A biodegradable superabsorbent polymer

Abstract

The present disclosure relates to a superabsorbent polymer-based nanocomposite for use in controlled irrigation in agriculture, comprising a polymer of one or more water-soluble and ionizable monomers graft copolymerized on one or more biopolymers and / or copolymerized with one or more biodegradable polymers. A combined amount of the one or more biopolymers and the one or more biodegradable polymers is within a range between 5 wt.% and 50 wt.% with regard to a dry weight of the nanocomposite. The present disclosure further relates to a method for obtaining such nanocomposites.

Description

[0001] A BIODEGRADABLE SUPERABSORBENT POLYMER

[0002] Technical Field

[0003] The present disclosure relates to superabsorbent polymers. In particular, the present disclosure relates to a biodegradable superabsorbent polymer nanocomposite as a water and nutrient reservoir for plants.

[0004] Background

[0005] In 2023, several major agricultural basins in Turkiye experienced droughts. Marmara, Southern Aegea, Mediterranean, and Eastern Anatolia regions all received less rain than respective historical averages and the previous years. The gravity of the situation was particularly felt in the large and high-value-added Cukurova region, which experienced severe droughts.

[0006] The 2023 regional map of farming suitability based on water irrigation in Turkiye highlights significant disparities (Topcu, S., Kibaroglu, A., Kadirbeyoglu, Z. (2019). Turkey. In: Molle, F., Sanchis-lbor, C., Avella-Reus, L. (eds) Irrigation in the Mediterranean. Global Issues in Water Policy, vol 22. Springer, Cham, doi: 10.1007 / 978-3-030-03698-0_7). Northern Europe and Northern Asia exhibit high suitability due to abundant water resources, while much of Africa, the Middle East, and South Asia face severe irrigation challenges due to water scarcity (https: / / www.wri.org / insights / highest-water-stressed-countries , accessed on July 12, 2024). This underscores the critical need for innovative water management and irrigation solutions in less suitable regions to enhance agricultural productivity.

[0007] Superabsorbent polymers are employed in various areas including controlled release of water. WO2021 / 167577 relates to production of a superabsorbent polymer structure.

[0008] In the literature, there are studies that report composite SAPs incorporating fertilizers. Various micro- and macronutrients can be combined. However, mostly the utilization of macronutrients such as urea, NPK, and DAP is reported in several studies. Fertilizers are incorporated in SAPs at varying doses throughout these studies, although most papers only report one or a few similar fertilizer:SAP ratios. Water absorption performances of such composite SAPs are generally inferior compared to commercial SAPs. Globally, the average fertilizer application dose per hectare is reported as 140 kg, of which urea and NPK are the major constituents. In comparison, SAP application is suggested to be between 15-45 kg / ha. The highest fertilizer incorporation in SAP reported in the literature is approximately 60 wt%, which significantly deteriorates water absorption and renders them impractical for agricultural applications.

[0009] On the other hand, calcium and zinc fertilizers are applied at much lower doses compared to urea and NPK. With a single application of fertilizer incorporating composite SAPs, the majority of the calcium and zinc needs of the soil can be met.

[0010] Accordingly, the present disclosure is directed to provide an improved superabsorbent polymer nanocomposite design.

[0011] Summary

[0012] The primary object of the present disclosure is to overcome the above-mentioned shortcomings of the prior art. Another object of the present disclosure is to propose a superabsorbent polymer nanostructure (SAP) that provides an enhanced extent of swelling in comparison with those in prior art; that is, a SAP that swells up to 2000 times of its own (that is, dry) weight.

[0013] A further object of the present disclosure is to propose a SAP that provides sustained release of 2+ valenced micro- and / or macro- nutrients. An even further object of the present disclosure is to propose a SAP that fully releases its nutrient content within a short period such as four days.

