Producing bacterial cellulose foam objects

Abstract

The present disclosure presents a method of producing an object of bacterial cellulose foam (i.e. bacterial cellulose foam objects). The method comprises the steps of: - providing a bacterial cellulose pellicle which was grown from a growth medium for supporting bacterial growth inoculated with a cellulose producing bacterial culture; - forming the bacterial cellulose pellicle into a shape which corresponds to the object to be produced; and - freeze-drying the formed bacterial cellulose pellicle while in said shape to obtain the object of bacterial cellulose foam. The disclosure further presents an object of bacterial cellulose foam obtainable by this method.

Description

[0001] PRODUCING BACTERIAL CELLULOSE FOAM OBJECTS

[0002] The present disclosure relates to objects of bacterial cellulose foam (i.e. bacterial cellulose foam objects) that are shaped into a desired form and methods of producing such objects.

[0003] In an effort to reduce consumption of materials which have ecological impact, the inventors of the technology disclosed herein have considered bacterial cellulose to replace conventional foam-like materials based on synthetic polymers. However, there is currently no evidence of successful production of bacterial cellulose foam objects to date, let alone at a commercially relevant scale. Existing methods related to bacterial cellulose foam exhibit various disadvantages, such as complexity and poor scalability.

[0004] In a first aspect, a method of producing an object of bacterial cellulose foam is presented. The method comprises the steps of: providing a bacterial cellulose pellicle which was grown from a growth medium for supporting bacterial growth inoculated with a cellulose producing bacterial culture; forming the bacterial cellulose pellicle into a shape which corresponds to the object to be produced; and freeze-drying the formed bacterial cellulose pellicle while in said shape to obtain the object of bacterial cellulose foam.

[0005] As is customary in biology, the term pellicle here refers to the growth on the surface of an aqueous culture. A bacterial cellulose pellicle is wet and thus contains water which is removed by freeze-drying to obtain the bacterial cellulose foam. In the method, the shape of the formed bacterial cellulose pellicle is maintained as it is freeze-dried into the foam. Foam is a solid porous structure. In particular, the bacterial cellulose foam that can be obtained by the method is self-supporting and dry.

[0006] This method exhibits enhanced simplicity and / or scalability as the object of bacterial cellulose foam (i.e. bacterial cellulose foam object) is obtained already once the formed, wet bacterial cellulose pellicle is freeze-dried. In some embodiments, the bacterial cellulose foam object is acquired in a single step through freeze-drying the formed, wet bacterial cellulose pellicle while eliminating the need for further shaping. This may avoid one or more additional steps in the production of bacterial cellulose foam objects, presenting a significant opportunity for both environmental and economic impact in a positive way. Furthermore, material characteristics of the bacterial cellulose foam object that originate from the bacterial cellulose pellicle can be maintained in the presently disclosed method. Post-processing steps such as cutting, folding, bending and / or gluing techniques can be avoided which, if applied after the production of the foam material, would otherwise significantly impact these material characteristics. Further shaping of the foam by taking away material could even be avoided altogether, thus improving material usage.

[0007] The object may form a final product or an intermediate product or a part of such final or intermediate product. Multiple freeze-dried bacterial cellulose pellicles may be combined to from the object / product.

[0008] Forming the bacterial cellulose pellicle into the shape which corresponds to the object to be produced, is a pre-forming operation prior to setting the yet wet bacterial cellulose pellicle in its solid foam form by freeze-drying. This forming is preferably a mechanical macroscopic deformation of the bacterial cellulose pellicle while leaving its internal, microscopic structure of networked cellulose fibres intact. The produced object benefits from this intact cellulose fibre network which has merely been deformed to comply to the desired shape of the object.

[0009] As the bacterial cellulose pellicle will usually grow in a flat shape of a particular thickness, the forming may in particular refer to deforming, bending, rolling, folding and / or stacking the flat bacterial cellulose pellicle into three dimensions. Its thickness may be maintained or may be compressed to some extend during the forming operation. Additionally or alternatively, the forming or deforming may involve stacking one or more than one bacterial cellulose pellicle or sections thereof.

[0010] The shape which corresponds to the object to be produced may in particular refer to the exterior shape or form of the object that is to be produced by the method.

[0011] The grown medium usually is a liquid or gelled material. Growth medium should contain adequate nutrients, buffers and / or other substances to facilitate production of cellulose by bacteria of the bacterial culture in the growth medium.

[0012] Various growth media for supporting bacterial growth can be used. As an example, Hestrin-Schramm (HS) medium can be used. Other media are known and can be selected based on the cellulose producing bacterial culture that is used. The growth medium may typically contain water, a carbon source and salts, which may vary among bacteria species and growing conditions. These salts generally provide essential elements such as magnesium, nitrogen, phosphorus and sulphur to allow the bacteria to synthesize protein and nucleic acids. Alternatively or additionally, a source of amino acids and nitrogen can be included in the growth medium. The carbon source may be a sugar such as glucose or a less energy-rich source such as succinate.

[0013] The growth medium is preferably sterilized prior to inoculation by the cellulose producing bacterial culture, more preferably by filter sterilization. Filter sterilization has provided the surprising effect of an outer surface of the bacterial cellulose foam which exhibits enhanced smoothness, at least when compared to sterilization by other means, such as autoclave sterilization. Autoclave sterilization is heat treatment under increased pressure which avoids boiling of water present in the treated material (i.e. the bacterial cellulose pellicle). When boiling is avoided, the internal network of bacterial cellulose fibres is maintained.

