Increasing the double layer capacitance of titanium by laser-based generation of a titanium nitride layer and simultaneous nano-structuring and upstream laser ablation

Abstract

The present invention relates to a method for treating a surface (10a) of a part (10) of an implantable medical device (1), the method comprising the steps of: providing the part (10), the part (10) comprising a surface (10a) comprising titanium, exposing the surface to a gas (G) containing nitrogen, and applying laser light (L) to the surface (10a) to create a titanium nitride (TiN) layer (11) on the surface (10a) having an increased double layer capacitance compared to the untreated surface (10a).

Description

[0001] Applicant: BIOTRONIK SE & Co. KG

[0002] Increasing the double layer capacitance of titanium by laser-based generation of a titanium nitride layer and simultaneous nano-structuring and upstream laser ablation

[0003] The present invention relates to a method for treating a surface of a part of an implantable medical device to increase its double-layer capacitance.

[0004] An electrical double layer typically forms due to a separation of charges at an interface, e.g., when a metallic surface is immersed in an electrolyte solution. Ions contained in the solution then arrange themselves near the surface so that two layers of charge are created, namely one on the metallic surface and the other one in the electrolyte. The region where this charge separation occurs is called the double layer. As the electrical double layer is able to store charge at the interface between the metallic surface and the electrolyte solution, it comprises a capacitance C which is denoted as double layer capacitance and can be described by the following formula wherein e is the dielectric constant of the medium between the charges (relative permittivity), e0is the vacuum permittivity, A is the area of the metallic surface, and d is the effective thickness of the electrical double layer.

[0005] In the prior art, generation of a fractal iridium layer by sputtering is known to increase the double layer capacitance. Furthermore, creating a fractal titanium nitride layer by sputtering is also known. Further, it is proposed in the prior art to increase the double layer capacitance by laser nano-structuring of platinum (substrate material). Further, the generation of titanium nitride coatings to improve wear protection, tribology or biocompatibility has also been suggested in the prior art. However, generating a fractal iridium coating by sputtering takes place in a vacuum, wherein before the sputtering a relatively high vacuum of approx. 10'6mbar is needed, and during sputtering a fine vacuum of approximately 1 mbar. The areas of the component that are not to be coated must be masked during the process. The coating process is batch-based at component level, which means that the fractal coating may have to be masked and unmasked again for protection during subsequent processes (e.g. in case of a silicone, parylene or polyurethane coating at the end of the process chain).

[0006] Additional production aids are required for masking and unmasking, both during sputtering and in the subsequent processes. Unmasking during the subsequent coating process (e.g., silicone, parylene, polyurethane) can lead to damage to the edge area of the insulating layer. This makes an additional visual inspection process necessary.

[0007] As the component volume increases, the possible batch size per sputtering run decreases and the amount of iridium required per component increases. Moreover, the price of iridium has risen sharply in recent years. This has a negative impact on the economic efficiency of the sputtering process.

[0008] Based on the above, the problem to be solved by the present invention is to provide a more efficient surface treatment for increasing the double layer capacitance. Particularly, it is desirable to avoid batch-based machining and to enable machining of individual parts, to avoid machining in a high vacuum (1 O’3to 10'7mbar), and to avoid masking of parts to be coated. Particularly, regarding the overall process chain it is also desirable to enable processing at the product level instead of the component level.

[0009] The problem according to the present invention is solved by a method having the features of claim 1. Preferred embodiments of this aspect of the present invention are stated in the corresponding dependent claims and are described below.

[0010] According to claim 1 a method for treating a surface of a part of an implantable medical device is disclosed, the method comprising the steps of: providing the part, the part comprising an initial surface comprising titanium, exposing the surface to a gas containing nitrogen, and irradiating the surface with laser light to create a titanium nitride (TiN) layer on the surface having an increased double layer capacitance compared to the initial surface, wherein particularly the increased double layer capacity is in the range of 10 pF / mm2to 100 pF / mm2

[0011] Particularly, the untreated / initial surface corresponds to the titanium surface without the titanium nitride layer generated thereon. Furthermore, particularly, the surface is formed out of titanium or a titanium alloy, with titanium being the main component.

[0012] Particularly, the titanium nitride layer on the surface is characterized by a thickness in the range of in the range of 0.1 pm to 10 pm.

[0013] Particularly, processing of the surface is carried out with a laser. Laser-based processes generally enable localized processing of the substrate, which means that no additional production aids are required for masking the surface. Thus, particularly, according to a preferred embodiment of the method the laser light is applied to the surface of the part, the surface being an unmasked surface.

