JP6533908B2 - Method of manufacturing molded body - Google Patents

Description

  The present invention relates to a molded article excellent in strength, and more particularly to a molded article having an optimum strength for a medical molded article and various fastening members excellent in biocompatibility, biodegradability and strength.

In recent years, plastic materials have been widely used in various fields, and are widely used not only in conventional containers but also in fields requiring strength such as substitutes for metal bolts and nuts. It is supposed to be.
Especially in the present day where importance of recycling is screamed, there is a concern about using metal fastening members in plastic containers and automobile parts, and movement to use plastic material as a substitute material for metal fastening members There is.
However, in the case of conventionally proposed plastic sails, the strength as required by only plastics can not yet be achieved, and at present, other materials such as carbon fibers are combined.
Furthermore, in Japan, a rapidly aging society is advancing, and with the increase of elderly people, problems such as an increase in bone fracture caused by bone loss caused by a decline in biological function and damage such as tooth damage are becoming problems.
In the current medical field, depending on the type and degree of fracture, treatments such as fractures use fracture fixation methods such as external fixation, internal fixation, and external fixation.
Among them, the internal fixation method is a method of directly fixing a bone by a bone fixation device or the like after restoring the position of the bone by surgery. The material of the bone fixation device used in the internal fixation method is called a fracture fixation material or a bone fixation material, and this material is roughly classified into three types of metal materials, ceramic materials, and plastic materials. Among the materials used for bone fixing materials, metal materials are most commonly used in bone fixing materials in terms of high strength and reliability.
However, in a corrosive environment such as a living body, fatigue is promoted and the fatigue limit tends to be significantly reduced as compared with the atmosphere. In addition to this, it is also feared that stress shielding occurs due to the high modulus of elasticity of the metal material, and the bone after treatment is weakened. Because of these problems, it is necessary to remove the metallic bone fixative for a long time after the fracture has healed, without leaving it in the body for a long time, but re-surgery to remove the metallic bone fixative It is a physical, mental and financial burden for the patient. Particularly in the internal fixation method, in the current medical field, as a recent trend, aiming at the quality improvement of the living standard of patients (Quality Of Life (= QOL)), the biodegradation which does not require removal after treatment (reoperation) Replacement of metal materials by plastic plastics has been carried out, and various proposals have been made on biodegradable plastics.
For example, in Patent Document 1, a polymer material containing carbon as a constituent element is used as a polymer material whose tissue compatibility has been improved by ion beam irradiation for preventing rupture of an aneurysm at risk of rupture, and the surface is Materials for treating aneurysms have been proposed, wherein at least a portion of the material is modified by ion bombardment.
Also, for example, Patent Document 2 prevents blood or cerebrospinal fluid leakage more quickly by improving the affinity between a living tissue implant material such as an artificial blood vessel or an artificial dura mater and a biological tissue adhesive. A polymer material which is used in combination with a biological tissue adhesive and which is made of a polymer material containing carbon or silicon as a constituent element, and in which at least a part of the surface is modified by ion bombardment Proposed.
Also, for example, Patent Document 3 prevents blood or cerebrospinal fluid leakage more quickly by improving the affinity between a living tissue implant material such as an artificial blood vessel or an artificial dura mater and a biological tissue adhesive. A polymer material which is used in combination with a biological tissue adhesive and which is made of a polymer material containing carbon or silicon as a constituent element, and in which at least a part of the surface is modified by ion bombardment Proposed.
Further, for example, in Patent Document 4, a polymer material containing carbon as a constituent element as a material adhering to cells accompanied by morphological and histochemical changes over time by bringing it into close contact with bones and muscles. There is proposed a material having adhesiveness to bone and / or fascia, which is composed of at least a part of the surface modified by ion bombardment.
In addition, for example, in Patent Document 5, an initial compressive bending strength of 200 MPa or more is maintained in a living body for about 3 to 4 months by molecular orientation of polymer chains uniaxially or multiaxially, and after about 6 months. As a biodegradable and bone-retaining material that promotes decomposition and absorption and complete decomposition and loss of the molded product within 3 years at maximum, polylactic acid or L-lactide / DL-lactide copolymer and alkali-treated hydroxy A rod or sheet obtained by blending apatite in appropriate proportions, extruding or injection molding, and further obtaining the composite at a deformable temperature by uniaxial stretching, compression deformation or solid extrusion, in vivo Degradable and absorbable bone fixing materials have been proposed.
Also, for example, in Patent Document 6, biodegradable filaments such as polylactic acid and polyglycolic acid can be made of ultrafine biodegradable filamentene by a simple means without requiring a special, high-precision and high-level device. As a method of manufacturing, it has been proposed to heat a biodegradable filament with an infrared light flux, and an ultrafine filament in which the heated original filament is drawn 100 times or more by a tension of 10 MPa or less.

JP 2007-020590A JP, 2005-034256, A JP, 2004-089361, A Japanese Patent Application Laid-Open No. 2002-315821 Japanese Patent Application Laid-Open No. 11-206871 WO 2005/083165

However, although the medical materials according to the proposals of Patent Documents 1 to 4 exhibit biodegradability, they have a problem that the decomposition rate is extremely slow, and a problem that the strength is low.
Further, the medical material proposed in Patent Document 5 is for molecular orientation of polymer chains uniaxially or multiaxially, and when used as a bone fixing material, the strength is still insufficient.
Moreover, since the medical material proposed according to Patent Document 6 is a microbiodegradable filament, it was not suitable for use as a bone fixing material.
Furthermore, these proposed materials do not have sufficient strength as a substitute for metal fastening members of various industrial products that are not living bodies.
In short, a molded body made of a conventionally proposed plastic material does not sufficiently satisfy both the biodegradability and the fastening strength as a bone fixing material, and is excellent in biocompatibility, biodegradability and strength. There is a demand for development of medical materials, and there is currently a demand for development of molded articles made of materials exhibiting sufficient strength even when used as fastening members for various industrial products.

  Therefore, an object of the present invention is to provide a molded article having an optimum strength for medical molded articles and various fastening members which are excellent in biodegradability and strength.

