MEDIATION OF IN VIVO ANALYTE SIGNAL DEGRADATION

CROSS-REFERENCE TO RELATED APPLICATION [0001] The present application claims the benefit of priority to U.S. Provisional Application Serial No. 62/935,140, filed on November 14, 2019, which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Field of lnvention

[0003] The present invention relates generally to continuous reduction of in vivo degradation of analyte sensor moieties when measuring an analyte in a medium of a living animal using a system including a sensor implanted (partially or fully) or inserted into the living animal. Specifically, the present invention relates to a sensor that utilizes one or more additives, which may be incorporated within an analyte indicator, and/or a material covering at least a portion of the analyte indicator.

[0004] Discussion of the Background

[0005] A sensor may be implanted (partially or fully) within a living animal (e.g, a human) and used to measure an analyte (e.g, glucose, oxygen, cardiac markers, low-density lipoprotein (LDL), high-density lipoprotein (HDL), or triglycerides) in a medium (e.g., interstitial fluid (ISF), blood, or intraperitoneal fluid) within the living animal. The sensor may include a light source (e.g, a light-emitting diode (LED) or other light emitting element), indicator molecules, and a photodetector (e.g, a photodiode, phototransistor, photoresistor or other photosensitive element). Examples of implantable sensors employing indicator molecules to measure an analyte are described in U.8. Pat. Nos. 5,517,313 and 5,512,246, which are incorporated herein by reference in their entirety.

[0006] A sensor may include an analyte indicator, which may be in the form of indicator molecules embedded in a graft ( i.e., layer or matrix). For example, in an implantable fluorescence-based glucose sensor, fluorescent indicator molecules may reversibly bind glucose and, when irradiated with excitation light (e.g., light having a wavelength of approximately 378 nm), emit an amount of light (e.g., light in the range of 400 to 500 nm) that depends on whether glucose is bound to the indicator molecule.

[0007] If a sensor is implanted in the body of a living animal, the animal’s immune system may begin to attack the sensor. For instance, if a sensor is implanted in a human, white blood cells may attack the sensor as a foreign body, and, in the initial immune system onslaught, neutrophils may be the primary white blood cells attacking the sensor. The defense mechanism of neutrophils includes the release of highly caustic substances known as reactive oxygen species. The reactive oxygen species include, for example, hydrogen peroxide and superoxide. [0008] Hydrogen peroxide and other reactive species such as reactive oxygen and nitrogen species may degrade the indicator molecules of an analyte indicator. For instance, in indicator molecules having a boronate group, hydrogen peroxide and other reactive species may degrade the indicator molecules by oxidizing the boronate group, thus disabling the ability of the indicator molecule to bind glucose.

[0009] There is presently a need in the art for improvements in reducing analyte indicator degradation. There is also a need in the art for continuous analyte sensors having increased longevity. SUMMARY

[0010] The present invention overcomes the disadvantages of prior systems by providing, among other advantages, reduced analyte indicator degradation.

[0011 ] One aspect of the present, invention provides a sensor that may be for implantation or insertion within a living animal and measurement of an analyte in a medium within the living animal. The sensor may include an analyte indicator and one or more additives that reduce deterioration of the analyte indicator. In some embodiments, the analyte indicator and one or more additives that reduce deterioration of the analyte indicator are provided on a substrate. The substrate may be an electrode or a sensor surface. In some embodiments, the sensor may include a sensor housing, and the analyte indicator may cover at least a portion of the sensor housing. [0012] In some embodiments, the sensor may include at least one additive-containing polymer graft, and the one or more additives may be co-polymerized with or dispersed within the additive-containing polymer graft. In some embodiments, the additive-containing polymer graft may cover at least a portion of the sensor housing. In some embodiments, the additive- containing polymer graft may be within the sensor housing.

[0013] In some embodiments, the one or more additives may be incorporated with the analyte indicator, e.g., as a co-monomer. In some embodiments, the sensor may include a material, e.g., a membrane, covering at least a portion of the analyte indicator, and the one or more additives are incorporated within the material.

