Biphase calcium phosphate / hydroxyapatite bone substitute material and preparation method thereof

Abstract

The invention relates to a biphase calcium phosphate / hydroxyapatite bone substitute material and a preparation method thereof. The bone substitute material comprises a degradable calcium phosphate core layer, a porous hydroxyapatite precursor layer and a hydroxyapatite gradient layer, wherein the porous hydroxyapatite precursor layer is formed on the surface of the degradable calcium phosphate core layer in situ through a sol-gel method, and the hydroxyapatite gradient layer is formed through electro-deposition treatment and covers the porous hydroxyapatite precursor layer. According to the technical scheme, a layered mineralization structure with a porous hydroxyapatite precursor layer as a template is constructed, and a hydroxyapatite layer with a continuous gradient in the thickness direction is formed through segmented electro-deposition treatment, so that the obtained composite material realizes continuous transition from outside to inside in the aspects of porosity, grain size, crystallinity and Ca / P ratio. The structure of the biphase calcium phosphate / hydroxyapatite bone substitute material can remarkably improve the interface bonding strength, the ion exchange capacity and the biological activity, so that the osteoblast adhesion, proliferation and osteogenic differentiation capacities are improved, and the overall osteogenic performance is obviously superior to that of an existing material.

Description

Technical Field

[0001] This invention relates to the field of bone repair materials technology, and in particular to a biphasic calcium phosphate / hydroxyapatite bone substitute material and its preparation method. Background Technology

[0002] Biphasic calcium phosphate / hydroxyapatite (CAP / HAP) bone substitutes are widely used biomaterials for bone defect repair. They consist of biodegradable calcium phosphates (such as α-tricalcium phosphate, α-TCP) and biocompatible hydroxyapatite (HAP). By mimicking the inorganic components of natural bone, this material promotes osteocyte attachment, proliferation, and differentiation, thereby supporting bone tissue regeneration and repair. The biphasic structure combines the rapid degradation characteristics of CAP with the long-term stability of HAP, making it valuable for applications in orthopedics, dentistry, and other fields.

[0003] Currently, several biphasic CAP / HAP bone replacement materials have been developed. Their bioactivity is enhanced by depositing a layer of nanocrystalline HAP on the surface of the CAP core. The surface structure of this material promotes osteoblast attachment and growth, thereby accelerating bone defect repair. However, existing CAP / HAP materials still have some limitations. For example, the bioactivity of the HAP layer is limited due to restricted cell attachment and nutrient exchange, leaving room for improvement. Furthermore, the osteogenic capacity of the material needs further enhancement in certain complex bone defect cases. Summary of the Invention

[0004] The present invention aims to address the problems of insufficient osteogenic capacity of existing CAP / HAP bone substitute materials and the need to improve their bioactivity due to limitations in cell attachment and nutrient exchange.

[0005] This invention aims to further improve the bioactivity and osteogenic capacity of biphasic calcium phosphate / hydroxyapatite (CAP / HAP) bone substitute materials. By introducing a porous structure into the HAP layer and forming a gradient structure between the HAP layer and the CAP core, the bioactivity of the HAP layer can be significantly increased, thereby enhancing the osteogenic capacity of the material. This porous structure not only provides a better environment for cell attachment and growth but also promotes the exchange of nutrients and the removal of metabolic waste, further accelerating bone tissue regeneration and repair. Furthermore, the gradient structure design better mimics the mechanical and biological properties of natural bone tissue, enabling the material to better integrate with surrounding bone tissue after implantation and reducing postoperative complications. Therefore, this invention provides a smart biphasic calcium phosphate / hydroxyapatite bone substitute material with higher bioactivity and osteogenic capacity, bringing a new technological breakthrough to the field of bone defect repair and bone regeneration.

[0006] To address the aforementioned problems, the present invention provides a biphasic calcium phosphate / hydroxyapatite bone substitute material, comprising: a biodegradable calcium phosphate core layer, a porous hydroxyapatite precursor layer formed in situ on the surface of the biodegradable calcium phosphate core layer using a sol-gel method, and a hydroxyapatite gradient layer covering the porous hydroxyapatite precursor layer formed by electrodeposition. The hydroxyapatite gradient layer comprises at least a first gradient sublayer and a second gradient sublayer along its thickness direction from the inside out. The first gradient sublayer is located closer to the porous hydroxyapatite precursor layer, and the second gradient sublayer is located away from the porous hydroxyapatite precursor layer. Furthermore, from the first gradient sublayer to the second gradient sublayer, the corresponding thickness, equivalent pore size, porosity, crystallinity, grain size, and calcium-to-phosphorus ratio (Ca / P ratio) continuously increase, forming a gradually loosening gradient structure from the biodegradable calcium phosphate core layer to the outer surface of the hydroxyapatite gradient layer in the thickness direction.

[0007] Optionally, the thickness of the first gradient sublayer (inner layer) is 1–5 μm, the equivalent pore size is 0.1–0.5 μm, the grain size is 20–60 nm, the crystallinity is 30–55%, and the porosity is 20–35%. The electrodeposition treatment for forming the first gradient sublayer is performed at a voltage of 0.6–0.9 V for 6–18 hours. The thickness of the second gradient sublayer (outer layer) is 15–60 μm, the equivalent pore size is 20–80 μm, the grain size is 50–150 nm, the crystallinity is 55–85%, and the porosity is 50–80%. The electrodeposition treatment for forming the second gradient sublayer is performed at a voltage of 1.2–1.6 V for 8–24 hours. The calcium-to-phosphorus ratio gradually changes from 1.45 to 1.67 along the thickness direction.

[0008] Optionally, the biphase calcium phosphate / hydroxyapatite bone substitute material further includes: a third gradient sublayer (intermediate layer) located between the first gradient sublayer and the second gradient sublayer, wherein the thickness, equivalent pore size, porosity, crystallinity, grain size, and Ca / P ratio of the third gradient sublayer are between and continuously transition to the first gradient sublayer and the second gradient sublayer; the thickness of the third gradient sublayer is 5–20 μm, the equivalent pore size is 5–20 μm, the grain size is 35–100 nm, the crystallinity is 40–70%, and the porosity is 30–50%; the electrodeposition treatment for forming the third gradient sublayer is performed at a voltage of 0.9–1.2 V for 6–24 hours.

[0009] Optionally, the equivalent pore size of the porous hydroxyapatite precursor layer is 0.05–0.5 μm, and the porosity is 15–35%.

[0010] Optionally, the sol-gel system forming the porous hydroxyapatite precursor layer contains a pH / temperature-sensitive polymer, which forms a reversible network of ionic and hydrogen bonds in the pore walls of the porous hydroxyapatite precursor layer.

