Preparation method of gradient biological coating with controllable structure

Abstract

The invention provides a preparation method of a gradient biological coating with a controllable structure, which comprises the following steps: step 1, preparing uniformly mixed TC4 / HA powder by utilizing a low-energy ball milling method before coating deposition; 2, a TC4 / HA coating for relieving the thermal expansion coefficient is prepared on the surface of the titanium alloy through the atmosphere plasma spraying technology; and 3, preheating the base material deposited with the TC4 / HA transition layer, and preparing the HA biological coating with a controllable structure on the surface of the TC4 / HA coating.

Description

Technical Field

[0001] This invention relates to the field of bio-coating preparation and material surface protection, and in particular to a method for preparing a gradient bio-coating with controllable structure. Background Technology

[0002] Titanium alloys (such as TC4) are widely used as implant materials for hard tissue replacement or repair in orthopedics, dentistry, and other fields due to their high specific strength, good mechanical properties, and excellent biocompatibility. However, titanium alloys are inherently bioinert materials, and their surfaces are difficult to form strong chemical bonds with human bone tissue, meaning their osseointegration capacity is limited, which can easily lead to implant loosening and failure. Furthermore, titanium alloys have poor wear resistance, and during long-term use in the body, wear may release metal ions, posing potential biological risks.

[0003] To overcome the aforementioned shortcomings, preparing a hydroxyapatite (HA) bioactive coating on the surface of a titanium alloy substrate is currently the most effective solution. HA is a major inorganic component of human bone and possesses excellent biocompatibility and osteoconductivity. Atmospheric plasma spraying (APS) technology is a commonly used industrial method for preparing HA coatings due to its high efficiency and controllable coating thickness. However, this technology faces two key technical challenges that have long remained unresolved. First, there is a significant mismatch in thermophysical properties between HA and the titanium alloy substrate, especially a large difference in the coefficient of thermal expansion (CTE) (HA: ~13-15×10⁻⁻⁻⁴). 6 / K, TC4: ~8-9×10⁻ 6 / K). During the rapid heating and cooling process of plasma spraying, this mismatch generates huge residual thermal stress at the coating / substrate interface, directly leading to low coating bonding strength, easy cracking, and even peeling. Traditional single-component HA coatings are difficult to solve this problem. Secondly, the microstructure of the coating is closely related to its biological function, but traditional processes make it difficult to achieve precise control over the coating structure. HA is unstable at high temperatures; excessive heat input can cause it to decompose into an amorphous phase or a calcium phosphate phase with poor biological activity (such as TCP), reducing the long-term stability of the coating; while insufficient heat input may result in incomplete powder melting and weak bonding between the coating and the substrate (or transition layer). Therefore, how to reconcile the contradiction between high coating bonding strength and high biological activity structure is the core challenge for improving coating performance. Existing technologies lack an effective means to achieve interfacial metallurgical bonding (or quasi-metallurgical bonding) while ensuring the biological activity of the HA top layer.

[0004] To address the thermal mismatch issue, researchers have attempted to introduce a compositional gradient transition layer. However, transition layers prepared using traditional methods exhibit poor uniformity, and reliable theoretical basis and technological windows are still lacking for achieving high-strength bonding between the HA functional layer and the transition layer. Studies have shown that for ceramic coatings, deposition temperature is a key factor affecting interlayer bonding within the coating. By precisely controlling the deposition temperature during the spraying process to reach a critical bonding temperature, the spreading behavior of individual flat particles and interfacial reactions during ceramic coating spraying can be significantly improved, thereby achieving a strong interfacial bonding effect within the coating that approaches "metallurgical bonding." However, for the preparation of bioactive HA coatings on titanium alloy surfaces, existing technologies have not systematically combined this critical temperature control with the preparation of gradient coatings, thus failing to simultaneously optimize the mechanical properties and biological functions of the coating. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a method for preparing a structure-controllable gradient bio-coating. First, a TC4 / HA transition layer with uniform tissue structure is deposited by uniformly mixing TC4 and HA powders. Second, the HA functional layer structure is adjusted by controlling the deposition temperature to ensure it meets the bioactivity and biocompatibility requirements of artificial bone implants in different parts of the human body. This method solves the problem of precisely controlling the microstructure of coatings (especially the surface HA layer), which is difficult to achieve with traditional methods, resulting in a high-performance gradient bio-coating with strong adhesion, high bioactivity, and an ideal degradation rate. This overcomes the technical challenges of traditional preparation methods.

