WO2015168500A1

WO2015168500A1 - Ternary silicon-chromium eutectic alloys having molybdenum, copper or silver

Info

Publication number: WO2015168500A1
Application number: PCT/US2015/028706
Authority: WO
Inventors: James Michael Curtis; Vasgen A. Shamamian; Michael W. Toepke; Edward K. Nyutu; Joseph SOOTSMAN
Original assignee: Dow Corning Corp
Current assignee: Dow Silicones Corp
Priority date: 2014-05-02
Filing date: 2015-05-01
Publication date: 2015-11-05
Anticipated expiration: 2016-11-02

Abstract

Ternary silicon alloys and shape cast products made therefrom are disclosed. The ternary silicon alloys generally include silicon as the first alloying element, chromium as the second alloying element, and one of silver (Ag), copper (Cu) and molybdenum (Mo) as the third alloying element. The ternary silicon alloy includes a eutectic amount of the silicon and the chromium. The ternary silicon alloy also generally includes an amount of the third alloying element sufficient to realize at least one of (a) improved castability and (b) biomedical enhancement. Shape cast products made from the ternary silicon alloy may be used in various applications, such as biomedical applications (e.g., implantable medical products).

Description

TERNARY SILICON-CHROMIUM EUTECTIC ALLOYS HAVING

MOLYBDENUM, COPPER OR SILVER

BACKGROUND

[0001] Silicon (Si) eutectic alloys can be fabricated by melting and casting processes (see, e.g., WO 2011/022058). Such silicon eutectic alloys of WO2011/022058 may realize improved fracture toughness.

SUMMARY OF THE DISCLOSURE

[0002] Broadly, the present disclosure relates to ternary silicon alloys having silicon, chromium, and one of silver, copper, and molybdenum. The ternary silicon alloys may be useful, for instance, in biomedical applications, as described below.

[0003] As noted, the ternary silicon alloys include silicon as the first alloying element and chromium as the second alloying element. The ternary silicon alloys include a eutectic amount of the silicon and the chromium so as to produce a ternary silicon alloy product having a first phase comprising silicon and a second phase comprising chromium disilicide. As used herein, the phrase "a eutectic amount of the silicon and the chromium", and the like, means the amount of the silicon and the chromium contained in the alloy are such that a eutectic aggregation of silicon (Si) and chromium disilicide (CrSi₂) is realized in a casting made from the ternary silicon alloy composition, as verified by optical metallography. One example of "a eutectic amount of silicon and chromium" is about 76 wt. % Si and 24 wt. % Cr, which will result in a eutectic aggregation of silicon and chromium disilicide (CrSi₂). Silicon and chromium amounts similar to these amount may also realize a eutectic aggregation of silicon and chromium disilicide. WO2011/022058 to Schuh et al. and U.S. Patent No. 4,724,223 to Ditchek et al., each of which is incorporated herein by reference in its entirety, describe some methods for producing silicon eutectic alloys.

[0004] The ternary silicon alloy also includes one of silver (Ag), copper (Cu), and molybdenum as the third alloying element. The amount of the third alloying element included in the ternary silicon alloy may be any amount that facilitates one or more of (a) improved castability and (b) biomedical enhancement, as described below. The amount of the third alloying element is limited to an amount that still allows the formation of the eutectic aggregation of silicon and a chromium disilicide. If the ternary alloy contains too much of the third alloying element, the eutectic aggregation of silicon and chromium disilicide will not form.