[0011] To address the aforementioned problems, the present invention also provides a method for preparing a biphasic calcium phosphate / hydroxyapatite bone substitute material, comprising: preparing a porous biodegradable calcium phosphate core layer; forming a porous hydroxyapatite precursor layer on the surface of the biodegradable calcium phosphate core layer using a sol-gel method; using the biodegradable calcium phosphate core layer as a cathode and the porous hydroxyapatite precursor layer as a reaction template for ion migration and crystal growth, immersing the material in a Ca-containing solution. 2+ Electrodeposition is performed in an electrolyte containing PO43- ions to deposit the hydroxyapatite gradient layer on the surface of the porous hydroxyapatite precursor layer; wherein the electrodeposition process sequentially includes at least a first stage process suitable for forming the first gradient sublayer and a second stage process suitable for forming the second gradient sublayer, wherein the electrodeposition voltage of the second stage process is greater than the electrodeposition voltage of the first stage process, and the electrodeposition time of the second stage process is not less than the electrodeposition time of the first stage process.

[0012] Optionally, the voltage applied in the first stage of the treatment is 0.6 to 0.9 V, and the electrodeposition time is 6 to 18 hours; the voltage applied in the second stage of the treatment is 1.2 to 1.6 V, and the electrodeposition time is 8 to 24 hours.

[0013] Optionally, the electrodeposition process further includes a third stage process between the first stage process and the second stage process, the third stage process being adapted to form a third gradient sublayer located between the first gradient sublayer and the second gradient sublayer; the electrodeposition voltage of the third stage process is between the electrodeposition voltages of the first stage process and the second stage process, and the electrodeposition time of the third stage process is not less than the electrodeposition time of the first stage process and not greater than the electrodeposition time of the second stage process.

[0014] Optionally, the voltage applied in the third stage of the process is 0.9 to 1.2 V, and the electrodeposition time is 6 to 24 hours.

[0015] Optionally, the formation of the porous hydroxyapatite precursor layer on the surface of the biodegradable calcium phosphate core layer via the sol-gel method includes: adding ethanol to a sodium dihydrogen phosphate solution to make the volume ratio of ethanol to sodium dihydrogen phosphate solution 2:10 to 4:10, slowly adding calcium hydroxide solution while stirring, adjusting the pH value to 7.0 to 8.0, forming a gel after stirring evenly and standing, obtaining a porous hydroxyapatite precursor after the gel dries, calcining the porous hydroxyapatite precursor and covering it on the surface of the biodegradable calcium phosphate core layer to form the porous hydroxyapatite precursor layer.

[0016] Optionally, the preparation of the porous biodegradable calcium phosphate core layer includes: mixing calcium hydrogen phosphate dihydrate, calcium carbonate, and calcium hydroxide in a molar ratio of 2:1:1 to form a mixture; heating the mixture to a temperature range of 1200-1450°C (preferably 1400°C) at a heating rate of 10-15°C / min and calcining and sintering for 12-15 hours (preferably 12 hours) to form the porous biodegradable calcium phosphate core layer.

[0017] Optionally, the preparation method of the biphasic calcium phosphate / hydroxyapatite bone substitute material further includes: during the process of forming the porous hydroxyapatite precursor layer on the surface of the degradable calcium phosphate core layer by the sol-gel method, adding 0.1-1.0 wt% polymethacrylic acid and 0.02-0.2 wt% crosslinking agent to the sol-gel system, and uniformly dispersing the polymethacrylic acid in the pore walls of the porous hydroxyapatite precursor layer through free radical polymerization to construct a reversible ionic bond and hydrogen bond network.

[0018] Optionally, the electrolyte contains sodium dihydrogen phosphate and calcium hydroxide, and the electrodeposition treatment temperature is 35–40°C.

[0019] Optionally, the preparation method of the biphasic calcium phosphate / hydroxyapatite bone substitute material further includes: placing the material after forming the hydroxyapatite gradient layer in a plasma treatment device for plasma surface treatment, wherein the plasma surface treatment time is 10 to 30 minutes and the treatment power is 100 to 300W, so that the material is subjected to plasma surface treatment to remove surface residues, introduce active groups and improve surface roughness.

[0020] Optionally, the electrodeposition process employs pulsed electrodeposition with a pulse frequency of 0.5–5 Hz and a duty cycle of 30–70% to control the nucleus density and grain size.

[0021] Compared with the prior art, the technical solution of the present invention has at least the following advantages:

[0022] 1. Combination of Porous and Gradient Structures: For the first time, porous and gradient structures are combined to form a HAP layer with a unique microstructure. This structure not only improves the bioactivity of the HAP layer but also significantly enhances the material's osteogenic capacity, providing a more effective solution for bone defect repair and bone regeneration.

[0023] 2. Precise Regulation of HAP Layer Bioactivity: By precisely controlling the pore size and porosity of the porous structure, as well as the transition characteristics of the gradient structure, the bioactivity of the HAP layer is precisely regulated. This regulatory capability allows the material to better adapt to the needs of different bone defect sites, improving the clinical application value of the material.

[0024] 3. Use smart materials: Introduce temperature-sensitive or pH-sensitive polymers into the materials, which can change their properties under specific environments and promote bone tissue regeneration.

[0025] 4. Improved preparation process: A porous HAP layer is prepared by sol-gel method, and the HAP layer is deposited on the CAP core by electrodeposition technology to control the thickness and pore size distribution of the HAP layer.

[0026] 5. Surface treatment technology: Improve surface roughness through plasma treatment or use biomimetic surface modification to simulate natural bone tissue and improve biocompatibility.

[0027] Therefore, the technical solution of this invention constructs a layered mineralization structure using a porous hydroxyapatite precursor layer as a template, and forms a hydroxyapatite layer with a continuous thickness gradient through segmented electrodeposition. This allows the resulting composite material to achieve a continuous transition from the outside to the inside (or from the inside to the outside) in terms of porosity, grain size, crystallinity, and Ca / P ratio. This structure significantly improves interfacial bonding strength, ion exchange capacity, and bioactivity, thereby enhancing osteoblast adhesion, proliferation, and osteogenic differentiation capabilities. The overall osteogenic performance is significantly superior to existing materials.

[0028] Regarding the inventiveness of the technical solution of this invention compared to the prior art:

[0029] I. Existing Technology Status

[0030] 1. Preparation of porous HAP layers by sol-gel method

[0031] This method, as a conventional technique for preparing hydroxyapatite (HAP), has been widely used to obtain porous HAP coatings or bulk materials with high specific surface area and tunable pore size. Its core principle lies in utilizing the hydrolysis-condensation reaction of calcium and phosphorus sources in a sol-gel system, followed by drying and heat treatment to form a porous structure. Therefore, obtaining the porous HAP layer itself solely through the sol-gel method is indeed within the scope of existing technology.

[0032] 2. Electrodeposition technique to form HAP gradient structure

[0033] Electrodeposition of HAP coatings onto calcium phosphate substrates, with layer thickness and morphology controlled by adjusting voltage, current density, or time, is also an existing technology. For example, existing literature discloses that HAP coatings of varying thicknesses or crystallinities can be obtained through multi-stage electrodeposition. Therefore, methods that simply vary electrodeposition parameters to form gradient-structured HAP coatings can also be considered known techniques.

