AU2020104317A4 - Method for Making personalized degradable metal stent or internal fixing device based on 3D printing - Google Patents

Abstract

The invention discloses a method for making a personalized degradable metal stent or an internal fixing device based on 3D printing. This method includes the following steps: (1) Obtain the corresponding size parameters of the lesion in the human body through the QCA technology, and obtain the structure of the blood vessel stent, other metal stents or internal fixation devices through the three-dimensional reconstruction; (2) Build the 3D models for wax prototypes including blood vessel stents, other metal stents, or internal fixation devices in the computer, and decompose the 3D model into a series of two dimensional thin-film models; (3) Use 3D printing technology to make wax prototypes; (4) introduce plaster to the wax prototypes. After the plaster is hardened, bake it to completely evaporate the wax model prototype, and then the alloy melt is cast. After the casting is completed, the plaster shell is broken to obtain a metal stent or internal fixing device. The invention can be customized according to the patient's diseased blood vessels, and the obtained metal stent or internal fixation device is degradable, with high precision, good mechanical properties as well as good corrosion properties. 19 Drawings Figure 1 Figure Figure 3 Page 1 of 2

Description

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Figure 1

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Method for Making personalized degradable metal stent or internal fixing device based on

3D printing

Technical field

This invention is within the technical field of implantable medical devices, and particularly

relates to using 3D printing as an approach for making a personalized degradable metal stent or internal fixation device.

Technical Background

Vascular stents are devices that used in the body to prevent stenosis and occlusion of blood vessels, reduce the elastic retraction and reshaping of blood vessels, and maintain smooth blood flow in the lumen.

These devices are mainly divided into four categories include coronary stents, cerebrovascular stents, renal

artery stents, aortic stents, etc. Intravascular stent implantation has now become the main treatment for cardiovascular diseases caused by atherosclerosis, which greatly reduces the mortality of myocardial

infarction and the risk of serious or fatal cardiac events. Since the first successful coronary stent operation

in Sigwait in 1987, vascular stents have undergone rapid development, where it upgraded from permanent bare metal stents (BMS), drug-eluting stents (DES) to biodegradable stents (BDS). Although permanent

metal stents can effectively treat local vascular stenosis, further development is restricted for issues such as

thrombosis reoccurrence due to tissue damage caused by permanent implantation (or secondary surgery), metal ions generated by corrosion and dissociation, and material properties are incompatible with the

working conditions, as well as unsatisfactory clinical efficacy such as high reoccurring restenosis rate.

Emphasis on focusing on the development of a new generation of fully degradable vascular stents has been stated from the National Administration in the "Made in China 2025" and the Ministry of Science

and Technology in the "Thirteenth Five-Year Plan for Scientific and Technological Innovation of Medical

Devices". In addition, the "'Thirteenth Five-Year" Biological Industry Development Plan' illustrates the need to promote the additive manufacturing (3D printing) technology in implementing (introduction) into

new products.

Currently, research on degradable stents in terms of materials are focusing on the development of polymer stents and metal stents. Manufacturing process for polymer stents is relatively mature, but it has a

slow degradation rate (3 to 5 years), which affects the growth of the blood vessel itself and prolongs the inflammatory response of the walls of blood vessels. At the same time, due to the low polymer support strength, the stent can shrink easily. To improve its performance requires increasing wall thickness, which limits its use in small blood vessel lumens. In March 2017, the U.S. Food and Drug Administration announced that the incidence of degradable polymer stents for adverse cardiovascular events and thrombosis was significantly higher than that of existing drug eluting metal stents. In addition, the biodegradable polymer stent is known for bad for imaging because it does not develop image by itself, heavy metal tantalum is required to add before developing any image, which inevitably bring difficulties to the operation of bringing the two stents to connect in position, thus limits its application of long-vessel disease. The tantalum, which serves a marker after the stent degradation, will also remain in the body as a foreign part.

The difference is that the fully degradable metal stent can theoretically cure vascular stenosis within

a certain period, and then it can be completely degraded. The degradation products have good

biocompatibility, which fundamentally overcomes many of disadvantages and complications caused by the

permanent metal stents. Current degradable magnesium alloy stents and degradable iron alloy stents are

difficult to be widely used clinically due to issues such as degradation occurs too fast or too slow and

material causes inflammation response. Zinc-based stents has attracted wide attention for their good

biocompatibility and moderate degradation rate. The domestic and international patents related to zinc

based biodegradable alloys mainly include binary alloy of Zn-Ca, Zn-Mg and ternary alloys Zn-Fe (CN

102234746 A, CN 104888282 A, CN 104689378 A, US6287332 B1, US 8002821B2). However, research

on the design, 3D printing, and surface modification of the degradable zinc and its alloy stents is rarely

reported. Furthermore, there are no public reports about making biodegradable and absorbable zinc-based

alloy vascular stents using 3D printing laser stereo molding technology one-time molding process.

