Communications

Polymer Nanocomposites with Nanowhiskers Isolated fromMicrocrystalline Cellulose

Jeffrey R. Capadona,†,‡,§,| Kadhiravan Shanmuganathan,†,‡ Stephanie Trittschuh,‡

Scott Seidel,‡ Stuart J. Rowan,‡,⊥ and Christoph Weder*,‡,⊥

Departments of Macromolecular Science and Engineering, Biomedical Engineering, and Chemistry, CaseWestern Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, and Rehabilitation Research

and Development, Louis Stokes Cleveland DVA Medical Center, 10701 East Blvd. Cleveland, Ohio 44106

Received September 25, 2008; Revised Manuscript Received February 5, 2009

The ability to produce polymer nanocomposites, which comprise a percolating, three-dimensional network ofwell-individualized nanofibers, is important to maximize the reinforcing effect of the nanofibers. Whilemicrocrystalline cellulose (MCC) has been previously shown to improve the mechanical properties of polymercomposites, the formation of fibrous percolating networks within the nanocomposites has been stifled. Throughthe utilization of a template approach, nanocomposites based on an ethylene oxide/epichlorohydrin copolymerand nanowhiskers isolated from MCC were produced that display the maximum mechanical reinforcement predictedby the percolation model.

Introduction

The incorporation of small amounts of high-stiffness, high-aspect-ratio nanometer-sized fillers into polymers is a designapproach that has rapidly emerged to a broadly exploitedframework for the creation of new materials with tailoredmechanical properties.1-3 Crystalline cellulose nanofibers areattracting significant interest in this context, mainly due totheir intriguing mechanical properties and the abundance ofcellulose in the biomass.4 These fiber-like crystals, oftenreferred to as nanowhiskers, display an elastic modulus of120-150 GPa5 and are readily obtained from renewablebiosources such as bacteria, wood, cotton, and sessile seacreatures called tunicates.4 Owing to their strongly interactingsurface hydroxyl groups,6 cellulose nanowhiskers have asignificant tendency for self-association, which is advanta-geous for the formation of load-bearing percolating archi-tectures within the host polymer matrix: the spectacularreinforcement of polymers observed for this class of materialsis attributed to the formation of rigid nanowhisker networksin which stress transfer is facilitated by hydrogen-bondingbetween the nanowhiskers;7 van der Waals interactions alsohave been shown to play a significant role.8 However, thesesame nanowhisker-nanowhisker interactions can also leadto aggregation during the nanocomposite fabrication,9 whichsignificantly reduces the mechanical properties of the result-ing materials compared to predicted values.7 The traditionalapproach to solve this problem is surface functionalization,

which mediates particle-particle and particle-polymerinteractions and significantly influences nanoparticle dis-persion.10-13 However, the advantages of surface groups areoften negated because they suppress desirable nanoparticleinteractions and limit their reinforcing impact. To solve thisdilemma, we recently explored a template approach tonanocomposite fabrication.14 The process is based on theformation of a three-dimensional scaffold of well-individual-ized nanowhisker, which is subsequently filled with a polymerof choice. We demonstrated that this technique, which issomewhat different from other recently developed “impreg-nation schemes”,15 is applicable to cellulose nanowhiskersisolated from tunicates16 and cotton4 (both exhibit averagediameters of 20-26 nm, and lengths of 2.2 µm or ∼210 nm,respectively). Both nanowhisker types were incorporated intoa range of polymers, and the resulting nanocomposites displaysignificantly improved mechanical properties. We here reportthat the template approach is also suitable for the fabricationof polymer nanocomposites with commercially availablemicrocrystalline cellulose (MCC). MCC is produced bypartially hydrolyzing cellulose pulp, for example, from wood,with mineral acids. The properties of the resulting particlesare influenced by the conditions of the hydrolysis process.17

Typical MCC features particles with dimensions on the orderof 10-100 µm.18 However, the material can be dispersedby ultrasonication so that mainly nanowhiskers with dimen-sions on the order of 20 × 200 nm are obtained.18,19 Thenanowhiskers produced here from MCC were of similardimensions (23 × 260 nm, Figure 1a). The main applicationsof MCC are as an excipient in the formulation of tablets,emulsifier, stabilizer, and anticaking agent. The commercialavailability of MCC has also triggered significant interest inits use as reinforcing filler in polymer composites.20-22

Unfortunately, the dramatic reinforcement effects displayedby cellulose nanowhiskers from other sources have hitherto

* To whom correspondence should be addressed. Tel.: (216) 368 6374.E-mail: christoph.weder@case.edu.

