CA2181984C - Treatment of contact lenses with supercritical fluid - Google Patents
Treatment of contact lenses with supercritical fluid Download PDFInfo
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- CA2181984C CA2181984C CA002181984A CA2181984A CA2181984C CA 2181984 C CA2181984 C CA 2181984C CA 002181984 A CA002181984 A CA 002181984A CA 2181984 A CA2181984 A CA 2181984A CA 2181984 C CA2181984 C CA 2181984C
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- Prior art keywords
- supercritical
- lens
- carbon dioxide
- contact lens
- supercritical fluid
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
- B29D11/00—Producing optical elements, e.g. lenses or prisms
- B29D11/00009—Production of simple or compound lenses
- B29D11/00038—Production of contact lenses
- B29D11/00125—Auxiliary operations, e.g. removing oxygen from the mould, conveying moulds from a storage to the production line in an inert atmosphere
- B29D11/00192—Demoulding, e.g. separating lenses from mould halves
- B29D11/00201—Demoulding, e.g. separating lenses from mould halves using cooling means
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C37/00—Component parts, details, accessories or auxiliary operations, not covered by group B29C33/00 or B29C35/00
- B29C37/0003—Discharging moulded articles from the mould
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C71/00—After-treatment of articles without altering their shape; Apparatus therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C71/00—After-treatment of articles without altering their shape; Apparatus therefor
- B29C71/009—After-treatment of articles without altering their shape; Apparatus therefor using gases without chemical reaction
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
- B29D11/00—Producing optical elements, e.g. lenses or prisms
- B29D11/00009—Production of simple or compound lenses
- B29D11/00432—Auxiliary operations, e.g. machines for filling the moulds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C71/00—After-treatment of articles without altering their shape; Apparatus therefor
- B29C71/0009—After-treatment of articles without altering their shape; Apparatus therefor using liquids, e.g. solvents, swelling agents
- B29C2071/0027—Removing undesirable residual components, e.g. solvents, unreacted monomers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C71/00—After-treatment of articles without altering their shape; Apparatus therefor
- B29C71/0009—After-treatment of articles without altering their shape; Apparatus therefor using liquids, e.g. solvents, swelling agents
- B29C2071/0054—Supercritical fluid treatment, i.e. using a liquid in which distinct liquid and gas phases do not exist
Abstract
A method of treating contact lenses made from polymerizable materials by providing supercritical fluids to the lenses.
Description
WO95120476 2 1 8 1 9 8 IIT 1_1/11.,,~._ T~ . OF C021TAC~r T.T~-~R~ lII5~ DU~ nl r~-T FLIIID
BAr~o~ _ OF Trl~ T-JVENTION
This invention relates to improved methods o~ manufacturing or processing contact lens materials employing a supercritical f luid .
Polyme~ized contact lens materials must not only have ~ufficient optical clarity, bu~ also must be suitable for contact with the eye for xtended peril~ds. The contact lenses made from such materials must be su~ficiently hydrophilic at the lens surface to properly "wet". Wel:ting is the char~cteristic understood to relate to the colltact lens' ability to be lubricated by the eye's natural tears so l:hat the lens may move freely over the eye during its use. This freedom of movement over the eye keeps the lens from adhering to the eye and allows a continuous strea~ of tears to wash under ~nd over the lens, resulting in maximum comfort.
The ability of a lens to properly wet and be "comfortable" in the eye is difficult to predict. Much work in the field has been directed to achieving and maint~ining a hydrophilic environment on the contact len5 surface. Inc~rporation of a variety of hydrophilic monomers into the honomer mix, as w~ll as post-L~L ts ~iuch as plasma L,~ ~l c have been attempted, with ~ome success, to maintain hydrophilicity at the lens surface.
WO95120~76 2 1 8 1 9 ~ 4 However, attempts to improve and maintain adequate hydrophilicity must not , ; ce the other important lens characteri~tics, such ~s optical clarity. C~ ly, atte~pts to improve or retain a high degree of optical clarity, oxygen permeability, tear 6trength, etc., while maintaining the proper modulus, must not adversely affect the lens' wetting capabili~ies.
A method of lens ~L~at which would not adversely affect the lens' wetting or other physical charactQristics, but which could improve the lens' optical clarity would be desirable. In addition, a lens LLe:a~ t which could improve the hydrophilicity of ~ lens, thereby eliminating or ~t least reducing the need for z~dditives or post-tL~at -~ would be advantageous.
Because of certain processing li=itations, most so~t hydrogel contact lens production results in a molded lens which must be handled, ;nsr^ct~ and shipped in a wet state. This processing limitation adds ti~e and cost to the overall lens production.
However, a cost-e~fective len6 ~L~:at ~ which could produce a dry lens could simplify lens production and reduce the cost o~ lenses.
It will also be appreciated that large-scale manufacturing ~L~ _;f - ~i reguire disposal of relatively high volu~es of the extraction solutions used to remove impurities and residual materials (fiometimes referred to as residuals or extractables) from the lenses. In addition, various materials used as solvents provide pot~nti~lly hazardous conditions to working environments W09~120~76 2 i 8 1 9 8 4 P~ u.. ! Lj.U
due to material toxicity to humans or fl~mm~bility, for example.
An extraction t~' hni i using a non-toxic, preferentially recyclable extraction solvent would be desirnble.
~CTTMM~RV OF T~ Ihv~
The present invention pr~vides methods of treating contact lenses and contact lens materials. More specifically, in one aspect of the invention, a method of treating a contact lens material is r}i~rlo~ecl comprising treating the contact lens m~terial with a supercritical fluid.
In /mother ~spect of the invention a method of producing an optically ~lear contact lens is disclosed comprising treating the contact lens with a supercritical fluid.
In a still further aspect of the invention a method of dry releasing a contact lens from a mold in which the lens was molded is ~ , comprising treating the contact lens and mold with a ~upercritical fluid.
In yet another aspect of the present invention, a method of extracting incompletely polymerized materialc from a contact lens is disclosed comprising treating the contact lens with a supercritical fluid.
WO gS1204~6 1 ~ l021 0 DETATT Fn DESCRIPTIoN OF T}~F INVENTION
A gas is considered to be in a supercritical state when it is subjected to such a combination of pressure and t~ ,Lu.~ that its density ~y~rc,~ s that of a liquid ~where a liguid and gas gtate coexist). When a gas is _ubjected to such condition6, it is called a supercritical fluid (SCF~. It has now been discovered that exposing a contact lens to supercritical carbon dioxide ~CO2) produces a contact lens with enhanced optical clarity. It was ~lso discovered that supercritical ~luids could extract the unreacted or incompletely polymerized material in the polymeric a~Lu.Lu.~: of various contact lens materialg.
Carbon dioxide is a pre~erred candidate for supercriticality since its critical t~ Lu~_ is 31C. A gas' critical t LUL~ is the t~ c~Lu~ at which a change in phases takes place causing an appreciable change in the gas' physic~l propertie6. While ~11 of the experimentation ~icc~cc~d below was ~nr~ llc t~d with C02 it is understood that many other gases under ~upercritical conditions m~y be used to treat contact lens polymeric materials, including supercritical nitrous oxide IN2O), ethane and propane, or A combination thereo~.
As is known ln the field of supercritical fluids, the solubility of a particular solid in a SCF depends upon the density and polarity o~ the SCF. Therefore, when a supercritical fluid is to be u~ed to extract a particul~r L fron a material, the ~ wo ssno476 2 1 8 1 9 8 4 ~ ~J
specific solubility of the -t Dlust be experimentally determined .
For the extraction of in~ompletely polymerized residual material from contact lens m~terials, it has now been ~t~rm;n~
that the C02 should be pressurized to from about 1000 psi to about 4000 psi, and is preferably from about 2000 psi to ~bout 4000 psi when the t~ L~ILe is kept within the r~nge of from about 40C
to about 90C, ~nd preferably from about 50C to ~bout 80C.