[0014] A further object of the present disclosure is to propose a SAP that provides sustained or controlled release of water for a prolonged period such as fifty days or longer. An even further object of the present disclosure is to propose a SAP that shows an enhanced extent of biodegradability.

[0015] The present disclosure achieves this object with the features that constitute the appended independent claims.

[0016] The present disclosure proposes a superabsorbent polymer-based nanocomposite for use in controlled irrigation in agriculture. The nanocomposite comprises a polymer of one or more water-soluble and ionizable monomers that are graft copolymerized on one or more biopolymers and / or copolymerized with one or more biodegradable polymers. A combined amount of the one or more biopolymers and the one or more biodegradable polymers is within a range between 5 wt.% and 50 wt.% with regard to a dry weight of the nanocomposite. Here, the term 'dry weight' refers to the weight of the nanocomposite before swelling with water for provision of sustained release, such as when in use for agricultural irrigation.

[0017] In a possible embodiment, the combined amount of the one or more biopolymers and the one or more biodegradable polymers can be within a range between 10 wt.% and 45 wt.% with regard to the dry weight of the nanocomposite. This provides a great extent of biodegradability without compromising a prolonged sustained release of water.

[0018] In a possible embodiment, the one or more water-soluble and ionizable monomers can be selected from vinylic, acrylic and allylic monomers. In a further possible embodiment, the one or more water-soluble and ionizable monomers are selected from acrylic acid, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

[0019] A possible embodiment can be arranged for providing one or more divalent cations selected from calcium and zinc ions when swollen with water, thereby providing sustained release of these divalent cations as agricultural nutrient when in use.

[0020] In a possible embodiment, the one or more biodegradable polymers can be selected from polyethylene glycol diacrylate, polyethylene glycol and polylactic acid. In a further possible embodiment, the one or more biodegradable polymers can be selected from polyethylene glycol diacrylate and polyethylene glycol.

[0021] In a possible embodiment, the one or more biopolymers can be selected from cellulose derivatives, chitin, chitosan and gelatin. In a further possible embodiment, the one or more biopolymers can be selected from cellulose derivatives. In an even further possible embodiment, the one or more biopolymers can comprise carboxymethyl cellulose. An even further possible embodiment comprises carboxymethyl cellulose as the biopolymer.

[0022] Accordingly, the present disclosure proposes a method for production of the superabsorbent polymer-based nanocomposite for use in controlled irrigation in agriculture. The method comprises graft copolymerization of one or more water-soluble and ionizable monomers on one or more biopolymers and / or copolymerization of the one or more water-soluble and ionizable monomers on one or more biodegradable polymers. The method further comprises the arrangement of a combined amount of the one or more biopolymers and the one or more biodegradable polymers to be within a range between 5 wt.% and 50 wt.% with regard to a dry weight of the nanocomposite.

[0023] The method can comprise the arrangement of the combined amount of the one or more biopolymers and the one or more biodegradable polymers to be within a range between 10 wt.% and 45 wt.% with regard to the dry weight of the nanocomposite.

[0024] The one or more water-soluble and ionizable monomers can be selected from from vinylic, acrylic and allylic monomers. In a possible implementation of the method comprises the selection of the one or more water-soluble and ionizable monomers from from acrylic acid, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

[0025] The method can comprise the arrangement of the nanocomposite for provision of one or more divalent cations selected from calcium and zinc ions when swollen with water. So, sustained release of calcium and / or zinc ions from a swollen state of the resulting SAP is rendered available.

[0026] In a possible implementation of the method, the one or more biodegradable polymers can be selected from polyethylene glycol diacrylate, polyethylene glycol and polylactic acid. In a further possible implementation of the method, the one or more biodegradable polymers can be selected from polyethylene glycol diacrylate and polyethylene glycol.

[0027] In a possible implementation of the method, the one or more biopolymers can be selected from from cellulose derivatives, chitin, chitosan and gelatin. The one or more biopolymers can be selected from cellulose derivatives. The method can comprise selection of carboxymethyl cellulose as the biopolymer.

