JP2015085098A - Implant for living body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain high mechanical strength for a predetermined period after implantation.SOLUTION: An implant for living body has a base material comprising magnesium or magnesium alloy, and an amorphous coat covering the surface of the base material. In the coat, the total content of magnesium element, oxygen element and phosphorus element is 95 wt.% or more.

Description

  The present invention relates to a biological implant.

  Conventionally, as a suitable material for an implant to be implanted in a living body, application of magnesium or a magnesium alloy which is light and strong and has biodegradability has been studied. Magnesium is highly reactive with water and proceeds in an environment where water is present. However, decomposition also proceeds in vivo in response to moisture such as body fluids and blood. Therefore, in order to use magnesium or a magnesium alloy as an implant material that requires strength over a predetermined period, it is necessary to control the decomposition rate. Then, the technique which suppresses the decomposition rate of a magnesium alloy by covering the surface of a magnesium alloy with the film | membrane which has corrosion resistance is known (for example, refer patent document 1, 2).

  In Patent Documents 1 and 2, a base material made of magnesium or a magnesium alloy is anodized to form an anodized film containing an oxygen element and a phosphorus element on the surface of the base material. According to Patent Document 1, the decomposition rate of the magnesium alloy when immersed in the simulated body fluid is suppressed by film formation, and the amount of decrease in the bending strength of the magnesium alloy when immersed in the simulated body fluid for 12 weeks does not include the film. In some cases, it was 40.0%, but when a film is present, it is reported to be suppressed to 28.7%. On the other hand, according to Patent Document 2, it is reported that high corrosion resistance can be obtained against salt spray.

US Patent Application Publication No. 2013/0116696 Japanese Patent No. 4686727

  In fracture treatment, it is said that it takes about 3 months to repair autologous bone. Therefore, an implant for joining bones needs to maintain strength in vivo for at least three months. However, in Patent Document 1, the strength decreases by about 1/3 in 12 weeks, and it cannot be said that the strength necessary for an implant is sufficiently maintained. Patent Document 2 is intended to improve the corrosion resistance of products in a living environment for industrial products, and it is difficult to exhibit sufficient corrosion resistance even in vivo. As described above, the techniques of Patent Documents 1 and 2 have a problem that the corrosion resistance in the living environment is insufficient, and the necessary strength cannot be maintained over a period required for treatment.

  This invention is made | formed in view of the situation mentioned above, Comprising: It aims at providing the biomedical implant which can maintain high mechanical strength over a predetermined period after implantation.

In order to achieve the above object, the present invention provides the following means.
One embodiment of the present invention includes a base material made of magnesium or a magnesium alloy, and an amorphous film covering the surface of the base material, and the total content of magnesium element, oxygen element, and phosphorus element in the film is A biomedical implant that is 95% by weight or more is provided.
According to this aspect, the amorphous film having the above composition suppresses a decrease in the mechanical strength of the living body implant due to corrosion after implantation in the living body for at least a predetermined period. Thereby, high mechanical strength can be maintained over a predetermined period after implantation.

In the above aspect, the magnesium element content in the coating is 25 wt% or more and 49 wt% or less, the oxygen element content is 46 wt% or more and 51 wt% or less, and the phosphorus element content The rate is preferably 1% by weight or more and 22% by weight or less.
By setting the content ratio of the main component exhibiting effective corrosion resistance in the living environment within the above range, the amount of elution due to biodegradation can be suppressed over a long period from the initial stage of implantation, and the structural strength can be further maintained. Specifically, a mechanical strength of 80% or more can be maintained with respect to the mechanical strength before implantation even after 120 days have elapsed since implantation.

In the above aspect, the magnesium element content in the coating is 25 wt% or more and 34 wt% or less, the oxygen element content is 46 wt% or more and 51 wt% or less, and the phosphorus element More preferably, the content of is 16 wt% or more and 22 wt% or less.
By making the content ratio of the main component exhibiting effective corrosion resistance in the living environment within the above range, the structural strength can be further maintained. Specifically, a mechanical strength of 85% or more with respect to the mechanical strength before implantation can be maintained even after 90 days have elapsed since implantation.