At present, the widely used intravascular stents are generated mainly by extrusion and drawing

methods to prepare raw models, and then process them by laser cutting technology. However, this method

is complicated in procedures and very expensive in cost, the products generated using this method are

limited in their structure design, where complex-shaped vascular stents are hard to achieve as well as key

performances such as precision and smoothness, resulting in thrombosis and blockage in clinical use.

3D printing technology is an emerging rapid prototyping technology. Based on the different raw

materials used, 3D printing can be divided into metal printing, ceramic printing, plastic printing, and sand printing, etc. For metal stents, the SLM method is a direct printing method, which can be only used in titanium alloys currently. Materials like cobalt-chromium alloys, stainless steel and aluminum need to develop powders and process parameters that can be used for metal 3D printing. Patent CN 104224412 A discloses a method for producing stainless steel and nickel-titanium alloy intravascular stents based on 3D printing technology. Indirect printing is a fusion manufacturing method that combines 3D printing technology with traditional casting, and integrated casting products can be obtained through a wax model printed by fused deposition (SLS) and photopolymerization (DPL) modes, and combined with traditional casting methods such as lost wax combining casting.

3D printing has great developmental potential in the fields of bioengineering and biomedicine.

However, the production of medical devices generally has very stringent requirements for materials. The

materials produced by 3D printing molding often results in imperfections, such as fuzzy surface, warping

deformation, dimensional deformation, uneven surface, fine structure defects, broken, staggered layer and

other defects, due to different materials selected, improper binders selected during molding, and poor

control of process parameters. These limitations are essential factors for preventing the use of 3D printing

technology in the manufacture of medical devices. Moreover, it is difficult to control the dimensional

accuracy of the product since the product still shrinks and deforms during the sintering process. Therefore,

the combination of 3D printing and traditional casting can bring novel ideas to solve this problem.

As one of the essential trace elements of the human body, zinc element is involved in all

physiological metabolic processes in the body. In addition to catalyzing or constructing various metal

enzymes, transcription factors and other proteins, zinc also functions as a neurotransmitter or modulator.

The feasibility of pure zinc as a metal material for stents is demonstrated in various perspectives, including

its mechanical properties and imaging developability which both are more optimal than polymers, a

moderate corrosion rate compare to magnesium and iron, and it has a good biocompatibility. However, the

mechanical properties of pure zinc are poor. For example, the tensile strength of as-cast pure zinc is only

MPa, and the elongation at break is 0.2%. Therefore, alloying and processing procedures are needed to

enhance its mechanical properties.

The existing zinc alloys at present all contain aluminum, an element that is toxic and can cause

allergy in the human body, resulting the existing zinc alloys cannot be used as materials for degradable

metal stents. Thus, it is necessary to develop a new type of zinc alloy that does not contain harmful components such as Al.

Content of the invention

The primary goal of this invention is to provide a method for making a personalized degradable

metal stent or internal fixation device based on 3D printing by overcoming the shortcomings and

deficiencies of the current technologies. The stent structure can be optimized by three-dimensional

modeling method using 3D printing combined with casting integrated forming, and the shape can be

customized according to the patient's malfunctioning blood vessel, thus effectively meeting the structural

requirement of various abnormal blood vessels.

Another goal of this invention is to provide personalized degradable metal stents or internal fixation

devices generated using the method mentioned from the primary goal.

The goal of this invention is to be achieved by the following technical solution: a method for

making a personalized degradable metal stent or internal fixation device based on 3D printing. The detailed

procedures are shown as following:

1. Structural analysis:

QAccording to coronary angiography, the vascular morphology data of the lesion in the human

body is obtained through QCA technology, and then the vascular stent structure is determined

through three-dimensional reconstruction;

or

©According to the CT scan image, the corresponding size parameters of the malfunctioning parts

in the human body is obtained through the QCA technology, and the structure of metal stents or

internal fixation devices is obtained through three-dimensional reconstruction;

2. Modeling: Build 3D models for vascular stents, other metal stents, or wax model prototypes of

internal fixation devices in the computer, and decompose the 3D model into a series of two

dimensional models of thin films with a thickness of 10 to 80 m;

3. 3D printing wax model: Import the model data obtained in step 2 into the computer of the printing

device and then set the printing program, to make the wax model prototype using 3D printing

technology;

4. Casting: Directly put the wax prototype made in step 3 into a container (casting cylinder), or put it into a container (casting cylinder) after assembling it into a wax tree, then shape it by introducing the plaster, and bake the plaster model to vaporize the wax prototype after the plaster is hardened, then the alloy melt is casted. After the casting is completed, a personalized degradable metal stent or internal fixation device can be obtained by breaking the shell.

