Plastic for living body and process for producing the same

Abstract

Super engineering plastics are excellent in mechanical properties and heat resistance, but have a problem that they are poor in biocompatibility and are not suitable for use as biomaterials.SOLUTION: The plastic for a living body having a super engineering plastic as a base material and a crystallized hydroxyapatite layer formed on the surface of the super engineering plastic can provide a lightweight material for a living body excellent in biocompatibility, mechanical strength and heat resistance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to bioplastics that can be used as substitute materials for bones, teeth, etc. in the fields of orthopedics and dentistry. [Background technology]

[0002] Super engineering plastics, such as polyetheretherketone (PEEK), exhibit excellent mechanical properties (especially elastic modulus), high chemical resistance, inherent radiopacity, and in vivo stability. Therefore, super engineering plastics have attracted attention as biomaterials that can replace conventional metal implants made of pure titanium or titanium alloys for patients with metal allergies. However, the poor biocompatibility of the surfaces of super engineering plastics has hindered their application in orthopedics and dentistry.

[0003] To date, physical methods such as sandblasting, acid etching, ultraviolet irradiation, laser surface modification, and plasma treatment have been investigated to improve the biocompatibility of super engineering plastic surfaces. In addition, attempts have been made to coat the surfaces of super engineering plastics with bioactive glass and polydopamine (PDA).

[0004] Furthermore, in recent years, attempts have been made to coat hydroxyapatite (HAp) by sputtering or dip coating. Specifically, Patent Document 1 discloses a method in which a Ti layer is formed on the surface of PEEK, a hydroxyapatite film is formed by sputtering, and then hydrothermal treatment is performed.

[0005] Patent Document 2 also discloses a method in which a liquid crystal phase is formed on the surface of a liquid phase via a surfactant, nano-sized crystalline calcium phosphate is formed therein, an object is immersed in the solution to form a coating layer of nano-sized crystalline calcium phosphate on the surface of the object, and then the surfactant is removed by heating.

[0006] Patent Document 3 discloses a method for forming a strontium apatite film on the surface of PEEK by forming strontium apatite particles into ink on the surface of PEEK, dipping the PEEK material in the ink, drying it, and then heating it with a laser. Note that this document also states that a hydroxyapatite film is simultaneously formed by the same method. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-29754 [Patent Document 2] U.S. Patent No. 8,206,813 [Patent Document 3] Patent Publication No. 2021-029750 Summary of the Invention [Problem to be solved by the invention]

[0008] However, physical methods such as sandblasting, acid etching, UV irradiation, laser surface modification, and plasma treatment carry the risk of reducing the mechanical properties of PEEK (a super engineering plastic).In addition, methods that coat the surface of PEEK (a super engineering plastic) with bioactive glass or polydopamine (PDA) carry the risk of coating film peeling and degradation of the base PEEK (a super engineering plastic).

[0009] Furthermore, in Patent Document 1, an intermediate layer such as Ti must be formed on the surface of PEEK (super engineering plastic), which increases manufacturing costs. Furthermore, in sputtering, the base resin material is exposed to high temperatures, which increases the risk of deterioration in shape and mechanical properties. In addition, in Patent Document 2, problems remain, such as peeling of the coating film due to the low crystallinity of HAp and the use of physical adsorption. In addition, in Patent Document 3, the high temperatures during laser heating cause problems similar to those of sputtering. In the first place, the hydroxyapatite film in Patent Document 3 is not considered worthy of use. [Means for solving the problem]

[0010] The present invention provides a bioplastic material in which a crystallized HAp film is formed directly on the surface of a super engineering plastic by pulsed laser deposition (PLD) using an ultraviolet laser.

[0011] More specifically, according to the present invention, the bioplastic is The base material is super engineering plastic, The super engineering plastic is characterized by having a crystallized hydroxyapatite layer formed on the surface thereof.

[0012] Further, the method for producing bioplastic according to the present invention comprises the steps of: forming an amorphous hydroxyapatite layer on the surface of a super engineering plastic substrate by a pulsed laser deposition method to obtain a substrate plastic with an amorphous hydroxyapatite layer; The method is characterized by comprising a step of subjecting the substrate plastic with the amorphous hydroxyapatite layer to hydrothermal treatment to obtain a substrate plastic with a crystallized hydroxyapatite layer as a bioplastic. [Effects of the Invention]

[0013] In this invention, a hydroxyapatite film is formed on a super engineering plastic (PEEK) substrate by pulsed laser deposition (PLD) using an ultraviolet laser, so there is little difference between the composition of the hydroxyapatite target and the composition of the thin film deposited on the substrate surface. Furthermore, because the deposited thin film is less susceptible to damage from re-ablation from the substrate, a high-quality hydroxyapatite thin film with relatively high adhesion strength can be produced on the surface of the super engineering plastic.