[0014] Further variations encompassed within the systems and methods are described in the detailed description of the invention below. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various, non-limiting embodiments of the present invention. In the drawings, like reference numbers indicate identical or functionally similar elements.

[0016] FIG. 1 is a schematic view illustrating a sensor system embodying aspects of the present invention.

[0017] FIG, 2 illustrates a perspective view of a sensor embodying aspects of the present invention.

[0018] FIG. 3 illustrates an exploded view of a sensor embodying aspects of the present invention.

[0019] FIG. 4 is a schematic view illustrating a sensor embodying aspects of the present invention.

[0020] FIG. 5 plots % signal modulation remaining in explanted sensors made using the following test compounds: EUK-8 (CAS #53177-12-1); Trolox (CAS # 53188-07-01), MnP (manganese porphyrin); EUK-134 (CAS # 81065-76-1); and N-acetyl -1 -cysteine, compared to bare indicator hydrogel as a control.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0021] FIG. 1 is a schematic view of a sensor system embodying aspects of the present invention. In some non-limiting embodiments, as shown in FIG. 1, the system may include a sensor 100 and an external transceiver 101. In some embodiments, the sensor 100 may be an implantable sensor configured to be fully or partially implanted in a living animal (e.g, a living human). The sensor 100 may be implanted, for example, in a living animal’s arm, wrist, leg, abdomen, peritoneum, or other region of the living animal suitable for sensor implantation. For example, in some non-limiting embodiments, the sensor 100 may be implanted beneath the skin (i.e., in the subcutaneous or peritoneal tissues). However, this is not required, and, in some alternative embodiments, the sensor 100 may be a transcutaneous sensor.

[0022] In some embodiments, a transceiver 101 may be an electronic device that communicates with the sensor 100 to power the sensor 100, provide commands and/or data to the sensor 100, and/or receive data from the sensor 100. In some embodiments, the received data may include one or more sensor measurements. In some embodiments, the sensor measurements may include, for example and without limitation, one or more light measurements from one or more photodetectors of the sensor 100 and/or one or more temperature measurements from one or more temperature sensors of the sensor 100. In some embodiments, the transceiver 101 may calculate analyte (e.g., glucose) concentrations from the measurement information received from the sensor 100.

[0023] In some non-limiting embodiments, the transceiver 101 may be a handheld device or an on-body/wearable device. For example, in some embodiments where the transceiver 101 is an on-body /wearable device, the transceiver 101 may be held in place by a band (e.g., an armband or wristband) and/or adhesive, and the transceiver 101 may convey (e.g., periodically, such as every two minutes, and/or upon user initiation) measurement commands (i.e., requests for measurement information) to the sensor 100. In some embodiments where the transceiver 101 is a handheld device, positioning (i.e., hovering or swiping/waving/passing) the transceiver 101 within range over the sensor implant site (i.e., within proximity of the sensor 100) may cause the transceiver 101 to automatically convey a measurement command to the sensor 100 and receive a data from the sensor 100. [0024] In some embodiments, as shown in FIG. 1, the transceiver 101 may include an inductive element 103, such as, for example, a coil. In some embodiments, the transceiver 101 may generate an electromagnetic wave or electrodynamic field (e.g, by using a coil) to induce a current in an inductive element 114 of the sensor 100. In some non-limiting embodiments, the sensor 100 may use the current induced in the inductive element 114 to power the sensor 100. However, this is not required, and, in some alternative embodiments, the sensor 100 may be powered by an internal power source (e.g., a battery),

[0025] In some embodiments, the transceiver 101 may convey data (e.g., commands) to the sensor 100. For example, in some non-limiting embodiments, the transceiver 101 may convey data by modulating the electromagnetic wave generated by the inductive element 103 (e.g., by modulating the current flowing through the inductive element 103 of the transceiver 101). In some embodiments, the sensor 100 may detect/extract the modulation in the electromagnetic wave generated by the transceiver 101. Moreover, the transceiver 101 may receive data (e.g., one or more sensor measurements) from the sensor 100. For example, in some non-limiting embodiments, the transceiver 101 may receive data by detecting modulations in the electromagnetic wave generated by the sensor 100, e.g., by detecting modulations in the current flowing through the inductive element 103 of the transceiver 101.