† These authors contributed equally.‡ Department of Macromolecular Science and Engineering, Case Western

Reserve University.§ Department of Biomedical Engineering, Case Western Reserve University.| Louis Stokes Cleveland DVA Medical Center.⊥ Department of Chemistry, Case Western Reserve University.

Biomacromolecules 2009, 10, 712–716712

10.1021/bm8010903 CCC: $40.75 2009 American Chemical SocietyPublished on Web 03/03/2009

not been observed in the case of MCC-based composites.Wu et al. attributed this shortcoming to the inability of MCCto form percolating fibrous networks within the nanocom-posites.21 The present study supports this finding for materialsthat comprise small volume fractions of ultrasonicated, butnot fractionated MCC dispersions. We further demonstratethat MCC nanocomposites with properties that appear toreach the theoretical limit can be fabricated by fractionationof the MCC and using the template approach.

Experimental Section

Materials. All reagents, except acetone, were used as received.Dimethyl formamide (DMF, water <50 ppm), acetone (dried withpotassium carbonate), sulfuric acid, and potassium hydroxide werepurchased from Sigma Aldrich (Milwaukee, WI). The ethylene oxide/epichlorohydrin copolymer (EO-EPI copolymer, Epichlomer, comono-mer ratio ) 1:1, δ ) 1.39 g/mL) was received from Daiso Co. Ltd.(Osaka, Japan). Cotton nanowhiskers were isolated from Whatman filterpaper and lyophilized as previously described.14a,23 Microcrystallinecellulose (MCC) was received from FMC Biopolymer under the brandname Avicel (Lattice NT-100). A value of 1.46 g/mL was assumedfor the density of crystalline cellulose nanowhiskers.24

Instrumentation. Transmission electron micrographs (TEMs) wereacquired using a JEOL 1200EX Transmission Electron Microscope.Briefly, TEM samples were prepared by deposition of 5 µL (∼0.01mg/mL) of the appropriate nanowhisker dispersions on Formvar/carbon-coated copper grids (aqueous dispersions) or a 400 mesh carbon-coatedcopper grid (DMF dispersions). After 2 min, the excess dispersion wasremoved from the grids with a small piece of filter paper. Next, sampleswere stained using a standard uranyl acetate negative staining method(three 5 min treatments with 1% uranyl acetate)25 and were then allowedto dry for 15 min. For ultrasonication of nanowhisker dispersions, a

Fischer Scientific FS60H ultrasonic bath (100 W, 9.5 L bath) was used.Mechanical measurements were performed on rectangular nanocom-posite films (ca. 15 × 3 x 0.30 mm) using a TA Instruments DMA2980.

Cotton Cellulose Nanowhiskers. Cellulose nanowhiskers fromcotton were prepared using the procedure by Dong et al.23 with minormodifications. Briefly, 5.2 g of Whatman No. 1 filter paper wascombined with 250 mL of deionized water and blended in a Waringblender at high speed until a lumpy pulp was formed. In a beaker,sulfuric acid (98%, 140 mL) was slowly added under vigorousmechanical stirring to the cooled filter paper pulp (250 mL, 20 °C).After this addition, the suspension was heated to 50 °C for 3.5 h whilestirring. The mixture was then cooled to room temperature, filteredover a small-pore fritted glass filter, and washed with deionized wateruntil the pH was neutral. The resulting dispersion was then dialyzed infour successive 24 h treatments with deionized water to remove anyremaining salts and sonicated for approximately 7 h. After the dispersionwas left to settle at ambient temperature for at least 16 h, the supernatantdispersion was decanted off. The concentration of the nanowhiskers inthat dispersion was determined gravimetrically to be ∼20 mg/mL.Dispersions of this concentration were used for the fabrication of gels.Further, aliquots of this solution were lyophilized and the aerogel thusproduced was dispersed in DMF at a concentration 5 mg/mL viasonication for approximately 7 h. These DMF solutions were employedfor the production of solution cast nanocomposites.

