Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Canadian patent application Serial No. 330,888 dis-
closes a transparent liquid dressing material, specially
suitable for the treatment of wounds, but also useful for the
after-treatment of skin tumors, for the desensitization of
allergies, cosmetic purposes, keeping exposed bones and tendons
moist, psoriasis, and as carrier for cell cultures.
The material comprises a hydrophilic, organic, trans-
parent gel in film or strip form, swollen with an aqueous
solution, which can contain buffer substances, active rnaterials
usual in the treatment of wounds, nutrient materials and/or
growth materials and may contain reinforcing material in the
form of threads or mesh.
An advantage of this dressing material is that it is
simple to employ and can be removed or changed without trouble,
makes possible with visual observation of the underlying parts
of the body or celllcultures, brings about an improved wound
healing without excessive granulation and enables the applica-
tion of active substances through the material itself.
Its large liquid content is sometimes a disadvantage
during storage retention. Furthermore, the application of
active substances and the removal of secretions is relatively
slow. Therefore, an aim of the present invention is, while
retaining all the advantages of the transparent liquid dressing
material, to provide a more easily storable form which permits
quick application of active substances and removal of secretions.
According to the invention, this is accomplished by
providing a transparent liquid dressing material of the type
described in the form of a dry, clear, swellable film.
More specifically, the invention provides a trans-
parent dressing material which is especially useful for thetreatment of wounds, comprising a dry, swellable, clear film
1.~\
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of a hydrophilic, organic transparent gel in the form of a
sheet or strip, in which the gel comprises:
(a3 at least one of a gellable polysaccharide,
protein or polypeptide, and
(b) a polymer of a hydrophilic acrylic or metha-
crylic acid derivative polymerized in the
presence of said component (a).
The invention also contemplates a process for the
preparation of a dressing material as described. This process
comprises dissolving at least one polymerizable monomer or
monomer mixture comprising a hydrophilic acrylic or metha-
crylic acid and at least one of a gellable polysaccharide,
protein or polypeptic as starting substances for the gel, in
an aqueous medium, permitting the solution to thicken to the
degree desired for the sheet, and starting the gel-forming
reaction by the addition of an initiator for the polymeriza-
tion of the polymerizable monomer, and then drying the swollen
gel material obtained. The resulting product may then be
dried.
A dressing material, according to the invention,
exists in the form of a skin-thin, glass-clear film havin~ the
ability to swell again. In a short time, i.e. within the course
of an hour, it absor~s up to 10 times its weight and more of
-la-
liquid and is almost completely reconstituted so that it
possesses all the mechanical and structural properties of the
swollen starting ma-terial. In general, the weight of the dried
film accounts for 2 to 10, preferably 3 to 7% of the weight of
the swollen, moist, starting material. In general, its thick- '
ness lies between about 0.5 and 0.01 mm., preferably 0.3 to
0.003 mm., discounting reinforcing material.
The com~osition and production of the gel conforrn to
the description of application Serial No. 330,888. Thus, a gel
of a mixture of hydrophilic polymer and at least one gelable,
high molecular substance is preferred. Especially preferred,
is a gel of a gelable polysaccharide and/or protein or poly-
- peptide and a polymer of a hydrophilic acrylic or methacrylic
acid derlvative produced by polymerization in the presence of a
polysaccharide and/or protein or polypeptide. The hydrophilic
acrylic or methacrylic acid derivative is expediently an amide
or an ester with an alkanol possibly containing one or more
additional free hydroxyl groups. As gelable polysaccharide,
agarose is preferred, as gelable protein gelatine.
As in the case of the prior a~plication mentioned,
the gel may also consist of 10 to 90 wt.% of polymerized acrylic
or methacrylic acid derivative and 90 to 10 wt.% of polysaccha-
ride and/or protein. However, especially favourable drying and
reconstituting properties are available when the polymerized
acrylic or methacrylic acid derivative is present in at least
the same amount by weight as the polysaccharide and/or protein
and preferably accounts for 60 to 90 wt.% of the total gel dry
mass.