[0026] In some embodiments, as shown in FIG. 1, the sensor 100 may include a sensor housing 102 (i.e., body, shell, capsule, or encasement), which may be rigid and biocompatibie. In exemplary embodiments, sensor housing 102 may be formed from a suitable, optically transmissive polymer material, such as, for example, acrylic polymers (e.g., polymethylmethacrylate (PMMA)). [0027] In some embodiments, as shown in FIG. 1, the sensor 100 may include an analyte indicator 106. In some non-limiting embodiments, the analyte indicator 106 may be a polymer graft coated, diffused, adhered, or embedded on at least a portion of the exterior surface of the sensor housing 102. The analyte indicator 106 (e.g., polymer graft) may cover the entire surface of sensor housing 102 or only one or more portions of the surface of housing 102. As an alternative to coating the analyte indicator 106 on the outer surface of sensor housing 102, the analyte indicator 106 may be disposed on the outer surface of the sensor housing 102 in other ways, such as by deposition or adhesion, in some embodiments, the analyte indicator 106 may be a fluorescent glucose indicating polymer. In one non-limiting embodiment, the polymer is biocompatible and stable, grafted onto the surface of sensor housing 102, designed to allow for the direct measurement of glucose in interstitial fluid (ISF), blood, or intraperitoneal fluid after implantation of the sensor 100. In some embodiments, the analyte indicator 106 may comprise a hydrogel.

[0028] In some embodiments, the analyte indicator 106 (e.g., polymer graft) of the sensor 100 may include indicator molecules 104, The indicator molecules 104 may be distributed throughout the entire analyte indicator 106 or only throughout one or more portions of the analyte indicator 106. The indicator molecules 104 may be fluorescent indicator molecules (e.g, TFM having the chemical name 9-[N-[6-(4,4,5,5,-tetramethyl-I,3,2-dioxaborolano)-3- (trifluoromethyl)benzyl]-N-[3-(methacrylamido)propylamino]me thyl]-10~[N-[6~(4, 4,5,5,- tetramethyl-l,3,2-dioxaborolano)-3-(trifluoromethyl)benzyl]- N-[2- (carboxyethy[)amino]methyl]anthracene sodium salt) or light absorbing, non-fluorescent indicator molecules. In some embodiments, the indicator molecules 104 may reversibly bind an analyte (e.g., glucose, oxygen, cardiac markers, low-density lipoprotein (LDL), high-density lipoprotein (HDL), or triglycerides). When an indicator molecule 104 has bound an analyte, the indicator molecule may become fluorescent, in which case the indicator molecule 104 is capable of absorbing (or being excited by) excitation light 329 and emitting light 331. In one non- limiting embodiment, the excitation light 329 may have a wavelength of approximately 378 nm, and the emission light 331 may have a wavelength in the range of 400 nm to 500 nm. When no analyte is bound, the indicator molecule 104 may be only weakly fluorescent.

[0029] In some embodiments, the sensor 100 may include a light source 108, which may be, for example, a light emitting diode (LED) or other light source that emits radiation, including radiation over a range of wavelengths that interact with the indicator molecules 104. In other words, the light source 108 may emit the excitation light 329 that is absorbed by the indicator molecules in the matrix layer/polymer 104. As noted above, in one non-limiting embodiment, the light source 108 may emit excitation light 329 at a wavelength of approximately 378 nm. [0030] In some embodiments, the sensor 100 may also include one or more photodetectors (e.g., photodiodes, phototransistors, photoresist ors or other photosensitive elements). For example, in the embodiment illustrated in FIG. 1, sensor 100 has a first photodetector 224 and a second photodetector 226. However, this is not required, and, in some alternative embodiments, the sensor 100 may only include the first photodetector 224. In the case of a fluorescence-based sensor, the one or more photodetectors may be sensitive to fluorescent light emitted by the indicator molecules 104 such that a signal is generated by a photodetector (e.g., photodetector 224) in response thereto that is indicative of the level of fluorescence of the indicator molecules and, thus, the amount of analyte of interest (e.g., glucose).