Dispersion of MCC in Solvents. The MCC powder received fromFMC Biopolymer had a particle size of the order of 100 µm, with apH of 6.6. The MCC was added to deionized water at a concentrationof 20-21 mg/mL, or to DMF at a concentration of 15 mg/mL, andwas dispersed via ultrasonication for 4-6 h. The temperature of thewater bath increased during sonication and was not monitored norcontrolled. The suspensions were allowed to settle overnight (typically12 h) before the well-dispersed top layer was collected by decanting,

Figure 1. Transmission electron microscopy (TEM) images of cellulose nanowhiskers prepared by (a) dispersion of microcrystalline cellulose(MCC) in water and subsequent fractionation; (b) dispersion of microcrystalline cellulose (MCC) in DMF; (c) hydrolysis of cotton and dispersionin water; scale bars (a,c) ) 500 nm; (b) ) 2 µm.

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leaving behind any sediments at the bottom (especially in the case ofaqueous dispersions). The final concentrations of the nanowhiskerdispersions created from MCC dispersions were determined gravi-metrically to be 5.0 g/mL (stder ) 1.3, N ) 12) and 15 mg/mL (stder) 0.5, N ) 12) in water and DMF, respectively. The dimensions ofthe isolated nanowhiskers were evaluated with TEM.

Formation of Cotton Nanowhisker Organogels. Cotton whiskerorganogels were prepared from aqueous dispersions using a solvent-exchange sol-gel process, previously described.14a

Formation of MCC Nanowhisker Organogels. MCC nanowhisker/acetone gels were prepared in a similar fashion as the cottonnanowhisker gels with slight modifications, that is, by using a solvent-exchange sol-gel process in which gelation was induced through theaddition of a water-miscible nonsolvent to the whisker dispersion.14a

In a typical example, the aqueous MCC nanowhisker dispersion (5.0mg/mL) was heated to evaporate water and increase the MCCconcentration to 7.4 mg/mL. A total of 150 mL of this dispersion wasadded to a large beaker (1000 mL), followed by brief sonication toremove air bubbles. After cooling to room temperature (RT; ∼23-25°C), acetone (850 mL) was gently added on top of the aqueous MCCnanowhisker dispersion to form an organic layer on top of the aqueousdispersion. The organic layer was exchanged 1-2 times daily untilthe bottom portion had assembled into a mechanically coherentnanowhisker-acetone gel (typically 4-5 days). During that process,the acetone layer was gently agitated (1-2 times daily) to facilitatethe solvent exchange. The absence of refractive index gradients at thesol/gel interface was taken as an indication that the solvent exchangewas complete. At this point, the MCC nanowhisker gel was releasedfrom the beaker, and the solvent was exchanged two more times withdry acetone (overnight, in same beaker). The resulting MCC nano-whisker gel was cut into pieces of about 1 × 0.75 × 1.5 cm for polymerinfusion.

Determination of Cellulose Content in Organogels. The cottonnanowhisker or MCC nanowhisker content of the organogels wasdetermined gravimetrically. The gels were weighted in their swollenand dried state and the whisker to total weight ratio was determined asan average of at least three independently prepared samples.

Fabrication of Polymer/Cellulose Nanocomposites by SolutionCasting. Lyophilized cotton nanowhiskers or MCC (vide supra) weredispersed in DMF at a concentration of 5 or 15 mg/mL for cotton andMCC, respectively. EO-EPI was dissolved in DMF (5% w/w) by stirringfor two days. Nanocomposites were prepared by combining the desiredamounts (to yield materials containing 0.9-33.3% v/v whiskers) ofthe colloidal nanowhisker dispersion and polymer solution and solution-casting the resulting mixture into Teflon Petri dishes. The dishes wereplaced into a vacuum oven (60 °C, 15 mbar, 48 h) to evaporate thesolvent and dry the resulting films before the material was compression-molded between spacers in a Carver laboratory press (at 80 °C and6000 psi for 2 min) to yield 300-400 µm thin nanocomposite filmswhich were stored in a vacuum oven (40 °C, 15 mbar) until they weretested.