[0005] In one approach, the ternary silicon alloy includes a sufficient amount of silver, copper, or molybdenum to improve castability of the ternary silicon alloy. The improved castability may be realized in the form of reduced (or no) ingot cracking / surface defects relative to casting made from a binary Si-Cr alloy having 76 wt. % Si and 24 wt. % Cr. In this regard, a method may include flowing a molten mixture into a shape casting mold, wherein the molten mixture comprises (and in some instances consists essentially of) the silicon, the chromium, and the third alloying element. The method may include solidifying the molten mixture into a shape cast part corresponding to the shape of the shape casting mold, wherein the shape cast part comprises an eutectic aggregation of silicon and chromium disilicide. The method may include extracting the shape cast part from the shape casting mold, wherein the shape cast part is crack-free. As used herein, "crack-free" means that the shape cast part is sufficiently free of cracks that it can be used for its intended purpose. For example, when the shape casting mold is in the form of an medical product, the medical product is crack-free when it can be used as the medical product for which it was intended. In one embodiment, the shape cast part is crack-free to the unaided, naked eye. To facilitate improved castability, the ternary silicon alloy may include at least 0.10 wt. % of the third alloying element in the final product, as measured by the Composition Test Procedure, described in the examples section, below. In one embodiment, the ternary silicon alloy includes at least 0.15 wt. % of the third alloying element. In another embodiment, the ternary silicon alloy includes at least 0.20 wt. % of the third alloying element. In yet another embodiment, the ternary silicon alloy includes at least 0.25 wt. % of the third alloying element.

[0006] In one approach, the amount of the third alloying element in the ternary silicon alloy is sufficient to promote a biomedical enhancement of castings made from the ternary silicon alloy. As used herein, an amount sufficient to realize "biomedical enhancement", and the like, means that the ternary silicon alloy includes an amount of the third alloying element such that:

(a) a casting made from the ternary silicon alloy realizes the eutectic aggregation of silicon and chromium disilicide (as defined above); and

(b) the casting made from the ternary silicon alloy realizes at least one of the following properties: (I) a cytotoxity rating of zero (0) when measured in accordance with ISO- 109935; or

(II) a "passing" rating when tested in accordance with the Leaching Test Procedure (described in the Examples section, below); or

(III) at least a 1.3 Log reduction of the bacteria Pseudomonas aeruginosa (ATCC 9027), within 24 hours, as compared to a control of stainless steel (316), when tested in in accordance with ISO 22196; or

(IV) a stem cell (Dl ORL UVA) density no less than 90% lower than a polystyrene control (cells/mm²) when tested in accordance with The Cell Attachment Test Procedure (described in the Examples section, below); or

(V) a calcium mineralization deposition amount that covers at least 50% of the area of a 1 cm x 1 cm test coupon after 28 days when tested in in accordance with the Calcium Mineralization Test Procedure (described in the Examples section, below). In one embodiment, the calcium deposition amount covers at least 60% of the area of the test coupon. In another embodiment, the calcium deposition amount covers at least 70% of the area of the test coupon. In yet another embodiment, the calcium deposition amount covers at least 80% of the area of the test coupon. In another embodiment, the calcium deposition amount covers at least 90% of the area of the test coupon.

In one embodiment, a casting made from a ternary silicon alloy realizes at least two of the properties of (b)(I)-(b)(V). In another embodiment, a casting made from a ternary silicon alloy realizes at least three of the properties of (b)(I)-(b)(V). In yet another embodiment, a casting made from a ternary silicon alloy realizes at least four of the properties of (b)(1)- (b)(V). In another embodiment, a casting made from a ternary silicon alloy realizes all of the properties of (b)(I)-(b)(V).

[0007] In one approach, the casting is a shape cast part in the form of an implantable medical product. In one embodiment, the implantable medical product realizes at least biomedical enhancement properties (b)(1) and (b)(II). In another embodiment, the implantable medical product realizes at least biomedical enhancement properties (b)(1) and (b)(II), and at least one of properties (b)(III)-(b)(V). In yet another embodiment, the implantable medical product realizes at least biomedical enhancement properties (b)(1) and (b)(II), and at least two of properties (b)(III)-(b)(V). In another embodiment, the implantable medical product realizes all of biomedical enhancement properties (b)(1)- (b)(V).

[0008] In one embodiment, the medical product is surgical equipment and/or instrumentation, and at least realizes biomedical enhancement properties (b)(1) and (b)(II). In one embodiment, the medical product is a liner or tray for an autoclave, and realizes at least one of biomedical enhancement properties (b)(II) and (b)(III). In one embodiment, the medical product is an incubator tray, or a liner for an incubator, and realizes at least one of biomedical enhancement properties (b)(II) and (b)(III).

