This work was supported by Technologico de Monterrey and the University of California at Irvine.

1. 3D Human Hair-derived Carbon Structure Fabrication
NOTE: Use personal protective equipment. Follow laboratory instructions to use the instruments and to work inside the laboratory.
<ol>
	<li>Prepare collected human hair by washing it with DI water and drying it with N2 gas.</li>
	<li>Arrange the hairs as desired, such as in parallel strands, cross over, with two hairs wound together, etc.</li>
	<li>Attach the hairs to a silicon substrate using SU8 or keep them directly in a ceramic boat.</li>
	<li>Place the hair-attached silicon substrate or boat into a furnace.</li>
	<li>Turn on the furnace and open the valve of an inert gas (N2) tank. 
	NOTE: The optimal gas flow rate is dependent upon the volume of the furnace tube. A 6 L/min flow rate was applied for a tube volume of 6 L. To establish a completely inert environment in the furnace tube, a gas flow rate 1.5 times higher than the optimal gas flow rate was applied for the first 15 min.</li>
	<li>Set the parameters, including maximum pyrolysis temperature, temperature ramp rate, and inert gas flow rate, and run the furnace.
	<ol>
		<li>For example, increase temperature from room temperature to 300 &#176;C at a 5 &#176;C/min ramp rate. Keep it at 300 &#176;C for 1 h for stabilization. Further increase the temperature to 900 &#176;C and maintain it for 1 h more for carbonization.</li>
		<li>Cool the furnace down to 300 &#176;C at a rate of 10 &#176;C/min and turn off the heater of the furnace, as the controlled cooling is not necessary after 300 &#176;C. Leave the samples in the furnace until the temperature reaches room temperature by N2 flow only.</li>
	</ol>
	</li>
	<li>Turn off the furnace and gas flow upon the completion of the pyrolysis process.</li>
	<li>Take the samples out of the furnace.</li>
</ol>
2. 3D Polymer Structure Fabrication: Photolithography
<ol>
	<li>Design a 2D layout of the desired 3D photoresist structure using an appropriate software package and prepare the printed mask (i.e., a polyethylene photofilm mask). 
	NOTE: A commercial service was used to get the design printed. The size of the mask generally depends on the design.</li>
	<li>In a clean laboratory facility, turn on two hot plates and set the temperatures to 65 &#176;C and 95 &#176;C, respectively.</li>
	<li>Switch on a spin coater and a vacuum pump. Ensure that the vacuum pump is connected through a tube to the spinner head.</li>
	<li>Set the parameters of the two-step spin, such as the spinning speed, ramp, and duration. For the first step, set the spinning speed to 500 rpm, the ramp to 100 rpm/s, and the spin time to 10 s to begin the spin cycle. For the next step, set the spinning speed to 1,000 rpm, the ramp to 100 rpm/s, and the spin time to 30 s to evenly spread the photoresist.</li>
	<li>Place a substrate (i.e., a 4 inch x 4 inch and 550 &#181;m &#177; 25 &#181;m-thick Si wafer with a 1 &#181;m-thick SiO2 layer) at the center of the holder.</li>
	<li>Deposit photosensitive polymer (i.e., SU8 photoresist) directly onto the center of the substrate. Use enough to cover the surface.</li>
	<li>Push the &#34;vacuum&#34; button to hold the substrate.</li>
	<li>Push the &#34;run&#34; button to coat the substrate with SU8 and to achieve a final thickness of 250 &#181;m.</li>
	<li>After the completion of spinning process, press the &#34;vacuum&#34; button again to release the coated substrate from the holder.</li>
	<li>Hold the coated substrate carefully using a tweezer to keep the surface smooth and clean. Transfer the substrate directly onto the hot plate at 65 &#176;C temperature for 6 min and then onto the hot plate at 95 &#176;C temperature for 40 min (soft bake). 
	NOTE: Baking at 65 &#176;C is required to ensure the slow evaporation of the solvent, resulting in the better coating and better adhesion to the substrate, while baking at 95 &#176;C further densifies the SU8.</li>
	<li>In the meantime, press the switch to turn on the UV-exposure system and set the time of exposure to &#34;12 s&#34; using the set button in the system. 
	NOTE: For a 250 &#181;m-thick SU8 layer, the exposure energy must be 360 mJ/cm2.</li>
	<li>Once the baking step (step 2.10) is completed, put the substrate into the UV-exposure system and place the printed side of a photomask (from step 2.1) onto it. Use the whole mask area to cover the coated substrate and press gently to ensure that there is no gap between the mask and substrate.</li>
	<li>Expose the SU8-coated substrate to UV radiation through the photomask using predefined UV settings.</li>
	<li>Heat the substrate again by placing it directly on the hotplate at 65 &#176;C for 5 min and at 95 &#176;C for 14 min for a post-exposure bake (PEB). 
	NOTE: The PEB increases the degree of cross-linking in the UV-exposed areas and makes the coating more resistant to solvents in the development step.</li>
	<li>Remove the unexposed photoresist regions by dipping the substrate in the dedicated developer solution, placed in a beaker, for 20 min. Continuously shake the solution (carefully) to ensure the complete removal of the un-exposed resist areas.</li>
	<li>Dry the developed structures by holding the substrate and blowing nitrogen or compressed air onto it.</li>
	<li>Inspect the wafer under a microscope with 50X magnification to compare the patterns transferred to the photoresist with the desired patterns.</li>
</ol>
3. 3D Carbon Structure Fabrication: Pyrolysis
<ol>
	<li>Place the samples prepared using photolithography (steps 2.1-2.17) inside a pressurized, open-ended tube furnace.</li>
	<li>Turn on the furnace and set the parameters for pyrolysis, as mentioned above in step 1. Repeat the process from step 1.6-1.8.</li>
	<li>Handle the samples carefully using tweezers and proceed to characterization.</li>
</ol>

