Multi-phase bacterially-synthesized-nanocellulose biomaterials and method for producing the same

Abstract

Multi-phase biomaterials based on bacterially synthesized nanocellulose and method for producing same.

Claims

1. A multi-phase biomaterial, comprising bacterially synthesized nanocellulose (BNC) comprising a plurality of different bacterial cellulose networks arranged in a plurality of phases, wherein the plurality of different bacterial cellulose networks are integrally combined in a homogeneous phase system or wherein the plurality of different bacterial cellulose networks are formed as a layered phase system comprising at least one combined homogeneous phase and at least one single phase, wherein said BNC has a transparency to an extent that more than 50% of visible light passes through the biomaterial at a thickness of greater than 2 mm of the biomaterial, and wherein said BNC has a thickness greater than 2 mm.

2. The multi-phase biomaterial of claim 1, wherein the plurality of different bacterial cellulose networks differ in their molecular structure.

3. The multi-phase biomaterial of claim 1, wherein the plurality of different bacterial cellulose networks differ in their supra-molecular structure.

4. The multi-phase biomaterial of claim 1, comprising cellulosic structures on the basis of modified C-sources.

5. The multi-phase biomaterial of claim 4, wherein said C-sources comprise one or both of N-acetyl glucosamine or glucosamine.

6. The multi-phase biomaterial of claim 1, wherein said bacterial cellulose networks are produced by a plurality of different Gluconacetobacter strains.

7. The multi-phase biomaterial of claim 6, wherein said strains comprise ATCC 23769 and DSM 11804.

8. The multi-phase biomaterial of claim 1, wherein said BNC has a thickness greater than 5 mm.

9. The multi-phase biomaterial of claim 8, wherein said BNC has a thickness greater than 10 mm.

10. The multi-phase biomaterial of claim 9, wherein said BNC has a thickness greater than 20 mm.

11. The multi-phase biomaterial of claim 10, wherein said BNC has a thickness greater than 30 mm.

12. The multi-phase biomaterial of claim 11, wherein said BNC has a thickness greater than 50 mm.

13. A wound dressing, comprising the multi-phase biomaterial of claim 8.

14. The multi-phase biomaterial of claim 1, wherein said BNC has solids content of at least 5%.

15. The multi-phase biomaterial of claim 14, wherein said BNC has solids content of at least 6%.

16. The multi-phase biomaterial of claim 15, wherein said BNC has solids content of at least 8%.

17. The multi-phase biomaterial of claim 16, wherein said BNC has solids content of at least 10%.

18. The multi-phase biomaterial of claim 17, wherein said BNC has solids content of at least 15%.

19. The multi-phase biomaterial of claim 1, wherein said BNC has a tensile strength in the native wet state of at least 0.1 MPa.

20. The multi-phase biomaterial of claim 19, wherein said BNC has a tensile strength in the native wet state of at least 0.15 MPa.

21. The multi-phase biomaterial of claim 20, wherein said BNC has a tensile strength in the native wet state of at least 0.2 MPa.

22. The multi-phase biomaterial of claim 21, wherein said BNC has a tensile strength in the native wet state of at most 0.9 MPa.

23. The multi-phase biomaterial of claim 22, wherein said BNC has a tensile strength in the native wet state of at most 0.7 MPa.

24. The multi-phase biomaterial of claim 23, wherein said BNC has a tensile strength in the native wet state of at most 0.5 MPa.

25. The multi-phase biomaterial of claim 21, wherein said BNC has a tensile strength in the native wet state of from 0.2 MPa to 0.5 MPa.

26. The multi-phase biomaterial of claim 19, wherein said BNC has a water absorption capacity (WAC) of at least 80%.

27. The multi-phase biomaterial of claim 26, wherein said BNC has a water absorption capacity (WAC) of at least 120%.

28. The multi-phase biomaterial of claim 27, wherein said BNC has a water absorption capacity (WAC) of at least 150%.

29. The multi-phase biomaterial of claim 26, wherein said BNC has a water absorption capacity (WAC) of at most 300%.

30. The multi-phase biomaterial of claim 29, wherein said BNC has a water absorption capacity (WAC) of at most 250%.

31. The multi-phase biomaterial of claim 30, wherein said BNC has a water absorption capacity (WAC) of at most 200%.

32. The multi-phase biomaterial of claim 28, wherein said BNC has a water absorption capacity (WAC) of from 150% to 200%.

