A method for preparing gradient HA / ZrO2 bioceramics and the bioceramics themselves

Abstract

This invention provides a method for preparing gradient HA / ZrO2 bioceramics and the bioceramics themselves, relating to the field of ceramic material preparation technology. The method includes: conducting sintering experiments with different solid contents and different combinations of HA and ZrO2 component ratios to obtain sintering shrinkage data and establishing a sintering shrinkage control model; determining the component ratio of each layer of the ceramic gradient structure according to biomechanical requirements; performing reverse design of the gradient structure based on the component ratio of each layer of the ceramic gradient structure using the sintering shrinkage control model to obtain the required solid content for each layer of the ceramic gradient structure; and preparing HA / ZrO2 composite ceramic slurries with different solid contents according to the required solid content for each layer of the ceramic gradient structure to prepare gradient HA / ZrO2 bioceramics. This invention enables the ZrO2-rich layer and the HA-rich layer to achieve equal shrinkage during co-sintering, fundamentally eliminating interlayer stress and preventing cracking and warping.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation technology, specifically to an additive manufacturing method for multiphase bioceramics, and more particularly to a method for preparing gradient HA / ZrO2 bioceramics and the bioceramics themselves. Background Technology

[0002] Hydroxyapatite (HA) possesses excellent bioactivity and osteoconductivity, but is brittle and has low fracture toughness; zirconia (ZrO2) exhibits excellent mechanical properties, but is highly bioinert. Combining these two materials to prepare functionally graded materials allows for a performance transition from a high-strength ZrO2 core to a highly bioactive HA surface, making it an ideal bone repair material. With the development of additive manufacturing technology, Digital Light Processing (DLP) technology, due to its high forming precision and ability to fabricate complex structures, has become the primary method for preparing bioceramic gradient structures.

[0003] In related technologies, the conventional process for preparing HA / ZrO2 gradient materials typically employs a strategy of "fixed solid content, varied component ratio," meaning that the same solid content is used in each gradient layer, and the compositional gradient is achieved only by adjusting the ratio of HA to ZrO2. When the two components differ significantly, a transition layer is added in the middle to reduce the risk of cracking caused by differences in sintering shrinkage. However, the number, thickness, and ratio of the transition layer often depend on exploratory experiments, resulting in long development cycles and significant waste. Furthermore, the focus of process design is often limited to optimizing the rheological properties of the slurry and adjusting printing parameters to ensure the molding accuracy of the green body, failing to fundamentally solve the shrinkage mismatch problem.

[0004] Therefore, how to solve the interlayer cracking problem caused by inconsistent intrinsic sintering shrinkage of different gradient layers in HA / ZrO2 gradient materials during DLP photocuring preparation has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a method for preparing gradient HA / ZrO2 bioceramics and the bioceramics themselves, in order to solve the problem of interlayer cracking caused by inconsistent intrinsic sintering shrinkage of different gradient layers in HA / ZrO2 gradient materials during DLP photocuring preparation.

[0006] In a first aspect, embodiments of the present invention provide a method for preparing gradient HA / ZrO2 bioceramics, comprising:

[0007] By constructing sintering experiments with different solid contents and different combinations of HA and ZrO2 composition ratios, sintering shrinkage rate data were obtained, and a sintering shrinkage rate control model was established based on the sintering shrinkage rate data.

[0008] Obtain biomechanical requirements and determine the composition ratio of each layer of the ceramic gradient structure based on these requirements;

[0009] Based on the composition ratio of each layer of the ceramic gradient structure, the gradient structure is reverse-designed using a sintering shrinkage rate control model to obtain the required solid content of each layer of the ceramic gradient structure.

[0010] Based on the required solid content of each layer of the ceramic gradient structure, HA / ZrO2 composite ceramic slurries with different solid contents were prepared, and gradient HA / ZrO2 bioceramics were prepared using the HA / ZrO2 composite ceramic slurries.

[0011] In one possible implementation, based on the component ratios of each layer of the ceramic gradient structure, a sintering shrinkage control model is used for inverse design of the gradient structure to obtain the required solid content of each layer of the ceramic gradient structure, including:

[0012] Obtain the target volume shrinkage rate;

[0013] By inputting the component ratios and target volume shrinkage rates of each layer of the ceramic gradient structure into the sintering shrinkage rate control model, the required solid content of each layer of the ceramic gradient structure can be calculated.