Further, in the above aspect, in the film, the remainder excluding the magnesium element, the oxygen element, and the phosphorus element may contain a carbon element as an inevitable element, and the content of the carbon element in the film is It may be 0.5% by weight or less.
By doing in this way, higher corrosion resistance can be exhibited in a living environment.

Moreover, in the said aspect, the said membrane | film | coat may have a thickness of 1.6 micrometers or more and 16 micrometers or less.
By doing in this way, while having high mechanical strength for a predetermined period, it can be rapidly extinguished by biodegradation after the affected part has healed.

In the above aspect, the biomedical implant may be a screw, pin, or plate-shaped osteosynthesis device, or may be a substantially cylindrical stent having a mesh structure.
In this way, it can be applied to bone treatment or vascular treatment.

  According to the present invention, there is an effect that high mechanical strength can be maintained for a predetermined period after implantation.

It is a partial front view of the biomedical implant which concerns on one Embodiment of this invention, and an expanded sectional view which shows the D section detail. It is a graph which shows the composition of the film | membrane of sample A, B, C, D which concerns on the Example of this invention, and the sample E which concerns on a comparative example. It is a graph which shows the relationship between the etching time obtained by XPS analysis of the film | membrane of the sample A, and the detection amount of each element. It is a graph which shows the time change of the detection amount of each element obtained by XPS analysis of the membrane | film | coat of the sample A. It is an XPS spectrum of each element in each depth of the film of sample A. 4 is a spectrum showing the result of XRD measurement of sample A. FIG. 7 is an enlarged view of the spectrum of FIG. 6 in a measurement angle range of 20 ° to 40 °. 4 is a spectrum showing the result of XRD measurement of sample E. It is the SEM image which observed the cross section of the surface vicinity of the sample D, and the line analysis result by EDX. It is a chart which shows the film thickness of sample A, B, C, D, and E. It is a graph which shows the relationship between the immersion period and bending strength of the sample A, B, C, D, and E to the pseudo body fluid. It is the pathological image of the implantation site | part 90 days after it implants the biomedical implant which has the same membrane | film | coat as the sample A. FIG.

A biological implant 1 according to an embodiment of the present invention will be described below with reference to the drawings.
A living body implant 1 according to this embodiment is an osteosynthesis material implanted in a fracture site or the like, and as shown in FIG. 1, a base material 2 formed into a screw shape, a pin shape, or a plate shape. And a coating 3 formed on the entire surface of the base material 2.

The base material 2 is made of magnesium or a magnesium alloy containing magnesium as a main component.
The film 3 includes a magnesium (Mg) element, an oxygen (O) element, and a phosphorus (P) element, and the total content of the Mg element, the O element, and the P element is 95% by weight or more. By doing in this way, corrosion of the membrane | film | coat 3 and the base material 2 after implantation in a living body is suppressed, and the fall of the mechanical strength of the implant 1 for living organisms after implantation is suppressed. When the total content of the above three types of elements is less than 95% by weight, sufficient corrosion resistance cannot be obtained with respect to the environment in the living body, and as a result, necessary for treatment after implantation of the living body implant 1 It is difficult to maintain the structure over a predetermined period. Such a coating 3 is formed, for example, by using an electrode made of pure Mg and anodizing the base material 2 in an electric field solution containing ammonium ions and phosphate ions.

  In the coating 3, the Mg element content is 25 wt% or more and 49 wt% or less, the O element content is 46 wt% or more and 51 wt% or less, and the P element content is 1 wt% or more and 22 wt%. % Or less is preferable. By doing in this way, the fall amount of the mechanical strength of the implant 1 for biological bodies for the predetermined period after implantation in a biological body can be reduced more.

  In the coating 3, the Mg element content is 25 wt% or more and 34 wt% or less, the O element content is 46 wt% or more and 51 wt% or less, and the P element content is 16 wt% or more and 22 wt%. More preferably, it is% or less. By doing in this way, the reduction | decrease amount of the mechanical strength of the implant 1 for biological bodies for the predetermined period after implantation in a biological body can further be reduced.

  The remainder of the film 3 excluding Mg element, O element and P element contains carbon (C) element. This C element is derived from an organic substance or the like attached to the surface of the base material 2 or an unavoidable element included in the manufacturing process of the biological implant 1. The content of inevitable elements contained in the balance is preferably 0.5% by weight or less.

