Preparation method of two-way reinforced high-stability slurry 3D printing hydroxyapatite scaffold

Abstract

The invention relates to a preparation method of a bidirectional reinforced high-stability slurry 3D printing hydroxyapatite scaffold, which comprises the following steps: calculating the optimal grading proportion of nanospheres HA and microspheres HA according to the Furnas theory, carrying out grading, mixing a light-cured resin monomer and a diluent monomer according to different proportions, adding a first dispersant and a photoinitiator, stirring in a dark place, adding a second dispersant and a photoinitiator, and carrying out uniform mixing to obtain the bidirectional reinforced high-stability slurry 3D printing hydroxyapatite scaffold. Then ball-milling the powder and resin, adding a second dispersing agent, uniformly mixing to obtain hydroxyapatite slurry, finally printing the hydroxyapatite slurry into a stent by using a 3D printer, and cleaning, degreasing and sintering the printed stent to obtain the bidirectional reinforced high-stability slurry 3D printed hydroxyapatite stent. The porosity of the prepared porous scaffold is 62%, the compressive strength can reach 14.2 MPa, meanwhile, the stability of the slurry is synergistically enhanced by combining the double dispersing agents with the spherical powder, the flowability and solid content of the slurry can be effectively improved, and the quality and stable consistency of the printed scaffold are improved.

Description

Technical Field

[0001] The present invention belongs to the field of 3D printing biomedical materials, and specifically relates to a method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold. Background Art

[0002] With the rapid development of additive manufacturing technology, 3D printing has seen breakthroughs in the fields of biomedicine, aerospace, and more. Compared to traditional molding processes (such as injection molding and compression molding), photo-curing 3D printing technology achieves complex structure formation through layer-by-layer stacking, making it particularly suitable for personalized customization and the manufacture of fine porous structures. For example, in bone tissue engineering, the pore size, shape, and connectivity of porous bone scaffolds have a decisive influence on cell proliferation and nutrient delivery, and 3D printing technology can precisely control these parameters.

[0003] Hydroxyapatite (HA), the main inorganic component of human bone, is widely used in biomedical fields such as artificial bone implants and dental restorations due to its excellent biocompatibility, osteoconductivity, and chemical stability. However, traditional sintering processes make it difficult to produce HA ceramic components with complex geometries, and their mechanical properties have limited compatibility with natural bone. Light-curing 3D printing technology, by mixing HA powder with photosensitive resin to form a ceramic slurry, can directly form high-precision blanks, which are then degreased and sintered to obtain dense ceramic parts, providing a new approach for customized bone repair.

[0004] Despite this, the preparation of ceramic slurries remains a technical bottleneck. This is primarily due to the non-spherical HA powder, which leads to uneven slurry viscosity and poor leveling. This lack of stability during long-term use leads to sedimentation, and the tendency for interlayer delamination and porosity defects to occur during printing. Scaffolds printed with HA slurries of a single particle size also suffer from insufficient mechanical properties and high brittleness. Therefore, developing HA slurries with both high stability and excellent light-curing properties, and optimizing powder morphology and printing parameters, are key to improving the mechanical properties of ceramic scaffolds.

[0005] The Chinese patent "A method for preparing a porous calcium phosphate scaffold" (application number: 201810214780.8, authorization number: CN108638494B, announcement date: 2020.05.12) discloses a method for preparing a porous calcium phosphate scaffold. First, polycaprolactone is dissolved in acetone to prepare a concentrated polycaprolactone solution, and a suspension is obtained by uniformly mixing a mixed powder of calcium hydrogen phosphate and tetracalcium phosphate with a concentrated polycaprolactone solution as a 3D printing slurry, and then a direct-write 3D printer is used to form the porous scaffold. However, the solid content of the slurry prepared by this process is less than 20%, resulting in poor mechanical properties of the printed scaffold, and the printed scaffold obtained by the slurry requires complex post-processing processes such as removing the template, and cannot be sintered into porcelain.

[0006] The Chinese patent "A mechanically reinforced 3D printed calcium phosphate ceramic scaffold, its preparation method and application" (application number: CN202310713596.9, authorization number: CN116606130B, announcement date: 2025.01.28) discloses a mechanically reinforced 3D printed calcium phosphate ceramic scaffold, its preparation method and application. First, different acrylate monomers and dispersants are fully mixed, then hydroxyapatite powder and whisker growth inducing components are added, and finally a photoinitiator is added for vacuum degassing to obtain a 3D printing slurry and a light-curing 3D printer is used to prepare a porous scaffold. However, this method requires the addition of whisker growth inducing components to prepare the slurry, which is costly and cannot be applied on a large scale.

