Interpenetrating polymer network microneedle compositions for biosensing devices

Abstract

Microneedle patches and methods of fabrication are provided. A microneedle patch includes a plurality of microneedles formed from an interpenetrating polymer network having a primary network comprising zwitterionic polymerizable components and a secondary network of polyvinyl methyl ether maleic acid chains crosslinked with polyethylene glycol. The microneedles can include a microporous microstructure that accelerates swelling and interstitial fluid uptake while providing mechanical robustness and resistance to biofouling. In some embodiments, a method includes preparing a precursor mixture comprising at least one zwitterionic monomer or zwitterionic crosslinker together with additional polymerizable components, combining the precursor mixture with a Gantrez–polyethylene glycol solution, and dispensing the casting composition into a microneedle mold. Free-radical polymerization is initiated by ultraviolet exposure and thermal activation, optionally using a gas-evolving porogen initiator to generate microporosity under mold confinement, followed by post-polymerization thermal cycling to form ester crosslinks between Gantrez and polyethylene glycol.

Description

INTERPENETRATING POLYMER NETWORK MICRONEEDLECOMPOSITIONS FOR BIOSENSING DEVICESFIELD

[0001] Embodiments of the present disclosure generally relate to interpenetrating polymer network microneedle compositions, and in particular to interpenetrating polymer network microporous zwitterionic microneedle compositions for biosensing devices and methods of fabricating microneedle patches.BACKGROUND

[0002] Microneedle devices have been explored to access interstitial fluid for biomarker monitoring with reduced pain and minimal invasiveness. Hydrogel microneedles can swell within the dermis and take up fluid for subsequent analysis or for coupling to biosensors. In some scenarios, molecular biomarkers in interstitial fluid may be used for predicting various health conditions such as heart disease, diabetes, or pulmonary disease, among other examples.

[0003] Existing hydrogel microneedle materials, including alginate, poly(L-lactide) (PLLA), poly(hydroxyethyl methacrylate) (pHEMA), dextran, gelatin, hydroxypropyl cellulose (HPC), carboxymethylcellulose (CMC), hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA), and poly-L-glutamic acid (y-PGA) [1,2], can exhibit limited swelling kinetics and reduced mechanical robustness, resulting in slow interstitial fluid extraction and an elevated risk of needle fracture during skin insertion. Reported extraction volumes can be on the order of up to about 1 pL per 100 microneedles of interstitial fluid over several hours in certain implementations [3],

[0004] Methacrylated hyaluronic acid (MeHA) microneedles have demonstrated improved extraction in some cases; for example, such devices may extract approximately 10 pL per 100 microneedles of interstitial fluid in about 20 minutes. The inclusion of osmolytes like maltose can enhance ex vivo interstitial fluid extraction to about 20 pL per 100 microneedles in about 20 minutes [3], However, these devices can remain mechanically soft and may require lengthy and costly processing due to slow dissolution of long polymer chains, which can limit throughput.Osmolyte-biomarker interactions may affect recovery and accurate sensing, and the generally soft nature of such microneedles may make skin penetration challenging.

[0005] Interpenetrating polymer network microneedles have been proposed to enhance mechanical properties and swelling; for example, systems involving poly(vinyl methyl ether-co-maleic acid) (PVME / MA, commercially available as Gantrez AN- 139) crosslinked with poly(ethylene glycol) (PEG) in combination with a secondary network of neutralized poly(acrylic acid) (PAA) can extract on the order of 12 pL per 100 microneedles after 30 minutes ex vivo. Such superswelling interpenetrating polymer network microneedles may provide desirable mechanical strength and interstitial fluid extraction but can remain susceptible to biofouling, leading to non-specific protein adsorption or bacterial adhesion that impairs sensing.