[0014] The cellulose producing bacterial culture may be selected from cellulose producing Gramnegative bacteria such as from the genus Acetobacter, Alcaligenes, Azotobacter, Komagataeibacter, Pseudomonas, Rhizobium or Salmonella and Gram-positive bacteria such as from the genus Sarcina. For example, the cellulose producing bacteria can be selected from Komagataeibacter hansenii, Komagataeibacter xylinus or Sarcina ventriculi.

[0015] In an embodiment of the method, providing the bacterial cellulose pellicle comprises providing a bacterial cellulose pellicle which was grown from a filter-sterilized growth medium inoculated with the cellulose producing bacterial culture.

[0016] In an embodiment of the method, providing the bacterial cellulose pellicle comprises: providing a receptacle containing the growth medium inoculated with the cellulose producing bacterial culture; incubating said receptacle containing said growth medium to grow bacterial cellulose from the cellulose producing bacterial culture and form the bacterial cellulose pellicle; and optionally, separating the bacterial cellulose pellicle from the growth medium. The receptable can be selected based on a desired outline of the bacterial cellulose pellicle so that subsequent forming operations can be minimized. Moreover, a separate forming operation may even be avoided altogether when the object to be produced has a roughly planar shape. In general, the step or operation of forming the bacterial cellulose pellicle into the shape which corresponds to the object to be produced may then already be performed during the step or operation of growing bacterial cellulose from the cellulose producing bacterial culture in such a receptacle to form the bacterial cellulose pellicle in conforming to the selected receptacle.

[0017] Preferably, the step of providing the receptacle containing the growth medium with the bacterial culture for producing bacterial cellulose comprises: providing the growth medium; sterilizing the growth medium; and inoculating the sterilized growth medium with the bacterial culture.

[0018] Further, sterilizing the growth medium preferably comprises sterilization by filtering the growth medium. The effect of filter sterilization is a surprisingly smooth outer surface of bacterial cellulose foam object that is produced. This smoothness exhibits a more glossy or reflective appearance. Alternatively, sterilization can be performed by autoclave treatment, which however does not result in such a smooth outer surface.

[0019] In an embodiment, the method further comprises at least one of: rinsing the bacterial cellulose pellicle with water; and autoclaving the rinsed bacterial cellulose pellicle.

[0020] Rinsing serves to remove residual constituents of the growth medium from the bacterial cellulose pellicle. Autoclaving serves to sterilize the bacterial cellulose pellicle, preferably prior to obtaining the product. Rinsing and / or autoclaving may be performed after providing the bacterial cellulose pellicle and / or forming the provided bacterial cellulose pellicle, yet before freeze-drying the formed bacterial cellulose pellicle. Alternatively or additionally, autoclaving may be performed after freeze-drying the formed bacterial cellulose pellicle.

[0021] Rinsing the bacterial cellulose pellicle with water and / or autoclaving the rinsed bacterial cellulose pellicle may follow or be performed after providing the bacterial cellulose pellicle, more in particular after separating the bacterial cellulose pellicle from the growth medium. When both rinsing and autoclaving are performed, it is preferred that said rinsing precedes said autoclaving. The effect of this order is an increased whiteness of the resulting foam. Autoclaving without prior rinsing is possible and can result in caramelization of residual sugars from the growth medium.

[0022] In an embodiment of the method, forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises deforming or bending the bacterial cellulose pellicle while maintaining its thickness within a deviation of at most 20%, preferably 10%, more preferably 5%.

[0023] Forming may be defined as mechanical deformation of the bacterial cellulose pellicle while preserving the internal structure of the bacterial cellulose pellicle, in contrast to comminuting or macerating techniques such as is the case when using resuspended bacterial cellulose hydrogels. In some embodiments, the bacterial cellulose hydrogen may however be trimmed at its edged or cut into macroscopic sections (e.g. larger than 5 mm) to facilitate forming the bacterial cellulose pellicle into the desired shape.

[0024] In an embodiment of the method, forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises cutting at least one section from the bacterial cellulose pellicle to form said shape. Said cutting may include trimming of edges of the bacterial cellulose pellicle. In some cases, even cutting the bacterial cellulose pellicle into the desired shape may be sufficient to obtain the object after freeze- drying. In other embodiments, trimming or cutting can be avoided by selecting an appropriately shaped receptacle to grow the bacterial cellulose pellicle.

[0025] In an embodiment of the method, forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises: cutting sections (i.e. multiple sections) from the bacterial cellulose pellicle; and arranging at least two of the sections (e.g. the multiple sections, though some may be waste and not used for forming the shape of the object) into the shape. In this way, more intricate shapes can be obtained. Further, bacterial cellulose pellicle or sections thereof can be stacked to provided increased thickness.

[0026] In an embodiment of the method, forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises providing and forming one or more than one further bacterial cellulose pellicle, optionally at least one section thereof, into the shape corresponding to the object to be produced. The object of bacterial cellulose foam may thus be formed of multiple bacterial cellulose pellicles or of section from multiple bacterial cellulose pellicles.