[0007] The Chinese patent "A light-cured bioceramic composite material for 3D printing, its application and printing system" (application number: CN201911093041.9, authorization number: CN110981463B, announcement date: 2020.08.28) discloses a light-cured bioceramic composite material for 3D printing, its application and printing system. First, the modified nano-tricalcium phosphate and modified nano-hydroxyapatite are respectively ball-milled with the light-curing resin, and then bone morphogenetic protein (BMP), material support, dispersant, nano-zirconium oxide, and water-soluble rheological additive are added. After multiple ball milling, ultrasonic dispersion, stirring, and low-temperature degassing, a light-cured bioceramic precursor solution is obtained. However, this method is complicated, requires multiple ball milling and mixing, is costly, and cannot be prepared in batches. Summary of the Invention

[0008] In response to the above problems, the present invention aims to provide a micro-nano spherical HA compound slurry, and prepare a bidirectionally reinforced and highly stable hydroxyapatite slurry through a suitable dispersant. By regulating the ratio of micro-nano spherical powder, the type and amount of dispersant, the ratio of resin monomer, etc., the problems of insufficient mechanical properties of single-particle HA slurry printed brackets in the prior art, difficulty in uniformly dispersing HA powder, resulting in poor stability of HA slurry, low fluidity, and pore defects in printed parts are solved.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold is specifically implemented according to the following steps:

[0011] Step 1, powder compounding: nano-sphere HA and micro-sphere HA are graded in different proportions to obtain compounded HA powder;

[0012] Step 2, resin preparation: Mix the photocurable resin monomer and the diluent monomer in different proportions, add the first dispersant and the photoinitiator, and stir in the dark;

[0013] Step 3, ball milling and mixing: adding the HA powder compounded in step 1 to the resin prepared in step 2, adding a second dispersant, placing in a planetary ball mill and mixing evenly to obtain a hydroxyapatite slurry;

[0014] Step 4, 3D printing and debinding and sintering: The hydroxyapatite slurry obtained in step 3 is used to print a bracket using a sinking DLP-3D printer, and then the printed bracket is cleaned in an ultrasonic bath to remove the uncured suspension. Finally, the printed bracket is debinded and sintered to obtain a bidirectionally reinforced and highly stable slurry 3D printed hydroxyapatite bracket.

[0015] Furthermore, the particle size of the nanosphere HA in step 1 is 100-300 nm, the particle size of the microsphere HA is 1-3 μm, the nanosphere HA accounts for 15%-30% of the total mass of the compounded HA powder, and the microsphere HA accounts for 70%-85% of the total mass of the compounded HA powder.

[0016] Furthermore, in step 2, the photocurable resin monomer is one or more of TMPTA and ACMO; and the diluent monomer is one or more of HDDA and HEA.

[0017] Furthermore, in step 2, the first dispersant is one of BYK-111, KOS-110, and Solsperse 41000, and the amount of the first dispersant added is 1%-5% of the total mass of the compounded HA powder.

[0018] Furthermore, the photoinitiator in step 2 is one of TPO or TMO, and the added amount of the photoinitiator is 2%-6% of the total mass of the photocurable resin monomer and the diluent monomer.

[0019] Furthermore, the light-proof stirring time in step 2 is 2-6 hours.

[0020] Furthermore, in step 3, the second dispersant is one of BYK-333, KOS-110, and Solsperse 41000, and the added amount of the second dispersant is 0.2%-3% of the total mass of the photocurable resin monomer and the diluent monomer.

[0021] Furthermore, in step 3, the ball milling speed of the planetary ball mill is 200 r / min-1000 r / min, and the ball milling time is 2-12 h.

[0022] Furthermore, the hydroxyapatite slurry prepared in step 3 is a suspension, and the solid loading thereof is 30%-55% of the total mass of the hydroxyapatite slurry.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention provides a method for preparing a bidirectionally reinforced, highly stable slurry for 3D printing of hydroxyapatite scaffolds. Using nanosphere and microsphere hydroxyapatite as ceramic powders, the optimal gradation ratio is calculated using Furnas' compounding theory, achieving bidirectional reinforcement through micro-nano gradation. The slurry prepared at a micro / nano ratio of 85:15, after 3D printing, yields a maximum porosity of 62% and a maximum compressive strength of 14.2 MPa. This material exhibits the properties of being porous yet highly strong. This exceeds the compressive strength of typical cancellous bone, which is 2-9 MPa, and meets the mechanical property requirements for subsequent bone scaffold printing.

