3
5 Methyl paraben Preservatives 0.2
6 Propyl paraben Preservatives 0.02
7 Talcum powder Softening agent 2.0
8 Triethalonamine Alkali 1-2 ml
9 Water Base 100
5.3.2 Preparation of the Topical Peel-off Gel (disodium edetate / DTPA) Formulation
After optimisation of the polymer ingredients, peel-off gel formulation was prepared.
Carbopol 934 dispersed in water with the halp of mechanical stirrer and stirred
continuously until carbopol swell. Polyvinyl alcohol (cold), methyl paraben sodium and
propyl paraben sodium were added in carbopol solution and stirred gently until PVA
swells. To this, Disodium edetate / DTPA (solubilised into 1M NaOH) were loaded gently
and dissolved. Drug solution along with carbopol and PVA were added slowly in swelled
NaCMC under continuous stirring. Triethalonamine added to the obtained solution to
maintain pH and to achieve desired consistency of the formulation. Talcum powder mixed
it to give the formulation opacity. Final volume was made up with the purified water.
After addition of whole ingredients, stirred continuously until a smooth dispersion
obtained. Prepared formulation filled in lacquered plastic containers for further analysis.
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5.3.3 Pharmaceutical Characterisation of Peel-off gel
(i) pH
The pH value of topical peel off gel was determined by using digital pH meter. One gram
of gel was dissolved in 100 ml distilled water and stored for two hours. The
measurements of pH of the formulation were done in triplicate and average values
calculated as given in table.
Table 5.5: Measurement of pH of the formulation
Water 7.6 7.5 7.6 7.5 ± 1
Placebo peel-off gel 7.5 7.5 7.5 7.0 ±0.3
Disodium edetate peel-off gel 7.1 7.5 7.6 7.1±0.3
DTPA peel-off gel 7.4 7.4 7.5 7.1±0.4
(ii) Spreadability
Spreadability of the peel-off gel was found to be 2.1±0.4 cm respectively.
Table 5.6: Spreadability of the Peel-off gel
Parameters Spreadability Weight (g) Length (cm) Time (sec)
Placebo Peel-off
Gel
0.22 1 2.5 11
Na2EDTA Peel-off
gel
0.27 1 2.5 11
DTPA Peel-off gel 0.26 1 2.5 10
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(iii)Viscosity
Table 5.7: Viscosity of the formulations
S. No. Parameters EDTA Peel-off gel DTPA Peel-off gel
1 Sample (g) 1 1
2 Speed (rpm) 70 70
3 Run Triple Triple
4 Run time (sec) 60 60
5 Temperature (0C) 30±0.5 30±0.5
6 Shear rate (min-1
) 815.23 720.57
7 Viscosity (cps) 795±25 770±35
(iv) Visual observation
Visual observation was performed once in 15 days for six months and was recorded in the
following manner
Table 5.8: Visual observation data for peel off gel formulation
Trials Days
0 1 15 30 45 60 90 105 120 135 150 165 180
Gelatin CTG S S S S S S S S S S S S
PVA(6%) FG FG CG CG CG CG CG CG CG CG CG CG CG
Na CMC
(0.3%)
CTG CTG CTG CG CG CG CG CG CG CG CG CG CG
Carbopol-
934
(0.5%)
CTG CTG CG CG CG CG CG CG CG CG CG CG CG
(vi) Accelerated stability studies of optimized Peel-off gel formulation
Accelerated stability studies were performed according to the ICH Q1A guideline.
Table 5.9: Accelerated stability of disodium edetate Peel-off gel
Mean ±S.D.(Shear rate), formulation stored at 40±20C and 75±5% RH
S. No. Time (days) Mean viscosity ± S.D.
(shear rate)
%drug
remained
Log % drug
remained
1 0 815±2.14 100.00 2.0000
2 30 815±2.22 99.58 1.9981
3 60 815±231 99.30 1.9969
4 90 815.68±2.10 99.10 1.9961
Optimisation and Development of the Peel-off Gel Formulation for
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Self-life was determined as the time at which the 95% one-sided confidence limit for the
mean curve intersects the acceptance criterion of 90% percentage label claim. Data were
evaluated using sigmaplotTM
10 software (Cranes Software International, Bangalore,
India). Percentage label claim (% drug remaining) was plotted against time in months to
determine the shelf-life to be 24 months.
Table 5.10: Accelerated stability of DTPA Peel-off gel
Mean ±S.D.(Shear rate), formulation stored at 40±20C and 75±5% RH
S. No. Time
(days)
Mean viscosity ± S.D.