The manufacture of the dressing material proceeds as
described in the earlier application. As starting materials, a
monomer or monomer mixture and at least one gelable, hydrophilic,
high molecular substance are dissolved in a~ueous medium. The
,r~ ~s~
solution is laid down on a substrate to the desired thickness
for the sheet or strip. Ihen, the gel formation is started by
the addition of an initiator or of an initiator mixture for the
polymerization of the polymexizable monomers. A reinforcing
material may be added before, during, or after the addition of
the initiator. The swollen gel is then dried.
The drying is preferably from both sides uniformly
and simultaneously. Distortion, e.g. buckling may be prevented
by drying the gel between two porous supporting bodies. This
is important in fast drying. Suitable supporting elements are,
for example, porous synthetic resin plates, perforated metal
plates or sheets, and the like. If the porous supporting
elements are thin films, then they, in turn, are carried by
suitable supporting means.
According to another form of the invention, the wet
gel is dried while stretched on a thread- or mesh-like rein~
forcing material. The drying itself can be carried out at room
or at elevated temperature, in a vacuum or at normal pressure.
In the case of the use of the described "sandwich technique"
drying between two porous supporting elements, it has been
ascertained that a vacuum of down to 1 to 10 mm. Hg can be
employed without impairing the properties of the dried film
in recovering the mechanical and structural properties of the
wet starting material. If drying is effected without using a
vacuum, for example, in a current of warm air, for the purpose
of better heat transmission, metal plates or sheets are pre-
ferably employed as supporting elements.
Gels with an initial thickness of between about 0.5
and about 3 mm. have proven especially sui-table for the drying
process. The best results in the case of the use of porous
supporting elements were achieved with 1 to 2 mm. thick gels.
In this range, with increasing thickness, better properties
are achieved by Lhe use of a vacuum -than without a vacuum.
When drying wi-thout a vacuwn in a current of warm air, the
best results are achieved wi-th a thickness of 1 mm. or less.
The invention provides considerable improvement
over that disclosed in the parent application. In the case of
the dried film packaging is easier. Sterilization is also
simpler. The moisture-saturated gel is,relatively slow in
taking up active materials, such as e.g. antibiotics, cyto-
statics, wound hormones, nutrient substances and the like.
This is because a mixing of the liquid carrying the applied
substances must take place with that enclosed in the gel.
In the case of the dry film this exchange is faster since the
aqueous carrier solution is absorbed immediately.
! The dressing material according to the invention
in the dry form is also effective without previous rehydra-'
tion or, with partial rehydration, in the case of heavily
suppurating woulds,since it absorbs the discharged secretions
to a greater extent than the fully swollen materialO In this
way, it is possible to absorb the same amount of secretion
as can only be achieved in the case of the dressing material
of the earlier application only by the use of escape holes.
The following Examples further ex~lain the invention.
EXAMPLES 1 to 6
As described in Example 2 of application Serial No.
330,888, a dressing material was produced, the gel of which
consisted of polyacrylamide and agarose. Apart from the
composition of Example 2, five further gels were also pro-
duced which differed with regard to the contents of poly-
acrylamide P and agarose A. The compositions are given in
the following table.
The individual gels were brought to a thickness of
1 to 2 mm. and then laid betweçn porous synthetic resin plates
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of polyethylelle (pro~ucer the firm Pharmacia, Sweden) and dried
at a vacuum of 2 to 5 mm. Hg and rooM temperature. The weight
of the films obtained as percentage of the moist weight of the
starting material is also shown in the table.
The reswelling took place by soaking in water. The
period of time and degree of reswelling achieved are also given
in the table.
TABLE
P % 2.5 3.5 5 3.5 3.5 3.5
A % 1 1 1 0.5 1.5 2
dry wt.
in % of 3.4 4.8 6.6 3.8 5.4 6.1
wet wt.
reswelling to % of the starting weight
before drying
time(h) 46.7 56.5 50.3 58.5 51.1 55.5
6 54.2 82.9 95.6 81.0 75.5 72.2
24 55.7 84.9 97.1 8203 78.6 74.1
