CC BY
13
UDC 615.462.011
K. Z. Gumargalieva, G. E. Zaikov, M. I. Artsis, L. A. Zimina, Kh. S. Abzaldinov
EFFICIENCY AND PHYSICO-CHEMICAL CRITERIA OF POLYMER BURN DRESSINGS
Keywords: burn dressings, adhesion, physical-chemical criteria, methods of investigation, sorbtion, desorbtion, mechanical properties,
application.
Based on theoretical and experimental data we found that maximal sorptional ability of burn dressing equals the free volume of the dressing material, calculated from the value of the material density. We found that the study sorption ability water can be used as a model liquid instead of the blood plasma medium. Kinetic parameters were determined from the sorption curves. These parameters showed that the first aid burn dressings markedly differ in the value of the rate or liquid media sorption at stages close to the sorption limits. We established that the air penetrability parameter in wet state decreases abruptly by 2 - 3 orders of magnitude for the majority of tested dressings. We recommended that the air penetrability parameter be determined in wet state which represents the common condition of action for the first air burn dressing. The value of adhesive strength after the end of its action on the wound must not exceed 20 N/m.
Ключевые слова: ожоговые повязки, адгезия, физико-химические критерии, методы исследования, сорбция, десорбция,
механические свойства, применение.
На основании теоретических и экспериментальных данных обнаружено, что максимальная сорбционная способность ожоговой повязки равна свободному объему перевязочного материала, рассчитанному по значению плотности материала. Обнаружено, что вода при исследовании сорбционной способности может быть использована в качестве модельной жидкости вместо среды плазмы крови. Из кривых сорбции определены кинетические параметры, которые показали, что ожоговые повязки для первой помощи заметно отличаются по значениям скорости или сорбции жидких сред на этапах, близких к пределам сорбции. Установлено, что параметр воздухопроницаемости во влажной среде резко уменьшается на 2-3 порядка для большинства проверенных повязок. Рекомендовано определять параметр воздухопроницаемости во влажной среде, которая представляет собой общее условие применения ожоговых повязок для первой помощи. Значение адгезионной прочности после окончания ее действия на рану не должно превышать 20 Н/м.
1 Introduction
The principal medical treatment of burns is the use of dressings, which often worsen the effects of the injury.
It is difficult to estimate the effectiveness of the new burn dressings. Their physico-chemical properties are not usually presented in literature.
This Section firstly discusses this subject. The authors address the complexity of physico-chemical methods of analysis in order to create criteria for an efficienty dressings for a burnier wound surface.
2 Experimental Results and Discussion
2.1 Determination of Sorption Ability of Burn Dressings
At applying the dressings on the burn wound there occurs first the wetting of the surface layer of the material and then sorption of the wound exudate into the dressing volume. In this connection it is necessary to answer the following two questions:
1) What are the components of the exudate of wound and burns, being able to sorb by the material, and what is the way of sorption?
2) What is the maximum sorption of the separate components of the exudate by the dressing material?
The first question had not yet been addressed in the published literature. In regard to the second question, the maximum water sorption of different materials as follows was previously determined [1]. The sample was immersed into the water, dried fast by filter paper and then weighted. Such method did not allow
one to measure the sorption kinetics, and its accuracy of the maximum sorption was low.
The exudate of the wounds contains water, salts, proteins, cells the damaged cells and various low-and high-molecular substances in relatively lower amounts. The composition of edema liquid changes in dependence on the burn degree: the worse the bum is, the higher the content of protein and the lower albumine to globulin ratio [2].
Sorption of wounds exudate may proceed via filling of micro- and macropores, or dissolving in the material matrix.
Let consider sorption of different components of the wound exudate by the dressing material.
Water fills pores and dissolves in the material matrix. Water solubility is defined by the material hydrophilicity.
The solubility of water, salts and other low molecular substances in polymers is the subject to the following rules:
- solubility in hydrophilic polymers is defined by size and charge of low molec ular substance;
- in hydrophobic polymers it is defined by vapor elasticity (the higher vapor elasticity is, the higher is the solubility) [3].
Protein fills the pores of the size up to 10-2 m and may dissolve only in hydrogels of "Hydron" type with water content over 30% by mass.
Cells fill only open pores of the size over 0.1 -
0.2 |im.
Solubility of water in polymers
As above mentioned modern burn dressings represent heterogeneous materials, usually consisting of
several layers. The upper one having the air is, as a rule, more hydrophobic and less porous than the others.
Solubility of water in this layer will define its evaporation from the dressing surface and the heat exchange between the wound and the surrounding. The information about solubility of water in various polymers (Table 1) are shown in the paper [4].
Solubility of water was determined by the sorption method. Extreme values of sorption at the definite pressures of water vapors were calculated from the sorption curves, and then the sorption isotherms were constructed using the method described in the paper [5].
Extreme values of solution ^H o at the saturation pressure were determined by extrapolation of
^H o to P/Ps = 1. The value ^H O equals to the H 2 O 2
solubility of water in polymer.
Table 1 - Solubility of water in various polymers
®
C® _ mc
Cc _
V®P c
-1,
(2.2)
Polymer Solubility, 102 g/g T, K
Cellophane 40 303
Viscose fiber 46 303
Cotton 23 303
Cellulose diacetate 18 303
Cellulose triacetate 11.5 303
Polycaproamide 8.5 303
Polyethyleneterphthalate 0.3 303
Polydimethylsiloxane 0.07 308
Poly(2-oxyethylmethacrylate) 40* 310
Polypropylene 0.007 298
Polytetrafluoroethylene 0.01 293
Polyethylene (= 0.923) 0.006 298
Polyurethane 1* 298
Polyvinylchloride 1.5 307
Note: * is measured by the authors
Maximum sorption ability of burn dressings
Modern burn dressings represent large-porous or fibrillar heterogeneous materials, possessing high free volume. At the contact with the wound the exudate will fill the free volume of the dressing, filling degree being defined by hydrophilicity of the material, the size and geometry of the free volume fraction.
Theoretical
Consider the filling process of the entire free volume of the material by liquid medium. The maximum sorption of the medium by the dressing will be calculated in the following way. Mass of the medium, sorbed by the dressing material, me equals
mc = V„Pc - V0po, (2.1)
where Vw and V0 are the volumes of the dressing after and before sorption of the liquid medium, respectively; pc and p0 are the density of the liquid medium and the dressing material, respectively.
Maximum sorption of the liquid medium in this
case is
mo VqPQ where m0 is the initial material mass.
Two particular cases are possible.
