WO2015078930A1

WO2015078930A1 - Electrolyte composition and method for the electropolishing treatment of nickel-titanium alloys and/or other metal substrates including tungsten, niob and tantal alloys

Info

Publication number: WO2015078930A1
Application number: PCT/EP2014/075710
Authority: WO
Inventors: Ulf Fritz
Original assignee: Abbott Laboratories Vascular Enterprises Limited
Priority date: 2013-11-28
Filing date: 2014-11-26
Publication date: 2015-06-04
Also published as: EP2878713A1; EP3074553A1

Abstract

The present invention relates to an electrolyte composition and an electropolishing method in the presence of said composition, which is directed towards the surface treatment of medical devices. The electrolyte composition comprises methanesulfonic acid and a surface selective (anode specific) masking agent. The medical devices in question are formed from high-strength medical grade alloys, wherein the metals comprising said alloys are selected from a group of Nickel, Titanium, Cobalt, Chromium, Tantalum, Niobium, Tungsten, and whereas said alloys may contain one or more of said metals.

Description

TITLE

Electrolyte composition and method for the electropolishing treatment of Nickel- Titanium alloys and/or other metal substrates including tungsten, niob and tantal alloys

BACKGROUND OF THE INVENTION

The present invention relates to an Electrolyte composition and to a method for electropolishing in the presence of said electrolyte composition, which is directed towards the surface treatment of medical devices. The electrolyte composition comprises methanesulfonic acid and at least one phosphonic acid derivative. The medical devices in question are formed from high-strength medical grade alloys, wherein the metals comprising said alloys are selected from a group of Nickel, Titanium, Cobalt, Chromium, Tantalum, Niobium, Tungsten, and whereas said alloys may contain one or more of said metals.

FIELD OF THE INVENTION

Nitinol, a Nickel-Titanium alloy (often abreviated: NiTi) is used in a wide variety of medical device applications, because of a favourable combination of mechanical and surface properties, which include among others, shape memory capability, superelasticity and increased corrosion resistance.

Concerning the use of NiTi in medical device applications, several studies have demonstrated that implants composed of NiTi exhibit a good biocompatibility along with good corrosion resistance. However, concerns exist, that the high Nickel content within the NiTi alloy along with potential dissolution during corrosion could pose potential health risks [S. A. Shabalovskaya, Surface, corrosion and biocompatibility aspects of Nitinol as an implant material, Bio-Med. Mater. Eng. 12 (2002) 69-109]. Nitinol is available in different surface conditions, depending on the type of treatment employed. Typical commercially available surface conditions are Native, Sandblasted, Black Oxide, Air Aged, Heat Treated, Electropolished, and Surface Passivated.

It is known, that conventional surface finishing techniques, such as grinding and polishing can introduce surface defects which actually promote localized corrosion upon contact with physiological environments and / or test electrolytes. Phenomena such as pitting and crevice corrosion have been reported for NiTi surfaces when submitted to such conventional finishing techniques. These phenomena are highly undesirable, due to their impact on the fatigue life of medical devices formed from NiTi. Also, it is known that cellular adhesion, migration and proliferation often can be triggered by increased implant surface roughness, because surface defects, scratches and the like can act as an anchoring motif for cells. In the case of vascular implants, such as coronary or peripheral stents, excessive neointima formation and subsequent cellular growth could minder the clinical success following implantation. Therefore, it is highly desirable that the implant surface is as smooth as possible, so that the cellular response is accordingly minimized.

Surface treatments, such as electropolishing and surface passivation, can be performed on the NiTi implants, to improve corrosion resistance (and thus the ability to decrease Nickel ion leaching from the surface) because it has been recognized that the corrosion resistance of NiTi is very dependent upon the quality and quantity of the passive oxide layer formed on its surface. These surface treatment techniques also have a benign effect on the ability to 'heal' the Titanium oxide layer during deployment, as it is actually known that electropolished and passivated Nitinol exhibits at least an equivalent static corrosion behaviour and ability to resist and repassivate (repair) surface damage when compared with 316L stainless steel [Shabalovskaya, 2002].

Additionally, the ability of the aforementioned surface treatment techniques to minimize the implant material's surface corrugation and roughness is a crucial factor for clinical device performance following implantation. Since electropolishing is capable of rendering the implant surface with a smooth surface finish as well as reducing the number and magnitude of potential surface defects, the implants flow characteristics and fatigue life performance will accordingly be improved.

Therefore, the preferred surface treatments involve electropolishing and surface passivation of the NiTi implant, in an effort to achieve a smooth implant surface finish as well as building both a Nickel- depleted, passive Titanium oxide layer. The surface treatments are intended to generate a titanium oxide layer which a) shares the same biocompatibility characteristics as a native Titanium oxide layer and b) renders the surface with an increased corrosion resistance and c) minders the surfaces' ability to leach out Nickel - ions [Shabalovskaya, 2002].

Still, when considering the electrolyte compositions of the art and their use in standard electropolishing methods many disadvantages persist, in that electrolyte compositions of the art allow formation of passive oxide layers with uneven thickness during the electropolishing process, thus reducing metal dissolution rates and therefore hindering formation of a desirable diffusion layer on the substrate. The presence of the oxide layer thus hinders effective electropolishing, yielding inferior results (rough surfaces, uneven polishing effect etc.). In practiced art, the formation of oxide layers is often addressed by the incorporation of specific agents into the electrolyte formulation that are capable of dissolving away the oxide layer. Such agents typically include, for example, hydrofluoric acid and organic or inorganic salts thereof. Some electrolyte formulations have addressed the suppression of oxide layer formation via the incorporation of a methylating species as a surface masking agent, such as dimethyl sulphate, which is a known carcinogenic and mutagenic substance. Other formulations that have been known to produce good electropolished surfaces include very strong acids, such as perchloric acid in combination with organic solvents such as n-butanol, the particular combination requiring strict temperature control to prevent explosions. These agents are of a rather hazardous, volatile or corrosive nature, which can represent itself as both an undesired health- as well as an environmental hazard.

It would therefore be desirable to obtain an electrolyte composition capable of generating a smooth, even, protective film on the surface of the material to be electropolished during electropolishing methods, and which composition can suppress or reduce and thus control the formation of undesired oxide films during electropolishing. Common surface masking agents in the art are typically a) rather unspecific as to the mechanism of action and binding mode incurred on the electrode or work piece surface(s), b) require a certain minimum concentration within the electrolyte composition in order to be effective, and are c) often quantitatively consumed/spent during electropolishing operations in relation to the amount of work piece material dissolved.

It would thus be highly desirable to employ a selective surface masking agent which would allow for a

(I) targeted deposition of a monolayer or multilayer film on the electrode and/or work piece surface, thus

(II) allowing the surface masking agent to be used at a much lower concentration ranges (typical for use in monolayer generation e.g. in the 0.1 - 10 millimolar range). Also, it would be desirable to identify a selective surface masking agent that would (III) adsorb both rapidly and quantitatively on the surface within the time span of the electropolishing operation, that could be (IV) 'tailored' to the specific surface chemistries of both work piece and electrode surface involved, and (V) that would prolong the work life of the electrolyte composition. The surface masking agent should also have a protective effect on the electrode surfaces, in that sludge formation and dissolution of the electrode surfaces should be reduced, thus prolonging the work life of electrode materials in the process, and allowing cheaper electrode materials, such as stainless steel (as compared to inert, but very expensive materials such as gold or platinum) to be used for the electrodes and contacting circuits.

This object is achieved by the electrolyte compositions of the present invention. BRIEF SUMMARY OF THE INVENTION

In a first aspect the invention refers to a electrolyte composition, comprising methane sulfonic acid; and at least one phosphonic acid derivative; wherein said phosphonic acid derivative contains at least three (n>2) phosphonic acid groups.

In a preferred embodiment of the invention the at least one phosphonic acid derivative has the structure according to Formula I:

(I)

wherein

Ri is a substituted C1-3 alkyl group; wherein substituents are selected from -PO(OH)2 or NR4Rb, wherein Px4 and Rb, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -PO(OH)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)₂ groups;

R2 is a substituted C1-3 alkyl group; wherein substituents are selected from -PO(OH)2 or NR4Rb, wherein R4 and Rb, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -PO(OH)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)2 groups;R3 is a substituted C1-3 alkyl group; wherein substituents are selected from PO(OH)2 or NR4Rb, wherein R4 and Rb, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -PO(OH)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)2 groups; with the proviso that the compound according to formula (I) contains at least three (n>2) -PO(OH)2 groups.

