Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Web – sheet or filament bases; compositions of bandages; or...
Reexamination Certificate
1997-10-22
2001-05-29
Dees, Jose′ G. (Department: 1616)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Web, sheet or filament bases; compositions of bandages; or...
C424S423000
Reexamination Certificate
active
06238691
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hydrogel wound dressing and a method of making and using the same. More particularly, the present invention relates to a flexible hydrogel wound dressing which is highly absorptive, contours to a wound site and maintains the wound in a moist state to promote healing thereof and the method of producing and using the same.
BACKGROUND OF THE INVENTION
The treatment of draining wounds is a problem in the medical profession. Wound exudate such as blood, serum and purulent matter from a draining wound can lead to bacterial growth and delayed healing if not treated properly. Often times it is difficult to maintain wounds free of such wound secretions to allow for healing. Another concern in treating such draining wounds is that some believe that allowing a wound to heal in a slightly moist state may actually accelerate healing. Accordingly, the medical profession desires a means for maintaining draining wounds in a clean, moist protected state.
Currently in an attempt to meet such wound treatment needs there are wound exudate absorption compositions which comprise hydrogel materials in powder form. One example of such a powder material includes dextranomer beads. Dextranomer beads are hydrophilic spherical beads which are applied to a wound to absorb wound exudate. Disadvantages noted in using materials in powder form include difficulty in even application, lumping and clumping of the material after application and difficulty in removal of the material from the wound site without damaging the newly formed tissues of the wound.
U.S. Pat. No. 4,226,232 discloses the blending of a hydrogel material with a liquid curing agent such as polyethylene glycol prior to introducing the material to the wound. A difficulty of using this material is that it can not be sterilized by irradiation due to the formation of free radicals within the gel material. The free radicals within the gel material cause instability of the product and thereby shortens the shelf life thereof.
U.S. Pat. No. 5,059,424 discloses a wound dressing comprising a backing member with an adhesive layer and hydrogel material of 15-30% polyhydric alcohol, 8-14% iso phorone diisocyanate prepolymer, 5-10% polyethylene oxide-based diamine, 0-1% salt and the balance water. Difficulties associated with the use of this wound product includes the limitation of not being able to cut the dressing to a size appropriate for the particular wound and still have the backer intact. Additionally, the hydrogel material disclosed in this patent lacks the necessary strength to be used and removed, without the added support of the backer material.
The need exists for a sterile wound dressing that provides a size a appropriate protective covering for a draining wound capable of absorbing exudate from the wound. It is also desirable to have a wound dressing suitable to protect a wound from debris and foreign matter capable of contaminating the wound. It is also desirable to have a wound dressing that cushions the wound from pressure. It is also desirable to have a wound dressing that does not adhere to the new tissue forming in the wound. It is also desirable to have a wound dressing that maintains a wound in a slightly moist state to promote healing.
SUMMARY OF THE INVENTION
The present invention relates to a hydrogel wound dressing capable of absorbing exudate from a draining wound without becoming adhered thereto. The wound dressing maintains the wound in a slightly moist state to promote healing of the wound while retaining its overall strength to allow for removal thereof in a unitary fashion.
The hydrogel wound dressing of the present invention is a polyurethane hydrogel material comprising polyurethane prepolymer, deionized water, glycols and optionally an antimicrobial and/or a bacteriostatic agent.
The method of producing the hydrogel material of the present invention involves hydrolysis and addition reactions to produce a three-dimensional cross-linked polyurethane hydrogel as described in more detail below. The resultant polyurethane hydrogel material is blended and cast molded to allow for gelation thereof in fewer than 180 minutes at room temperature. The subject wound dressing is then optionally subjected to temperatures below 0° C. to remove excess water and then packaged and sterilized using radiation sterilization or other suitable sterilization technique, prior to distribution.
DETAILED DESCRIPTION OF THE INVENTION
The polyurethane hydrogel wound dressing of the present invention is capable of absorbing moisture from a wound site until the overall composition comprises approximately 95 percent to 99 percent water or fluid. The subject non-adhesive hydrogel dressing provides for moist wound healing, absorbs wound exudate, allows for fewer dressing changes, allows for easy removal with no trauma to the wound, protects the wound from contamination and minimizes odor.
The polyurethane hydrogel material of the present invention is generally produced through a hydrolysis and an addition reaction. The hydrolysis and addition reactions are achieved by blending polyurethane prepolymer with polypropylene glycol, water and propylene glycol in accordance with the following reactions:
STEP 1:
O═C—N—R
1
—N═C═O + 2 R
2
OH → R
2
OOC—HN—R
1
—NH—COOR
2
+ O═C—N—R
1
—N═C═O
Prepolymer
+ Alcohol
Polyurethane
Unreacted Prepolymer
STEP 2:
R
1
—NH—COOR
2
+ O═C═N—R
1
—N═C═O + 2 H
2
O → R
1
NH
2
+ 2 CO
2
+ O═C═N—R
1
—N═C═O + R
1
—NHCOOR
2
Polyurethane + Unreacted Prepolymer + Water
Polyamine(unstable intermediate) +
Carbon Dioxide + Unreacted
Prepolymer + Polyurethane
STEP 3:
R
1
—NH—COOR
2
+ O═C═N—R
1
—N═C═O + 2 R
1
NH
2
→ R
1
HNOC—HN—R
1
NH—CONHR
1
+ R
1
—NH—COOR
2
Polyurethane + Unreacted Prepolymer
Polyurea (stable) + Polyurethane
+ Polyamine (unstable intermediate)
wherein the R
1
groups may be the same or different selected from the group consisting of C
1-12
alkyl repeating groups such as for example methyl, ethyl, or propyl, but preferably propyl to increase clarity; C
1-12
mono or poly hydroxyalkyl repeating groups, such as for example hydroxymethyl or dihydroxypropyl but preferably dihydroxypropyl, to increase clarity; C
1-12
acyl repeating groups, such as for example, acetyl or proprionyl, but preferably proprionyl to increase clarity; C
1-12
alkoxyalkyl repeating groups, such as, for example, methoxyethyl or ethoxypropyl, but preferably ethoxypropyl to increase clarity; C
1-12
aminoalkyl repeating groups, such as, for example, aminomethyl or aminopropyl, but preferably aminopropyl to increase clarity; C
1-12
acylaminoalkyl repeating groups, such as, for example, acetylaminomethyl or proprionylaminomethyl but preferably proprionylaminomethyl to increase clarity; C
1-12
oxyalkyl repeating groups, such as, but not limited to, oxyethylene, oxypropylene or oxybutylene, but preferably oxyethylene and/or oxypropylene to increase clarity, such repeating units having an average molecular weight of about 7,000 to about 30,000 capped with aromatic, aliphatic, or cycloaliphatic isocyanates, diisocyanates, or polyisocyanates, but most preferably diisocyanate- or polyisocyanate-capped repeating units, as described above, having molecular weights of at least 10,000. The use of aliphatic polyisocyanates is preferred in the present invention to achieve a greater degree of handling freedom, since aliphatic isocyanate-capped prepolymers typically require longer periods of time to gel. In addition, aliphatic polyisocyanates will be preferred when the material is intended to be used in medical applications, because of decreased toxicological considerations. By contrast, prepolymers capped with aromatic polyisocyanates will gel in about 30 to 60 seconds as opposed to 20 to 90 minutes as typical for the aliphatic isocyantes. Gelation within 30 to 60 seconds is a disadvantage for use in the present ap
Dees Jose′ G.
Denninger Douglas E.
Shelborne Kathryne E.
Sherwood Services AG
Vacca Rita D.
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