[0028] The method can comprise the use of one or more coupling agents selected from vinyl alkoxysilanes, bis-acrylamides and dihydrazides, as (in-situ) cross-linking agent. In a possible implementation of the method, the one or more coupling agents can be selected from vinyltriethoxysilane, vinyltrimethoxy silane and tri(2-methoxyethoxy)vinylsilane), methylene bisacrylamide and adipic acid dihydrazide. The one or more cross-linking agents provide enhanced water adsorbance and impedance in release of water. Detailed Description

[0029] The present disclosure proposes a superabsorbent polymer-based nanocomposite structure for use in controlled irrigation in agriculture, and a method for obtaining the same. Within the context of the present disclosure, the superabsorbent polymer-based nanocomposite structure can be also referred to as superabsorbent polymer, nanocomposite or SAP.

[0030] The method includes the use of one or more water-soluble and ionizable monomers in production of the SAP. The one or more monomers can be selected from vinylic, allylic and acrylic monomers. In an embodiment, the one or more monomers can be selected from acrylic acid (abbreviated as AA), acrylamide (abbreviated as AM) and 2-acrylamido-2- methylpropanesulfonic acid (AMPS).

[0031] The method can be considered to further include the use of one or more vinyl alkoxysilanes as coupling agent or cross-linking agent.

[0032] The method can further include the use of one or more divalent ions when preparing the SAP. In an embodiment, the divalent ions can be selected from calcium (Ca2+) and zinc (Zn2+). The one or more divalent ions serve as micro / macro nutrients.

[0033] The method further includes graft copolymerization of the one or more monomers on one or more natural polymers (in other words, biopolymers); and / or copolymerization of the one or more monomers on one or more biodegradable polymers. The graft copolymerization on the biopolymer(s) and / or copolymerization on the biodegradable polymer(s) provides an enhanced biodegradability. It is hereby sought to enhance the biodegradability without compromising water absorbency.

[0034] The one or more biopolymers can be selected from one or more cellulose derivatives, chitin, chitosan and gelatin. In an embodiment, the one or more biopolymers comprises one or more cellulose derivatives. In an embodiment, the one or more cellulose derivative is carboxymethyl cellulose (abbreviated as CMC).

[0035] In an embodiment, the amount of natural biopolymers is within the range between 5 wt.% and 50 wt.%, with regard to a total weight of the SAP. This measure provides an enhanced biodegradability along with water absorbency. In an embodiment, the amount of natural biopolymers is within the range between 10 wt.% and 45 wt.%, with regard to a total weight of the SAP. This range provides an even This measure provides an even enhanced biodegradability along with a high extent of water absorbency. The higher end of this range, that is, around 40 wt.% (e.g., 35-45 wt.%) biopolymers with regard to the total weight of the SAP provides a sweetspot in terms of complete biodegradability and high water absorption ability.

[0036] In an embodiment, the one or more biodegradable polymers can be selected from polyethylene glycol diacrylate, polyethylene glycol and polylactic acid. In an embodiment, the one or more biodegradable polymers can be selected from polyethylene glycol diacrylate and polyethylene glycol.

[0037] EXAMPLES

[0038] The following examples are provided for better understanding of the present disclosure without intention to delimit the scope of protection that is defined by the appended claims.

[0039] EXAMPLE 1: Materials

[0040] As exemplary monomers, commercially available acrylic acid (CAS 79-10-7), acrylamide (CAS 79- 06-1) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, CAS 15214-89-8) were used. Sodium ions can displace other mineral nutrients in the soil, which leads to nutrient deficiencies. So, sodium is not desired in farming. On the other hand, potassium is one of the essential macronutrients. Therefore, to make the SAP formulation more suited for agricultural applications, potassium hydroxide was preferred as a neutralizing agent, instead of sodium hydroxide. Reagent grade potassium hydroxide (CAS 1310-58-3) is used. For provision of an exemplary vinyl alkoxysilane as coupling agent (or, cross-linking agent) commercially available vinyltrimethoxysilane, (VTMS, CAS 2768-02-7) was used. As an initiator, commercially available ammonium persulfate (APS), ACS reagent, (CAS 7727-54-0) was used. As an exemplary biopolymer, carboxymethyl cellulose (CMC, CAS 9004-32-4) was used.