33. The multi-phase biomaterial of claim 26, wherein said BNC has a moist vapor transmission rate in the wet state of at least 100 g/(m2*24 h).

34. The multi-phase biomaterial of claim 33, wherein said BNC has a moist vapor transmission rate in the wet state of at least 200 g/(m2*24 h).

35. The multi-phase biomaterial of claim 34, wherein said BNC has a moist vapor transmission rate in the wet state of at least 500 g/(m2*24 h).

36. The multi-phase biomaterial of claim 35, wherein said BNC has a moist vapor transmission rate in the wet state of at most 3000 g/(m2*24 h).

37. The multi-phase biomaterial of claim 36, wherein said BNC has a moist vapor transmission rate in the wet state of at most 2000 g/(m2*24 h).

38. The multi-phase biomaterial of claim 37, wherein said BNC has a moist vapor transmission rate in the wet state of at most 1000 g/(m2*24 h).

39. The multi-phase biomaterial of claim 35, wherein said BNC has a moist vapor transmission rate in the wet state of from 500 g/(m2*24 h) to 1000 g/(m2*24 h).

40. The multi-phase biomaterial of claim 1, wherein the plurality of different BNC networks differ in their molecular structure according to at least one of degree of polymerization (DP.sub.n), polydispersity index (PDI) or both.

41. The multi-phase biomaterial of claim 40, wherein at least one BNC network is characterized by a DP.sub.n of at least 4000.

42. The multi-phase biomaterial of claim 41, wherein at least one BNC network is characterized by a DP.sub.n of at least 6000.

43. The multi-phase biomaterial of claim 42, wherein at least one BNC network is characterized by a DP.sub.n of at least 8000.

44. The multi-phase biomaterial of claim 40, wherein at least one BNC network is characterized by a DP.sub.n of at most 2000.

45. The multi-phase biomaterial of claim 44, wherein at least one BNC network is characterized by a DP.sub.n of at most 1000.

46. The multi-phase biomaterial of claim 45, wherein at least one BNC network is characterized by a DP.sub.n of at most 500.

47. The multi-phase biomaterial of claim 40, wherein a first BNC network has a higher DP.sub.n and a second BNC network has a lower DP.sub.n, wherein the DP.sub.n of the first BNC network is higher by a factor of at least 2.

48. The multi-phase biomaterial of claim 47, wherein the DP.sub.n of the first BNC network is higher by a factor of at least 5.

49. The multi-phase biomaterial of claim 40, wherein at least one BNC network is characterized by a PDI of at least 1.5.

50. The multi-phase biomaterial of claim 49, wherein at least one BNC network is characterized by a PDI of at least 1.7.

51. The multi-phase biomaterial of claim 50, wherein at least one BNC network is characterized by a PDI of at least 2.0.

52. The multi-phase biomaterial of claim 51, wherein at least one BNC network is characterized by a PDI of at most 8.

53. The multi-phase biomaterial of claim 52, wherein at least one BNC network is characterized by a PDI of at most 6.

54. The multi-phase biomaterial of claim 53, wherein at least one BNC network is characterized by a PDI of at most 4.

55. The multi-phase biomaterial of claim 40, wherein a first BNC network has a higher PDI and a second BNC network has a lower PDI, wherein the PDI of the first BNC network is higher by a factor of at least 1.5.

56. The multi-phase biomaterial of claim 55, wherein the PDI of the first BNC network is higher by a factor of at least 2.

57. The multi-phase biomaterial of claim 55, wherein the PDI of the first BNC network is higher by a factor of at least 3.

58. The multi-phase biomaterial of claim 40, wherein a first BNC network has a higher PDI and a lower DP.sub.n as compared to a second BNC network.

59. The multi-phase biomaterial of claim 1, wherein the plurality of different BNC networks differ in their degree of crystallinity.

60. The multi-phase biomaterial of claim 59, wherein at least one BNC network is characterized by a degree of crystallinity of at least 55%.

61. The multi-phase biomaterial of claim 60, wherein at least one BNC network is characterized by a degree of crystallinity of at least 60%.

62. The multi-phase biomaterial of claim 61, wherein at least one BNC network is characterized by a degree of crystallinity of at least 65%.

63. The multi-phase biomaterial of claim 59, wherein a plurality of BNC networks of the multi-phase biomaterials have a degree of crystallinity of at most 95%.

64. The multi-phase biomaterial of claim 63, wherein a plurality of BNC networks of the multi-phase biomaterials have a degree of crystallinity of at most 80%.

