Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND SYSTEMS FOR LEACHING AND RELBASING SILICONE
HYDROGEL OPHTHALMIC LENSES WITH ALCOHOL SOLUTIONS
FIELD OF THE INVENTION
This invention relates to a process to produce ophthalmic lenses made from
silicone hydrogels. More specifically, the present invention relates to
methods and -
systems for leaching components from an ophthalmic lens and releasing the
lenses
from mold parts in which they were formed.
BACKGROUND OF THE INVENTION
It is well known that contact lenses can be used to improve vision. Various
contact lenses have been commercially produced for many years. Early designs
of
contact lenses were fashioned from hard materials. Although these lenses are
still
currently used in some applications, they are not suitable for all patients
due to their
poor comfort and relatively low permeability to oxygen. Later developments in
the
field gave rise to soft contact lenses, based upon hydrogels.
Hydrogel contact lenses are very popular today. These lenses are often more
comfortable to wear than contact lenses made of hard materials. Malleable soft
contact lenses can be manufactured by forming a lens in a multi-part mold
where the
combined parts form a topography consistent with the desired final lens.
Multi-part molds used to fashion hydrogels into a useful article, such as an
ophthalmic lens, can include for example, a first mold portion with a convex
surface
that corresponds with a back curve of an ophthalmic lens and a second mold
portion
with a concave surface that corresponds with a front curve of the ophthalmic
lens. To
prepare a lens using such mold portions, an uncured hydrogel lens formulation
is
placed between the concave and convex surfaces of the mold portions and
subsequently cured. The hydrogel lens formulation may be cured, for example by
exposure to either, or both, heat and light. The cured hydrogel forms a lens
according
to the dimensions of the mold portions.
Following cure, traditional practice dictates that the mold portions are
separated and the lens remains remains adhered to one of the mold portions. A
release process detaches the lens from the remaining mold part. The extraction
step
removes unreacted components and diluents (hereinafter referred to as "UCDs")
from
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the lens and affect clinical viability of the lens. If the UCDs are not
extracted from
the lens, they may make the lens uncomfortable to wear.
According to prior art, release of the lens from the mold can be facilitated
by
exposure of the lens to aqueous or saline solutions which act to swell the
lens and
loosen adhesion of the lens to the mold. Exposure to the aqueous or saline
solution
can additionally serve to extract UCDs and thereby make the lens more
comfortable
to wear and clinically acceptable.
New developments in the field have led to contact lenses that are made from
silicone hydrogels. Known hydration processes using aqueous solutions to
effect
release and extraction have not been efficient with silicone hydrogel lenses.
Consequently, attempts have been made to release silicone lenses and remove
UCDs
using organic solvents. Processes have been described in which a lens is
immersed in
an alcohol (ROH), ketone (RCOR'), aldehyde (RCHO), ester (RCOOR'), amide
(RCONR'R") or N-alkyl pyrrolidone for 20 hours-40 hours and in the absence of
water, or in an admixture with water as a minor component (see e.g., U.S. Pat.
No.
5,258,490).
However, although some success has been realized with the known processes,
the use of highly concentrated organic solutions can present drawbacks,
incllluding,
for example: safety hazards; increased risk of down time to a manufacturing
line; high
cost of release solution; and the possibility of collateral damage, due to
explosion.
Therefore, it would be advantageous to find a method of producing a silicone
hydrogel contact lens which requires the use of little or no organic solvent,
avoids the
use of flammable agents, that effectively releases lenses from the molds in
which they
were formed, and which removes UCDs from the lens.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides methods of leaching a silicone
hydrogel ophthalmic lens of UCDs without soaking the lens in organic solvents.
According to the present invention, release of a silicone hydrogel lens from a
mold in
which the lens is formed is facilitated by exposing the lens to an aqueous
solution of
an effective amount of a release aid. In addition, leaching of UCDs from the
lens is
also facilitated by exposing the lens to an aqueous solution of an effective
amount of a
leach aid.
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In addition, the present invention relates generally to ophthalmic lenses
fashioned from materials including wettable silicone hydrogels formed from a
reaction mixture including at least one high molecular weight hydrophilic
polymer
and at least one hydroxyl-fi-nctionalized silicone-containing monomer. In some
embodiments, the ophthalmic lenses are formed from a reaction mixture
including a
high molecular weight hydrophilic polymer and an effective amount of an
hydroxyl-
functionalized silicone-containing monomer.
In other embodiments, the present invention relates to a method of preparing
an ophthalmic lens which includes mixing a high molecular weight hydrophilic
polymer and an effective amount of a hydroxyl-functionalized silicone-
containing
monomer to form a clear solution, and curing said solution. Some embodiments
can
therefore include one or more of (a) mixing a high molecular weight
hydrophilic
polymer and an effective amount of an hydroxyl-functionalized silicone-
containing
monomer; and (b) curing the product of step (a) to form a biomedical device
and
curing the product of step (a) to form a wettable biomedical device.
In some embodiments, the present invention still further relates to an
ophthalmic lens formed from a reaction mixture including at least one hydroxyl-
functionalized silicone-containing monomer and an amount of high molecular
weight
hydrophilic polymer sufficient to incorporate into the lens, without a surface
treatment, an advancing contact angle of less than about 80°
DETAILED DESCRIPTION OF THE INVENTION
It has been found that a silicone hydrogel ophthalmic lens can be released
from a mold in which it was cured by exposing the cured lens to an aqueous
solution
of an effective amount of a release aid. It has also been found that adequate
removal
of Leachable Materials from the silicone hydrogel ophthalmic lens can be
realized by
exposing the cured lens to an aqueous solution of an effective amount of a
leach aid.
Definitions
As used herein, "adequate removal of Leachable Materials" means that at least
50%, of the Leachable Materials have been removed from a lens after treating
the
lens.
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As used herein, "Leachable Material" includes UCD's and other material
which is not bound to the polymer and may be extracted from the polymer
matrix, for
example, by leaching with water or an organic solvent.
As used herein, a "Leaching Aid" is any compound that if used in an effective
amount in an aqueous solution to treat a ophthalmic lens can yield a lens with
an
adequate amount of removal of Leachable Materials.
As used herein the term "monomer" is a compound containing at least one
polymerizable group and an average molecular weight of about less than 2000
Daltons, as measured via gel permeation chromatography refractive index
detection.
Thus, monomers can include dimers and in some cases oligomers, including
oligomers made from more than one monomeric unit.
As used herein, the term "Ophthalmic Lens" refers to devices that reside in or
on the eye. These devices can provide optical correction, wound care, drug
delivery,
diagnostic functionality, cosmetic enhancement or effect or a combination of
these
properties. The term lens includes but is not limited to soft contact lenses,
hard
contact lenses, intraocular lenses, overlay lenses, ocular inserts, and
optical inserts.
As used herein, a "release aid" is a compound or mixture of compounds,
excluding organic solvents, which, when combined with water, decreases the
time
required to release a ophthalmic lens from a mold, as compared to the time
required to
release such a lens using an aqueous solution that does not comprise the
release aid.
As used herein, "released from a mold" means that a lens is either completely
separated from the mold, or is only loosely attached so that it can be removed
with
mild agitation or pushed off with a swab.
As used herein, the term "treat" means to expose a cured lens to an aqueous
solution including at least one of: a leaching aid and a release aid.
As used herein and also defined above, the term "UCD" means unreacted
components and diluents.
Treatment
According to the present invention, treatment can include exposing a cured
lens to an aqueous solution which includes at least one of: a leaching aid and
a release
aid. In various embodiments, treatment can be accomplished, for example, via
immersion of the lens in a solution or exposing the lens to a flow of
solution. In
various embodiments, treatment can also include, for example, one or more of:
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heating the solution; stirring the solution; increasing the level of release
aid in the
solution to a level sufficient to cause release of the lens; mechanical
agitation of the
lens; and increasing the level of leach aid in the solution to a level
sufficient to
facilitate adequate removal of UCDs from the lens.