[0014] In one possible implementation, sintering shrinkage rate data is obtained by constructing sintering experiments with different solid contents and different combinations of HA and ZrO2 composition ratios. Based on the sintering shrinkage rate data, a sintering shrinkage rate control model is established, including:

[0015] Sintering experiments were conducted under m groups of different solid contents and n groups of different combinations of HA and ZrO2 composition ratios to obtain m×n groups of sintering shrinkage rate data; the sintering shrinkage rate data included volume shrinkage rate, solid content, and composition ratio of HA and ZrO2.

[0016] A multiple linear regression analysis was performed on the sintering shrinkage rate data to obtain a sintering shrinkage rate control model.

[0017] In one possible implementation, the sintering shrinkage rate control model is expressed as:

[0018]

[0019] Where y is the volume shrinkage rate; Solid content; The composition ratio of HA to ZrO2; These are the fitting constant coefficients; The solid content coefficient; is the component coefficient.

[0020] In one possible implementation, the HA / ZrO2 composite ceramic slurry is composed of HA powder, ZrO2 powder, and a photosensitive resin premix; the photosensitive resin premix includes resin monomers, acrylate prepolymers, dispersants, and photoinitiators.

[0021] In one possible implementation, the resin monomers include 4-acryloylmorpholine, ethoxylated trimethylolpropane triacrylate, and propoxylated neopentyl glycol diacrylate; the acrylate prepolymers include polyurethane acrylates.

[0022] 4-Acryloylmorpholine:ethoxylated trimethylolpropane triacrylate:propoxylated neopentyl glycol diacrylate:polyurethane acrylate = 2:3:3:2.

[0023] In one possible implementation, the solid content required for each layer of the ceramic gradient structure, calculated based on the target volume shrinkage rate, is within the printing range of the slurry; the solid content adjustment range corresponding to the printing range of the slurry is 19 vol.% to 41 vol.%.

[0024] In one possible implementation, the composition ratio of HA to ZrO2 is expressed as the mass fraction of HA, with the mass fraction of HA ranging from 0.3 to 0.7; the particle size of the HA powder is 4.5 μm; and the ZrO2 powder is 3 mol% yttrium oxide-stabilized zirconium oxide with a particle size of 1 μm.

[0025] In one possible implementation, gradient HA / ZrO2 bioceramics are prepared using HA / ZrO2 composite ceramic slurry, including:

[0026] By using a photopolymerization 3D printer, different gradient layers are printed sequentially by changing HA / ZrO2 composite ceramic slurry with different solid contents, resulting in green bodies with gradient changes in both composition and solid content.

[0027] The green body was degreased and co-sintered at high temperature to obtain gradient HA / ZrO2 bioceramics.

[0028] Secondly, embodiments of the present invention provide a gradient HA / ZrO2 bioceramic prepared by any of the methods described in the above embodiments.

[0029] In this embodiment of the invention, a sintering shrinkage rate control model is constructed, with solid content as an active adjustment variable. The solid content of each layer in the ceramic gradient structure is designed in reverse for different component ratios, ensuring that the ZrO2-rich layer and the HA-rich layer achieve equal shrinkage during co-sintering. This fundamentally eliminates interlayer stress and prevents cracking and warping. Quantitative design replaces traditional trial-and-error, significantly shortening the R&D cycle and reducing costs. Simultaneously, it considers both the bioactivity of HA and the mechanical properties of ZrO2, enabling the fabrication of gradient structures with a wide compositional range, numerous layers, and tight interfacial bonding. This achieves optimized distribution of bioactivity and mechanical properties within a single component. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the preparation method of gradient HA / ZrO2 bioceramics provided in this embodiment of the invention.

[0031] Figure 2 This is a process flow diagram for preparing gradient HA / ZrO2 bioceramics provided in an embodiment of the present invention;

[0032] Figure 3 This is a cylindrical sample containing five layers of compositional gradients provided in the embodiments of the present invention;

[0033] Figure 4 This is the microstructure of a cylindrical sample with five layers of compositional gradient formed by five different component ratios provided in the embodiments of the present invention; Figure 4 (a) shows the microstructure of HA:3YSZ = 7:3; Figure 4 (b) shows the microstructure of HA:3YSZ = 6:4. Figure 4 (c) shows the microstructure of HA:3YSZ=5:5; Figure 4 The middle (d) shows the microstructure of HA:3YSZ=4:6; Figure 4 In the middle (e), the microstructure of HA:3YSZ=3:7 is shown. Detailed Implementation

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] The method for preparing gradient HA / ZrO2 bioceramics provided in this invention can be applied in the fields of biomedical engineering and bone tissue engineering. Ideal bone implant materials need to possess both excellent biocompatibility and sufficient mechanical properties. HA, as the main inorganic component of vertebrate bones and teeth, has excellent bioactivity and osteoconductivity, and can form chemical bonds with bone tissue. However, the inherent brittleness and low fracture toughness of HA ceramics limit their application in the repair of weight-bearing bone defects. In contrast, ZrO2, especially 3 mol% yttrium oxide-stabilized tetragonal zirconia polycrystalline (3YSZ), is known as "ceramic steel" due to its excellent fracture toughness and high flexural strength, but its bioinertness results in weaker bonding with host bone tissue.

