Note: Descriptions are shown in the official language in which they were submitted.
lc~5g~53
BACKGROUND OF THE INVENTION
_
The primary concern is with the treatment of human
patients and, to some extent, animals, which have incurred se-
vere burns or tissue damage which leaves a substantially expo-
;5 sed wound. One purpose is to convert the contaminated and
open wound to a clean and closed wound in the shortest time
possible.
It has been customary to use cadaver skin or porcineskin among other to protect wounds and to aid in the develop-
ment oE granulation tissue prior to autografting.
- The wound dressing should decrease pain, reduce pro-
tein loss, reduce evaporative heat and water losses from the
wound surface and prevent further contamination. It is desir- ~ -
able that the use of the dressing results in decreasing exist
`,15 ing bacterial growth in the wound. At times a bleeding wound
or wound losing plasma rapidly is present as a part of a larger
wound and the dressing should aid in minimizing blood or plasma
loss. It is desirable that the dressing remain flexible and
adherent to the wound at all times and be sufficiently flex- ;
~$
ible to permit at least some flexing of the wound surface.
'`1
The desired degree of flexing to some extent varies with the
location of the wound. For example, a wound surface adjacent ~
.,j : '.
a joint should preferably have greater flexibility than a
wound adjacent a less flexed area such as a chest or back.
r~ 25 In general, the requirements for a wound dressing,
particularly a burn dressing, are known and recognized.
DESCRIPTION OF THE PRIOR ART
The use of polyglycolic acid is disclosed in a
series of patents and applicatio~ to Schmitt, et al:
U.S. Patent 3,297,033, Schmitt and Polistina,
January 10, 1967, SVRGICAL SUTURES, discloses polyhydroxy-
-- 1 --
, , .
... . . . .
~9~53 :;
acetic ester absorbable sutures. The material is also called
polyglycolic acid, and is disclosed as permitting small quanti-
ties of comonomers to be present, such as dl-lactic acid, its
optically active forms, homologs and analogs. A small quantity
is recognized by the art as up to 15%, as shown by United States
Patent 2,668,162, Lowe, February 2, 1954, PREPARATION OF HIGH
MOLECULAR WEIGHT POLY~NDROXY-ACETIC ESTER.
United States Patent 3,463,158, Schmitt and Polistina,
August 26, 1969, POLYGLYCOLIC ACID PROSTHETIC DEVICES, dis-
closes surgical uses of polyglycolic acid, and incorporates
definitions of some terms.
United States Patent 3,620,218, Schmitt and Polistina, ~-
November 16, 1971, CYLINDRICAL PROSTHETIC DEVICES OP POLY
- GLYCOLIC ACID, lists many uses of polyglycolic acid.
United States Patent 3,736,646, Schmitt and Epstein,
June 5, 1973, METHOD OF ATTACHING SURGICAL NEEDLES TO MULTIFILA-
MENT POLYGLYCOLIC ACID ABSORBABLE SUTURES, discloses surgical
elements of a copolymer containing from 15 to 85 mol percent
- glycolic acid and 85 to 15 mol percent lactic acid.
United States Patent 3,739,773, Schmitt and Polistina,
June 19, 1973, POI.YGLYCOLIC PROSTHETIC DEVICES, claims parti-
~, cularly bone pins, plates, nails and screws of polyg~l~ycolic acid. --
United States Patent 3,875,937, Schmitt and Polistina,
SURGICAL DRESSINGS OF ABSORBABLE POLYMERS, discloses additional
~ "
subject matter on surgical dressings of polyglycolic acid. ;
United States Patent 3,739,773, supra, lists a number
of United States Patents on methods for preparing polyglycolic
acid and starting materials therefor.
In United States Patent 3,620,218, supra, in Column 2 ~ -
are listed a number of medical uses of polyglycolic acids, in-
. , .
- 2 -
~S~ 3
cluding in Column 2; line 52, knit-ted or woven ~ibrillar products, including
ve].ours, and mentioning specifically in line 53, burn dressings, line 57,
felt or sponge for liver hemostasis; line 63, foam as absorbable prosthesis;
and in lines 74 and 75, burn dressings (in combination with other polymeric
films).
