DE10064096A1 - Permanent hydrophilization of contact lenses involves forming a surface coating of diamond-like carbon in a reducing plasma containing a carbon source followed by treatment in oxidizing, oxygen-containing plasma - Google Patents

Abstract

A method for the surface coating of contact lenses, especially silicone contact lenses, with a layer of diamond-like carbon (DLC) involves (a) treatment of the lens surface in a reducing plasma containing a source of carbon and (b) further treatment in an oxidizing, oxygen-containing plasma. An Independent claim is also included for silicone contact lenses coated with a layer of oxidized DLC, especially lenses made by the above method.

Description

The invention relates to a method for permanently stable Hydrophilization of a contact lens surface as well a silicone contact lens with such a stabilized hydrophilized surface.

Silicone contact lenses, e.g. B. from polydimethylsiloxane, ha compared to other contact lens materials such as Polymethyl methacrylate or the like, the advantage of a particular high oxygen permeability, which is an aerobic Glycolysis in the corneal epithelium ensures without it this can lead to hypoxia. The oxygen Permeable DK value can be well over 300 stride. The DK value is the product of diffusion coefficient and solubility constant of Oxygen in the polymer. They also have silicone contact lenses outstanding biocompatibility, so that also with long-term wear of the contact lens hardly ever occur. The deformation of silicone contactlin sen when wearing is low. Furthermore, they are quite right resistant to the accumulation of bacteria.

A disadvantage of silicone contact lenses is that their ba sismaterial per se is an extremely strong hydrophobic Surface and it leads to droplet formation of the tears liquid is coming. The lens can become defective Tight wetting on the cornea so that it only can still be removed with difficulty. The hy drophobic surface can cloud quickly and is in Other difficult to maintain.  

Silicone contact lenses are usually molded process manufactured. This will be the first liquid starting material in one of the later lens given a correspondingly large pot, one of the eye crumbs mung adapted concave bottom surface. After encore a stamp is placed on the reaction partner, which the inner curvature facing the surface of the eye is defi niert (contact lens back surface). By using it different molds with different curvatures floors and stamps with different curvatures Convex and concave shapes can be created in this way Contact lenses with different lens powers and un different eye curvatures. To this Any contact lenses are as needed produced. After shaping and polymerization / vul The contact lenses are cannulated with tetrahydro furan (THF) removed. This THF must be removed from the mold be extracted. Then the lens is in aqueous solution solution washed with ultrasound and then dried net.

Because the contact lens thus obtained is extremely hydrophobic has areas, it must be hydrophilized to them to be able to wear at all.

For example, it is known to coat silicone rubber lenses by means of an immersion process. So z. B. from the company SurModics Inc., 9924 West 74 ^th Street, Eden Prairie, MN 55344 to 3523 USA a method of photo-copo lymerisation of surfaces of films and membranes and for hydrophilizing among others silicone contact lenses known as in WO 9734935 and WO 9716544 A1 are described.

Furthermore, the so-called hydromer immersion process (HYDROMER® coatings for medical devices; 35 Columbia Road, Branchburg, New Jersey 08876 USA). there are by means of coatings with hydrogel polymers Slippery surfaces and partly antimicrobial modified (US 4,100,309; 4,119,094; 4,642,267; 4,769,013).

Also the chemical modification of surfaces using Gas flame, corona discharge or plasma excitation is known.

From US 4,822,359 a polymethyl methacrylate (PMME) contact lens is known, the surfaces of which are coated with a layer of diamond-like carbon (so-called diamond-like carbon or DLC layer) with the aim of protecting the eye from UV radiation , The DLC layer is produced in a plasma coating process (PE-CVD process or plasma enhanced chemical vapor deposition) in an H ₂ and hydrocarbon gas plasma. However, such DLC layers are hydro phobic.

In medical technology, it is also known to be silicone coated surfaces with a DLC layer, about the scratch resistance of the material or solution to improve medium durability, or to improve the per se to reduce the very high gas permeability of silicone. These layers are significantly thicker than 50 nm.

