This work is funded in part by the USDA National Institute for Food and Agriculture, National Competitive Grants Program, National Research Initiative Program 71.1 FY 2007 as Grant No. 2007-35503-18392, and National Institutes of Health, Institute for Allergy and Infectious Disease, R33AI94514-03.

1. Spinning Dope Preparation
<ol>
	<li>Prepare a range of biopolymer concentrations to be investigated (0.1% to 30%, w/v) and be sure to consider moisture content of the biopolymer powder in these calculations. For each concentration, weigh the biopolymer (starch or pullulan) powder into a 50 ml test tube. Add aqueous dimethyl sulfoxide (DMSO) solution and a stir bar.</li>
	<li>Place the tube into boiling water with constant stirring on a magnetic stirrer hotplate.</li>
	<li>After about 1 hr, turn off heat and allow the dispersion to cool to room temperature. The dispersion is then ready for rheological testing and electrospinning.</li>
</ol>
2. Steady Shear Rheology
<ol>
	<li>Warm up the rheometer and set the stage temperature at 20 &#176;C. Calibrate the gap between the probe (25 mm cone used) and the stage (plate).</li>
	<li>Load 0.41 ml of the biopolymer dispersion onto the center of the stage and lower the probe to set the position (0.053 mm gap for 25 mm cone). Make sure that the dispersion evenly spreads within the gap.</li>
	<li>Perform the rheological test with the following experimental parameters: sweep mode: log, initial rate: 100 sec-1, final rate: 0.1 sec-1, points per decade: 10, delay before measure: 5 sec, measure time: 10 sec, and directions per measure: two (both clockwise and counterclockwise).</li>
	<li>Analyze rheological data to estimate appropriate dispersion concentrations for electrospinning trials.
	<ol>
		<li>Plot apparent shear viscosities against shear rates as a function of polymer concentrations. For each flow curve, approximate zero shear viscosities, &#951;0, by the actual or extrapolated values (e.g., at low concentrations where the low shear rate data are unreliable) for apparent viscosity at 0.1 sec&#8722;1.</li>
		<li>Calculate specific viscosity: &#951;sp = (&#951;0&#8722; &#951;s)/&#951;s, where &#951;s is the viscosity of the solvent.</li>
		<li>Plot specific viscosities as a function of concentration. Identify semidilute unentangled and entangled regimes. The semidilute unentangled regime begins from the low concentration end with a small slope, and the semidilute entangled regime has a greater slope following the unentangled regime. Fit power-law regression models in both regimes. The power values are the slopes (concentration dependence) in semidilute unentangled and entangled regimes on a log-log plot. The intersection of the two fitted lines is the entanglement concentration, ce.</li>
	</ol>
	</li>
</ol>
3. Electrospinning Parameter Variation
<ol>
	<li>Assemble the electrospinning setup as shown in Figure 1. Load the syringe with dispersion of appropriate composition, e.g., 15% (w/v) starch or pullulan in 100% DMSO, onto the syringe pump. Clip the high voltage wire (positive) to the needle. Connect the coagulation bath containing pure ethanol to ground by immersing the ground wire (negative) into the bath. Use a lab jack to adjust the distance between the syringe needle and coagulation bath. Immerse a metal mesh in the bath to collect the fiber mat after electrospinning.</li>
	<li>Spin the biopolymer in the following parameter ranges: feed rate from 0.1 to 0.4 ml/hr, spinning distance from 5 to 10 cm, and voltage from 0 to 15 kV.
	<ol>
		<li>Start with a spinning distance of 5 cm. For the first feed rate (0.1 ml/hr), ramp the voltage up slowly from 0 V. Pay attention to the shape of the dispersion extruded at the needle tip and note when the dripping dispersion is accelerated and then elongated.</li>
		<li>Note the voltage at which a tiny jet initiated from the drop surface, indicating electrospinnability of the solution. Record the voltage at which a continuous jet initiates, if any.</li>
		<li>Examine the complete range for each of the three parameters and note successful spinning conditions. Collect the fibers only when there is a continuous jet from the tip.</li>
	</ol>
	</li>
	<li>After a few minutes of collecting, rinse the fiber mat with pure ethanol. Place the fiber mat into a desiccator containing desiccant under vacuum.</li>
	<li>Repeat for each biopolymer concentration for complete characterization.</li>
</ol>
<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/51933/51933fig1highres.jpg" width="500" /> 
Figure 1.&#160;Schematic drawing of the electro-wet-spinning setup. The biopolymer dispersion is extruded from a syringe pump. A high voltage DC power supply provides high voltage to the blunt needle and grounds the coagulation bath. The polymer jet from the needle tip travels through a straight path and then develops a rapid whipping path (aka whipping instability).
4. Morphological Characterization
<ol>
	<li>Cut a piece of dried fiber mat and immobilize it onto a SEM stub using carbon tape.</li>
	<li>Load the sample stub into the SEM instrument and obtain images for analysis.</li>
</ol>