[0025] 2. The hydroxyapatite slurry prepared by this invention achieves enhanced stability through the synergistic effect of a dual dispersant combined with spherical powder. This dual effect stabilizes the slurry viscosity below 4 Pa·s and achieves an absolute zeta potential of 32 mV. After standing for one month, the slurry exhibits no sedimentation. Furthermore, the spherical powder exhibits improved dispersion within the printing slurry matrix, resulting in excellent fluidity, effectively increasing the slurry's solids content and enhancing printing quality and stability.

[0026] 3. The raw materials used in this preparation method are low in cost, cheap and easily available, the slurry preparation process range is wide, the slurry has good stability, and is easy to mass produce and store for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a technical roadmap for the preparation method of a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold of the present invention;

[0028] Figure 2 Graph showing the dynamic viscosity test results of the hydroxyapatite slurries prepared in Examples 3 and 4 of the present invention;

[0029] Figure 3 Graph showing the Zeta potential test results of the hydroxyapatite slurries prepared in Examples 3 and 4 of the present invention;

[0030] Figure 4 3 is a graph showing the rheological properties of the hydroxyapatite slurries prepared in Examples 3 and 4 of the present invention;

[0031] Figure 5 Thixotropic ring analysis diagram of the hydroxyapatite slurry prepared in Example 3 and Example 4 of the present invention;

[0032] Figure 6 This is a macroscopic image of the static sedimentation experiment of the hydroxyapatite slurry prepared in Examples 1-4 of the present invention;

[0033] Figure 7 Schematic diagram of the porosity of the scaffolds obtained by 3D printing in Example 3 and Example 4 of the present invention;

[0034] Figure 8Schematic diagram of the compressive strength of the stents obtained by 3D printing in Example 3 and Example 4 of the present invention;

[0035] Figure 9 These are sample images of the embryo, degreasing stage, and sintering stage of the scaffold obtained by 3D printing in Example 4 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] like Figure 1 As shown, the present invention proposes a method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold, which is specifically implemented by the following steps:

[0038] Step 1, powder compounding: nanosphere HA with a particle size of 100-300nm and microsphere HA with a particle size of 1-3μm are graded in different proportions, wherein the nanosphere HA accounts for 15%-30% of the total mass of the compounded HA powder, and the microsphere HA accounts for 70%-85% of the total mass of the compounded HA powder.

[0039] Step 2, Resin Preparation: Mix the photocurable resin monomer and diluent monomer in different proportions, add the first dispersant and photoinitiator, and stir in the dark for 2-6 hours. The photocurable resin monomer is one or more of TMPTA (trimethylolpropane triacrylate) and ACMO (4-acryloylmorpholine). The diluent monomer is one or more of HDDA (1,6-hexanediol diacrylate) and HEA (hydroxyethyl acrylate). The first dispersant is one of BYK-111, KOS-110, or Solsperse 41000, and the amount of the first dispersant added is 1%-5% of the total weight of the compounded HA powder. The photoinitiator is one of TPO (2,4,6-trimethylbenzoyl)diphenylphosphine oxide) and TMO (2,4,6-trimethylbenzoyl-di(p-tolyl)phosphine oxide), and the amount of the photoinitiator added is 2%-6% of the total weight of the photocurable resin monomer and diluent monomer.

[0040] Step 3, ball milling: The HA powder compounded in step 1 is added to the resin prepared in step 2, followed by a second dispersant. The mixture is then placed in a planetary ball mill and mixed until uniformly mixed to obtain a hydroxyapatite slurry. The prepared hydroxyapatite slurry is a suspension having a solid loading of 30% to 55% of the total mass of the hydroxyapatite slurry. The second dispersant is selected from the group consisting of BYK-333, KOS-110, and Solsperse 41000, and the amount of the second dispersant added is 0.2% to 3% of the total mass of the photocurable resin monomer and the diluent monomer. The planetary ball mill is operated at a speed of 200 to 1000 rpm for a milling time of 2 to 12 hours.