The corresponding vascular stents described in step 1 ( include coronary stents, cerebrovascular

stents, renal artery stents, aortic stents, etc.

The corresponding size parameters of the human body lesions described in step 1 are the size

parameters of the human trachea, esophagus, bile duct, urethra anorectal, and other malfunctioning parts.

The other metal stents mentioned in step 1 include tracheal stents, esophageal stents, bile duct

stents, urethral stents, and anorectal stents, etc.

The internal fixation device described in step 1 includes a bone nail and a bone plate.

The material for making the wax prototype model in step 3 is a castable lost wax photosensitive

resin, preferably a UV photosensitive resin; a UV photosensitive resin with a melting point higher than

600°C would be the best.

The 3D printing technology described in step 3 includes fused deposition modeling technology

(PDM), powder selective sintering technology (SLS), photopolymerization (DLP) technology, or 3D

printing molding based on injection/deposition technology of other materials. As the printing platform for

wax molds and casting shells, products generated by the photopolymerization (DLP) process have the

highest forming accuracy and smoothness.

The method of making the 3D printing-based personalized degradable metal stent further includes

the following steps after step 3: remove remaining powder from the wax prototype, and then immersing it

in a low-temperature wax liquid to obtain a paraffin wax surface layer. After cooling, polish the surface of

the wax prototype, smoothening to improve the finish of the product.

The low-temperature wax liquid is preferably a wax liquid at 55-60°C.

The method of making the 3D printing-based personalized degradable metal stent further includes

the following steps before step 4: using casting process simulation software to simulate the casting

procedures or determining the casting process plan according to the existing process parameters.

The container described in step 4 is preferably a stainless-steel container.

The plaster baking process described in step 4 is to set a calcination and heating process to bake the plaster, which is suitable for wax mold demolding, drying, and casting insulation.

The corresponding conditions for demolding the wax mold are as follows: raise the temperature to

the melting point of the wax mold with the increasing speed of 100-200°C/hour, then put in a fully hardened plaster mold, and raise the temperature with a speed of 30-50°C/hour to a point that is lower than the plaster

pyrolysis temperature, temperature holding time is about 1-12 hours; the preferably demolding conditions

are: heating up to 600°C with the temperature increasing speed of 100°C/hour, then put in the fully hardened plaster mold, and then increase the temperature to 780°C at temperature increasing speed of 30-50°C/hour,

and the holding time is 1 hour.

The melting point of the wax mold is 600°C. The temperature point that is lower than the plaster pyrolysis temperature is 750-800°C.

The drying conditions are: 550-750°C for 1 to 5 hours; the preferable drying conditions are: 620°C

for 3 hours; The conditions of the casting insulation are: Heat preservation time of 1 to 5 hours at temperature

350-550°C; preferably, 350°C for 1 hour.

The alloy melt described in step 4 is an alloy melt of degradable metals which include Zn, Mg, Fe and other degradable metals; Optimal ally melt is a zinc alloy melt.

The zinc alloy is composed of Zn and one or more of the following elements: Mg, Zr, Mn, Mo, Cu,

Ag, Ga, Sr, Nd, Li; Optimal compositions are Zn and one or more of the following elements with their mass percentage of each component shown below: Mg (0-6.5 wt.%), Zr (0-0.5 wt.%), Mn (0-0.3 wt.%),

Mo (0-0.3 wt.%), Cu (0-1 wt.%), Ag (0-10 wt.%), Ga (0-1.5 wt.%), Sr (0-1.5 wt.%), Nd (0~1.5

wt.%), Li (0-4 wt.%), the balance will be filled with Zn. The best composition is Zn-lMg alloy, Zn-1Li

alloy or Zn-4Cu alloy.

The melting temperature of the zinc alloy is 550°C to 750°C, and the zinc alloy melt at 550°C to

750°C can be poured along the casting gate to obtain the model, or the zinc alloy can be heated to higher than the melting temperature then pour into the casting channel to make the model.