(shear rate)
%drug remained Log % drug
remained
1 0 720.57±2.14 100.00 2.0000
2 30 719.76±2.22 99.44 1.9976
3 60 715.29±231 99.04 1.9958
4 90 715.68±2.10 98.78 1.9947
(vii) Thermodynamic Stability studies
This experiment was performed to see the stress effect and stability on formulations at
low and high temperature of prepared peel off gels. Six cycle between refrigerator
temperature (4°C) and accelerated temperature (40°C) with storage at each temperature
for not less than 24 hours performed. The formulations that were found to be stable at
these temperatures were subjected to Freeze thaw stress test found stable (Shakeel et al, a,
b, c).
Table 5.11: Stability studies of the optimised formulations
Trials Days
1 (4°C) 2 (40°C) 3 (4°C) 4 (40°) 5(4°C) 6 (40°)
Na CMC (0.3) Gel Gel Gel Gel Gel Gel
Carbopol
(0.5%)
Gel Gel Gel Gel Gel Gel
PVA (6%) Gel Liquid Gel Liquid Gel Liquid
Status of the formulation during studies
EDTA Gel Gel Gel Gel Gel Gel Gel
DTPA Gel Gel Gel Gel Gel Gel Gel
Optimisation and Development of the Peel-off Gel Formulation for
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Table 5.12: Effect of Preservatives on optimised formulation
Trials
0 1 15 30 45 60 75 90 105 120 135 150 165 180
EDTA Gel
(without
preservatives)
CTG CG CG CG CG CG CG CG CG CG CG CG CG CG
DTPA Gel
(without
preservatives)
CTG CG CG CG CG CG CG CG CG CG CG CG CG CG
EDTA Gel (with
preservatives)
CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG
DTPA Gel (with
preservatives)
CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG CTG
Result: Visual observation of optimised formulation was found to be clear and stable till 180th
day without any physical damage and fungal
growth.
Optimisation and Development of the Peel-off Gel Formulation for
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5.3.4 Decontamination Efficacy (DE) of Topical Peel-off gel (POG) Containing EDTA /
DTPA
Peel-off gel formulation was primarily screened for decontamination efficacy against
99mTc,
131I and
201Tl. over the human tissue equivalent and rat experimental model using
nuclear medicine technique. DE of Placebo formulation (without decontamination agent),
disodium edetate and DTPA peel-off gel formulations were studied and compared
between groups and within groups. Similarly, solution of disodium edetate / DTPA (0.5-
5.0%) were also applied as negative control. Results of the control data compared with
POG containing disodium edetate / DTPA. EDTA solution was able to decontaminate 40-
55% while DTPA solution could reduced up to 55-65%. Data of DE between both the
models as well as between both the formulations (disodium edetate/DTPA) were
analysed.
Fig. 5.3: Decontamination efficacy of the peel-off gel formulation evaluated against 99mTc found to be 65±3%. Data was found to be significant (p <0.05) compared with the placebo.
Optimisation and Development of the Peel-off Gel Formulation for
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Fig. 5.4: Decontamination efficacy of the peel-off gel determined in percentage of applied radioactivity removal from the contaminated surfaces. EDTA and DTPA peel-off gel formulations were found effective to decontamination up to 55±4% quantitatively recorded to be significant than the placebo (p <0.05).
Status of the peel-off film
After drying, film becomes was able to remove from the applied site and it was soft to
hard. Drying time took longer time (30-35 min).
Optimisation and Development of the Peel-off Gel Formulation for
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Fig. 5.5: Peel-off Gel film drying time was 30-35 min and thickness measured to be
0.05±0.01 mm.
Formulation was found to be significant when compared when the control. Formulation
with the Na2EDTA / DTPA was found not to be effective against the 99m
Tc applied as
radiological contaminant in both the experimental models. A complete film was not
found for the human tissue equivalent model decided to further not investigated for the
toxicity studies.
The epidermis is the most superficial layer of the skin and is composed of stratified
keratinised squamous epithelium which varies in thickness in different parts of the body.
The skin forms a relatively waterproof layer that protects the deeper and more delicate
structures. Blood vessels are distributed profusely beneath the skin. Especially important
is a continuous venous plexus that is supplied by inflow of blood from the skin capillaries.
Optimisation and Development of the Peel-off Gel Formulation for
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In the most exposed areas of the body—the hands, feet, and ears blood is also supplied to
the plexus directly from the small arteries through highly muscular arterio-venous
anastomoses.