[0036] The intrinsic sintering behavior differences between HA and 3YSZ stem from their different powder characteristics and densification kinetic mechanisms. HA powder typically has a large particle size (micrometer scale), low sintering activity, and is prone to high-temperature decomposition. Its densification process mainly relies on volume diffusion, with a high initial shrinkage temperature and a gradual shrinkage rate. In contrast, submicrometer-sized 3YSZ has a high specific surface area and defect chemical activity, resulting in strong sintering driving force and a fast densification rate, preferentially completing shrinkage under the same heating conditions. Related technologies reduce the difference in sintering shrinkage by setting an intermediate transition layer. During high-temperature co-sintering, the shrinkage rate and amount of the HA-rich layer and the 3YSZ-rich layer are inconsistent. When the 3YSZ-rich layer has completed most of its shrinkage while the HA-rich layer has not yet been sufficiently densified, significant shear and tensile stresses will accumulate at the interface. This asynchronous densification behavior leads to huge mismatch stresses at the gradient layer interface. If these stresses exceed the interlayer bonding strength, macroscopic cracking, delamination, or severe warping deformation will inevitably occur, greatly reducing the yield and mechanical reliability of the material.

[0037] Solid content refers to the volume percentage of ceramic powder (HA and ZrO2) in the ceramic slurry, expressed as vol.%. The remainder is a photosensitive resin premix. Volume shrinkage rate refers to the percentage decrease in volume of the ceramic green body after high-temperature sintering into a dense ceramic part.

[0038] Solid content, as a key parameter of ceramic slurry, not only affects the forming performance and density of green bodies, but also plays a decisive role in the volume shrinkage rate during sintering. Theoretically, the higher the solid content, the greater the particle packing density in the green body, and the smaller the volume shrinkage rate during sintering; conversely, the lower the solid content, the greater the volume shrinkage rate during sintering.

[0039] The inventors discovered that related technologies generally treat solid content as a fixed parameter, merely considering it as a process parameter to maintain the printability of the slurry, failing to recognize that solid content can be an effective variable for actively controlling sintering shrinkage. In fact, by rationally adjusting the solid content of each gradient layer, the intrinsic shrinkage differences between layers of different compositions can be compensated. Specifically, a higher solid content is used for 3YSZ-rich layers to suppress excessive shrinkage, while a lower solid content is used for HA-rich layers to promote sufficient densification, thus achieving a synergistic matching of shrinkage behavior among layers. However, how to implement this compensation mechanism is a problem that needs to be solved. Therefore, the inventors established a quantitative relationship model to mathematically characterize the relationship between "composition-volume shrinkage rate-solid content," thereby enabling precise reverse design of solid content to achieve consistent shrinkage of different composition gradient layers during co-sintering, resulting in high-performance gradient bioceramics with intact structures and no cracks.

[0040] See Figure 1 The document illustrates a flowchart of the preparation method for gradient HA / ZrO2 bioceramics provided in this embodiment of the invention, detailed below:

[0041] A method for preparing gradient HA / ZrO2 bioceramics, comprising:

[0042] Step 101: By constructing sintering experiments with different solid contents and different combinations of HA and ZrO2 composition ratios, sintering shrinkage rate data is obtained, and a sintering shrinkage rate control model is established based on the sintering shrinkage rate data.

[0043] For example, multiple sets of sintering shrinkage rate data are obtained by setting up multiple sets of orthogonal sintering experiments. Among them, the sintering shrinkage rate data includes volume shrinkage rate, solid content, and composition ratio of HA to ZrO2.

[0044] Step 102: Obtain biomechanical requirements and determine the composition ratio of each layer of the ceramic gradient structure based on biomechanical requirements.

[0045] For example, in the field of bone tissue engineering, ideal implant materials need to meet the specific biomechanical requirements of the implantation site. That is, the material needs to have excellent bioactivity in the area in contact with the host bone to promote bone healing, while it needs to have sufficient mechanical strength in the load-bearing area to support the load. Human natural bone tissue itself is a typical gradient structure, such as the transition from dense cortical bone to porous cancellous bone. Therefore, designing biomimetic gradient materials is an effective strategy to achieve structure-function matching.