[0041] All chemicals were used without necessitating further purification. Cellulase enzymes used in this experimental work is commercially available.

[0042] EXAMPLE-2: Synthesis of the SAPs

[0043] A copolymer of AA, AM and AMPS was synthesized through free-radical polymerization. To prepare the polymerization solution, first, the monomers were mixed in deionized (DI) water. Acrylamide and AMPS were weighed and transferred to a beaker. DI water was added to obtain a reaction medium, and monomers were dissolved by magnetic stirring of the reaction medium. Next, acrylic acid was transferred into the reaction medium. Next, the pH of the reaction medium was brought to between 6-7 by addition of potassium hydroxide. Subsequently, as an exemplary biopolymer, carboxymethyl cellulose (CMC) was added into the reaction medium. This addition is performed very slowly and under constant stirring, in order to prevent a possible coagulation. Then, the pH of the reaction medium was adjusted again to between 7-8. The reaction medium was then transferred into a reactor.

[0044] After purging with an inert gas (e.g., nitrogen, for ca.10 minutes), vinyltrimethoxysilane (VTMS) was added as an exemplary cross-linking agent. The purging was continued (e.g., for five more minutes), and then ammonium persulfate (APS), was added as an exemplary initiator. To minimize material loss, both VTMS and APS were mixed with (e.g., 2 mL of) DI water and added to the reactor (e.g., using a syringe). Upon APS addition, the temperature was set to a reaction temperature (e.g., 75 °C, using an oil bath). Purging was continued (e.g., for another five minutes), and the reaction was allowed to proceed for a reaction time (e.g., two hours, under constant magnetic stirring). Upon completion of the reaction time, the temperature was allowed to drop (e.g., by shutting down the heating and the bringing the reactor out of the oil bath).

[0045] The resulting polymer solution was then subjected to a cross-linking along with drying (e.g., by pouring into a rectangular Teflon mold and drying in a drying oven, at 70 °C, for 18 hours, where further crosslinking takes place).

[0046] Because of the fact that one of the objects of the present disclosure can be considered as developing Calcium- and / or Zinc-SAP composites; after the polymerization reaction was complete, suitable fertilizers (e.g., that include salts of calcium and / or zinc) were mixed with the polymer solution and dried together. So, the resulting SAPs are arranged for provision of one or more divalent cations selected from calcium and zinc ions when swollen with water.

[0047] Hence, possible embodiments of the superabsorbent polymer-based nanocomposites were obtained as the products.

[0048] The dried products are observed to be brittle. The products were broken by hand and placed in closed falcon tubes, to prevent any moisture absorption. Only the CMC and solvent quantities were changed throughout different formulations. This was done to deduce the effect of increasing only the CMC content, on the physical properties and performance of SAPs. The CMC ratios to be tested were selected as 5, 10, 20, 30, 40, 50, and 60 wt% of resulting (dry) SAP.

[0049] A fully synthetic (that is, pure) SAP without biopolymer (that is, out of the intended scope of patent protection), was also synthesized to act as the reference, or control.

[0050] EXAMPLE-3: Morphological remarks

[0051] The morphological properties of the SAPs were evaluated through Scanning Electron Microscopy (SEM). Since the aim was to inspect the topography of the samples' surface, the CMC-SAPs were viewed by using secondary electron detection.

[0052] CMC mostly has a fibrous structure. The diameter of most fibers approximately ranges from 10 to 30 micrometers.

