This work was supported by the AFOSR Young Investigator Program under FA9550-12-1-0352 and a 3M Non-Tenured Faculty Award. The authors would like to thank Lalisa Stutts and Janine Tom for helpful discussion relating to this project. The authors thank the Calit2 Microscopy Center and Laser Spectroscopy Facility at the University of California, Irvine for allowing use of its facilities. Hodge Harland and the UCI Physical Sciences Machine Shop are acknowledged for the fabrication of tools. Poly(lactic) acid fibers were generously provided by Teijin Monofilament.

1. Catalyzing Sacrificial Fibers
<ol>
	<li>Wrap the desired amount of poly(lactic) acid fibers around the lower &#190; of customized spindle. Reduce fiber overlap to provide the maximum surface area exposure.</li>
	<li>Mix deionized H2O with 40 ml of Disperbyk 130 in a closed bottle and shake until a homogenous solution is obtained. Then place a 1,000 ml beaker in a water bath at 37 &#176;C and pour trifluoroethanol into the beaker. The amount of H2O and TFE to use depends on the PLA fiber diameter used.
	<table border="1">
		<tbody>
			<tr>
				<td>Fiber Diameter</td>
				<td>Amount of H2O (ml)</td>
				<td>Amount of TFE (ml)</td>
			</tr>
			<tr>
				<td>200</td>
				<td>400</td>
				<td>400</td>
			</tr>
			<tr>
				<td>300</td>
				<td>360</td>
				<td>440</td>
			</tr>
			<tr>
				<td>500</td>
				<td>320</td>
				<td>480</td>
			</tr>
		</tbody>
	</table>
	</li>
	<li>Add the H2O/Disperbyk 187 solution to the beaker and stir until uniform.</li>
	<li>Add 1 g of Malachite Green to the mixture and stir until dissolved.</li>
	<li>Place the custom spindle with fibers in the beaker &#189; inch&#160;from the bottom and attach the spindle to a digital mixer. Then start the digital mixer at 400 rpm.</li>
	<li>Slowly add 1.3 g of tin (II) oxalate (SnOx) catalyst to the mixture. The addition of SnOx must be gradual in order to prevent large agglomerations of material from crashing out of the solution.</li>
	<li>Adjust the pH in the mixture using NaOH until the pH is ~6.8-7.2.</li>
	<li>Secure a lid to the beaker and increase the spindle rotation to 500 rpm&#160;for 24 hr. If an agglomeration of SnOx is observed, manually break it up within the first 2 hr.</li>
	<li>Remove spindle and dry in oven at 35 &#176;C overnight.</li>
	<li>Unwrap and remove excess catalyst from the catalyzed PLA fibers.</li>
</ol>
2. Microvascular Gas Exchange Unit Fabrication
<ol>
	<li>Obtain a pair of laser-cut brass patterning brass plates with the desired microvascular pattern and affix the plates on clip holders.</li>
	<li>Cut a 10 inch&#160;length of catalyzed fiber per microchannel and remove any remaining catalyst using a thicker plate cut to the fiber diameter (draw plate).</li>
	<li>Taper the edges of the fibers by using the tip of a hot glue gun to slowly extrude the fiber tips.</li>
	<li>Thread the fibers through matching holes in the brass patterning plate pairs.</li>
	<li>Screw the plates onto a molding box. Make sure the fibers are not twisted when attaching the plates.</li>
	<li>String the fiber tips through the tuning pegs of the custom tensioning board.</li>
	<li>Tension the PLA fibers until taut. Be careful not to over-tension and snap the fibers.</li>
	<li>Remove excess particulates from the fiber pattern using compressed air.</li>
	<li>Mix polydimethylsiloxane (PDMS) base with curing agent in a 10:1, v:v ratio.</li>
	<li>Degas the mixture under vacuum in a desiccator jar for 10 min.</li>
	<li>Pour the PDMS mixture into the mold box. Do not pour directly over the fibers in order to reduce the trapping of air bubbles.</li>
	<li>Using a 26 G needle, remove any bubbles within the molding box or between the fibers.</li>
	<li>Cure the PDMS mixture at 85 &#176;C for 30 min.</li>
	<li>Unfasten the brass plates from the mold box, making sure not to bend the plates or pull too hard. Remove the cured 1st stage from the mold box.</li>
	<li>Thread the fibers through an RTV end-cap by puncturing holes in the end-cap with a hypodermic needle. Depending on fiber size, use a needle gauge that has at least 2x&#160;the inner diameter of the outer diameter of your fiber. Maintain a similar pattern as the brass patterning plate, but more widely spread out.</li>
	<li>Fasten the end-caps to the ends of a larger mold box and pour a 2nd stage of PDMS.</li>
	<li>Remove any remaining gas bubbles and cure at 85 &#176;C for 30 min.</li>
	<li>Cut any excess PLA fibers from the sample and place in a vacuum oven at 210 &#176;C for 24 hr, or until the PLA fibers have been mostly evacuated.</li>
	<li>If any PLA cannot be removed, gently dissolve out of the microchannels using an injection of 1 ml of chloroform.</li>
</ol>

