EP4683966A1

EP4683966A1 - Biodegradable film and method for manufacturing it

Info

Publication number: EP4683966A1
Application number: EP24714978.4A
Authority: EP
Inventors: Vinay Kumar; Aayush JAISWAL; Akio Yamamoto; Mohammadhossein BEHFAR
Original assignee: VTT Technical Research Centre of Finland Ltd
Current assignee: VTT Technical Research Centre of Finland Ltd
Priority date: 2023-03-21
Filing date: 2024-03-20
Publication date: 2026-01-28
Also published as: FI20235332A1; WO2024194531A1

Abstract

A biodegradable film and a method for manufacturing as biodegradable film that includes a substrate region and an integral local region. The integral local region is formed of an immersed pattern of biodegradable material that has a different elastic modulus than the elastic modulus of the biodegradable material in the substrate region.

Description

BIODEGRADABLE FILM AND METHOD FOR MANUFACTURING IT

TECHNICAL FIELD

The application relates to flexible films made of biodegradable materials.

BACKGROUND

Printed, flexible, and hybrid electronic technologies are advancing rapidly leading to remarkable developments in, for example, smart wearables, intelligent textiles, and health monitoring systems. Flexible electronics have been conventionally fabricated on petroleum-derived polymeric substrates. However, in the light of global environmental concerns regarding fossil raw materials, there is a need to drive the production of flexible electronics devices based on more sustainable materials.

Biodegradable materials, or biobased and biodegradable materials like nanocellulose, with their renewable nature are an excellent alternative to plastics in several flexible electronics applications. The term biobased in this context refers to products that are wholly or partly derived from materials of biological origin, excluding materials embedded in geological formations and/or fossilised (cf. https://single-market- economy.ec. europa.eu/sectors/biotechnology/bio-based-products_en). The term biodegradable in this context refers to products that are capable of decomposing rapidly by microorganisms under natural conditions (aerobic and/or anaerobic) (cf. https://www.eea.eu opa.eu/help/qlossarv/eea-qlossary/biodeQradable). However, adoption of biodegradable films has been slowed down due to their poor mechanical properties, for instance due to the inherently low tear resistance of biodegradable films. It seems that with conventional technologies, it may be easier to make compromises in sustainability than risk having failures in manufacturing stages, like converting and printing processes. Possible brittleness of biodegradable films has also been considered to compromise durability and reliability of the end products.

Mechanical strength of any type of films can naturally be improved by simply making the film thicker. However, in many applications, thickness of the film cannot be increased without compromising other important product parameters, like elasticity, conformability, transparency and cost. Another conventional way to improve resilience of elastic sheets is to reinforcing wires or strings in or on the elastic sheet. Alternatively, one can adhesively attach a reinforcing patch on an elastic sheet. Again, for many implementations that are based on biodegradable materials, these conventional solutions are not applicable, because they tend to compromise the desired electrical, optical and/or mechanical properties of the end product. Strength of films can also be modified by adjusting chemical composition of the film material, and significant advantages have been made with this respect in the field of nanocellulose films. For example, article “Biodegradable Cellulose Nanocomposite Substrate for Recyclable Flexible Printed Electronics” (https://onlinelibrary.wiley.com/doi/full/10.1002/aelm.202201Q94) discloses a fully biobased and biodegradable substrate that is based on a nanocomposite of cellulose nanofibril (CNF) and hydroxyethyl cellulose (HEC) and shows excellent mechanical and optical properties for sustainable printed flexible electronics applications.

Even so, further advances would be welcome. Specifically, it would be important to provide local reinforcing or softening effects in a biodegradable film but minimally compromise electrical, optical and/or mechanical properties of the resulting biodegradable film. Optimally, such local effects should be provided in a way that integrates to existing casting and curing processes of biodegradable films so that any additional post-processing needed to locally alter mechanical properties of the film is minimised.

