WO2015031196A1

WO2015031196A1 - Method and device for surface modification by cold plasma treatment at ambient pressure

Info

Publication number: WO2015031196A1
Application number: PCT/US2014/052321
Authority: WO
Inventors: Subrata Roy
Original assignee: University Of Florida Research Foundation, Inc.
Priority date: 2013-08-26
Filing date: 2014-08-22
Publication date: 2015-03-05

Abstract

A method for plasma treatment of an object, for example, a contact lens or other device, involves the generation of plasma on one or more surfaces by a dielectric barrier discharge (DBD). The object undergoes surface reactions in the plasma which modifies the chemical composition of its surface. For example, a hydrophobic surface of a contact lens can be rendered hydrophilic by removal or conversion of non-polar functionality to expose or form polar and ionic functionality. The cold plasma treatment allows surface modification without distortion of or reaction within the bulk of the object. The method can be carried out in air or other desired gas environment.

Description

DESCRIPTION

METHOD AND DEVICE FOR SURFACE MODIFICATION BY COLD PLASMA TREATMENT AT AMBIENT PRESSURE

CROSS-REFERENCE TO RELATED APPLICATION The present application claims the benefit of U.S. Provisional Application Serial No. 61/870,003, filed August 26, 2013, which is hereby incorporated by reference herein in its entirety, including any figures, tables, or drawings.

BACKGROUND OF INVENTION

Gas permeable contact lenses and intraocular lenses made from silicone-containing materials can be subdivided into various classes, for example, hydrogels and non-hydrogels or rigid and soft. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels absorb and retain water. Such silicone devices tend to have relatively hydrophobic surfaces that have a high affinity for lipids, which is a problem for contact lens wear.

Various methods have been pursued to modify the surface of contact lenses to improve their compatibility against the eye by increasing the surface hydrophilicity. Increasing the hydrophilicity can improve the comfort of wearing contact lenses and diminish deposition of lipids and proteins from the tear film. The surface properties of an extended wear lens are especially critical for retaining comfort and the health of the eye.

Plasma treatment of the lenses has been pursued to improve surface properties. Examples of plasma treatments include plasmas from: inert gas or oxygen (U.S. Pat. Nos. 4,055,378, 4,122,942, and 4,214,014); various hydrocarbons and halohydrocarbons (U.S. Pat. No. 4, 143,949, 4,312,575, 5,153,072, 5,091,204, 5,034,265, and 4,565,083); oxidizing agents and solvents (WO 95/04609 and U.S. Pat. No. 4,632,844); and treatment with a hydrogen plasma followed by an oxidizing plasma (U.S. Pat. No. 7,094,458). Plasma treating operations are often performed in large, batch reactors, for example as disclosed in U.S. Pat. No. 5,503,515. Alternatively, plasma treatment of individual lenses has been disclosed, for example, in U.S. Pat. No. 7,250,197.

Recently Shin et al. J. Korean Phys. Soc. 55(6), 2009, 2436-40, has disclosed the use of a cold plasma for treating contact lenses in air at room temperature, where ridged glass permeable (RGP) lenses were treated using a discharge type plasma system using a lens positioned on a rotating sample holder. A decrease of the wetting angle resulted with a plasma power of 200W and an exposure of about 4 minutes. The wetting increase was correlated to the decrease in SiC bonds and the increase of SiO bonds upon plasma treatment. A more efficient process for plasma treating lenses is desirable. It is desirable to perform the plasma treatment at atmospheric pressure and in air or other gas atmospheres and to use less power to effectively plasma treat a lens or other device surfaces than that employed in the disclosed literature. DETAILED DISCLOSURE

Embodiments of the invention are directed to the surface modification of contact lenses and other devices, where a wettable or more hydrophilic surface is required, by cold plasma in air and a plasma generation device for the treatment of objects. The plasma is generated by a dielectric barrier discharge (DBD), a non-thermal discharge, where a dielectric layer between electrodes causes the plasma discharge to occur at and immediately above a surface comprising at least one electrode, generally, a multiplicity of electrodes. The surface modification device can comprise a container or holder for the object with the container configured to hold and present the contact lenses or other devices to the plasma and can be a moving device to aid in translating the object over and on and off of the area of the plasma surface.

In an embodiment of the invention, the device for surface modification comprises at least one first electrode that is exposed at a surface in the presence of air or other desired gas and is separated from one or more second electrodes by a dielectric layer. The electrodes generate plasma at the surface of the first electrodes by the application of a voltage across the first electrodes being powered electrodes and the second electrodes being ground electrodes. The surfaces can be flat or have any shape, for example, one that facilitates the placement of movement of one or more contact lenses or other devices over the surface. The voltage can be applied as an A.C. voltage. The frequency of the current establishes a period of the A.C. cycle where electrons must travel to the electrodes and generate a charge but where heavier ions cannot. In air or other gases at normal atmospheric pressure a homogeneous glow can be maintained at 3 to 20 kHz RF and rms electrode voltage between 2 to 15 kV, with an electric field of about 30 kV/cm. Although the voltage is high, only a few milliamps current is required to sustain a RF driven barrier discharge.