[0006] There remains a need for microneedle compositions and fabrication methods that provide rapid and efficient interstitial fluid extraction, mechanical robustness suitable for skin penetration without breakage, and resistance to biofouling, while maintaining processability and compatibility with biosensing modalities.SUMMARY

[0007] The present disclosure provides interpenetrating polymer network microneedle compositions, microneedle patches, and methods of fabrication. In certain embodiments, the microneedle composition includes a primary network comprising one or more zwitterionic polymerizable components together with one or more additional polymerizable components, and a secondary network formed by polyvinyl methyl ether maleic acid chains crosslinked with polyethylene glycol. In some embodiments, polymerization is carried out in microneedle molds and may optionally employ a gas-evolving porogen initiator to generate a microporous microstructure under mold confinement, which can accelerate swelling and interstitial fluid uptake while preserving microneedle geometry. The zwitterionic chemistry of the primary network can further confer antibiofouling properties.

[0008] In one aspect, a method of fabricating a microneedle patch includes preparing a precursor mixture comprising at least one zwitterionic monomer or zwitterionic crosslinker and at least oneadditional polymerizable component; combining the precursor mixture with a polyvinyl methyl ether maleic acid and polyethylene glycol solution to form a microneedle casting composition; dispensing the composition into a microneedle mold; initiating free-radical polymerization by exposing the composition to ultraviolet radiation in the presence of a photoinitiator and by heating in the presence of a thermal initiator, the thermal initiator optionally being a porogen initiator effective to generate microporosity; removing the polymerized microneedle patch from the mold; and subjecting the microneedle patch to post-polymerization thermal cycling to form ester crosslinks between polyvinyl methyl ether maleic acid and polyethylene glycol.

[0009] In another aspect, a microneedle patch is provided comprising a plurality of microneedles extending from a substrate, each microneedle comprising an interpenetrating polymer network that includes a primary network comprising one or more zwitterionic polymerizable components together with one or more additional polymerizable components, and a secondary network comprising polyvinyl methyl ether maleic acid chains crosslinked with polyethylene glycol. In some embodiments, the microneedles include a microporous microstructure and may exhibit a mean pore size between about 0.1 micrometres and about 5 micrometres, a pore volume fraction between about 5 percent and about 60 percent, a failure force greater than about 0.1 newtons per microneedle under compression, and extraction of at least about 12 microlitres per 100 microneedles in about 20 minutes ex vivo.DESCRIPTION OF THE FIGURES

[0010] FIG. 1 illustrates a schematic of the interpenetrating polymer network architecture of a microporous microneedle patch, showing a primary zwitterionic network and a secondary Gantrez-PEG support network, and the formation of ester crosslinks between Gantrez chains and PEG following post-polymerization thermal processing.

[0011] FIG. 2 illustrates representative chemical structures of zwitterionic monomers, comonomers, zwitterionic crosslinkers, and support networks for use in the microneedle compositions, including examples of DMAPS, MPC, CBMA, acrylic and methacrylic acids and salts, zwitterionic crosslinkers CL-1 and CL-2, and support networks based on Gantrez-PEG, hyaluronic acid, or poly(vinyl alcohol).

[0012] FIG. 3 illustrates, for embodiments and comparative examples, charts 300 showing (a) swelling ratio over time and (b) phosphate-buffered saline (PBS) extraction per 100 microneedles at 20 minutes.

[0013] FIG. 4 illustrates microscopic images 400 of microneedle patches highlighting microporous and non-porous microstructures, including, in some embodiments, images of embodiment devices in panels a, b, and c and images of comparative devices in panels d, e, and f.

[0014] FIG. 5 illustrates charts 500 showing mechanical properties of microneedle patches, including load-displacement curves, slope in the initial linear region, and failure load for embodiments and comparative examples.DETAILED DESCRIPTION

[0015] Microneedles (MNs) may be configured with devices for accessing molecular biomarkers in interstitial fluid (ISF) of a user. For example, microneedles may be combined with biosensor devices and configured for monitoring of key metabolites on a substantially continuous basis. Microneedles may be configured as relatively short needles and may be configured to interface with a user through the stratum comeum (SC), the topmost layer of skin, into the dermis. Microneedle devices may be configured with features to swell and sample the user’s interstitial fluid. In some scenarios, interstitial fluid may include biomarkers and other metabolites for predicting a plurality of health conditions, such as heart disease, diabetes, and pulmonary disease.