<ol>
	<li>Greiner, A., Wendorff, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+self-assembled+nanofibers+by+electrospinning.">Functional self-assembled nanofibers by electrospinning.</a> Self-aseembled nanomaterials. 1, 107-171 (2008).</li><li>Ramakrishna, S., Fujihara, K., Teo, W. E., Lim, T. C., Ma, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> An Introduction to Electrospinning and Nanofibers. , (2005).</li><li>Klossner, R. R., Queen, H. A., Coughlin, A. J., Krause, W. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlation+of+Chitosan&#8217;s+Rheological+Properties+and+Its+Ability+to+Electrospin.">Correlation of Chitosan&#8217;s Rheological Properties and Its Ability to Electrospin.</a> Biomacromolecules. 9 (10), 2947-2953 (2008).</li><li>McKee, M. G., Wilkes, G. L., Colby, R. H., Long, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlations+of+Solution+Rheology+with+Electrospun+Fiber+Formation+of+Linear+and+Branched+Polyesters.">Correlations of Solution Rheology with Electrospun Fiber Formation of Linear and Branched Polyesters.</a> Macromolecules. 37 (5), 1760-1767 (2004).</li><li>McKee, M. G., Hunley, M. T., Layman, J. M., Long, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solution+rheological+behavior+and+electrospinning+of+cationic+polyelectrolytes.">Solution rheological behavior and electrospinning of cationic polyelectrolytes.</a> Macromolecules. 39 (2), 575-583 (2006).</li><li>Kong, L., Ziegler, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+pure+starch+fibers+by+electrospinning.">Fabrication of pure starch fibers by electrospinning.</a> Food Hydrocolloids. 36, 20-25 (2014).</li><li>Singh, R. S., Saini, G. K., Kennedy, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pullulan:+microbial+sources,+production+and+applications.">Pullulan: microbial sources, production and applications.</a> Carbohydrate Polymers. 73 (4), 515-531 (2008).</li><li>Leathers, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biotechnological+production+and+applications+of+pullulan.">Biotechnological production and applications of pullulan.</a> Applied Microbiology and Biotechnology. 62 (5), 468-473 (2003).</li><li>Karim, M. R., Lee, H. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+characterization+of+electrospun+pullulan/montmorillonite+nanofiber+mats+in+aqueous+solution.">Preparation and characterization of electrospun pullulan/montmorillonite nanofiber mats in aqueous solution.</a> Carbohydrate Polymers. 78 (2), 336-342 (2009).</li><li>Stijnman, A. C., Bodnar, I., Hans Tromp, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrospinning+of+food-grade+polysaccharides.">Electrospinning of food-grade polysaccharides.</a> Food Hydrocolloids. 25 (5), 1393-1398 (2011).</li><li>Kong, L., Ziegler, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+molecular+entanglements+in+starch+fiber+formation+by+electrospinning.">Role of molecular entanglements in starch fiber formation by electrospinning.</a> Biomacromolecules. 13 (8), 2247-2253 (2012).</li><li>Kong, L., Ziegler, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rheological+aspects+in+fabricating+pullulan+fibers+by+electro-wet-spinning.">Rheological aspects in fabricating pullulan fibers by electro-wet-spinning.</a> Food Hydrocolloids. 38, 220-226 (2014).</li><li>Han, C. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Fiber Spinning Rheology and Processing of Polymeric Materials: Volume 2: Polymer Processing. , 257-304 (2007).</li><li>Morris, E. R., Cutler, A. N., Ross-Murphy, S. B., Rees, D. A., Price, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Concentration+and+shear+rate+dependence+of+viscosity+in+random+coil+polysaccharide+solutions.">Concentration and shear rate dependence of viscosity in random coil polysaccharide solutions.</a> Carbohydrate Polymers. 1 (1), 5-21 (1981).</li><li>Thompson, C. J., Chase, G. G., Yarin, A. L., Reneker, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+parameters+on+nanofiber+diameter+determined+from+electrospinning+model.">Effects of parameters on nanofiber diameter determined from electrospinning model.</a> Polymer. 48 (23), 6913-6922 (2007).</li></ol>

The authors declare that they have nothing to disclose.

Rheology is an essential tool to study the processing of polymers, including conventional fiber spinning and electrospinning13. From the steady shear rheological studies, polymer conformation and their interactions in different solvents can be resolved (Figures 2&#160;and&#160;3). At concentrations not high enough for biopolymer molecules to overlap with one another, their concentration dependence was around 1.4 (Figure 3), which was in good agreement with reported values of other polymers in good solvent3,4. After the biopolymer molecules start to entangle, the specific viscosity showed a much higher dependence on concentration. A greater n value indicates a stronger intermolecular interaction. Many random coil polysaccharides showed similar concentration dependence, with an n value of approximately 3.3&#160;14. Pullulan showed stronger interaction than starch in solvents of high DMSO content, possibly due to the molecular nature of the two biopolymers. The starch used had some highly branched components (~20% amylopectin), while the pullulan should be linear. Of course, the molecular weights, which were unknown, would also have an influence.
The entanglement concentration would depend on the conformation of the biopolymer in the dispersion. For example, the entanglement concentration of starch in 92.5% (w/v) DMSO aqueous solution is much lower than that in pure DMSO11. It implies that starch molecules exist in a more extended conformation in 92.5% (w/v) DMSO aqueous solution so that they occupy a larger hydrodynamic volume and tend to overlap more easily. The entanglement concentrations of pullulan did not vary as drastically as those of starch with varying solvent quality, probably because both water and DMSO are good solvents for pullulan and have little effect on the molecular conformation. Water, which is not a good solvent for starch, made the scenario much complicated, since undissolved starch molecules would affect the rheological response.
To spin good fibers, the concentration had to be 1.2-2.7 and 1.9-2.3x&#160;the entanglement concentration for starch and pullulan, respectively (Figures 4 &#38; 5). This range is narrower for pullulan, probably also due to less conformation difference in the solvents. It was interesting to note that a dispersion at entanglement concentration, when polymers start to entangle with one another, was not electrospinnable. Probably, high shear force involved in electrospinning impede chain overlap and long range polymer interaction that might have already been established at static and low shear conditions, and thus an enhanced and sufficient entanglement is required. In addition, shear viscosity also played an important role (Figure 6). The electrospinnable starch and pullulan dispersions fall into a similar range of shear viscosity at 100 sec-1, with an upper boundary of 2.2 Pa&#183;sec.
The procedure described herein can be modified in correspondence with the equipment and materials used in other studies. The dissolution of polymers is the first critical step in this protocol, because we found that partially dissolved starch dispersions (e.g., in 85% (w/v) DMSO) produced unstable steady shear viscosity data that prevented an accurate determination of ce. While conducting steady shear measurements, we prefer to start from the highest shear rate. By doing so, the dispersion is evenly distributed within the gap by the help of a high shear rate. The electrospinning step required much practice. Attention should be paid to the shape change of the droplet at the needle tip. Safety precautions during electrospinning should not be neglected. The main danger of electrospinning comes from the high voltage used in the process, although the current is relatively low. Electrospinning experiments should be performed in a fume hood in order to expel solvent vapor that may pose health hazards if one is exposed to it for a long time. Avoid close distance and even contact between the charged needle tip and the coagulation bath, because these will result in a short and fire hazard.
The rheological methods employed in the current study do have limitations. For instance, it should be noted that the actual shear rate involved in electrospinning is much higher than 100 sec-1&#160;1. In addition to shear rheology studied, elongational rheology, which characterize the stretching of dispersion along the trajectory, may also play an important role15. The rheometer used in this study is not capable of characterizing elongational viscosity.
Rheological studies can provide valuable information on biopolymer conformation in dispersions and their processing properties. This protocol is potentially useful in electrospinning of many other biopolymers and their blends, in terms of solvent system selection, optimization of parameters, and fiber forming mechanism on a molecular level.