BRIEF DESCRIPTION

The following examples disclose an improved film structure and a method for manufacturing that film structure so as to meet at least some of the above-described requirements.

Improvements are achieved through the combination features included in the independent claims.

An independent claim defines a biodegradable film including a substrate region and an integral local region, wherein the area of the integral local region is smaller than the area of the biodegradable film. The substrate region is formed of a first biodegradable material that has a first elastic modulus and the integral local region is formed of a pattern of second biodegradable material that has a different elastic modulus than the first elastic modulus. The pattern is immersed into the first biodegradable material of the substrate region.

Another independent claim defines a method for manufacturing a biodegradable film. The method includes: forming into the biodegradable film a substrate region and an integral local region, wherein the area of the integral local region is smaller than the area of the biodegradable film; forming the substrate region of a first biodegradable material that has a first elastic modulus; and forming the integral local region of a pattern of second biodegradable material that has a different elastic modulus than the first elastic modulus of the substrate region, the pattern being immersed into the first biodegradable material of the substrate region. Some exemplary embodiments are disclosed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following some examples will be described in greater detail with reference to the accompanying drawings, in which

Figure 1 is a schematic drawing that illustrates a conventional solution for providing local mechanical reinforcement to a flexible film;

Figure 2 illustrates schematically stages of an example method applying the claimed features;

Figure 3 illustrates schematically stages of another example method applying the claimed features;

Figure 4 illustrates schematically stages of a further example method applying the claimed features; and

Figure 5 illustrates schematically stages of a further example method applying the claimed features;

Figure 6 illustrates a top view to an example of a biodegradable film resulting from any of the example methods of figures 2 to 5;

Figure 7 illustrates a top view to another example of a biodegradable film resulting from any of the example methods of figures 2 to 5.

Figure 8 illustrates a top view to a further example of a biodegradable film with two integral local regions.

DETAILED DESCRIPTION

Figure 1 is a schematic drawing that illustrates a conventional solution to provide an integral local region with different elasticity to a biodegradable flexible film. The term film in this text refers to a thin layer of film material that has been cast in fluidic form on a flat carrier substrate and cured into an elastic solid. Curing refers herein generally to processes through which an elastic solid product can be obtained from a fluidic formulation. A flexible film has a flat form wherein two larger surfaces of the film are essentially parallel and remain essentially parallel even if the film is flexed. A film may have a tape-like, continuous structure that can be rolled in and out of a reel in a roll-to-roll process, or it may be a separate sheet, or a patch processed in various different forms. The term layer indicates here that the thickness T of the film is essentially constant in the width W and length L dimensions of the film, and the term thin in this context means that the thickness of the film is less than one tenth of the smaller of the width and the length of the film. Typical thicknesses of biodegradable films vary in the range of five micrometers to ten millimeters. The term integral in this context means that the flexible film includes one or more integral local regions and one or more substrate regions and parts of the film that form the one or more local regions are partially or completely immersed into the material of the one or more substrate regions. For example, a film patch that is adhesively attached or cast on a substrate film does therefore not provide an integral local region.

Figure 1 shows a conventional combination of a flexible film 100 and an interface element 102 adhesively attached on the film 100. In conventional applications, the interface element 102 is also flexible but made to be mechanically stronger than the flexible film 100. The interface element 102 is thus provided on the film to provide local mechanical reinforcement to the structure but let the rest of the film maintain the original characteristics of the film material. Such reinforcement may be needed, for example, to provide support for a rigid component 104 installed on a stretchable film. The interface element can further be structured into a desired specific form to specifically control local tensions and forces in the surrounding, more elastic film during its use.

