U.S. patent number 3,903,882 [Application Number 05/462,490] was granted by the patent office on 1975-09-09 for composite dressing.
This patent grant is currently assigned to American Cyanamid Company. Invention is credited to Thomas Anthony Augurt.
United States Patent |
3,903,882 |
Augurt |
September 9, 1975 |
Composite Dressing
Abstract
A flexible, tissue surface conformable, water vapor permeable,
composite dressing for wounds, particularly major burns, is formed
from a knitted fabric of a tissue absorbable polymer, such as
polyglycolic acid, having on the non-tissue contacting surface a
water vapor permeable elastomeric film, such as polyurethane,
silicone, poly(caprolactone) and natural rubber, which excludes
microorganisms and dirt, while controlling water vapor permeation
to approximately that of the intact human skin. The dressing is
tissue surface conformable, minimizes pooling of liquids between
the dressing and the wound, minimizes infections, is readily
removable to permit a change of dressing, and permits granulation
tissue to form under the dressing and subsequent autografting. If
any of the tissue absorbable material is trapped within the wound,
it is absorbed with no deleterious effects.
Inventors: |
Augurt; Thomas Anthony
(Stamford, CT) |
Assignee: |
American Cyanamid Company
(Stamford, CT)
|
Family
ID: |
23836598 |
Appl.
No.: |
05/462,490 |
Filed: |
April 19, 1974 |
Current U.S.
Class: |
602/43;
128/DIG.8; 602/48 |
Current CPC
Class: |
A61F
15/001 (20130101); A61F 13/00046 (20130101); A61F
13/00038 (20130101); A61L 15/26 (20130101); A61L
15/26 (20130101); C08L 67/04 (20130101); A61F
2013/530992 (20130101); A61F 2013/00238 (20130101); A61F
2013/00561 (20130101); A61F 2013/00157 (20130101); A61F
2013/00221 (20130101); A61F 2013/00519 (20130101); A61F
2013/51411 (20130101); A61F 2013/00876 (20130101); A61F
13/551 (20130101); A61F 2013/00727 (20130101); A61F
2013/0091 (20130101); Y10S 128/08 (20130101); A61F
2013/00263 (20130101) |
Current International
Class: |
A61F
15/00 (20060101); A61F 13/00 (20060101); A61L
15/16 (20060101); A61L 15/26 (20060101); A61F
13/15 (20060101); A61F 013/00 () |
Field of
Search: |
;128/149,153-157,268,165 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trapp; Lawrence W.
Attorney, Agent or Firm: Walker; Samuel Branch
Claims
I claim:
1. 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 moisture of the order of
that of the intact human skin (approximately 2.2 mg/sq. cm./hr.),
which comprises: an elastomeric layer of the order of 0.1 to 5 mils
thick, and which elastomeric layer has bonded thereto a fabric
knitted of continuous fibers of the order of 1/2 to 12 denier 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 10 days, and which knitted fabric has
a tissue contacting surface free from upstanding loops, and which
has interstitial spaces into which granulating tissue can grow, but
which readily releases granulating tissue 4 to 10 days after
emplacement.
2. The wound dressing of claim 1 in which the tissue compatible
material is a polymer subject to hydrolytic degradation to
non-toxic, tissue compatible absorbable components, said polymer
having glycolic acid ester linkages.
3. The wound dressing of claim 2 in which the tissue compatible
material is homopolymeric polyglycolic acid.
4. The wound dressing of claim 2 in which the tissue compatible
material is a polymer of 3-methyl-1,4-dioxane-2,5-dione.
5. The wound dressing of claim 1 in which the tissue compatible
material is a polymer of N-acetyl-D-glucosamine.
6. An interiorly sterile strippable package having therein in
sterile condition 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
moisture of the order of that of the intact human skin
(approximately 2.2 mg/sq. cm./hr), which comprises: an elastomeric
layer of the order of 0.1 to 5 mils thick, and which elastomeric
layer has bonded thereto a fabric knitted of continuous fibers of
the order of 1/2 to 12 denier 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 10
days, and which knitted fabric has a tissue contacting surface free
from upstanding loops, and which has interstitial spaced into which
granulating tissues can grow, but which readily releases
granulating tissue 4 to 10 days after emplacement.