By way of non-limiting examples, various implementations can include
release and UCD removal that is accomplished by way of a batch process wherein
lenses are submerged in a solution contained in a fixed tank for a specified
period of
time or in a vertical process where lenses are exposed to a continuous flow of
a
solution that includes at least one of a leach aid and a release aid.
In some embodiments, the solution can be heated with a heat exchanger or
other heating apparatus to further facilitate leaching of the lens and release
of the lens
from a mold part. For example, heating can include raising the temperature of
an
aqueous solution to the boiling point while a hydroget lens and mold part to
which the
lens is adhered are submerged in the heated aqueous solution. Other
embodiments
can include controlled cycling of the temperature of the aqueous solution.
Some embodiments can also include the application of physical agitation to
facilitate leach and release. For example, the lens mold part to which a lens
is
adhered, can be vibrated or caused to move back and forth within an aqueous
solution.
Other embodiments may include ultrasonic waves through the aqueous solution.
These and other similar processes can provide an acceptable means of
releasing the lens and removing UCDs from the lens prior to packaging.
Release
According to the present invention, release of a silicone hydrogel lens is
facilitated by treating the lens with a solution including one or more release
aids
combined with water at concentrations effective for causing release of the
lens. In
some embodiments, release can be facilitated by the release solution causing a
silicone hydrogel lens to swell by 10% or more in which percentage of swelling
is
equal to 100 times the diameter of lens in release aid solution/diameter of
lens in
borate-buffered saline.
In some embodiments, the release aid can include alcohols, such as, for
example, C5 to C7 alcohols. Some embodiments can also include alcohols that
are
useful as release aids and include primary, secondary and tertiary alcohols
with one to
9 carbons. Examples of such alcohols include methanol, ethanol, n-propanol, 2-
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propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-pentanol, 3-
pentanol, 2-
methyl-l-butanol, tert-amyl alcohol, neopentyl alcohol, 1-hexanol, 2-hexanol,
3-
hexanol, 2-methyl-l-pentanol, 3-methyl-lpentanol, 4-methyl-l-pentanol, 2-
methyl-2-
pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol, 1-heptanol, 2-heptanol, 3-
heptanol, 4-heptanol, 1-octanol, 2-octanol, 1-nonanol, and 2-nonanol. IN some
embodiments, phenols may also be used.
In addition, in some embodiments of the present invention Leach Aids, which
are further discussed below, can also be combined with alcohols to improve the
rate
of release. In some cases leach aids may be used as release aids without the
addition
of alcohols. For example, leach aids at concentrations greater than about 12%,
or
when used to release lenses with water soluble diluents such as t-amyl
alcohol.
Lens materials
Ophthalmic lenses suitable for use with the current invention include those
made from silicone hydrogels. Silicone hydrogels offer benefits to ophthalmic
lens
wearers as compared to conventional hydrogels. For example, they typically
offer
much higher oxygen permeability, Dk, or oxygen oxygen/transmissibility, Dk/l,
where I is the thickness of the lens. Such lenses cause reduced corneal
swelling due
to reduced hypoxia, and may cause less limbal redness, improved comfort and
have a
reduced risk of adverse responses such as bacterial infections. Silicone
hydrogels are
typically made by combining silicone-containing monomers or macromers with
hydrophilic monomers or macromers.
Examples of silicone containing monomers include SiGMA (2-propenoic acid,
2-methyi-,2-hydroxy-3-[3-[1,3,3,3-tetramethyl-l-
[(trimethylsilyl)oxy]disiloxanyl]propoxy]propyl ester), a,a)-
bismethacryloxypropylpolydimethylsiloxane, mPDMS (monomethacryloxypropyl
terminated mono-n-butyl terminated polydimethylsiloxane) and TRIS (3-
methacryloxypropyltris(tri methylsi loxy)si lane).
Examples of hydrophilic monomers include HEMA (2-
hydroxyethylmethacrylate), DMA (N,N-dimethylacrylamide) and NVP (N-
vinylpyrrolidone).
In some embodiments, high molecular weight polymers may be added to
monomer mixes and serve the function of internal wetting agents. Some
embodiments can also include additional components or additives, which are
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generally known in the art. Additives can include, for example: ultra-violet
absorbing
compounds and monomer, reactive tints, antimicrobial compounds, pigments,
photochromic, release agents, combinations thereof and the like.
The silicone monomers and macromers are blended with the hydrophilic
monomers or macromers, placed into ophthalmic lens molds, and cured by
exposing
the monomer to one or more conditions capable of causing polymerization of the
monomer. Such conditions can include, for example: heat and light, wherein the
light
may include one or more of: visible, ionizing, actinic, X-ray, electron beam
or ultra
violet (hereinafter "UV") light. In some embodiments, the light utilized to
cause
polymerization can have a wavelength of about 250 to about 700 nm. Suitable
radiation sources include UV lamps, fluorescent lamps, incandescent lamps,
mercury
vapor lamps, and sunlight. In embodiments, where a UV absorbing compound is
included in the monomer composition (for example, as a UV block), curing can
be
conducted by means other than UV irradiation (such as, for example, by visible
light
or heat).
In some embodiments a radiation source, used to facilitate curing can be
selected from UVA (about 315 - about 400 nm), UVB (about 280-about 315) or
visible light (about 400 -about 450 nm), at low intensity. Some embodiments
can
also include a reaction that mixture includes a UV absorbing compound.
In some embodiments, wherein the lenses are cured using heat then a thermal
initiator may be added to the monomer mix. Such initiators can include one or
more
of: peroxides such as benzoyl peroxide and azo compounds such as AIBN
(azobisisobutyronirile).
In some embodiments, lenses can be cured using UV or visible light and a
photoinitiator may be added to the monomer mix. Such photoinitiators may
include,
for example, aromatic alpha-hydroxy ketones, alkoxyoxybenzoins, acetophenones,
acyl phosphine oxides, and a tertiary amine plus a diketone, mixtures thereof
and the
like. Illustrative examples of photoinitiators are 1-hydroxycyclohexyl phenyl
ketone,
2-hydroxy-2-methyl-i-phenyl-propan-l-one, bis(2,6-dimethoxybenzoyl)-2,4-4-
trimethylpentyl phosphine oxide (DMBAPO), bis(2,4,6-trimethylbenzoyl)-
phenylphosphineoxide (Irgacure 819), 2,4,6-trimethylbenzyldiphenyl phosphine
oxide
and 2,4,6-trimethylbenzyoyl diphenylphosphine oxide, benzoin methyl ester and
a
combination of camphorquinone and ethyl 4-(N,N-dimethylamino)benzoate.
Commercially available visible light initiator systems include Irgacure 819,
Irgacure
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1700, Irgacure 1800, Irgacure 819, Irgacure 1850 (all from Ciba Specialty
Chemicals)
and Lucirin TPO initiator (available from BASF). Commercially available UV
photoinitiators include Darocur 1173 and Darocur 2959 (Ciba Specialty
Chemicals).
In some embodiments, it may also be useful to include diluents in the
monomer mix, for example to improve the solubility of the various components,
or to
increase the clarity or degree of polymerization of the polymer to be formed.
Embodiments can include secondary and tertiary alcohols as diluents
Various processes are known for processing the reaction mixture in the
production of ophthalmic lenses, including known spincasting and static
casting. In
some embodiments, a method for producing an ophthalmic lens from a polymer
includes molding silicone hydrogels. Silicone hydrogel molding can be
efficient and
provides for precise control over the final shape of a hydrated lens.