[0014] Furthermore, this laser processing in a nitrogen, nitrogen-argon or nitrogen-helium atmosphere leads to a chemical reaction and the formation of a titanium nitride layer if the surface temperature and holding time are sufficient. Particularly, the surface temperature and the holding interact with each other. The holding time is the duration for which the temperature on the surface of the component is keep at the target value. The chemical reaction will occur at temperatures above 1200 °C or higher on the surface of the component, wherein, the chemical reaction is accelerated with higher temperatures. Preferably, surface temperatures above the melting point of titanium (approx. 1650 °C) are applied which lead to a short holding time in the range of 0.1 to 1.0 seconds. Surface temperatures between the melting point of titanium and 1200 °C will reduce the speed of the chemical reaction and hence require an increased holding time of 1 second to 1 minute. The upper temperature limit of the reaction is given by the boiling point of titanium nitride (approx. 2930 °C). The set parameters of surface temperature and holding time are limited by an acceptable warming of the part of the medical device to be treated with the method according to the invention. This may be of importance if the part is more temperature sensitive, e.g., if the part is a battery, than other parts of the medical device to be treated.

[0015] According to a preferred embodiment, during applying the laser light to the surface, a relative movement between a laser light beam (or a laser providing the laser light beam) impinging on the surface (to apply laser light to the surface) and the part is performed.

[0016] In addition to the relative movement between the laser light beam or laser and the part, the laser light beam may perform a superimposed movement, which may influence the energy input and thus the properties of the TiN layer. Superimposed movement may be achieved by a transversal movement of the laser beam superimposed by a movement of the workpiece, e.g., a rotation. Additionally, the laser beam may oscillate crosswise to its moving direction at a high frequency (“wobbling”).

[0017] According to a preferred embodiment, the part is provided in a processing chamber, and exposing the surface to said gas is conducted by introducing the gas into the processing chamber.

[0018] Furthermore, according to a preferred embodiment, the gas further comprises argon or helium. Particularly, the properties of the TiN layer (e.g., surface structure, layer thickness, adhesive strength) may be influenced by the composition of the gas and the gas pressure.

[0019] According to a preferred embodiment, the gas comprises 10 % v / v to 100 % v / v nitrogen.

[0020] Furthermore, in a preferred embodiment, the gas comprises 10 % v / v to 100 % v / v nitrogen and 0 % v / v 90% v / v argon. Particularly, with the sum of the concentrations of nitrogen and argon being smaller or equal to 100% v / v.

[0021] According to yet another preferred embodiment, the gas comprises 10 % v / v to 100 % v / v nitrogen and 0 % v / v to 90% v / v helium. Particularly, with the sum of the concentrations of nitrogen and helium being smaller or equal to 100% v / v. Furthermore, in a preferred embodiment, during applying / irradiating the laser light onto the surface of the part, the gas comprises a pressure in the range from 1 mbar (rough vacuum) to 10'7mbar (high vacuum).

[0022] According to a further embodiment, the laser light is applied to the surface. Depending on the energy density, a nano-structure is formed into the surface of the part which leads to an enlargement of the surface and hence to an increasing of the double layer capacitance. The characteristic of the nano-structure may be formed differently depending on the parameter set (e.g. dot-like, lines, cone, pillar, hierarchical). The pitch and depth of the nano structure may be in the range of 0.1 pm to 100 pm. Due to the presence of the gas, the TiN layer for further increasing the double layer capacitance of the part at is formed by chemical reaction its outer surface (formed by the TiN layer). Particularly, this combination (nanostructuring and formation of a TiN layer) may be achieved at sufficiently high energy density per unit area (fluence), particularly in the range of 0.1 J / cm2to 1 J / cm2

[0023] Particularly, according to a preferred embodiment, the laser is femtosecond laser configured to emit ultrashort pulses with durations in the femtosecond range (10‘15s), or alternatively a picosecond laser configured to emit pulses with durations in the picosecond range (10‘12s). In an alternative embodiment, the laser is a continuous wave laser.

[0024] Furthermore, according to a preferred embodiment, the wavelength of the laser light is in the range of 150 nm to 1100 nm.

