METHOD FOR PRODUCING BACTERIALLY SYNTHESIZED CELLULOSE NON-WOVEN

Abstract

The present invention relates to a method for producing bacterially synthesized cellulose (BC) non-woven as well as to BC non-woven produced by the method and uses of such BC non-woven. The present invention also relates to an apparatus for production of the BC non-woven. Preferably, the bacterially synthesized cellulose (BC) of the present invention is biotechnologically produced nano-structured cellulose (BNC).

Claims

1. A method for producing bacterially synthesized cellulose (BC) non-woven, the method comprising the steps of: a) synthesizing BC by incubating a bacterial culture in a culture vessel, wherein the bacterial culture comprises liquid culture medium and BC-synthesizing bacteria, b) adding fresh or recycled culture medium and/or removing consumed culture medium during the incubation as an optional step, c) removing produced BC non-woven having an average thickness of at least 0.5 mm from the culture vessel, wherein at least during step a) the gaseous atmosphere above the bacterial culture is kept at a temperature that is at most 10 K below the highest temperature of the culture medium in the culture vessel within a distance from the interface of BC and gaseous atmosphere of from 0 to 2 cm measured perpendicular to the interface and/or wherein at least during step a) the gaseous atmosphere above the bacterial culture is kept at a relative humidity of at least 70% within a distance from the interface of BC and gaseous atmosphere of from 0 to 2 cm measured perpendicular to the interface.

2. The method according to claim 1, wherein synthesis of BC in the culture vessel continues during removal of produced BC non-woven having an average thickness of at least 0.5 mm from the culture vessel and wherein non-finished BC non-woven remains in the culture vessel and is separated from the BC non-woven that is removed, the method further comprising the following steps: d) continuing synthesis of BC in the culture vessel by continuation of incubation of the bacterial culture in the culture vessel, e) adding fresh or recycled culture medium and/or removing consumed culture medium during the continued incubation as an optional step, f) removing produced BC non-woven having an average thickness of at least 0.5 mm from the culture vessel, wherein synthesis of BC optionally continues during removal and wherein optionally non-finished BC non-woven remains in the culture vessel and is separated from the BC non-woven that is removed, and g) repeating steps d) to f) at least once as an optional step.

3. The method according to claim 1, wherein the temperature of the culture medium is from 20 C. to 40 C.

4. The method according to claim 1, wherein during step a) the gaseous atmosphere above the bacterial culture is kept at a temperature that is at most 10 K below the temperature of the culture medium in the culture vessel and/or at a relative humidity of at least 70% within a distance from the interface of BC and gaseous atmosphere of from 0 to 5 cm measured perpendicular to the interface.

5. The method according to claim 1, wherein the culture vessel is covered with a cover.

6. The method according to claim 1, wherein non-finished BC non-woven is separated from removed BC non-woven by fluid jet cutting.

7. The method according to claim 1, wherein the produced BC non-woven is removed from the culture vessel in step c) after at least three and at most ten days of incubation.

8. The method according to claim 2, wherein synthesis of BC in the culture vessel is continued in step d) by continuation of incubation of the bacterial culture in the culture vessel for at least 12 hours and at most 100 hours.

9. The method according to claim 1, wherein the method further comprise the step of sterilizing the BC non-woven by e-beam sterilization subsequent to step c).

10. Bacterially synthesized cellulose (BC) non-woven characterized by the standard deviation of WAC and/or WRC being at most 15% of the corresponding mean value of WAC or WRC, respectively, wherein mean value and standard deviation are determined from at most 25 independent measured values and wherein the independent measured values are obtained by cutting essentially equally sized samples of 2 cm2 cm from the BC non-woven and determining the WAC and/or WRC value for each sample independently.

11. The BC non-woven according to claim 10, wherein the BC non-woven is produced by a method comprising the steps of: a) synthesizing BC by incubating a bacterial culture in a culture vessel, wherein the bacterial culture comprises liquid culture medium and BC-synthesizing bacteria, b) optionally adding fresh or recycled culture medium and/or removing consumed culture medium during the incubation, c) removing produced BC non-woven having an average thickness of at least 0.5 mm from the culture vessel, wherein at least during step a) the gaseous atmosphere above the bacterial culture is kept at a temperature that is at most 10 K below the highest temperature of the culture medium in the culture vessel within a distance from the interface of BC and gaseous atmosphere of from 0 to 2 atmosphere above the bacterial culture is kept at a relative humidity of at least 70% within a distance from the interface of BC and gaseous atmosphere of from 0 to 2 cm measured perpendicular to the interface.