[0046] For example, based on biomimetic bone structures, and utilizing the material properties that HA content is directly proportional to bioactivity and ZrO2 content is directly proportional to mechanical strength, the composition ratio of HA and ZrO2 can be set to continuously vary along the gradient layer. The qualitative requirements for biomimetic bone structures are quantified into the specific component ratios of each layer of the gradient structure. This ensures that the biological and mechanical functions of the gradient structure are rationally distributed along the thickness direction, paving the way for subsequent back-calculation of the solid content of each layer based on the sintering shrinkage rate model. This lays the foundation for achieving crack-free co-sintering manufacturing.

[0047] Step 103: Based on the composition ratio of each layer of the ceramic gradient structure, the gradient structure is reverse-designed using a sintering shrinkage rate control model to obtain the required solid content of each layer of the ceramic gradient structure.

[0048] For example, the solids content is no longer a fixed value, but is used as a tool to actively regulate shrinkage. By changing the solids content of different gradient layers, intrinsic shrinkage differences caused by compositional variations can be compensated for.

[0049] Step 104: Based on the required solid content of each layer of the ceramic gradient structure, prepare HA / ZrO2 composite ceramic slurries with different solid contents, and use the HA / ZrO2 composite ceramic slurries to prepare gradient HA / ZrO2 bioceramics.

[0050] This embodiment constructs a sintering shrinkage rate control model, using solid content as an active adjustment variable. It designs the solid content of each layer in reverse for different component ratios, ensuring equal shrinkage between the ZrO2-rich and HA-rich layers during co-sintering. This fundamentally eliminates interlayer stress and prevents cracking and warping. Quantitative design replaces traditional trial-and-error, significantly shortening the R&D cycle and reducing costs. Simultaneously, it balances the bioactivity of HA with the mechanical properties of ZrO2, enabling the fabrication of gradient structures with a wide compositional range, numerous layers, and tight interfacial bonding. This achieves optimized distribution of bioactivity and mechanical properties within a single component.

[0051] In one embodiment, the specific process of the sintering shrinkage rate control model is described. Step 101 specifically includes:

[0052] First, sintering experiments were conducted under m groups of different solid contents and n groups of different combinations of HA and ZrO2 composition ratios to obtain m×n groups of sintering shrinkage rate data.

[0053] For example, a photosensitive resin premix and ceramic powder are prepared. The ceramic powder is selected from hydroxyapatite (HA) powder and ZrO2 powder. The composition ratio of HA to ZrO2 is expressed as the mass fraction of HA, with the mass fraction of HA ranging from 0.3 to 0.7; the particle size of the HA powder is 4.5 μm; the ZrO2 powder is 3 mol% yttrium oxide-stabilized zirconium oxide with a particle size of 1 μm.

[0054] The photosensitive resin premix comprises resin monomers, acrylate prepolymers, dispersants, and photoinitiators, as shown in Table 1. The resin monomers, acrylate prepolymers, dispersants, and photoinitiators are magnetically stirred until homogeneous to form the photosensitive resin premix for later use. The resin monomers include 4-acryloylmorpholine, ethoxylated trimethylolpropane triacrylate, and propoxylated neopentyl glycol diacrylate; the acrylate prepolymers include polyurethane acrylates. The photoinitiator includes phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0055] Table 1 Composition of photosensitive resin premix

[0056]

[0057] The ratio of 4-acryloylmorpholine: ethoxylated trimethylolpropane triacrylate: propoxylated neopentyl glycol diacrylate: polyurethane acrylate is 2:3:3:2. This specific ratio allows the photosensitive resin system to maintain high curing activity at low viscosity, and it can still have excellent flowability and molding precision even with high solids content ceramic powder filling, ensuring strong interlayer bonding in the green body and no cracking after degreasing.

[0058] The photosensitive resin premix also includes diluents, including octamethylcyclotetrasiloxane and polyethylene glycol 400, to reduce viscosity, improve flowability, and adjust the flexibility of the cured product. Thixotropic agents can also be added to the photosensitive resin premix to increase viscosity when the slurry is at rest and to increase flowability under shear.

[0059] PEG400 comprises 30% of the total mass of monomers and prepolymers, SP710 comprises 1-5% of the total mass of powder, D4 comprises 1% of the total mass of powder, and the photoinitiator comprises 2% of the total mass of resin. Unless otherwise specified, all raw materials used in this invention are commercially available in the art.

