Method for additive manufacturing of 3D-printed articles

Abstract

The present invention provides a method of additive manufacturing a 3D-printed article, comprising: (a) printing and depositing one or more layers of a slurry by using a 3D printer, wherein the slurry comprises a ceramic powder composition; (b) further injecting an oil around the one or more layers of slurry, wherein the height of the injected oil is lower than the height of the slurry; (c) repeating steps (a) and (b) until a main body with desired geometric shape is obtained; and (d) sintering the main body by heating to obtain the 3D-printed article wherein the temperature of a printing carrier of the 3D printer is from 30 to 80° C.

Claims

1. A method for additive manufacturing a 3D-printed article, comprising: (a) printing and depositing one or more layers of a slurry by using a 3D printer to obtain a printed ceramic object, wherein the slurry comprises a ceramic powder composition; (b) covering outer periphery of the printed ceramic object with an oil; and (c) sintering the oil-covered printed ceramic object from step (b) by heating to obtain the 3D-printed article wherein the temperature of a printing carrier of the 3D printer is from 30 to 80° C.

2. The method of claim 1, wherein the ceramic powder comprises hydroxylapatite, tricalcium phosphate, high density alumina, zirconia, bioglass, carbide ceramic materials, nitride ceramic materials, aluminum silicate, boride ceramic materials or silicide ceramic materials.

3. The method of claim 1, wherein the oil comprises polyglycol, silicone oil, fluorinated oil, phosphoric ester, polyether, paraffin, dodecyl alcohol, olive oil, soybean oil, hydrocarbon mineral oil, liquid paraffin, or synthetic hydrocarbon.

4. The method of claim 1, wherein the viscosity of the slurry ranges from 100 to 900 cP.

5. The method of claim 1, wherein the size of a nozzle of the 3D printer ranges from 19 to 30G.

6. The method of claim 1, wherein the printing speed of the 3D printer ranges from 0.1 to 5 cm/s.

7. The method of claim 1, wherein the slurry in step (a) comprises a ceramic powder composition and a hydrogel, and the slurry is prepared by following steps: (1) synthesizing poly(N-isopropylacrylamide) (p(NiPAAm)) or poly(N-isopropylacrylamide-co-methacrylic acid) (p(NiPAAm-MAA)); (2) mixing a dispersant with hydroxylapatite; (3) mixing the p(NiPAAm) or the p(NiPAAm-MAA) of step (a) with water to obtain a hydrogel solution; (4) mixing the hydrogel solution of step (c) with product of step (b) to produce a mixture; and (5) stirring the mixture of step (4) to produce the slurry.

8. The method of claim 7, which further comprise adding polymer particles to the mixture of step (4) prior to step (5).

9. The method of claim 7, wherein the hydroxylapatite and the dispersant of step (2) are mixed in a weight ratio ranging from 25:1 to 25:5.

10. The method of claim 7, wherein the dispersant of step (2) is polyacrylic acid (PAA), polymethacrylic acid (PMA), or polyvinyl alcohol (PVA).

11. The method of claim 7, wherein the p(NiPAAm-MAA) and the water of step (3) are mixed in a volume ratio ranging from 1:10 to 2:1.

12. The method of claim 7, which further comprises adding a photocuring initiator to the hydrogel solution of step (3) to allow the slurry to be photocured and molded after being irradiated by UV light.

13. The method of claim 12, wherein the photocuring initiator is a radical type photocuring initiator or a cationic type photocuring initiator.

14. The method of claim 13, wherein the radical type photocuring initiator comprises acrylic acid or unsaturated polyester, the cationic photocuring initiator comprises an epoxy compound, oxetane or vinyl ether.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows condition parameters for 3D printing of the bio-hydrogel ceramic material.

(2) FIG. 2 shows that the 3D printing technology can effectively control the size, spacing and pattern of bio-ceramic pores.

(3) FIG. 3 shows an embodiment of uniform shrinkage and enhanced sintered density.

(4) FIG. 4 shows a comparison of the shrinkage rate of phosphate ceramics with or without oil.

(5) FIG. 5 shows a comparison of the shrinkage rate of zirconia ceramics with or without oil.

(6) FIG. 6 shows a 3D printing of calcium phosphate bioceramic composite scaffold having interpenetrating pores.