The casting method described in step 4 is a traditional lost wax casting method, which includes

planting wax trees, pouring plaster, baking plaster, casting, crushing plaster molds, cleaning and shearing castings, etc.; The optimal option is achieved by the following methods :

a. Directly put the wax prototype made in step 3 into a container (casting tube) or assembling it into a wax tree then put it into a container (casting tube), shape it by introducing in plaster, and let it sit for 1 to 2 hours until the plaster completely hardens; b. Set up a calcination and heating process for baking and dewaxing; c. After dewaxing, pour the 550-750°C zinc alloy melt along the casting gate and keep it for

1-2 hours;

d. After the liquified metal solidifies, take out the plaster mold, let the high-temperature plaster

mold sit for 10-30 minutes, then knock and crush the plaster shell, take out the stent, and further clean

the plaster remaining on the surface of the stent and dry it to obtain personalized biodegradable metal

stents or internal fixation devices.

The calcining and heating process set in step b is: heating up to 600°C at a temperature increasing

speed of 100°C/hour, then put in the plaster mold obtained in step a, then heating up to 750-800°C at

temperature increasing speed of 30-50°C/hour, and keeping it warm 1 to 12 hours; finally drying the mold

at 550 to 750°C for 1 to 5 hours.

The casting mentioned in step 4 includes common casting methods such as vacuum suction casting

and vacuum induction centrifugal casting; the casting process can be assisted with the vacuum device to

help the liquified metal flow; or superimpose mechanical oscillation or electromagnetic at a certain

frequency (0-500Hz) vibration refines the solidified structure.

The baked plaster process described in step 4 can be combined with a forging process to improve

the dimensional accuracy and surface finish of the casting.

A personalized degradable metal stent or internal fixation device based on 3D printing can be

generated by any one of the methods described above.

The 3D printing-based personalized degradable metal stent has a uniform wall thickness, and the

preferable thickness is 0.2-2 mm.

The 3D printing-based personalized degradable metal stent should meet geometric structure

matching with excellent mechanical properties as well as the hemodynamic requirements, and its preferable

structures are "S"-shaped, diamond-shaped grid, wave-folded, and tapered structure/ heteromorphic

bifurcation structure.

Compared with the existing technology, the present invention has the following advantages:

1. The present invention discloses a design and manufacturing method for generating a degradable metal (zinc alloy) stent based on 3D printing technology. The method is to first establish a 3D model of the stent in a computer, then import the model into a 3D printer to set printing program.

The wax mold of the stent then is printed out through the 3D printing program, followed by a

traditional casting method to obtain the integrated casting model of the stent. This invention adopts

3D printing and traditional casting method to manufacture degradable metal (zinc alloy) stent with

complex thin-walled structure, which solves the problems of insufficient precision and complicated

procedures when processing complex thin-walled parts in traditional processing methods, and

effectively improves processing efficiency and reduces production costs. Additionally, it avoids

processing defects caused by multiple processing procedures. For example, laser cutting causes

local metal melting, reducing surface accuracy and smoothness and further affecting the

biocompatibility of materials.

2. This invention applies 3D printing integrated forming technology, which optimizes the stent

structure using three-dimensional modeling method. The shape of the stent can be customized

according to the patient's malfunctioning blood vessel, which efficiently meets the structural

requirements of various abnormal blood vessels.

3. This invention aims at solving clinical issues such as thrombosis and blood vessel blockage caused

by the traditional stents, whose manufacturing cost is high, structural design is limited, and accuracy,

smoothness and biocompatibility are compromised due to laser cutting melting the local metal,

with limitations to meet the requirements of complicated blood vessel. Although the direct 3D

printing method can achieve integrated one-step molding, it also has problems such as narrow trial

range, difficulty in metal powder manufacturing, and high cost. Furthermore, due to the low melting

point of zinc alloy, laser printing will cause part of the zinc to vaporize and make the final product

composition inaccurate. Therefore, it is still not suitable for printing zinc-based metal stents. After

repeated trial and research, the inventor finally decided to choose the 3D printing with casting

method to prepare the metal stent, which can design a personalized model according to the actual

needs of the patient, quickly and accurately prepare the required stent wax model perfectly. After

wax shell molding, demolding and casting, a bare stent is obtained with high precision, smooth

surface, no defects such as deformation and cracking, and good biocompatibility. Compared with

traditional bare metal stents that are not degradable in the body and remain in the body as a foreign part for a long time, and degradable polymer stent has poor mechanical support performance and does not help the imaging, this invention is undoubtedly an excellent solution.