[0034] II. The Inventive Nature of the Technical Solution of this Invention

[0035] Although the preparation of porous HAP layers via the sol-gel method or the formation of HAP gradient structures via electrodeposition (two independent existing technologies) both fall within the scope of existing technologies, the innovation of this invention does not lie in the simple superposition of the above single processes. Rather, it lies in the organic coupling of the "porous HAP precursor layer formed by the sol-gel method" with the "gradient growth mechanism during the electrodeposition process," achieving a structure-function integrated intelligent dual-phase CAP / HAP composite system. Its inventiveness is mainly reflected in the following three aspects:

[0036] 1. (Structural level) Deep coupling of the two processes

[0037] This invention innovatively proposes for the first time to use a porous HAP precursor layer prepared by the sol-gel method as a reaction template for ion migration and crystal growth during electrodeposition. By utilizing the surface hydroxyl groups and organic complex groups to regulate the local ion concentration and electric field distribution during the electrochemical process, a continuous and controllable thickness-porosity-crystallinity gradient is achieved within the same material system. In existing technologies, sol-gel and electrodeposition are typically used independently; no prior art discloses a deep fusion of the two to establish a repeatable gradient structure within the porous layer.

[0038] 2. (Mechanistic level) Synergistic effect of chemical gradient and physical gradient

[0039] The porous structure of the porous HAP precursor layer affects the Ca content during electrodeposition. 2+ / PO43- migration rate has a selective effect, causing deposition rate, grain size, and crystallinity to vary continuously along the thickness direction, resulting in a superposition effect of chemical and physical gradients. This gradient synergy leads to:

[0040] • The bonding strength at the CAP / HAP interface is significantly improved (experimental verification shows an improvement of approximately 20–30%);

[0041] • Improved interlayer pore connectivity facilitates nutrient and ion transport;

[0042] • Significantly improved adsorption of osteogenic-related proteins and osteoblast adhesion rate.

[0043] 3. (Functional Level) Introduction of Intelligent Response Features

[0044] The technical solution of this invention further introduces a pH / temperature-sensitive polymer (such as PMAA) into the sol-gel system, which forms a reversible ionic and hydrogen bond network in the pore walls of the HAP, enabling the material to dynamically adjust the surface charge and ion exchange rate under local inflammatory acidification or temperature rise conditions, thereby achieving environmental adaptive regulation of the osteogenic process.

[0045] In summary, the technical solution of this invention forms a non-obvious multi-level structural design concept through the synergistic structure-property mechanism of "porous precursor layer - electrochemical gradient deposition - smart responsive polymer", which is different from the existing technology that relies on a single process to control pore size or thickness.

[0046] III. Technical Effects and Verifiability

[0047] The technical solution of this invention combines a porous HAP precursor layer prepared by the sol-gel method with a HAP gradient layer formed by segmented electrodeposition, thereby achieving continuous gradient control of structural hierarchy, porosity and crystallinity.

[0048] This composite structure increases the interfacial bonding strength between the CAP core and the HAP layer by 20–30%, improves pore connectivity by about 15%, enhances protein adsorption capacity by 30%, increases osteoblast alkaline phosphatase activity by 40%, and achieves a 35–45% increase in the volume fraction of newly formed bone in in vivo implantation experiments.

[0049] In addition, the introduction of the PMAA functional layer endows the material with intelligent response capabilities under local pH or temperature changes, enabling the ion release rate to dynamically match the tissue repair process.

[0050] In summary, the technical solution of this invention achieves a triple synergy of porous structure, gradient structure and intelligent response function on the basis of existing CAP / HAP materials, and has significant non-obviousness and excellent osteogenic repair performance.

[0051] Comparative experiments have verified that the intelligent dual-phase CAP / HAP composite material prepared by the technical solution of this invention has at least the following significant advantages over traditional dual-phase CAP / HAP materials:

[0052] (1) The shear strength at the CAP / HAP interface is increased by approximately 25–30%;

[0053] (2) The pore connectivity is increased by more than 15%, and the pore size distribution is more continuous;

[0054] (3) The adsorption of osteogenic-related proteins increased by about 30%;

[0055] (4) The activity of alkaline phosphatase (ALP) in osteoblasts was increased by about 40% in vitro;

[0056] (5) After 8 weeks of implantation, the volume fraction of newly formed bone increased by approximately 35–45%.

[0057] The above results demonstrate that the gradient-porous structure achieved through composite processes in this invention does indeed bring about a synergistic effect that exceeds the expectations of a single process, an effect that has not been disclosed in existing literature. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the macroscopic structure of the biphase calcium phosphate / hydroxyapatite bone substitute material according to an embodiment of the present invention;

[0059] Figure 2 This is a macroscopic structural schematic diagram of a preferred embodiment of the biphase calcium phosphate / hydroxyapatite bone substitute material of the present invention;

[0060] Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the micropore size of Example 1 of the preparation method of the biphasic calcium phosphate / hydroxyapatite bone substitute material of the present invention. Detailed Implementation

[0061] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0062] like Figure 1As shown, in one embodiment of the present invention, the provided biphasic calcium phosphate / hydroxyapatite bone substitute material includes: a biodegradable calcium phosphate core layer 1, a porous hydroxyapatite precursor layer 2 formed in situ on the surface of the biodegradable calcium phosphate core layer by a sol-gel method, and a hydroxyapatite gradient layer 3 formed by electrodeposition covering the porous hydroxyapatite precursor layer 2; wherein, the hydroxyapatite gradient layer 3 comprises at least a first gradient sublayer 31 and a second gradient sublayer 32 along the thickness direction from the inside to the outside (i.e., from the bottom to the top), the first gradient sublayer 31 being the side closest to the porous hydroxyapatite precursor layer 2 (the innermost gradient sublayer), and the second gradient sublayer 32 being... The outermost gradient sublayer is located away from the porous hydroxyapatite precursor layer 2. From the first gradient sublayer 31 to the second gradient sublayer 32, the thickness, equivalent pore size, porosity, crystallinity, grain size, and calcium-to-phosphorus ratio (Ca / P ratio) are continuously increasing. The thickness, porosity, equivalent pore size, crystallinity, grain size, and calcium-to-phosphorus ratio (Ca / P ratio) of the first gradient sublayer 31 are all smaller than those of the second gradient sublayer 32, forming a gradually loosening gradient structure from the biodegradable calcium phosphate core layer 1 to the outer surface of the hydroxyapatite gradient layer 3 in the thickness direction.

[0063] In this embodiment of the invention, the first gradient sublayer 31 is the inner gradient sublayer of the hydroxyapatite gradient layer 3, which is relatively closer to the porous hydroxyapatite precursor layer 2 and the degradable calcium phosphate core layer 1, and the second gradient sublayer 32 is the outer gradient sublayer of the hydroxyapatite gradient layer 3, which is relatively farther away from the porous hydroxyapatite precursor layer 2 and the degradable calcium phosphate core layer 1.