1. There is no swelling of the polymer during sorption, i.e. liquid medium fills the free volume space only. In this case Vw = V0 and
f100 _ Cc _
P c
(2.3)
0.1 g/cm3
C® _ p c Cc " '
P 0
P0
2. For materials possessing low density, p0 <
(2.4)
Maximal sorption of water by burn dressings
Sorption of water by burn dressings is measured using a device developed for this purpose by the authors.
Experiments were performed in the following way. First, the weights of different mass were placed on the perforated plate of the device and the relative device immersing to the water was measured with the help of a horizontal microscope HM. Calibrating curve was represented in "weights masses - depth of device immersing" coordinates in the units of eyepiece of microscope. Angle coefficient equals 0.70 ± 0.02 g/unit.
Subsequently, the sample of a dressing was placed into the device, and the depth of the device immersing during time "h" was measured. The mass of the medium sorted by the material was calculated from the correlation:
mc - 0.70h. (2.5)
The extreme value of the sorted medium mass was determined at t ^ ro. Maximal sorption of the medium by the material was calculated from Equations (2.3) and (2.4).
Table 2 shows experimental and theoretical (calculated from (2.5)) values of CH 2 o and values of
p0, determined experimentally and used for theoretical calculation.
Good correlation was observed between the experimental and theoretical values of CH 2 o for the
majority of dressings. This shows that practically the entire free volume is filled by liquid medium at the contact of dressings with water.
The exception is the "Algipore" dressing, the large pores of which become denser on filling of water entering because of collapse of the pore walls. In the end this leads to the decrease of the total volume of the dressing. Liquid medium may fill not the whole volume of dressings, if the material is sufficiently hydrophobic and poorly wetted with water.
To test this assumption 7 collagen materials were investigated, which differed in the production method.
Table 2 - Experimental and theoretical data of the maximum sorption of water by burn dressings
Covering name (material) CH 2 O, g/g pc, g/cm3
Expe rimental Theo retical
Helitrex (collagen) 32 ± 2 33 ± 2 0.030 ± 0.007
Helitrex (collagen sponge) 58 ± 3 55 ± 3 0.018 ± 0.005
Collagen dressing 1.8 ± 0.1 2.8 ± 0.3 0.350 ± 0.07
Corretium-2 (collagen) 3.5 ± 0.3 3.3 ± 0.3 0.300 ± 0.07
Corretium-3 (collagen) 2.1 ± 0.2 3.0 ± 0.1 0.330 ± 0.05
Combutec-2 (collagen) 77.0 ± 5.0 66.0 ± 3.0 0.015 ± 0.005
Epigard (foamy polyurethane 10.0 ± 0.3 15.0 ± 1.0 0.067 ± 0.005
Silicon-nylon composite 7.5 ± 0.2 7.7 ± 0.5 0.130 ± 0.03
Syspurderm (foamy polyurethane) 6.2 ± 0.2 7.1 ± 0.5 0.140 ± 0.03
Syncrite (foamy polyurethane) 20.0 ± 2.0 22.0 ± 1.5 0.050 ± 0.01
Farmexplant (foamy polyurethane) 12.0 ± 0.5 15.6 ± 3.0 0.064 ± 0.007
Johnson-Johnson (cellulose) 11.4 ± 0.5 10.0 ± 1.5 0.100 ± 0.03
Blood stopping (cellulose) 15.7 ± 0.9 12.5 ± 0.7 0.080 ± 0.006
Tunneling (cellulose) 4.3 ± 0.2 5.0 ± 0.4 0.200 ± 0.005
Switin (cellulose) 18.0 ± 2.0 20.0 ± 1.0 0.050 ± 0.005
Metallized (cellulose-paper) 12.4 ± 0.7 10.0 ± 0.5 0.100 ± 0.04
Needle-perforated (cellulose-viscose) 28.0 ± 2.5 30.0 ± 2.0 0.033 ± 0.007
Viscose 100% 25.0 ± 2.0 30.0 ± 2.0 0.033 ± 0.007
70% of cotton + 30% of viscose 31.0 ± 3.0 33.3 ± 3.0 0.030 ± 0.007
50% of cotton + 50% of viscose 25.0 ± 2.0 28.5 ± 2.0 0.035 ± 0.007
30% of cotton + 70% of viscose 28.0 ± 2.0 27.7 ± 2.0 0.036 ± 0.007
Algipore (vegetable) 30.0 ± 3.0 90.0 ± 5.0 0.011 ± 0.0002
We investigated: density, maximal water sorption, wetting angle and heat effect of water sorption by the material. The latter was determined using the microcalorimeter LKB 2107 as follows. The sample of definite mass was exposed to vacuum in the Butch type
cell, thermostated, and then the excess amount of water was introduced into the cell causing a forced filling of the material volume. The obtained results are presented in the Table 3 and on the Fig. 1.
Table 3 - Density, maximal water sorption, wetting angle and heat effect of sorption of water by different collagens
po, g/cm3 œ / ch 2 о, g/g ф° AH, cal/g
Experimental Theoretical
0.011 74 91 170 34.6
0.016 53 62.5 70 25.4
0.013 49 77 90 30.2
0.013 47 77 110 31.9
0.013 8 77 120 31.2
0.014 4 71.4 110 29.8
0.014 30 71.4 50 27.2
The following conclusions can be made on the basis of tile data presented in the Table 3:
1. Experimental value of CH2 o , is lower than
the "theoretical" one. This may be explained by two causes: the decrease of the total volume (as in the case of "Algipore") and non-filling of a part of the material free volume by water.
2. A satisfactory correlation exists between
the theoretical values of CH2o and AH. Thus, the main reason of the difference between experimental and theoretical values of CH 2 o is evidently the non-filling
of a part of the material free volume by water.
3. The absence of correlation between maximal water sorption and wetting angle, defined on the external surfaces of the material, shows that the values, obtained as mentioned above, do not reflect real interaction of water with internal surface of collagen.
Fig. 1 - The dependence of maximum sorption of water by collagen materials on heat effect sorption
Thus, it may be concluded that for the most number of burn dressings from hydrophilic materials, the maximum sorptional capacity with reference to water may be predicted satisfactorily. To fulfill this it is sufficient to use the Eq. (2.4). For example, the
experimental values of CH o , correlate well with the
free volume part of the materials (Fig. 2). The correlation coefficient is 0.96.
Maximal sorption of plasma by burn dressings Sorption of the blood plasma by burn dressings was determined by a similar method. Plasma was obtained by centrifugation of the conserved blood. The treatment of the experimental results was carried out similarly to the case of the investigation of maximal
Dressing name R, cmx10-2 N, pore/cm
Epigard 2.2 + 0.2 370 + 10
Syspurderm 1.8 + 0.2 266 + 5
Syncrite 2.8 + 0.2 275 +5
Farmexplant 2.2 + 0.2 300 + 10
why the data for C plasma are not shown in Table 3.