  The coating 3 is amorphous. In general, it is known that a material having a crystal grain boundary promotes corrosion when impurities accumulate in the grain boundary or a corrosion medium enters the grain boundary. On the other hand, an amorphous material does not have a crystal grain boundary, so that corrosion is not easily promoted, and has higher corrosion resistance than a crystalline material. Therefore, when the film 3 is amorphous, excellent corrosion resistance can be obtained as compared with the crystalline film.

  Further, since the film 3 is amorphous, it is possible to obtain higher wear resistance than the crystalline film. When the living body implant 1 is implanted, medical instruments such as forceps and a driver come into contact with the coating 3. At this time, the crystalline film is easily peeled off by contact with a medical device, whereas the amorphous film 3 is hardly peeled off even when it comes into contact with a hard object such as a medical device. Therefore, it is possible to prevent the film 3 from falling off by an operation before or at the time of implantation.

  The film 3 has a thickness of 1.6 μm or more and 16 μm or less. When the thickness of the film 3 is less than 1.6 μm, there is a possibility that the corrosion resistance cannot be obtained for a predetermined period necessary for treatment after the living body implant 1 is implanted. On the other hand, when the thickness of the coating 3 is larger than 16 μm, it may take too much time for the living body implant 1 to disappear due to biodegradation after the treatment.

Here, the durability period of the biodegradable biomedical implant 1 will be described.
Although there are individual differences, the period until the fractured bone is repaired takes about 90 days according to Gurlt. That is, it is not preferable that the mechanical strength of the biomedical implant 1 rapidly decreases for about 90 days until the fracture portion is healed.

  Currently, polylactic acid materials are clinically used as biodegradable implants. According to the document "Y. Shikinami, et al. Biomaterials 20 (1999) 859-877" It has been reported that it decreased by 16% from the initial strength and decreased by 20.4% from the initial strength after about 120 days. From the above literature, the initial bending strength of polylactic acid is reported to be 270 MPa. On the other hand, the initial bending strength of the Mg alloy is 400 MPa or more. Therefore, as long as the degradation rate is at least equal to that of polylactic acid, it has a higher initial bending strength than polylactic acid, so that the load applied is greater than the therapeutic range in which the existing bone cement made of polylactic acid is used. It can also be applied to osteosynthesis treatments that require durability. That is, in an implant material using Mg or Mg alloy as a base material having a high initial bending strength, the decrease in strength from the initial stage of implantation is less than 16.3% after 3 months, and 20.4 after 4 months. If it is less than%, it can be said that it has a sufficient function as a biodegradable implant.

  According to the living body implant 1 according to the present embodiment, for example, when the living body tissue is implanted in a fractured part of a bone tissue, the coating 3 provided on the surface of the base material 2 first becomes a body fluid. It contacts and protects so that the corrosion of Mg or Mg alloy which comprises the base material 2 may be suppressed.

  In this case, the coating 3 is amorphous and the total content of Mg element, O element and P element in the coating 3 is 95% by weight or more, so that the coating 3 is corroded for at least 4 months. Is sufficiently suppressed, and the decrease in the mechanical strength of the biological implant 1 is suppressed to less than 20% compared to immediately after implantation.

In particular, the Mg element has a content of 25 wt% or more and 49 wt% or less, the O element content is 46 wt% or more and 51 wt% or less, and the P element content is 1 wt% or more and 22 wt% or less. In such a case, the decrease in mechanical strength after 90 days from the time of implantation is suppressed to less than 15% of that immediately after implantation. Further, the Mg element content is 25 wt% or more and 34 wt% or less, the O element content is 46 wt% or more and 51 wt% or less, and the P element content is 16 wt% or more and 22 wt% or less. In some cases, the decrease in mechanical strength when 120 days have elapsed after implantation is suppressed to less than 16% of that immediately after implantation.
Thus, according to the biomedical implant 1, the load applied to the fractured part can be firmly supported by the biomedical implant 1 until the fractured part is healed, and a high therapeutic effect can be obtained.

