ZHU YejiaMA YanxueGUAN GuopingMENG FenyeLI Yuling

1 Engineering Research Center of Technical Textiles,Ministry of Education,Shanghai 201620,China 2 College of Textiles,Donghua University,Shanghai 201620,China

Abstract:In order to explore the feasibility of tungsten filament as biomedical metal material,this article conducted a series of performance tests on two different thicknesses of black tungsten filament and two different thicknesses of white tungsten filament. It mainly tested the basic physical properties of the tungsten filament including the longitudinal cross-section of the fiber,the fiber diameter,the mechanical properties of the fiber and the biodegradability,and analyzed the results. The results showed that the breaking force of tungsten filament was about 3000MPa. And whether it was black tungsten filament or white tungsten filament,the larger the diameter,the greater the breaking force,and the breaking strength of the tungsten filament was much larger than the breaking strength of the steel wire. The larger the diameter of the tungsten filament,the slower the degradation rate. During the two months,the mass loss rate of the thick black tungsten filament was 59.40%,thin black tungsten filament was 83.88%,thick white tungsten filament was 47.39%,thin white tungsten filament was 72.29%,the degradation rate of thick tungsten wire was nearly half of the thin,and degradation mainly occured in the first months.

Key words:tungsten;filament;degradation performance;mechanical properties;diameter

Introduction

Biomedical materials can be implanted into or connected to biological tissues in medical,which play a role in diagnosing,treating,repairing or replacing diseased tissues,organs or functions in living organisms.Biomedical materials currently used in clinical fields mainly include biomedical metal materials,biomedical organic polymer materials,biomedical inorganic non-metallic materials[1-2],and can also be classified into two categories:degradable and non-degradable.Generally,biomedical metal fibers,such as stainless steel,cobalt-based alloys,titanium and titanium alloys,have excellent toughness,radiation impermeability,excellent processing properties,and other polymer materials cannot be replaced[2].However,in the case of low mass density of these metallic materials,the mechanical properties will be lower than many polymer materials with the same linear density.Therefore,the application fields of commonly used metal materials are subject to relatively large restrictions.Tungsten is the highest melting point material and a high tensile strength material[3].Usually the knowledge about tungsten filament is basically on the tungsten filament of the bulb.An article published by Matthias Peuster on the biocompatibility study of tungsten shows that there is no question about the toxicity or unexplained clinical symptoms after implantation of tungsten filament,indicating that tungsten filament can be used as biomedical metal fiber[4].Other reports on the use of tungsten filament as a biomedical material confirm this view[5-6].However,tungsten filaments have not entered the market for clinical use.This paper studies the basic physical properties and biodegradability of fiber-grade tungsten filament produced by Xiamen Honglu Tungsten &Molybdenum Industry Co.,Ltd.,Xiamen,China.It provides a basis for the use of tungsten filament as biomedical material,and it also provides a direction for research and development of new medical metal materials.

1 Experimental Design

1.1 Experimental materials

The material used in this test comes from Xiamen Honglu Tungsten &Molybdenum Industry Co.,Ltd.,Xiamen,China.There are four different specifications of tungsten filament.The package form is shown in Fig.1 and the specifications are shown in Table 1.The black tungsten filament is formed by using graphite as a lubricant during the processing,using natural gas or electric heating to oxidize the surface of the tungsten filament,and the graphite and tungsten oxide are attached to the surface of the tungsten filament.The white tungsten filament is a tungsten filament after the black tungsten filament is subjected to alkali washing or electrolytic polishing.Compared with black tungsten filament,the white tungsten filament has a smooth,bright,clean surface with a silver-gray metallic luster.The surface morphology of the two materials is shown in Fig.2.

The specifications in Table 1 refer to the number of milligrams of fiber in the length of 200 mm,that is,the linear density of the fiber.Fiber diameter and strength data are provided according to the factory’s test methods.

Fig.1 Different specifications of tungsten filament

Table 1 Specifications of tungsten filament

Fig.2 SEM images of tungsten filament:(a) 30 μm black tungsten;(b)20 μm black tungsten;(c)30 μm white tungsten;(d) 20 μm white tungsten

1.2 Basic physical properties test

The basic physical properties examined here are fiber longitudinal section,fiber diameter and basic mechanical properties.The fiber cross section was observed by continuous zoom stereo microscope(PXS8-T,China).Fiber longitudinal section and fiber diameter were tested according to international standard ISO137—1975.The instrument was inverted microscope(VAB-100-1,China).The basic mechanical properties were tested in accordance with GB/T 10573—1989.The instrument was high strength and high modulus fiber strength extensometer(XQ-1C,Shanghai New Fiber Instrument Co.,Ltd.,Shanghai,China).In addition,the commercially available 304 stainless steel wire with a diameter of 0.06 mm was used as the control group for the same mechanical properties test.