~Zhe use of gauzes, felts, and knitted fabrics as a wound dressing
is quite conventional. The use of collagenous products as a sponge or pad
has been disclosed. The requirements for surgical dressings are varied and
more satisfactory dressings than presently available are constaNtly in demand.
U.S. Patent 3,526,224, R. M. Potts, September 1, 1970, DRESSI~G,
discloses an occlusive dressing designed to act as a synthetic skin which has
an elastomeric polyurethane film having a water vapor transmission rate of
150 to 500 g/m /2~ hrs. laminated to a knitted velour fabric. A tricot fabric
of 30 denier textured 6.6 nylon yarn is suggested. The pile or nap side of
the knitted velour forms the wound-contacting side of the dressing.
Studies are being made by and for governmental agencies on burn ;~
protection. One such "Development of a Synthetie Polymer Burn Covering"
Z prepared by Dynateck R/D Company, ~or the Office of ~aval Research, June 1973,
~ational Technical Information Service AD-76L,631 discloses the use o~ poly-
meric films, including lactic acid polymers, and 75/25 lacticlglycolic co-
polymers, and the disadvantages of flat, solvent cast films. A normal ~-
insensible water loss from the human body is given as 2.2 mg/hr c~ , ~uoting
Treger, " hysical Y~nctions of the Skin", Acsdemic Press, ke~ ~ork.
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9853
SU~R~ OF T~IE INVENTION
This invention relates to a wound dressing, particularly
adapted for major burns in humans in which at least a part of the
skin has been destroyed or removed and which underlying tissue is
~ subject to moisture and liquid loss and bacterial contamination which
; dressing comprises an exterior surface of an elastomeric material
such as polyurethane which has a moisture permeability of the order of
that of the intact human skin and to which is adhesively flocked a layer
` of fibers of a tissue compatible and absorbable material which fibers
are preferably predominantly at about right angles to the elastomeric
layer and which are so spaced as to permit the invasion of granulation
;; tissue and which can be removed from the granulation tissue without
.
pulling off such granulation tissue and with minimum damages to the
developing granulation tissue to leave a bed for autografting or other .
', subsequent treatment.
Thus, according to the present invention, there is provided
a wound dressing for the surface of living tissue from which at least
part of the skin has been removed and which tissue is subject to moisture,
loss, and bacterial contamination, which dressing is sufficiently flexible
that it will conform and adapt to the surface of the tissue to minimize
pools of fluid or air between the dressing and the tissue surface, which
pools generate problems of infection, and which has a permeability to mois-
ture of the order of that of the intact human skin ~approximately 2.2
mg/sq./cm./hr,) which comprises an eiastomeric layer which elastomeric
layer has adhesively flocked to its surface a layer of fibers and which ;
fibers are of a tissue compatible material which is substantially absorbed
by living tissue within about 90 days, and which fibers maintain their
integrity for at least about 3 days.
The fibers themselves are absorbable by living tissue so that
any of the fibers which are trapped within the wound are absorbed by the
~.~
.
1~59~3~;i3
living tissue without deletcrious effects.
The present wound dressing may be used on almost any ~ype of
wound in which the skin is broken and body fluids, particularly blood
and serum, are released by the wound. It is primarily designed for
major burns in which a substantial area of the skin of a human is destroy-
ed, a third degree burn, leaving underlying tissues which are either contam-
inated, or subject to contamination by bacteria, or other contaminants,
and which wound is of such a size that immediate protection of the tissue
surface is required. It is desirable to change the wound from a contam-
inated and open wound to a clean and closed wound in the shortest time
possible, to de- -
'~
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., ~
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.
~59~
crease pain, and to minimi?.e protein loss, reduce ev~poratlve heat
and water losses, and prevent furt~er contamination during the
time required for the underlying tissues to build up a granu- ~-
lating surface which will accept a skin autograft.
y skin autograft is meant skin taken from another
area of the sub~ect, and which is living so that when placed
on the granulating tissueJ the skin will graft to the granu-
lating tissue and grow providing a skin surface at the wound
area. With rare exceptions, the s~in of any other subject
will be rejected and not graft to thewo~ed subject. The
; subject's own skin grafts to properl~ prepared granulatlng
tissue and will grow so as to enlarge the skin covered area.