[0027] In general, forming the wet bacterial cellulose hydrogen into the desired shape preferably comprises using a mould. The mould may serve to bend the bacterial cellulose pellicle from a generally flat or planar shape into a three-dimensional bended form. The bacterial cellulose pellicle, optionally one or more than one section of the bacterial cellulose pellicle, are formed by the mould. Alternatively, multiple bacterial cellulose pellicles (or sections thereof) can be combined to form the desired shape. The shape may thus be formed by a patchwork of (sections of) bacterial cellulose pellicles, even when no mould is used. The three-dimensional bended form can be defined by a moulding surface of the mould, which may be a single moulding surface of a single mould part, though a two-part mould may also be employed.

[0028] In an embodiment of the method, forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises arranging the bacterial cellulose pellicle or at least one section thereof, and optionally a further bacterial cellulose pellicle or at least one section thereof, at one or more than one moulding surface of a mould defining the shape corresponding to the object to be produced. For example, the wet bacterial cellulose pellicle may be placed in, around or against a mould of one or more parts, each part having a moulding surface to jointly define the shape of at least a part of the object that is to be produced of bacterial cellulose foam.

[0029] Preferably, arranging the bacterial cellulose pellicle or the at least one section thereof, and optionally the further bacterial cellulose pellicle or the at least one section thereof, in the mould comprises arranging the bacterial cellulose between an inner mould part and an outer mould part of the mould. At least a part of the shape corresponding to the object to be produced may be defined between the inner mould part and the outer mould part.

[0030] Preferably, at least one of the one or more than one moulding surface of the mould is permeable to water, in particular water vapour. For example, the moulding surface of the inner mould part and / or the moulding surface of the outer mould part, preferably both, may be permeable. Alternatively or additionally, the mould may have walls which are permeable or the mould may be permeable itself. Permeability facilitates sublimation of water from the freeze-dried bacterial cellulose material from all sides. Use of a permeable mould for forming bacterial cellulose pellicles, or even bacterial cellulose hydrogels, is considered an innovation on its own for which protection may be sought in isolation of the method as disclosed herein. A further aspect of the disclosure thus presents a mould for forming a wet bacterial cellulose hydrogel or pellicle, which mould has one or more than one permeable moulding surface. Any of the features of the mould as disclosed herein can be combined with this general definition.

[0031] Preferably, at least one of the one or more than one moulding surface of the mould is configured to impart a surface texture to the bacterial cellulose pellicle in addition to defining the shape of the object to be produced. In this way, a surface texture as well as a shape may be imparted to the bacterial cellulose foam object produced with the method.

[0032] Preferably, freeze-drying the formed bacterial cellulose pellicle comprises freeze-drying the formed bacterial cellulose pellicle while arranged in the mould.

[0033] In an embodiment of the method, freeze-drying the formed bacterial cellulose pellicle comprises: arranging the formed bacterial cellulose pellicle inside a freeze-drier chamber; evacuating the freeze-drier chamber to freeze water in the bacterial cellulose pellicle; and cooling the freeze-drier chamber to condense sublimated water from the bacterial cellulose.

[0034] Freeze-drying serves to prevent water in the bacterial cellulose pellicle from boiling. In other words, freeze-drying avoids the liquid-to-gas transition which would disrupt the internal structure of the bacterial cellulose pellicle.

[0035] Freeze-drying as such is a known technology. When applied to a wet bacterial cellulose pellicle, the following is noted, which applies irrespective of whether a mould is used to shape said pellicle. The start of freeze-drying can be observed visually by the pellicle freezing over. Conditions of freeze-drying are selected such that water in the pellicle does not boil (i.e. pass from liquid to vapour phase) but rather sublimates from solid to vapour. Water vapour is removed by condensation with a cooling unit. As freeze-drying proceeds, water is removed from the bacterial cellulose pellicle and its internal network of bacterial cellulose fibres is laid bare. This network forms the bacterial cellulose foam. Once freeze- drying is completed, the chamber is repressurized and the freeze-dried bacterial cellulose pellicle, now in the form of a bacterial cellulose foam, is removed from the chamber. If the mould is used, it is also removed from the mould in which it was formed into the object.

[0036] Freeze-drying should be performed until the bacterial cellulose foam is sufficiently dry. The duration of the freeze-drying process depends on volume and shape of the bacterial cellulose pellicle as well as the conditions imposed in the freeze-drying chamber. In general, such parameters can be established by routine experimentation to ensure that no collapse of the bacterial cellulose foam occurs after freeze-drying is completed.

[0037] In an embodiment, the method further comprises processing the object of bacterial cellulose foam into a final product, such as by machining, surface treatment, impregnation, painting or cutting (e.g. by a blade or a laser). For example, the bacterial cellulose foam object may require a through hole or other further processing operation to arrive at the final product for which the object is only intermediate.

[0038] In an embodiment, the method comprising producing a packaging object, such a container or cover, or an insulation object. In other words, the object may be a packaging object, such a container or cover, or an insulation object.

[0039] In a second aspect, an object of bacterial cellulose foam (i.e. a bacterial cellulose foam object) is presented. Said object is preferably obtainable by the method according to the first aspect. Correspondingly, the method as disclosed herein may be configured to provide the object as disclosed herein. Feature of the method may thus define features of the object and vice versa.

[0040] In an embodiment, the object, in particular the bacterial cellulose foam thereof, has a density in the range of 10 - 50 kg / m3, preferably 15 - 25 kg / m3and / or 20 - 30 kg / m3. The density of the bacterial cellulose foam can be tuned in various ways, for example by compressing the bacterial cellulose pellicle when forming it into the shape (this increases the density). Further, the density can be reduced by gas formation when the bacterial cellulose is grown from the growth medium or by processing the foam, such as by laser cutting.