[0014] Furthermore, because the melting point of the super engineering plastic (PEEK) is low, it is difficult to crystallize the hydroxyapatite film by high-temperature heat treatment, so a hydrothermal treatment method that allows crystallization at low temperatures is used for crystallization. Specifically, a batch hydrothermal synthesis method using an autoclave pressure vessel is used, and the effect of pressure is used to crystallize the hydroxyapatite at a temperature lower than that in air.

[0015] By using the UV PLD method to prepare a hydroxyapatite thin film and hydrothermal treatment to crystallize the hydroxyapatite thin film, we succeeded in preparing a highly crystalline hydroxyapatite thin film with high adhesive strength on a super engineering plastic (PEEK).The biocompatibility of the surface-modified super engineering plastic (PEEK) coated with the crystallized hydroxyapatite film was evaluated in vitro, and it was found that the surface biocompatibility was improved.This result indicates that early osseointegration can be promoted. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a conceptual diagram showing a part of the method for producing bioplastic according to the present invention (a step of forming a hydroxyapatite film by the PLD method). [Figure 2] These are photographs of the results of observation using a scanning electron microscope (SEM) of the PEEK surface before film deposition (Figures 2(a) and 2(b)) and the PEEK surface after film deposition (Figures 2(c) and 2(d)). [Figure 3] FIG. 1 shows X-ray diffraction (XRD) results for a PEEK substrate, HAp-PEEK, and annealed HAp-PEEK. [Figure 4] These are the results of composition evaluation using energy dispersive X-ray spectroscopy (EDS). Figure 4(a) shows the composition mapping results, which are mapping photographs of "field of view SEM image," "Ca: calcium," "O: oxygen," and "P: phosphorus." Figure 4(b) shows the results of composition analysis. [Figure 5] FIG. 1 shows the results of chemical structure analysis by Fourier transform infrared spectroscopy (FT-IR). [Figure 6] FIG. 10 is a diagram showing the results of a film adhesion strength test performed by a tensile test method. [Figure 7] These are photographs of the results of SEM observation of the morphology of cells on PEEK 24 hours after cell seeding and on HAp-PEEK after annealing. [Figure 8] 1 is a graph showing the results of evaluating cell proliferation 1, 3, and 7 days after cell seeding. [Figure 9] Figure 9(a) shows the quantification results of ALP activity / DNA amount, which is an early marker of hard tissue differentiation induction, and Figure 9(b) is a graph showing the measurement results of calcium precipitation amount, which is a late marker of hard tissue differentiation induction. [Figure 10] 1 is a graph showing the results of analyzing gene expression related to hard tissue differentiation induction on the material surface of annealed HAp-PEEK. [Figure 11] An example of screw use (Fig. 11(a)) and a photograph (Fig. 11(b)). [Figure 12] The results show the biocompatibility of the screws implanted in rats. Figure 12(a) is the bone volume fraction (BV / TV) of newly formed bone, Figure 12(b) is the number of trabeculae (Tb.N), and Figure 12(c) is a graph showing the results of the spacing between trabeculae (Tb.Sp). DETAILED DESCRIPTION OF THE INVENTION

[0017] The bioplastic according to the present invention will be described below with reference to drawings and examples. Note that the following description illustrates one embodiment of the present invention and one example, and the present invention is not limited to the following description. The following description can be modified within the scope of the present invention. Note that in the following description, "A to B" for numerical values ​​A and B means "A or more (greater than A including A)" and "B or less (smaller than B including B)."

[0018] The bioplastic of the present invention is a super engineering plastic having a hydroxyapatite (hereinafter also simply referred to as "crystallized HAp") layer formed directly on the surface thereof.

[0019] Super engineering plastics, also known as super engineering plastics, are resin materials with higher heat resistance than regular engineering plastics.

