Contact lens material

Details Contact lens material Contact lens material

1995-06-06

2002-07-23

Mulcahy, Peter D. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S547000, C526S277000, C526S287000

Reexamination Certificate

active

06423761

ABSTRACT:

The present invention relates to copolymers, in particular suitable for use in contact lenses.
The use of synthetic hydrogels for contact lenses was first demonstrated by Wichtecte and Lim in the 1960's. Early hydrogels employed 2-hydroxyethyl methacrylate (HEMA) as principal monomer, together with some of the homologous esters of the glycol monomethacrylate series such as diethylene glycol monomethacrylate and tetraethylene glycol monomethacrylate. It was later found that slightly cross-linked copolymers of the higher glycol monomethyacrylates and 2-hydroxyethyl methacrylate yielded transparent hydrogels that swelled in water to a higher hydration than the hydrogels of 2-hydroxyethyl methacrylate.
The water content of hydroxyalkyl methacrylate based gels can be further increased by the addition of vinyl lactams, methacrylic acids, acrylic acids, acrylamides and methacrylamides. Although the required degree of gel hydration can be achieved by the addition of anionic monomers, it is well known that these gels display high levels of protein deposition on and occasionally within the gel matrix.
It has now surprisingly been found that effective contact lens materials which have both good transparency and a high degree of water swellability are provided by copolymers which have a permanent positive charge built into them. Such polymers are formed by polymerising and crosslinking a neutral diluent monomer, for example HEMA, with a co-monomer bearing a centre of permanent positive charge. These formulations have been found to have a high level of protein resistance to tear component deposition and a reduction in lens water loss.
Accordingly, the present invention provides a crosslinked copolymer which is obtainable by polymerising a neutral diluent monomer or monomers, a monomer or monomers bearing a centre of permanent positive charge, and a bifunctional or trifunctional crosslinking agent.
The crosslinked copolymers of the present invention therefore comprise residues of a diluent monomer or monomers, a monomer or monomers bearing a centre of permanent positive charge, and a bifunctional or trifunctional crosslinking agent.
The copolymers of the invention may be xerogels which do not contain any water. Alternatively, they may be in the form of hydrogels which do contain water.
The invention also provides a process for producing such a crosslinked copolymer, a contact lens material comprising such a copolymer, a contact lens made from such a copolymer, and use of such a copolymer or contact lens material in the production of a contact lens.
Diluent Comonomer
The diluent monomer can act as a solvent for the comonomers during copolymerisation to produce the copolymer if no additional solvent is present. Where the diluent monomer and monomer bearing the centre of permanent positive charges are immiscible a solvent can be used to aid mixing.
Particular examples of diluent comonomers include alkyl (alk)acrylate preferably containing 1 to 12, more preferably 1 to 4, carbon atoms in the alkyl group of the ester moiety, such as a methyl (alk)acrylate and butyl (alk)acrylate; a dialkylamino alkyl (alk)acrylate, preferably containing 1 to 4 carbon atoms in each alkyl moiety of the amine and 1 to 4 carbon atoms in the alkylene chain, e.g. 2(dimethylamino)ethyl (alk)acrylate; an alkyl (alk)acrylamide preferably containing 1 to 4 carbon atoms in the alkyl group of the amide moiety; a hydroxyalkyl (alk)acrylate preferably containing from 1 to 4 carbon atoms in the hydroxy moiety, e.g. a 2-hydroxyethyl (alk)acrylate; or a vinyl monomer such as an N-vinyl lactam, preferably containing from 5 to 7 atoms in the lactam ring for instance vinyl pyrrolidone; styrene or a styrene derivative which for example is substituted on the phenyl ring by one or more alkyl groups containing from 1 to 4 carbon atoms, and/or by one or more halogen, such as fluorine atoms.
