Dressing system

Abstract

The present invention relates to skin dressings that are useful in the treatment of conditions associated with tissue ischaemia and skin lesions including those that are infected, such as burns and surgical wounds and chronic wounds such as but not limited5 to diabetic foot ulcers and venous leg ulcers. The skin dressings are also useful to effect transdermal delivery of pharmaceutically active agents.

Claims

1. A system comprising: (i) a layer containing a nitrite, wherein the layer containing the nitrite is a mesh or a dissolvable film; and (ii) a layer comprising a source of hydrogen ions, wherein the layer is not a hydrogel.

2. The system according to claim 1, wherein the layer containing the nitrite is a mesh.

3. The system according to claim 2, wherein the mesh is formed of a polymer.

4. The system according to claim 1, wherein the layer containing the nitrite is a dissolvable film.

5. The system according to claim 4, wherein the dissolvable film is formed of a polyvinyl alcohol, polyvinylpyrrolidone, a cellulose-based polymer or cellulose.

6. The system according to claim 1, wherein the nitrite is an alkaline metal nitrite or an alkaline earth metal nitrite.

7. The system according to claim 6, wherein the nitrite is sodium nitrite.

8. The system according to claim 1, wherein the system comprises a plurality of layers containing a nitrite.

9. The system according to claim 1, wherein the nitrite is present as a nitrite solution.

10. The system according to claim 1, wherein the layer comprising the source of hydrogen ions is a superabsorbent dressing based on sodium polyacrylate.

11. The system according to claim 1, wherein the layer comprising the source of hydrogen ions is a honey-based dressing.

12. A method for the treatment of a condition associated with tissue ischaemia or a wound, comprising administering the system according to claim 1 to a subject in need thereof.

13. The method according to claim 12, wherein the wound is an ulcer.

14. The method according to claim 13, wherein the ulcer is a leg ulcer, pressure ulcer, or diabetic ulcer.

15. The method according to claim 12, wherein the wound is a skin donor site, a surgical wound, a burn, a laceration, or an abrasion.

16. The method according to claim 12, wherein the condition associated with tissue ischaemia is Raynaud's syndrome, or tissue ischaemia caused by septic shock, irradiation, or a peripheral vascular disease.

17. The system according to claim 1, further comprising a pharmaceutically active agent.

18. A method for the treatment of a disease or medical condition, comprising administering the system according to claim 17 to a subject in need thereof.

19. A kit comprising: (i) a layer containing a nitrite, wherein the layer containing the nitrite is a mesh or a dissolvable film, and (ii) a layer comprising a source of hydrogen ions, wherein the layer is not a hydrogel, as a combined preparation for simultaneous, separate or sequential use in treating a disease or condition, wherein the layer containing the nitrite and/or the layer comprising the source of hydrogen ions comprises a pharmaceutically active agent.

20. A system comprising: (i) a layer containing a nitrite, wherein the layer containing the nitrite is a mesh or a dissolvable film; and (ii) a layer comprising a source of hydrogen ions, wherein the layer is not a hydrogel, in combination with an anaesthetic.

21. A method of treatment or prevention of pain comprising administering a system comprising: (i) a layer containing a nitrite, wherein the layer containing the nitrite is a mesh or a dissolvable film; and (ii) a layer comprising a source of hydrogen ions, wherein the layer is not a hydrogel, and an anaesthetic to a subject in need thereof.

Description

(1) The present invention will now be described by way of illustration only with reference to the following Examples and Figures, in which:

(2) FIG. 1 shows a plot of results for analysis of HONO using 1 quarter dressing (4 repeats) at 660 mL/min flow rate with synthetic air (A); and a plot of results for analysis of HONO using 1 quarter dressing (4 repeats) at 660 mL/min flow rate with synthetic air rescaled for baseline comparison (B).