7. A method of protecting the surface of living tissue during a
healing process which comprises: during a preliminary period,
covering and protecting the surface of damaged tissue by emplacing
thereon 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 moisture of the order
of that of the intact human skin (approximately 2.2 mg/sq.
cm./hr.), which comprises: an elastomeric layer of the order of 0.1
to 5 mils thick, and which elastomeric layer has bonded thereto a
fabric knitted of continuous fibers of the order of 1/2 to 12
denier 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 10 days, and which
knitted fabric has a tissue contacting surface free from upstanding
loops, and which has interstitial spaces into which granulating
tissue can grow, but which readily releases granulating tissue 4 to
10 days after emplacement, permitting granulation tissue to grow
thereunder to give a clean wound closed by said dressing, stripping
off said dressing, to expose granulation tissue, then autografting
living skin to said exposed granulation tissue.
8. The process of claim 7 in which the tissue compatible material
is homopolymeric polyglycolic acid.
Description
BACKGROUND OF THE INVENTION
This invention relates to the treatment of mammals, particularly
humans, and, to some extent, animals, which have incurred severe
burns or tissue damage which leaves an exposed wound whose skin
cover has been damaged. One purpose is to convert a contaminated
and open wound to a clean and closed wound in the shortest time
possible, protect the wound from outside infection, and maintain it
in such condition that the healing process will proceed to a point
where coverage by and the taking of autograft skin becomes
possible.
It has been customary to use human cadaver skin or porcine skin
among other devices to dress and protect wounds and to aid in the
development of granulation tissue prior to autografting.
The wound dressing should make the patient more comfortable, reduce
protein loss, reduce evaporative heat and water losses from the
wound surface and prevent further contamination. It is desirable
that the use of the dressing results in decreasing existing
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 flexible to permit at least
some flexing of the wound surface. The desired degree of flexing to
some extent varies with the location of the wound. For example, a
wound surface adjacent a joint should preferably have greater
flexibility than a wound adjacent a less flexed area such as the
chest or back.
In general, the characteristics of a wound dressing, particularly a
burn dressing, are known and recognized -- but improvements are
very much in demand.
DESCRIPTION OF THE PRIOR ART
The use of polyglycolic acid is disclosed in a series of patents
and applications to Schmitt, et al:
U.S. Pat. No. 3,297,033, Schmitt and Polistina, Jan. 10, 1967,
SURGICAL SUTURES, discloses polyhydroxyacetic ester absorbable
sutures. The material is also called polyglycolic acid, and is
disclosed as permitting small quantities 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 percent, as shown by U.S. Pat. No. 2,668,162, Lowe, Feb.
2, 1954, PREPARATION OF HIGH MOLECULAR WEIGHT POLYHYDROXY-ACETIC
ESTER.
U.S. Pat. No. 3,463,158, Schmitt and Polistina, Aug. 26, 1969,
POLYGLYCOLIC ACID PROSTHETIC DEVICES, discloses surgical uses of
polyglycolic acid, and incorporates definitions of some terms.
U.S. Pat. No. 3,620,218, Schmitt and Polistina, Nov. 16, 1971,
CYLINDRICAL PROSTHETIC DEVICES OF POLYGLYCOLIC ACID, lists many
uses of polyglycolic acid.
U.S. Pat. No. 3,736,646, Schmitt and Epstein, June 5, 1973, METHOD
OF ATTACHING SURGICAL NEEDLES TO MULTIFILAMENT POLYGLYCOLIC ACID
ABSORBABLE SUTURES, discloses surgical elements of a copolymer
containing from 15 to 85 mol percent glycolic acid and 85 to 15
percent lactic acid.
U.S. Pat. No. 3,739,773, Schmitt and Polistina, June 19, 1973,
POLYGLYCOLIC ACID PROSTHETIC DEVICES, claims particularly bone
pins, plates, nails and screws of polyglycolic acid.
U.S. Application Ser. No. 365,656, Schmitt and Polistina, May 31,
1973, SURGICAL DRESSINGS OF ABSORBABLE POLYMERS, now U.S. Pat. No.
3,875,937, Apr. 8, 1945, discloses additional subject matter on
surgical dressings of polyglycolic acid.
U.S. Pat. No. 3,739,773, supra, lists a number of U.S. patents on
methods for preparing polyglycolic acid and starting materials
therefor.
In U.S. Pat. No. 3,620,218, supra, in Column 2 are listed a number
of medical uses of polyglycolic acids, including in Column 2; line
52, knitted or woven fibrillar products, including velours, 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).