As a result of intensive studies to solve the above problems, the present inventors have found that the strength can be improved by modifying the surface of a molded article made of a polymer material by ion implantation, and further studies are conducted. As a result, it was found that the biocompatibility and biodegradability are improved while maintaining strength, particularly when a biodegradable material is used, and the conditions of ion implantation and the forging method are examined, and the present invention It came to complete.
That is, the present invention provides the following inventions.
1. A molded body formed of a polymer material,
A molded article characterized in that ions are implanted into at least a part of the surface of the polymer material by ion beam irradiation.
2. The molded article according to 1, wherein the ion species in the ion beam irradiation is a rare gas or an ion species contained in a human body.
3. The molding according to 2, wherein the noble gases are Ar (argon) or He (helium), and the ion species contained in the human body is N (nitrogen), P (phosphorus) or C (carbon). body.
4. The molded article according to any one of 1 to 3, wherein the ion implantation amount in the ion beam irradiation is 10 ⁸ to 10 ¹⁸ ion / cm ² .
5. The molded product according to any one of 1 to 4, wherein the conditions for accelerating voltage of ions in the ion beam irradiation are 10 keV to 300 keV.
6. The molded article according to any one of 1 to 5, wherein the polymer material is a low-degradable biomaterial.
7. The molded article according to 6, wherein the low-degradable biomaterial is polylactic acid or polycaprolactone.
8. The formed body according to any one of 1 to 7, wherein the formed body is obtained by twist-stretching a polymer material.
9. The molded body according to 8, wherein the extrusion pressure in the twist drawing is 100 to 200 kN.
10. The molded article according to 8 or 9, wherein a helical angle in the torsional stretching is 15 to 75 degrees.
11. The molded article according to any one of claims 8 to 10, wherein the molded article is a fastening member, and the twisting direction of the twisting in the twisting and stretching is the same as the twisting direction of the screw.
12. The molded object in any one of 1-11 whose said molded object is a medical molded object.

The molded article of the present invention is a molded article which has optimum strength for medical molded articles and various fastening members which are excellent in biodegradability and strength.
In particular, when the molded article of the present invention is a medical molded article, it is excellent in biocompatibility, biodegradability and strength made of biodegradable materials. In addition, the medical molded product in this case is subjected to surface modification by ion implantation, and its biocompatibility and biodegradation rate are controlled while maintaining its strength by changing the injection amount and injection depth. It is.
Therefore, when used for internal fixation of fracture treatment, re-surgery is not necessary because it is degraded in vivo, and mechanical strength is gradually reduced, so it does not inhibit bone growth and metal material is used. Since there is no adverse effect such as tissue reaction due to corrosion or stress shielding due to excessive rigidity, there is little risk of bone porosity, and there is no influence on X-rays and MRI.
Further, the molded product of the present invention is a fff capable of further improving shear and torsional strength by optimizing molecular orientation and its angle by a twisting drawing method.
In addition, when polylactic acid is used as a polymer material, unlike the conventional self-reinforcing polylactic acid, it is possible to improve the shear and torsional strength of the polylactic acid material, and therefore, it can be manufactured at low cost.

FIG. 1 is a view showing an embodiment of a medical molded article of the present invention. FIG. 2 is an explanatory view of the twist drawing, (a) is an extrusion drawing, and (b) is a drawing of the twist processing. FIG. 3 is an explanatory view of an ion beam irradiation method (a) and an ion beam irradiation object (b) in Examples 1 to 5. FIG. 4 is a graph showing the results of surface roughness in Examples 1 to 3 and in the target experiment. FIG. 5 is a graph showing the results of contact angles in Examples 1 to 3 and in the target experiment. FIG. 6 is a graph showing the contact angle results in Examples 2, 4 and 5 and in the target experiment. FIG. 7: is explanatory drawing of the natural decomposition test of Examples 1-5, (a) is a medical molded article of this invention used by a test, (b) is explanatory drawing of immersion test and level | step difference. FIG. 8 is a graph showing the results of natural decomposition tests of Examples 1 to 3. FIG. 9 is a graph showing the results of natural decomposition tests of Examples 2, 4 and 5 FIG. 10 is a graph showing the results of tensile strength in Examples 6 to 9 and Comparative Example 1. FIG. 11 is an explanatory view of extrusion stretching in Experimental Example 1. FIG. 12 is an explanatory diagram of preparation of a measurement sample in Experimental Example 1. FIG. 13 is a graph showing the results of the orientation function and the extrusion ratio in Experimental Example 1. FIG. 14 is an explanatory view of the twisting process in the first experimental example. FIG. 15 is an explanatory view of a shear strength test in Experimental Example 2. FIG. 16 is a graph showing the results of shear strength in Experimental Example 2. FIG. 17 is an explanatory view of a torsional strength test in Experimental Example 3. FIG. 18 is a graph showing the results of torsional strength in Experimental Example 3. FIG. 19 is a graph showing the relationship between the torsional strength and the maximum helix angle. FIG. 20 is a graph showing the relationship between the maximum helical angle and the shear strength.

1: Medical molding, 10: Axis, 11: Thread, 20: Head

Hereinafter, the present invention will be described in more detail.
A medical molded article as an example of an embodiment of the molded article of the present invention will be described with reference to FIG.
<Overall configuration>
The medical molded article as the molded article of the present invention is a medical molded article formed of a biodegradable material as a polymer material, and the biodegradable material is an ion formed on at least a part of the surface thereof. Ions are implanted by beam irradiation.
The medical molded body 1 of the present embodiment is a screw as a bone fixing tool used for internal fixation of bone at the time of a fracture etc., and has a shaft 10 provided with a screw thread 11 on the whole and a head having a bearing surface It consists of 20 and.

(Polymer material)
The molded body of the present invention is formed of a polymer material.
The polymer material that can be used here can be used without particular limitation as long as it is used for ordinary plastic moldings, but in addition to biodegradable materials described later, polypropylene (PP), polyethylene (PE) And polystyrene (PS), polyetheretherketone (PEEK), polycarbonate, polyester and the like.
And as a fastening member of various industrial products, in particular, polypropylene (PP), polystyrene (PS), polyetheretherketone (PEEK) and the like are preferable, and a biodegradable material is preferable as a medical molding.
In the following description, an example of a medical molded article is shown and described. Other molded articles will be described separately.
(Biodegradable material)
As used herein, biodegradable material refers to materials that are degraded in vivo. As a result, since they are eventually degraded or absorbed in the living body, they do not need to be recovered.
The biodegradable material used in the medical molding of the present invention is not particularly limited, but for example, a resin comprising the following components may be used, and they may be used alone or in combination. .
Polylactic acid (PLA), polyglycolic acid, polycaprolactone, polyhydroxyalkanoate, modified polyvinyl alcohol, casein, modified starch and the like.
That is, the low degradable biocompatible material in the present invention means a material which is gradually degraded in vivo, and specifically preferably polylactic acid (PLA), polyglycolic acid, polycaprolactone, polyhydroxyalkanoate A modified polyvinyl alcohol, casein, modified starch, and a material selected from the group consisting of mixtures thereof. Among them, polylactic acid, polycaprolactone and the like are preferable from the viewpoint of degradability.
By performing ion beam irradiation described later on such a material having low in vivo degradability, the biodegradation rate can be improved while maintaining the strength, and the material is modified to be more suitable as a biocompatible material. can do.
In the polylactic acid, poly L lactic acid (PLLA) consisting only of L body and poly D lactic acid (PDLA) consisting only of D body, and PLA consisting of both exist, and any of them can be used without particular limitation.
In the medical molded article 1 of the present embodiment, a resin composed of PLLA and PDLA is used.

