US-12623004-B2 - Surface treatment method for surgical implant and surgical implant

US12623004B2US 12623004 B2US12623004 B2US 12623004B2US-12623004-B2

Abstract

Provided is a surface treatment method for a surgical implant that improves fatigue strength of the surgical implant while maintaining the microscopic surface structure of the surgical implant. A surface treatment method for a surgical implant, including: placing an additive manufactured surgical implant in a processing liquid, the surgical implant including a microscopic surface structure having a complete penetration area and an incomplete penetration area; and causing a nozzle immersed in the processing liquid to eject a cavitation jet of the processing liquid to the surgical implant to remove the incomplete penetration area remaining on a surface of the surgical implant and apply a compressive residual stress to the surface of the surgical implant.

Inventors

Taiki MATSUI

Assignees

SUGINO MACHINE LIMITED

Dates

Publication Date: 20260512
Application Date: 20240102
Priority Date: 20230106

Claims (10)

1 . A surface treatment method for a surgical implant, the method comprising: placing an additive manufactured surgical implant in a processing liquid, the surgical implant including a microscopic spherical structure having a complete penetration area and an incomplete penetration area, the microscopic spherical structure including a spherical portion, a substrate, and a base portion connecting the spherical portion and the substrate; and causing a nozzle immersed in the processing liquid to eject a cavitation jet of the processing liquid to the surgical implant to remove the incomplete penetration area remaining on a surface of the surgical implant while maintaining the structure of the complete penetration area and apply a compressive residual stress to the surface of the surgical implant.
2 . The surface treatment method for the surgical implant according to claim 1 , wherein the base portion in the incomplete penetration area has a dimension equal to or smaller than 70% of a diameter of the spherical portion.
3 . The surface treatment method for the surgical implant according to claim 1 , wherein the surgical implant is formed of bioinert metal.
4 . The surface treatment method for the surgical implant according to claim 3 , wherein the bioinert metal is pure titanium, or titanium alloy.
5 . The surface treatment method for the surgical implant according to claim 1 , wherein the nozzle ejects the processing liquid at a pressure of 50 MPa to 70 MPa.
6 . The surface treatment method for the surgical implant according to claim 2 , wherein the surgical implant is formed of bioinert metal.
7 . The surface treatment method for the surgical implant according to claim 2 , wherein the nozzle ejects the processing liquid at a pressure of 50 MPa to 70 MPa.
8 . The surface treatment method for the surgical implant according to claim 1 , wherein the placing the additive manufactured surgical implant in the processing liquid includes placing the additive manufactured surgical implant in an immersion depth of 300 mm to 900 mm, the immersion depth being a distance from a processing liquid level to a surface of the additive manufactured surgical implant.
9 . The surface treatment method for the surgical implant according to claim 1 , wherein the compressive residual stress measured by X-ray stress measurement (cos α method) is −20 MPa to −200 MPa.
10 . The surface treatment method for the surgical implant according to claim 1 , wherein the residual stress is applied on the surface of the surgical implant and a back surface of the surgical implant as viewed from the nozzle.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to Japanese Patent Application No. 2023-000956, filed on Jan. 6, 2023, the entire contents of which are hereby incorporated by reference. BACKGROUND 1. Technical Field The present invention relates to a surface treatment method for surgical implant and a surgical implant. 2. Description of the Background Incomplete penetration areas may remain on a surface of surgical implants produced by additive manufacturing. Surgical implants implanted in vivo may also be destroyed by fracture, work hardening, fatigue, and erosion (Hanawa, Biocompatibility of Titanium—favorable properties, Journal of The Japan Institute of Light Metals, Vol. 62, No. 7 (2012), 285-290). BRIEF SUMMARY A surgical implant preferably has a microscopic surface structure. An object of the present invention is to provide a surface treatment method for a surgical implant that improves the fatigue strength of the surgical implant while maintaining the microscopic surface structure of the surgical implant. A first aspect of the present invention provides a surface treatment method for a surgical implant, the method including: placing an additive manufactured surgical implant in a processing liquid, the surgical implant including a microscopic surface structure having a complete penetration area and an incomplete penetration area; andcausing a nozzle immersed in the processing liquid to eject a cavitation jet of the processing liquid to the surgical implant to remove the incomplete penetration area remaining on a surface of the surgical implant and apply a compressive residual stress to the surface of the surgical implant. A second aspect of the present invention provides a surgical implant formed of pure titanium or titanium alloy, the surgical implant including: an additive manufactured microscopic surface structure,wherein the surgical implant has a surface residual stress of negative value measured by X-ray stress measurement (cos α method). The surgical implants are, for example, artificial bones, artificial joints, artificial vertebral bodies, or artificial intervertebral disc. The bioinert metal is, for example, pure titanium, a titanium alloy, a cobalt chromium alloy or stainless steel. The titanium alloy is, for example, a Ti-6Al-4V alloy, a Ti-6Al-7Nb alloy, or a Ti-15Mo-5Z4-3Al alloy. The incomplete penetration area is formed on the surface of the surgical implant. The incomplete penetration area is formed of the same material as the surgical implant. The incomplete penetration area is, for example, a metal particle. The incomplete penetration area is partially integral with the surgical implant. The incomplete penetration area includes manufacturing defects. Within the microscopic spherical structure, a narrow base portion means that, for example, the diameter of the narrowest portion of the base portion is 70% or less than the diameter of the spherical portion. The additive manufacturing methods are, for example, 3D printing, or additive manufacturing by thermal spraying. The surface of the surgical implants produced by additive manufacturing has a tensile residual stress. The surgical implant is immersed in the processing liquid and the processing liquid is ejected from the nozzle immersed in the processing liquid. At this time, cavitation occurs due to a pressure difference around the jet of the processing liquid. The processing liquid is pure water or an aqueous solution containing a rust inhibitor. Examples of the rust inhibitor include amines and amine salts. In the cavitation processing, when the pressure becomes lower than the saturated vapor pressure for a very short time in the flow of the liquid, a large number of fine bubbles are generated by boiling of the liquid or liberation of the dissolved gas using the fine bubble nucleus as a nucleus. The bubbles collide with the surgical implant with the force of the jet. The bubbles repeatedly expand and contract to become smaller. The bubble is depressed to generate a micro jet flow, and the bubble is split and disappears. The micro jet flow erodes the surface of the surgical implant. It also imparts a compressive residual stress to the surface of the surgical implant. The cavitation removes the incomplete penetration area of the surgical implant. The jet containing bubbles generated by cavitation is referred to as a cavitation jet. The surface treatment method for the surgical implant according to the present invention improves the fatigue strength of the surgical implant while maintaining the microscopic surface structure of the surgical implant. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a flowchart showing a manufacturing method of a surgical implant according to an embodiment. FIG. 2 is a schematic diagram showing a microscopic spherical structure of the surgical implant according to the embodiment. FIG. 3 shows a peening processing machine for the surgical implant according to the embodiment.