[0041] Step 4, 3D printing and debinding and sintering: The hydroxyapatite slurry obtained in step 3 is used to print a bracket using a sinking DLP-3D printer, and then the bracket is cleaned in an ultrasonic bath to remove the uncured suspension. Finally, the printed bracket is debinded and sintered to obtain a bidirectionally reinforced and highly stable slurry 3D printed hydroxyapatite bracket.

[0042] The present invention provides a method for preparing a bidirectionally reinforced, highly stable slurry 3D-printed hydroxyapatite scaffold. Nanospheres and microspheres of hydroxyapatite are used as ceramic powders. The optimal gradation ratio is calculated through Furnas compounding theory to achieve micro-nano grading bidirectional reinforcement. The microspheres of HA serve as the skeleton to support the structural strength, while the nanospheres of HA fill the pores and enhance the interfacial bonding strength.

[0043] The Furnas theory aims to optimize the mixing ratio of bimodal particles, so that small particles fill the gaps between large particles and achieve maximum packing density. According to the Furnas theory, when a powder with a mixed bimodal particle size distribution (PSD) reaches the most dense packing, the ideal volume concentration φ1 of the large particles and the ideal volume concentration φ2 of the small particles are calculated as follows:

[0044]

[0045] Where ε1 is the porosity of the large particles, ε2 is the porosity of the small particles, φ1 is the ideal volume concentration of the large particles, and φ2 is the ideal volume concentration of the small particles.

[0046] In actual research, the above formula, combined with the experimentally measured porosity data of large and small particles, can be used to calculate the ratio of the two particle sizes when they are closely packed. Porosity is the ratio of pore volume to the total volume of the material, which can be measured by BET to obtain pore volume / V pore The calculations were performed using the following formulas and the results are shown in Table 1.

[0047] The volume of HA is:

[0048] Total volume V total =V total =V HA +V Proe (4)

[0049] Porosity calculation formula:

[0050] Among them, V HA is the volume of HA, m HA is the mass of HA, ρ HA is the density of HA, V total is the total volume of HA material, VProe is the pore volume and ε is the porosity.

[0051] Table 1 shows the BET test results and porosity calculation results.

[0052] Table 1 shows the BET surface area test results and porosity calculation results of hydroxyapatite powder. pore is the pore volume per unit mass measured by the BET method (cm 3 ·g -1 ), which reflects the capacity of the pores inside the material; d represents the average pore size (nm), which characterizes the size characteristics of the pore structure; ε is the porosity calculated based on formula (5), which reflects the proportion of the pore volume in the material to the total volume. For microsphere HA, its lower V pore (0.156cm 3 ·g -1 ) and a larger average pore size (249.542 nm) corresponding to a porosity of 33%, indicating that its particles are densely packed; while the nanosphere HA has a higher V pore (0.589cm 3 ·g -1 ) and a small pore size (21.848 nm) resulted in a significant increase in porosity to 65%, revealing a richer microporous structure between the particles. The difference in porosity between the two groups of samples directly affects the subsequent calculation of the optimal ratio of bimodal particles in Furnas theory.

[0053] Table 1 BET test results and porosity calculation results

[0054]

[0055] Substituting ε1 = 0.33 and ε2 = 0.65 into formula (1) and formula (2), we can calculate φ1 = 85.3% and φ2 = 14.7%. At this time, the micro-nano ratio is approximately μ-HA:n-HA = 85:15. This result was verified by subsequent examples. The hydroxyapatite slurry prepared at a micro-nano ratio of 85:15 had a maximum porosity of 62% after sintering by 3D printing, but had a maximum compressive strength of 14.2 MPa. The material exhibited porous but high-strength characteristics. This exceeded the compressive strength of ordinary cancellous bone, which is 2-9 MPa, and met the mechanical properties requirements of subsequent bone scaffold printing.

[0056] The hydroxyapatite slurry synthesized in this invention achieves synergistically enhanced stability through the combination of dual dispersants and spherical powders. A first dispersant is pre-coated on the HA surface to reduce agglomeration, while a second dispersant is introduced to create steric hindrance during ball milling. These dual effects stabilize the slurry viscosity below 4 Pa·s and achieve an absolute zeta potential of 32 mV. After standing for one month, the slurry exhibits no sedimentation, meeting the requirements of DLP-3D printing and addressing the sedimentation problem of high-solids content (above 45%) slurries. Furthermore, the spherical powder exhibits improved dispersion and fluidity within the printing slurry matrix, effectively increasing the slurry's solids content and enhancing print quality and stability.