4. The degradable zinc-based metal material of this invention achieves controllable mechanical

properties and corrosion performance by adjusting the content of alloying elements in the zinc and

zinc alloy used, the tensile strength ranges from 200-400MPa, and the elongation at room

temperature ranges from 0.3 -60%, the degradation rate in simulated body fluid is 0.01-1.5mm/year,

and the degradation time is controlled at 18-24 months. Its performance is better than the existing

degradable polymer materials, magnesium alloys and iron-based biological materials.

5. The degradable zinc alloy stent of this invention can be well visualized in the human body, which

is convenient for the operation of minimally invasive surgery and conducting of postoperative

related examinations.

Description of the supplement figures

Fig. 1 A schematic diagram of the structure of the "S"-shaped stent in example of this invention.

Fig. 2 A schematic diagram of the structure of the diamond-shaped grid stent in example 2 of this invention.

Fig. 3 A schematic diagram of the structure of the tapered stent in example 3 of this invention.

Fig. 4 A schematic diagram of the structure of a heteromorphic bifurcated stent in example 3 of this

invention.

Figure 5 A schematic diagram of a titanium alloy bone plate prepared by the method described in this

invention.

Fig. 6 A schematic diagram of a magnesium alloy bone nail and a bone plate prepared by the method

described in this invention.

Detailed Implementing Process

This invention will be further described in detail below in conjunction with examples, but the examples of

this invention are not limited thereto.

Example 1: Zn-lMg alloy "S" shaped stent

1. Structural analysis and modeling of degradable metal stents

O) The casting material is zinc alloy (Zn-Mg alloy), which is made by melting pure zinc (99.99+%)

and pure magnesium (99.99+%). The melting point is around 420°C, the wall thickness of the stent is uniform about 0.5 mm. According to designed structure of the stent and technical requirements for casting of low melting point thin-walled parts, the casting process determined to use is lost wax casting; According to coronary angiography, the diameter of the malfunctioning blood vessel was measured by QCA (qualitative comparative analysis) technology, the morphological data of the diseased blood vessel was obtained, and the personalized degradable stent was designed. The diameter of the diseased blood vessel was measured to be 10mm. Figure 1 shows the "S"-shaped stent structure suitable for the patient's blood vessel determined by three-dimensional reconstruction;

® Simulating a 3D model of the wax prototype of the intravascular stent in the computer, and decompose the 3D model into a series of two-dimensional model of thin films with a thickness of

35 im;

2. 3D printing wax model and size precision control J5Import the model data from step 1 into the computer of the 3D printing device to set the printing

program and use the 3D printing molding process of photopolymerization (DLP) technology to

make the wax prototype. The material used is 3D printing UV photosensitive resin (melting point higher than 600°C);

After prototype printing, take the wax model out, blow off the remaining powder, and immerse it in a low-temperature wax liquid (55°C) to obtain the paraffin wax surface layer. After cooling,

polish the wax model prototype surface to enhance product's smoothness finish;

3. Casting process design and casting process simulation analysis

Use casting process simulation software to simulate the casting process, then design the process layout, riser size, pouring system size, and determine feasible pouring process plans;

4. Precision casting process of degradable metal stent

First step is to generate the shell for the wax mold and drying it, then calcinating and heating to dewax, followed by pouring zinc alloy melt at 550-750°C along the casting channel. The casting process is

assisted by vacuuming to promote the flow of molten metal. It also can superimpose 0-500Hz mechanical

vibration or electromagnetic vibration to refine the solidification structure. After the casting is completed and cooled, the shell is broken to obtain the stent with the structure exactly as the wax mold prototype; the

specific steps are as follows:

Put the processed wax model prototype into a stainless-steel container (casting cylinder), introduce

gypsum, and let it sit for 1 hour until the plaster is completely solidified and hardened;

Set the calcinating and heating process: set the dewaxing temperature to 780°C, heat up to 600°C

at temperature rising speed of 100°C/hour, put in the plaster mold, and then heat up to 780°C at

temperature rising speed of 30-50°C/hour, and the holding time is 1 hour; The drying temperature

is 620°C, and the holding time is 3 hours, which the wax mold prototype inside should be

completely vaporized;

Set up the pouring channel and riser, and pour zinc alloy melt into the channel gate, the pouring

temperature should be controlled in range of 550°C-750°C (or put the zinc alloy material in the

runner position first, and heat it together to a temperature that is higher than the melting point of

the zinc alloy), followed by the zinc alloy melt flows into the plaster along the runner, and the

temperature is kept at 350°C for 1 hour;

After the molten metal has solidified, take out the plaster mold, let the high temperature plaster

mold sit for 20 minutes, then use a plaster removal machine to push the plaster body out of the

casting cylinder, break the plaster shell and take out the stent, then clean the remaining surface of

the stent and dry, to obtain an "S"-shaped product.

