Biopolymeric optical fiber for humidity sensing

Abstract

A method for quantitatively measuring humidity is provided, the method comprising providing a sensing apparatus (600) comprising a biopolymeric optical fiber (650) as a sensing element, measuring transmittance of the biopolymeric optical fiber (650) at selected wavelength(s) at standard conditions to obtain reference data, measuring transmittance of the biopolymeric optical fiber at the selected wavelength(s) at target conditions to obtain target measurement data, and obtaining quantitative humidity value by comparing the target measurement data to the reference data. An apparatus, a biopolymeric optical fiber, and a method for manufacturing the fiber are also provided.

Description

[0001] BIOPOLYMERIC OPTICAL FIBER FOR HUMIDITY SENSING

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to optical fibers. The disclosure relates particularly, though not exclusively, to biopolymeric optical fibers for sensing applications.

[0004] BACKGROUND

[0005] This section illustrates useful background information without admission of any technique described herein representative of the state of the art.

[0006] Generally, optical fibers act as waveguides and effectively transmit light. This property is readily usable both in signaling and data transmission and for illumination purposes.

[0007] Today, state-of-the-art glass optical fibers (GOFs) can transmit signals across hundreds of kilometers with extremely low optical losses in the range of approximately 0.14-0.2 dB / km. Hence, GOFs are ideal for long-range communication enabling high-bandwidth data transmission. However, for short-range or local applications, for instance, in indoor networks, medical devices or automobiles, plastic optical fibers (POFs) are typically preferred over GOFs. In certain short-range applications, the brittleness of GOFs may also become an issue.

[0008] Plastic optical fibers (POFs) are routinely prepared from synthetic polymers, such as poly(methyl methacrylate) (PMMA) or polystyrene. POFs typically have good fatigue tolerance and higher transmission losses than GOFs. POFs are also relatively cost-effective and suitable for illumination purposes.

[0009] However, manufacturing of GOFs and POFs requires specialized infrastructure and is energy intensive due to the required high temperatures (2000 °C for GOFs and 200-300 °C for POFs), and POFs are typically manufactured from non-renewable fossil-based raw materials. Toxic chemicals may also be required in fiber fabrication. Further, to achieve sensing in either GOFs or POFs traditionally requires extensive post-fabrication modifications. The present disclosure aims to address at least some of these issues. SUMMARY

[0010] It is an object of certain embodiments of the present disclosure to provide optical fibers (for short-range applications) that are manufactured from renewable sources and enable environmental sensing or at least to provide an alternative to existing technology.

[0011] The appended claims define the scope of protection. Any examples and technical descriptions of apparatuses, products and / or methods in the description and / or drawings not covered by the claims are presented not as embodiments of the invention but as background art or examples useful for understanding the invention.

[0012] According to a first example aspect there is provided an apparatus for quantitative measuring of humidity, comprising a biopolymeric optical fiber, BOF, as a sensing element. Advantageously, humidity may be directly, rapidly, and accurately quantified.

[0013] In certain embodiments, the biopolymeric optical fiber is a single component biopolymeric optical fiber, wherein the single component is a polysaccharide.

[0014] In certain embodiments, the biopolymeric optical fiber is a composite biopolymeric optical fiber comprising at least two (different) polysaccharides. In certain embodiments, the biopolymeric optical fiber comprises two polysaccharides (first polysaccharide and second polysaccharide). In certain embodiments, the biopolymeric optical fiber comprises three polysaccharides (first polysaccharide, second polysaccharide, and third polysaccharide). In certain embodiments, the polysaccharides differ from each other by at least polysaccharide type. In certain embodiments, the polysaccharides differ from each other by at least their degree of substitution. In certain embodiments, the polysaccharides differ from each other by at least molecular weight. Advantageously, the mechanical and optical properties of the biopolymeric optical fiber may be adjusted by adjusting the fiber composition.

[0015] In certain embodiments, the biopolymeric optical fibers is a single component biopolymeric optical fiber, wherein the single component is a polysaccharide, or a composite biopolymeric optical fiber comprising at least two polysaccharides.

[0016] In certain embodiments, the biopolymeric optical fiber is (fully) made of polysaccharide(s). In certain embodiments, the polysaccharide(s) account for (substantially) 100% (by weight) of the total dry mass of a biopolymeric optical fiber. Advantageously, only minor residues from coagulation solutions or ions from ionic cross-linking may be present in the fiber besides the polysaccharide(s). Further, other components may not be needed besides the polysaccharide(s) and suitable solvents, and possible ions for ionic cross-linking in certain embodiments. Thus, the manufacturing process may be kept simple.

[0017] In certain embodiments, the biopolymeric optical fiber is replaceable. In certain embodiments, the biopolymeric optical fiber is biodegradable. Advantageously, the sensing element of a sensing apparatus may be feasibly replaced without discarding the entire apparatus. Further, the amount of waste may be reduced.

[0018] In certain embodiments, the apparatus comprises a casing. In certain embodiments, the apparatus is portable. In certain embodiments, the apparatus comprises a replaceable power source. In certain embodiments, the apparatus comprises a rechargeable power source. In certain embodiments, the apparatus comprises a replaceable power source. In certain embodiments, the apparatus is remotely operable by a mobile phone. Advantageously, the apparatus may be feasibly operated in and transported to various locations.

[0019] In certain embodiments, the apparatus is configured to measure transmittance of light through the biopolymeric optical fiber to determine humidity.

[0020] In certain embodiments, the apparatus is configured to measure transmittance of the biopolymeric optical fiber at selected wavelength(s) at target conditions to obtain target measurement data, the apparatus comprising: a control unit configured to control the apparatus to obtain quantitative humidity value(s) by comparing the target measurement data to reference data obtained by measuring transmittance of the biopolymeric optical fiber at the selected wavelength(s) at standard conditions.

[0021] In certain embodiments, the apparatus comprises a source element to provide the sensing element with light. In certain embodiments, the control unit is connected to or connectable with the source element.

[0022] In certain embodiments, the apparatus comprises an output element to measure said transmittance(s). In certain embodiments, the control unit is connected to or connectable with the output element.

[0023] In certain embodiments, the apparatus comprises a plurality of sensing apparatuses configured to be used in combination to provide data simultaneously from multiple measurement points. In certain embodiments, the apparatus comprises a control unit configured to control the plurality of sensing apparatuses. In certain embodiments, the control unit configured to control the plurality of sensing apparatuses is a separate external control unit. Advantageously, data may be gathered at several target positions within a larger measurement area, thus allowing area mapping and more accurate and reliable results.

[0024] According to a second example aspect, there is provided a method for measuring humidity, the method comprising providing a sensing apparatus comprising a biopolymeric optical fiber as a sensing element, measuring transmittance of the biopolymeric optical fiber at selected wavelength(s) at standard conditions to obtain reference data, measuring transmittance of the biopolymeric optical fiber at the selected wavelength(s) at target conditions to obtain target measurement data, and obtaining quantitative humidity value by comparing the target measurement data to the reference data. In certain embodiments, the selected wavelength comprises (only) a single wavelength. In certain embodiments, the selected wavelengths comprise a plurality of wavelengths. In certain embodiments, the selected wavelengths comprise a range of wavelengths.

[0025] In certain embodiments, providing the sensing apparatus comprising a biopolymeric optical fiber, BOF, as a sensing element further comprises selecting the biopolymeric optical fiber according to the humidity sensitivity properties of the biopolymeric optical fiber. Advantageously, the most suitable biopolymeric optical fiber for certain humidity conditions or for a certain measurement wavelength may be used and, thus, measurement accuracy improved.

[0026] In certain embodiments, the measuring transmittance of the biopolymeric optical fiber at selected wavelength(s) at standard conditions to obtain reference data is performed at predetermined intervals. The interval may be, for instance, 1 , 2, 3, or 4 weeks. In certain embodiments, the reference data is obtained each time the biopolymeric optical fiber is replaced. In certain embodiments, the reference data is measured centrally and then shared to the apparatus(es). Advantageously, the reference data may not be required to be obtained separately for each humidity measurement.

[0027] According to a third example aspect there is provided a biopolymeric optical fiber for sensing applications wherein the biopolymeric optical fiber is a composite fiber comprising at least two polysaccharides. In certain embodiments, the biopolymeric optical fiber comprises two polysaccharides (first polysaccharide and second polysaccharide). In certain embodiments, the biopolymeric optical fiber comprises three polysaccharides (first polysaccharide, second polysaccharide, and third polysaccharide). In certain embodiments, the polysaccharides differ from each other by at least polysaccharide type, degree of substitution or molecular weight. In certain embodiments, the polysaccharide(s) account for substantially 100% (by weight) of the total dry mass of a biopolymeric optical fiber. In certain embodiments, the polysaccharides are selected from a group comprising alginate, chitosan, agarose, and water-soluble cellulose derivatives. In certain embodiments, the water-soluble cellulose derivatives include methylcellulose, carboxymethylcellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, and hydroxyethyl cellulose.

[0028] In certain embodiments, the alginate content of the biopolymeric optical fiber is at most 25% (by weight) based on the total dry mass of the biopolymeric optical fiber. In certain embodiments, the alginate content of the biopolymeric optical fiber is at most 50 % (by weight) based on the total dry mass of the BOF. In certain embodiments, the alginate content of the biopolymeric optical fiber is at most 60%, 70%, 80%, or 90% (by weight) based on the total dry mass of the BOF. In certain embodiments, the alginate content of a composite biopolymeric optical fiber is at least 1 .0 % (by weight) of the total dry mass of the biopolymeric optical fiber.

[0029] In certain embodiments, the biopolymeric optical fiber, BOF, is a composite of a first polysaccharide and a second polysaccharide, the biopolymeric optical fiber comprises 5- 95% (by weight) of the first polysaccharide, and 5-95% (by weight) of the second polysaccharide of the total dry mass of the biopolymeric optical fiber. In certain embodiments, the biopolymeric optical fiber is a composite of a first polysaccharide and a second polysaccharide, the biopolymeric optical fiber comprises 25-75% (by weight) of the first polysaccharide, and 25-75% (by weight) of the second polysaccharide of the total dry mass of the biopolymeric optical fiber. In certain embodiments, the BOF is a composite of a first polysaccharide, a second polysaccharide and a third polysaccharide, comprising 10- 50% (by weight) of the first polysaccharide, 10-50% (by weight) of the second polysaccharide, and 10-50% (by weight) of the third polysaccharide of the total dry mass of the biopolymeric optical fiber.

[0030] In certain embodiments, the composite biopolymeric optical fiber is manufactured from an aqueous spinning dope. In certain embodiments, preparing the spinning dope comprises dissolving the biopolymer raw material in water. In certain embodiments, the total polysaccharide content of the spinning dope is 0.5-30.0% (w / v), preferably 1.0-20.0% (w / v). In certain embodiments, the composite biopolymeric optical fiber is manufactured by wetspinning or dry-jet spinning. In certain embodiments, the biopolymeric optical fiber comprises a coating or a cladding.

[0031] According to a fourth example aspect there is provided a method for manufacturing a biopolymeric optical fiber, the method comprising selecting a polysaccharide raw material based on optical properties of a BOF manufactured from said raw material, preparing a spinning dope from the selected raw material, continuously extruding the spinning dope to a coagulation bath to prepare a fiber, collecting the extruded fiber from the coagulation bath, and drying the fiber.

[0032] In certain embodiments, selecting the polysaccharide raw material comprises selecting at least one of first polysaccharide, second polysaccharide, and third polysaccharide. In certain embodiments, the first polysaccharide, second polysaccharide, and third polysaccharide differ from each other by at least polymer type. In certain embodiments, the first polysaccharide, second polysaccharide, and third polysaccharide differ from each other by at least degree of substitution. In certain embodiments, the first polysaccharide, second polysaccharide, and third polysaccharide differ from each other by at least molecular weight. In certain embodiments, the first polysaccharide, second polysaccharide, and third polysaccharide differ from each other by polysaccharide type, degree of substitution, or molecular weight. In certain embodiments, the first polysaccharide, second polysaccharide, and third polysaccharide are selected from a group comprising alginate, chitosan, agarose, and water-soluble cellulose derivatives. In certain embodiments, selecting the polysaccharide raw material comprises selecting the polysaccharide raw material to obtain a BOF with a predetermined humidity sensitivity properties.

[0033] In certain embodiments, the extrusion step comprises wet spinning or dry-jet spinning. In certain embodiments, the extruded spinning dope is coagulated simultaneously by extrusion in ethanol and ionic cross-linking. In certain embodiments, the method comprises rinsing the fiber after coagulation. In certain embodiments, the method further comprises cutting the fiber to a predetermined length. In certain embodiments, the method further comprises coating the fiber.