[0057] The raw materials used in the preparation process of the present invention are low-cost and readily available, the slurry preparation process has a wide range, and the slurry has good stability, which makes it easy to mass produce and store for a long time. There is no need to worry about the problem of high-solid content slurry easily settling when stored for a long time.

[0058] Example 1

[0059] Step 1, powder compounding: grading 20 wt% of nanosphere HA with a particle size of 100-300 nm and 80 wt% of microsphere HA with a particle size of 1-3 μm, the total of the above components being 100%.

[0060] Step 2, resin preparation: diluent monomer HDDA and photocurable resin monomers TMPTA and ACMO are mixed in a mass ratio of 4:4:2, BYK-111 (1 wt% compounded HA powder) and TPO (2 wt% total mass of photocurable resin monomer and diluent monomer) are added to the mixture, stirred in the dark for 2 h, and mixed evenly to obtain a solvent.

[0061] Step 3, ball milling: Add the HA powder compounded in Step 1 to the resin solvent prepared in Step 2, then add KOS-110 (0.2 wt% total weight of the photocurable resin monomer and diluent monomer). Mix in a planetary ball mill at 200 rpm for 12 hours. The final hydroxyapatite slurry is adjusted to a solids content of 30 wt% by weight by adjusting the ratio of HA powder to resin.

[0062] Step 4, 3D printing and debinding and sintering: The hydroxyapatite slurry obtained in step 3 is used to print a bracket using a sinking DLP-3D printer, and then the printed bracket is cleaned in an ultrasonic bath to remove the uncured suspension. Finally, the printed bracket is debinded and sintered to obtain a bracket sample.

[0063] Example 2

[0064] Step 1, powder compounding: grading 25wt% of nanosphere HA with a particle size of 100-300nm and 75wt% of microsphere HA with a particle size of 1-3μm, the total of the above components is 100%.

[0065] Step 2, resin preparation: Mix the diluent monomer HEA with the photocurable resin monomers TMPTA and ACMO in a mass ratio of 2:5:3, add Solsperse 41000 (5wt% compounded HA powder) and TMO (6wt% total mass of photocurable resin monomer and diluent monomer) to the mixture, stir in the dark for 6 hours, and mix evenly to form a solvent.

[0066] Step 3, ball milling: Add the HA powder compounded in Step 1 to the solvent prepared in Step 2, along with BYK-333 (3 wt% total weight of the photocurable resin monomer and diluent monomer). Mix in a planetary ball mill at 1000 rpm for 2 hours. The final hydroxyapatite slurry is adjusted to a solids content of 40 wt% by weight by adjusting the ratio of HA powder to resin.

[0067] Step 4, 3D printing and debinding and sintering: The hydroxyapatite slurry obtained in step 3 is used to print a bracket using a sinking DLP-3D printer, and then the printed bracket is cleaned in an ultrasonic bath to remove the uncured suspension. Finally, the printed bracket is debinded and sintered to obtain a bracket sample.

[0068] Example 3

[0069] Step 1, powder compounding: grading 30 wt% of nanosphere HA with a particle size of 100-300 nm and 70 wt% of microsphere HA with a particle size of 1-3 μm, the total of the above components being 100%.

[0070] Step 2, resin preparation: diluent monomers HDDA, HEA and photocurable resin monomer ACMO are mixed in a mass ratio of 3:3:4, BYK-111 (2 wt% compounded HA powder) and TMO (4 wt% total mass of photocurable resin monomer and diluent monomer) are added to the mixture, stirred in the dark for 5 hours, and mixed evenly to form a solvent.

[0071] Step 3, ball milling: Add the HA powder compounded in Step 1 to the solvent prepared in Step 2, add Solsperse 41000 (1.2 wt% total weight of the photocurable resin monomer and diluent monomer), and stir in a planetary ball mill at 600 rpm for 10 hours. The final hydroxyapatite slurry is adjusted to a solids content of 55 wt% by weight by adjusting the ratio of HA powder to resin.

[0072] Step 4, 3D printing and debinding and sintering: The hydroxyapatite slurry obtained in step 3 is used to print a bracket using a sinking DLP-3D printer, and then the printed bracket is cleaned in an ultrasonic bath to remove the uncured suspension. Finally, the printed bracket is debinded and sintered to obtain a bracket sample.

[0073] Example 4

[0074] Step 1, powder compounding: grading 15 wt% of nanosphere HA with a particle size of 100-300 nm and 85 wt% of microsphere HA with a particle size of 1-3 μm, the total of the above components being 100%.