In another preferred embodiment the at least one phosphonic acid derivative is selected from Amino- tris-(methylene phosphonic acid) (ATMP), Ethylenediamine tetra(methylene phosphonic acid) (EDTMP), Tetramethylenediamine tetra (methylene phosphonic acid) (TDTMP), Diethylenetriamine- penta(methylenephosphonic acid (DTPMP), Hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP), and phytic acid (IP6) or respective salts thereof.

In another preferred embodiment the concentration of methane sulfonic acid is between 20-98% (v/v).

In another preferred embodiment the concentration of the at least one phosphonic acid derivative is between 0.1 % and 10% (m/v).

In another preferred embodiment the at least one phosphonic acid derivative is Ethylenediamine tetra(methylene phosphonic acid) (EDTMP).

In another preferred embodiment the composition further contains at least one additional additive selected from the group of viscosifying agents, chelating agents, stabilizer agents, buffering agents; and/or at least one other helping agents, selected from solvents and water.

In another preferred embodiment the composition contains polyethylene glycol as a viscosifying agent.

In a very preferred embodiment the composition is consisting of

20-40% (v/v) methane sulfonic acid,

0,1-5% (m/v) Ethylenediamine tetra(methylene phosphonic acid) (EDTMP),

1% (m/v) polyethylene glycol having a molecular weight of 1000g/mol (PEG-1000), an alcohol, selected from MeOH, EtOH, IprOH, and n-BuOH, and, preferably,

H2O in an amount of between 0.1-10 % (v/v).

In a second aspect the invention refers to a method of electropolishing comprising the steps of

a) bringing a metal substrate into contact with the electrolyte composition

according to the first aspect in an apparatus, said apparatus comprising: at least one cathode and a cathode current conducting member attached to said cathode;

at least one anode and an anode current conducting member; and b) supplying a voltage difference between said cathode current conducting member and said anode current conducting member.

In a preferred embodiment the metal substrate is immersed in the electrolyte solution. In another preferred embodiment the metal is selected from Nickel Titanium, Cobalt, Chromium.Tantalum, Niobium, Tungsten.Vanadium, or alloys thereof, wherein said alloys can contain one or more of said metals.

In another preferred embodiment the metal is a nickel, titanium or an alloy thereof, preferably a nickel- titanium alloy.

In another preferred embodiment the nickel-titanium alloy is Nitinol.

In a very preferred embodiment the metal substrate is a medical device, preferably a stent.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 :

Schematic Drawing of Electropolishing Cell with components denoted hereafter as

100 Implant (Anode)

110 Electrolyte

120 Magnetic Stirring Rod

130 Magnetic Stirrer

140 Thermostate Bath

150 Thermostate Heat Transfer Fluid (Inlet/Outlet marked by Arrows)

160 Thermostate Casing

170 Cathode

180 Wiring to Negative Potential

190 Wiring to Positive Potential

Figure 2:

Molecular Structure of HEDP Figure 3:

Molecular Structure of ATMP

Figure 4:

Molecular Structure of EDTMP Figure 5:

Molecular Structure of DTPMP Figure 6:

Proposed Surface Binding Mechanism

with the following elements contained in the drawing

600 Implant Surface (NiTi) with surface bound EDTMP

610 Nitrogens complexing Ni

620 Phosphonate Group(s) binding to Titanium

Figure 7:

Surface Quality of NiTi Implant prior to Electropolishing via Example 1 (Top view, visualized at 10Ox Magnification Level)

Figure 8:

Surface Quality of NiTi Implant after Electropolishing via Example 1 (Top view, visualized at 10Ox Magnification Level)

Figure 9:

Surface Quality of NiTi Implant prior to Electropolishing via Example 1 (Edge on - view, visualized at 300x Magnification Level)

Figure 10:

Surface Quality of NiTi Implant after Electropolishing via Example 1 (Edge-on view, visualized at 300x Magnification Level) Figure 11 :

Figure 12:

Figure 13:

Surface Quality of NiTi Implant after Electropolishing via Example 2 (Edge-on view, visualized at 500x Magnification Level)

Figure 14:

Surface Quality of NiTi Implant after Electropolishing via Example 3 (Edge-on view, visualized at 500x Magnification Level)

Figure 15:

Surface Quality of NiTi Implant after Electropolishing via Example 4 (Edge-on view, visualized at 500x Magnification Level)

Figure 16:

Surface Quality of NiTi Implant after Electropolishing via Example 5 (Edge-on view, visualized at 500x Magnification Level)

Figure 17:

Surface Quality of Nickel foil before Electropolishing via Example 6 (Edge-on view, visualized at 200x Magnification Level)

Figure 18:

Surface Quality of Nickel foil after Electropolishing via Example 1 (Edge-on view, visualized at 200x Magnification Level) DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the invention refers to an electrolyte composition, comprising methane sulfonic acid; and at least one phosphonic acid derivative; wherein said phosphonic acid derivative contains at least three (n>2) phosphonic acid groups.

Phosphonic acid derivatives which contain at least three (n>2) phosphonic acid groups possess a high binding affinity to metal surfaces, particularly those that form multivalent metal ions during anodic dissolution, such as Titanium, Chromium, Tungsten, and the like, with the phosphonic acids having the ability to form Mono- or Multilayers, and on the other hand, phosphonic acid derivatives which contain at least three (n>2) phosphonic acid groups also possess good complexation capability for Nickel or other multivalent ions.

If in the following, surface passivation agents, complexing agents, or masking agents of the invention are mentioned, the respective disclosure thus reads on phosphonic acid derivatives which contain at least three (n>2) phosphonic acid groups.

Also, any mentioning of phosphonic acid derivatives, if not indicated otherwise, refers to phosphonic acid derivatives which contain at least three (n>2) phosphonic acid groups.

The electrolyte composition of the invention is unique in that the selected complexing agents are predominantly surface bound, i.e. selective to the anode respectively work piece or medical device surface. As compared to regular complexing agents, phosphonic acid derivatives which contain at least three (n>2) phosphonic acid groups, serve as surface selective masking agents capable of rendering the medical device surface with a protective film to resist the formation of hardly soluble oxide films during electropolishing, while simultaneously being capable of complexing the metal ions released from the surface to allow for constant mass transfer into solution.

A distinctive feature of the masking agents of the invention is that, since the binding affinity of the masking agent can be qualitatively and quantitatively tailored towards the element composition of the medical device surface, a selective depletion of one or more elements of the elemental surface composition can be afforded during electropolishing. Also, the formation of hardly soluble oxide films, which can cause an inhomogeneous material dissolution from the anode (work piece, medical device surface) can be suppressed. The proposed mechanism is provided in Figure 6. While not wishing to be bound by theory, it is assumed, that the desired effect of phosphonic acid derivatives which contain at least three (n>2) phosphonic acid groups, namely the ability to form stable passivation layers on the anode surface, as well as to the ability to deplete surface-bound Nickel from the Nitinol (implant) surface by complexation, is more pronounced, the higher the magnitude of the complex formation constant of said phosphonic acid derivative is towards Nickel.

Further, it is assumed, that Tri- (Example: ATMP, Figure 3), Tetra- (Example: Ethylendiamine- tetra(methylenephosphonic acid, EDTMP, Figure 4), and Penta- (Example: Diethylenetriamine- penta(methylenephosphonic acid, DTPMP, Figure 5) and other multivalent phosphonic acids and their derivatives possess a higher effectiveness to form stable passivation layers as compared to mono- or divalent phosphonic acids, such as for example 1 -Hydroxyethane-(1 , 1 -di-phosphonic acid (HEDP, Figure 2), because by multiplication of the number of possible phosphonic acid anchor groups of a given phosphonic acid or derivative thereof, the Nitinol surface is masked more efficiently - because such compounds have a higher binding capability to form mono- or multilayers on the Nickel-depleted, Titanium-enriched anode surface.