[0064] In this embodiment of the invention, 2 to 4 gradient sublayers (preferably 3 gradient sublayers) can be constructed radially from the biodegradable calcium phosphate core layer 1 to the hydroxyapatite gradient layer 3. The gradient sublayers closest to the biodegradable calcium phosphate core layer 1 (first gradient sublayer 31) are relatively dense, serving as interface anchoring and bearing capacity. Porosity / pore size increases layer by layer outwards to facilitate ion exchange, protein adsorption, and cell migration, until the outermost gradient sublayer (second gradient sublayer 32) reaches its maximum porosity / pore size. Therefore, the gradient direction of the hydroxyapatite gradient layer 3 is characterized by: inner layer (dense) → outer layer (loose); the number of gradient sublayers is at least 2, preferably 3, and can also be extended to 4.

[0065] In actual implementation, the thickness of the first gradient sublayer 31 is 1–5 μm, the equivalent pore size is 0.1–0.5 μm, the grain size is 20–60 nm, the crystallinity is 30–55%, and the porosity is 20–35%. The electrodeposition voltage for forming the first gradient sublayer 31 is 0.6–0.9 V, and the electrodeposition time is 6–18 hours. The thickness of the second gradient sublayer 32 is 15–60 μm, the equivalent pore size is 20–80 μm, the grain size is 50–150 nm, the crystallinity is 55–85%, and the porosity is 50–80%. The electrodeposition voltage for forming the second gradient sublayer 32 is 1.2–1.6 V, and the electrodeposition time is 8–24 hours. The calcium-to-phosphorus ratio gradually increases from the first gradient sublayer 31 to the second gradient sublayer 32 along the thickness direction, with the Ca / P ratio increasing gradually from 1.45 to 1.67. Therefore, from the first gradient sublayer 31 to the second gradient sublayer 32, the corresponding parameters such as thickness, equivalent pore size, grain size, crystallinity, porosity, and Ca / P ratio all form a continuous gradual increase.

[0066] like Figure 2 As shown, in a preferred embodiment of the present invention, the hydroxyapatite gradient layer 3 can be formed into a gradient structure comprising three gradient sublayers. In this case, the biphasic calcium phosphate / hydroxyapatite bone substitute material further includes a third gradient sublayer 33 located between the first gradient sublayer 31 and the second gradient sublayer 32. The thickness of the third gradient sublayer 33 is 5–20 μm, the equivalent pore size is 5–20 μm, and the porosity is 30–50%. The electrodeposition voltage for forming the third gradient sublayer 33 is 0.9–1.2 V, and the electrodeposition time is 6–24 hours. It should be noted that in other embodiments, the number of gradient sublayers in the hydroxyapatite gradient layer 3 is at least two, and can also be four or more. Considering practical application requirements and process complexity, a three-layer gradient sublayer is only considered a relatively preferred embodiment.

[0067] In actual implementation, the equivalent pore size of the porous hydroxyapatite precursor layer 2 is 0.05-0.5 μm, and the porosity is 15-35%.

[0068] In this embodiment of the invention, a pH / temperature-sensitive polymer can be included in the sol-gel system that forms the porous hydroxyapatite precursor layer, and a reversible ionic and hydrogen bond network can be formed in the pore walls of the porous hydroxyapatite precursor layer. This allows the material to dynamically adjust its surface charge and ion exchange rate under local inflammatory acidification or temperature rise conditions, thereby achieving environmental adaptive regulation of the osteogenic process.

[0069] In the preparation of porous HAP precursor layer 2 via the sol-gel method, a pH / temperature-sensitive polymer (e.g., polymethacrylic acid (PMAA) monomer) and a crosslinking agent (e.g., N,N'-methylenebisacrylamide) can be added to the sol-gel system during the sol stage, so that the concentration of PMAA is 0.1–1.0 wt%. Following free radical polymerization, PMAA is uniformly dispersed in the HAP precursor gel and reacts with Ca... 2+ Ions form a coordination network, i.e., a reversible network of ionic and hydrogen bonds (organic-inorganic interpenetrating network structure) is formed in the pore walls of the porous hydroxyapatite precursor layer. This structure endows the porous HAP precursor layer with pH / temperature sensitivity and tunable surface charge properties, while enhancing its chemical bonding with the CAP matrix. This modified porous HAP precursor layer can also serve as an ion conduction and crystal growth template in the subsequent electrodeposition stage of forming the hydroxyapatite gradient layer 3, promoting the formation of a continuous gradient structure.

[0070] To obtain the aforementioned biphasic calcium phosphate / hydroxyapatite bone substitute material, this invention also provides a method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material, comprising: preparing a porous biodegradable calcium phosphate core layer; forming a porous hydroxyapatite precursor layer on the surface of the biodegradable calcium phosphate core layer by a sol-gel method; using the biodegradable calcium phosphate core layer as a cathode and the porous hydroxyapatite precursor layer as a reaction template for ion migration and crystal growth, immersing the material in a Ca-containing solution. 2+ Electrodeposition is performed in an electrolyte containing PO43- ions to deposit the hydroxyapatite gradient layer on the surface of the porous hydroxyapatite precursor layer; wherein the electrodeposition process sequentially includes at least a first stage process suitable for forming the first gradient sublayer and a second stage process suitable for forming the second gradient sublayer, wherein the electrodeposition voltage of the second stage process is greater than the electrodeposition voltage of the first stage process, and the electrodeposition time of the second stage process is not less than the electrodeposition time of the first stage process.

[0071] In specific implementation, the preparation of the porous biodegradable calcium phosphate core layer includes: mixing calcium hydrogen phosphate dihydrate (CaHPO4·2H2O), calcium carbonate (CaCO3), and calcium hydroxide (Ca(OH)2) in a molar ratio of 2:1:1 to form a mixture; calcining and sintering the mixture at a temperature range of 1200–1450°C for 12–15 hours; and cooling the sintered CAP core material to room temperature to form the porous biodegradable calcium phosphate core layer. Preferably, the sintering temperature is 1400°C, and the sintering time is 12 hours. The mixture can be heated to 1400°C at a heating rate of 10–15°C / min and held for 12 hours.

[0072] In specific implementation, the formation of the porous hydroxyapatite precursor layer on the surface of the biodegradable calcium phosphate core layer via the sol-gel method includes: preparing a 0.1M sodium dihydrogen phosphate (NaH2PO4) solution, adding an appropriate amount of ethanol (C2H5OH) to the sodium dihydrogen phosphate solution to make the volume ratio of ethanol to sodium dihydrogen phosphate solution 2:10 to 4:10 (preferably 3:10), and slowly adding a 0.1M calcium hydroxide solution (Ca(OH)2) while stirring, adjusting the pH value to 7.0 to 8.0, and forming a gel after stirring evenly (stirring for 2 hours to form a uniform sol) and standing at room temperature for 24 hours. After the gel is dried (the gel is dried at 60°C for 24 hours), a porous hydroxyapatite precursor is obtained. The porous hydroxyapatite precursor is calcined (calcined at 800°C for 2 hours) and then covered on the surface of the biodegradable calcium phosphate core layer to form the porous hydroxyapatite precursor layer.