[0009] In one approach, the third alloying element is molybdenum. When only improved castability is required, the ternary silicon alloy may include at least 0.10 wt. % Mo, or at least 0.15 wt. % Mo, or at least 0.20 wt. % Mo, or at least 0.25 wt. % Mo, as described above, up to an amount that still allows the formation of the eutectic aggregation of silicon and a chromium disilicide (e.g., up to 5.0 wt. % Mo). When biomedical enhancement is required, the ternary silicon alloy may include from 0.20 to 5.0 wt. % Mo. In one embodiment, the ternary silicon alloy includes 0.6 to 3.0 wt. % Mo. In another embodiment, the ternary silicon alloy includes 1.0 to 2.5 wt. % Mo. In yet another embodiment, the ternary silicon alloy include about 1.5 to 2.5 wt. % Mo. In another embodiment, the ternary silicon alloy includes about 2.0 wt. % Mo.

[0010] In another approach, the third alloying element is copper. When only improved castability is required, the ternary silicon alloy may include at least 0.10 wt. % Cu, or at least 0.15 wt. % Cu, or at least 0.20 wt. % Cu, or at least 0.25 wt. % Cu, as described above, up to an amount that still allows the formation of the eutectic aggregation of silicon and a chromium disilicide (e.g., up to 5.0 wt. % Cu). When biomedical enhancement is required, the ternary silicon alloy may include from 0.20 to 3.0 wt. % Cu. In one embodiment, the ternary silicon alloy includes from 0.5 to 2.0 wt. % Cu. In another embodiment, the ternary silicon alloy includes from 0.6 to 1.7 wt. % Cu. In yet another embodiment, the ternary silicon alloy include about 0.7 to 1.6 wt. % Cu. In another embodiment, the ternary silicon alloy includes about 1.0 wt. % Cu.

[0011] In yet another approach, the third alloying element is silver. When only improved castability is required, the ternary silicon alloy may include at least 0.10 wt. % Ag, or at least 0.15 wt. % Ag, or at least 0.20 wt. % Ag, or at least 0.25 wt. % Ag, as described above, up to an amount that still allows the formation of the eutectic aggregation of silicon and a chromium disilicide (e.g., up to 10.0 wt. % Ag). When biomedical enhancement is required, the ternary silicon alloy may include from 0.20 to 2.0 wt. % Ag. In one embodiment, the ternary silicon alloy includes from 0.4 to 1.2 wt. % Ag. In another embodiment, the ternary silicon alloy includes about 0.8 wt. % Ag.

[0012] Shape cast products may be produced from the ternary silicon alloys using shape cast molds. As used herein, a shape casting mold means any mold capable of producing a shape cast part from the ternary silicon alloys. Such molds include die casting molds, sand casting molds, investment casting molds, permanent graphite casting molds, rotary casting molds, and the like. The shape cast products may include a eutectic aggregation of a first phase consisting essentially of silicon and a second phase comprising chromium disilicide. The silicon of the aggregation may be in the form of crystalline silicon and/or amorphous silicon (generally crystalline). The chromium disilicide may be in the form of rods. Such rods may be interpenetrated (cannot pass through the body without contacting at least one of these structures). The chromium disilicide rods may have an averaging diameter of from about 0.5 to about 5 microns and a characteristic spacing (λ) of from about 1.5 to about 15 microns. When the third alloying element is molybdenum, at least some of the molybdenum is in solid solution with at least some of the second phase. When the third alloying element is copper, at least some of the copper defines a copper-rich third phase having copper and silicon, and at least some of this third phase is located adjacent some of the second phase. A "copper-rich" phase is a phase having at least 50 at. % copper (e.g., at least 85 at. % Cu). When the third alloying element is silver, at least some of the silver may be in metallic form, and at least some of this silver may be located adjacent some of the second phase.

[0013] The shape cast products may be in any suitable form. In one embodiment, the shape casting mold is in the form of a medical product, and the corresponding resulting shape cast part comprising the ternary silicon alloy is a crack-free medical product. In one embodiment, the medical product is an implantable medical product. In one embodiment, the implantable medical product is a dental implant. In another embodiment, the implantable medical product is an orthopedic implant. In one embodiment, the orthopedic implant is one of a spinal fusion implant, a large joint implant, a small joint implant, a jaw implant, and a shoulder implant. In one embodiment, the medical product is an implantable fixation device. In one embodiment, the fixation device is one of a rod, screw, plate, and combinations thereof. In one embodiment, the medical product is surgical equipment and/or instrumentation, such as scalpels, clamps, surgical tools, hemostats, and rib spreaders, among others. In one embodiment, the medical product is an incubator tray, or a liner for an incubator. In another embodiment, the medical product is a liner and/or tray for an autoclave.

