Inkjet 3D printing of microbial mineralization composites and methods of making the same

Abstract

This invention relates to a microbial mineralization composite material for inkjet 3D printing and its preparation method. The composite material comprises powder materials and a binder. The powder materials, by weight, include: 70-85 parts magnesium phosphate cement powder, 10-25 parts fine aggregate, 0.5-3 parts a porous protective carrier loaded with urease-producing Bacillus licheniformis spores, 0.05-0.5 parts a nutrient protectant, and 1-5 parts a calcium source. The binder, by weight, includes: 94-98 parts deionized water, urea, 0.02-0.2 parts nutrients, 0.01-0.5 parts a pH adjuster, 0.5-5 parts a viscosity adjuster, and 0.01-0.2 parts a surface tension adjuster. The concentration of urea in the binder is 0.02-0.10 mol / L. This invention solves the problems of existing inkjet 3D printing materials having internal pores, microcracks, and weak interlayer interfaces after molding, limiting the improvement of the mechanical properties of printed parts in the later stages, and the difficulty in adapting the microbial mineralization system to the inkjet 3D printing process.

Description

Technical Field

[0001] This invention relates to the fields of additive manufacturing and microbial mineralization materials technology, specifically to an inkjet 3D printed microbial mineralization composite material and its preparation method. Background Technology

[0002] 3D printing technology boasts advantages such as high printing speed, customizable structures, and mold-free operation, making it a crucial technological support for the digital and flexible development of manufacturing. It is widely used in fields such as architecture, decoration, mold making, and engineering material molding. Inkjet 3D printing, in particular, achieves rapid manufacturing of complex structures by layer-by-layer powder deposition and selectively spraying binders to bond powder materials according to a pre-defined model. However, existing inkjet 3D printing materials largely rely on physical deposition, binder bonding, or hydration and consolidation of cementitious materials to achieve molding. This often leads to the formation of pores, microcracks, and weak interlayer interfaces within the printed parts, limiting their density and mechanical properties. Therefore, there is an urgent need to develop material systems that can further enhance the performance of printed parts after molding.

[0003] Microbial-induced calcium carbonate deposition is a green mineralization technology characterized by mild reaction conditions, environmental friendliness, and the ability to fill pores in situ, showing potential applications in soil and rock reinforcement, concrete repair, and building material reinforcement. This technology typically utilizes urease-producing microorganisms to decompose urea, generating carbonate ions which react with calcium ions to form calcium carbonate precipitates. These precipitates then fill internal pores, microcracks, and interfacial gaps in the material, improving its density and mechanical properties. Combining this technology with inkjet 3D printing promises to maintain the advantages of rapid prototyping of complex structures while achieving post-printing reinforcement through in-situ microbial mineralization. Existing microbial mineralization systems are primarily designed for crack repair or overall reinforcement of existing concrete structures, and are not specifically tailored to the characteristics of inkjet 3D printing processes such as powder spreading, binder spraying, hydration consolidation, and subsequent curing, making them difficult to directly apply to inkjet 3D printing material systems.

[0004] Based on the above problems, there is an urgent need to develop a microbial mineralization composite material suitable for inkjet 3D printing and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide an inkjet 3D printing microbial mineralization composite material and its preparation method, so as to solve the problems that existing inkjet 3D printing materials are prone to having pores, microcracks and weak interlayer interfaces after molding, which limits the improvement of mechanical properties of printed parts in the later stage, and that microbial mineralization systems are difficult to adapt to inkjet 3D printing processes.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A microbial mineralization composite material for inkjet 3D printing, the composite material comprising powder material and binder; The powder material comprises, by weight: 70-85 parts magnesium phosphate cement powder, 10-25 parts fine aggregate, 0.5-3 parts urease-producing Bacillus licheniformis spore-loaded porous protective carrier, 0.05-0.5 parts nutrient protectant, and 1-5 parts calcium source. The magnesium phosphate cement powder comprises magnesium oxide powder, ammonium dihydrogen phosphate powder, and a retarder. The mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder is 1.40:1-2.80:1, and the amount of retarder is 0.5%-1.5% of the total mass of magnesium oxide powder and ammonium dihydrogen phosphate powder. The binder comprises, by weight: 94-98 parts deionized water, urea, 0.02-0.2 parts nutrients, 0.01-0.5 parts pH adjuster, 0.5-5 parts viscosity adjuster, and 0.01-0.2 parts surface tension adjuster; the concentration of urea in the binder is 0.02-0.10 mol / L.

[0007] The adhesive has a pH of 7.0-7.6, a viscosity of 3-15 mPa·s, and a surface tension of 35-55 mN / m.

[0008] Furthermore, the magnesium oxide powder is calcined magnesium oxide powder obtained by calcining magnesite at 1600-1950℃ for 60-180 min, followed by cooling, grinding, and sieving; both the magnesium oxide powder and the ammonium dihydrogen phosphate powder are powders that can pass through a 125μm sieve.

[0009] Furthermore, the retarder is at least one of borax or boric acid; the fine aggregate is at least one of quartz sand, silica sand or limestone powder; and the particle size of the fine aggregate is 75-125 μm.

[0010] Furthermore, the porous protective carrier for the urease-producing Bacillus licheniformis spores is obtained by loading urease-producing Bacillus licheniformis spores onto a porous protective carrier through adsorption, impregnation, embedding, or freeze-drying; the porous protective carrier is one or more of diatomaceous earth, zeolite, biochar, or porous calcium carbonate; and the content of urease-producing Bacillus licheniformis spores in the powder material is 10%. 6 -10 8 CFU / g dry powder.

[0011] Furthermore, the nutritional protectant is at least one of trehalose, sucrose, sodium alginate, or skim milk powder; the calcium source is at least one of calcium lactate powder, calcium acetate powder, porous calcium carbonate, diatomaceous earth loaded with calcium source, or zeolite loaded with calcium source.