Therefore, within the scope of the disclosure, by usage of multivalent alkyl-based phosphonic acids and / or derivatives (with n>2 acid groups) as surface selective masking agent, it is intended to facilitate a selective Nickel depletion of the anode surface while simultaneously masking the in-situ forming, Titanium-enrichened NiTi surface, so that in a subsequent passivation step, a well-defined, stable titanium oxide layer of decreased surface roughness can be formed on the electropolished NiTi implant surface.

The term "Electrolyte composition", according to the invention, refers to any liquid composition containing at least one electrolyte. An electrolyte according to the invention is a compound that is capable of forming ionized species when subjected to an electric current . Therefore, most soluble salts, acids, and bases can function as electrolytes. Some gases, such as hydrogen chloride, under conditions of high temperature or low pressure can also function as electrolytes. Electrolyte compositions can e.g. be formed when a salt is placed into a solvent such as water and the individual components dissociate due to the thermodynamic interactions between solvent and solute molecules, in a process called solvation. For example, when table salt, NaCI, is placed in water, the salt (a solid) dissolves into its component ions, according to the dissociation reaction

NaCI(s)→Na+(aq) + CI-(aq) When electrodes are placed in an electrolyte and a voltage is applied, the electrolyte will conduct electricity. Lone electrons normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the cathode consuming electrons from the anode. Another reaction occurs at the anode, producing electrons that are eventually transferred to the cathode. As a result, a negative charge cloud develops in the electrolyte around the cathode, and a positive charge develops around the anode. The ions in the electrolyte neutralize these charges, enabling the electrons to keep flowing and the reactions to continue.

It was surprisingly found that phosphonic acid derivatives which contain at least three (n>2) phosphonic acid groups can be used as surface passivation or masking agents in electrolyte compositions, which are capable of generating a protective film or passivation layer on the surface of the material or substrate during electropolishing. In particular, it was found that phosphonic acid derivatives which contain at least three (n>2) phosphonic acid groups, used as surface passivation or masking agents in electrolyte compositions, are capable of forming stable passivation layers on the anode surface, as well as to the ability to deplete surface-bound Nickel from the Nitinol (medical device) surface by complexation, when employed in electropolishing-methods of Nitinol-substrates, Thus employing the electrolyte compositions of the invention can protect the anode surface from formation of undesired oxide films during electropolishing - and avoid or reduce oxygen generation, gassing, in-situ oxide film formation and suppression of water at the anode interface While not wishing to be bound by theory, the surface masking agent competes with present oxygen on a molecular level for the anode surface, thus effectively reducing or suppressing said oxide layer formation tendency either in the absence or presence of water. Water is the main source for gassing effects in the form of both hydrogen and oxygen generation during electropolishing operations at the electrode surfaces. Hydrogen formation can cause so-called hydrogen embrittlement, which can negatively affect mechanoelastical properties and premature failure of either electrodes and/or work piece due to material fatigue, while oxygen formation increases the level of dissolved oxygen in the electrolyte, favoring oxide film formation at the electrode interfaces. Generally gas formation will physically prevent the contact of the electrolyte with the electrodes and /or work pieces by forming gas bubbles on their surfaces, thus leading to an uneven material dissolution or a generally less controlled material ablation process. While water-less electrolyte formulations are desirable on the basis of the given argumentation, water can and is not always excluded in electrolyte formulations, for the following reasons: Many electrolyte components are hygroscopic (Examples include sulfuric acid, methane sulfonic acid, ethylene glycol derivatives) and will attract water over prolonged exposure to ambient conditions. In some electrolyte formulations, water acts as solvent for electrolyte additives. It also represents a cheap and easily available solvent. While not wishing to be bound by theory, it may actually be needed to facilitate mass transport of water- soluble byproducts of the electropolishing process away from the electrode surfaces. Hence, the role of the surface masking agent is not to suppress the presence on water in the electrolyte formulation, but rather to suppress effects of gassing at the electrode interface, along with the dissolution and/or complexation of hardly soluble oxide species away from the surface .

The term "Methane sulfonic acid', according to the invention, refers to a compound with the chemical formula CH3SO3H

The term "Phosphonic acid group", according to the invention, refers to a chemical group having the following structure: -PO(OH)2. Thus, according to the invention, phosphonic acid groups can be defined as -PO(OH2) groups which, in a preferred embodiment of the invention, are covalently linked to a carbon atom, e.g. as they replace a hydrogen atom on a carbon atom, or in other words, the -PO(OH2) groups are substituents of aliphatic radicals or groups, alkyl-, alkenyl-, alkynyl-, cycloalkyl- , heterocyclyl or aryl-groups, as defined herein.

The term "Phosphonic acid derivative" or "phosphonates", according to the invention, refer to any organic compound containing at least three (n>2) -PO(OH)2 groups or to any organic compound in which at least three (n>2) -PO(OH2) groups are covalently linked to (a) carbon atom(s), e.g. as they replace a hydrogen atom on a carbon atom, or in other words, the -PO(OH2) groups are substituents of aliphatic radicals or groups, alkyl-, alkenyl-, alkynyl-, cycloalkyl- , heterocyclyl or aryl-groups, as defined herein.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[PO(OH)2]_n with n>2, wherein R is an aliphatic group, a cycloalkyl group, a heterocyclic group, or an aryl group.

The phosphonic acid derivative or phosphonate may either be used in its protonated state or in form of a salt.The respective counter ion may either be an inorganic or organic cation.

In another aspect of the invention, the structural aspects of the term "phosphonic acid group", as defined herein, may interchangeably be applicable to phosphinic acid groups R-P(OH)3 , therefore, any disclosure, aspect, embodiment or definition of the invention regarding phosphonic acid derivatives having phosphonic acid groups also applies to the respective compounds having phosphinic acid groups instead of phosphonic acid groups. The term "aliphatic group", according to the present invention, refers to alkyl-, alkenyl- or alkynyl-groups.

In the context of this invention, "alkyl", "alkyl radical' or -group is understood as meaning saturated, linear or branched hydrocarbons, which can be unsubstituted or mono- or polysubstituted. Alkyl groups encompass e.g. -CH3 and -CH2-CH3. In these radicals, Ci-2-alkyl represents Ci- or C2-alkyl, Ci-3-alkyl represents C1-, C2- or C3-alkyl, Ci-4-alkyl represents C1-, C2-, C3- or C4-alkyl, Ci-5-alkyl represents C1-, C2-, C3-, C4-, or C5-alkyl, Ci-6-alkyl represents C1-, C2-, C3-, C4-, C5- or C6-alkyl, Ci-7-alkyl represents Ci- , C2-, C3-, C4-, C5-, C6- or C7-alkyl, Ci-8-alkyl represents C1-, C2-, C3-, C4-, C5-, C6-, C7- or Cs-alkyl, C1-9- alkyl represents C1-, C2-, C3-, C4-, C5-, C6-, C7-, Ce, or Cg-alkyl; and Ci-10-alkyl represents C1-, C2-, C3-, C4-, C5-, C6-, C7-, Ce-, C9- or Cio-alkyl.

The term "alkenyl groups" according to the invention refers to, unsaturated, linear or branched, hydrocarbons, which can be unsubstituted or mono- or polysubstituted, like e.g. -CI- CH-CH3. In these radicals, C2-3-alkenyl represents C2- or C3-alkenyl, C2-4-alkenyl represents C2-, C3- or C₄-alkenyl,

alkenyl represents C2-, C3-, C4-, or Cb-alkenyl, C2-6-alkenyl represents C2-, C3-, C4-, C₀- or Ce-alkenyl, C2 -^-alkenyl represents C2-, C3-, C4-, C₀-, C6- or Cralkenyl, C2-e-alkenyl represents C2-, C3-, C4-, C₀-, C6- , Ci- or Ce-alkenyl, C2-9-alkenyl represents C2-, C3-, C4-, C₀-, C6-, Ci-, Ce, or Cg-alkenyl; and C2-io-alkenyl represents C2-, C3-, C4-, C₀-, C6-, d-, Ce-, Cg- or Cio-alkenyl.