[0031] Some part of the excitation light 329 emitted by the light source 108 may be reflected from the analyte indicator 106 back into the sensor 100 as reflection light 333, and some part of the absorbed excitation light may be emitted as emitted (fluoresced) light 331. In one non- limiting embodiment, the emitted light 331 may have a different wavelength than the wavelength of the excitation light 329. The reflected light 333 and emitted (fluoresced) light 331 may be absorbed by the one or more photodetectors (e.g., first and second photodetectors 224 and 226) within the body of the sensor 100.

[0032] Each of the one or more photodetectors may be covered by a filter 112 (see FIG. 3) that allows only a certain subset of wavelengths of light to pass through. In some embodiments, the one or more filters 112 may be thin glass filters. In some embodiments, the one or more filters 112 may be thin film (e.g, dichroic) filters deposited on the glass and may pass only a narrow band of wavelengths and otherwise reflect most of the received light. In some embodiments, the filters may be thin film (dichroic) filters deposited directly onto the photo detectors and may pass only a narrow band of wavelengths and otherwise reflect most of the light received thereby. The filters 112 may be identical (e.g, both filters 112 may allow signals to pass) or different (e.g., one filter 112 may be a reference filter and another filter 112 may be a signal filter).

[0033] In one non-limiting embodiment, the second (reference) photodetector 226 may be covered by a reference photodiode filter that passes light at the same wavelength as is emitted from the light source 108 (e.g., 378 nm). The first (signal) photodetector 224 may detect the amount of fluoresced light 331 that is emitted from the molecules 104 in the analyte indicator 106. In one non-limiting embodiment, the peak emission of the indicator molecules 104 may occur around 435 nm, and the first photodetector 224 may be covered by a signal filter that passes light in the range of about 400 nm to 500 nm. In some embodiments, higher glucose levels/concentrations correspond to a greater amount of fluorescence of the molecules 104 in the analyte indicator 106, and, therefore, a greater number of photons striking the first photodetector 224.

[0034] In some embodiments, as shown in FIG. 1, the sensor 100 may include a substrate 116. In some embodiments, the substrate 116 may be a circuit board (e.g., a printed circuit board (PCB) or flexible PCB) on which circuit components (e.g., analog and/or digital circuit components) may be mounted or otherwise attached. However, in some alternative embodiments, the substrate 116 may be a semiconductor substrate having circuitry? fabricated therein. The circuitry may include analog and/or digital circuitry. Also, in some semiconductor substrate embodiments, in addition to the circuitry fabricated in the semiconductor substrate, circuitry' may be mounted or otherwise attached to the semiconductor substrate 116. In other words, in some semiconductor substrate embodiments, a portion or ail of the circuitry?, which may include discrete circuit, elements, an integrated circuit, (e.g., an application specific integrated circuit (ASIC)) and/or other electronic components, may be fabricated in the semiconductor substrate 116 with the remainder of the circuitry is secured to the semiconductor substrate 116, which may provide communication paths between the various secured components.

[0035] In some embodiments, the one or more of the sensor housing 102, analyte indicator 106, indicator molecules 104, light source 108, photodetectors 224, 226, temperature transducer 670, substrate 116, and inductive element 114 of sensor 100 may include some or all of the features described in one or more of U.S. Application Serial No. 13/761,839, filed on February 7, 2013, U.S. Application Serial No. 13/937,871, filed on July 9, 2013, and U.S. Application Serial No. 13/650,016, filed on October 11, 2012, all of which are incorporated by reference in their entireties. Similarly, the structure and/or function of the sensor 100 and/or transceiver 101 may be as described in one or more of U S. Application Serial Nos. 13/761,839, 13/937,871, and 13/650,016.

[0036] In some embodiments, the sensor 100 may include a transceiver interface device, and the transceiver 101 may include a sensor interface device. In some embodiments where the sensor 100 and transceiver 101 include an antenna or antennas (e.g, inductive elements 103 and 114), the transceiver interface device may include the inductive element 114 of the sensor 100, and the sensor interface device may include the inductive element 103 of the transceiver 101. In some of the transcutaneous embodiments where there exists a wired connection between the sensor 100 and the transceiver 101, the transceiver interface device and sensor interface device may include the wired connection.