The range of tensile strength of the alloy stent in the Example 1 measured by uniaxial stretching was 230

MPa, the range of elongation at room temperature was 10 5%, and the degradation rate of the stent in

simulated body fluids was 0.7 0. 2 mm/year, the degradation time was controlled within 6-24 months.

Example 2: Zn-lLi alloy diamond grid support

1. Structural analysis and modeling of degradable metal stents

J)The casting material is zinc alloy (Zn-Li alloy), which is made with pure zinc (99.99+%) and

pure lithium (99.99+%) through vacuum melting. The melting point is around 420°C. The stent

wall thickness is uniform, which is 1 mm. According to designed structure of the stent and

technical requirements for casting of low melting point thin-walled parts, the casting process

determined to use is lost wax casting;

According to coronary angiography, the morphological data of the malfunctioning blood vessel

is obtained through QCA technology, and the personalized degradable stent was designed. The diameter of the diseased blood vessel was measured to be 10mm. Figure 2 shows the diamond shaped grid stent structure with slightly larger openings at both ends determined by three dimensional reconstruction;

® Simulating a 3D model of the wax prototype of the intravascular stent in the computer, and decompose the 3D model into a series of two-dimensional model of thin films with a thickness

of50 im; 2. 3D printing wax model and size precision control

Import the model data from step1 into the computer of the 3D printing device to set the printing

program and use the 3D printing molding process of photopolymerization (DLP) technology to make the wax prototype. The material used is 3D printing UV photosensitive resin (melting point higher than 600°C);

After prototype printing, take the wax model out, blow off the remaining powder, and immerse it in a low-temperature wax liquid (55°C) to obtain the paraffin wax surface layer. After cooling,

polish the wax model prototype surface to enhance product's smoothness finish;

3. Casting process design and casting process simulation analysis Use casting process simulation software to simulate the casting process, then design the process layout,

riser size, pouring system size, and determine feasible pouring process plans;

4. Precision casting process of degradable metal stent First step is to generate the shell for the wax mold and drying it, then calcinating and heating to dewax, followed by pouring zinc alloy melt at 550°C along the casting channel. The casting process is assisted by

vacuuming to promote the flow of molten metal. After the casting is completed and cooled, the shell is broken to obtain the stent with the structure exactly as the wax mold prototype; the specific steps are as

follows;

Put the processed wax model prototype into a stainless-steel container (casting cylinder), introduce gypsum, and let it sit for 2 hours until the plaster is completely solidified and hardened;

Set the calcinating and heating process: same as Example 1;

Set up the pouring channel and riser, and put the zinc alloy prepared in advance on the runner position, and heat up to 550°C, let the zinc alloy melt flows into the gypsum along the runner, and

keep it at 350°C for 1 hour;

The method of taking the mold out is the same as that of Example 1, and a diamond-shaped grid

stent is obtained.

The tensile strength of the stent from Example 2 measured by uniaxial stretching was 200±50 MPa, the

elongation range at room temperature was 10±5%, and the degradation rate of the stent in simulated body

fluid was 0.9+0.2 mm/year. The degradation time was controlled within 6-24 months.

Example 3: Zn-4Cu alloy cone structure and special-shaped bifurcation structure bracket

1. Structural analysis and modeling of degradable metal stents

The casting material is zinc alloy (Zn-4Cu alloy), which is made with pure zinc (99.99+%) and

H62 brass (Cu-38wtZn). The melting point is around 420°C. The wall thickness of the stent is

uniform, which is 0.5 mm. According to designed structure of the stent and technical requirements

for casting of low melting point thin-walled parts, the casting process determined to use is lost wax

casting;