The term "alkynyl groups" according to the invention refers to, unsaturated, linear or branched, hydrocarbons, which can be unsubstituted or mono- or polysubstituted, like e.g. -CEC-Chb. In these radicals, C2-3-alkynyl represents C2- or C3-alkynyl, C2 4-alkynyl represents C2-, C3- or C₄-alkynyl, C2-5- alkynyl represents C2-, C3-, C4-, or Cs-alkynyl, C2-6-alkynyl represents C2-, C3-, C4-, C5- or C6-alkynyl, C2- 7-alkynyl represents C2-, C3-, C4-, C5-, C6- or Cz-alkynyl, C2-e-alkynyl represents C2-, C3-, C4-, C5-, C6-, C7- or Cs-alkynyl, C2-9-alkynyl represents C2-, C3-, C4-, C5-, C6-, C7-, Ce, or Cg-alkynyl; and C2 10-alkynyl represents C2-, C3-, C4-, C5-, C6-, C7-, Ce-, Cg- or Cio-alkynyl.

An "aryl group", according to the present invention, is understood as meaning an aromatic ring.

Preferred aryl groups are phenyl, naphthyl, fluoranthenyl, fluorenyl, tetralinyl or indanyl, which can be unsubstituted or monosubstituted or polysubstituted. A "heterocyclic group", according to the present invention, is understood as meaning a heterocyclic ring system which contain one or more heteroatoms from the group consisting of nitrogen, oxygen, phosphorus, and/or sulfur in the ring or ringsystem, and can also be mono- or polysubstituted.

Preferred heterocyclyl groups are furan, thiophene, pyrrole, pyridine, piperazine, pyrimidine, pyrazine morpholine,

In the context of this invention "cycloalkyi group" or "radical" is understood as meaning saturated and unsaturated (but not aromatic) cyclic hydrocarbons (without a heteroatom in the ring), which can be unsubstituted or mono- or polysubstituted. Furthermore, C₄ 5-cycloalkyl represents C4- or Cs-cycloalkyl, C₄-6-cycloalkyl represents C4-, C5- or C6-cycloalkyl, C₄-7-cycloalkyl represents C4-, C5-, C6- or C7- cycloalkyl, C₄-8-cycloalkyl represents C4-, C5-, C6-, C7- or Cs-cycloalkyl, C₄-5-cycloalkyl represents C4- or Cs-cycloalkyl, C₄-6-cycloalkyl represents C4-, C5- or C6-cycloalkyl, C₄-7-cycloalkyl represents C4-, C5-, C6- or C -cycloalkyl, C₄-8-cycloalkyl represents C4-, Cb-, C6- C/- or Cs-cycloalkyl, Cb-6-cycloalkyl represents Cb- or C6-cycloalkyl and Cb-rcycloalkyl represents Cb-, C6- or Crcycloalkyl. However, mono- or polyunsaturated, preferably monounsaturated, cycloalkyls also in particular fall under the term cycloalkyi as long as the cycloalkyi is not an aromatic system.

Preferred cycloalkyi groups are cyclopropyl, 2-methylcyclopropyl, cyclopropylmethyl, cyclobutyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, cycloheptyl, and cyclooctyl. Particularly preferred is cyclohexyl.

In connection with aliphatic radicals or groups, alkyl-, alkenyl-, alkynyl-, cycloalkyi- , heterocyclyl or aryl- groups - unless defined otherwise - the term "substituted" in the context of this invention is understood as meaning replacement of at least one hydrogen radical by -PC Oh ) groups, F, CI, Br, I, NH, NH2, NH3, SH or OH; within that "monosubstituted" means the substitution of exactly one hydrogen radical, whereas "polysubstituted" means the substitution of more than one hydrogen radical with "polysubstituted" radicals being understood as meaning that the replacement takes effect both on different and on the same atoms several times with the same or different substituents, for example three times on the same C atom, as in the case of CF3, or at different places, as in the case of e.g. -CH(OH)- CH=CH-CHC .

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is selected from the group consisting of a substituted or unsubstituted aliphatic group, or a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted aryl group, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises n>0 primary, secondary or tertiary amino groups.

The expression "wherein in R one or more "C-atoms" may be replaced by a nitrogen" refers to the possibility that in a given linear, branched or cyclic organic molecule, e.g. an aliphatic group, an alkyl group, an alkenyl group, an alkenyl group, a cycloalkyl group, a heterocyclic group, an aryl group etc. as defined herein, a carbon atom can be replaced by a nitrogen atom, such that, in relevant part, the hydrocarbon molecule is modified from CH2-CH2-CH2 to CH2-NH-CH2, or to CH2-NHR-CH2, or the like, as will be readily understood by the skilled person.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[PO(OH)2]_n with n>2, wherein R is selected from the group consisting of an substituted or unsubstituted, linear or branched, alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted heterocyclic group or a substituted or unsubstituted aryl group; wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises n>0 primary, secondary or tertiary amino groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is selected from the group consisting of a substituted or unsubstituted, linear or branched, C1-10 alkyl, C2-10 alkenyl, C2-10 alkynyl; wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises n>0 primary, secondary or tertiary amino groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R represents a substituted or unsubstituted, linear or branched, C1-10 aminoalkyl, C2-10 aminoalkenyl, C2-10 aminoalkynyl; a substituted or unsubstituted, linear or branched, C1-10 iminoalkyl, C2-10 iminoalkenyl, C2-10 iminoalkynyl, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises n>0 primary, secondary or tertiary amino groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is an aryl group selected from substituted or unsubstituted, cyclic C4-12 aryl, or R is a substituted or unsubstituted C4-8 cycloalkyl group, or a substituted or unsubstituted C4-8 heterocyclyl group, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises n>0 primary, secondary or tertiary amino groups.

In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is an aliphatic group selected from a substituted or unsubstituted, linear or branched, C1-10 aminoalkyl, C2-10 aminoalkenyl, C2-10 aminoalkynyl, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises at least one primary, secondary or tertiary amino groups..

In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is an aliphatic group selected from a substituted or unsubstituted, linear or branched, C1-10 aminoalkyl, C2-10 aminoalkenyl, C2-10 aminoalkynyl, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises at least two primary, secondary or tertiary amino groups..

In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is an aliphatic group selected from a substituted or unsubstituted, linear or branched, C1-10 aminoalkyl, C2-10 aminoalkenyl, C2-10 aminoalkynyl, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises at least three primary, secondary or tertiary amino groups..

In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is an aliphatic group selected from a substituted or unsubstituted, linear or branched, C1-10 aminoalkyl, C2-10 aminoalkenyl, C2-10 aminoalkynyl, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein the number of primary, secondary or tertiary amino groups in R equals the number of phosphonic acid groups in the phosphonic acid derivative .

In a very preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is an aliphatic group selected from a substituted or unsubstituted, linear or branched, C1-10 aminoalkyl, C2-10 aminoalkenyl, C2-10 aminoalkynyl, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein the number of primary, secondary or tertiary aminogroups in R equals the number of phosphonic acid groups in the phosphonic acid derivative, and wherein the phosphonic acid groups each bind covalently to an aminogroup.

In an even even more preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is an aliphatic group selected from a substituted or unsubstituted , branched, C1-10 aminoalkyl, C2-10 aminoalkenyl, C2-10 aminoalkynyl, wherein in R one or more "C-atoms" may be replaced by a nitrogen, wherein the number of primary, secondary or tertiary aminogroups in R equals the number of phosphonic acid groups in the phosphonic acid derivative, and wherein the phosphonic acid groups each bind covalently to an aminogroup.

In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is a substituted or unsubstituted mono-cyclic C4-8 cycloalkyl group and, preferably, R is cyclohexyl and n=6.

In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is a substituted or unsubstituted mono-cyclic C4-8 heterocyclyl group, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises n>0 primary, secondary or tertiary amino groups.

In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure R-[P0(0H)2]_n with n>2, wherein R is a substituted or unsubstituted mono-cyclic C4-12 aryl group, wherein in R one or more "C-atoms" may be replaced by a nitrogen, and wherein R comprises n>0 primary, secondary or tertiary amino groups.