[0020] More specifically, examples include PPS (polyphenylene sulfide), PSU (polysulfone), PPSU (polyphenylene sulfone), PAR (polyarylate), PES (polyethersulfone), PEI (polyetherimide), PAI (polyamideimide), LCP (liquid crystal polymer), PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane polymer), PEEK (polyetheretherketone), PEK (polyetherketone), PEKK (polyetherketoneketone), and the like. The present invention can utilize at least one material from among these. Note that, in this specification, these super engineering plastics are also referred to as bioplastic substrates.

[0021] <Hydroxyapatite: Crystallized HAp> Hydroxyapatite is known as a type of apatite that contains hydroxyl groups as monovalent anions. In the bioplastic of the present invention, a hydroxyapatite target with a predetermined composition ratio of Ca, P, hydroxyl groups, etc. is prepared, and the hydroxyapatite layer is deposited on a substrate by the PLD (Pulsed Laser Deposition) method.

[0022] It should be noted that the hydroxyapatite layer immediately after deposition cannot be said to be in a crystalline state. Therefore, the hydroxyapatite layer immediately after deposition is called an "amorphous hydroxyapatite layer (amorphous HAp layer)." Furthermore, the amorphous HAp layer can be crystallized by hydrothermal treatment, which will be described later. The crystallized HAp layer is called a "crystallized hydroxyapatite layer (crystallized HAp layer)."

[0023] In the bioplastic of the present invention, an amorphous HAp layer is provided on a substrate and then crystallized to form a crystallized HAp layer. The thickness of the amorphous HAp layer provided on the substrate is preferably 0.2 μm to 1.0 μm. If the thickness is too thin, the plastic surface cannot be completely covered, and if the thickness is too thick, cracks and peeling occur due to stress during deposition.

[0024] Furthermore, in the bioplastic of the present invention, the crystallized HAp layer on the substrate is crystallized, and peaks specific to HAp polycrystals can be confirmed by X-ray diffraction. Furthermore, in the bioplastic of the present invention, the crystallized HAp layer is produced by depositing an amorphous HAp layer directly on the substrate. In other words, no inorganic intermediate layer is provided between the substrate and the crystallized HAp layer. Therefore, in the bioplastic of the present invention, only peaks due to the substrate, peaks due to the crystallized HAp layer, and noise are observed by X-ray diffraction, and no other peaks are observed. Here, the peak refers to the peak at which the intensity of X-ray diffraction increases and decreases.

[0025] Even if a film has already been formed on a substrate, it can be determined whether the film on the substrate is a crystallized HAp layer by first measuring the intensity profile against 2θ using X-ray diffraction, then peeling off the formed portion and measuring the X-ray diffraction of only the substrate. More specifically, it is sufficient to confirm the characteristic peaks of the already known crystallized HAp, namely, the 201, 211, 112, 300, and 202 planes. Note that if at least the 211 and 112 planes are confirmed, it can be said to be the crystallized HAp of the present invention. Furthermore, if no peaks other than the characteristic peaks of the crystallized HAp layer and the substrate are detected, it can be said that the crystallized HAp layer is directly formed on the substrate. Furthermore, elemental analysis can be used to confirm the absence of elements other than Ca, P, and O.

[0026] <Pulsed laser deposition method (PLD method)> In the PLD method, a pulsed laser wave is irradiated onto a target in a vacuum, ablating the target and depositing it onto a substrate. The composition ratio of the deposited film on the substrate is almost the same as that of the target material, and the temperature of the substrate does not increase. Therefore, by using a target with a predetermined composition ratio of the desired elements, an amorphous HAp layer with almost the same composition ratio as the target can be formed on the substrate.

[0027] An overview of the PLD method is shown in Figure 1. A target 14 and a substrate 16 are placed in a vacuum processing space 10. The substrate 16 is fixed to a holder 20. The film formation atmosphere in the vacuum processing space 10 is preferably O2 gas containing water (O2 + H2O). The pulsed laser device 12 does not need to be located inside the vacuum processing space 10, as irradiation through a viewing window is also possible in the case of a laser.

[0028] When a pulsed laser 30 is irradiated onto the target 14 from the pulsed laser device 12, a decomposition and separation reaction (ablation) occurs on the surface of the target 14, and the constituent materials of the target 14 fly off from the surface of the target 14 as atoms, molecules, and clusters (scattered particles 32).