[0060] For example, with m and n both set to 5, five different HA to 3YSZ composition ratios were designed, with HA mass fractions of 0.7, 0.6, 0.5, 0.4, and 0.3, and five different solid contents of 20 vol.%, 25 vol.%, 30 vol.%, 35 vol.%, and 40 vol.%. These composition ratios and solid contents were combined in pairs to prepare 25 sets of ceramic photosensitive slurries. A DLP photopolymerization 3D printer was used, with a light source wavelength of 405 nm and an exposure intensity of 32.5 mW / cm². A standard test strip of 36 mm × 4 mm × 3 mm was printed under the same printing parameters. The printing parameters included layer thickness, single-layer exposure time, squeegee spreading speed, squeegee zeroing speed, and bottom layer exposure settings. For example, the layer thickness was 0.04 mm, the exposure time was 5 s, the squeegee spreading speed was 6 mm / s, the squeegee zeroing speed was 65 mm / s, and the bottom layer exposure was set to 3 layers, with each layer exposed for 10 s. The test specimens were degreased and sintered at high temperature. The sintering shrinkage data were measured, and the volume shrinkage rate y was calculated.

[0061] Then, a multiple linear regression analysis was performed on the sintering shrinkage rate data to obtain the sintering shrinkage rate control model.

[0062] For example, the sintering shrinkage rate control model is expressed as follows:

[0063]

[0064] Where y is the volume shrinkage rate; Solid content; The composition ratio of HA to ZrO2; These are the fitting constant coefficients; The solid content coefficient; is the component coefficient.

[0065] For example, to investigate the quantitative influence of solid content and component ratio on sintering shrinkage rate of a certain compositional gradient structure, 25 sets of orthogonal experimental data containing 5 component ratios (HA:3YSZ) and 5 volumetric solid contents are listed in Table 2. Sintering shrinkage rate data may also include flexural strength. Volumetric shrinkage rate was calculated by measuring the dimensions of the standard test specimen before and after sintering with vernier calipers. Flexural strength was measured using a three-point bending strength test on the standard test specimen.

[0066] Table 2. 25 sets of orthogonal experimental data for a certain compositional gradient structure

[0067]

[0068] Furthermore, multiple linear regression analysis was performed on the above 25 sets of data using Origin software, and the sintering shrinkage rate was set. yThe dependent variable is the volumetric solids content. and the proportion of HA components Let be the independent variable. The fitted sintering shrinkage rate control model is as follows: .

[0069] The coefficient of determination R of the model 2 =0.99304, indicating that the model has extremely high fitting accuracy and can accurately predict shrinkage behavior under different process parameters. This model is based on a specific experimental system, but its method is universal. For different raw material systems, those skilled in the art can reconstruct similar models according to the method disclosed in this invention.

[0070] For example, The absolute value is greater than 1. The absolute value is less than 1. Preferably, 1.02383 can be obtained. It can be -1.21133. It can be -0.33422.

[0071] The data shows that, at the same solid content, the volume shrinkage rate decreases significantly with increasing HA content. Similarly, at the same composition, the volume shrinkage rate decreases significantly with increasing solid content. This confirms that it is feasible to compensate for shrinkage differences caused by composition by adjusting the solid content in this embodiment. The sintering shrinkage rate control model in this embodiment is not only a mathematical fit but also a state equation guiding gradient structure design, providing a theoretical quantitative basis for achieving equal shrinkage rates.

[0072] This embodiment constructs a precise mathematical regression model of "composition-volume shrinkage rate-solid content" based on a large amount of experimental data. Using this mathematical model, the required solid content of each layer can be directly calculated in reverse according to the designed composition gradient. This digital and quantitative process design method eliminates blind spots, significantly shortens the process development cycle, reduces the raw material loss of expensive bioceramic powder and photosensitive resin, and achieves precise control of the process.

[0073] For a clearer understanding of the specific process flow of the above and following embodiments of the present invention, please refer to... Figure 2 .

[0074] In one embodiment, the gradient structure is reverse-designed based on the sintering shrinkage rate control model obtained in step 101 and the component ratio of each layer of the ceramic gradient structure obtained in step 102, and the required solid content of each layer of the ceramic gradient structure is calculated. Step 103 includes:

[0075] First, obtain the target volume shrinkage rate.

[0076] For example, a target sintering shrinkage rate y is selected. 目标 The principle for selecting the target sintering shrinkage rate is that the required solid content for each layer of the ceramic gradient structure, calculated based on the target volume shrinkage rate, must be within the printing range of the slurry. Specifically, the solid content adjustment range corresponding to the printing range of the slurry is 19 vol.% to 41 vol.%.