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<li>Jong, K. P. D., Geus, J. W. <a target="_blank" href="http://www.tandfonline.com/doi/abs/10.1081/CR-100101954">Carbon nanoﬁbers: catalytic synthesis and applications.</a> Catal Rev Sci Eng. 42, 481-510 (2000).</li>
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<li>Baughman, R. H., Zakhidov, A. A., Heer, W. A. D. <a target="_blank" href="http://science.sciencemag.org/content/297/5582/787.full">Carbon nanotubes-the route toward applications.</a> Science. 297, 787-792 (2002).</li>
<li>Kumar, R., Singh, R. K., Singh, D. P. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S1364032115015038">Natural and waste hydrocarbon precursors for the synthesis of carbon based nanomaterials: graphene and CNTs.</a> Renew Sustain Energy Rev. 58, 976-1006 (2016).</li>
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<li>Sharma, S., Kalita, G., Hirano, R., Hayashi, Y., Tanemura, M. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0167577X12016692">Influence of gas composition on the formation of graphene domain synthesized from camphor.</a> Mater Lett. 93 (0), 258-262 (2013).</li>
<li>Ghosh, P., Afre, R. A., Soga, T., Jimbo, T. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0167577X06015084">A simple method of producing single-walled carbon nanotubes from a natural precursor: eucalyptus oil.</a> Mater Lett. 61 (17), 3768-3770 (2007).</li>
<li>Kumar, R., Tiwari, R., Srivastava, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Scalable+synthesis+of+aligned+carbon+nanotubes+bundles+using+green+natural+precursor%3A+neem+oil%5BTitle%5D)+AND+%22Nanoscale+Res+Lett%22%5BJournal%5D)">Scalable synthesis of aligned carbon nanotubes bundles using green natural precursor: neem oil.</a> Nanoscale Res Lett. 6 (1), 92-97 (2011).</li>
<li>Liang, Y., Wu, D., Fu, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Carbon+microfibers+with+hierarchical+porous+structure+from+electrospun+fiber-like+natural+biopolymer%5BTitle%5D)+AND+%22Sci+Rep%22%5BJournal%5D)">Carbon microfibers with hierarchical porous structure from electrospun fiber-like natural biopolymer.</a> Sci Rep. 3, 1-5 (2013).</li>
<li>Gupta, A. <a target="_blank" href="https://www.hindawi.com/archive/2014/498018/">Human hair "waste" and its utilization: gaps and possibilities.</a> J Waste Manag. 2014, 1-17 (2014).</li>
<li>Qian, W., Sun, F., Xu, Y., Qiu, L., Liu, C., Wang, S., Yan, F. <a target="_blank" href="http://pubs.rsc.org/en/Content/ArticleLanding/2014/EE/c3ee43111h">Human hair-derived carbon flakes for electrochemical supercapacitors.</a> Energy Environ Sci. 7, 379-386 (2014).</li>
<li>Pramanick, B., Cadenas, L. B., Kim, D. M., Lee, W., Shim, Y. B., Martinez-Chapa, S. O., Madou, M. J., Hwang, H. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0008622316305504">Human hair-derived hollow carbon microfibers for electrochemical sensing.</a> Carbon. 107, 872-877 (2016).</li>
<li>Miura, N., Numaguchi, T., Yamada, A., Konagai, M., Shirakashi, J. <a target="_blank" href="http://iopscience.iop.org/article/10.1143/JJAP.37.L423/meta">Room temperature operation of amorphous carbon-based single-electron transistors fabricated by beam-induced deposition techniques.</a> Jpn J Appl Phys. 37 (2), L423-L425 (1998).</li>
<li>Irie, M., Endo, S., Wang, C. L., Ito, T. <a target="_blank" href="https://www.deepdyve.com/lp/elsevier/fabrication-and-properties-of-lateral-p-i-p-structures-using-single-03o6EWw2pN">Fabrication and properties of lateral p-i-p structures using single crystalline CVD diamond layers for high electric ﬁeld applications.</a> Diamond Rel Mater. 12, 1563-1568 (2003).</li>
<li>Tay, B. K., Sheeja, D., Yu, L. J. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0925963503000219">On stress reduction of tetrahedral amorphous carbon ﬁlms for moving mechanical assemblies.</a> Diamond Rel Mater. 12 (2), 185-194 (2003).</li>
<li>Kamath, R. R., Madou, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Three-dimensional+carbon+interdigitated+electrode+arrays+for+redox-amplification%5BTitle%5D)+AND+%22Anal+Chem%22%5BJournal%5D)">Three-dimensional carbon interdigitated electrode arrays for redox-amplification.</a> Anal Chem. 86 (6), 2963-2971 (2014).</li>
<li>Sharma, S., Khalajhedayati, A., Rupert, T. J., Madou, M. J. <a target="_blank" href="http://ecst.ecsdl.org/content/61/7/75.short">SU8 derived glassy carbon for lithium ion batteries.</a> ECS Trans. 61 (7), 75-84 (2014).</li>
<li>Kim, D., Pramanick, B., Salazar, A., Tcho, I. -W., Madou, M. J., Jung, E. S., Choi, Y. -K., Hwang, H. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/admt.201600160/abstract">3D carbon electrode based triboelectric nanogenerator.</a> Adv Mater Technol. 1 (8), 1-7 (2016).</li>
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<li>Pramanick, B., Martinez-Chapa, S. O., Madou, M. <a target="_blank" href="http://ma.ecsdl.org/content/MA2016-01/14/902.abstract">Fabrication of biocompatible hollow microneedles using the C-MEMS process for transdermal drug delivery.</a> ECS Trans. 72 (1), 45-50 (2016).</li>
</ol>