In-house attempts to use a silicone contact lens with a to provide hydrophilic coating, in particular by Plasma polymerisation with HMDS / HMDS-O (HMDS = Hexamethy lendisilazane and HMDS-O = hexamethylene disiloxane)  Lenses that are either optically unsatisfactory or were not stable in storage. A plasma treatment with sow raw material or noble gases alone led to short-term hydrophilic contact lenses, however, their good benet properties within a few days, at the latest after four weeks of storage, more than 70% ver lost.

The object of the invention is therefore to initiate a method give which for a durable hydrophilicity the contact lens surface. Beyond that the procedure the oxygen permeability of the lens not or only slightly hinder. The so obtained Lenses should also have a high level of comfort and can be worn continuously for a long time.

To achieve the object, a method for surface coating of a contact lens, in particular a silicon contact lens, with a layer of diamond-like carbon (DLC) is proposed, which comprises the steps of:

• a) Treating the contact lens surface in a redu ornamental, a carbon-providing agent the plasma and
• b) post-treatment of the contact lens surface in one oxidizing, oxygen-containing plasma.

The resulting contact lens lasts for months permanently hydrophilic, shows a high oxygen permeability liquidity and also points one towards me surface resistant to mechanical influences.

Surprisingly, it was found that with the inventions method according to the invention the oxygen permeability  Lentils are hindered so little that even the tall pig non-permeability of silicone contact lenses is affected.

Except for silicone contact lenses, this is coating procedure also for flexible hard contact lenses from others Ren polymer materials such as thermosets can be used materials. These lenses also often have only slightly wettable lens surfaces, so too where hydrophilization is necessary. Especially because with these other contact materials the oxygen permeability does not reach as high values as with Si silicone material, but still for gas exchange on the Cornea surface is important, must be particularly ge be careful that the hydrophilizing coating does not affect oxygen permeability.

In the first step a), a plasma polymer layer which is a nano-diamond cluster with flexible Chain forms. In the second step b) DLC layer obtained after-treated oxidizing, whereby the wettability of the contact lens surface permanently is improved.

As carbon-providing agents in the process according to the invention, all carbon-containing sources can be used which, under the reduced conditions used, form nano-diamond clusters in the plasma, such as CO, CO ₂ and in particular hydrocarbons. The hydrocarbons can be aliphatic and / or aromatic.

However, aliphatic hydrocarbons are preferably used, with short-chain hydrocarbons such as methane and / or acetylene being particularly preferred. It has also proven to be advantageous to additionally add H ₂ and / or noble gases to the plasma used in step a), preferably before argon.

The plasma gas used in step b) can, in addition to oxygen, also hydrocarbons or / and Noble gases contain, for simplicity and around to reduce the expenditure on equipment, it is preferred to use the same gases as in step a).

The optical properties of the layer become special well if the energy used to excite the plasma in step a) is greater than in step b) or / and the Step a) is carried out longer than step b).

In order to temper the contact lens on both sides, there is the Possibility that in a first sequence of steps a) and b) the one lens side is then reimbursed the contact lens turned over and then in a second Follow steps a) and b) the second side of the con tact lens is remunerated.

Alternatively, there is the option of both sides first to treat the contact lens one after the other according to step a) deln, and then both sides in sequence according to step b).

A particularly good oxygen permeability becomes common usually with a layer of only 5 to 50 nm thickness, preferably 10 to 30 nm thick. However, there are thicker layers are also possible without the oxygen through to noticeably hinder casualness.  

It has proven to be advantageous in the method according to the invention proven as the basic material for the production of the Kon tactile lens materials with a low content to use on Pt. The Pt content is preferably below 20 ppm, in particular <10 ppm, with Pt contents of <5 ppm are particularly preferred. Such materials are sold as medical grade and are as silicones for example from Bayer, Germany or from Nusil Technology, Germany available.