[0014] These and other aspects and advantages, and novel features of this new technology are set forth in part in the description that follows and will become apparent to those skilled in the art upon examination of the following description and figures, or may be learned by practicing one or more embodiments of the technology provided for by the present disclosure.

DETAILED DESCRIPTION

EXAMPLES

A. Alloy Materials

i. Binary Si-Cr and Si-Ti alloys

[0015] Several Si-Cr eutectic binary alloys were produced, each having about 76 wt. % Si and 24 wt. % Cr. The alloys were generally produced by melting silicon (about 1292 grams, Dow Corning, PV1101) and chromium metal (about 408 grams, Atlantic Metals, Electrolytic Flake) in a graphite crucible heated with an induction power supply to form the Si-CrSi₂ eutectic mixture. The mixture was heated to about 1500°C and held for about 5 minutes to homogenize the melt, after which the melt was poured into a casting die, under vacuum, to form an ingot. The ingot generally contained a first phase comprising silicon and a second phase comprising SiCr₂ rods. Based on historical data, it is expected that the CrSi₂ rods had a diameter of about 0.5 to 5.0 micron(s) and a characteristic spacing (λ) of about 1.5 to 15 microns. The Si-Cr ingots were prone to ingot cracking.

[0016] A Si-Ti eutectic binary alloy was produced, the Si-Ti eutectic alloy having about 78.3 wt. % Si and about 21.7 wt. % Ti. The alloy was produced by melting silicon (about 1487.7 grams, Dow Corning, PV1101) and titanium metal (about 413.2 grams, Atlantic Metals, 99.99% Chunk) in a graphite crucible heated with an induction power supply to form the Si-TiSi₂ eutectic mixture. The mixture was heated to about 1500°C and held for about 5 minutes to homogenize the melt, after which the melt was poured into a casting die, under vacuum, to form an ingot. The ingots generally contained a first comprising silicon and a second phase comprising TiSi₂ lamella. Based on historical data, it is expected that the TiSi₂ lamella had a diameter of about 1 to 5 micron(s) and a characteristic spacing (λ) of about 1 to 5 micron(s). The Si-Ti ingots were prone to ingot cracking. ii. Ternary Si-Ti-Al alloys

[0017] A Si-Ti-Al ternary alloy was prepared using a vacuum melt pouring system. Specifically, a composition of about 76.7 wt. % Si (Dow Corning, PV1101), about 21.3 wt. %. Ti ( Atlantic Metals, 99.99% ) , and about 2 wt. % Al (Atlantic Metals, 99.99% ) was melted in a graphite crucible heated with an induction power supply to form the Si- TiSi₂ eutectic mixture. The mixture was heated to about 1500°C and held for about 5 minutes to homogenize the melt, after which the melt was poured into a casting die, under vacuum, to form an ingot. The Si-Ti-Al alloy realized negligible ingot cracking.

Hi. Ternary Si-Cr and Si-Ti alloys

[0018] Three ternary Si-Cr- alloys were prepared using a vacuum melt pouring system, where X is one of Ag, Cu, or Mo. Specifically, a Si-CrSi₂ eutectic alloy having a composition similar to that of the alloy of Section (A)(i), above, was melted, after which about 2 wt. % of Ag, or Cu, or Mo was added to the melt, and heated, as necessary, to form a homogenous melt. The melt was then poured into a casting die, under vacuum, to form an ingot. All of these ternary alloys realized reduced ingot surface cracking.