(Other ingredients)
The medical molded articles according to the present invention include ions, low molecular weight compounds, human-body-containing substances such as proteins and nucleic acids, cytokines, growth factors, vitamin D related to bone growth, physiologically active substances such as prostaglandins and pharmacologically active substances And the like may be blended without departing from the spirit of the present invention.

(Medical molded body)
As used herein, a medical molded body refers to a molded body used for repairing at least a part of a human or animal body.

(Ion beam irradiation)
As described above, the medical molded article of the present invention is formed by implanting ions into at least a part of the surface of the biodegradable material by ion beam irradiation.
As used herein, the term “ion beam irradiation” refers to irradiating the surface of the biodegradable material with an ion beam to implant ions or ion particles onto the surface.
By performing the ion beam irradiation, ions can be more strongly introduced onto the surface of the biodegradable material than simple adhesion or adsorption, and the surface can be reformed more effectively than before. it can. This makes it possible to improve biocompatibility (hydrophilicity) and biodegradability while maintaining strength.
As the ion beam irradiation, a known ion beam irradiation apparatus can be used without particular limitation as long as the apparatus is capable of irradiating the surface of the biodegradable material with an ion beam and injecting ion microparticles onto the surface. Among them, from the viewpoint of controlling the modification state of the surface of the medical molded article of the present invention, it is preferable to use an apparatus capable of controlling the conditions such as ion species, ions, and accelerating voltage to be irradiated.
In the present embodiment, the ion beam irradiation may be an ion source that generates ions of a target element, a mass analyzer that extracts only necessary ions, an accelerator that accelerates ions to electrically necessary energy, and an object. An apparatus is used which comprises a high vacuum chamber or the like on which a target is mounted, and which can control conditions such as the ion species, the ion implantation amount, and the acceleration voltage of ions to be irradiated.
Thereby, as described in detail below, by controlling the conditions such as the ion species, the ion implantation amount, and the acceleration voltage of ions in the ion beam irradiation, the modification state of the surface of the medical molded article of the present invention is controlled. Control the biodegradability, biocompatibility, properties of implanted ions, etc.
Although the said ion beam irradiation is performed during the manufacturing process of the medical molded object of this invention, the timing which performs the said ion beam irradiation can be performed without a restriction | limiting especially in the range which does not deviate from the meaning of this invention For example, it can carry out to the said biodegradable material etc. after temporary shaping | molding. In this embodiment, it is carried out after forming a screw thread by forging an extension-processed product which has been subjected to a twisting extension described later.
The site to which the ion beam irradiation is performed is not particularly limited without departing from the scope of the present invention, and for example, irradiation to the entire surface, irradiation to a part of the surface, and the like can be performed. Conditions such as ion species, ion implantation amount, and acceleration voltage of ions, which will be described later, may be changed for each portion to be irradiated.

(Ion species)
In the medical molded article of the present invention, the diameter of the pores formed on the surface can be controlled by the ion species used in the ion beam irradiation to change the modification state of the surface. Thereby, characteristics such as biodegradability of biodegradation rate and biocompatibility are made.
Specifically, when ions are implanted at the same number (ion number) and depth, the larger the ion radius of the implanted ions, for example, the larger the pore diameter formed, and the biodegradation rate is higher. Is expensive.
The ions that can be used in the ion beam irradiation are not particularly limited as long as they do not deviate from the spirit of the present invention, and for example, rare gases (such as Ar (argon) and He (helium)) and ion species contained in the human body For example, ions that can be generated using N (nitrogen), P (phosphorus), C (carbon), or a group 2 group (such as Ca) as an ion source can be used, and one or more ions may be used. It can be used as a mixture of seeds. Among them, from the viewpoint of the safety to the living body, it is preferable to be an ion species contained in the human body such as rare gases of group 8 such as Ar and He, N (nitrogen), P (phosphorus) and C (carbon). .
Further, depending on the type of ions to be injected, new functions can be imparted to the medical molded article of the present invention. For example, when ions of Group 2 (such as Ca) are injected, functions such as bone bonding can be imparted.
In the present embodiment, Ar is used as an ion source.

(Ion implantation amount)
The medical molded article of the present invention can change the number of pores formed on the surface, etc. depending on the ion implantation amount in the ion beam irradiation. As a result, the biodegradability, biocompatibility, properties of injected ions, etc. of the biodegradable material are controlled.
Specifically, in the case of injecting the same ion species, the larger the number of ions to be injected, the larger the number of pores formed, and the higher the biodegradation rate.
The ion implantation amount in the ion beam irradiation is not particularly limited as long as it does not deviate from the spirit of the present invention, but it is preferably 10 ⁸ to 10 ¹⁸ ion / cm ² and 10 ¹⁰ to 10 ¹⁶ ion / cm ² . It is more preferably present, and 10 ¹² to 10 ¹⁵ ion / cm ² is particularly preferred.
Within this range, the biocompatibility (hydrophilicity) and the biodegradability can be further improved while maintaining the strength without damaging or damaging the material by ion implantation.
In addition, in this embodiment, it shape | molds on the conditions shown in Example 10. FIG.

(Acceleration voltage of ion)
In the medical molded article of the present invention, the acceleration amount of ions to be implanted is changed by controlling the acceleration voltage of ions in the ion beam irradiation to change the depth of pores formed on the surface. it can. Thereby, the biodegradability of biodegradation rate, biocompatibility, properties by injected ions, etc. are controlled.
The conditions for the acceleration voltage of the ions are not particularly limited as long as they do not deviate from the gist of the present invention, but are preferably in the range of 10 keV to 300 keV, and more preferably in the range of 10 keV to 300 keV.
Within this range, biocompatibility (hydrophilicity) and biodegradability can be further improved while maintaining strength. Also, by controlling the acceleration voltage condition and the ion implantation amount simultaneously, the ion implantation depth is obtained to the extent that the desired effect is sufficiently exhibited without damaging the material (to be within the preferable range described later) In order to achieve this, it is preferable to make the optimum balance between the applied voltage condition and the ion implantation amount. Specifically, when the pressurization voltage is in the range of 10 keV to 300 keV, it is preferable to control so that the ion implantation amount becomes smaller as the pressurization voltage is increased.
In the present embodiment, molding is performed under the conditions shown in Example 10.