The problem with these conventional structures is that the reinforcing patch is a separate structural element and tends to bring about also properties that are not useful or may even be detrimental for the end product. For example, dimensions (e.g. thickness) of the overall structure reinforced in this conventional way deviate from the original one. Even if the reinforcing structure would be made very thin, it anyhow bulges to some extent out of the underlying film and forms an additional surface structure to it. It is also difficult to control the reduction to elasticity caused by the interface element and the adhesive used for attaching it. Such thickening and/or stiffening structures may be harmful for many applications, for example, for films used for ultra-thin conformal skin patches. Furthermore, the film and the adhesively attached reinforcing structure form a laminate structure which may easily unravel in use. Conventional structures also provide very little possibility for customization or for creating complex geometries with elastically differing regions.

With methods disclosed herein, a biodegradable film can be made to provide regions with different elastic moduli while minimally compromising the integral form of the film. The flexible biodegradable film can, for example, be made to include an integral local region that is stronger, meaning withstands applied mechanical stress without breaking or plastic deformation better than bulk substrate regions of the film. Alternatively, an integral local region in a flexible biodegradable film may be made to be more flexible and thus provide a softer or more conformal feeling when, for example, applied on the skin. With the proposed methods, this possibility to customize additional functional properties to a film and thus improve flexible film designs can be achieved integrally, with minimal effect to overall properties of the film.

The solution is based on forming into the biodegradable film a substrate region and an integral local region. The substrate region is formed of a first biodegradable material that has a first elastic modulus and the integral local region is formed of a pattern of second biodegradable material that has a different elastic modulus than the first elastic modulus.

Elastic modulus is a measurable material property, a physical property that describes stiffness of the material but does not depend on the amount. Elastic modulus is the ratio of stress to a corresponding strain when deformation is totally elastic. This means that the greater the elastic modulus, the stiffer the material, or the smaller the elastic strain that results from the application of a given stress. Accordingly, when the pattern is immersed into the first biodegradable material of the substrate region, the integral local region within boundaries of the pattern functions as if it were made of material with different elastic properties than the first biodegradable material of the substrate region. Accordingly, the effect of locally changed elasticity can be controlled both by choice of materials and by form of the pattern immersed into the substrate material.

The thickness of the biodegradable film may be 50 - 500 pm. The thickness of the biodegradable film may be more than 50 pm, more than 150 pm, more than 250 pm, more than 350 pm. The thickness of the biodegradable film may be less than 500 pm, less than 400 pm, less than 300 pm, less than 200 pm or less than 100 pm. The biodegradable film may be flexible in-plane with, for example, 0.5% elastic deformation limit, and out-of-plane, with capability of bending to 0 - 180 degrees angle.

Figure 2 illustrates schematically stages of an example method for producing a fully biodegradable film that includes at least one integral local region with adjusted elastic properties. The method begins by preparing (stage 200) a first biodegradable fluid, in other words a biodegradable formulation, for example a nanocellulose based formulation, in fluidic form. The first biodegradable fluid may be cured to provide the bulk of the final film product and include, for example, a nanocomposite of cellulose nanofibril (CNF) and hydroxyethyl cellulose (HEC) that is fully biobased and biodegradable and shows excellent mechanical and optical properties for flexible films. A non-exhaustive list of examples of other applicable biodegradable and even biobased materials that can be cast in fluidic form and cured into an elastic solid include cellulose fibers, dissolved cellulose, microfibrillated cellulose (MFC), nanofibrillated cellulose (NFC), cellulose nanocrystals (CNC), bacterial cellulose (BC), cellulose derivatives like (but not limited to) carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), hydroxypropylmethyl cellulose (HPMC), methyl cellulose (MC), and non-cellulosic materials like chitin, chitosan, lignin, suberin, cutin, alginate, hemicelluloses, modified and native starch, proteins, polyhydroxyalkanoates (PHAs), polybutylene succinate (PBS), polybutylene succinate-co- adipate (PBSA), polylactic acid (PLA) and its copolymers, etc. The first biodegradable fluid is cast (stage 202) on a planar support substrate so that it spreads or can be mechanically spread into a layer of essentially even thickness. In this example, while the first biodegradable fluid is still in the fluidic form, meaning not cured into elastic solid, one or more integral local regions are formed (stage 204) into the layer that is carried by the support structure. The materials applied in this example process are selected so that after curing (stage 206) of the combination of materials, the integral local regions form parts where the resulting film has different elasticity than in other parts of the film. The curing stage refers here to a process in which the combination of fluids transforms into an elastic solid. For example, the fluids can be transformed into combined elastic solid via removal of a solvent phase, for example, through drying under ambient conditions, or by using heating or vacuum.