[0034] According to another example aspect, there is provided a sensing apparatus, comprising a biopolymeric optical fiber as a sensing element. Different non-binding example aspects and embodiments have been illustrated in the foregoing. The embodiments in the foregoing are used merely to explain selected aspects or steps that may be utilized in different implementations. Some embodiments may be presented only with reference to certain example aspects. It should be appreciated that corresponding embodiments apply to other example aspects as well.

[0035] BRIEF DESCRIPTION OF THE FIGURES

[0036] Some example embodiments will be described with reference to the accompanying figures, in which:

[0037] Fig. 1 a and 1 b show a structural formula of alginate polymer chain and schematically the coordination of alginate polymer chains with metal ions, respectively;

[0038] Fig. 2 shows general structural formula of cellulose derivatives;

[0039] Fig. 3 schematically shows a fiber spinning apparatus for manufacturing biopolymeric optical fibers according to certain embodiments;

[0040] Fig. 4 shows polarized light microscopy and scanning electron microscopy micrographs of biopolymeric fibers of certain embodiments;

[0041] Fig. 5 shows a photograph of an experimental setup for measuring optical properties of biopolymeric optical fibers;

[0042] Fig. 6 schematically shows a system for measuring optical properties of biopolymeric optical fibers according to certain embodiments;

[0043] Fig. 7 shows normalized transmission spectra of biopolymeric optical fibers of certain embodiments;

[0044] Fig. 8 shows an attenuation spectrum and correlation coefficient of a composite biopolymer optical fiber of certain embodiments;

[0045] Fig. 9a-d show attenuation measurement data of composite biopolymer optical fibers of certain embodiments;

[0046] Fig. 10a-d show attenuation measurement data of carboxymethylcellulose fibers of certain embodiments:

[0047] Fig. 11 a-c show tensile test data of biopolymeric optical fibers of certain embodiments;

[0048] Fig. 12a-d show thermal analysis of biopolymeric optical fibers of certain embodiments; Fig. 13a-c show humidity sensitivity of single component and composite biopolymer optical fibers according to certain embodiments;

[0049] Fig. 14 show humidity sensitivity per wavelength of biopolymeric optical fiber according to certain embodiments;

[0050] Fig. 15 schematically shows a sensing apparatus according to certain embodiments;

[0051] Fig. 16 schematically shows another sensing apparatus according to certain embodiments;

[0052] Fig. 17a-b show experimental breathing and touch sensor data, respectively, according to certain embodiments;

[0053] Fig. 18 shows a flow chart of a method for manufacturing biopolymeric optical fibers according to certain embodiments; and

[0054] Fig. 19 shows a flow chart of method of measuring humidity according to certain embodiments.

[0055] DETAILED DESCRIPTION

[0056] In the following description, like reference signs denote like elements or steps.

[0057] The use of optical fibers, both glass optical fibers (GOFs) and plastic optical fibers (POFs), is widespread due to their several benefits, such as immunity to electromagnetic interference, light weight, large bandwidth, and low optical losses. However, more environmentally friendly alternatives to GOFs and POFs are desired. Further, inertness and impermeability of GOFs and POFs may be challenging for adapting the fibers as such for sensing applications. Advantageously, biopolymer-based fibers may provide the desired properties in short range applications.

[0058] BIOPOLYMERS

[0059] The biopolymers used to manufacture biopolymeric optical fibers (BOFs) of the present disclosure comprise polysaccharide(s). In certain embodiments, the BOF is a single component fiber comprising only one type of polysaccharide. In certain embodiments, the BOF is a composite fiber comprising at least two polysaccharides. In certain embodiments, the BOF comprises three polysaccharides. Preferably, polysaccharides account for substantially 100% of the total dry mass of a BOF. In certain embodiments, the polysaccharides are coagulated or ionically cross-linked to form the BOF. Preferably, polysaccharides are configured to form the BOF by non-covalent interactions. The polysaccharides are present in a spinning dope, of which the BOF is prepared, in a fully dissolved state, that is, as substantially individual polysaccharide chains. A BOF prepared from the polysaccharide spinning dope has a homogeneous structure. That is, the polysaccharide content and density is substantially the same throughout the BOF. In other words, the polysaccharides are not present in the spinning dope or the resulting BOF as crystals or crystal-like particles or solid aggregates.

[0060] For the sake of clarity, it is noted that herein BOF refers to an unclad optical fiber unless stated otherwise. That is, the BOF is analogous with, for example, the glass core of commercial GOFs. However, the BOF may further comprise a coating or a cladding as described with respect to certain embodiments.

[0061] In certain embodiments, a BOF comprises (only) one type of polysaccharide (i.e., a first polysaccharide). In certain embodiments, a BOF is a composite of a first polysaccharide and a second polysaccharide. In certain embodiments, the composite BOF further comprises a third polysaccharide. In certain embodiments, the dry mass of a BOF essentially equals the total polysaccharide mass of the BOF. In certain embodiments, the (ratios and types of) first, second, and third polysaccharides are selected based on optical properties of a BOF manufactured from said polysaccharides. In certain embodiments, the first, second, and third polysaccharides are selected such that the mixture is configured to provide BOFs with predetermined optical and mechanical properties. Advantageously, BOFs optimal for certain humidity and measurement conditions and / or measurement wavelengths may be manufactured.

[0062] In certain embodiments, the polysaccharides are selected such that transmission at a predetermined wavelength range is achieved. In certain embodiments, the wavelength range is 150 - 550 nm, above 550 - 650 nm, above 650 - 900 nm, or above 900 nm. For instance, when operating with light below 500 nm wavelengths, more MC is preferably included to a BOF to increase transmission in the visible wavelength range. In certain embodiments, the polysaccharides are selected such that the resulting fiber is optimized for measuring humidity at a pre-determined wavelength range. In certain embodiments, the wavelength range is below 600 nm, 600 nm - 950 nm, or above 950 nm. In certain embodiments, the polysaccharides are selected such that the resulting BOF is optimized for measuring humidity at certain humidity conditions. In certain embodiments, the humidity condition is relative humidity range from 5% RH to 95% RH, preferably from 10 % RH to 90% RH. In certain embodiments the humidity condition is relative humidity below 50% RH. In certain embodiments the humidity condition is relative humidity above 50% RH. In certain embodiments, polysaccharides are selected to achieve BOF with predetermined elastic modulus, maximum strain, maximum stress, and / or modulus of toughness.

[0063] In certain embodiments, a BOF comprises alginate. Alginates are water-soluble edible natural polymers which can be isolated from either bacteria or brown algae. When dissolved in water, alginate typically forms white-yellowish solution. Due to the typical color and slightly hazy appearance in solution and gels alginate may not be an obvious choice for optical fiber preparation. However, surprising optical benefits have been observed. Alginate is a linear copolymer which consists of a-L-guluronic (G-block) and p-D-mannuronic (M- block) acid residues covalently linked together into different sequences or blocks. The ratio of mannuronic acid to glucuronic acid in alginate may be in the range from 0.43 to 2.52. The ratio may depend on the alginate source. In certain embodiments, the alginate has a molecular weight in the range from 120 000 to 190 000 g / mol. However, the use of alginate having other molecular weights is possible too.

[0064] Fig. 1a shows a structural formula of a short sequence of an alginate polymer chain. Alginate is readily available commercially, for instance, as sodium alginate. Advantageously, the sodium ions of sodium alginate may be exchanged to calcium which results in gelation of an aqueous alginate due to ionic cross-linking. Fig. 1 b schematically shows the coordination of alginate polymer chains with metal ions, such as calcium (Ca2+) ions, which results in the ionic crosslinking. Ionic cross-linking is herein referred to also as ionic coagulation. The ionic cross-linking enables fast and near-immediate fiber formation in fiber spinning and good mechanical strength.

[0065] In certain embodiments, a BOF comprises chitosan. Chitosan is a linear polysaccharide obtained by deacetylation of chitin containing randomly distributed p-linked D-glucosamine and N-acetyl-D-glucosamine. In certain embodiments, chitosan is obtained from the wastes of seafood processing industry. The polycationic nature of chitosan may allow interfacial polyelectrolyte complexation with anionic polymers such as alginate and carboxymethyl cellulose. Advantageously, in certain embodiments, fiber formation is supported and promoted by polyelectrolyte interactions. The cationic nature also makes chitosan antimicrobial. Advantageously, in certain embodiments, BOFs resistant for bacterial accumulation and growth are prepared. In certain embodiments, chitosan has molecular weight in the range of 50 000 - 190 000 g / mol, 190 000-300 000 g / mol, or 310 000-375 000 g / mol. Advantageously, the viscosity of the chitosan-comprising spinning dope may be adjusted by selecting low, medium, or high molecular weight chitosan, respectively. Chitosan may also be used for preparing BOF cladding or coatings, for instance, with antimicrobial properties.

[0066] In certain embodiments, the BOF comprises agarose. Agarose is a linear heteropolysaccharide extracted from seaweed. It consists of alternating D-galactose and 3,6-anhydro-L-galactopyranose units linked by a-(1 -> 3) and 0-(1 -> 4) glycosidic bonds. Agarose shows strain stiffening properties. Advantageously, mechanical performance of composite fibers may be improved. In certain embodiments, agarose is used for preparing fiber cladding or coatings.

[0067] In certain embodiments, the BOF comprises a water-soluble cellulose derivative. In certain embodiments, the BOF comprises more than one water soluble cellulose derivative. In certain embodiments, the water-soluble cellulose derivative is methylcellulose (MC), carboxymethylcellulose (CMC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), or hydroxyethyl cellulose (HEC).

[0068] In certain embodiments, the BOF comprises methylcellulose (MC). MC is a water-soluble cellulose derivative. Aqueous solutions of MC are typically clear and colorless. Aqueous MC is also thermoresponsive; When heated above a critical temperature, sol-gel transition occurs. The gelation is reversible by cooling the gel below the critical temperature. Aqueous MC can be coagulated in ethanol, which is beneficial in manufacturing BOFs according to certain example embodiments.

[0069] In certain embodiments, the BOF comprises carboxymethylcellulose (CMC). Aqueous solutions of CMC are typically clear and colorless. CMC may be ionically crosslinked by divalent or trivalent cations, such as Ca2+, Fe3+or Al3+.

[0070] In certain embodiments, the BOF comprises hydroxypropyl cellulose (HPC). In certain embodiments, the BOF comprises hydroxypropyl methylcellulose (HPMC). In certain embodiments, the BOF comprises hydroxyethyl cellulose (HEC).

[0071] Fig. 2 shows general structural formula of cellulose derivatives. For instance, in the case of MC, the “R” in Fig. 2 is either hydrogen (-H) or a methyl group (-CH3) depending on the substitution pattern and degree of substitution of the particular MC polymer. Typically, the degree of substitution of water-soluble MC is in the range of 1.5 - 1.9. Analogously, for CMC, the “R” in Fig. 2 is either hydrogen (H) or carboxymethyl groups (-CH2COOH). The degree of substitution of CMC may be, for instance, in the range of 0.7 - 1 .2. For HPC, the R is either hydrogen (-H) or hydroxypropyl group (-OCH2CH(OH)CH3), respectively. In certain embodiments, the second polysaccharide is a water-soluble cellulose derivative different from the first polysaccharide. In certain embodiments, the second polysaccharide is the same polysaccharide as the first polysaccharide but has a different molecular weight. In certain embodiments, the second polysaccharide is the same polysaccharide as the first polysaccharide but has a different degree of substitution.

[0072] In certain embodiments, the third polysaccharide comprises a water-soluble cellulose derivative different from the first and second polysaccharide. In certain embodiments, the third polysaccharide comprises the same polysaccharide as the first polysaccharide or the second polysaccharide but has a different molecular weight or degree of substitution. In certain embodiments, first, second, and third polysaccharide comprise the same polysaccharide, but they all have different molecular weights. For instance, if the first polysaccharide is MC having a molecular weight (MW) of 88 000 g / mol, the second polysaccharide may be MC having a MW of 41 000 g / mol. Further, the third polysaccharide may also be MC but having MW of 14000, or perhaps CMC which is a different polysaccharide, or MC having a different degree of substitution from the first and second polysaccharides.

[0073] In certain embodiments, the ratio (by mass) of the first and second polysaccharide in a two- component composite BOF is in the range from 1 : 10 to 1 : 1 . In certain embodiments, the ratio of the amounts (by mass) of the first polysaccharide and the second polysaccharide is 1 : 1 . In certain embodiments, the ratio of the amounts (by mass) of the first polysaccharide and the second polysaccharide is 1 : 3.

