Patent Application
20190308141
The present disclosure relates generally to porous materials and autonomous control of the permeability of these materials.
Porous materials have numerous uses crossing over from the chemical and/or biologically protective to the recreational and even industrial uses. As an example, chemical and biological protective clothing utilizes layering technology, wherein static barrier materials are stacked to mitigate contaminant breakthrough. In recent years these materials have been enhanced, but these enhancements do not provide the speed, selectivity, or molecular capacity to address complex threats as they arise in dynamic environments. In addition, the complexity of production and limited lifetime of these older materials may result in unsustainable financial costs that limit the benefits of protective technologies to small numbers of personnel. An additional challenge, however, is that these enhancements do not address the significant physical burden to the user due to the poor water vapor transport, heat management, and sheer bulk of the material. As a result of these shortcomings, users typically can only operate in full protective state for less than an hour at a time.
The present disclosure provides autonomous localized permeability material systems that can provide superior performance to that of the existing material systems.
Autonomous localized permeability material systems are provided that can include: a dynamically permeable porous material; and immobilized reagents operatively associated with the porous material in sufficient proximity to trigger a localized change in material pore size upon reagent reaction.
Autonomous localized permeability material system preparation methods are provided that can include operatively associating immobilized reagents with a dynamically permeable porous material.
Methods for autonomously modifying localized permeability of material are also provided. These methods can include: providing a dynamically permeable porous material operatively associated with immobilized reagents; reacting the reagents with a reactant to form a product; and exposing the product to the dynamically permeable porous material, with the exposing of the product modulating the permeability of the material.
Embodiments of the disclosure are described below with reference to the following accompanying drawings.
The present disclosure provides autonomous localized permeability material systems and methods for using and making same. In accordance with example implementations, these systems can be used as part of a protective material which only at the point of contact with a reagent, locally switches into a closed protective state. Other example configurations include but are not limited to industrial and/or recreational uses.
In accordance with example implementations, the material systems of the present disclosure can include a dynamically permeable porous material, and one or more immobilized reagents operatively associated with the porous material in sufficient proximity to trigger a localized change in material pore size upon reagent reaction. The material systems can be considered membranes and/or membrane systems. The material systems can be an entirety of a material or a portion of a material, such as a layer of same.
The material systems of the present disclosure can be considered an autonomous self-decontaminating selectively responsive porous material system that senses and reacts with target analyte(s) in the environment to produce triggers for material response.
The responsive porous material can include immobilized reagent(s) chemically configured to recognize and/or convert target analytes (reactants) into chemical triggers. The target analytes or reactants can include but not limited to the chemical warfare agents sarin, soman, sulfur mustard; pesticides parathion, paraoxon, diisopropyl fluorophosphate, and biomolecules including glucose, carbon dioxide, and glutathione. These reactants can be converted into triggers to actuate a material response such as the modulation of porosity of the material.
Referring to
As one example, triblock terpolymer such as poly(isoprene-b-styrene-b-4-vinylpyridine) (ISV) (P4VP) can serve as the basis for the porous material.
In accordance with other implementations, ISV can be the porous material. The P4VP part of the ISV can also be 3-amino or 2-amino pyridine, as shown in the tetrablock quarterpolymer. Other embodiments of the responsive polymer include isoprene-styrene-PDMAEMA and isoprene-styrene-HEMA, both of which are triblock terpolymers.
With reference to 10a, porous material 12 may have reagent 14 integrated therein with at least some of reagent 14 being located sufficiently proximate a surface of porous material 12 to react with a reactant upon exposure of the system to the reactant. This form of integration can be the modification of the porous material itself, such as the modification of the terminal ends of block polymers used in formation of the porous material. For example, reagents may be included during the porous material forming process, such as at least partially inorganic materials that may remain reactive upon porous material formation. Such materials can include metals and/or metal organic frameworks.