The authors have nothing to disclose.

In this paper the methods for manufacturing a variety of carbon microstructures based on the pyrolysis of natural precursor materials or photo-patterned polymer structures were reported. The carbon materials resulting from both the traditional and non-conventional C-MEMS/C-NEMS processes are typically found to be glassy carbons. Glassy carbon is a widely used electrode material for electrochemistry and also for high-temperature applications. The microstructure of glassy carbon is composed of both crystalline and amorphou...

Carbon has many allotropes and, depending on the particular application, one of the following allotropes can be chosen: carbon nanotubes (CNTs), graphite, diamond, amorphous carbon, lonsdaleite, buckminsterfullerene (C60), fullerite (C540), fullerene (C70), and glassy carbon1,2,3,4. Glassy carbon is one of the most widely used allotropes because of its physical properties, including high isotropy. It also has the following properties: good electrical conductivity, low thermal expansion coefficient, and gas impermeability.
There has been a continuous search for carbon-rich precursor materials to obtain carbon structures. These precursors can be manmade materials or natural products that are available in particular shapes, and even include waste products. A wide variety of micro/nanostructures are formed via biological or environmental processes in nature, resulting in unique features that are extremely difficult to create using conventional manufacturing tools. As patterning took place naturally in this case, the synthesis of nanomaterials using natural and waste hydrocarbon precursors could be carried out using an easy, one-step process of thermal decomposition in an inert or vacuum atmosphere, called pyrolysis5. High-quality graphene, single-walled CNTs, multi-walled CNTs, and carbon dots have been produced by thermal decomposition or the pyrolysis of plant-derived precursors and wastes, including seeds, fibers, and oils, such as turpentine oil, sesame oil, neem oil (Azadirachta indica), eucalyptus oil, palm oil, and jatropha oil. Also, camphor products, tea-tree extracts, waste foods, insects, agro wastes, and food products have been utilized6,7,8,9 Recently, researchers have even used silk cocoons as a precursor material to prepare porous carbon microfibers10. Human hair, usually considered a waste material, was recently used by this team. It is made up of approximately 91% polypeptides, which contain more than 50% carbon; the rest are elements such as oxygen, hydrogen, nitrogen, and sulphur11. Hair also comes with several interesting properties, such as very slow degradation, high tensile strength, high thermal insulation, and high elastic recovery. Recently, it has been used to prepare carbon flakes employed in supercapacitors12 and to create hollow carbon microfibers for electrochemical sensing13.
