Note: Descriptions are shown in the official language in which they were submitted.
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OPHTHALMIC DEVICE COMPRISING A HOLOGRAPHIC SENSOR
Field of the Invention
This invention relates to an ophthalmic device comprising a holographic
sensor.
Background to the Invention
Ophthalmic devices, for example contact lenses, comprising holographic
elements are known. Typically, a holographic element is used to focus incoming
light. The holographic element may have a programmed activating angle
providing two or more optical powers. The use of a holographic element allows
the user to see clear and unimpaired images, thereby overcoming many of the
shortfalls of traditional simultaneous vision and translating lenses.
Holographic
optical inserts are described, for example, in WO-A-99/34239, WO-A-99/34244,
WO-A-02/054137 and WO-A-99/34248.
The need for minimally invasive, easy-to-use glucose sensors has
motivated the investigation of numerous approaches. One particular area of
interest is ophthalmic glucose sensors, i.e. those for the detection of
glucose in
the eye. The levels of glucose in the eye are known to correlate with those in
the
blood, and thus blood levels of glucose can be monitored indirectly by
measuring
the levels in an ocular fluid such as tears.
US-A-200310027240 describes an ocular insert for the detection of
glucose. The insert comprises a polymerised crystalline colloidal array (PCCA)
which is polymerised in a hydrogel, and a molecular recognition component
capable of responding to glucose. The array has a lattice spacing that changes
when the volume of the hydrogel changes, causing the diffracted wavelength of
the array to change.
WO-A-95/26499 discloses a holographic sensor, based on a volume
hologram. This sensor comprises an analyte-sensitive matrix having an optical
transducing structure disposed throughout its volume. Because of this physical
arrangement of the transducer, the optical signal generated by the sensor is
very
sensitive to volume changes or structural rearrangements taking place in the
analyte-sensitive matrix as a result of interaction or reaction with the
analyte.
For example, a sensor comprising a gelatin-based holographic medium may be
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used to detect trypsin. Trypsin acts on the gelatin medium, irreversibly
destroying the integrity of the holographic support medium. Holographic
sensors
may also be used to detect changes in, for example, pH.
Although sensors of the kind described in US-A-2003/0027240 may be
used to detect levels of glucose in the eye, there remains the need for
ophthalmic sensors which allowfor accurate, real-tim a detection of analytes
such
as glucose.
Summary of the Invention
The present invention is based on the realisati on that holographic sensing
technology, when incorporated into a contact lens or other ophthalmic device,
provides an accurate yet minimally invasive method of detection of an ocular
analyte. Such sensing technology may allow for the continuous, real-time
sensing of glucose or other carbohydrates. The invention thus may improve the
lives of patients having diabetes and decrease such patients' risk of
developing
hypoglycemia or hyperglycemia.
Afirst aspect of the invention is an ophthalmic device which comprises a
holographic element comprising a medium and, dis posed therein, a hologram,
wherein an optical characteristic of the element changes as a result of a
variation of a physical property of the medium, and wherein the variation
arises
as a result of interaction between the medium and an analyte present in an
ocular fluid. The device may be a contact lens or an ocular implant.
Another aspect of the invention is a method of detection of an analyte in
an ocular fluid, the method comprising detecting any change of the optical
characteristic of the holographic element of a device of the invention with
the
fluid, in the eye.
Another aspect of the invention is a method for the production of a device
of the invention which comprises contacting the holographic element with a
contact lens, wherein the contacted regions of the element and the lens are
cross-linkable; and cross-linking said regions. Preferably, at least one of
the
contacted regions comprises PVA, more preferably Nelfilcon.
The invention may be used for the detection of ocular analytes such as
glucose or lactate. The interaction is preferably reversible so that both the
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interaction and reverse interaction can occur, allowing the analyte to be
continuously detected, preferably in real time. The interaction is preferably
a
chemical reaction.
Description of the Invention
The term "glucose" as used herein refers to the known cyclic and linear
forms of glucose.
w The term "ophthalmic device" as used herein refers to contact lenses
(both hard and soft), corneal onlays, implantable ophthalmic devices and the
like.
