Wound dressing

Abstract

The invention relates to a sterile wound dressing having a backing and a nonabsorbent elastomer wound contact layer, wherein the elastomer matrix is formed by a synthetic three-block elastomer, preferably a copolymer of polystyrene block and polyolefin block (SEPS, SEBS, SEEPS, etc.) or mixtures thereof, wherein the total polymer content is less than 3.2 wt %, in particular 3.0 wt % or less, preferably 2.6 wt % or less, and is plasticized by an apolar oil and/or petroleum jelly.

Claims

1. A wound dressing comprising: a) a backing; and b) a non-absorbent elastomeric wound contact layer, said wound contact layer comprising an elastomeric matrix plasticized by an apolar oil, petroleum jelly or mixture thereof; said elastomeric matrix formed from a mixture of: at least one high molecular weight synthetic triblock elastomer with an average molecular weight of less than 300,000 daltons and at least one ultrahigh molecular weight synthetic triblock elastomer with an average molecular weight of more than 300,000 daltons, said synthetic triblock elastomers selected from the group consisting of polystyrene-polyethylene-polybutylene-polystyrene (SEBS), polystyrene-b-poly(ethylene/propylene)-b-polystyrene (SEEPS), polystyrene-polyethylene-polypropylene-polystyrene (SEPS) and mixtures thereof; the total polymer content of the elastomeric matrix is less than 3.2% by weight; the ultrahigh molecular weight synthetic triblock elastomer comprises approximately 10% to approximately 50% of the total polymer content; and said elastomeric matrix having a molecular weight of 150,000 to 600,000.

2. The wound dressing according to claim 1, wherein at least one of the high molecular weight synthetic tri-block elastomer or ultrahigh molecular weight synthetic tri-block elastomer has a Brookfield viscosity of 5000 mPas or more for a 10% solution in toluene at 30 C.

3. The wound dressing according to claim 1, wherein the elastomeric matrix comprises an ionic or non-ionic hydrocolloid that is dispersed homogeneously in the matrix.

4. The wound dressing according to claim 1, wherein the backing comprises a material selected from a group consisting of open mesh knit, a woven fabric, a non-woven fabric, polyurethane foam, and mixtures thereof.

5. The wound dressing according to claim 1 wherein the elastomeric matrix has an active ingredient in a therapeutically effective amount.

6. The wound dressing according to claim 5, wherein the active ingredient is dissolved, dispersed or distributed homogeneously in the elastomeric matrix.

7. The wound dressing according to claim 5, wherein the elastomeric matrix does not contain active ingredient in all areas.

8. The wound dressing according to claim 5, wherein the active ingredient comprises metals, metal compounds, or mixtures thereof.

9. The wound dressing according to claim 8, wherein the metals or metal compounds comprise metal salts.

10. The wound dressing according to claim 5, wherein the active ingredient is selected from the group consisting of an oligomeric/polymeric biguanide, an oligomeric/polymeric guanide, a broad spectrum antiseptic and mixtures thereof.

11. The wound dressing according to claim 10, wherein the active ingredient is polyhexamethylene biguanide (PHMB).

12. The wound dressing according to claim 10, wherein the active ingredient is octenidine.

13. The wound dressing according to claim 1, wherein the elastomeric matrix contains a tackifier in order to increase the adhesive strength.

14. The wound dressing according to claim 1, wherein the wound dressing exhibits improved cohesion and elasticity upon radiation sterilization compared to a wound dressing that does not include an ultrahigh molecular weight synthetic triblock elastomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) In an especially preferred embodiment of the invention, thermoplastic elastomers (TPE) and/or elastomer mixtures with an especially high molecular weight are used to counteract the negative effects of radiation sterilization on cohesion of the matrix. It has surprisingly been found that the addition/use of the preferred ultrahigh molecular elastomers such as Septon 4077 greatly improves cohesion after sterilization.

(2) Due to the content of relatively temperature-sensitive components such as petroleum jelly or CMC in the matrix, the processing temperature is limited (preferably max. approximately 140-145 C.). The expected increase in the processing temperature when using an ultrahigh molecular elastomer is only minor, however, and is within the acceptable range.

(3) The wound contact layer of a wound dressing according to the invention according to the invention preferably comprises, in addition to an organic polymer matrix, a plasticizer, and hydrophilic organic and/or inorganic microparticles which form a gel on contact with an aqueous solution.