[0025] Furthermore, according to a preferred embodiment, the wavelength of the applied laser light may be in the near-infrared range (NIR) e.g. between 800 nm to 1064 nm (e.g. a Ti laser at 800 nm, a Yb-doped fiber laser at 1030 nm, or an Nd laser at 1064 nm). Furthermore, in a preferred embodiment, the wavelength may also in the ultraviolet range (UV) e.g. between 150 nm (Excimer laser) and 355 nm (frequency-tripled Nd laser). Furthermore, the wavelength may also in the range of 400 to 1000 nm (diode laser). Furthermore, according to a preferred embodiment, the laser light comprises pulses, particularly with a pulse duration of 10 fs to 1000 fs (e.g. when a femtosecond laser is used) or a pulse duration of 1 ps to 100 ps (e.g. when a picosecond laser is used) or a pulse duration of 1 ns to 1000 ns (e.g. when a nanosecond laser is used). Alternatively, the laser is a continuous wave laser.

[0026] Furthermore, according to a preferred embodiment, the pulses comprise a pulse energy in the range from 0.1 pj to 1000 pj.

[0027] Furthermore, according to yet another preferred embodiment, the pulses comprise a repetition rate in the range from 1 kHz to 100 MHz.

[0028] Furthermore, the applied laser light forms a spot on the surface comprising a spot size (i.e. diameter), wherein preferably the spot size of the laser light (e.g. pulses) is in the range from 1 pm to 100 pm, or for a continuous wave laser in the range of 50 pm to 1 mm

[0029] According to yet another embodiment, the laser light spot on the surface is moved relative to the surface (e.g., either by moving the spot / laser light beam(s) or by moving the part or by moving both the spot and the part), wherein preferably a scan speed of the laser light with respect to the surface is in the range from 0.001 m / s to 100 m / s.

[0030] Particularly, in case the spot size used is relatively large (e.g. when employing a diode laser), the intensity on the surface is relatively low, and the scan speed is relatively slow the increase in double layer capacitance is predominantly achieved by creating the titanium nitride layer. In this case, the energy density per unit area (fluence) as a result of energy input and spot size, is below the material specific ablation threshold. On the other hand, in case the spot size used is relatively small (e.g. when employing an ultrashort pulse laser), the intensity on the surface of the part is relatively high, the scan speed is relatively high, the increase in double layer capacity is achieved by nano-structuring and the generation of the titanium nitride layer. In this case, the energy density per unit area (fluence) is near to or above the material specific ablation threshold. Furthermore, according to a preferred embodiment, the laser light is applied to the surface of the part by direct laser interference patterning (DLIP), wherein at least two laser light beams are intersected at the surface creating an interference pattern to generate periodic modulation in intensity of the laser light at the surface so that the titanium nitride layer is periodically patterned.

[0031] According to yet another preferred embodiment, the laser light comprising pulses is applied to the surface to create laser-induced periodic surface structures (LIPSS), wherein the laser light pulses interact with the surface, and an interference between the incident laser light pulses and waves scattered from the surface results in the formation of said periodic structures. Particularly, these structures may be aligned perpendicular to the laser's polarization direction, and depend on the parameters of the laser, such as wavelength, energy density per unit area (fluence), and pulse duration, as well as the properties of the titanium surface.

[0032] Furthermore, in a preferred embodiment, the surface of the part is a surface of an electrode of the implantable medical device, particularly for sensing a human or animal electrophysiological signal and / or for applying electrical stimulation to human or animal tissue.

[0033] Particularly, the surface of the part or the implantable medical device comprising said part can be surface-treated at any point in the production chain.

[0034] In a preferred embodiment, the part is a housing of an implantable medical device, wherein particularly the implantable medical device is an implantable cardiac monitor (ICM) or an implantable intracardiac (leadless) pacemaker. Particularly, the ICM is configured to detect and store an electrophysiological signal generated by a human or animal heart. Furthermore, particularly, the ICM is configured to analyze the signal and exchange data with a remote device via wireless communication. Particularly, the surface is an electrode surface and forms a portion of a housing of the ICM. Furthermore, particularly, in case of an intracardiac pacemaker, the surface also is an electrode surface and forms a portion of a housing of the intracardiac pacemaker. Particularly, in a preferred embodiment, the housing accommodates an electronic circuit and / or a battery during applying of said laser light. Particularly, this means that the surface treatment can also be applied on the product level, i.e., when the device has essentially been completely assembled regarding components accommodated in the housing of the implantable medical device. However also individual parts prior to assembly can be processed with the method according to the present invention.