The term "contact lens" as used herein refers to any hard or soft lens used
on the eye or ocular vicinity for vision correction, diagnosis, sample
collection,
drug delivery, wound healing, cosmetic appearance or other ophthalmic
application. The lens may be a daily-disposable, daily-wear or extended-wear
lens.
The term "implantable ophthalmic device" as used herein refers to an
ophthalmic device which is used in, on or about the eye or ocular vicinity.
Such
devices include intraocular lenses, subconjunctival lenses, intracorneal
lenses,
and shunts/implants (e.g. a stent or glaucoma shunt) that can rest in the cul
de
sac of an eye.
In a preferred embodiment, the insert is in the form of a contact lens. The
lens may be manufactured using any suitable material known in the art. The
lens
material may be formed by the polymerisation of one or more monomers and
optionally one or more prepolymers. The material may comprise a
photoinitiator,
visibility tinting agent, UV-blocking agent and/or a photosensitiser.
A preferred group of lens materials are prepolymers which are water-
soluble and/or meltable. It is preferred that the material comprises one or
more
prepolymers which are in a substantially pure form (e.g. purified by
ultrafiltration). Preferred prepolymers include water-soluble crosslinkable
polyvinyl alcohol) prepolymers (as described in US5583163 and US6303687);
a water-soluble vinyl group-terminated polyurethane, obtainable by reacting an
isocyanate-capped polyurethane with an ethylenically unsaturated amine
(primary or secondary amine) or an ethylenically unsaturated monohydroxy
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compound, wherein the isocyanate-capped polyurethane can be a
copolymerisation product of at least one polyalkylene glycol, a compound
containing at least 2 hydroxyl groups, and at least one compound with two or
more isocyanate groups; derivatives of a polyvinyl alcohol, polyethyleneimine
or
polyvinylamine (see, for example, US5849841); a water-soluble crosslinkable
polyurea prepolymer as described in US6479587; crosslinkable polyacrylamide;
crosslinkable statistical copolymers of vinyl lactam, MMA and a comonomer, as
disclosed in EP-A-0655470 and US5712356; crosslinkable copolymers of vinyl
lactam, vinyl acetate and vinyl alcohol, as disclosed in EP-A-0712867 and
US5665840; polyether-polyester copolymers with crosslinkable side chains, as
disclosed in EP-A-0932635; branched polyalkylene glycol-urethane prepolymers,
as disclosed in EP-A-0958315 and US6165408; polyalkylene glycol
tetra(meth)acrylate prepolymers, as disclosed in EP-A-0961941 and
US6221303; and crosslinkable polyallylamine gluconolactone prepolymers, as
disclosed in WO-A-00/31150.
The lens may comprise a hydrogel material. Typically, hydrogel materials
are polymeric materials which are capable of absorbing at least 10% by weight
of water when fully hydrated. Hydrogel materials include polyvinyl alcohol)
(PVA), modified PVA (e.g. nelfilcon A), poly(hydroxyethyl methacrylate),
polyvinyl pyrrolidone), PVA with a poly(carboxylic acid) (e.g. carbopol),
polyethylene glycol), polyacrylamide, polymethacrylamide, silicone-containing
hydrogels, polyurethane, polyurea, and the like.
Alternatively, the device may be an implantable ophthalmic device.
Glucose levels in tears may be much lower than blood glucose levels. With an
implantable ophthalmic sensor, one can monitor glucose levels in aqueous
humor or interstitial fluid, where glucose levels can be much higher than
glucose
levels in tears. Preferably, the device is in the form of a subconjunctive
implant,
intracorneal lens, stent or glaucoma shunt.
The holographic support medium is one in which a hologram can be made
and which is capable of exhibiting one or more of the properties of the
sensitive
mechanisms described herein. The hologram may be disposed on or in, part of
or throughout the bulk of the volume of the support medium. Particularly in
the
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case of a contact lens, the support medium may be an integral part of the
device,
e.g. the body of a lens may itself comprise or form a holographic support
medium.
The support medium preferably comprises a native or modified matrix with
5 viscoelastic properties which alter as a result of an interaction with an
analyte
species. For example, the matrix may be formed from the copolymerisation of
(meth)acrylamide and/or (meth)acrylate-derived comonomers. In particular, the
monomer HEMA (hydroxyethyl methacrylate) is readily polymerisable and cross-
linkable. PoIyHEMA is a versatile support material since it is swellable,
hydrophilic and widely biocompatible.