According to the coronary angiography, the morphological data of the malfunctioning blood vessel

is obtained through the QCA technology, and the personalized degradable stent is designed. The

shape of the two diseased coronary vessels is not a traditional single cylindrical shape based on the

measurement data. One has a tapered shape with a diameter of 3cm at the big end, 2cm at the small

end, and the stent length of 5cm; the other has a heteromorphic bifurcated structure, which is

derived from a thick tube into two thinner tubes with different diameters. The three diameters from

large to small are 1.87 cm, 1.33 cm, and 1.25 cm, respectively. As shown in Figure 3 and Figure 4,

a special-shaped bifurcated stent structure suitable for the patient's pathological alteration is

determined by three-dimensional reconstruction;

Simulating a 3D model of the wax prototype of the intravascular stent in the computer, and

decompose the 3D model into a series of two-dimensional model of thin films with a thickness of

35 im;

2. 3D printing wax model and size precision control

JImport the model data from step 1 into the computer of the 3D printing device to set the printing

program and use the 3D printing molding process of photopolymerization (DLP) technology to

make the wax prototype. The material used is 3D printing UV photosensitive resin (melting point higher than 600°C);

After prototype printing, take the wax model out, blow off the remaining powder, and immerse it

in a low-temperature wax liquid (55°C) to obtain the paraffin wax surface layer. After cooling,

polish the wax model prototype surface to enhance product's smoothness finish;

3. Casting process design and casting process simulation analysis

Use casting process simulation software to simulate the casting process, then design the process layout,

riser size, pouring system size, and determine feasible pouring process plans;

4. Precision casting process of degradable metal stent

First step is to generate the shell for the wax mold and drying it, then calcinating and heating to dewax,

followed by pouring zinc alloy melt at 550°C along the casting channel. The casting process is assisted by

vacuuming to promote the flow of molten metal. After the casting is completed and cooled, the shell is

broken to obtain the stent with the structure exactly as the wax mold prototype; the specific steps are as

follows:

Put the processed wax model prototype into a stainless-steel container (casting cylinder), introduce

gypsum, and let it sit for 2 hours until the plaster is completely solidified and hardened;

Set the calcining temperature rise process: set the dewaxing temperature to 780°C, heat up to 600°C

at a temperature increasing speed of 100 C /hour, put the casting cylinder into the furnace, and then

heat up to 780°C at a temperature increasing speed of 30-50°C /hour, let it forge for 8 hours ;

Set up the pouring channel and riser, and put the zinc alloy prepared in advance on the runner

position, and heat up to a temperature that is higher than the melting point, let the zinc alloy melt

flows into the gypsum along the runner, and keep it at 350°C for 1 hour;

The method of taking the mold out is the same as that of Example 1, and stents with tapered

structure and the special-shaped bifurcated shape are obtained.

The tensile strength of the stent from Example 3 measured by uniaxial stretching was 250+20 MPa, the

elongation range at room temperature was 30±5%, and the degradation rate of the stent in simulated body

fluid was 0.5±0.1 mm/year. The degradation time was controlled within 6 to 24 months.

The method described in this invention greatly reduced the processing procedures of the traditional

technology, and complex stents, such as special-shaped stents, bifurcated stents, etc., can be made through

integrated forming one step technology. Furthermore, it can fully utilize the personalized advantages of 3D printing technology. The other applications of this method include generating other degradable medical implants. According to CT scan images, the data of the corresponding size parameters of the malfunctioning parts in the human body can be obtained through QCA technology, therefore, accurate metal stents or internal fixation devices such as personalized bone nails, bone plates, tracheal stents, esophageal stents, bile duct stents, urethral stents, anorectal stents, etc can be obtained through three-dimensional reconstruction.

Among them, metal bone nail and bone plates, as commonly used medical orthopedic implants, include

permanently implanted bone nail and bone plates made by titanium alloy, cobalt-chromium alloy etc., as

well as the degradable magnesium alloy. Fig. 5 is a titanium alloy Ti6Al4V bone plate prepared by the

method of this invention, and Fig. 6 is a magnesium alloy AZ91 and WE43 bone nail and bone plate

prepared by the method of this invention. Above applications not only illustrate that this invention using

the 3D printing combined with casting method is more in line with the needs of personalized customization,

but also imply that this method has a broad application range.

The above-mentioned examples are preferred implementary process of the present invention, but

the executions of the present invention are not limited by the above-mentioned examples. Any other changes,

modifications, substitutions, combinations, and simplifications, etc., made without departing from the

original spirit and principle of the present invention, all should be equivalent replacement methods, which

are all included in the protection scope of the present invention.