[0053] On the other hand, pure SAP (that is, without any fillers, biopolymer or biodegradable polymer), has a very smooth cross-sectional surface, as expected. Only small surface cracks can be observed, due to fractures. With increasing incorporation of CMC in the SAP structure, we start to see some fiber-like fillers in the matrix.

[0054] At 5 wt% CMC, no dramatic difference was observed when compared to the pure SAP sample. In cross-sectional images, CMC particles can be observed along the edges. There are also few clusters of CMC fibers penetrating through the surface in the middle of the SAP. However, other than these regions, the surface was very smooth, similar to pure SAP.

[0055] As the CMC content is increased to 10 wt.%, a significant increase in the roughness of the outer surface is observed. However, the CMC fibers were still neither widespread nor clearly visible. When the CMC ratio is increased to 20 wt.%, more CMC fibres were observed throughout the entire cross-sectional surface. As the CMC ratio is further increased to 30 wt.%, more fillers were observed to penetrate through the cross-sectional surface, in comparison with 20 wt.% of CMC. However, the instances of CMC fillers present on the outer surface were significantly less than one would expect from a material containing 30 wt.% CMC. Also, the overall roughness of the outer surface did not seem to increase noticeably. As the CMC ratio reached 40 wt.%, total instances of CMC fillers on the outer surface did not significantly increase. However, the cross-sectional surface appeared to be rougher, overall. Yet, the appearance of the SAP was highly uniform, despite a high ratio of CMC fillers.

[0056] The cross-sectional surface of the SAP with 50 wt.% CMC displays noticeably more occurrences of fillers when compared to SAPs with lower contents of CMC. Also, the overall appearance of the outer surface was rougher. Yet, the appearance of the SAP was highly homogeneous, despite a very high concentration of the CMC fillers. At 60 wt.% CMC, highest extent of instances of CMC fillers were observable on the outer surface, and the cross-sectional surface appeared to be rougher than all the other samples. However, the surface still appears to be notably coherent, especially considering the fact that 60 wt% of this material is made up of CMC.

[0057] The fact that we observe a highly coherent or homogeneous cross-sectional surface throughout all CMC-SAP samples, suggests that the incorporation of CMC as biopolymer in the nanocomposite was successful during the syntheses.

[0058] EXAMPLE-4: Remarks on the superabsorbent polymer nanocomposites prepared for the present experiments

[0059] The Table-1 below shows qualitative evaluation of water absorption ability and quantitative information on biodegradation for various superabsorbent polymer nanocomposites. The SAPs shown in Table-1 vary with regard to one another in their biopolymer content (here: CMC) only. The biopolymer contents are given in CMC wt.% with regard to a total weight of the respective (dried) SAP.

[0060] EXAMPLE-5: Remarks on water absorption abilities

[0061] Water absorption ability (g / g) is calculated by dividing the difference between a temporary weight (Wt) of swollen SAP and the initial weight (Wi) thereof before swelling, to said initial weight (Wi). Thus, the water absorption ability is equal to (Wt-Wi) / Wi.

[0062] The qualitative evaluations of water absorption abilities (shortly: water absorption) for samples #1 to #5 are compared with those for the samples #6 and #7. Comparative samples #6 and #7 show only a weak and short-term water absorption. On the other hand, water absorption achieved by all of the samples #1 to #5 are highly acceptable for time periods of up to 90 days.

[0063] Referring to the water absorption behavior difference between sample #5 and sample #6, it is contemplated that a biopolymer (e.g., CMC) content of 45 wt.% with regard to total weight of the respective SAP will show an enhanced long-term water absorption when compared to sample #6.

[0064] For sample #1 to sample #4, water absorption is monitored for 180 days.

[0065] EXAMPLE-6: Remarks on biodegradabilities

[0066] Sample #5 shows complete biodegradation within 5 days. Samples #3 and #4 show an almost complete extent of biodegradation at the end of 5 days; and it is contemplated that complete biodegradation can be achieved within a short term (that is, even at the end of several further days). It is contemplated that samples #1 and #2 will also provide a complete or at least very advanced extent of biodegradation in short term.