A device in the form of a contact lens is preferably obtained by forming a
holographic element and then embedding the element into a contact lens. For
example, a contact lens sensor may be obtained using the following protocol:
(a) forming a polymeric holographic sensor(e.g. using phenylboronate
ligands) on a glass slide or similar surface;
(b) coating a layer of polyvinylalcohol (PVA), preferably "Nelfilcon",
onto the surface of the sensor, with subsequent cross-linking of
the layer;
(c) extracting any toxic components from the coated sensor (e.g. using
1:1 mixture of methanol:water overnight at 40°C), followed by
autoclaving;
(d) removing the sensor from the slide and cutting from it a disc of
about 4mm diameter; and
(e) inserting a disc into a contact lens mould containing a contact lens
and PVA, preferably Nelfilcon, then cross-I inking and autoclaving
the components to form the finished lens.
A holographic sensor of the type used in the invention generally
comprises a medium and, disposed throughout the volume of the medium, a
hologram. The support medium may interact with an analyte resulting in a
variation of a physical property of the medium. This variation induces a
change
in an optical characteristic of the holographic element, such as its
polarisability,
reflectance, refractance or absorbance. If any change occurs whilst the
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hologram is being replayed by incident broad band, non-ionising
electromagnetic
radiation, then a colour or intensity change, for example, may be observed.
The sensor may be prepared according to the methods disclosed in WO
A-95/26499, WO-A-99/63408 and WO-A-03/087789. The contents of these
specifications are incorporated herein by reference.
More than one hologram may be supported on, or in, a holographic
element. Means may be provided to detect the or each variation in radiation
emanating from the or each hologram, arising as a result of a variation in the
or
each optical characteristic. The holographic elements may be dimensioned and
arranged so as to sense two independent events/species and to affect,
simultaneously, or otherwise, radiation in two different ways. Holographic
elements may be provided in the form of an array.
An illuminating source of non-ionising radiation, for example visible light,
may be used to observe variations) in the, or each, optical characteristic of
the
holographic element. The extent of interaction between the holographic medium
and the analyte species is reflected in the degree of change of the physical
property, which is detected as a variation in an optical characteristic,
preferably
a shift in wavelength of non-ionising radiation.
The property of the holographic element which varies may be its charge
density, volume, shape, density, viscosity, strength, hardness, charge,
hydrophobicity, swellability, integrity, cross-link density or any other
physical
property. Variation of the or each physical property, in turn, causes a
variation
of an optical characteristic, such as the polarisability, reflectance,
refractance or
absorbance of the holographic element.
There are a number of basic ways to change a physical property, and thus
vary an optical characteristic. The physical property that varies is
preferably the
volume of the support medium and, in turn, the spacing of the holographic
fringes of the holographic element. This variation may be achieved by
incorporating specific groups into the support matrix, where these groups
undergo a change in, for example, conformation, charge or the degree of cross-
linking upon interaction with the analyte, and cause an expansion or
contraction
of the support medium. An example of such a group is the specific binding
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conjugate of an analyte species. Another variation is in th a active water,
solvent
or charge content of the support medium. In this case, the holographic support
medium is preferably in the form of a gel.
Analyte molecules that can react with at least two functional groups in the
element may form a reversible cross-link between separate parts of the support
matrix, thereby altering the visco-elastic properties of the support matrix.
Consequently, if present within a solvent-containing environment, and the
support matrix changes, the support matrix contracts and the separation of
the fringes is reduced. Specificity may be provided by ensuring that specific
binding sites are provided within the medium.
The support medium may comprise a receptor which is capable of binding
or interacting specificallywith the analyte. Suitable receptors include
antibodies,
lectins, hormone receptors, drug receptors, enzymes, aptamers, nucleic acids,
nucleic acid analogues, and fragments thereof.
A receptor may be incorporated into a support med ium using any suitable
method known in the art. For example, a prepolymer and receptor may comprise
matching functional groups; the two components can then be covalently linked
with one another. Alternatively, a receptor may be incorporated in a vinylic
monomer which a component of the lens-forming material.