[0074] In certain embodiments, a two-component BOF comprises 5-95% (by weight) of the first polysaccharide, and 5-95% (by weight) of the second polysaccharide of the total dry mass of the biopolymeric optical fiber. In certain embodiments, a two-component BOF comprises 25-75% (by weight) of the first polysaccharide, and 25-75% (by weight) of the second polysaccharide of the total dry mass of the biopolymeric optical fiber. The combined total amount of polysaccharides in a BOF corresponds to substantially 100 % of the total dry mass of the BOF.

[0075] In certain embodiments, a three-component BOF comprises 10-50% (by weight) of the first polysaccharide, 10-50% (by weight) of the second polysaccharide, and 10-50% (by weight) of the third polysaccharide of the total dry mass of the biopolymeric optical fiber. In certain embodiments, a three-component BOF comprises 20-40% (by weight) of the first polysaccharide, 20-40% (by weight) of the second polysaccharide, and 20-40% (by weight) of the third polysaccharide of the total dry mass of the biopolymeric optical fiber. Preferably, the sum of the amounts of the polysaccharide components of a BOF is substantially equal to the total dry mass of the BOF. Advantageously, the BOF may be substantially fully made of renewable and biodegradable material.

[0076] In certain embodiments, a three-component BOF comprises equal amounts of each polysaccharide component, i.e. in a 1 : 1 : 1 ratio. In certain embodiments, at least one polysaccharide component of a three-component BOF accounts for at least 40% of the total dry mass of the BOF. In certain embodiments, one polysaccharide component of a three- component BOF accounts for at least 40% of the total dry mass of the BOF. In certain embodiments, one polysaccharide component of a three-component BOF accounts for at least 50% of the total dry mass of the BOF. In certain embodiments, one polysaccharide component of a three-component BOF accounts for at least 60% of the total dry mass of the BOF. In certain embodiments, one polysaccharide component of a three-component BOF accounts for at least 70% of the total dry mass of the BOF. In certain embodiments, the polysaccharide accounting for the at least 40, 50, 60, or 70 % of the total dry mass of a BOF is methylcellulose. In certain embodiments, the alginate content (by weight) of a BOF is at most 50%. Advantageously, different fiber compositions may enable transmission of light at different wavelengths ranges.

[0077] In certain embodiments, the polysaccharide components of a BOF, i.e., the first, second, and third polysaccharides, are different polysaccharides and / or have different molecular weights and / or degrees of substitution. A mixture of different types of polysaccharides may provide advantages in processing, decreased surface roughness, and / or mechanical properties in addition to the optical characteristics. The co-existence of polysaccharides with smaller and larger MW facilitates the prevention of voids and inhomogeneities inside the resulting fiber. Advantageously, homogeneous structure contributes to both light transmission and mechanical durability. For clarity, it is noted that typically the MW of an amount of a polysaccharide is generally a distribution, and not an exact value of each polymer chain present in the amount. The skilled person appreciates that the MW is to be understood as the representative MW of the used polysaccharide(s).

[0078] In certain embodiments, a BOF comprises MC having a MW in the range from 14 000 g / mol to 130 000 g / mol. In certain embodiments, the first, second and / or third polysaccharide is MC having MW of 14 000 g / mol, 41 000 g / mol, or 88 000 g g / mol. In certain embodiments, MC having MW higher than 88 000 g / mol is used. In certain embodiments, the BOF comprises MC having a MW up to 300 000 g / mol. In certain embodiments, first, second, and / or the third polysaccharide comprises CMC having a MW in the range from 90 000 g / mol to 250 000 g / mol. In certain embodiments, the first, second, and / or third polysaccharide is CMC having MW of 90 000 g / mol, 150 000 g / mol, or 250 000 g g / mol. In certain embodiments, CMC having MW higher than 250 000 g / mol is used.

[0079] In certain embodiments, the BOF comprises HPC having a MW in the range from 75 000 g / mol to 400 000 g / mol. In certain embodiments, the first, second, and / or third polysaccharide is HPC having MW of 75 000 g / mol, or 370 000 g / mol. In certain embodiments, HPC having MW higher than 370 000 g / mol is used.

[0080] In certain embodiments, the BOF comprises HPMC having a MW in the range from 10 000 to 150 000 g / mol. In certain embodiments, the first, second, and / or third polysaccharide is HPMC having MW of 10 000 g / mol, 22 000 g / mol, or 86 000 g / mol. In certain embodiments, the HPMC has a methoxy content of 28-30% and a hydroxypropyl content of 7-12%.

[0081] In certain embodiments, the BOF comprises HPMC having viscosity of 145 mPa-s, 3400 - 5000 mPa-s, or 4500 - 6500 mPa-s, as measured from 1 % of HPMC in water at 20 °C.

[0082] FIBER SPINNING DOPE

[0083] Biopolymeric optical fibers (BOFs) of the present disclosure are manufactured by wetspinning or dry-jet spinning. Advantageously, the spinning processes do not require heating. In other words, the spinning may be performed in ambient conditions and without significant energy investments. However, heating may be optionally applied to facilitate polysaccharide dissolution, fiber formation and / or drying. For example, aqueous spinning dopes prepared comprising MC and HPMC may be thermally responsive. The fiber spinning equipment is also relatively simple and affordable. Generally, the spinning of a BOF comprises extrusion of a spinning dope into a coagulation bath, wherein the spinning dope coagulates into a fiber. A fiber spinning apparatus 300 according to certain embodiments is shown in Fig. 3. A flow chart for manufacturing a BOF according to certain embodiments is shown in Fig. 18. The method may be performed, for example, by using the fiber spinning apparatus 300.

[0084] To prepare spinning dope 115, polysaccharide(s) in a powder form is (are) portion wise added to a known volume of water under continuous stirring until a desired concentration (weight per volume) is reached. Preferably, highly purified water free of contaminants, such as distilled water or ultrapure water is used. The polysaccharide comprises at least one polysaccharide selected from the first, second, and third polysaccharide. The first, second, and third polysaccharide may comprise any of the polysaccharide discussed herein. Polysaccharides in powder form are commercially readily available. In a case where more than one polysaccharide is used to prepare a composite BOF, the powders are preferentially mixed together in dry state, and the mixed powder is then added to the water portion wise under vigorous stirring. For the stirring, for instance, a magnetic stirrer with a stirring speed of 1000 - 1500 rpm may be used.

[0085] After having added all the polysaccharide powder to the water, the stirring is continued until a clear homogeneous solution is achieved. In the fully dissolved state, the polysaccharide chains are present in the solution as essentially individual polymer chains. That is, crystals, particles or solid aggregates of the polysaccharide or polysaccharides are not present in the spinning dope. Thus, inhomogeneities and undesirable scattering in the BOFs may also be minimized.

[0086] Preferably, the amount of added polysaccharide is chosen such that the spinning dope remains liquid-like and flowing after the polysaccharide dissolution is complete, i.e., very high concentrations and unintentional gelation are avoided. This way even distribution and proper mixing may be ensured. Advantageously, homogeneous spinning dope may be achieved, and clump formation avoided. The liquid-like state also facilitates the handling and extrusion of the spinning dope. Preferably, the spinning dope is stored at low temperatures, such as +4 °C, until the spinning.

[0087] In certain embodiments, the spinning dope preparation involves heating. For instance, to dissolve MC or HPMC, heating may be used to facilitate powder dissolution in water. For instance, the water may be heated up to 80 - 85 °C before adding the MC or HPMC powder. After a homogeneous solution is acquired, the spinning dope may be cooled down to promote hydration of the polysaccharides. For example, ice bath may be used to cool down the solution.

[0088] The total polysaccharide content of the spinning dope 115 is 0.5% (w / v) - 30.0% (w / v), preferably 1.0 % (w / v) - 20.0 % (w / v), more preferably 2.0 % (w / v) - 15.0 % (w / v), even more preferably 3.0 %(w / v) - 10.0 % (w / v). The total polysaccharide content refers to the combined amount of polysaccharides (the first polysaccharide, the second polysaccharide, and the third polysaccharide; by weight) present in the spinning dope divided by the volume of the spinning dope. For instance, a 4.0 % (w / v) polysaccharide solution consists of 4 grams of polysaccharide in 100 ml of water. Advantageously, by tuning the total polysaccharide content and composition of the spinning dope 115, the viscosity and spinning characteristics of the spinning dope may be adjusted. For instance, at low total polysaccharide contents low viscosity spinning dope is achieved that is easy to handle, degas and extrude. On the other hand, spinning dopes with higher total polysaccharide contents are more viscous, more difficult to degas, and may require more powerful pumps and more pressure-resistant equipment to extrude but often retain the extruded fiber shape better. The skilled person appreciates, however, that in addition to the polysaccharide content, the type, degree of substitution and molecular weights of the selected polysaccharides may also affect the viscosity of the spinning dope which should be considered in the preparation of the spinning dope.

[0089] FIBER MANUFACTURING

[0090] In certain embodiments, BOFs are manufactured by wet-spinning. In certain embodiments, BOFs are manufactured by dry-jet spinning. A fiber spinning apparatus 300 is schematically shown in Fig. 3 In general, wet-spinning and dry-jet spinning are fiber forming processes in which the raw material, such as polymer powder, is dissolved in a solvent to form a spinning dope 325. The spinning dope 325 is then extruded into a coagulation or cross-linking solution 345 (in a coagulation bath 340) to form a continuous fiber 335. In wet-spinning, the spinning dope 325 is extruded directly to the coagulation solution 345. In dry-jet spinning the spinning dope 325 is extruded first through a non-coagulating fluid, such as air, and then into the coagulation solution 345. The spinning process may be driven continuously as long as there is sufficient spinning dope 325 and coagulation solution 345 available. Advantageously, a very long fiber 335 may be prepared. In the present disclosure, the raw material for spinning comprises polysaccharide(s) dissolved in water. That is, water is used as the solvent to prepare the spinning dope 325. The water is preferably highly pure water, for instance, Milli-Q® (Type I) water or distilled water.

[0091] In certain embodiments, the spinning of BOFs is performed in ambient conditions. That is, any particular temperature control is preferably not required, and the spinning, in certain embodiments, is performed at room temperature, i.e., approximately 20-24 °C. Advantageously, energy may be saved as energy-intensive heating or cooling may not be required.

[0092] In certain embodiments, the coagulation solution 345 is ethanol. In certain embodiments, the ethanol content of the coagulation solution is 90.0 % (v / v) - 99.7 % (v / v), preferably 94.0 % (v / v) - 98.0 % (v / v), more preferably 96.0 % (v / v) - 97.0 % (v / v). In certain embodiments, the ethanol content is 96.1 % (v / v). Higher ethanol content results in more effective solvent exchange and thus faster fiber coagulation. Lower ethanol content enables gentler coagulation but as a trade-off allows the nascent fiber 335 more time to deform. Advantageously, the coagulation rate and shape retention of the extruded nascent fibers may be controlled by the ethanol content of the coagulation solution 345.

[0093] In certain embodiments, the coagulation solution 345 is an aqueous ionic solution comprising ions suitable for crosslinking at least one of the first polysaccharide, second polysaccharide, and / or third polysaccharide present in the spinning dope 325. For instance, 2% (w / v) calcium chloride (CaCh) solution may be used as the coagulation solution 345 to cross-link spinning dope 325 comprising sodium alginate. As another example, 2% (w / v) aluminum sulfate (Ah(SO4)3) may be used to cross-link a spinning dope 325 comprising CMC. Other ions and concentrations of ions suitably selected according to the spinning dope composition may also be used. In certain embodiments, only one type of cross-linking ion is used. In certain embodiments, two different types of cross-linking ions are present simultaneously in the coagulation solution 345. For instance, CaCh and Ah(SO4)3 may be used together to crosslink two different components, e.g., alginate and CMC, of the extruded spinning dope 325. Advantageously, denser cross-linking may be achieved by using more than one ionic species suitable for crosslinking more than one polysaccharide, respectively.

[0094] The skilled person appreciates that the ions and ionic concentration of the coagulation solution 345 are selected suitably according to the polysaccharide(s) of the spinning dope 325. The cross-linking may be performed, for example, depending on the selected polysaccharides, with various divalent cations, such as Ca2+, Ba2+, Cu2+, Fe2+, Zn2+, Sr2+, Sn2+, Ni2+, Co2+, and Cd2+.

[0095] In certain embodiments, the coagulation solution 345 comprises ions suitable for crosslinking dissolved in ethanol. For instance, CaCh is soluble in ethanol up to 25.8 g / 100 ml of water at 20 °C. Advantageously, fiber formation upon extrusion to the coagulation bath may be promoted by both coagulation in ethanol and by ionic cross-linking simultaneously providing more efficient fiber formation. For instance, a spinning dope 325 comprising both MC and alginate as the first and second polysaccharides, respectively, may be feasibly coagulated by such double coagulation.

