Methods for surface modification

Abstract

A method of modifying surfaces of a device, for example, a medical device, is disclosed. The method includes modifying a surface of a device by providing a device, exposing the device to a reactive gas and plasma energy to create a plasma deposited surface on the device, and quenching the device with the reactive gas. The device exhibits changes in its surface properties thereby making it more desirable for an intended use.

Description

[0001] The present invention relates to methods for surface modification. More particularly, the present invention relates to methods for surface modification of medical materials, such as, for example, biomaterials.DESCRIPTION OF RELATED ART[0002] For devices used in many fields, it is desirable to use materials having particular surface properties suitable for a given purpose so that the device optimally functions without causing adverse effects. One such field where it is desirable to have specific properties for the surface material of the devices is the medical field, where the surface characteristics of biomaterials are particularly important.[0003] Biomaterials are typically made of inert metals, polymers, or ceramics to ensure durability. Furthermore, biomaterials are often desirably constructed of materials that do not adversely react with the physiological environment with which they come into contact, such as with blood or tissues. More particularly, many biomedical devic...

AI Technical Summary

Benefits of technology

[0024] Another advantage of the present invention over conventional coating techniques is that the present invention is universal. Conventional coating techniques are restricted by the device to be coated, that is, the techniques must be necessarily different for each material or device in order to modify its surface properties. However, the present invention is applicable to all types of materials and devices and, thus, makes it possible to treat a wide variety of materials and devices with the same process.

[0025] The coating methods of the present invention also result in uniform application of an altered surface property. Conventional surface coating procedures suffer from surface abnormalities and inconsistencies as a result of uneven distribution of surface coating during the coating process. These surface abnormalities affect the function of the materials and prevent uniform property characteristics. In contrast to conventional techniques, the process of the present invention produces a highly controlled and pure surface free from contaminants.

[0026] The inventive methods also allow the treated surface of a material, such as, for example, a medical device, to be layered with a particular substrate in order to give the entire device surface the property of the substrate. Stated by example, the process of the present invention enables a medical device to have a surface area that is covered by a particular substrate that alternatively may be connected to biologically-active species. Furthermore, as stated previously, a bioactive molecule can be attached to the grafted surface in an optimal manner through several well known affinity chromatography schemes to result in a high degree of conformational integrity and thus biological activity.

[0027] The methods of the present invention use the unique properties of plasma-polymerized surfaces and their ability, when generated by the method described in this invention, to promote optimal free radical grafted surfaces, and to perform such grafting without first treating the plasma-polymerized surface to additional plasma activation that is suggested by the state of the art. The methods also create conformal coatings that do not release the surface modification as is the case with common coating techniques. The method of the present invention creates a plasma deposited surface that can be directly grafted thereupon by using catalysts and vinyl monomers. Biomedical devices can, thus, be treated to be blood compatible, infection resistant, and tissue compatible.

[0028] Another advantage of the method of the present invention is that depositing a plasma film using a propylene gas onto a surface yields a treated surface that is capable of a direct and high density grafting that can be applied long after deposition, as long as, for example, up to and over one week post-deposition. The fact that a high-density graft can be applied directly after plasma deposition and without activation, and that this ability is long lived is clearly counterintuitive to the teaching of the art. Observing the unexpected performance on non-activated control samples for plasma deposited films that were subsequently activated discovered this.

[0029] Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.

Problems solved by technology

For example, disposable surgical tools may become infected with bacteria during a course of a long operation and reuse of the tool during the operation may promote bacterial infection in the patient.

For example, one type of biomaterial, polyolefin, can result in devices that have non-polar properties and therefore may result in poor adhesion, printability, and adaptability of its surface for coatings.

These methods have proven to have limited success due to their general ineffectiveness and expense.

Conventional techniques for coating a biomedical device with a desired surface layer typically are expensive, time-consuming, inconsistent in results, and do not ensure either a uniform layer of a surface material on the medical device or that the coating does not wear off in time.

Thus, the properties of the surface layer of the device may vary between areas and thereby affect the overall surface property of the device.

Furthermore, different devices subject to the same coating technique may result in different properties.

Another disadvantage of typical processes for applying a coating to a biomedical device is that each material requires a different technique to modify its surface.

For example, metals, ceramics, and polymers have different surface properties and do not lend themselves to a common coating process.

Polymers typically are hydrophobic or, at best, have relatively poor wetting, and therefore are difficult to coat from solutions.

Furthermore, the majority of polymers used for medical devices also are relatively inert and do not possess functional groups that readily enter into direct chemical coupling reactions that could modify their surfaces.

These free radicals however are short lived and lacking in surface density.

Attempts to effect a chain reaction polymerization on such surfaces (graft) with monomers such as acrylamide only works on a few materials and poorly on those few materials.

The results are a slight and patchy grafting with significant areas of no grafting.

First, the plasma itself is a highly reactive state and so many radicals are produced that they end up reacting with each other, resulting in termination and / or neutralization of free radicals.

Biomolecules require a mobile three-dimensional environment to react, and simple adsorption based on charge attraction results in a multipoint spread out attachment that compromises the conformational integrity of the molecule.

The primary limitation is that the most common biomaterials such as PTFE (polytetrafluoroethylene), silicone, PVC (polyvinylchloride), metals, and ceramics do not effectively generate free radicals on their surfaces.

An additional disadvantage to commercial polymers is the additives present contaminate the surfaces and make direct coupling to the native polymer unstable and unpredictable.

Finally, free radicals generated on a polymeric surface by plasma treatment are short lived, and this makes it very difficult to attain optimal free radical grafted surfaces.

Plasma polymerized films can uniformly cover the surface of a polymer with a new composition, but these surfaces as mentioned previously are highly ordered, and attempts to further directly couple molecules at high loadings are difficult.

Attempts to plasma activate a plasma polymerized film and subsequently free radical graft to this surface remove some of the disadvantages, but still suffer from the problems of short lived free radicals, and difficulty in adjusting plasma conditions to obtain optimal graft densities.

Conventional surface coating procedures suffer from surface abnormalities and inconsistencies as a result of uneven distribution of surface coating during the coating process.

These surface abnormalities affect the function of the materials and prevent uniform property characteristics.

The fact that a high-density graft can be applied directly after plasma deposition and without activation, and that this ability is long lived is clearly counterintuitive to the teaching of the art.

This continued flow consumes (quenches) excessive and uncontrollable free radical reactions, and paradoxically leaves the surface more reactive to further grafting reactions, and for a relatively long period of time.

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