[0037] FIGS. 2 and 3 illustrate a non-limiting embodiment of a sensor 100 embodying aspects of the present invention that may be used in the sensor sy stem illustrated in FIG. 1.

FIGS. 2 and 3 illustrate perspective and exploded views, respectively, of the non-limiting embodiment of the sensor 100.

[0038] In some embodiments, as illustrated in FIG, 3, the sensor housing 102 may include an end cap 113. In some embodiments, the sensor 100 may include one or more capacitors 118.

The one or more capacitors 118 may be, for example, one or more tuning capacitors and/or one or more regulation capacitors. The one or more capacitors 118 may be too large for fabrication in the semiconductor substrate 116 to be practical . Further, the one or more capacitors 118 may be in addition to one or more capacitors fabricated in the semiconductor substrate 116.

[0039] In some embodiments, as illustrated in FIG. 3, the sensor 100 may include a reflector 119 (i.e., mirror). Reflector 119 may be attached to the semiconductor substrate 116 at an end thereof. In a non-limiting embodiment, reflector 119 may be attached to the semiconductor substrate 116 so that a face portion 121 of reflector 119 is generally perpendicular to a top side of the semiconductor substrate 116 ( i.e ,, the side of semiconductor substrate 116 on or in which the light source 108 and one or more photodetectors 110 are mounted or fabricated) and faces the light source 108. The face 121 of the reflector 119 may reflect radiation emitted by light source 108. In other words, the reflector 119 may block radiation emitted by light source 108 from exiting the axial end of the sensor 100.

[0040] According to one aspect of the invention, an application for which the sensor 100 was developed (although by no means the only application for which it is suitable) is measuring various biological analytes in the living body of an animal (including a human). For example, sensor 100 may be used to measure glucose, oxygen, toxins, pharmaceuticals or other drugs, hormones, and other metabolic analytes in, for example, the human body.

[0041] In some embodiments, the specific composition of the analyte indicator 106 and the indicator molecules 104 may vary depending on the particular analyte the sensor is to be used to detect and/or where the sensor is to be used to detect the analyte (e.g., in the in subcutaneous tissues, blood, or peritoneum). In some embodiments, the analyte indicator 106 facilitates exposure of the indicator molecules 104 to the analyte. In some embodiments, the indicator molecules 104 may exhibit a characteristic (e.g., emit an amount of fluorescence light) that is a function of the concentration of the specific analyte to which the indicator molecules 104 are exposed.

[0042] in some embodiments, the sensor 100 may include at least one drug eluting polymer matrix and/or a layer of catalyst and/or one or more therapeutic agents that may be provided on, adjacent to, incorporated in, or dispersed within the analyte indicator or sensor housing as described in U.S. Pat. No. 9,931,068 (Huffstetler et ah), which is incorporated herein by reference in its entirety. In some embodiments, the one or more therapeutic agents may be incorporated in the analyte indicator 106. In some embodiments, the sensor 100 may include a membrane covering at least a portion of the analyte indicator 106, and the one or more therapeutic agents may be incorporated within the membrane. In some embodiments, the one or more therapeutic agents include dexamethasone, triamcinolone, betamethasone, methylprednisolone, beciometasone, fludrocortisone, derivatives thereof, and analogs thereof, a glucocorticoid, an anti-inflammatory drug, e.g., a non-steroidal anti-inflammatory drug including but not limited to acetyfsaiicylic acid, isobutylpheny!propanoic acid.