[0096] Further, whenever MC or HPMC is present in a spinning dope 325, shape retention and coagulation of the nascent fiber may also be facilitated by heating the coagulation bath 340 and the coagulation solution 345 therein. Generally, heating up to the range from 30 °C to 45 °C is sufficient to induce reversible sol-gel transition in MC. Due to thermoresponsivity of MC, the nascent fiber then reversibly gelates in the coagulation solution 345, thus, supporting the coagulation reaction driven by ethanol and / or ionic cross-linking. For HPMC, the respective gelation temperature is typically in the range from 75 °C to 90 °C. In certain embodiments, MC-containing or HPMC-containing spinning dope 325 is extruded into a heated coagulation bath.

[0097] The fiber spinning apparatus 300 comprises a sample container 320. The sample container 320 is configured to contain fiber spinning dope 325. The spinning dope may be prepared as described in the foregoing. The sample container 320 is connected to a pump 310 and a capillary tube 330. The capillary tube 330 connects the sample container 320 to a coagulation bath 340. The coagulation bath 340 contains coagulation solution 345. The pump 310 is configured to pump, i.e., extrude, the spinning dope 325 from the sample container 320 through the capillary tube 330 to the coagulation bath 340. Upon emerging from the capillary tube 330 to the coagulation bath 340, the spinning dope 325 interacts with the coagulation solution 345. In wet spinning, the capillary tube 330 end is immersed in the coagulation solution 345 such that the spinning dope 325 is extruded directly into the coagulation solution. In dry-jet spinning, the spinning dope 325 may exit the capillary tube, for example, above the coagulation solution 345 surface such that the dope 325 is extruded first into air (a non-coagulating medium) and only then to the coagulation solution 345.

[0098] As a result, the extruded spinning dope 325 is continuously coagulated into a fiber 335 in the coagulation bath 340. A collector 360 is configured to collect the nascent wet fiber 335 from the coagulation bath 340. The collector 360 pulls the fiber through a rinsing bath 350 after the coagulation bath 340 to remove chemical residues. After rinsing, a dryer 370 is configured to dry the wet fiber 335, for example, by hot air flow. A cutter 380 is configured to cut the continuous fiber 335 into sections of desired length, for instance, to lengths suitable for commercial products such as sensing elements. Advantageously, wet spinning enables continuous production of BOFs with relatively safe chemicals and without the need for extreme temperatures. A coater 190 is configured to provide coating, cladding, or other surface modifications to the extruded BOF.

[0099] The spinning dope 325 is an aqueous solution comprising the selected polysaccharide(s) homogeneously dissolved in water. In certain embodiments, the spinning dope 325 comprises only first polysaccharide. In certain embodiments, the spinning dope 325 comprises first polysaccharide and second polysaccharide. In certain embodiments, the spinning dope 325 comprises first, second, and third polysaccharide. The solvent used to prepare the spinning dope 325 is water. In certain embodiments, the spinning dope 325 is degassed before extrusion to remove gas bubbles by using a suitable degassing method. For instance, a vacuum-guided centrifuge, vacuum chamber, or sonification may be used.

[0100] The pump 310 may be an extrusion pump, syringe pump or any other suitable pump capable of providing a stable extrusion flow. The pump 310 is adjusted to enable a desired extrusion flow rate from the capillary tube 330. In certain embodiments, the flow rate is 1.0 ml / min. In certain embodiments, the flow rate is 1.8 ml / min. In certain embodiments, the flow rate is in the range of 0.5 ml / min - 2.0 ml / min. In certain embodiments, the flow rate is at least 1.0 ml / min. In certain embodiments, the flow rate is at least 2.0 ml / min. In adjusting the extrusion flow rate, the inner diameter of the capillary tube 330 needs to be considered. By adjusting the pump 310, different extrusion flow rates may be achieved. Advantageously, by adjusting the flow rate, shear forces within the capillary tube 330 and consequently alignment of the polysaccharide(s) in the resulting BOF 335 may be controlled.

[0101] The capillary tube 330 may be made of polyether ether ketone (PEEK). However, other inert materials that enable corresponding capillary tubes capable of enduring high pressures may also be used. The capillary tube 330 may comprise a nozzle.

[0102] The inner diameter of a capillary tube 330 determines, at least partially, the cross-sectional dimensions of the extruded fiber 335. The swelling and drying of the fiber 335 also may play a role to a certain extent. In certain embodiments, the inner diameter of the capillary tube 330 is 1 .0 mm. In certain embodiments, the inner diameter of the capillary tube 330 is 0.727 mm. In certain embodiments, the inner diameter of the capillary tube 330 is 0.5 mm. In certain embodiments, the inner diameter of the capillary tube 330 is 0.14 mm. In certain embodiments, the inner diameter of the capillary tube 330 is in the range of 0.1 mm - 2.0 mm. Advantageously, BOFs having different cross-sectional diameters may be manufactured by using capillary tubes 330 having different inner diameters.

[0103] In certain embodiments, the length of the capillary tube 330 is at least 0.5 m. In certain embodiments, the length of the capillary tube 330 is 1 .0 m, 1 .5 m, 2.0 m, or 3.0 m. In certain embodiments, the length of the capillary tube 330 is in the range from 0.5 m to 4.0 m. Advantageously, longer capillary tubes may enable better shear-induced alignment of the polysaccharide(s) in the extruded fiber. In certain embodiments, the extruded fiber 335 is equilibrated in the coagulation bath 340 for a predetermined period of time before removing it from the coagulation bath 340. In certain embodiments, the equilibration time is 2 min, 5 min, 10 min, 15 min, 20 min, 30 min, or 45 min. In certain embodiments, the equilibration time is in the range from 2 s to 50 min. Typically, when using ethanol as the coagulation solution 345, longer equilibration time, such as 15-30 min, is beneficial to ensure proper fiber coagulation, whereas in ionic crosslinking the extruded fiber 335 may be almost immediately collected from the coagulation bath 340. Extruded fiber 335 thickness and density may also affect the access of the coagulation solution 345 to the fiber core and solvent exchange speed, thus also the needed equilibration time.

[0104] In certain embodiments, the collector 360 is an automatic collecting reel, drum, or rack. The collecting speed of the collector 360 may be matched with the extrusion flow rate. In certain embodiments, the collector 360 may be configured to collect the fiber 335 at a faster rate than the extrusion rate determined by the pump 310. Advantageously, stretching may be applied to the extruded fiber 335 further enhancing the internal alignment.

[0105] In certain embodiments, a plurality of rinsing baths 350 is provided after the coagulation bath 340. In certain embodiments, 1 , 2, 3, or 4 separate rinsing baths 350 are provided. The fiber 335 may be continuously pulled and guided through the rinsing bath(s) 350 or alternatively allowed to soak stationery in each bath for a predetermined period of time. In certain embodiments, the rinsing time is 0.5, 1 , 3, 5, or 15 min per rinsing bath 350. In certain embodiments, the rinsing time is in the range from 2 s to 5 min. In certain embodiments, the fiber 335 is dipped to the rinsing bath 350. Advantageously, chemical residues may be effectively removed by guiding the extruded fiber 335 through the rinsing bath(s) 350, particularly after ionic coagulation. Some of the rinsing baths 350 may also be cleaned or have the rinsing solution exchanged while the other rinsing baths 350 are in use.

[0106] In certain embodiments, collected fiber 335 is directly subjected to drying once collected from the coagulation bath 340. That is, there is no rinsing bath 350. This applies particularly to ethanol coagulation, where rinsing in water may begin to re-dissolve the coagulated fiber 335. Advantageously, ethanol coagulation also does not introduce other chemicals or components beyond ethanol that would need to be removed. Alternatively, other solvents than water, such as ethanol, may be used for rinsing ethanol coagulated fibers 335. Advantageously, the rinsing process may be adapted according to the materials and spinning process to ensure purity of the BOF. The drying step comprises removing from the fiber 335 the excess coagulation and rinsing fluids still present in the fiber 335. In certain embodiments, the collector 360 comprises the dryer 370. That is, there is no separate dryer 370 but the collector 360 includes a dryer setup suitable for drying the collected fiber 335 and storing the fiber 335 for the duration of the drying. In certain embodiments, the dryer 370 is a rack, a drum, or a spool onto which the extruded fiber 335 is wrapped onto. In certain embodiments, the fiber 335 is dried at ambient temperature and humidity at normal indoor conditions. That is, a separate temperature or humidity controller may not be required. In certain embodiments, the drying is performed at a controlled temperature and relative humidity environment. In certain embodiments, the drying temperature is in the range from 15 °C to 80 °C. In certain embodiments, the relative humidity for drying is in the range from 15% to 60%. In certain embodiments, the drying time is 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, or 20 h. In certain embodiments, the drying time is in the range from 15 min to 24 h. Advantageously, even and controlled drying of the extruded fiber 335 may be ensured.

[0107] In certain embodiments, the cutting of the fiber by cutter 380 is performed after the drying has taken place (as in Fig. 3). In such case, the fiber 335 may be fully dried into its final form as BOF before the cutting. That is, a continuous dried fiber 335 is cut to desired lengths. In alternative embodiments, the cutter 380 is positioned before the dryer 370. In such cases, a wet fiber 335 is cut already before drying.

[0108] A coater 390 may be used continuously in conjunction with the fiber spinning, or alternatively as a separate post-processing stage once the extruded fiber 335 is fully dried. In certain embodiments, coating is performed by dip-coating, drop-coating, spray-coating, or vapor deposition. In certain embodiments, a protective layer is provided to protect the BOF 335 against mechanical abrasion. Generally, the coating or cladding may be used to provide mechanical and chemical protection, modify the surface chemistry of the BOF 335, and / or to facilitate or provide sensing capabilities, e.g., by providing a specific binding capability. Cladding may also improve signal transmission within the BOF and reduce scattering.

[0109] Fig. 4 shows polarized light microscopy (POM) and scanning electron microscopy (SEM) micrographs of biopolymeric fibers 335 prepared from alginate, methylcellulose, and a mixture of alginate and methylcellulose. Fibers in the top row are made of 4% (w / v) methylcellulose by wet-spinning into 96% (v / v) ethanol. Fibers in the middle row are made of 4% (w / v) alginate by wet-spinning into 2% (w / v) CaCh solution. Fibers in the bottom row are composite fibers of methylcellulose and alginate (MC to alginate ratio 3:1 , from a spinning dope having a total polysaccharide content 4% (w / v)) prepared by wet-spinning into 96% (v / v) ethanol. For SEM imaging, the fibers have been further coated with a 6 nm- thick platinum-Palladium sputter coating. The first column shows non-cross-polarized bright-field polarized optical microscopy (POM BF) micrographs of the sides of the BOFs. The second column shows cross-polarized polarized optical microscopy (POM) micrographs of the sides of the BOFs. The third column shows SEM micrographs of the sides of the BOFs. The fourth column shows SEM micrographs of tips of the BOFs cut by a razor blade. As shown, all the fibers have relatively smooth surfaces which is advantageous for reducing signal losses. Ethanol coagulation especially provides particularly smooth surfaces which is advantageous for light signal propagation inside a fiber and to reduce scattering.

[0110] The cross-sectional shape of the ethanol coagulated fibers is not fully circular as shown in Fig. 4. However, this is acceptable for short-range applications. The non-circular shape is due to slower nature of the ethanol coagulation process and resulting fiber deformation in the coagulation bath 340. Ionically crosslinked alginate-containing fibers show more circular cross-section, preferably fully circular. Advantageously, polysaccharides or polysaccharide composites that support ionic cross-linking may be selected for purposes where circular shape of the fiber is especially desired, for instance, to ensure uniform cross-sectional shape and diameter or accurate fit with connectors to minimize coupling losses. Further, by selection of the coagulation process and polysaccharides, BOF surface smoothness may be adjusted. Through selection of polysaccharides and manufacturing parameters, a balance between coagulation efficacy, fiber appearance, optical properties and mechanical properties may be tuned.

[0111] BOF CHARACTERISTICS

[0112] A measurement setup used for measuring and studying the optical properties of the BOFs according to certain embodiments is shown in Fig. 5. The numbered parts in Fig. 5 are the following:

[0113] 1 : Light source. A LED light source (CoolLED pE-4000, 15 -30 nm FWHM) was typically used. Alternatively, a laser or white light source, such as halogen lamp, may be used;

[0114] 2: Fiber collimator. Collimator couples the light from the light source to an optical fiber.