Generally, in the r-m~f~-t~lre of contact lenses, some of the monomer mix is not fully polymerized. The incompletely polymerized material from the polymerization proc~ss may affect optical clarity or may be harmful to the eye. Residual material may include solvents or unre~cted monomers from the monomeric mixture, or oligomers present as by-product~ from the polymeriz~tion process.
The residual material may be hydrophilic or l.rdL~hoLic.
Convention~l methods to ~xtract ~uch residual m~teri~ls from the polymerized cont~ct lens material include extraction with water tfor extr~ction of hydrophili.c residual material) or an alcohol solution ~for extr~ction of ~-y-lL~ hObic residual m~lteri~l).
However, ome of the ~lcohol extraction solution remains in the polymeric network of the pol~merized contact lens material, and must ~180 be extracted from 1:he lens material before the lens may be worn s~fely ~nd comfortab:Ly on th~ eye. T~lis requires ~n WO9C/20476 2 1 8 1 q84 PCrlUS95/OIOtl o additional extraction of the alcohol from the lens, generally using heated water for up to 4 hours or more. Frequently, however, the conventional methods may not ~deguately remove the residual m~terial.
Contact lens materials are formed from the polymerization produc of a mixture of monomers or prepolymers. (For purposes of ConVeniQnC-, the term " ~~ " as used hereafter shall include prepolymers. ) The monomeric mixture may also include m2terials other than monomers that aid in thc polymerization process, such ~s a 601vent or a diluent. Contact lens materials include materials for "hard" ~nd "soft" lenses. The hard lens classification typically includes lenses such as rigid gas pe- hl-~ (RGP) contact lenses, which are generally formed of cror6linlr~d ~ilicone acrylate or fluorn~ilic~ crylate copolymers. Soft lenses include "soft" hydrogel contact lenses.
Hydrogels are hydrophilic polymers that absorb water to an equilibrium value ~nd are insoluble in water due to the presence of a cr~Cl;n?--~ three-dimensional network. HYdL~, ~C are generally formed of a copolymer of at least one hydrophilic monomer and a crosslinking monomer. The hydrophilicity is due to the presence of hydrophilic groups, 6uch as alcohols, carboxylic acids, amides and sulfonic acids. The swollen equilibrated state results from a balance between the osmotic driving forces that cause the water to enter the hydrophilic polymer and the forces xerted by the polymer chains in resisting ~ nC j on . In the case of silicone hydrogel contact lenses, the copolymeric material ~ WO9'i/20~76 ~ 2 1 8 1 9~4 P~l/G.,!~I 2l further includes a silio~ ,,tA;ninq monomer. Lenses in this class are generally formed of a copolymer of at least one hydrophillc monomer And a cro~linking monomer. Hydrophilic monomers include: unsaturated carboxylic acids, such as methacrylic acid and acrylic acid; (meth)acrylic substituted alcohols or glycols, such as 2 h~d.~A~ lmethacrylate, 2-~ t~ hylacrylate, glyceryl methacrylate, and polyethyleneglycol methacryla~e; vinyl lactams, such as N-vinyl-2-pyrrolidone; and acrylamides, ~uch as methacrylamide and N,N-dimethylacrylanide. Further ,exanples of such hydrophilic monomers can be found in U.S. Patent Nos. 4,153,641; 4,740,533; 5,034,461;
and 5, 070, 215.
The crosslinking monomer may be a material having nultiple polymerizable ~unctionalities, preferably vinyl functionalities.
r ~, Le~L..Lative croC~ i nki nq m~nomers include: divinylbenzene;
allyl methacrylate; ethyleneglycol ditneth)acrylate, tetraethyleneglycol di~meth)a~rylate, polyethyleneglycol di (meth) acrylzlte; and vinylcarbonate derivatives of the glycol di(meth)~crylates. In the ca~e of silicone hydrogel contact lenses, the copolymeric material further includes at least one 8il i~ --e ~ ~" ~A i n i nq monomer .
Extracting hydrogel lens~s with solutions may restrict processing flexibility; the l~nse6 muGt be p.~.~ e.~cd, inspected and ~hipped in ~ "wet" state. From a m~ fa~L .ing perspective, it may be de~irable to packag~ and ship hydrogel lenses in the dry W095~0476 2 1 8 1 9 8 4 PCT/11595/01021 ~
~tate. However, known extraction methods frustrate the ability to p~ck~ge and ship hydrogel lenses in the dry state. As ohown by the cxperiment outlined in Example 4 below, it was determined that ~ contact lens could be released rrom a lens-in-mold ~ssembly in the dry ~t~te using supercritical C02. While the phy6ical propertles of the released lenses were not recorded, it is believed that supercritic~l fluid t~ lo~y could be used to release the lens from its mold ~nd have residuals extracted from the lens all in one step.
The incomplete extraction of residual material from lenses may contribute ~dversely to the useful life of the lens. It is thought that some residuals may not be fully extracted and may, over time, migrate through the polymeric network of the lens toward the surface. The residuals may impact lens performance and comfort by interfering with optical clarity or the desired unifor~
hydrophilicity of the lens surface. Therefore the use of ~upercritical C02 or other acceptable supercritical rluids will provide ~ more complete extraction of the contact lens material.
Such lm extraction would be highly preferable to known extraction protocols, and could result in a contact lens that is initially more hydrophilic, and which i5 able to remain hydrophilic for longsr duration.
Supercritical fluids may rurther incc,Lt,oL~.te amounts of ~dditional ~ for the purpose of -nhAnrinq the SCF's ~xtraction efficiency. This is sometimes referred to as "spiking"
~ Wo g~s/20476 2 1 ~ 1 9 8 4 F~ e~ 021 the SCF. Ely adding a compound to the SCF, the 6pecific properties of the SCF, ;nrlu~;nrJ behavior as a solvent, m~y be favorably altered. In this way, a wider range of impurities or ~ '-may be extracted from the lens material. Any organic solvent may be placed in the chamber for the purpose of mixing with the SCF.
Particul~rly useful ~ . '~ used for such SCF "spiking" include propanol, ethanol, methylene chloride and others as would be apparent to one 6killed in thla field of SCF technology.
If a contact lens is to remain comfortable for extended periods on the ye, the lens ~ust properly wet. To achieve this wetting, lenses often ir.ouL~o~c.te hydrophilic monomers into the monomer mix in an attempt to increase and maintain uniform wetting on the lens surface. Contact lenses have also been post-treated to achieve proper wetting. Plasma treating of contact lenses has been investigated and has yielded lenses with enhanced wetting.
Supercritical fluids were used to extract contact lenses both before and after plasma treating the lenses. See Ex~mple 3 below.
With respect to the extraction of residuals from contact lenses, Lolvents must be chosen by their ability to extract either hydrophilic, lI~dL~ JLiC or both types of unreacted residual material rrom the polymeric 2i~LU Lu-~:. However, the solvent itself must be able to be rerloved or flushed from the polymeric D~LU~UL~. Even if a particular liolvent car~ be flushed from the polymeric aLLU~LUL~, it may adversely affect the ~LLU~,LULe in a way that leaves the lens appearing cloudy. It is important that _g_ WO~/20476 2 1 8 1 984 1~ C1021 o the selected solvent in no way adver~ely affect the optical cl~rity of the lens. Optical clarity is subjectively understood to be the lev~l of clarity observed when the lens is inspected.
Trained inspectors in the field in~pect contact lense~ for their clarity. The len~es which had been extracted with supercritical C2 appeared at least as R optical ly clearR when viewed next to conventionally extracted contact lenses.
There is evidence shown in the following Examples that the l;upercritical C02 extracted residuals fron the contact lenses, under certain conditions up to ten times, better than conventional isopropyl alcohol and water extractions. See Example l, Table l.