[0077] Assuming that the calculated solid content of all gradient layers is within the printable range of the slurry, the target sintering shrinkage rate is determined by considering functional requirements or process stability. For example, based on the flexural strength requirements of the ceramic to be prepared, a value that achieves a balanced distribution of solid content across all layers is selected. If the solid content of any layer exceeds the printable range, the target volume shrinkage rate needs to be adjusted until the solid content of all layers falls within a reasonable, printable range.

[0078] For example, under the same component ratio distribution, different selected target sintering shrinkage rates result in different solid contents in different component gradient structures. As shown in Table 3, the target shrinkage rates of component gradient structure 1, component gradient structure 2, and component gradient structure 3 are different. The smaller the target shrinkage rate, the higher the overall solid content of each layer in the entire gradient; the larger the target shrinkage rate, the lower the overall solid content.

[0079] Table 3. Solid content and composition ratio of the three component gradient structures

[0080]

[0081] Then, the composition ratio of each layer of the ceramic gradient structure and the target volume shrinkage rate are input into the sintering shrinkage rate control model to calculate the required solid content of each layer of the ceramic gradient structure.

[0082] For example, step 102 designs a cylindrical sample containing 5 layers of compositional gradients, such as... Figure 3 As shown, each layer is 1.2 mm high, with a total height of 6 mm. The composition ratio of each layer of the ceramic gradient structure from the bottom to the top is as follows:

[0083] Layer 1: HA:3YSZ=3:7 ;

[0084] Layer 2: HA:3YSZ=4:6 ;

[0085] Layer 3: HA:3YSZ=5:5 ;

[0086] Layer 4: HA:3YSZ=6:4 ;

[0087] Layer 5: HA:3YSZ=7:3 .

[0088] For example, taking composition gradient structure 1 as an example, Figure 4 The microstructures of cylindrical samples with five compositional gradients formed by the five compositional ratios described above are displayed at the same magnification and scale bar of 3 μm. As the HA to 3YSZ ratio changes from 7:3 to 3:7, the microstructure of the ceramics exhibits a significant evolution in phase distribution. HA particles, being large-diameter particles, form a continuous or semi-continuous skeletal structure in HA-rich regions, while fine 3YSZ particles fill the gaps in the HA skeletal structure, forming a typical multiphase structure of large particles supporting and small particles filling. As the HA content decreases and the 3YSZ content increases, the microstructure gradually transitions to a morphology with 3YSZ as the continuous matrix and HA particles dispersed within it, with a tight bond between the two phases and no obvious pores or microcracks. This compositional gradient-driven microstructure evolution ensures that the material macroscopically possesses both the bioactivity of HA and the mechanical strength of 3YSZ, while also providing a structural basis for the isoshrinkage behavior of each gradient layer during co-sintering.

[0089] Using the solid content of 25 vol.% and component ratio of 5:5 in Table 2 as a reference, the volume shrinkage rate is 0.62376, which is set as the target volume shrinkage rate. y 目标 =0.62376.

[0090] According to the sintering shrinkage rate control model in the above embodiments Back-calculate the required solid content for each layer :

[0091]

[0092] The calculation results are as follows:

[0093] Level 1 ( ): ;

[0094] 2nd floor ( ): ;

[0095] 3rd floor ( ): ;

[0096] 4th floor ( ): ;

[0097] 5th floor ( ): .

[0098] This embodiment takes into account that the biomechanical requirements of each layer are determined during the preparation of gradient materials, such as decreasing bioactivity and increasing strength from the surface layer to the inner layer. Therefore, the appropriate HA / ZrO2 ratio for each layer is directly specified, meaning the distribution of the component ratio can be determined by the biomimetic structural design of the bone scaffold. The solid content itself does not have functional significance; its main role is to serve as a compensating tool for adjusting shrinkage rate after the component ratio is determined, offsetting the differences in intrinsic shrinkage rates of different component layers to achieve the goal of equal shrinkage. Therefore, by first determining the component ratio based on biomechanical requirements and then back-calculating the solid content using a mathematical model, both the biological and mechanical properties of the scaffold are guaranteed, and the sintering cracking problem is solved.

[0099] Furthermore, this embodiment fully considered the limitations of the slurry rheological properties when establishing the sintering shrinkage rate control model. The set solid content adjustment range of 19 vol.% to 41 vol.% not only covers the adjustable range of shrinkage rate but also falls within the optimal viscosity range for photopolymerization printing. This ensures that the reverse-designed slurry not only has consistent shrinkage but also suitable viscosity, no sedimentation, and uniform spreading, guaranteeing the operability and robustness of this method in actual industrial production.