[0067] To mimic the biodegradation-related microbial activity in soil, cellulase enzymes were used to degrade CMC incorporating SAPs. To assess the cellulase degradation of CMC-based SAPs, a modified version of the method described in the article of Fujita et. al. was used (Fujita, S.; Tazawa, T.; Kono, H. Preparation and Enzyme Degradability of Spherical and Water-Absorbent Gels from Sodium Carboxymethyl Cellulose. Gels 2022, 8 (5), 321. https: / / doi.org / 10.3390 / gels8050321). To dissolve the cellulase enzyme and contain the SAPs, a buffer solution was prepared. For this experiment, a 50 mM sodium acetate buffer was prepared, and its pH was brought to approximately 5.25 by the addition of acetic acid. Later, this solution was transferred to a glass container, which was sterilized in an autoclave at 121 °C for 20 minutes. Biodegradation tests were carried out in 15 mL, sterilized falcon tubes. In each tube 9.8 mL of buffer solution and 0.2 mL of cellulase enzyme were added, which translates to 2% v / v enzyme. For each test, approximately 0.2 grams of SAP was used.

[0068] Measurements were taken after 1 day, 2 days, 3 days, and 5 days. All temporal biodegradation tests were performed in triplicates. Falcon tubes containing each respective SAP and enzyme were shaken constantly at 150 rpm in a heated incubator. The temperature was set at 50 °C for the complete duration of the test, to activate the cellulase enzyme.

[0069] At the end of the enzymatic biodegradation tests, buffer solutions containing the SAP and the enzyme were filtered using a vacuum filter with a 200-mesh nylon filter, corresponding to a pore size of 75 microns. Therefore, SAPs with a size of more than 75 microns were considered in the final weight, whereas smaller SAP particles were considered degraded. Next, the SAP that stayed on the nylon filter was put back into their respective falcon tubes.

[0070] After the filtration step was complete, all the test tubes containing the filtered SAPs were frozen at -80 °C for 4 hours and freeze-dried for 3 days. Since 15 mL falcon tubes have very small openings, and the depth of the SAP inside the tubes is very high, it would have taken a very long time to dry these samples in a drying oven. Therefore, freeze-drying method was preferred. The test tubes were covered with Parafilm to prevent sample discharge due to high vacuum. However, 4-5 holes were opened at the top of the tubes, with a needle, to allow water vapor to be released easily.

[0071] Although it may not be completely straightforward to convert the degradation time in enzyme containing buffer solution to the expected degradation time in soil, determining the correlation between the cellulose content of the SAPs and their degradation kinetics is the sought-after outcome from this test.

[0072] Samples #6 and #7 are outside the intended scope of protection merely because of containing 50 wt.% or more of biopolymer (here: CMC) with regard to total weights of the respective SAPs. On the other hand, all of the samples #1 to #5 contain less than 50 wt.% of biopolymer (here: CMC) with regard to total weights of the respective SAPss, thereby being within the intended scope of protection.

[0073] So, all of the samples #1 to #5 within the scope of the present disclosure are biodegradable. The Table-1 also implies that biopolymer (e.g., CMC) contents that are higher than that of the sample #5 (that is, values greater than 40 wt.% and up to 50 wt.%) would inherently show an even quicker biodegradation.

Claims

Claims1. A superabsorbent polymer-based nanocomposite for use in controlled irrigation in agriculture, comprising a polymer of one or more water-soluble and ionizable monomers graft copolymerized on one or more biopolymers and / or copolymerized with one or more biodegradable polymers; a combined amount of the one or more biopolymers and the one or more biodegradable polymers being within a range between 5 wt.% and 50 wt.% with regard to a dry weight of the nanocomposite.