Surfaces having an array of embedded electrodes for producing a plasma are formed. In an embodiment of the invention, a voltage between 2-20 kV can be applied across electrodes with 1-50 kHz RF A.C. voltage. The powered electrodes and the ground electrodes form a crossing pattern. Driving the powered electrodes with a voltage relative to the grounded electrodes produces plasma that can modify the surface of a device. In an embodiment of the invention, the plasma surface electrodes can have a thin insulating layer, for example, Teflon®, or other thin dielectric material layer coating over the electrodes. The DBD device can comprise a pair of surfaces having the working electrodes, such that the device can be placed between the two surfaces. As desired, the electrodes can be placed in a manner that generates a thrust, promoting a gas flow over the surface if desired. Such a flow can be used to promote transport of contact lenses or other devices across a surface or between two surfaces and/or to draw the desired gas volume over the surface or between surfaces where the plasma is formed. Electrodes can be oriented to induce a rotation of the contact lenses or other devices by the gas flow while situated within the plasma. Transport of the devices through the generated plasma can be carried out by a mechanical device with a container for the contact lens or other device, where the container or the entire mechanical device passes through the plasma. Generally, the container is constructed to have minimum physical contact with the contact lenses or other devices to be modified.

The DBD plasma device can be of a construction similar to that disclosed in Roy et al. International Publication No. WO 2009/067682, which is incorporated herein by reference. The DBD plasma device can be portable and can be powered by a power supply as described in Roy et al. International Publication No. WO 2013/096956, which is incorporated herein by reference. The position of the electrodes can induce the flow of gases over the surface or between surfaces, as taught in Roy et al. U.S. Patent Application Publication No. 2013/0038199, which is incorporated herein by reference.

In an embodiment of the invention, contact lenses or other devices are treated by the plasma when placed upon or immediately above the surface of the DBD plasma device. The contact lens can be a rigid or soft lens and can be an oxygen permeable lens and can comprise hydrogels, silicone hydrogels or other materials. The devices can be treated individually or where a plurality of devices is treated simultaneously or where devices can be treated in a continuous manner where unmodified devices are continuously introduced to the plasma surface(s) and surface modified devices are continuously removed. The method comprises placement of at least one object on or above the DBD surface such that the plasma contacts the object. The method is carried out at ambient pressure or at a modestly elevated or reduced pressure, for example, from 0.5 to about 1.5 atmospheres. The atmosphere can be air or it can be any desired gas, such as nitrogen, argon, or other gas, and can include other components to promote specific modifications of the device surfaces as desired. For example, air can be wet or dry, and can be combined with other gases, including oxygen or nitrogen to have a desired concentration of oxygen. Other gases that can be included are ammonia, sulfur oxides, nitrogen oxides, halogens, carbon dioxide, or any other gases determined to be beneficial for the modification of a device's surface. The period of contacting of the contact lens or other device with the plasma can be for any necessary period of time and that period can be one of constant or continuous contact or can be discontinuous, where the contacting time is divided into portions of the entire time needed for treatment in portions that are equal or different lengths. The periods for contacting can be controlled by removing the device from the plasma or by stopping the plasma being generated. The period of time is sufficient for chemically modifying the surface and not only removing impurities absorbed on or residing on the surface of the object. The period of time can be, for example, one to ten minutes.

Devices to be so modified by plasma treatment can be polymeric in nature, including homopolymers, block copolymers, polymer blends, branched polymers, or hyper branched polymers. The polymers can be organic, inorganic, or any combination thereof. All surfaces of the devices can be modified or portions of the devices can be materials incapable of being modified. Coatings that resist modification can be placed of a portion of the device's surface. The coating may be readily removed, or are sacrificial coatings that allow the resulting device to have portions that are modified and other portions that are not modified. Modification can be carried out by a variety of methods, including, but not limited to, printing, painting or other coating techniques; for example coatings can be selectively placed on a device by ink- jet printing.

All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification. It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.

Claims

CLAIMS I claim:

1. A method of modifying surfaces of a device, comprising:

generating a plasma by dielectric barrier discharge (DBD) on at least one plasma surface of at least one electrode of a plasma generating device, wherein the surface is in the presence of a gas or gas mixture;

placing at least one device in contact with the plasma of the plasma surface; retaining the contact of the device with the plasma for a period, wherein the plasma promotes reaction that modifies the surfaces of the device to form a surface modified device; and

removing the surface modified device from the plasma surface.

2. The method of claim 1, wherein the device is a contact lens.

3. The method of claim 1 , wherein the gas mixture is air.

4. The method of claim 1, wherein the device is retained in a container that also contacts the plasma.

5. The method of claim 1, wherein the period of retaining is continuous or discontinuous.

6. The method of claim 1, further comprising transporting the device over the plasma surface.

7. A plasma treatment device, comprising: at least one dielectric barrier discharge (DBD) plasma generator comprising at least two electrodes and a dielectric layer; a power supply; and a passive or active gas supply, wherein the plasma resides above a surface comprising at least one of the electrodes, and wherein the surface is configured to receive at least one object for surface modification.

8. The plasma treatment device of claim 8, wherein the gas supply is air.