[0115] Thorlabs F11 OFC-633 collimator was used; 3: Commercial POF. A commercial POF was used as an intermediate fiber to guide light to a BOF to be measured. For instance, Thorlabs M124L01 (0400 pm, 0.50 NA) multimode fiber was used;

[0116] 4: Coupling ferrule. POF was coupled to the BOF to be measured by a custom-made 3D-printed ferrule. Alternatively, commercially available stainless steel or ceramic fiber optic ferrules may be used;

[0117] 5: BOF to be measured. The BOF may be a single-component fiber or a composite of two or three polysaccharides;

[0118] 6: Silicon photodiode power sensor. For instance, Thorlabs S151 C (400 - 1100 nm operating range with 20 mW maximum power and 100 pW resolution) was used; and

[0119] 7: Power meter. Thorlabs PM100D was used. With this type of setup, the transmission power through the BOF was measured. Accordingly, Attenuation and transmission losses could be monitored.

[0120] A measurement system 600 according to certain embodiments for measuring optical properties of BOFs is schematically shown in Fig. 6.

[0121] The measurement system 600 comprises a light source 610. In certain embodiments, the light source 610 is a laser, or an LED light source. In certain embodiments, the light source 610 is a white light source, such as deuterium and halogen lamp. In certain embodiments, the light source 610 is configured to emit only certain wavelength or wavelength range of light. In certain embodiments, the light source 610 emits light in the wavelength range from 180 to 2600 nm. In certain embodiments, the light intensity is adjustable. Advantageously, optimal wavelength and light intensity may be selected depending on the application and used BOF characteristics.

[0122] In certain embodiments, the measurement system 600 comprises a fiber collimator 620 configured to collimate and launch the light from the light source 610 into an optical fiber after the collimator.

[0123] The measurement system 600 optionally comprises a section of a commercial optical fiber 630, preferably a POF, into which the fiber collimator 620 guides the light before the BOF 650 to be measured. Advantageously, POF 630 enables flexibility in implementing the measurement / sensing system. The sensing BOF section 650 may not need to be immediately adjacent to the light source 610 thus providing positional operational freedom. In certain embodiments, a commercial fiber 630 is alternatively or additionally located after the BOF 650 and before a photodetector 660.

[0124] In certain embodiments, ferrule 640 couples the fiber collimator 620 or the commercial optical fiber 630 to a first end of a wet-spun BOF 650.

[0125] The second end of the BOF 650 is connected, either directly or via a commercial optical fiber, to the photodetector 660. The photodetector 660 detects the transmitted light. A computing device 670 may visualize and / or calculate light transmission characteristics and changes from the signals detected by the photodetector 660.

[0126] It has been observed that a similar or an analogous system may be used as a sensing system for sensing applications to provide, for instance, humidity, vapor, or touch sensing.

[0127] The BOF 650 is any biopolymeric optical fiber according to the present disclosure. For instance, it may comprise one, two, or three polysaccharides and it may have been manufactured by wet-spinning or dry-jet spinning. The BOF 650 operates as a sensing element to measure e.g., humidity, and the measurement system 600 enables quantitative humidity measurement.

[0128] In certain embodiments, the computing device 670 stores and / or comprises reference data for quantitative determination of humidity and is configured to convert measured transmission signals to quantitative humidity values. The photodetector 660 may be, for instance, a silicon photodiode, a spectrometer, or a spectral analyzer. The computing device 670 may be for instance, a personal computer, mobile phone, or a power meter. The computing device 670 may be connected by a cable or wirelessly to the measurement system 600. The computing device may be configured to control the measurement system 600. The computing device 670 may be connected to and interact with a further computing device, server, or a cloud service or storage.

[0129] Fig. 7 shows normalized transmission spectra of biopolymeric optical fibers according to certain embodiments. Transmission spectra show which wavelengths of light are least attenuated as they propagate through the biopolymer fibers. Surprisingly, the composition of the BOF affects which wavelengths of light propagate the best. BOFs prepared from pure alginate (spectrum A) show a sharp drop in transmission below 900 nm and generally transmission is very low across the visible spectrum (350 - 750 nm). In comparison BOFs prepared from MC (spectrum B) have relatively high transmission down to 650 nm and their transmission drops more gradually across the visible spectrum. Therefore, transmission in MC is better retained in the visible light range. Neither single component (i.e., BOF comprising only first polysaccharide) alginate BOFs (spectrum A) nor single component MC BOFs (spectrum B) show considerable ultraviolet light transmission (below 400 nm). Further, alginate and MC BOFs both display good transmission in near-infrared above 900 nm.

[0130] The transmission spectra of composite BOFs, in Fig. 7 the MC-AIg fibers which are a composite of MC and alginate (spectrum C), lies between the spectra of the single component polysaccharide fibers. Advantageously, the transmission spectra of the BOFs may be tuned by adjusting the BOF composition, particularly, by adjusting the type and ratios of the first, second, and third polysaccharide. Alginate fibers typically appear as not fully clear and slightly yellowish. Alginate fibers are typically also produced for mechanical purposes which is supported by the relatively poor transmission at visible wavelength range. Thus, they would not logically be considered as suitable for optical fibers. However, they perform surprisingly well in the near-infrared wavelengths as observed here, while also providing mechanical reinforcement by enabling efficient ionic crosslinking. Further, by mixing alginate with for instance MC, the transmission window in the composite fibers may be better extended also to the visible range. At the same time, MC may benefit from the ionic cross-linking provided by alginate. In certain embodiments, a single component alginate fiber is used as a biopolymeric optical fiber. In certain embodiments, single component MC or CMC fiber is used as a biopolymeric optical fiber.

[0131] Fig. 8 shows attenuation measurement spectrum of a composite BOF consisting of alginate and MC in 1 : 5 ratio (by weight). Also, R-squared correlation factor is shown. Attenuation reveals how much transmitted light is lost per fiber length. The attenuation coefficient was determined by measuring transmitted light from fiber samples at various lengths. Therefrom, the fiber length dependence of light transmission could be calculated. Preferably, a cutback method was used. The attenuation coefficient can be determined numerically from the data of light power and fiber length data pairs by applying the Beer-Lambert law P Li = Poe~aLl, where Po is the input power, P(Lj) is the output power at length Lhand a is the attenuation. Applying the Beer-Lambert law involves the assumptions of constant input power and coupling efficiencies. The representative attenuation spectrum is shown in Fig. 8.

[0132] Fig. 9a-d and 10a-d show attenuation measurement data of composite biopolymer optical fibers according to certain embodiments. Fig. 9a-d show photon counts per fiber length at b) 470 nm (blue), c) 635 nm (red), d) 900 nm (near-infrared), and e) 1100 nm (near-infrared) of BOFs consisting of alginate and MC in 1 : 5 ratio (by weight). Blue data is direct photon counts from spectrometer with exponential fit, and red data is photon count converted into transmission loss in dB with linear fit. Notably, depending on the used wavelength, the photon count decreases at different rates. Notice the different Y-axis scales. The blue curves show direct photon counts from spectrometer with exponential fit. The red curves show photon count converted into transmission loss in dB with linear fit. Advantageously, it is observed that measuring single-wavelength attenuation, as in Figs. 9a-d, enables less noisier data than measuring attenuation spectra, as in Fig. 8. Therefore, improved measurement accuracy may be achieved with single-wavelength attenuation measurements.

[0133] Figs. 10a-d show attenuation measurement data from CMC fibers. Power-length datasets from the cutback method at (a) 470 nm (blue), (b) 635 nm (red), and (c) 770 nm (nearinfrared) are shown. Red data is measured power in pW with exponential fit from Beer- Lambert law, and blue data is power converted into transmission loss in dB with linear fit. Fig. 10d shows attenuation coefficients per wavelength (datapoints) and a spline interpolation to guide the eye. Advantageously, lower attenuation coefficients may be achieved closer to the infrared wavelengths.

[0134] In certain embodiments, the attenuation coefficients of BOFs according to the present disclosure reside in the range from 3.0 dB / cm to 12 dB / cm. In certain embodiments, the attenuation coefficient is below 1.0 dB / cm, even 0.19 dB / cm. For instance, the 0.19 dB / cm attenuation has been achieved with a BOF prepared from 7% (w / v) CMC spinning dope by ionic coagulation in Ah(SO4)3 coagulation solution, wherein the attenuation was determined at the wavelength 770 nm. Corresponding attenuation measurement data is shown in Fig. 10c. In certain embodiments, the attenuation coefficient is less than 12.0 dB / cm, preferably less than 8.0 dB / cm, even more preferably less than 4.0 dB / cm, even more preferably less than 2.0 dB / cm, or less than 1 .0 dB / cm. While the attenuation is still significantly larger than the attenuation coefficient of the commercially available GOFs or POFs, it is still advantageously suitable for local sensing applications and short-range data transmission.

[0135] In certain embodiments, the operation length scale of BOFs is less than 1 meter. In certain embodiments, the operation length scale of BOFs is 1 - 5 meters. In certain embodiments, the operation length scale of BOFs is 5 - 10 meters. In certain embodiments, the operation length scale of BOFs is more than 10 meters. That is, the BOFs may be best implemented at various types of devices and sensors and local applications. Generally, with BOFs lowest attenuation is achieved with near-infrared and infrared light. Therefore, biopolymeric optical fibers are best suited for use in near-infrared and infrared light ranges but poorly suited for ultraviolet light. In the visible wavelength range, the losses typically increase towards the lower wavelengths (closer to blue). Advantageously, the transmission is generally improving towards the commonly used telecom wavelengths beyond the 1000 - 1100 nm range, up to above 1600 nm or even above 2000 nm. Further, through selection and adjusting the polysaccharide components, the attenuation and transmission ranges may be adjusted. Some representative attenuation coefficients determined for a series of BOFs according to certain embodiments are given in Table 1.

[0136] Mechanical properties of BOFs were characterized by tensile tests at 50% relative humidity and 22-23 °C. Each sample (sample length 1.0 cm) was elongated at a constant elongation speed of 0.5 mm / min until failure, and the corresponding load (N) was measured. Maximum stress, maximum strain, Young’s modulus, and the modulus of toughness were resolved.

[0137] Fig. 11 a-c show representative stress-strain curves of some BOFs of different compositions prepared according to certain embodiments. Fig. 11 a shows data for pure alginate fiber prepared from a spinning dope with a total polysaccharide content of 3.0% (w / v) by ionic crosslinking; Fig. 11 b for one-, two-, and three-component fibers prepared from a spinning dope with a total polysaccharide content of 4.0% (w / v) by ionic crosslinking; and Fig. 11 c for one-, two-, and three-component fibers prepared from a spinning dope with a total polysaccharide content of 4.0% (w / v) by ethanol coagulation.

[0138] Whereas ionically cross-linked alginate-containing BOFs can withstand over 150 MPa of stress before plastic deformation occurs (Figs. 11 a-b), ethanol coagulated BOFs comprising only MC begin to plastically deform already after 40 MPa (Figs. 11 b-c). Mixture of two MCs having different MW also provides higher strain than single-component MC fiber. Thus, mixing of similar polysaccharides with different MWs enables bigger plastic deformation. In general, higher alginate content translates to higher Young’s modulus, while higher methylcellulose content and ethanol coagulation produces tougher fibers due to higher maximum strain. In terms of ultimate tensile strength (breaking point) the BOFs are relatively weak thus limiting their applicability in physically straining applications. Advantageously, the mechanical properties may be tuned by adjusting the polysaccharide composition and by coagulation method.

[0139] Further material composition, coagulation methods, and measured mechanical and optical properties of BOFs manufactured according to certain embodiments are given in Table 1. The BOFs in Table 1 have been manufactured of pure alginate, pure MC with MW of 88 000 g / mol (MC88), or different two- or three-component mixtures of alginate, MC88, and MC having MW of 41 000 g / mol (MC41 ). In each case the total polysaccharide content of the spinning dope has been 4% (w / v) (to enable feasible handling and extrusion), and the used component ratios have been given in the material composition column. Thus, for instance, material composition MC88-Alg (3:1 ) means that the spinning dope of that particular fiber consisted of 3% (w / v) of MC88 and 1% / w / v) of alginate (total polysaccharide content of 4% (w / v). The other columns show used coagulation method, maximum stress, maximum strain, Young’s modulus, modulus of toughness, transmission window, attenuation coefficient (measured at 770 nm), and refractive index (the value shown in the table is measured at 633 nm from a film cast from the spinning dope), respectively. Evidently, the measured parameters shown in Table 1 depend on and are adjustable by selection of the polysaccharides and their ratios and processing.

