Name: casting protocols for the production of open cell aluminum foams by the replication technique and the effect on porosity
Uploaded: 2014-12-11T13:00:00.000+00:00
Duration: 9 min 22 s
Description: Watch this Scientific Journal Video about Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity at JoVE.com

The corresponding author would like to acknowledge the Mexican Government&#8217;s National Council of Science and Technology CONACYT for provision of a scholarship.

NOTE: The instructions below are for Protocol A (Figure 1). Modifications for Protocol B, C, and D are listed as well.
1. Aluminum Bar Preparation
<ol>
	<li>Place a large piece (500 g &#8211; 1 kg) of commercial purity aluminum ingot into a crucible.</li>
	<li>Place the crucible in a furnace at 800 &#176;C for about 1 hr, until molten.</li>
	<li>Take the crucible out of the furnace and pour the molten aluminum into a cylindrical mold that is 50 mm in diameter, slightly smaller than the final diameter of the chamber to be used for infiltration (51 mm) giving a gap of about &#189; mm.</li>
	<li>Wait 1 hr for the bar to cool down.</li>
	<li>Remove the bar from the mold.</li>
	<li>Using a band saw, cut it into 4 same-size pieces.</li>
	<li>Sand the edges of each piece to ensure a good fit in the infiltration mold.</li>
</ol>
2. Furnace Preparation
<ol>
	<li>Program the furnace to reach a 740 &#176;C plateau for at least 2 hr.</li>
	<li>Set the heating rate of the furnace to 20 &#176;C/min.</li>
</ol>
3. Preform Preparation
NOTE: Depending on the height of the foam aimed for, vary the amount of NaCl to use for infiltration between 100 g and 300 g.
<ol>
	<li>Choose the infiltration NaCl to use, with a diameter corresponding to the pore size range required (for example a range between 1.4 mm and 1.7 mm). The material can be obtained from chemical suppliers in high purity, or supermarket bought table salt can be used (such material will have additives such as iodine and anti-caking agents, but these do not in practice influence the process to a significant extent).</li>
	<li>Select sieves of an appropriate size range and stack on a base container with the smaller opening size at the bottom.</li>
	<li>From the suppliers&#8217; bag of NaCl, take approximately 500 g and pour it in the stacked sieves.</li>
	<li>Agitate the sieves, either manually or using a sieve shaker, for 1 min.</li>
	<li>Discard the NaCl left in the larger aperture size sieve and the bottom container, the NaCl left in the smaller aperture sieve is used for infiltration.</li>
	<li>Weigh the amount of infiltration NaCl obtained.</li>
	<li>If the amount is insufficient, repeat steps 3.4 to 3.7. 
	NOTE: For Protocols B, C or D, obtain 100 g of fine NaCl (&#60; 500 &#181;m). This creates an extra space in the mold for air trapped in the preform during infiltration in case the air in the preform does not escape the chamber adequately.</li>
</ol>
4. Mold Preparation
<ol>
	<li>Using sandpaper and laboratory paper roll, clean the mold cylinder (Figure 2), taking special consideration for both the top and bottom edges, and keeping the mold free of any noticeable impurities from previous use.</li>
	<li>Spray the inside of the mold cylinder with boron nitride aerosol spray, creating a thin coat covering the inside of the mold. 
	NOTE: This is achieved when the original color of the mold is replaced by a white layer of the spray; it is not necessary to measure its specific concentration.</li>
	<li>Let the mold cylinder dry for at least 5 min at RT (heating to around 100 &#176;C for up to 1 hr may be applied for further drying if desired).</li>
	<li>Using fine sandpaper, remove any residue of boron nitride from the edges of the mold cylinder, to improve the seal between the mold cylinder and the mold base. 
	NOTE: The next 3 steps are for Protocols A and B; for Protocols C and D cut only one gasket ring for the lid.</li>
	<li>Cut 2 gasket rings from 1 mm thick graphite sheet (OD = 60 mm, ID = 51 mm), one for the union between the top edge of the mold cylinder and the mold lid leading up to the valve system, the other for the union between the bottom edge of the mold cylinder and the mold base.</li>
	<li>Place one of the gaskets in the mold base groove.</li>
	<li>Place the bottom of the mold cylinder into the groove with the gasket.</li>
	<li>Tap lightly with a mallet on the top of the mold cylinder to secure the bottom to the base groove. 
	NOTE: For Protocol B, C, or D, add the following step.
	<ol>
		<li>Pour the 100 g of fine NaCl (&#60; 500 &#181;m) into the mold cylinder and flatten the top with an uncut aluminum bar tapping the top of it lightly with the mallet to ensure the fine NaCl is packed to a high density. 