65. The multi-phase biomaterial of claim 63, wherein a plurality of BNC networks of the multi-phase biomaterials have a degree of crystallinity of at most 70%.

66. The multi-phase biomaterial of claim 59, wherein a degree of crystallinity of a first BNC network with a highest degree of crystallinity of said plurality of BNC networks is higher by a factor of at least 1.2 than a degree of crystallinity of a second BNC network with a lowest degree of crystallinity of said plurality of BNC networks.

67. The multi-phase biomaterial of claim 66, wherein said factor is at least 1.5.

68. The multi-phase biomaterial of claim 67, wherein said factor is at least 2.

69. The multi-phase biomaterial of claim 1, wherein said plurality of different BNC networks comprise a plurality of different thicknesses of microfibrils.

70. The multi-phase biomaterial of claim 1, wherein said plurality of different BNC networks comprise a plurality of different pore sizes, determined as an average cross sectional area of pores of said networks.

71. The multi-phase biomaterial of claim 70, wherein at least one BNC network is characterized by an average cross sectional pore area of at least 15 m.sup.2.

72. The multi-phase biomaterial of claim 71, wherein at least one BNC network is characterized by an average cross sectional pore area of at least 20 m.sup.2.

73. The multi-phase biomaterial of claim 72, wherein at least one BNC network is characterized by an average cross sectional pore area of at least 25 m.sup.2.

74. The multi-phase biomaterial of claim 70, wherein a plurality of BNC networks of the multi-phase biomaterials have an average cross sectional pore area of at most 50 m.sup.2.

75. The multi-phase biomaterial of claim 74, wherein a plurality of BNC networks of the multi-phase biomaterials have an average cross sectional pore area of at most 40 m.sup.2.

76. The multi-phase biomaterial of claim 75, wherein a plurality of BNC networks of the multi-phase biomaterials have an average cross sectional pore area of at most 30 m.sup.2.

77. The multi-phase biomaterial of claim 70, wherein an average cross sectional pore area of a first BNC network is higher by a factor of at least 1.2 than for a second BNC network.

78. The multi-phase biomaterial of claim 77, wherein said average cross sectional pore area is at least 1.5 times greater.

79. The multi-phase biomaterial of claim 78, wherein said average cross sectional pore area is at least 2 times greater.

80. A method for producing multi-phase biomaterials comprised of bacterially synthesized nanocellulose (BNC), comprising inoculating a culture medium with at least two different cellulose-producing bacterial strains, which have been commonly or separately prepared, thereby to synthesize BNC comprised of a plurality of different bacterial cellulose networks wherein BNC structure and BNC properties of the multi-phase biomaterials are predetermined by selection of the at least two different bacterial strains, by their preparation and inoculation and by selection of conditions of the synthesis, wherein said BNC has a transparency to an extent that more than 50% of visible light passes through the biomaterial at a thickness greater than 2 mm of the biomaterial, and wherein said BNC has thickness greater than 2 mm.

81. The method of claim 80, wherein the at least two different bacterial cellulose networks are prepared independently from each other and subsequently combined and commonly synthesized.

82. The method of claim 80, wherein the at least two different bacterial cellulose networks are combined for co-synthesis already before the inoculation.

83. The method of claim 80, wherein said bacterial strains are selected to generate cellulose-like structures on the basis of modified C-sources.

84. The method of claim 83, wherein said C-sources are selected from the group consisting of N-acetyl glucosamine and glucosamine.

85. The method of claim 80, wherein said plurality of different bacterial strains comprise a plurality of different Gluconacetobacter strains.

86. The method of claim 85, wherein said strains comprise ATCC 23769 and DSM 11804.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of embodiments of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout.

(2) In the accompanying drawings:

(3) FIG. 1: Bacterially synthesized nanocellulose (BNC) featuring a plurality of different bacterial cellulose networks that form a common homogeneous phase system;

(4) FIG. 2: BNC featuring two different bacterial cellulose networks each of them forming a separate layered single phase;

(5) FIG. 3: BNC with two different bacterial cellulose networks that form a layered phase system featuring two layered single phases and one combined, homogeneous phase;

(6) FIGS. 4A and 4B show images of BNC prepared as described with regard to FIG. 1, in which the BNC features two different individual cellulose networks that form a common homogeneous phase; and

(7) FIGS. 5A and 5B show images of BNC prepared as described with regard to FIG. 3, in which the BNC features two different bacterial cellulose networks that form a layered phase system of two layered single phases and one combined homogeneous phase.