12. The BC non-woven according to claim 10, wherein the non-woven has an average thickness of at least 0.5 mm and at most 8 mm.

13. Use of BC non-woven according to claim 10 in dermatological, medical, pharmaceutical, diagnostic, nutrition, cosmetic, technical and protective equipment products.

14. Apparatus for producing BC non-woven, wherein the apparatus comprises: A) at least one culture vessel, B) means for adding fresh or recycled culture medium and/or removing consumed culture medium from the culture vessel, and C) means for removing produced BC non-woven from the culture vessel.

15. The apparatus of claim 14, wherein the culture vessel has a substantially rectangular shape with a length of at least 100 cm and a width of at least 10 cm, wherein the aspect ratio of length to width is from 1.5 to 10,000.

16. The method according to claim 1, wherein the temperature of the culture medium is from 25 C. to 33 C.

17. The method according to claim 2, wherein during step d) the gaseous atmosphere above the bacterial culture is kept at a temperature that is at most 10 K below the temperature of the culture medium in the culture vessel and/or at a relative humidity of at least 70% within a distance from the interface of BC and gaseous atmosphere of from 0 to 5 cm measured perpendicular to the interface.

18. The method according to claim 4, wherein during step a) the gaseous atmosphere above the bacterial culture is kept at a temperature that is at most 5 K below the temperature of the culture medium in the culture vessel and/or at a relative humidity of at least 95%.

19. The method according to claim 17, wherein during step d) the gaseous atmosphere above the bacterial culture is kept at a temperature that is at most 5 K below the temperature of the culture medium in the culture vessel and/or at a relative humidity of at least 95%.

20. The method according to claim 2, wherein the method further comprise the step of sterilizing the BC non-woven by e-beam sterilization subsequent to step f).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0158] FIG. 1 shows scanning electron microscope images that allow comparison of cut edges obtained by fluid jet cutting (right panel) with cut edges obtained by cutting with a scalpel (left panel). The scanning electron microscope images show the cut edges with a magnification of 300 (upper panel) and 3000 (lower panel), respectively.

[0159] FIG. 2 shows scanning electron microscope images of BC non-woven sterilized with steam (upper panel) or e-beam (lower panel). The scanning electron microscope images show the BC with a magnification of 300 (left panel) and 3000 (right panel), respectively. Notably, the BC network structure is not compromised by e-beam sterilization in comparison to sterilization with steam.

EXAMPLES

Example 1

[0160] BC non-woven was produced by the method of the present invention. Produced BC non-woven having an average thickness of 2 mm was removed from the culture vessel and separated from the BC non-woven that remained in the culture vessel. Separation was either done by cutting with a scalpel or by fluid jet cutting. The cut edges were investigated by scanning electron microscopy. It was found that the cut edges produced by fluid jet cutting were smoother as compared to the cut edges produced by cutting with a scalpel. The results are shown in FIG. 1.

Example 2

[0161] BC non-woven was produced by the method of the present invention. In particular, BC non-woven was sterilized with e-beam or by exposure to steam after removal from the culture vessel and separation from the BC that remained in the culture vessel. The BC network structure was investigated with scanning electron microscopy. It was found that the network structure was neither disturbed by sterilization with steam nor by e-beam sterilization.

Example 3

[0162] Three distinct BC non-woven materials were produced by the method of the present invention, which were characterized by a range of WAC and WRC values. Six samples of essentially equal size of 2 cm2 cm were cut from each of the BC non-woven materials and WAC and WRC values were obtained independently for each of the six samples of each of the BC non-woven materials. For each sample, mean and standard deviation of WRC and WAC were calculated. Table 1 and 2 demonstrate the quality and homogeneity of the BC non-woven materials in view of standard deviations (SD) below 5% for both characteristic material property values.