Furthermore, eventu has proven to be advantageous all impurities and / or not or not completely dig polymerized low molecular weight components from the Lens removed after polymerization or vulcanization NEN. This removal is conveniently done before DLC coating according to the invention and is preferred carried out by means of an extraction. Suitable extract agents are easy to determine and by the specialist are especially liquids or fluid mixtures, in which the impurities dissolve well. An esp extraction fluid is particularly suitable for silicone lenses Water and tetrahydrofuran, the multi-stage either can be used in succession or as a mixture.

According to the invention, it has proven to be expedient Perform extraction in an ultrasonic bath. Prinzi However, other extraction methods such as z. B. heating and / or stirring the extraction solution, if necessary even possible under reflux.

The invention also relates to a contact lens as used with the method described above is obtained.

The invention will now be described in exemplary embodiments of the accompanying drawings. Show it:

Figure 1 is a schematic cross section through the upper surface of a silicone contact lens, provided with a DLC coating according to the invention. and

Fig. 2 is a diagram from which the durability of the hydrophilized surface can be seen, the abscissa shows the storage time and the ordinate shows the water contact angle as a measure of the hydrophilization, it corresponds to the following Table 1.

Table 1

The DLC layer is applied to the surface of silicone chew Tschuk contact lenses preferably using high pure starting components with an extremely low Ka catalyst content applied. In the present example the lenses were made using 1 part by weight of Si silicone component B500A from GE Bayer Silicones and 1  Part by weight of the associated silicone component B500B ver mixes, and in an impression system using Molding tools for a spherical contact lens in the case range from +40 to -40 dpt. After dosing The vulcanization of the liquid silicone rubber took place within 45 minutes at 110 ° C in a heating oven. The lenses were then cooled and demolded.

To avoid impurities or low molecular weight components remove, followed preferably a multi-stage extract tion in tetrahydrofuran and deionized water. That so material obtained is purely aliphatic polydimethylsi Loxan. Then the lenses were used for coating prepared dry.

For the adherent, hydrophilic coating of the silicone lenses treated as before with a DLC layer, these were placed in a high-frequency hollow cathode plasma coating system, model PlasCon HCD from PlasmaConsult GmbH. For this purpose, the silicone lenses were placed manually on the sample holder with tweezers with the concave surface facing upwards. The vacuum chamber of the system was closed and evacuated to 0.2 mbar. Then the process-controlled coating of the concave lens surface began. For this purpose, the lens surface with noble gas, e.g. B. Argon, excited and with 30 sccm (standard cm ³ ). Me thanplasma coated under a power of 40 W within 5 minutes and an excitation frequency of 13.56 MHz ( Fig. 1). This was followed immediately by a second process step, also with an argon stream and 30 sccm methane, but additionally with 20 sccm oxygen at a power of 10 W for 2 minutes.

This two-step process was made after manual flipping of the lenses by 180 ° C for the convex lens surface repeated once.

Then the lenses could be removed and placed in physio logical saline solution. The fat the DLC layer on the lens surface was in each case 10 to 30 nm. Read with such a coating system 100 to 150 contact lenses in batches coat per hour.

The plasma coating process allows the application a uniformly thick layer even on non-planar or complicated shaped substrates, such as contact lenses. With the so-called "cold plasma", the Ab occurs Storage at high rates at low temperatures during the coating. The resulting layer forms a hydrophilic with excellent optical transparency Surface, so that the silicone contact lenses also Room temperature are long-term storable and also mechani withstands loads such as the manual Lin Sen care with suitable care products. The high gas permeability of the silicone substrate is determined by the Be stratification not affected.

The layer thickness is 10 to 50 nm, preferably in the loading range from 25 to 45 nm, with a continuous Layer thickness of approximately 35 nm is particularly advantageous has according to the desire, on the one hand, the surfaces to make the contact lens compensation hard and permanent, on the other hand, the oxygen permeability does not increase affect.  

The contact lenses produced according to the invention have permanently hydrophilic properties and are in any aqueous storage solutions, such as preserved ones physiological saline, or usual storage solutions for hard contact lenses Long-term storage ig. However, these solutions should not contain organic solvents Ownership of solvent because, for example, silicone swell the lenses and the coating structure is burdened. The lenses according to the invention can be individually duels can be worn continuously for up to approx. 4 weeks.