[0016] Swellable hydrogel microneedles can be limited by inadequate swelling, relatively low biocompatibility, or biofouling. Some hydrogel microneedle devices may include physical properties that result in relatively slow interstitial fluid extraction and may include properties that are prone to needle fractures during skin insertion. Some microneedle devices may be prone to biofouling resulting in attraction of proteins, bacteria, or cells to device surfaces.

[0017] Hydrogel microneedles have been fabricated from polymers such as alginate, poly(L- lactide) (PLLA), poly(hydroxyethyl methacrylate) (pHEMA), dextran, gelatin, hydroxypropylcellulose (HPC), carboxymethylcellulose (CMC), hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA), and poly-L-glutamic acid (y-PGA), and such microneedles may extract up to about 1 pL per 100 microneedles of interstitial fluid over several hours in certain implementations [1-3],

[0018] Hydrogel microneedles based on methacrylated hyaluronic acid (MeHA) may extract approximately 10 pL per 100 microneedles of interstitial fluid in about 20 minutes, and the inclusion of osmolytes like maltose can enhance extraction ex vivo to about 20 pL per 100 microneedles in about 20 minutes [3], However, osmolyte-biomarker interactions may affect recovery and accurate sensing, and the generally soft nature of such microneedles may make skin penetration challenging. Fabrication may be prone to higher costs and time-consuming processes due to the extended dissolution time of long hyaluronic acid chains, thereby reducing the practicality of such devices for interstitial fluid collection.

[0019] Superswelling interpenetrating polymer network microneedles (IPN MNs) using poly(vinyl methyl ether-co-maleic acid) (PVME / MA or Gantrez) crosslinked with polyethylene glycol) (PEG) as a primary network and neutralized poly(acrylic acid) (PAA) as a secondary network have demonstrated desirable mechanical strength and interstitial fluid extraction on the order of 12 pL per 100 microneedles after about 30 minutes ex vivo, but may be susceptible to biofouling that limits biosensing applications.

[0020] Embodiments of the present disclosure address these limitations with interpenetrating polymer network microporous zwitterionic microneedle compositions comprising polymerizable zwitterionic monomers and crosslinkers to provide highly swellable and robust MN compositions. In some embodiments, the compositions include improved mechanical properties by employing an interpenetrating polymer network approach using a secondary support network to provide mechanical strength. In certain embodiments, the compositions provide antibiofouling features based on zwitterionic monomers and crosslinkers; due to an even distribution of charges, strong attraction between the super-hydrophilic anions and cations and water molecules may provide a dense hydrated layer on a surface that prevents non-specific adsorption of proteins and the adhesion of bacteria or cells. In some embodiments, the compositions provide enhancedinterstitial fluid extraction rates by creating a microporous microstructure within microneedles using a porogen initiator.

[0021] In some embodiments, interpenetrating polymer network microporous microneedle patches are produced by free-radical polymerization of zwitterionic co-monomers and a zwitterionic crosslinker in a solution containing Gantrez and PEG. The polymerization may be initiated by a combination of ultraviolet (UV) exposure in the presence of a photoinitiator and thermal activation in the presence of a thermal initiator. In some embodiments, the thermal initiator comprises a porogen initiator that evolves gas to generate a microporous microstructure; in other embodiments, a non-porogenic thermal initiator may be used. When a porogen initiator is employed, confinement within polydimethylsiloxane (PDMS) microneedle mold cavities inhibits bubble coalescence and promotes formation of a uniformly distributed microporous microstructure while preserving microneedle geometry.

[0022] Post-polymerization thermal processing may promote formation of ester crosslinks between Gantrez chains mediated by PEG molecules, thereby forming a secondary support network. In some embodiments, the zwitterionic monomer may be chosen from [2- (methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide (DMAPS), 2- methacryloyloxyethyl phosphorylcholine (MPC), or 3-[[2- (methacryloyloxy)ethyl]dimethylammonio]propionate (CBMA). Co-monomer options may include acrylic acid (AA), methacrylic acid (MAA), sodium methacrylate (SMA), and sodium acrylate (SA), either individually or in combination. Zwitterionic crosslinkers may include N,N- bis(methacryloxyethyl) N-methyl N-(3-sulfopropyl)ammonium betaine (CL-1) or N,N- bis(methacryloxyethyl) N-methyl N-(4-sulfobutyl)ammonium betaine (CL-2). The support network may be selected from Gantrez-PEG (PVME / MA+PEG), hyaluronic acid (HA), or poly(vinyl alcohol) (PVA).