The machining of a bulk carbon material to fabricate three-dimensional (3D) structures is a difficult task, as the material is very brittle. Focused ion beam14,15 or reactive ion etching16 may be useful in this context, but they are expensive and time-consuming processes. Carbon microelectromechanical system (C-MEMS) technology, which is based on the pyrolysis of patterned polymeric structures, represents a versatile alternative. In the past two decades, C-MEMS and carbon nanoelectromechanical systems (C-NEMS) have received much attention because of the simple and inexpensive fabrication steps involved. The conventional C-MEMS fabrication process is carried out in two steps: (i) patterning a polymer precursor (e.g., a photoresist) with photolithography and (ii) pyrolysis of the patterned structures. Ultraviolet (UV)-curable polymer precursors, such as SU8 photoresists, are often used to pattern structures based on photolithography. In general, the photolithography process includes steps for spin coating, soft bake, UV exposure, post bake, and development. In the case of C-MEMS; silicon; silicon dioxide; silicon nitride; quartz; and, more recently, sapphire have been used as substrates. The photo-patterned polymer structures are carbonized at a high temperature (800-1,100 &#176;C) in an oxygen-free environment. At those elevated temperatures in a vacuum or inert atmosphere, all of the non-carbon elements are removed, leaving only carbon. This technique allows for the attainment of high-quality, glassy carbon structures, which are very useful for many applications, including electrochemical sensing17, energy storage18, triboelectric nanogeneration19, and electrokinetic particle manipulation20. Also, the fabrication of 3D microstructures with high aspect ratios using C-MEMS has become relatively easy and has led to a wide variety of carbon electrodes applications18,21,22,23, often replacing noble metal electrodes.
In this work, the recent development of a simple and cost-effective way to fabricate hollow carbon microfibers from human hair using non-conventional C-MEMS technology13 is introduced. The conventional SU8 polymer-based C-MEMS process is also described here. Specifically, the fabrication procedure for high-aspect ratio solids and hollow SU8 structures is described24.

<table><tbody><tr><td>SU8-2100</td><td>Microchem</td><td>Product number-Y1110750500L</td><td></td></tr><tr><td>Spinner</td><td>Laurell Technologies Corporation</td><td>Model-WS650HZB-23NPP/UD3</td><td></td></tr><tr><td>Hotplate</td><td>Torrey Pines Scientific</td><td>HS61</td><td></td></tr><tr><td>UV-exposer</td><td>Mercury Lamp, SYLVANIA</td><td>H44GS-100M, P/N-34-0054-01</td><td></td></tr><tr><td>Photomask</td><td>CAD/Art</td><td></td><td>No number</td></tr><tr><td>Developer&amp;nbsp;</td><td>Microchem</td><td>Y020100 4000L&amp;nbsp;</td><td></td></tr><tr><td>DI water system</td><td>Milli Q</td><td>ZOOQOVOTO</td><td></td></tr><tr><td>IPA</td><td>CTR Sientific</td><td>CTR 01244</td><td></td></tr><tr><td>N&lt;sub&gt;2&lt;/sub&gt; gas</td><td>AOC Mexico</td><td></td><td>No number</td></tr><tr><td>Furnace</td><td>PEO 601, ATV Technologie GMBH</td><td>Model-PEO 601, Serial no.-195</td><td></td></tr><tr><td>Si/SiO&lt;sub&gt;2&lt;/sub&gt;</td><td>Noel Technologies</td><td></td><td></td></tr></tbody></table>

fabrication of 3d carbon microelectromechanical systems (c-mems)

