Methods for geometrically varied hydrogel membrane production

Abstract

A method for producing a hydrogel membrane includes adding a volume of alginate solution to a solution containing calcium ions, maintaining the volume of alginate solution in the solution containing calcium ions until a hydrogel membrane forms on an exterior surface of the volume of alginate solution by the cross-linking of alginate in the volume of alginate solution by the calcium ions, and recovering the hydrogel membrane. In aspects, the recovered hydrogel membrane is in the shape of a bead, a net, threads, or grains.

Description

METHODS FOR GEOMETRICALLY VARIED HYDROGEL MEMBRANE PRODUCTIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of, and priority to, U.S. Provisional Patent Application No. 63 / 587,457, filed on October 3, 2023, the entire contents of which are hereby incorporated herein by reference.TECHNICAL FIELD

[0001] The present disclosure relates to hydrogel membranes. More specifically, an aspect of the present disclosure provides methods for producing hydrogel membranes of various geometric shapes and dimensions which result in improved efficiency.BACKGROUND

[0002] Hydrogels are three-dimensional network structures capable of absorbing large amounts of water, thereby functioning as small water containers enclosed within semipermeable osmotic membranes which permit the transport of water. Alginate-based hydrogels have demonstrated elevated levels of efficiency in controlling moisture within a respective system and are environmentally friendly, thus, being of great use in the agricultural sector in particular. Hydrogels that are implanted into soil have the ability of absorbing and retaining water and, thereafter, releasing the contained water when the soil begins to dry out, thereby reducing the need for frequent irrigation and the labor and costs associated with irrigation systems. Oftentimes, flooding may negatively impact the quality of soil by causing soil erosion as a result of the sheer power that the flow of water results in, thereby tearing away valuable layers of nutrient-rich soil. Hydrogels possess the added benefit of reducing the likelihood of flood-caused erosion, ultimately mitigating the detrimental effects thatflooding may have on soil and the associated livelihood of those involved in the agricultural sector. Additionally, hydrogels are capable of improving the overall hydro-physical properties of soil, such as the soil’s porosity, and may stimulate, through biodegradation, microbial activity within the soil.SUMMARY rooo3] An aspect of the present disclosure provides a method for producing a hydrogel membrane. The method includes adding a volume of an alginate solution to a solution containing calcium ions, maintaining the volume of alginate solution in the solution containing calcium ions until a hydrogel membrane forms on an exterior surface of the volume of alginate solution by the cross-linking of alginate in the volume of alginate solution by the calcium ions, and recovering the hydrogel membrane. The method further includes recovering a bead having un-reacted alginate solution contained within the hydrogel membrane, the bead having a size of 0.5 mm to about 5 mm.

[0004] In aspects, the viscosity of the alginate solution may be from about 400 milli- Pascal-second (mPas) to about 12,000 mPas.

[0005] In aspects, a concentration of alginate in the alginate solution may range from about 5 to about 50 g / L.

[0006] In aspects, the method may further include grinding alginate powder and adding the ground alginate powder to distilled water to form the alginate solution.

[0007] In another aspect of the present disclosure, a method for producing a hydrogel membrane is provided. The method includes adding a volume of an alginate solution to a fluid-absorbent mold which was previously soaked in a solution containing calcium ions, a portion of the mold in contact with the volume of alginate solution and having a patternformed therein. The method further includes maintaining the volume of alginate solution in the previously soaked fluid-absorbent mold until a hydrogel membrane forms on an exterior surface of the volume of alginate solution by the cross-linking of alginate in the volume of alginate solution by the calcium ions released from the previously soaked fluid-absorbent mold. The method further includes exposing a portion of the alginate solution not in contact with the mold to a solution containing calcium ions to form a hydrogel membrane on the portion of the alginate solution not in contact with the mold. The method includes recovering the hydrogel membrane, the hydrogel membrane encasing un-reacted alginate solution and having a shape determined by the pattern formed in the portion of the mold in contact with the volume of alginate solution.