[0012] Furthermore, the nutrient is at least one of yeast extract or peptone; The pH adjuster is at least one of sodium hydroxide, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium bicarbonate, or tris(hydroxymethyl)aminomethane; the viscosity adjuster is at least one of polyvinylpyrrolidone, polyethylene glycol, or polyvinyl alcohol; and the surface tension adjuster is at least one of nonionic surfactants, polysorbate surfactants, or polyether-modified siloxane surfactants.

[0013] This invention also protects a method for preparing the inkjet 3D printed microbial mineralization composite material, comprising the following steps: (1) Urease-producing Bacillus licheniformis spores were loaded onto a porous protective carrier by means of adsorption, impregnation, embedding or freeze drying to obtain a porous protective carrier loaded with urease-producing Bacillus licheniformis spores. (2) Weigh magnesium oxide powder and ammonium dihydrogen phosphate powder according to the mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder of 1.40:1-2.80:1, add a retarder, the amount of the retarder is 0.5%-1.5% of the total mass of the magnesium oxide powder and the ammonium dihydrogen phosphate powder, mix for 5-10 min to obtain magnesium phosphate cement powder; (3) By weight, place 70-85 parts of magnesium phosphate cement powder obtained in step (2), 10-25 parts of fine aggregate, 0.5-3 parts of urease-producing Bacillus licheniformis spore-loaded porous protective carrier obtained in step (1), 0.05-0.5 parts of nutrient protectant and 1-5 parts of calcium source into a mixing device and continue mixing for 10-20 min to obtain powder material; (4) By weight, add urea, 0.02-0.2 parts of nutrients, 0.01-0.5 parts of pH adjuster, 0.5-5 parts of viscosity adjuster and 0.01-0.2 parts of surface tension adjuster to 94-98 parts of deionized water, stir or sonicate until uniform to obtain a first mixture, wherein the amount of urea added is such that the urea concentration in the first mixture is 0.02-0.10 mol / L; (5) The first mixture obtained in step (4) is filtered sequentially through a 10-15 μm filter membrane and a 0.45-0.5 μm microporous filter membrane, and then subjected to vacuum degassing to obtain the binder.

[0014] (6) Add the powder material to the powder material feed hopper of the inkjet 3D printer, add the binder to the liquid supply system of the inkjet 3D printer, set the printing program and printing parameters; start the inkjet 3D printer, the powder spreader evenly spreads the powder material on the printing base plate, the print head sprays the binder onto the first layer of powder material, so that the magnesium oxide powder and ammonium dihydrogen phosphate powder undergo a hydration reaction and form a magnesium phosphate cement cement phase, while Bacillus licheniformis spores absorb water and are activated; after the first layer of the set path of the print head is printed, the printing platform descends by one printing layer thickness, and the steps of powder spreading by the powder spreader, printing head spraying binder and printing platform descending are repeated until the printing is completed and the printed blank is obtained; During the printing process, the printing layer thickness is 0.1-0.2 mm, the printing head speed is 300-1000 mm / s, and the mass ratio of binder to powder material is 0.12-0.25:1. (7) After printing, remove the unbonded powder material and wet-cur the resulting printed blank so that the calcium carbonate induced by Bacillus licheniformis is deposited in the pores, particle contact points and interlayer interfaces of the printed blank. After wet curing, the inkjet 3D printed microbial mineralization composite material is obtained.

[0015] The wet curing conditions are as follows: after the printed blank is sealed and wet-cured for 12-24 hours, it is continued to be cured for 7 days in an environment with a temperature of 20-35℃ and a relative humidity of not less than 90%.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention combines magnesium phosphate cement powder, fine aggregate, urease-producing Bacillus licheniformis spore-loaded porous protective carrier, nutrient protectant and calcium source to form a powder material, and uses it in conjunction with a binder containing urea, nutrients and functional adjustment components, so that the inkjet 3D printing process is combined with the microbial induced mineralization process, and the printed blank can be further mineralized and enhanced in situ after printing.

[0017] (2) Based on the process characteristics of "powder spreading - binder spraying - local wetting and consolidation - wet curing and mineralization" in inkjet 3D printing, this invention partitions the solid active components and soluble nutrient components in the microbial mineralization system. Specifically, urease-producing Bacillus licheniformis spores are placed in the powder material in the form of a porous protective carrier, while urea, nutrients, pH adjusters, viscosity adjusters, and surface tension adjusters are placed in the binder. Thus, on the one hand, it can avoid nozzle clogging, filtration retention, sedimentation, or spray instability caused by directly adding microbial particles to the binder; on the other hand, after the binder is sprayed onto the powder layer, it can provide moisture, urea, and nutrients in situ in the printing area, so that the Bacillus licheniformis spores in the powder material are activated after printing and induce calcium carbonate deposition, thereby simultaneously meeting the requirements of printability of inkjet 3D printing and secondary calcium production and consolidation by microorganisms after printing.

[0018] (3) In this invention, urease-producing Bacillus licheniformis spores are loaded onto a porous protective carrier, transforming the trace amounts of easily agglomerated microbial spores into composite particles with a certain particle size and surface structure. This facilitates the uniform dispersion of spores in the magnesium phosphate cement powder and fine aggregate system, reducing local agglomeration and local enrichment. Simultaneously, the porous protective carrier buffers and protects the spores during powder mixing, feeding, spreading, and binder spraying, maintaining good flowability and spreadability of the powder material, which is beneficial for obtaining a printing powder layer with stable thickness, smooth surface, and continuous interlayer layers. After printing, the porous protective carrier can also serve as a local carrier for microbial attachment and mineral deposition, promoting the uniform formation of calcium carbonate at pores, particle contact points, and interlayer interfaces.