In accordance with example implementations, the immobilized reagent can be stoichiometric or catalytic. The immobilized reagent can include one or more of enzymes, metal organic frameworks, metal oxides, nucleophilic amines, and oximes. In accordance with example implementations, the reagent can generate products, such as stimulus (triggers), upon reaction with the reactant; the reaction products can include but are not limited to acids, bases, and/or thiols. Other implementations of the disclosure include systems with reagents that degrade reactants but generate by-products that have no impact on the porous material. In some of these configurations, multiple reagents can be incorporated, with at least one reagent generating a product upon exposure to a reactant, and the product initiating a change in the porous material.
With reference to 10b, porous material 12 may have reagent 14 bonded and/or adsorbed thereto. The bonding may be covalent in nature and/or non-covalent. Just one example of the reagents that may be bonded to the porous material include a hydrolase such as a phosphotriesterase enzyme, haloalkane dehalogenase enzyme or other enzymes.
With reference to 10c, porous material 12 may have another layer bonded thereto that may include integrated and/or bonded reagents 14. In accordance with example implementations, one or more of the implementations of 10a-10c can be supported by another layer 16. Layer 16 may be woven nylon for example.
The porous material can respond to exposure to triggers including but not limited to pH, redox potential, and group polarity. The reagents immobilized with the material can be selected and/or configured to produce products that initiate such triggers (pH changes for example).
Operatively associated with the porous materials can be specified reagents. With reference to
Select variants of these reagents are capable of generating large changes in pH with reactant (substrate, for example) specificity and response times toward a number of chemical and biological agents of interest. In accordance with example configurations, coupling the selectivity and response of enzymes with stimuli responsive materials, the dynamic material system can be prepared which responds only to reactants (e.g., enzyme substrates) with high sensitivity. Phosphotriesterase (PTE, EC 3.1.8.1) can be selected for the rapid detoxification of a wide range of reactants such as organophosphate pesticides and chemical agents. Hydrolysis of these reactants via PTE catalysis can generate strong and weak acid products. Incorporation of PTE into the ISV materials can effectively create a lock-and-key-type permeability barrier to chemical diffusion.
The materials are compatible with large area fabrication and integration with other support and protective materials to achieve required properties including material strength, moisture vapor transmission rates (MVTR), as well as fast response times. In accordance with example implementations, the material system can include the porous material on nylon-based support structures, such as casting on macroporous woven nylon support layers. The material system can have an elastic moduli of greater than 300 MPa.
With reference to
With reference to
Critical textile properties of the material systems can be evaluated including moisture vapor transport rate (MVTR), intrinsic water vapor resistance and durability (
Referring next to
In
In general, material systems can provide MVTR values similar to those of standard commercial textiles, such as PTFE (MVTR ˜550 g/m2/day). Evaluation of MVTR across several material systems compositions (ranging in molecular weight from 43, 99, and 119) revealed a range of accessible vapor transport (˜500-800 g/m2/day) and demonstrated the tunable properties of the material systems as a function of polymer molar mass, casting conditions and material system pore size. Elastic moduli (E ˜400 MPa) and ductility (λ max ˜0.5) were found to be comparable to commercial materials, such as GoreTex™, and approximately independent of strain rate. Permeability response of the supported material systems can be practically unaffected by repeated (10×) flex deformation to film curvatures of 3 cm−1. The scalability of the material system can be demonstrated through the fabrication of mid-gauge material system swatches. These samples can be produce, in a single continuous casting process, measuring approximately 4″×5″ and displaying virtually the same homogeneity, consistent pore structure, and permeability response observed at smaller scales.
Referring to
As described herein, material system 10 can include reagents and upon exposure to one or more of these reagents, a product 52 is formed. Product 52, may, for example be a by-product of the degradation of a reactant, such as protons upon the degradation of an organophosphorous neurotoxin when reacted with a phosphotriestrerase reagent. This product can initiate the porous material to locally swell or collapse, modulating permeability as shown in swollen portion 54. In accordance with this example, the product can be acidic and the pores of the porous material can swell and close upon decrease in pH. Where the porous material is formed of poly(4-vinylpyridine), chains of the poly(4-vinylpyridine) may stretch to close the pores, for example.