[0140] Table 1. The material composition, coagulation methods, mechanical and optical properties of single component Alginate, MC fibers, and Alginate-MC composite fibers according to certain embodiments.

[0141] MC88 i EtOH 1.8 167.5 38.6 4.2 44.5 500 - 4.14 1.499

[0142] (4) ±56 ±15.5 ±0.6 ±27.9 1100 9

[0143] Alg (4) i CaCh 1.0 195.3 13.8 11.3 23.3 700 - 8.84 1.521

[0144] ±23.3 ±2.8 ±1.3 ±6.5 1100 6

[0145] Alg (4) i CaCh 1.8 175.8 13.2 10.8 20 700 - 6.91 1.521

[0146] ±21.1 ±2.5 ±1.2 ±5.4 1100 6

[0147] Alg (4) i EtOH 1.0 149 22.2 8.7 25.5 700 - 4.43 1.521

[0148] ±30.3 ±1.2 ±1.2 ±5.8 1100 6

[0149] MC88- i EtOH 1.0 117.7 36.2 3.1 28.9 500 - 3.34

[0150] MC41 i ±46.5 ±12.8 ±0.9 ±15.9 1100

[0151] (2:2) j

[0152] MC88- i EtOH 1.8 118.4 40.5 3.3 40 500 - 3.35

[0153] MC41 i ±91 ±26.6 ±1.6 ±44.6 1100

[0154] (2:2) j

[0155] MC88- i EtOH 1.0 168.8 47.9 3.5 51.2 500 - 3.06

[0156] MC41 i ±50.5 ±8.7 ±0.9 ±22 1100

[0157] (3:1) j

[0158] MC88- i EtOH 1.8 129.7 58 2.8 51.4 500 - 4.37

[0159] MC41 i ±49.9 ±23.1 ±0.9 ±32.5 1100

[0160] (3:1) j

[0161] MC88- i EtOH 1.0 146.7 40.7 4.1 40.7 700 - 11.6

[0162] Alg (3:1) i ±23.7 ±7.9 ±0.6 ±11.5 1100

[0163] MC88- i EtOH 1.8 176.8 52.5 5.1 63 700 - 7.94

[0164] Alg (3:1) i ±25.4 ±9.9 ±0.6 ±14.2 1100

[0165] MC88- i CaCh 1.0 111.1 36.7 3.8 28.6 700 - 4.37

[0166] Alg (3:1) i ±27.1 ±7.8 ±0.9 ±8.3 1100 Material Coag. Flow £f E Wf Trans- a Refra compos soluti rate (Mpa (%) (GP (MJ / m mission (dB / c dive ition on (ml / ) a)3) (nm) m) index w / v%).

[0167] MC88- 130.5 28.9 4.8 26.9 700 - 5.65

[0168] Alg (3:1) ±7.9 ±4.4 ±0.4 ±3.6 1100

[0169] MC88- 139.3 40.5 4.5 39.9 700 - 8.32

[0170] MC41- ±43.1 ±9.4 ±0.8 ±12.5 1100

[0171] Alg

[0172] (1.5: 1.5:

[0173] 1)

[0174] MC88- 137.4 42.4 4.7 41.5 700 - 9.48

[0175] MC41- ±29.7 ±12.1 ±0.8 ±13.8 1100

[0176] Alg

[0177] (1.5: 1.5:

[0178] 1)

[0179] MC88- 79.6 38 2.7 700 - 4.24

[0180] MC41- ±12.3 ±8.3 ±0.6 1100

[0181] Alg

[0182] (1.5: 1.5:

[0183] 1)

[0184] MC88- 95 33.5 3.2 700 - 4.86

[0185] MC41- ±15. ±6 ±0. 1100

[0186] Alg 7 9

[0187] (1.5:1.5:1

[0188] )

[0189] MC88- 149.1 42.7 5.1 700 - 11.8

[0190] MC41- ±42. ±7.4 ±1. ±18.1 1100

[0191] Alg 5 2 (2:1:1) MC88- 145.3 46.8 5+1 50.2 700 - 5.90

[0192] MC41- ±33. ±10. ±19 1100

[0193] Alg 6 5 (2:1:1) MC88- 130.1 33.8 4.3 31.5 700 - 5.11

[0194] MC41- ±12. ±7 ±0. ±7.5 1100

[0195] Alg 1 5 (2:1:1) MC88- 99.7 31 3.5 22.2 700 - 5.68

[0196] MC41- ±27. ±6.1 ±1 ±7.2 1100

[0197] Alg 2 (2:1:1)

[0198] Fig. 12a-d show thermal analysis results of BOFs manufactured according to certain embodiments. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) curves are shown: In Fig. 12a for single component fiber manufactured from 4% (w / v) spinning dope of MC having MW of 88 000 g / mol at 1 .8 ml / min extrusion rate and by ethanol coagulation; in Fig. 12b for single component fiber manufactured from 4% (w / v) spinning dope of sodium alginate at 1 .8 ml / min extrusion rate and by CaCh cross-linking; in Fig. 12c for composite fiber manufactured from 4% (w / v) spinning dope consisting of 2% (w / v) of MC with MW of 88 000 g / mol, 1% (w / v) of MC with MW of 41 000 g / mol, and 1% (w / v) of sodium alginate at 1.0 ml / min extrusion rate and by ethanol coagulation; and in Fig. 12d for composite fiber manufactured from 4% (w / v) spinning dope consisting of 2% (w / v) of MC with MW of 88 000 g / mol, 1 % (w / v) of MC with MW of 41 000 g / mol, and 1% (w / v) of sodium alginate at 1.0 ml / min extrusion rate and by CaCh cross-linking.

[0199] In the thermal analysis, pieces of BOF were gradually heated in a crucible up to 600 °C, and the sample weight as well as heat flow were simultaneously measured. Perkin Elmer STA 6000 simultaneous thermogravimetric / differential scanning calorimetric (TG / DSC) analyzer was used to carry out the measurements. The heating was performed under air and nitrogen atmospheres (flow rate of 40 mL / min) with a heating rate of 10 °C / min using temperature range of 20 - 600 °C. Melting points of indium and zinc metal standards were used to calibrate the device temperature. Standard weight of 50.00 mg was used to calibrate the weight. Sample weights used in the measurements were about 1 - 2 mg.

[0200] Single component MC BOF (Fig. 12a) showed only 1 mass-% water evaporation (mass loss around 100 °C), while single component alginate fiber’s (Fig. 12b) mass steadily decreased by 15 mass-% below 200 °C. The two materials also differed by decomposition steps: over 80% of the mass rapidly decomposed from single component MC BOF between 250 - 350 °C with heat flow peak in this second decomposition step, while the alginate fiber gradually lost 40 mass-% between 200 - 500 °C with the heat flow peak focused on the third, relatively more rapid step of 10 % mass reduction around 520 °C. Similar, albeit more gradual step occurred for the MC fiber between 350 - 450 °C for almost 20% mass decomposition.

[0201] Apparently, the gradual first decomposition step at lower temperatures is due to ionic coagulation. For example, the composite fiber containing MC and alginate fabricated using ethanol coagulation (Fig. 12c) has only 3 mass-% decomposition presumably due to water evaporation before 200 °C. On the other hand, the same composition fabricated using ionic coagulation (Fig. 12d) has almost 20% mass change below 200 °C. The second decomposition step is more rapid for ethanol coagulated fibers with almost 60 mass-% decomposition between 230 - 350 °C. Only a gradual 25 mass-% decomposition between 200 - 300 °C was observed for the ionically coagulated composite fibers. For all alginate- containing fibers, the remaining sample mass at the end of the thermal analysis at 600 °C remains at 20 - 40 mass-%. However, for pure methyl cellulose fiber almost all fiber mass is decomposed by 450 °C. As alginate-containing fibers show remaining mass at 600 °C regardless of the coagulation method, the remaining mass is not due to ions from ionic coagulation. Advantageously, ethanol coagulation enables good thermal stability up to approximately 200 °C. Further, loss of signal transmission due to thermal expansion may be minimized. Advantageously, in addition to tuning the optical properties and depending on the desired other properties (such as thermal stability, coagulation time and efficacy, smoothness, and cross-sectional shape), one may accordingly choose the most suitable coagulation method and polysaccharide raw materials. Overall, the thermal properties of BOFs appear to be close to or even better than commercial POFs, such as PMMA or polystyrene fibers.

[0202] SENSING APPLICATIONS

[0203] The BOFs of the present disclosure are not rigid but rather soft and the BOFs enable interaction directly with the environment, for instance, by absorbing humidity and moisture from air by an absorption-desorption process. The absorbed humidity directly affects the transmission properties of the BOF and thus the transmitted signal. Further, the absorbed humidity may swell the BOF to further affect signal transmission, particularly if the BOF is exposed to high humidity for extended periods of time. In a less humid environment, moisture may be again released from the fiber, thus, recovering the initial transmission properties. Therefore, the BOFs are suitable to be used as humidity or moisture sensors. Exemplary data of a qualitative humidity measurement by a BOF from breathing is shown in Fig. 17a. Such direct humidity or material absorption measurement is not possible with the GOFs or POFs. The GOFs and POFs are inert and do not absorb humidity or substantially swell even if immersed in liquid. Therefore, GOFs and POFs as such are not suitable for such direct humidity measurements.

[0204] Since humidity directly affects the signal transmission of a BOF through the absorptiondesorption process, the changes in humidity may be advantageously detected and measured in seconds due to change in light signal transmission through the fiber. That is, the measurement response of a BOF-based may be faster than with the typical commercial averaging capacitance humidity sensors whose response time may be in tens of seconds or even minutes. Advantageously, observation of changes in humidity may be detected very rapidly as demonstrated in Fig. 17a. Direct measurement of the changes in signal transition may also reduce measurement errors as mathematical fittings are not required to interpret the measurement data.

[0205] BOFs are relatively soft and may be compressed by touch or pressure. By touching, the refractive index difference across the surface of the BOF is also changed. As a result, transmission loss may be increased and thus pressure or touch to the fiber detected. Exemplary data of a qualitative touch sensing (i.e., sensing if the fiber is touched or not) measurement is shown in Fig. 17b. Further, effects of touching and alterations in humidity may affect and be simultaneously detected with a BOF. Any chemical modifications are not needed for the humidity or touch sensing abilities. Only a measurement system, such as the system shown in Figs. 5-6, capable of detecting and analyzing the changes in transmission is needed.

[0206] In addition to qualitative monitoring (e.g., detecting whether an action, such as a touch or breathing, occurs or not), environmental conditions can also be determined quantitatively (e.g., measuring the magnitude of the change in pressure or humidity caused by the action, respectively) by characterizing the material response to a given condition. In terms of humidity, light transmission through the fiber is measured at selected wavelengths as it is exposed to various controlled humidity levels. Thereby, in certain embodiments, a correlation, or a reference data or standard data, is established. In certain embodiments, target measurements results based on BOF absorption are then compared with the reference data to correlate and convert, for instance, measured light intensity to a certain relative humidity value. That is, in certain embodiments, humidity is quantitatively determined.

[0207] Therefore, in certain embodiments, the BOFs are used as quantitative humidity or moisture sensors. By comparing the measured signal transmission (or attenuation) to a reference data, the measured signal transmission or attenuation coefficient may be quantitatively converted to humidity. The reference data comprises the correlation of signal transmission and / or attenuation (measured at selected wavelength(s)) to humidity for the particular material of which the BOF is made of. The reference data is determined under controlled humidity conditions by changing the humidity and measuring the corresponding transmittance (or attenuation) for each particular material composition.

[0208] Fig. 13a shows humidity sensitivity of single component and composite biopolymer optical fibers according to certain embodiments at 900 nm. For pure MC BOFs, the humidity response is linear across the relative humidity range from 10% RH (relative humidity) to 80% RH (the linear fitting in Fig. 13). Advantageously, MC BOFs appear highly suitable for quantifying relative humidity at broad range at least from 10% to 80% RH. In comparison, humidity response of composite BOFs comprising alginate is non-linear, as shown in Fig. 13 (the curved fitting). Accordingly, the alginate-containing fibers have higher sensitivity in the high humidity range (> 50% RH). By providing a calibration curve, potentially highly precise quantitative measurements in higher humidity conditions, that is, above 50 % RH, are enabled. Advantageously, the BOF may be prepared to be most suitable for certain kind of humidity conditions, such as high humidity above 50%, or even performance across the full humidity range from below 5% RH up to above 95% RH by selecting an appropriate polysaccharide composition.