Table 5.13: Dry film thickness of the peel-off gel formulation
Formulation Dry film
thickness (mm)
95% C. I.
(+/-
thickness)
% reduction in
thickness
Placebo 0.01±0.002 1.28 80
Disodium edetate
Peel-off gel
0.015±0.001 1.95 75
DTPA Peel-off gel 0.014±0.003 1.29 80
5.3.5 Skin Toxicity
All animals survived, gained weight and appeared active and healthy. There were no signs
of gross toxicity, adverse pharmacologic effects or abdominal behavior. Skin patch where
formulation was applied was found to be normal, e. g., no erythema or edema. No adverse
health effects or deaths recorded during the study.
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Table 5.14: Erythema and edema scoring method for skin reaction
Skin Reaction Score
(A) Erythema and Eschar formation
No erythema 0
Very slight erythema (barely perceptible) 1
Well defined erythema 2
Moderate to severe erythema 3
Severe erythema beet redness to eschar formation 4
(B) Edema formation
No edema 0
Very slight edema (barely perceptible) 1
Slight edema (edges of area well raised) 2
Moderate edema(raised approx. 1 mm) 3
Severe edema (raised more than 1 mm and
extending beyond area of exposure)
4
Table 5.15: Evaluation of reactions (Draize’s method) for Disodium edetate and
DTPA Formulations
Primary Irritation Index (PII)
All animals appeared clinically normal throughout the study. No irritation was observed
on the skin of the rabbits. The Maximum Irritation Response was not applicable. The
Primary Irritation Index of the test formulations was calculated to be 0.0. The irritation
Rabbits number
Aver
age
Combined
Index
1 M 2 M 3 M
24 Hrs
Erythema Score
Edema Score
0
0
0
0
0
0
0.00
0.00
0.00
0.00
48 Hrs
Erythema Score
Edema Score
0
0
0
0
0
0
0.00
0.00
0.00
0.00
72 Hrs
Erythema Score
Edema Score
0
0
0
0
0
0
0.00
0.00
0.00
0.00
Optimisation and Development of the Peel-off Gel Formulation for
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calculations are shown above. Under the conditions of this study, no erythema and no
oedema were observed on the skin of the rabbits. The Primary Irritation Index for the test
article was calculated to be 0.0. The response of the test article was categorised as
negligible.
Table 5.16: Evaluation of Primary Skin Irritation Index (PII)
Evaluations Score
Non irritant 0.0
Negligible irritant 0.1-0.4
Slight irritant 0.41-1.9
Moderate irritant 2.0-4.9
Severe irritant 5.0-8.0
5.4 Discussion
Radioactive contamination results when loose particles of radioactive material settle on
surfaces, skin, or clothing. Internal contamination may result if these loose particles are
inhaled, ingested, or lodged in an open wound. A person who has received a significant
dose from an external source(s) includes an exposure to a large radiation source over a
short period of time or exposure to a smaller radioactive source over a longer time frame.
Such exposure will cause symptoms that depend on the amount of exposure. This includes
nausea, reddening of the skin and fatigue. An extremely high exposure may result in death
of the victim. These symptoms may not appear immediately; it may take several days or
weeks before symptoms are observed. Contaminated people are radioactive and should be
decontaminated as quickly as possible. However, unavailability of equipment or space in
a medical facility related to radioisotope contamination is costly and can impact the
person contaminated. Although liquid decontamination agents can be used to address this
problem, they often require multiple applications with attendant scrubbing and wiping
which can produce large volumes of low-level radioactive waste (Matanoski 1991; Hall
1994; Akleyev 1995; Pollycove 1998; Martin 2006; Kohli 2009; Tazrart et al 2013).
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The guide of the French Nuclear Safety Authority (ASN 2008) is more focused on
decorporation than on decontamination. However, it recommends the use of an acid soap
or Ca-DTPA solution at 25% (10% for eye contaminations), regardless the radionuclide.
At the European level, the European training for health professional on rapid response to
health threats (ETHREAT 2008) also recommends the use of 0.1% bleach or saline.