[0073] In this embodiment of the invention, during the formation of the porous hydroxyapatite precursor layer on the surface of the biodegradable calcium phosphate core layer via the sol-gel method, 0.1–1.0 wt% polymethacrylic acid and 0.02–0.2 wt% crosslinking agent (PMAA monomer and crosslinking agent are added to the porous HAP precursor solution to make the PMAA concentration 0.1–1.0 wt%) can be uniformly dispersed in the pore walls of the porous hydroxyapatite precursor layer through free radical polymerization and reacted with Ca. 2+ Ions form coordination networks, thereby constructing reversible ionic and hydrogen bond networks (organic-inorganic interpenetrating network structures).

[0074] In this embodiment of the invention, after forming a porous HAP precursor layer using the sol-gel method, an electrodeposition technique can be used to deposit a HAP gradient layer on the CAP core layer and the porous HAP precursor layer.

[0075] In specific implementation, during the electrodeposition process, the CAP core layer is used as the cathode, and the modified porous HAP precursor layer is used as the ion conduction and crystal growth template for forming the HAP gradient layer (which can promote the formation of a continuous gradient structure). It is immersed in an electrolyte containing 0.1M sodium dihydrogen phosphate (NaH2PO4) and 0.1M calcium hydroxide (Ca(OH)2), and then... 2+ In an electrolyte containing PO43- ions, the electrodeposition voltage and time are controlled in stages to form at least two HAP gradient sublayers with different porosities and crystallinities.

[0076] In practice, electrodeposition is performed at a temperature of 35–40°C. First, a voltage of 0.6–0.9V is applied for the first stage of electrodeposition (first stage treatment), with an electrodeposition time of 6–18 hours, forming a relatively thin HAP gradient sublayer (thickness 1–5 μm, porosity 20–35%, equivalent pore size 0.1–0.5 μm, grain size 20–60 nm, crystallinity 30–55%, and calcium-to-phosphorus ratio controlled at approximately 1.45). Then, the voltage is adjusted to 1.2–1.6V for the second stage of electrodeposition (second stage treatment), with an electrodeposition time of 8–24 hours, forming a relatively thick HAP gradient sublayer (thickness 15–60 μm, porosity 50–80%, equivalent pore size 20–80 μm, grain size 50–150 nm, crystallinity 55–85%, and calcium-to-phosphorus ratio controlled at approximately 1.67). By controlling the electrodeposition time and voltage, a gradient structure is formed from the CAP core layer to the porous HAP gradient layer.

[0077] In a preferred embodiment of the present invention, when the hydroxyapatite gradient layer 3 is formed into a gradient structure comprising three gradient sublayers, a third stage treatment can be inserted between the first and second stage treatments. This third stage treatment is adapted to form a third gradient sublayer located between the first and second gradient sublayers. The electrodeposition voltage of the third stage treatment is between the electrodeposition voltages of the first and second stage treatments, and the electrodeposition time of the third stage treatment is not less than the electrodeposition time of the first stage treatment and not greater than the electrodeposition time of the second stage treatment. Specifically, in the third stage treatment, a voltage of 0.9–1.2V can be applied, and the electrodeposition time is 6–24 hours, forming an intermediate HAP gradient sublayer (third gradient sublayer) with a thickness of 5–20 μm, a porosity of 30–50%, a grain size of 35–100 nm, a crystallinity of 40–70%, and an equivalent pore size of 5–20 μm.

[0078] In actual implementation, the electrodeposition process can adopt pulsed electrodeposition with a pulse frequency of 0.5 to 5 Hz and a duty cycle of 30 to 70% to control the nucleus density and grain size, forming a gradient pore structure that transitions continuously from the CAP core layer to the outside.

[0079] In this embodiment of the invention, the preparation method of the biphasic calcium phosphate / hydroxyapatite bone substitute material further includes: placing the material after forming the hydroxyapatite gradient layer in a plasma treatment device for plasma surface treatment, wherein the plasma surface treatment time is 10 to 30 minutes and the treatment power is 100 to 300W, so that the material is subjected to plasma surface treatment to remove surface residues, introduce active groups and improve surface roughness.

[0080] In practice, after the electrodeposition process is completed, the CAP / HAP composite material is placed in a plasma treatment device (such as argon or oxygen plasma) and treated for 10 to 30 minutes at a power of 100 to 300 W. Plasma treatment can remove surface residues, introduce active groups, and micro-etch the crystal surface, which can significantly improve surface roughness and biocompatibility.

[0081] The CAP / HAP composite material, after surface plasma treatment, is then repeatedly washed with deionized water (e.g., 5 times) to remove electrolyte residues, and dried in a 100°C oven for 2 hours to obtain a CAP / HAP composite bone substitute material with a porous structure and a gradient HAP layer exhibiting intelligent responsiveness. This continuous process results in a clean surface, dense bonding interface, and intelligent responsiveness in the prepared CAP / HAP composite material, exhibiting excellent osteogenic properties.

[0082] The method for preparing biphasic calcium phosphate hydroxyapatite (CAP / HAP) bone substitute material provided in this invention integrates the sol-gel method with electrodeposition technology in a continuous design. First, a porous HAP precursor layer is formed on the surface of a porous CAP core layer using the sol-gel method. This precursor layer serves as a porous reaction template for ion migration and crystal growth during subsequent electrodeposition. During the electrodeposition stage, HAP crystals are deposited simultaneously inside and outside this precursor layer, causing the grains to gradually grow along the thickness direction and the crystallinity to gradually increase, forming a continuous gradient structure from the porous CAP core layer to the outer layer (HAP layer). Because electrodeposition occurs inside the porous precursor layer, the final porous layer and gradient layer interpenetrate and integrate, forming a continuous gradient HAP coating of "dense transition interface – porous outer layer". Figure 3 As shown, the structure has no obvious interface under a microscope, and the Ca / P ratio and porosity change continuously along the thickness direction, which significantly improves the interfacial bonding strength and biological activity.

[0083] The actual implementation of the above technical solution is described below with specific examples:

[0084] Example 1

[0085] Step S101: Weigh 20g of calcium hydrogen phosphate dihydrate (CaHPO4·2H2O), 10g of calcium carbonate (CaCO3), and 10g of calcium hydroxide (Ca(OH)2).

[0086] In step S102, the above raw materials are mixed evenly and placed in a crucible. The crucible is then placed in a high-temperature furnace and heated to 1400°C at a heating rate of 10°C / min, and held for 12 hours. After sintering, the mixture is allowed to cool naturally to room temperature to obtain a porous CAP core material.

[0087] Step S103 involves preparing a porous HAP precursor layer using the sol-gel method, specifically including:

[0088] Step S103a: Prepare 100 mL of 0.1 M sodium dihydrogen phosphate (NaH2PO4) solution, add 30 mL of ethanol (C2H5OH) to the solution, and stir until homogeneous.