  Further, by using the base material 2 made of Mg or Mg alloy, a thin and small living body implant 1 that can withstand practical use can be manufactured. Compared with polylactic acid known as a material for existing biodegradable implants, Mg or Mg alloy has a high specific strength as described above. Therefore, the volume necessary for obtaining the same strength is smaller than that of the polylactic acid implant, and the living body implant 1 can be thinned and reduced in size. The foreign body feeling and discomfort given to the patient can be reduced.

  In addition, titanium is known as a material for existing biodegradable implants, but titanium does not have biodegradability, so titanium implants require re-operation for removal after implantation. become. According to the present embodiment, the polylactic acid implant can be suitably applied to a site that is difficult to apply due to insufficient strength, and the removal re-operation can be made unnecessary.

  In addition, the formation method of the film | membrane 3 is not limited to an anodic oxidation process, The various film-forming methods which form an amorphous film | membrane are employable. For example, a wet method such as an electrolytic deposition method, a sol-gel method, or a dip coating method may be used. Alternatively, a dry method such as a sputtering method, a pulse laser deposition method, or an electron beam deposition method may be used. When the dry method is used, the coating 3 with higher purity can be formed.

  Further, in the present embodiment, the bone joint device has been described as the living body implant 1, but instead, the living body implant 1 according to the present embodiment is implanted in a narrowed part of a coronary artery or a peripheral blood vessel. It may be a stent. In this case, the base material 2 is formed into a cylindrical shape having a mesh structure, and the coating 3 is formed on the entire surface of the base material 2.

  According to Japanese Translation of PCT International Publication No. 2012-533408, it is desired that a vascular stent should continue to reinforce a blood vessel for at least 2 months, preferably about 4 months, in order to prevent restenosis after treatment. . That is, the living body implant 1 according to the present embodiment can maintain necessary mechanical strength over a period required for treatment even when used as a stent.

  Next, as an example of the biological implant 1 according to the present embodiment, as shown in FIG. 2, four samples A, B, C, and D having coatings having different compositions were prepared. Moreover, the sample E was created as a comparative example with respect to the samples A, B, C, and D according to the present invention. The composition of the film of Sample E corresponds to the composition range of the film disclosed in Patent Document 1 (Japanese Patent No. 4686727).

(Sample preparation)
Five types of samples A, B, C, D, and E were obtained by anodizing a test piece (base material 2) made of WE43 in ASTM standard using an electrolytic solution containing ammonium ions and phosphate ions, respectively. . The test piece is a test piece having a shape shown in JIS Z 2248 (metal material bending test method). Samples A, B, C, which have coatings having different compositions by changing the concentration, purity, processing voltage, current density, etc. of the electrolyte solution to pure Mg to control the mixed elements and their amounts D and E were created. Taking the sample A as an example, the preparation conditions will be described below. Moreover, the preparation conditions of the sample E of a comparative example are also shown.

Preparation conditions for sample A Base material: WE43 (Mg-Y-RE-Zr alloy)
Electrolytic solution: ammonium ion 1.9 mol / L
Phosphate ion 0.01 mol / L
Energizing jig: Made of pure Mg to prevent contamination by impurities
1. Immersion in phosphoric acid solution (pretreatment)
2. Sodium hydroxide solution immersion (pretreatment)
3. Anodizing temperature 10 ° C, current density 20A / dm ² , voltage 400V, treatment time 40 seconds

Preparation conditions of sample E Base material: WE43 (Mg-Y-RE-Zr alloy)
Electrolytic solution: ammonium ion 1.9 mol / L
Phosphate ion 0.25 mol / L
Energizing jig: Pure Mg
procedure:
1. Immersion in phosphoric acid solution (pretreatment)
2. Sodium hydroxide solution immersion (pretreatment)
3. Anodizing temperature 15 ° C, current density 20A / dm ² , voltage 450V, treatment time 118 seconds

  In the preparation methods of Samples A, B, C, and D of Examples of the present invention and E of Comparative Example, the test pieces were acid-treated as pretreatment. By this acid treatment, impurities on the surface of the test piece are dissolved and removed, and a uniform chemical conversion treatment film is formed on the surface of the test piece. This is expected to increase the corrosion resistance. Furthermore, when an electrolytic solution containing ammonium ions and phosphate ions is used in anodic oxidation, it is preferable to use phosphoric acid in the acid treatment. After forming magnesium phosphate on the surface of the base material by treating with phosphoric acid, it was confirmed that the corrosion resistance of the product is improved by carrying out anodization using ammonium ions and phosphate ions as the electrolyte. ing.