It has been thought that lenses may lose their wetting properties and become more ~,~dL~,~hoLic at the surface, over time, due to the leaching out of 1-~L~,~hobic segments which were not satisfactorily extracted previously. It is possible that the enhanced extraction of residuals effected by the supercritical C02 may obviate the ne~d to post-treat a lens. This could l~ad to both longer lasting and more comfortable lenses with excellent wetting properties.
Such lenses would also require fewer processing steps which could greatly reduce cost.
It i~ contemplated that the SCF ~.LL ~' i~n may be in~L~L~ted into any contact lens r-n~f~t~ring protocol, at any point in the protocol, although it is preferable that the SCF
extr~ction take place as the final step in the process to provide a final cleaning of the lens.
WO9~120476 2181 984 r~ "~2~
While data was obtained only for poly6iloxane hydrogel contact lens material6, it is understood that supercritical fluids may be used for extr~cting ~ny contact lens m~terial. Therefore any lens-forming mzteri~l can be employed in the present invention. The materials m~y be hydrophilic, or l.~.lLv}.l.oLic, or mixtures of both. The resulting contact lenses may be hard lenses as exemplified by the rigid acrylic plastics including poly(methyl methacrylate); or such contact lenses may be flexible, ~y.lL~,~hobic lenses exemplified by the unsubstituted and fl~loL., _ baLituted polyethylenes, the silicone elastomers, and the like; or such lenses may be soft hydrogel lenses.
It WAS further discovered that contact lenses could be ~ubjected to SCF extraction while still in the mold in which the lens was cast. See Example 3. The complete lens-in-mold Assembly WA5 placed into the SCF pressurized chamber. Therefore, the SCF
extraction t~^hnnlo-AJy can be used to effect dry lens release from the mold, which m~y be ~.lvAnl-J~ with respect to p~ AJin~ and inA, ~nnci~ ations. The method may be used to release any type of contact lens from molds made of any material, in which it w~s cast. Polyvinyl chloride and polypropylene are preferred mold materials with polypropylene being p~rticularly preferred.
Often, contact lenses ~re released by contacting the lens and mold with ~ release solution, preferably by immersing the mold and lens ~sèmbly in the solution. This "wet" release step may be accomplished at room t ALUL~ lthough in some cases it may be WO95/20476 21 81 q84 r~ 1021 0 advantageous to conduct the release at othor temperatures, for example, at an elevated bath t~ u-_6 Up to about 125C.
Following release of the lens from the mold, the lens is hydrated with water or burfered saline. S- ~s~1v~ ly, the lens is ~terilized 6uch as by autoclaving in water or saline. The6e 6teps al60 effect remov~l of any re6idual isvylvy~l.ol from the lens. As already m ntioned, "wet" processing of contact len6es ib labor intensive and may add to the cost o~ processing. Dry release, as facilitated by the pre6ent invention, would present an 9 ~ lly ~ùv~,nLa.~:uu. alternative to the known lens release method6 .
The pre6ent invention further contemplates the use of supercritical fluid technology to facilitate the de-blocking pLV~m:~UL~O currently used for lathed contact lenses. If a contact len6 edge or surface must be altered by using a lathe, the lens is often fixed or "blocked" to a holding implement, typically using a curable wax material. This material h~rdens and holds the lens in place whlle it is rotated at high speeds against the lathe. After the lathing is complete, the len6 must be removed, or "de-blocked"
from the holding implement. Ecologically unfavorable materials including chlorofluorocarbons ~CFCs) were widely used for such de-blocking. After the de-blocking, the len6es must then be cleaned, followed by extraction p-v- ~duLæs as already described. It is now thought that supercritical liquids including supercritical C02 could be u~ed to di6solve the blocking wax while at the 6ame time WO 9~no476 2 1 8 1 9 8 4 PCT/U595/01021 cleaning the lens and al~o removing residual materials rom the lens .
The contact lens~s treat~ad by the PLV~,6_3l3S of the present lnvention may be Lu,~.d by the ~pincasting IJL~ uch aS those ~licrl~s~ in U.S. Pat. Nos. 3,408,429 ~nd 3,496,254 and other convelltional ~ethods, ~uch as compression molding ~s disclosed in t~.S. Pat. Nos. 4,084,459 ~nd 4 ,197, 266 .
Polymarization may be r ~ either in a spinning mold, or ~ stationary mold CV~.L- . 'in~ to a des$red contact lens shape. The obtained conl:act l~ns may be further subjected to zl -nir~ finSshing, as desired. Al~;o, the polymeriz~tion may be ~n~ ct 1 in an appropriate mold or vessel to give a lens materiaL in the form o f hutton, plate or rod, which may then be pL~- eas3~ (e.g., cut or polished via l~the or laser) to give a cont:act lens havin~ a desired shape.
The Il~.IL~ produced b~ the present invention are oxygen tL~r,-~vL~ing, hydrolytically stAble, }~iologically inert, and tr~nsp~rent. The ~lonomers and copolymers employed in ~vL~ance with this invent:ion, ~re readily polymerized to rorm three rli~ -ion~l networks which permit the tLarl ".)LL of oxygen And Are optically clear, strong and hydrophilic.
W0~5/20476 2 1 8 1 q 84 P~
The present invention provides materials which can be usefully employed for the fabrication of prostheses such as heart v~lves And intraocular lenses, ~s optical contact lenses or ala fllms. More particularly, the present invention concerns contact lenses.
The present invention may further assist in the m-n--f~ re of material~ which can be used for bi~ At~
devices, such as, surgical devices, heart v~lves, vessel ~ubstitutes, intrauterine devices, ` ~ 3 and other films, di~phr~gms, ~urgical implant6, blood vessels, ~rti~icial ureters, ~rtifici~l breast tissue and ~ 8 intended to come lnto contact with body fluid outside of the body, e.g., a5 for kidney dialysis and h-art/lung machines and the like, c~theters, mouth guards, denture liners, intraocular devic~s, ~nd especially contact lenses.
~ t i~ known that blood, for ~xample, is readily and r~pidly damaged when it comes into contact with ~rtificial Lurfaces. The design of a ~ynthetic ~urface which is ~ntithL. `, ic ~nd nonhemolytic to blood is necessary for prosthe~es ~nd devices u5ed with blood.
The following Examples further illustrate various preferred _'~ Ls of the invention. Although certain preferred _ A; have been described, it ili understood that the WO 95/2(~4~6 2 1 8 1 9 8 4 PCT/US9~01021 invention is not limited thereto and modifici~tions and variations would be ~vident to a person of ordinzrY skill in the art.
F~lUtPLEi 1 Det~r~in-tion of ~-ln_r Critic~l Fl~ Lens rYtraction EfficiencY
An ex"eriment was designed to ~-t-rn~-- whether t.~LL - ~ion of contact lenses would be enhanced by uring supercritical fluids.
Ten polysiloxane hydrogel lenses to serve as controls were extracted with isopropyl alco~lol (IPA~ and then water. The lenses were first placed in IPA at room t, ~ tULe for 1 hour, followed by pl~- into a water tank at 85C for 4 hours. Ten polysiloxane hydrogel lenses were then extracted with super critical carbon dioxide (C02), in batches at vnrious t-, ~tULeS
and ~. F .,:; as shown below. Each t~n lens batch, inrll~Aini the control was static extracted i n 3 mL of tetrAhydrofuran (THF) for a minimum of 24 hours. Four hundred microliters of the THF for each batch including the cont~ol were sequentially injected into the SEC. The total area of the distribution of the THF lens extract was used to determine the efficiency of the super critical fluid extractions as compared to the IP~ L~ol extractions. The -rêa of the test lens THF extracts were divided into the area of the control lens extract to give an extraction efficiency ratio (EER) . Th~ extraction ef f iciency ratios were determined by dividing the total area (normi~lized ~rea) of the molecular weight distribution of the test lens THF extracts into the total area (n~ area) of the molecular weight distribution of the control lens THF extracts. Thie 1~= of the control lens was wogs/20476 2 1 8 1 98~ F~ e,.,~ . O
~rt~h~ ~ r~ l to be 1. 00 . EER values greater than 1. 00 are less ~fficient than the IPA extraction method: EER values less than 1.00 are more e~ficient. For ~ch SCF C02 extraction, the chamber was filled with SCF C02 ~nd purged 3 times with each purge/fill cycle lasting 1 hour.