2. The nanocomposite according to claim 1; wherein the combined amount of the one or more biopolymers and the one or more biodegradable polymers is within a range between 10 wt.% and 45 wt.% with regard to the dry weight of the nanocomposite.

3. The nanocomposite according to any of claims 1 or 2; wherein the one or more water- soluble and ionizable monomers are selected from vinylic, acrylic and allylic monomers.

4. The nanocomposite according to claim 3; wherein the one or more water-soluble and ionizable monomers are selected from acrylic acid, acrylamide and 2-acrylamido-2- methylpropanesulfonic acid.

5. The nanocomposite according to any of claims 1 to 4; arranged for providing one or more divalent cations selected from calcium and zinc ions when swollen with water.

6. The nanocomposite according to any of claims 1 to 5; wherein the one or more biodegradable polymers are selected from polyethylene glycol diacrylate, polyethylene glycol and polylactic acid.

7. The nanocomposite according to claim 6; wherein the one or more biodegradable polymers are selected from polyethylene glycol diacrylate and polyethylene glycol.

8. The nanocomposite according to any of claims 1 to 7; wherein the one or more biopolymers are selected from cellulose derivatives, chitin, chitosan and gelatin.

9. The nanocomposite according to any of claims 1 to 8; wherein the one or more biopolymers are selected from cellulose derivatives.

10. The nanocomposite according to any of claims 1 to 9; wherein the one or more biopolymers comprise carboxymethyl cellulose.

11. The nanocomposite according to any of claims 1 to 10; comprising carboxymethyl cellulose as the biopolymer.

12. A method for production of a superabsorbent polymer-based nanocomposite for use in controlled irrigation in agriculture, comprising graft copolymerization of one or more water-soluble and ionizable monomers on one or more biopolymers and / or copolymerization of the one or more water-soluble and ionizable monomers on one or more biodegradable polymers; the method further comprising the arrangement of a combined amount of the one or more biopolymers and the one or more biodegradable polymers to be within a range between 5 wt.% and 50 wt.% with regard to a dry weight of the nanocomposite.

13. The method according to claim 12; comprising the arrangement of the combined amount of the one or more biopolymers and the one or more biodegradable polymers to be within a range between 10 wt.% and 45 wt.% with regard to the dry weight of the nanocomposite.

14. The method according to any of claims 12 or 13; comprising selection of the one or more water-soluble and ionizable monomers from vinylic, acrylic and allylic monomers.

15. The method according to claim 14; comprising the selection of the one or more water- soluble and ionizable monomers from from acrylic acid, acrylamide and 2-acrylamido-2- methylpropanesulfonic acid.

16. The method according to any of claims 12 to 15; comprising the arrangement of the nanocomposite for provision of one or more divalent cations selected from calcium and zinc ions when swollen with water.

17. The method according to any of claims 12 to 16; comprising selection of the one or more biodegradable polymers from polyethylene glycol diacrylate, polyethylene glycol and polylactic acid.

18. The method according to claim 17; comprising selection of the one or more biodegradable polymers from polyethylene glycol diacrylate and polyethylene glycol.

19. The method according to any of claims 12 to 18; comprising selection of the one or more biopolymers from cellulose derivatives, chitin, chitosan and gelatin.

20. The method according to any of claims 12 to 19; comprising selection of the one or more biopolymers from cellulose derivatives.

21. The method according to any of claims 12 to 20; comprising selection of carboxymethyl cellulose as the biopolymer.

22. The method according to any of claims 12 to 14; comprising the use of one or more coupling agents selected from vinyl alkoxysilanes, bis-acrylamides and dihydrazides, as an in-situ cross-linking agent.

23. The method according to claim 22; wherein the one or more coupling agents are selected from vinyltriethoxysilane, vinyltrimethoxy silane and tri(2-methoxyethoxy)vinylsilane), methylene bisacrylamide and adipic acid dihydrazide.

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