While the present disclosure describes the exemplary use of Tri-, Tetra- and / or Multifunctional phosphonic acids and /or derivatives thereof, the concept can be extended to include other possible anchor groups instead of the phosphonic acid component, such as, but not limiting to, phosphinic-, sulfamic-, and hydroxamic-, carboxylic acid based components, that can subsequently be derivatized with one ore more alkane-, amino-, hydroxyl-, or thiol- functional groups and /or combinations thereof.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative according to the above embodiments of compounds with the structure R-[P0(0H)2]_n contains at least three (n=3) phosphonic acid groups. In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative according to the above embodiments of compounds with the structure R-[P0(0H)2]_n contains three (n=3) phosphonic acid groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Amino-tris-(methylene phosphonic acid) (ATMP) or a respective salt thereof.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative according to the above embodiments of compounds with the structure R-[P0(0H)2]_n contains at least four (n=4) phosphonic acid groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative according to the above embodiments of compounds with the structure R-[P0(0H)2]_n contains four (n=4) phosphonic acid groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is selected from Ethylenediamine tetra(methylene phosphonic acid) (EDTMP), Tetramethylenediamine tetra (methylene phosphonic acid) (TDTMP), Hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP) or respective salts thereof.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Ethylenediamine tetra(methylene phosphonic acid) (EDTMP) or a respective salt thereof.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Tetramethylenediamine tetra (methylene phosphonic acid) (TDTMP) or a respective salt thereof.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP) or a respective salt thereof. In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative according to the above embodiments of compounds with the structure R-[P0(0H)2]_n contains at least five (n=5) phosphonic acid groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative according to the above embodiments of compounds with the structure R-[P0(0H)2]_n contains five (n=5) phosphonic acid groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Diethylenetriamine-penta(methylenephosphonic acid (DTPMP) or a respective salt thereof.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative according to the above embodiments of compounds with the structure R-[P0(0H)2]_n contains at least six (n=6) phosphonic acid groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative according to the above embodiments of compounds with the structure R-[P0(0H)2]_n contains six (n=6) phosphonic acid groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is phytic acid (IP6) or a respective salt thereof.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is selected from Amino-tris-(methylene phosphonic acid) (ATMP), Ethylenediamine tetra(methylene phosphonic acid) (EDTMP), Tetramethylenediamine tetra (methylene phosphonic acid) (TDTMP), Diethylenetriamine-penta(methylenephosphonic acid (DTPMP), Hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP), and phytic acid (IP6) or respective salts thereof. In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure according to Formula I: ,N ""

R₃ (I)

wherein

Ri is a substituted C1-3 aliphatic group; wherein substituents are selected from -P0(0H)2 or NR4R5, wherein R4 and R5, independent from each other, can be H or a C1-3 aliphatic group, wherein the C1-3 aliphatic group is optionally substituted with -P0(0H)2; wherein both the C1-3 aliphatic groups are substituted with a total of 0, 1 or 2 -PO(OH)2 groups;

R2 is a substituted C1-3 aliphatic group; wherein substituents are selected from -PO(OH)2 or NR4R5, wherein R4 and R¾, independent from each other, can be H or a C1-3 aliphatic group, wherein the C1-3 aliphatic group is optionally substituted with -PO(OH)2; wherein both the C1-3 aliphatic groups are substituted with a total of 0, 1 or 2 -PO(OH)2 groups;

R3 is a substituted C1-3 aliphatic group; wherein substituents are selected from -PO(OH)2 or NR4Rb, wherein R4 and R¾, independent from each other, can be H or a C1-3 aliphatic group, wherein the C1-3 aliphatic group is optionally substituted with -PO(OH)2; wherein both the C1-3 aliphatic groups are substituted with a total of 0, 1 or 2 -PO(OH)2 groups; with the proviso that the compound according to formula (I) contains at least three (n>2) -PO(OH)2 groups.

As defined herein, aliphatic groups comprise alkyl-, alkenyl-, and akiynyl groups. Therefore, the above feature of an C1-3- aliphatic group reads on C1-3 alkyl groups, C2-3 alkenyl groups and C2-3 alkynyl groups, as will be readily understood by the skilled person. In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has the structure according to Formula I: ,N ""

R₃ (I)

wherein

Ri is a substituted C1-3 alkyl group; wherein substituents are selected from -P0(0H)2 or NR4R5, wherein Px4 and R5, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -P0(0H)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)₂ groups;

R2 is a substituted C1-3 alkyl group; wherein substituents are selected from -PO(OH)2 or NR4R5, wherein R4 and Rb, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -PO(OH)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)₂ groups;

R3 is a substituted C1-3 alkyl group; wherein substituents are selected from -PO(OH)2 or NR4Rb, wherein R4 and Rb, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -PO(OH)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)₂ groups; with the proviso that the compound according to formula (I) contains at least three (n>2) -PO(OH)2 groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is selected from Amino-tris-(methylene phosphonic acid) (ATMP), Ethylenediamine tetra(methylene phosphonic acid) (EDTMP), Tetramethylenediamine tetra (methylene phosphonic acid) (TDTMP), Diethylenetriamine-penta(methylenephosphonic acid (DTPMP), and Hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP), or respective salts thereof.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has a structure according to formula (I) and contains three -PO(OH)2 groups. In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Amino-tris-(methylene phosphonic acid) (ATMP) or a respective salt thereof.

In another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has a structure according to formula (I) and contains at least four -P0(0H)2 groups.

In yet another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has a structure according to formula (I) and contains four -P0(0H)2 groups.

In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP) or a respective salt thereof.

In a particularly preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Ethylenediamine tetra(methylene phosphonic acid) (EDTMP) or a respective salt thereof.

In yet another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has a structure according to formula (I) and contains at least five -P0(0H)2 groups.

In yet another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has a structure according to formula (I) and contains five -P0(0H)2 groups. In a preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative is Diethylenetriamine-penta(methylenephosphonic acid (DTPMP) or a respective salt thereof.

In yet another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has a structure according to formula (I) and contains at least six -P0(0H)2 groups.

In yet another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative has a structure according to formula (I) and contains six -P0(0H)2 groups.

In yet another preferred embodiment of the electrolyte composition of the invention the at least one phosphonic acid derivative, preferably according to the above structure R-[P0(0H)2]_n and/or according to formula (I), as defined herein, are two phosphonic acid derivatives.

In another preferred embodiment of the electrolyte composition of the invention the two phosphonic acid derivatives are Amino-tris-(methylene phosphonic acid) (ATMP) and Ethylenediamine tetra(methylene phosphonic acid) (EDTMP) or respective salts thereof.

In another preferred embodiment of the electrolyte composition of the invention the two phosphonic acid derivatives are Amino-tris-(methylene phosphonic acid) (ATMP) and Tetramethylenediamine tetra (methylene phosphonic acid) (TDTMP) or respective salts thereof.

In another preferred embodiment of the electrolyte composition of the invention the two phosphonic acid derivatives are Amino-tris-(methylene phosphonic acid) (ATMP) and Diethylenetriamine- penta(methylenephosphonic acid (DTPMP) or respective salts thereof.

In another preferred embodiment of the electrolyte composition of the invention the two phosphonic acid derivatives are Amino-tris-(methylene phosphonic acid) (ATMP) and (HDTMP) or respective salts thereof.

In another preferred embodiment of the electrolyte composition of the invention the two phosphonic acid derivatives are Amino-tris-(methylene phosphonic acid) (ATMP) and phytic acid (IP6) or respective salts thereof. In another preferred embodiment salts of the phosphonic acid derivatives as defined herein are inorganic salts. Preferably inorganic salts are formed from alkali metal species, such as sodium or potassium.

In another preferred embodiment.salts of the phosphonic acid derivatives as defined herein are organic salts. For example they can be formed via an organic cationic species (e.g. ionic liquids or complexing cationic counterions).

In a preferred embodiment of the electrolyte composition of the invention the concentration of the at least one phosphonic acid derivative is between 0.1 % and 10% (m/v).

In a preferred embodiment of the electrolyte composition of the invention the concentration of the at least one phosphonic acid derivative is between 0.1 % and 5% (m/v).

In another preferred embodiment of the electrolyte composition of the invention the concentration of methane sulfonic acid in the electrolyte composition is between 20-98% (v/v).

In another preferred embodiment of the electrolyte composition of the invention the concentration of methane sulfonic acid in the electrolyte composition is between 20-80% (v/v).