One parameter determining the response of the system is the extent of
cross-linking. The number of cross-linking points due to polymerisation of
monomers should not be so great that complex formation between polymer and
analyte-binding groups is relatively low, since the polymer film may become
too
rigid. This may inhibit the swelling of the support medium.
By way of example of a glucose sensor, a hydroge 1-based hologram may
have a support medium comprising pendant glucose groups and a lectin,
preferably concanavalin A (con A). The lectin binds to the pendant glucose
groups and acts as a cross-linker in the polymer structure. In the presence of
freely diffusible glucose, the extent of cross-linking will decrease as
glucose in
solution displaces polymer-attached glucose from the binding sites on the
lectin,
resulting in swelling of the polymer. Volume changes in hydrogel films
containing
pendant glucose groups and con A can be observed using a reflection hologram.
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A volume change in the hydrogel alters the fringe separation of the
holographic
structure and can be followed as a shift in the peak wavelength of the
spectral
reflected response.
Water-based systems are preferred in such a holographic sensor, since
they protect the lectin from exposure to organic solvents. Examples of
suitable
glucose components are high molecular weight dextran, and the monomers
allylglucoside and 2-glucosyloxyethyl methacrylate (GEMA). Dextran, having no
inherent polymerisable functionality, can be entrapped during the
polymerisation
of acrylamide-based monomers; allylglucoside and GEMA can be polymerised
either individually or together with comonomers. The polymers are preferably
prepared as thin films on glass supports.
A holographic glucose sensor may comprise any suitable glucose
receptor, particularly one which allows a reversible change in a physical
property
of the support medium upon binding with glucose. For example, the support
medium may comprise pendant boronic acid groups, such as phenylboronic acid
or a derivative thereof. Two adjacent diol groups in glucose bind with a
boronic
acid group in a reversible condensation reaction. Thus in a holographic
element,
reaction of glucose with pendant phenylboronic acid groups causes an
expansion of the support medium, due to the formation of boronate esters.
Without wishing to be bound by theory, it is believed that the boronate esters
are
negatively charged and effect a Donan potential, causing water to partition
into
the support medium. This expansion is observed as a shift in the reflectance
maxima to longer wavelengths. The sensing ability of boronic acid groups is
strongly dependent on the molecular geometry and the aromatic species where
the boronic acid group is present. Thus, glucose sensitive probes can be made
with a variety of affinities, in the mM range for blood glucose, and in the pM
range for tear glucose. Preferred boronic acid groups include those described
in WO-A-04/081624.
Boronic acid compounds, in particular phenylboronicacid compounds, are
versatile receptors since they may be used for the detection of a variety of
carbohydrates. In physiological fluids, this lack of selectivity is not a
problem
because most sugars are found on glycoproteins and other macromolecular
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structures, i.e. they are already bound and thus cannot bind to the boronic
groups of the support medium. Glucose is the only sugar that is found free in
relatively high concentration. Lactate (lactic acid), however, may pose a
problem
since it is an a-hydroxy acid which binds to boronic acid groups and is, in
ocular
fluids, generally present in a greater concentration than glucose.
The problem of lactate interference can be addressed by incorporating,
in the device, a group which repels lactate. Lactate carries an overall
negative
charge in physiological fluids and thus, for example, the support medium may
carry a group having a negative charge, the magnitude of which will be
apparent
to those skilled in the art. An example of such a group is glycolic acid,
which can
be incorporated into the support medium by the polymerisation of monomers
including, for example, acrylamidoglycolic acid. The glycolic acid moiety
competes with glucose and lactate for available phenylboronic acid sites
however, since the moiety carries a negative charge, it repels lactate but not
glucose. Alternatively, the boronic receptor may itself carry a substantial
negative charge or polarisation, e.g. by coordinating the boron atom with
suitable
electron-donating groups. An example of such a boronic acid is 5-fluoro-2-
methylacrylamidophenylboronic acid. Another option is to attach negatively
charged groups to the phenyl group of a phenylboronate receptor. The surface
of the holographic element or the device may be negatively charged, to reduce
the effects of lactate interference.
A sensor can also be made more selective for glucose by incorporating
pendant amine groups in the support medium. The nitrogen atom of the amine
group may form an intramolecular bond with the boron atom, thereby promoting
formation of the more reactive tetrahedral conformation about the boron atom.