Autonomously, the material systems of the present disclosure can degrade a material hazardous to human health to non-hazardous material and also prevent the hazardous material from traversing the material system. As
These material systems may be considered actively-gated material systems with molecular recognition that mimics skin-like functionality by integration of enzymes into mesoporous and pH-responsive asymmetric polymeric films. Theses bio-mimetic material systems can perform a rapid and spatially selective response to specific threat agents and can be integrated into robust material systems consistent with clothing, suit, mask, and/or protective textile applications.
Referring to
The porous material of the material system can be sensitive to environmental changes and the products of the reactants and the reagents can provide these changes. With reference to
Referring to
Visual detection of bound enzyme activity can be demonstrated through the use of a pH-sensing cyanine indicator dye (1) (
With reference to
Transduction of enzyme-mediated substrate hydrolysis into a permeability response can be evaluated by measurement of the pressure-driven water flux across material systems in aqueous solution at varying simulant concentration. Within one minute a reduction of liquid permeability to about 1 dB of the original value can be observed, demonstrating the rapid self-regulating characteristics of enzyme-actuated material systems (
In accordance with example implementations, materials system 10 can be prepared by operatively associating immobilized reagents with a dynamically permeable porous material. These methods can include first preparing the dynamically permeable porous material and then operatively associating reagents with the porous material. These methods also include integrating the reagents with the porous material, and these methods also can include providing another material, such as a layer upon the porous material with the layer including immobilized reagents. For example, this layer may be considered a reagent support material and this reagent support material may be operatively associated with the porous material. In the above example implementations, at least a portion of the reagents may be immobilized when associated with the porous material.
In accordance with at least one example implementation, non-solvent induced phase separation can be used to form the dynamically permeable porous material from triblock terpolymers. Porous materials can be prepared using SNIPS (self-assembly with non-solvent induced phase separation) of five ISV terpolymers (triblock terpolymers such as poly(isoprene-b-styrene-b-4-vinylpyridine) with molar masses in the range of 40-120 kg/mol (ISV43, ISV99, ISV117, ISV118 and ISV119). The porous material exhibited a hierarchical structure that can include a thin top surface separation layer of vertically aligned uniform mesopores and a substructure of graded meso- to macropores, with all surfaces lined by the poly-4-vinylpyridine (V) block of the terpolymer.
Two types of substructures with either a densely packed “sponge-like” or largely open “finger-like” morphology can be observed depending on fabrication conditions. Variation in polymer composition and porous material casting conditions can be used to control pore size, shape, density and substructure architecture to match the permeability profile of the resulting porous material to respective specifications.
Preparation of the triblock terpolymer ISV and mesoporous asymmetric membranes derived from ISV can be performed in accordance with Tuning Structure and Properties of Graded Triblock Terpolymer-Based Mesoporous and Hybrid Films, Nano Lett, 2011, 11 2892-2900 and/or Understanding the Structure and Performance of Self-Assembled Triblock Terpolymer Membranes, J. Membrane Sci. 2013, 444, 461-468 the entirety of each of which is incorporated by reference herein.
In accordance with example implementations, multiple ISV triblock terpolymers can be synthesized by anionic polymerization. Total number average molar mass, Mn, weight fraction, f, and polydispersity index, PDI, for these terpolymers as experimentally determined by gel permeation chromatography (GPC) and proton nuclear magnetic resonance (1H NMR) are summarized in Table 1 below.