Claims (7)

Claims

1. A method for making a personalized degradable metal stent or internal fixation device based on 3D printing, the features comprise the following steps:

(1) Structural analysis: QAccording to coronary angiography, the vascular morphology data of the malfunctioning parts in the

human body is obtained through QCA technology, and then the vascular stent structure is determined

through three-dimensional reconstruction;

or @According to the CT scan image, the data of the corresponding size parameters of the malfunctioning

parts in the human body is obtained through the QCA technology, and the structure of other metal stents

or internal fixation devices is obtained through three-dimensional reconstruction; (2) Modeling: Build 3D models of vascular stents, other metal stents, or wax model prototypes of internal

fixation devices in the computer, and decompose the 3D model into a series of two-dimensional thin-film

models with a thickness of 10 to 80 mi; (3) 3D printing wax model: Import the model data obtained in step (2) into the computer of the 3D

printing device to set the printing program, and then use 3D printing technology to make the wax model

prototype; (4) Casting: Put the wax model prototype made in step (3) directly into a container or assembling it into a

wax tree then put it into a container, shape it by introducing in plaster, bake the plaster when it is

completely hardened to vaporize the wax model prototype, and then cast the melt alloy. After the casting is completed, break the shell to obtain a personalized biodegradable metal stent or internal fixation

device;

The casting described in step (4) is achieved by the following method: a. Put the wax model prototype made in step (3) directly into a container or assembling it into a wax tree then put it into a container, shape it by introducing in plaster, and let it stand for 1 to 2 hours until the

plaster is fully solidified and hardened; b. Set a calcinating and heating process for baking and dewaxing; c. After dewaxing, pour the 550-750°C zinc alloy melt along the casting gate and keep it for 1-2 hours; d. After the liquified metal solidifies, take out the plaster mold, let the high-temperature plaster mold sit for

-30 minutes, followed by quenching in cold water and knocking and crushing the plaster shell, take out the stent, and further clean the plaster remaining on the surface of the stent and dry it to obtain personalized biodegradable metal stents or internal fixation devices;

The calcining and heating process set in step b is: heating up to 600°C at a temperature increasing speed of

100°C/hour, then put in the plaster mold obtained in step a, then heating up to 750-800°C at temperature increasing speed of 30-50°C/hour, and keeping it warm 1 to 12 hours; finally drying the mold at 550 to

750°C for I to 5 hours; The vascular stents described in step (1) ( are coronary stents, cerebrovascular stents, renal artery stents

or aortic stents; The other metal stents mentioned in step (1) @ are tracheal stents, esophageal stents, bile duct stents,

urethral stents or anorectal stents; The internal fixation device described in step (1) @ is a bone nail or a bone plate.

2. According to the Right Claim 1 stating features of the method for making personalized degradable

metal stents or internal fixation devices based on 3D printing, the alloy melt in step (4) is a zinc alloy melts and the zinc alloy are composed of Zn and one or more of the following elements: Mg, Zr, Mn, Mo,

Cu, Ag, Ga, Sr, Nd, Li.

3. According to the Right Claim 2 stating features of the method for making personalized degradable metal stents or internal fixation devices based on 3D printing, the zinc alloy is composed of Zn and one or more of the following elements and their mass percentages are: Mg 0-6.5wt.%, Zr 0-0.5wt.%, Mn 0

0.3wt.%, Mo 0-0.3wt.%, Cu 0~-1wt.%, Ag 0-1l0wt.%, Ga 0~-1.5wt.%, Sr 0-1.5wt.%, Nd 0~ 1.5wt.%, Li 0-4wt.% and the remaining balance is filled by Zn.

4. According to the Right Claim 1 stating the features of the method for making a personalized degradable

metal stent or internal fixation device based on 3D printing, the method further comprises the following steps after step (3): blowing the wax mold prototype to remove remaining powder, followed by

immersing the mold in a low-temperature wax liquid to obtain a paraffin surface layer, then cool it,

followed by polishing the surface of the wax model prototype to a smooth finish.

5. According to the Right Claim 1 stating the features of the method for making a personalized degradable

metal stent or internal fixation device based on 3D printing, the material for making the wax model prototype in step (3) is UV photosensitive resin;

The 3D printing technology described in step (3) is fused deposition forming technology, powder

selective sintering technology, and photopolymerization technology.

6. The feature of a personalized degradable metal stent or internal fixation device based on 3D printing is

that this device is prepared by the method stated by any one of the Right Claims I to 5.

7. According to Right Claim 6 stating the features of the 3D printing-based personalized degradable metal

stent or internal fixation device, the thickness of the 3D printing-based personalized degradable metal

stent is 0.2-2 mm.