The t~ .,tu.~ and pl~ ~, used for the super critical C2 extraction, ~Ireas from the SEC, and EER values are listed in Table 1.
Table 1 ./Pr~e~l~re(Dsi~ Area (SEC~ ~3 Control 24707992 1.00 50C/2000 18817108 0.81 70C/3000 18753486 0 . 81 80C/2000 2093090 0.09 80C/4000 24676496 1.08 A. SCF/P1 a~- Treatment Ninety soft hydrogel contact lenses were made without initial plasma L,e:ai ~ ~. Twenty of the5e lenses were set aside le~ving 70 l-n~es. The i;eventy lenses were supercritically e,.L,e,- Led using C02 at 4500 psi, 60C. The chamber was ~illed with ~upercritical C02 and purged 3 times with each filling/purge cycle laE~ting 1 hour. The seventy lenses were then plasma treated, W0 95~20476 2 1 8 1 9 8 4 r~ o21 followed by water extraction Por 4 hour~ at 190C. The plasma tL~i L protocol followed iE as described im~ediately below.
Pl~C - Treatin~ of Soft l~yrlroc~el C~st Molded Contact ~-A plasma is A complex mixture of zltoms ~nd molecules in both ground and excited states which reach a steady state after the di=charge h~s begun . The CO~C ~ rlltiOn of ionC is about six orders of m~gnitude lower thar~ neutrals. The primary reactants in ~n air or oxygen plasma are oxygen atoms. The action of an air plasma will cause primarily oxygen, and to a lesser extent nitrogen, ir~v~v~tiOn into the polymeric l.LLu~LuLe of the material in the chamber. As is u-.deL-Lood in the field, plasmas can be produced by passing an electrical discharge, usually at radio LL-, y through ~ g~s At low pressure (0.005 to 5.0 torrj.
The ~pplie~ RF power is absor~ed by atoms and ~olecules in the gas state . The circulating electr ical f ield cauEes these excited atoms and molecules to collide with one another as well as the walls of the chamber and the ~urface of the ~aterials placed into the chamber. The lenses were removed ~rom handling trays and placed concave side up on an aluminum coated tray. The tray was then placed into the pl~sma L..:ai L chamber. The lenses were then treated in a direct current DC chamber. The chamber pressure w~s reduced to 0.1 torr ~nd stabilized for ~t least 30 seconds.
The lenses were treated ~t 400 watts for 4 minutes at 0.1 torr.
The chamber wai; then backfilled to ambient pressure. The tray was then removed from the chamber, the lenses inverted ~nd the repeated to plasma treat the other side of the lens.
W09~120~76 2 1 8 1 9~4 J ~ 2l o Ten lenses were ~ubmitted for measurement of residual extractables in tetral-r.lL~,ru.~l, (THF) and for ~ . ' of physical char~cteristics .
B. Plasma Tre-' ' /SCF
Soft hydrogel lenses were manufactured using plasma LL. a~ L . Ten lenses were set aside. Ten lenses were subjected to Alcohol and water extractions to ~;erve as control lenses.
Another ten lcnses were plasma treated, then subjected to cupercritical C02 and THF extractions, using the 6ame conditions ~s listed ~bove in part A. The THF extracts were then ev~luated ~or L~ ~ inin~ extractables using Size Exclusion Chromatography tSEC) as set forth in Exallple 1 above. The following data was obtained. The weight column (wt) Le~LeS IlLs the starting total weight of 10 lenses. The column marked N.A. is the normalized average of lenses arrived at by dividing the weight into the area.
The EER ratio is as described in Example 1 with the dry lenses accorded an arbitrary rating of 1. 00 for co~parative purposes .
The final colu~n L~ LeS~ S the lens batches normalized to the IPA
tisopropanol/H20 extracted lenses) control batch.
Table 2 ~earSEC~ wt N.A. FF~ TPA
1.Non-Extracted 27362822 0.2153 1.27x108 1.00 6.00 2.IPA/H20 4386309 0.2092 2.10alO7 0.17 1.00 3.Pl~sma/SCF 5687337 0.21436 2.65x107 0.21 1.26 4 . SCF/Pla~ma 4481289 0 . 21153 2 .12x107 0.17 1. 01 WO 9C12047~ 2 1 8 1 q 8 ~ r~
The physical characteristics of the lenses i n groups 2, 3 and 4 were as follows:
IPA/H20 Plasma/SCF SCF/Plasma Modulus (g/mm2) 91 llO 105 Elongation (~ N/A 70 63 Tensile (g/mm~) 21/A 42 3~
Tear (g/mm) g B 7 ~ aXPL~ 3 Descri~tion of Drv ~elease fro~ Lens-In-Mold ~~ ` lv A lens-in-mold assembly was placed in an upright position in the ~upercritical fluid chamber. The polysiloxane hydrogel contact lens was positioned in the polypropylene mold such that the concave side of the lens was exposed to the a~ ,. The chamber was filled with C02 and pressurized to 2000 psi at 50C
for l hour. The chamher was purged of the C02 and replaced with fresh C02 3 times. The chamber was then purged a final time and the lens-in mold ~ ' ty was removed from the chamber. The lens remained in the mold but was clearly ~ n~ d f ro~ the mold such th~t the lens dropped from th~ mold when the assembly was inverted. The lens appeared dimpled ~nd hazy toward the center o~
the lens. However, inspection of the lenses following hydration revealed that the lenses dry released from the mold looked indist~n~~ hl~ from lenses released from the mold via standard hydration .
WO9S/20~76 21 81984 r~
M~ny other modific~tlons ~nd v~ri~tions of the present invention ~re possible to the skilled pr~ctitioner in the field in light of the t~ hir7~ herein. It is therefore u--d ~DL~od that, within the scope of the cl~ims, the present invention c~n be practiced other th~n ~s herein specif ic~lly described .
--2 o--
BAr~o~ _ OF Trl~ T-JVENTION
This invention relates to improved methods o~ manufacturing or processing contact lens materials employing a supercritical f luid .
Polyme~ized contact lens materials must not only have ~ufficient optical clarity, bu~ also must be suitable for contact with the eye for xtended peril~ds. The contact lenses made from such materials must be su~ficiently hydrophilic at the lens surface to properly "wet". Wel:ting is the char~cteristic understood to relate to the colltact lens' ability to be lubricated by the eye's natural tears so l:hat the lens may move freely over the eye during its use. This freedom of movement over the eye keeps the lens from adhering to the eye and allows a continuous strea~ of tears to wash under ~nd over the lens, resulting in maximum comfort.
The ability of a lens to properly wet and be "comfortable" in the eye is difficult to predict. Much work in the field has been directed to achieving and maint~ining a hydrophilic environment on the contact len5 surface. Inc~rporation of a variety of hydrophilic monomers into the honomer mix, as w~ll as post-L~L ts ~iuch as plasma L,~ ~l c have been attempted, with ~ome success, to maintain hydrophilicity at the lens surface.
WO95120~76 2 1 8 1 9 ~ 4 However, attempts to improve and maintain adequate hydrophilicity must not , ; ce the other important lens characteri~tics, such ~s optical clarity. C~ ly, atte~pts to improve or retain a high degree of optical clarity, oxygen permeability, tear 6trength, etc., while maintaining the proper modulus, must not adversely affect the lens' wetting capabili~ies.