The porous materials can be fabricated by employing a combination of self-assembly and non-solvent induced phase separation, now referred to as SNIPS. An ISV polymer casting solution can be prepared by dissolving ISV polymer into a co-solvent mixture comprised of a 7:3 ratio (by weight) of 1,4-Dioxane (DOX) and tetrahydrofuran (THF). The solution can be pipetted onto a glass substrate for neat, unsupported material. Supported material can be cast directly onto porous nylon substrates, purchased from Sterlitech Inc., taped to glass substrates. The polymer solution can be cast by a doctor blade with a gate height of 220 μm and allowed to evaporate for a specified amount of time before the films are immersed into a deionized water bath. Unless mentioned otherwise, materials can be cast from a 16% (ISV43), 12% (ISV99 and ISV118) or 11% (ISV117 and ISV119) (by weight) polymer solution. These materials can be cast on top of a 0.2 μm (ISV117), 0.1 μm (ISV43, ISV99, ISV119) or 0.04 μm (ISV118) nylon support.
Referring to
Referring to
Additional values for the absolute permeabilities in the “open” and “closed” state of neat and supported ISV117 and ISV119 materials are indicated in Table 2 below.
Referring to
Additional values for the absolute permeabilities in the “open” and “closed” state of neat and supported ISV118 materials are provided in Table 3 below.
Preparation of the material system can also include adsorbing the reagents to the porous material. This can include covalently bonding the reagents to the porous material as well as integrating the reagent into the porous material. Accordingly, the reagents can be immobilized on to the surface of the material using methods including but not limited to adsorption, bio-affinity or covalent conjugation. As described, the reagent can include more than one co-immobilized reagent including but not limited to enzymes, metal organic frameworks (MOFs), metal oxides, nucleophilic amines and oximes.
Adsorption can be used as a reagent (enzyme) immobilization method to attach a broad array of protein structures to polymer surfaces. Enzyme coupling can be accomplished by immersion of porous materials into concentrated enzyme solutions, harnessing the strong interactions between enzymes and P4VP on the outer surface of the ISV material. Coupling can also be accomplished by dropcasting, printing or other similar deposition methods.
To impart target-specific response characteristics, supported ISV materials can be conjugated to hydrolase enzymes, which have demonstrated use in the identification, quantitation, and decontamination of threat agents. In specific embodiments, due to the pH-based material response mechanism, functionalization of the ISV material may focus primarily on enzymes that act on relevant substrates to produce highly acidic products.
In accordance with example implementations, porous materials can be incubated in solutions of PTE enzyme (1-20 mg mL−1, 10 mM CAPSO, pH 9.4, 500 μL per 100 mm2 material system surface area) for 16 hours at 4° C. on an orbital shaker at low speed. For samples containing dye 1, 100 μL of a 10 mg mL−1 stock solution in water can be added to the protein solution for every 100 mm2 material system surface area. Post-immobilization, samples can be washed (3×) with 10 mM CAPSO, pH 9.4 buffer for 30 minutes at 4° C. on an orbital shaker at low speed prior to testing.
Direct phosphotriesterase hydrolysis assays can be performed on a Molecular Devices SpectraMax M2e spectrophotometer in 96 well plates for solution-phase enzyme samples (100 μL reaction volume, 0.35 mm path length, 5 min kinetic duration) and on a Beckman Coulter DU530 UV/VIS spectrophotometer, transferring aliquots of assay solution samples to a cuvette for solid-phase enzyme samples (1 mL volume, 1 cm path length, 10 min kinetic duration). All assays can be completed at 25° C. against ethyl paraoxon and the rates measured by monitoring the release of p-nitrophenol (ε405=17100 M−1cm−1). Substrate stock solutions can be prepared by the dissolution of diethyl paraoxon in dry methanol (152 mM) followed by dilution of the methanol stock in deionized water (15.2 mM). For the enzymatic reaction, aliquots of the 15.2 mM paraoxon stock can be added to a mixture of enzyme in reaction buffer (50 mM CAPSO, 50 μM CoCl2, pH 9.0) to give a final concentration of 1.52 mM. A dilution series of enzyme concentrations can be used for solution-phase samples (final enzyme concentrations range from 1 ng-10 μg mL−1) to achieve a linear rate. For solid-phase samples, a section of material can be submerged in an adequate volume as to maintain a linear rate over the course of the kinetic assay (typical conditions: 3 mm diameter circle, 2 mg mL−1 enzyme incubation, 12 mL assay buffer). The initial enzymatic rates can be corrected for the background rate of spontaneous paraoxon hydrolysis in the absence of enzyme. Specific activity values of the solution-phase samples can be calculated using the following formula:
Specific Activity (umol min−1.mg−1)=ΔmAU min−1×(1×106)×DF×(1000×17100×0.35×C)−1, where ΔmAU min−1=ΔmAU min−1 test−ΔmAU min−1 blank, DF is the dilution factor, 17,100 M−1 cm−1 is the molar extinction coefficient of p-nitrophenol, C (in mg L−1) is the protein concentration of enzyme stock solution and 0.35 cm is the path length of light.