(Ion implantation depth, pore)
It is considered that the medical molded article of the present invention formed by applying ion beam irradiation as described above has ions implanted and fine pores formed on the surface by the ion beam irradiation.
The depth to which this ion is injected and the depth of the formed pore can be adjusted by variously changing the conditions of the above-mentioned ion beam irradiation, whereby the biodegradability of biodegradation rate, biocompatibility, It is possible to control the sex and so on.
In the present invention, the implantation depth of the ions is preferably 30 nm to 1000 nm, and particularly preferably 50 nm to 600 nm. Within this range, it is possible to further improve the biocompatibility (hydrophilicity) and the biodegradability while maintaining the strength, and to impart the characteristics of the ions.
In addition, although the diameter and the like of the pores can not be accurately measured at present, they are modified from the surface to the ion implantation depth according to simulation results described later and measurement results such as cross-sectional observation with a transmission type microscope It is clear that a thick layer is formed. The reason is that although the ion beam irradiation causes the ions to reach a certain depth and a hole having a diameter equal to or slightly larger than the ion diameter is formed, a very fine particle having a diameter slightly larger than the ion diameter is formed. It is assumed that it is difficult to measure each diameter because it is a hole.

(Twist drawing)
The medical molded article of the present invention is preferably obtained by subjecting a biodegradable material to torsional stretching. Thereby, the strength can be increased.
An example of the torsional stretching will be described with reference to FIG.
In the twisting and stretching process, first, as shown in FIG. 2 (a), an extrusion process is performed by extruding and stretching a temporary formed body such as a compression-formed product obtained by forming a molten raw material by compression molding or the like. Get things. Next, as shown in FIG. 2 (b), one end of the extruded product is fixed, the extruded product is heated, and the other end is twisted in the twist direction of the arrow in the figure (γ in the figure The twisting process is performed by rotating at.

(Extrusion extrusion)
The extrusion stretching is not particularly limited, and can be performed by a known method or apparatus. For example, the resin can be heated to a temperature above the glass transition temperature and below the melting point, and deformed and drawn so as to squeeze out the material using a mold and an indenter.
Thereby, the molecule | numerator of the said biodegradable material in the medical molded object of this invention can be orientated, and strength can be made higher.
The material used for the extrusion stretching is not particularly limited without departing from the scope of the present invention, and for example, a material formed by compression molding from a resin raw material can be used.
The extrusion pressure in the extrusion and stretching is not particularly limited without departing from the scope of the present invention, but is preferably 100 to 200 kN from the viewpoint of molecular orientation, strength and the like.
The stretching ratio in the extrusion stretching is not particularly limited without departing from the scope of the present invention, but in the case where the biodegradable material is polylactic acid, from the viewpoint of molecular orientation, strength, etc. 10 is preferred.
The orientation function in the extrusion stretching is not particularly limited without departing from the scope of the present invention, but in the case where the biodegradable material is polylactic acid, it is 0.5 to 0.5 from the viewpoint of molecular orientation, strength, etc. It is preferably 0.8.
In addition, the orientation function of the said polylactic acid is calculated | required by the method described in the Example.
The medical molded article of the present embodiment is drawn under the conditions of Example 10.

(Torsion processing)
The twisting process used in the present invention is performed on the extrusion-treated product molecularly oriented by the above-described extrusion stretching. Thereby, the shear strength of the medical molded article of the present invention can be maintained, and the torsional strength can be increased.
The rotation of the material in the twisting process can be performed by fixing one end with respect to the long axis direction of the material by adhesion or the like, heating the material and rotating the other end, etc. It can carry out using the extending | stretching apparatus used when processing a seed | species without a restriction | limiting in particular.
In the present embodiment, one end is fixed as shown in FIG. 2 (b), FIG. 14 or the like, and many ends are rotated by a torque load machine while heating the material by a heater.
The heating temperature in the above-mentioned twist processing is not particularly limited, but is preferably 50 to 200 ° C. from the viewpoint of processing ease and the like.
In the present embodiment, the twisting process is performed by applying torque at a molding temperature of about 100 ° C., a rotation speed of 0.2 rpm, and a rotation direction clockwise.
The twisting process is preferably performed at a helical angle of 15 to 75 degrees, and is particularly preferably 45 degrees in theory. When the helix angle is in this order, the torsional strength is higher.
In the present specification, the helical angle means an angle θ generated when one end of the material is rotated to the angle γ in the arrow direction as shown in FIG. 2B, and, for example, in the case of a cylinder , And can be measured by the following method.
The helix angle can be measured as follows. First, a straight line in the axial direction of the cylinder before twisting is drawn. After torsional stretching, an axial straight line is drawn starting from the fixed end. Wrap tracing paper around a cylinder, trace the lines drawn before and after torsional stretching, and separate it from the cylinder. And a helix angle can be measured by measuring the angle of the line (line before and behind twist draw) drawn before and behind torsion draw using a protractor.
Also, the average value of the helix angles is called the average helix angle, and the helix angles are measured at a plurality of points in the longitudinal direction of the cylinder as described above, and the average is calculated. In the present embodiment, the average helix angle is 23 degrees.
Further, in the case where the medical molded article of the present invention is a fastening member such as a screw in the present embodiment, the twisting direction in the above-mentioned twist processing is the same direction as the screw spiral from the viewpoint of strength etc. preferable. Thereby, the torsional strength in the twisting direction (screw spiral direction) can be increased.
In addition, in this specification, a fastening member means a member used for fastening, and a bolt, a nut, a screw etc. are specifically mentioned.

(Description of the product)
The medical molded article 1 of the present invention obtained as described above has high hydrophilicity and improved strength. In this embodiment, the contact angle is changed from about 75 degrees to about 60 degrees by ion beam irradiation to improve the hydrophilicity. In addition, the torsional strength (torque) is increased from about 1.0 N · m to about 1.2 N · m by torsional drawing, and the strength is improved.

(Shape and size)
The shape and size of the medical molded article of the present invention are not particularly limited, and any may be used depending on the application. In the present embodiment, the screw is about 20 mm in length and 6 mm in diameter.