Molding an ophthalmic lens from a silicone hydrogel can include placing a
measured amount of monomer mix in a concave mold part. A convex mold part is
then placed on top of the monomer and pressed to close and form a cavity that
defines
a contact lens shape. The monomer mix within the mold parts is cured to form a
contact lens. As used herein, curing the monomer mix includes a process or
condition
which allows or facilitates the polymerization of the monomer mix. Examples of
conditions which facilitate polymerization include one or more of: exposure to
light
and application of thermal energy.
When the mold halves are separated the lens typically adheres to one or the
other mold half. It is typically difficult to physically remove the lens from
this mold
half, and it is generally preferred to place this mold half into a solvent to
release the
lens. The swelling of the lens that results when the lens absorbs some of this
solvent
typically facilitates release of the lens from the mold.
Silicone hydrogel lenses may be made using relatively hydrophobic diluents
such as 3,7-dimethyl-3-octanol. If one attempts to release such lenses in
water, such
diluents prevent absorption of water, and do not allow sufficient swelling to
case
release of the lens.
Alternatively, silicone hydrogels may be made using relatively hydrophilic
and water soluble diluents such as ethanol, t-butanol or t-amyl alcohol. When
such
diluents are used and the lens and mold are placed into water, the diluent may
more
easily dissolve and the lens may more easily release in water than if more
hydrophobic diluents are used.
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Leachable Material
After a lens is cured the polymer formed typically contains some amount of
material that is not bound to or incorporated into the polymer. Leachable
Material not
bound to the polymer may be extracted from the polymer matrix for example by
leaching with water or an organic solvent (hereinafter "Leachable Material").
Such
Leachable Material may not be favorable to the use of the contact lens in an
eye. For
example, Leachable Material may slowly be released from a contact lens when
the
contact lens is worn in an eye and may cause irritation or a toxic effect in
the eye of
the wearer. In some cases, Leachable Material may also bloom to the surface of
a
contact lens where it may form a hydrophobic surface and may attract debris
from
tears, or may interfere with wetting of the lens.
Some material may be physically trapped in the polymer matrix and may not
be able to be removed for example by extracting with water or an organic
solvent. As
used herein, trapped material is not considered Leachable Material.
Leachable material typically includes most or all of the material included in
the monomer mix that does not have polymerizable functionality. For example, a
diluent may be a Leachable Material. Leachable material may also include
nonpolymerizable impurities which were present in the monomer. As
polymerization
approaches completion, the rate of polymerization will typically slow and some
small
amount of the monomer may never polymerize. Monomer that never polymerizes can
be included in the material that will be leached from the polymerized lens.
Leachable
material may also include small polymer fragments, or oligomers. Oligomers can
result from the termination reactions early in the formation of any given
polymer
chain. Accordingly, Leachable Materials can include any or all of a mixture of
the
above described components, which may vary one to another in their properties
such
as toxicity, molecular weight or water solubility.
Leach aids
According to the present invention, leaching of a silicone hydrogel lens is
facilitated by exposing the lens to a solution including one or more leaching
aids
combined with water at concentrations effective to remove UCDs from the lens.
For example, in some embodiments, ophthalmic lenses can be subjected to a
treatment exposing the lenses to a leach aid and a GC Mass Spectrometer can be
used
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to measure the level of one or more UCDs in the ophthalmic lenses. The GC Mass
Spectrometer can determine whether treatment with a particular leaching aid is
effective to reduce an amount of particular UCDs present in the lenses to a
maximum
threshold amount.
Accordingly, in some embodiments, a GC Mass Spectrometer can be used to
check for a maximum threshold of UCDs, such as SiMMA, mPDMS, SiMMA glycol,
and epoxide, of approximately 300 ppm. A minimum hydration treatment time
period
necessary to reduce the presence of such UCDs to 300 ppm or less in specific
lenses
can be determined by the periodic measurements. In additional embodiments,
other
UCDs, such as, for example, D30 or other diluents, can be measured to detect
the
presence of a maximum amount of approximately 60 ppm. Embodiments can also
include setting a threshold amount of a particular UCD at the minimum
detection
level ascertainable by the testing equipment.
Examples of leaching aids, according to the present invention include:
ethoxylated alcohols or ethoxylated carboxylic acids, ethoxylated glucosides
or
sugars, optionally with attached C8 to C14 carbon chains, polyalkylene oxides,
sulfates, carboxylates or amine oxides of C8-C10 compounds. Examples include
cocoamidopropylamine oxide, C12_14 fatty alcohol ethoxylated with 10 ethylene
oxides, sodium dodecyl sulfate, polyoxyethylene-2-ethyl hexyl ether,
polypropylene
glycol, polyethylene glycol monomethyl ether, ethoxylated methyl glucoside
dioleate,
and the sodium salt of n-octylsulfate, sodium salt of ethylhexyl sulfate.
In order to illustrate the invention the following examples are included.
These
examples do not limit the invention. They are meant only to suggest a method
of
practicing the invention. Those knowledgeable in contact lenses, as well as
other arts,
may find other methods of practicing the invention, those methods are deemed
to be
within the scope of this invention.
High Molecular Weight Hydrophilic Polymer
As used herein, "high molecular weight hydrophilic polymer" refers to
substances having a weight average molecular weight of no less than about
100,000
Daltons, wherein said substances upon incorporation to silicone hydrogel
formulations, increase the wettability of the cured silicone hydrogels. The
preferred
weight average molecular weight of these high molecular weight hydrophilic
polymers is greater than about 150,000; more preferably between about 150,000
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about 2,000,000 Daltons, more preferably still between about 300,000 to about
1,800,000 Daltons, most preferably about 500,000 to about 1,500,000 Daltons.
Alternatively, the molecular weight of hydrophilic polymers of the invention
can be also expressed by the K-value, based on kinematic viscosity
measurements, as
described in Encyclopedia of Polymer Science and Engineering, N-Vinyl Amide
Polymers, Second edition, Vol 17, pgs. 198-257, John Wiley & Sons Inc. When
expressed in this manner, hydrophilic monomers having K-values of greater than
about 46 and preferably between about 46 and about 150. The high molecular
weight
hydrophilic polymers are present in the formulations of these devices in an
amount
sufficient to provide contact lenses, which without surface modification
remain
substantially free from surface depositions during use. Typical use periods
include at
least about 8 hours, and preferably worn several days in a row, and more
preferably
for 24 hours or more without removal. Substantially free from surface
deposition
means that, when viewed with a slit lamp, at least about 70% and preferably at
least
about 80%, and more preferably about 90% of the lenses worn in the patient
population display depositions rated as none or slight, over the wear period.
Suitable amounts of high molecular weight hydrophilic polymer include from
about I to about 15 weight percent, more preferably about 3 to about 15
percent, most
preferably about 5 to about 12 percent, all based upon the total of all
reactive
components.
Examples of high molecular weight hydrophilic polymers include but are not
limited to polyamides, polylactones, polyimides, polylactams and
functionalized
polyamides, polylactones, polyimides, polylactams, such as DMA functionalized
by
copolymerizing DMA with a lesser molar amount of a hydroxyl-functional monomer
such as HEMA, and then reacting the hydroxyl groups of the resulting copolymer
with materials containing radical polymerizable groups, such as
isocyanatoethylmethacrylate or methacryloyl chloride. Hydrophilic prepolymers
made
from DMA or n-vinyl pyrrolidone with glycidyl methacrylate may also be used.