(3) FIG. 2 shows plot of results for analysis of NO using 1 quarter dressing (4 repeats) at 660 mL/min flow rate with synthetic air rescaled (A); and plot of results for analysis of NO using 1 quarter dressing (4 repeats) at 660 mL/min flow rate with synthetic air rescaled for baseline comparison (B).

(4) FIG. 3 shows plot of results for NO.sub.2 analysis using 1 quarter dressing (4 repeats) at 660 mL/min flow rate using synthetic air.

(5) FIG. 4 shows a plot of results for dressing analysis, dressing 1 at 660 mL/min air flow rate, concentration in nmol/mL.

(6) FIG. 5 shows a plot of results for dressing analysis, dressing 2 at 660 mL/min air flow rate, concentration in nmol/mL.

(7) FIG. 6 shows a plot of results for dressing analysis, dressing 3 at 660 mL/min air flow rate, concentration in nmol/mL.

(8) FIG. 7 shows a plot of results for dressing analysis, dressing 4 at 660 mL/min air flow rate, concentration in nmol/mL.

(9) FIG. 8 shows a plot for a dressing analysis, quarter dressing at the 50 mL/min synthetic air flow rate.

(10) FIG. 9 a plot for a dressing analysis of the full dressing stuck over sampling tube (A) and a plot for a dressing analysis for a quarter dressing face down over sampling tube (B).

(11) FIG. 10 shows the output from SIFT-MS over time for a nitrite mesh/Aquacel system. As can be seen, the production of NO is favourable compared to NO.sub.2 and HNO.sub.2 production.

(12) FIG. 11 shows the output from SIFT-MS over time for a nitrite mesh/Medihoney HCS system. As can be seen, the production of NO is favourable compared to NO.sub.2 and HNO.sub.2 production.

EXAMPLE 1

Selected Ion Flow Tube Mass Spectrometry Analysis of Nitric Oxide Generating Wound Dressing

(13) The production of NO, NO.sub.2 and HNO.sub.2 by a dressing based on a hydrogel system (as described in WO/2014/188174) was tested using Selected Ion Flow Tube Mass Spectrometry (SIFT-MS).

(14) Method

(15) The SIFT-MS system was calibrated for the detection of the compounds of interest using reference samples.

(16) The compounds generated by the dressing system were then tested in a flow cell set up. Briefly, a 670 mL plastic (BPA free) clip lock tub with silicone seal (Tesco) was used and cleaned with low concentration of Virkon detergent before being rinsed with deionised water and dried with paper towel. Two holes were drilled one on either side, one for synthetic air in and one for sample air out. Synthetic air from the cylinder (BOC, the Linde group) (<0.1 parts per million (ppm) NOx) flowed into the chamber whilst a NMP05B micro-pump (KNF Neuberger U.K. Ltd) draws the sample air out of the chamber over the SIFT-MS inlet capillary. The flow rate of air into the chamber was set according to the experiment (either 50 mL/min or 660 mL/min) and sample air was drawn over the capillary at the set flow rate, depending on the experiment (N.B. the SIFT-MS draws air through the capillary at a constant rate of 2.7 mL per minute). In order to achieve higher flow rates two pumps were required. Table 1 shows the various permutations of the undertaken analysis;

(17) TABLE-US-00001 Dressing Dressing Re- size Air Flow Pump flow Position Analyte peats 2.5 2.5/5 5 50 mL/min 50 mL/min Face up NO/NO.sub.2 2 2.5 2.5/5 5 50 mL/min 50 mL/min Face up HONO 2 2.5 2.5/5 5 None None Face down NO/NO.sub.2 1 2.5 2.5/5 5 None None Face down HONO 1 Full dressing 50 mL/min 50 mL/min Face up NO/NO.sub.2 1 Full dressing 50 mL/min 50 mL/min Face up HONO 1 Full dressing None None Face down NO/NO.sub.2 1 Full dressing 50 mL/min 50 mL/min Face up HONO 1 Full dressing None None Face down HONO 1 Full dressing 660 mL/min 660 mL/min Face up NO/NO.sub.2 2 Full dressing 660 mL/min 660 mL/min Face up HONO 2 2.5 2.5/5 5 660 mL/min 660 mL/min Face up NO/NO.sub.2 4 2.5 2.5/5 5 660 mL/min 660 mL/min Face up HONO 4 Table 1, showing the various permutations of analysis carried out.