Wi~h major burns, a sufficientl~ large portion of the subject
may be burned so that sites for donor skin are limited and it
is necessar~ to protect burned areas for a prolonged period
until graft donor sites can regenerate and be used for a sub- ~ ;
sequent graft.
The generalized subject of burn treatement of this
type is fairly well recogni~ed as are mcm~ of the requirements
for such a wound dressing. T~e medical profession recognizes
the need for improvements in burn site protection during burn
treatment, Survivabilit~ after major burns has been lmprovlng
-- the present invention contributes towards suc~ improvement.
The use of a synthetic tissue absorbable dressing
eliminates man~ disadvantages of prior art dressings, partic-
ularl~ as to availabilit~, and represents a substantial step
- forward in burn treatment.
The dressing should conform to the surface of the
` tissue. Conformation comprises an assessment of the supple-ness, ~esilienc~, and dressing~s ability to mimic the topo-
graph~ of the wound in such a fashion that there is a minimum
., .
', ' ~
53
gap between the -tissue and the clressing which minimizes air
gaps and pools of li~uid. If pools of liquid build up, whether
of serum or blood, such pools become sites for the growth of
undesirable microorganisms. If the dressing conforms aaequat-
ely to the surface of the wound, the body's own defense mech-
anisms are effective up to the zone of contact with the dress-
ing, and bacterial contamination is minimized. In many in-
stances, the body's defense mechanisms can clean a protected
contaminated wound and permit the growth of granulation tissue
even though the wound was initially contaminated.
In modern hospital technology, any area not known
to be surgically clean must be regarded as contaminated or at
least suspect, and treated as if contaminated.
For proper protection of the tissue surface, the
gross escape of liquids such as serum or blood needs to be
prevented by the dressing and the tissue needs to be protected
from the atmosphere, but at the same time just as natural skin
permits the escape of a certain amount of moisture, a wound
dressing must permit the escape of at least some moisture to
prevent the dressing from being lifted by the underlying flow
'!
of fluids. If the rate of moisture loss is too high, there
is a cooling effect from the heat required to convert the
liquid to vapor; and electrolytes, proteins, and other mater-
- ials in the underlying fluid concentrate and crust on the
surface, or under the dressing, which leads to complications.
It is desirable that the permeability be of at least approx-
~' imately that of the intact human skin (which is found to be
about 2.2 mg./sq. cm./hr.) and may be several times this value.
A permeability of 4.7 mg./sq. cm./hr. has been found effec-
tive under many conditions. The values are approximate as
different skin areas lose moisture at a different rate and,
'
~5~S3
depending upon the temperature of the subject, the tempera-
ture o~ the atmosphere, the movement of ambient air and under
other variables, the natural skin has a considerable range
of skin moisture loss. ~he natural skin is adaptable to a
wide range of environmental conditions so that if the wound
dressing has a moisture loss which is approximately that of
the intact human skin and remains within this range of ac-
ceptable conditions, the underlying tissues are protected
; and regenerate. There is a fine and, perhaps, unascertain-
able line between the regenerative processes of the tissue
when protected from ad~erse effects and the increase that
might be caused by dressing characteristics and environ-
mental factors. It is not necessary to ascribe the rate of
; healing to any special set of factors~ It is merely found
that by using the present wound dressing, rapid healing is
encouraged.
For adequate conformation, the wound dressing must
be flexible so that it can conform to the topography of the
wound and at the same time it must be sufficiently flexible
that as the tissues move, the wound dressing can move with
them. For instance, if the skin adjacent to a joint is in-
jured, flexing of the joint and movement of the underlying
tissues requires that the wound dressing have some flexibil-
ity. The minimum required flexibility is exceeded by the
present dressing and the dressing is sufficiently flexible
for tissue movement over joints and other areas.
Basically, the tissue-contacting portion of the
dressing is a flock of tissue compa-tible material which is
substantially absorbed by living tissue within a period of
about 90 days and which fibers maintain their intPgrity for
at least about three days.