The
glycidyl methacrylate ring can be opened to give a diol which may be used in
conjunction with other hydrophilic prepolymer in a mixed system to increase
the
compatibility of the high molecular weight hydrophilic polymer, hydroxyl-
functionalized silicone containing monomer and any other groups which impart
compatibility. The preferred high molecular weight hydrophilic polymers are
those
that contain a cyclic moiety in their backbone, more preferably, a cyclic
amide or
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cyclic imide. High molecular weight hydrophilic polymers include but are not
limited
to poly-N-vinyl pyrrolidone, poly-N-vinyl-2-piperidone, poly-N-vinyl-2-
caprolactam,
poly-N--vinyl-3-methyl-2-caprolactam, poly-N-vinyl-3-methyl-2-piperidone, poly-
N-
vinyl-4-methyl-2-piperidone, poly-N-vinyl-4-methyl-2-caprolactam, poly-N-vinyl-
3-
ethyl-2-pyrrolidone, and poly-N-viny14,5-dimethyl-2-pyrrol- idone,
polyvinylimidazole, poly-N-N-dimethylacrylamide, polyvinyl alcohol,
polyacrylic
acid, polyethylene oxide, poly 2 ethyl oxazoline, heparin polysaccharides,
polysaccharides, mixtures and copolymers (including block or random, branched,
multichain, comb-shaped or star shaped) thereof where poly-N-vinylpyrrolidone
(PVP) is particularly preferred. Copolymers might also be used such as graft
copolymers of PVP.
The high molecular weight hydrophilic polymers provide improved
wettability, and particularly improved in vivo wettability to the medical
devices of the
present invention. Without being bound by any theory, it is believed that the
high
molecular weight hydrophilic polymers are hydrogen bond receivers which in
aqueous environments, hydrogen bond to water, thus becoming effectively more
hydrophilic. The absence of water facilitates the incorporation of the
hydrophilic
polymer in the reaction mixture. Aside from the specifically named high
molecular
weight hydrophilic polymers, it is expected that any high molecular weight
polymer
will be useful in this invention provided that when said polymer is added to a
silicone
hydrogel formulation, the hydrophilic polymer (a) does not substantially phase
separate from the reaction mixture and (b) imparts wettability to the
resulting cured
polymer. In some embodiments it is preferred that the high molecular weight
hydrophilic polymer be soluble in the diluent at processing temperatures.
Manufacturing processes which use water or water soluble diluents may be
preferred
due to their simplicity and reduced cost. In these embodiments high molecular
weight
hydrophilic polymers which are water soluble at processing temperatures are
preferred.
Hydroxyl-functionalized Silicone Containing Monomer
As used herein a "hydroxyl-functionalized silicone containing monomer" is a
compound containing at least one polymerizable group having an average
molecular
weight of about less than 5000 Daltons as measured via gel permeation
chromatography, refractive index detection, and preferably less than about
3000
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Daltons, which is capable of compatibilizing the silicone containing monomers
included in the hydrogel formulation with the hydrophilic polymer. Hydroxyl
functionality is very efficient at improving hydrophilic compatibility. Thus,
in a
preferred embodiment hydroxyl-functionalized silicone containing monomers of
the
present invention comprise at least one hydroxyl group and at least one "-Si-O-
Si-
"group. It is preferred that silicone and its attached oxygen account for more
than
about 10 weight percent of said hydroxyl-functionalized silicone containing
monomer, more preferably more than about 20 weight percent.
The ratio of Si to OH in the hydroxyl-functionalized silicone containing
monomer is also important to providing a hydroxyl functionalized silicone
containing
monomer which will provide the desired degree of compatibilization. If the
ratio of
hydrophobic portion to OH is too high, the hydroxyl-functionalized silicone
monomer
may be poor at compatibilizing the hydrophilic polymer, resulting in
incompatible
reaction mixtures. Accordingly, in some embodiments, the Si to OH ratio is
less than
about 15:1, and preferably between about 1:1 to about 10: l. In some
embodiments
primary alcohols have provided improved compatibility compared to secondary
alcohols_ Those of skill in the art will appreciate that the amount and
selection of
hydroxyl-functionalized silicone containing monomer will depend on how much
hydrophilic polymer is needed to achieve the desired wettability and the
degree to
which the silicone containing monomer is incompatible with the hydrophilic
polymer.
In some embodiments, reaction mixtures of the present invention may include
more than one hydroxyl-functionalized silicone containing monomer. For
monofunctional hydroxyl functionalized silicone containing monomer the
preferred R'
is hydrogen, and the preferred R2,R3, and R4, are C'-6alkyl and triC'-
6alkylsiloxy,
most preferred methyl and trimethylsiloxy. For multifunctional (difunctional
or
higher) R'-R4 independently comprise ethylenically unsaturated polymerizable
groups
and more preferably comprise an acrylate, a styryl, a Ci.6alkylacrylate,
acrylamide,
CI.6alkylacrylamide, N-vinyllactam, N-vinylamide, C2_12alkenyl,
C2_iZalkenylphenyl,
C2-12alkenylnaphthyl, or C2.6alkenylphenyl Q-6alkyl. In some embodiments R5 is
hydroxyl, --CH2OH or CH2CHOHCH2OH.
In some other embodiments, R6 is a divalent Cl.6alkyl, Ct.6alkyloxy, Cl-
6alkyloxyQ.6alkyl, phenylene, naphthalene, CI.12 cycloalkyl,
Ct.6alkoxycarbonyl,
amide, carboxy, CI-6 alkylcarbonyl, carbonyl, Ci_6atkoxy, substituted
Q.6alkyl,
substituted CI-6alkyloxy, substituted Q-6alkyloxyQ.6a1ky1, substituted
phenylene,
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substituted naphthalene, substituted Q_12cycloalkyl, where the substituents
are
selected from one or more members of the group consisting of CI.6
alkoxycarbonyl,
CI.6alkyl, C1..6alkoxy, amide, halogen, hydroxyl, carboxyl, CI-6alkylcarbonyl
and
formyl. The particularly preferred R6 is a divalent methyl (methylene).
In some embodiments, R7 comprises a free radical reactive group, such as an
acrylate, a styryl, vinyl, vinyl ether, itaconate group, a CI-6alkylacrylate,
acrylamide,
Ct.balkylacrylamide, N-vinyllactam, N-vinylamide, , C2-12alkenyl,
C2_i2alkenylphenyl-
, C2_12alkenylnaphthyl, or C2.6alkenylphenylCi_6alkyl or a cationic reactive
group such
as vinyl ether or epoxide groups. The particulary preferred R7 is
methacrylate.
In some embodiments, R8 is a divalent CI-6alkyl, Cl-6alkyloxy, Cl-6
alkyloxyCl_
6alkyl, phenylene, naphthalene, Ci_12cycloalkyl, Ci 6alkoxycarbonyl, amide,
carboxy,
Cl.6alkylcarbonyl, carbonyl, CI.6alkoxy, substituted Q-6alkyl, substituted Cl_
6alkyloxy, substituted Q.6alkyloxyCj.6alkyl, substituted phenylene,
substituted
naphthalene, substituted C1_12cycloalkyl, where the substituents are selected
from one
or more members of the group consisting of C]_6alkoxycarbonyl, Q-6alkyl, Ci_
6alkoxy, amide, halogen, hydroxyl, carboxyl, CI.6alkylcarbonyl and formyl. The
particularly preferred R8 is Q-6alkyloxyQ-6alkyl.
Examples of hydroxyl-functionalized silicone containing monomer of Formula
I include 2-propenoic acid, 2-methyl-,2-hydroxy-3-[3-[1,3,3,3-tetramethyl-l-
[(trimethylsilyl)oxy]disi- loxanyl]propoxy]propyl ester (which can also be
named (3-
methacryloxy-2-hydroxypropyloxy)propylbis(trimethylsiloxy)methylsilane- ) 2.
The
compound, (3-rnethacryloxy-2-hydroxypropyloxy)propylbis(tr-
imethylsiloxy)methylsilane can be formed from an epoxide, which produces an
80:20
mixture of the compound shown above and (2-methacryloxy-3-hydroxypr-
opyloxy)propylbis(trimethylsiloxy)methylsilane. In some embodiments of the
present
invention it is preferred to have some amount of the primary hydroxyl present,
preferably greater than about 10 wt % and more preferably at least about 20 wt
%.