[0008] In aspects, the method for producing a hydrogel membrane may include submerging the mold containing the volume of alginate solution in a solution containing calcium ions, and maintaining the mold containing the volume of alginate solution in the solution containing calcium ions until a hydrogel membrane forms on an exterior surface of the volume of alginate solution not in contact with the mold by the cross-linking of alginate in the volume of alginate solution by calcium ions in the solution containing calcium ions.

[0009] In other aspects, the method for producing a hydrogel membrane may include spraying a solution containing calcium ions into the mold forming a hydrogel membrane on an exterior surface of the volume of alginate solution not in contact with the mold by the cross-linking of alginate in the volume of alginate solution by calcium ions in the solution containing calcium ions, thereby completely encasing the exterior surface of the volume of alginate solution.

[0010] In aspects, a viscosity of the alginate solution added to the fluid-absorbent mold isfrom about 400 milli-Pascal-second (mPas) to about 12,000 mPas.

[0011] In aspects, the pattern formed in the portion of the fluid-absorbent mold in contact with the volume of alginate solution may define a mesh.

[0012] In aspects, the method further includes drying the recovered the hydrogel membrane.

[0013] In another aspect of the present disclosure, a method for producing a hydrogel strand is provided. The method includes adding strand-shaped volumes of alginate solution to a solution containing calcium ions. The method further includes maintaining the strandshaped volume of alginate solution in the solution containing calcium ions until a strandshaped hydrogel membrane forms on an exterior surface of each strand-shaped volume of alginate solution by the cross-linking of alginate in the strand-shaped volumes of alginate solution by the calcium ions. The method also includes recovering the strand-shaped hydrogel membranes encasing un-reacted alginate solution.

[0014] In aspects, a viscosity of the alginate solution is from about 400 milli-Pascal- second (mPas) to about 12,000 mPas.

[0015] In aspects, a concentration of alginate in the alginate solution may range from about 5 to about 50 g / L.

[0016] In aspects, the method for producing a hydrogel strand may include grinding alginate powder and adding the ground alginate powder to distilled water to form the alginate solution.

[0017] In aspects, adding strand-shaped volumes of alginate solution to a solution containing calcium ions may include injecting, dipping, or dripping alginate solution into the solution containing calcium ions to form a plurality of a strand-shaped volumes of alginatesolution of different diameters and lengths.

[0018] In aspects, the method for producing a hydrogel strand may include drying the recovered the strand-shaped hydrogel membranes.

[0019] In aspects, the method for producing a hydrogel strand may include grinding the dried the strand-shaped hydrogel membranes into grains.

[0020] In aspects, the method for producing a hydrogel strand may include sieving the grains and recovering grains of a desired size.

[0021] Further details and aspects of the present disclosure are described in more detail below with reference to the appended figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] A better understanding of the features and advantages of the present disclosure will be obtained by reference to the following detailed description that sets forth illustrative aspects, in which the principles of the present disclosure are utilized, and the accompanying figures of which:

[0023] FIG. 1 illustrates a system for hydrogel membrane production, in accordance with aspects of the present disclosure;

[0024] FIG. 1 A schematically illustrates a cross-section of a bead having a alginate-based hydrogel membrane encasing un-reacted alginate solution in accordance with aspects of the present disclosure;

[0025] FIG. 2 illustrates a system for net-shaped hydrogel membrane production, in accordance with aspects of the present disclosure;

[0026] FIG. 3 is an image of a dry and wet hydrogel net, in accordance with aspects of the present disclosure;

[0027] FTG. 3A schematically illustrates a cross-section of a hydrogel net having an alginate-based hydrogel membrane encasing un-reacted alginate solution in accordance with aspects of the present disclosure;

[0028] FIG. 4 illustrates a system for granular hydrogel membrane production, in accordance with aspects of the present disclosure;

[0029] FIG. 4A schematically illustrates a grain having an alginate-based hydrogel membrane surrounding un-reacted alginate solution in accordance with aspects of the present disclosure;

[0030] FIG. 5A is an image of wet hydrogel strands, in accordance with aspects of the present disclosure;

[0031] FIG. 5B is an image of dry hydrogel strands, in accordance with aspects of the present disclosure;

[0032] FIG. 6 is an image of hydrogel powder, in accordance with aspects of the present disclosure; and

[0033] FIG. 7 shows a hydrogel membrane in the shape of a flat coil in accordance with aspects of the present disclosure.DETAILED DESCRIPTION

[0034] The present disclosure relates to hydrogel membranes. Aspects of the present disclosure are described in detail with reference to the figures wherein like reference numerals identify similar or identical elements.