Fabrication of Polymer/Cellulose Nanocomposites byTemplate Approach. Cotton or MCC nanowhisker acetone gels,prepared as described above, were placed at room temperature intosolutions of between 1.0 and 30.0 mg/mL of EO-EPI in tetrahydrofuranfor 16-36 h. The gels were subsequently removed from the polymersolutions and dried at room temperature in air for up to 2 h to remove(most of) the solvent before the material was compression-molded at60 °C between spacers (above the Tg of the neat polymer at 9000 psi)for 2 min to yield 300-400 µm thin nanocomposite films which werestored in a vacuum oven (40 °C, 15 mbar) until they were tested. Thenanowhisker content of the nanocomposites was determined gravi-metrically from the weights of the wet acetone gel and the final driedmaterial.

Dynamic Mechanical Thermal Analyses (DMTA). DMTA mea-surements were performed on rectangular films (ca. 15 × 3 × 0.3 mm)using a TA Instruments DMA 2980 in tensile mode with an oscillation

frequency of 1 Hz, a static force of 10 mN, an oscillation amplitude of15.0 µm, and an automatic tension setting of 125%. Measurements werecarried out at a heating rate of 3°/min (range of 15-45 °C). Shearstorage moduli G′ were calculated from the experimentally determinedtensile storage moduli E′, utilizing the relationship E′ ) 2G′(ν + 1),where ν ) 0.3 is the Poisson’s ratio.26

Conductometric Titration of Cotton and MCC Nanowhiskers.Surface charge densities of both cellulose nanowhiskers derived from

cotton and MCC were quantified by conductometric titration to betterunderstand their ability to disperse in aqueous and organic solvents.Between 6.6 and 8.8 mL of aqueous dispersions of either cellulosesource (∼15 mg/mL) was placed into a 250 mL beaker with ∼200 mLof deionized water (in the case of the MCC, 0.3 mL of 0.01 M HClwas added to the beaker to ensure a counterion for titration).Suspensions were placed on a magnetic stir plate, and stirred duringthe entire titration to increase homogeneity. Ionic equilibrium wasdetermined from measurements of pH and conductivity made against50 µL additions of 0.01 M KOH using an Accumet AR50 (FisherScientific; accuTupH pH probe #13-620-183; accumet conductivityprobe #13-620-163).

Results and Discussion

The analysis of transmission electron micrographs (TEMs)reveals that the nanowhiskers produced through sonication ofcommercially available MCC in water and subsequent fraction-ation (cf. Experimental Section, yield 25%) exhibit a width (d)of ∼23 ( 1 nm and a length (L) of ∼260 ( 12 nanometers(Figure 1a, L/d ) 11; N ) 32). Unfractionated dispersions ofMCC in DMF appear homogeneous to the eye and do not showany settlements upon standing for several days. TEM imagesdisplay well separated nanowhiskers of similar dimensions andalso occasional larger aggregates (Figure 1b). Attempts toseparate these aggregates by filtration showed only a minor (ofthe order of 10%) weight loss, suggesting that a substantialfraction of the MCC has indeed been dispersed into nanoscalewhiskers. The MCC nanowhiskers display similar dimensionsas cellulose nanowhiskers derived from cotton (Figure 1c, d )20 ( 1 nm, L ) 210 ( 19 nm, and L/d ) 10.5; N ) 106). TheTEMs of both cellulose sources reveal that MCC nanowhiskersmore readily forms small bundles or fibers, compared to thewell-individualized nanowhiskers obtained from cotton. Thelatter were isolated by hydrolysis with sulfuric acid, whichintroduces negatively charged sulfate groups to the whiskersurface (∼67 mmol SO4

-/Kg cellulose). The electrostaticrepulsion among these groups greatly enhances the whiskerdispersibility in aqueous and organic solvents,4,27 which isinstrumental for the formation of nanocomposites with welldispersed whisker networks.4,7,9,14,16 Conductometric titrationrevealed no net surface charge for the MCC nanowhiskers usedhere. This major difference in surface charge density is the resultof different hydrolysis protocols and likely to be a key factorfor differences in their dispersibility and the morphology ofpolymer nanocomposites produced from such dispersions (videinfra).