<Other molded body>
Moreover, the case where the molded object of this invention is molded objects other than a medical molded object is demonstrated below.
Even when the molded article of the present invention is an industrial molded article or the like which is not the above-mentioned medical molded article (for example, a fastening member such as a bolt or a nut), the above-mentioned polymeric material Can be used. In addition, ion beam irradiation, ion implantation amount, ion acceleration voltage, ion implantation depth and pore size, twist drawing, extrusion drawing, and twist processing can be performed under the same conditions as the above-mentioned medical molded article.
The ion species that can be used at this time can be the same as those of the above-mentioned medical molded product, but in particular, noble gases (Ar (argon), He (helium), etc.) are preferable.
The strength of the resulting molded body can be variously changed depending on the polymer material used, and in the molded body of the present invention, it is possible to adjust to a desired strength.

The production method and the application will be described below without distinction of molded articles.
(Production method)
The formed body of the present invention comprises a stretching step of subjecting the biodegradable material to a twisting process to obtain a temporary formed body;
And an irradiation step of irradiating the obtained temporary formed body with an ion beam.
The stretching step can be carried out by performing the above-described extrusion stretching and twisting.
The said irradiation process can be implemented by performing the above-mentioned ion beam irradiation.
The temporary formed body can be subjected to processing such as forging and cutting without departing from the scope of the present invention.
In the present embodiment, ion beam irradiation is performed after forming a thread by forging.
Further, in the case where the medical molded article does not require a twisting process such as a flat plate, the twisting process can be omitted.

(Use etc.)
The molded article of the present invention is useful as a fastening member such as a screw, a bolt, or a nut because it has the above-mentioned characteristics. When a biodegradable material is used as the polymer material, it can be suitably used as a medical molded article used in vivo. Among them, it can be further suitably used as a fixing plate for medical fixings and parts used for internal fixation of fractures mentioned above, screws, bolts, nuts, pins, cages, etc. The medical molded article of the present invention is particularly suitably used for a fastening member such as a screw, a bolt, or a nut, or a molded article provided with a screw hole, from the viewpoint of imparting torsional strength in a predetermined rotational direction. Can.

The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the spirit of the present invention.
For example, although the example in which the screw thread was provided in the whole main part was explained, it is considered as the shape in which the screw thread was formed only in the tip part, etc. The formation places of the screw thread are arbitrary.

  Hereinafter, the present invention will be described more specifically by showing Examples and Comparative Examples, but the present invention is not limited thereto.

[Examples 1 to 5]
Ion beam irradiation was performed using the injection-molded articles shown below to obtain medical molded articles as molded articles of the present invention.
Changes in the surface state of the portion of the obtained molded article for medical use after modification by ion beam irradiation were examined by measuring the surface roughness and contact angle of the surface of the ion beam irradiated portion after ion beam irradiation.
(Method of producing injection molded product)
PLA pellets with a weight average molecular weight of 95000 were used. This pellet alone is injection-molded into a dumbbell shape with a length of about 30 mm, a width of about 5 mm and a thickness of about 2 mm using an ultra-precise compact molding machine (NP7 Real Mini) manufactured by Nissei Plastic Industry under the conditions shown below A molded product (a pseudo-molded product of a bolt and a nut) or a fixed plate is obtained.
conditions:
Injection Pressure [MPa]: 82
Fusion Temperature [° C]: 200
Clamping Temperature [° C]: 50
Cooling Time [s]: 30

(Ion beam irradiation)
Ion beam irradiation was performed on a part of the surface of the obtained injection-molded biodegradable material.
The ion beam irradiation was performed using an ion beam irradiation apparatus. The ion beam irradiation apparatus used is equipped with an ion source that generates ions of a target element, a mass analyzer that extracts only necessary ions, an accelerator that accelerates ions to necessary energy, and a target that is an object. It is an apparatus which comprises a high vacuum chamber and the like, and can control conditions such as the ion species, the ion implantation amount, and the acceleration voltage of ions to be irradiated.
Further, as shown in FIG. 3 (a), in the portion subjected to ion beam irradiation, a portion of the surface of the injection molded product is a mask (material (aluminum foil, plate, etc.), size about 100 × 100 × 1 mm The portion coated and masked according to (1) was carried out so that the ion beam was not irradiated, and an ion beam irradiated product as a medical molded product as the molded product of the present invention shown in FIG. (The dotted part in the figure shows the part irradiated with the ion beam.)
The ion beam irradiation was performed under the conditions shown in Table 1.

[Test Example 1]
(Measurement of surface roughness and contact angle of surface)
The change of the surface state in the portion modified by ion beam irradiation in the medical molded body was investigated by measuring the surface roughness and the contact angle of the surface of the ion beam irradiated portion.
Also, in order to examine the difference in the effect due to the difference in the ion implantation amount and the acceleration voltage of the ions under the ion beam irradiation conditions,
Ion implantation amount: 10 ¹³ ions / cm ² , ion accelerating voltage: 50, 100, 150 keV surface roughness of the surface of the portion irradiated with the ion beam (Examples 1 to 3),
Ion implantation amount: 10 ¹³ ions / cm ² , accelerating voltage of ions: contact angle of the surface of the ion beam irradiated portion under each condition of 50, 100 and 150 keV (Examples 1 to 3),
Ion accelerating voltage: 100 keV, ion implantation amount: 10 ¹³ ions, 10 ¹⁴ ions, 10 ¹⁵ ions / cm ² , contact angles of the surface of the ion beam irradiated portion (Examples 2, 4 and 5) ,
The test was conducted at In addition, as a control test, measurement of surface roughness and contact angle of the surface in a portion not subjected to ion beam irradiation was performed.
The surface roughness of the surface and the contact angle were measured by the following method.
Surface roughness measurement:
The surface roughness was measured by a tapping method using an atomic force microscope (AFM) (device name: ICON, manufactured by Bico).
Contact angle measurement:
The contact angle was measured by dropping 20 μL of distilled water and using a contact angle meter (device name: DM-301, manufactured by Kyowa Interface Science Co., Ltd.) by a dropping method.
The results of the surface roughness of the obtained surface are shown in FIG. 4 (Examples 1 to 3: comparison of acceleration voltages of ions), and the results of the contact angle are shown in FIG. 5 (Examples 1 to 3: comparison of acceleration voltages of ions) And FIG. 6 (Examples 2, 4 and 5: comparison of the amount of implanted ions).
Note that the experimental results at 0 keV in the figure mean the experimental results in a portion not subjected to ion beam irradiation as a control experiment (a portion under the mask in FIG. 3A).
In addition, all the tests were conducted in 5 trials.