[0100] In one embodiment, in step 104, HA / ZrO2 composite ceramic slurry is prepared according to the solid content required for each layer of the ceramic gradient structure calculated in reverse, and bioceramics are prepared.

[0101] For example, the composition of the HA / ZrO2 composite ceramic slurry is consistent with that of the ceramic photosensitive slurry used in the sintering experiment described in the above embodiments. The HA / ZrO2 composite ceramic slurry consists of HA powder, ZrO2 powder, and a photosensitive resin premix; the photosensitive resin premix includes resin monomers, acrylate prepolymers, dispersants, and photoinitiators.

[0102] For example, the resin monomers include 4-acryloylmorpholine, ethoxylated trimethylolpropane triacrylate, and propoxylated neopentyl glycol diacrylate; the acrylate prepolymers include polyurethane acrylates.

[0103] For example, 4-acryloylmorpholine: ethoxylated trimethylolpropane triacrylate: propoxylated neopentyl glycol diacrylate: polyurethane acrylate = 2:3:3:2.

[0104] For example, the preparation of gradient HA / ZrO2 bioceramics using HA / ZrO2 composite ceramic slurry includes:

[0105] Using a photopolymerization 3D printer, different gradient layers were printed sequentially by changing the HA / ZrO2 composite ceramic slurry with different solid contents, resulting in green bodies with gradient changes in both composition and solid content. The green bodies were then degreased and co-sintered at high temperature to obtain gradient HA / ZrO2 bioceramics.

[0106] For example, five different slurries are prepared according to the calculated solid content. Using a DLP printer, the first layer of slurry is added and printed to a thickness of 1.2 mm. After pausing printing, the remaining slurry is removed and the slurry container is cleaned. Then, the second layer of slurry is added and printing continues. Alternatively, the slurry container can be changed directly, replacing it with the next layer of slurry after each layer is printed, repeating the above steps until all five layers are printed. The above operations are examples of how to replace HA / ZrO2 composite ceramic slurries with different solid contents layer by layer, and do not constitute a limitation of the present invention.

[0107] In the degreasing and high-temperature co-sintering process, the material was first ultrasonically cleaned three times with 75% alcohol for 10 minutes each time. After drying, a two-step degreasing process was adopted. The first degreasing step was carried out in a nitrogen atmosphere, with the temperature increased to 200℃ at 0.2℃ / min, and then increased to 600℃ at 0.1℃ / min and held for 2 hours. After cooling in the furnace, the material was transferred to an air atmosphere and heated to 600℃ at 5℃ / min and held for 4 hours to remove residual carbon. After degreasing, high-temperature sintering was performed: the temperature was increased to 1400℃ at 5℃ / min and held for 4 hours, and then cooled to 200℃ at 5℃ / min and cooled in the furnace to obtain a dense gradient composite material with uniform shrinkage.

[0108] The method for preparing gradient HA / ZrO2 bioceramics proposed in this application breaks the limitation of "fixed solid content" and uses solid content as an active adjustment variable. By using a sintering shrinkage rate control model to precisely match the shrinkage rate of each layer, even with different compositions, each layer can maintain synchronous shrinkage during sintering. Moreover, the thickness value of each component can be arbitrarily set without affecting shrinkage, thereby solving the cracking problem.

[0109] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0110] This invention provides a gradient HA / ZrO2 bioceramic prepared by any of the methods described in the above embodiments.

[0111] Along the thickness direction, the composition ratio and microstructure packing density of this gradient bioceramic exhibit continuous or stepwise gradient changes. Specifically, from the ZrO2-rich end to the HA-rich end, the HA content gradually increases and the ZrO2 content gradually decreases, while the solid content of the corresponding layer shows an inverse trend, forming a composite gradient structure with synergistic regulation of composition and density.

[0112] By employing an iso-shrinkage model to precisely match the solid content of each layer, different composition layers achieve synchronous shrinkage during high-temperature co-sintering, eliminating interlayer shrinkage stress. Therefore, the resulting gradient bioceramic product exhibits tight interlayer bonding, no macroscopic cracks, no warping deformation, and no stress concentration zones at the interfaces caused by significant compositional abrupt changes.

[0113] This gradient bioceramic achieves an optimal distribution of bioactivity and mechanical properties along its thickness. The HA-rich end exhibits excellent bioactivity and osteoconductivity, facilitating chemical bonding with host bone tissue; the ZrO2-rich end possesses high fracture toughness and flexural strength, meeting the mechanical requirements of load-bearing components. The intermediate transition layer ensures a smooth transition in properties, avoiding the risk of interfacial failure caused by abrupt performance changes in traditional bilayer materials.