[0019] A fourth ternary alloy having about 0.5 wt. % Mo was also produced, and as per above. The 0.5 wt. % Mo ingot realized reduced ingot surface cracking. a. Silver

[0020] In the Si-Cr- Ag ingot, it appears that there was less silver in the cast material due to the high vapor pressure of silver during the casting process, which resulted in a surface coating on the inside of the vacuum tilt pour chamber. Despite adding silver just prior to pouring of the ingot (described above), EDS analysis of a cross section of the silver sample showed an average silver content of about 0.8 wt. % Ag (standard deviation of ±0.4 wt. % Ag. SEM/EDS and XRD results indicated that the silver was present as separate elemental metallic phase in the ingot, and the silver appeared to preferentially associated with the chromium silicide phase. About the same composition is expected if tested in accordance with the Composition Test Procedure, described below. I. Composition Test Procedure

The composition of the third alloying element of a ternary silicon alloy product is tested as follows. The entire cast product (ingot, shape casting, or otherwise) is dissolved and analyzed using ICP (inductively-coupled plasma).

b. Copper

[0021] In the Si-Cr-Cu ingot, an EDS analysis of a cross section of the copper sample showed an average copper content of about 1.1 wt. % Cu (standard deviation of ± 0.5 wt. % Cu). In the Si-Cr-Cu ingot, due to the copper addition, a copper-based phase is formed, the copper-based phase being copper rich and with a small amount of silicon. The copper- based phase tended to preferentially associate with the chromium silicide phase. Notably, the Si-Cr-Cu ingot did not pest in open air over the course of five months.

c. Molybdenum

[0022] In the 2 wt. % (target) Si-Cr-Mo ingot, EDS analysis showed that the ingot contained about 1.8 ± 1.2 wt. % Mo. The Si-Cr-Mo ingot contained a first phase of silicon, a second phase of a SiCr₂, and the molybdenum appears to be in solid solution with various ones of the CrSi₂ phase.

[0023] In the 0.5 wt. % (target) Si-Cr-Mo ingot, EDS analysis showed that the ingot contained about 0.5 ± 0.2 wt. % Mo. The Si-Cr-Mo ingot contained a first phase of silicon, a second phase of a SiCr₂, and the molybdenum appears to be in solid solution with various ones of the CrSi₂ phase.

iv. Ti6Al4V

[0024] As a point of reference, control samples of Ti6A14V alloy was purchased from McMaster-Carr, machined into test coupons, and rinsed with acetone, followed by water. Ti6A14V is commonly used in a variety of biomedical implants, including orthopedics and dental applications.

v. Samples

[0025] Samples from each of the silicon-based eutectic ingots were obtained by cutting the ingot, through thickness, and with the appropriate geometry for the various assays (described below). The samples were sonicated in water and acetone to remove any residual material (e.g., left over from the cutting).

B. Etching [0026] Samples of the alloys of (A)(i) were selectively chemically etched to create surface porosity in the sample. KOH etching was used to remove the silicon phase from some samples (approx. 50 microns removed), while HF was used to remove the CrSi₂ or the TiSi₂ silicide phase (approx. 100 microns removed), as applicable, from other samples. In either case, the samples were etched for a short amount of time in order to limit the etch depth to several microns.

C. Cytotoxicity

[0027] All of the alloys of Section A (i.e., the Si-Cr, Si-Ti, Si-Ti-Al, Si-Cr-Ag, Si-Cr- Cu, and Si-Cr-Mo alloys) were evaluated for cytotoxicity, per ISO 10993-5. None of the alloys showed a cytopathic effect (i.e., had a cytotoxicity rating of zero (0)).

D. Leaching studies

[0028] Several replicate bars (approx. 4 mm x 4 mm x 25 mm; at least triplicate specimens) were prepared from each of the above described silicon alloys of Section A. The bars were tested in accordance with the Leaching Test Procedure, described below. The test results are provided below.

I. Leaching Test Procedure

The leaching test procedure is as follows. Each alloy sample is held in an individual, isolated sample chamber having simulated body fluid. The alloy sample must have both silicon and chromium disilicide phases. If the alloy sample is derived from a ternary alloy, the alloy sample must also include any metal phase (e.g., metallic silver when the alloy is a Si-Cr-Ag alloy, molybdenum in solid solution with chromium disilicide with the alloy is a Si-Cr-Mo alloy, a copper-rich phase when the alloy is a Si-Cr-Cu alloy). The simulated body fluid is as follows:

The temperature of the simulated body fluid during testing is held at 37°C ± 1°C. Slow agitation is used to equilibrate the solution concentration (Varian 400-DS USP Dissolution Apparatus). The simulated body fluid in each chamber is removed on days 1, 3, 7, 14, 21 , and 28 of the 28-day testing period, and replaced with fresh simulated body fluid (except on day 28). For each removal, the concentration of metal and silicon in the removed simulated body fluid is measured using ICP.