[0019] (4) This invention controls the type and amount of nutrients in the binder, enabling the binder to meet the requirements of inkjet printing for viscosity, surface tension, filtration, and jetting stability, while also providing the necessary nutritional conditions for the water absorption activation and metabolic calcium production of urease-producing Bacillus licheniformis spores after printing. When the nutrient content is too low, spore activation is insufficient, and the amount of microbially induced calcium carbonate deposition decreases; when the nutrient content is too high, the solid content of the binder increases, which can easily cause viscosity changes, nozzle end face residue, satellite droplets, or jetting instability. This invention controls the nutrient content at 0.02-0.2 parts, and coordinates it with the urea concentration, pH, viscosity, and surface tension range to ensure that the binder pH is 7.0-7.6, viscosity is 3-15 mPa·s, and surface tension is 35-55 mN / m, so that the binder has both jettisonability and microbial activation promotion effects.

[0020] (5) The composite material described in this invention can achieve microbial-induced calcium carbonate deposition under normal temperature and humidity curing conditions, without the need for high-temperature sintering or complex post-processing, which is beneficial to reduce energy consumption and provides a new material system and process method for improving the performance of inkjet 3D printed parts in the later stage. Attached Figure Description

[0021] Figure 1 This is a sample image of the inkjet 3D printed microbial mineralization composite material obtained in Example 3.

[0022] Figure 2 This is a sample image of the printed specimen obtained in Comparative Example 1.

[0023] Figure 3 This is a sample image of the printed specimen obtained in Comparative Example 2. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments, but this is not intended to limit the scope of protection of this application. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are all within the scope of protection of the present invention. Unless otherwise specified, all quantities mentioned below are by weight.

[0025] This invention provides an inkjet 3D printing microbial mineralization composite material, which includes powder material and binder. The powder material comprises, by weight: 70-85 parts magnesium phosphate cement powder, 10-25 parts fine aggregate, 0.5-3 parts urease-producing Bacillus licheniformis spore-loaded porous protective carrier, 0.05-0.5 parts nutrient protectant, and 1-5 parts calcium source.

[0026] The magnesium phosphate cement powder is an unhydrated magnesium phosphate cement precursor powder before inkjet printing, comprising magnesium oxide powder, ammonium dihydrogen phosphate powder, and a retarder. The mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder is 1.40:1-2.80:1, and the amount of retarder is 0.5%-1.5% of the total mass of magnesium oxide powder and ammonium dihydrogen phosphate powder. When the binder is sprayed onto the powder material, the magnesium oxide powder and ammonium dihydrogen phosphate powder undergo a hydration reaction to form a magnesium phosphate cement binder phase, thereby enabling the printed area to quickly solidify and form.

[0027] The magnesium oxide powder is recalcined magnesium oxide powder obtained by calcining magnesite at 1600-1950℃ for 60-180 min, followed by cooling, grinding, and sieving. Both the magnesium oxide powder and ammonium dihydrogen phosphate powder are capable of passing through a 125μm sieve. The retarder is borax or boric acid. The fine aggregate is one or more of quartz sand, silica sand, and limestone powder, with a particle size of 75-125 μm. The fine aggregate is used to improve the spreadability, skeletal stability, and volume stability of the printed preform.

[0028] The porous protective carrier for urease-producing Bacillus licheniformis spores is obtained by loading Bacillus licheniformis spores onto a porous protective carrier through adsorption, impregnation, embedding, or freeze-drying. The porous protective carrier is one or more of diatomaceous earth, zeolite, biochar, and porous calcium carbonate. The porous protective carrier provides attachment space for the Bacillus licheniformis spores and protects the spores during powder mixing, spreading, binder spraying, and curing. The content of Bacillus licheniformis spores in the powder material is 10%. 6 -10 8 CFU / g dry powder.

[0029] The nutrient protectant is one or more of trehalose, sucrose, sodium alginate, and skim milk powder. The nutrient protectant is used to improve the stability of spores in the dry powder state and during the printing process. The calcium source is one or more of calcium lactate powder, calcium acetate powder, porous calcium carbonate, calcium-supported diatomaceous earth, and calcium-supported zeolite. The calcium source provides calcium ions for microbial-induced calcium carbonate deposition during wet curing.

[0030] The binder comprises, by weight: 94-98 parts deionized water, urea, 0.02-0.2 parts nutrients, 0.01-0.5 parts pH adjuster, 0.5-5 parts viscosity adjuster, and 0.01-0.2 parts surface tension adjuster. The concentration of urea in the binder is 0.02-0.10 mol / L. The nutrients are at least one of yeast extract powder, peptone, etc.; the pH adjuster is one or more of sodium hydroxide, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium bicarbonate, and tris(hydroxymethyl)aminomethane; the viscosity adjuster is one or more of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol; and the surface tension adjuster is one or more of nonionic surfactants, polysorbate surfactants, and polyether-modified siloxane surfactants.

[0031] The binder has a pH of 7.0-7.6, a viscosity of 3-15 mPa·s, and a surface tension of 35-55 mN / m. The binder serves both as a liquid phase component in the inkjet printing process and as a source of urea, nutrients, and a suitable liquid environment for the subsequent activation and mineralization of urease-producing Bacillus licheniformis.

[0032] The present invention also provides a method for preparing the above-mentioned inkjet 3D printed microbial mineralization composite material, the method comprising the following steps: (1) Urease-producing Bacillus licheniformis spores are loaded onto a porous protective carrier by means of adsorption, impregnation, embedding or freeze-drying to obtain a porous protective carrier loaded with urease-producing Bacillus licheniformis spores. Specifically, the porous protective carrier can be sterilized and added to a suspension of urease-producing Bacillus licheniformis spores. After shaking adsorption or impregnation treatment, solid-liquid separation and drying are performed to load the spores onto the pores and surface of the porous protective carrier.