[0035] Furthermore, according to a preferred embodiment of the method, the part is processed in the processing chamber as a single part or as a component of a single workpiece arranged in the processing chamber, i.e., no further part of the same kind to be surface-treated is arranged in the processing chamber upon applying said laser light to the surface of the part. However, as described above, the part can form a component of a workpiece / assembly that is placed in the processing chamber.

[0036] Furthermore, in a preferred embodiment, prior to applying said laser light to the surface of the part, an insulating layer being arranged on said surface is removed, particularly ablated, by applying laser light on this insulating layer. Particularly, said insulating layer comprises one of: silicone, parylene, polyurethane.

[0037] According to yet another preferred embodiment, removing of said insulating layer by applying laser light on the insulating layer is performed under atmosphere, thereby forming a titanium oxide layer on the surface. Particularly, this offers the advantage of uniform input conditions for the next processing step (i.e. generation of the TiN-layer).

[0038] According to a further aspect of the present invention, an implantable medical device is disclosed, the implantable medical device comprising a surface treated with the method according to the present invention, wherein particularly said surface is an electrode surface of the implantable medical device. Particularly, according to a preferred embodiment of the implantable medical embodiment, the implantable medical device is an implantable cardiac monitor or an implantable leadless pacemaker.

[0039] In the following, embodiments of the present invention as well as further features and advantages shall be described with reference to the Figure, wherein

[0040] Fig. 1 shows a schematic illustration of a system for conducting a method according to the present invention for treating a surface of a part to increase the double layer capacitance of the resulting surface.

[0041] Fig. 1 shows a schematic representation of a system 100 for carrying out the method according to the present invention. The method aims at treating a surface 10a of a part 10 of an implantable medical device 1, such as a housing 10 to increase a double layer capacitance of the (treated / coated) surface 10a. Particularly, the implantable medical device 1 may be an implantable cardiac monitor (ICM) as indicated in Fig. 1 but may also be an intracardiac pacemaker or another implantable medical device. Particularly, as indicated in Fig. 1 said surface may be an electrode surface 10a of the device that may be arranged at an end of a housing 10 of the device. In particular, the method comprises the steps of: providing the part 10 (e.g. either as a single part or as a component of an already assembled device 1), exposing the surface 10a to a gas G containing nitrogen, and applying laser light L to the surface 10a to create a titanium nitride (TiN) layer 11 on the surface 10a (see detail of Fig. 1 on the upper right hand side) having an increased double-layer capacitance compared to the untreated surface 10a. For exposing the part 10 to the gas, the part 10 is preferably arranged in a processing chamber 107 of a system 100 for conducting the method, wherein said exposing is achieved by introducing the gas G into the processing chamber 107.

[0042] The processing chamber 107 may be formed from stainless steel or other inert materials to avoid contamination. It can be properly sealed to maintain the inert gas atmosphere inside the processing chamber 107 provided by introduction of the gas G. For introducing the gas G into the processing chamber 107, the latter may comprise a gas inlet 104 connected to a suitable gas source 104 being configured to provide the desired gas mixture G. Furthermore, the processing chamber may comprise a gas outlet 106 for removing gas G from the processing chamber. Both the gas inlet 105 and the gas outlet 106 may be provided with valves to adjust the flow of gas G into the chamber 107 and the gas pressure in the chamber 107 and to facilitate removal of the gas G from the processing chamber 107.

[0043] For irradiating the surface 10a with laser light L, the system 100 further comprises a laser 101 as specified herein. The laser beam(s) may be delivered into the processing chamber via a suitable optics 102 and a window 108 provided in the processing chamber. It is also conceivable to accommodate the laser 101 inside the processing chamber 107. Furthermore, the system may comprise a control unit 103 for adjusting laser parameters specified herein such as (pulse) energy, pulse duration, scan speed etc. Furthermore, the gas composition and pressure may be adjusted via the control unit 103.

[0044] Furthermore, the system 100 may comprise a suitable gas source 104 storing the gas G containing nitrogen that is to be introduced into the processing chamber 107 to cover the surface 10a and allow formation of the titanium nitride layer 11. The composition of the gas G (e.g. mixture of nitrogen and argon or helium as specified herein) may be controlled via corresponding valves at the gas inlet 105 and particularly gas outlet 106. Particularly, the properties of the TiN layer 11 (e.g., surface structure, layer thickness, adhesive strength) may be influenced by the gas mixture and pressure ratio. Particularly, the gas G may comprise 10 % v / v to 100 % v / v nitrogen and 0 % v / v to 90% v / v helium or 0 % v / v to 90% v / v argon. Moreover, the gas G may have a pressure in the processing chamber 107 in the range of 1 mbar (rough vacuum) to 10'7mbar (high vacuum).