(4) According to one of the features of the invention, the wound dressing comprises a flexible open mesh fabric, wherein the fabric comprises fibers sheathed with an elastomeric cohesive and nonsticking gel/matrix, so that the mesh essentially cannot be clogged, i.e., remains permeable.

(5) The polymer matrix may contain a synthetic thermoplastic hydrophobic three-block copolymer A-B-A, in which the polymer matrix preferably contains no more than 3.2 parts by weight, in particular no more than 2.6 parts by weight of a block polymer, in which the terminal block A may be of the polystyrene type and the central block B may be of the saturated polyolefin type and the styrene component is between 25% and 40%.

(6) To obtain a hydrophobic matrix according to the invention with adequate cohesion even after radiation sterilization, three-block elastomers of the polystyrene-polyethylene-polybutylene-polystyrene (SEBS) type, or polystyrene-polyethylene-polypropylene-polystyrene (SEPS) type and/or polystyrene-b-poly(ethylene/propylene)-b polystyrene (SEEPS) type with high and ultrahigh molecular weights are used.

(7) It is expedient to use hydrogenated polystyrene-polyethylene-polybutylene-polystyrene copolymers (SEBS, e.g., G1651, MD 6933, Kraton). Within the scope of the invention, hydrogenated polystyrene-b-poly(ethylene/propylene)-b-polystyrene copolymers (SEEPS, Septon 4055 and Septon 4077, Kuraray) are preferred.

(8) To obtain a hydrophobic matrix according to the invention, at least one three-block elastomer of the SEBS or SEPS type, especially SEEPS with a very high molecular weight (at least 200,000 dalton, preferably at least 400,000 dalton) and with a Brookfield viscosity of at least 5000 mPas (for a 10% solution in toluene a 30 C.) is selected.

(9) Such polymer compositions allow good inclusion of the fibers of the fabric as the backing, which thus remain completely isolated from the wound, so that no direct contact between fiber and regenerated tissue is risked at any time, which could result in a fiber inclusion in the wound, resulting in painful destruction of the tissue when the dressing is pulled away.

(10) By using a mixture of the high-molecular and ultrahigh-molecular thermoplastic elastomers (TPE), a very soft compress is obtained which conforms well to the surface that is to be protected, while on the other hand, because of the strong cohesion and elasticity of the matrix even after radiation sterilization, is at no time so harmful, when applied to the wound according to the invention, that the fibers are exposed and come in direct contact with the wound. The amount of the ultrahigh-molecular polymer with a molecular weight of more than 300,000 dalton in the total polymer content is less than 50 wt %, in particular less than 25 wt % to maintain adequate processability. The desired improvement in sterilization stability under radiation sterilization is achieved when the amount of ultrahigh molecular polymer with a molecular weight of more than 300,000 dalton in particular approximately 400,000 to 450,000 dalton in relation to the total polymer content is more than 5%, in particular more than 10%, especially preferably 20% or more.

(11) Due to the high oily plasticizer content, which is preferably obtained by starting with a mixture of mineral oil and petroleum jelly, in combination with a very low polymer/elastomer content, the matrix also acts like a pure fatty substance, which thus ensures very good tissue tolerability and properties of nonadhesion to the surface of the compress.

(12) Of the products/plasticizers that are readily suitable for plasticizing the elastomer, reference may be made in particular to fatty substances that are liquid or solid at room temperature, in particular paraffin oils, medicinal white oils, mineral oils, ointment paraffins, petroleum jelly, silicone oils or silicone fats and/or waxes as well as mixtures thereof. Plasticizers such as petroleum jelly, whose drop point is between 35 C. and 70 C., are preferred. Medicinal white oils, whose purity requirements conform to Ph. Eur., are also preferred.

(13) The matrix may also contain antioxidants. Suitable antioxidants include the sulfur antioxidants, for example, the zinc dibutyl dithiocarbamate marketed by the company Akzo Nobel Chemicals under the brand name Perkacit ZDBC and/or the phenolic antioxidants, for example, the products marketed under the brand names Irganox 1010, Irganox 565, Irganox 1035 by the company BASF may also be mentioned as suitable antioxidants.

(14) The compound in Irganox 1010 is preferred within the scope of the present invention.