[0035] Although the present disclosure will be described in terms of specific aspects and examples, it will be readily apparent to those skilled in this art that various modifications,rearrangements, and substitutions may be made without departing from the spirit of the present disclosure.

[0036] For purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to exemplary aspects illustrated in the figures, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended. Any alterations and further modifications of the novel features illustrated herein, and any additional applications of the principles of the present disclosure as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the present disclosure.

[0037] FIG. 1 illustrates a system 100 for production of hydrogel membrane, arranged in accordance with at least some embodiments described herein. An alginate solution 104 may be formed by mixing alginate powder 112 with distilled water 114 within chamber 116. Alginate powder 112 may be an extract from brown seaweed that is commonly grown on the east coast of the United States. Alginate powder 112 may be mixed with distilled water 114 using various mechanical devices or hand-operated tools 102 (e.g., manual, magnetic, electric mixers, manual mixing spatulas and bowls). In creating alginate solution 104, the concentration of alginate powder 112 in distilled water 114 may be between about 5 and about 50 g / L, with the concentration being dependent upon the requirements of a respective application method (e.g., the need for alginate solutions of varying viscosities). In aspects, the concentration of alginate powder 1 12 may be adjusted to produce a more or less viscous alginate solution 104 such that alginate solution 104 may be immersed into the calcium ions solution bath 106 in shapes of varying geometry and dimensions (e.g., strands, nets, noodles) and by utilizing various instruments and methods (e.g., syringes, molds, pipettes).

[0038] A volume of alginate solution 104 may be immersed in a calcium ions solution bath 106. Calcium ions solution bath 106 may be a solution including calcium chloride. A hydrogel membrane 101 may form on an exterior surface 103 of alginate solution 104 when alginate solution 104 is immersed in a calcium ions solution bath 106. As those skilled in the art reading this disclosure will understand, the interaction of alginate solution 104 with calcium ions solution bath 106 will produce an alginate-based hydrogel. Calcium ions solution bath 106 may have a concentration of calcium ions ranging from about 1 to about 20 g / L, dependent upon an amount of time to be spent on the formation of hydrogel membrane 101. In examples, a higher concentration of calcium ions may require a lesser time to form hydrogel membrane 101. Alginate solution 104 may be immersed in calcium ions solution bath 106 by way of injection, piping 108, dipping, dripping, or within a mold, which may produce alginate solutions 104 within respective hydrogel membranes 101 of varying geometric shapes and dimensions depending on the amount of alginate solution used, and method of delivery of the alginate solution into the calcium ions solution bath 106. Within calcium ions solution bath 106, exterior surface 103 of alginate solution 104 may interact with the calcium ions by cross-linking through the binding of calcium ions, which in turn, may result in hydrogel membrane 101 forming. Hydrogel membrane 101 may be similar in chemical and physical structure to synthetic hydrogel (e.g., poly hydroxyethyl methacrylate, polyethylene glycol hydrogels, and poly acrylic acid).