[0033] (2) Weigh magnesium oxide powder and ammonium dihydrogen phosphate powder according to the mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder of 1.40:1-2.80:1, and add a retarder. The amount of the retarder is 0.5%-1.5% of the total mass of magnesium oxide powder and ammonium dihydrogen phosphate powder. Mix for 5-10 min to obtain magnesium phosphate cement powder, i.e. magnesium phosphate cement precursor powder.

[0034] (3) By weight, 70-85 parts of magnesium phosphate cement powder obtained in step (2), 10-25 parts of fine aggregate, 0.5-3 parts of urease-producing Bacillus licheniformis spore-loaded porous protective carrier obtained in step (1), 0.05-0.5 parts of nutrient protectant and 1-5 parts of calcium source are placed in a mixing device and mixed for 10-20 min to obtain powder material.

[0035] (4) By weight, add urea, 0.02-0.2 parts of nutrients, 0.01-0.5 parts of pH adjuster, 0.5-5 parts of viscosity adjuster and 0.01-0.2 parts of surface tension adjuster to 94-98 parts of deionized water, stir or sonicate until uniform to obtain a first mixture, wherein the amount of urea added is such that the urea concentration in the first mixture is 0.02-0.10 mol / L.

[0036] (5) The first mixture obtained in step (4) is filtered through a 10-15 μm filter membrane and a 0.45-0.5 μm microporous filter membrane in sequence, and then subjected to vacuum degassing to obtain the binder.

[0037] (6) Add the powder material to the powder material feed hopper of the inkjet 3D printer, add the binder to the liquid supply system of the inkjet 3D printer, set the printing program and printing parameters; start the inkjet 3D printer, the powder spreader evenly spreads the powder material on the printing base plate, the print head sprays the binder onto the first layer of powder material, so that the magnesium oxide powder and ammonium dihydrogen phosphate powder undergo a hydration reaction and form a magnesium phosphate cement cement phase, while Bacillus licheniformis spores absorb water and are activated; after the first layer of the set path of the print head is printed, the printing platform descends by one printing layer thickness, and the steps of powder spreading by the powder spreader, printing head spraying binder and printing platform descending are repeated until the printing is completed and the printed blank is obtained.

[0038] During the printing process, the printing layer thickness is 0.1-0.2 mm, the printing head speed is 300-1000 mm / s, and the mass ratio of binder to powder material is 0.12-0.25:1.

[0039] (7) After printing, remove any unbonded powder material and wet-cur the resulting printed blank to allow the calcium carbonate induced by Bacillus licheniformis to deposit in the pores, particle contact points, and interlayer interfaces of the printed blank. The wet curing conditions are as follows: after sealing and wet curing the printed blank for 12-24 hours, continue curing for 7 days in an environment of 20-35℃ and relative humidity not less than 90%.

[0040] Example 1 This embodiment provides an inkjet 3D printing microbial mineralization composite material.

[0041] The powder material comprises, by weight: 80 parts magnesium phosphate cement powder, 16 parts quartz sand, 1.5 parts diatomaceous earth loaded with urease-producing Bacillus licheniformis spores, 0.2 parts trehalose, and 2.3 parts calcium lactate powder. The particle size of the quartz sand is 75-125 μm. The content of urease-producing Bacillus licheniformis spores in the powder material is 1×10⁻⁶. 7 CFU / g dry powder.

[0042] In the magnesium phosphate cement powder, the mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder is 2.00:1, and the retarder is borax, with the amount of borax being 1.0% of the total mass of magnesium oxide powder and ammonium dihydrogen phosphate powder. The magnesium oxide powder is recalcined magnesium oxide powder obtained by calcining magnesite at 1800℃ for 120 min, followed by cooling, grinding, and sieving; both the magnesium oxide powder and the ammonium dihydrogen phosphate powder are powders that can pass through a 125μm sieve.

[0043] The binder comprises, by weight, 96 parts deionized water, urea, 0.1 parts yeast extract powder, 0.08 parts disodium hydrogen phosphate, 0.02 parts sodium dihydrogen phosphate, 2 parts polyvinylpyrrolidone, and 0.05 parts polysorbate surfactant. The amount of urea added makes the urea concentration in the binder 0.05 mol / L. The binder has a pH of 7.3, a viscosity of 8.5 mPa·s, and a surface tension of 42 mN / m.

[0044] The preparation method in this embodiment is as follows: (1) After sterilizing the diatomaceous earth, add it to the suspension of urease-producing Bacillus licheniformis spores, shake to adsorb, then perform solid-liquid separation and freeze-drying to obtain diatomaceous earth loaded with urease-producing Bacillus licheniformis spores; (2) Weigh magnesium oxide powder and ammonium dihydrogen phosphate powder according to the mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder of 2.00:1, add borax, mix for 10 min to obtain magnesium phosphate cement powder. (3) Place 80 parts magnesium phosphate cement powder, 16 parts quartz sand, 1.5 parts diatomaceous earth loaded with urease-producing Bacillus licheniformis spores, 0.2 parts trehalose and 2.3 parts calcium lactate powder in a mixing device and continue mixing for 15 min to obtain powder material; (4) Add urea, 0.1 parts yeast extract powder, 0.08 parts disodium hydrogen phosphate, 0.02 parts sodium dihydrogen phosphate, 2 parts polyvinylpyrrolidone and 0.05 parts polysorbate surfactant to 96 parts deionized water, stir and sonicate until uniform to obtain the first mixture. (5) The first mixture is filtered through a 15 μm filter membrane and a 0.5 μm microporous filter membrane in sequence, and then subjected to vacuum degassing to obtain the binder.