To investigate to what extent the successful processingprotocols for nanocomposites comprising cellulose nanowhiskersisolated from tunicates and cotton (solution-casting from di-methyl formamide, DMF, and the template approach) could beapplied to MCC, we prepared a series of nanocomposites basedon a rubbery 1:1 ethylene oxide-epichlorohydrin copolymer(EO-EPI). Given the similar dimensions of cotton-based andMCC derived nanowhiskers, these two fillers were studied in acomparative mode. Between 0 and 35% v/v of either cellulosetype were incorporated into the matrix polymer via solution

714 Biomacromolecules, Vol. 10, No. 4, 2009 Communications

casting from DMF. The mechanical properties of these materialswere established by dynamic mechanical thermal analysis(DMTA). Figure 2 shows the shear storage moduli (Gc′) of dryEO-EPI nanocomposites extracted from the DMTA traces fora temperature of 25 °C, that is, in the rubbery regime of thematrix. In case of the cotton nanowhisker nanocomposites, Gc′increased with the nanowhisker content from 1.6 (neat polymer)to 43 MPa (24% v/v whiskers). By contrast, Gc′ of the MCCnanowhisker nanocomposites increased from 1.6 MPa (neatpolymer) to just 17 MPa at a similar whisker content (25% v/vMCC). Thus, while in both cases a significant increase instiffness is observed, the reinforcing effect of the cottonnanowhiskers is more than twice as large as that observed forthe MCC.

The reinforcement observed in the cotton nanowhiskernanocomposites is, as we demonstrated before,14 related to theformation of a percolating nanofiber network in which stresstransfer is facilitated by hydrogen-bonding between the nano-whiskers. Under these circumstances, the mechanical propertiescan be predicted by calculations obtained using a percolationmodel.16 Within the framework of the model, Gc′ can beexpressed as28,29

with

where ψ is the volume fraction of nanowhiskers that participatein the load transfer, Xr is the volume fraction of the randomlyorientated filler, G′s is the experimentally determined shearstorage modulus of the neat EO-EPI (1.6 MPa), and Xc is thecritical whisker percolation volume fraction calculated by 0.7/A. A is the aspect ratio of the filler (10.5 for cotton nanowhiskersand 11 for MCC nanowhiskers). The shear storage modulus ofthe network formed by the rigid phase, G′r, for the EO-EPI/

cotton whisker nanocomposites was determined to be 250 MPafrom a least-squares fit of eq 1.14a The fit utilized experimentalvalues for A, Xc, Xr, and G′s and experimental results for G′c.The determined value for G′r was slightly higher than the valuereported by Yamanaka et al. for cotton whiskers (85 MPa).30

While the experimental results for the solution-cast EO-EPI/cotton nanowhisker nanocomposites match with the percolationmodel (above the onset of percolation),14a the solution-cast EO-EPI/MCC nanocomposites do not exhibit the predicted rein-forcement (Figure 2). The limited reinforcing effect of the MCCnanowhiskers can, in principle, be related to a lower stiffnessof the individual nanofibers, lower interactions among them(and/or with the matrix) when incorporated into the polymermatrix, or as discussed above and suggested by others,21 stifledformation of a percolating network due to particle aggregation.Note that below the percolation threshold, the nanocompositessurpass the predictions of the percolation model, which neglectsthe reinforcing effect achieved by the incorporation of nonin-teracting reinforcing agents.31

As pointed out above, TEM images of the neat MCCnanowhiskers (Figure 1), and the absence of surface chargesindeed suggest that aggregation may be at play. Moreover, thedata points of the solution-cast MCC nanowhisker nanocom-posites (Figure 2, open circles) would be difficult to fit to thepercolation model, even if a lower intraparticle interactionstrength or lower nanofiber stiffness was assumed. The data areconsistent with the hypothesis that at low MCC concentrations,the fraction of not dispersed MCC particles plays a morepronounced role than at higher concentrations, in that it lowersthe actual contribution of nanowhiskers that participate in thepercolating network. Finally, the solution-cast EO-EPI nano-composite comprising 35% v/v MCC reached a Gc′ of 73 MPa,matching that of a cellulose nanowhisker nanocomposite ofsimilar concentration; because at high loading levels increasedfiller content only marginally increases Gc′, this data point seemsto suggest that at higher loading levels percolation is in factachieved in the MCC-based nanocomposites. To demonstratethis point, we sought to compare the properties of nanocom-posites fabricated from preformed percolating networks of cottonand MCC nanowhiskers, respectively, utilizing the templateapproach.14a Despite their rather low aspect ratio, cellulosenanowhiskers isolated from cotton are able to form robustmacroscopic gels (Figure 3) if the dispersing solvent (water) iscarefully exchanged with a miscible nonsolvent (acetone). Wepreviously exploited the fact that such gels form porous scaffoldsand can be imbibed with any polymer if placed in a solventthat does not redisperse the nanowhiskers (see ExperimentalSection for nanocomposite fabrication).14a Unfortunately, onlynanowhisker-rich compositions could be created on account ofthe high molecular weight of the host polymer used (resultingin high viscosity solutions).14a Indeed here, EO-EPI/cottonwhisker nanocomposites created with the template approachexhibit the predicted reinforcement of the percolation modeland match the mechanical properties of solution-cast materials