[0209] Figs. 13b and 13c show normalized transmission spectra of single-component MC BOF and MC-alginate composite BOF, respectively, measured in the relative humidity range from 10% to 80%. The humidity sensitivity was studied by coupling the BOF to be studied with commercial optical fibers into a white light source (Ocean Optics DH-2000-BAL, 230-2500 nm balanced deuterium and halogen lamps) and a spectrometer (Avantes AvaSpec ULS2048L, 200-1100 nm). Spectra were measured periodically while ambient humidity was ramped with 1 h steps of 10 %RH increments. The spectra of Figs. 13b-c are from 50 min into each humidity level to allow the humidity controller to stabilize. Single component (MC) fiber shows a more linear response to humidity, while Alg-containing composite fiber has greater transmission changes at higher humidities. Hence, confirming the observations related to Fig. 13a.

[0210] A humidity sensitivity graph per wavelength for single-component MC BOF (“Sensor type I”) and alginate-comprising composite BOF (“Sensor type II”) is shown in Fig. 14. The humidity sensitivity graph has been prepared by taking the humidity dependence data, similar to data shown in Fig. 13, for each wavelength and plotting the fitting slopes per wavelength. While for composite fibers comprising alginate (“Sensor type II") the highest sensitivity range is approximately from 700 to 960 nm and poor performance is observed below 650 nm, for single-component MC BOFs (“Sensor type I”), the highest humidity sensitivity is around 600 nm. Accordingly, the transmission window of a BOF may be adjusted by adjusting the BOF composition.

[0211] Fig. 15 schematically shows a sensing apparatus according to certain embodiments. The sensing apparatus may be used to measure environmental humidity (see also Fig. 6 measurement system, Fig. 17a humidity sensing data and 19 for humidity sensing method). The sensing apparatus 1300 comprises a biopolymeric optical fiber (BOF) as a sensing element 1520. The sensing element 1520 absorbs and / or releases humidity depending on the surrounding humidity. As a consequence, the signal transmission of the sensing element and the intensity of the transmitted signal changes. This results in a measurable change in the BOF’s light transmission. In certain embodiments, the BOF of the sensing element is replaceable. The BOF of the sensing element 1520 may be any BOF herein disclosed. In certain embodiments, the BOF comprises only first polysaccharide. In certain embodiments, the single component BOF is made of alginate, MC, CMC, HPMC, HPC, HEC, agarose, or chitosan. In certain embodiments, the BOF is a composite of a first polysaccharide and a second polysaccharide. In certain embodiments, the BOF is a composite of a first polysaccharide, a second polysaccharide, and a third polysaccharide. In certain embodiments, the BOF comprises substantially 100% (by weight) of the coagulated polysaccharide or polysaccharides based on the total dry mass of the BOF. In certain embodiments, the BOF is renewable. In certain embodiments, the BOF is biodegradable. In certain embodiments, the polysaccharides BOF is non-toxic.

[0212] In certain embodiments, the first polysaccharide, second polysaccharide, and / or third polysaccharide is alginate. In certain embodiments, the first polysaccharide, second polysaccharide, and / or third polysaccharide is water-soluble cellulose derivative. In certain embodiments, the BOF is a composite comprising alginate and water-soluble cellulose derivative. In certain embodiments, the BOF is a composite comprising alginate and MC. In certain embodiments, the BOF is a composite comprising alginate and MC having a first molecular weight and MC having a second molecular weight (wherein the first and second molecular weight are different from each other). In certain embodiments, the cellulose derivative is selected from the group of MC, CMC, HPC, HPMC, and HEC. For instance, MC may be coagulated by ethanol and CMC by ionic coagulation. Aqueous MC and HPMC may also be reversibly gelated by heating. Advantageously, combining heating and ethanol, BOF coagulation and shape-retention may be improved during fiber manufacturing.

[0213] In certain embodiments, first polysaccharide, second polysaccharide, and third polysaccharide each are different polysaccharides. In certain embodiments, at least two of the first polysaccharide, second polysaccharide, and / or third polysaccharide are the same polysaccharide but have different molecular weights. That is, the first polysaccharide, second polysaccharide, and third polysaccharide may differ from each other by at least polysaccharide type, degree of substitution, and / or molecular weight.

[0214] In certain embodiments, the sensing apparatus 1500 comprises a source element 1510. The source element 1510 is configured to provide light to the sensing element 1520. The source element 1510 provides light of certain wavelength or a certain wavelength range or a certain spectrum of light. The source element 1510 is connected to the first end of the sensing element 1520. In certain embodiments, the source element is connected to a control unit 1540 which is configured to control the source element 1510. In certain embodiments, the source element is an LED light source. In certain embodiments, the source element is a laser light source. In certain embodiments, the source element is a white light source. The source element 1510 may comprise a POF configured to transmit light from the light source to the sensing element 1520. In certain embodiments, the source element 1510 comprises a fiber collimator configured to focus the light from the light source to an optical fiber, either to the BOF of the sensing element 1520 directly or to a POF which transmits the light to the sensing element 1520.

[0215] In certain embodiments, the sensing apparatus 1500 comprises an output element 1530. The output element 1530 is connected to the second end of the sensing element 1320. The output element 1530 is also connected to the control unit 1540. The output element 1530 is configured to receive and measure the light transmitted through the sensing element 1520. The output element 1530 may be, for instance, a photodetector, photodiode, power meter or a spectral detector. The output element 1530 transmits the measured signals to the control unit 1540.

[0216] In certain embodiments, the sensing apparatus 1500 comprises a control unit 1540. The control unit 1540 is configured to control the operation of the sensing apparatus 1500 by controlling the source element 1510 and the output element 1530. The control unit 1540 is configured to store the measured data from the output element 1530. The control unit 1540 is configured to analyze and report quantitative values, such as humidity, based on the measured output of the output element 1530 and reference data. The control unit 1540 stores reference data and measurement data. The reference data, aka. standard measurement data may be correlation data showing the attenuation coefficient or transmittance of a BOF of a predetermined composition at certain relative humidity. The reference data may not need to be re-measured at each measurement cycle, but stored correlation data may be used to quantify target measurement data. The reference data may be updated and calibrated at predetermined intervals, e.g., weekly or monthly, or upon replacing the sensing element 1520.

[0217] In certain embodiments, a plurality of sensing apparatuses 1500 are used in combination, to provide data simultaneously from multiple measurement points. Therefore, data may be gathered at several target positions within a larger measurement area, thus allowing area mapping and more accurate and reliable results. In certain embodiments, a control unit 1540 of one sensing apparatus 1500 is configured to control the plurality of sensing apparatuses 1500. In certain embodiments, an external separate control unit is configured to control a plurality of sensing apparatuses 1500. The external separate control unit may be a personal computer or a mobile phone comprising suitable software.

[0218] Fig. 16 schematically shows another sensing apparatus 1500 according to certain embodiments. The sensing apparatus 1500 comprises a BOF as a sensing element 1520. In certain embodiments, the sensing apparatus 1500 is portable.

[0219] The sensing apparatus comprises a source element 1510. The source element 1510 is connected to a first end of the sensing element 1520. The source element 1510 is configured to provide light to the sensing element 1520. In certain embodiments, the source element is an LED light source. In certain embodiments, the source element is a laser light source. In certain embodiments, the source element is a white light source.

[0220] The sensing apparatus 1500 comprises an output element. The output element 1530 is connected to the second end of the sensing element 1520. The output element 1530 is configured to receive and measure the light transmitted through the sensing element 1520.

[0221] The sensing apparatus comprises a processor 1610. The sensing apparatus comprises a memory 1620. The memory comprises program code 1630. The program code 1630 comprises instructions for the sensing apparatus to operate, for instance, to measure humidity. The program code 1630, together with the memory 1620 and the processor 1610, is configured to cause the sensing apparatus to operate, for instance, to perform a humidity measurement. Accordingly, the processor (or at least one processor) 1610 and the memory 1620 comprising the program code 1630 are understood to implement a control unit (or part of a control unit) similar to the preceding control unit 1540.

[0222] The memory 1620 comprises a data storage 1640. The storage is configured to store measured raw data from the output element 1530. The storage is configured to store measurement results analyzed by the output element 1530 and / or the processor 1610. In certain embodiments, the memory comprises a cloud-based data storage 1640. In certain embodiments, the storage 1640 is configured to store the reference data for quantitative humidity determination.

[0223] The sensing apparatus comprises an interaction element 1650. In certain embodiments, the interaction element 1650 comprises user interaction means. The user interaction means may be, for instance, a keyboard, touch screen, or a headset. The interaction element 1650 may further comprise wireless and wired communication means, such as Bluetooth, USB ports, HDMI, and Wi-Fi. In certain embodiments, the sensing apparatus is remotely operable, via the interaction element, by a mobile phone (comprising a suitable control application). Through the interaction element 1650, the user may operate the sensing apparatus 1500. The user may also extract and transmit data from the sensing apparatus 1500, such as measurement results. The sensing apparatus 1500 may be configured to directly communicate with a cloud storage via the interaction element 1650. Reference data and new correlation measurement values may be uploaded to the sensing apparatus 1500 through the interaction element 1650.

[0224] The sensing apparatus 1500 comprises a casing 1660. The casing 1660 protects the sensing apparatus 1500. The casing 1660 is configured to allow the sensing element 1520 to be exposed to the surrounding atmosphere for the measurements. In certain embodiments, the casing 1660 covers and protects the sensing element 1520 when the sensing apparatus 1500 is not in use. In certain embodiments, the casing 1660 comprises a door 1665 (drawn with a dashed line in Fig. 16) to protect the sensing element 1520. The door 1665 may be closed when the sensing apparatus 1500 is not in use and opened to allow measurements. Advantageously, the casing 1660 protects the interior of the sensing apparatus from dirt and mechanical damages. In certain embodiments, the sensing element 1520 is replaceable.

[0225] The sensing apparatus comprises a power source 1670. The power source 1670 provides power to the sensing apparatus 1500. The power source may be, for instance, a Li-ion battery. In certain embodiments, the power source (battery) 1670 is replaceable. Advantageously, battery of a portable sensing apparatus 1500 may be changed in case no charging station is available. In certain embodiments, the power source (battery) 1670 is rechargeable. Advantageously, the sensing apparatus does not need to be constantly connected to an external power source.

[0226] Fig. 17a and 17b show experimental qualitative data of breathing and touch sensor applications, respectively, according to certain embodiments. Note the inverted y-axes. The measurements could be performed by an apparatus like the sensing apparatus 1500, for example.

[0227] In the breathing sensor data of Fig. 17a, breathing onto the fiber results in moisture absorption, reducing transmission and causing increased losses. Quickly after breathing the moisture evaporates and fiber transmission recovers to its initial level, allowing for measuring breaths every two seconds. Advantageously, changes in humidity may be detected in seconds. In the touch sensor data of Fig. 17b, transmission losses increase as the fiber is touched, and immediately recover back to the level before touching after pressure is relieved. Advantageously, BOFs react and recover quickly to environmental changes thus providing efficient sensors. The BOFs are not degraded in the measurement.

[0228] METHODS

[0229] Fig. 18 shows a flow chart of a method for manufacturing a BOF according to certain embodiments. For instance, a spinning apparatus 300 may be used to manufacture the BOF. The BOF may be implemented, for example, as the sensing element of sensing apparatus 1500 according to Figs. 15-16. The details discussed earlier with respect to the other embodiments are equally applicable in the method shown in Fig. 18, and vice versa.

[0230] 1810. Selecting biopolymer raw material based on the optical properties of a BOF manufactured from said raw material. In certain embodiments, only first polysaccharide is selected as raw material. In certain embodiments, a mixture of first polysaccharide and second polysaccharide is selected. In certain embodiments, a third polysaccharide is further selected. In certain embodiments, the first, second, and third polysaccharide are selected from a group of alginate, chitosan, agarose, and water-soluble cellulose derivatives. In certain embodiments, the cellulose derivative(s) is / are selected from the group of MC, CMC, HPC, HPMC, and HEC. The selected polysaccharides of a mixture differ from each other by polysaccharide type and / or molecular weight. In certain embodiments, at least two of the first, second, and third polysaccharide are the same polysaccharide, but each has a different molecular weight.