TABLE-US-00001 TABLE 1 Mean of water absorption capacity (in %) and corresponding standard deviations (in %) of different BC non-woven materials (n = 6 samples for each material) Mean of WAC SD WAC Material [%] [%] Material 1 9,827 358 Material 2 7,100 292 Material 3 6,644 241

TABLE-US-00002 TABLE 2 Mean of water retention capacity (in %) and corresponding standard deviations (in %) of different BC non-woven materials (n = 6 samples for each material) Mean of WRC SD WRC Sample [%] [%] Material 1 832 17 Material 2 798 24 Material 3 719 22

Example 4

[0163] The influence of covering the culture vessel with a lid on evaporation of water from the culture vessel was tested under laminar air flow conditions at a temperature of 28 C. The results are shown in table 3. It can be seen that covering the culture vessel with a lid reduced the amount of water that evaporated from the culture vessel by a factor of almost 50.

TABLE-US-00003 TABLE 3 Evaporation of water in L per m.sup.2 culture vessel per day at T = 28 C. under laminar air flow conditions Evaporation Test [L/(m.sup.2 .Math. d)] Test 1 (culture vessel without cover) 4.9 Test 2 (culture vessel with cover) 0.1

Example 5

[0164] Two distinct BC non-woven materials were produced by the method of the present invention, which were characterized by a range of WAC and WRC values. The materials were produced under the conditions listed in table 4. In particular, the humidity of the gaseous atmosphere above the culture medium was kept at 79-80% and the temperature of the gaseous atmosphere 3 cm above the culture medium was kept at a temperature not more than 1 K below the temperature of the culture medium. The humidity and the temperature of the gaseous atmosphere at a distance from 0 to 2 cm measured perpendicular to the interface was not lower than the listed values in table 4. The samples of essentially equal size of 2 cm2 cm were cut from each of the BC non-woven materials and WAC and WRC values were obtained independently for each of the samples of each of the BC non-woven materials. For each material, mean and standard deviation of WRC and WAC were calculated. Table 5 demonstrates the quality and homogeneity of the BC non-woven materials in view of standard deviations (SD) below 5% for both characteristic material property values. Materials 4 and 5 show a smooth and even surface.

TABLE-US-00004 TABLE 4 Experimental conditions to obtain material 4 and 5 ( = relative humidity of the gaseous atmosphere above the bacterial culture, T.sub.GA = temperature of the gaseous atmosphere at a distance from the interface of BC and gaseous atmosphere of 3 cm measured perpendicular to the interface, T.sub.CM = temperature of the culture medium in the culture vessel, h.sub.BC = average thickness of the BC non-woven material, t = cultivation time relative to material 4) T.sub.GA T.sub.CM h.sub.BC t Material [%] [ C.] [ C.] [mm] [%] Material 4 79 28 29 4 100 Material 5 80 28 29 4 100

TABLE-US-00005 TABLE 5 Mean and standard deviations of water absorption capacity and water retention capacity of BC non-woven material 4 (n = 10 samples) and BC non-woven material 5 (n = 6 samples) Mean of WAC SD WAC Mean of WRC SD WRC Material [%] [%] [%] [%] Material 4 9,419 352 841 25 Material 5 10,141 472 818 32

Example 6

[0165] Two distinct BC non-woven materials were produced as in example 5 with modifications of the experimental conditions to evaluate the influence of the humidity of the gaseous atmosphere. Namely, the gaseous atmosphere above the culture medium was kept at 31-33% and the cultivation time was extended to 225% relative to material 4. Table 6 demonstrates the insufficient quality and poor homogeneity of the BC non-woven materials in view of standard deviations (SD) above 15% for water absorption and retention capacity as well as varying thickness between 2 two 6-7 mm. Material 6 and material 7 show an uneven surface.

TABLE-US-00006 TABLE 6 Experimental conditions to obtain material 6 and 7 ( = relative humidity of the gaseous atmosphere above the bacterial culture, T.sub.GA = temperature of the gaseous atmosphere at a distance from the interface of BC and gaseous atmosphere of 3 cm measured perpendicular to the interface, T.sub.CM = temperature of the culture medium in the culture vessel, h.sub.BC = average thickness of the BC non-woven material, t = cultivation time relative to material 4) T.sub.GA T.sub.CM h.sub.BC t Material [%] [ C.] [ C.] [mm] [%] Material 6 31 28 29 2-6 225 Material 7 33 28 29 2-7 225

TABLE-US-00007 TABLE 7 Mean and standard deviations of water absorption capacity and water retention capacity of BC non-woven material 6 (n = 10 samples) and BC non-woven material 7 (n = 6 samples) Mean of WAC SD WAC Mean of WRC SD WRC Material [%] [%] [%] [%] Material 6 10,298 2,087 802 141 Material 7 9,633 1,914 838 149