Electrospinning is a technique that is capable of producing continuous micro- to nano-scale fibers from a wide variety of materials. It has gained increasing academic and industrial interest1. Though the setup and practice of electrospinning seem straightforward, the ability to predict electrospinnability and control fiber properties remains a challenge. The reason may lie in the fact that there are many factors influencing the electrospinning process2 and the process, especially the path travelled by the fiber, is chaotic1. Often an empirical &#8220;cook-and-look&#8221; approach is used for screening potential electrospinnable materials. However, to gain better control over the electrospinning process and resultant fiber properties, a more complete understanding of the mechanisms that govern electrospinnability is required. Several researchers have found that molecular entanglement of polymers in the spinning dope is an essential prerequisite for successful electrospinning3-5.
Rheology is a powerful tool to probe molecular conformation and interaction in polymer dispersions. For instance, McKee et al. investigated the molecular conformation of linear and branched poly(ethylene terephthalate-co-ethylene isophthalate) copolymers in a solvent containing chloroform/dimethyl terephthalate (7/3, v/v), and determined that the polymer concentration had to be 2-2.5x&#160;the entanglement concentration for successful electrospinning4.
There is currently renewed interest in fibers from biopolymers because of their advantages in biodegradability, biocompatibility, and renewability vis-&#224;-vis their synthetic counterparts. Yet practitioners confront many challenges arising generally from their structural complexity, difficulty in thermal processing and inferior mechanical properties. Starch, found in plant tissues, is among the most abundant and inexpensive biopolymers on earth. Pure starch fibers fabricated using an electro-wet-spinning apparatus were recently described6. Pullulan is a linear polysaccharide produced extracellularly by certain bacteria. The regular alternation of (1&#8594;4) and (1&#8594;6) glucosidic bonds are believed to be responsible for several distinctive properties of pullulan, including excellent fiber/film forming capability7,8. Electrospinning of pullulan fibers from aqueous dispersion has been reported by a number of researchers9,10. In our previous publications, the electrospinnability of two biopolymers, starch11 and pullulan12, has been discussed. This report focuses on demonstrating the protocol for utilizing rheological principles in the investigation of the electrospinnability of these two biopolymers.

<table border="0" cellpadding="0" cellspacing="0" width="762">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Name of Reagent/ Equipment</td>
			<td style="width:253px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:175px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Gelose 80 starch</td>
			<td style="width:253px;">Ingredion</td>
			<td style="width:119px;"></td>
			<td>Used as it is</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Pullulan</td>
			<td style="width:253px;">Hayashibara Co. Ltd</td>
			<td style="width:119px;"></td>
			<td>Used as it is</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Dimethyl Sulfoxide</td>
			<td style="width:253px;">BDH Chemicals</td>
			<td style="width:119px;">BDH1115-4LP</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:216px;">Ethanol</td>
			<td style="width:253px;">VWR International</td>
			<td style="width:119px;">89125-172</td>
			<td>200 proof</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;"></td>
			<td style="width:253px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Rheometer</td>
			<td style="width:253px;">TA Instruments</td>
			<td style="width:119px;">ARES&#160;</td>
			<td>50 mm cone and plate geometry</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Syringe (10 mL)</td>
			<td style="width:253px;">Becton, Dickinson and Company</td>
			<td style="width:119px;">309604</td>
			<td>Syringe with Luer-Lok&#174; Tip</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:216px;">High voltage generator</td>
			<td style="width:253px;">Gamma High Voltage Research, Inc.</td>
			<td style="width:119px;">ES40P</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Syringe pump</td>
			<td style="width:253px;">Hamilton Company</td>
			<td style="width:119px;">81620</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Environmental scanning electron microscope</td>
			<td style="width:253px;">FEI Company</td>
			<td style="width:119px;">Quanta 200</td>
			<td>for starch fibers</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Environmental scanning electron microscope</td>
			<td style="width:253px;">Phenom-World</td>
			<td style="width:119px;">Phenom G2 Pro</td>
			<td>for pullulan fibers</td>
		</tr>
	</tbody>
</table>