<ol>
	<li>Bellan, L. M., Singh, S. P., Henderson, P. W., Porri, T. J., Craighead, H. G., Spector, J. A. <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+an+artificial+3-dimensional+vascular+network+using+sacrificial+sugar+structures.">Fabrication of an artificial 3-dimensional vascular network using sacrificial sugar structures.</a> Soft Matter. 5 (7), 1354 (2009).</li><li>Bellan, L. M., Strychalski, E. A., Craighead, H. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nano-channels+fabricated+in+polydimethylsiloxane+using+sacrificial+electrospun+polyethylene+oxide+nanofibers.">Nano-channels fabricated in polydimethylsiloxane using sacrificial electrospun polyethylene oxide nanofibers.</a> J. Vac. Sci. Technol. B Microelectron. Nanometer Struct. Process. Meas. Phenom. 26 (5), 1728 (2008).</li><li>Borenstein, J. T., Weinberg, E. J., Orrick, B. K., Sundback, C., Kaazempur-Mofrad, M. R., Vacanti, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfabrication+of+three-dimensional+engineered+Scaffolds.">Microfabrication of three-dimensional engineered Scaffolds.</a> Tissue Eng. 13 (8), 1837-1844 (2007).</li><li>Wu, H., Odom, T. W., Chiu, D. T., Whitesides, G. M. <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+complex+three-dimensional+microchannel+systems+in+PDMS.">Fabrication of complex three-dimensional microchannel systems in PDMS.</a> J. Am. Chem. Soc. 125 (2), 554-559 (2003).</li><li>Trask, R. S., Bond, I. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomimetic+self-healing+of+advanced+composite+structures+using+hollow+glass+fibres.">Biomimetic self-healing of advanced composite structures using hollow glass fibres.</a> Smart Mater. Struct. 15 (3), 704-710 (2006).</li><li>Dong, H., Esser-Kahn, A. P., 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=Chemical+treatment+of+poly(lactic+acid)+fibers+to+enhance+the+rate+of+thermal+depolymerization.">Chemical treatment of poly(lactic acid) fibers to enhance the rate of thermal depolymerization.</a> ACS Appl. Mater. Interfaces. 4 (2), 503-509 (2012).</li><li>Esser-Kahn, A. P., Thakre, P. R., 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=Three-dimensional+microvascular+fiber-reinforced+composites.">Three-dimensional microvascular fiber-reinforced composites.</a> Adv. Mater. 23 (32), 3654-3658 (2011).</li><li>White, S. R., Blaiszik, B. J., Kramer, S. L. B., Olugebefola, S. C., Moore, J. S., Sottos, N. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-healing+polymers+and+composites.">Self-healing polymers and composites.</a> Am. Sci. 99 (5), 392 (2011).</li><li>Nguyen, D. T., Leho, Y. T., Esser-Kahn, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+three-dimensional+microvascular+gas+exchange+unit+for+carbon+dioxide+capture.">A three-dimensional microvascular gas exchange unit for carbon dioxide capture.</a> Lab Chip. 12 (7), 1246 (2012).</li><li>Nguyen, D. T., Leho, Y. T., Esser-Kahn, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+membrane+thickness+on+a+microvascular+gas+exchange+unit.">The effect of membrane thickness on a microvascular gas exchange unit.</a> Adv. Funct. Mater. , (2012).</li></ol>

We have filed for a provisional patent on this technology und US patent U.S. Provisional Application Serial No. 61/590,086.

The introduction of the SnOx catalyst into the PLA fibers allows the fibers to depolymerize at a lower temperature. This prevents the degradation of the embedding resin, in this case PDMS. A custom spindle is required to properly mix the treatment solution (Figure 5A). The spindle is composed of six supporting rods surrounding a central core which attaches to a digital mixer. The fibers are wrapped around the support rods so that the surface area of the wrapping fibers in contact with the catalytic solut...