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long and hollow glassy carbon microfibers derived from human hairs is introduced. The long and hollow carbon structures were made by the pyrolysis of human hair at 900 &#176;C in a N2 atmosphere. The morphology and chemical composition of natural and pyrolyzed human hairs were investigated using scanning electron microscopy (SEM) and electron-dispersive X-ray spectroscopy (EDX), respectively, to estimate the physical and chemical changes due to pyrolysis. Raman spectroscopy was used to confirm the glassy nature of the carbon microstructures. Pyrolyzed hair carbon was introduced to modify screen-printed carbon electrodes ; the modified electrodes were then applied to the electrochemical sensing of dopamine and ascorbic acid. Sensing performance of the modified sensors was improved as compared to the unmodified sensors. To obtain the desired carbon structure design, carbon micro-/nanoelectromechanical system (C-MEMS/C-NEMS) technology was developed. The most common C-MEMS/C-NEMS fabrication process consists of two steps: (i) the patterning of a carbon-rich base material, such as a photosensitive polymer, using photolithography; and (ii) carbonization through the pyrolysis of the patterned polymer in an oxygen-free environment. The C-MEMS/NEMS process has been widely used to develop microelectronic devices for various applications, including in micro-batteries, supercapacitors, glucose sensors, gas sensors, fuel cells, and triboelectric nanogenerators. Here, recent developments of a high-aspect ratio solid and hollow carbon microstructures with SU8 photoresists are discussed. The structural shrinkage during pyrolysis was investigated using confocal microscopy and SEM. Raman spectroscopy was used to confirm the crystallinity of the structure, and the atomic percentage of the elements present in the material before and after pyrolysis was measured using EDX.

A schematic of the fabrication process for human hair-derived hollow carbon microfibers is shown in Figure 1. The carbonized human hair was characterized using SEM to estimate the shrinkage. The hair diameter shrank from 82.88 &#177; 0.003 &#181;m to 31.42 &#177; 0.003 &#181;m due to the pyrolysis. Scanning electron microscopic (SEM) images of various patterns made using hair-derived carbon microfibers are shown in Figure 2. The ...

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Fabrication of 3D Carbon Microelectromechanical Systems C-MEMS

Long and hollow glassy carbon microfibers were fabricated based on the pyrolysis of a natural product, human hair. The two fabrication steps of carbon microelectromechanical and carbon nanoelectromechanical systems, or C-MEMS and C-NEMS, are: (i) photolithography of a carbon-rich polymer precursor and (ii) pyrolysis of the patterned polymer precursor.

Fabrication of 3D Carbon Microelectromechanical Systems (C-MEMS)

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long ...

fabrication-of-3d-carbon-microelectromechanical-systems-c-mems

Research

JoVE Journal

Engineering

12.2K Views.  Tecnologico de Monterrey. Long and hollow glassy carbon microfibers were fabricated based on the pyrolysis of a natural product, human hair. The two fabrication steps of carbon microelectromechanical and carbon nanoelectromechanical systems, or C-MEMS and C-NEMS, are: (i) photolithography of a carbon-rich polymer precursor and (ii) pyrolysis of the patterned polymer precursor. 

Video: Fabrication of 3D Carbon Microelectromechanical Systems C-MEMS

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

Microfabricated Platforms for Mechanically Dynamic Cell Culture

The ability to systematically probe in vitro cellular response to combinations of mechanobiological stimuli for tissue engineering, drug discovery or fundamental cell biology studies is limited by current bioreactor technologies, which cannot simultaneously apply a variety of mechanical stimuli to cultured cells. In order to address this issue, we have developed a series of microfabricated platforms designed to screen for the effects of mechanical stimuli in a high-throughput format. In this protocol, we demonstrate the fabrication of a microactuator array of vertically displaced posts on which the technology is based, and further demonstrate how this base technology can be modified to conduct high-throughput mechanically dynamic cell culture in both two-dimensional and three-dimensional culture paradigms.

In this protocol, we demonstrate the fabrication of a microactuator array of vertically displaced posts on which the technology is based, and how this base technology can be modified to conduct high-throughput mechanically dynamic cell culture in both two-dimensional and three-dimensional culture paradigms.