In another preferred embodiment of the electrolyte composition of the invention the concentration of methane sulfonic acid in the electrolyte composition is between 20-60% (v/v).

In even more preferred embodiment of the electrolyte composition of the invention the concentration of methane sulfonic acid in the electrolyte composition is between 20-40% (v/v).

In another preferred embodiment of the invention the electrolyte composition further contains at least one additional additive selected from the group of viscosifying agents, chelating agents, stabilizer agents, buffering agents; and/or at least one other helping agents, selected from solvents and water.

Solvents can be any organic solvent, or alcohol. Particularly preferred are alcohols selected from methanol (MeOH), ethanol (EtOH), isopropanol (IprOH); n-butanol (n-BuOH), propan-1,2-diol (pr-1,2- diOH), propan-1 ,3-diol (pr-1 ,3-diOH), 2-Methyl-1-butanol (2-Me-1-BuOH), 3-Methyl-2-butanol(3-Me-2- BuOH), 2-Methyl-1-pentanol (2-Me-PeOH), or tert-butyl (t-BuOH). Buffering agents are typically chosen for their ability to control the desired pH strength and buffering capacity of the electrolyte composition. Typical pH buffering agents may include citrate, oxalate, borate compositions and the like. In one embodiment of the present disclosure, the electrolyte composition itself or the electropolishing cell can contain buffering species bound to polymeric resins, i.e. in the form of anion or cation exchange resins that are capable of removing predominantly multivalent metal ions from the electrolyte solution, as well as replenishing or stabilizing the available proton concentration to a desired level. In one preferred embodiment, the electrolyte cell may contain separate compartment(s) for either a cation- or anion exchange resin or both, which are immersed into the electrolyte, but placed outside of the electrode working space, i.e. the space between anode and cathode.

Complexing agents for use in electrolyte compositions are typically chosen for their ability to chelate metal ions in solution (and thus to prevent (re-) precipitation of hardly soluble residues that may form on the surface or in solution during electropolishing). Such complexing agents are rather well known and documented and can include agents such as Oxychinolines, Catecholes, Quadrol, 1,2-Ethanediamine, Ethanolamines, Triisopropanolamines, N,N,N',N'-tetrakis(2-aminoethyl)-EDA, EDTA, NTA, N,N'-Bis(2- hydroxyethyl)ethylenediamines, N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamines, Ν,Ν,Ν',Ν'- Tetrakis(2-Hydroxypropyl)ethylenediamines and the like. In one preferred embodiment, the electrolyte composition may include 0-5 % of a non-surface bound complexing agent, more preferably between 0- 2% of one or more of the aforementioned agents in combination or alone.

Stabilizers and additional Helping Agents/Additives for use in electrolyte compositions according to the invention can include aliphatic, alicyclic or aromatic mono-, di-, tri- or multivalent alcohols, including, but not limited to compounds such as ethanediol, glycerine, sugars, dextrines, cyclohexanol, benzyl alcohol, aliphatic, alicyclic, or aromatic mono-, di-, tri- or multivalent amines, for example compounds such as ethylendiamine, ethanoldiamine, urea, tetramethyl urea, aliphatic, alicyclic or aromatic mono-, di-, tri- or multivalent thiol containing compounds, for example Thiourea, methylating agents, such as Dimethyl Sulfate, 1 ,3-Dimethyl-3,4,5,6-tetrahydro-2(1 H)-pyrimidinone (DMPU), chelating acids, such as glycolic or oxalic acid and others. In one preferred embodiment, the electrolyte composition may include 0-10 % of additional helping agents, more preferably between 0-5% of one or more of the aforementioned agents in combination or alone.

In another preferred embodiment of the invention the electrolyte composition contains polyethylene glycol as a viscosifying agent. In another preferred embodiment of the invention the electrolyte composition contains polyethylene glycol 1000 (PEG-1000) or polyethylene glycol 1500 (PEG 1500), as a viscosifying agent.

In another preferred embodiment of the invention the electrolyte composition contains polyethylene glycol 1000 (PEG-1000) or polyethylene glycol 1500 (PEG 1500) as a viscosifying agent, in a concentration between about 0,1-2,5% (m/v).

In another preferred embodiment of the invention the electrolyte composition contains polyethylene glycol 1000 (PEG-1000) as a viscosifying agent, in a concentration between about 0,1 -2,5% (m/v), preferably in a concentration between about 0,1-1% (m/v), more preferably in a concentration of about 1% (m/v).

In another preferred embodiment of the invention the electrolyte composition consists of

20-40% (v/v) methane sulfonic acid,

0,1-5% (m/v) Ethylenediamine tetra(methylene phosphonic acid) (EDTMP),

1% (m/v) polyethylene glycol having a molecular weight of 1000g/mol (PEG-1000), and an alcohol, selected from MeOH, EtOH, IprOH, and n-BuOH, and, preferably,

H2O in an amount of between 0.1-10 % (v/v).

In a second aspect, the invention refers a method of electropolishing comprising the steps of

a) bringing a metal substrate into contact with the electrolyte composition of the first aspect in an apparatus, said apparatus comprising:

at least one cathode and a cathode current conducting member attached to said cathode;

at least one anode and an anode current conducting member; and

b) supplying a voltage difference between said cathode current conducting member and said anode current conducting member.

The term "Electropolishing", also known as electrochemical polishing or electrolytic polishing, according to the invention, refers to an electrochemical process that removes material from a metallic workpiece. It is used to polish, passivate, and deburr metal parts. It is often described as the reverse of electroplating. It may be used in lieu of abrasive fine polishing in microstructural preparation. Electropolishing streamlines the microscopic surface of a metal object by removing metal from the object's surface through an electrochemical process similar to, but the reverse of, electroplating. In electropolishing, the metal is removed ion by ion from the surface of the metal object in question. Electrochemistry and the fundamental principles of electrolysis replace traditional mechanical finishing techniques, including grinding, milling, blasting and buffing as the final finish.

Typically, the object to be electropolished is immersed in an electrolyte and subjected to a direct electrical current. The object is maintained anodic, with the cathodic connection being made to a nearby metal conductor. During electropolishing, the polarized surface film is subjected to the effects of gassing (oxygen), which occurs with electrochemical metal removal, saturation of the surface with dissolved metal and the agitation and temperature of the electrolyte. Smoothness of the metal surface is a primary and very advantageous effect of electropolishing. During the process, a film of varying thickness covers the surfaces of the metal. This film is thickest over microdepressions and thinnest over microprojections. Electrical resistance is at a minimum wherever the film is thinnest, resulting in the greatest rate of metallic dissolution. Electropolishing selectively removes microscopic high points or "peaks" much faster than the corresponding rate of attack on the corresponding micro-depressions or "valleys." As a result of applying electropolishing methods, the surface of the metal is microscopically featureless, with not even the smallest speck of a torn surface remaining. The basic metal surface is subsequently revealed - bright, clean and microscopically smooth. By contrast, even very fine mechanically finished surfaces will show smears and other directionally oriented patterns or effects.

In a preferred embodiment of the method according to the invention the metal substrate is immersed in the electrolyte solution.

In a preferred embodiment of the method according to the invention the metal is selected from Nickel Titanium, Cobalt, Chromium.Tantalum, Niobium, Tungsten.Vanadium, or alloys thereof, wherein said alloys can contain one or more of said metals.

In a preferred embodiment of the method according to the invention the metal is a nickel, titanium or an alloy thereof.

In a preferred embodiment of the method according to the invention the metal is a nickel-titanium alloy. In a preferred embodiment of the method according to the invention the nickel-titanium alloy is Nitinol. In a preferred embodiment of the method according to the invention the metal substrate is a medical device.

In a preferred embodiment of the method according to the invention the medical device is a medical implant.

In a preferred embodiment of the invention the medical implant is selected from the group consisting of vascular implants, preferably stents, filters, coils, closure devices, clips; orthopaedic implants or - prosthesis; or a mechanical heart valve.