• For binary Si-Cr alloys, the alloy "passes" the leaching test if no sample contains more than 5 ppm silicon and no more than 1 ppm chromium.

• For Si-Cr-Cu alloys, the alloy "passes" the leaching test if (a) all samples pass the binary Si-Cr alloy requirement (above), and (b) no sample contains more than 5 ppm of copper.

• For Si-Cr-Mo alloys, the alloy "passes" the leaching test if (a) all samples pass the binary Si-Cr alloy requirement (above), and (b) no sample contains more than 1 ppm of molybdenum.

• For Si-Cr-Ag alloys, the alloy "passes" the leaching test if (a) all samples pass the binary Si-Cr alloy requirement (above), and (b) no sample contains more than 1 ppm of silver.

i. Si-Cr and Si-Ti alloys (both etched and un-etched)

[0029] For the Si-Cr and Si-Ti binary alloys, both etched and un-etched, neither chromium nor titanium ions were detected during the ICP analysis. The un-etched Si-Cr alloy did show a statistically higher concentration of silicon (+1 ppm) in solution relative to the blank cell control on days 14 and 28. However, this low rate of silicon loss may be beneficial in an implant as it will be non-toxic and may actually allow bone to grow and form a strong interface. Likewise, the HF etched Si-Cr samples did realize slightly higher levels of silicon in solution, but not statistically different from the control (p = 0.06 on day 21, p = 0.07 on day 28) due to a high degree of variance. Similarly, the KOH etched Si-Cr samples showed a statistically significant increase in silicon leaching (+2 ppm) on day 28.

ii. Si-Ti-Al alloy [0030] Visual observation of the Si-Ti-Al alloy showed evidence of corrosion. A white crystalline material formed on the outer surface of the Si-Ti-Al samples, and the samples were brittle. Testing of the Si-Ti-Al samples was discontinued based on the brittle nature of the materials upon exposure to simulated body fluid.

Hi. Si-Cr-Cu alloy

[0031] The Si-Cr-Cu alloy samples turned the simulated body fluid blue, indicating copper ion leaching. This observation was confirmed by ICP results, which showed copper concentration was significantly higher (~ 200 ppm on average) than control samples for day 14 onward. The high rate of copper leaching may make the material unsuitable for long-term implant use, but the material could potentially find use in short- term applications or as a minor surface coating component. For example, the copper silicide might be useful as a sustained release antimicrobial coating.

iv. Si-Cr-Ag alloy and the 2 wt. % Si-Cr-Mo alloy

[0032] ICP analysis indicated that neither silver nor molybdenum were in solution over the course of the 28 day leaching experiments.

E. Antimicrobial testing

[0033] Si-Cr-Mo alloys (both the 0.5 wt. % (target) and the 2.0 wt. % (target)) were submitted for antimicrobial testing against Pseudomonas aeruginosa (ATCC 9027), and also in accordance with ISO 22196. The 0.5 wt. % Mo alloy did not realize a decrease in bacterial count relative to the control. The 2.0 wt. % Mo alloy realized a 1.3 fold (log) reduction in bacteria.

[0034] Similar tests were conducted in accordance with ISO 22196 relative to the bacteria staphylococcus epidermidis, a bacterial strain that is often associated with implant infections. Various ones of the silicon alloys were tested. Neither the Si-Cr nor the Si-Ti alloys were found to have intrinsic antimicrobial properties. However, all of the Si-Cr-Cu, the Si-Cr-Mo, and the Si-Cr-Ag alloys showed antimicrobial properties.

F. Cell attachment/proliferation

[0035] Cell attachment of Dl ORL UVA cells (ATCC) to various ones of the alloys was tested in accordance with the cell attachment procedure, described below. The results are provided below.