[0045] The powder material is added to the powder material feed hopper of the inkjet 3D printer, and the binder is added to the inkjet 3D printer's liquid supply system. The printing layer thickness is set to 0.15 mm, the print head speed is 600 mm / s, and the mass ratio of binder to powder material is 0.18:1. After starting the inkjet 3D printer, the powder spreader evenly spreads the powder material on the printing plate, and the print head sprays the binder according to the set path, printing layer by layer to obtain the printed blank. After printing, the unbonded powder material is removed, and the printed blank is sealed and wet-cured for 18 hours, and then cured for another 7 days in an environment of 30℃ and relative humidity not less than 90%.

[0046] Example 2 This embodiment provides an inkjet 3D printing microbial mineralization composite material. The difference between this embodiment and Embodiment 1 lies in the different ratios of powder material and binder.

[0047] The powder material comprises, by weight: 70 parts magnesium phosphate cement powder, 25 parts silica sand, 0.5 parts zeolite loaded with urease-producing Bacillus licheniformis spores, 0.05 parts sucrose, and 4.45 parts zeolite loaded with a calcium source. The silica sand has a particle size of 75-100 μm. The content of urease-producing Bacillus licheniformis spores in the powder material is 1×10⁻⁶. 6 CFU / g dry powder.

[0048] In the magnesium phosphate cement powder, the mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder is 1.40:1, the retarder is boric acid, and the amount of boric acid is 0.5% of the total mass of magnesium oxide powder and ammonium dihydrogen phosphate powder.

[0049] The binder comprises, by weight, 98 parts deionized water, urea, 0.02 parts peptone, 0.01 parts sodium bicarbonate, 0.5 parts polyethylene glycol, and 0.01 parts nonionic surfactant. The amount of urea added ensures a urea concentration of 0.02 mol / L in the binder. The pH of the binder is adjusted to 7.0, the viscosity is controlled at 10.5 mPa·s, and the surface tension is 45 mN / m.

[0050] The preparation method of this embodiment is the same as that of Example 1, except that: the urease-producing Bacillus licheniformis spores are loaded onto zeolite by impregnation, the fine aggregate is silica sand, the nutrient protectant is sucrose, and the calcium source is zeolite loaded with calcium source.

[0051] The printing layer thickness was 0.1 mm, the print head speed was 1000 mm / s, and the mass ratio of binder to powder material was 0.12:1. After printing, the unbonded powder material was removed, and the printed blank was sealed and wet-cured for 12 hours, followed by continued curing for 7 days in an environment at 20℃ and a relative humidity of not less than 90%.

[0052] Example 3 This embodiment provides an inkjet 3D printing microbial mineralization composite material. The difference between this embodiment and Embodiment 1 lies in the different ratios of powder material and binder.

[0053] The powder material comprises, by weight: 85 parts magnesium phosphate cement powder, 10 parts limestone powder, 3 parts porous calcium carbonate supported on urease-producing Bacillus licheniformis spores, 0.5 parts skim milk powder, and 1.5 parts calcium acetate powder. The limestone powder has a particle size of 75-125 μm. The content of urease-producing Bacillus licheniformis spores in the powder material is 1×10⁻⁶. 8 CFU / g dry powder.

[0054] In the magnesium phosphate cement powder, the mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder is 2.80:1, the retarder is borax, and the amount of borax is 1.5% of the total mass of magnesium oxide powder and ammonium dihydrogen phosphate powder.

[0055] The binder comprises, by weight, 94 parts deionized water, urea, 0.1 parts yeast extract, 0.1 parts peptone, 0.5 parts tris(hydroxymethyl)aminomethane, 5 parts polyvinyl alcohol, and 0.2 parts polyether-modified siloxane surfactant. The amount of urea added ensures a urea concentration of 0.10 mol / L in the binder. The pH of the binder is adjusted to 7.6, the viscosity is controlled within the range of 3-15 mPa·s, and the surface tension is controlled within the range of 35-55 mN / m.

[0056] The preparation method in this embodiment is the same as in Example 1, except that: urease-producing Bacillus licheniformis spores are loaded onto porous calcium carbonate via embedding or freeze-drying; the fine aggregate is limestone powder; the nutrient protectant is skim milk powder; and the calcium source is calcium acetate powder. The printing layer thickness is 0.2 mm, the print head speed is 300 mm / s, and the mass ratio of binder to powder material is 0.25:1. After printing, unbonded powder material is removed, and the printed blank is sealed and wet-cured for 24 h, then cured for another 7 days at 35°C and a relative humidity of not less than 90%.

[0057] Example 4 This embodiment provides an inkjet 3D printing microbial mineralization composite material. The difference between this embodiment and Embodiment 1 lies in the porous protective carrier, nutrient protectant, and calcium source in the powder material.

[0058] The powder material comprises, by weight: 78 parts magnesium phosphate cement powder, 18 parts quartz sand, 1 part urease-producing Bacillus licheniformis spore-supported biochar, 0.3 parts sodium alginate, and 2.7 parts porous calcium carbonate. The particle size of the quartz sand is 75-125 μm. The content of urease-producing Bacillus licheniformis spores in the powder material is 5 × 10⁻⁶. 7 CFU / g dry powder.

[0059] In the magnesium phosphate cement powder, the mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder is 2.20:1, the retarder is boric acid, and the amount of boric acid is 1.2% of the total mass of magnesium oxide powder and ammonium dihydrogen phosphate powder.

[0060] The binder comprises, by weight: 95 parts deionized water, urea, 0.05 parts yeast extract, 0.05 parts peptone, 0.15 parts disodium hydrogen phosphate, 1 part polyethylene glycol, 1 part polyvinylpyrrolidone, and 0.08 parts nonionic surfactant. The amount of urea added ensures a urea concentration of 0.08 mol / L in the binder. The pH of the binder is adjusted to 7.4, the viscosity is controlled at 7.5 mPa·s, and the surface tension is 42 mN / m.