1.3 Biodegradability test

Biodegradability is a fundamental property that must be understood as a biomedical material.The method for detecting theinvitrodegradation properties of materials usually uses different degradation solutions.The main types of solution include:0.9% NaCl aqueous solution,simulated body fluid(SBF),Hank’s,phosphate buffered saline(PBS),DMEM and so on[7].The solution selected here was PBS.The method was to dissolve 1.65 g KH2PO4and 19.53 g NaHPO4·H2O in 1 000 mL distilled water to prepare a solution,pH 7.4,and put the sample as shown in Fig.3 and subjected to shaker degradation at a temperature of 37 ℃[7-9].The test equipment was KY-100B air constant temperature culture shaker (China),84-1A pH meter (China),DZF-6030B vacuum drying oven (China),electronic analytical balance (China).Degradation characteristics were characterized by the mass loss rate of the sample.

Fig.3 Phosphate buffer containing materials

2 Results and Discussion

2.1 Basic physical characteristics

The cross section of the fiber is shown in Fig.4.The magnification of the microscope is 50 times.It can be seen from Fig.4 that the fiber cross section is close to a circle.The longitudinal section of the fiber is shown in Fig.5.The magnification of the microscope is 750 times,and the fiber diameter is measured for the longitudinal section.The basic physical index measurement data of the fiber is shown in Table 2.The diameters of four kinds of tungsten fibers measured under inverted microscope belong to micron scale.The two kinds of thin tungsten filament have a diameter of about 20 μm,and the two kinds of thick tungsten filament are about 30 μm,but there is a deviation from the factory identification data,and there are basically lower deviations.It can be seen from Table 2 that under the same diameter specification,the breaking force of white tungsten filament is larger than that of black tungsten filament,and the larger the diameter,the greater the difference in strength.In addition,whether it is white tungsten filament or black tungsten filament,the breaking force increases as the diameter increases.Compared with the steel wire material in Table 2,the breaking strength of the two kinds of tungsten filament is larger than the strength of the 60 μm steel wire material,indicating that the tungsten filament is a metal material with a large tensile breaking strength and has good mechanical properties.

Fig.4 Cross section of the fiber:(a) 30 μm black tungsten;(b) 20 μm black tungsten;(c) 30 μm white tungsten;(d) 20 μm white tungsten

Fig.5 Optical surface morphology of fiber:(a) 30 μm black tungsten;(b) 20 μm black tungsten;(c) 30 μm white tungsten;(d) 20 μm white tungsten

Table 2 Material physical property data sheet

2.2 Biodegradability test

The surface state of the material after degradation is shown in Fig.6.After the black tungsten filament was washed by distilled water,a black substance was removed from the surface,and white tungsten filament was not visible.In solutions of neutral and alkaline pH values,a native WO3metal oxide film forms but continually dissolves away,and is thus non-passivating,the WO3surface species formed soluble tungstate ions,which resulted in the continual dissolution of surface material;and these were products of WO3as well as active W metal dissolution at higher pHs[10-13].

Fig.6 Degraded material

The data results are shown in Table 3.The mass loss rate refers to the ratio of the dry weight difference before and after degradation to the dry weight before degradation.As can be seen from Table 3,the metal material of tungsten filament is a degradable material which degrades rapidly.From the perspective of degradation rate,in the first month,the mass loss rate of No.2 has reached about 80%,and that of No.4 is about 70%.The other two materials are relatively slow.The second month was much slower than the first month,indicating that the degradation process occurred mainly in the first month.It can also be seen from Table 3 that,in the case of the same degradation time,it is obtained from the mass loss rate,whether it is black tungsten or white tungsten,the finer the diameter,the faster the degradation.Tungsten filament might develop a pronounced fiber texture in the forming process,caused anisotropic deformation of single grains.The finer tungsten wire is formed with more texture,and more corrosive surface[11].

Due to the influence of time and external factors,the results of this degradation test only temporarily measured the mass loss rate of the material.Subsequent changes will be made to the results of the test,such as changing the degradation solution,changing the degradation environment and making changes in characterization such as characterizing strength,morphology,and degrading liquid ionic components[10],especially the analysis of ionic components in the degradation fluid will be analyzed.Because the metal material contains more alloying elements,when implanted in the human body,metal ions are eluted due to corrosion,abrasion,etc.,metal ions entering the tissue fluid will cause some biological reactions,and the ion components should be reasonably analyzed to provide a basis for animal experiments.

Table 3 Biodegradability test data

3 Conclusions

In the study,basic physical properties of tungsten filaments were tested.According to the results,tungsten filament is a kind of metal material with strong tensile breaking strength and good mechanical properties,and the tungsten materials are degradable.In the degradation process of tungsten filaments,an uncertain substance would be produced on the surface,and components and reasons of the substance need to be further investigated.In the case of the same degradation time,it was obtained from the mass loss rate,whether it was black tungsten or white tungsten,the finer the diameter,the faster the degradation.In future study,more properties will be explored,and usage of the tungsten filaments in biomedical textiles will be discussed.