The term “biodegradable” in this application may refer to material that may be broken down into simpler compounds by the action of microorganisms such as bacteria, fungi, or other living organisms. Biodegradable materials may be broken down into natural substances like water, carbon dioxide, and biomass or mineral salts through biological processes in the presence of oxygen. Alternatively, at least the first material may be biocompatible.

The term “biobased” in this application may refer to material which is wholly or partly of biogenic origin. Specifically, it may refer to materials that consist of a substance (or substances) derived from living matter (biomass) and either occur naturally or are synthesized, or it may refer to products made by processes that use biomass.

In the example of Figure 2, the integral local regions are formed (stage 204) by depositing in or on the layer of first biodegradable fluid a pattern of a second biodegradable fluid. The material composition of the second biodegradable fluid can be selected so that its viscosity is higher than viscosity of the first biodegradable fluid. This means that the volume of the essentially second biodegradable fluid maintains the form in which it has been deposited on the layer of first biodegradable fluid but becomes at least partially immersed into the layer of first biodegradable fluid so that the combination of the first biodegradable fluid and the second biodegradable fluid assumes the essentially level form of the film. To achieve such performance, the viscosity of the first and the second fluids may be more than 1000 mPa.s at zero shear. A shear thinning and a thixotropic nature may or may not be present in either the first or the second liquid. However, it is preferred in the second fluid where it can be easily dispensed by applying shear and when the shear forces are removed, the fluid can be immobilized in the dispensed position. The volume of the second biodegradable fluid may immerse to align with the top surface of the resulting layer with the first biodegradable fluid, it may be fully enveloped into the layer so that both surfaces of the resulting layer include the first biodegradable fluid only, or it may sink into the first biodegradable fluid to align with the bottom surface of the resulting layer with the first biodegradable fluid. As shown in Figure 2, the first biodegradable fluid and the deposited second biodegradable fluid can be cured in a common curing stage.

The second biodegradable fluid can be deposited to form a plate-like formation that immerses into the layer of first biodegradable fluid and becomes integral part of the film. On the other hand, the second biodegradable fluid can be deposited with a nozzle that extrudes material to a limited area on the receiving film. During deposition, the nozzle and the receiving layer of first biodegradable fluid can be made to move in relation to each other so that the extruded second biodegradable fluid forms a pattern. The pattern may include various types of lines and/or dots. The easiest way to provide the relative motion is to move the nozzle above the layer of first biodegradable fluid. Different nozzle forms, pressures and all three dimensions can be used to form a desired pattern into the biodegradable film.

Figure 3 illustrates another exemplary method for forming a biodegradable film with integral local regions. The method includes stages 300 to 306 that correspond with stages 200 to 206 of Figure 2, but now stage 204 is replaced by two sub-stages 304a and 304b. The method begins again by preparing (stage 300) a first biodegradable fluid, a biodegradable formulation in fluidic form. The first biodegradable fluid is cast (stage 302) on a planar support substrate so that it spreads or can be mechanically spread into a layer of essentially even thickness. While the first biodegradable material is still in the fluidic form, meaning not cured into elastic solid, integral local regions are formed (stages 304a, 304b) into the layer carried by the support structure.