molecular entanglement and electrospinnability of biopolymers

Electrospinning is a fascinating technique to fabricate micro- to nano-scale fibers from a wide variety of materials. For biopolymers, molecular entanglement of the constituent polymers in the spinning dope was found to be an essential prerequisite for successful electrospinning. Rheology is a powerful tool to probe the molecular conformation and interaction of biopolymers. In this report, we demonstrate the protocol for utilizing rheology to evaluate the electrospinnability of two biopolymers, starch and pullulan, from their dimethyl sulfoxide (DMSO)/water dispersions. Well-formed starch and pullulan fibers with average diameters in the submicron to micron range were obtained. Electrospinnability was evaluated by visual and microscopic observation of the fibers formed. By correlating the rheological properties of the dispersions to their electrospinnability, we demonstrate that molecular conformation, molecular entanglement, and shear viscosity all affect electrospinning. Rheology is not only useful in solvent system selection and process optimization, but also in understanding the mechanism of fiber formation on a molecular level.

Flow curves of the biopolymer dispersions as a function of biopolymer concentration and DMSO concentration in solvent were obtained. Two representative figures show the flow curves of starch (Figure 2A) and pullulan (Figure 2B) as a function of their concentration in pure DMSO solvent. The specific viscosities were plotted against biopolymer concentration (Figure 3A&#160;for starch and Figure 3B&#160;for pullulan). From these plots, entanglement concentrations were obtained as the intercept of the fitted lines in the semidilute unentangled and the semidilute entangled regimes.
<img alt="Figure 2" fo:content-width="5in" src="/files/ftp_upload/51933/51933fig2highres.jpg" width="500" /> 
Figure 2.&#160;Flow curves of (A) Gelose 80 starch and (B) pullulan in pure DMSO as a function of concentration (%, w/v) at 20 &#176;C. In both figures, starch and pullulan of low concentrations were less viscous to produce sufficient torque at low shear rates. These unreliable data were thus not plotted. In general, the two biopolymers showed Newtonian behavior at low concentrations, i.e. the apparent shear viscosity was independent of shear rate. Shear thinning became apparent as their concentration increases, especially beyond 10% (w/v). Yet the shear thinning behavior was weak. The 15% and 20% (w/v) pullulan dispersions only showed the early phase of the power law region upon high shear rates, while the starch dispersions did not show significant reduction in viscosity over the shear rate range from 0.1 to 100 sec-1. Reprinted with permission from ref 11, Copyright (2012) American Chemical Society, and with permission from ref 12, Copyright (2014) Elsevier.
<img alt="Figure 3" fo:content-width="5in" src="/files/ftp_upload/51933/51933fig3highres.jpg" width="500" /> 
Figure 3.&#160;Plot of specific viscosity versus (A) Gelose 80 starch and (B) pullulan concentration in pure DMSO. The slopes of the fitted lines in semidilute unentangled (left side) and the semidilute entangled (right side) regimes indicate the concentration dependence of specific viscosity, aka scaling dependence4. Pullulan showed stronger concentration dependence than starch in the entangled regime. The intercept of the two fitted lines was termed as the entanglement concentration (ce) at which biopolymers start to overlap in the dispersion. Starch required a higher concentration than pullulan to start entangling. Reprinted with permission from ref 11, Copyright (2012) American Chemical Society, and with permission from ref 12, Copyright (2014) Elsevier.
Electrospinning was attempted for all of the biopolymer dispersions, and results judged in terms of electrospinnability, i.e. jet forming ability during electrospinning, and morphology of the fibers formed. A dispersion of good electrospinnability formed a stable and continuous jet that resulted in continuous and smooth fibers without droplets. A dispersion that was not able to electrospin could not form a stable jet or develop whipping instability. Either tiny droplets or thick fibers were deposited into the coagulation bath. Figure 4 shows representative good and poor fibers evaluated from their appearance. Figure 5 summarizes evaluation of electrospinnability at varying concentrations of DMSO in solvent and the biopolymer in dispersion for starch and pullulan, respectively. In addition to entanglement concentrations, shear viscosities at 100 sec-1 were plotted against biopolymer concentration, where regions of electrospinnability were denoted (Figure 6).
<img alt="Figure 4" fo:content-width="5in" src="/files/ftp_upload/51933/51933fig4highres.jpg" width="500" /> 
Figure 4: Scanning electron micrographs of good (left) and poor (right) starch and pullulan fibers. Good fibers are smooth, continuous, and randomly oriented, while poor fibers may have beads, breaks, and droplets as shown in the figure (red circles). (a) 10% (w/v) Gelose 80 starch in 95% (v/v) DMSO, (b) 8% (w/v) Gelose 80 starch in 80% (v/v) DMSO, (c) 17% (w/v) pullulan in 40% (v/v) DMSO, and (d) 9% (w/v) pullulan in 80% (v/v) DMSO. Reprinted with permission from ref 11, Copyright (2012) American Chemical Society, and with permission from ref 12, Copyright (2014) Elsevier.
<img alt="Figure 5" fo:content-width="5in" src="/files/ftp_upload/51933/51933fig5highres.jpg" width="500" /> 
Figure 5.&#160;Evaluation of electrospinnability of (A) Gelose 80 starch and (B) pullulan dispersions as a function of DMSO concentration in solvent and biopolymer concentration in the dispersion: good electrospinnability (circles), poor electrospinnability (diamonds), and unable to electrospin (X&#39;s). Shaded areas roughly represent electrospinnable regions. Entanglement concentrations are also approximately labeled. Reprinted with permission from ref 11, Copyright (2012) American Chemical Society, and with permission from ref 12, Copyright (2014) Elsevier.
<img alt="Figure 6" fo:content-width="5in" src="/files/ftp_upload/51933/51933fig6highres.jpg" width="500" /> 
Figure 6.&#160;Shear viscosity (at 100 sec-1) of (A) Gelose 80 starch and (B) pullulan dispersions as a function of biopolymer concentration in different DMSO/water solvents. Shaded areas roughly represent the electrospinnable region. Reprinted with permission from ref 11, Copyright (2012) American Chemical Society, and with permission from ref 12, Copyright (2014) Elsevier.