The ability to systematically probe in vitro cellular response to combinations of mechanobiological stimuli for tissue engineering, drug discovery or ...

Bioengineering

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.

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 ...

Manufacturing of Three-dimensionally Microstructured Nanocomposites through Microfluidic Infiltration

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite in&#64257;ltration of 3D interconnected microfluidic networks. The manufacturing of the reinforced beams begins with the fabrication of microfluidic networks, which involves layer-by-layer deposition of fugitive ink filaments using a dispensing robot, filling the empty space between filaments using a low viscosity resin, curing the resin and finally removing the ink.&#160;Self-supported 3D structures with other geometries and many layers (e.g.&#160;a few hundreds layers) could be built using this method. The resulting tubular micro&#64258;uidic networks are then infiltrated with thermosetting nanocomposite suspensions containing nanofillers (e.g.&#160;single-walled carbon nanotubes), and subsequently cured. The infiltration is done by applying a pressure gradient between two ends of the empty network (either by applying a vacuum or vacuum-assisted microinjection). Prior to the infiltration, the nanocomposite suspensions are prepared by dispersing nanofillers into polymer matrices using ultrasonication and three-roll mixing methods. The nanocomposites (i.e.&#160;materials infiltrated) are then solidified under UV exposure/heat cure, resulting in a 3D-reinforced composite structure. The technique presented here enables the design of functional nanocomposite macroscopic products for microengineering applications such as actuators and sensors.

Three-dimensional (3D) microstructured composite beams are fabricated through the directed and localized infiltration of nanocomposites into 3D porous microfluidic networks. The flexibility of this manufacturing method enables the utilization of different thermosetting materials and nanofillers in order to achieve a variety of functional 3D reinforced nanocomposite macroscopic products.

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite ...

Chemistry

Micro-masonry for 3D Additive Micromanufacturing

Transfer printing is a method to transfer solid micro/nanoscale materials (herein called &#8216;inks&#8217;) from a substrate where they are generated to a different substrate by utilizing elastomeric stamps. Transfer printing enables the integration of heterogeneous materials to fabricate unexampled structures or functional systems that are found in recent advanced devices such as flexible and stretchable solar cells and LED arrays. While transfer printing exhibits unique features in material assembly capability, the use of adhesive layers or the surface modification such as deposition of self-assembled monolayer (SAM) on substrates for enhancing printing processes hinders its wide adaptation in microassembly of microelectromechanical system (MEMS) structures and devices. To overcome this shortcoming, we developed an advanced mode of transfer printing which deterministically assembles individual microscale objects solely through controlling surface contact area without any surface alteration. The absence of an adhesive layer or other modification and the subsequent material bonding processes ensure not only mechanical bonding, but also thermal and electrical connection between assembled materials, which further opens various applications in adaptation in building unusual MEMS devices.

This paper introduces a 3D additive micromanufacturing strategy (termed &#8216;micro-masonry&#8217;) for the flexible fabrication of microelectromechanical system (MEMS) structures and devices. This approach involves transfer printing-based assembly of micro/nanoscale materials in conjunction with rapid thermal annealing-enabled material bonding techniques.

Transfer printing is a method to transfer solid micro/nanoscale materials (herein called &#8216;inks&#8217;) from a substrate where they are generated to ...

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-&#954; dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive ...