[0039] Within calcium ions solution bath 106, hydrogel membrane 101 may form and seal the exterior surface 103 of the alginate solution 104. Specifically, outside surface 103 of the alginate solution 104 may be sealed when alginate solution 104 is entirely submerged in calcium ions solution bath 106. Thus, in accordance with this aspect of the present disclosure, abead-like structure is formed having un-reacted alginate solution 104 encased by an alginate-based hydrogel membrane 101. A volume of alginate solution 104 sufficient to form a bead having a width of about 0.5 mm to about 5 mm may be added to the calcium ions solution bath 106. In order to produce a bead-like structure, the viscosity of the alginate solution 104 should be from about 400 mPas to about 12,000 mPas. Alginate solution 104 may be placed within calcium ions solution bath 106 for anywhere from about 1 to about 20 minutes. Hydrogel membrane 101 thickness may be dependent upon a concentration of calcium ions solution bath 106 and an amount of time that alginate solution 104 is in calcium ions bath solution 106. Over time, calcium ions within calcium ions solution bath 106 may penetrate outer formed hydrogel membrane 101 and react with alginate solution 104 within the formed membrane to increase a thickness of hydrogel membrane 101. Development of hydrogel membrane 101 may be temperature and pressure insensitive and may not be dependent on external humidity conditions. Hydrogel membrane 101 formed on the exterior surface 103 of the alginate solution 104 may serve to prolong the lifespan of alginate solution 104 sealed within, and the resulting hydrogel. The alginate-based hydrogel formed in accordance with the present disclosure may advantageously possess osmotic properties. An external thickness of osmotic hydrogel membrane 101 may regulate a liquid release rate of the resulting hydrogel. For example, a thicker exterior thickness of osmotic hydrogel membrane 101 may result in a slower release rate of water and may result in a longer life span of the resulting alginate-based hydrogel. An osmotic alginate-based hydrogel membrane 101 may provide the added benefit of preventing clumping during use of the the resulting beads, for example when incorporated into soil or used within diapers.

[0040] FIG. 1A schematically illustrates a cross-section of a bead 150 having an alginate-based hydrogel membrane 101 encasing un-reacted alginate solution 104 in accordance with aspects of the present disclosure.

[0041] Referring to FIGS. 2-3, a system for net-shaped hydrogel membrane production and hydrogel nets are shown. System 200 may be similar’ to system 100 described above. A fluidabsorbent open mold 202 may be submerged in a chamber 206 containing calcium ions solution bath 106. Fluid-absorbent open mold 202 may be composed of any fluid-absorbent material, such as, for example, ceramic or plaster. Fluid-absorbent open mold 202 may soak in calcium ions solution bath 106 for a predetermined amount of time, from about 2 minutes to about 10 minutes. Fluid-absorbent open mold 202 may be removed from chamber 206 and calcium ions solution bath 106, and excess calcium ions solution bath 106 may be removed from fluid-absorbent open mold 202 by, for example, patting down mold 202 with a dry material.

[0042] Cavity 204 of the fluid-absorbent open mold 202 may be defined by an internal perimeter of fluid-absorbent open mold 202 and may include a bottom surface 207 having a negative volume or void suitable for producing a hydrogel of a desired shape when filled with an alginate solution. For example, a bottom surface 207 may include a series of perpendicular, intersecting troughs to produce a hydrogel in the shape of a mesh when filled with an alginate solution. Those skilled in the art reading this disclosure will envision configurations for bottom surface 207 suitable to produce other shapes and patterns of varying dimensions (e.g., flat coils) upon which alginate solution 104 can be disposed. Accordingly, bottom surface 207 of the fluid-absorbent open mold 202 may be configured to produce a net-shaped hydrogel membrane 201 disposed upon exterior surface 103 of the resulting hydrogel net 250.

[0043] Alginate solution 104, prepared as previously described, may be placed within a cavity204 of fluid-absorbent open mold 202. In order to produce a net-like structure, the viscosity ofthe alginate solution 104 should be from about 400 mPas to about 12,000 mPas. Those skilled in the art reading this disclosure will envision other viscosities suitable for forming other shapes within mold 202. Alginate solution 104 may be in fluid communication with calcium ions retained by fluid-absorbent open mold 202. This will result in the formation of an alginate-based hydrogel on the surface of alginate solution 104 wherever it is in contact with the surface of fluidabsorbent mold 202. To fully encase alginate solution 104 within a hydrogel membrane, the portions of alginate solution not in contact with mold 202 are exposed to calcium ions. To do this, a solution containing calcium ions may be sprayed into mold 202 thereby causing reaction of the alginate solution 104 with calcium ions in the sprayed solution thereby forming a hydrogel in areas where the alginate solution is not in contact with mold 202. Alternatively, fluid- absorbent open mold 202 containing the alginate solution 104 may be placed within calcium ions solution bath 106 in chamber 206, thereby forming a hydrogel in areas of the alginate solution is not in contact with mold 202. Once an alginate-based hydrogel membrane 201 is disposed upon the entire exterior surface 103 of alginate solution 104, a hydrogel net 250 may be recovered from mold 202. As in the previously described bead-like hydrogel membranes, the hydrogel membrane on this embodiment may encase un-reacted alginate solution. Additionally, the alginate-based net- shaped hydrogel membrane formed in accordance with the present disclosure may advantageously possess osmotic properties.