[0061] The preparation method in this embodiment is the same as in Example 1, except that: urease-producing Bacillus licheniformis spores are loaded onto biochar via adsorption, sodium alginate is used as the nutrient protectant, and porous calcium carbonate is used as the calcium source. The printing layer thickness is 0.18 mm, the print head speed is 800 mm / s, and the mass ratio of binder to powder material is 0.20:1. After printing, unbonded powder material is removed, and the printed blank is sealed and moist-cured for 20 h, then cured for another 7 days at 25°C and a relative humidity of not less than 90%.

[0062] Comparative Example 1: Powder without the addition of urease-producing Bacillus licheniformis spore-loaded porous protective carrier The difference between this comparative example and Example 1 is that no urease-producing Bacillus licheniformis spore-loaded diatomaceous earth was added to the powder material, while the composition of other raw materials and the preparation method are the same as in Example 1.

[0063] This comparative example illustrates the effect of urease-producing Bacillus licheniformis spore-loaded porous protective carrier on microbial-induced mineralization enhancement in the later stages of printing.

[0064] Comparative Example 2: No calcium lactate powder added to the powder material The difference between this comparative example and Example 1 is that calcium lactate powder is not added to the powder material, and an equal amount of quartz sand is used to make up the difference. The composition of other raw materials and the preparation method are the same as in Example 1.

[0065] This comparative example illustrates the effect of calcium source on calcium carbonate deposition during the wet curing stage.

[0066] Comparative Example 3: No urea added to the adhesive The difference between this comparative example and Example 1 is that urea is not added to the adhesive, while the composition of the other raw materials and the preparation method are the same as in Example 1.

[0067] This is used to illustrate the effect of urea on the calcium carbonate deposition process induced by urease-producing Bacillus licheniformis.

[0068] Comparative Example 4: Free spores were directly added to the powder without loading onto a porous carrier. The difference between this comparative example and Example 1 is that: instead of loading urease-producing Bacillus licheniformis spores onto diatomaceous earth, freeze-dried free urease-producing Bacillus licheniformis spore powder is directly added to the powder material, along with sterilized diatomaceous earth in an amount equivalent to that used in Example 1, so that the content of urease-producing Bacillus licheniformis spores in the powder material remains 1×10⁻⁶. 7 CFU / g dry powder. The composition of other raw materials and the preparation method are the same as in Example 1.

[0069] This demonstrates the effect of loading urease-producing Bacillus licheniformis spores onto a porous protective carrier on improving the uniformity of spore dispersion in powder materials, enhancing powder spreadability, and improving the uniformity of subsequent mineralization deposition.

[0070] Comparative Example 5: Bacterial spores were added to the adhesive, rather than to the powder material. The difference between this comparative example and Example 1 is that the powder material does not contain diatomaceous earth loaded with urease-producing Bacillus licheniformis spores. Instead, the urease-producing Bacillus licheniformis spores are added to the binder, so that theoretically, the number of urease-producing Bacillus licheniformis spores sprayed onto the printing area is comparable to that in Example 1. Since spore particles are difficult to pass through a 0.45-0.5 μm microporous membrane, the binder in this comparative example is only filtered through a 10-15 μm membrane and subjected to vacuum degassing. The remaining raw material composition and preparation method are the same as in Example 1.

[0071] This illustrates the importance of placing microbial spores in the powder material, rather than in the binder, to avoid nozzle clogging, reduce spore filtration loss, improve jetting stability, and ensure post-printing microbial mineralization.

[0072] Comparative Example 6: Nutrients were added to the powder material, rather than to the binder. The difference between this comparative example and Example 1 is that yeast extract is not added to the binder; instead, the same amount of yeast extract as in Example 1 is added to the powder material, and the amount of quartz sand is reduced accordingly to ensure that the total weight of the powder material remains unchanged. The remaining raw material composition and preparation method are the same as in Example 1.

[0073] This is used to illustrate the importance of incorporating soluble nutrients into the binder, allowing them to enter the printing area along with the binder droplets, for improving nutrient utilization efficiency, preventing powder from absorbing moisture and clumping, maintaining powder spreadability, and promoting local microbial activation after printing.

[0074] Comparative Example 7: The nutrient content in the adhesive is too low. The difference between this comparative example and Example 1 is that the amount of yeast extract added to the binder is reduced from 0.1 parts to 0.005 parts, which is below the range of nutrient usage specified in this invention. The remaining raw material composition and preparation method are the same as in Example 1.

[0075] This illustrates that when the nutrient content in the binder is too low, although the binder can still meet the requirements of inkjet printing, it is difficult to provide sufficient nutrition for the post-printing activation of urease-producing Bacillus licheniformis spores, resulting in insufficient microbial-induced calcium carbonate deposition and a decrease in the later mineralization enhancement effect.

[0076] Comparative Example 8: The nutrient content in the adhesive is too high. The difference between this comparative example and Example 1 is that the nutrients in the binder are 0.5 parts yeast extract and 0.5 parts peptone, and the total amount of nutrients added is 1.0 part, which is higher than the range of nutrient dosages defined in this invention; the composition of the remaining raw materials and the preparation method are the same as in Example 1, and the pH of the binder is adjusted to 7.3.

[0077] Table 1 Performance parameters of the printed specimens obtained in Examples 1-4 and Comparative Examples 1-8

[0078] As shown in Table 1, the printed specimens obtained in Examples 1-4 all exhibited good mechanical properties and molding quality after wet curing. The compressive strength remained within the range of 24.8-26.3 MPa, the dimensional error was controlled within the range of 0.30-0.70 mm, and the porosity was 34.6%-36.5%. This indicates that within the range of powder material composition, binder composition, and printing and curing parameters defined in this invention, the printing process can proceed stably, the printed blank can obtain good early molding strength, and further enhancement can be achieved through microbial-induced calcium carbonate deposition during subsequent wet curing. Among them, Example 3 showed the highest compressive strength and the lowest porosity, indicating that under suitable spore content, calcium source content, urea concentration, and curing conditions, microbially induced calcium carbonate can improve the density and strength of the printed specimen.