DETAILED DESCRIPTION OF THE INVENTION

(8) Various examples of embodiments of the present invention will be explained in more detail by virtue of the following embodiments illustrated in the figures and/or described below.

(9) FIG. 1 shows bacterially synthesized nanocellulose (BNC biomaterial) that, according to the invention, consists of a plurality of different bacterial cellulose networks, of which two are shown for illustration only and without wishing to be limited in any way, forming a common phase system of one combined homogeneous phase (reference number 1combined homogeneous phase).

(10) This exemplary, illustrative phase system is synthesized from two kinds of Gluconacetobacter strains, in the example ATCC 23769 and DSM 11804, in a not shown cultivation vessel with a synthesis area of 7 cm.sup.2. However, the area can be freely selected for the special phase formation in this embodiment. Also optionally any suitable Gluconacetobacter strain may be used, including but not limited to ATCC 10245, ATCC 23769, DSM 11804 and DSM 14666.

(11) After separate preparation the two bacterial strains were added together into the cultivation vessel and thus they were inoculated for co-synthesis. An added cultivation medium included a carbon source (preferentially different sugars and their derivatives), a nitrogen source (preferentially peptone) and, if required, a buffer system (preferentially disodium hydrogen phosphate and citric acid). The biosynthesis was carried out at a temperature ranging from 28 to 30 C. during a period from 3 to 21 days and it was tested for both a discontinuous and a continuous synthesis procedure.

(12) A very stable and transparent combined homogenous BNC phase system (see FIG. 1) of the two synthesized BNC networks was reliably obtained with exemplary volume ratios of 5:1 and 2:1 of the culture medium and the bacterial strains, defining an optional range of from 5:1 to 2:1 of the culture medium and bacterial strains.

(13) The inoculation ratio is the volume ratio of the inoculated strains to each other. For example an inoculation ratio of 80:20 means that the volume of one strain used for inoculation was four times higher as compared to the volume of the other strain used for inoculation.

(14) The inoculation ratio is 50:50 (ATCC 23769:DSM 11804), i.e. the quantities of the bacterial strains that take part in the synthesis are identical. A change of this inoculation ratio would additionally allow the control of the pore system and thus of the stability as well as of the transparency of the homogenous BNC biomaterial. With an inoculation ratio of 10:90, for example, a solid/stable, transparent and simultaneously elastic BNC carded web was generated. If the inoculation ratio is reversed (e.g. 90:10), both the strength and the elasticity can be reduced without changing the transparency.

(15) Furthermore, the optional addition of glacial acetic acid in an amount of up to 2% volume/volume can improve the homogeneity of the generated BNC material.

(16) FIGS. 4A and 4B show images of BNC prepared as described with regard to FIG. 1, in which the BNC features two different individual cellulose networks that form a common homogeneous phase. FIG. 4A shows a photograph of actual BNC material, shown with a human hand for scale, indicating the flexibility of the material. FIG. 4B shows electron micrographs of the structure of the material.

(17) FIG. 2 shows a BNC material that, as proposed, also features two different bacterial cellulose networks which, however, have been synthesized to a layered phase system comprising separate single phases 2, 3. Each of the separate single phases 2, 3 corresponds to one BNC carded web and its properties known per se and are firmly combined with each other.

(18) This phase system was synthesized from two kinds of Gluconacetobacter strains, ATCC 10245 and DSM 14666 in this example, in the cultivation vessel that was mentioned in the first example and that has a synthesis area that can be freely selected for this special phase formation. In this embodiment, the two bacterial strains are separately prepared, too, and are added together into the cultivation vessel for co-synthesis. The added cultivation medium again features a carbon source (preferentially different sugars and their derivatives), a nitrogen source (preferentially peptone), a vitamin source (preferentially yeast extract) and, if required, a buffer system (preferentially disodium hydrogen phosphate and citric acid).

(19) Biosynthesis was performed at a temperature ranging from 28 to 30 C. during a period from 3 to 21 days and was tested with both a discontinuous and continuous synthesis procedure. During the procedure, a stable layered system was obtained from the two separated but firmly combined single phases 2, 3 with a volume ratio of 20:1 between the cultivation medium and the mentioned bacterial strains. Also the Gluconacetobacter strains were different from the ones used in the first embodiment, in that in the first embodiment, ATCC 23769 and DSM 11804 were used. In contrast, in the second embodiment, ATCC 10245 and DSM 14666 were used. In the material produced according to this second embodiment, the single phases 2, 3 were externally almost not visible as separate layers. Thus, the synthesized BNC biomaterial visually appears to be a homogenous carded web but structurally features the two different bacterial cellulose networks.