Figure 2 - The dependence of cH o on free volume
of the material various burn dressings: 1 - collagen dressing Helitrex; 2 - collagen sponge neutron; 3 -collagen dressing Braun; 4, 5 - artificial leather Corretium 2 and 3; 6 - Combutek-l1; 7 - synthetic dressing Epigard; 8 - foamy polyurethane dressing Syspurderm; 9 - synthetic dressing Syncrite; 10 -foamy polyurohane dressing Famlexplant; 1 - burn face mask; 12 - compositional dressing Biobrant; 13 -cellulose dressing Johnson-Johnson; 14 - cellulose dressing Candall; 15 - cellulose non-adhesive dressing Torcatee; 16 - blood-stopping cellulose dressing: 17 - cotton balling dressing Mesorb; 18 -dressing with tunneling effect; 19 - cellulose dressing with nonadhesive synthetic layer; 20 - cotton balling dressing Svutyn; 21, 22 - metallized dressings; 23, 24 - needle perforated fabric with atraumatic layer; 25 -viscose 100%; 26-29 - viscose + cotton balling
2.2 Study of the Kinetics of the Sorption of Liquid Media by Burn Dressings
The study of the kinetics of the sorption of the wound exudate by burn dressings is of great importance for the estimation of their efficiency.
The difficulties occurs at the mathematical description of the kinetics of the sorption process, connected with the absence of strictly quantitative description of the dressings structure.
Structure of burn dressings
Burn dressings are heterogeneous systems, consisting of several component-phases. As the general attention in dressings must be paid to the material
possessing the maximum penetrability with reference to liquid medium, it is necessary to classify the types of heterogeneous systems.
For example, the penetrable parts of the material are placed under the layer of another weakly penetrable material in the way that diffusing flow is perpendicular to the surface layer. This is the case of double-layered dressings with a dense external layer. The penetrable parts of the material can be dispersed in a continuous weakly penetrable phase.
Dressings, based on collagen and cellulose, possess fibrillar structure and the fibers are randomly placed. In some cases spatial orientation of fibers is present. The sufficient amount of open pores in the dressings of such type is large but the open pores possess irregular form and great tortuosity in the direction of mass transfer. Modern burn dressings are multilayered with more dense external layer. Table 4 shows the mean-radius of macropores and their amount per unit of square for dressings, based on polyurethane.
Table 4 - Mean-radius of macropores and their amount per unit of square N for dressings, based on polyurethane
Dressing name
Epigard
Syspurderm
Syncrite
Farmexplant
R, cmx10-
2.2 + 0.2
1.8 + 0.2
2.8 + 0.2
2.2 + 0.2
N, pore/cm2
370 + 10
266 + 5
275 +5
300 + 10
All dressings possess a mean-radius of macropores in the range of (2.0 4 3.0)x10-2 cm and a sufficiently narrow distribution (Fig. 3).
N 3.0
2.0
1.0
0
0.5 1.0 d, mm
0.4 0.6 d, mm
1,0 d, mm 2,0 0 0,1 0 3 °'5 <>,mm
Fig. 3 - Curves of distribution of pores by sizes for different dressings: 1 -Farmexplant; 2 - Syncrite; 3 - collagen dressing Braun; 4 - Syspurderm
Theoretical
The detailed analysis of a number of mathematical models and results of experimental investigations of heterogeneous systems was performed by Barrer [6].
Dressings are of a membrane form. If a membrane is in contact with the solution in a way that
or
m
the concentration at one of its surfaces equals C0 and at the other equal 0 at t = 0, then the total amount of the substance entered the membrane during time t( mt), is
given by the equation:
m 8
—1 -—rexp
mt n2
Dn 21
l
2
(2.6)
where mœ is the amount of substance, entered the membrane at t ^ œ, i.e. in the equilibrium; D is the coefficient of substance diffusion in the membrane; l is the membrane thickness.
The following correlation is satisfactory for the initial part of the kinetic curve of sorption:
m,
m.
• = 2
Dt nl2
12
(2.7)
The Eq. (2.6) was obtained for homogeneous material assuming that D does not depend on concentration of the substance in membrane. From Eq. (2.6) it is possible to calculate D value and time of membrane saturation by the substance up to a definite limit. For example, time of saturation up to
mt
m.
= 0.85 is calculated from the correlation:
^ 0.85
6D
(2.8)
and m 1 = 0.97 is reached during the time
m r
T 0.97 -
3D '
(2.9)
Both these correlations may be applied for practical calculations.
As it was mentioned above, the calculation of diffusion coefficient in heterogeneous systems is very difficult.
According to ideas accepted in the present time, the penetration of liquid into porous body is ruled by the laws of capillarity. These ideas are successfully applied for interpreting the penetration of water into paper, leather, fabrics, etc. [7].
Capillary pressure, which is the driving force of liquid to rise, is determined from the Jurene equation [8]:
2y i cos0
Pk -
(2.10)
where yi is the surface tension of liquid; 0 is the wetting angle; r is the capillary radius.
The equation, taking into account real structure of porous body, was obtained by Deriagin [8].
Experimental
Kinetics of sorption of water and blood plasma was investigated using the device for the maximal sorption of water.
Fig. 4 shows typical kinetic curves of sorption of water and plasma by various dressings. All curves are satisfactorily described by Eq. (2.7). Table 5 shows the
values of
D
l
^L and the value of x08
2
calculated
according to Eq.2.8).
Table 5 - Values of D eff and x0 85 for different burn i2 ' dressings in water and plasma at 37°C
Dressing name (material) Deff • 103, s l2 T 0.85 • 10 3, s
Water Plasma Water Plasma
Helitrex (collagen) 2.5 ± 0.3 1.3 ± 0.2 3.9 ± 0.2 7.0 ± 0.3
Helitrex (collagen sponge) 6.6 ± 0.6 3.3 ± 0.4 1.5 ± 0.1 3.0 ± 0.15
Corretium-2 (collagen) 4.7 ± 0.4 2.5 ± 0.3 4.1 ± 0.2 8.0 ± 0.4
Combutek (collagen) 7.0 ± 0.7 3.5 ± 0.4 1.4 ± 0.1 3.0 ± 0.15
Syspurderm (foamy polyurethane) 2.3 ± 0.3 1.1 ± 0.1 4.3 ± 0.2 8.6 ± 0.4
Syncrite (foamy polyurethane) (9.8 ± 0.8)* (5.0 ± 0.5)* 90 ± 10 200 ± 10
Switin (cellulose) (4.5 ± 0.4)* (2.2 ± 0.2)* 210 ± 20 420 ± 35
Needle-perforated (cellulose) 35 ± 3 17 ± 1.7 0.3 ± 0.02 0.6 ± 0.05
* Must be multiplied by 1С
4 t,min
5 10 t,s 2 4 6 8 t,min
Fig. 4 - Curves of solution of water and blood plasma by different burn dressings: 1 - water - by needle perforated material; 2 - plasma - by needle perforated material; 3 - water - by polyurethane dressing Syspurderm; 4 - plasma - by Syspurderm dressing
The following conclusions could be made from the Table 5 data:
1. Burn dressings differ significantly in their rates of sorption of liquid media.
r
2. The rate of sorption is determined by the pores size and the material hydrophilicity.
2.3 Determination of Vapor Penetrability of Burn Dressings
With multilayered dressings, the external layer of is more dense than lower one which regulates the mass transfer of water from the wound into the surrounding. The process of mass transfer of water through the material layer is often called aquapenetrability or vapor penetrability.
Penetrability and diffusion of water in polymers were the subject of numerous investigations, the results of which are generalized in the list of reviews and monographs [4, 9] and are presented in Table 6. The mass transfer of water molecules in polymers possess a list of features. In hydrophilic matrices the interaction between water molecules and the material matrix is weak (low solubility). Nevertheless, the interaction of water molecules with each other stipulate a specific transfer mechanism.
Table 6 - Penetrability and diffusion of water vapors in polymers [9]
Polymer T, K P 0 P-1015, mol-m/ m2-s Pa D-1012, m2/s
Cellulose 298 1.0 8500 —
Regenerated cellulose 298 0.2 5700 0.1
Cellulose acetate 303 0.5 - 1.0 2000 1.7
Cellulose diacetate 298 1.0 15.7 —
Cellulose triacetate 298 1.0 5.5 —
Ethylcellulose 298 0.84 7950 18
Polydimethyl organosiloxane 308 0.2 14400 7000
Polyethylene (= 0.922) 298 0 - 0.1 30 23
Polyethylene terephthalate 298 0 - 0.1 58.6 0.39
Polypropylene 298 0 - 0.1 17 24
Polyvinyl chloride 303 — — 2.3
Poly caproamide 298 0.5 134 0.097
In hydrophilic materials the interaction between water molecules and hydrophilic groups of the material matrix stipulates high solubility of water in the matrix and increased aquapenetrability.
Thus, high aquapenetrability may be the property of hydrophobic as well as of hydrophilic materials, however the causes will be different. For example, in hydrophilic polydimethylorgano-siloxane the high mobility of water molecules is stipulated by high mobility of the chain units in this polymer. That is why despite low solubilities of water in
polydimethylorganosiloxane the coefficient of aqua penetrability is significant.
On the opposite, in regenerated cellulose the diffusion coefficient is low because only the dissolved water molecules which are not connected with the matrix of this polymer participate in the mass transfer. In this case high value of aquapenetrability is stipulated by increasing the desolved water content in regenerative cellulose which increases the part of water molecules participating in the mass transfer. This in turn leads to the increase of both diffusion coefficient and penetrability coefficient.
Theoretical
The mass transfer of water through a porous body is practically equal to that of gases in a polymer, provided there is no interaction between water molecules and the matrix of polymeric material.
Since the hydrophilic materials are commonly used for the production of dressings, which actively interact with water molecules, the diffusion should be considered simultaneously with absorption.
As a rule, the rate of the absorption process is significantly higher than the diffusion rate. Therefore, it can be assumed that the absorption equilibrium is immediately reached, and the concentration of water in the material ch O is obtained from the following
equation: acH2о _
at "
D
a2 с
H 2 о
H 2 O"
ax2
acH 2 о
at
(2.11)
where D is the coefficient of water diffusion in the
H 2 O
material; x is the diffusion coordinate; ca is the
H 2 O
concentration of the absorbed water.
The concentration of the absorbed water can be
calculated for the particular cases. For example, if the
concentration of functional groups, capable to link water
mole cules irreversibly, is limited and equals Cf, we can
assume that the bonded water molecules no longer
participate in the diffusion process, but form domains
on which fast absorption occurs.
For the case when the concentration of water
on one of the surfaces (x=0) is constant and equals
C0 , the reaction zone reaches the second surface of H 2 O
the membrane, which is l thick, during the time t [10].
Thus, during the time t there will be no water flow through the surface X = 1 on the membrane exit, and then stationary flow will be set immediately. The amount of water passed through the membrane will equal
'h , о
D
aC
h , о
H , о
l
• S • t,
(2.12)
ACH
where S is the square of the membrane; 2O is the
l
concentration gradient. If the solubility of water in the material is ruled by the Henry law: Ch 2 o =°P, (213)
where P is the pressure of water vapors over the material; then substituting (2.13) into (2.12) we obtain the following equation:
aP,
mH2O - DH2O H2O_pSt
(2.14)
Considering the diffusional coefficient Dh о
being equal:
h 2 о
D
H2O UH2O'
we obtain
PH 2 O
mH 2 O
AP•S • t
(2.15)
(2.16)
Experimental
Aquapenetrability of burn dressings was determined on the device. The values of penetrability coefficients were cal culated from the Equation (2.16).
Table 7 shows the values of coefficients of aquapenetrability PH 0 for various burn dressings.
Table 7 - Values of aquapenetrability coefficients of burn dressings at 37°C
Dressing name (material) Ph2o • 109, mol-m/m2-s-Pa
Helitrex (collagen) 1.6 + 0.1
Helitrex sponge (collagen) 11.0 + 1.0
Brown dressing (collagen) 6.6 + 0.6
Syspurderm (foamy polyurethane) 0.8 + 0.2
Syncrite (foamy polyurethane) 1.2 + 0.2
Epigard (foamy polyurethane) 4.3 + 0.4
Farmexplant (foamy polyurethane) 3.3 + 0.3
Biobrant (silicon- 1.6 + 0.16
polyamide)
Johnson-Johnson 2.0 + 0.2
(cellulose)
Perforated metallized 9.0 + 0.7
dressing (cellulose)
Face mask 2.5 + 0.2
dressing (cellulose)
Burn towel (cellulose) 5.4 + 0.5
50% cotton + 50% viscose 8.0 + 0.7
70% cotton + 30% viscose 8.0 + 0.7
100% viscose 7.0 + 0.7
2.4 Determination of the Air Penetrability of Burn Dressing
As it was mentioned in the Sect. 2.1, active sorption of the wound exudate occurs during several minutes after the burn wound is closed by dressing. Further on, there proceeds the evaporation of water from the external side of the dressing. This leads to the change of the state of exudate in the material mass. On the whole, this changes penetrability of the dressing with respect to air. In this case in order for anaerobic conditions not to be created in the wound, it is necessary to provide optimal air penetrability during the entire period of application.