Microfabrication of Chip-sized Scaffolds for Three-dimensional Cell cultivation

Using microfabrication technologies is a prerequisite to create scaffolds of reproducible geometry and constant quality for three-dimensional cell cultivation. These technologies offer a wide spectrum of advantages not only for manufacturing but also for different applications. The size and shape of formed cell clusters can be influenced by the exact and reproducible architecture of the microfabricated scaffold and, therefore, the diffusion path length of nutrients and gases can be controlled.1 This is unquestionably a useful tool to prevent apoptosis and necrosis of cells due to an insufficient nutrient and gas supply or removal of cellular metabolites.
Our polymer chip, called CellChip, has the outer dimensions of 2 x 2 cm with a central microstructured area. This area is subdivided into an array of up to 1156 microcontainers with a typical dimension of 300 m edge length for the cubic design (cp- or cf-chip) or of 300 m diameter and depth for the round design (r-chip).2
So far, hot embossing or micro injection moulding (in combination with subsequent laborious machining of the parts) was used for the fabrication of the microstructured chips. Basically, micro injection moulding is one of the only polymer based replication techniques that, up to now, is capable for mass production of polymer microstructures.3 However, both techniques have certain unwanted limitations due to the processing of a viscous polymer melt with the generation of very thin walls or integrated through holes. In case of the CellChip, thin bottom layers are necessary to perforate the polymer and provide small pores of defined size to supply cells with culture medium e.g. by microfluidic perfusion of the containers.
In order to overcome these limitations and to reduce the manufacturing costs we have developed a new microtechnical approach on the basis of a down-scaled thermoforming process. For the manufacturing of highly porous and thin walled polymer chips, we use a combination of heavy ion irradiation, microthermoforming and track etching. In this so called "SMART" process (Substrate Modification And Replication by Thermoforming) thin polymer films are irradiated with energetic heavy projectiles of several hundred MeV introducing so-called "latent tracks" Subsequently, the film in a rubber elastic state is formed into three dimensional parts without modifying or annealing the tracks. After the forming process, selective chemical etching finally converts the tracks into cylindrical pores of adjustable diameter.

We present two processes for the microfabrication of porous polymer chips for three-dimensional cell cultivation. The first one is hot embossing combined with a solvent vapour welding process. The second one uses a recently developed microthermoforming process combined with ion track technology leading to a significant simplification of manufacture.

Using microfabrication technologies is a prerequisite to create scaffolds of reproducible geometry and constant quality for three-dimensional cell ...

Biology

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

Fabrication of Carbon-Based Ionic Electromechanically Active Soft Actuators

Ionic electromechanically active capacitive laminates are a type of smart material that move in response to electrical stimulation. Due to the soft, compliant and biomimetic nature of this deformation, actuators made of the laminate have received increasing interest in soft robotics and (bio)medical applications. However, methods to easily fabricate the active material in large (even industrial) quantities and with a high batch-to-batch and within-batch repeatability are needed to transfer the knowledge from laboratory to industry. This protocol describes a simple, industrially scalable and reproducible method for the fabrication of ionic carbon-based electromechanically active capacitive laminates and the preparation of actuators made thereof. The inclusion of a passive and chemically inert (insoluble) middle layer (e.g., a textile-reinforced polymer network or microporous Teflon) distinguishes the method from others. The protocol is divided into five steps: membrane preparation, electrode preparation, current collector attachment, cutting and shaping, and actuation. Following the protocol results in an active material that can, for example, compliantly grasp and hold a randomly shaped object as demonstrated in the article.

This article describes a fast and simple manufacturing process of ionic electromechanically active composite materials for actuators in biomedical, biomimetic and soft robotics applications. The key fabrication steps, their importance for the actuators&#39; final properties, and some of the main characterization techniques are described in detail.

Ionic electromechanically active capacitive laminates are a type of smart material that move in response to electrical stimulation. Due to the soft, ...

Melt Electrospinning Writing of Three-dimensional Poly(&#949;-caprolactone) Scaffolds with Controllable Morphologies for Tissue Engineering Applications

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology with great potential for biomedical applications. The technique facilitates the direct deposition of biocompatible polymer fibers to fabricate well-ordered scaffolds in the sub-micron to micro scale range. The establishment of a stable, viscoelastic, polymer jet between a spinneret and a collector is achieved using an applied voltage and can be direct-written. A significant benefit of a typical porous scaffold is a high surface-to-volume ratio which provides increased effective adhesion sites for cell attachment and growth. Controlling the printing process by fine-tuning the system parameters enables high reproducibility in the quality of the printed scaffolds. It also provides a flexible manufacturing platform for users to tailor the morphological structures of the scaffolds to their specific requirements. For this purpose, we present a protocol to obtain different fiber diameters using melt electrospinning writing (MEW) with a guided amendment of the parameters, including flow rate, voltage and collection speed. Furthermore, we demonstrate how to optimize the jet, discuss often experienced technical challenges, explain troubleshooting techniques and showcase a wide range of printable scaffold architectures.

This protocol serves as a comprehensive guideline to fabricate scaffolds via electrospinning with polymer melts in a direct writing mode. We systematically outline the process and define the appropriate parameter settings for achieving targeted scaffold architectures.

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology ...

Fabrication of 3D Carbon Microelectromechanical Systems (C-MEMS)

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