It is to be understood that throughout the specification (alk)acrylate, (alk)acrylic and (alk)acrylamide mean acrylate or alkacrylate, acrylic or alkacrylic and acrylamide or alkacrylamide respectively. Preferably alkacrylate, alkacrylic and alkacrylamide groups contain from 1 to 4 carbon atoms in the alkyl group thereof and are most preferably methacrylate, methacrylic or methacrylamide groups. Similarly (meth)acrylate, (meth)acrylic and (meth)acrylamide shall be understood to mean acrylate or methacrylate, acrylic or methacrylic and acrylamide or methacrylamide respectively.
Preferably the diluent monomer is selected from vinylpyrrolidone, 2-hydroxyethyl methacrylate, methyl methacrylate and mixtures thereof, most preferably 2-hydroxyethyl methacrylate, methyl methacrylate and mixtures thereof. In one embodiment diluent monomers are vinylpyrrolidone, 2-hydroxyethyl methacrylate and mixtures thereof.
Comonomers Bearing A Centre of Permanent Positive Charge
The comonomer bearing the centre of permanent positive charge can either be cationic or zwitterionic. In the latter case the monomer includes within its structure not only a centre of permanent positive charge but also a centre of negative charge. Typically the centre of permanent positive charge in both cationic and zwitterionic comonomers is provided by a quaternary nitrogen atom.
Preferred comonomers which bear a centre of positive charge are of general formula (I)
Y—B—X  (I)
wherein
B is a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene chain or if X contains a carbon-carbon chain between B and the centre of permanent positive charge or if Y contains a terminal carbon atom, a valence bond,
X is a group bearing a centre of permanent positive charge and
Y is an ethylenically unsaturated polymerisable group selected from
wherein:
R is hydrogen or a C
1
-C
4
alkyl group;
A is —O— or —NR
1
— where R
1
is hydrogen or a C
1
-C
4
alkyl group or R
1
is —B—X where B and X are as defined above.
K is a group —(CH
2
)
p
CO(O)—, —(CH
2
)
p
C(O)O—, —(CH
2
)
p
OC(O)O—, —(CH
2
)
p
NR
2
—, —(CH
2
)
p
NR
2
C(O)—, —(CH
2
)
p
C(O)NR
2
—, (CH
2
)
p
NR
2
C(O)O—, —(CH
2
)
p
OC(O)NR
2
—, —(CH
2
)
p
NR
2
C(O)NR
2
— (in which the groups R
2
are the same or different), —(CH
2
)
p
O—, —(CH
2
)
p
SO
3
—, or, optionally in a combination with B, a valence bond, and p is from 1 to 12 and R
2
is hydrogen or a C
1
-C
4
alkyl groups
The proviso on whether B may be a valence bond ensures that the centre of permanent positive charge in X is not directly bonded to a heteroatom, such as an oxygen or nitrogen atom in Y.
Preferred monomers which bear a centre of positive charge are those of general formula (II) or (III).
where R, A, B and X are as defined with reference to formula (I).
Preferably R is hydrogen, methyl, or ethyl , more preferably methyl, so that the monomer of formula (II) is an acrylic acid, methacrylic acid or ethacrylic acid derivative.
In the compounds of formula (III) K may be a valence bond and B a group, K may be a group and B a valence bond, both K and B may be groups or K and B may together be a valence bond. Preferably B is a group where K is a valence bond. Where K is a group then preferably p is from 1 to 6, more preferably 1, 2 or 3 and most preferably p is 1. When K is a group —(CH
2
)
p
NR
2
—, —(CH
2
)
p
NR
2
C(O)—, —(CH
2
)
p
C(O)NR
2
—, —(CH
2
)
p
NR
2
C(O)O—, —(CH
2
)
p
OCNR
2
— or —(CH
2
)
p
NR
2
C(O)NR
2
— then R
2
is preferably hydrogen, methyl or ethyl, more preferably hydrogen.
Preferably B is:
an alkylene group of formula —(CR
3
2
)
a
—, wherein the groups —(CR
3
2
)— are the same or different, and in each group —(CR
3
2
)— the groups R
3
are the same or different and each group R
3
is hydrogen or C
1-4
alkyl, preferably hydrogen, and a is from 1 to 12, preferably 1 to 6;
an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety, more preferably —CH
2
O(CH
2
)
4
—;
an oligo-oxaalkylene group of formula —[(CR
4
2
)
b
O]
c
(CR
4
2
)
b
— where the groups —(CR
4
2
)— are the same or different and in each group —(CR
4
2
)— the groups R
4
are the same or different and each group R
4
is hydrogen or C
1-4
alkyl, pr

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