[0043] FIG. 4 is a schematic view of a sensor 100 embodying aspects of the present invention. In some non-limiting aspects, as shown in FIG. 4, the sensor 100 may include a drug eluting region 401 covering at least a portion of the sensor housing 102. In some non-limiting aspects, as shown in FIG. 4, the sensor 100 may include an analyte indicator 106, and the analyte indicator 106 may include a hydrogel entrapping an additive of the present disclosure. In some non-limiting aspects, as shown in FIG. 4, the sensor 100 may include sensor electronic components, which may include any of the electronic components described in the present disclosure, including in FIG. 1 and FIG. 3 (e.g., the light source 108, the one or more photodetectors 110, the inductive element 114, and/or the one or more capacitors 118), as well as those described in one or more of U.S. Application Serial No. 13/761,839, filed on February' 7, 2013, U.S. Application Serial No. 13/937,871, filed on July 9, 2013, and U.S. Application Serial No. 13/650,016, filed on October 11, 2012, all of which are incorporated by reference in their entireties. In some non-limiting aspects, as shown in FIG. 4, the sensor 100 may include a metal coating 403 covering at least a portion of the sensor housing 102. In some non-limiting aspects, the metal coating 403 may include one or more metals selected from Cu, W, Pt Fe, Mo, Co, oxides, alloys, and complexes thereof. In some non-limiting aspects, the metal coating 403 may be coated on the hydrogel entrapping an additive of the present disclosure.

[0044] The implantation or insertion of a medical device, such as a bio-sensor, into a user/patient’s body can cause the body to exhibit adverse physiological reactions that are detrimental to the functioning of the device. The reactions may range from infections due to implantation surgery to the immunological response of a foreign object implanted in the body. That is, the performance of the implantable bio-sensor can be hindered or permanently damaged in vivo via the immunological response to an infection or the device itself. In particular, the performance of the analyte indicator 106 may be deteriorated by the immunological response of the body into which the sensor 100 is implanted. For example, as explained above, white blood cells, including neutrophils, may attack an implanted sensor 100. The neutrophils release reactive species including, inter alia , hydrogen peroxide, which may degrade indicator molecules 104 (e.g, by oxidizing a boronate group of an indicator molecule 104 and disabling the ability of the indicator molecule 104 to bind glucose).

[0045] In some embodiments, the analyte indicator 106 may include one or more additives that interact, or react with one or more degradative species without compromising signal integrity or performance of the sensor device. In some embodiments, the one or more additives may be incorporated into the analyte indicator 106 that may cover at least a portion of the sensor housing 102, The one or more degradative species may include one or more of hydrogen peroxide, a reactive oxygen species, a reactive nitrogen species, a free radical, enzymes, and a metal ion. In some aspects, the degradative species may include superoxide, hydrogen peroxide, hypochlorite, peroxynitrite, or a combination thereof. In some embodiments, the additive may be copolymerized with the indicator molecule 104. In some embodiments, the one or more additives may be provided in the analyte indicator 106 (e.g., polymer graft). In some embodiments, the one or more additives may interact and/or react with degradative species. In some embodiments, the one or more additives may neutralize the degradative species. In some embodiments, the one or more additives may bind to the degradative species. In some embodiments, the one or more additives may sequester the degradative species so as to inhibit, reduce, and/or prevent degradation of the analyte indicator by the degradative species. Accordingly, in some embodiments, the one or more additives reduce degradation of the analyte indicator 106.

[0046] In some non-limiting embodiments, the one or more additives may be one or more of the following compounds:

(Formula I), wherein in the compound of Formula I, X is a halide, each R3, R4, R5, and R6 is independently selected from H, C1-C20 alkyl, C1-C20 alkoxy, carboxy, aryl, alkoxy, halide, SH, aryloxy, alkylthio, amino, substituted amino, aikoxy carbonyl, alkanoylamido, aroylamido, heterocyclocarbonylamido, heteroaroylamido, alkanoyl(alkyl substituted) amido, aroyl(alky!substituted)amido, heteroaroyl(alkylsubstituted)amido, and heterocyclocarbonyl(alkyl substituted)amido, and formula I may be optionally substituted with C1 -5 alkyl, alkoxy, eyano, halo and/or trifluoromethyl at. any position.