[0029] These particles 32 scattered from the target 14 are deposited on the substrate 16 to form the deposited thin film 18. This PLD method is characterized by the fact that the use of short-wavelength ultraviolet light makes it difficult for the composition of the target 14 and the composition of the deposited thin film 18 to differ, and is also less susceptible to damage such as re-ablation to the surface of the deposited thin film 18 during film formation. At this stage, the deposited thin film 18 is amorphous. The substrate immediately after deposition is also called a substrate plastic with an amorphous HAp layer.

[0030] <Hydrothermal treatment> The HAp film deposited on the substrate by the PLD method is still amorphous, so an annealing process is required for crystallization. However, because the glass transition temperature of super engineering plastics is generally lower than the melting point of metals, annealing and baking, which involves applying thermal energy in a typical electric furnace to crystallize the plastic, cannot be used. Therefore, when manufacturing the bioplastic of the present invention, a hydrothermal treatment method is used. In this method, pressure and a temperature below the melting point of the substrate 16 (343°C) are applied to the object to be treated placed in a hydrothermal reaction vessel. The temperature is preferably 120°C or higher and 160°C or lower. The substrate after hydrothermal treatment is also called a substrate plastic with a crystallized HAp layer. [Example]

[0031] In the PLD method of FIG. 1, the substrate 16 was made of PEEK material, and a KrF excimer laser (wavelength: 248 nm) was used for the pulse laser device 12. The pulse repetition frequency was 10 Hz. A circular HAp disk (CELL YARD: manufactured by HOYA Technosurgical Co., Ltd.) was used for the target 14. The substrate temperature of the substrate 16 was room temperature, and the film formation atmosphere was O2 gas containing water (O2 + H2O) at a gas pressure of 1.3 × 10 -2 The thickness of the deposited thin film 18 (deposited HAp film) formed on the PEEK surface was approximately 1 μm.

[0032] To crystallize the deposited thin film 18, a hydrothermal treatment was carried out at 140°C for 3 hours, because the PEEK of the substrate 16 has a melting point of 343°C and a heat distortion temperature of 315°C.

[0033] Figure 2 shows the results of scanning electron microscope (SEM) observations of the PEEK surface before film deposition (Figures 2(a) and 2(b)) and after film deposition (Figures 2(c) and 2(d)). Figures 2(b) and 2(d) are enlarged photographs of the areas enclosed by dotted lines in Figures 2(a) and 2(c), respectively. Hereinafter, the PEEK sample after film deposition (Figures 2(c) and 2(d)) will be referred to as HAp-PEEK. Note that the sample after annealing HAp-PEEK by hydrothermal treatment will be referred to as "annealed HAp-PEEK."

[0034] Figures 2(a) and 2(b) show cutting marks on the PEEK surface. On the other hand, Figures 2(c) and 2(d) show scattered particle droplets with a diameter of 2 to 3 μm, which are characteristic of the pulsed laser deposition method, on the HAp-PEEK surface. This shows that the HAp-PEEK is a PEEK in which a thin HAp film is formed uniformly on the PEEK surface through the above process.

[0035] Figure 3 shows the X-ray diffraction (XRD) results for the PEEK substrate, HAp-PEEK, and annealed HAp-PEEK. The horizontal axis represents 2θ, and the vertical axis represents intensity (arbitrary units). The diffraction peaks for HAp-PEEK after film deposition are nearly identical to those for the PEEK substrate, and HAp is no longer visible after film deposition.

[0036] However, in the diffraction results for annealed HAp-PEEK, in addition to the PEEK peak (downward triangle (▼) in the figure), a HAp peak (downward arrow) was observed, which indicates that in annealed HAp-PEEK, a crystallized HAp film is formed on the PEEK substrate.

[0037] Figure 4 shows the results of composition evaluation using energy dispersive X-ray spectroscopy (EDS). Figure 4(a) shows the composition mapping results, which are "field-of-view SEM image," "Ca: calcium," "O: oxygen," and "P: phosphorus" mapping photographs. Figure 4(b) shows the composition analysis results.

[0038] Figure 4(a) shows that the constituent elements of HAp, Ca, P, and O, are uniformly detected on the surface. Figure 4(b) also shows peaks for Ca, P, O, and C, and the ratio of Ca to P (Ca / P) is 1.63, which is close to the Ca / P molar ratio of 1.67 for stoichiometric HAp. These findings indicate that a crystallized HAp film has formed on the PEEK surface.