Other suitable hydroxyl-functionalized silicone containing monomers include
(3-methacryloxy-2-hydroxypropyloxy)propyltris(trimethylsiloxy)sil- ane 3 bis-3-
methacryloxy-2-hydroxypropyloxypropyl polydimethylsiloxane 4 3-methacryloxy-2-
(2-hydroxyethoxy)propyloxy)propylbis(trimethylsilo- xy)methylsilane 5
N,N,N',N'-
tetrakis(3-methacryloxy-2-hydroxypropyl)-.alpha.,.omega.-- bis-3-aminopropyl-
polydimethylsiloxane.
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The reaction products of glycidyl methacrylate with amino-functional
polydimethylsiloxanes may also be used as a hydroxyl-functional silicone
containing
monomer. Still additional structures which may be suitable hydroxyl-
functionalized
silicone containing monomers include those similar to compounds having the
following structure: 6 where n=I-50 and R independently comprise H or a
polymerizable unsaturated group, with at least one R comprising a
polymerizable
group, and at least one R, and preferably 3-8 R, comprising H. These
components
may be removed from the hydroxyl-functionalized monomer via known methods such
as liquid phase chromatography, distillation, recrystallization or extraction,
or their
formation may be avoided by careful selection of reaction conditions and
reactant
ratios.
Suitable monofunctional hydroxyl-functionalized silicone monomers are
commercially available from Gelest, Inc. Morrisville, Pa. Suitable
multifunctional
hydroxyl-functionalized silicone monomers are commercially available from
Gelest,
Inc, Morrisville, Pa. or may be made using known procedures.
While hydroxyl-functionalized silicone containing monomers have been found
to be particularly suitable for providing compatible polymers for biomedical
devices,
and particularly ophthalmic devices, any functionalized silicone containing
monomer
which, when polymerized and/or formed into a final article is compatible with
the
selected hydrophilic components may be used. Suitable functionalized silicone
containing monomers may be selected using the following monomer compatibility
test. In this test one gram of each of mono-3-methacryloxypropyl terminated,
mono-
butyl terminated polydimethylsiloxane (mPDMS MW 800-1000) and a monomer to
be tested are mixed together in one gram of 3,7-dimethyl-3-octanol at about
20° C. A mixture of 12 weight parts K-90 PVP and 60 weight parts DMA is
added drop-wise to hydrophobic component solution, with stirring, until the
solution
remains cloudy after three minutes of stirring. The mass of the added blend of
PVP
and DMA is determined in grams and recorded as the monomer compatibility
index.
Any hydroxyl-functionalized silicone-containing monomer having a compatibility
index of greater than 0.2 grams, more preferably greater than about 0.7 grams
and
most preferably greater than about 1.5 grams will be suitable for use in this
invention.
An "effective amount" or a "compatibilizing effective amount" of the
hydroxyl-functionalized silicone-containing monomers of the invention is the
amount
needed to compatibilize or dissolve the high molecular weight hydrophilic
polymer
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and the other components of the polymer formulation. Thus, the amount of
hydroxyl-
functional silicone containing monomer will depend in part on the amount of
hydrophilic polymer which is used, with more hydroxyl-functionalized silicone
containing monomer being needed to compatibilize higher concentrations of
hydrophilic polymer. Effective amounts of hydroxyl-functionalized silicone
containing monomer in the polymer formulation include about 5% (weight
percent,
based on the weight percentage of the reactive components) to about 90%,
preferably
about 10% to about 80%, most preferably, about 20% to about 50%.
In addition to the high molecular weight hydrophilic polymers and the
hydroxyl-functionalized silicone containing monomers of the invention other
hydrophilic and hydrophobic monomers, crosslinkers, additives, diluents,
polymerization initators may be used to prepare the biomedical devices of the
invention. In addition to high molecular weight hydrophilic polymer and
hydroxyl-
functionalized silicone containing monomer, the hydrogel formulations may
include
additional silicone containing monomers, hydrophilic monomers, and cross
linkers to
give the biomedical devices of the invention.
Additional Silicone Containing Monomers
With respect to the additional silicone containing monomers, useful amide
analogs of TRIS can include, 3-rnethacryloxypropyltris(trimethylsiloxy)silane
(TRIS),
monomethacryloxypropyl terminated polydimethylsiloxanes,
polydimethylsiloxanes,
3-methacryloxypropylbis(trimethylsiloxy)methylsila- ne,
methacryloxypropylpentamethyl disiloxane and combinations thereof are
particularly
useful as additional silicone-containing monomers of the invention. Additional
silicone containing monomers may be present in amounts of about 0 to about 75
wt
%, more preferably of about 5 and about 60 and most preferably of about 10 and
40
weight %.
Hydrophilic Monomers
Additionally, reaction components of the present invention may also include
any hydrophilic monomers used to prepare conventional hydrogels. For example
monomers containing acrylic groups (CH2=CRCOX, where R is hydrogen or Cl_
6alkyl an X is 0 or N) or vinyl groups (--C=CH2) may be used. Examples of
additional hydrophilic monomers are N,N-dimethylacrylamide, 2-hydroxyethyl
methacrylate, glycerol monomethacrylate, 2-hydroxyethyl methacrylamide,
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polyethyleneglycol monomethacrylate, methacrylic acid, acrylic acid, N-vinyl
pyrrolidone, N-vinyl-N-methyl acetamide, N-vinyl-N-ethyl acetamide, N-vinyl-N-
ethyl formamide, N-vinyl formamide and combinations thereof.
Aside the additional hydrophilic monomers mentioned above,
polyoxyethylene polyols having one or more of the terminal hydroxyl groups
replaced
with a functional group containing a polymerizable double bond may be used.
Examples include polyethylene glycol, ethoxylated alkyl glucoside and
ethoxylated
bisphenol A, reacted with one or more molar equivalents of an end-capping
group
such as isocyanatoethyl methacrylate, methacrylic anhydride, methacryloyl
chloride,
vinylbenzoyl chloride, and the like, produce a polyethylene polyol having one
or more
terminal polymerizable olefinic groups bonded to the polyethylene polyol
through
linking moieties such as carbamate, urea or ester groups.
Still further examples include the hydrophilic vinyl carbonate or vinyl
carbamate monomers, hydrophilic oxazolone monomers and polydextran.
Additional hydrophilic monomers can include N,N-dimethylacrylamide
(DMA), 2-hydroxyethyl methacrylate (HEMA), glycerol methacrylate, 2-
hydroxyethyl methacrylamide, N-vinylpyrrolidone (NVP), polyethyleneglycol
monomethacrylate, methacrylic acid, acrylic acid and combinations thereof.
Additional hydrophilic monomers may be present in amounts of about 0 to about
70
wt %, more preferably of about 5 and about 60 and most preferably of about 10
and
50 weight %.