[0041] In an embodiment, the object, in particular the bacterial cellulose foam thereof, has a Young’s Modulus below 100 MPa, preferably in the range of 10 - 50 MPa, more preferably in the range of 15 - 40 MPa. The lower end of these ranges may be as low as 5 MPa. Young’s Modulus can be measured with a tensile test using standard equipment. The tensile test is preferably performed in the plane corresponding to the flat shape of the original bacterial cellulose as grown.

[0042] In an embodiment, the object, in particular the bacterial cellulose foam thereof, has a compression modulus below 1 MPa or even below 0.5 MPa. Preferably, the compression modulus is in the range of 0.01 MPa - 0.05 MPa, more preferably 0.02 - 0.04 MPa.

[0043] An elastic point of the bacterial cellulose foam may be below 0.5 MPa, in particular in the range of 0.1 - 0.3 MPa.

[0044] In an embodiment of the object of bacterial cellulose foam, bacterial cellulose fibres of the bacterial cellulose foam are non-homogenously arranged or have a preferred orientation. This can be observed by microscopy, e.g. optical or electron microscopy. The nonhomogeneity or preferred orientation of the distribution of the bacterial cellulose fibres can for example be observed in cross-section over the thickness of the bacterial cellulose foam, i.e. in the direction in which the bacterial cellulose pellicle was grown from the growth medium. For example, when a roughly flat bacterial cellulose pellicle is bend into the shape of the object to be produced, layers can be observed in cross-section perpendicular to the thickness of the foam object (thickness referring to this distance from one surface of the object to an opposite surface of the object).

[0045] In an embodiment, the object of bacterial cellulose foam has a layered microscopic structure of bacterial cellulose fibres. Layers arise from growth of the bacterial cellulose pellicle at the liquid / air interface. Once the bacterial cellulose pellicle is formed (e.g. deformed or bend to comply to the shape of the object to be produced), this layered structure is maintained. In alternative methods, involving destructive processing methods such as nanofibrilation, ultrasonication and / or homogenisation, such internal microscopic structure or network is lost.

[0046] The layers of bacterial cellulose fibres may have a thickness in the range of 1 - 50 pm, preferably 2 - 10 pm. This layer thickness can be measured by microscopy, e.g. optical microscopy or (scanning) electron microscopy. In an embodiment, the object of bacterial cellulose foam is a packaging object, such a container or cover, or an insulation object.

[0047] Some embodiments of the present disclosure are based on the insight that a wet bacterial cellulose pellicle that can be or is obtained from a bacterial culture in a growth medium is deformed while wet into a shape corresponding to a desired object and subsequently freeze-drying this formed wet bacterial cellulose pellicle while in said shape to obtain a bacterial cellulose foam having the shape of the desired object. In particular, a mould can be used to form the bacterial cellulose pellicle and maintain the form during freeze-drying. Though a single bacterial cellulose pellicle may be employed, multiple pellicles can be combined. Further, a bacterial cellulose pellicle may be trimmed or cut into sections, which may be combined to define the shape of the desired object.

[0048] The following figures are presented to further explain the technology present herein: FIG. 1 shows a flow diagram for the method of producing a bacterial cellulose foam object;

[0049] FIG. 2A - 2D shows a schematic illustration for the method;

[0050] FIG. 3 shows a photograph of a bacterial cellulose foam object produced according to a first example;

[0051] FIG. 4 shows a photograph of a bacterial cellulose foam object produced according to a second example;

[0052] FIG. 5A-5B show stress-strain curves from tensile testing of BC foam samples; and

[0053] FIG. 6A-6B show stress-strain curves from compression testing of BC foam sample, in which the data of FIG. 6A was collected in the normal direction (i.e. growth direction of the BC pellicle from which the BC foam is made) and the data of FIG. 6B was collected in the across direction perpendicular to the normal direction (i.e. in the plane of the BC foam).

[0054] The following reference signs are used throughout.

[0055] 1 bacterial cellulose pellicle

[0056] 2 receptacle

[0057] 3 growth medium

[0058] 4 incubator chamber

[0059] 5 shape of object to be produced

[0060] 6 object to be produced 7 section of bacterial cellulose pellicle

[0061] 8 mould

[0062] 9 moulding surface

[0063] 10 inner mould part

[0064] 11 outer mould part

[0065] 12 first moulding surface

[0066] 13 second moulding surface

[0067] 14 freeze-dryer chamber

[0068] 15 first exterior surface

[0069] 16 second exterior surface

[0070] 100 providing bacterial cellulose pellicle

[0071] 110 providing receptacle containing growth medium

[0072] 111 providing growth medium

[0073] 112 sterilizing growth medium

[0074] 113 inoculating sterilized growth medium

[0075] 120 incubating receptacle containing growth medium

[0076] 130 separating bacterial cellulose pellicle from growth medium

[0077] 140 rinsing bacterial cellulose pellicle

[0078] 150 autoclaving bacterial cellulose pellicle

[0079] 200 forming bacterial cellulose pellicle into shape

[0080] 210 cutting at least one section from bacterial cellulose pellicle

[0081] 220 cutting sections from bacterial cellulose pellicle

[0082] 230 arranging at least two sections into shape

[0083] 240 providing and forming further bacterial cellulose pellicle

[0084] 250 arranging bacterial cellulose pellicle at moulding surface of mould

[0085] 260 arranging bacterial cellulose pellicle between inner and outer mould parts

[0086] 300 freeze-drying formed bacterial cellulose pellicle while in shape

[0087] 310 arranging formed bacterial cellulose pellicle inside freeze-drier chamber

[0088] 320 evacuating freeze-drier chamber

[0089] 330 cooling freeze-drier chamber

[0090] 400 processing object of bacterial cellulose foam

[0091] FIG. 1 and 2A - 2D illustrate the method including various optional steps or operations. The method includes a step 100 of providing a bacterial cellulose pellicle 1 which was grown from a growth medium 3 for supporting bacterial growth inoculated with a cellulose producing bacterial culture (see e.g. FIG. 2A - 2B).