(18) All the dressings were treated in the same way; the layers were combined as quickly as possible before the chamber was sealed, though no significant delays were noted it is possible there may have been a few seconds difference between the dressing being combined and the sealing of the chamber. Dressing LOT numbers D020715C/D030515C.

(19) Analysis

(20) The data from the quarter dressing at the 660 mL/min flow rate was converted into excel data. This was used to generate one graph for each dressing showing the production of all three target analytes; and one graph per analyte comparing all four dressings (see results). Duplicate graphs were created with only visible trend lines which have been created using a 25 point moving average in order to smooth out the results by reducing the noise, this step proved useful for performing visual analysis.

(21) Each compound for each dressing was also converted into micrograms (g) per minute evolved both over the course of the testing duration (1.5 hours) and for the initial 15 minutes (to encompass the initial peak). This was then used to calculate the total quantities in g for the respective time frames.

(22) Results

(23) The following shows the results for the face up, quarter dressing at the 660 mL/min flow rate method. Four analyses for each analyte were performed using different dressings. Table 2 below shows the quantities calculated for the four different dressings.

(24) TABLE-US-00002 TABLE 2 quantification of the compounds evolved from each dressing, each analysis performed with same method. 1 quarter dressing with 660 mL/min flow rate using synthetic air. Dressing Dressing Dressing Dressing 1 2 3 4 Total AverageHONO (ppm) 4.23 2.47 2.18 3.18 Average first 15 minutes 17.20 9.94 8.43 12.65 HONO (ppm) Amount evolved g/min 5.28 3.09 2.72 3.97 total HONO Amount evolved g/min 21.47 12.40 10.52 15.79 first 15 mins HONO Total HONO evolved g 474.89 277.94 244.42 357.44 Total HONO evolved first 15 322.05 186.07 157.77 236.84 min (g) Total Average NO (ppm) 7.70 9.60 6.54 7.79 Average NO first 28.00 37.78 25.73 28.72 15 minutes (ppm) Amount NO 6.12 7.62 5.19 6.18 evolved g/min total Amount NO 22.23 30.00 20.43 22.80 evolved g/min first 15 mins Total NO evolved 550.44 686.05 467.04 556.34 g Total NO evolved 333.50 449.93 306.41 342.07 first 15 min (g) Total Average 0.41 0.41 0.38 0.41 NO.sub.2 (ppm) Average NO.sub.2 first 0.26 0.37 0.30 0.29 15 minutes (ppm) Amount NO.sub.2 0.49 0.50 0.46 0.50 evolved g/min total Amount NO.sub.2 0.32 0.45 0.36 0.35 evolved g/min first 15 mins Total NO.sub.2 evolved 44.55 45.01 41.48 44.88 g Total NO.sub.2 evolved first 15 4.74 6.71 5.42 5.28 min (g)

(25) TABLE-US-00003 Dressing Dressing Dressing Dressing 1 2 3 4 Total production (g) 1069.88 1009 752.94 958.66 Total production first 15 mins 660.29 642.71 469.6 584.19 (g) Total dressing productiontotal 832.73 726.85 547.74 759.76 empty chamber production (over 90 mins) (g) Total dressing productiontotal 620.77 595.68 435.4 551.04 empty chamber production (first 15 mins) (g) Table 3, the total quantity of measured compounds released over the course of 90 minutes and during the first fifteen minutes, for each dressing. i.e. The value is the result of HONO, NO, NO.sub.2 production added together.