Watch this Scientific Journal Video about Molecular Entanglement and Electrospinnability of Biopolymers at JoVE.com

Molecular Entanglement and Electrospinnability of Biopolymers

Electrospinning is a fascinating technique used to fabricate micro- to nano-scale fibers from a wide variety of materials. Molecular entanglement of the constituent polymers in the spinning dope is essential for successful electrospinning. We present a protocol for utilizing rheology to evaluate the electrospinnability of two biopolymers, starch and pullulan.

Electrospinning is a fascinating technique to fabricate micro- to nano-scale fibers from a wide variety of materials. For biopolymers, molecular ...

molecular-entanglement-and-electrospinnability-of-biopolymers

Nanyang Technological University

Research

JoVE Journal

Bioengineering

13.7K Views.  Pennsylvania State University. Electrospinning is a fascinating technique used to fabricate micro- to nano-scale fibers from a wide variety of materials. Molecular entanglement of the constituent polymers in the spinning dope is essential for successful electrospinning. We present a protocol for utilizing rheology to evaluate the electrospinnability of two biopolymers, starch and pullulan.

Video: Molecular Entanglement and Electrospinnability of Biopolymers

Fluorescence Lifetime Imaging of Molecular Rotors in Living Cells

Diffusion is often an important rate-determining step in chemical reactions or biological processes and plays a role in a wide range of intracellular events. Viscosity is one of the key parameters affecting the diffusion of molecules and proteins, and changes in viscosity have been linked to disease and malfunction at the cellular level.1-3 While methods to measure the bulk viscosity are well developed, imaging microviscosity remains a challenge. Viscosity maps of microscopic objects, such as single cells, have until recently been hard to obtain. Mapping viscosity with fluorescence techniques is advantageous because, similar to other optical techniques, it is minimally invasive, non-destructive and can be applied to living cells and tissues.
Fluorescent molecular rotors exhibit fluorescence lifetimes and quantum yields which are a function of the viscosity of their microenvironment.4,5 Intramolecular twisting or rotation leads to non-radiative decay from the excited state back to the ground state. A viscous environment slows this rotation or twisting, restricting access to this non-radiative decay pathway. This leads to an increase in the fluorescence quantum yield and the fluorescence lifetime. Fluorescence Lifetime Imaging (FLIM) of modified hydrophobic BODIPY dyes that act as fluorescent molecular rotors show that the fluorescence lifetime of these probes is a function of the microviscosity of their environment.6-8 A logarithmic plot of the fluorescence lifetime versus the solvent viscosity yields a straight line that obeys the F&ouml;rster Hoffman equation.9 This plot also serves as a calibration graph to convert fluorescence lifetime into viscosity.
Following incubation of living cells with the modified BODIPY fluorescent molecular rotor, a punctate dye distribution is observed in the fluorescence images. The viscosity value obtained in the puncta in live cells is around 100 times higher than that of water and of cellular cytoplasm.6,7 Time-resolved fluorescence anisotropy measurements yield rotational correlation times in agreement with these large microviscosity values. Mapping the fluorescence lifetime is independent of the fluorescence intensity, and thus allows the separation of probe concentration and viscosity effects. 
In summary, we have developed a practical and versatile approach to map the microviscosity in cells based on FLIM of fluorescent molecular rotors.

Fluorescence Lifetime Imaging (FLIM) has emerged as a key technique to image the environment and interaction of specific proteins and dyes in living cells. FLIM of fluorescent molecular rotors allows mapping of viscosity in living cells.

Diffusion is often an important rate-determining step in chemical reactions or biological processes and plays a role in a wide range of intracellular ...

In vitro Assembly of Semi-artificial Molecular Machine and its Use for Detection of DNA Damage

