United States Patent:   6,011,082

Assignee:  Pharmacia & Upjohn AB (Stockholm, SE)

Filed:  June 2, 1997

A process for forming a surface modification on a polymer substrate and polymer substrates having such surface modifications. The process comprises the steps of absorbing a swelling monomer into the polymer substrate for a period of time in order to swell the polymer substrate; removing the swollen polymer from the swelling monomer; transferring the swollen polymer to a reaction mixture containing at least one functional monomer; polymerizing the functional monomer in the reaction mixture containing the swollen polymer substrate for a period of time; and removing the polymer from the reaction mixture. Because the surface modification produced by the process is a surface interpenetrating polymer network, the process is not sensitive to the reactive groups located on the surface of the polymer substrate. Further, the surface interpenetrating network bonds to the polymer substrate through caternary connections or other forms of chain entanglement and thus is quite stable. Polymer substrates having the surface modification of the present invention are capable of having a surface modification agent, such as heparin, adhere to the surface of the polymer substrate.

SUMMARY OF THE INVENTION

In accordance with the present invention, a process for forming a surface modification on a polymer is provided. The process modifies the properties of the polymer at its surface. The process can be used to increase the ability of a surface modification agent, such as heparin, to adhere to the surface of the polymer. The surface of the polymer is modified by a surface interpenetrating polymer network, which provides for the indirect bonding of the polymer network with the surface of the polymer substrate in a caternary connection or other form of chain entanglement. There are no direct bonds to any reactive groups located on the surface of the polymer substrate, so the process is not sensitive to the particular reactive groups located on the surface of the polymer substrate. Further, the surface modification of the present invention affects only the surface of the polymer, rather than the bulk of the polymer. Thus, the desirable physical properties of the bulk polymer are maintained. The process also yields uniform surfaces on the polymer, does not weaken or discolor the polymer material, is relatively simple and inexpensive, and provides a surface modification that has long-term stability.

The present invention provides a process for the surface modification of a polymer involving the use of surface interpenetrating polymer networks. An interpenetrating polymer network is a combination of two polymers in the network form, at least one of which is polymerized in the immediate presence of the other. An interpenetrating polymer network is distinguished from simple polymer blends, blocks, or grafts in two ways: (1) an interpenetrating polymer network swells, but does not dissolve in solvents, and (2) creep and flow are suppressed.

In general, the interpenetrating polymer networks of the present invention are prepared by the introduction of a swelling monomer into the surface of a polymer substrate in order to swell the polymer substrate at its surface. The swelling occurs in a solvent, although the solvent may not always be necessary, because the monomer should be able to diffuse into the substrate surface with or without the aid of a solvent. The swelling process occurs at a particular temperature and for a particular time period. The swelling monomer is then catalyzed in the presence of an initiator that has been introduced into the reaction mixture. The swelling monomer may be a crosslinking monomer, a functional monomer, or a combination of both.

In another embodiment of the present invention, the polymer substrate may be removed from the surface modification process of the present invention following swelling and placed in a reaction medium containing a functional monomer, and, in some cases, a solvent. The functional monomer is then polymerized in a polymerization reaction which may be initiated by a catalyst, or by UV radiation, heat, or ionization radiation. The polymerization of the swelling monomer and the functional monomer occurs at a particular temperature for a particular period of time. Upon initiation, polymerization proceeds in the solution resulting in a soluble polymer. On the surface of the polymer, however, the polymerization results in an interpenetrating polymer network due to the presence of the swelling monomer, which polymerizes together with the functional monomer at the surface interface of the polymer substrate.

The surface interpenetrating network formed on the polymer substrate is quite stable. The bonding between the functional monomer and the polymer is indirect, in that catenary connection and other forms of chain entanglement are responsible for the bonding of the coupling agent and the polymer. Because the functional monomer does not chemically react with the substrate, this interpenetrating polymer network process is rather insensitive to the substrate surface, as long as the surface swells to a certain extent. Thus, in order to break the surface interpenetrating polymer network, a covalent bond on the interpenetrating polymer must be broken. Even if such a covalent bond is broken, the interpenetrating polymer will still be entrapped within the surface of the polymer substrate and thus the surface modification to the polymer substrate will remain virtually intact.

The surface modification process of the present invention is useful for modifying the surface of a silicone polymer. Thus, silicone intraocular lenses, silicone contact lenses, silicone particles for a chromatography column, and other medical devices may be formed. Further, the surface modification process is useful for permitting a surface modification agent, such as heparin, to adhere to the surface of a silicone lens having the surface interpenetrating polymer network of the present invention, for instance.

Claim 1 of 8 Claims

1. A process for producing an ocular lens by modifying the surface of a polymer substrate to provide a semi-interpenetrating polymer network therein suitable for coupling with a surface modification agent, said process comprising the steps of:

absorbing a swelling monomer into the surface of a silicon polymer substrate to swell said silicon polymer substrate surface;

polymerizing said absorbed swelling monomer within said polymer substrate surface to produce an semi-interpenetrating network of polymerized swelling monomer having free ends including reactive functional groups extending from said surface wherein said swelling monomer is selected from the group consisting of: reactive functional acrylamindes, substituted reactive functional acrylamides, reactive functional acrylates, substituted reactive functional acrylates, reactive functional allyl crosslinkers, and reactive functional vinyl crosslinkers;

bonding a surface modification agent to said extending functional groups.

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