(15) The wound contact layer of a wound dressing according to the invention according to the invention may also comprise an additive selected from the group consisting of another stabilizer, extrusion aids, fillers, pigments, dyes, crosslinking agents, odor suppressants, tackifiers, tolerability mediators, and combinations therefore.

(16) The hydrocolloids, which are known in general (CMC, alginates, gelatin, xanthan, pectins) but also silicates such as bentonites, aerosils, or superabsorbers may be used as the hydrophilic organic and/or inorganic microparticles that bind water and undergo gelation in the process. Microparticles with a diameter of 50 to 300 m (assuming a spherical shape), in particular with a diameter of 50 to 200 m, are preferred.

(17) The hydrocolloid dispersed in the elastomer matrix in a relatively small amount makes it possible to retain a slightly hydrophilic character, which is sufficient to maintain a moist wound environment that promotes wound healing, but is not sufficient to enable the gel to absorb a great deal of water. In fact, this absorption capacity is not desirable because it leads to swelling of the gel, which would cause a gradual clogging of the openings left in the structure of the compress. The compress would thus become occlusive which would thus suppress the option of eliminating the exudates while also increasing the risk of maceration and would clog the passages formed in the contact layer and cause maceration of the wound.

(18) According to the present invention, a polymer composition comprising a nonabsorbent elastomer matrix/wound contact layer is made available.

(19) With respect to the elastomer polymer matrix, the term nonabsorbent means that the hydrophobic matrix absorbs less than 35%, preferably less than 25% of the saline solution (aqueous 0.8% NaCl solution) in 24 hours, based on the dry weight of the matrix.

(20) In elastomeric thermoplastic compositions, cohesion refers to the forces which hold the mass together. These cohesive forces are responsible for the toughness (viscosity) and flow behavior (rheology) of the elastomer matrix in processing and are also responsible for the strength of the matrix under stress. The cohesive forces in such systems are described by characteristic values such as the elastic modulus, tensile elongation, tensile strength and breaking strength/tensile force, or Shore hardness.

(21) Tensile Strength and Tear Strength Testing

(22) The tear strength is the quotient of the force F.sub.R (tearing force) measured at the moment of tearing and the initial cross section A.sub.0 of the test sample, which is measured at the thinnest location.

(23) The tensile strength is the quotient of the measured maximum force and the initial cross section of the sample body, which is measured at the thinnest location. In elastomers, the tearing force is usually also the maximum force.

(24) Using a Zwick tensile testing machine, the tear strength and elongation at tear of the elastomer matrix were measured using sterile and nonsterile test bodies at an initial cross section A.sub.0 of 100 mm.sup.2. In determining the elongation at break, the length of a test body with an original length of 8 mm is determined on reaching the tearing force.

(25) TABLE-US-00001 TABLE 1 Tear strength and elongation at tear of sterile and unsterile samples Type of steril- radiation ization unsterile sterilization (gamma) Dose 25-30 kGy Feature F.sub.R Tear Elongation F.sub.R Tear Elongation max strength at tear max strength at tear Sample [N] [cN/mm.sup.2] [mm] [N] [cN/mm.sup.2] [mm] Example 1 2.97 2.97 614 1.69 1.69 544 Example 1 2.80 2.80 579 1.48 1.48 395 Example 1 2.80 2.80 581 1.55 1.55 490 Average 2.86 2.86 591 1.57 1.57 476 Example 2 5.14 5.14 669 2.72 2.72 486 Example 2 4.69 4.69 686 3.09 3.09 516 Example 2 4.11 4.11 621 3.10 3.10 563 Average 4.65 4.65 659 2.97 2.97 522

(26) Replacing small amounts (e.g., 0.6%) of the elastomer with a high molecular weight (as in example 1) with an ultrahigh molecular elastomer (as in example 2) completely compensates for the decline in tear strength and cohesion and increases stability of the polymer elastomer matrix with respect to radiation sterilization (sample of example 1, unsterile 2.86 cN/mm.sup.2; sample of example 2, sterile 2.97 cN/mm.sup.2). The negative effect of radiation sterilization on the elongation at tear is partially compensated.

(27) Absorption of Saline Solution (NaCl0.8%) in Wound Dressings After a Contact Time of 2 Hours, 4 Hours and 24 Hours

(28) A 10 cm.sup.2 sample is weighed using an analytical balance (w1). A crystallizing dish is filled with saline solution so that the sample is completely covered with the test solution and there are only a few small air bubbles on it. At certain points in time, the sample is removed from the solution and patted carefully using a soft paper towel until all the water drops have been removed. The dry sample is then weighed using the analytical balance (w2).