Naturally occurring bio-molecular machines work in every living cell and display a variety of designs 1-6. Yet the development of artificial molecular machines centers on devices capable of directional motion, i.e. molecular motors, and on their scaled-down mechanical parts (wheels, axels, pendants etc) 7-9. This imitates the macro-machines, even though the physical properties essential for these devices, such as inertia and momentum conservation, are not usable in the nanoworld environments 10. Alternative designs, which do not follow the mechanical macromachines schemes and use mechanisms developed in the evolution of biological molecules, can take advantage of the specific conditions of the nanoworld. Besides, adapting actual biological molecules for the purposes of nano-design reduces potential dangers the nanotechnology products may pose. Here we demonstrate the assembly and application of one such bio-enabled construct, a semi-artificial molecular device which combines a naturally-occurring molecular machine with artificial components. From the enzymology point of view, our construct is a designer fluorescent enzyme-substrate complex put together to perform a specific useful function. This assembly is by definition a molecular machine, as it contains one 12. Yet, its integration with the engineered part - fluorescent dual hairpin - re-directs it to a new task of labeling DNA damage12.
Our construct assembles out of a 32-mer DNA and an enzyme vaccinia topoisomerase I (VACC TOPO). The machine then uses its own material to fabricate two fluorescently labeled detector units (Figure 1). One of the units (green fluorescence) carries VACC TOPO covalently attached to its 3'end and another unit (red fluorescence) is a free hairpin with a terminal 3'OH. The units are short-lived and quickly reassemble back into the original construct, which subsequently recleaves. In the absence of DNA breaks these two units continuously separate and religate in a cyclic manner. In tissue sections with DNA damage, the topoisomerase-carrying detector unit selectively attaches to blunt-ended DNA breaks with 5'OH (DNase II-type breaks)11,12, fluorescently labeling them. The second, enzyme-free hairpin formed after oligonucleotide cleavage, will ligate to a 5'PO4 blunt-ended break (DNase I-type breaks)11,12, if T4 DNA ligase is present in the solution 13,14 . When T4 DNA ligase is added to a tissue section or a solution containing DNA with 5'PO4 blunt-ended breaks, the ligase reacts with 5'PO4 DNA ends, forming semi-stable enzyme-DNA complexes. The blunt ended hairpins will interact with these complexes releasing ligase and covalently linking hairpins to DNA, thus labeling 5'PO4 blunt-ended DNA breaks.
This development exemplifies a new practical approach to the design of molecular machines and provides a useful sensor for detection of apoptosis and DNA damage in fixed cells and tissues.

In vitro Assembly of Semi-artificial Molecular Machine and its Use for Detection of DNA Damage

We demonstrate the assembly and application of a molecular-scale device powered by a topoisomerase protein. The construct is a bio-molecular sensor which labels two major types of DNA breaks in tissue sections by attaching two different fluorophores to their ends.

Naturally occurring bio-molecular machines work in every living cell and display a variety of designs 1-6. Yet the development of artificial molecular ...

Low Molecular Weight Protein Enrichment on Mesoporous Silica Thin Films for Biomarker Discovery

The identification of circulating biomarkers holds great potential for non invasive approaches in early diagnosis and prognosis, as well as for the monitoring of therapeutic efficiency.1-3 The circulating low molecular weight proteome (LMWP) composed of small proteins shed from tissues and cells or peptide fragments derived from the proteolytic degradation of larger proteins, has been associated with the pathological condition in patients and likely reflects the state of disease.4,5 Despite these potential clinical applications, the use of Mass Spectrometry (MS) to profile the LMWP from biological fluids has proven to be very challenging due to the large dynamic range of protein and peptide concentrations in serum.6 Without sample pre-treatment, some of the more highly abundant proteins obscure the detection of low-abundance species in serum/plasma. Current proteomic-based approaches, such as two-dimensional polyacrylamide gel-electrophoresis (2D-PAGE) and shotgun proteomics methods are labor-intensive, low throughput and offer limited suitability for clinical applications.7-9 Therefore, a more effective strategy is needed to isolate LMWP from blood and allow the high throughput screening of clinical samples. 
Here, we present a fast, efficient and reliable multi-fractionation system based on mesoporous silica chips to specifically target and enrich LMWP.10,11 Mesoporous silica (MPS) thin films with tunable features at the nanoscale were fabricated using the triblock copolymer template pathway. Using different polymer templates and polymer concentrations in the precursor solution, various pore size distributions, pore structures, connectivity and surface properties were determined and applied for selective recovery of low mass proteins. The selective parsing of the enriched peptides into different subclasses according to their physicochemical properties will enhance the efficiency of recovery and detection of low abundance species. In combination with mass spectrometry and statistic analysis, we demonstrated the correlation between the nanophase characteristics of the mesoporous silica thin films and the specificity and efficacy of low mass proteome harvesting. The results presented herein reveal the potential of the nanotechnology-based technology to provide a powerful alternative to conventional methods for LMWP harvesting from complex biological fluids. Because of the ability to tune the material properties, the capability for low-cost production, the simplicity and rapidity of sample collection, and the greatly reduced sample requirements for analysis, this novel nanotechnology will substantially impact the field of proteomic biomarker research and clinical proteomic assessment.

We developed a technology based on mesoporous silica thin film for the selective recovery of low molecular weight proteins and peptides from human serum. The physico-chemical properties of our mesoporous chips were finely tuned to provide substantial control in peptide enrichment and consequently profile the serum proteome for diagnostic purposes.

The identification of circulating biomarkers holds great potential for non invasive approaches in early diagnosis and prognosis, as well as for the ...

Flexural Rigidity Measurements of Biopolymers Using Gliding Assays

Microtubules are cytoskeletal polymers which play a role in cell division, cell mechanics, and intracellular transport. Each of these functions requires microtubules that are stiff and straight enough to span a significant fraction of the cell diameter. As a result, the microtubule persistence length, a measure of stiffness, has been actively studied for the past two decades1. Nonetheless, open questions remain: short microtubules are 10-50 times less stiff than long microtubules2-4, and even long microtubules have measured persistence lengths which vary by an order of magnitude5-9.
	Here, we present a method to measure microtubule persistence length. The method is based on a kinesin-driven microtubule gliding assay10. By combining sparse fluorescent labeling of individual microtubules with single particle tracking of individual fluorophores attached to the microtubule, the gliding trajectories of single microtubules are tracked with nanometer-level precision. The persistence length of the trajectories is the same as the persistence length of the microtubule under the conditions used11. An automated tracking routine is used to create microtubule trajectories from fluorophores attached to individual microtubules, and the persistence length of this trajectory is calculated using routines written in IDL.
	This technique is rapidly implementable, and capable of measuring the persistence length of 100 microtubules in one day of experimentation. The method can be extended to measure persistence length under a variety of conditions, including persistence length as a function of length along microtubules. Moreover, the analysis routines used can be extended to myosin-based acting gliding assays, to measure the persistence length of actin filaments as well.