[0231] In certain embodiments, a polysaccharide is selected to provide a single component BOF with predetermined optical properties. In certain embodiments, a polysaccharide mixture is selected to provide a BOF with predetermined optical properties. In certain embodiments, selecting comprises selecting the polysaccharide raw material to result in a BOF with a predetermined transmission window. In certain embodiments, a polysaccharide is selected to provide a single component BOF with predetermined optical and mechanical properties. In certain embodiments, the polysaccharide mixture is selected to provide a BOF with predetermined optical and mechanical properties. In certain embodiments, polysaccharide raw material is selected to provide a BOF with predetermined humidity sensitivity properties, such as high sensitivity at high humidity conditions (> 50% RH). In certain embodiments, polysaccharide raw material is selected to provide a BOF with high humidity sensitivity at a certain wavelength or wavelength range. In certain embodiments, the polysaccharides are selected to provide highest humidity sensitivity at a pre-determined wavelength or wavelength range, for instance, above 700 nm, or at 900 nm. The ratio of polysaccharides in a mixture may be adjusted to achieve, for example, a desired transmission spectrum. It is generally not obvious to combine different materials together to obtain an optical fiber, as it typically reduces transmission properties due to, for example, inhomogeneities or refractive index incompatibilities. However, BOFs prepared from polysaccharide mixtures herein described enable surprising synergistic effects in both optical and mechanical properties.

[0232] In certain embodiments, the polysaccharides are selected such that transmission at predetermined wavelength range is maximized. In certain embodiments, the wavelength range is 550 - 650 nm, above 650 - 900 nm, or above 900 nm. For example, to enable better transmission closer to the blue light, more MC is preferably included instead of alginate. In certain embodiments, humidity sensing accuracy at predetermined humidity conditions is maximized. In certain embodiments, the humidity conditions are the relative humidity range 5% - 40%, 30% - 60 %, or above 50%. Preferably, composite fibers comprising alginate are preferred for humidity measurements at the higher humidity conditions. In certain embodiments, maximum strain is pursued. In certain embodiments, the maximum strain is more than 30%, more than 35%, or more than 40%. In certain embodiments, a predetermined maximum stress is pursued. Preferably, MC or a mixture of MCs with different MWs are selected and coagulated with ethanol to provide high maximum strain. On the other hand, alginate and ionic crosslinking are preferred for optimizing elastic modulus and high strength. In certain embodiments, polysaccharides suitable for ionic coagulation are selected.

[0233] 1820. Preparing a spinning dope from the selected polysaccharide raw material. To prepare the spinning dope, the polysaccharides are mixed and dissolved in ultrapure water under stirring. In certain embodiments, the spinning dope is degassed. Details of spinning dope preparation already discussed in the foregoing apply also here.

[0234] 1830: Continuously extruding the spinning dope to a coagulation bath to prepare a fiber. In certain embodiments, wet-spinning is used. In certain embodiments, dry-jet spinning is used. The coagulation may be implemented as extrusion into ethanol or by ionic coagulation. In certain embodiments, the extruded spinning dope is coagulated simultaneously by extrusion in ethanol bath and ionic cross-linking (in a sense by “double coagulation"). Advantageously, coagulation efficacy may be improved.

[0235] 1840. Collecting the extruded fiber from the coagulation bath. 1845. Optionally, rinsing the fiber.

[0236] 1850. Drying the fiber. After drying, the BOF comprises essentially only the selected biopolymer raw material in the form of a fiber. Thus, the biopolymer-content of a BOF is approximately 100% (ionic residues, ethanol residues, and some moisture may be present).

[0237] 1860. Optionally, cutting the fiber to pieces of desired length. For instance, 3 cm, 5 cm, or 10 cm pieces may be used in a humidity measurement system. In certain embodiments, the fibers are cut before drying.

[0238] 1860. Optionally, coating the fiber. In certain embodiments, coating is performed by dipcoating, drop coating, spray-coating, or vapor deposition. In certain embodiments, a protective layer is provided to protect the BOF against mechanical abrasion.

[0239] Fig. 19 shows a flow chart of a method for measuring humidity with a sensing apparatus according to certain embodiments.

[0240] 1910. Providing a sensing apparatus comprising a BOF as a sensing element. The measurement system may be, for instance, the sensing system 1500 of Fig. 15 or Fig. 16. The fiber may have been manufactured by using spinning apparatus 300 of Fig. 3 according to the method of Fig. 18. In certain embodiments, providing the sensing apparatus comprising a BOF as a sensing element, comprises selecting the BOF according to the humidity sensitivity properties of the BOF. For example, for measurements in high relative humidity conditions (> 50% RH) composite BOFs comprising alginate may be preferred, whereas for low humidity conditions (<50% RH) single component MC BOFs may be more preferable. Further, for example, depending on the available light source, it may be desirable to use a BOF composition that has high humidity sensitivity at certain wavelength or wavelength range.

[0241] 1920. Measuring transmittance of the biopolymeric optical fiber at a selected wavelength(s) at standard conditions. This way calibration data may be provided. Correlation of humidity to transmittance (or attenuation) of the BOF is acquired. For instance, transmission spectra at various humidity conditions are measured at predetermined wavelengths to establish a correlation between relative humidity and BOF transmittance at the predetermined wavelengths. Preferably, the reference data of a BOF is composition or material specific. That is, BOFs having the same composition may use the same refence data. Advantageously, the reference data may not need to be measured separately for each individual BOF. This reference data is used to quantify later measurements by converting the measured transmittance (or determined attenuation coefficient) to a quantitative humidity value. Step 1920 may not need to be performed before each measurement. In certain embodiments, step 1920 is performed at predetermined intervals to calibrate the reference data and the sensing apparatus. The reference data may be stored in or uploaded to a memory of the sensing apparatus. The reference data enables quantifying the humidity based on the measured light transmission.

[0242] 1930. Measuring transmittance of the biopolymeric optical fiber at the selected wavelength(s) at target conditions. Data from the desired location is acquired.

[0243] 1940. Obtaining humidity value based on the measurements at standard and target conditions. By correlating the target measurement results with the reference data, the humidity value at the target location can be determined. The humidity may be reported for instance, as a number, as a graph, or both.

[0244] Without limiting the scope and interpretation of the patent claims, certain technical effects of one or more of the example embodiments disclosed herein are listed in the following. A technical effect is providing optical fibers from environmentally friendly sources. Further technical benefit is providing simple and energy efficient manufacturing method for biopolymeric optical fibers. Still further benefit is providing BOFs whose optical and mechanical properties may be adjusted by the selection of polysaccharides, their ratios, and processing. Yet another benefit is providing direct and fast humidity sensing.

[0245] Various embodiments have been presented. It should be appreciated that in this document, words comprise, include, and contain are each used as open-ended expressions with no intended exclusivity.

[0246] The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented in the foregoing, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention.

[0247] Furthermore, some of the features of the afore-disclosed example embodiments may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

CLAIMS1 . An apparatus for quantitative measuring of humidity, comprising: a biopolymeric optical fiber as a sensing element.

2. The apparatus of claim 1 , wherein the biopolymeric optical fiber is a single component biopolymeric optical fiber, wherein the single component is a polysaccharide.

3. The apparatus of claim 1 , wherein the biopolymeric optical fiber is a composite biopolymeric optical fiber comprising at least two polysaccharides.

4. The apparatus of any preceding claim, wherein the biopolymeric optical fiber is replaceable.

5. The apparatus of any preceding claim, wherein the biopolymeric optical fiber is biodegradable.

6. The apparatus of any preceding claim comprising a casing.

7. The apparatus of any preceding claim, wherein the apparatus is portable.

8. The apparatus of any preceding claim, comprising a replaceable power source.

9. The apparatus of any preceding claim, wherein the apparatus is remotely operable.

10. The apparatus of any preceding claim, configured to measure transmittance of the biopolymeric optical fiber at selected wavelength(s) at target conditions to obtain target measurement data, the apparatus comprising: a control unit configured to control the apparatus to obtain quantitative humidity value(s) by comparing the target measurement data to reference data obtained by measuring transmittance of the biopolymeric optical fiber at the selected wavelength(s) at standard conditions.

11. The apparatus of claim 10, comprising a source element to provide the sensing element with light.

12. The apparatus of claim 10 or 11 , comprising an output element to measure said transmittance(s).

13. The apparatus of any preceding claim, comprising a plurality of sensing apparatuses configured to be used in combination to provide data simultaneously from multiple measurement points.

14. The apparatus of claim 13, comprising a control unit configured to control the plurality of sensing apparatuses.

15. A method for quantitatively measuring humidity, the method comprising: providing a sensing apparatus comprising a biopolymeric optical fiber as a sensing element; measuring transmittance of the biopolymeric optical fiber at selected wavelength(s) at standard conditions to obtain reference data; measuring transmittance of the biopolymeric optical fiber at the selected wavelength(s) at target conditions to obtain target measurement data; and obtaining quantitative humidity value by comparing the target measurement data to the reference data.

16. The method of claim 15, wherein providing the sensing apparatus comprising a biopolymeric optical fiber as a sensing element, further comprises selecting the biopolymeric optical fiber according to the humidity sensitivity properties of the biopolymeric optical fiber.

17. A biopolymeric optical fiber for sensing applications, wherein the biopolymeric optical fiber is a composite fiber comprising at least two polysaccharides.

18. The biopolymeric optical fiber of claim 17, wherein the polysaccharides differ from each other by at least polysaccharide type, degree of substitution, or molecular weight.

19. The composite biopolymeric optical fiber of any one of the claims 17-18, wherein the polysaccharides are selected from a group comprising alginate, chitosan, agarose, and water-soluble cellulose derivatives.

20. The composite biopolymeric optical fiber of claim 19, wherein the water-soluble cellulose derivatives include methylcellulose, carboxymethylcellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, and hydroxyethyl cellulose.21 . The composite biopolymeric optical fiber of any one of the claims 17-20, wherein the alginate content of the biopolymeric optical fiber is at least 1 .0 % (by weight) of the total dry mass of the biopolymeric optical fiber.

22. The composite biopolymeric optical fiber of any one of the claims 17-21 , wherein the biopolymeric optical fiber is a composite of the first polysaccharide and the second polysaccharide, the biopolymeric optical fiber comprising 5-95% (by weight) of the first polysaccharide, and 5-95% (by weight) of the second polysaccharide of the total dry mass of the biopolymeric optical fiber.

23. The composite biopolymeric optical fiber of any one of the claims 17-22 wherein the biopolymeric optical fiber is a composite of the first polysaccharide, the second polysaccharide and the third polysaccharide, comprising 10-50% (by weight) of the first polysaccharide, 10-50% (by weight) of the second polysaccharide, and 10-50% (by weight) of the third polysaccharide of the total dry mass of the biopolymeric optical fiber.

24. The composite biopolymeric optical fiber of any one of the claims 17-23, wherein the composite biopolymeric optical fiber is manufactured from an aqueous spinning dope.

25. The composite biopolymeric optical fiber of claim 24, wherein the total polysaccharide content of the spinning dope is 0.5-30.0% (w / v).

26. The composite biopolymeric optical fiber of any one of the claims 17-25 wherein the composite biopolymeric optical fiber is manufactured by wet-spinning or dry-jet spinning.

27. The composite biopolymeric optical fiber of any one of the claims 17-26, comprising a coating or a cladding.

28. A method for manufacturing a biopolymeric optical fiber, the method comprising: selecting a polysaccharide raw material based on optical properties of a biopolymeric optical fiber manufactured from said raw material; preparing a spinning dope from the selected raw material; continuously extruding the spinning dope to a coagulation bath to prepare a fiber; collecting the extruded fiber from the coagulation bath; and drying the fiber.

29. The method of claim 28, wherein selecting the polysaccharide raw material comprises selecting at least one of first polysaccharide, second polysaccharide, and third polysaccharide.

30. The method of claim 28 or 29, wherein the first polysaccharide, second polysaccharide, and third polysaccharide differ from each other by at least polymer type, degree of substitution or molecular weight.31 . The method of any one of the claims 28-30, wherein the first polysaccharide, second polysaccharide, and third polysaccharide are selected from a group comprising alginate, chitosan, agarose, and water-soluble cellulose derivatives.

32. The method of any one of the claims 28-31 , wherein selecting the polysaccharide raw material comprises selecting the polysaccharide raw material to obtain a biopolymeric optical fiber with a predetermined humidity sensitivity properties.

33. The method of any one of the claims 28-32, wherein preparing the spinning dope comprises dissolving the biopolymer raw material in water.

34. The method of claim 33, wherein the total polysaccharide content of the spinning dope is 0.5-30.0% (w / v).

35. The method of any one of the claims 28-34, wherein the extrusion step comprises wet spinning or dry-jet spinning.

36. The method according to any one of the claims 28-35, wherein the extruded spinning dope is coagulated simultaneously by extrusion in ethanol and by ionic cross-linking.

37. The method of any one of the claims 28-36, further comprising rinsing the fiber after coagulation.

38. The method of any one of the claims 28-37, further comprising cutting the fiber to a predetermined length.

39. The method of any one of the claims 28-38, further comprising coating the fiber.

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