(7) FIG. 7 is a UV photo-cured and molded 3D printing of calcium phosphate bioceramic composite scaffold.

(8) FIG. 8 shows a comparison of the shrinkage rate of an UV-cured and molded ceramic phosphate ceramics containing oil.

(9) FIG. 9 is a schematic drawing of a ceramic crack after uneven shrinkage. (Drying too quickly causes the specimen to bend or crack due to uneven shrinkage).

(10) FIG. 10 is a schematic diagram of the shrinkage of a dry powder dried without oil film. During the heating process, the hydrogel on the outer periphery of the preformed blank shrinks first, but while the temperature is increasing, the surrounding moisture also dissipates, which makes it difficult for the outer particles to have a high degree of shrinkage and densification. The pores tend to generate easily in the internal powder during the subsequent temperature increasing process.

(11) FIG. 11 is a schematic diagram of the shrinkage of a dry powder dried with oil film. During the heating process, the outer periphery of the preformed blank is coated with an oil film, which facilitates the shrinkage of the entire hydrogel and the dissipation of water to the outer periphery. Therefore, it is easier to have a high shrinkage rate, improving the densification of sintering. During the subsequent temperature increasing process, the porosity of the internal powder reduces significantly due to high temperature sintering and diffusion.

EXAMPLES

(12) The examples below are non-limiting and are merely representative of various aspects and features of the present invention.

(13) The present invention relates to preparing bioceramics by a 3D printing technology molding (additive manufacturing), i.e., bioceramics. For the method for preparing a composition comprising porous ceramic with thermo-responsive hydrogel, please refer to U.S. Pat. No. 8,940,203. The present invention utilizes the combination of a thermo-responsive hydrogel and the 3D printing technology to prepare a porous ceramic. Therefore, the goals of the present invention are: (1) adjustment of the ratio range of the negative thermo-responsive hydrogel/ceramic powder for the optimal condition of 3D printing and molding; (2) the range of the optimal control conditions during a 3D printing manufacturing process; (3) 3D printing and manufacturing of bioceramics (HAp/β-TCP)/negative thermo-responsive hydrogel (p(NiPAAm-MMA)), and detection and analysis; (4) 3D printing and manufacturing of oil-containing (such as silicone oil) bioceramics (HAp/β-TCP)/thermo-responsive hydrogel (p(NiPAAm-MMA)), and detection and analysis; (5) 3D printing and manufacturing of bioceramics (zirconia, ZrO.sub.2)/negative thermo-responsive hydrogel (p(NiPAAm-MMA)), and detection and analysis; (6) 3D printing and manufacturing of oil-containing (such as silicone oil) bioceramics (zirconia, ZrO.sub.2)/negative thermo-responsive hydrogel (p(NiPAAm-MMA)), and detection and analysis; (7) addition of a UV photo-curing initiator to the negative thermo-responsive hydrogel ceramics for proceeding a photo-curing printing. The mixing ratio of the negative thermo-responsive hydrogel solution and the ceramic powder was the weight percentage (wt %) of the negative thermo-responsive hydrogel solution and the weight of the ceramic powder. The condition of the 3D printing of negative thermo-responsive hydrogel/bioceramics was designed with the thermo-responsive properties of the negative thermo-responsive hydrogel, the temperature control on the printing carrier was adjusted so as to undergo phase transformation and shrinkage of the negative thermo-responsive hydrogel, allowing tightness among ceramic powders and achieving the molding effect. Other printing control conditions included the pressure of material extruding discharger of printing head, the printing speed, and the size of needle on a printing material discharge end. After 3D printing and manufacturing of the bioceramics, the high temperature sinter activities performed with or without added oil (silicon oil as the example) to cover the bioceramics were used as comparing groups, the ratio of shrinkage in the presence or absence of oil coverage before and after sintering were examined and compared Two different ceramic powders were used to verify the combinations of the negative thermo-responsive hydrogel system and the 3D printing technology for different ceramic powders. The preliminary results showed that after the negative thermo-responsive hydrogel and the bioceramics were mixed and agitated, the viscosity of the hydrogel needed to reach about 100 to 900 cP, which was in line with the material discharge range of 50 to 200,000 mPa.Math.s driven by the gas of a 3D printing machine. According to the particle size of the bioceramic powder and the thickness of printed lines, it was suitable to select a printing needle size ranging from 19G to 30G for proceeding the manufacturing. The movement speed of a printing head for 3D printing and manufacturing was one of the determining factors of the line thickness. After being physically tested, the best printing speed was in the range of 0.1 to 5 (cm/s). The shrinkage rate of oil containing—(silicon oil, hydrocarbon mineral oil, liquid paraffin, paraffin, synthetic hydrocarbons, etc.) or oil free-bioceramics (HAp/β-TCP)/negative thermo-responsive hydrogel (p(NiPAAm-MMA) or p(NiPAAm)) manufactured by 3D printing before and after sintering were compared, wherein the oil-covering group had a higher shrinkage rate, a shrinkage rate up to 27.9%. When different bioceramic powders were compared, the shrinkage rate of the oil containing- or oil free-bioceramics (zirconia, ZrO.sub.2)/negative thermo-responsive hydrogel (p(NiPAAm-MMA)) manufactured by 3D printing before and after sintering were compared, similarly, the oil-covering group had a higher shrinkage rate, a shrinkage rate up to 36%. At present, when the sintered ceramics were observed with a scanning electron microscope (SEM), the size of the pores was approximately 500 μm from a front view, and then the surface morphology was observed from a side view, a stacked pattern having interlaced bars specific to 3D printing and molding could be observed. The present invention successfully manufactured a system suitable for 3D printing of bioceramic. This negative thermo-responsive hydrogel of the system was able to use in combination with a variety of bioceramic materials, and multivariate patterns were printed by temperature-control of a 3D printing equipment, in which the use of negative thermo-responsive hydrogel in combination with an oil phase solution further enhanced the shrinkage effect of the bioceramics.