[0023] To create porosity in the IPN MNs, 2,2'-azobis(2-amidinopropane) dihydrochloride (AIBA), a water-soluble azo initiator that dissociates into cationic free radicals and nitrogen (N2) at temperatures above approximately 60 °C, may be used as the porogen. The UV photoinitiator may be lithium phenyl 2,4,6-trimethylbenzoylphosphinate (LAP), a water-soluble, non-cytotoxicphotoinitiator that is also configurable for producing UV-curable hydrogels for cell-scaffolding applications.

[0024] In representative embodiments, the microneedle casting composition is dispensed into a PDMS microneedle mold and centrifuged at approximately 4,000 rpm for approximately 3 minutes to promote cavity filling prior to UV exposure. In some embodiments, the mold may additionally or alternatively be subjected to reduced pressure (vacuum evacuation) to assist in drawing the casting composition into the mold cavities. UV curing may be performed, for example, using a Blak-Ray® B-100AP high-intensity (100 watt) UV lamp for approximately 10 minutes, followed by a thermal cure at approximately 70 °C for approximately 2 hours, demolding, and a post-cure at approximately 80 °C for approximately 24 hours to promote formation of ester crosslinks between Gantrez and PEG.

[0025] In some embodiments, the microneedle mold may be placed in a chamber and evacuated to reduce the pressure within the microneedle cavities before or while a microneedle casting composition or polymeric precursor composition is applied to the mold. Upon introducing the composition to the evacuated mold and subsequently allowing the pressure to return toward ambient, the pressure differential drives the composition into and fills the mold cavities. This evacuation-assisted filling approach may be used instead of, or in combination with, centrifugation to promote complete filling of the microneedle cavities prior to ultraviolet exposure and thermal curing

[0026] In some embodiments, the microneedles may be configured within an array with representative dimensions including a microneedle height of about 500 pm to about 800 pm, a base width of about 250 pm to about 400 pm, a tip radius of not more than about 20 pm, and an array pitch of about 500 pm to about 800 pm. These ranges are non-limiting and may vary with application and mold geometry.

[0027] Embodiments may exhibit a microporous microstructure characterized by a mean pore size between about 0.1 pm and about 5 pm and a pore volume fraction between about 5% and about 60%. The microneedles may exhibit a failure force greater than about 0.1 N per microneedle under compression and a stiffness sufficient for penetration of mammalian skinwithout fracture. In some embodiments, the patches may extract at least about 12 pL per 100 microneedles from porcine skin in about 20 minutes ex vivo.