I. Cell Attachment Test Procedure The cell attachment procedure is as follows. Dl ORL UVA cells (ATCC) are used. The cells are to be used between passage 4 and 20 and are expanded in Dulbecco's Modified Eagle's Medium (DMEM) with 10% fetal bovine serum and 100 U/ml penicillin/streptomycin. Cells are passaged using 0.5% trypsin-EDTA and counted using a hemacytometer. Alloy sample are to be sterilized using an autoclave (exposed to a temperature of about 121°C for at least 30 minutes) after which the samples are to be transferred to individual wells in a 24-well plate. A polystyrene sample is to be used in one of the wells as a control. Cells are to be seeded in each well at a concentration of ~ 5 x 10⁴ cells per well. Samples are to be cultured for 5 days and then fixed with 10% neutral buffered formalin (Sigma), permabilized with 0.1 % Triton X 100 (Sigma), and stained with DAPI (Invitrogen). The samples are then imaged on a Leica fluorescent microscope and the number of cells on the surface of the samples is to be determined using Image J software (NIH).

• An alloy "passes" the cell attachment test if the alloy realizes at least 90% of the cell attachment density of the polystyrene control. For instance, if the polystyrene control realized a cell attachment density of 2398 cells per mm², then the any alloy realizing a cell attachment density of 2158 cells/mm², or higher, would pass the cell attachment test.

[0036] As shown in Table 1, below, cells readily attached to the un-etched Si-Cr and Si-Ti samples. However, significantly fewer cells attached to the HF etched samples. This lower amount of cell attachment may be due to surface topography and/or the cells may be able to more readily dissolve high surface area silicon. The KOH etched version of the Si-Cr alloy also had low cell attachment as compared to the un-etched sample. In contrast, the KOH etched Si-Ti alloy had a large number of cells on the surface of the test sample. Given the high cell density on the surface of the KOH etched Si-Ti alloy, it is likely that some of the cells grew into the pores of the material.

Table 1: Cell density on substrates after 5 days of culture

G. Osteoconductivity

[0037] The ability of a medical implant to support bone ingrowth is referred to as osteoconductivity. To test for osteoconductivity, various ones of the samples were cultured with mesenchymal stem cells (MSC). MSC can turn into bone (via osteoblast cells, which synthesize bone), cartilage (chondrocytes), or fat (adipocytes), depending on culture exposure conditions. In the present example, alizarin red stain was used to determine if calcium mineral has been deposited onto the surface of a material. MSCs were cultured on each of the test materials for 28 days in cell osteogenic differentiation medium (composition below). The samples were then fixed in neutral buffered formalin, stained using Alizarin Red S (Alcon), and imaged with a Zeiss SteREO Lumar vl2 microscope.

I. Calcium Mineralization Test Procedure

A 1 cm x 1 cm coupon of the alloy is placed in the "Cell osteogenic differentiation medium", described below, for 28 days, with the cell osteogenic differentiation medium being replaced with fresh medium every 2-3 days. The coupon is then removed and then fixed in neutral buffered formalin, rinsed with DI water, stained using Alizarin Red S (Alcon), and imaged under DI water. The whole 1 cm x 1 cm coupon is imaged with a Zeiss SteREO Lumar vl2 microscope using a Axiocam HRc high resolution color camera (12MP) using Axio Vision or Zeiss Zen software. Image analysis software (Olympus Stream Motion) was used in order to determine what percentage of the coupon's surface is covered by calcium mineralization. The total amount of pixels for the 1 cm x 1 cm coupon image should be around 1.4 million total pixels, with each pixel having a size of about 70 μιη². All red pixels are counted, after which the amount of red pixels is divided by the total amount of pixels to determine the percentage covered by red pixels. Duplicate coupons are measured, and the results are averaged. Whether a pixel is "red" is determined by the human eye. "Pink" pixels are a species of red, and are thus counted.