[0114] After high-temperature sintering, the material has low internal porosity, well-developed grains, and uniform distribution of the HA and ZrO2 phases, forming a dense multiphase ceramic structure that ensures the mechanical reliability and long-term stability of the material.

[0115] This gradient bioceramic can serve as an ideal implant material for repairing weight-bearing bone defects, possessing both excellent biocompatibility and mechanical load-bearing capacity, and has promising prospects for clinical application.

[0116] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0117] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for preparing gradient HA / ZrO2 bioceramics, characterized in that, include: Sintering experiments were conducted with different solid contents and different combinations of HA and ZrO2 composition ratios to obtain sintering shrinkage rate data. Based on this data, a sintering shrinkage rate control model was established. The sintering shrinkage rate control model is expressed as follows: ； Where y is the volume shrinkage rate; Solid content; The composition ratio of HA to ZrO2; These are the fitting constant coefficients; The solid content coefficient; These are the component coefficients; Obtain biomechanical requirements and determine the composition ratio of each layer of the ceramic gradient structure based on the biomechanical requirements; Based on the component ratio of each layer of the ceramic gradient structure, the gradient structure is reverse-designed using the sintering shrinkage rate control model to obtain the required solid content of each layer of the ceramic gradient structure; including: obtaining the target volume shrinkage rate; inputting the component ratio of each layer of the ceramic gradient structure and the target volume shrinkage rate into the sintering shrinkage rate control model to back-calculate the required solid content of each layer of the ceramic gradient structure. Based on the required solid content of each layer of the ceramic gradient structure, HA / ZrO2 composite ceramic slurries with different solid contents are prepared, and gradient HA / ZrO2 bioceramics are prepared using the HA / ZrO2 composite ceramic slurries.

2. The method for preparing gradient HA / ZrO2 bioceramics according to claim 1, characterized in that, The sintering experiments were conducted with different solid contents and different combinations of HA and ZrO2 composition ratios to obtain sintering shrinkage data. Based on this sintering shrinkage data, a sintering shrinkage control model was established, including: Sintering experiments were conducted under m groups of different solid contents and n groups of different combinations of HA and ZrO2 composition ratios to obtain m×n groups of sintering shrinkage rate data; the sintering shrinkage rate data included volume shrinkage rate, solid content, and composition ratio of HA and ZrO2. A multiple linear regression analysis was performed on the sintering shrinkage rate data to obtain the sintering shrinkage rate control model.

3. The method for preparing gradient HA / ZrO2 bioceramics according to claim 1, characterized in that, The HA / ZrO2 composite ceramic slurry is composed of HA powder, ZrO2 powder and photosensitive resin premix; the photosensitive resin premix includes resin monomers, acrylate prepolymers, dispersants and photoinitiators.

4. The method for preparing gradient HA / ZrO2 bioceramics according to claim 3, characterized in that, The resin monomers include 4-acryloylmorpholine, ethoxylated trimethylolpropane triacrylate, and propoxylated neopentyl glycol diacrylate; the acrylate prepolymers include polyurethane acrylates. 4-Acryloylmorpholine:ethoxylated trimethylolpropane triacrylate:propoxylated neopentyl glycol diacrylate:polyurethane acrylate = 2:3:3:

2.

5. The method for preparing gradient HA / ZrO2 bioceramics according to claim 1, characterized in that, The solid content required for each layer of the ceramic gradient structure, calculated based on the target volume shrinkage rate, is within the printing range of the slurry; the solid content adjustment range corresponding to the printing range of the slurry is 19 vol.% to 41 vol.%.

6. The method for preparing gradient HA / ZrO2 bioceramics according to claim 3, characterized in that, The composition ratio of HA to ZrO2 is expressed as the mass fraction of HA, and the mass fraction of HA ranges from 0.3 to 0.

7. The particle size of the HA powder is 4.5 μm. The ZrO2 powder is 3 mol% yttrium oxide stabilized zirconium oxide with a particle size of 1 μm.

7. The method for preparing gradient HA / ZrO2 bioceramics according to claim 1, characterized in that, The preparation of gradient HA / ZrO2 bioceramics using the HA / ZrO2 composite ceramic slurry includes: Using a photopolymerization 3D printer, by changing the HA / ZrO2 composite ceramic slurry with different solid contents layer by layer, each gradient layer is printed sequentially to obtain a green body with gradient changes in both composition and solid content. The green body was subjected to degreasing and high-temperature co-sintering treatment to obtain gradient HA / ZrO2 bioceramics.

8. A gradient HA / ZrO2 bioceramic, characterized in that, Prepared by the method described in any one of claims 1 to 7.

Images