A method to measure the persistence length or flexural rigidity of biopolymers is described. The method uses a kinesin-driven microtubule gliding assay to experimentally determine the persistence length of individual microtubules and is adaptable to actin-based gliding assays.

Microtubules are cytoskeletal polymers which  play a role in cell division, cell mechanics, and intracellular transport. Each of these functions requires ...

Aplysia Ganglia Preparation for Electrophysiological and Molecular Analyses of Single Neurons

A major challenge in neurobiology is to understand the molecular underpinnings of neural circuitry that govern a specific behavior. Once the specific molecular mechanisms are identified, new therapeutic strategies can be developed to treat abnormalities in specific behaviors caused by degenerative diseases or aging of the nervous system. The marine snail Aplysia californica is well suited for the investigations of cellular and molecular basis of behavior because neural circuitry underlying a specific behavior could be easily determined and the individual components of the circuitry could be easily manipulated. These advantages of Aplysia have led to several fundamental discoveries of neurobiology of learning and memory. Here we describe a preparation of the Aplysia nervous system for the electrophysiological and molecular analyses of individual neurons. Briefly, ganglion dissected from the nervous system is exposed to protease to remove the ganglion sheath such that neurons are exposed but retain neuronal activity as in the intact animal. This preparation is used to carry out electrophysiological measurements of single or multiple neurons. Importantly, following the recording using a simple methodology, the neurons could be isolated directly from the ganglia for gene expression analysis. These protocols were used to carry out simultaneous electrophysiological recordings from L7 and R15 neurons, study their response to acetylcholine and quantitating expression of CREB1 gene in isolated single L7, L11, R15, and R2 neurons of Aplysia.

Aplysia Ganglia Preparation for Electrophysiological and Molecular Analyses of Single Neurons

Marine snail Aplysia californica has been widely used as a neurobiology model for the studies on cellular and molecular basis of behavior. Here a methodology is described for exploring the nervous system of Aplysia for the electrophysiological and molecular analyses of single neurons of identified neural circuitry.

A major challenge in neurobiology is to understand the molecular underpinnings of neural circuitry that govern a specific behavior. Once the specific ...

Microscale Vortex-assisted Electroporator for Sequential Molecular Delivery

Electroporation has received increasing attention in the past years, because it is a very powerful technique for physically introducing non-permeant exogenous molecular probes into cells. This work reports a microfluidic electroporation platform capable of performing multiple molecule delivery to mammalian cells with precise and molecular-dependent parameter control. The system&#8217;s ability to isolate cells with uniform size distribution allows for less variation in electroporation efficiency per given electric field strength; hence enhanced sample viability. Moreover, its process visualization feature allows for observation of the fluorescent molecular uptake process in real-time, which permits prompt molecular delivery parameter adjustments in situ for efficiency enhancement. To show the vast capabilities of the reported platform, macromolecules with different sizes and electrical charges (e.g., Dextran with MW of 3,000 and 70,000 Da) were delivered to metastatic breast cancer cells with high delivery efficiencies (&#62;70%) for all tested molecules. The developed platform has proven its potential for use in the expansion of research fields where on-chip electroporation techniques can be beneficial.

A microfluidic vortex assisted electroporation platform was developed for sequential delivery of multiple molecules into identical cell populations with precise and independent dosage control. The system&#8217;s size based target cell purification step preceding electroporation aided to enhance molecular delivery efficiency and processed cell viability.

Electroporation has received increasing attention in the past years, because it is a very powerful technique for physically introducing non-permeant ...

Biofunctionalized Prussian Blue Nanoparticles for Multimodal Molecular Imaging Applications

Multimodal, molecular imaging allows the visualization of biological processes at cellular, subcellular, and molecular-level resolutions using multiple, complementary imaging techniques. These imaging agents facilitate the real-time assessment of pathways and mechanisms in vivo, which enhance both diagnostic and therapeutic efficacy. This article presents the protocol for the synthesis of biofunctionalized Prussian blue nanoparticles (PB NPs) - a novel class of agents for use in multimodal, molecular imaging applications. The imaging modalities incorporated in the nanoparticles, fluorescence imaging and magnetic resonance imaging (MRI), have complementary features. The PB NPs possess a core-shell design where gadolinium and manganese ions incorporated within the interstitial spaces of the PB lattice generate MRI contrast, both in T1 and T2-weighted sequences. The PB NPs are coated with fluorescent avidin using electrostatic self-assembly, which enables fluorescence imaging. The avidin-coated nanoparticles are modified with biotinylated ligands that confer molecular targeting capabilities to the nanoparticles. The stability and toxicity of the nanoparticles are measured, as well as their MRI relaxivities. The multimodal, molecular imaging capabilities of these biofunctionalized PB NPs are then demonstrated by using them for fluorescence imaging and molecular MRI in vitro.