(Formula III), wherein in the compound of Formula III, X is O, N, S, and each of R and R.i is independently selected from H, C1-C20 alkyl, C1-C20 a!koxy, carboxy, aryl, alkoxy, halide, SH, aryloxy, alkylthio, amino, substituted amino, alkoxy carbonyl, alkanoylamido, aroylamido, heterocyclocarbonylamido, heteroaroylamido, alkanoyl(alkylsubstituted) aniido, aroyl(alkylsubstituted)amido, heteroaroyl (alkylsubstituted)amido, and heterocyclocarbonyl(alkyl substituted)amido, and formula I may be optionally substituted with Cl -5 alkyl, alkoxy, cyano, halo and/or trifluoromethyl at any position. In some embodiments, each of R and R1 is independently absent, or a bond or linker for polymerizing the compound of Formula III to a polymer backbone.

(Formula IV).

[0047] In some non-limiting embodiments, a sensor 100 for measurement of an analyte (e.g., glucose) in a medium (e.g., interstitial fluid) within a living animal (e.g., a human) contains one or more of the following components: a sensor housing 102, a light source 108 within the sensor housing 102 configured to emit excitation light 329; an analyte indicator 106 covering a portion of the sensor housing 102, one or more indicator molecules 104 that are part of the analyte indicator 106, reversibly bind the analyte, are positioned to be irradiated by the excitation light, and are configured to emit light 331 indicative of the amount of the analyte in the medium within the living animal; a photodetector 224 within the sensor housing 102 that is sensitive to light 331 emitted by the one or more indicator molecules 104 and configured to generate a signal indicative of the amount of the analyte in the medium within the living animal, and one or more compounds of Formulae I-IV to interact with degradative species without compromising signal integrity or performance of the sensor 100. In some non-limiting embodiments, the sensor 100 may include a drug eluting region 401, e.g., a drug eluting matrix, collar, and/or a layer of catalyst provided on, adjacent to, or incorporated in the analyte indicator 106.

[0048] In some non-limiting embodiments, the one or more compounds of Formulae I-IV may be provided in the analyte indicator 106 (e.g., hydrogel) of the analyte sensor 100. In some non-limiting embodiments, one or more compounds of Formulae I-IV may be incorporated into the analyte indicator 106 by polymerizing the one or more compounds of Formulae I-IV as a co~ monomer with indicator monomer and one or more acrylate monomers. In some non-limiting embodiments, one or more compounds of Formulae I-IV may be provided as co-monomers of four monomers according to Formula V:

A-B-C-D [Formula V], wherein A is an indicator monomer, B is a methacrylate monomer, C is a polyethylene glycol monomer, and D is a compound of one or more of Formulae I-IV monomer, wherein A is 0.001 to 10 % by weight, B is I to 99 % by weight, C is 1 to 99 % by weight, and D is 0.001 to 99% by weight of the total polymer. In som e aspects, A is 0.01 to 10 % by weight, B is 1 to 99 % by weight, C is 1 to 99 % by weight, and D is 0.01 to 99% by weight of the total polymer.

[0049] In some non-limiting embodiments, the analyte indicator 106 may contain four monomers: (i) the TFM fluorescent indicator, (ii) bydroxyethylmethacrylate (HEMA), which is a methacrylate, (iii) polyethylene glycol (PEG), and (iv) a compound of Formula I or a compound of Formula III. In some embodiments, the PEG may be polyethylene glycol methacrylate (PEG- methacrylate) or polyethylene glycol diacrylate (PEG-diacrylate or PEGDA), and the one or more compounds of Formulae I-IV may be a compound of Formula I or a compound of Formula Ill. In some embodiments, the four monomers may be in specific molar ratios. For example, in some non-limiting embodiments in which the analyte indicator 106 is opaque, the analyte indicator 106 may comprise 0.001 to 10 molar percent, HEMA may comprise 10 to 90 molar percent, PEGDA may comprise 10 to 90 molar percent, and the compound of Formula I or a compound of Formula III may comprise 0.001 to 90 molar percent. With this formulation, the combined (i.e., total) monomers may, in one example, be 30% by volume of the polymerization solution used for the polymerization reaction with the remainder of the polymerization solution being water (i.e,, the polymerization solution may be 70% water by volume). For another example, in one non-limiting embodiment, the analyte indicator 106 may be made using a polymer solution that is 50% water by volume and 50% monomers by volume.