Crosslinkers
Suitable crosslinkers are compounds with two or more polymerizable
functional groups. The crosslinker may be hydrophilic or hydrophobic and in
some
embodiments of the present invention mixtures of hydrophilic and hydrophobic
crosslinkers have been found to provide silicone hydrogels with improved
optical
clarity (reduced haziness compared to a CSI Thin Lens). Examples of suitable
hydrophilic crosslinkers include compounds having two or more polymerizable
functional groups, as well as hydrophilic functional groups such as polyether,
amide
or hydroxyl groups. Specific examples include TEGDMA (tetraethyleneglycol
dimethacrylate), TrEGDMA (triethyleneglycol dimethacrylate), ethyleneglycol
dimethacylate (EGDMA), ethylenediamine dimethyacrylamide, glycerol
dimethacrylate and combinations thereof Examples of suitable hydrophobic
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crosslinkers include multifunctional hydroxyl-functionalized silicone
containing
monomer, multifunctional polyether-polydimethylsiloxa- ne block copolymers,
combinations thereof and the like. Specific hydrophobic crosslinkers include
acryloxypropyl terminated polydimethylsiloxane (n=10 or 20) (acPDMS),
hydroxylacrylate functionalized siloxane macromer, methacryloxypropyl
terminated
PDMS, butanediol dimethacrylate, divinyl benzene, 1,3-bis(3-
methacryloxypropyl)-
tetrakis(trimethylsiloxy) disiloxane and mixtures thereof. Preferred
crosslinkers
include TEGDMA, EGDMA, acPDMS and combinations thereof. The amount of
hydrophilic crosslinker used is generally about 0 to about 2 weight % and
preferably
from about 0.5 to about 2 weight % and the amount of hydrophobic crosslinker
is
about 0 to about 5 weight %, which can alternatively be referred to in mol %
of about
0.01 to about 0.2 mmole/gm reactive components, preferably about 0.02 to about
0.1
and more preferably 0.03 to about 0.6 mmole/gm.
Increasing the level of crosslinker in the final polymer has been found to
reduce the amount of haze. However, as crosslinker concentration increases
above
about 0.15 mrnole/gm reactive components modulus may increase above generally
desired levels (greater than about 90 psi). Thus, in some embodiments of the
present
invention the crosslinker composition and amount is selected to provide a
crosslinker
concentration in the reaction mixture of between about 0.01 and about 0.1
mmoles/gm
crosslinker.
Additional components or additives, which are generally known in the art may
also be included. Additives include but are not limited to ultra-violet
absorbing
compounds and monomer, reactive tints, antimicrobial compounds, pigments,
photochromic, release agents, combinations thereof and the like.
Additional components include other oxygen permeable components such as
carbon-carbon triple bond containing monomers and fluorine containing monomers
which are known in the art and include fluorine-containing (meth)acrylates,
and more
specifically include, for example, fluorine-containing C2-C12 alkyl esters of
(meth)acrylic acid such as 2,2,2-trifluoroethyl (meth)acrylate, 2,2,2,2',2',2'-
hexafluoroisopropyl (meth)acrylate, 2,2,3,3,4,4,4-heptafluorobutyl
(meth)acrylate,
2,2,3,3,4,4,5,5,6,6,7,7,8,- 8,8-pentadecafluorooctyl (meth)acrylate,
2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-h- exadecafluorononyl (meth)acrylate and the
like.
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Diluents
The reaction components (hydroxyl-functionalized silicone containing
monomer, hydrophilic polymer, crosslinker(s) and other components) are
generally
mixed and reacted in the absence of water and optionally, in the presence of
at least
one diluent to form a reaction mixture. The type and amount of diluent used
also
effects the properties of the resultant polymer and article. The haze and
wettability of
the final article may be improved by selecting relatively hydrophobic diluents
and/or
decreasing the concentration of diluent used. As discussed above, increasing
the
hydrophobicity of the diluent may also allow poorly compatible components (as
measured by the compatibility test) to be processed to form a compatible
polymer and
article. However, as the diluent becomes more hydrophobic, processing steps
necessary to replace the diluent with water will require the use of solvents
other than
water. This may undesirably increase the complexity and cost of the
manufacturing
process. Thus, it is important to select a diluent which provides the desired
compatibility to the components with the necessary level of processing
convenience.
Diluents useful in preparing the devices of this invention include ethers,
esters,
alkanes, alkyl halides, silanes, amides, alcohols and combinations thereof.
Amides
and alcohols are preferred diluents, and secondary and tertiary alcohols are
most
preferred alcohol diluents. Examples of ethers useful as diluents for this
invention
include tetrahydrofuran, tripropylene glycol methyl ether, dipropylene glycol
methyl
ether, ethylene glycol n-butyl ether, diethylene glycol n-butyl ether,
diethylene glycol
methyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether,
propylene
glycol methyl ether acetate, dipropylene glycol methyl ether acetate,
propylene glycol
n-propyl ether, dipropylene glycol n-propyl ether, tripropylene glycol n-butyl
ether,
propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene
glycol
n-butyl ether, propylene glycol phenyl ether dipropylene glycol dimetyl ether,
polyethylene glycols, polypropylene glycols and mixtures thereof. Examples of
esters
useful for this invention include ethyl acetate, butyl acetate, amyl acetate,
methyl
lactate, ethyl lactate, i-propyl lactate. Examples of alkyl halides useful as
diluents for
this invention include methylene chloride. Examples of silanes useful as
diluents for
this invention include octamethylcyclotetrasiloxane.
Examples of alcohols useful as diluents for this invention include those
having
the formula 7 wherein R, R' and R" are independently selected from H, a
linear,
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branched or cyclic monovalent alkyl having 1 to 10 carbons which may
optionally be
substituted with one or more groups including halogens, ethers, esters, aryls,
amines,
amides, alkenes, alkynes, carboxylic acids, alcohols, aldehydes, ketones or
the like, or
any two or all three of R, R and R" can together bond to form one or more
cyclic
structures, such as alkyl having I to 10 carbons which may also be substituted
as just
described, with the proviso that no more than one of R, R' or R" is H.
It is preferred that R, R' and R" are independently selected from H or
unsubstituted linear, branched or cyclic alkyl groups having I to 7 carbons.
It is more
preferred that R, R', and R" are independently selected form unsubstituted
linear,
branched or cyclic alkyl groups having I to 7 carbons. In certain embodiments,
the
preferred diluent has 4 or more, =more preferably 5 or more total carbons,
because the
higher molecular weight diluents have lower volatility, and lower
flammability. When
one of the R, R' and R" is H, the structure forms a secondary alcohol. When
none of
the R, R' and R" are H, the structure forms a tertiary alcohol. Tertiary
alcohols are
more preferred than secondary alcohols. The diluents are preferably inert and
easily
displaceable by water when the total number of carbons is five or less.
Examples of
useful secondary alcohols include 2-butanol, 2-propanol, menthol,
cyclohexanol,
cyclopentanol and exonorborneol, 2-pentanol, 3-pentanol, 2-hexanol, 3-hexanol,
3-
methyl-2-butanol, 2-heptanol, 2-octanol, 2-nonanol, 2-decanol, 3-octanol,
norborneol,
and the like.
Examples of useful tertiary alcohols include tert-butanol, tert-amyl, alcohol,
2-
methyl-2-pentanol, 2,3-dimethyl-2-butanol, 3-methyl-3-pentanol, 1-
methylcyclohexanol, 2-methyl-2-hexanol, 3,7-dimethyl-3-octanol, I-chloro-2-
methyl-
2-propanol, 2-methyl-2-heptanol, 2-methyl-2-octanol, 2-2-methyl-2-nonanol, 2-
methyl-2-decanol, 3-methyl-3-hexanol, 3-methyl-3-heptanol, 4-methyl-4-
heptanol, 3-
methyl-3-octanol, 4-methyl-4-octanol, 3-methyl-3-nonanol, 4-methyl-4-nonanol,
3-
methyl-3-octanol, 3-ethyl-3-hexanol, 3-methyl-3-heptanol, 4-ethyl-4-heptanol,
4-
propyl-4-heptanol, 4-isopropyl-4-heptanol, 2,4-dimethyl-2-pentanol, 1-
methylcyclopentanol, 1-ethylcyclopentanol, 1-ethylcyclopentanol, 3-hydroxy-3-
methyl-l-butene, 4-hydroxy-4-methyl-l-cyclopentanol, 2-phenyl-2-propanol, 2-
methoxy-2-methyl-2-propanol 2,3,4-trimethyl-3-pentanol, 3,7-dimethyl-3-
octanol, 2-
phenyl-2-butanol, 2-methyl-l-phenyl-2-propanol and 3-ethyl-3-pentanol, and the
like.