(20) The selected inoculation ratio between the bacterial strains used was 50:50 (ATCC 10245:DSM 14666). If this ratio is changed in favor of one bacterium, the thickness of the single phases 2 or 3 and the resulting properties (water absorption and water retention, etc.) can be specifically controlled. Furthermore, an inoculation ratio of 70:30 between the strains (the volume ratio of 20:1 between the cultivation medium and the bacterial strains was maintained) resulted in an improved transparency without a change of the thickness of the BNC carded web (data not shown).

(21) FIG. 3 shows a BNC that again features two different bacterial cellulose networks which, however, have been synthesized to form a special layered phase system. In this system the two separate single phases (2, 3) were combined via a combined homogenous phase (1). This special phase system was synthesized from the two Gluconacetobacter strains ATCC 23769 and DSM 14666, again in the previously mentioned but not shown cultivation vessel, again with a synthesis area of 7 cm.sup.2. If this synthesis area is changed, the formation of the single phases 2, 3 can be deliberately influenced as follows. Increasing the area (with an inoculation ratio of 50:50) supports the formation of the single phase 2 (corresponding to the bacterial strain DSM 14666) more than the formation of the single phase 3 (corresponding to bacterial strain ATCC 23769).

(22) The phase system of the BNC biomaterial shown in FIG. 3 is achieved by the use of the bacterial strains mentioned before and by their separate preparation and subsequent common inoculation. However, a common cultivation of these bacterial strains, common preparation included, would generate a combined homogeneous phase system as shown in FIG. 1.

(23) The cultivation medium used here was again a mixture of a carbon source (preferentially different sugars and their derivatives), a nitrogen source (preferentially peptone), a vitamin source (preferentially yeast extract) and, if required, a buffer system (preferentially disodium hydrogen phosphate and citric acid). The biosynthesis was carried out at a temperature ranging from 28 to 30 C. during a period from 3 to 21 days with a volume ratio of 20:1 between the cultivation medium and the bacterial strains and was tested both for a discontinuous and continuous synthesis procedure.

(24) The inoculation ratio of 50:50 between the bacterial strain led to the externally visible layered BNC phase system (FIG. 3) comprising the aforementioned two single phases 2, 3 and the homogenous phase 1 located between them. Moreover, with this inoculation ratio the proportions of the single phases are identical. The change of the inoculation ratio in favor of one bacterial strain allows the deliberate control of the thickness of the single phases 2, 3 and of the resulting properties (water absorption and water retention, etc.).

(25) FIGS. 5A and 5B show images of BNC prepared as described with regard to FIG. 3, in which the BNC features two different bacterial cellulose networks that form a layered phase system of two layered single phases and one combined homogeneous phase. FIG. 5A shows a photograph of actual BNC material. FIG. 5B shows electron micrographs of the structure of the material, with the phases labeled. Bacterial strain one is shown at the top right while strain two is shown at the lower right (ATCC 23769 and DSM 14666, respectively).

(26) In order to obtain the multi-phase biomaterials, preferably suitable cellulose-producing bacterial strains are selected for conjoint cultivation (co-cultivation). According to at least some embodiments of the present invention, two or more different cellulose-producing bacterial strains are co-cultivated in order to obtain the inventive multi-phase biomaterials comprising at least two different BNC networks. Preferably, the two or more different cellulose-producing bacterial strains are Gluconacetobacter strains. Notably, the international nomenclature has been recently amended and Gluconacetobacter has been renamed to Komagataeibacter. Preferably, the two or more different cellulose-producing bacterial strains are selected from the group consisting of ATCC 10245, ATCC 23769, DSM 11804 and DSM 14666.

(27) In a preferred embodiment, two cellulose-producing bacterial strains are co-cultivated in order to obtain multi-phase biomaterials comprising exactly two different BNC networks. Preferably, ATCC 23769 is co-cultivated with DSM 11804 or with DSM 14666. Preferably, ATCC 10245 is co-cultivated with DSM 14666.