[0044] After soaking in the calcium ions solution bath 106 for a concentration-dependent amount of time from about 10 seconds to about 30 seconds, the resulting wet alginate-based hydrogel net 252 may be removed from the fluid-absorbent open mold 202 while the mold is still submerged in the calcium ions solution bath 106. The resulting wet hydrogel net 252 may be allowed to dry. Drying may be performed on a non-sticky and non-water absorbent surface (e.g.,wax paper, parchment paper, stainless steel sheets). Wet hydrogel net 252 may reduce in size while drying, and in an example wet hydrogel net 252 may reduce in size to a size of about 4x4 cm2. FIG. 3 illustrates a difference in size between wet hydrogel net 252 and dried hydrogel net 250.

[0045] FIG. 3A schematically illustrates a cross-section of a hydrogel net 252 having an alginate-based hydrogel membrane 201 encasing un-reacted alginate solution 104 in accordance with aspects of the present disclosure

[0046] Referring to FIGS. 4-6, a system for production of hydrogel membrane strands and grains, as well as example strand and grains are shown. Alginate solution 104, prepared as previously described, may be immersed in calcium ions solution bath 106 by injection, dipping, or dripping from a syringe 302. Alginate solution 104 may be immersed within calcium ions solution bath 106 such that alginate solution 104 is in fluid communication with calcium ions present within calcium ions solution bath 106 and the calcium ions may create an alginate- based hydrogel membrane 301 upon an exterior surface 303 of the alginate solution 104 resulting in membrane- sealed alginate solution 104 in the form of hydrogel strand 310. Alginate solution 104 may be injected, dropped, or dripped into calcium ions solution bath 106 in strands of varying diameters and lengths. Alginate solution 104 may be prepared with a lower viscosity than the alginate solution used in the foregoing membrane and mesh examples. In order to produce a thread-like structure, the viscosity of the alginate solution 104 should be from about 400 mPas to about 12,000 mPas. After soaking in calcium ions solution bath 106 for a concentration-dependent amount of time, the resulting hydrogel strand 310 may be removed from calcium ions solution bath 106 and dried on a non-sticky and non-water absorbent surface 302 at room temperature of about 25 °C and a relative humidity between about 30% and 50%.Drying may also be performed in a low-temperature oven at about 40°C. Once thoroughly dried,the resulting hydrogel strand 310 may be shredded or ground to form grains 304 of specific sizes. Shredding or grinding may be performed using a variety of different mechanical devices and handoperated tools 307 (e.g., mechanical grinder, manual grain mill, or electric coffee grinder). Grains 304 may be sieved through mesh sieves 306 of varying grits to obtain grains 304 of specified sizes, such as, for example, between about 100 to about 500 micrometers, or flakes of about 0.5 mm to about 5 mm. Grains 304 of the finest size (-100-200 micrometers) may be classified as powder 311. Mechanical grinding may allow partial breaking of the hydrogel membrane 301 to increase water absorption capacity and speed of grains 304 and powder 311. Hydrogel strands 310 that are ground down to powder 311 or grains 304 may have multiple applications in absorbent hygiene products, baby diapers, wound care dressings, biohazardous liquid absorption, fuel and oil dewatering, ice packs, and flood sacks. The grain size employed may depend on the final application of the grains. Smaller size grains (e.g., between about 100 to about 500 micrometers) may be suitable for inclusion within soil, while larger grain sizes (e.g., over 5 mm) may be suitable for incorporation on diapers or wound dressings. FIG. 4A schematically illustrates a grain 304 having an alginate-based hydrogel membrane 301 surrounding unreacted alginate solution 104 in accordance with aspects of the present disclosure. Grains containing an osmotic alginate-based hydrogel membrane 101 may provide the added benefit of preventing clumping of the grains during use of the grains, for example when incorporated into soil or used within diapers.