A method of lens ~L~at which would not adversely affect the lens' wetting or other physical charactQristics, but which could improve the lens' optical clarity would be desirable. In addition, a lens LLe:a~ t which could improve the hydrophilicity of ~ lens, thereby eliminating or ~t least reducing the need for z~dditives or post-tL~at -~ would be advantageous.
Because of certain processing li=itations, most so~t hydrogel contact lens production results in a molded lens which must be handled, ;nsr^ct~ and shipped in a wet state. This processing limitation adds ti~e and cost to the overall lens production.
However, a cost-e~fective len6 ~L~:at ~ which could produce a dry lens could simplify lens production and reduce the cost o~ lenses.
It will also be appreciated that large-scale manufacturing ~L~ _;f - ~i reguire disposal of relatively high volu~es of the extraction solutions used to remove impurities and residual materials (fiometimes referred to as residuals or extractables) from the lenses. In addition, various materials used as solvents provide pot~nti~lly hazardous conditions to working environments W09~120~76 2 i 8 1 9 8 4 P~ u.. ! Lj.U
due to material toxicity to humans or fl~mm~bility, for example.
An extraction t~' hni i using a non-toxic, preferentially recyclable extraction solvent would be desirnble.
~CTTMM~RV OF T~ Ihv~
The present invention pr~vides methods of treating contact lenses and contact lens materials. More specifically, in one aspect of the invention, a method of treating a contact lens material is r}i~rlo~ecl comprising treating the contact lens m~terial with a supercritical fluid.
In /mother ~spect of the invention a method of producing an optically ~lear contact lens is disclosed comprising treating the contact lens with a supercritical fluid.
In a still further aspect of the invention a method of dry releasing a contact lens from a mold in which the lens was molded is ~ , comprising treating the contact lens and mold with a ~upercritical fluid.
In yet another aspect of the present invention, a method of extracting incompletely polymerized materialc from a contact lens is disclosed comprising treating the contact lens with a supercritical fluid.
WO gS1204~6 1 ~ l021 0 DETATT Fn DESCRIPTIoN OF T}~F INVENTION
A gas is considered to be in a supercritical state when it is subjected to such a combination of pressure and t~ ,Lu.~ that its density ~y~rc,~ s that of a liquid ~where a liguid and gas gtate coexist). When a gas is _ubjected to such condition6, it is called a supercritical fluid (SCF~. It has now been discovered that exposing a contact lens to supercritical carbon dioxide ~CO2) produces a contact lens with enhanced optical clarity. It was ~lso discovered that supercritical ~luids could extract the unreacted or incompletely polymerized material in the polymeric a~Lu.Lu.~: of various contact lens materialg.
Carbon dioxide is a pre~erred candidate for supercriticality since its critical t~ Lu~_ is 31C. A gas' critical t LUL~ is the t~ c~Lu~ at which a change in phases takes place causing an appreciable change in the gas' physic~l propertie6. While ~11 of the experimentation ~icc~cc~d below was ~nr~ llc t~d with C02 it is understood that many other gases under ~upercritical conditions m~y be used to treat contact lens polymeric materials, including supercritical nitrous oxide IN2O), ethane and propane, or A combination thereo~.
As is known ln the field of supercritical fluids, the solubility of a particular solid in a SCF depends upon the density and polarity o~ the SCF. Therefore, when a supercritical fluid is to be u~ed to extract a particul~r L fron a material, the ~ wo ssno476 2 1 8 1 9 8 4 ~ ~J
specific solubility of the -t Dlust be experimentally determined .
For the extraction of in~ompletely polymerized residual material from contact lens m~terials, it has now been ~t~rm;n~
that the C02 should be pressurized to from about 1000 psi to about 4000 psi, and is preferably from about 2000 psi to ~bout 4000 psi when the t~ L~ILe is kept within the r~nge of from about 40C
to about 90C, ~nd preferably from about 50C to ~bout 80C.
Generally, in the r-m~f~-t~lre of contact lenses, some of the monomer mix is not fully polymerized. The incompletely polymerized material from the polymerization proc~ss may affect optical clarity or may be harmful to the eye. Residual material may include solvents or unre~cted monomers from the monomeric mixture, or oligomers present as by-product~ from the polymeriz~tion process.
The residual material may be hydrophilic or l.rdL~hoLic.
Convention~l methods to ~xtract ~uch residual m~teri~ls from the polymerized cont~ct lens material include extraction with water tfor extr~ction of hydrophili.c residual material) or an alcohol solution ~for extr~ction of ~-y-lL~ hObic residual m~lteri~l).
However, ome of the ~lcohol extraction solution remains in the polymeric network of the pol~merized contact lens material, and must ~180 be extracted from 1:he lens material before the lens may be worn s~fely ~nd comfortab:Ly on th~ eye. T~lis requires ~n WO9C/20476 2 1 8 1 q84 PCrlUS95/OIOtl o additional extraction of the alcohol from the lens, generally using heated water for up to 4 hours or more. Frequently, however, the conventional methods may not ~deguately remove the residual m~terial.
Contact lens materials are formed from the polymerization produc of a mixture of monomers or prepolymers. (For purposes of ConVeniQnC-, the term " ~~ " as used hereafter shall include prepolymers. ) The monomeric mixture may also include m2terials other than monomers that aid in thc polymerization process, such ~s a 601vent or a diluent. Contact lens materials include materials for "hard" ~nd "soft" lenses. The hard lens classification typically includes lenses such as rigid gas pe- hl-~ (RGP) contact lenses, which are generally formed of cror6linlr~d ~ilicone acrylate or fluorn~ilic~ crylate copolymers. Soft lenses include "soft" hydrogel contact lenses.
Hydrogels are hydrophilic polymers that absorb water to an equilibrium value ~nd are insoluble in water due to the presence of a cr~Cl;n?--~ three-dimensional network. HYdL~, ~C are generally formed of a copolymer of at least one hydrophilic monomer and a crosslinking monomer. The hydrophilicity is due to the presence of hydrophilic groups, 6uch as alcohols, carboxylic acids, amides and sulfonic acids. The swollen equilibrated state results from a balance between the osmotic driving forces that cause the water to enter the hydrophilic polymer and the forces xerted by the polymer chains in resisting ~ nC j on . In the case of silicone hydrogel contact lenses, the copolymeric material ~ WO9'i/20~76 ~ 2 1 8 1 9~4 P~l/G.,!~I 2l further includes a silio~ ,,tA;ninq monomer. Lenses in this class are generally formed of a copolymer of at least one hydrophillc monomer And a cro~linking monomer. Hydrophilic monomers include: unsaturated carboxylic acids, such as methacrylic acid and acrylic acid; (meth)acrylic substituted alcohols or glycols, such as 2 h~d.~A~ lmethacrylate, 2-~ t~ hylacrylate, glyceryl methacrylate, and polyethyleneglycol methacryla~e; vinyl lactams, such as N-vinyl-2-pyrrolidone; and acrylamides, ~uch as methacrylamide and N,N-dimethylacrylanide. Further ,exanples of such hydrophilic monomers can be found in U.S. Patent Nos. 4,153,641; 4,740,533; 5,034,461;
and 5, 070, 215.
The crosslinking monomer may be a material having nultiple polymerizable ~unctionalities, preferably vinyl functionalities.
r ~, Le~L..Lative croC~ i nki nq m~nomers include: divinylbenzene;
allyl methacrylate; ethyleneglycol ditneth)acrylate, tetraethyleneglycol di~meth)a~rylate, polyethyleneglycol di (meth) acrylzlte; and vinylcarbonate derivatives of the glycol di(meth)~crylates. In the ca~e of silicone hydrogel contact lenses, the copolymeric material further includes at least one 8il i~ --e ~ ~" ~A i n i nq monomer .