The data on penetrability of dressings according to dry air are known in literature. Thus, for example, it is recommended [11] to determine air penetrability with the help of industrially produced VPTM-2 device. This device records automatically the amount of the air, passed through the dressing of the known square during time t at pressure oscillations of about 5 mm H2O. However the application of such device does not allow us to investigate the air penetrability of dense materials such as foamy polyurethane compositions, and most importantly of dressings in wet state.
Penetrability of various materials according to oxygen and nitrogen
The coefficient of gas penetrability (as well as of vapor penetrability) is calculated according to the formula (2.16).
The literature data on penetrability or various polymers according to the oxygen and nitrogen are given in Table 8.
Table 8 - The literature data on penetrability or various polymers according to the oxygen and nitrogen
Polymer Penetrability coefficient, (mol-m/m2-s-Pa) x1015 Separation coefficient
O2 n2 O2 - N2
Polycaproamide 0.013 0.0033 3.8
Polyvinylchloride 0.022 0.008 2.8
Polyurethanic elastomer 0.032 0.10 3.2
Polyethylene (p = 0.922) 0.35 0.13 2.7
Polystyrene 3.13 0.73 2.9
Teflon 2.07 0.67 3.1
Ethylcellulose 3.2 0.93 3.4
Polydimethyl siloxane 168 83.0 2.0
Silicon rubber 200 87.0 2.3
As it is seen from the data presented in the Table 8, the penetrability of polymers may differ by four orders of magnitude. Special attention should be paid to high gas penetrability of polydimethylsiloxane and compositions on its basis, which is the result of the increased solubility of gases in them at high rate of diffusion (Table 9).
Table 9 - Values of penetrability coefficients P (mol-m/m2-s-Pa), diffusion D (m2/s) and solubility ct (mol/m3Pa) of gases into polydimethylsiloxane at 20°C [12]
Gases P-1015 D-1010 CT-106
O2 83 23.3 36
N 164 30 55.6
CO2 720 — —
Penetrability of porous materials, filled by liquid medium
A short list of studies considering the investigations of gas penetrability of polymeric membranes, in con tact with a liquid is given in [13].
It was observed, that the sorption of liquid by a polymer leads to a decrease of gas penetrability coefficient in comparison with the liquid free polymer.
Theoretical
Let us consider the mass transfer of the air through porous body in two cases: one in which the free volume of all pores is filled by the air and the other with free volume filled by liquid medium. Porous body may be presented as consisting of two phases: the material forming the body's carcass and free space.
We also assume that pores possess cubic form and are disposed in the volume of the body, not joining each other. Such model is sufficiently suitable for porous burn dressings.
Let us determine the total thickness of the body in the direction of the mass transfer, total thickness of free space, occupied by pores, and total thickness of the layer, occupied by the material.
The total thickness of the body in the direction of the mass transfer is V
l Z
S
(2.17)
where V and S are the volume and surface, respectively. Total thickness of the free space occupied by pores is
(2.18)
Q pores = l Z Q13 = V • Q13
v
where q = pores is porosity.
pores V
The total thickness of the layer, occupied by the material, is
V'
S
Thus the air passing through the porous body will overcome the resistance of two layers, each possessing its own penetrability coefficient with respect to air.
Total penetrability coefficient Ps or the porous body equals
mat
l Z
-l = V (1 _ Q1/3 )
■pores с \ I
(2.19)
1
pores
mat
Pv lvP
AZ Z pores
l Z Pmat
(2.2G)
where Ppores and Pmat are penetrability coefficients of the medium, presenting in pores; and the material, forming the body's carcass, respectively.
Let determine the ratio of penetrability coefficients of the porous body according to air, when its pores are filled by liquid and air.
P
Z(l)
P Pa
mat
+1
P
Z(a
where
Pm
Pi
Q
1/3
1 - Q13
Values of Pmat are shown in Table 10.
(2.21)
(2.22)
Table 10 - Values of the coefficients of penetrability, diffusion and solubility of the oxygen in air, water, plasma and blood at 37°C (dimensions as in Table 9)
Medium P D CT
Air 2.54G-9 2.74G-5 9.44G-5
Water 7.4^1G-14 3.G•1G-9* 2.54G-5*
Plasma — 2.G4G-9* —
Blood 1.4•1G-14 1.4•1G-9* LG^m-5*
* The values were taken from [13]
Values of Pair and Pl can be estimated from the coefficients of diffusion and solubility of oxygen in air, water, plasma and blood at 37°C.
Values of penetrability coefficients of the oxygen in various media may be calculated according to the following expression:
P = Da. (2.23)
For any material Pair>>Pmat, so we obtain more simple expression:
PZ(air) _ Pm
Pz( l)
4
mat
1
(2.24)
As for the majority of the dressings §>>1, and Pmat and Pl are of the same degree, the decrease of air penetrability of the dressing at pores filling by liquid must be then significant.
Experimental
Air penetrability of burn dressings was determined using the de vice developed for this purpose.
Two types of experiments were performed: determination of air penetrability for dry air and determination of air penetrability of dressings, preliminarily saturated by water (in conditions of maximal sorption of water), for humid air.
It has been shown by special experiment that air humidity (from 40 to 100%) does not practically influence the rate of penetration.
The experiments were performed according to the following scheme. At first we determined the time of filling by air of polyethylene sack of 45 1 volume in conditions, when the sample was not in the cell. This time (the constant of the device) depended on pressure in the system (p):
lg1 = -2.00 + 0.44lg p. (2.25)
The time of polyethylene sack filling at p=100 Pa was selected as the standard. At T=(21±l)°C, to=16.0 ± 0.1 min.
Subsequently the time of polyethylene sack filling with the sample was placed into the cell was similarly determined (Fig. 5).
It was observed (Fig. 5) that the dependence of tx on p is described with the same slope as in (2.25) for all investigated dressings in conditions of the dry air penetration:
lg f = _ A,
0.44lg p
(2.2б)
where Ax is the constant depending on structure and properties of the dressing material.
Thus
4.1 4.3
IgAP, Pa
Fig. 5 - The dependence of l/lg(x) on pressure in the system for dry air: 1 - needle perforated material; 2 -collagen sponge; 3 - Syspurderm; 4 - Syncrite; 5 -cellulose dressing Svulyn; 6 - Farmexplant; 7 -Epigard
At bubbling humid air through the dressing saturated by water, the slope increased significantly. That is why it is necessary to perform several experiments for each dressing at different pressures in order to extrapolate tx to the pressure of 100 Pa with the required accuracy (Fig. 6).
f i >
The increase the slope of lg _ — lg p at air
V tx J
bubbling through the dressing saturated by water was attributed to the change of the material structure of the dressing resulting from the change of forms and sizes of macropores. This is often accompanied by a decrease of the total volume of the dressing.