The 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. Pat. No. 3,526,224, R. M. Potts, Sept. 1, 1970, DRESSING,
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.sup.2 /24 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.
U.S. Pat. No. 3,648,692, L. M. Wheeler, Mar. 14, 1972,
MEDICAL-SURGICAL DRESSING FOR BURNS AND THE LIKE, discloses a
thrombogenic open-cell foam, such as a reticulated open-cell
polyurethane foam backed by a microporous polypropylene film, but
also disclosing natural rubber and silicone rubber of specified
pore size. A permeability of a 5 mil thick silicone rubber of 6.2
grams of liquid water per square foot per hour is disclosed and
oxygen penetration of 20 liters per 24 hours per 100 square inches
per 5 mil thickness per atmosphere. This patent shows a clear
recognition of many of the problems of burn dressings.
Studies are being made by and for governmental agencies on burn
protection. One such "Development of a Synthetic Polymer Burn
Covering" prepared by Dynateck R/D Company, for the Office of Naval
Research, June 1973, National Technical Information Service
AD-761,631 discloses the use of polymeric films, including lactic
acid polymers, and 75/25 lactic/glycolic copolymers, and the
disadvantages of flat, solvent cast films. A normal insensible
water loss from the human body is given as 2.2 mg/hr cm.sup.2,
quoting Treger, "Physical Functions of the Skin," Academic Press,
New York.
The complete disclosures of the above patents and articles are
hereby herein incorporated by this reference thereto.
SUMMARY OF THE 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 or silicone or natural rubber or poly(caprolactone)
which has a moisture permeability of the order of that of the
intact human skin and to which is adhesively united a knitted
fabric of a tissue compatible and absorbable material having a
close knit stitch so spaced as to permit slight 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.
The fibers themselves are absorbable by living tissue so that
fibers which are trapped within the wound are absorbed by the
living tissue without deleterious effects.
The present wound dressing may be used on almost any type 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
destroyed leaving underlying tissues which are either contaminated,
or subject to contamination by bacteria, or other contaminants, and
which wound is of such a size that new skin covered for it may not
form spontaneously, or that immediate protection and dressing is
required. Decubitus ulcers, sometimes called bedsores, are
effectively dressed with the subject dressing. It is desirable to
change the wound from a contaminated and open wound to a clean and
closed wound in the shortest time possible, to minimize protein
loss, control evaporative heat and water losses, and prevent
further contamination during the time required for the underlying
tissues to build up a granulating surface which will accept a skin
autograft.
By skin autograft is meant skin taken from another area of the
subject, and which is living so that when placed on the granulating
tissue, the skin will graft to the granulating tissue and grow
providing a skin surface at the wound area. With rare exceptions,
the skin of any other subject will be rejected and not permanently
graft to the wounded subject. With major burns, a sufficiently
large portion of the subject may be burned so that sites for donor
skin are limited and it is necessary to protect burned areas for a
prolonged period until graft donor sites can regenerate and be used
for a subsequent graft.
The generalized subject of burn treatment of this type is fairly
well recognized as are many of the requirements for such a wound
dressing. The medical profession recognizes the need for
improvements in burn site protection, during burn treatment.
Survivability after major burns has been improving -- the present
invention contributes towards such improvement.
The use of a synthetic tissue absorbable dressing eliminates many
disadvantages of prior art dressings, particularly as to
availability, and size, 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 suppleness, resiliency,
and the dressing's ability to mimic the topography of the wound in
such a fashion that there is a minimum gap between the tissue and
the dressing which minimizes air gaps and pools of liquid. 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 adequately to the surface of the wound, the body's own
defense mechanisms are effective in reducing the bacteria
population even in a contaminated wound.
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 loss of body
fluids such as serum or blood needs to be prevented by the dressing
but at the same time just as natural skin is permeable to moisture
vapor, a wound dressing must permit the escape of at least some
moisture to prevent pooling of body fluids which pools become sites
for infection. If the rate of moisture loss is too high, there is a
cooling effect from the heat required to convert the liquid to
vapor. If the wound is not covered so as to reduce moisture loss,
electrolytes, proteins, and other materials concentrate and crust
on the surface, leading to eschar formation. It is desirable that
the permeability be of at least approximately 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 effective under many conditions. A permeability of
about 0.4 mg./sq. cm./hr. to about 6 mg./sq. cm./hr. as measured by
ASTM method E96 gives good water vapor loss control. The values are
approximate as different skin areas lose moisture at a different
rate and, depending upon the temperature of the subject, the
temperature of the atmosphere, the movement of ambient air and
under other variables, the natural skin has a considerable range of
skin moisture loss. The 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 acceptable conditions, the
underlying tissues are protected and regenerate. There is a fine
and, perhaps, unascertainable line between the regenerative
processes of the tissue when protected from adverse effects and the
increase that might be caused by dressing characteristics and
environmental 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 injured, flexing of the joint and movement
of the underlying tissues requires that the wound dressing have
some flexibility. The minimum required flexibility is exceeded by
the present dressing and the dressing is sufficiently flexible for
tissue movement over joints and other areas.