Quantitation of active enzyme loading of solid-phase samples can be calculated using a calibration curve prepared from the rates of enzymatic paraoxon hydrolysis (linear regression of absorbance vs. time) for a series of solution-phase enzyme standards of known concentration and identical specific activity as that incubated with the material system. The resulting equation can then be compared against the hydrolysis rates obtained for the solid-phase samples to calculate enzyme mass loading (ng) per unit area (mm2).
Referring to
The ellipsometry measurements can be conducted using a Beaglehole Instruments Picometer phase-modulated ellipsometer equipped with a helium-neon laser (λ=632.8 nm). The angle of incidence was varied from 70-80°, and analysis was completed using TF Companion software (Version 3.0, Semicon Software, Inc.) and a four layer, homogeneous film model (semi-infinite silicon+silicon dioxide+polymer+adsorbed enzyme+semi-infinite air). Thin film material systems of PI, PS, P4VP, and ISV with thicknesses between 10-20 nm can be spin cast from 0.1 wt. % solutions in toluene (PI, PS, and ISV) and a 1:1 mixture of acetone and ethanol (P4VP) onto silicon wafers. The polymer-coated wafers can incubated in a solution of PTE enzyme (9.7 mg mL−1, 10 mM CAPSO, pH 9.4) for 16 hours at 4° C. on an orbital shaker at low speed. The layer thickness can be successively determined for the silicon dioxide layer (2-3.5 nm), the material layer (10-20 nm), and the adsorbed enzyme. Literature values of refractive indices for PI (1.51), PS (1.59), P4VP (1.581), ISV (1.5707), and dry enzyme (1.53) were used for the analysis.
Referring next to
As shown, the material system retained activity in solution and upon drying, even after extended storage (
Samples can be incubated at 4, 25, 40, or 60° C. for up to 30 days, with activity time points collected on days 0, 10, and 30. At each time point the enzyme activity can be assessed by >4 replicates. Pretreatment of samples with excipient significantly helped to maintain enzyme activity of the dried samples as measured on day 0.
As indicated, material system 10 can also include a support structure such as a nylon-based support structure. This support structure can be included before or after the association of the immobilized reagents.
Phosphotriesterase (PTE) can be obtained from Novozymes (Davis, CA) and exchanged into 50 mM potassium phosphate, 100 uM cobalt chloride, pH 8.0 for storage at 4° C. until use. Enzyme variants PTE(RN-YT) and PTE(C23) can be prepared in-house according to known procedures. pH-sensitive dye 1 can be custom synthesized and purchased from American Dye Source, Inc. (Quebec, Canada). Ethyl paraoxon (Chem Service, Inc., >98%), Diisopropylfluorophosphate (Sigma-Aldrich, >97%)
An evaporative dish method, based on the British Standard BS 7209, was used to determine the MVTR in material system samples. The Turl dish assembly consists of a dish, triangular support, and cover ring. The test specimen is comprised of two circular material system samples, with a total area of 402 mm2, anchored to a circular transparency film, purchased from C-Line Products, Inc. (No. 60837), using epoxy. The test specimen was sealed over the mouth of the dish containing deionized water and the triangular support to maintain a ˜10 mm air gap. The cover ring was placed above the test specimen and adhesive tape was applied around the circumference of the competed assembly. The assembly was positioned into a turntable and the experiment was conducted in a controlled atmosphere of 20° C. and 65% relative humidity. The assemblies were weighed on a balance with a resolution of 0.01 g. Each assembly was weighed daily up to five days in order to assure full equilibration. Data for calculation of MVTR values were taken on day five.