(26) TABLE-US-00004 Pre- Pre- Pre- Pre- Dressing 1 Dressing 2 Dressing 3 Dressing analysis analysis analysis 4 analysis Total Average HONO 0.21 0.32 0.15 0.14 (ppm) Amount evolved 0.26 0.40 0.19 0.17 g/min total HONO Total HONO evolved 0.53 0.80 0.39 0.34 g Total Average NO 2.38 2.94 1.91 1.85 (ppm) Amount NO evolved 1.89 2.34 1.52 1.47 g/min total Total NO evolved g 3.81 4.71 3.07 2.97 Total Average NO.sub.2 0.38 0.31 0.45 0.45 (ppm) Amount NO.sub.2 evolved 0.46 0.38 0.54 0.55 g/min total Total NO.sub.2 evolved g 0.93 0.76 1.10 1.11 Total evolved over 5.27 6.27 4.56 4.42 120 seconds (g) Total evolved over 237.15 282.15 205.2 198.9 1.5 hours (same as sample time)(g) Total evolved over 39.53 47.03 34.2 33.15 first 15 minutes g Table 4, quantity of HONO, NO and NO.sub.2 produced by the empty chamber sealed over a 120 second sampling time using synthetic air at a flow rate of 660 mL/min.

(27) TABLE-US-00005 Dressing 1 Dressing 2 Dressing 3 Dressing 4 HONO Total 0.173 0.101 0.064 0.093 average nmol/mL per second HONO total 10.375 6.075 3.816 5.582 average nmol/mL per min Total amount 933.714 546.776 343.410 502.390 evolved nmol 90 mins NO total average 0.315 0.392 0.267 0.318 nmol/mL per second NO total average 18.883 23.506 16.033 19.102 nmol/mL per min Total amount 1699.456 2115.520 1442.926 1719.174 evolved nmol 90 min NO.sub.2 total average 0.016 0.017 0.015 0.017 nmol/mL per second NO.sub.2 total average 0.990 1.002 0.924 0.997 nmol/mL per minute NO.sub.2 total evolved 89.068 90.176 83.147 89.757 nmol 90 mins Table 5, showing quantification for each compound in nmol.

(28) In order to obtain the g per minute value the following calculations took place. The molecular weight of the compound at an assumed temperature of 299K was used to calculate the mass per cm.sup.3 (1.222 mg for NO). This was then multiplied by the flow rate (average of 650 mL/min) to arrive at 794 mg per minute, for 100% NO i.e. 106 ppm. Thus the equation to convert ppm into mg per minute for NO was therefore 794*(X/10.sup.6)=mg per minute (where X is the ppm). In order to use uniform significant figures milligrams were converted to micrograms. The same formulae with appropriate coefficients were applied to all three compounds e.g. 1222*(X/10.sup.6) for NO.sub.2 and 1248*(X/10.sup.6) for HONO.

(29) Dressing 3 appears to be an outlier with less production of all three compounds than the other dressings. Excluding dressing 3 the quantities for HONO and NO production shown in table 2 appear to follow an inverse correlation, the dressing with the highest NO value over 1.5 hours also has the lowest HONO value (dressing 2). Likewise the highest HONO producer shows the lowest NO production (dressing 1). This is likely indicative of the conversion of HONO into NO. NO.sub.2 appears to have no such relationship with the other compounds produced as the readings were remarkably similar for all 4 dressings.

(30) Table 4 shows the production of HONO, NO and NO.sub.2 over 120 seconds with air flow into the sealed chamber before the dressing was added to act as a baseline level. As the sealed chamber with synthetic air flow was not recorded for the same duration as the dressing the average production over the course of 120 seconds was used to calculate the average production over 1.5 hours (the same as testing time). It is worth noting the average production, in ppm is significantly less than seen in table 2. Moreover the total evolved is similar for each test run suggesting there is very limited if any residual detection from the previous sampling. Table 3 shows the total production of the monitored gases over 1.5 hours and the first 15 minutes of a sample run. During the first 15 minutes of sampling there is a spike in production (discussed in detail below). Table 3 also shows the total production of monitored compounds minus the average production from the sealed empty chamber with synthetic air flow at a rate of 660 mL/min (e.g. the same conditions as per sample test).