Cell osteogenic differentiation medium :

• 100 ug/ml ascorbic acid

• 5 mM beta-glycerophosphate

• 90% DMEM-low glucose, without glutamine, modified to contain o 4 mM L-glutamine

o 3.7 g/L sodium bicarbonate

o 1 mM sodium pyruvate

• 10% fetal bovine serum

• 100 U/ml penicillin-streptomycin

[0038] The un-etched Si-Cr binary alloy showed a large amount of calcium mineralization on the surface after 28 days (average of 71%). Conversely, there was no significant mineralization on the surface of the un-etched Si-Ti binary alloy (0%). Likewise, the HF etched Si-Cr (0%>) and Si-Ti (0%>) binary alloys did not show any significant calcium mineral deposition.

[0039] The Si-Cr-Cu alloy was brittle and only showed staining along grain boundaries. For the Si-Cr-Ag alloy, it appeared that cells did not initially adhere to the sample; rather the cells seemed to have grown onto the sample from the periphery.

[0040] In contrast, calcium mineralization appeared to be fairly uniform across the surface of the 2 wt. % Si-Cr-Mo alloy samples (average of 82%). Calcium mineralization also appeared to be fairly uniform across the surface of the KOH etched Si-Cr samples (single sample - 85%).

[0041] While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.

Claims

CLAIMS What is claimed is:

1. A ternary silicon alloy comprising:

a first alloying element, wherein the first alloying element is silicon;

a second alloying element, wherein the second alloying element is chromium; and a third alloying element, wherein the third alloying element is selected from the group consisting of silver (Ag), copper (Cu) and molybdenum (Mo);

wherein the ternary silicon alloy comprises a eutectic amount of the silicon and the chromium;

wherein the ternary silicon alloy includes an amount of the third alloying element sufficient to realize at least one of (a) improved castability and (b) biomedical

enhancement.

2. The ternary silicon alloy of claim 1, wherein the third alloying element is molybdenum.

3. The ternary silicon alloy of claim 2, comprising from 0.1 to 5.0 wt. % Mo.

4. The ternary silicon alloy of claim 2, comprising from 0.6 to 3.0 wt. % Mo.

5. The ternary silicon alloy of claim 1, wherein the third alloying element is copper.

6. The ternary silicon alloy of claim 5, comprising from 0.1 to 5.0 wt. % Cu.

7. The ternary silicon alloy of claim 5, comprising from 0.5 to 2.0 wt. % Cu.

8. The ternary silicon alloy of claim 1, wherein the third alloying element is silver.

9. The ternary silicon alloy of claim 8, comprising from 0.1 to 10.0 wt. % Ag.

10. The ternary silicon alloy of claim 8, comprising from 0.4 to 1.2 wt. % Ag.

11. A shape cast product made from the ternary silicon alloy of claim 2, wherein the shape cast product comprises:

a first phase consisting essentially of silicon; and

a second phase comprising chromium disilicide;

wherein the shape cast product comprises a eutectic aggregation of the first phase and the second phase;

wherein at least some of the molybdenum is in solid solution with at least some of the second phase.

12. A shape cast product made from the ternary silicon alloy of claim 5, wherein the shape cast product comprises:

a first phase consisting essentially of silicon; and

a second phase comprising chromium disilicide; wherein the shape cast product comprises a eutectic aggregation of the first phase and the second phase;

wherein at least some of the copper defines a copper-rich third phase having copper and silicon, wherein at least some of the third phase is located adjacent some of the second phase.

13. A shape cast product made from the ternary silicon alloy of claim 8, wherein the shape cast product comprises:

a first phase consisting essentially of silicon; and

a second phase comprising chromium disilicide;

wherein at least some of the silver is in metallic form, and wherein at least some of the silver is located adjacent some of the second phase.

14. The shape cast product of any of claims 11-13, wherein the shape cast product is in the form of a medical product.

15. The shape cast product of claim 14, wherein the medical product is an implantable medical product.

16. The shape cast product of claim 15, wherein the implantable medical product is a dental implant.

17. The shape cast product of claim 15, wherein the implantable medical product is an orthopedic implant.

18. The shape cast product of claim 17, wherein the orthopedic implant is one of a spinal fusion implant, a large joint implant, a small joint implant, a jaw implant, and a shoulder implant.

19. The shape cast product of claim 15, wherein the implantable medical product is an implantable fixation device.

20. The shape cast product of claim 19, wherein the fixation device is one of a rod, screw, plate, and combinations thereof.