GB2451060A

GB2451060A - Dual coatings applied to medical devices

Info

Publication number: GB2451060A
Application number: GB0713434A
Authority: GB
Inventors: Anthony Walter Anson
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-07-11
Filing date: 2007-07-11
Publication date: 2009-01-21
Anticipated expiration: 2027-07-11
Also published as: GB2451060B; GB0713434D0

Abstract

Medical device 1 having a diffusion barrier 4 and biocide coating 6 jointly applied thereto. The diffusion barrier can be diamond like carbon (DLC) and the biocide coating can for example be silver or gold. The coatings can be deposited on different selected areas of the medical device by using masks eg, copper wire (2, fig 1). The DLC may be deposited using PACVD and the silver/gold may be electro-deposited.

Description

Dual Coatings Applied To Medical Devices

Background

Medical devices for maintenance or repair of the living organism are constructed of metals, polymers and ceramics. Efficacy of a prostheses is determined by several factors; particularly important among these factors, is biocompatibility. Degradation (corrosion) of a medical implant has been directly associated with biocompatibility1' according to the literature.

Corrosion effects with metal alloys, such as titanium-vanadium-aluminium, cobalt-chrome, nickel-titanium and various stainless steels alloys, commonly used as prostheses, facilitate protection by means of a naturally occurring oxide layer, (titanium oxide, and chromium oxide) or enhanced or additional oxide films on exposed surfaces.

Oxide, thin films act as barriers between biological tissue and the prostheses, affording protection of the metal object for example, with a consequent reduction in the release of metal species (in ionic form) from implant to tissue, in the presence of biological fluids.

This is a two-way effect: protection of the prostheses from the potential corrosion effects of biological fluids and protection of surrounding tissue when in contact with toxic materials comprising the medical implant.

Established and approved metallic biomaterials are often implanted with the essential metal structure in close contact with surrounding tissue or body fluids. All metallic biomaterials contain bulk or trace elements that readily oxidise, for example titanium and chromium, forming a barrier film, giving a some protection. Further protection can be facilitated by increasing the thickness of these oxides or by applying an additional thin or thick film. Improved corrosion resistance of the medical implant is also improved by additional or thicker oxide or additional coatings. Among these coatings, well known in the art, comprise titanium oxide, titanium nitride, diamond-like carbon, hydroxyapatite, silicone carbide and other polymers such as polyethertertraphthalate. A barrier film can be applied to a medical device using several techniques, equally well known and established in the art: plasma vapour and plasma assisted chemical vapour deposition, sputtering, ion beam, laser beam, metal spraying metal evaporation and others.

However, another factor infection, associated with medical prostheses may be due to invasive introduction at the site of a medical implant: the mechanisms of infection are well known in the interventional and surgical arena's and have three essential routes: resident micro-organisms [in the host organism], infective species introduced on the implant and infectious species [airborne or already attached to a solid surface] resident in an operating theatre or other clinical environment.

To reduce the incidence of infection, biocides can be applied to a medical device.

Silver7 in elemental form as a wrought product, colloidal forms and as a compound, has a well recorded history in the medical field, Orthodontic, orthopaedic,8'9 cardiovascular7 devices and medicinal compounds have benefited from the antibacterial properties of silver. The use of metals, including silver, copper and zinc has been recorded in several and diverse public documents during the last 2000 years: military wounds being treated with a number of biocidal materials, in elemental or as a silver salt such as silver nitrate: preventing or reducing the effects of infection, in Roman times, silver, in elemental form was also used as a means to prevent bacterial degradation of water and wine and food, by the use of a silver insert into a container (coin) or indeed the entire container being made of silver. Other metals and compounds comprising zinc and iron have also found use at anti-infection agents.

Description

This disclosure reveals a method whereby two or more coatings are applied to the surfaces of medical prostheses to reduce potential ion or polymer migration from prostheses to tissue and to facilitate release of biocides from a suitable additional coating to reduce potential infection. Said coatings, referred to as dual coatings are, preferably thin films, ranging from 10 nanometres to 4 micron thickness. It is necessary to adjust the biocide coating volume as a means to adjust the quantity of ions released; this will be determined by the nature of the intervention, the biological status of a patient and the severity and type of infection.

The object of this disclosure is to apply a diffusion barrier and anti-bacterial agent on a common substrate to improve the performance of a medical device. The diffusion barrier is a static, thin-film coating, preferably diamond-like carbon. This film, acting as a barrier, reducing potential metal ion or polymer (in the case of plastic implants) migration or leaching. Intimately associated with the diffusion barrier is a dynamic anti-bacterial coating, preferably silver. This is termed dynamic as metal ions are continuously released from implant-to-tissue, when in the biological environment, offsetting potential infection.

Diamond-like carbon, applied to a substrate, using Plasma Assisted Chemical Vapour Deposition, (PACVD), well known in the art, is used to deposit thin films in the range nanometres -4 microns, onto a metal, polymer or ceramic substrate. Prior to coating, a mask is applied to the substrate, preventing DLC coating in the masked area. Copper wire of suitable cross section and diameter is wound onto or around the medical implant substrate. The length and geometrical arrangement of the copper, acting as a mask, will, in part, determine the quantity of silver, co-deposited onto a medical device.