[0092] The step 100 of providing the bacterial cellulose pellicle 1 may comprises at least one of: an optional step 110 of providing a receptacle 2 containing the growth medium 3 inoculated with the cellulose producing bacterial culture; an optional step 120 of incubating said receptacle 2 containing said growth medium 3 to grow bacterial cellulose from the cellulose producing bacterial culture and form the bacterial cellulose pellicle 1 (e.g. in an incubator chamber 4, see FIG. 2A); and an optional step 130 of separating the bacterial cellulose pellicle from the growth medium (see e.g. FIG. 2B).

[0093] The step 110 of providing the receptacle 2 containing the growth medium 3 with the bacterial culture for producing bacterial cellulose may comprise at least one of: an optional step 111 of providing the growth medium 3; an optional step 112 sterilizing the growth medium 3, in particular sterilization by filtering the growth medium 3; and an optional step 113 inoculating the sterilized growth medium with the bacterial culture.

[0094] The step 100 of providing the bacterial cellulose pellicle 1 may alternatively or additionally comprise providing a bacterial cellulose pellicle 1 which was grown from a filter-sterilized growth medium 3 inoculated with the cellulose producing bacterial culture.

[0095] The method may further comprise at least one of: an optional step 140 of rinsing the bacterial cellulose pellicle 1 with water; and an optional step 150 of autoclaving the rinsed bacterial cellulose pellicle 1 .

[0096] The method further includes a step 200 of forming the bacterial cellulose pellicle 1 into a shape 5 which corresponds to the object 6 to be produced (see e.g. FIG. 2C - 2D).

[0097] The step 200 of forming the bacterial cellulose pellicle 1 into the shape corresponding to the object to be produced may comprise deforming or bending the bacterial cellulose pellicle while maintaining its thickness within a deviation of at most 20%, preferably 10%, more preferably 5%. The step 200 of forming the bacterial cellulose pellicle 1 into the shape 5 corresponding to the object 6 to be produced may comprise an optional step 210 of cutting at least one section from the bacterial cellulose pellicle 1 to form said shape 5.

[0098] The step 200 of forming the bacterial cellulose pellicle 1 into the shape 5 corresponding to the object 6 to be produced may comprise at least one of: an optional step 220 of cutting sections 7 from the bacterial cellulose pellicle 1 ; and an optional step 230 of arranging at least two of the sections 7 into the shape 5.

[0099] The step 200 of forming the bacterial cellulose pellicle 1 into the shape 5 corresponding to the object 6 to be produced may comprise an optional step 240 of providing and forming one or more than one further bacterial cellulose pellicle 1 , optionally at least one section 7 thereof, into the shape 5 corresponding to the object 6 to be produced (see e.g. FIG. 2C where two section 7 of bacterial cellulose pellicle 1 jointly form said shape 5).

[0100] The step 200 of forming the bacterial cellulose pellicle 1 into the shape 5 corresponding to the object 6 to be produced may comprise an optional step 250 of arranging the bacterial cellulose pellicle 1 or at least one section 7 thereof, and optionally a further bacterial cellulose pellicle 1 or at least one section 7 thereof, at one or more than one moulding surface 9 of a mould 8 defining the shape 5 corresponding to the object 6 to be produced.

[0101] The step 250 of arranging the bacterial cellulose pellicle 1 or the at least one section 7 thereof, and optionally the further bacterial cellulose pellicle 1 or the at least one section 7 thereof, in the mould 8 may comprise an optional step 260 of arranging said bacterial cellulose pellicle 1 and / or section 7 between an inner mould part 10 and an outer mould part 11 of the mould 8, wherein at least a part of the shape 5 corresponding to the object 6 to be produced is defined between the inner mould part 10 and the outer mould part 11 . As illustrated in FIG. 2C, the inner mould part 10 may have a first moulding surface 12 and the outer mould part 11 may have a second moulding surface 13.

[0102] At least one of the one or more than one moulding surface 9 of the mould 8 may be permeable to water, in particular water vapour. Alternatively or additionally, at least one of the one or more than one moulding surface 9 of the mould 8 is configured to impart a surface texture to the bacterial cellulose pellicle 1 in addition to defining the shape 5 of the object 6 to be produced.

[0103] The method further includes a step 300 of freeze-drying the formed bacterial cellulose pellicle 1 while in said shape 5 to obtain the object 6 of bacterial cellulose foam (see e.g. FIG. 2C - 2D).

[0104] The step 300 of freeze-drying the formed bacterial cellulose pellicle 1 may comprise freeze-drying the formed bacterial cellulose pellicle 1 while arranged in the mould 8 (e.g. in a freeze-dryer chamber 14 of FIG. 2C).