Extracting hydrogel lens~s with solutions may restrict processing flexibility; the l~nse6 muGt be p.~.~ e.~cd, inspected and ~hipped in ~ "wet" state. From a m~ fa~L .ing perspective, it may be de~irable to packag~ and ship hydrogel lenses in the dry W095~0476 2 1 8 1 9 8 4 PCT/11595/01021 ~
~tate. However, known extraction methods frustrate the ability to p~ck~ge and ship hydrogel lenses in the dry state. As ohown by the cxperiment outlined in Example 4 below, it was determined that ~ contact lens could be released rrom a lens-in-mold ~ssembly in the dry ~t~te using supercritical C02. While the phy6ical propertles of the released lenses were not recorded, it is believed that supercritic~l fluid t~ lo~y could be used to release the lens from its mold ~nd have residuals extracted from the lens all in one step.
The incomplete extraction of residual material from lenses may contribute ~dversely to the useful life of the lens. It is thought that some residuals may not be fully extracted and may, over time, migrate through the polymeric network of the lens toward the surface. The residuals may impact lens performance and comfort by interfering with optical clarity or the desired unifor~
hydrophilicity of the lens surface. Therefore the use of ~upercritical C02 or other acceptable supercritical rluids will provide ~ more complete extraction of the contact lens material.
Such lm extraction would be highly preferable to known extraction protocols, and could result in a contact lens that is initially more hydrophilic, and which i5 able to remain hydrophilic for longsr duration.
Supercritical fluids may rurther incc,Lt,oL~.te amounts of ~dditional ~ for the purpose of -nhAnrinq the SCF's ~xtraction efficiency. This is sometimes referred to as "spiking"
~ Wo g~s/20476 2 1 ~ 1 9 8 4 F~ e~ 021 the SCF. Ely adding a compound to the SCF, the 6pecific properties of the SCF, ;nrlu~;nrJ behavior as a solvent, m~y be favorably altered. In this way, a wider range of impurities or ~ '-may be extracted from the lens material. Any organic solvent may be placed in the chamber for the purpose of mixing with the SCF.
Particul~rly useful ~ . '~ used for such SCF "spiking" include propanol, ethanol, methylene chloride and others as would be apparent to one 6killed in thla field of SCF technology.
If a contact lens is to remain comfortable for extended periods on the ye, the lens ~ust properly wet. To achieve this wetting, lenses often ir.ouL~o~c.te hydrophilic monomers into the monomer mix in an attempt to increase and maintain uniform wetting on the lens surface. Contact lenses have also been post-treated to achieve proper wetting. Plasma treating of contact lenses has been investigated and has yielded lenses with enhanced wetting.
Supercritical fluids were used to extract contact lenses both before and after plasma treating the lenses. See Ex~mple 3 below.
With respect to the extraction of residuals from contact lenses, Lolvents must be chosen by their ability to extract either hydrophilic, lI~dL~ JLiC or both types of unreacted residual material rrom the polymeric 2i~LU Lu-~:. However, the solvent itself must be able to be rerloved or flushed from the polymeric D~LU~UL~. Even if a particular liolvent car~ be flushed from the polymeric aLLU~LUL~, it may adversely affect the ~LLU~,LULe in a way that leaves the lens appearing cloudy. It is important that _g_ WO~/20476 2 1 8 1 984 1~ C1021 o the selected solvent in no way adver~ely affect the optical cl~rity of the lens. Optical clarity is subjectively understood to be the lev~l of clarity observed when the lens is inspected.
Trained inspectors in the field in~pect contact lense~ for their clarity. The len~es which had been extracted with supercritical C2 appeared at least as R optical ly clearR when viewed next to conventionally extracted contact lenses.
There is evidence shown in the following Examples that the l;upercritical C02 extracted residuals fron the contact lenses, under certain conditions up to ten times, better than conventional isopropyl alcohol and water extractions. See Example l, Table l.
It has been thought that lenses may lose their wetting properties and become more ~,~dL~,~hoLic at the surface, over time, due to the leaching out of 1-~L~,~hobic segments which were not satisfactorily extracted previously. It is possible that the enhanced extraction of residuals effected by the supercritical C02 may obviate the ne~d to post-treat a lens. This could l~ad to both longer lasting and more comfortable lenses with excellent wetting properties.
Such lenses would also require fewer processing steps which could greatly reduce cost.
It i~ contemplated that the SCF ~.LL ~' i~n may be in~L~L~ted into any contact lens r-n~f~t~ring protocol, at any point in the protocol, although it is preferable that the SCF
extr~ction take place as the final step in the process to provide a final cleaning of the lens.
WO9~120476 2181 984 r~ "~2~
While data was obtained only for poly6iloxane hydrogel contact lens material6, it is understood that supercritical fluids may be used for extr~cting ~ny contact lens m~terial. Therefore any lens-forming mzteri~l can be employed in the present invention. The materials m~y be hydrophilic, or l.~.lLv}.l.oLic, or mixtures of both. The resulting contact lenses may be hard lenses as exemplified by the rigid acrylic plastics including poly(methyl methacrylate); or such contact lenses may be flexible, ~y.lL~,~hobic lenses exemplified by the unsubstituted and fl~loL., _ baLituted polyethylenes, the silicone elastomers, and the like; or such lenses may be soft hydrogel lenses.
It WAS further discovered that contact lenses could be ~ubjected to SCF extraction while still in the mold in which the lens was cast. See Example 3. The complete lens-in-mold Assembly WA5 placed into the SCF pressurized chamber. Therefore, the SCF
extraction t~^hnnlo-AJy can be used to effect dry lens release from the mold, which m~y be ~.lvAnl-J~ with respect to p~ AJin~ and inA, ~nnci~ ations. The method may be used to release any type of contact lens from molds made of any material, in which it w~s cast. Polyvinyl chloride and polypropylene are preferred mold materials with polypropylene being p~rticularly preferred.
Often, contact lenses ~re released by contacting the lens and mold with ~ release solution, preferably by immersing the mold and lens ~sèmbly in the solution. This "wet" release step may be accomplished at room t ALUL~ lthough in some cases it may be WO95/20476 21 81 q84 r~ 1021 0 advantageous to conduct the release at othor temperatures, for example, at an elevated bath t~ u-_6 Up to about 125C.
Following release of the lens from the mold, the lens is hydrated with water or burfered saline. S- ~s~1v~ ly, the lens is ~terilized 6uch as by autoclaving in water or saline. The6e 6teps al60 effect remov~l of any re6idual isvylvy~l.ol from the lens. As already m ntioned, "wet" processing of contact len6es ib labor intensive and may add to the cost o~ processing. Dry release, as facilitated by the pre6ent invention, would present an 9 ~ lly ~ùv~,nLa.~:uu. alternative to the known lens release method6 .
The pre6ent invention further contemplates the use of supercritical fluid technology to facilitate the de-blocking pLV~m:~UL~O currently used for lathed contact lenses. If a contact len6 edge or surface must be altered by using a lathe, the lens is often fixed or "blocked" to a holding implement, typically using a curable wax material. This material h~rdens and holds the lens in place whlle it is rotated at high speeds against the lathe. After the lathing is complete, the len6 must be removed, or "de-blocked"
from the holding implement. Ecologically unfavorable materials including chlorofluorocarbons ~CFCs) were widely used for such de-blocking. After the de-blocking, the len6es must then be cleaned, followed by extraction p-v- ~duLæs as already described. It is now thought that supercritical liquids including supercritical C02 could be u~ed to di6solve the blocking wax while at the 6ame time WO 9~no476 2 1 8 1 9 8 4 PCT/U595/01021 cleaning the lens and al~o removing residual materials rom the lens .
The contact lens~s treat~ad by the PLV~,6_3l3S of the present lnvention may be Lu,~.d by the ~pincasting IJL~ uch aS those ~licrl~s~ in U.S. Pat. Nos. 3,408,429 ~nd 3,496,254 and other convelltional ~ethods, ~uch as compression molding ~s disclosed in t~.S. Pat. Nos. 4,084,459 ~nd 4 ,197, 266 .