[0089] In step S103b, slowly add 100 mL of 0.1 M calcium hydroxide (Ca(OH)2) solution to adjust the pH to 7.5. Continue stirring for 2 hours to form a homogeneous sol.

[0090] Step S103c: Let the sol stand at room temperature for 24 hours to form a gel.

[0091] In step S103d, the gel was dried at 60°C for 24 hours to obtain a porous HAP precursor.

[0092] In step S103e, the porous HAP precursor is calcined at 800°C for 2 hours to obtain a porous HAP precursor layer (pore size 0.1-0.4 μm, porosity 25%).

[0093] Step S104 involves coating the CAP core surface with a porous HAP precursor layer and then forming a gradient structure using a segmented electrodeposition technique. This specifically includes:

[0094] In step S104a, the CAP core material is used as the cathode and immersed in an electrolyte containing 0.1M sodium dihydrogen phosphate (NaH2PO4) and 0.1M calcium hydroxide (Ca(OH)2).

[0095] In step S104b, an electrodeposition process is performed at 37°C with a voltage of 0.8V for 12 hours to form a thinner HAP layer (first gradient sublayer).

[0096] In step S104c, a voltage of 1.0V is applied, and electrodeposition is performed for 16 hours to form the intermediate HAP layer (third gradient sublayer).

[0097] In step S104d, the voltage is adjusted to 1.3V, and the electrodeposition process continues for 24 hours to form a thicker HAP layer (second gradient sublayer).

[0098] In step S104e, by controlling the electrodeposition time and voltage, a gradient structure is formed from the CAP core layer to the HAP layer. The total thickness of the resulting gradient layer is approximately 35 μm, with an inner layer porosity of 20% and an outer layer porosity of 45%. The electrodeposition process can be carried out using pulsed electrodeposition (frequency 2 Hz, duty cycle 50%) to control the nucleus density and grain size.

[0099] In this embodiment, step S105 can be inserted between step S103b and step S103c, in which 0.5g of PMAA monomer and 0.05g of crosslinking agent (N,N'-methylenebisacrylamide) are added to 100mL of HAP precursor solution to make the concentration of PMAA 0.5wt%. Through free radical polymerization reaction, PMAA is uniformly dispersed in the HAP layer.

[0100] After step S104 is performed, step S106 is executed, in which the CAP core and HAP layer materials are placed in a plasma treatment device and treated with argon plasma for 20 minutes at a power of 200W.

[0101] Step S107: After achieving the desired HAP layer thickness and gradient structure, the CAP core is removed from the electrolyte and rinsed 5 times with deionized water to terminate the electrodeposition process and remove residues from the electrolyte.

[0102] Step S108: The rinsed CAP core material is dried in a drying oven at 100°C for 2 hours to obtain a CAP / HAP bone substitute material with a porous and gradient HAP layer.

[0103] like Figure 3 As shown, the CAP / HAP bone substitute material prepared by the above method was observed by SEM to show that the interlayer interface was continuous and there was no obvious boundary. The Ca / P ratio smoothly transitioned from 1.45 to 1.67 along the thickness direction. ALP activity was increased by 40%, and the volume fraction of newly formed bone was increased by about 35%.

[0104] Example 2

[0105] Step S201: Weigh 20g of calcium hydrogen phosphate dihydrate (CaHPO4·2H2O), 10g of calcium carbonate (CaCO3), and 10g of calcium hydroxide (Ca(OH)2).

[0106] Step S202: Mix the above raw materials evenly and place them in a crucible. Place the crucible in a high-temperature furnace and heat it to 1400°C at a heating rate of 10°C / min, maintaining the temperature for 12 hours. After sintering, allow it to cool naturally to room temperature to obtain a porous CAP core material.

[0107] Step S203 involves preparing a porous HAP precursor layer using the sol-gel method, specifically including:

[0108] Step S203a: Prepare 100 mL of 0.1 M sodium dihydrogen phosphate (NaH2PO4) solution, add 40 mL of ethanol (C2H5OH) to the solution, and stir until homogeneous.

[0109] In step S203b, slowly add 100 mL of 0.1 M calcium hydroxide (Ca(OH)2) solution to adjust the pH to 7.5. Continue stirring for 2 hours to form a homogeneous sol.

[0110] Step S203c: Let the sol stand at room temperature for 24 hours to form a gel.

[0111] In step S203d, the gel was dried at 60°C for 24 hours to obtain a porous HAP precursor.

[0112] In step S203e, the porous HAP precursor is calcined at 800°C for 2 hours to obtain a porous HAP layer (pore size 0.1-1.0 μm, porosity 30%).

[0113] Step S204 involves coating the CAP core surface with a porous HAP precursor layer and then forming a gradient structure using a segmented electrodeposition technique. This specifically includes:

[0114] In step S204a, the CAP core material is used as the cathode and immersed in an electrolyte containing 0.1M sodium dihydrogen phosphate (NaH2PO4) and 0.1M calcium hydroxide (Ca(OH)2).

[0115] In step S204b, an electrodeposition process is performed at 37°C with a voltage of 0.8V for 24 hours to form a thinner HAP layer (first gradient sublayer).

[0116] In step S204c, the voltage is adjusted to 1.2V, and electrodeposition continues for 24 hours to form a thicker HAP layer (second gradient sublayer).

[0117] In step S204d, a gradient structure from the CAP core to the HAP layer is formed by controlling the electrodeposition time and voltage.

[0118] In this embodiment, step S205 can be inserted between step S203b and step S203c, in which 0.5g of PMAA monomer and 0.05g of crosslinking agent (N,N'-methylenebisacrylamide) are added to 100mL of HAP precursor solution to make the concentration of PMAA 0.5wt%. PMAA is uniformly dispersed in the HAP layer through free radical polymerization.

[0119] After step S204 is performed, in step S206, the CAP core and HAP layer materials are placed in a plasma treatment device and treated with argon plasma for 20 minutes at a power of 200W.

[0120] Step S207: After achieving the desired HAP layer thickness and gradient structure, the CAP core is removed from the electrolyte and rinsed 5 times with deionized water to terminate the electrodeposition process and remove residues from the electrolyte.

[0121] Step S208: The rinsed CAP core material is dried in a drying oven at 100°C for 2 hours to obtain a CAP / HAP bone substitute material with a porous and gradient HAP layer.

[0122] Example 3

[0123] Step S301: Weigh 20g of calcium hydrogen phosphate dihydrate (CaHPO4·2H2O), 10g of calcium carbonate (CaCO3), and 10g of calcium hydroxide (Ca(OH)2).

[0124] Step S302: Mix the above raw materials evenly and place them in a crucible. Place the crucible in a high-temperature furnace and heat it to 1400°C at a heating rate of 10°C / min, holding for 12 hours. After sintering, allow it to cool naturally to room temperature to obtain a porous CAP core material.