[0028] For comparison to embodiments, processes for fabricating example comparative microneedle patches are described. In a first comparative process (comparative example 1 - MeHA), a fabrication process includes steps for fabricating approximately 30 microneedle patch devices:1. Dissolving 300 mg MeHA, 12 mg N,N-methylene-bis-acrylamide (BIS), and 12 mg LAP in 6 mL of water.2. Sonicating the mixture until complete dissolution of the monomers.3. Adding 100 pL of the mixture to a PDMS microneedle mold.4. Centrifuging the mold in a swing-bucket centrifuge at 4,000 rpm for 3 minutes.5. Adding an additional 100 pL of the mixture to the PDMS microneedle mold.6. Removing the water overnight in a space protected from light.7. Removing the dried microneedle array from the PDMS mold and curing it with a Blak- Ray® B-100AP high-intensity (100 watt) UV lamp for 10 minutes.In a second comparative process (comparative example 2 - non-porous IPN), a fabrication process includes steps for fabricating approximately 30 microneedle patch devices:1. Adding 670 mg SA, 330 mg DMAPS, and 20 mg CL-1 crosslinker to a 20 mL vial.2. Adding 10 g of a mixture of 20% Gantrez AN-139 (Ashland, Mn-1,080,000 g / mol, hydrolyzed to the maleic acid form prior to use) and 5% PEG (Mn-20,000 g / mol) solution.3. Sonicating the mixture until complete dissolution of all components in the Gantrez / PEG solution.4. Adding 45 mg ammonium persulfate (APS) and 45 mg LAP as thermal and photoinitiators to the solution prepared in step 3.5. Adding 100 pL of the mixture to a PDMS microneedle mold.6. Centrifuging the mold in a swing-bucket centrifuge at 4,000 rpm for 3 minutes.7. Curing the hydrogel with a Blak-Ray® B-100AP high-intensity (100 watt) UV lamp for 10 minutes.8. Curing the hydrogel at 70 °C for 2 hours in an oven.9. Taking the samples out of the molds.10. Curing the hydrogel at 80 °C for 24 hours in an oven to ensure crosslinking of Gantrez with PEG.In a third comparative process (comparative example 3 - non-IPN-1), a fabrication process includes steps for fabricating approximately 30 microneedle patch devices:1. Preparing 10 g of hydrolyzed 20% Gantrez AN-139 (Ashland, Mn-1,080,000 g / mol) and 5% PEG (Mn-2,000 g / mol) solution.2. Adding 100 pL of the solution to a PDMS microneedle mold.3. Centrifuging the mold in a swing-bucket centrifuge at 4,000 rpm for 3 minutes.4. Drying the sample overnight.5. Taking the samples out of the molds.6. Curing the hydrogel at 80 °C for 24 hours in an oven.In a fourth comparative process (comparative example 4 - non-IPN-2), a fabrication process includes steps for fabricating approximately 30 microneedle patch devices:1. Adding 670 mg SA, 330 mg DMAPS, 20 mg CL-1 crosslinker, and 10 g water to a 20 mL vial.2. Sonicating the mixture until complete dissolution of all components.3. Adding 20 mg APS and 20 mg LAP to the solution prepared in step 2.4. Adding 100 pL of the mixture to a PDMS microneedle mold.5. Centrifuging the mold in a swing-bucket centrifuge at 4,000 rpm for 3 minutes.6. Curing the hydrogel with a Blak-Ray® B-100AP high-intensity (100 watt) UV lamp for 10 minutes.7. Curing the hydrogel at 70 °C for 2 hours in an oven.8. Taking the samples out of the molds.9. Curing the hydrogel at 80 °C for 24 hours in an oven.In some cases, including comparative example 4, non-interpenetrating patches failed to remain intact after molding, highlighting the crucial role of the interpenetrating polymer network in maintaining physical integrity.

[0029] In an embodiment, the process of fabricating the interpenetrating polymer network microporous microneedle patch includes adding 670 mg sodium acrylate, 330 mg DMAPS, and 20 mg CL-1 crosslinker to a 20 mL vial; adding 10 g of a mixture of hydrolyzed 20% Gantrez AN-139 (Ashland, Mn-1,080,000 g / mol, hydrolyzed to the maleic acid form prior to use) and 5% PEG having a number average molecular weight of approximately 20,000 g / mol; sonicating the mixture until complete dissolution of all components in the Gantrez-PEG solution; adding 20 mg AIBA and 20 mg LAP; dispensing approximately 100 pL of the mixture to a PDMS microneedle mold; centrifuging at approximately 4,000 rpm for approximately 3 minutes; UV curing, for example with a Blak-Ray® B-100AP high-intensity (100 watt) UV lamp, for approximately 10 minutes; thermal curing at approximately 70 °C for approximately 2 hours; demolding; and post-curing at approximately 80 °C for approximately 24 hours to form ester crosslinks between Gantrez and PEG.

[0030] For evaluating properties of embodiments, the interstitial fluid extraction performance was compared with the comparative microneedle devices. A 4 cm by 4 cm rectangular piece of porcine skin was cut and soaked overnight in phosphate-buffered saline (PBS) solution. Microneedle patches were applied to the porcine skin and secured with a bandage (e.g., a bandaid). After approximately 20 minutes, 120 minutes, and 24 hours, three patches were removed at each interval, and their weight gain was measured to calculate swelling ratio.