Coefficient of air penetrability of the dressing (Px) was calculated according to the equation: n mlx
Px = o--n-\ (2.27)
X S-t •(( — 10)
where m is the polyethylene sack bulk equal 2 moles of air at (21±l)°C; S the surface square contacting with the bubbling air, equal 1.8-10"3 m2; p=100 Pa.
IgAP, Pa
Fig. 6 - The dependence of 1/lg(x) on pressure in the system for humid air: 1 - needle perforated material; 2 - Farmexplant; 3 - Combutek; 4 - Syspurderm; 5 -compositional dressing Biobrant (silicon-polyamide); 6 - Epigard
Px = 11-
l.
(2.28)
(tx — 10)
The value of air penetrability coefficients for the dressings dry and saturated by water are shown in Table 11.
From the data shown in Table 11 we see that on saturation with water a significant decrease of air penetrability takes place for all dressings, except for the "Biobrant"
Penetrability coefficient for dry dressings can be calculated according to the following equation:
QV3 (1 + q1/3)
_1
PE(air
■ + ±-(2.29)
p
lair I "air xmat
Pair is obtained from the expression (2.23) using D=2.7-10-5 m2/s and 45 mol/m3 (solubility at the atmosphere pressure). The value of Pair is 1.2-10"3 mol-m/m2-s-Pa. The values of Pi(ajr) were taken from Table 11.
Values of Pmat were calculated from Eq. (2.24).
Table 11 - Coefficients of air penetrability for dry and water-saturated burn dressings at temperature of (21±l)°C
Dressing name (material) Coefficient of air penetrability, mol-m/m2-s-Pa
Dry Swollen
Helitrex (collagen) 2.7-10-5 0
Combutek (collagen) 1.1-10-3 0
Epigard (foamy polyurethane) 1.3-10-4 1.3-10-5
Syspurderm (foamy polyurethane) 1.3-10-4 1.0-10-6
Syncrite (foamy polyurethane) 1.1-10-3 4.0-10-5
Farmexplant (foamy polyurethane) 4.5-10-5 0
Biobrant (polyamide + silicon) 1.8-10-4 7.0-10-5
Johnson-Johnson (cellulose) 1.6-10-4 3.0-10-6
Needle-perforated material (cellulose) 1.1-10-3 —
The values of P can be obtained from
X(H 2 °j
the following equation:
1 Q
1/3 (1 + Q1/3 )
P
Z(H 2 о)
(2.30)
- mat
According to the calculations of , its
Z(H 2 O)
values fall close to 10-8 mole-m/m2- s-Pa for the majority of dressings. It is this result which reveals the extremely low air penetrability for the listed dressings.
For some dressings the value of p
Z(H 2 O)
is
significantly higher than 10- mole-m/m • s-Pa. This can be explained by two effects:
1. The presence of the air flow along the surface of pores (surface flow) [10];
2. The pressure of channels in the materials that are free of water.
To test these suppositions additional investigations are required.
2.5 Determination of Adhesion of Burn Dressings
Adhesion properties play a key role in the dressing performance. On one hand the lower layer of the dressing must be easily wetted, providing good adhesion of the dressing to the wound. On the other hand, the surface energy on the dressing - wound interface must be minimal to provide the smallest trauma on its removal from the wound.
Theoretical
The adhesive strength characterizes the ability of an adhesive structure to preserve its integrity. The adhesive strength as well as the strength of homogeneous solids is of kinetic nature. That is why the rate of tension increase and temperature affect the adhesive strength and the scale factor (i.e. sample dimensions) are also of great importance.
Different theories of adhesion of polymers were previously suggested [14].
1. Mechanical theory (MacBain), according to which the main role is devoted to mechanical filling of defects and pores of the surface (dressing) by the adhesive (blood).
2. Adsorptional theory (Mac-Loren) considering adhesion as a result of the performance of molecular interaction forces between contacting phases. According to this theory low adhesion, for example, may be reached between a substrate (dressing) with nonpolar groups and polar adhesive (blood).
3. Electrical theory (Deriagin) is based on the idea that the main factor controlling the strength of adhesive compounds rests in the double electrical layer which is formed on the adhesive-substrate interface.
4. Diffusional theory (Vojytzky) considers the adhesion as a result of interweaving of the polymers chains.
5. Molecular-kinetic theory (Lavrentiev) assumes that a continuous process of restoration and breakage of bonds proceeds in the zone of adhesive-substrate contact. Thus, the adhesive strength is defined by the difference between activation energies of the breakage and formation of bonds, and also depends on the correlation between the amount of segments participating in the formation of bonds and averge amount of molecular bonds per unit of the contact area.
In recent years, the thermodynamic concept received the most attention. There, the main role is devoted to the correlation of surface energies of adhesive and substrate.
Thermodynamic work of adhesion of a liquid to a solid (Wa) is described by the Dupret-Jung equation:
Wa = y l (1 - cos9), (2.31)
where yi is the surface tension of liquid; 0 is the wetting angle.
Substituting Jung's equation into (2.31)
y s-1 =y s -y s-1 cos0, (2 32)
we obtain the correlation
Wa =y s +y l-y s -1, (2.33)
where y s and y s _ l are the surface tension of solid
and of the solid-liquid interface, respectively.
It follows from Eq. (2.33) that the higher is Wa,
the larger are the values of y s and y l while y s -1
are smaller. However, according to (2.33) the increase
of y s must, on one hand, lead to the growth of Wa,
and, on the other hand, to an increase of y s -1. That is
why the increase of the surface tension of the substrate is accompanied by the action of two effects. The necessary condition of the adhesive strength is
y l >> y s.
Values of y 1 and Ws- H O for different materials are shown in Table 12.
Table 12 - Values of the surface tension and thermodynamic work of adhesion of various materials [15]
Material ys, mN/m Ws - H 2 O > mN/m
Polytetrafluoroethylene 18.5 83
Silicon rubber 21.0 78
Polyethylene 31.0 99
Polystyrene 33.0 105
Polymethylmethacrylate 39.0 103
Polyvinyl chloride 39.0 101
Polyethylene terephthalate 43.0 104
Polycaproamide 46.0 107
Glass 170.0 222
The value of y 1 for blood is 55.0 [16].
Experimental
Table 13 shows adhesive strength of various burn dressings and the angle of wetting by water also.