[0079] Compared to Example 1, Comparative Example 1, without the addition of a porous protective carrier loaded with urease-producing Bacillus licheniformis spores, relied primarily on magnesium phosphate cement for strength in the printed specimens, lacking the subsequent microbial mineralization enhancement. Consequently, the compressive strength decreased to 20.4 MPa, and the porosity increased to 43.8%. Comparative Example 2, without a calcium source, despite the presence of microbial components and urea, suffered from insufficient calcium ions available for reaction during wet curing, resulting in reduced calcium carbonate deposition and a decrease in compressive strength to 18.9 MPa, while the porosity increased to 45.1%. Comparative Example 3, without urea, struggled to fully induce calcium carbonate deposition with urease-producing Bacillus licheniformis, further reducing the compressive strength of the printed specimens to 17.6 MPa, increasing the porosity to 46.3%, and increasing dimensional errors. These results indicate that the synergistic effect of urease-producing Bacillus licheniformis spores, calcium source, and urea is crucial for achieving microbial-induced calcium carbonate deposition and secondary mineralization reinforcement after printing.

[0080] In Comparative Example 4, the urease-producing Bacillus licheniformis spores were not loaded onto a porous protective carrier, but were directly added to the powder material as free spore powder. Compared to Example 1, although Comparative Example 4 still contained bacterial spores, calcium source, and urea, its compressive strength decreased to 22.1 MPa, and its porosity increased to 41.7%. This is because the free spore powder is prone to agglomeration, resulting in uneven distribution of effective bacteria in the printed blank and affecting the uniformity of calcium carbonate deposition. This demonstrates that loading bacterial spores onto a porous protective carrier can not only protect the bacterial spores but also improve their dispersion uniformity in the powder material, thereby improving powder spreadability and mineralization deposition uniformity.

[0081] In Comparative Example 5, urease-producing Bacillus licheniformis spores were added to the binder instead of the powder material. Compared to Example 1, the compressive strength of Comparative Example 5 decreased to 19.8 MPa, the porosity increased to 44.5%, and the jetting stability during printing decreased. This is because bacterial spores are particulate biological components, which are prone to sedimentation, filtration retention, or nozzle clogging after being added to the binder, affecting the jetting stability of the binder. This indicates that a component allocation method that places bacterial spores in the powder material and urea and nutrients in the binder is more suitable for inkjet 3D printing, ensuring the jettability of the binder while allowing bacteria to participate in secondary mineralization and reinforcement after printing.

[0082] In Comparative Example 6, nutrients were added to the powder material instead of the binder. Compared to Example 1, the compressive strength of Comparative Example 6 decreased to 21.5 MPa, the porosity increased to 42.6%, and the uniformity of mineralization deposition decreased. This is because nutrients such as yeast extract and peptone are hygroscopic, and direct addition to the powder material can easily affect the powder's storage stability and spreading uniformity. Simultaneously, the nutrients cannot be directed into the printing area with the binder droplets, resulting in insufficient bacterial activation and mineralization deposition. This demonstrates that incorporating nutrients into the binder improves nutrient utilization efficiency and promotes bacterial activation and calcium carbonate deposition within the printing area.

[0083] In Comparative Example 7, the nutrient content in the binder was lower than the range specified in this invention. Although the binder spraying was relatively stable, the insufficient nutrients resulted in lower bacterial spore activation during the wet curing stage, reduced calcium carbonate deposition, and consequently, a decrease in compressive strength to 21.9 MPa and an increase in porosity to 41.3%. In Comparative Example 8, the nutrient content in the binder was higher than the range specified in this invention. Although it provided more nutrients, the excessively high nutrient content affected the binder's spraying compatibility, leading to increased dimensional errors and a decrease in compressive strength to 20.7 MPa. This demonstrates that a higher nutrient content in the binder is not necessarily better. This invention controls the nutrient content to 0.02-0.2 parts, and, in conjunction with urea concentration, pH, viscosity, and surface tension parameters, can ensure the binder's sprayability while meeting the needs for bacterial activation and secondary calcium production reinforcement after printing.

[0084] The results of Examples 1-4 and Comparative Examples 1-8 show that the technical effects of this invention are achieved through the rational component distribution of powder materials and binders, early hydration and consolidation of magnesium phosphate cement, bacterial loading on a porous protective carrier, calcium source supply, urea substrate supply, and regulation of nutrient content. Magnesium phosphate cement powder provides early bonding strength after binder spraying; urease-producing Bacillus licheniformis spores loaded on a porous protective carrier improve the uniformity and stability of bacterial dispersion in the powder material and enhance powder spreadability; calcium source, urea, and nutrients synergistically promote calcium carbonate deposition during the wet curing stage, allowing mineralized products to fill pores, particle contact points, and interlayer interfaces. Therefore, this invention can achieve secondary mineralization enhancement of the printed body in the later stages while ensuring the printability and forming accuracy of inkjet 3D printing.

[0085] Furthermore, this invention incorporates bacterial spores and calcium sources into the powder material, and urea and soluble nutrients into the binder. This keeps the powder areas not wetted by the binder relatively dry and stable, reducing premature reactions, moisture absorption and clumping, and ineffective nutrient consumption in areas before or before printing. In the printed areas wetted by the binder, urea and nutrients are directionally introduced with the droplets and work synergistically with the bacterial spores and calcium sources in the powder material, thereby triggering bacterial activation and mineralization reactions. This component allocation method is fully adapted to the process characteristics of inkjet 3D printing: "powder first, then liquid spraying, layer-by-layer molding, and post-curing." It ensures that the powder spreading, binder spraying, hydration consolidation, and microbial mineralization processes are matched, thereby improving the compressive strength of the printed specimen, reducing porosity, and improving interlayer bonding performance.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions or conventional adjustments made to the types and amounts of raw materials, mixing methods, printing parameters, and curing conditions in the above embodiments under the technical concept of the present invention, as long as they do not depart from the scope defined by the claims of the present invention, shall fall within the scope of protection of the present invention.