(31) FIGS. 1 and 2 show the results for all four dressings for HONO and NO production respectively. Both these compounds show similar traits, both show a rapid sharp peak in production almost instantly upon the dressing being assembled and the chamber being sealed. Likewise both compounds appear to drop reasonably rapidly to a steady state of production just above the baseline. The NO production appears to drop to this steady state more rapidly than HONO production; at approximately 1500 seconds and 3000 seconds respectively. There also appears to be a reasonable overlap of the traces at later stages of testing suggesting reasonably consistent production between dressings. However during the initial production spike there are visible differences between the dressings. Furthermore during the first portion of HONO production there is very little noise when compared to NO; however over time the level of noise in HONO production increases.

(32) The results for NO.sub.2 are shown in FIG. 3, in this instance the pattern of production is unlike the other compounds in that there appears to be a slight dip below the baseline in the initial phase of production. Following this initial phase the levels to rise a steady state; while FIG. 3 may appear very noisy is should be noted the scale is considerably smaller than that of FIGS. 1 and 2. FIGS. 4-7 show the results per dressing allowing a visual representation of how each compound relates to one another, in this context the NO.sub.2 production is significantly lower.

(33) FIGS. 4-7 show a plot of NO, HONO and NO.sub.2 production at ca. 299K for each dressing converted into nmol/mL. This was calculated using the equation X ppm=0.0408*X nmol/mL. Total quantification for each compound (in nmol) is shown in table 5. As noted earlier all dressings show consistent patterns in the production of all three compounds of interest. It is worth noting that across the whole testing time frame the production of NO appears to be significantly greater than that of the other compounds. This is highlighted by the yield calculations of table 2. It is known that at the lower levels of detection (e.g. sub parts per million) NO detection becomes difficult on SIFT-MS due to interference from the NO+ reagent ion. This is mitigated by the proportionally large production of NO from the dressing.

(34) As mentioned all four repeats discussed thus far have been with airflow over the dressing of 660 mL/min. In the initial phase of testing a run was done with a significantly lower flow of the same synthetic air at approximately 50 mL/min (FIG. 8). At the lower flow the patterns in production are broadly similar to that of the higher flow rate in so far as there is an almost instant spike upon sealing the chamber followed by a drop in production to a steady state (with the exception of NO.sub.2). However in this instance the steady state of production occurs at a significantly higher level than at the higher flow rate. This is most likely attributed to the possibility that production occurs at a more rapid rate than the air can leave the chamber and thus the gases are collected and in effect concentrated. Alternatively the higher flow rate may be providing a dilution effect which would also result in this pattern. Following this method of testing the chamber takes significantly longer to return to an appropriate baseline level than after higher flow rate testing. This therefore provides us with evidence that for this particular permutation of testing the higher 660 mL/min flow rate is more appropriate.

(35) In order to achieve something of an analogue to an in vivo test the dressing was also analysed face down stuck over the sample inlet tube; the gathered results can be seen in FIG. 9. For this experiment no air flow was used and the chamber lid was removed, thus eliminating any concentration effects from the chamber. The HONO trace is not included for the full dressing analysis as this was part of another trace and would make for an inappropriate comparison. Once again we see a familiar pattern in the production of each compound. The NO peak while monitoring facedown is very sharp, it is also notable that the difference between the peak production for the full and quarter dressing is not as large as anticipated; approximately 280 to 260 ppm respectively. The full dressings steady state is significantly higher (125 ppm full dressing 40 ppm quarter dressing), though this this is not as big as expected. If a quarter dressing on average produces 40 ppm one might expect the whole dressing to produce 160 ppm (4 times the amount), we find this does not occur and thus hypothesis that there may be a relationship between the edges surface area and NO production. HONO production during the steady state for the full dressing was approximately 100 ppm compared to approximately 25 ppm for the quarter dressing; these proportions are what one would expect from a linear relationship between surface area and HONO production.