		NOTE: For Protocol D add the following step.</li>
		<li>Cut 2 circles of soft 2 mm thick ceramic Kaowool blanket the size of the mold diameter (51 mm) and place them on top of the fine NaCl, use the uncut aluminum bar and the mallet to press them against the fine NaCl.</li>
	</ol>
	</li>
	<li>Pour the NaCl to be infiltrated into the mold cylinder. 
	NOTE: For Protocol D add the following step.
	<ol>
		<li>Attach the mold and base to a vibrating table, making sure the mold cylinder does not move from the base groove. Vibrate for 1 min at 50 Hz with a 0.01 m amplitude.</li>
	</ol>
	</li>
	<li>Holding the top of the cylinder in place, pick up the base and shake lightly until the NaCl inside the mold forms a flat surface at the top.</li>
	<li>Place the prepared aluminum bar on top of the NaCl preform.</li>
	<li>Place a graphite gasket in the groove of the mold lid.</li>
	<li>By hand screw the 4 stainless steel studs to the base and secure them with 4 sets of stainless steel nuts and washers on the top of the base using a wrench and place the mold lid on top of the mold cylinder through the studs.</li>
	<li>With a torque wrench set at 16 N&#183;m, screw the 4 sets of steel nuts and washers on the 4 threaded rods screwed into the base and extending up through the lid, where the nuts are tightened to lock the mold lid in place.</li>
	<li>Attach the top of the lid to the valve system with the gasket, clamp, bolt and butterfly nut.</li>
	<li>Close all the valves of the system.</li>
	<li>Open the valve leading to the vacuum pump and the mold (valve 3).</li>
	<li>Turn on the vacuum pump until the dial gauge of the valve system indicates the lowest pressure possible.</li>
	<li>Turn off the vacuum pump.</li>
	<li>If the loss of vacuum in the system is lower than a rate of 50 Torr/sec for the first 10 sec after shutting down the vacuum pump the seal is sufficiently good for infiltration.</li>
	<li>Leave the lid valve open (valve 3) to keep the system at ambient pressure and close the vacuum pump valve (valve 1).</li>
	<li>Without detaching the valve system, place the mold in the preheated furnace and wait for 1 hr.</li>
</ol>
5. Infiltration
<ol>
	<li>Close all the valves of the system (Figure 3).</li>
	<li>Open the valve leading to the argon gas cylinder (valve 2).</li>
	<li>Open the main valve on the argon gas tank and set the infiltration pressure with the regulator valve (for a range of 1.4 mm to 1.7 mm of NaCl particle size, use a pressure of 3.5 bars). 
	NOTE: For Protocol B, an infiltration pressure of 3 bar is used. Use a pressure of 1 bar for Protocols C and D.</li>
	<li>In a swift manner, open the lid valve (valve 3).</li>
	<li>After 1 min, remove the mold from the furnace and place it on top of a cooling surface (in this case a copper block). 
	NOTE: While cooling, the pressure in the system will change. For the first 5 min of this process, pay close attention to the pressure indicated by the regulator and adjust back to the infiltration pressure if necessary.</li>
</ol>
6. Sample Extraction
<ol>
	<li>After 30 min, when the mold is cool enough to handle with light heat resistant gloves, detach the valve system and place the mold base on a workbench vise. Unscrew the lid from the top of the cylinder.</li>
	<li>With the lid off, lightly tap the top of the mold cylinder with a mallet in a perpendicular direction to the vise&#8217;s grip to loosen the mold cylinder from the base groove.</li>
	<li>Remove the mold base from the vise and place the mold cylinder in the vise grip.</li>
	<li>With the mallet tap the remaining aluminum on top of the sample to push it out of the mold cylinder.</li>
	<li>Using a band saw, cut the bottom part of the foam sample, removing the surplus aluminum.</li>
	<li>Depending on the height of foam required, cut where desired, close to the top of the sample.</li>
	<li>Place the infiltrated foam in a beaker with water and a magnetic stirring bar on a stirring hot plate to dissolve the NaCl preform.</li>
	<li>Set the temperature of the hot plate to 60 &#176;C. Change the water every 10 min until there is no NaCl left in the foam. 
	NOTE: To ensure there is no NaCl left in the foam, change the water approximately 10 times. It is also possible to make periodic checks of the sample weight after a brief drying stage. When this ceases to change significantly with further immersion, the NaCl must be completely removed.</li>
	<li>Finally using an electric air drier remove all the water left in the foam. The foam sample is ready.</li>
</ol>