[0087] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A microbial mineralization composite material for inkjet 3D printing, characterized in that, The composite material includes powder materials and binders; The powder material comprises, by weight: 70-85 parts magnesium phosphate cement powder, 10-25 parts fine aggregate, 0.5-3 parts urease-producing Bacillus licheniformis spore-loaded porous protective carrier, 0.05-0.5 parts nutrient protectant, and 1-5 parts calcium source. The magnesium phosphate cement powder comprises magnesium oxide powder, ammonium dihydrogen phosphate powder, and a retarder. The mass ratio of magnesium oxide powder to ammonium dihydrogen phosphate powder is 1.40:1-2.80:1, and the amount of retarder is 0.5%-1.5% of the total mass of magnesium oxide powder and ammonium dihydrogen phosphate powder. The binder comprises, by weight: 94-98 parts deionized water, urea, 0.02-0.2 parts nutrients, 0.01-0.5 parts pH adjuster, 0.5-5 parts viscosity adjuster, and 0.01-0.2 parts surface tension adjuster; The concentration of urea in the binder is 0.02-0.10 mol / L.

2. The inkjet 3D printed microbial mineralization composite material according to claim 1, characterized in that, The magnesium oxide powder is calcined magnesium oxide powder obtained by calcining magnesite at 1600-1950℃ for 60-180 min, followed by cooling, grinding, and sieving; both the magnesium oxide powder and the ammonium dihydrogen phosphate powder are powders that can pass through a 125 μm sieve; the retarder is at least one of borax or boric acid; the fine aggregate is at least one of quartz sand, silica sand, or limestone powder; and the particle size of the fine aggregate is 75-125 μm.

3. The inkjet 3D printed microbial mineralization composite material according to claim 1, characterized in that, The urease-producing Bacillus licheniformis spore-loaded porous protective carrier is obtained by loading urease-producing Bacillus licheniformis spores onto a porous protective carrier through adsorption, impregnation, embedding, or freeze-drying; the porous protective carrier is one or more of diatomaceous earth, zeolite, biochar, or porous calcium carbonate; the content of urease-producing Bacillus licheniformis spores in the powder material is 10%. 6 -10 8 CFU / g dry powder.

4. The inkjet 3D printed microbial mineralization composite material according to claim 1, characterized in that, The nutritional protectant is at least one of trehalose, sucrose, sodium alginate, or skim milk powder; the calcium source is at least one of calcium lactate powder, calcium acetate powder, porous calcium carbonate, calcium-supported diatomaceous earth, or calcium-supported zeolite. The nutrient is at least one of yeast extract or peptone; The pH adjuster is at least one of sodium hydroxide, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium bicarbonate, or tris(hydroxymethyl)aminomethane; The viscosity modifier is at least one of polyvinylpyrrolidone, polyethylene glycol, or polyvinyl alcohol. The surface tension modifier is at least one of a nonionic surfactant, a polysorbate surfactant, or a polyether-modified siloxane surfactant.

5. The inkjet 3D printed microbial mineralization composite material according to claim 1, characterized in that, The mass ratio of binder to powder material is 0.12-0.25:

1.

6. A method for preparing an inkjet 3D printed microbial mineralization composite material according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: Weigh each component of the powder material by weight and place it in a mixing device to continue mixing for 10-20 minutes to obtain the powder material. Weigh each component of the binder by weight, stir or sonicate until homogeneous to obtain a first mixture, wherein the urea concentration in the first mixture is 0.02-0.10 mol / L; filter the obtained first mixture sequentially through a 10-15 μm filter membrane and a 0.45-0.5 μm microporous filter membrane, and perform vacuum degassing to obtain the binder; The powder material is added to the powder material feed hopper of the inkjet 3D printer, and the binder is added to the liquid supply system of the inkjet 3D printer. The printing program and printing parameters are set. The inkjet 3D printer is started, and the powder spreader evenly spreads the powder material on the printing plate. The print head sprays the binder onto the first layer of powder material, causing the magnesium oxide powder and ammonium dihydrogen phosphate powder to undergo a hydration reaction and form a magnesium phosphate cement binder phase. At the same time, the Bacillus licheniformis spores are activated by absorbing water. After the first layer of the set path is printed, the printing platform descends by one printing layer thickness. The steps of powder spreading by the powder spreader, printing head spraying binder, and printing platform descent are repeated until printing is completed, and a printed blank is obtained. After printing, the unbonded powder material is removed, and the resulting printed blank is wet-cured to allow the calcium carbonate induced by Bacillus licheniformis to deposit in the pores, particle contact points, and interlayer interfaces of the printed blank. After wet curing, the inkjet 3D printed microbial mineralization composite material is obtained.

7. The preparation method according to claim 6, characterized in that, The wet curing conditions are as follows: after the printed blank is sealed and wet-cured for 12-24 hours, it is continued to be cured for 7 days in an environment with a temperature of 20-35℃ and a relative humidity of not less than 90%.

8. The preparation method according to claim 7, characterized in that, During the printing process, the printing layer thickness is 0.1-0.2mm, and the printing head speed is 300-1000mm / s.

9. The composite material obtained by the preparation method according to any one of claims 6-8, characterized in that, The compressive strength of the composite material is maintained in the range of 24.8-26.3 MPa, the dimensional error is controlled in the range of 0.30-0.70 mm, and the porosity is 34.6%-36.5%.

10. An article obtained by the preparation method according to any one of claims 6-8.

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