In the example of Figure 3, the integral local regions are formed by depositing (stage 304a) onto the layer of first biodegradable fluid a pattern of second biodegradable fluid that in this case is a mixture of a biodegradable precursor and a photocurable agent. Photocurable agent in this context refers to substances that mix with the precursor and cause the mixture to respond to interaction with electromagnetic radiation in the visible and near-visible range (typically light in the ultraviolet range) by curing. A non-exhaustive list of examples of applicable photocurable agents include modified lignin, acrylates, methacrylates, epoxies, urethanes, vanillin, rosin, and terpenes. The material composition of the second biodegradable fluid may be selected so that its viscosity is higher than viscosity of the first biodegradable fluid. Due to this, the volume of the second biodegradable fluid maintains the form in which it has been deposited on the layer of first biodegradable fluid but becomes at least partially immersed into the layer of first biodegradable fluid so that the combination of the first biodegradable fluid and the second biodegradable fluid assumes the essentially level form of the film.

The integral local regions are cured (stage 304b) into the layer in a first curing stage by exposing parts of the layer of first biodegradable fluid to a light source. In this example, the light source does not need to move, it can be configured to emit a local beam of light with a specific intensity and wavelength and direct it towards the surface of the layer of first biodegradable fluid. The pattern of the second biodegradable fluid becomes illuminated and thus cured to form a pattern that is immersed into the layer of first biodegradable fluid. The layer that includes the photocured pattern of second biodegradable material and the uncured bulk of first biodegradable fluid is then cured (stage 306) in a second curing stage so that also the remaining parts of the film materials become cured. A fully biodegradable film that includes an immersed pattern that forms the integral local region but resembles mostly to a film of first biodegradable material is thus created. This is achieved with minor additions to the conventional film casting process.

Figure 4 illustrates schematically stages of a further example for forming a biodegradable film with integral local regions. The method includes stages 400 to 406 that correspond again with stages 200 to 206 of Figure 2. However, in the example of Figure 4, in the beginning of the method, the first biodegradable fluid is prepared (stage 400) by mixing into biodegradable precursor, for example a nanocellulose precursor, a portion of at least one photocurable agent. As explained earlier, photocurable agent in this context refers to substances that mix with the precursor and cause the mixture to respond to interaction with electromagnetic radiation in the visible and near-visible range (typically light in the ultraviolet range) by curing. The non-exhaustive list of examples of applicable photocurable agents include modified lignin, vanillin, rosin, and terpenes. In the example of Figure 4, the layer cast on the support substrate undergoes two curing stages. A first curing is a selective pre-curing stage implemented through exposure to a movable beam of light, intensity of which is in a predefined range and wavelength of which is in a predefined range to which the photocurable agent is responsive. Each of these parameters is adjustable for a specific mixture of a precursor(s) and photocurable agent(s). The second curing is a common curing stage applied for the whole layer carried on the support substrate. Applied materials and process parameters are adjusted so that parts of the resulting film that have been exposed to the first and second curing stages have a different elastic modulus than parts of the resulting film that have been exposed only to the second curing stage. For example, materials and process parameters can be adjusted so that the achieved mechanical strength (in other words ability to withstand applied forces without breakage or plastic deformation) of regions cured with the first and second curing processes is better than the strength of the regions that become cured only in the second curing process.

Also in this embodiment, the first biodegradable fluid is cast (stage 402) into a layer of essentially even thickness. While the first biodegradable material is still in the fluidic form, meaning not cured into elastic solid, the integral local regions are formed (stage 404) into the layer by exposing parts of the layer of first biodegradable fluid to a moving light source. The light source is configured to emit a beam of light with a specific intensity and wavelength and direct it towards the surface of the layer of first biodegradable fluid. The illuminated parts on and underneath the surface become cured and form a pattern of precured material into the layer. The light beam may be controlled in many ways. As the pattern is formed by moving the light source above the layer of first biodegradable fluid, a great variety of patterns can be implemented simply by re-programming motion of the light source. After the first curing in stage 404 has been completed, the whole layer of first biodegradable fluid can be cured (stage 406) in the second curing stage so that all parts of the film become cured. However, the parts of the pattern, pre-cured with light, have an elastic modulus that is different from the elastic modulus in the bulk substrate regions and thus form into the resulting film an integral local region.