  The alkali treatment using a sodium hydroxide solution aims to remove insoluble substances formed in the acid treatment. In addition, as a result of evaluating the corrosion resistance of the product when the alkali treatment is performed after the acid treatment and when the alkali treatment is not performed, if the anodic oxidation conditions are the same, a difference superior to the corrosion resistance of the product is not confirmed. It was.

(Coating composition analysis)
The composition of the prepared samples A, B, C, D, and E was analyzed by X-ray photoelectron spectroscopy (XPS) using Quantera II manufactured by ULVAC-PHI, while ion etching the sample surface. Since the sample surface is contaminated by contact with the external environment, an accurate component cannot be obtained even if the sample surface is analyzed. Therefore, XPS analysis was performed while cutting the film by ion etching, and the composition of the film was determined from the composition ratio in the etching time period when the detected amount of the main element was constant.

FIG. 3 shows the relationship between the ion etching time and the detected amount (unit: weight percentage) of each element of Sample A. FIG. 4 is a graph showing the change over time in the detected amount of each element. Furthermore, FIG. 5 shows multiple recording of the detected electronic spectrum of each element.
3, 4, and 5 are all the analysis results of the sample A, but the analysis results having the same tendency as the analysis results of the sample A were obtained for the samples B, C, and D. Therefore, the description of the analysis results regarding the samples B, C, and D is omitted.

  In FIG. 3, carbon (C) is detected at 10.1 wt% on the outermost surface of the sample (etching time = 0 min), but as the amount of detected carbon decreases after the etching starts, other elements ( The detected amounts of oxygen (O), magnesium (Mg), phosphorus (P), and yttrium (Y) increased. In the etching time of 15 min to 20 min, relatively large amounts of oxygen and phosphorus were temporarily detected. From this, it is considered that the constituent elements are different between the vicinity of the base material of the film and the vicinity of the surface. In FIG. 4, no significant change was observed in the detected amount of phosphorus. After the etching time of 30 minutes, the amount of each element was almost constant.

  The amount of each element was stably detected in the etching time range of 100 min or more. Therefore, the composition of the film shown in FIG. 1 was determined from the average of the detected values of each element in the etching time range of 100 min to 180 min.

  Next, the results shown in FIG. 5 will be described. Regarding the C element, a large detection energy spectrum was observed only on the outermost surface of the sample A, but the amount of energy decreased with the progress of ion etching. In FIG. 5, the lowermost line shows the spectrum of the outermost surface of the film of Sample A, and the upper line shows the spectrum of the deeper position of the film.

  Next, for the O element and the P element, the spectrum pattern changes with the progress of ion etching with respect to the energy spectrum observed on the outermost surface. That is, it is considered that the presence state of the O element and the P element is different between the outermost surface and the inside of the coating. This is because the O and P elements on the outermost surface of the sample are adsorbed on the surface, and the internal O and P elements constituting the film exist with different chemical bonds from the adsorbed on the surface. It is guessed that this is because.

  Next, regarding the Mg element and the Y element, the spectrum pattern was almost constant, but the energy amount was observed to vary with the ion etching time and increase with time. The Mg element and the Y element are elements that exist in the base material, and are not elements that are mixed from the outside during film formation. Therefore, it is considered that the Mg element and Y element in the coating are derived from the base material. In FIG. 5, the notation in parentheses indicates orbital electrons to be detected.

(Crystal analysis of film)
Next, the crystallinity of the film of Sample A was analyzed by X-ray diffraction (XRD) measurement. For the measurement, MiniFlex II manufactured by Rigaku Corporation was used. The measurement results are shown in FIGS.
As shown in FIG. 6, peaks indicating the crystal structure of the Mg alloy contained in the base material were observed, but peaks indicating the crystal structures of the other components were not observed. If the O element, Mg element, and P element, which are the main components of the film, are crystalline components of magnesium oxide or magnesium phosphate, peaks indicating the crystal structure of the magnesium oxide or magnesium phosphate compound are observed in the XRD measurement. As expected, no such peak was observed.