[0105] The step 300 of freeze-drying the formed bacterial cellulose pellicle 1 may comprise at least one of: an optional step 310 of arranging the formed bacterial cellulose pellicle 1 inside a freeze-drier chamber 14; an optional step 320 of evacuating the freeze-drier chamber 14 to freeze water in the formed bacterial cellulose pellicle 1 ; and an optional step 330 of cooling the freeze-drier chamber 14 to condense sublimated water from the formed bacterial cellulose pellicle inside the freeze-drier chamber 14.

[0106] Optionally, the method further comprises a step 400 of processing the object of bacterial cellulose foam obtained from step 300 into a final product, such as by machining, surface treatment, impregnation, painting or cutting.

[0107] The method results in a bacterial cellulose foam object 6 which is shaped as desired. In particular when the mould 8 is used its moulding surface(s) 9 impart the desired shape to said object 6. For example, when the mould 8 with the inner mould part 10 and the outer mould part 11 is employed, the first moulding surface 12 of the inner mould part 10 has served to form a first exterior surface 15 of the object 6 while the second moulding surface 13 of the outer mould part 11 has served to form a second exterior surface 16 of the object 6 (see e.g. FIG. 2D). The first exterior surface 15 may form in interior space of the object 6.

[0108] As is evident from these relatively simple examples, the method as disclosed herein allows for many variations in shape of the object 6 and thus has great versatility. FIG. 3 shows a photograph of a bacterial cellulose foam object 6 produced according to a first example in which the growth medium 3 was sterilized by autoclave treatment prior to inoculation with the cellulose producing bacterial culture.

[0109] Komagataeibacter hansenii was grown in HS medium statically at 30 °C. A bacterial cellulose (BC) pellicle was produced at the air-liquid interface, vertically increasing in thickness with time. After 10 days, the BC pellicle was harvested (i.e. manually removed from the medium), washed in demineralised water and autoclaved for 25 min. at 122 °C under increased pressure to avoid boiling.

[0110] The autoclaved BC pellicle in its wet state was formed at a moulding surface 9 of a mould 8 to impart a desired shape 5.

[0111] The autoclaved and formed BC pellicle was freeze-dried (lyophilized) to remove water while retaining the thickness of the wet BC pellicle. Freeze-drying was performed by lowering the ambient pressure (set to 0.2 mbar) resulting in freezing of the pellicle. The BC pellicle was kept at the lowered ambient pressure for 48 hours to allow sublimation of practically all water content. Water was removed by condensation at a cooling unit (set to -55°C).

[0112] The resulting bacterial cellulose foam object 6 is shown in FIG. 3. The first exterior surface 15 reflects the shape imparted by the moulding surface 9 of the mould 8. The illustrated object 6 may serve as packaging or insulation coat for a bottle. Other shapes can be devised for other purposes, such as packaging boxes, corrugated insulation slabs, formed-fitted packaging inserts for (electronic) products, etc.

[0113] The thickness of the bacterial cellulose foam object 6, as measured across the object 6 from the first exterior surface 15 to an opposing second exterior surface, was within ±10% of the thickness of the original bacterial cellulose pellicle 1 used in this example.

[0114] Mechanical testing was performed on obtained bacterial cellulose foam material. Seven samples were cut from bacterial cellulose foam and tensile testing was performed in the plane corresponding to the flat shape of the original bacterial cellulose as grown (i.e. along the plane of the microscopic layers structure). To calculate Young's Modulus for the obtained bacterial cellulose foam material, the slope of the linear part of the measured stress-strain curve was calculated. Table 1 presents the results.

[0115] The density of the bacterial cellulose foam material was 22 kg / m3. Further batches had a density of (19.4 ± 0.8) kg / m3, (23.0 ± 0.8) kg / m3and (17 ± 1 ) kg / m3, respectively. These batches are further described below.

[0116] The bacterial cellulose foam material compares very favourably in terms of relatively low density and relative high Young’s Modulus when compared to other foam materials.

[0117] FIG. 4 shows a photograph of a bacterial cellulose foam object 6 in which the growth medium 3 was filter-sterilized prior to inoculation with the cellulose producing bacterial culture. A 0.2 pm polyether sulfone capsule filter was used for this purpose. No autoclaving was performed.

[0118] The planar shape of the bacterial cellulose foam object 6 shown in FIG. 4 is imparted by the receptacle 2 in which it was grown. Said receptacle 2 has a rectangular outline with rounded corners.

[0119] As is apparent from comparing the photographs of FIG. 3 and 4, the exterior surface 16 of the bacterial cellulose foam object 6 of FIG. 4 is smoother than the exterior surface (e.g. exterior surface 15) of the bacterial cellulose foam object 6 of FIG. 3. It is particularly noted that this smoothness effect arises even without performing the step of forming the bacterial cellulose pellicle 1 into the shape 5 corresponding to the object 6 to be produced.

[0120] Use of filter-sterilization of the growth medium for growing bacterial cellulose pellicles is considered an innovation on its own for which protection may be sought in isolation of the method as disclosed herein. In general, the disclosure thus also presented a further aspect in a method for preparing a bacterial cellulose foam involving filter-sterilizing the growth medium from which a bacterial cellulose pellicle is grown and which is subsequently freeze-dried to obtain the bacterial cellulose foam. The other steps of the method as disclosed herein may still apply, except for the step 200 of forming the bacterial cellulose pellicle into the shape, which step can be omitted. In this case, a bacterial cellulose pellicle as grown from the growth medium may be employed (generally of a flat or planar shape) without performing the forming step.