[0075] Step 2, resin preparation: Mix the diluent monomers HDDA and HEA with the photocurable resin monomer TMPTA in a mass ratio of 6:3:1, add KOS110 (3 wt% of compounded HA powder) and TPO (3 wt% of the total mass of the photocurable resin monomer and the diluent monomer) to the mixture, stir in the dark for 4 hours, and mix well to form a solvent.

[0076] Step 3, ball milling: Add the HA powder compounded in Step 1 to the solvent prepared in Step 2, along with BYK-333 (0.3 wt% total weight of the photocurable resin monomer and diluent monomer). Mix in a planetary ball mill at 400 rpm for 8 hours. The ratio of HA powder to resin was adjusted to achieve a final hydroxyapatite slurry with a solids content of 50 wt%.

[0077] Step 4, 3D printing and debinding and sintering: The hydroxyapatite slurry obtained in step 3 is used to print a bracket using a sinking DLP-3D printer, and then the printed bracket is cleaned in an ultrasonic bath to remove the uncured suspension. Finally, the printed bracket is debinded and sintered to obtain a bracket sample.

[0078] Figure 2 The figure shows the dynamic viscosity test results of the hydroxyapatite slurry prepared in Example 3 and Example 4 of the present invention. Group S2 is Example 4, Group S3 is Example 3, and Group C1 is a control group in which a single nanosphere powder and a single dispersant are added. Figure 2 As can be seen, group S2 has the lowest viscosity and the best fluidity. Group C1 has the highest viscosity, which further confirms that ungraded single nanosphere powder is difficult to evenly disperse in the resin, and a single dispersant clearly cannot achieve the best dispersion effect. The results show that group C1 has the worst fluidity. Adding only a single nanosphere powder and a single dispersant significantly increases the viscosity of the slurry and reduces its fluidity.

[0079] Figure 3The Zeta potential test results of the hydroxyapatite slurry prepared in Example 3 and Example 4 of the present invention are shown in Figure 1. The S2 group is Example 4, the S3 group is Example 3, and the C1 group is a control group to which a single nanosphere powder and a single dispersant are added. The absolute value of the Zeta potential of C1 is the lowest, which is 7mV, while the absolute value of the Zeta potential of the S2 group is 32mV, which is about 4 times that of the slurry in the C1 group. This shows that the synergy of the dual dispersants can effectively increase the absolute value of Zeta and improve the stability of the slurry. The absolute value of the Zeta potential of the S3 group is 28mV, which is lower than that of the S2 group. The excessively high n-HA content exacerbates the agglomeration of the slurry itself, resulting in the overall stability of the S3 group being inferior to that of the S2 group.

[0080] Figure 4 The rheological properties analysis diagram of the hydroxyapatite slurry prepared in Examples 3 and 4 of the present invention, Group S2 is Example 4, Group S3 is Example 3, and Group C1 is a control group with the addition of a single nanosphere powder and a single dispersant. Obvious shear thinning phenomenon can be observed in all three groups of slurries. At the beginning, the viscosity of Group S2 was the lowest. As the shear rate increased, the viscosity of Group S2 dropped to about 2.6 Pa·s. The viscosity of Group C1 was the highest, at 5.5 Pa·s, indicating that the dual dispersants can synergistically reduce the slurry viscosity and improve fluidity. Compared with Group S2, Group S3 had a lower slurry fluidity due to the excess n-HA, with a viscosity of 3.6 Pa·s.

[0081] Figure 5 Thixotropic ring analysis diagram of hydroxyapatite slurry prepared in Example 3 and Example 4 of the present invention. Group S2 is Example 4, Group S3 is Example 3, and Group C1 is a control group with a single nanosphere powder and a single dispersant added. The stability of the slurry can be verified by measuring the size of the thixotropic ring of the three groups of slurries. The smaller the area, the more stable the shear spreading process of the slurry during printing, and the easier it is to recover after shearing, which can avoid the formation of defects inside the printed part. Figure 5 It can be seen that the thixotropic ring area of group S2 is the smallest at 39.48, which allows for rapid printing and laying of materials. Group S3 has a lower stability in the rheological process than group S2 due to the excessive addition of n-HA, while group C1 has the worst stability due to its higher viscosity.