[0045] Furthermore, the system may comprise a sample holder 109 to hold the part 10, wherein the sample holder 109 may comprise an xyz stage allowing precise positioning of the part 10 with respect to the laser light L. The holder 109 may also comprise a rotary stage to offer the ability to position the part 10 at different angles / spatial orientations to the laser beam(s). Particularly, the system and method according to the present invention allow to increase the double layer capacitance of electrically active surfaces 10a of implantable medical devices 1, wherein such surfaces 10 can be coated locally with a TiN layer 11 and, if necessary, structured at the same time. Preferably, the material forming the surface(s) 10a to be treated is titanium or a titanium alloy. In a preferred embodiment, the surface 10a to be treated may be covered by an existing insulating layer (e.g. silicone, parylene, polyurethane) that has been generated in a preceding manufacturing step of the implantable medical device 1, wherein this insulating layer may be removed / ablated with the same laser that will be used for generating the TiN layer 11 afterwards. Particularly, a rising / flushing step in the processing chamber 107 may be performed between removal / ablation of the insulating layer and forming of the titanium nitride layer 11.

[0046] After removal of the insulating layer (if necessary). The surface 10a is then processed locally with the laser in a nitrogen, nitrogen-argon or nitrogen-helium atmosphere. To this end, the gas G comprising a corresponding composition of these inert gases as specified herein. If the surface temperature and holding time are sufficient as specified herein, a titanium nitride layer 11 is formed by chemical reaction. For example, if a surface temperature above the melting point of titanium (approx. 1650 °C) is applied the holding time is in the range of 0.1 to 1.0 seconds. In an alternative example, if a between the melting point of titanium and 1200 °C is applied, an increased holding time of 1 second to 1 minute is required.

[0047] To enhance the effect of increasing the double layer capacitance, a nano-structure may be created on the surface 10a at the same time, provided that the energy density per unit area (fluence) of the laser light L and the movement of the laser beam and the workpiece on the surface is set sufficiently high as specified herein. For example, a sufficiently high energy density per unit area (fluence) may be in the range of 0.1 J / cm2to 1 J / cm2

[0048] Due to the fact that processing is carried out with a laser 101, no additional production aids are required for masking the part 10 to be treated since the laser processing may take place locally limited areas on the workpiece. Preferably, the part 10 is processed as component of a single workpiece (or is the actual single workpiece) and may be processed at any point in the process chain.

[0049] Furthermore, applying the laser light L to the surface 10a may in particular be conducted to ablate an insulating layer (e.g. comprising one of: silicone, parylene, polyurethane) under atmosphere, thereby forming a titanium oxide layer on the surface 10 to facilitate uniform input conditions for the next process step.

[0050] Further, during processing, a relative movement between the laser beam(s) L and the part 10 may be performed (e.g., utilizing either optics 102 and / or the holder 109). In addition to the relative movement between the laser beam(s) L and the part 10, the laser beam(s) L may perform a superimposed movement, particularly an oscillation (e.g. by means of the optics 102), which may influence the energy input and thus the properties of the coating 11.

[0051] Depending on the selected parameters, the following processing variants may be utilized. In case the spot size used is relatively large (e.g. diode laser), the intensity on the surface 10a is relatively low, and the relative movement (e.g. scan speed) is relatively slow, the increase in double layer capacity is predominantly achieved by creating the titanium nitride layer 11. In this case, the energy density per unit area (fluence) as a result of energy input and spot size, is below the material specific ablation threshold. Furthermore, in case the spot size used is relatively small (e.g., ultrashort pulse laser), the intensity on the substrate surface is relatively high, and the relative movement is relatively fast, the increase in double layer capacitance can be achieved by nano-structuring and the generation of the titanium nitride layer 11. In this case, the energy density per unit area (fluence) is near to or above the material specific ablation threshold.

[0052] Furthermore, in particular, periodic structures can be created using a superposition of at least two laser beams (DLIP), or using of an ultrashort pulse laser and suitable parameters (LIPSS). The properties of the TiN layer 11 (e.g. surface structure, coating thickness, adhesive strength) may be influenced by the following conditions; if necessary, an interaction with the permissible workpiece temperature is taken into account:

[0053] Pressure (1 mbar to 10'7mbar) in the processing chamber 107,

[0054] Nitrogen-argon or nitrogen-helium mixing ratio (10 % v / v to 100 % v / v nitrogen and 0 % v / v 90% v / v argon or helium), energy density per unit area (fluence) of the laser light L on the surface 10a (0.1 J / cm2to 1 J / cm2),

[0055] Scan speed (0.001 m / s to 10 m / s) of the laser light L on the surface 10a, and

[0056] Overall processing strategy, see above: relative movement between laser beam(s) L and part 10, possibly superimposed movement of the laser beam(s) L, use of DLIP or LIPSS.