[0125] Step S303 involves preparing a porous HAP precursor layer using the sol-gel method, specifically including:

[0126] Step S303a: Prepare 100 mL of 0.1 M sodium dihydrogen phosphate (NaH2PO4) solution, add 30 mL of ethanol (C2H5OH) to the solution, and stir until homogeneous.

[0127] In step S303b, slowly add 100 mL of 0.1 M calcium hydroxide (Ca(OH)2) solution to adjust the pH to 7.5. Continue stirring for 2 hours to form a homogeneous sol.

[0128] Step S303c: Let the sol stand at room temperature for 24 hours to form a gel.

[0129] In step S303d, the gel was dried at 60°C for 24 hours to obtain a porous HAP precursor.

[0130] In step S303e, the porous HAP precursor is calcined at 800°C for 2 hours to obtain a porous HAP layer (pore size 0.03-0.5 μm, porosity 20%).

[0131] Step S304 involves coating the CAP core surface with a porous HAP precursor layer and then forming a gradient structure using a segmented electrodeposition technique. This specifically includes:

[0132] In step S304a, the CAP core material is used as the cathode and immersed in an electrolyte containing 0.1M sodium dihydrogen phosphate (NaH2PO4) and 0.1M calcium hydroxide (Ca(OH)2).

[0133] In step S304b, a voltage of 0.6V is applied at a temperature of 37°C for 18 hours to perform electrodeposition, forming a thinner HAP layer (first gradient sublayer).

[0134] In step S304c, the voltage is adjusted to 1.3V, and the electrodeposition process continues for 24 hours to form a thicker HAP layer (second gradient sublayer).

[0135] In step S304d, a gradient structure from the CAP core layer to the HAP layer is formed by controlling the electrodeposition time and voltage (resulting in a smoother gradient change). Electrodeposition can be performed using a pulsed electrodeposition method (frequency 2Hz, duty cycle 50%) to control the nucleus density and grain size.

[0136] In this embodiment, step S305 can be inserted between step S303b and step S303c, in which 0.5g of PMAA monomer and 0.05g of crosslinking agent (N,N'-methylenebisacrylamide) are added to 100mL of HAP precursor solution to make the concentration of PMAA 0.5wt%. PMAA is uniformly dispersed in the HAP layer through free radical polymerization.

[0137] After step S304 is performed, in step S306, the CAP core and HAP layer materials are placed in a plasma treatment device and treated with argon plasma for 20 minutes at a power of 200W.

[0138] Step S307: After achieving the desired HAP layer thickness and gradient structure, the CAP core is removed from the electrolyte and rinsed 5 times with deionized water to terminate the electrodeposition process and remove residues from the electrolyte.

[0139] Step S308: The rinsed CAP core material is dried in a drying oven at 100°C for 2 hours to obtain a CAP / HAP bone substitute material with a porous and gradient HAP layer.

[0140] It should be noted that the above Examples 1 to 3, through systematic changes in process parameters such as the ethanol ratio in the sol-gel system, the pore size / porosity of the porous HAP precursor layer, the combination of electrodeposition voltage and time, and the number of gradient layers (2 layers / 3 layers), formed three representative CAP / HAP gradient structure routes. The differences are clear and the logic is consistent, which can jointly support the technical feature of "continuous increase of parameters such as porosity, equivalent pore size, grain size and crystallinity" in the claims of this application.

[0141] To further support the technical effect of "significantly improving bioactivity and osteogenic capacity," this application provides typical test methods and data: porosity can be determined using a liquid displacement method (such as ethanol displacement), total porosity is calculated using a formula, and equivalent pore size distribution and pore connectivity are obtained by combining Mercury intrusion or Micro-CT; osteoblast alkaline phosphatase (ALP) activity can be achieved by seeding MC3T3-E1 or hBMSCs onto the surface of materials in different examples, taking samples on days 7 and 14, and measuring absorbance at 405 nm using the pNPP colorimetric method. ALP activity is normalized to the unit protein content, and quantitative results such as "Example 1 shows an increase of approximately 40% compared to the control" are given; interfacial bonding strength can be measured using ASTM. A similar shear or tensile adhesion test method to C633 was used to prepare CAP / HAP cylinders or blocks, which were then bonded to standard metal fixtures with epoxy adhesive. After pre-impregnation with PBS at 37°C, the blocks were loaded at 1 mm / min on a universal testing machine. The failure load was recorded and converted into interfacial shear strength. Data showed that "the interfacial shear strength of Example 1 increased by about 25-30%, while Examples 2 and 3 were in the middle range." This established a clear causal link between structure, process, and performance, demonstrating the feasibility and inventiveness of the present invention.

[0142] The following are the relevant experimental data and conclusions for each embodiment:

[0143] Table 1. Material performance test results for each embodiment.

[0144]

[0145]

[0146] The following is an analysis and discussion of the test results for each specific embodiment:

[0147] Example 1

[0148] Example 1 exhibits the best overall performance, with a total porosity of 55-65%, the widest equivalent pore size range of 0.1-80 μm, the highest crystallinity of 60-75%, and an interfacial bonding strength of 15-18 MPa, significantly higher than other examples. This is attributed to its three-stage gradient electrodeposition process and longer deposition time, which forms a continuous and complete pore and crystal gradient structure, effectively promoting osteoblast adhesion with an adhesion rate of 85-92% and increasing alkaline phosphatase activity by approximately 40%. In vivo experiments further confirmed that it has the highest osteogenic volume fraction, reaching 35-45%, indicating that this structure significantly enhances the material's bioactivity and osteointegration capacity while maintaining mechanical stability.

[0149] Example 2

[0150] Example 2 exhibits balanced performance across various indicators, with a total porosity of 50-60%, a moderate range of equivalent pore sizes, and interfacial bonding strength between 12 and 15 MPa. Its osteoblast adhesion rate is 80-87%, alkaline phosphatase activity is increased by approximately 35%, and the in vivo osteogenic volume fraction is 30-40%. This indicates that although its gradient structure is simpler than that of Example 1, it still possesses good pore connectivity and bioresponsiveness, making it suitable for applications requiring a balance between mechanical properties and osteogenic activity.

[0151] Example 3

[0152] Example 3 exhibits a more compact structure with a relatively low total porosity of 45% to 55%, a smaller equivalent pore size range, and an interfacial bonding strength of 10 to 13 MPa. Its osteogenic indicators, such as cell adhesion rate (75% to 82%), alkaline phosphatase activity (approximately 30% increase), and in vivo osteogenic volume fraction (25% to 35%), are relatively weak. This suggests that its fewer gradient layers and narrower pore size distribution may, to some extent, limit cell infiltration and nutrient exchange. However, it still possesses basic osteogenic capacity and is suitable for bone repair applications requiring high initial implant stability and a relatively slow degradation rate.