(36) Conclusion

(37) The nitric oxide producing dressing has been analysed for production of NO, NO.sub.2 and HONO under a number of different permutations. The proportions of the compounds produced remained very similar: NO.sub.2 production is by far the least abundant regardless of methodology. HONO is produced in significant quantities and appears to have an inverse relationship with NO; thus it is important when considering the chemical processes taking place. As expected NO production is by far the most consistent and abundant compound (of those monitored).

(38) The finding that high levels of NO and very low levels of NO.sub.2 are produced is surprising, since until now it was assumed that acidification of nitrite would give rise to equimolar ratios of NO and NO.sub.2.

EXAMPLE 2

Production of Dressing System Using Hydrogel Compositions

(39) Primary Layer: Wound Contact Mesh (containing 1M Sodium Nitrite)

(40) The Mesh is a polypropylene mesh (RKW-Group), imbibed with 1M Sodium Nitrite solution, from Sodium Nitrite Extra Pure ph Eur, USP Merck and deionised water.

(41) Description of Manufacturing Process

(42) Sodium nitrite is weighed into a suitably sized vessel and then transferred carefully into a known volume of deionised water, which is then stirred until dissolution is complete to make a solution of appropriate concentration. In this embodiment the sodium nitrite solution is dispensed onto the mesh and then is placed into each petri dish for a minimum time to imbibe the mesh with the sodium nitrite solution. The finished products are sterilised by irradiation.

(43) Secondary Layer: Hydrogel Top Layer

(44) The hydrogel chosen for this study has high capability for absorption and facilitates a moist wound-healing environment. The hydrogel comprises a cross-linked anionic copolymer, circa 30% water and circa 30% glycerol. It has an outer polyurethane film that provides a bacterial barrier and aesthetically pleasing outer surface to the dressing. The gels have an acidic surface pH circa 2-5 arising from the presence of some sulfonic acid groups. These groups provide the acidity for the conversion of Sodium Nitrite to Nitric Oxide. As the sulfonic acid groups are covalently bound to the hydrogel network they are not released into the wound.

(45) Description of Manufacturing Process

(46) The hydrogel is manufactured from the list of ingredients set out below. The process of manufacture is as according to patents EP1100555B1 and EP110556B1, which are incorporated by reference in their entirety herein.

(47) The ingredients are dispensed into a suitable mixing vessel (dispensing is controlled by weight) and stirred overnight. Once mixed, a portion of the liquid solution is dispensed onto a moving substrate (clear polyurethane film, Inspire 2304) at the required coat weight. Then a mesh made of polypropylene (RKW 20 g/m.sup.2) is laid onto the top of the liquid formulation, which is then exposed to UV light and cured. A second layer is coated on top of the first at the required coat weight and exposed to UV light, thus making a sandwich with the mesh in the middle.

(48) The hydrogel is cut to the required size and pouched, sealed and sterilised. The finished products are sterilised by gamma irradiation.