Figure 5 illustrates schematically stages of a further example for the method disclosed herein. The method corresponds with the one described with Figure 4, but here the order of the curing processes is changed. Also in this process, the first biodegradable fluid is prepared (stage 500) by mixing into a biodegradable precursor, for example a nanocellulose precursor, a portion of at least one photocurable agent. The first biodegradable fluid is cast (stage 502) into a layer of essentially even thickness. In a first curing stage, the whole layer of first biodegradable fluid is cured (stage 504) so that all parts of the film become cured to an elastic solid film. After this, the integral local regions are formed (stage 506) into the layer by exposing parts of the elastic solid film to a moving light source. The light source is configured to emit a beam of light with a specific intensity and wavelength and direct it towards the surface of the elastic solid film. The illuminated parts become cured for a second time and form an integral pattern that is fully immersed into the elastic solid film. The pattern, cured in two curing stages, form into the elastic solid film an integral local region with an elastic modulus that is different from the bulk substrate regions that were cured only in the first curing stage.

Figure 6 illustrates a top view to an example of a biodegradable film resulting from any of the example methods of Figures 2 to 5. The film includes a substrate region 600 and an integral local region 602. The substrate region 600 and the integral local region 602 have been cured into elastic solids. This means that in the film form where the thickness of the film is less than one tenth of the smaller of the width and the length of the film, the substrate region and the integral local region will deform in response to applied forces, but after removal return to their initial shape and size. Both the substrate region 600 and the integral local region 602 are formed of biodegradable materials, but the integral local region 602 provides different elastic properties than the substrate region 600.

The substrate region 600 is formed of a first biodegradable material that has a first elastic modulus. As may be seen from Figure 6, the integral local region 602 is formed of a pattern of biodegradable material that is immersed into the first biodegradable material of the substrate region. Local region in this context means that the area of the integral local region is smaller than the area of the biodegradable film. Conventionally, local reinforcement has been provided by additional layer elements attached on a cured film substrate, or by incast visible wires in the substrate. The present invention enables providing biodegradable films local reinforcement through biodegradable patterns that can be formed to adjust elasticity in part of the film, but as much as possible maintain overall mechanical properties of the substrate in the film. As shown with Figures 2 to 5, stages needed to provide this improved structure can be easily streamlined to conventional manufacturing processes, including roll-to-roll processes.

In biodegradable films resulting from the example method of Figure 2, the second biodegradable material has a different chemical composition than the first biodegradable material. The materials are selected so that at the time of deposition, meaning before the curing stage, viscosity of the second biodegradable fluid is higher than viscosity of the first biodegradable fluid. Due to this the pattern of second biodegradable fluid that is deposited on the first biodegradable fluid maintains its form but immerses into the first biodegradable fluid. The result is the cast-in element 602 cured into the biodegradable substrate material 600. In biodegradable films resulting from the example method of Figure 3, the second biodegradable material has a different chemical composition than the first biodegradable material. Also in this case, the materials are selected so that the curing stage, viscosity of the second biodegradable fluid is higher than viscosity of the first biodegradable fluid. However, the photocurable agent is now mixed into the second biodegradable fluid. At the manufacturing stage the whole film can be exposed to the light source, but only the immersed pattern is responsive to it. The immersed photocured pattern changes locally the elastic modulus so that an integral local region 602 into the substrate 600 is formed into the biodegradable film.

In biodegradable films resulting from the example method of Figure 4, the second biodegradable material and the first biodegradable material have the same chemical composition, which results from a mix of a biodegradable precursor and a photocurable agent. The pattern is in this case formed by exposing the layer of first biodegradable fluid to a light source that cures exposed parts of the first biodegradable fluid to form the immersed pattern. The photocuring can be made more intensive than the later curing on the whole film, or to further intensify with the later curing so that a pattern that forms a local integral local region 602 is formed into the second biodegradable flexible film.