Table 13 - Adhesive strength (A) and the angle of wetting by water (0) of various burn dressings
Dressing name (material) A, mN/m 9°
1 2 3
Corretium (collagen) 220 + 20 75 + 2
Syspurderm (foamy 210 + 20 —
polyurethane)
Epigard 350 + 50 125 + 3
(foamy polyurethane)
Farmexplant (foamy 200 + 20 130 + 2
polyurethane)
End table 13
1 2 3
Bern-pack (cellulose) 170 + 20 —
Biobrant 70 + 10 —
(silicon-polyamide)
Johnson-Johnson (cellulose) 20 —
Blood stopping non-adhesive dressing (cellulose) 20
Dressing with metallized lower layer (cellulose) 170 + 50 —
3 The Model of a Burn Dressing Action
Three main processes proceed at the application of a dressing to the wound:
1. Sorption of the wound exudate by dressing.
2. Water evaporation from the dressing
surface.
3. Mass transfer of gases through the dressing in conditions of the proceeding of sorption and evaporation processes.
It was found that sorption of the liquid media (water, plasma) proceeds fast and reaches the limiting value (maximal sorption ability) after several minutes for the most number of dressings, i.e. during the time sufficiently lower than that of the dressing action (2-3 days).
The mass transfer of gases (oxygen and nitrogen) through the dressing, is 2-4 orders of magnitude slower with wet samples, than with the dry ones in similar conditions.
Next, we consider the water evaporation from the dressing surface.
3.1 Evaporation of Water from the Dressing Surface
The dressing is saturated with water in air at 20°C temperature and 50% humidity. The temperature of the dressing surface is 32°C. This condition is chosen to take into account the temperature gradient in the matrix of the dressing.
Let us determine the amount of water, evaporating from the surface of the dressing during a given time period under stationery air, atmospheric pressure, and the dressing surface is completely saturated by water.
The partial pressure of air at 20°C and 50% relative humidity equals:
Ph2o = 1.26-10—3 kg/cm2, Pair = 1.02 kg/cm2.
P
For air at 32°C in the saturation state: H 2 O = 4.85-10-2 kg/cm2,
Pair = 0.98 kg/cm2.
The values for density, viscosity, heat conductivity and heat capacity of the air at the average temperature of 26°C equal:
p = 1.185 kg/cm3; ^ = 1.861-10-6 g/m • s;
X = 6.1-10—6 kcal/m - s - grad;
Cp = 0.24 kcal/k - grad.
After mathematical transformations using the method, described in [17], we may obtain the following equation for the mass transfer of water in dressing:
P
"(Pi -P2) '
(3.1)
W = amR T
R - T Pav
where am is the coefficient of heat conductivity; pav is the average value of the mixture density over the surface and near the surface of the dressings; p-i and p2 is the partial pressure ph o at 37°C and 20°C,
respectively; R is the universal gas constant; P is normal pressure.
Substituting numerical values for the dressing of 1x1 m size, we obtain:
W = 1.2-10-1 g/m2s.
If the dressing surface is not completely occupied by water, we should apply the following correlation:
Cs
w =
C0
îf((2O). 1.2-10-1 g/m2s
rf (H 2 O)
(3.2)
where C and C0 are the surface
surf (H 2 O) surf(H 2 O)
concentration of water on the external side of the dressing and free water surface, respectively.
3.2 Sorption of Fluids by Burn Dressing from Bulk Containing a Definite Amount of Fluid
Let us consider the case, where the burn dressing is applied to a wound containing a definite amount of liquid. Assume that the dressing of a membrane of a given size (thickness and surface area S) is in contact with the solution of the restricted bulk V,
which contains a C0
concentration of diffusive
'0(s—s)
substance. As the dressing is saturated by this substance, the concentration of the latter in the bulk will decrease.
The solution of the diffusional equation has the following form [17]:
m 2a(1 — a)
= 1 --
m.
2 2 a q
exp
4Dq21
2
(3.3)
1 + a-
where q is the positive solution of the characteristic equation
t V
tgq = aq; a = —, oSl
where o is the coefficient of distribution of the substance between the membrane and the solution.
When a sufficient part of the substance in solution is sorbed by the membrane, the value of a is small and a more simple expression can be used:
mt
; m
1 --
(4rcD1 /12 )
12
(3.4)
From Eqs. (3.3) and (3.4) we obtain two important correlations. Sorptional ability of the
a
dressing, i.e. the part of the substance sorbed from the solution in the equilibrium conditions, equals:
X 1
— = (3.5)
m0 1 + a ' '
Thus, for the efficient action of the dressing it is necessary that the concentration C to be as high as possible in relation to the products of metabolism and toxins. Relating to water Ch o ~1, it is desirable the
dressing volume (l-S) to be close to that of the exudate of wounds V.
The time of reaching 0.85 degree of maximum sorption of liquid media by the dressing equals:
Т 0.S5 = 12
a 2 • 12 rnD
= 12
V2
wDCT 2S 2
(3.6)
It depends on many parameters, each being able to affect in order the time of completion of the sorption process.
3.3 Mass transfer of water from wound info the surrounding
Generally the change of the water amount
under the dressing in the wound (mH 2 o ) is
determined from the correlation derived from Eqs. (3.2) and (3.4):
m(„_O) = V • C„ _ - m,
и 2O "'и 2 O(dressing)
1 --
(4wDt /12 )
V2
(3.7)
Cs,
fM x 1.240-1 • S• t.
C°
rf (и 2O)
Let consider the application of the correlation (3.7) for the following case. The wound characteristics are:
S = 10-2 m-2,
CH2O = 106 g/m3, m H 2 o = 50 g, V = 5^-5 m3
a3, m H
12 о ~ H 2 о
-2 ™-2 i _ in-3 ,
S = 10-2 m-2, l = 10-3 m, CT H 2 O = 1
C
sur]
f (и 2 о)
C
= 0.5.
0
surf (H 2 O)
For these conditions
25 •Ю-10 2 Т = 12---г = 9.5 • 102 s (or ~ 15 min),
m
-9 1 n-4
Я 10^ • 10 1
m
1 +
5 • 10
-5
= 0.17 or S.5 g.
10-2 -10"3
During the same time the following amount of water will evaporate from the dressing surface:
m evap(H 2 O) < 05 • I-2 • I0-' • 950 • I0-' = 06 g,
i.e. the rate of evaporation is signillcantly (14 times) lower than that of water sorption by the dressing. All the amount of water from the wound (wound exudate) will evaporate during the time:
50
0.5 • 1.2 • 10-1 •Ю-2
= S.3-104 s or ~ 23 hours.