(49) The components of the hydrogels are:

(50) Monomer, Sodium AMPS 2405A (58% solution in water) (Lubrizol)

(51) Monomer, 2-acrylamido-2-methylpropane sulfonic acid (Sigma-Aldrich)(AMPS Acid)

(52) Monomer, Acrylic Acid (BASF)

(53) Glycerine BP, EP (H. Fosters)

(54) Darocur 1173, 2-hydroxy-2-methylpropiophenone (BASF) (D1173)

(55) SR 344, poly (ethylene glycol) diacrylate (Sartomer) (PEG diacylate)

(56) Mesh, Carded non-woven 20 gsm (RKW-Group)

(57) Inspire 2304, polyurethane film (Coveris)

(58) 70 micron, low density polyethylene, siliconised (Adcoat)

(59) NeoCarta, peelable laminate (Safta)

(60) The components of the nitrite layer are:

(61) Mesh, Carded non-woven 20 gsm (RKW-Group)

(62) NeoCarta, peelable laminate (Safta)

(63) Sodium Nitrite, extra pure, Ph Eur, USP (Merck)

(64) De-ionised water (First Water Ltd)

(65) Example Hydrogel Compositions

(66) TABLE-US-00006 Sample 1 Sample 2 Sample 3 Sample 4 Component Parts (g) Parts (g) Parts Parts (g) Na AMPS 2405A 66 67 67 67 AMPS Acid 1.03 0.4 0.05 Acrylic Acid 2 Glycerol 30 30 30 30 D1173 and PEG 0.12 0.12 0.12 0.12 diacrylate (in a 4:20 w/w ratio) Table 6, example hydrogel compositions.

EXAMPLE 3

Production of a Wound Dressing

(67) A wound dressing of the invention can be made by placing the first layer, made by imbibing a 5 cm5 cm nitrite mesh of Example 2 with 0.05 to 1 g of 0.01M to 2M sodium nitrite, (specific example 0.2 g of 1M sodium nitrite) onto a wound and covering the first layer with a second layer comprising a source of hydrogen ions. The second layer may be for example Medihoney HCS (11 cm11 cm) (Derma Sciences),

(68) AQUACEL (10 cm10 cm) (ConvaTec), AQUACEL Ag (10 cm10 cm) (ConvaTec),

(69) AQUACEL Ag Foam (10 cm10 cm (ConvaTec)), AQUACEL Foam (10 cm10 cm) (ConvaTec), AQUACEL EXTRA (10 cm10 cm) (ConvaTec), Granuflex (10 cm10 cm) (ConvaTec).

EXAMPLE 4

Selected Ion Flow Tube Mass Spectrometry Analysis of Alternative Nitric Oxide Generating Dressing Systems

(70) The production of NO, NO.sub.2 and HNO.sub.2 by dressings based on either Medihoney or AQUACEL was tested using Selected Ion Flow Tube Mass Spectrometry (SIFT-MS).

(71) SIFT-MS was carried out as described with respect to Example 1, using a flow rate of 660 ml/min.

(72) AQUACEL is carboxymethyl cellulose based fibre, in which carboxylic acid groups are copolymerised into the polymer network. In this experiment, a dry AQUACEL (10 cm10 cm) (ConVatec) dressing was cut in half to form a 5 cm5 cm square and placed into the sample chamber. A 2.5 cm2.5 cm (0.0145 mg) of polypropylene non-woven mesh imbibed with 34.5 mg of a 1M sodium nitrite solution was placed on top of the Aquacel sample and the sample chamber then closed and SIFT-MS data collected. FIG. 10 shows the output from SIFT-MS for this experiment. As can be seen, the production of NO is favourable compared to NO.sub.2 and HNO.sub.2 production.

(73) Medihoney HCS is a gel dressing comprising greater than 50% Manuka honey. In the following experiment Medihoney HCS was used as the sole source of hydrogen ions. A Medihoney HCS (10 cm10 cm) (Derma Sciences) dressing was cut in half to form a 5 cm5 cm square and placed into the sample chamber. A 2.5 cm2.5 cm (0.0145 mg) of polypropylene non-woven mesh imbibed with 34.5 mg of a 1M sodium nitrite solution was placed on top of the Medihoney sample and the sample chamber then closed and SIFT-MS data collected. FIG. 11 shows the output from SIFT-MS for this experiment. As can be seen, the production of NO is favourable compared to NO.sub.2 and HNO.sub.2 production.