[0006] This invention is achieved through the following technical solution: a method for preparing a structure-controllable gradient bio-coating, comprising: Step 1: Before coating deposition, prepare uniformly mixed TC4 / HA powder using a low-energy ball milling method; Step 2: Prepare a TC4 / HA coating on the surface of the titanium alloy substrate to mitigate the coefficient of thermal expansion using atmospheric plasma spraying technology; Step 3: Preheat the substrate material for depositing the TC4 / HA transition layer to prepare a structurally controllable HA bio-coating on the surface of the TC4 / HA coating.

[0007] Specifically, in the process of preparing TC4 / HA mixed powder by the low-energy ball milling method, the ball mill speed is 50-100 r / min, and the ball milling time is 60-180 min.

[0008] Specifically, step 2 includes: Step 2-1: Before spraying, the powder is first dried to obtain dry TC4 / HA mixed powder. The uniformly mixed TC4 / HA powder is dried in an oven to improve the flowability of the powder during spraying. The drying temperature is 80-120℃ and the drying time is 2-4 hours.

[0009] Step 2-2: Pre-treat the surface of the substrate material to remove surface contaminants.

[0010] Steps 2-3: Use the dried TC4 / HA mixed powder to perform atmospheric plasma spraying on the surface of the pretreated substrate material to deposit a dried TC4 / HA coating on the substrate surface.

[0011] Specifically, the volume content of HA powder in the mixed powder is 30-60%, and the volume content of TC4 powder is 40-70%.

[0012] Specifically, the HA powder in the mixed powder has a particle size of 15-75 μm, and the TC4 powder has a particle size of 15-75 μm.

[0013] Specifically, the current during the atmospheric plasma spraying process is 480-700A, the arc power of the spraying is 25-45kW, the spraying distance is 80-140mm, and the thickness of the TC4 / HA transition layer is 80-150μm.

[0014] Specifically, before depositing the controllable HA coating, the substrate material with the TC4 / HA transition layer deposited should be preheated to 200-600°C using a heating table.

[0015] Specifically, the top layer of the structure-controllable layer HA is prepared by atmospheric plasma spraying technology, and the thickness of the structure-controllable layer is 50-120μm.

[0016] Specifically, the atmospheric plasma spraying current is 500-650A, the spraying arc power is 20-40kW, and the spraying distance is 80-140mm.

[0017] Compared with the prior art, the present invention has the following beneficial effects: First, the invention achieves synergistic optimization of coating interface bonding strength and bioactivity: The core innovation lies in introducing the concept of a "critical bonding temperature" and precisely controlling it. Before depositing the HA functional layer, the substrate with the prepared TC4 / HA transition layer is preheated to a specific temperature range (200-600℃). This temperature is the "critical point" for achieving optimal wetting and interfacial diffusion between molten HA particles and the transition layer surface. At this temperature, HA particles have sufficient kinetic energy and time to spread, forming a strong metallurgical-like bonding interface with the transition layer, significantly improving the bonding strength between the functional layer and the transition layer. Simultaneously, this preheating temperature is far below the temperature window that leads to severe HA decomposition, providing a crucial guarantee for maintaining the high crystallinity and phase purity of HA during subsequent spraying, thus resolving the fundamental contradiction in traditional processes where high bonding strength and high bioactivity are difficult to achieve simultaneously.

[0018] Second, by precisely controlling the deposition temperature, the microstructure of the HA functional layer is actively and precisely regulated: This invention overcomes the limitation of the traditional process of "passively forming" the HA coating structure. The preheating temperature of the substrate is a key process parameter for controlling the cooling and solidification behavior of HA particles. By matching and optimizing the preheating temperature with parameters such as the arc power and spraying distance of atmospheric plasma spraying, the cooling rate and solidification process after the molten HA particles impact the substrate can be actively controlled, thereby achieving precise design of the final coating microstructure. For example, at a lower preheating temperature, a coating with higher porosity and specific surface area can be obtained, which is conducive to rapid cell ingrowth; at a higher preheating temperature, a denser coating with higher bonding strength can be obtained. This temperature-based structural control capability is a significant advantage of this invention.