[0031] The swelling ratio is calculated as:Swelling ratio (%) = (Wt- Wo) / Wo x 100 where Wo and Wtrepresent the initial weight and the weight at time t of the patch, respectively.

[0032] Reference is made to FIG. 3, which illustrates charts 300 showing (a) the swelling ratio of embodiments of the present disclosure as compared to identified comparative examples over time and (b) PBS extraction per 100 microneedles at 20 minutes for embodiments andcomparative examples. FIG. 3(a) shows that embodiments swell as quickly as the MeHA-based comparative devices initially. However, while the swelling ratio of the MeHA devices levels off at around 100%, embodiments continue to swell significantly more. As shown in FIG. 3(b), the MeHA devices extract approximately 6 pL per 100 microneedles of PBS from porcine skin in approximately 20 minutes, whereas embodiments extract approximately 16 pL per 100 microneedles in the same timeframe. The greater swelling performance of embodiments compared to the non-porous interpenetrating polymer network devices underscores the importance of the porous microstructure in the swelling rate.

[0033] Reference is made to FIG. 4, which illustrates microscopic images 400 of microneedle patches. In some embodiments, FIG. 4(a)-(c) show embodiment devices and FIG. 4(d)-(f) show comparative devices. Rougher surfaces and small holes observed in embodiment devices (for example in FIG. 4(b)) indicate the porous microstructure, whereas smoother surfaces observed in non-porous comparative devices (for example in FIG. 4(e)) indicate an absence of such microporosity. The enhanced swelling performance of embodiments, compared to the noninterpenetrating network devices (comparative example 3), highlights the significance of the primary zwitterionic network (for example poly(SA-DMAPS)) in the IPN for ISF extraction.

[0034] Reference is made to FIG. 5, which shows charts 500 depicting mechanical properties of microneedle patches. A Dynamic Mechanical Analyzer (DMA 3200, TA Instruments) with a 500 N load cell was used to perform compression tests on the samples. The MN patches were positioned with their tips facing upward on a flat stainless-steel platen, and a vertical force was applied to the tips of the MNs at a strain rate of approximately 0.5 mm / min. FIG. 5(a) shows load versus displacement curves for the embodiment devices and comparative example devices. The steeper slope of the load-displacement curves in the initial linear region for the embodiment devices, compared to the comparative example devices, indicates higher stiffness, which is necessary for skin penetration without breakage, as further illustrated in FIG. 5(b). FIG. 5(c) shows failure force of the MN patches, with the embodiment devices demonstrating a higher failure force than the comparative example devices, highlighting desirable properties for skin penetration without fracture. MN patches of comparative example 4 devices failed to remain intact after molding, which further shows the crucial role of the IPN in maintaining physical integrity of the microneedle patches.

[0035] Embodiments described herein provide an interpenetrating polymer network microporous microneedle patch that ensures rapid and efficient ISF extraction, superior mechanical strength, and resistance to biofouling. In particular, embodiments combine an interpenetrating polymer network architecture with a microporous microstructure in a zwitterionic antibiofouling formulation. Creating a microporous hydrogel to enhance swelling speed and using porogen initiators to generate bubbles during hydrogel synthesis are known techniques; however, their application within microneedle molds for forming fine microneedle structures yields unexpected results. Bubble formation and coalescence could be expected to create large pores that disrupt microneedle formation, but the high pressure and confinement within the PDMS mold cavities inhibit bubble growth, maintaining intact needle shape while producing a beneficial microporous microstructure. Therefore, using a porogen initiator for microneedle fabrication represents an unexpected approach or combination of operations in view of the potential for pore-induced structural disruption.

[0036] Embodiments may be paired with electrochemical or colorimetric biosensors for continuous point-of-care biomarker monitoring and may be adapted for combination with wearable biosensing devices to monitor various ISF biomarkers, including metabolites, electrolytes, proteins, and hormones.