(14) 1. The ratio for mixing and agitating the negative thermo-responsive hydrogel solution and the ceramic powder was measure by the weight percentage concentration (wt %) of the negative thermo-responsive hydrogel solution and the weight of the ceramic powder, the best example would be adjusted according to the characteristic difference of the ceramic powder. The following was the actually implemented ratio:

(15) (1) Tricalcium Phosphate (β-TCP) ceramic powder: In 1 mL of 15% negative thermo-responsive hydrogel solution, 2.0 g of calcium phosphate ceramic powder was added and agitated for 8 minutes under vacuum to obtain a printable slurry.

(16) (2) Zirconia (ZrO.sub.2) ceramic powder: In 1 mL of 10% negative thermo-responsive hydrogel solution, 1.8 g of zirconia ceramic powder was added and agitated for 8 minutes under vacuum to obtain a printable slurry.

(17) (3) Hydroxylapatite (HAp) ceramic powder: In 1 mL of 15% negative thermo-responsive hydrogel solution, 2.0 g of hydroxylapatite ceramic powder was added and agitated for 8 minutes under vacuum to obtain a printable slurry.

(18) 2. The condition of the 3D printing negative thermo-responsive hydrogel/bioceramics was designed with the thermo-responsive properties of the negative thermo-responsive hydrogel, the temperature control on the printing carrier was adjusted so as to proceed phase transformation and shrinkage of the negative thermo-responsive hydrogel, allowing tightness among ceramic powders and achieving the molding effect. Other printing control conditions included the pressure of material extruding discharger of printing head, the printing speed, and the size of needle on a printing material discharge end.

(19) (1) The movement speed of a printing head for 3D printing and manufacturing was one of the determining factors of the line thickness. After being physically tested, the best printing speed was in the range of 0.1 to 5 (cm/s).

(20) (2) The material discharge speed of a printing head for 3D printing and manufacturing was one of the determining factors of the line thickness. After being physically tested, the best material discharge speed was 23G of needle primarily (internal diameter 25 mm), and the air pressure required to pneumatically push the material to be discharged was ±4.5 bar.

(21) (3) The curing and molding conditions for 3D printing and manufacturing of the negative thermo-responsive hydrogel was to increase the temperature of the printing carrier so that the negative thermo-responsive hydrogel underwent phase transformation and shrinkage, the temperature was ±40° C. In another preferred embodiment, the temperature of the printing carrier was heated to 30 to 80° C.