Continuous fibers of about 1/2 to 12 denier per filament in a yarn
which is neither spun nor bulked nor textured are conveniently
used.
It is desirable that the fibers be absorbable by living tissue as
some of the fibers may remain in the wound, and non-absorbable
materials can be the source of undesirable side effects.
A preferred tissue absorbable polymer is polyglycolic acid, such as
described in the Schmitt patents above and which is meeting with
commercial 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. Pat. No.
3,736,646, supra.
A polymer having an ordered configuration of glycolic acid units
and lactic acid units which is tissue absorbable is described at
length in Ser. No. 435,365, Jan. 24, 1974, Augurt, Rosensaft, and
Perciaccante, UNSYMMETRICALLY SUBSTITUTED
1,4-DIOXANE-2,5-DIONES.
Another absorbable polymer which may be used for the graft is
poly(N-acetyl-D-glucosamine) such as described in U.S. Ser. No.
441,717 filed Feb. 11, 1974, Richard Carl Capozza,
POLY(N-ACETYL-D-GLUCOSAMINE) PRODUCTS.
The important 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, and it has sufficient strength
to maintain its integrity during the manufacture of the wound
dressing, that it maintains its integrity in contact with the
tissue long enough for granulation tissue to form and the dressing
removed, about 4 to 10 days and yet is absorbable within a
reasonable length of time, for instance, about 90 days, so that no
fragments remain as a foreign body trapped in tissue after the
wound has healed. The dressing may be changed after 24 hours, or
less, but mature granulation tissue does not form in such a short
time.
The above two patent applications, the disclosures of which are
herein incorporated by this reference thereto, give examples of
such materials.
Inasmuch as the useful characteristics of such materials 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 at about 1/2 to about 12
denier per filament, are in a non-textured continuous yarn which is
knitted as described below. The knitted fabric may be adhesively
united to the elastomeric layer as it is formed. More conveniently,
when the elastomeric layer is formed, a separate adhesive layer is
placed thereon and the knitted fabric is placed on such adhesive
layer. Evaporation of the solvent in the polyurethane layer unites
the knitted absorbable fabric to the moisture-controlling
polyurethane layer.
The elastomeric layer may be any material which is permeable to
moisture vapor, has a low Young's modulus, and is thus readily
conformable to the wound surface. Elastomers with a Young's modulus
of between about 200 pounds per square inch per inch and about
40,000 pounds per square inch per inch give acceptable results. A
particularly useful material is polyurethane. A soft, flexible
elastomeric layer of polyurethane of the order of 1 mil thick (0.1
to 5 mil) provides a barrier to excessive water loss, is permeable
to moisture within the range of that of the intact human skin,
which is approximately 2.2 mg./sq. cm./hr., to two to four times
this value, which permits moisture vapor to pass through the
backing layer at such a rate that formation of liquid pools under
the dressing is minimized, and yet the water loss is within a
desirable range as regards heat loss and concentration of dissolved
components in the body fluids which are underneath the
dressing.
At the time of use, the wound should be debrided in accordance with
the usual techniques. Some surgeons prefer to use antimicrobial
agents such as silver nitrate or Sulfamylon
(alpha-amino-p-toluenesulfonamide acetate). Then, the knitted
surface of the wound dressing is placed in contact with the wound,
being sure that it conforms 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,
additional bandages, or suturing. A low pressure bandage may be
used to hold the dressing in place, depending upon the location of
the dressing and the condition of the patient. The dressing is
permitted to remain in place for up to approximately 7 days. There
are times when many dressing changes are required before the wound
is in condition for autografting or before skin for autografting
becomes available. For major burns or traumatic tissue damage,
prolonged treatment may be required before the wound is ready for
final grafting.