[0039] Figure 5 shows the results of chemical structure analysis by Fourier transform infrared spectroscopy (FT-IR). The horizontal axis shows the wave number (cm -1 ) and the vertical axis is the transmittance (%). After annealing, the transmittance of HAp-PEEK was 3608 cm -1 Nearby OH - Peak, 1008cm -1 and 569cm -1 PO4 nearby 3- The peaks indicate that a crystallized HAp film is formed on the PEEK.

[0040] Figure 6 shows the results of a film adhesion strength test using the tensile test method. The horizontal axis is the amount of elongation (displacement) (mm) and the vertical axis is the stress (MPa). Figure 6 shows that the adhesion strength of the crystallized HAp film on the PEEK is approximately 2.90 MPa. Since tensile forces are rarely applied to films inside the oral cavity, this value is sufficient for adhesion strength.

[0041] Figures 7 and 8 show the results of an in vitro biocompatibility evaluation using rat bone marrow mesenchymal stem cells (rBMMSCs).

[0042] Figure 7 shows the results of SEM observations of cell morphology on PEEK and annealed HAp-PEEK 24 hours after cell seeding. Figure 7(a) is a photograph of PEEK before cell seeding, and Figures 7(b) and 7(c) are photographs 24 hours after cell seeding. Figures 7(b) and 7(c) are photographs at different magnifications. Figure 7(d) is a photograph of annealed HAp-PEEK before seeding. This is a photograph of a crystallized HAp thin film. Figures 7(e) and 7(f) are photographs 24 hours after cell seeding. Figures 7(e) and 7(f) are photographs at different magnifications.

[0043] It was confirmed that cells adhered to the material surface regardless of whether or not a crystallized HAp thin film was applied. However, on the annealed HAp-PEEK surface with a crystallized HAp layer, the number of cells was higher than on the PEEK surface, and the extension of cell processes was observed, extending several filopodia to adhere to the surface. These results suggest that the crystallized HAp thin film coating promotes cell proliferation and exhibits good biological activity.

[0044] Figure 8 shows the results of cell proliferation evaluation 1, 3, and 7 days after cell seeding. The horizontal axis represents the number of days and scaffold material type (PEEK and annealed HAp-PEEK), and the vertical axis represents the number of cells. 1, 3, and 7 days after cell seeding, the number of cells was higher in the annealed HAp-PEEK group than in the PEEK control group. In other words, it was clear that the annealed HAp-PEEK with a crystallized HAp thin film had statistically significantly better cell proliferation than the control group.

[0045] Figure 9(a) shows the quantitative results of ALP activity / DNA content, an early marker of hard tissue differentiation induction. The horizontal axis shows the number of days and scaffold material type, and the vertical axis shows ALP activity / DNA content (μmol / ml). The relative ALP activity / DNA content of annealed HAp-PEEK was significantly higher than that of PEEK on days 7 and 14.

[0046] Figure 9(b) shows the measurement of calcium precipitation, a late marker of hard tissue differentiation induction. The horizontal axis shows the number of days and scaffold material type, and the vertical axis shows the amount of calcium precipitation (mg / dL). The amount of calcium precipitation 21 and 28 days after cell seeding was significantly higher for annealed HAp-PEEK than for PEEK.

[0047] Figure 10 shows the results of analyzing gene expression related to hard tissue differentiation induction on the surface of annealed HAp-PEEK materials. The mRNA expression levels of osteogenesis-related genes, including alkaline phosphatase (ALP) (Figure 10(a)) and runt-related transcription factor (Runx2) (Figure 10(b)), were evaluated by qRT-PCR in cells cultured on different surfaces for 3 and 7 days.

[0048] Referring to Fig. 10(a), the horizontal axis represents the scaffold material type, and the vertical axis represents the mRNA expression level. In Fig. 10(b), the horizontal axis represents the number of days and the scaffold material type, and the vertical axis represents the amount of runt-related transcription factor. Note that in both Fig. 10(a) and Fig. 10(b), the vertical axis is the value normalized by the mRNA amount of GAPDH. Significantly higher gene expression was observed on the material surface of annealed HAp-PEEK at all measurement times.

[0049] <In vivo evaluation> Lag screws (hereinafter simply referred to as "screws") used in surgical treatments for femoral trochanter fractures are currently made of titanium, but the bioplastic according to the present invention is considered promising as an alternative material in terms of strength and biocompatibility. Fig. 11 shows the screw. Fig. 11(a) is a conceptual diagram showing an example of a screw 50 drilled into a femur 52.