This protocol describes the synthesis of biofunctionalized Prussian blue nanoparticles and their use as multimodal, molecular imaging agents. The nanoparticles have a core-shell design where gadolinium or manganese ions within the nanoparticle core generate MRI contrast. The biofunctional shell contains fluorophores for fluorescence imaging and targeting ligands for molecular targeting.

Multimodal, molecular imaging allows the visualization of biological processes at cellular, subcellular, and molecular-level resolutions using multiple, ...

Engineering Molecular Recognition with Bio-mimetic Polymers on Single Walled Carbon Nanotubes

Semiconducting single-wall carbon nanotubes (SWNTs) are a class of optically active nanomaterial that fluoresce in the near infrared, coinciding with the optical window where biological samples are most transparent. Here, we outline techniques to adsorb amphiphilic polymers and polynucleic acids onto the surface of SWNTs to engineer their corona phases and create novel molecular sensors for small molecules and proteins. These functionalized SWNT sensors are both biocompatible and stable. Polymers are adsorbed onto the nanotube surface either by direct sonication of SWNTs and polymer or by suspending SWNTs using a surfactant followed by dialysis with polymer. The fluorescence emission, stability, and response of these sensors to target analytes are confirmed using absorbance and near-infrared fluorescence spectroscopy. Furthermore, we demonstrate surface immobilization of the sensors onto glass slides to enable single-molecule fluorescence microscopy to characterize polymer adsorption and analyte binding kinetics.

We present a protocol for engineering the corona phase of near infrared fluorescent single walled carbon nanotubes (SWNTs) using amphiphilic polymers and DNA to develop sensors for molecular targets without known recognition elements.

Semiconducting single-wall carbon nanotubes (SWNTs) are a class of optically active nanomaterial that fluoresce in the near infrared, coinciding with the ...

Methods for the Self-integration of Megamolecular Biopolymers on the Drying Air-LC Interface

Living organisms that use water are always prone to drying in the environment. Their activities are driven by biopolymer-based micro- and macro-structures, as seen in the cases of moving water in vascular bundles and moisturizing water in skin layers. In this study, we developed a method for assessing the effect of aqueous liquid crystalline (LC) solutions composed of biopolymers on drying. As LC biopolymers have megamolecular weight, we chose to study polysaccharides, cytoskeletal proteins, and DNA. The observation of biopolymer solutions during drying under polarized light reveals milliscale self-integration starting from the unstable air-LC interface. The dynamics of the aqueous LC biopolymer solutions can be monitored by evaporating water from a one-side-open cell. By analyzing the images taken using cross-polarized light, it is possible to recognize the spatio-temporal changes in the orientational order parameter. This method can be useful for the characterization of not only artificial materials in various fields, but also natural living tissues. We believe that it will provide an evaluation method for soft materials in the biomedical and environmental fields.

A method for the drying-induced self-integration of megamolecular biopolymers on the air-liquid crystalline interface is provided here. This methodology will be useful not only for understanding the macroscopic potentials of biopolymers, but also as an evaluation method for soft materials in biomedical and environmental fields.

Living organisms that use water are always prone to drying in the environment. Their activities are driven by biopolymer-based micro- and ...

Bioparticle Microarrays for Chemotactic and Molecular Analysis of Human Neutrophil Swarming in vitro

Neutrophil swarming is a cooperative process by which neutrophils seal off a site of infection and promote tissue reorganization. Swarming has classically been studied in vivo in animal models showing characteristic patterns of cell migration. However, in vivo models have several limitations, including intercellular mediators that are difficult to access and analyze, as well as the inability to directly analyze human neutrophils. Because of these limitations, there is a need for an in vitro platform that studies swarming with human neutrophils and provides easy access to the molecular signals generated during swarming. Here, a multistep microstamping process is used to generate a bioparticle microarray that stimulates swarming by mimicking an in vivo infection. The bioparticle microarray induces neutrophils to swarm in a controlled and stable manner. On the microarray, neutrophils increase in speed and form stable swarms around bioparticle clusters. Additionally, supernatant generated by the neutrophils was analyzed and 16 proteins were discovered to have been differentially expressed over the course of swarming. This in vitro swarming platform facilitates direct analysis of neutrophil migration and protein release in a reproducible, spatially controlled manner.

This protocol generates bioparticle microarrays that provide spatially controlled neutrophil swarming. It provides easy access to the mediators that neutrophils release during migration and allows for quantitative imaging analysis.

Neutrophil swarming is a cooperative process by which neutrophils seal off a site of infection and promote tissue reorganization. Swarming has classically ...

Molecular Entanglement and Electrospinnability of Biopolymers

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Chapters in this video

Fluorescence Lifetime Imaging of Molecular Rotors in Living Cells

In vitro Assembly of Semi-artificial Molecular Machine and its Use for Detection of DNA Damage

Low Molecular Weight Protein Enrichment on Mesoporous Silica Thin Films for Biomarker Discovery

Flexural Rigidity Measurements of Biopolymers Using Gliding Assays

Aplysia Ganglia Preparation for Electrophysiological and Molecular Analyses of Single Neurons

Microscale Vortex-assisted Electroporator for Sequential Molecular Delivery

Biofunctionalized Prussian Blue Nanoparticles for Multimodal Molecular Imaging Applications

Engineering Molecular Recognition with Bio-mimetic Polymers on Single Walled Carbon Nanotubes

Methods for the Self-integration of Megamolecular Biopolymers on the Drying Air-LC Interface

Bioparticle Microarrays for Chemotactic and Molecular Analysis of Human Neutrophil Swarming in vitro