In other instances, a wound may be fairly minimal and the present
wound dressing may be applied even though a less adequate wound
dressing could have been used, and a single application of the
wound dressing permits substantial healing.
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. The covering does not interfere with normal physiological
processes conducive to wound healing and autograft
conditioning.
The composite structure provides both a good moisture control layer
and bacteria barrier. The conformability resulting from the
elastomeric backing permits conformation to nearly any wound
topography.
DRAWINGS
FIG. 1 shows a fabric face view of a polyglycolic acid knit wound
dressing at about 30 diameters magnification, using a scanning
electron microscope.
FIG. 2 is part of the same structure as claim 1, at about 60
diameters magnification.
FIG. 3 is a lateral cross section view of the wound dressing of
FIG. 1, at 50 diameters magnification, using reflected light on a
section in an epoxy matrix.
FIG. 4 is a longitudinal cross section of the wound dressing of
FIG. 1.
FIG. 5 is a drawing showing the wound dressing in a double envelope
package.
FIG. 6 is a drawing in a pictorial, partly broken away, showing the
sterile wound dressing in a strippable envelope.
As shown in the drawings, a polyurethane such as described in U.S.
Pat. 3,582,423, Wang, June 1, 1971, PROCESS FOR COATING POROUS
SUBSTRATES, and sold as Helastic 13141 polyurethane, is cast on a
release coated paper to form a film with a thickness of 1 mil. The
material is a reaction product of a hydroxy terminated polyester
such as diethylene glycol adipate and p,p'-methylene dianiline and
a mixture of 2,4- and 2,6-toluene diisocyanates, at about 25
percent solids. The polyester type segmented polyurethane is
permitted to harden to form a water vapor permeable elastomer
layer, and then coated with an additional half a mil thickness of
the same polyurethane on which is placed the knit fabric of
absorbable polymer.
The polyurethane structure may be graphically described as:
NH.sub.2 -R.sub.1 --NH-CO-NH-R.sub.2 -NH-CO-O-R.sub.3
-O-CO-NH-R.sub.2 -NH---CO-NH-R.sub.1 ].sub.n NH.sub.2
where, ##SPC1##
or
--CH.sub.2 -CH.sub.2 -CH.sub.2 -CH.sub.2 -- O-CH.sub.2 -CH.sub.2
-CH.sub.2 -CH.sub.2 ].sub.m
The polyurethane film is cast by pouring the resin dissolved in
solvent on a release paper such as a silicone coated release paper,
which is pulled through rollers set to leave about 4 mils of 25
percent solids solution on the release paper, so that when dry a 1
mil layer remains. After a second pass to leave an additional
adhesive coat which dries to about 0.5 mil thickness, the knitted
fabric is placed with the loop side in contact with the still tacky
adhesive layer and pressed into place.
The knitted structure embodied in the wound dressing may be a
tricot knit, as is formed in a conventional flat warp knitting
machine. As shown in FIGS. 1 and 2, the fabric comprises a system
of yarns which is fully threaded on a 28 gauge knitting machine so
as to knit on all of the needles of the machine and which is
controlled to knit in a pattern 1-2/1-0. A second system of yarns
is likewise fully threaded so as to knit on every needle and is
controlled to knit 0-1/4-3. Thus, as shown in FIGS. 1 and 2, the
first system of yarns are knit to provide knitted loops as
alternately placed in adjacent wales. The second system of yarns
are knit alternately to provide knitted loops in laterally-spaced
wales with underlaps spanning between these wales and across the
intermediate wales. Because of the tension in the yarns and the
overfeeding of the second system of yarns, the knitted loops are
canted alternately left and right along each wale. Furthermore, the
overfeeding of the yarn causes the loops to project from the
surface to provide a relatively loose looped pile effect. In the
illustrated embodiment, the overfeed of the second system yarns is
at least twice the feed of the first system of yarns so that
overall coverage is provided on the looped side of the fabric by
the projecting loops.
The knitted base fabric may take other forms, and other knitting
mechanisms may be used for making the fabric. For example, the base
fabric structure may be knitted on a warp knitter having a terry
attachment or other pile-forming mechanism, or on a weft knitter
with a fleece or other attachment. Of prime importance is the
location of projecting yarn portions of one yarn system to
substantially cover the interknitted structure with a degree of
freedom to be displaced relative thereto.