The MVTR(g m−2 day−1) was calculated as: MVTR=24M(At)−1, where M is the loss in mass of water in grams, t is the time period in hours, and A is the area of the material system sample in m2.
In addition to the three nylon-supported ISV materials (ISV43, ISV99, and ISV199), dishes were evaluated in the open and closed states for reference. Values obtained from these measurements were used as benchmarks in addition to literature values reported for relevant commercially available material (i.e. PTFE and PU, see
Intrinsic water vapor resistance was calculated as: Ret=Rf(RT)(MwΔHvap)−1, where Rf is the intrinsic mass transfer resistance of the sample, R is the universal gas constant, T is temperature, Mw is molar mass of water, and ΔHvap is the enthalpy of vaporization of water.
Tensile testing of the materials can be performed on an Instron (model 4442) equipped with a 1 kN load cell with loading strain rates of 1, 10, and 100 mm min−1. The samples were 13 mm×20 mm with a thickness of 0.11 mm. Stress-strain curves were constructed, and the Young's Modulus was determined by calculating the slope within the proportionality limit of the curve. The toughness can be calculated by integrating the stress-strain curve over the entire deformation range. Samples can be fixed and repeatedly flexed (three sets of 10 flexes) to a curvature of 3 cm−1 at a rate of 0.5 Hz.
The entirety of both “Biocatalytic Stimuli-Responsive Asymmetric Triblock Terpolymer Membranes for Localized Permeability Gating” by Poole et al, Macromolecular Rapid Communications, 2017, 1700364, and Supporting Information for Macromol. Rapid Commun., DOI: 10.1002/marc.201700364 “Biocatalytic Stimuli-Responsive Asymmetric Triblock Terpolymer Membranes for Localized Permeability Gating” by Poole et al, are both incorporated herein by reference.
Enzymes can be incorporated into ISV membranes to test their ability to hydrolyze simulants on the surface of the membrane in low (<20%) and high (>90%) humidity. For example, 8 mm ISV membranes can be coated with phosphotriesterase (PTE), haloalkane dehalogenase(DHG), or both and allowed to dry. In accordance with one example, enzyme can be provided at 51.7 μg/mm2, 25.9 μg/mm2, and 5.2 μg/mm2. The enzyme coated membranes and a breakthrough membrane can be incorporated into the cap of a GC vial containing artificial sweat. This vial can then be placed into a 20 mL vial containing another GC vial with either water (>90% humidity) or saturated lithium chloride (<20% humidity). The larger vial may be capped, and the internal environment allowed to equilibrate for 15 minutes. 500 μg of Diethyl VX per mm2 can then be added the membrane and allowed to incubate overnight. The membranes may then be extracted for GC-MS analysis.