[0037] In accordance with an aspect, there is provided a method of fabricating a microneedle patch comprising preparing a precursor mixture that includes at least one zwitterionic polymerizable component selected from a zwitterionic monomer and a zwitterionic crosslinker together with at least one additional polymerizable component; combining the precursor mixture with a solution comprising polyvinyl methyl ether maleic acid and polyethylene glycol to form a microneedle casting composition; dispensing the microneedle casting composition into a microneedle mold; initiating free-radical polymerization of the microneedle casting composition by exposing the composition to ultraviolet radiation in the presence of a photoinitiator and by heating in the presence of a thermal initiator, the thermal initiator optionally being a gasevolving porogen initiator effective to generate a microporous microstructure under mold confinement; removing the polymerized microneedle patch from the mold; and subjecting the microneedle patch to post-polymerization thermal cycling to form ester crosslinks betweenpolyvinyl methyl ether maleic acid and polyethylene glycol to provide a secondary support network.

[0038] In accordance with another aspect, there is provided a microneedle patch comprising a plurality of microneedles extending from a substrate, each microneedle comprising an interpenetrating polymer network including a primary network comprising one or more zwitterionic polymerizable components together with one or more additional polymerizable components, and a secondary network comprising polyvinyl methyl ether maleic acid chains crosslinked with polyethylene glycol, the microneedles optionally including a microporous microstructure.

[0039] In accordance with a further aspect, there is provided a microneedle composition comprising a primary network of an interpenetrating polymer network that includes one or more polymerizable components selected from zwitterionic monomers, comonomers, and crosslinkers, and a secondary network formed by polyvinyl methyl ether maleic acid chains crosslinked with polyethylene glycol or another support network.

[0040] It will be appreciated that any feature described in relation to one aspect or embodiment may be combined with any other aspect or embodiment.REFERENCES[1] Y. Hu, et al., Adv. Sci. (2024), 2306560[2] X. Hu, et al., Biomedicines (2023), 11, 2119[3] M. Zeng, et al., Adv. Healthcare Mater. (2020), 1901683[4] E. Laszlo, et al., Adv. Funct. Mater. (2021), 2106061[5] P. Ghavami Nejad, et al., Adv. Healthcare Mater. (2023), 12, 2202362[6] E. Shirzadi, Adv. Sensor Res. (2023), 2300122

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A method of fabricating a microneedle patch comprising: preparing a precursor mixture comprising at least one zwitterionic component selected from a zwitterionic monomer and a zwitterionic crosslinker, and further comprising at least one additional polymerizable component selected from a comonomer and a crosslinker; combining the precursor mixture with a solution comprising polyvinyl methyl ether maleic acid and polyethylene glycol to form a microneedle casting composition; dispensing the microneedle casting composition into a microneedle mold and distributing the composition into mold cavities; initiating free-radical polymerization of the microneedle casting composition by exposing the composition to ultraviolet radiation in the presence of a photoinitiator and by heating in the presence of a thermal initiator, the thermal initiator being optionally a porogen initiator that evolves gas, such that when a porogen initiator is present, confinement within the mold cavities inhibits bubble coalescence and preserves microneedle geometry while generating a microporous microstructure; removing the polymerized microneedle patch from the mold; and subjecting the microneedle patch to post-polymerization thermal cycling effective to form ester crosslinks between polyvinyl methyl ether maleic acid chains and polyethylene glycol to provide a secondary support network.

2. The method of claim 1, wherein the zwitterionic monomer is selected from the group consisting of [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide (DMAPS), 2-methacryloyloxyethyl phosphorylcholine (MPC), and 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propionate (CBMA).

3. The method of claim 1, wherein the comonomer is selected from the group consisting of acrylic acid (AA), methacrylic acid (MAA), sodium methacrylate (SMA), and sodium acrylate (SA).

4. The method of claim 1, wherein the zwitterionic crosslinker is selected from the group consisting of N,N-bis(methacryloxyethyl) N-methyl N-(3-sulfopropyl)ammonium betaine (CL-1) and N,N-bis(methacryloxyethyl) N-methyl N-(4-sulfobutyl)ammonium betaine (CL-2).