[Test Example 2]
A natural degradation test was conducted to investigate the biodegradability of the molded article for medical use.
(Natural decomposition test)
It is known that the degradation rate of polylactic acid in vivo and the degradation rate in phosphate buffer are equal, and the degradation rate of the medical molded article of the present invention in phosphate buffer is in vivo It is considered to be equivalent to the decomposition rate of Therefore, natural decomposition experiments were conducted by immersing the medical molded article of the present invention in 200 mL of a phosphate buffer solution (pH 7.4) with a concentration of 0.067 M as shown in FIG.
The molded article for medical use is taken out of the buffer solution 1, 2, 4 and 6 weeks after immersion in the phosphate buffer solution, and the difference in thickness between the portion irradiated with the ion beam and the portion not irradiated with the ion beam (FIG. It carried out by measuring "the level | step difference" in the figure. The phosphate buffer solution was replaced once a week.
The thickness was measured using an atomic force microscope (AFM) apparatus (trade name: ICON, manufactured by Bico).
In order to examine the difference in the effect due to the difference in ion beam irradiation conditions, the test
Amount of implanted ions: 10 ¹³ ions / cm ² , accelerating voltage of ions: 50, 100, 150 keV medical molded articles (Examples 1 to 3), ion accelerating voltage: 100 keV, ion implantation Amount: Medical molded articles (Examples 2, 4 and 5) manufactured under the conditions of 10 ¹³ ions, 10 ¹⁴ ions and 10 ¹⁵ ions / cm ² , respectively.
The results are shown in FIG. 8 (Examples 1 to 3: comparison of acceleration voltage of ions) and FIG. 9 (Examples 2, 4 and 5: comparison of injected ion amount).

[Examples 6 to 9]
(Production of Medical Molded Article as a Molded Article of the Present Invention)
An injection molded product is produced from PLA pellets in the same manner as in Example 1, and the injection molded product is subjected to ion beam irradiation on the entire surface of the molded product under the conditions shown in Table 2 below. Examples 6 to 9) were obtained.
The ion beam irradiation conditions in each example (Examples 6 to 9) are shown in Table 2.
(Ion implantation depth by simulation)
In addition, when the ion implantation depth by the ion beam irradiation was simulated by SRIM 2006 (JF Ziegler et al., Http://www.srim.org/), it was as follows.
Example 6: about 80 (± 20 nm) nm, Example 7: about 160 (± 30 nm) nm,
Example 8: about 80 (± 20 nm) nm, Example 9: about 160 (± 30 nm) nm.

Comparative Example 1
An injection molded article was produced from PLA pellets in the same manner as in Example 1 except that ion beam irradiation was not performed, and the obtained injection molded article was referred to as Comparative Example 1.

[Test Example 3]
The strength of the medical molding was examined by measuring the tensile strength.
The measurement of tensile strength was performed on the medical molded articles obtained in Examples 6 to 9 and the compression molded article obtained in Comparative Example 1.
(Tensile strength measurement)
The tensile strength was measured by the following method.
Methods: Performed according to JIS K7162 (Plastics-Test methods for tensile properties, Part 2: Test conditions for molding, extrusion and cast plastic).
Test device: Device name: Universal testing device, Model name: AGS 1000-A, manufactured by Shimadzu Corporation, the tensile strength was the maximum tensile stress applied during the tensile test.
The obtained result is shown in FIG.
The test was conducted three times.

[Experimental Example 1] Analysis of Molecular Orientation State at Various Extrusion Stretching Ratios in Torsional Stretching In order to optimize the molecular orientation at the torsional stretching, the molecular orientation state by the extrusion ratio at the time of extrusion stretching in the torsional stretching was examined.
(Production of compression molded products)
The compression molded product is compression molded using the PLA pellet of Example 1 with a cylindrical mold (diameter: 6 mm, length 40 mm), and the cylindrical compression molded product (diameter: 6 mm, length 40 mm).

(Production of extruded products)
The obtained compression molded product was extruded and drawn at various draw ratios (draw ratio: 1.0, 1.3, 2.0, 4.0, 8.0) by an extrusion method. In addition, extrusion stretching was performed so as to have a diameter of 6 mm at all stretching ratios.
An outline of extrusion stretching is shown in FIG. Extrusion molding uses a mold consisting of four parts: a body, a guide of a bulk body, an indenter, and a tapered part, the mold is heated to 105 ° C. using a self-made hot press, and the compression molding is performed in the mold. Heating was performed for 10 minutes with the object set, and after heating, the hydraulic jack of the hot press was manually operated to apply a load and press the indenter.
After extrusion drawing, the mold was taken out of the hot press, and the mold was cooled to 50 ° C. using a heat absorbing metal plate, and then taken out of the mold to obtain an extruded product (diameter 6 mm, length 40 mm) . In addition, the thing of draw ratio 1.0 is what heat-treated only, and did not perform extrusion stretch.

(Analysis of molecular orientation)
The molecular orientation of the obtained extruded product was analyzed by the total reflection method (ATR method) of Fourier transform infrared spectroscopy (FTIR).
The details of the analysis are shown below.
In FTIR, light emitted from an infrared light source portion enters an interferometer, becomes an interference wave (interferogram), and passes through a sample. At that time, light of a specific frequency corresponding to the vibrational energy of the atoms or atomic groups in the molecules constituting the sample is absorbed. The signal obtained by the detector is subjected to Fourier transform in the computer unit to obtain an infrared spectrum unique to the sample. Thereby, identification of the sample substance can be performed, and further, analysis of molecular orientation can be performed by using polarized infrared light. The ATR method is one of the measurement methods of FTIR, and is a method of obtaining information of about 1 to 2 μm on the sample surface by totally reflecting infrared rays on the sample surface.
In the oriented film consisting of alpha crystals of PLA, an absorption band of 923 cm ⁻¹ assigned to the CH ₃ vibration mode exhibiting a transition moment perpendicular to the molecular chain axis is observed (S. Kang et al., Macromolecues 34, 4542 ( 2001)), in films consisting of highly oriented β crystals, an absorption band of 912 cm ⁻¹ assigned to the CH ₃ vibration mode of β crystals is observed (Daisuke Sawai et al., Macromolecules, 36, 3601-3605 ( 2003) has been reported. Therefore, the orientation function of each of the α crystal and the β crystal can be determined by using the infrared dichroic ratio.
The dichroic ratio R is defined as the following equation (Equation 1).

Where A _p and A _s are absorbances determined using infrared light polarized parallel to and perpendicular to the sample surface.
The orientation function f _c can be obtained from the dichroic ratio R using the following equation (Equation 2).

In the formula, θ is the angle between the molecular chain axis and the stretching direction, R ₀ = ² cot ² α, and α is the angle between the transition moment of the infrared absorption band and the molecular chain, α = 90 °.