In accordance with another example, ten different levels of enzyme were loaded within the membranes ranging from 50-2.5 μg/mm2 (See Table 6 Below) These membranes were then tested for surface decontamination of the simulant diethyl VX at a load of 500 ug/cm2 under high (>90%) or low (<20%) humidity conditions. After a 24 incubation the membrane and breakthrough material were both extracted per the above protocol to quantitate decontamination and agent breakthrough within the sample. The graphs of
Using the same format as described above, the study can be expanded to include contamination of simulants diisopropylfluorophosphate (DFP), ethyl paraoxon, and dibromoethane (DBE), in addition to DEVX. Each simulant can be tested under both high and low humidity environment. Under the loading conditions of 51 μg/mm2 for PTE and 20 μg/mm2 for Haloalkane Dehalogenase (DHG), membranes were separately challenged with 500 μg/cm2 of Diisopropyl fluorophosphate (DFP), Paraoxon or Dibromoethane (DBE) under dry (<20% humidity) and humid (>90% humidity) conditions. GC-MS analysis demonstrated that full hydrolysis of each simulant occurs under humid conditions. The data presented in
Under humid conditions, 500 μg/cm2 DEVX can be added to phosphotriesterase loaded membranes. Samples were analyzed by GC-MS analysis at 0, 1, 5, 10, 30 and 60 minutes. With 51 μg/cm2 enzyme loaded onto an ISV membrane, a hydrolysis of >99% of a 500 μg/cm2 challenge can be observed within the first 30 minutes of the challenge with decontamination rates for this time ranging from 135 to 0.3 μg/cm2*min, as shown in
To determine the ability of the enzyme-loaded membranes to respond to sequential DEVX challenges, phosphotriesterase enzyme was loaded onto ISV membranes at 51 μg/mm2. Additive challenges of 500 μg/cm2 (250 μg per 8 mm membrane) can be performed at 0, 1 and 2 hours (1.5 mg/cm2 cumulative challenge). Membranes may be analyzed for the presence of remaining DEVX at 1, 2 and 3 hours.
The results demonstrate that DEVX hydrolysis continues after the initial challenge and even after the third challenge of 500 μg/cm2, >90% of the DEVX is hydrolyzed with no breakthrough observed as shown in
Moving toward assessing the ability of the material to address multiple types of challenges in a single form factor, the best method of performing challenges with a mix of agents may be determined. 500 μg/cm2 of DEVX and DBE, as well as serial dilutions of each, can be either mixed or added separately to a chloroform extraction with internal standard and analyzed by GC-MS and the resulting data shown in
Methods used to quantitate agent permeation can include the following:
Samples analyzed by this method are shown in
The headspace gas chromatography method outlined by the ECBC may be used to analyze DFP simulant permeation through ISV membrane and several control samples. Enzymatic loading can be performed via drop-casting. Horseradish Peroxidase (HRP) {E.C. 1.11.17} was utilized as a control for Phosphotriesterase (PTE). HRP has a molecular weight of 44 g/mol as compared with PTE, which has a molecular weight of 35.90 g/mol. Analyzing the protein electrostatics, the overall protein charges are also similar with PTE having an overall charge of −2.6 while HRP contains an overall charge of −2 under neutral conditions.
Upon receiving the membranes, they may be treated for the vial-in-vial protocol. This entailed as mentioned previously rinsing the membranes with water, drying the membranes to remove any residual moisture, drop-casting enzyme onto the membrane and then drying the enzyme loaded membranes. Once dried the membranes can then conditioned for 24-48 hours in a humid environment at 37° C. Enzyme loading within the material may be performed at a protein loading concentration of 7 μg/mm2. This concentration dried upon the membrane produces a uniform enzyme coating which does not appear to flake or clump. The membranes may than be tested in the previously described vial-in-vial experimentation setup with 500 μg/cm2 Diisopropyl flurophosophate (DFP) to monitor vapor permeation across the enzyme loaded ISV membrane. Triisopropyl Phosphate (TIPP) was utilized as the internal standard reference. The temperature of analysis was 37° C.