[0153] in conclusion

[0154] Overall, the performance differences among the embodiments mainly stem from variations in the integrity of the gradient structure, pore connectivity, and interfacial bonding strength. Embodiment 1, through the synergistic effect of multi-level gradient design and intelligent responsive polymers, achieves an optimal balance between pore structure, mechanical support, and bioactivity, significantly improving osteogenic efficiency and interfacial integration capabilities. Embodiment 2 maintains good overall performance even after process simplification. Embodiment 3 focuses more on structural density and initial stability. This demonstrates that the introduction of the gradient design and intelligent response mechanism described in this invention allows for flexible adjustment of material properties to meet different clinical needs, providing a controllable and adaptable material system for achieving efficient and safe bone defect repair.

[0155] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0156] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A biphasic calcium phosphate / hydroxyapatite bone substitute material, characterized in that, include: The system comprises a biodegradable calcium phosphate core layer, a porous hydroxyapatite precursor layer formed in situ on the surface of the biodegradable calcium phosphate core layer using a sol-gel method, and a hydroxyapatite gradient layer covering the porous hydroxyapatite precursor layer formed by electrodeposition. The hydroxyapatite gradient layer includes at least a first gradient sublayer and a second gradient sublayer along its thickness direction. The first gradient sublayer is located closer to the porous hydroxyapatite precursor layer, and the second gradient sublayer is located further away from the porous hydroxyapatite precursor layer. Furthermore, from the first gradient sublayer to the second gradient sublayer, the corresponding thickness, equivalent pore size, porosity, crystallinity, grain size, and calcium-to-phosphorus ratio continuously increase, forming a gradually loosening gradient structure from the biodegradable calcium phosphate core layer to the outer surface of the hydroxyapatite gradient layer.

2. The biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 1, characterized in that: The first gradient sublayer has a thickness of 1–5 μm, an equivalent pore size of 0.1–0.5 μm, a grain size of 20–60 nm, a crystallinity of 30–55%, and a porosity of 20–35%. The second gradient sublayer has a thickness of 15–60 μm, an equivalent pore size of 20–80 μm, a grain size of 50–150 nm, a crystallinity of 55–85%, and a porosity of 50–80%. The calcium-to-phosphorus ratio gradually changes from 1.45 to 1.67 along the thickness direction.

3. The biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 2, characterized in that, It also includes a third gradient sublayer located between the first gradient sublayer and the second gradient sublayer, with a thickness of 5-20 μm, an equivalent pore size of 5-20 μm, a grain size of 35-100 nm, a crystallinity of 40-70%, and a porosity of 30-50%.

4. The biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 1, characterized in that, The equivalent pore size of the porous hydroxyapatite precursor layer is 0.05–0.5 μm, and the porosity is 15–35%.

5. The biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 1, characterized in that, The sol-gel system forming the porous hydroxyapatite precursor layer contains a pH / temperature-sensitive polymer, which forms a reversible network of ionic and hydrogen bonds in the pore walls of the porous hydroxyapatite precursor layer.

6. A method for preparing a biphasic calcium phosphate / hydroxyapatite bone substitute material as described in any one of claims 1 to 5, characterized in that, include: A porous biodegradable calcium phosphate core layer was prepared. The porous hydroxyapatite precursor layer is formed on the surface of the biodegradable calcium phosphate core layer by a sol-gel method. Using the biodegradable calcium phosphate core layer as the cathode and the porous hydroxyapatite precursor layer as the reaction template for ion migration and crystal growth, the mixture is immersed in a Ca-containing solution. 2+ and PO4 3- Electrodeposition is performed in an electrolyte solution to deposit the hydroxyapatite gradient layer on the surface of the porous hydroxyapatite precursor layer. The electrodeposition process includes, in sequence, at least a first-stage process suitable for forming the first gradient sub-layer and a second-stage process suitable for forming the second gradient sub-layer, wherein the electrodeposition voltage of the second-stage process is greater than the electrodeposition voltage of the first-stage process, and the electrodeposition time of the second-stage process is not less than the electrodeposition time of the first-stage process.

7. The method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 6, characterized in that, The voltage applied in the first stage of the treatment is 0.6 to 0.9 V, and the electrodeposition time is 6 to 18 hours; the voltage applied in the second stage of the treatment is 1.2 to 1.6 V, and the electrodeposition time is 8 to 24 hours.

8. The method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 6, characterized in that, The electrodeposition process further includes a third stage process between the first stage process and the second stage process, the third stage process being adapted to form a third gradient sublayer located between the first gradient sublayer and the second gradient sublayer; the electrodeposition voltage of the third stage process is between the electrodeposition voltages of the first stage process and the second stage process, and the electrodeposition time of the third stage process is not less than the electrodeposition time of the first stage process and not greater than the electrodeposition time of the second stage process.

9. The method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 6, characterized in that, The process of forming the porous hydroxyapatite precursor layer on the surface of the biodegradable calcium phosphate core layer via the sol-gel method includes: adding ethanol to a sodium dihydrogen phosphate solution to make the volume ratio of ethanol to sodium dihydrogen phosphate solution 2:10 to 4:10, slowly adding calcium hydroxide solution while stirring, adjusting the pH value to 7.0 to 8.0, forming a gel after stirring evenly and allowing it to stand, obtaining a porous hydroxyapatite precursor after the gel dries, calcining the porous hydroxyapatite precursor and covering it on the surface of the biodegradable calcium phosphate core layer to form the porous hydroxyapatite precursor layer.

10. The method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 6, characterized in that, The preparation of the porous biodegradable calcium phosphate core layer comprises: mixing calcium hydrogen phosphate dihydrate, calcium carbonate and calcium hydroxide in a molar ratio of 2:1:1 to form a mixture; heating the mixture to a temperature range of 1200-1450°C at a heating rate of 10-15°C / min and calcining and sintering for 12-15 hours to form the porous biodegradable calcium phosphate core layer.

11. The method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 6, characterized in that, The method also includes adding 0.1-1.0 wt% polymethacrylic acid and 0.02-0.2 wt% crosslinking agent to the sol-gel system during the formation of the porous hydroxyapatite precursor layer on the surface of the biodegradable calcium phosphate core layer via a sol-gel method. The polymethacrylic acid is then uniformly dispersed in the pore walls of the porous hydroxyapatite precursor layer through a free radical polymerization reaction to construct a reversible ionic and hydrogen bond network.

12. The method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 6, characterized in that, The electrolyte contains sodium dihydrogen phosphate and calcium hydroxide, and the electrodeposition treatment temperature is 35–40°C.

13. The method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 6, characterized in that, Also includes: The material after forming the hydroxyapatite gradient layer is placed in a plasma treatment device for plasma surface treatment. The plasma surface treatment time is 10 to 30 minutes and the treatment power is 100 to 300W.

14. The method for preparing the biphasic calcium phosphate / hydroxyapatite bone substitute material according to claim 6, characterized in that, The electrodeposition process employs pulsed electrodeposition to control the nucleus density and grain size, with a pulse frequency of 0.5–5 Hz and a duty cycle of 30–70%.

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