The illustrated embodiment of the fabric comprises a base fabric
structure knitted on a 28 gauge tricot warp knitter, with two bars
fully threaded. The front bar was operated to knit 1-2/1-0 and the
back bar was operated to knit 0-1/4-3. Both bars of the machine
were threaded with 25 denier 12 filament non-textured polyglycolic
acid having a tenacity of 6.8 grams per denier. The feed ratio
between the front and back bars was set to 0.345:1, and the
knitting density was 80 courses on the machine with a quality of 6
inches.
The knitted fabric is pressed into the polyurethane while still
containing enough solvent to be soft and adhesive. The looped face
of the fabric is embedded in the moisture control layer.
FIG. 1 shows the smoother surface of the knit fabric which is the
face contacting the wound. This figure is at 30 diameters
magnification and shows the wound contacting face. FIG. 1 is from a
scanning electron microscope, which gives a great depth of field to
a photomicrograph.
FIG. 2 is similar but at 60 diameters magnification. The individual
fibers are clearly seen, as in the knit construction. The structure
of the knit permits granulation tissue to grow closely to the knit,
but separate smoothly and readily when the wound dressing is
removed.
FIG. 3 is a cross section of the same wound dressing as in FIGS. 1
and 2. The wound dressing was embedded in an epoxy matrix, which
was permitted to harden, then sliced and polished. The epoxy resin
tends to distort the smooth surface of the polyurethane film 16.
The embedment of the polyglycolic acid fibers 17 in the knit loops
in the polyurethane film keeps the laminate together. The picture
is a photomicrograph by reflected light from a polished surface at
50 diameters magnification. Most of the individual fibers are cut
at nearly right angles.
FIG. 4 is a similar section at right angles to FIG. 3, and shows a
number of fibers 17 cut nearly lengthwise. Again the barrier layer
of polyurethane is nearly flat, but is distorted by the epoxy resin
used as a matrix for the cross section.
The laminate should have a delamination pull of at least about 1
pound per inch of width. The delamination resistance may drop
somewhat during use, but when the wound dressing is used, should be
high enough to pull the knit fabric from the wound.
As a surgical device, it is obviously desirable, almost mandatory,
that the wound dressing be sterile at the time of use. The wound
dressing may be sterilized by an appropriate sterilizing cycle
using ethylene oxide as a sterilizing agent. Radiation
sterilization may be used, as may heat sterilization.
If ethylene oxide is used to sterilize, it is convenient that the
ethylene oxide be diluted with carbon dioxide or a
chlorofluoroalkane to such an extent that the sterilizing gas is
non-explosive. For storage stability, it is desirable that the
wound dressing be protected from atmospheric influences. Because
the wound dressing contains hydrolyzable polyglycolic acid ester
linkages, the linkages can be hydrolyzed by ambient moisture under
room storage. The wound dressing requires that the knitted fabric
retain sufficient strength to be separated from the wound when the
dressing is changed. Preferably, it should retain strength at least
10 days to two weeks. It is desirable that such storage conditions
be used as to maintain the wound dressing in a dry environment so
that whether used immediately after packaging or after a storage
period of several years, the wound dressing has the same
characteristics and, hence, has known predictable attributes as far
as the using surgeon is concerned.
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. Pat. No. 3,728,839, Arthur Glick, Apr. 24, 1973, STORAGE
STABLE SURGICALLY ABSORBABLE POLYGLYCOLIC ACID PRODUCTS. As there
described, the polyglycolic acid product is stored in a moisture
proof envelope in which conveniently the product is packaged except
for one open side and sterilized using ethylene oxide diluted so as
to be non-explosive, and then while protecting sterility, the
product is vacuum dried and the envelope sealed. By having the foil
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. Conveniently, but not
necessarily, the wound dressing may be placed between two sheets of
paper, or a single sheet of paper with a fold, so that the wound
dressing is held in flat condition between the sheets during
storage and service to the using surgeon.
As shown in FIGS. 5 and 6, the polyglycolic acid-polyurethane
laminate wound dressing 11 is placed in a folded sheet of paper 12,
which is sealed in an inner envelope 13, which is sealed in an
outer strippable envelope 14. The package is similar to those used
for sutures.
A single envelope can be used, which, on stripping, releases the
wound dressing folded in a sheet of paper 12. Such a single
envelope package is shown in U.S. Pat. 3,017,990, Singerman, Jan.
23, 1962, STERILE PACKAGE FOR SURGICAL FABRIC.