[0121] Further BC pellicles were prepared to a thickness of about 7 mm using the above methods. After autoclaving, the BC pellicles were cooled to room temperature and washed by remaining submerged in demineralized water for 3 days. The BC pellicles were then freeze-dried as described above for 4 days, however without deforming the BC pellicles into a particular shape. The resulting BC foam also exhibited a thickness of 7 mm and was cut into samples for mechanical testing. Two batches were prepared.

[0122] Tensile and compressions tests were conducted on a number of these samples from these batches. Tensile properties can be determined by the ISO 1926:2009 standard. Compression properties can be determined by the ISO 844:2021 standard. Both standards refer to rigid cellular plastics. ‘Rigid cellular plastics’ here refers to materials that are either open or closed cell foams which show plastic deformation when subjected to high forces. These properties best describe the BC foam material for which these test standards are suitable. Irregular shapes were removed or accounted for in the analysis.

[0123] For tensile testing, samples of 7.5 mm thickness were cut into rectangles of 7.5 mm wide and 45 mm long. The samples were pulled by their longitudinal ends (i.e. in the plane of the BC foam) at a speed of 1 mm / min until failure (i.e. breaking). A Zwick-Roell tensile testing machine equipped with a static load cell of 500 N was used. The tension test results were first obtained in the form of force / displacement data, this was then processed using the dimensions of the samples into stress / strain data which is plotted in the graphs shown in FIG. 5A and 5B for a sample set of each batch.

[0124] The stress / strain data was used to calculate the elastic slope by linear regression, calculate the intersection point, calculate the elongation point and the toughness.

[0125] To calculate the yield point of the material, the slope of the initial section was calculated and a parallel line from 0.2% strain was drawn, the intersection of this line with the stress strain curve gave the yield points for every sample.

[0126] The ultimate stress, which in this case also equals the breaking stress, is given by the maximum stress of the curve. This is due to the material undergoing brittle failure at maximum stress.

[0127] The toughness of the material is represented by the area under the curve between the curve and the elastic line from point of failure. This is also calculated for every sample.

[0128] The elongation point, which is the intersection point between the elastic slope line from maximum stress at the X-axis, indicates the amount of plastic deformation.

[0129] These metrics are summarized for the two batches in Table 2 (for FIG. 5A) and Table 3 (for FIG. 5B). The average and standard deviation (st. dev.) are also indicated for each parameter.

[0130] During tensile testing, the BC foam material exhibits two distinct behaviours: an initial phase of linear elasticity and a subsequent phase that appears to be plastic deformation. Variability in Young's modulus across batches ranges from approximately 7 MPa to 18 MPa, with ultimate stress values varying between 0.65 MPa and 1 .3 MPa. Despite this variability, the material generally behaves consistently under tension with minor deviations likely due to residual stresses near the protective tapes used to clamp the samples in the claws of the testing apparatus. Using ISO standardized sample geometries helped ensure more reliable data.

[0131] For compression testing, cylindrical or disc-shaped samples were cut. Compression testing was performed in two orthogonal direction of the samples: normal (i.e. the thickness of the BC foam in the direction of growth) and across (i.e. perpendicular to the normal or thickness direction in the plane of the BC foam). For normal compression testing, disc-shaped samples of 7 mm thick and 14.4 mm in diameter were used, while for across compression testing, samples of 5 mm thick and 9 mm in diameter were used. A DMA Q800 of TA instruments was used with a load capacity of up to 18 N and compression plate diameter of up to 9.5 mm, and at 1 mm / min loading speed until 10% of the initial thickness was achieved (i.e. 90% strain).

[0132] The raw force / displacement data was converted to stress / strain data using the dimensions of the samples. The stress / strain data is presented in FIG. 6A and 6B for the normal direction and the across direction of the samples, respectively.

[0133] The stress / strain data is used to calculate the elastic slope (by linear regression), the slope of the plateau region, the slope of the densification region, the intersection point of the elastic and plateau lines, and the intersection point of the plateau and densification lines. Elasticity calculations began from 2% strain to remove any artefacts at the beginning of a test cycle.

[0134] The intersection point of the elastic and plateau lines give the elastic strain and elastic stress of each sample. The intersection point of the plateau and densification lines give the densification strain and densification stress of each sample.

[0135] These metrics are summarized for the normal and across directions in Table 4 (for FIG. 6A) and Table 5 (for FIG. 6B), respectively. The average and standard deviation (st. dev.) are again indicated for each parameter. Samples 3.8 - 3.16 were tested using ARG 2 Rheometer with a 50 N load cell and larger sample accommodation.

[0136] The BC foam initially compresses elastically, followed by a phase where it compresses more easily with minimal resistance increase, and finally densifies with a sharp increase in resistance. In the normal direction, the material shows an elastic point around 0.045 MPa and a compression modulus of approximately 0.004 MPa. In the across direction, these values increase significantly to an elastic point ranging from 0.15 - 0.2 MPa, and a compression modulus ranging from 0.023 - 0.033 MPa. Compared to the behaviour under tension, the material exhibits a similar yield point (~0.1 MPa) but significantly lower stiffness, approximately three orders of magnitude weaker.

[0137]

Claims

CLAIMS1 . A method of producing an object of bacterial cellulose foam, the method comprising the steps of:(100) providing a bacterial cellulose pellicle which was grown from a growth medium for supporting bacterial growth inoculated with a cellulose producing bacterial culture;(200) forming the bacterial cellulose pellicle into a shape which corresponds to the object to be produced; and(300) freeze-drying the formed bacterial cellulose pellicle while in said shape to obtain the object of bacterial cellulose foam.