The contact lenses coated according to the invention, in particular especially those made of silicone keep their extreme Gas permeability with the best hydrophilic surfaces properties without the basic properties of the lenses endanger, such as their dimensional stability, rebound resilience strength, tear resistance, optical transparency and optical Imaging properties. In addition, the DLC layer does the silicone lenses are biocompatible, without inclination to one Corneal adsorption, high deposition rates of approximately Pro complexion and lipid structures of the tear film on the lenses surface and the like. In contrast to so-called hydro Gel contact lenses require the herge according to the invention lenses provided only a small amount of tear fluid, to wet the surface. All of this causes an au Exceptional comfort, so that the lenses over can be worn permanently in the eye for a long time.

A diagram for the comparison of the stability under different surface treatments on silicone rubber lenses is shown in FIG. 2, the storage time in days at 23 ° C. being indicated on the abscissa and the water contact angle in degrees on the ordinate. The contact angle is understood to be the angle formed between the surface of the contact lens and the surface tangent at the base of a water droplet adhering to it, measured on the inside of the droplet. At the very top (curve A) is the water contact angle of an untreated silicone contact lens. It is constantly about 120 °. The middle curve B relates exclusively to contact lenses hydrophilized in the oxygen plasma, which were treated with a physiological saline solution after the plasma treatment and stored therein. Here, too, the water contact angle increases slowly and after a longer storage period reaches a value in the range between 90 and 100 °. The lower curve C relates to DLC-coated silicone contact lenses according to the invention. This curve shows a much slower increase in the water contact angle, which adjusts to a much lower range between 50 and 60E and is essentially retained even after a very long storage period of more than 100 days.

Claims (14)

1. A method for the surface coating of a contact lens, in particular a silicone contact lens, with a layer of diamond-like carbon (DLC), which comprises the steps:

• a) treating the surface of the contact lens in a reducing plasma containing a carbon source and
• b) post-treatment of the contact lens surface in an oxidizing, oxygen-containing plasma.

2. The method according to claim 1, characterized in that the carbon source used in step a) comprises graphite, CO, CO ₂ and / or hydrocarbons. 3. The method according to claim 1 or 2, characterized in that the hydrocarbons aliphatic hydrocarbons and / or aromatic Are hydrocarbons. 4. The method according to any one of the preceding claims, characterized in that in step a) the Kon tactile lens surface additionally with hydrogen or / and noble gas, preferably argon, is treated. 5. The method according to any one of the preceding claims, characterized in that the plasma in step b), in addition to oxygen, hydrocarbons or / and noble gases.   6. The method according to any one of the preceding claims, characterized in that in step b) - except Oxygen - the same gases as in step a) be used. 7. The method according to any one of the preceding claims, characterized in that the plasma excitation power in step a) is greater than in step b). 8. The method according to any one of the preceding claims, characterized in that the process time of Step a) is longer than the process time from Step b). 9. The method according to any one of the preceding claims, characterized in that the contact lenses both be surface-coated on one side. 10. The method according to claim 9, characterized in that in a first episode Steps a) and b) one side of the contact lens is tempered, then the contact lens vice versa rotates and in a second sequence of steps a) and b) the second side of the contact lens is tempered. 11. The method according to claim 9, characterized in that both sides of the Kon tactile lens successively treated according to step a) and then both sides of the contact lens treat each other in accordance with step b). 12. The method according to any one of the preceding claims, characterized in that the lenses used material polydimethylsiloxane or a thermosetting  Plastic is, preferably polymethyl methacrylic lat (PMMA) or hydroxyethyl methacrylate (HEMA). 13. The method according to any one of the preceding claims, characterized in that by the steps a) and b) layer 5 to 50 nm obtained, preferred 10 to 30 nm thick is stored. 14. Silicone contact lens, in particular manufactured according to any of the preceding claims, characterized in that their surface with an oxidizing treated diamond-like carbon material layer (DLC) is coated.