Biodegradable films resulting from the example method of Figure 5 are similar to the ones from the example method of Figure 4. The second biodegradable material and the first biodegradable material have the same chemical composition, which results from a mix of a biodegradable precursor and a photocurable agent. The pattern is formed by first curing the mix into an elastic solid and then exposing the elastic solid to a light source that cures exposed parts of the first biodegradable fluid to form the immersed pattern. The photocuring can be made more intensive than the common curing on the whole film, or to further intensify with the earlier common curing so that a pattern that forms a local integral local region 602 is formed into the second biodegradable flexible film.

When such deposited pattern includes a closed shape that forms a perimeter around the pattern, and this pattern becomes cast-in to the film, the integral local region 602 can be considered to include only the pattern, or the integral local region 602 can be considered to be formed of the combination of the immersed pattern and parts 600a of the film enclosed by the pattern.

It is known that tears typically initiate from edges of a film. However, by means of a simple immersed pattern that includes a closed shape, the tear-resistance of the resulting film can be considerably increased, with minimal adverse overall effects from use of reinforcing material in the film. With the proposed solution, a pattern including a closed peripheral shape can be immersed integrally into the film at edges or close to the edges of the film to increase tear resistance of almost the whole of the resulting film. On the other hand, as shown in Figure 6, an integral local region 602 may be formed to enclose only a limited inner part 600a in the resulting film. The closed shape in the pattern can be used to protect this inner region 600a from tears that could progress from edges of the film towards the inner region. The inner region 600a can be made to carry, for example, electric wiring that cannot be stretched as much as the bulk part of the film or needs to be protected from stresses progressing from edges of the film.

On the other hand, in some applications, there is no need for reinforcement or closed shapes in the pattern. Elastic modulus of the second biodegradable material of the immersed pattern may be smaller than the elastic modulus of first biodegradable material of the substrate region to provide added flexibility in the integral local region. Furthermore, the pattern may include a matrix of dots, weave patterns, wave patterns, and/or curves, etc. Figure 7 illustrates a top view to an example of a biodegradable film resulting from any of the example methods of Figures 2 to 5. The film includes a substrate region 700 and an integral local region 702. In this example, the pattern that forms the integral local region 702 includes separate pattern elements 704 so that the integral local region can be identified as a region within a boundary drawn around the pattern elements. In this example the pattern elements are dots, but other forms may be applied. Elastic modulus of the second biodegradable material of the immersed pattern is in this example smaller than elastic modulus of the first biodegradable material of the substrate region so that the integral local region is more flexible than regions around it.

The above Figures 6 and 7 are only descriptive and illustrate some basic structural ways to implement the claimed features. A person skilled in the art can easily generate many other variations based on the methods and structural features described herein. Figure 8 illustrates an example showing how to combine methods of Figure 2 and Figure 5 and structural features of Figures 6 and 7 to manufacture a biodegradable film including two integral local regions. An inner integral local region 702 would be formed of pattern elements 704 with smaller elastic modulus material to provide locally more elasticity to the film, and an outer integral local region 602 would be formed of a closed shape pattern 602 to protect the more elastic part from tears and stresses progressing from the edge of the film. For this structure the method of Figure 2 only needs to be complemented with the stage wherein the first biodegradable fluid is prepared (stage 500) by mixing into a biodegradable precursor a portion at least one photocurable agent, and the stage wherein the integral local regions are formed (stage 506) into the layer by exposing parts of the elastic solid film to a moving light source.

The common advantageous aspect for all these examples is that both the substrate region and the integral local region are formed of biodegradable elastic solids. By varying the form and extent of the immersed pattern, mechanical strength of these biodegradable elastic films can be locally increased in a way suitable for many particular purposes of the elastic biodegradable film. It is thus possible increase resilience or flexibility to selected positions where it is needed but compromises that have to be made to the overall properties of the film for the locally adjusted mechanical properties are minimised.