-- 7 --
~L~59~3~ii3
A flock of fibers of` the order o~ 0.5 to 12 denier and
from 10 to 30 mils long which are flocked onto an elastomeric layer
gives protection to the wound surface.
It is desirable that the fibers be absorbable by living
tissue as characteristics of a flocked surface are such -that some
fibers are not tightly held, and some Or the fibers may remain in
the wound, and non-absorbable materials can be the source of un-
desirable side effects.
A preferred tissue absorbable polymer is polyglycolic
acid, such as described in the Schmitt patents above and which is
meeting with commerical success as a suture. Polymers in which tissue
absorption results from the hydrolytic degradation of glycolic acid
`, ester linkages give good results. Because strength of the fibers is
not a maJor requirement, a copolymer containing considerable lactic
acid makes a good dressing. Such polymers are disclosed in U.S.
Patent 3,736,646, supra.
A polymer having an ordered configuration Or glycolic acid ~-~
units and lactic acid units which is tissue absorbable is described
.
: ~ :
at length in Canadian Serial No. 216,765, December 24, 1974, Augurt,
Rosensa~t, and Perciaccante, UNSYMMETRICALLY SUBST~TUTED 1,4-DIOXANE-2,
5-DIONES.
Another absorbable polymer ~hich may be used for the graft
is poly(N-acetyl-D-glucosamine) such as described in U.S. Patent
3~988,411, Richard Carl Capozza~ POLY(N-ACETYL-D-GLUCOSA~INL) PRODUCTS. '~
The i~portant thing about the tissue absorbable polymer is
that it be of a material which is not deleterious to living human
tissue and that it be spinnable as a fiber which forms a ~ine
structure such that blood and other fluids do not flow rapidly there-
through and it has su~ficient -~
:
- 8 _
. ,f~
" .
5~
strength to malntain its integrity during the manufacture of a flock and
that it maintains its integrity in contact ~ith the tissue long enough for
granulation tissue to form ancl yet is absorbable within a reasonable length
of time, for instance, about 90 days, so that it does not remain as a foreign
body after the wound has healed.
Canadian Serial No. 216,765 and United States Patent 3,988,411
give examples of such materials.
Inasmuch as the use~ul characteristics of such ma-terials are
largely as a function of size, shape and structure, these materials may be
substituted for the polyglycolic acid fibers described in more detail in the
following examples. ~ `
The fibers which conveniently are spun in abou-t 1 to about 12 denier
are adhesively flocked to the elastomeric backing layer. By using an electro-
static charge, as is conventional in flocking systems, the fibers are caused
to stand on end and are predominantly at right angles to the elastomeric
layer. The fibers may be adhesively united to the elastomeric layer by using
the adhesive characteristics Or the elastomeric layer as it is ~ormed. ~ore
conveniently, when the elastomeric layer is formed, a separate adhesive layer
is placed thereon and the flocked fibers are placed on such adhesive layer
and caused to stand on end electrostatically.
The elastomeric layer may be any material which is permeable to
; moisture, has a low Young's modulus and is thus readily conformable to the
wound surface. A particularly useful material is polyurethane. A soft,
~lexible elastomeric layer of polyurethane o~ the order o~ 2 mils thick
provides a barrier to excessive water loss, is permeable to
.
, '.
:~ '
._ g _
,~ t,~
~ 59y35i3
moisture within the range o tha-t of the intact human skin,
which is approximately 2.2 mg./sq. cm./hr., to two to four times
this value, which permits moisture to pass through the backing
la~er at such a rate that formation of liquid pools under the
dressing is minimized, and yet the water loss is within a de-
sirable range as regards heat loss and concentration oE dis-
solved components in the body fluids which are underneath the
dressing.
At the time of use, the wound shculd be debrided in
accordance with usual techniques and substantially dried
so that there is no standing liquid on the surface of the
`l wound. Then, the soft flocked surface of the wound dressing
is placed in contact with the wound, ~eing sure that it con-
forms to the topography of the wound surface so that there
are no gaps or spaces between the tissue and the dressing;
with the dressing being held in place by adhesive tape, add-
tional bandages, or suturing. A low pressure bandage may be
used to hold the dressing in place, depending upon the loca~
- tion of the dressing and the condition of the patient. The
dressing is permitted to remain in place for approximately
seven da~s. If less than four days in most subjects, there
is not suff~cient time for adequate granulation tissue to
grow under a dressing and if more than fourteen days,.;
much granulation tissue may grow and result in scar tissue.