Polymarization may be r ~ either in a spinning mold, or ~ stationary mold CV~.L- . 'in~ to a des$red contact lens shape. The obtained conl:act l~ns may be further subjected to zl -nir~ finSshing, as desired. Al~;o, the polymeriz~tion may be ~n~ ct 1 in an appropriate mold or vessel to give a lens materiaL in the form o f hutton, plate or rod, which may then be pL~- eas3~ (e.g., cut or polished via l~the or laser) to give a cont:act lens havin~ a desired shape.
The Il~.IL~ produced b~ the present invention are oxygen tL~r,-~vL~ing, hydrolytically stAble, }~iologically inert, and tr~nsp~rent. The ~lonomers and copolymers employed in ~vL~ance with this invent:ion, ~re readily polymerized to rorm three rli~ -ion~l networks which permit the tLarl ".)LL of oxygen And Are optically clear, strong and hydrophilic.
W0~5/20476 2 1 8 1 q 84 P~
The present invention provides materials which can be usefully employed for the fabrication of prostheses such as heart v~lves And intraocular lenses, ~s optical contact lenses or ala fllms. More particularly, the present invention concerns contact lenses.
The present invention may further assist in the m-n--f~ re of material~ which can be used for bi~ At~
devices, such as, surgical devices, heart v~lves, vessel ~ubstitutes, intrauterine devices, ` ~ 3 and other films, di~phr~gms, ~urgical implant6, blood vessels, ~rti~icial ureters, ~rtifici~l breast tissue and ~ 8 intended to come lnto contact with body fluid outside of the body, e.g., a5 for kidney dialysis and h-art/lung machines and the like, c~theters, mouth guards, denture liners, intraocular devic~s, ~nd especially contact lenses.
~ t i~ known that blood, for ~xample, is readily and r~pidly damaged when it comes into contact with ~rtificial Lurfaces. The design of a ~ynthetic ~urface which is ~ntithL. `, ic ~nd nonhemolytic to blood is necessary for prosthe~es ~nd devices u5ed with blood.
The following Examples further illustrate various preferred _'~ Ls of the invention. Although certain preferred _ A; have been described, it ili understood that the WO 95/2(~4~6 2 1 8 1 9 8 4 PCT/US9~01021 invention is not limited thereto and modifici~tions and variations would be ~vident to a person of ordinzrY skill in the art.
F~lUtPLEi 1 Det~r~in-tion of ~-ln_r Critic~l Fl~ Lens rYtraction EfficiencY
An ex"eriment was designed to ~-t-rn~-- whether t.~LL - ~ion of contact lenses would be enhanced by uring supercritical fluids.
Ten polysiloxane hydrogel lenses to serve as controls were extracted with isopropyl alco~lol (IPA~ and then water. The lenses were first placed in IPA at room t, ~ tULe for 1 hour, followed by pl~- into a water tank at 85C for 4 hours. Ten polysiloxane hydrogel lenses were then extracted with super critical carbon dioxide (C02), in batches at vnrious t-, ~tULeS
and ~. F .,:; as shown below. Each t~n lens batch, inrll~Aini the control was static extracted i n 3 mL of tetrAhydrofuran (THF) for a minimum of 24 hours. Four hundred microliters of the THF for each batch including the cont~ol were sequentially injected into the SEC. The total area of the distribution of the THF lens extract was used to determine the efficiency of the super critical fluid extractions as compared to the IP~ L~ol extractions. The -rêa of the test lens THF extracts were divided into the area of the control lens extract to give an extraction efficiency ratio (EER) . Th~ extraction ef f iciency ratios were determined by dividing the total area (normi~lized ~rea) of the molecular weight distribution of the test lens THF extracts into the total area (n~ area) of the molecular weight distribution of the control lens THF extracts. Thie 1~= of the control lens was wogs/20476 2 1 8 1 98~ F~ e,.,~ . O
~rt~h~ ~ r~ l to be 1. 00 . EER values greater than 1. 00 are less ~fficient than the IPA extraction method: EER values less than 1.00 are more e~ficient. For ~ch SCF C02 extraction, the chamber was filled with SCF C02 ~nd purged 3 times with each purge/fill cycle lasting 1 hour.
The t~ .,tu.~ and pl~ ~, used for the super critical C2 extraction, ~Ireas from the SEC, and EER values are listed in Table 1.
Table 1 ./Pr~e~l~re(Dsi~ Area (SEC~ ~3 Control 24707992 1.00 50C/2000 18817108 0.81 70C/3000 18753486 0 . 81 80C/2000 2093090 0.09 80C/4000 24676496 1.08 A. SCF/P1 a~- Treatment Ninety soft hydrogel contact lenses were made without initial plasma L,e:ai ~ ~. Twenty of the5e lenses were set aside le~ving 70 l-n~es. The i;eventy lenses were supercritically e,.L,e,- Led using C02 at 4500 psi, 60C. The chamber was ~illed with ~upercritical C02 and purged 3 times with each filling/purge cycle laE~ting 1 hour. The seventy lenses were then plasma treated, W0 95~20476 2 1 8 1 9 8 4 r~ o21 followed by water extraction Por 4 hour~ at 190C. The plasma tL~i L protocol followed iE as described im~ediately below.
Pl~C - Treatin~ of Soft l~yrlroc~el C~st Molded Contact ~-A plasma is A complex mixture of zltoms ~nd molecules in both ground and excited states which reach a steady state after the di=charge h~s begun . The CO~C ~ rlltiOn of ionC is about six orders of m~gnitude lower thar~ neutrals. The primary reactants in ~n air or oxygen plasma are oxygen atoms. The action of an air plasma will cause primarily oxygen, and to a lesser extent nitrogen, ir~v~v~tiOn into the polymeric l.LLu~LuLe of the material in the chamber. As is u-.deL-Lood in the field, plasmas can be produced by passing an electrical discharge, usually at radio LL-, y through ~ g~s At low pressure (0.005 to 5.0 torrj.
The ~pplie~ RF power is absor~ed by atoms and ~olecules in the gas state . The circulating electr ical f ield cauEes these excited atoms and molecules to collide with one another as well as the walls of the chamber and the ~urface of the ~aterials placed into the chamber. The lenses were removed ~rom handling trays and placed concave side up on an aluminum coated tray. The tray was then placed into the pl~sma L..:ai L chamber. The lenses were then treated in a direct current DC chamber. The chamber pressure w~s reduced to 0.1 torr ~nd stabilized for ~t least 30 seconds.
The lenses were treated ~t 400 watts for 4 minutes at 0.1 torr.
The chamber wai; then backfilled to ambient pressure. The tray was then removed from the chamber, the lenses inverted ~nd the repeated to plasma treat the other side of the lens.
W09~120~76 2 1 8 1 9~4 J ~ 2l o Ten lenses were ~ubmitted for measurement of residual extractables in tetral-r.lL~,ru.~l, (THF) and for ~ . ' of physical char~cteristics .
B. Plasma Tre-' ' /SCF
Soft hydrogel lenses were manufactured using plasma LL. a~ L . Ten lenses were set aside. Ten lenses were subjected to Alcohol and water extractions to ~;erve as control lenses.
Another ten lcnses were plasma treated, then subjected to cupercritical C02 and THF extractions, using the 6ame conditions ~s listed ~bove in part A. The THF extracts were then ev~luated ~or L~ ~ inin~ extractables using Size Exclusion Chromatography tSEC) as set forth in Exallple 1 above. The following data was obtained. The weight column (wt) Le~LeS IlLs the starting total weight of 10 lenses. The column marked N.A. is the normalized average of lenses arrived at by dividing the weight into the area.
The EER ratio is as described in Example 1 with the dry lenses accorded an arbitrary rating of 1. 00 for co~parative purposes .
The final colu~n L~ LeS~ S the lens batches normalized to the IPA
tisopropanol/H20 extracted lenses) control batch.