[0050] In some embodiments, the relative molar percent of the compound of Formulae I-IV may be within a specific range. In some embodiments, the relative molar percent of the compound of one or more of Formulae I-IV ranges between 0.1 and 100 molar percent. If the relative molar percent of the compound of one or more of Formulae I-IV is greater than this range, the hydrogel is not formed. If the relative molar percent of the compound of one or more of Formulae I-IV is lower than this range, the unexpected longevity and functionality-boosting effects described in this disclosure may not obtained.

[0051] In some embodiments, the PEGDA may act as a cross-linker and create a sponge-like matrix/hydrogel. In some non-limiting embodiments, the PEG-containing graft/hydrogel may become clear if a sufficient amount, of additional PEG is added to the mixture (i.e., if it is fabricated with a higher concentration of PEG), and a clear analyte indicator 106 may be made from such a formulation. For example, in one non-limiting embodiment, the polymer graft 106 may be made using a polymer solution that is 50-60% water by volume and 40-50% monomers by volume, where the TFM fluorescent, indicator, HEMA, PEG-methacrylate, and one or more compounds of Formulae I-IV may comprise 0.01 to 10 %, 1 to 99 %, 1 to 99 %, and 0.01 to 99% by weight, of the monomers in the solution. In some embodiments, the polymer graft may be synthesized using conventional tree radical polymerization.

[0052] In some instances, the amount of the one or more compounds of Formulae I-IV incorporated into the analyte indicator is in the range of about 1 to about 5 mg.

[0053] In some instances, sensors loaded with one or more compounds of Formulae I-IV reduce oxidation of analyte indicator molecules by degradative species including superoxide, hydrogen peroxide, hypochlorite, and peroxynitrite. In some instances, loading sensors with low loadings, e.g., less than 2 mg or less than 1 mg of a compound of Formulae I-IV is effective to significantly reduce oxidation of analyte indicator molecules by degradative species including superoxide, hydrogen peroxide, hypochlorite, and peroxynitrite. Analyte indicator loaded [0054] An implanted sensor including an additive-containing analyte indicator may have improved performance over a sensor that does not include an additive-containing analyte indicator. For instance, in some non-limiting embodiments, the additive improves the longevity and functionality of the sensor 100.

[0055] Example

[0056] An in vivo study was performed in female guinea pigs in which mock sensors with variable amounts (1- 5mg) of the tested compounds were entrapped and implanted to assess protection of the indicator signal over time. Manganese porphyrin and N-acetyl-l-cysteine are not part of the invention and were found to have a detrimental effect on indictor signal over time. Implantation was executed subcutaneously in the back of each guinea pig (4 samples per guinea pig) with the Senseonics insertion tool kit according to manufacturer's instructions. These mock sensors were sterilized before implantation. The samples were then explanted after 15 days from the Guinea pigs and were washed and disinfected using Enzol enzymatic detergent and glutaraldehyde solution. The explanted samples were then analyzed by fluorimetry to evaluate fluorescence intensity changes and then rank ordered with respect to the % modulation loss to bare indicator hydrogel as controls as shown in FIG. 5.

[0057] Embodiments of the present invention have been fully described above with reference to the drawing figures. Although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions could be made to the described embodiments within the spirit and scope of the invention. For example, although in some embodiments, the analyte sensor 100 may be an optical sensor, this is not required, and, in one or more alternative embodiments, the analyte sensor may be a different type of analy te sensor, such as, for example, an electrochemical sensor, a diffusion sensor, or a pressure sensor. Also, although in some embodiments, the analyte sensor 100 may be an implantable sensor, this is not required, and, in some alternative embodiments, the analyte sensor may be a transcutaneous sensor having a wired connection to an external transceiver. For example, in some alternative embodiments, the analyte sensor 100 may be located in or on a transcutaneous needle {e.g., at the tip thereof). In these embodiments, instead of wirelessly communication using an antenna (e.g., inductive element 114), the analyte sensor may communicate with the external transceiver using one or more wires connected between the external transceiver and a transceiver transcutaneous needle including the analyte sensor. For another example, in some alternative embodiments, the analyte sensor may be located in a catheter (e.g., for intravenous blood glucose monitoring) and may communicate (wirelessly or using wires) with an external transceiver.