(28) As described above and also shown in FIGS. 1 to 3, in different embodiments of the present invention, the at least two different bacterial cellulose networks may optionally be formed as a combined homogeneous phase system, as a layered phase system comprising firmly combined separate single phases or as a layered phase system comprising at least one combined homogeneous phase and at least one single phase. The particular phase system formed depends mainly on the kinetics of cellulose production of the different cellulose-producing bacterial strains. For example, if bacterial strains with comparable kinetics of cellulose production are used, the resulting different bacterial cellulose networks are formed as a combined homogeneous phase system. In contrast, if one strain with fast kinetics of cellulose production is combined with a strain with slow kinetics of cellulose production it might be that the slow strain starts production of cellulose only when the fast strain has already substantially finished production of cellulose. In such a case, the different bacterial cellulose networks are formed as a layered phase system comprising firmly combined separate single phases. If the slow strain starts production of cellulose when the fast strain is still producing cellulose, the different bacterial cellulose networks are formed as a layered phase system comprising at least one combined homogeneous phase and at least one single phase. If in such a case the slow strain continues cellulose production when the fast strain has stopped to produce cellulose, the different bacterial cellulose networks are formed as a layered phase system comprising a combined homogeneous phase and two single phases as shown in FIG. 3.

(29) In a preferred embodiment of the present invention, two cellulose-producing bacterial strains are co-cultivated, whose initial kinetics of cellulose production are so similar that the quotient of the initial kinetics of cellulose production of the strain with the faster initial kinetics (dividend) and the initial kinetics of cellulose production of the strain with the slower initial kinetics (divisor) is at most 2, more preferably at most 1.5, more preferably at most 1.2. According to this embodiment, multi-phase biomaterials may be obtained that comprise two different bacterial cellulose networks that are formed as a combined homogeneous phase system.

(30) In another embodiment of the present invention, two cellulose-producing bacterial strains are co-cultivated, whose initial kinetics of cellulose production are so different that the quotient of the initial kinetics of cellulose production of the strain with the faster initial kinetics (dividend) and the initial kinetics of cellulose production of the strain with the slower initial kinetics (divisor) is at least 2.5, more preferably at least 3, more preferably at least 5, more preferably at least 10. According to this embodiment, multi-phase biomaterials may be obtained that comprise two different bacterial cellulose networks that are formed as a layered phase system.

(31) Preferably, the initial kinetics of cellulose production of a cellulose-producing bacterial strain are determined as the weight of cellulose produced by such bacterial strain within 96 hours after beginning of cultivation, more preferably within 72 hours after beginning of cultivation, more preferably within 48 hours after beginning of cultivation, more preferably within 24 hours after beginning of cultivation, more preferably within 12 hours after beginning of cultivation.

(32) The co-cultivated cellulose-producing bacterial strains may also differ in the maximum bacterial cell number that is reached during cultivation. According to at least one embodiment of the present invention, the maximum bacterial cell number of the fast growing strain that is reached during cultivation is preferably higher by a factor of between about 5 to about 15, more preferably by a factor of about 10, in comparison to the maximum bacterial cell number of the slow growing strain that is reached during cultivation.

(33) The properties of the obtained multi-phase biomaterials may optionally be influenced by the inoculation ratio.

(34) Preferably, comparable volumes of the different cellulose-producing strains are used for inoculation. Thus, the inoculation ratio is preferably at most 90:10 and at least 10:90, more preferably at most 80:20 and at least 20:80, more preferably at most 70:30 and at least 30:70, more preferably at most 60:40 and at least 40:60, even more preferably about 50:50.

(35) The properties of the obtained multi-phase biomaterials may also be influenced by the volume ratio of the culture medium to the bacterial strains used for inoculation. Preferably, the volume ratio is at least 2:1, more preferably at least 5:1, more preferably at least 10:1, more preferably at least 15:1. Preferably, the volume ratio is at most 50:1, more preferably at most 30:1, more preferably at most 20:1.

(36) The properties of the obtained multi-phase biomaterials may also be influenced by the composition of the culture medium. Preferably, the culture medium comprises a carbon source, a nitrogen source and a vitamin source and optionally a buffer system. Preferably, the carbon source is selected from different sugars and their derivatives. Preferably, the nitrogen source is peptone. Preferably, the vitamin source is yeast extract. Preferably, the buffer system is disodium hydrogen phosphate and citric acid.

(37) Preferably, the culture medium is liquid.