Table 2 ~earSEC~ wt N.A. FF~ TPA
1.Non-Extracted 27362822 0.2153 1.27x108 1.00 6.00 2.IPA/H20 4386309 0.2092 2.10alO7 0.17 1.00 3.Pl~sma/SCF 5687337 0.21436 2.65x107 0.21 1.26 4 . SCF/Pla~ma 4481289 0 . 21153 2 .12x107 0.17 1. 01 WO 9C12047~ 2 1 8 1 q 8 ~ r~
The physical characteristics of the lenses i n groups 2, 3 and 4 were as follows:
IPA/H20 Plasma/SCF SCF/Plasma Modulus (g/mm2) 91 llO 105 Elongation (~ N/A 70 63 Tensile (g/mm~) 21/A 42 3~
Tear (g/mm) g B 7 ~ aXPL~ 3 Descri~tion of Drv ~elease fro~ Lens-In-Mold ~~ ` lv A lens-in-mold assembly was placed in an upright position in the ~upercritical fluid chamber. The polysiloxane hydrogel contact lens was positioned in the polypropylene mold such that the concave side of the lens was exposed to the a~ ,. The chamber was filled with C02 and pressurized to 2000 psi at 50C
for l hour. The chamher was purged of the C02 and replaced with fresh C02 3 times. The chamber was then purged a final time and the lens-in mold ~ ' ty was removed from the chamber. The lens remained in the mold but was clearly ~ n~ d f ro~ the mold such th~t the lens dropped from th~ mold when the assembly was inverted. The lens appeared dimpled ~nd hazy toward the center o~
the lens. However, inspection of the lenses following hydration revealed that the lenses dry released from the mold looked indist~n~~ hl~ from lenses released from the mold via standard hydration .
WO9S/20~76 21 81984 r~
M~ny other modific~tlons ~nd v~ri~tions of the present invention ~re possible to the skilled pr~ctitioner in the field in light of the t~ hir7~ herein. It is therefore u--d ~DL~od that, within the scope of the cl~ims, the present invention c~n be practiced other th~n ~s herein specif ic~lly described .
--2 o--
Claims (20)
1. A method of producing an optically clear contact lens, comprising moulding the lens from a monomeric mixture, and treating the moulded contact lens with a supercritical fluid.
2. The method of Claim 1 wherein the supercritical fluid is selected from the group consisting of supercritical carbon dioxide, supercritical nitrous oxide, supercritical ethane and supercritical propane.
3. The method of Claim 1 wherein the supercritical fluid comprises supercritical carbon dioxide.
4. The method of Claim 3 wherein the supercritical fluid further comprises a compound selected from the group consisting of propanol, ethanol and methylene chloride.
5. The method of Claim 3 wherein the supercritical carbon dioxide is pressurized to from about 2000 to about 4000 psi.
6. The method of Claim 3 wherein the temperature of the supercritical carbon dioxide is from about 50°C to about 80°C.
7. The method of Claim 1, wherein the contact lens is retained in the mold in which the lens was molded, and the improvement comprises treating the contact lens while still in the mold with the supercritical fluid, and disengaging the contact lens from the mold without the use of a release solution.
8. The method of Claim 7 wherein the supercritical fluid is selected from the group consisting of supercritical carbon dioxide, supercritical nitrous oxide, supercritical ethane and supercritical propane.
9. The method of Claim 7 wherein the supercritical fluid comprises supercritical carbon dioxide.
10. The method of Claim 7 wherein the supercritical fluid additionally comprises a compound selected from the group consisting of propanol, ethanol and methylene chloride.
11. The method of claim 1, wherein the improvement comprises treating the molded contact lens with a supercritical fluid to remove incompletely polymerized materials from the contact lens.
12. The method cf Claim 11 wherein the residual materials include at least one member selected from the group consisting of organic solvents, unreacted monomers and oligomers.
13. The method of Claim 11 wherein the supercritical fluid is selected from the group consisting of supercritical carbon dioxide, supercritical nitrous oxide, supercritical ethane and supercritical propane.
14. The method of Claim 13 wherein the supercritical fluid comprises supercritical carbon dioxide.
15. The method of Claim 14 wherein the supercritical fluid additionally comprises a compound selected from the group consisting of propanol, ethanol and methylene chloride.
16. The method of Claim 14 wherein the supercritical carbon dioxide is pressurized to from about 2000 to about 4000 psi.
17. The method of Claim 14 wherein the temperature of the supercritical carbon dioxide is from about 50°C to about 80°C.
18. The method of Claim 1 wherein the lens has been prepared from mixtures of both hydrophilic and hydrophobic materials.
19. The method of Claim 18 wherein the lens is a silicone hydrogel contact lens.
20. The method of claim 18, wherein the improvement comprises contacting the molded contact lens in the dry state and while still in the mold with a supercritical fluid to remove both hydrophilic and hydrophobic residues remaining on the lens after polymerization.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US18934794A | 1994-01-31 | 1994-01-31 | |
| US08/189,347 | 1994-01-31 | ||
| PCT/US1995/001021 WO1995020476A1 (en) | 1994-01-31 | 1995-01-24 | Treatment of contact lenses with supercritical fluid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2181984C true CA2181984C (en) | 2000-06-13 |
Family
ID=22696923
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002181984A Expired - Fee Related CA2181984C (en) | 1994-01-31 | 1995-01-24 | Treatment of contact lenses with supercritical fluid |
Country Status (13)
| Country | Link |
|---|---|
| US (3) | US6071439A (en) |
| EP (1) | EP0741637B1 (en) |
| JP (2) | JP3447296B2 (en) |
| KR (1) | KR100346485B1 (en) |
| CN (1) | CN1061589C (en) |
| AU (1) | AU689850B2 (en) |
| BR (1) | BR9507054A (en) |
| CA (1) | CA2181984C (en) |
| DE (1) | DE69511067T2 (en) |
| ES (1) | ES2137495T3 (en) |
| HK (1) | HK1013809A1 (en) |
| MX (1) | MX9603063A (en) |
| WO (1) | WO1995020476A1 (en) |
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- 1995-01-24 AU AU16076/95A patent/AU689850B2/en not_active Ceased
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- 1995-01-24 WO PCT/US1995/001021 patent/WO1995020476A1/en active IP Right Grant
- 1995-01-24 KR KR1019960704113A patent/KR100346485B1/en not_active IP Right Cessation
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- 1995-01-24 BR BR9507054A patent/BR9507054A/en not_active IP Right Cessation
- 1995-01-24 JP JP52015795A patent/JP3447296B2/en not_active Expired - Fee Related
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- 1995-01-24 CN CN95191428A patent/CN1061589C/en not_active Expired - Fee Related
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1997
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1998
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2000
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2003
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| AU1607695A (en) | 1995-08-15 |
| CN1142209A (en) | 1997-02-05 |
| DE69511067T2 (en) | 1999-12-09 |
| US6180031B1 (en) | 2001-01-30 |
| US6071439A (en) | 2000-06-06 |
| JPH09511000A (en) | 1997-11-04 |
| WO1995020476A1 (en) | 1995-08-03 |
| HK1013809A1 (en) | 1999-09-10 |
| CN1061589C (en) | 2001-02-07 |
| AU689850B2 (en) | 1998-04-09 |
| EP0741637B1 (en) | 1999-07-28 |
| MX9603063A (en) | 1997-05-31 |
| EP0741637A1 (en) | 1996-11-13 |
| KR100346485B1 (en) | 2002-11-30 |
| BR9507054A (en) | 1997-09-16 |
| JP3447296B2 (en) | 2003-09-16 |
| US6610221B2 (en) | 2003-08-26 |
| JP2004004814A (en) | 2004-01-08 |
| US20010048506A1 (en) | 2001-12-06 |
| ES2137495T3 (en) | 1999-12-16 |
| DE69511067D1 (en) | 1999-09-02 |
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