Claims

1. A biodegradable film including a substrate region and an integral local region, wherein the area of the integral local region is smaller than the area of the biodegradable film; the substrate region is formed of a first biodegradable material that has a first elastic modulus; the integral local region is formed of a pattern of second biodegradable material that has a different elastic modulus than the first elastic modulus, the pattern being immersed into the first biodegradable material of the substrate region.

2. The biodegradable film of claim 1 wherein the second biodegradable material has a different chemical composition than the first biodegradable material and the second biodegradable material is immersed as a cast-in pattern in the first biodegradable material of the substrate region.

3. The biodegradable film of claim 2 wherein the second biodegradable material includes also a photocurable agent.

4. The biodegradable film of claim 1 wherein the second biodegradable material and the first biodegradable material have the same chemical composition; the chemical composition includes a photocurable agent.

5. The biodegradable film of claim 3 or 4 wherein the photocurable agent is a substance that changes elastic modulus of a precursor to which it is mixed in response to exposure to light, intensity of which is in a predefined range and wavelength of which is in a predefined range.

6. The biodegradable film of any of claims 1 to 5 wherein the pattern includes a closed shape.

7. The biodegradable film of any of claims 1 to 5 wherein the pattern includes separate pattern elements and the integral local region is formed within a boundary around the pattern elements.

8. A method for manufacturing a biodegradable film, including: forming into the biodegradable film a substrate region and an integral local region, wherein the area of the integral local region is smaller than the area of the biodegradable film; forming the substrate region of a first biodegradable material that has a first elastic modulus; forming the integral local region of a pattern of second biodegradable material that has a different elastic modulus than the first elastic modulus of the substrate region, the pattern being immersed into the first biodegradable material of the substrate region.

9. The method of claim 8, including: casting a layer of first biodegradable fluid on a support substrate; before curing of the layer of first biodegradable fluid, depositing in or on the layer of first biodegradable fluid a pattern of a second biodegradable fluid that has a different chemical composition than the first biodegradable fluid; curing the first biodegradable fluid and the second biodegradable fluid so that the substrate region and the integral local region are formed.

10. The method of claim 8 or 9, including curing the first biodegradable fluid and the deposited second biodegradable fluid in a common curing stage.

11 . The method of claim 10, including mixing into the second biodegradable fluid a photocurable agent and exposing the second biodegradable fluid and the first biodegradable fluid before the common curing stage the to a light source that cures the second biodegradable fluid but does not cure the first biodegradable fluid.

12. The method of claim 10, including mixing into the second biodegradable fluid a photocurable agent and exposing the second biodegradable fluid and the first biodegradable fluid after the common curing stage the to a light source that cures the second biodegradable fluid but does not cure the first biodegradable fluid.

13. The method of claim 8, including mixing into a first biodegradable fluid a photocurable agent; casting a layer of a mix of the first biodegradable fluid and the photocurable agent on a support substrate; exposing the mix of the first biodegradable fluid and the photocurable agent to a movable light source that pre-cures exposed parts of the first biodegradable fluid to form the pattern immersed into the mix of the first biodegradable fluid and the photocurable agent; curing the mix of the first biodegradable fluid and the photocurable agent with the immersed pattern in a common curing stage.

14. The method of claim 8, wherein the common curing stage cures further the immersed pattern.

15. The method of claim 8, including mixing into a first biodegradable fluid a photocurable agent; casting a layer of a mix of the first biodegradable fluid and the photocurable agent on a support substrate; curing the mix of the first biodegradable fluid and the photocurable agent; exposing the layer of the mix of the first biodegradable fluid and the photocurable agent to a movable light source configured to further cure exposed parts of the first biodegradable fluid to form the pattern immersed into the first biodegradable material.

16. The method of any of claims 8 to 16, including forming the immersed pattern to include a closed shape that forms a boundary of the pattern.