Figure 2. Shear storage moduli, Gc′, of EO-EPI nanocompositescomprising either cellulose nanowhiskers isolated from cotton (tri-angles) or microcrystalline cellulose (MCC, circles) at 25 °C. Thenanocomposites were created via either solution-casting (openshapes) or the template approach (filled shapes). The experimentaldata were fit to the percolation model for mechanical reinforcement(solid line). Error bars represent standard error, and are only shownfor samples with at least three repeated measurements.

Gc′ )

(1 - 2ψ + ψXr)G′sG′r + (1 - Xr)ψG′r2

(1 - Xr)G′r + (Xr - ψ)G′s(1)

ψ ) Xr(Xr - Xc

1 - Xc)0.4

(2)

Figure 3. Pictures of cellulose gels created from nanowhiskersisolated from cotton (left) or microcrystalline cellulose (MCC, right).

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(Figure 2).14a For template-made EO-EPI/cotton whisker nano-composites, Gc′ increases from 1.6 MPa (neat polymer) to 56MPa for a 32.4% v/v cotton whisker nanocomposite, and up to74 MPa for material comprising 48.1% v/v whiskers. Weproduced MCC gels in the same manner (Figure 3) and wereable to fabricate EO-EPI/MCC nanocomposites by the templateapproach. These materials display significantly higher modulithan the solution-cast materials. For example, the Gc′ of EO-EPI/MCC nanocomposites with ∼25% v/v MCC increased from18 MPa for solution-cast materials to 39 MPa for template-made materials. Figure 2 shows that Gc′ of EO-EPI/MCCnanocomposites created with the template approach follows thepredicted reinforcement of the percolation model. EO-EPI/MCCnanocomposites with 42.3% v/v MCC reach a Gc′ of 73 MPa,which is similar to the 74 MPa for the nanocomposite compris-ing 48.1% v/v cotton whiskers.

The data shown in Figure 2 clearly demonstrate that ifappropriately processed, for example, by fractionating thenanowhiskers and employing the template approach, MCC-basednanocomposites can display virtually identical mechanicalproperties as nanocomposites comprising cellulose nanowhiskersisolated from cotton. The excellent agreement of the experi-mental Gc′ with predictions of the percolation model suggeststhat the percolating network of the MCC nanoparticles formedin a sol/gel process is maintained through the steps of imbibingwith polymer, drying, and compression molding into filmsamples. The results imply that the percolating network formedby the MCC fibrils is comparable to that of cellulose isolatedfrom cotton.

Conclusions

The ability to produce polymer nanocomposites, whichcomprise a percolating, three-dimensional network of well-individualized nanofibers, is important to diverse areas ofpolymer science. While MCC has been previously shown toimprove the mechanical properties of polymer composites, ithas thus far not been reported to form fibrous percolatingnetworks within the nanocomposites. This limitation has resultedin polymer composites that did not exploit the full reinforcingpotential of MCC. Through the utilization of optimized process-ing conditions, nanowhisker fractionation and the templateapproach, we here describe for the first time the formation ofEO-EPI/MCC nanocomposites, which achieve the maximummechanical reinforcement predicted by the percolation model.The materials reported display significantly improved mechan-ical properties, which are of interest in their own right. However,more importantly, the application of the template approach toMCC nanocomposite fabrication promises to expand upon theabundant uses of MCC in composite applications, while furthersupporting the significance of the newly developed technique.

Acknowledgment. We thank Dr. Midori Hitomi for the TEMcharacterization and acknowledge generous financial supportthrough an Ohio Innovation Incentive Fellowship (to K.S.), a

SOURCE fellowship (to S.S.), and from the Department ofVeterans Affairs Career Development Program (to J.C.).

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