optimisation and development of the peel-off gel...

Optimisation and Development of the Peel-off Gel Formulation for

the Decontamination of Radiological Contaminants from Skin

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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



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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



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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



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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



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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171

(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



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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



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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.



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174

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.



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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).



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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.



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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



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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



CHAPTER 5

184

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.

optimisation and development of the peel-off gel...

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