Control of volume of silver is realised by the masking arrangement, [determining surface area] and the thickness of the coating Copper wire or other forms of the metal, such as sheets or electroplating masking arrangements are preferred as the diamond-like carbon, deposited by PACVD, does not readily bond with copper. This leaves a defined geometry and surface area on the uncoated substrate surface. Other. metals such as ferrous based materials, titanium and its alloys, refractory and noble metals in nickel and its alloys, as wires or other suitable shapes and fabrications, are also capable of use as a mask.

Subsequent to DLC coating, the mask is removed, showing a bare metal, uncoated substrate. Silver is then deposited onto the uncoated substrate surface using, preferably electroplating techniques. Silver ions in an electrolyte will be preferentially attracted to an electrically conductive substrate surface: it will not readily bond to the carbon surface as the carbon allotropes comprising DLC has, typically a high electrical resistance.

For example, a round metal rod, made from an approved metal biomaterial, has a small diameter wire, preferably copper, attached in a helical form along the entire length of a sample medical device. The device is then coated with DLC. When completed, the copper wire is careftully removed. The DLC coated object is then placed in an electrolyte, suitable for silver plating. Silver will deposited, preferentially onto the exposed metal substrate; it will not coat the DLC as the film is not electrically conductive and therefore will not act as a cathodic element in the electroplating process Masking a suitable substrate can also facilitated by other means. Adhesive labels, resins, paints or metal or polymer forms can be attached to the surface or surfaces of a medical device, prior to DLC coating. Said alternative masks being removed after initial coating, in preparation for silver coating. Surface area being masked and the time that electroplating takes place, are the prime methods to control the volume of silver deposited. Equally, the geometry of the masking media will determine the exposed surface area of the subsequently coated silver.

Alternatively, if small quantities of silver are required, the medical device can be coated with DLC on all exposed surfaces. The DLC process has significant compressive stresses in its structure. Relaxation of the substrate occurs under the influence of these stresses, generating voids and fissures. Small areas of uncoated substrate exist under the DLC coating, allowing silver ions to be attracted during an electroplating process. Voids and fissures will thus contain silver.

A further method of producing an integrated mixture of carbon and silver is made possible by the plasma coating process. DLC coatings are produced by the disassociation of hydrogen and carbon from a precursor gas such as acetylene or methane: carbon ions are attracted to a suitable target by mean of a bias voltage, the target being at lower DC potential than the carbon ions, causing said ions to be energetically attracted to the target, forming a covalent bond. Elemental silver or its compounds, introduced into the plasma will form silver ions with a similar attraction force to the target. However, silver ions now entrapped with the forming carbon film and are retained by mechanical forces, not by chemically bonding with carbon.

A metal implants constructed of a suitable metal alloy, used for example as orthopaedic articular devices, trauma devices for fractured bones, reconstruction instruments and devices: cardiovascular stents, guide wires, occlusion coils, pacemakers, in-dwelling defibrillators, ventricular assist devices, other stents, general and special surgical instruments, have a dual coating consisting of diamond-like carbon applied to all tissue exposed metal surfaces. However, prior to the carbon coating, the medical artefact has a metal wire, preferably copper, wrapped around it and secured by tying terminal ends or by other fixation arrangements. Other surfaces that do not require DLC coating may be equally masked using suitable barrier materials.

The artefact is then coated, preferably using plasma assisted chemical deposition with a DLC coating, until it is sufficiently thick, in the range 10 nanometers-4.Omicrons: the coating process is stopped, the artefact removed from coating facility and the masking arrangement removed. The artefact is then coated with silver using, preferably using established industrial electroplating techniques; the deposited metal attaching only to exposed metal surfaces. If there are other surfaces, for example, bearing surfaces as in the case of articular implants used for joint replacement, said surfaces are masked by other means, such as the commonly used paints, well known in the art, covering an area that would not benefit or be deleterious from silver coating.

By way of example, the following drawings disclose the means to apply two coatings onto a sample metal substrate.

Fig 1.

I shows a plain metal rod.

2, a spiral of copper wire as a mask formed on:- 3, rod's outer surface. Fig 2

1 shows a plain metal rod.

4 shows diamond like carbon coating, coated only on to unmasked shows an uncoated metal surface. Fig 3

1 shows a plain metal rod.

4 shows diamond like carbon coating surface 6 shows a track of silver, electrodeposited onto masked area, 2.

R.EFS.

Bailey L.O. Lippiat S. Biancanello F.S. Ridder S.D. Washburn N.R.

The quantification of cellular viability and inflammatory response to stainless steel alloys.