At times a wound must have a first dressing applied and be
:: .
permitted to heal so that granulation tissue is formed in
part on the wound and then additional debridement or other
treatment is undertaken in other areas, requiring a second
wound dressing application to encourage the growth of addi-
tional granulation tissue. There are times when many treat-
ments are required hefore the wound is in condition for
autografting or before skin for autografting becomes avail~
- 10 -
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9~i3
able. For ma~or burlls or traumatic tissue damage, prolonged treatment
; may be required before the wound is ready for final grafting.
In other instancesJ a wound may be fairly minimal and the
present ~OUIId dressing ma~ be applied even though a less adequate
wound dressing could have been used and a single applicatiorl permits
substantial healing Different areas of the same wound ma~ require
different treatment.
The present wound dressing in particular functions as a
temporary synthetic skin, giving a protective covering to any area
of a body from which the skin is removed and the underlying tissues
are exposed with the covering not interfering with normal physiological
processes conducive to wound healing and autograft conditioning.
; The composite structure provides both a good moisture
barrier and bacteria barrier. The conformability resulting from the
elastomeric backing permits conformation to nearly any wound topography
while the short fibers protruding from the flocked surface insure
intimate contact and wetting at the wound surface which provides an
intimate contact with the tissue absorbable fiber during the healing
process~ Because the flocked surface is absorbable, there is no
-/ 20 problem resulting from biological rejection of the flocked material
and there can be no deleterious entrapment in regenerating tissue
` in tangled fibers, as can be the case of a sponge or woven web.
As shown in the attached drawing, a polyurethane
~: : .,
such as described in U,S. Patent 3,582,423, Wang, June 1, 1971,
- PROCESS FOR COATING POROUS SUBSTRATES, and sold as Helastic
` 13141 polyurethane, iâ cast on release coated paper to form a
film with a thickness of 2 nils. The material is a reaction
product of a hydrox~ terminated polyester such as diethylene
- glycol adipate and p,p'-methylene dianilane and a mixture of
-' 11 -.
2,4- and 2,6-toluene diisocyanates~ at about 25% solids. The
polyester type segmented polyurethane is per~itted to harden
to form a water vapor permeable elastomer layer, and then
coated with an additional half a ~il thickness of the same
polyurethane.
The polyurethane structure may be graphically de-
scribed as:
NH2-Rl--ENH-CO-NH~ -NE~-CO-O-R3-Q-CO-NH-R2-NH-
-CO-NH-Rl ~NH2
where,
Rl= ~ 2
CH
lS or ~ 2 ~
;, o o
.~ " ,
3 2 2~ CH2 CH2-CH2- CH2-C--CH -CH
or O O
:~ -CH-CH2~ 0-$-CH2-CH2-cH2-cH2-c-o CH-CH2 ~ ~
CH CH
3 3
or
-CEI2-CH2-cH2 CH2~ O C 2 2 2 2 m
The polyurethane film is cast by pouring the resin
~J dissolved in solvent on a release paper such as ~ silicone ~ ~ -
'I i .
coated release paper, which is pulled through rollers set to
leave about 4 mils of 25% solids solution on the release pap-
er, so that when dry a 2 mil layer remains. After a second
pass to leave an additional adhesive coat which dries to
about 0.5 mils thickness, there are flocked 2 denier poly-
glycolic acid fibers approximately 25 mils long with the fib-
ers being subjected to a strong electrostatic field, in accord-
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~q~5~ 3
ance with conventional procedures, to cause the fibers to
stand at approximately right angles to the field and, hence,
at right angles to the backing, while the polyurethane ad-
hesi~e layer cures. The thus formed flock is shaken and then
blown with air to remove any loose fibers, after which the
flocked sheet is cut into 2" X 3" rectangles for indi~idual
dressings.
As a surgical device, it is obviously desirable,
almost mandatory, that the wound dressing be sterile at the
~ime of use. The wound dressing may be sterilized by an ap-
propriate sterilizing cycle using ethylene oxide as a steril-
izing agent. Radiation sterilization may be used, as may
heat sterilization.