The support medium may comprise one or more macrocyclic groups such
as crown ethers, which reversibly bind a range of ionic species. Crown ethers
are well known to reversibly bind Group I and Group II metal ions. Therefore a
crown ether which is specific to an ionic analyte can be immobilised in the
support medium and used to continuously monitor the presence of the analyte.
The following Examples illustrate the invention.
Example 1
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A contact lens was produced according to the protocol described above.
The embedded holographic element comprised 12% mol of 3-
acrylamidophenylboronic acid, the synthesis of which is described in WO-A-
04/081624.
5 The lens was placed into the eye of a human volunteer, who then
ingested a 44g bolus of glucose. The response of the contact lens sensor was
measured in terms of the shift in the wavelength of reflection. Blood glucose
levels were also monitored directly using a conventional glucose sensor.
Fig. 1 shows the response of the contact lens sensor, Fig. 2 that of the
10 blood glucose sensor. It is evident that the responses of the two sensors
are
similar, the peak level of glucose being absorbed at around t = 25 minutes.
Example 2
An experiment similar to that of Example 1 was performed, using an
ophthalmic implant comprising the sensor. The support medium was coated with
Nelfilcon (Cibavision).
The experiment was conducted on a rabbit, instead of a human volunteer,
the device implanted subcutaneously just below the eye. The rabbit was then
anaesthetised using an xylazine-based protocol which causes blood levels of
glucose to rise to a level commonly seen in diabetic patients (see Cameron et
al, Diabetes Technology & Therapeutics, 2001, 3, 2O1-207). The concentration
of glucose was then monitored using the implant. Again, blood levels of
glucose
were also monitored directly.
Fig. 3 shows the response of the holographic implant, Fig. 4 that of the
blood glucose sensor. As in Example 1, the responses of the two sensors are
similar.
Example 3
A holographic support medium was formed by copolymerising 13 mol%
5-fluoro-2-methylacrylamidophenylboronic acid (the synthesised according to
WO-A-04/081624) and 3% MBA in acrylamide. A holographic image was then
recorded in the resulting medium and the sensor used to detect glucose in PBS
at pH 7.4 and a temperature of 30°C. A similar experiment was performed
to
test the sensor's response to lactate.
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The results are shown in Fig. 5. The improved selectivity to glucose over
lactate is attributable to the oxygen- and nitrogen-based electron-donating
groups coordinated to the boron atom of the phenylboronate receptor. These
groups increase the negative change around the boron atom.
Example 4
A medium was obtained by polymerising 12 mol% 3-
acrylamidophenylboronic acid, 12 mol% acrylamidoglycolic acid and 76 mol%
acrylamide, using 2% (w/v) of 2-dimethoxy-2-phenyl-acetophenone (a free
radical initiator) in dimethyl sulphoxide. A hologram was recorded in the
medium, and the resulting sensor tested for its response to glucose and
lactate.
The results are shown in Fig. 6. The presence of acrylamidoglycolic acid
reduced the response of the sensor to the two analytes, as the negative charge
of the acidic moiety causes a significant degree of swelling of the polymeric
medium. However, the sensor was more responsive to glucose than lactate,
because the glycolic acid component carries a negative charge which repels
lactate, without significantly affecting glucose binding.
Example 5
A support medium was formed by copolymerising 11.9 mol% 3
acrylamidophenylboronicacid, 9.2 mol% N-[3-(dimethylamino)propyl]acrylamide,
2.9 mol% methylenebisacrylamide and 76 mol % acrylamide, by exposure to UV
light for 1 hour. Silver ions, present in an acetic acid solution, were
diffused into
the medium, the acidic solution present to prevent "fogging" of the silver by
the
amine component. A hologram was recorded in the medium, and the resulting
sensor tested for its response to glucose and lactate.
The results are shown in Fig. 7. The sensor was selective for glucose
over lactate; the peak wavelength shift for lactate was only about 12% of that
for
glucose at the same concentration. Also, the wavelength shift is a negative
shift
for glucose, whereas the binding of lactate effects a positive shift. The
presence
of "background" (4mM) lactate had a negligible effect of the sensor's response
to glucose.