(Measurement and analysis)
A measurement sample was prepared to perform the measurement. As shown in FIG. 12 (a), a measurement sample is obtained by mixing the obtained extruded product with a resin in which Epicoat (registered trademark) 828 (manufactured by Mitsubishi Chemical Corporation) and triethylenetetramine are mixed at a weight ratio of 100: 11. After embedding, in order to obtain a cross section in the longitudinal direction, a part is cut out using a lab cutter as shown in FIG. 12 (b), and further, as shown in FIG. 12 (c), the extruded product is in the longitudinal direction The surface of a portion of the extruded product exposed by cutting out is polished in the order of # 800, # 1000, # 2000 using a water-resistant abrasive paper, and the buff is finally buffed. It is smoothed by polishing.
The measurement of the infrared spectrum was performed on the measurement sample by the total reflection method (ATR method) of Fourier transform infrared spectroscopy (FTIR). Specifically, a Fourier transform infrared spectrophotometer (trade name:) equipped with a horizontal total reflection measuring apparatus (ATR-8200HA, manufactured by Shimadzu Corporation) and an infrared polarizer (GPR-8000, manufactured by Shimadzu Corporation) The measurement sample was measured under the following conditions using IR Prestige-21 (manufactured by Shimadzu Corporation).
conditions:
Measurement Mode: Transmittance
Cumulated Number: 20
Resolution: 4.0 cm ^-1
Measuring Range: 700 to 4000 cm ^-1
The orientation function was calculated from the obtained infrared spectrum using the above-mentioned dichroic ratio. The results are shown in FIG.

Example 10 Production of Medical Molded Article as a Compact of the Present Invention by Torsional Stretching The strength in the torsional stretching direction in the torsionally stretched product was examined.
(Manufacturing of twist-stretched products)
(Raw material to extrusion drawing)
A compression-molded product was obtained from PLA pellets in the same manner as in Experimental Example 1 except that the draw ratio in extrusion was changed to 8, and the compression-molded product was extruded to obtain an extrusion-processed product.
(Torsion processing)
The obtained extruded product was subjected to twist processing.
In the twisting process, first, as shown in FIG. 14, hexagonal columnar metal tabs were bonded to both ends of the obtained extruded product so that a processed portion was 25 mm. In addition, a process part means the part without the tab of the obtained extrusion processing thing.
The extruded product with the tab attached is attached to the sample mounting unit of the self-made torque loading machine shown in FIG. 14, heated with a heater for 20 minutes, and subjected to a twisting process by applying a torque by a motor. A temporary formed body was obtained.
The twisting was performed by applying a torque such that the above-mentioned twisting angle becomes 192 degrees, with a forming temperature of 100 ° C., a rotational speed of 0.2 rpm, and a rotational direction of clockwise. The average helical angle in the twisting was 23 degrees.

(Forging)
A thread was formed on the twist-stretched product by forging.
To form a thread by forging, first, insert a twist-stretched product with one tab cut off from the top and bottom into a mold divided into two by cutting the thread of a coarse screw of M6. Heating was done for a minute. Thereafter, using a UH-1000 kNIR manufactured by Shimadzu Corporation, the surface of the twist-stretched product is transferred to a twist-stretched product by transferring a thread carved in a mold by cold pressing at a room temperature of 200 kN and room temperature. Formed a thread. Thereafter, when the mold temperature became 40 ° C. or less, the load was removed and taken out of the mold to obtain a forged product having a screw thread formed.

(Ion beam irradiation)
The obtained molded product was irradiated with ion beam to obtain a medical molded product of the present invention shown in FIG. The ion beam irradiation was carried out under the conditions of the ion implantation amount: 10 ¹³ ions / cm ² and the ion acceleration voltage: 50 keV after setting the molded product in the ion beam irradiation apparatus of Example 1 and then the first time. In order to irradiate the ion beam to the site where the ion beam irradiation was not performed, the formed product was rotated by 180 degrees and set in the apparatus, and the ion beam irradiation was performed again under the same conditions.

[Experimental Example 2] Strength According to Diameter Direction in Torsional Stretched Product In order to measure the shear strength of the torsional stretched processed product in the diametrical direction, a shear test on the torsionally stretched product obtained in Example 10 was performed. The outline is shown in FIG.
In the shear test, first, as shown in FIG. 15, the twist-stretched product was mounted on the sample mounting portion of the tester using a dedicated jig. A chucking load was removed from the mounted torsionally-stretched material, and a shear load was applied to the torsionally-stretched material by applying a compressive load using a tester with an indenter set at the top. As a testing machine, AGS-1000A manufactured by Shimadzu Corporation was used, and the crosshead speed was 0.5 mm / min. A 10 kN Load Cell was used to measure the load, and the measurement was performed at a measurement interval of 100 ms. From the obtained maximum load, shear strength S _s was calculated by the following equation (Equation 3).
The control test was conducted by similarly testing the extrudates obtained in Example 10, which were not subjected to the twist drawing. The obtained result is shown in FIG.
In the formula, F means the maximum load, and A is the effective cross-sectional area (22.5 mm ² ) of the twist-stretched product.

[Experimental Example 3] Strength According to Torsional Stretching Direction in Torsional Stretched Material In order to investigate the effect of the torsional stretching process, a twisting test of the torsionally stretched material obtained in Example 10 was conducted. The outline is shown in FIG.
In the torsion test, a hexagonal nut as a tab is bonded to both ends with an adhesive (trade name: Araldite (registered trademark), Huntsman Japan Ltd.) so that the length of the evaluation unit is 15 mm, and a dedicated jig is It used and was set to the tester. Next, in a testing machine, one side of the tab bonded to the twisting treatment was fixed, and the other was loaded with torque by a motor. Oriental Motor's M206-401 and gearhead 2GN180S are used as load motors, and a torque converter (model number: TP20kCE, manufactured by Kyowa Electric Industry Co., Ltd.) is used for torque measurement, and a rotation speed of 0.2 rpm and 100 ms are measured. Tests were conducted at intervals to determine the maximum torque. The shear strength S _τ in the axial direction was calculated from the obtained maximum torque by the following equation (Equation 4).
In the formula, T means the maximum torque (N · m), and Z _p is the pole section coefficient (30.07 mm ³ ) with respect to the effective diameter of the twist-stretched product.
In addition, in order to investigate the strength according to the twist direction in the twist-stretched product subjected to the twist stretching, a twist test was performed in both the stretch direction and the anti-stretch direction. Moreover, the twist test of the extending | stretching direction in the extrusion processing thing which did not perform a twist process was made comparative test.
The results are shown in FIG.