(38) Preferably, the culture medium comprises the carbon source in an amount of least 10 g/l, more preferably at least 15 g/l based on the volume of the culture medium. Preferably, the culture medium comprises the carbon source in an amount of at most 30 g/l, more preferably at most 25 g/l based on the volume of the culture medium.

(39) Particularly preferably, the culture medium comprises the carbon source in an amount of about 20 g/l.

(40) Preferably, the culture medium comprises the nitrogen source in an amount of least 2 g/l, more preferably at least 4 g/l based on the volume of the culture medium. Preferably, the culture medium comprises the nitrogen source in an amount of at most 10 g/l, more preferably at most 7 g/l based on the volume of the culture medium. Particularly preferably, the culture medium comprises the nitrogen source in an amount of about 5 g/l.

(41) Preferably, the culture medium comprises the vitamin source in an amount of least 2 g/l, more preferably at least 4 g/l based on the volume of the culture medium. Preferably, the culture medium comprises the vitamin source in an amount of at most 10 g/l, more preferably at most 7 g/l based on the volume of the culture medium. Particularly preferably, the culture medium comprises the vitamin source in an amount of about 5 g/l.

(42) Preferably, the culture medium comprises the buffer system in an amount of least 2 g/l, more preferably at least 4 g/l based on the volume of the culture medium. Preferably, the culture medium comprises the buffer system in an amount of at most 10 g/l, more preferably at most 5 g/l based on the volume of the culture medium. Particularly preferably, the culture medium comprises the buffer system in an amount of about 4.5 g/l.

(43) Particularly preferably, the culture medium comprises 20 g/l glucose, 5 g/l peptone, 5 g/l yeast extract, 3.4 g/l disodium hydrogen phosphate and 1.15 g/l citric acid.

(44) The properties of the obtained multi-phase biomaterials may also be influenced by the cultivation temperature. Preferably, the cultivation temperature is at least 20 C., more preferably at least 25 C., more preferably at least 28 C. If the cultivation temperature is too low, the bacterial strains do not grow properly. Preferably, the cultivation temperature is at most 36 C., more preferably at most 33 C., more preferably at most 30 C. If the cultivation temperature is too high, the bacterial strains do not grow properly.

(45) The properties of the obtained multi-phase biomaterials may also be influenced by the cultivation time. Preferably the cultivation time is at least 3 days, more preferably at least 7 days, more preferably at least 10 days. If the cultivation time is too short, not enough cellulose is produced. Preferably, the cultivation time is at most 30 days, more preferably at most 25 days, more preferably at most 20 days. Particularly preferably, the cultivation time is about 14 days.

(46) The properties of the obtained multi-phase biomaterials may also be influenced by the culture volume. Preferably, the culture volume is at least 20 ml, more preferably at least 500 ml, more preferably at least 2000 ml. Preferably, the culture volume is at most 200 l, more preferably at most 180 l, more preferably at most 100 l.

(47) The properties of the obtained multi-phase biomaterials may also be influenced by the cultivation vessel. Preferably, the cultivation vessel has a synthesis area of at least 1 cm.sup.2, more preferably at least 10 cm.sup.2, more preferably at least 100 cm.sup.2. Preferably, the cultivation vessel has a synthesis area of at most 50,000 cm.sup.2, more preferably at most 20,000 cm.sup.2, more preferably at most 1,000 cm.sup.2. Particularly preferably, the cultivation vessel has a synthesis area of about 7 cm.sup.2.

(48) As described above, the present invention relates to multi-phase biomaterials comprising at least two different BNC networks. Even if the different BNC networks are synthesized as a combined homogeneous phase according to one embodiment of the present invention, the different networks may be intertwined but they still remain their individual molecular and supra-molecular structure. Preferably, the multi-phase biomaterials comprise exactly two different BNC networks.

(49) As also described above, the multi-phase biomaterial of the present invention can be obtained by conjoint cultivation of at least two different cellulose-producing bacterial strains. Importantly, not every biomaterial resulting from a combination of two different bacterial species is necessarily a multi-phase material comprising two different BNC networks. Rather, generally no multi-phase materials are produced because the cellulose fibers are simultaneously generated and modified by both bacterial strains so that a single hybrid network is produced, which is homogeneous on both macroscopic and molecular level. Furthermore, in the predominant number of cases, conjoint cultivation of two different cellulose-producing bacterial strains results in cellulose materials characterized by the properties of only one strain because the more dominant strain will suppress the other strain as can be seen from the following comparative examples, in which strains were combined that are not preferred for combination according to the present invention.