In a preferred embodiment of the invention the medical implant is an orthopaedic implant or -prosthesis, selected from the group consisting of Austin-Moore prosthesis for fracture of the neck of femur; Baksi's prosthesis for elbow replacement; Buttress plate for condylar fractures of tibia; Charnley prosthesis: for total hip replacement; Condylar blade plate for condylar fractures of femur; Dynamic compression plate; Ender's nail for fixing inter-trochanteric fracture; Grosse-Kempf (GK) nail for tibial or femoral staff fracture; Gamma nail for peri-trochanteric fractures; Harrington rod: for fixation of the spine; Hartshill rectangle for fixation of the spine; Insall Burstein prosthesis for total knee replacement; Interlocking nail for femoral or tibial shaft fractures; Kirschner wire for fixation of small bones; Kuntscher nail for fracture of the shaft of femur; Luque rod for fixation of the spine; Moore's pin for fracture of the neck of femur; Neer's prosthesis for shoulder replacement; Rush nail for diaphyseal fractures of long bone; Smith Peterson (SP) nail for fracture of the neck of femur; Smith Peterson nail with McLaughlin's plate for inter-trochanteric fracture; Seidel nail for fracture of the shaft of humerus; Souter's prosthesis for elbow replacement; Steffee plate for fixation of the spine; Steinmann pin : for skeletal traction; Swanson prosthesis for the replacement of joints of the fingers; Talwalkar nail for fracture of radius and ulna; Thompson prosthesis for fracture of the neck of femur; Unicompartmental knee for partial knee replacement.

In a preferred embodiment of the invention the medical implant is a mechanical heart valve.

In a very preferred embodiment the mechanical heart valve is a -disc heart valve or a bileaflet heart valve.

In another very preferred embodiment of the invention the medical implant is a catheter.

In an even more preferred embodiment of the invention the medical implant the catheter is a peripheral venous catheter. In an even more preferred embodiment of the invention the medical implant is a vascular implant.

In an even more preferred embodiment of the invention the vascular implant is selected from the group consisting of stents, filters, coils, closure devices, clips.

In a very preferred embodiment of the invention the vascular implant is a stent.

A "stent' according to the invention, is a mesh tube inserted into a natural passage/conduit in the body to prevent or counteract a disease-induced, localized flow constriction. The term may also refer to a tube used to temporarily hold such a natural conduit open to allow access for surgery.

In an even more preferred embodiment of the method according to the invention the medical implant is a stent, selected from the group consisting of bare-metal stent, a drug-eluting stent, a bio engineered stent, a BVS or a Dual Therapy Stent (Combination of both Drug and bioengineered stent) or a covered stent.

In the most preferred embodiment of the method according to the invention the medical implant is a bare-metal stent, comprising Nitinol.

In the most preferred embodiment of the method according to the invention the medical implant is a bare-metal stent, consisting of Nitinol.

CITED REFERENCES

[1] S. A. Shabalovskaya, Surface, corrosion and biocompatibility aspects of Nitinol as an implant material, Bio-Med. Mater. Eng. 12 (2002) 69-109.

EXAMPLES

Description of preferred implant pre- and postconditioning steps:

In one preferred embodiment, the implant surface is subjected to a series of preconditioning steps prior to conducting electropolishing operations. First, the implant surface is subjected to mechanical deburring, which is then followed by implant surface cleaning and etching. The latter two steps are carried out as wet chemical processes, whereas preferred cleaning and etching formulations, along with process time are provided below.

Implant type: Nitinol

CD Mechanical Deburring

20+10 min

Alternatively, MSA 10 (v/v)% and Water 60 (v/v)%

Diluted with water in a 1 :2 (v/v) ratio

15+5 min

After carrying out the preferred electropolishing process, the implant surface is subjected to a series of preferred postconditioning steps, which comprise of surface passivation, rinsing and drying. The first two two steps are carried out as wet chemical processes, whereas preferred surface passivation formulations, along with process time are provided below.

Implant type: Nitinol

30+5 min

Description of preferred electrolyte embodiments

Electrolyte Composition:

Concentration % Target

Preferred Viscosifying Agent: PEG 1000-1500 (m/v)% [1 Og/I] Preferred Surface Masking Agent: EDTMP 0-5 (m/v)% [4 g/l] Preferred Dilution Solvent: EtOH, IprOH, n-BuOH 70-80 (v/v)% [75%]

Preferred Acid Component: MSA: 20-30 (v/v)% [25%]

Description of the preferred electropolishing cell configuration

Preferred Electrolyte Temperature: -10, 20, 50 °C

Agitation [rpm]: Yes [100-400] /No [0]

Electropolishing Cell Configuration

Electrode Material: Cathode: Stainless Steel

Anode: Work piece, attached by Titanium rods

Electrode Configuration: Cylindrical

Electrode Spacing Distance [cm]: 5-10

Electrode Surface [cm²]: tbd

Mechanical Stirrer

Description of the preferred electropolishing process parameters

Electropolishing Parameters:

Current Density [Acnr²]: see examples 1-6

Electropolishing Time [min]: see examples 1-6

Current / Charge [A]: see examples 1-6

Electrolyte Temperature [°C]: see examples 1-6

Dissolved Mass [%]: Preferably less than 50%, more preferably 20-40%, most preferably 25-35%

Cycles [#]: 1-10 cycles, more preferably 3-7 cycles and most preferably 5 cycles Cycle Time [s]: Preferably less than 3 min, more preferably less than 1 min and most preferably less than 0.5 min

Example 1 :

Electrolyte Composition: 125 ml MSA (25 %) 375 ml EtOH (75 %)

5.0 g PEG 1000

< 2.1 g EDTMP (Saturation Limit)

Substrate: NiTi based Stent

Substrate Cleaning according to Method ©

Substrate Etching according to Method ®

Electropolishing Parameters:

Electropolishing Time / cycle [min] 60 s

Number of Cycles [#]: 6

Current / Charge [A]: 7.0 V / variable current (Process Limit 1.5 A)

Electrolyte Temperature [°C]: 17 ± 2 °C

Stirring: 0 rpm

Substrate Weight after Etching and Cleaning: 206.8 mg

Substrate Weigth after Electropolishing: 145.8 mg

Dissolved Mass: 30%

Electrolyte performed as intended, yielding a very smooth and shiny surface finish. The results obtained are depicted in form of optical microscope images provided in Figures 7-11.

Example 2:

Electrolyte Composition: 250 ml MSA (25 %)

650 ml n-Butanol (65 %)

100 ml H₂0

10.0 g PEG 1000

< 4.2 g EDTMP (Saturation Limit)

Substrate(s): NiTi based Stents (NXP 0 5 x 80 mm)

Substrate Preparation: Substrate Cleaning according to Method ©

Substrate Etching according to Method ®

Electropolishing Parameters:

Number of Cycles [#]: 4

Rate of Ablation [mg/As]: 0.027

Polishing Voltage [V]: 8.0 V

Limiting Current [A]: 0.35 A

Electrolyte Temperature [°C]: 15 ± 2 °C

Stirring: 0 rpm

Substrate Weight after Etching and Cleaning: 162.8 mg

Substrate Weight after Electropolishing: 156.3 mg

Dissolved Mass: 4 %

The results obtained for Example 2 are depicted in form of optical microscope images provided in Figure 13. At 4% mass ablation, optical microscope images of the attained surface finish demonstrate a substantial improvement from the typical etched surface condition of the native substrate demonstrated in Fig.9.

Example 3:

Electrolyte Composition: 250 ml MSA (25 %)

650 ml n-Butanol (65 %)

100 ml H₂0

10.0 g PEG 1000

< 4.2 g EDTMP (Saturation Limit)

Substrate(s): NiTi based Stents (NXP 0 5 x 80 mm)

Substrate Preparation:

Substrate Etching according to Method Θ Electropolishing Parameters:

Number of Cycles [#]: 4

Rate of Ablation [mg/As]: 0.037

Polishing Voltage [V]: 8.0 V

Limiting Current [A]: 0.35 A

Electrolyte Temperature [°C]: 15 ± 2 °C

Stirring: 0 rpm

Substrate Weight after Etching and Cleaning: 180.6 mg

Substrate Weight after Electropolishing: 161.5 mg

Dissolved Mass: 10.5 %

The results obtained for Example 3 are depicted in form of optical microscope images provided in Figure 14. At around 10% mass ablation, optical microscope images of the attained surface finish demonstrate a substantial improvement from the typical etched surface condition of the native substrate demonstrated in Fig.9 combined with desired edge rounding as compared to the mass ablation of 4% shown in Fig. 13.