The results and discussion will be described in detail below.
(Change of surface condition by ion beam irradiation)
Changes in the surface state of the portion modified by ion beam irradiation were examined by measuring the surface roughness of the surface of the ion implanted portion immediately after ion beam irradiation, and the contact angle.
As a result, regarding the surface roughness of the surface, as shown in FIG. 4, no major change was observed due to the conditions of the acceleration voltage of ions in ion beam irradiation, that is, the amount of implantation acceleration.
Regarding the contact angle of the surface, in all the ion beam irradiation conditions shown in FIGS. 5 and 6, the contact angle in the part irradiated with the ion beam was lower than that in the part not irradiated with the ion beam. Furthermore, the contact angle of the surface decreased depending on the accelerating voltage (implantation acceleration amount) of the ions as shown in FIG. 5, and decreased depending on the implanted ion amount as shown in FIG.
The decrease in the contact angle in these results indicates that the hydrophilicity of the surface is highly modified, which means that the biocompatibility is increased.
Also, the fact that the surface has high hydrophilicity means that water is likely to penetrate to the surface, and when considered together with the fact that polylactic acid is degraded by water, it is likely that water is likely to penetrate. It shows that the biodegradability is improved.
And since the contact angle is lowered depending on the acceleration voltage (implantation acceleration amount) and the amount of implanted ions at the time of ion beam irradiation, the contact angle can be changed by changing those conditions at the time of ion implantation. That is, it is understood that biocompatibility and biodegradability can be controlled.

(Biodegradability of the medical molded article of the present invention)
The biodegradability of the medical molded article of the present invention was examined.
As a result, from FIG. 8 (Examples 1 to 3) and FIG. 9 (Examples 2, 4 and 5), in all the ion beam irradiation conditions tested, the ion implanted part is compared with the non-ion implanted part. Therefore, it can be understood that the decomposition speed is fast (steps are produced). In addition, it is understood that the decomposition rate is increased depending on the acceleration voltage (implantation acceleration amount) of the ions and the implanted ion amount. In particular, it can be seen that the degradation rate in 1 to 3 weeks from the start of the experiment is improved.
The medical molded article of the present invention has a high degradation rate and excellent biodegradability because the degradation rate of the ion-implanted portion is faster than that of the non-ion-implanted portion under all conditions in the ion beam irradiation. I understand that. In addition, since the decomposition rate increases depending on the acceleration voltage (implantation acceleration amount) and the amount of implanted ions of ions, it is understood that the decomposition rate can be controlled by the acceleration voltage conditions of ion implantation and the amount of implanted ions. .

(Strength of medical moldings as moldings of the present invention)
The tensile strength of the medical molded article as the molded article of the present invention was examined.
FIG. 10 shows the tensile strengths of the medical molded articles of the present invention in the case of ion beam irradiation and in the case of no ion beam irradiation under various conditions. From this result, it can be seen that the medical molded article of the present invention does not decrease in strength even when irradiated with an ion beam.

(Molecular orientation in extrusion stretching)
The state of molecular orientation in the extrusion stretching used in the present invention was examined.
As shown in FIG. 13, it can be seen that the orientation function is high even at a slight draw ratio such that the extrusion ratio in extrusion drawing is 1.3 or more. From this result, it is understood that the molecules of the extrusion-treated product are oriented by the extrusion stretching used in the present invention.

(Shear strength of twist drawing products)
The shear strength of the twist-stretched product was examined.
As shown in FIG. 16, it was confirmed that there is almost no difference in the shear strength of the twist-stretched product as compared with the product without twist-stretching. From this, it can be seen that the twist-stretched product maintains the shear strength improved by extrusion stretching.

(Torsion strength in twist drawing products)
The strength of the twist-stretched product in the twisting direction was examined.
As shown in FIG. 18, it is recognized that the twist-stretched product is improved in strength in the twisting direction by about 20% as compared with the non-twisted one. In addition, it can be seen that the torsional strength against the reverse rotation of the twist-stretched product is lower than that in the normal direction. This means that control of the twisting direction also enables control of the strength.

From the above, it can be seen that the medical molded article as the molded article of the present invention is excellent in biocompatibility, biodegradability and strength made of biodegradable materials.
The medical molded article as the molded article of the present invention is surface-modified by ion beam irradiation to change the conditions (ion species, implanted ion amount, ion acceleration amount (implantation depth), etc.) of the ion beam irradiation. From the above, it is understood that the biocompatibility and the biodegradation rate are excellent while maintaining the strength. Further, it is understood that the biocompatibility and the biodegradation rate can be controlled by the conditions of ion beam irradiation.
In addition, it is understood that the medical molded product as the molded product of the present invention has high shear strength and torsional strength by torsional stretching, and in particular, it is understood that the strength is high in the twisting direction.

[Example 11] (Relation between twisting helix angle and strength)
Further, molded articles were obtained in the same manner as in Example 10, respectively, except that the twisting helix angle was set to 0 °, 15 °, 30 °, 45 °, and 50 ° as shown in FIG.
The relationship between the torsional strength and the maximum helical angle and the relationship between the maximum helical angle and the shear strength were measured for the obtained molded body. The results are shown in FIGS.
The relationship between the torsional strength and the maximum helix angle is the same as the torsion test in Experiment 3 and the relationship between the maximum helix angle and the shear strength is the same shear test as that in Experiment 2. It measured by performing.
As apparent from the results shown in the respective drawings, it is understood that the torsional strength exhibits the highest value at the maximum helix angle of 40 to 50 °, and the shear strength exhibits the highest value at the maximum helix angle of 15 to 45 °.

Claims (5)

A method for producing a molded body formed of a polymer material, comprising:
Said polymer material, comprising a radiation step of implanting ions by ion beam irradiation at least a portion of its surface,
The ion species in the above ion beam irradiation is Ar (argon), He (helium), N (nitrogen), P (phosphorus), C (carbon) or Ca (calcium),
The ion implantation dose in the above-mentioned ion beam irradiation is 10 ¹² to 10 ¹⁵ ions / cm ² ,
The polymer material is polylactic acid or polycaprolactone,
The method for producing a molded body , wherein the ion implantation step is performed after a stretching step of subjecting the polymer material to torsional stretching . The method according to claim 1, wherein the extrusion pressure in the twist drawing is 100 to 200 kN. The method according to claim 1 or 2, wherein a helical angle in the torsional stretching is 15 to 75 degrees. The molded body is a fastening member,
The manufacturing method of the molded object according to any one of claims 1 to 3, wherein a twisting direction of twisting in the twisting and stretching is the same as a twisting direction of a screw. The method for producing a molded body according to any one of claims 1 to 4 , wherein the molded body is a medical molded body.