If ethylene oxide is used to sterilize, it is con-
venient that the ethylene oxide be diluted with carbon dioxideor a chlorofluoroalkane to such an extent that the steriliz-
ing gas is non-explosive. For st:orage stability, it is des-
irable that the wound dressing be protected from atmospheric
influences. Because the wound dressing contains hydrolyzable
;20 polyglycolic acid ester linkages, the lin~ages can be hydro-
lyzed by ambient moisture under room storage. The wound
dressing requires that the flocked fiber retain sufficient
strength to be separated from the wound when the dressing is
changed. Preferably, it should retain strength at least 10
25 days to two weeks. It is desirable that such storage condi- ~ -
tions be used as to maintain the wound dressing in a dry en- -
vironment so that whether used immediately after packaging
or after a storage period of several years, the wound dress-
ing has the same characteristics and, hence, has known pre-
dictable attributes as far as the using surgeon is concerned.
- 13 -
A good method of sterilizing and storage is the
same as is used for polyglycolic acid sutures on a commercial
scale and as disclosed in U.S. Patent 3,723,839, Arthur Glick,
April 24, 1973, STORAGE STABLE SURGICALLY ABSORBABLE POLYGLY-
COLIC ACID PRODUCTS. As there described, the polyglycolicacid product is stored in a moisture proof envelope in which
conveniently the product is packayed except for one open side
and sterilized using ethylene oxide diluted so as to be non-
j-explosive, and then while protecting sterility, the product ~- ~
10 is vacuum dried and the envelope sealed. By having the ~oil ~ -
envelope hermetically sealed, as there taught, the wound ~ ;
dressing may be maintained in a usable form with consistent
characteristics for a period of at least several years. Con-
veniently, but not necessarily, the wound dressing may be~ ~
15 placed between two sheets of paper, or a single sheet of paper ;
with a fold, so that the wound dressing is held in flat con-
`~dition between the sheets during storage and service to the
using surgeon.
IA single envelope can be used, which, on stripping,
'20 releases the wound dressing folded in a sheet of paper.
Such a single envelope package is shown in U.S. Patent 3,017,
990, Singerman, January 23, 1962, STERILE PACKAGE FOR SURGICAL
FABRIC.
:
For large sheets, the wound dressing may be fold-
ed~ but for sheets up to 3" X 5" it is conveniently placed
in an envelope large enough to hold the sheet flat. ~ plur-
ality o~ sheets may be packaged in a single envelope if de-
sired. Single sheets of about 3" X 5" are a surgically
acceptable size, with the wound dressing being cut to size - -
if necessary by the surgeon, or an assistant, at the time of
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i91~i3
use. For many surgical pxocedures, a single sheet is all
that is required. For major burned areas, either a number of
smaller sheets or a single layer sheet of the wound dressing
gives good results. A series of smaller dressings gives more
conformity on irregular areas. A single large sheet reduces
the number of seam lines. Convenientlyl the wound dressing
is made available in sterile form in sheets 3" X 5", 3" X
12", 3" X 18", 3" X 24" and continuous rolls, about 12" wide.
Other sizes and shapes can be provided to supply the using
surgeon with a choice of sizes, consistent with reasonable
inventory demands.
At the time of use, the enclosure is stripped open,
the individual dressing removed and placed in contact with
the wound surface. For burn areas with adjacent whole skin,
the wound dressing may be held in place by adhesive strips.
On burn test subjects, the wound is cleaned from
- burned tissue and other contaminants, in accordance with con-
~` ventional debriding proceedings, and the wound covered by the
wound dressing. After approxlmately seven days, the wound
dressing is removed from the wound gently to avoid stripping
granulation tissue, and the wound is ready for grafting, or
additional treatment.
The treatment of the wound before applying the
wound dressing may include antibacterial agents, anesthetics,
etc.
The time before dressing change varies with the
location o~ the wound, and the general condition of the pa-
, 1 . .
tient. Some heal more rapidly than others. The surgeon incharge must adapt the treatment to the speciflc patient.
-- 15 --
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