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A single alcohol or mixtures of two or.more of the above-listed alcohols or
two or more alcohols according to the structure above can be used as the
diluent to
make the polymer of this invention.
In certain embodiments, the preferred alcohol diluents are secondary and
tertiary alcohols having at least 4 carbons. In particular, some alcohol
diluents can
include tert-butanol, tert-amyl alcohol, 2-butanol, 2-methyl-2-pentanol, 2,3-
dimethyl-
2-butanol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol, 3,7-dimethyl-3-octanol.
Diluents can also include: hexanol, heptanol, octanol, nonanol, decanol, tert-
butyl alcohol, 3-methyl-3-pentanol, isopropanol, t amyl alcohol, ethyl
lactate, methyl
lactate, i-propyl lactate, 3,7-dimethyl-3-octanol, dimethyl formamide,
dimethyl
acetamide, dimethyl propionamide, N methyl pyrrolidinone and mixtures thereof.
In some embodiments of the present invention the diluent is water soluble at
processing conditions and readily washed out of the lens with water in a short
period
of time. Suitable water soluble diluents include 1-ethoxy-2-propanol, 1-methyl-
2-
propanol, t-amyl alcohol, tripropylene glycol methyl ether, isopropanol, l-
methyl-2-
pyrrolidone, N,N-dimethylpropionamide, ethyl lactate, dipropylene glycol
methyl
ether, mixtures thereof and the like. The use of a water soluble diluent
allows the post
molding process to be conducted using water only or aqueous solutions which
comprise water as a substantial component.
In some embodiments, the amount of diluent can be generally less than about
50 weight % of the reaction mixture and preferably less than about 40% and
more
preferably between about 10 and about 30%. In some embodiments, diluent may
also
include additional components such as release agents and can include water
soluble
and aid in lens deblocking.
Polymerization initiators can include, for example, compounds such as: lauryl
peroxide, benzoyl peroxide, isopropyl perearbonate, azobisisobutyronitrile,
and the
like, that generate free radicals at moderately elevated temperatures, and
photoinitiator systems such as aromatic alpha-hydroxy ketones,
alkoxyoxybenzoins,
acetophenones, acyl phosphine oxides, and a tertiary amine plus a diketone,
mixtures
thereof and the like. Illustrative examples of photoinitiators are 1-
hydroxycyclohexyl
phenyl ketone, 2-hydroxy-2-methyl-l-phenyl-propan-l-o- ne, bis(2,6-
dimethoxybenzoyl)-2,4-4-trimethylpentyl phosphine oxide (DMBAPO), bis(2,4,6-
trimethylbenzoyl)-phenylphosphineoxide (Irgacure 819), 2,4,6-
trimethylbenzyldiphenyl phosphine oxide and 2,4,6-trimethylbenzyoyl
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diphenylphosphine oxide, benzoin methyl ester and a combination of
camphorquinone
and ethyl 4-(N,N-dimethylamino)benzoate. Commercially available visible light
initiator systems include Irgacure 819, Irgacure 1700, Irgacure 1800, Irgacure
819,
Irgacure 1850 (all from Ciba Specialty Chemicals) and Lucirin TPO initiator
(available from BASF). Commercially available UV photoinitiators include
Darocur
1173 and Darocur 2959 (Ciba Specialty Chemicals). The initiator is used in the
reaction mixture in effective amounts to initiate photopolymerization of the
reaction
mixture, e.g., from about 0. I to about 2 parts by weight per 100 parts of
reactive
monomer. Polymerization of the reaction mixture can be initiated using the
appropriate choice of heat or visible or ultraviolet light or other means
depending on
the polymerization initiator used. Alternatively, initiation can be conducted
without a
photoinitiator using, for example, e-beam. However, when a photoinitiator is
used,
some embodiments can include a combination of 1-hydroxycyclohexyl phenyl
ketone
and bis(2,6-dimethoxybenzoyl)-2,4-4-trimethylpentyl phosphine oxide (DMBAPO),
and the method of polymerization initiation can include visible light. Other
embodiments can include: bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide
(Irgacure 819®).
In some embodiments, the present invention can further include ophthalmic
lenses of the formulae: I Wt % components HFSCM HMWHP SCM HM 5-90 1-15,
3-15 or 5-12 0 0 10-80 1-15, 3-15 or 5-12 0 0 20-50 1-15, 3-15 or 5-12 0 0 5-
90 1-15,
3-15 or 5-12 0-80, 5-60 or 10- 0-70, 5-60 or 10- 40 50 10-80 1-15, 3-15 or 5-
12 0-80,
5-60 or 10- 0-70, 5-60 or 10- 40 50 20-50 1-15, 3-15 or 5-12 0-80, 5-60 or 10-
0-70,
5-60 or 10- 40 50 HFSCM is hydroxyl-functionalized silicone containing monomer
HMWHP is high molecular weight hydrophilic polymer SCM is silicone containing
monomer HM is hydrophilic monomer.
The weight percents above can be based upon all reactive components. Thus,
in some embodiments, the present invention can include one or more of:
silicone
hydrogels, biomedical devices, ophthalmic devices and contact lenses, each of
one or
more of the compositions listed in the table, which describes ninety possible
compositional ranges. Each of the ranges considered can be prefixed with
"about",
whereby the range combinations presented with the proviso that the listed
components, and any additional components add up to 100 weight %.
A range of the combined silicone-containing monomers (hydroxyl-
functionalized silicone-containing and additional silicone-containing
monomers) can
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be from about 5 to 99 weight percent, more preferably about 15 to 90 weight
percent,
and in some embodiments about 25 to about 80 weight percent of the reaction
components. A range of hydroxyl-functionalized silicone-containing monomer can
be
about 5 to about 90 weight percent, preferably about 10 to about 80, and most
preferably about 20 to about 50 weight percent. In some embodiments a range of
hydrophilic monomer can be from about 0 to about 70 weight percent, more
preferably about 5 to about 60 weight percent, and most preferably about 10 to
about
50 weight percent of the reactive components. In other embodiments a range of
high
molecular weight hydrophilic polymer can be about I to about 15 weight
percent, or
about 3 to about 15 weight percent, or about 5 to about 12 weight percent. .
All of the
about weight percents are based upon the total of all reactive components.
In some embodiments, a range of diluent is from about 0 to about 70 weight
percent, or about 0 to about 50 weight percent, and or about 0 to about 40
weight
percent and in some embodiments, between about 10 and about 30 weight percent,
based upon the weight all component in the reactive mixture. The amount of
diluent
required varies depending on the nature and relative amounts of the reactive
components.
In some embodiments, the reactive components comprise 2-propenoic acid, 2-
methyl-,2-hydroxy-3-[3-[ 1,3,3,3-tetramethyl-l-[(trime-
thylsilyl)oxy]disiloxanyl)propoxy]propyl ester "SiGMA" .about.28 wgt. % of the
reaction components); (800-1000 MW monomethacryloxypropyl terminated mono-n-
butyl terminated polydimethylsiloxane, "mPDMS" (.about.31 %wt); N,N-
dimethylacrylamide, "DMA" (.about.24%wt); 2-hydroxyethyl methacryate, "HE1ViA"
(.about.6%wt); tetraethyleneglycoldimethacrylate, "TEGDMA" (.about.l.5%wt),
polyvinylpyrrolidone, "K-90 PVP" (.about.7%wt); with the balance comprising
minor
amounts of additives and photoinitiators. The polymerization can also be
conducted in
the presence of about 23% (weight % of the combined monomers and diluent
blend)
3,7-dimethyl-3-octanol diluent.