(22) 3. With respect to the 3D printing and manufacturing of negative thermo-responsive hydrogel/bioceramic, after completion of the printing and before the sintering was performed, the printed ceramics was covered by oil and sent to a high temperature furnace for sintering. The following were the differences in shrinkage with and without oil covering, and the ceramic sintering temperatures:

(23) (1) The agitated and mixed hydroxylapatite slurry was subjected to printing and molding, the object to be printed was about 14 mm in diameter and 3 mm in height, one of which was covered with silicone oil, sent to a high temperature furnace to be sintered at a gradient temperature of ±1250° C. for 6 to 8 hours. Upon completion, the diameter and height were measured to obtain the shrinkage rate (see FIG. 4). The shrinkage rate of the ceramic block without the addition of silicone oil and after being sintered was: 10% for diameter, 11.0% for height; the shrinkage rate of the ceramic block dripped and attached with silicone oil and after being sintered was: 27.9% for diameter, 21.3% for height.

(24) (2) The agitated and mixed zirconia slurry was subjected to printing and molding, the object to be printed was about 18.10 mm in diameter, one of which was covered with silicon oil, sent to a high temperature furnace to be sintered at a gradient temperature of ±1400° C. for 6 to 8 hours. Upon completion, the diameter and height were measured to obtain the shrinkage rate (FIG. 5). The shrinkage rate of the ceramic block without silicone oil and after being sintered was: 23.4% for diameter; the shrinkage rate of the ceramic block dripped and attached with silicon oil and after being sintered was: 36.08% for diameter.

(25) 4. 3D printing and molding technology of negative thermo-responsive hydrogel/bioceramic:

(26) With respect to previous curing technologies, the printing and manufacturing was performed by using temperature control. However, since the negative thermo-responsive hydrogel has a functional group structure for photo-curing mechanism, the printing and manufacturing could be converted into a printing performed in a photo-curing and molding manner by adding a photo-curing initiator.

(27) A photo-curing printing example, in which 1 to 5% of photo-curing initiator 12959 (UV absorption wavelength was 365 mm) was added to 15% of negative thermo-responsive hydrogel and agitated for 1 to 2 days, and then agitated with hydroxylapatite (HAp) ceramic powder, 2.0 g of hydroxylapatite ceramic powder was added to 1 mL of 15% negative thermo-responsive hydrogel solution, agitated and mixed under vacuum for 8 minutes to obtain a printable slurry.

(28) While printing, the photo-curing path and related irradiation time were provided by setting an UV module in order to cure and mold (see FIG. 7). A ceramic of 15 mm in diameter and 5 mm in height was printed, dripped and attached with silicon oil to cover, sent to a high temperature furnace to sintered at a gradient temperature of ±1250° C. for 6 to 8 hours. Upon completion, the diameter and height were measured, the size of ceramic block after sintered was 11.26 mm in diameter and 3.88 mm in height, and the shrinkage rate was 25% for diameter and 22.4% for height, respectively. (FIG. 8)

(29) Results:

(30) The above experimental results confirm that:

(31) (1) The 3D printing molding technology performed by using the negative thermo-responsive hydrogel mixed and agitated with ceramic powder of the present invention is a feasible 3D molding technology.

(32) (2) With respect to the 3D printing and molding process, printing parameters could be adjusted, the discharge rate of slurry, the movement rate of the printing head, the temperature of the carrier, the inner diameter of the printing needle, and other related parameters are controlled in order to proceed the manufacturing.

(33) (3) The negative thermo-responsive hydrogel system may be mixed and agitated with most ceramic powders for manufacturing and sintering, curing and molding for printing with the characteristics of phase transformation and shrinkage of the negative thermo-responsive hydrogel, and during the sintering process, the temperature is raised to further increase the shrinkage force, similar to the pressure equalization method in the traditional ceramic art, the shrinkage rate can be up to 10 to 20% as shown in the above experimental results.

(34) (4) In the experiment of the present invention, an action of covering a printed ceramic object by dripping and attaching an oil is proposed. This step can effectively improve the shrinkage effect of the ceramic sintering, and as shown in the above experimental results, the shrinkage rate can be up to 20 to 40%, having a greater shrinkage rate than the one with no oil dripped and attached.

(35) (5) The negative thermo-responsive hydrogel material used in the present invention can be added with a photo-curing initiator to convert it into a photocurable gel material. When being used in printing, the curing effect could be achieved by irradiation of the UV light, and the shrink capability remains the same.