  FIG. 7 is an enlarged view of the measurement angle range of 20 ° to 40 ° in FIG. As shown in FIG. 7, a broad peak was observed in the measurement angle range of 20 ° to 30 °. This broad peak was not observed when a sample having no film (that is, a sample consisting only of a base material) was measured. That is, this broad peak was observed by the formation of the film, indicating the crystalline state of the film, and it was confirmed that the film was amorphous. As for Samples B, C, and D, XRD measurement was performed in the same manner as Sample A, and as a result, it was confirmed that the film was amorphous.

  In anodic oxidation, although the threshold concentration at which the anodic oxide film crystallizes differs depending on the type of ions contained in the electrolytic solution, the higher the concentration of electrolyte ions in the electrolytic solution and the higher the processing voltage, The anodized film formed tends to crystallize as the treatment time increases.

  FIG. 8 shows the XRD measurement result of Sample E of the comparative example. Peaks corresponding to magnesium oxide, magnesium hydroxide and magnesium phosphate indicating that the film contained a crystalline structure were observed. In addition to these, crystal structures other than the base metal were also observed, although they could not be specified.

(Measurement of film thickness)
Next, for the prepared samples A, B, C, D, and E, the thickness of the film was measured by observation with a scanning electron microscope (SEM). Each sample was embedded with resin, and then the resin was cured, then cut, and the cut surface was observed by SEM. The SEM used was Hitachi High-Tech S-4000 (FE-SEM), and the acceleration voltage was 10 kV. FIG. 9 shows an SEM image of the cut surface of the sample D as an example. In FIG. 9, the thickness of the film (the width of the portion II in the figure) was measured to be an average of 1.6 μm, although it slightly varied depending on the position. For Samples A, B, C, and E, the thickness of the film was measured based on the SEM image as in Sample D. The measurement results are shown in FIG.

  The SEM image of the cut surface includes three parts I, II, and III of the base material, the film, and the resin. Therefore, by performing line analysis by energy dispersive elemental analysis (EDX) on the observed cut surface, it was specified which of the three portions I, II, and III was a film. The apparatus used for EDX was EX-250 manufactured by HORIBA, Ltd., and the line analysis capture time was 100 seconds and the integration time was 10 minutes.

  In FIG. 9, the result of the line analysis of Mg element, C element, and P element is shown. The characteristics of the composition of the base material, film and resin are different from each other. Specifically, the resin contains many C elements and does not contain Mg elements and P elements. The coating contains a trace amount of C element, and contains Mg element and P element. The base material contains a trace amount of C element, mainly composed of Mg element, and hardly contains P element. Therefore, the film can be specified based on the composition at each position.

  In FIG. 9, the Mg element rises from the left side (I) to the right side (III). The amount of C element is large in the left portion I, but is small in the right portion III. P element is large in the central part II and small in the right part III. From these, it was found that the resin, the film, and the base material were arranged in order from the left, and the portion II between the cracks was specified as the film. In addition, it is thought that a crack was produced at the time of the cutting | disconnection of the sample after embedding. Considering the composition, since the film is a layer in a state close to a ceramic containing a large amount of oxygen, it is considered that the film is more susceptible to cracking due to a load during cutting as compared with a resin and a metal base material.

(Bending test after immersion in simulated body fluid)
Next, after immersing samples A, B, C, D, and E in simulated body fluid (PBS (−) solution) for a predetermined period in order to simulate the change in strength after implantation in the body, JIS Z 2248 A bending test was performed according to (Metal material bending test method). Specifically, samples A, B, C, D, and E were immersed in simulated body fluid maintained at 37 ° C. for 30, 60, 90, and 120 days, and each sample after immersion was subjected to a bending test. The bending test result is shown in FIG. Note that the strengths of the samples A, B, C, D, E and the base material before immersion were substantially the same as 416 MPa, which is the average strength of WE43, and no difference in strength due to the presence or absence of the film was observed. In the graph of FIG. 11, the measured value (vertical axis) of the bending strength of each sample A, B, C, D, E is a value normalized with the bending strength at 0 days of immersion of each sample as 100.