(50) Two Gluconacetobacter strains (Komagataeibacter according to new nomenclature) were co-cultivated in each of comparative example 1 and comparative example 2. In comparative example 1 ATCC 23769 and ATCC 10245 were used. In comparative example 2, ATCC10245 and ATCC 53582 were used. The conjoint cultivation was done in Sueoka's high salt medium (HSM medium (pH 6), Sueoka, N. (1960) Proc. Natl. Acad. Sci. USA 46, 83-91) in a cultivation vessel with a synthesis area of 7 cm.sup.2. The total volume of the inoculated medium was 40 ml. Separate pre-cultures of the two bacterial strains were added together into the cultivation vessel and thus they were inoculated for co-synthesis. The ratio of the culture medium to the pre-cultures of the bacterial strains was 20:1. The inoculation ratio was 50:50 in both comparative examples, i.e. the quantities of the bacterial strains that take part in the synthesis were identical in each case.

(51) The biosynthesis was carried out at a temperature of 28 C. during a period of 14 days. It was found that neither the biomaterial obtained by combining ATCC 23769 and ATCC 10245 according to comparative example 1, nor the biomaterial obtained by combining ATCC10245 and ATCC 53582 according to comparative example 2, was a multi-phase biomaterial comprising at least two different bacterial cellulose networks. Instead, the bacterial cellulose was built only by the dominant strain.

(52) In contrast, a multi-phase biomaterial comprising two different bacterial cellulose networks was obtained according to example 1 that was performed as described above, except that the two Gluconacetobacter strains (Komagataeibacter according to the new nomenclature) that are preferred for co-cultivation were used. In example 1 ATCC 23769 and DSM 11804 were used. The conjoint cultivation was done in HSM medium in a cultivation vessel with a synthesis area of 7 cm.sup.2 as described above. The total volume of the inoculated medium was 40 ml. Separate pre-cultures of the two bacterial strains were added together into the cultivation vessel and thus they were inoculated for co-synthesis. The volume ratio of the culture medium to the pre-cultures of the bacterial strains was 5:1. The inoculation ratio was 20:80 (ATCC 23769:DSM 11804). The biosynthesis was carried out at a temperature of 28 C. during a period of 14 days. A transparent multi-phase biomaterial comprising two different bacterial cellulose networks was obtained.

(53) As noted above, a wound dressing according to various embodiments of the present invention preferably comprises the biomaterials as described herein. Such wound dressings may optionally be transparent, due to the combined homogeneous phase system as shown in FIG. 1. The transparency of the wound dressings enables visual inspection of the wound by the doctor without the need to remove the protective wound dressing. A wound dressing comprising such biomaterials may optionally remain transparent even at much greater thickness, which in turn enables production of wound dressings with significantly increased solid content by removal of liquid; that is, the percentage of the wound dressing material that comprises solids may optionally be much higher than for other biomaterials. The wound dressings become thinner by removal of water. However, as the BNC biomaterials as described herein are thicker than is known in the art, the decrease in thickness due to liquid removal still leaves a reasonable thickness for the wound dressing. In contrast, the transparent wound dressings that are known in the art are so thin, that the content of solids may not be increased by removal of water as the resulting BNC materials would be too thin for use as wound dressings. Thus, transparent wound dressings of increased content of solids have been provided by the present invention.

(54) Without wishing to be limited to a closed list, the increased content of solids is particularly advantageous for wound dressings that are used for covering severe burns (second and especially third degree burns). Such burns produce a high amount of exudates that need to be absorbed by the wound dressings. Higher content of solids of a wound dressing results in increased absorptive properties of the wound dressing. Consequently, the wound dressings as described herein that have an increased solids content need to be exchanged substantially less often so that the wound is protected for an increased length of time before the protective cover needs to be removed.

(55) These desirable properties are obtained by selecting and combining two or more cellulose-producing bacterial strains, thereby enabling exploitation of properties of BNC from strains that was not possible if those strains were cultivated alone. Some strains do produce BNC that does not have the mechanical strength necessary for the above application, other applications as described herein or otherwise. However, they might contribute to transparency or absorption properties in an advantageous manner. Therefore, the combination of such a strain with a strain that produces BNC with advantageous mechanical properties results in BNC biomaterial that combines the positive aspects of both BNCs.

(56) While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made, and that various combinations and subcombinations of embodiments are also possible and encompassed within the scope of this application.