[0082] Figure 6 This is a macroscopic image of the static sedimentation experiment of the hydroxyapatite slurry prepared in Examples 1-4 of the present invention. The four groups of slurries are Examples 1-4 respectively. It can be observed that the macroscopic stability of all slurries is good, and there is no sedimentation within one month of static standing, showing high stability.

[0083] Figure 7Schematic diagram of the porosity of 3D-printed scaffolds from Examples 3 and 4 of the present invention. Group S2 is Example 4, Group S3 is Example 3, and Group C1 is a control group containing a single nanosphere powder and a single dispersant. All three groups exhibited porosities ranging from 54% to 68%, indicating that all were porous scaffolds, with Group S2 exhibiting the highest porosity of 62%.

[0084] Figure 8 This figure shows the compressive strength of scaffolds obtained by 3D printing in Examples 3 and 4 of the present invention. Group S2 is Example 4, Group S3 is Example 3, and Group C1 is a control group that added a single nanosphere powder and a single dispersant. Group C1 had the lowest compressive strength of 6.4 MPa, while Group S3 had 11.0 MPa. Group S2 had the highest compressive strength of 14.2 MPa, indicating that bidirectional reinforcement with an optimal micro-nano ratio can effectively improve the mechanical properties of scaffolds printed with slurry. Its compressive strength exceeds the compressive strength of general cancellous bone, which is 2-9 MPa, meeting the mechanical properties requirements of scaffold printing.

[0085] Figure 9 This is a sample diagram of the embryo / degreasing stage / sintering stage (from left to right) of the scaffold obtained by 3D printing in Example 4 of the present invention. The final sintered scaffold has good precision, uniform layers, and good bonding. The prepared hydroxyapatite slurry can meet the requirements of precise molding of 3D printed scaffolds.

[0086] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold, characterized in that: Please follow the steps below to implement it: Step 1, powder compounding: nano-sphere HA and micro-sphere HA are graded in different proportions to obtain compounded HA powder; Step 2, resin preparation: Mix the photocurable resin monomer and the diluent monomer in different proportions, add the first dispersant and the photoinitiator, and stir in the dark; Step 3, ball milling and mixing: adding the HA powder compounded in step 1 to the resin prepared in step 2, adding a second dispersant, placing in a planetary ball mill and mixing evenly to obtain a hydroxyapatite slurry; Step 4, 3D printing and debinding and sintering: The hydroxyapatite slurry obtained in step 3 is used to print a bracket using a sinking DLP-3D printer, and then the printed bracket is cleaned in an ultrasonic bath to remove the uncured suspension. Finally, the printed bracket is debinded and sintered to obtain a bidirectionally reinforced and highly stable slurry 3D printed hydroxyapatite bracket.

2. The method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold according to claim 1, characterized in that: The particle size of the nanosphere HA in step 1 is 100-300 nm, the particle size of the microsphere HA is 1-3 μm, the nanosphere HA accounts for 15%-30% of the total mass of the compounded HA powder, and the microsphere HA accounts for 70%-85% of the total mass of the compounded HA powder.

3. The method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold according to claim 1, characterized in that: In step 2, the photocurable resin monomer is one or more of TMPTA and ACMO; the diluent monomer is one or more of HDDA and HEA.

4. The method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold according to claim 1, characterized in that: In step 2, the first dispersant is one of BYK-111, KOS-110, and Solsperse 41000, and the amount of the first dispersant added is 1%-5% of the total mass of the compounded HA powder.

5. The method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold according to claim 1, characterized in that: The photoinitiator in step 2 is one of TPO and TMO, and the amount of the photoinitiator added is 2%-6% of the total mass of the photocurable resin monomer and the diluent monomer.

6. The method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold according to claim 1, characterized in that: The stirring time in step 2 is 2-6 hours in the dark.

7. The method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold according to claim 1, characterized in that: In step 3, the second dispersant is one of BYK-333, KOS-110, and Solsperse 41000, and the amount of the second dispersant added is 0.2%-3% of the total mass of the photocurable resin monomer and the diluent monomer.

8. The method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold according to claim 1, characterized in that: In step 3, the ball milling speed of the planetary ball mill is 200 r / min-1000 r / min, and the ball milling time is 2-12 h.

9. The method for preparing a bidirectionally reinforced high-stability slurry 3D printed hydroxyapatite scaffold according to claim 1, characterized in that: The hydroxyapatite slurry prepared in step 3 is a suspension, and the solid loading thereof is 30%-55% of the total mass of the hydroxyapatite slurry.

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