[0047] FIG. 5A illustrates wet hydrogel strands drying on non-water absorbent surface 302. FIG. 5B illustrates dried hydrogel strands. FIG. 6 illustrates hydrogel powder. As in the previously described hydrogel membrane and meshes, alginate-based hydrogel grains formed in accordance with the present disclosure may advantageously possess osmotic properties,despite having open ends with un-reacted alginate solution exposed.

[0048] As noted above, the methoids described herein can be used to provide hydrogel membranes of shapes of varying geometry and dimensions. As seen in FIG. 7, the present hydrogel membranes may be created in the form of a flat coil 400. As in other embodiments, flat coil 400 includes an alginate-based hydrogel membrane surrounding un-reacted alginate solution. Coil 400 can be produced by the apparatus / method shown in FIG. 3, by providing a fluid-absorbent open mold that includes a bottom surface 207 having a negative volume or void suitable for producing a hydrogel in the shape of a flat coil. For example, a bottom surface 207 may include a single spiral-shaped trough to produce a hydrogel in the shape of a flat coil when filled with an alginate solution. Alternatively, a hydrogel thread produced produced by the apparatus / method shown in FIG. 4 can be wound into a coil shape and dried so that the coil shape is retained by the thread.

[0049] Beads, nets, grains, coils, or other shaped structures having an alginate-based osmotic hydrogel surrounding an alginate solution may be combined with soil and provide moisture control within the soil. The products made in accordance with the present disclosure can absorb and retain water during wet times, and release the retained water during dry times, thereby allowing plants that would otherwise suffer or even die under drought conditions to thrive and / or survive.

[0050] Certain aspects of the present disclosure may include some, all, or none of the above advantages and / or one or more other advantages readily apparent to those skilled in the art from the figures, descriptions, and claims included herein. Moreover, while specific advantages have been enumerated above, the various aspects of the present disclosure may include all, some, or none of the enumerated advantages and / or other advantages not specifically enumerated above.

[0051] The aspects disclosed herein are examples of the disclosure and may be embodied in various forms. For instance, although certain aspects herein are described as separate aspects, each of the aspects herein may be combined with one or more of the other aspects herein. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure. Like reference numerals may refer to similar or identical elements throughout the description of the figures.

[0052] The phrases “in an embodiment,” “in aspects,” “in various aspects,” “in some aspects,” or “in other aspects” may each refer to one or more of the same or different example Aspects provided in the present disclosure. A phrase in the form “A or B” means “(A), (B), or (A and B).” A phrase in the form “at least one of A, B, or C” means “(A); (B); (C); (A and B); (A and C); (B and C); or (A, B, and C).” As used herein, the term “about” is understood to include amounts up to about + or - 10 degrees from the amount or dimension indicated.

[0053] It should be understood that the foregoing description is only illustrative of the present disclosure. Various alternatives and modifications can be devised by those skilled in the art without departing from the disclosure. Accordingly, the present disclosure is intended to embrace all such alternatives, modifications, and variances. The aspects described with reference to the attached figures are presented only to demonstrate certain examples of the disclosure. Other elements, steps, methods, and techniques that are insubstantially different from those described above and / or in the appended claims are also intended to be within the scope of the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A method for producing a hydrogel membrane comprising: adding a volume of an alginate solution to a solution containing calcium ions; maintaining the volume of alginate solution in the solution containing calcium ions until a hydrogel membrane forms on an exterior surface of the volume of alginate solution by the cross-linking of alginate at the exterior surface of the volume of alginate solution by the calcium ions; and recovering a bead having un-reacted alginate solution contained within the hydrogel membrane, the bead having a size of from about 0.5 mm to about 5 mm.