5. The method of claim 1, wherein the microneedle casting composition comprises 670 mg SA, 330 mg DMAPS, and 20 mg CL-1, and the solution comprises 10 g of hydrolyzed 20% Gantrez AN-139 and 5% PEG having a number average molecular weight of about 20,000 g / mol.

6. The method of claim 1, wherein the photoinitiator comprises lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) and the thermal porogen initiator comprises 2,2'-azobis(2-amidinopropane) dihydrochloride (AIBA).

7. The method of claim 1, further comprising centrifuging the mold at about 4,000 rpm for about 3 minutes prior to ultraviolet exposure to promote filling of the mold cavities.

8. The method of claim 1, further comprising evacuating the mold and applying the polymeric precursor composition to the mold whereby the polymeric precursor composition fills the mold cavities prior to ultraviolet exposure.

9. The method of claim 1, wherein ultraviolet exposure is performed for about 10 minutes and thermal initiation is performed at about 70 °C for about 2 hours.

10. The method of claim 1, wherein the post-polymerization thermal cycling comprises curing at about 80 °C for about 24 hours to form ester crosslinks between Gantrez and PEG.

11. The method of claim 1, wherein the microneedles exhibit a mean pore size in a range of about 0.1 pm to about 5 pm and a pore volume fraction in a range of about 5% to about 60%.

12. A microneedle patch comprising a plurality of microneedles extending from a substrate, each microneedle comprising an interpenetrating polymer network that includes: a primary network formed from polymerization of polymerizable zwitterionic monomers, co-monomers and a zwitterionic crosslinker(s), and combinations thereof; anda secondary network comprising Gantrez chains crosslinked with polyethylene glycol), wherein the microneedles include a microporous microstructure distributed throughout the microneedle bodies.

13. The microneedle patch of claim 11, wherein the microporous microstructure comprises pores having a mean diameter between about 0.1 pm and about 5 pm and a pore volume fraction between about 5% and about 60%.

14. The microneedle patch of claim 11, wherein the microneedles exhibit a failure force greater than about 0.1 N per microneedle under compression and a stiffness sufficient for penetration of mammalian skin without fracture.

15. The microneedle patch of claim 11, wherein the microneedles extract at least about 12 pL per 100 microneedles from porcine skin in about 20 minutes ex vivo.

16. The microneedle patch of claim 11, wherein the zwitterionic monomer is selected from DMAPS, MPC, or CBMA and the zwitterionic crosslinker is selected from CL-1 or CL-2.

17. The microneedle patch of claim 11, wherein microneedle surfaces resist non-specific protein adsorption relative to a non-zwitterionic hydrogel control.

18. A microneedle precursor composition comprising sodium acrylate, a zwitterionic monomer selected from DMAPS, MPC, or CBMA, a zwitterionic crosslinker selected from CL-1 or CL-2, Gantrez, PEG, a photoinitiator comprising LAP, and a thermal porogen initiator comprising AIBA.

19. A biosensing system comprising the microneedle patch of claim 11 operatively coupled to an electrochemical or colorimetric biosensor configured to monitor one or more interstitial fluid biomarkers.

20. A microneedle composition comprising: a primary network of an interpenetrating polymer network that includes at least one zwitterionic monomer, at least one comonomer, at least one crosslinker, any two of them, or all of them; and a secondary network formed by Gantrez chains crosslinked with polyethylene glycol.

21. The microneedle composition of claim 19, wherein the zwitterionic monomer is selected from the group consisting of DMAPS, MPC, and CBMA.

22. The microneedle composition of claim 19, wherein the comonomer is selected from the group consisting of acrylic acid (AA), methacrylic acid (MAA), sodium methacrylate (SMA), and sodium acrylate (SA).

23. The microneedle composition of claim 19, wherein the zwitterionic crosslinker is selected from N,N-bis(methacryloxyethyl)-N-methyl-N-(3-sulfopropyl)ammonium betaine and N,N-bis(methacryloxyethyl)-N-methyl-N-(4-sulfobutyl)ammonium betaine.

24. The microneedle composition of claim 19, wherein the secondary network is selected from the group consisting of PVME / MA+PEG (Gantrez-PEG), hyaluronic acid (HA), and poly(vinyl alcohol) (PVA).

Images