After 45 minutes, the Free Diffusion samples recovered 83% of the 500 μg/cm2 initial DFP loaded in the challenge vial. The mere addition of the pristine ISV43 reduces the vapor permeation by 39.5% for the same time-course. Examining the enzyme loaded samples after 45 minutes, the HRP alone provided an 82% reduction in free diffusion. This is most likely due to steric hinderance and pore blockage since HRP shows little catalytic activity toward DFP as previously documented. The PTE loaded membranes for the same duration record values under the established calibration range. These effects are amplified as seen with the lower simulant challenge of 5 μg/cm2 DFP. In analyzing the vapor permeation after 45 minutes, free diffusion recovers approximately 64% of initial DFP challenge. See for example,
An extended time course examination was conducted monitoring vapor permeation from 1 hour after initial simulant loading up to 24 hours. For this experiment, twice the amount of the standard 500 μg/cm2 challenge was utilized 1000 μg/cm2 and the data is shown in
To determine the effect of enzyme loading on the MVTR of SNIPS membranes, pure and blended ISV membranes were loaded with protein solution and the change in MVTR was measured. This is an important factor as MVTR is directly related to the material's thermal burden performance specifications. Replicate membranes of pure ISV (YML644A and YML644B), blended ISV:ISO (9:1A ISV:ISO and 9:1B ISV:ISO), and blended ISV:IS(HEMA) (9:1A IS(HEMA) and 9:1B IS(HEMA)) were tested and the data shown in
Asymmetric membranes were fabricated by employing a hybrid process combining block copolymer self-assembly with a non-solvent induced phase separation process (SNIPS). Pure ISV membranes were cast from a 11% (by weight) ISV138 polymer solution in a solvent mixture of 1,4-dioxane (DOX) and tetrahydrofuran (THF) (7:3 by weight). For the ISV:ISO blend, a ternary solvent mixture of DOX, THF, and acetonitrile (MeCN) was used as the solvent system. The casting solutions were prepared by separately dissolving 11% and 18% of ISV and ISO, respectively, in a solvent system consisting of DOX/THF/MeCN (˜67/28/5 wt %) at 300 rpm overnight. The ISV:ISO weight ratios of 9:1 was maintained in the individual casting solutions prior to blending. The individual casting solutions containing the desirable blend weight ratios were then mixed and stirred together at 300 rpm for 10 minutes to form a hybrid casting solution. The dope solution was cast by doctor blade with a gate height of 220 μm onto a 0.1 micron nylon substrate using an automated set-up. After 100 seconds for pure ISV and 120 seconds for blended ISV:ISO membranes, the thin film was immersed into a coagulation bath of de-ionized water. Samples of ISV:IS(HEMA) membranes in a 9:1 weight ratio were prepared and supplied by Terapore.
An evaporative dish method, based on the British Standard BS 720921, was used to determine the MVTR in membrane samples. The Turl dish assembly consists of a dish, triangular support, and cover ring. The test specimen is comprised of two circular membrane samples, with a total area of 402 mm2, anchored to a circular transparency film, purchased from C-Line Products, Inc. (No. 60837), using epoxy. The test specimen was sealed over the mouth of the dish containing deionized water and the triangular support to maintain a ˜10 mm air gap. The cover ring was placed above the test specimen and adhesive tape was applied around the circumference of the completed assembly. The assemblies were positioned into a turntable and the experiment was conducted in a controlled atmosphere at 20° C. and 65% relative humidity. The assemblies were weighed on a balance with a resolution of 0.01 g. Each assembly was weighed daily up to six days in order to assure full equilibration. After six days, the pristine membranes were loaded with 60 microliters of protein solution (bovine serum albumin; BSA in 0.1 M PBS) with a concentration of 130 g/L. Each assembly was weighed daily. The reported MVTR values were averaged over five days. The MVTR (g/m2/day) was calculated as: MVTR=24M/At, where M is the loss in mass of water in grams, t is the time period in hours, and A is the area of the membrane sample in m2.
The MVTR values of the SNIPS membranes are not significantly affected by the loading of protein at such a high concentration. This result is encouraging as this indicates that enzyme may be loaded within the membrane at high concentrations without significantly impeding the moisture vapor flow through the membrane in the open state. It is important to note that the variability in the MVTR of the open reference can be due to the slight variability in ambient temperature and humidity of the room in the summer months.
This application claims priority to U.S. Provisional Patent Application Ser. No. 62/452,490 filed Jan. 31, 2017, entitled “Autonomous Localized Permeability Material Systems and Methods for Using and Making Same”, the entirety of which is incorporated by reference herein.
This invention was made with Government support under Contract No. HDTRAI-13-C-0003 awarded by the Defense Threat Reduction Agency (DTRA). The Government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/016153 | 1/31/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62452490 | Jan 2017 | US |