2. The method of claim 1, wherein a viscosity of the alginate solution is from about 400 mPas to about 12,000 mPas.

3. The method of claim 1, wherein a concentration of alginate in the alginate solution ranges from about 5 to about 50 g / L.

4. The method of claim 1, further comprising grinding alginate powder and adding the ground alginate powder to distilled water to form the alginate solution.

5. A bead having un-reacted alginate solution encased by an osmotic, alginate-based hydrogel membrane prepared in accordance with claim 1.

6. A method for producing a hydrogel membrane comprising:adding a volume of an alginate solution to a fluid-absorbent mold which was previously soaked in a solution containing calcium ions, a portion of the mold in contact with the volume of alginate solution and having a pattern formed therein; maintaining the volume of alginate solution in the previously soaked fluid- absorbent mold until a hydrogel membrane forms on an exterior surface of the volume of alginate solution in contact with the mold by the cross-linking of alginate in the volume of alginate solution by the calcium ions released from the previously soaked fluid- absorbent mold; exposing a portion of the alginate solution not in contact with the mold to a solution containing calcium ions to form a hydrogel membrane on the portion of the alginate solution not in contact with the mold; and recovering the hydrogel membrane, the hydrogel membrane encasing un-reacted alginate solution and having a shape determined by the pattern formed in the portion of the mold in contact with the volume of alginate solution.

7. The method of claim 6, wherein exposing the portion of the alginate solution not in contact with the mold to a solution containing calcium ions comprises: submerging the mold containing the volume of alginate solution in a solution containing calcium ions; and maintaining the mold containing the volume of alginate solution in the solution containing calcium ions until a hydrogel membrane forms on an exterior surface of the volume of alginate solution not in contact with the mold by the cross-linking of alginate in the volume of alginate solution by calcium ions in the solution containing calcium ions, thereby completely encasing the exterior surface of the volume of alginate solution.

8. The method of claim 6, wherein exposing the portion of the alginate solution not in contact with the mold to a solution containing calcium ions comprises: spraying a solution containing calcium ions into the mold to form a hydrogel membrane on an exterior surface of the volume of the alginate solution not in contact with the mold by the cross-linking of alginate in the volume of alginate solution by calcium ions in the solution containing calcium ions, thereby completely encasing the exterior surface of the volume of alginate solution.

9. The method of claim 6, wherein wherein a viscosity of the alginate solution is from about 400 mPas to about 12,000 mPas .

10. The method of claim 6, wherein the pattern formed in the portion of the fluidabsorbent mold in contact with the volume of alginate solution defines a mesh.

11. The method of claim 6, further comprising drying the recovered the hydrogel membrane.

12. A shaped structure having un-reacted alginate solution encased by an osmotic, alginate-based hydrogel membrane prepared in accordance with claim 6.

13. A method for producing a hydrogel strand comprising: adding strand- shaped volumes of an alginate solution to a solution containing calcium ions;maintaining the strand-shaped volume of alginate solution in the solution containing calcium ions until a strand- shaped hydrogel membrane forms on an exterior surface of each strand-shaped volume of alginate solution by the cross-linking of alginate in the strand-shaped volumes of alginate solution by the calcium ions; and recovering the strand-shaped hydrogel membranes encasing un-reacted alginate solution.

14. The method of claim 13, wherein a viscosity of the alginate solution is from about 400 mPas to about 12,000 mPas .

15. The method of claim 13, wherein a concentration of alginate in the alginate solution ranges from about 5 to about 50 g / L.

16. The method of claim 12, wherein adding strand-shaped volumes of alginate solution to a solution containing calcium ions comprises injecting, dropping, or dripping alginate solution into the solution containing calcium ions to form a plurality of a strand-shaped volumes of alginate solution of different diameters and lengths.

17. The method of claim 12, further comprising: drying the recovered the strand-shaped hydrogel membranes.

18. The method of claim 17, further comprising grinding the dried the strand-shaped hydrogel membranes into grains.

19. The method of claim 18, further comprising sieving the grains and recovering grains of a desired size.

20. Grains having un-reacted alginate solution encased by an osmotic, alginate-based hydrogel membrane prepared in accordance with claim 18.

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