In some embodiments, the polymerizations for the above formulations can be
conducted in the presence of tert-amyl-alcohol as a diluent comprising about
29
weight percent of the uncured reaction mixture.
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Processing
Embodiments can include ophthalmic lenses of the present invention which
are prepared by mixing the high molecular weight hydrophilic polymer, the
hydroxyl-
functionalized silicone-containing monomer, plus one or more of the following:
the
additional silicone containing monomers, the hydrophilic monomers, the
additives
("Reactive Components"), and the diluents (collectively, the "Reaction
Mixture"),
with a polymerization initiator and curing the Reaction Mixture by appropriate
conditions to form a product that can be subsequently formed into a predefined
shape
by lathing, cutting and the like. Alternatively, the reaction mixture may be
placed in a
mold and subsequently cured into an appropriate article.
Various processes are known for processing the reaction mixture in the
production of contact lenses, including spincasting and static casting. In
some
embodiments, the method for producing contact lenses of the polymer of this
invention is by the molding of the silicone hydrogels. During molding, the
Reaction
Mixture is placed in a mold having the shape of the final desired silicone
hydrogel,
i.e., water-swollen polymer, and the reaction mixture is subjected to
conditions
whereby the monomers polymerize, to thereby produce a polymer/diluent mixture
in
the shape of the final desired product. Then, this polymer/diluent mixture is
treated
with a solution to remove the diluent and ultimately replace it with water,
producing a
silicone hydrogel having a final size and shape which are quite similar to the
size and
shape of the original molded polymer/diluent article.
Curing
Another aspect of some embodiments of the present invention includes curing
silicone hydrogel formulations in a manner that provides enhanced wettability.
According to the present invention, it has been found that gel time for a
silicone
hydrogel may be correlated with cure conditions to provide a wettable
ophthalmic
device, and specifically a contact lens. As used herein, the gel time is the
time at
which a cross linked polymer network is formed, resulting in the viscosity of
the
curing reaction mixture approaching infinity and the reaction mixture becoming
non-
fluid. The gel point occurs at a specific degree of conversion, independent of
reaction
conditions, and therefore can be used as an indicator of the rate of the
reaction. It has
been found that, for a given reaction mixture, the gel time may be used to
determine
cure conditions which impart desirable wettability. Thus, in some embodiments
of the
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present invention, the reaction mixture can be cured at or above a gel time
that
provides improved wettability, an din some embodiments pf sufficient
wettability for
the resulting device to be used without a hydrophilic coating or surface
treatment
("minimum gel time"). In some embodiments, improved wettability can be a
decrease
in advancing dynamic contact angle of at least 10% compared to formulation
with no
high molecular weight polymer. In some embodiments, therefore, longer gel
times
are preferred as they provide improved wettability and increased processing
flexibility.
Gel times may vary for different silicone hydrogel formulations. Cure
conditions can also effect gel time. For example, in some embodiments, the
concentration of crosslinker will impact gel time, wherein increasing
crosslinker
concentrations decreases gel time. Increasing the intensity of the radiation
(for
photopolymerization) or temperature (for thermal polymerization), the
efficiency of
initiation (either by selecting a more efficient initiator or irradiation
source, or an
initiator which absorbs more strongly in the selected irradiation range) will
also
decrease gel time. Temperature and diluent type and concentration can also
effect gel
time in ways understood by those of skill in the art.
In some embodiments, a minimum gel time may be determined by selecting a
given formulation, varying one of the above factors and measuring the gel time
and
contact angles. The minimum gel time can therefore be the point above which
the
resulting lens is generally wettable. Below the minimum gel time, the lens may
not
wettable. In the context of this description, for a contact lens, "generally
wettable" is
a lens which displays an advancing dynamic contact angle of less than about 80
degrees, an in some embodiments less than 70 degrees and in still other
embodiments
less than about 60 degrees. Thus, those of skill in the art will appreciate
that minimum
gel point as defined herein may be a range, taking into consideration
statistical
experimental variability.
In certain embodiments, using visible light irradiation minimum gel times of
at
least about 30 seconds have been found to be advantageous.
In some embodiments, a mold containing the Reaction Mixture is exposed to
ionizing or actinic radiation, for example electron beams, Xrays, UV or
visible light,
i.e. electromagnetic radiation or particle radiation having a wavelength in
the range of
from about 150 to about 800 nm. In some embodiments, the radiation source is
UV or
visible light having a wavelength of about 250 to about 700 nm. Suitable
radiation
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sources can include UV lamps, fluorescent lamps, incandescent lamps, mercury
vapor
lamps, and sunlight. In embodiments where a UV absorbing compound is included
in
the composition (for example, as a UV block) curing is conducting by means
other
than UV irradiation (such as by visible light or heat). In some preferred
embodiments
the radiation source can be selected from UVA (about 315-about 400 nm), UVB
(about 280-about 315) or visible light (about 400-about 450 nm), at low
intensity.
In other embodiments, the reaction mixture includes a UV absorbing
compound, is cured using visible light and low intensity. As used herein the
term "low
intensity" means those between about 0.1 mW/cmZ to about 6 mW/cm2 and
preferably
between about 0.2 mW/cm2 and 3 mW/em2. The cure time can therefore be
relatively
long, generally more than about 1 minute and preferably between about 1 and
about
60 minutes and still more preferably between about I and about 30 minutes. In
some
embodiments, relatively slow, low intensity cure can provide compatible
ophthalmic
devices which display lasting resistance to protein deposition in vivo.
In some embodiments, the temperature at which the reaction mixture is cured
can be increased to above ambient, wherein the haze of the resulting polymer
decreases_ Temperatures effective to reduce haze include temperatures at which
the
haze for the resulting lens is decreased by at least about 20% as compared to
a lens of
the same composition made at 25 degrees C. Thus, in some embodiments, suitable
cure temperatures can include temperatures greater than about 25 degrees C.
Specifically embodiments can include ranges of between about 25 degrees C and
70
degrees C and between about 40 degrees C and 70 degrees C. The precise set of
cure
conditions (temperature, intensity and time) may depend upon the components of
lens
material selected and, with reference to the teaching herein, are within the
skill of one
of ordinary skill in the art to determine. Cure may be conducted in one or a
multiplicity of cure zones, and should preferably be suffcient to form a
polymer
network from the reaction mixture. Typically, the resulting polymer network
can be
swollen with the diluent and has the form of the mold cavity.
Examples:
Lenses made according to the descriptions above and with 24 parts N,N-
dimethylacrylamide and 0.48 ppm CGI 1850, using concave mold parts combined
with convex molds. After photocuring, the mold parts were removed, and the
lenses
in the concave mold part was were placed into stirring aqueous solutions as
shown in
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Table 1. Each aqueous solution included an alcohol as indicated in the column
labeled "Agent" in Table 1. The time until the lenses released and completely
separated from the molds was measured and is additionally shown in Table 1.
As indicated in Table 1, the exposure to the aqueous solutions including the
alcohols, additionally had the effect of leaching D30 from the lenses.
The lenses were stirred in the respective aqueous solutions for a total time
as
indicated in Table 1, then removed and extracted with isopropanol to remove
residual
D30 diluent. The isopropanol extract was analyzed for D30, and the results are
shown in Table I as a percentage of the level found in unleached control
lenses.
Table 1
Ex. Agent 1 Agent 2 Agent 3 Temp ml/lens Residual Release Leach
SCAW D30 time time
(min.) (min.)
19 4% 2-pentanol 0.5% 0.05% 90 C 35 3.2 - 5 6
C12E10 6.6%
19 4% 2-pentanol 90 C 35 5.6 - 6 6
39%
20 2% n-hexanol 1% 1% 90 C 167 14.6% 6 6
C12-E10
21 3% TAA 5% 90 C 35 22% 3 8
SCAW
Comp. 90 C 35 100% No 100%
release
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