  From the results of the bending test in FIG. 11, it was confirmed that the amount of decrease in bending strength after immersion differs depending on the coating even when the base material is the same. As a whole, the amount of decrease in bending strength tended to be large in the initial stage of immersion and decreased with increasing immersion time. One reason for this is that white magnesium phosphate was formed on the surface of each sample due to the reaction between the Mg ions eluted from the sample and the phosphate component in the simulated body fluid. It is considered that a new film was formed on the surface of the sample by reaction precipitation with the simulated body fluid, thereby suppressing the erosion of the sample and reducing the amount of decrease in strength.

Samples A, B, and C maintain a strength of 83.7% or more after being immersed in a simulated body fluid for 90 days, and 79.6% or more after 120 days, and have an effective structure as a biodegradable biological implant. It was confirmed that it could be retained.
Regarding sample D, the strength after 90 days immersion in simulated body fluid was less than 83.7%, but after 120 days immersion, the strength was maintained at 79.6% or more. From this result, although it may not be suitable as an osteosynthesis implant with a large load, it is considered that it can be effectively used as an implant for a digestive organ with a relatively small load.
Regarding sample E, which is a comparative example, the amount of decrease in strength from the initial stage of immersion is large, and it is difficult to maintain the structure after implantation in a living body, and it is considered that it is not effective as a biodegradable implant.

  As a result of the above bending test, the samples A, B, C, and D of the present invention provided with a film in which the total content of Mg element, O element and P element is 95% by weight or more and which is amorphous are as follows: Compared to Comparative Example E, it was confirmed that it has excellent corrosion resistance in the living environment and can maintain high strength over the treatment period.

(In vivo degradation test)
Next, the living body implant of the present invention was implanted in a living body, and a pathological examination of the transplanted site after a predetermined period of time was performed. Specifically, a pin-shaped biomedical implant created under the same conditions as in sample A was implanted in the femur of a minipig, and after 90 days from implantation, the implantation site was collected from the femur, and the obtained implant was obtained. The planting site was subjected to pathological examination. The result is shown in FIG.

  As shown in FIG. 12, a thin layer made of a substance such as magnesium phosphate was confirmed at the interface between the circular biomedical implant in the center and the surrounding bone tissue. This substance is produced by the biodegradation of the biomedical implant progressing and the components of the biomedical implant react with the body fluid. From this result, it was confirmed that the implant maintained the structure in the bone even after 90 days had elapsed after implantation, and the bone could be stably fixed. At the same time, it was also confirmed that no abnormality due to the biodegradation reaction of the implant occurred in the bone tissue around the implant.

1 Biomedical implant 2 Base material 3 Coating

Claims (8)

A base material made of magnesium or a magnesium alloy, and an amorphous film covering the surface of the base material,
A biomedical implant in which the total content of magnesium element, oxygen element and phosphorus element in the coating is 95% by weight or more.   In the film, the magnesium element content is 25 wt% or more and 49 wt% or less, the oxygen element content is 46 wt% or more and 51 wt% or less, and the phosphorus element content is 1 wt%. The biomedical implant according to claim 1, wherein the biomedical implant is at least 22% by weight.   In the film, the magnesium element content is 25 wt% or more and 34 wt% or less, the oxygen element content is 46 wt% or more and 51 wt% or less, and the phosphorus element content is 16 wt%. The biomedical implant according to claim 2, wherein the biomedical implant is at least 22% by weight.   The living body implant according to any one of claims 1 to 3, wherein in the coating, the remainder excluding the magnesium element, the oxygen element, and the phosphorus element contains a carbon element as an inevitable element.   The biomedical implant according to claim 4, wherein a content of the carbon element in the coating is 0.5% by weight or less.   The biological implant according to any one of claims 1 to 5, wherein the coating has a thickness of 1.6 µm or more and 16 µm or less.   The biomedical implant according to any one of claims 1 to 6, which is a screw, pin or plate-shaped bone connector.   The living body implant according to any one of claims 1 to 6, which is a substantially cylindrical stent having a mesh structure.