[0019] Third, it enables personalized coating customization for different clinical needs, expanding the application scope: Thanks to the precise control over the HA coating structure mentioned above, this invention makes "one preparation method, multiple coating structures" possible, thereby meeting the personalized needs of artificial bone implants in different locations. For example, for the joint stem portion requiring rapid osseointegration, a high-porosity, high-specific-surface-area HA coating can be prepared by adjusting process parameters to promote bone ingrowth and mechanical locking; for the dental implant neck requiring high shear stress, a denser and harder HA coating can be prepared to prioritize its mechanical properties and wear resistance. This flexibility of customizing coating performance on demand based on the same technology platform is unattainable by existing technologies, greatly expanding the application prospects of this coating technology.

[0020] Fourth: Scientifically designed gradient transition layer with synergistic multi-functional effects: This invention successfully constructs a gradient transition layer with continuously changing composition by using uniform TC4 / HA composite powder prepared through low-energy ball milling and an optimized plasma spraying process. This transition layer not only effectively alleviates the internal stress caused by the mismatch in thermal expansion coefficients between the titanium alloy substrate and the HA coating, fundamentally inhibiting coating cracking and peeling, but also acts as an effective physical barrier, preventing direct corrosion of the titanium alloy substrate by body fluids, reducing the free flow of metal ions to surrounding tissues, and improving the long-term biocompatibility of the implant.

[0021] Fifth: High degree of process integration, good reproducibility, and conducive to industrial production: This invention places the preparation of the gradient transition layer and the structural control of the HA functional layer within a continuous and synergistic process framework. From low-energy ball milling to transition layer spraying, and then to preheating and deposition of the functional layer, the entire process is tightly integrated with strong parameter correlation, forming a complete and reliable solution. This method has a clearly defined process window, and key parameters (such as preheating temperature) are easy to monitor and control online, ensuring the stability and reproducibility of product performance and possessing the potential for large-scale industrial application. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of a method for preparing a structure-controllable gradient bio-coating; Figure 2 This is a schematic diagram of a gradient bio-coating suitable for high shear stress environments (such as the neck of a dental implant) provided in an embodiment of the present invention; Figure 3 This is a coating provided by embodiments of the present invention suitable for sites requiring rapid osseointegration (such as the stem of an artificial joint); Detailed Implementation Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0024] Materials and equipment used in this invention: Substrate: Medical-grade TC4 (Ti-6Al-4V) titanium alloy plate, ultrasonically cleaned with acetone and anhydrous ethanol before use.

[0025] Powder: Spherical TC4 powder, medical grade hydroxyapatite (HA) powder, with a particle size range of 15-75μm.

[0026] Equipment: planetary ball mill, drying oven, sandblasting machine, atmospheric plasma spraying system (such as Sulzer Metco 9M), substrate heating table.

[0027] This invention provides a method for preparing a structure-controllable gradient bio-coating. The preferred embodiments of this invention will be described in detail below with reference to the accompanying drawings.

[0028] This invention provides a method for preparing a structure-controllable gradient bio-coating, such as... Figure 1 As shown, it includes: Step 1: Before coating deposition, prepare uniformly mixed TC4 / HA powder using a low-energy ball milling method; Step 2: Prepare a TC4 / HA coating on the surface of the titanium alloy substrate to mitigate the coefficient of thermal expansion using atmospheric plasma spraying technology; Step 3: Preheat the substrate material for depositing the TC4 / HA transition layer to prepare a structurally controllable HA bio-coating on the surface of the TC4 / HA coating.

[0029] Specifically, in the process of preparing TC4 / HA mixed powder by the low-energy ball milling method, the ball mill speed is 50-100 r / min, and the ball milling time is 60-180 min.

[0030] Specifically, step 2 includes: Step 2-1: Before spraying, the powder is first dried to obtain dry TC4 / HA mixed powder. The uniformly mixed TC4 / HA powder is dried in an oven to improve the flowability of the powder during spraying. The drying temperature is 80-120℃ and the drying time is 2-4 hours.