4 Criteria of Efficiency of the First Aid Burn Dressings
4.1 The Requirements to the First Aid Dressings
The first aid burn dressing must meet the following criteria:
1. Sorption of the wound exudate, containing products of metabolism and toxic substances, during the period of the dressing action (24 - 48 hours).
2. Wound isolation from infection of the external medium.
3. Optimum air and water transfer between the wound and the surrounding.
4. Easy removal from the wound, causing no damage to the wound surface.
4.2 Characteristics of Burn Dressings
Below we list the characteristics of the burn wounds based on approximate estimations, discussed above. Note that no quantitative data are reported in the literature.
4.3 Rational Criteria for the Efficiency of the First Aid Burn Dressings
Sorptional ability of dressings
The burn wound (II - III degree) releases on the average 5403 g/m2 of the exudate. As it is seen from the Table 1, the water amount is about 90%. The sorption of different components of the exudate proceeds with dif ferent rates. In this case, the free volume of the dressing material will be first filled with water. The diffusion of proteins and cells takes place in space occupied by water.
Modem burn dressings possess porosity of 0.9 (Table 2) and almost the entire free volume can be filled with water (Fig. 2). Maximum sorption ability for such dressings equals Ph 2 o
CH 2 о
p
and the amount of the liquid sorbed per square unit is:
m
CH2о -p-1 =
p и 2 о
p^ 1 « 106 • 1 g/m2
because pH O = 106 g/m3.
As the burn dressing of the first aid must sorb 5403 g/m3, it follows that
S^IO3 « 106l. (4.1)
Therefore the thickness of tile first aid bum dressing equals
l
5 • 103 106
5 • 10-3 m ( 0.5 cm).
Thus, the first criterion of the efficiency of the first aid burn dressing can be formulated as follows:
The burn dressing of the first aid must use its entire free volume for sorption. This volume must be 0.9 or more of the total volume of dressing. Dressing thickness must be 0.5 cm or more.
It should be mentioned that the majority of foreign first aid dressings fulfill this criterion.
t
a
Air penetrability of dressings The air penetrability of dry air of the most of dressings is ranged within 10-4 - 10-5 mole-m/m2-s-Pa (Table 11. The air penetrability of dressings filled with water is much lower and decreases to values between 10-6 - 10-5 mole-m/m2-s-Pa, that is 0.2 - 2 dm3/m2-s (this is for the dressing 5-10-3 m (0.5 cm) thick at pressure of 50 Pa (5 mm H2O) according to GOST 12088-77 (former USSR Standards).
Thus, the second criterion of the efficiency of the first aid bum dressings can be formulated as follows: The first aid burn dressing must possess air penetrability of 10-5 mole-m/m2-s-Pa or higher after the sorption of water. For example, Biobrant burn dressing fulfills this criterion.
Adhesion of dressing to wound Adhesion strength of dressings with respect to coagulated blood (Table 14) varies in a wide range, but it has the minimum value of ~ 20 N/m.
Table 14 - Characteristics of burn wounds [2]
This value should be accepted as the optimal one, because it corresponds to the minimal pain and damage on removal from the surface of natural skin. Thus, the third criterion of efficiency of the first aid burn dressings can be formulated as follows:
The first aid burn dressing must possess adhesive strength to the wound of 20 N/m or less after the end of its action.
The following burn dressings fulfill this criterion, for example: Biobrant, blood- stopping remedy, Johnson-Johnson.
Table 15 - Water losses by means of evaporation from burnt surfaces of different types
II-nd degree with no damage of fermentative layer 37
II - IV degree of burn 20 - 31
Isolation of wound from infection from external
medium
It is known, that microorganisms, causing the wound infection, do not penetrate through the filters, possessing average pores size ~ 0.5 |im. The fourth criterion of efficiency of the first aid burn dressings is then as follows:
The first air burn dressings must possess no open pores with average diameter larger than 5-10-7 m (0.5 |im).
Moreover, it is implied, that tile first aid bum dressings possess sufficient mechanical strength and elasticity both in dry and humid conditions [18-25].
5 Conclusion
The experimental methods to estimate the main physico-chemical properties were worked out.
Based on theoretical and experimental data we found that maximal sorptional ability of burn dressing equals the free volume of the dressing material, calculated from the value of the material density.
We found that the study sorption ability water can be used as a model liquid instead of the blood plasma medium.
Kinetic parameters were determined from the sorption curves. These parameters showed that the first aid burn dressings markedly differ in the value of the rate or liquid media sorption at stages close to the sorption limits.
We established that the air penetrability parameter in wet state decreases abruptly by 2-3 orders of magnitude for the majority of tested dressings. This is due to the filling of porous space by liquid medium.
We recommended that the air penetrability parameter be determined in wet state which represents the common condition of action for the first air burn dressing.
The value of adhesive strength after the end of its action on the wound must not exceed 20 N/m.
From the data obtained in this study we formulated the following criteria to estimate the efficiency of the fist aid bum dressing: maximum sorptional ability for water must be at least 10 g/g; optimal thickness of dressings, fulfilling this value of sorptional capacity, must be ~ 5-10-3 m, the adhesive strength must not exceed 20 N/min, and the average diameter of open (connected) pores must not exceed 5-10-7 m.
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Natural skin 1 - 2
I-st burn degree 1 - 2.5
II-nd burn degree with sac intacts 2.8
Burn degree Image of damage Physiological process Burn depth, mm
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© K. Z. Gumargalieva - Doctor of Chemistry, Full Professor, N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia, G. E. Zaikov - Doctor of Chemistry, Full Professor of Plastics Technology Department, Kazan National Research Technological University, Kazan, Russia, M. 1 Artsis - Ph.D, N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow, Russia, L. A. Zimina - N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow, Russia, Kh. S. Abzaldinov - Ph.D., Associate Professor of Plastics Technology Department, Kazan National Research Technological University, Kazan, Russia, abzaldinov@mail.ru.
© К. З. Гумаргалиева - доктор химических наук, профессор, Институт химической физики им. Н.Н. Семенова РАН, Москва, Россия, Г. Е. Заиков - доктор химических наук, профессор кафедры Технологии пластических масс, Казанский национальный исследовательский технологический университет, Казань, Россия, М. И. Арцис - кандидат химических наук, Институт биохимической физики им. Н.М. Эмануэля РАН, Москва, Россия, Л. А. Зимина - Институт биохимической физики им. Н.М. Эмануэля РАН, Москва, Россия, Х. С. Абзальдинов - кандидат химических наук, доцент, кафедра Технологии пластических масс, Казанский национальный исследовательский технологический университет, Казань, Россия, abzaldinov@mail.ru.