[0057] The present invention offers the advantages of reducing effort by avoiding processing in a high vacuum (10‘3to 10'7mbar) as well as preparation steps such as masking of the surfaces to be treated. Furthermore, the invention allows a flexible, lean production through single part processing. Based on the proposed method, an electrically active refined surface of the part / active implant can be provided as late as possible at product level, thus avoiding non-value-adding process steps in the subsequent processes, and visual inspection in subsequent processes (e.g. due to damage to the insulating layer caused by masking). Furthermore, the proposed process is a robust coating process due to uniform input conditions. Excessive costs for materials such as iridium can be avoided and processing is enabled at product level instead of the component level.

Claims

Claims1. A method for treating a surface (10a) of a part (10) of an implantable medical device(I), the method comprising the steps of:- providing the part (10), the part (10) comprising a surface (10a) comprising titanium,- exposing the surface (10a) to a gas (G) containing nitrogen,- applying laser light (L) to the surface (10a) to create a titanium nitride (TiN) layer(I I), particularly having a thickness in the range of 0.1 pm to 10 pm, on the surface (10a) having an increased double-layer capacitance compared to the untreated surface (10a), wherein particularly the increased double-layer capacitance is in the range of 10 pF / mm2to 100 pF / mm22. The method according to claim 1, wherein the part (10) is provided in a processing chamber (107), and exposing the surface (10a) to said gas (G) is conducted by introducing the gas (G) into the processing chamber (107).

3. The method according to claim 1 or 2, wherein the gas (G) further comprises argon or helium.

4. The method according to claim 3, wherein the gas (G) comprises a pressure in the processing chamber (107) in the range from 1 mbar to 10'7mbar.

5. The method according to one of the preceding claims, wherein applying the laser light to the surface (10a) forms a nano-structure into the surface (10a).

6. The method according to one of the preceding claims, wherein the wavelength of the laser light (L) is in the range from 150 nm and 1100 nm.

7. The method according one of the preceding claims, wherein the laser light (L) comprises pulses, particularly with a pulse duration in the range from 10 fs to 1000 fsor with a pulse duration in the range from 1 ps to 100 ps or with a pulse duration in the range from 1 ns to 1000 ns. Alternatively, the laser is a continuous wave laser.

8. The method according to claim 7, wherein the pulses comprise a pulse energy in the range from 0.1 pj to 1000 pj, and / or wherein the pulses comprise a repetition rate in the range from 1 kHz to 100 MHz.

9. The method according to one of the preceding claims, wherein the laser light (L) forms a spot on the surface (10a), wherein particularly the spot comprises a spot size in the range from 1 pm to 100 pm, or for a continuous wave laser in the range of 50 pm to 1 mm10. The method according to claim 9, wherein a scan speed of the laser light spot created by the laser light on the surface is in the range from 0.001 m / s to 100 m / s.

11. The method according to one of the preceding claims, wherein the laser light (L) is applied to the surface (10a) by direct laser interference patterning, wherein at least two laser light beams are intersected at the surface (10a) creating an interference pattern to generate periodic modulation in intensity of the laser light (L) at the surface (10a) so that the titanium nitride layer is periodically structured.

12. The method according to one of the claims 1 to 10, wherein the laser light (L) comprises pulses that are applied to the surface (10a) to create laser-induced periodic surface structures (LIPSS) on the surface (10a) and / or titanium nitride layer (11), wherein the laser light pulses interact with the surface (10a), and an interference between the incident laser light pulses and waves scattered from the surface (10a) results in the formation of said periodic surface structures.

13. The method according to one of the preceding claims, wherein the surface (10a) is a surface of an electrode of the implantable medical device (1).

14. The method according to one of the preceding claims, wherein prior to applying said laser light to the surface (10a), an insulating layer being arranged on said surface (10a) is removed by applying laser light on the insulating layer.

15. An implantable medical device (1) comprising a surface (10a) treated with the method according to one of the claims 1 to 14, wherein particularly said surface (10a) is an electrode surface.

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