For large sheets, the wound dressing may be folded, but for sheets
up to 3 .times. 5 inches it is conveniently placed in an envelope
large enough to hold the sheet flat. A plurality of sheets may be
packaged in a single envelope if desired. Single sheets of about 3
.times. 5 inches 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 use. For many surgical procedures, 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. Conveniently, the wound dressing
is made available in sterile form in sheets 3 .times. 5 inches, 3
.times. 12 inches, 3 .times. 18 inches, 3 .times. 24 inches and
continuous rolls, about 12 inches wide. Other sizes and shapes can
be provided to supply the using surgeon with a choice of sizes,
consistent with reasonable inventory commands.
Because it is not practical to purposely infect humans, tests were
conducted on rats which had wounds created by surgically excising
20 to 30 percent of the body surface. These wounds were seeded with
dosages of 10.sup.5 Pseudomonas Aeruginosa. After a 48 hour test
period, all of the control animals, that is, those in which the
wound was left bare, showed greater than 10.sup.7 colony forming
units per gram of tissue of Pseudomonas Aeruginosa. Porcineskin
dressed animals, that is, those in which porcineskin was used as a
dressing, had counts between 10.sup.3 and 10.sup.7 Pseudomonas per
gram of tissue whereas animals using the wound dressing of this
invention showed a marked reduction. Seven of the dressings showed
less than 10.sup.2, two had 10.sup.3, and one had 10.sup.5. These
results are extremely encouraging and show that the present wound
dressing aids dramatically in reducing contamination of wounds.
Usually, rats with values above 10.sup.5 do not survive.
An article Saymen, Nathan, Holder, Hill and MacMillan, Control of
Surface Wounds Infections: Skin versus Synthetic Grafts, Applied
Microbiology, June 1973 (V. 25, No. 6, pages 421 to 434), gives
considerable detail from others who have been experimenting on
surface wound infection. This article indicates that grafts may
lower bacterial levels in an established infection by modifying the
host response to the surface contamination.
In summary, the present wound dressing remains flexible and
adherent to a wound, has excellent conformity, including
suppleness, resiliency, and ability to mimic the wound topography,
controls the loss of water, prevents the loss of protein, and
protects against contamination of the wound. When removed after
about seven days, wounds showed granulation tissue covering 80
percent or more of the wound. Granulation tissue is a young
vascularized connective tissue formed in the process of healing of
wounds.
When applied to contaminated wounds, the subject wound dressing
reduced bacterial growth, allowing the host's own defense
mechanisms to deal with the surface infection effectively. When
removed after seven days, and autografted, 80 to 90 percent of the
grafted area was viable 21 days after transplantation.
In an additional preparation, polyglycolic acid yarn, from a suture
manufacturing run, was spun into fibers of about 2 denier per
filament, using a multiple orifice extrusion head yielding a 56
denier yarn with 28 filaments, an average tenacity of 6.8 grams per
denier, and an average elongation of 22 percent. The knit
scaffolding layer was knit on a tricot machine, of 28 needles per
inch, with a warp of 14 ends per inch, using a front bar pattern
2-3/1-0, a runner of 57.5 inches, and a threading of 1 in, 1 out,
and a back bar pattern of 1-0/7-8, a runner of 134 inches, and a
threading of 1 in, 1 out, take-up gears 108/104, a quality of 8.5
inches with a density of 3.0.+-.0.2 ounces per yard being
obtained.
The moisture control layer was cast of Helastic 13141 polyurethane
resin, having 25 percent solids, in dimethylformamide, and a
viscosity range of 6,000 to 15,000 centipoises. A film 0.6 mils dry
thickness was cast as a skin coat, on a release paper, dried at
150.degree.C. for four minutes then followed by a 0.4 mil dry
thickness tie coat, to which, dried at 85.degree.C. for about 10
seconds and while still soft, was applied the knit layer, with the
loop side toward the polyurethane film.
The polyglycolic acid knit was pressed into the still soft
polyurethane film. The laminate was cured at 150.degree.C. for
three minutes. The peel strength was 6 pounds per linear inch.
The laminate was cut to 3 .times. 5 inches size and sterilized as
above, in strippable packages.
The knit surface presented to the wound readily conforms to wound
topography. The knit absorbs some fluids from the wound, and
rapidly adheres by capillarity. The interstices fill with body
fluids, and are so close to the wound that host defense mechanisms
aid in controlling infection.
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