(29) Calculation of Absorption in % Based on the Polymer Matrix Weight (Pg) According to the Following Formula:

(30) The weight of the backing (43 g/m.sup.2) must be subtracted from the weight of the sample for this calculation.
Absorption (Pg)=[(w2w1)/(w10.043)]100

(31) TABLE-US-00002 TABLE 2 Absorption of the saline solution after 2, 4, and 24 hours Absorption (Pg) in % after Averages 2 h 4 h 24 h Example 1 0.2 0.7 5.5 Example 2 0.9 2.7 9.7

(32) The absorption data from Table 2 demonstrates clearly that in an especially preferred embodiment of the invention, the elastomer wound contact layer does not absorb any mentionable amount of saline solution and therefore is not absorbent. The small quantities of water absorbed are utilized to form a boundary layer which contains fat and hydrocolloid gel and does not stick to the wound.

(33) Wound dressings according to the invention can be obtained as follows:

EXAMPLE 1

(34) TABLE-US-00003 Amount (g) Parts by weight (%) Paraffin oil 1110 72.2 Copolymer 40 2.6 Antioxidant 1.5 0.1 Petroleum jelly 154 10.0 CMC 231 15.0

(35) The composition is prepared in a laboratory dissolver. 1110 g of the paraffin oil is placed in the dissolver and mixed with 40 g of an elastomer copolymer SEEPS (Septon 4055, Kuraray) and 1.5 g of an antioxidant (Irganox 1010) and stirred at approximately 135 C. until obtaining a clear homogeneous elastomer composition. After incorporating 154 g petroleum jelly (Vara AB, Sasol) 231 g of the sodium carboxymethyl cellulose (CMC, Blanose 7H4XF, Aqualon) is added. The resulting elastomer composition is stirred for 30 minutes more until obtaining a homogeneous composition.

(36) The composition may also be prepared in a kneader or similar installations/equipment known in general for processing hot melt compositions.

(37) The composition can be applied to the fabric (mesh tulle) in an immersion bath at approximately 140-145 C., so that the textile structure is completely sheathed but the interspaces/pores remain largely open to ensure that the exudate can flow through.

EXAMPLE 2

(38) Like example 1, except that a polymer mixture of 2% Septon 4055 and 0.6% Septon 4077 was used.

EXAMPLE 3

(39) Like example 1, except that 15% of a nonionic cellulose derivative (HPMC, Bonucel D15000) was used.

(40) Within the scope of the invention, it may be of particular importance for the wound dressings to absorb only in the range of 5% to 30% of the dry weight. This limits gelation and swelling (due to hydrocolloid solutions), so that the transport of exudate through the openings in the dressing and into the secondary dressing is not hindered.

(41) Within the scope of the invention, the aspect wherein the backing has an open mesh so that an exudate flow can be ensured even after the fibers forming the backing have been coated/sheathed with the elastomer composition.

(42) The invention is not limited to the exemplary embodiments described above. Instead, another idea involves the use of backing materials in the form of open mesh knits and woven fabrics and/or polyurethane foams, such as Vivo MCF 03 (AMS). The wound dressing according to the invention may also contain an additional active ingredient that is based on metals such as silver, copper, selenium, and/or based on metal compounds, in particular metal salts (Ag.sub.2O, AgCl, ZnO, MgO), and is dissolved/dispersed/distributed in the elastomer matrix.

(43) In an especially preferred embodiment of the invention the active ingredient comprises an oligomeric/polymeric biguanide, in particular polyhexamethylene biguanide (PHMB) (e.g., Cosmocil PQ, Arch) and/or an oligomeric/polymeric guanide and/or similar broad-spectrum antiseptics such as octenidine.

(44) From the foregoing it will be seen that this invention is one well adapted to attain all ends and objectives herein-above set forth, together with the other advantages which are obvious and which are inherent to the invention. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matters herein set forth are to be interpreted as illustrative, and not in a limiting sense. While specific embodiments have been shown and discussed, various modifications may of course be made, and the invention is not limited to the specific forms or arrangement of parts and steps described herein, except insofar as such limitations are included in the following claims. Further, it will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.