Among numerous guidelines and recommendations provide by International Atomic
Energy Agency (IAEA 1998) on radiological emergency, only one address the topic of
decontamination. The emergency preparedness response (WHO-IAEA 2002)
recommends a wide selection of products such as potassium permanganate (KMnO4),
DTPA, or hydrogen peroxide (H2O2). The triage, monitoring and treatment handbook
(TMT 2009) is summary of several guidelines, including the WHO-IAEA (2000). This is
a recent and very complete manual for triage and monitoring but lacks detail for use of
treatments in the field. The most comprehensive recommendations describing the view of
the United States about decontamination are those of the Armed Forces Radiobiology
Research Institute (AFFRI) and NCRP report 65, in which dry decontamination is
mentioned. The United Kingdom Health Protection Agency (HPA 2008) the reference
document for a CBRN incident, although no details are given for specific products for
decontamination. For most other countries, no document cites more specific products, and
the European or American documents are often referenced.
It is noted that the majority of authorities are fairly uniform with regard to the initial
method of skin decontamination (water + soap). However, there is less agreement about
more specific methods for certain products such as povidine iodine, which is not approved
by the FDA Food and Drug Administrator (DHS 2003), or bleach, which is discouraged
in certain documents (HPA 2008). Some other products are also used on the field (first
responders) but are not cited in the European recommendations, such as specific
decontamination soaps for the nuclear industry or chemical decontaminants. With regard
to damaged skin, most of the authorities also recommended the use of water or
physiological saline, which is not specific. Wound models are currently under
development using laboratory animals (Griffiths et al., 2012). Such a model would allow
evaluation of different modes of decontamination. Damaged skin is a delicate condition,
especially when the contamination is associated with a chemical burn (Kelsey et al.,
1998). The main action of decontaminating agents lies in the mechanical action of the
water. The water flow, with slight friction, will allow the removal of the contamination
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deposited on surface of the skin so as to avoid its penetration. To prevent internal
contamination, preserve the cutaneous barrier by performing soft washes. The
emulsifying properties of the soap can increase the action of water effectively by trapping
the contaminant and removing it with abundant rinses. The dry preparation cited in NCRP
report 65 (1980) and Fuller’s earth abrade the corneal layer, allowing the removal of
surface contamination only. Chemicals such as hydrogen peroxide, potassium
permanganate, or bleach have an oxidising effect on the radionuclide but may also help
denature organic complexes formed. After the application of an oxidant, a reducer such as
hydroxylamine or metabisulphite must be applied to eliminate the coloration and to
reduce the irritant effects.
Only the effectiveness of washing soap, bleach, and Ca-DTPA has been proven for
technetium, cesium, and some actinides (Gerasimo et al., 1997; Tymenet al., 2000;
Ruhman et al., 2010). Other products have been tested against chemical contaminants
such as the nerve agents VX or soman (GD) (Taysse et al., 2011; Wanger et al., 2007),
but they are not adopted to the needs of a nuclear or radiological emergency. The skin
models used are exclusively animal models (pigs, rats, or guinea pigs), who’s structure
and skin physiology differ from humans (Tymen 2002). These data highlight the need for
relevant tests to adjust their use and optimise their protocols. Furthermore, in case of a
mass casualty, the decontamination process with these products would take a long time
for an insufficient result. Considering the toxicity of a product is essential, because if the
skin barrier is damaged (micro lesions), it will allow a cutaneous transfer of the
contaminant, leading to the internal contamination and a potential on the other organism.
For instance, bleach,hydrogen peroxide, and potassium permanganate can cause burns if
the dilution is badly adjusted in case of panic or emergency. Reducing agents used after
potassium permanganate are also highly irritating, especially sodium metabisulphite or
hyposulphite. The hexachlorophene recommended by the DHS in 2003 was responsible
for the poisoning of several infants in the 1970s (talc Morhange case). Titanium dioxide
remains very volatile and therefore irritating to the respiratory tract,and it is classified as
2B by the IARC (compound may be carcinogenic to humans). Most of the
decontaminating agents do not have an adequate profile insofar as they present major side
effects and are not tested against radionuclides. These facts demonstrate the need for
developing products adapted to skin decontamination and specific for radionuclides that
would be tested on appropriate biological models (Tazrart et al., 2013).
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Therefore, research was conducted on the development of low-volume peel-off
decontamination formulation. Study was begun with an optimisation of different polymers
of the formulation (carbopol 934, sodium carboxymethyl cellulose and polyvinyl alcohol)
for the best application thickness, drying of the gel, minimum time requirements for peel-
off film removal, maximum drug release and decontamination start time for peel-off gel
formulation. In an effort to reduce the number of variables of the study, formulation was
tested side-by-side at a thickness of 0.5 mm and a contact/cure time. The thickness of the
film reduces and eases to peel-off from the surface (Grooms et al., 2005; Lovelady et al.,
2009; Ng et al., 2010).