2. The method according to claim 1 , wherein the step (100) of providing the bacterial cellulose pellicle comprises the steps of:(110) providing a receptacle containing the growth medium inoculated with the cellulose producing bacterial culture;(120) incubating said receptacle containing said growth medium to grow bacterial cellulose from the cellulose producing bacterial culture and form the bacterial cellulose pellicle; and optionally, (130) separating the bacterial cellulose pellicle from the growth medium.

3. The method according to claim 2, wherein the step (110) of providing the receptacle containing the growth medium with the bacterial culture for producing bacterial cellulose comprises:(111 ) providing the growth medium;(112) sterilizing the growth medium; and(113) inoculating the sterilized growth medium with the bacterial culture.

4. The method according to claim 3, wherein the step (112) of sterilizing the growth medium comprises sterilization by filtering the growth medium.

5. The method according to any of the previous claims, wherein the step (100) of providing the bacterial cellulose pellicle comprises providing a bacterial cellulose pellicle which was grown from a filter-sterilized growth medium inoculated with the cellulose producing bacterial culture.

6. The method according to any of the previous claims, further comprising: (140) rinsing the bacterial cellulose pellicle with water; optionally, (150) autoclaving the rinsed bacterial cellulose pellicle.

7. The method according to any of the previous claims, wherein the step (200) of forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises bending the bacterial cellulose pellicle while maintaining its thickness within a deviation of at most 20%, preferably 10%, more preferably 5%.

8. The method according to any of the previous claims, wherein the step (200) of forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises:(210) cutting at least one section from the bacterial cellulose pellicle to form said shape.

9. The method according to any of the previous claims, wherein the step (200) of forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises:(220) cutting sections from the bacterial cellulose pellicle; and (230) arranging at least two of the sections into the shape.

10. The method according to any of the previous claims, wherein the step (200) of forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises:(240) providing and forming one or more than one further bacterial cellulose pellicle, optionally at least one section thereof, into the shape corresponding to the object to be produced.11 . The method according to any of the previous claims, wherein the step (200) comprises bending the bacterial cellulose pellicle from a generally flat or planar shape into a three-dimensional bended form using a mould.

12. The method according to any of the previous claims, wherein the step (200) of forming the bacterial cellulose pellicle into the shape corresponding to the object to be produced comprises:(250) arranging the bacterial cellulose pellicle or at least one section thereof, and optionally a further bacterial cellulose pellicle or at least one section thereof, at one or more than one moulding surface of a mould defining the shape corresponding to the object to be produced.

13. The method according to claim 11 or 12, wherein the step (250) of arranging the bacterial cellulose pellicle or the at least one section thereof, and optionally the further bacterial cellulose pellicle or the at least one section thereof, in the mould comprises:(260) arranging said bacterial cellulose between an inner mould part and an outer mould part of the mould, wherein at least a part of the shape corresponding to the object to be produced is defined between the inner mould part and the outer mould part.

14. The method according to any of the claims 11 - 13, wherein at least one of the one or more than one moulding surface of the mould is permeable to water, in particular water vapour.

15. The method according to any of the claims 11 - 14, wherein at least one of the one or more than one moulding surface of the mould is configured to impart a surface texture to the bacterial cellulose pellicle in addition to defining the shape of the object to be produced.

16. The method according to any of the claims 11 - 15, wherein the step (300) of freeze-drying the formed bacterial cellulose pellicle comprises freeze-drying the formed bacterial cellulose pellicle while arranged in the mould.

17. The method according to any of the previous claims, wherein the step (300) of freeze-drying the formed bacterial cellulose pellicle comprises:(310) arranging the formed bacterial cellulose pellicle inside a freeze-drier chamber;(320) evacuating the freeze-drier chamber to freeze water in the bacterial cellulose pellicle; and(330) cooling the freeze-drier chamber to condense sublimated water from said bacterial cellulose.

18. The method according to any of the previous claims, further comprising:(400) processing the object of bacterial cellulose foam into a final product, such as by machining, surface treatment, impregnation, painting or cutting.

19. The method according to any of the previous claims, comprising producing a packaging object, such a container or cover, or an insulation object.

20. An object of bacterial cellulose foam obtainable by the method according to any of the previous claims.21 . The object of bacterial cellulose foam according to claim 20, wherein the object has a three-dimensional bended form.

22. The object of bacterial cellulose foam according to claim 20 or 21 , having a density in the range of 10 - 50 kg / m3, preferably 20 - 30 kg / m3.

23. The object of bacterial cellulose foam according to any of the claims 20 - 22, having a Young’s Modulus below 100 MPa, preferably in the range of 10 - 50 MPa, more preferably in the range of 15 - 40 MPa.

24. The object of bacterial cellulose foam according to any of the claims 20 - 23, wherein bacterial cellulose fibres of the bacterial cellulose foam are non-homogenously arranged or have a preferred orientation.

25. The object of bacterial cellulose foam according to any of the claims 20 - 24, having a layered microscopic structure of bacterial cellulose fibres.

26. The object of bacterial cellulose foam according to claim 25, wherein the layers of bacterial cellulose fibres have a thickness in the range of 1 - 50 pm, preferably 2 - 10 pm.

27. The object of bacterial cellulose foam according to any of the claims 20 - 25, wherein the object is a packaging object, such a container or cover, or an insulation object.

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