[0050] Also, Fig. 11(b) is a photograph taken with two screws 50 lined up side by side with a ruler. This is a PEEK screw 50 prototype made for rats described later.

[0051] The following in vivo evaluation was performed using PEEK screws in the experimental group and the control group. After drilling a diamond point into the femur of 8-week-old male SD rats (Shimizu Laboratory Supplies Co., Ltd.), the PEEK screws of each group were immediately implanted. At this time, the PEEK screw was brought into contact with the drilled part at several locations including the tip of the screw and implanted so as to obtain initial fixation. The experimental group is, of course, an annealed HAp-PEEK screw in which a HAp film was deposited on a PEEK screw 50 and crystallized by hydrothermal treatment.

[0052] <Spongy bone morphometry using CT> PEEK screws from each group were implanted into the femurs of 8-week-old male SD rats. Eight weeks after implantation, the rats were euthanized by intraperitoneal overdose of anesthetic, and the femurs were then excised. The excised femurs were then imaged using a microfocus X-ray CT SMX-130CT (Shimadzu Corporation). The bone volume fraction (BV / TV) of newly formed bone (Figure 12(a)), trabecular number (Tb.N) (Figure 12(b)), and trabecular spacing (Tb.Sp) (Figure 12(c)) were analyzed using TRI / 3D-BON (Ratoc System Engineering) trabecular structure measurement software.

[0053] For the bone volume fraction (Fig. 12(a)) and the number of trabeculae (Fig. 12(b)), the larger the value, the greater the amount of bone formation. For the gaps between trabeculae (Fig. 12(c)), the smaller the value, the denser the bone.

[0054] 12(a), 12(b), and 12(c), the horizontal axis represents the PEEK screws of the Example (annealed HAp-PEEK) and the Comparative Example (PEEK). The vertical axis represents the volume fraction (%) in Fig. 12(a), the number of trabeculae (1 / pixel) in Fig. 12(b), and the trabecular spacing (pixel) in Fig. 12(c).

[0055] The results of trabecular bone morphology measurement using CT, shown in Figures 12(a), 12(b), and 12(c), indicate that the annealed HAp-PEEK screw, which was coated with hydroxyapatite using the PLD method and had a crystallized HAp layer on its surface, showed greater bone formation than the untreated PEEK screw (Figures 12(a) and 12(b)). Also, because the bone was denser (Figure 12(c)), it was clear that the annealed HAp-PEEK screw formed more dense new bone around the screw than the untreated PEEK screw. [Industrial Applicability]

[0056] The bioplastic of the present invention can be used as a variety of biomaterials, including lag screws used in the treatment of femoral trochanteric fractures. In particular, it is promising as a bone substitute material because of its excellent mechanical properties and light weight. [Explanation of symbols]

[0057] 10 Vacuum processing space 12 Pulse laser device 14 Target 16 Base material 18 Hydroxyapatite (deposited thin film) 20 Holder 30 Laser 32 Scattered particles 50 lag screws 52 Femur

Claims

1. The base material is super engineering plastic, A bioplastic having a crystallized hydroxyapatite layer formed on the surface of the super engineering plastic.

2. 2. The bioplastic according to claim 1, wherein only peaks of the super engineering plastic and the crystallized hydroxyapatite layer are observed in X-ray diffraction of the surface (no peaks of other substances are observed except for noise).

3. 3. The bioplastic according to claim 2, wherein the peak of the crystallized hydroxyapatite layer includes the 211 plane.

4. 2. The bioplastic according to claim 1, wherein the adhesive strength between the crystallized hydroxyapatite layer and the super engineering plastic is 2 MPa or more.

5. forming an amorphous hydroxyapatite layer on the surface of a super engineering plastic substrate by a pulsed laser deposition method to obtain a substrate plastic with an amorphous hydroxyapatite layer; The method for producing a bioplastic comprises a step of subjecting the substrate plastic with the amorphous hydroxyapatite layer to hydrothermal treatment to obtain a substrate plastic with a crystallized hydroxyapatite layer as a bioplastic.

6. 6. The method for producing bioplastics according to claim 5, wherein the pulsed laser deposition method uses ultraviolet light.

7. 6. The method for producing bioplastics according to claim 5, wherein the hydrothermal treatment is carried out by exposing the substrate plastic with the amorphous hydroxyapatite layer to steam at a temperature of 120°C or higher and 160°C or lower.

Images