Beyond these conditions, concentration constants may be useful in estimating probable
effects to further optimise formula for better decontamination efficacy. The practical
significance of formation constant is that a high log K value means a large ratio of
chelated to un-chelated or free metal when equivalent amounts of metal and ligand are
present. Species in solution are generally in formation-dissociation equilibrium, and
displacement reactions of any given metal or ligand by another are possible (Kazantzi et
al., 2004). The addition of a chelating agent to a solution of two or more metal ions leads
to an order of metal ion complexation that is regulated by displacement equilibrium
constants. If the objective is to bind only a particular ion, then enough chelant to combine
with the target ion and all the other ions that are capable of displacing the target ion
should be added. For selective complexation of one metal in the presence of another, a
chelating agent with sufficiently different stability constants for the two metals is
necessary (Eljack et al., 2007; Suardin et al., 2007).
Non-fixed (loose) contamination is easier to remove than fixed. Fixed contamination is an
integral part of the surface and requires special or more aggressive techniques for
removal. In addition, the chemical form of the contamination (adherent particulate,
chemically bonded to surface, etc.) will also influence the choice of technique. If the
chemical form is not known, the general practice is to use the less aggressive techniques
first, then utilise more aggressive techniques only if required. The scale of
decontamination and the peelability complexity of the formulation will greatly affect the
personnel radiation exposure planning. If a person is highly contaminated and will result
in large radiation doses to personnel, a fast and ready to use self-usable decontamination
technique will require for the initial decontamination to lower the radiation dose rates to a
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safe working level. The radiation dose is primarily a function of exposure time and
working distance, so the selected technique should minimise the "hands on" working time
(Edgington et al., 2007; Nápoles-Rivera et al., 2010; Hanley et al., 2010; Edgington et al.,
2011).
Qualitative aspects of the decontamination peel-off gel formulation noted were ease of
application, peelability, odour, and overall user experience. These comments were based
on a wet film thickness of 0.05 mm and a drying time of 25 min. Placebo had the thinnest
consistency, was little bit difficult to apply, more challenging to peel. The consistency
was like that of a thin cake batter and air bubbles could be formed easily within the agent.
It came out of a bottle easily and could be easily spread with the wet film applicator. To
obtain the correct thickness, occasionally formulation with more quantity was added. It
peeled well, but was very elastic and would elongate as it was peeled off (Boone 2007;
Eljack et al., 2007; Suardin et al., 2007).
Disodium edetate was in the middle based on thickness consistency, was easy to apply,
easy to peel, had a low odour and overall user experience was excellent. The consistency
was like that of glue and very smooth. It was easy to squeeze out of a bottle and very easy
to spread over the contaminated areas with the wet film applicator. It was the easiest to
peel and come off in one piece or sheet without changing its shape. Developed Peel-off
gel formulations were the most consistent in decontamination of medical radioisotopes
from the surfaces. Peel-off decontamination formulation offers an advantage over liquid
decontamination agents by providing the potential for a reduced exposure for the people
performing the decontamination as well a substantial reduction in radioactive waste.
Overall, the Peel-off gel formulations worked well, achieving a decontamination
percentage of 60-70%. Radionuclide percent removals with the agents were more
consistent ranging from 50-70% while all three decontamination agents performed
exceptionally well on radionuclide removal from rat skin. Confidence intervals were
fairly small indicating consistency in removal and good laboratory practices were used.
API present in the formulation encapsulated the radionuclide very effectively. To develop
an effective and systematic model to synthesize a formulation of water soluble polymer
film coating for radioactive decontamination and waste reduction (El‐Halwagi et al.,
2004; Grooms et al., 2005; Lovelady et al., 2009; Ponce-Ortega et al., 2010). Quantitative
data were obtained for each of three different peelable decontamination agent
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formulations. Quantitative results concluded that on less porous stainless steel, all three
agents worked equally well performing at 55-65% of contaminants removal.
Ca-DTPA and EDTA are the most used decontaminating products after water. They form
a soluble complex with the radionuclide due to a metal chelation action. The mainly non-
specific action of these products allows a potential action on a broad spectrum of
contaminants that would justify their choice by the authorities. Since these compounds
acts only at the surface by chelation of the contaminants, they are ineffective in case of a
contamination in the upper layers of the skin or in the case of percutaneous penetration.
An osmotic Peel-off gel may be applied to treat these embedded contaminations as soon
as possible after suspicion of the radiological contamination.