Natural systems use extensive vascular networks to facilitate many biological functions. Mass transport can be achieved efficiently in such systems due to high surface area to volume ratios and optimized packing structures. While many synthetic fabrication techniques can produce microvascular structures, none can produce large-scale microvasculature while maintaining complexity and compatibility with existing manufacturing methods1-5. Structures such as the avian lung provide an inspiration. How do we fabricate structures of this complexity for enhancing mass transport?
The Vaporization of a Sacrificial Component (VaSC) can produce large-scale, complex microvascular structures6-7. This method uses the thermal depolymerization and evaporative removal of poly(lactic) acid fibers to form hollow channels that are the inverse of the fiber template. This is a sacrificial technique compatible with existing manufacturing methods. Meter long, cylindrical microchannel patterns can be formed using this fabrication process. This can be used to create vascularized devices such as self-healing polymers and 3D microvascular carbon capture units7-10.
The carbon capture units were inspired by the avian lung that provides an efficient gas-exchange-to-weight ratio owing to its use in flight. The parabronchus is composed of hexagonally patterned microchannels, which provides high gas exchange rates and structurally stable gas exchange units. In order to create exchange units with microscale features aligned in three-dimensions, we developed a method of independently tensioning fibers using a custom designed tension board with guitar tuners and laser-micromachined plates. Each fiber is held in place by external tension and the pattern is set by the placement of holes in the plate through which the fibers run.

<table border="1">
	<tbody>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Reagent</td>
		</tr>
		<tr>
			<td>Tin (II) oxalate</td>
			<td>Sigma-Aldrich</td>
			<td>402761</td>
			<td></td>
		</tr>
		<tr>
			<td>Disperbyk 130</td>
			<td>BYK Additives &#38; Instruments</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Trifluoroethanol</td>
			<td>Halocarbon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Malachite Green (technical grade)</td>
			<td>Sigma-Aldrich</td>
			<td>M6880</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide (&#8805;98%, pellets)</td>
			<td>Sigma-Aldrich</td>
			<td>S5881</td>
			<td></td>
		</tr>
		<tr>
			<td>Polydimethylsiloxane (PDMS)</td>
			<td>Dow Corning</td>
			<td>3097358-1004</td>
			<td>Distributed from Ellsworth Adhesives</td>
		</tr>
		<tr>
			<td>Poly(lactic) acid fibers</td>
			<td>Teijin Monofilament</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Material</td>
		</tr>
		<tr>
			<td>RW 20 Digital Mixer</td>
			<td>IKA</td>
			<td>3593001</td>
			<td></td>
		</tr>
		<tr>
			<td>Desiccator Jar</td>
			<td>Pyrex</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum Oven</td>
			<td>Fisher Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Third Hand</td>
			<td>Jameco Electronics</td>
			<td>26690</td>
			<td>Plate holder</td>
		</tr>
		<tr>
			<td>Glue Gun</td>
			<td>Stanley</td>
			<td>GR20L</td>
			<td></td>
		</tr>
		<tr>
			<td>PLA Spindle</td>
			<td></td>
			<td></td>
			<td>Custom made</td>
		</tr>
		<tr>
			<td>Tensioning Board</td>
			<td></td>
			<td></td>
			<td>Custom made</td>
		</tr>
	</tbody>
</table>

process of making three-dimensional microstructures using vaporization of a sacrificial component

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material fabrication techniques are able to mimic the complexity of these structures while maintaining scalability. The Vaporization of a Sacrificial Component (VaSC) process is able to do so. This process uses sacrificial fibers as a template to form hollow, cylindrical microchannels embedded within a matrix. Tin (II) oxalate (SnOx) is embedded within poly(lactic) acid (PLA) fibers which facilitates the use of this process. The SnOx catalyzes the depolymerization of the PLA fibers at lower temperatures. The lactic acid monomers are gaseous at these temperatures and can be removed from the embedded matrix at temperatures that do not damage the matrix. Here we show a method for aligning these fibers using micromachined plates and a tensioning device to create complex patterns of three-dimensionally arrayed microchannels. The process allows the exploration of virtually any arrangement of fiber topologies and structures.

This procedure provides a method of fabricating microvascular structures embedded within a resin. These structures can conform to a variety of patterns (Figure 2). The structure of the microvascular network is only limited by the structures that can be formed with the sacrificial fibers.
Using a parallel arrangement of microvascular channels, gas transport between fluid streams is facilitated as gases traverse a permeable inter-channel membrane. These devices can be fabricated...

Watch this Scientific Journal Video about Process of Making Three-dimensional Microstructures using Vaporization of a Sacrificial Component at JoVE.com

Process of Making Three-dimensional Microstructures using Vaporization of a Sacrificial Component

The Vaporization of a Sacrificial Component (VaSC) process is used to fabricate microvascular structures. This procedure uses sacrificial poly(lactic) acid fibers to form hollow microchannels with precise 3D geometric positioning provided by laser micromachined guide plates.

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material ...

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8.9K Views.  University of California, Irvine. The Vaporization of a Sacrificial Component (VaSC) process is used to fabricate microvascular structures. This procedure uses sacrificial poly(lactic) acid fibers to form hollow microchannels with precise 3D geometric positioning provided by laser micromachined guide plates.