[0031] Step 2-2: Pre-treat the surface of the substrate material to remove surface contaminants.

[0032] Steps 2-3: Use the dried TC4 / HA mixed powder to perform atmospheric plasma spraying on the surface of the pretreated substrate material to deposit a dried TC4 / HA coating on the substrate surface.

[0033] Specifically, the volume content of HA powder in the mixed powder is 30-60%, and the volume content of TC4 powder is 40-70%.

[0034] Specifically, the HA powder in the mixed powder has a particle size of 15-75 μm, and the TC4 powder has a particle size of 15-75 μm.

[0035] Specifically, the current during the atmospheric plasma spraying process is 480-700A, the arc power of the spraying is 25-45kW, the spraying distance is 80-140mm, and the thickness of the TC4 / HA transition layer is 80-150μm.

[0036] Specifically, before depositing the controllable HA coating, the substrate material with the TC4 / HA transition layer deposited should be preheated to 200-600°C using a heating table.

[0037] Specifically, the top layer of the structure-controllable layer HA is prepared by atmospheric plasma spraying technology, and the thickness of the structure-controllable layer is 50-120μm.

[0038] Specifically, the atmospheric plasma spraying current is 500-650A, the spraying arc power is 20-40kW, and the spraying distance is 80-140mm. Specific Implementation Example 1 This embodiment aims to prepare a gradient bio-coating suitable for high shear stress environments (such as the neck of dental implants), and its structural schematic diagram is shown below. Figure 2 As shown. A key feature is the relatively dense top layer structure of the HA layer, ensuring excellent bonding strength and wear resistance.

[0040] Step 1: Preparation of TC4 / HA mixed powder: First, weigh out powder according to a volume ratio of 60% TC4 and 40% HA, with a total mass of 500g. Next, place the mixed powder and zirconia grinding balls (ball-to-powder mass ratio 5:1) into a ball mill jar. Then, perform low-energy ball milling at a speed of 70 r / min for 150 minutes. These parameters aim to achieve uniform powder mixing while avoiding cold welding or component segregation caused by over-milling. After ball milling, a highly homogeneous TC4 / HA composite powder is obtained.

[0041] Step Two: Preparation of the TC4 / HA Transition Layer: First, the composite powder was placed in an oven and dried at 100°C for 3 hours to completely remove moisture and ensure good powder flowability during spraying. Next, the TC4 substrate was roughened by sandblasting, and then residual sand particles were blown away with compressed air. Finally, an atmospheric plasma spraying system was used to spray the pretreated substrate to prepare the transition layer. The dried powder was fed into the spray gun, and the spraying current was set to 600 A, the arc power to 40 kW, and the spraying distance to 100 mm. By controlling the spray gun scanning speed and the number of passes, a TC4 / HA transition layer with a thickness of approximately 120 μm was finally obtained.

[0042] Step 3: Preparation of a structurally controllable HA bio-coating: First, the substrate with the deposited TC4 / HA transition layer was fixed on a heating stage, and its surface temperature was monitored in real time using thermocouples. The substrate temperature was precisely preheated and stabilized at 450℃. This temperature is crucial (critical bonding temperature) for ensuring good interfacial bonding between the molten HA particles and the transition layer. Then, the HA top layer was sprayed using atmospheric plasma spraying, with a spraying current of 580 A, an arc power of 36 kW, and a spraying distance of 90 mm. This parameter combination, matched with the preheating temperature of 450℃, aims to fully melt the HA powder to form a dense structure while avoiding overheating and decomposition. Spraying was performed on the preheated substrate to prepare a HA bioactive top layer with a thickness of approximately 80 μm. Specific Implementation Example 2 This embodiment aims to prepare a coating suitable for sites requiring rapid osseointegration (such as the stem of an artificial joint), and its structural schematic diagram is shown below. Figure 3 As shown, the HA top layer is characterized by high porosity and specific surface area to promote bone ingrowth. The process includes the following steps: Step 1: Weigh TC4 and HA powders separately and mix them at a volume ratio of 1:1 to obtain a mixed powder; set the ball mill speed to 90 r / min and the ball milling time to 90 minutes to obtain a highly uniform TC4 / HA composite powder.