Biomaterials. 2005 Sep; 26 (26): 5296-302 Saldana L. Vilaboa N. Valles 0. Gon.zales J. Munuera L Osteob last response to thermally oxidized Ti6AI I 4V alloy J.Biomed. Mati Res. A 2005 Apr 1;73(1)97-107 Suba C. Velich N. Turi C. Szabo 0 Suthce analysis methods of biomaterials used in oral surgery: lit, review J. Craniofac Surg 2005 Jan;16(1):31-6 Hegadus C Lampe I Vitalyos G. Daroczi L. Beke D. Applicability of titanium in preparing dental prostheses for allergic patients Fogozy Sz 2004 Dec: 1997(6):239-45 Lappalamen R Santavirta S S. Potential of coating in total hip replacement Clinical Orthop. Relat. Res 2005Jan;(430):72-9.

Review.

Pourbaix M. Electrochemical corrosion of metallic biomaterials.

Biomaterials. 1984 May;5(3): 122-34.

Review.

Silver S, Phung Ic T. Silver G. Silver as biocides in wound and burn dressings and bacterial resistance to silver compounds J lad Microbial Biotechnol. 2006 Jul; 33(7):627-34.Epub 2006 May 25 Review Oloff's A, Gross-Siestrup C, Bisson S, Rinck M, Rudolph R, Gross U. Biocompatibility of silver coated polyurethane catheters and silver coated Dacron material.

Biomaterials. 1994 Aug; 15(1 0):753-8 Bosetti M, Masse A, Tobin E, Cannas M. Silver coated materials for external fracture devices: in vitro biocompatibility and genotoxcity.

Biomaterials. 2002 Feb; 23(3) 887-92

Claims

Claims.

1) A medical device for use inside or upon a living organism has two thin-films deposited onto its surface to protect biological tissue from undesirable molecules and migrating cationic or anionic species coming from the medical device.

2) As claimed in claim 1. a medical device made from a metal or polymer or ceramic or a combination of any of these materials, is furnished with biologically protecting films.

3) According to and as claimed in claims I and 2, protection of biological tissue is facilitated by one, thin-film to reduce ion, cation, monomer, polymer migration from implant to tissue.

4) As claimed in claim 3, a second coating consists of a non-organic biocide, electrodeposited and chemically bonded to a medical device.

5) As claimed in all preceding claims, a biologically protective diffusion barrier consists of a diamond-like carbon film, deposited by means of plasma assisted chemical vapour deposition, also referred to as plasma enhanced chemical vapour deposition. The film is deposited with a thickness of between 0.1 to 4.0 microns.

6) As claimed in claim 5, diamond-like carbon is deposited onto a medical device that is provided with a mask or shield to prevent coating in a desirably shielded or masked area.

7) As claimed in claim 6. A masking arrangement consists of a copper wire continuously or discontinuously wrapped around an implanted medical device.

8) As claimed in claim 7. a masking arrangement consists of copper sheet or strip, attached to a medical implant by mechanical means or adhesive means.

9) As claimed in claim 8, other metals wires, sheets or strip comprised of noble * metals, titanium and its alloys, ferrous-based alloys, nickel and nickel alloys, act as a mask or shield.

:. 10) As claimed in claim 6, diamond-like carbon is deposited in zones upon a * medical device using a masking arrangement consisting of one or more panels made of a metal or polymer with apertures arranged to advantageously permit * *** the passage and bonding of carbon ions onto the surface of said medical device. S*.* * *

11)As claimed in claim 4, an electro-deposited biocide is elemental silver, deposited on the site or sites that have not been coated by diamond like carbon.

12)As claimed in claim 4, a deposited biocide may also consist of other elemental metals such as zinc or copper.

13)As claimed in all preceding claims, a medical device that has non-electrically conductive surfaces, for example, a polymer or ceramic is first coated with an electrically conductive film. The medical devices in then masked and coated with diamond-like carbon 14) As in claimed in claim 13, Masking arrangements are removed from a medical device and the exposed electrically conductive coating is then coated with an elemental biocide.

15) As claimed in claim 1, 2 and 3, a dual coating applied to a medical device, consisting of a continuous plasma deposited thin-film, consisting of amorphous diamond-like carbon and elemental silver.

16) As claimed in claim 15, a method of co-depositing diamond like carbon and elemental silver by the vaporisation of metallic silver and the ionisation of silver vapour in a plasma, concurrently with carbon ions; a mixture of sp2 and sp3 carbon and silver are attracted to a preferred target by means of a DC bias current, anodically and cathodically applied to a target and plasma respectively.

17)As claimed in claim 16, a means of producing silver vapour is by melting a quantity from 0.5-50 grams. of silver in a suitable receptacle by mean of an electrically heated filament. A ceramic crucible is furnished with a heating element surrounding its outer surface and is able to reach a temperature is excess of the nominal melting point of silver.

18) As claimed in claim 15, a means of producing co-deposited elemental silver consists of a saturated solution of silver nitrate; helium gas is then directed through the silver compound to release silver nitrate vapour into a vacuum chamber containing plasma. Nitrogen is then disassociated from the silver compound, releasing silver ions into the plasma field. Silver and carbon ions are * then co-deposited onto a suitable target by means of a DC bias current as *,** claimed in claim 16. * S..

" 19)As claimed in claim 16, a DC bias applied to a plasma and target cathode and anode under vacuum, has a potentially difference of not less than 50 volts, not : ..* more than 600 Volts.

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