Example 4:

Electrolyte Composition: 250 ml MSA (25 %)

650 ml n-Butanol (65 %)

100 ml H₂0

10.0 g PEG 1000

< 4.2 g EDTMP (Saturation Limit)

Substrate(s): NiTi based Stents (NXP 0 5 x 80 mm)

Substrate Preparation:

Substrate Etching according to Method ® Electropolishing Parameters:

Number of Cycles [#]: 5

Rate of Ablation [mg/As]: 0.027

Polishing Voltage [V]: 16.0 V

Limiting Current [A]: 1.0 A

Electrolyte Temperature [°C]: 0 ± 2 °C

Stirring: 0 rpm

Substrate Weight after Etching and Cleaning: 178.9 mg

Substrate Weight after Electropolishing: 133.9 mg

Dissolved Mass: 25.1 %

The results obtained for Example 4 are depicted in form of optical microscope images provided in Figure 15. At around 25% mass ablation, optical microscope images of the attained surface finish demonstrate not only a substantial improvement from the typical etched surface condition of the native substrate shown in Fig.9, but also desired edge rounding and additional removal of surface corrugation when compared to the mass ablation level of 10% shown in Fig. 13.

The electrolyte composition employed in example 2, 3 and 4, using n-butanol as the major diluent of the formulation, demonstrate a remarkably high tolerance for water up to 10% in the presence of EDTMP, without compromising the desired level of surface quality (and also under the condition that the mass ablation is within the desired range of 20-40%).

Example 5:

Electrolyte Composition: 250 ml MSA (25 %)

650 ml EtOH (65 %)

100 ml H₂0

10.0 g PEG 1000

< 4.2 g EDTMP (Saturation Limit)

Substrate(s): NiTi based Stents (NXP 0 5 x 80 mm) Substrate Preparation:

Substrate Etching according to Method ®

Electropolishing Parameters:

Number of Cycles [#]: 5

Rate of Ablation [mg/As]: 0.026

Polishing Voltage [V]: 12.0 V

Limiting Current [A]: 1.3 A

Electrolyte Temperature [°C]: 15 ± 2 °C

Stirring: 0 rpm

Substrate Weight after Etching and Cleaning: 179.2 mg

Substrate Weight after Electropolishing: 134.4 mg

Dissolved Mass: 23.6%

The results obtained for Example 5 are depicted in form of optical microscope images provided in Figure 16. At around 24% mass ablation, optical microscope images of the attained surface finish demonstrate a stark contrast to the previous example 4: Surface corrugation has significantly increased, showing a 'granular' surface with smooth valleys and pointed spikes.

Example 6:

The surprising outcome observed in example 5 was investigated using a Nickel foil as substrate.

Electrolyte Composition 250 ml MSA (25 %)

650 ml EtOH (65 %)

100 ml H₂0

10.0 g PEG 1000

< 4.2 g EDTMP (Saturation Limit)

Substrate(s): Nickel foil, wall strength 0.127 cm Electropolishing Parameters:

Number of Cycles [#]: 10

Ablation per cycle [mg/#]: 50 mg

Polishing Voltage [V]: 22.0 V

Limiting Current [A]: 2.0 A

Electrolyte Temperature [°C]: 15 ± 2 °C

Stirring: 0 rpm

Initial Substrate Weight: 1376.1 mg

Substrate Weight after Electropolishing: 880.1 mg

Dissolved Mass: 36%

The results obtained for Example 6 are provided in form of optical microscope images, whereas Figure 17 depicts the typical surface of the native Nickel foil prior to electropolishing and Figure 18 the Nickel foil surface after electropolishing. On Nickel substrates a perfect mirror like finish is obtained.

Comparison between the different electrolyte formulations and substrates provided in examples 1 , 4, 5 and 6 lead to the conclusion, that a) In the absence of water, there is no preferential dissolution apparent, and the surface quality obtained is very smooth and with a mirror like finish as desired by the underlying invention (Example 1). b) In the presence of water, ethanol and EDTMP within the electrolyte formulation, Nickel is preferentially electropolished as compared to Titanium, demonstrating the role of EDTMP as a Ni-selective complexing agent as desired by the underlying invention (Example 6 vs Example

5).

In the presence of water, n-Butanol and EDTMP within the electrolyte formulation an addition of up to 10% water is tolerable without compromising the desired implant surface quality and constitutes a preferred solvent according to the invention (Example 4).

Claims

1. Electrolyte composition, comprising

methane sulfonic acid;

and at least one phosphonic acid derivative; wherein said phosphonic acid derivative contains at least three (n>2) phosphonic acid groups, wherein the concentration of methane sulfonic acid is between 20-98% (v/v).

2. Electrolyte composition according to claim 1 , wherein the at least one phosphonic acid derivative has the structure according to Formula I:

(I)

wherein

Ri is a substituted C1-3 alkyl group; wherein substituents are selected from -PO(OH)2 or NR₄Rs, wherein R₄ and R5, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -PO(OH)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)₂ groups;

R2 is a substituted C1-3 alkyl group; wherein substituents are selected from -PO(OH)2 or NR₄Rs, wherein R₄ and R5, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -PO(OH)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)₂ groups;

R3 is a substituted C1-3 alkyl group; wherein substituents are selected from -PO(OH)2 or NR₄Rs, wherein R₄ and R5, independent from each other, can be H or a C1-3 alkyl group, wherein the C1-3 alkyl group is optionally substituted with -PO(OH)2; wherein both the C1-3 alkyl groups are substituted with a total of 0, 1 or 2 -PO(OH)₂ groups; with the proviso that the compound according to formula (I) contains at least three (n>2) -PO(OH)2 groups.

3. Electrolyte composition according to claim 1 , wherein the at least one phosphonic acid derivative is selected from

Amino-tris-(methylene phosphonic acid) (ATMP), Ethylenediamine tetra(methylene phosphonic acid) (EDTMP), Tetramethylenediamine tetra (methylene phosphonic acid) (TDTMP), Diethylenetriamine-penta(methylenephosphonic acid (DTPMP), and Hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP),

or respective salts thereof.

4. Electrolyte composition according to claims 1 to 3, wherein the concentration of the at least one phosphonic acid derivative is between 0.1 % and 10% (m/v).

5. Electrolyte composition according to claims 1 to 4, wherein the at least one phosphonic acid derivative is Ethylenediamine tetra(methylene phosphonic acid) (EDTMP).

6. Electrolyte composition according to claims 1 to 5, wherein the composition further contains at least one additional additive selected from the group of viscosifying agents, chelating agents, stabilizer agents, buffering agents; and/or at least one other helping agents, selected from solvents and water.

7. Electrolyte composition according to claims 1 to6, wherein the composition contains polyethylene glycol as a viscosifying agent.

8. Electrolyte composition according to claims 1 to 7, wherein the composition is consisting of

20-40% (v/v) methane sulfonic acid,

0,1-5% (m/v) Ethylenediamine tetra(methylene phosphonic acid) (EDTMP),

1% (m/v) polyethylene glycol having a molecular weight of 1000g/mol (PEG-1000), and an alcohol, selected from MeOH, EtOH, IprOH, and n-BuOH, and, preferably, between 0.1 and

10% (v/v) H₂O.

9. A method of electropolishing comprising the steps of

a) bringing a metal substrate into contact with the electrolyte composition

according to claims 1 to 8 in an apparatus, said apparatus comprising:

at least one cathode and a cathode current conducting member attached to said cathode; at least one anode and an anode current conducting member; and b) supplying a voltage difference between said cathode current conducting member and said anode current conducting member.

10. The method according to claim 9, wherein the metal substrate is immersed in the electrolyte solution.

11. The method of claims 9 or 10, wherein the metal is selected from Nickel Titanium, Cobalt, Chromium,Tantalum, Niobium, Tungsten,Vanadium, or alloys thereof, wherein said alloys can contain one or more of said metals.

12. The method of claims 9 to 11 , wherein the metal is a nickel, titanium or an alloy thereof, preferably a nickel-titanium alloy.

13. The method of claim 12, wherein the nickel-titanium alloy is Nitinol.

14. The method of claims 8-13, wherein the metal substrate is a medical device, preferably a stent.