[0044] Step 2: The drying temperature was set to 90℃ for 3.5 hours to dry the highly homogeneous TC4 / HA composite powder. Then, the substrate was pretreated using the same method as in Example 1. Finally, a TC4 / HA transition layer was prepared using atmospheric plasma spraying technology. During the spraying process, the current was set to 520 A, the arc power to 37 kW, and the spraying distance to 120 mm. A transition layer with a thickness of approximately 150 μm was obtained.

[0045] Step 3: The substrate for depositing the TC4 / HA transition layer is preheated to 250°C on a heating stage. A porous HA top layer is then deposited using atmospheric plasma spraying technology. This relatively low preheating temperature accelerates the cooling rate of the molten HA particles after impact, facilitating the formation of a porous structure. During the spraying process, the current is set to 530 A, the arc power to 32 kW, and the spraying distance to 130 mm. The relatively large spraying distance and slightly lower power contribute to the formation of layered and porous structures, ultimately producing an HA top layer with a thickness of approximately 100 μm.

[0046] In summary, this invention discloses a method for preparing a structure-controllable gradient bio-coating, relating to the fields of bio-coating preparation and material surface protection. The method comprises three steps: Step 1: Preparing a uniformly mixed TC4 / HA powder using low-energy ball milling before coating deposition; Step 2: Preparing a TC4 / HA coating on a titanium alloy surface using atmospheric plasma spraying technology to mitigate the coefficient of thermal expansion; and Step 3: Preheating the substrate material for depositing the TC4 / HA transition layer to prepare a structure-controllable HA bio-coating on the TC4 / HA coating surface. This invention addresses the problem of coating cracking and peeling caused by the mismatch in the coefficients of thermal expansion between the titanium alloy substrate and the HA coating. More importantly, this invention allows for control of the HA functional layer structure by adjusting the deposition temperature, thereby enabling customized coating structures designed for different parts of the artificial bone, which has significant application value.

[0047] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a structure-controllable gradient bio-coating, comprising: Step 1: Before coating deposition, prepare uniformly mixed TC4 / HA powder using a low-energy ball milling method; Step 2: Prepare a TC4 / HA coating on the surface of the titanium alloy substrate to mitigate the coefficient of thermal expansion using atmospheric plasma spraying technology, as a TC4 / HA transition layer; Step 3: Preheat the substrate material for depositing the TC4 / HA transition layer to prepare a structurally controllable HA bio-coating on the surface of the TC4 / HA transition layer.

2. The preparation method according to claim 1, characterized in that, In the process of preparing TC4 / HA mixed powder by the low-energy ball milling method, the ball mill speed is 50-100 r / min, and the ball milling time is 60-180 min.

3. The preparation method according to claim 1, characterized in that, Step 2 specifically includes: Step 2-1: Before spraying, the powder is first dried to obtain dry TC4 / HA mixed powder. The uniformly mixed TC4 / HA powder is dried in an oven at a temperature of 80-120℃ for 2-4 hours. Step 2-2: Pre-treat the surface of the substrate material to remove surface contaminants; Steps 2-3: Atmospheric plasma spraying is performed on the surface of the pretreated substrate material using the dried TC4 / HA mixed powder to deposit a dried TC4 / HA coating on the surface of the substrate material.

4. The preparation method according to claim 3, characterized in that, The volume content of HA powder in the mixed powder is 30-60%, and the volume content of TC4 powder is 40-70%.

5. The preparation method according to claim 3, characterized in that, The HA powder in the mixed powder has a particle size of 15-75 μm, and the TC4 powder has a particle size of 15-75 μm.

6. The preparation method according to claim 3, characterized in that, The current during the atmospheric plasma spraying process is 480-700A, the arc power of the spraying is 25-45kW, the spraying distance is 80-140mm, and the thickness of the TC4 / HA transition layer is 80-150μm.

7. The preparation method according to claim 1, characterized in that, Before depositing the HA bio-coating with controllable deposition structure, the substrate material with the TC4 / HA transition layer deposited is preheated to 200-600°C using a heating table.

8. The preparation method according to claim 1, characterized in that, The thickness of the structure-controllable HA bio-coating is 50-120 μm.

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