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The authors declare that they have no competing financial interests.

The basic method described here has been used in different forms by other researchers. Some of the key variants that allow foams of different types to be created are discussed. In characterizing these foams we have measured the porosity, as this is a quick and easy assessment to make, but characterization of other structural characteristics, such as pore size, specific surface area or strut thickness might be required to obtain a full understanding of foam characteristics for different applications. In practice, for prod...

A journal reference was corrected in the publication of <a href="http://www.jove.com/video/52268">Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity</a>. Reference 21 and 22 were originally merged together as one reference. They have been separated into references 21 and 22 in the article. The reference numbers have been updated in the article to reflect this additional reference citation. It has been updated from:
<ol start="21"><li>LeMay, J.D., Hopper, R.W., Hrubesh, L.W., &#38; Pekala, R.W. Low-Density Microcellular Materials. Materials Research Society Bulletin. 15 (12), 19&#8211;20 (1990).Seliger, H., &#38; Deuther U. Die Herstellung von Schaum- und Zellaluminium. Feiburger Forschungshefte. 103&#8211;129 (1965).</li></ol>
to:
<ol start="21"><li>LeMay, J.D., Hopper, R.W., Hrubesh, L.W., &#38; Pekala, R.W. Low-Density Microcellular Materials. Materials Research Society Bulletin. 15 (12), 19&#8211;20 (1990).</li>
<li>Seliger, H., &#38; Deuther U. Die Herstellung von Schaum- und Zellaluminium. Feiburger Forschungshefte. 103&#8211;129 (1965).</li></ol>

Erratum: Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Metal foams have attracted a large amount of interest and research effort in recent years as shown by the large body of work cited in wide ranging review articles such as Banhart1, Conde et al.2 or more recently Goodall and Mortensen3. Among the methods used for production of the material, the replication process is distinguished by its experimental simplicity and the degree of control over the final foam structure that can be offered. It should be noted that although in the literature such materials are often described as foams (and are here) as they are not produced by bubbles of gas within a liquid they are more appropriately called porous metals or microcellular metals.
The first report of the replication process was in the early 1960s4, and it has been developed further at different stages since then, with notable advances by the research group of Mortensen at the Ecole Polytechnique Federale de Lausanne in Switzerland.
The process relies on the casting of the metal around a preform of particles that defines the shape of the porosity in the final material2, 5. After cooling the preform can be removed by solvent leaching or pyrolysis that causes oxidation. A popular use of this technique utilizes NaCl as a space holder to produce aluminum5-10 or aluminum alloy foams11-14. NaCl has several advantages such as being readily accessible, non-toxic and can be removed from the foam by dissolution in water. By having a melting point of 801 &#176;C, it can be used with metals that have a melting point lower than this value, most commonly aluminum, but examples also exist of the use with materials such as bulk metallic glasses, by humidifying a mix of liquid palladium-based bulk metallic glass alloy and NaCl granules15. Substitution of the NaCl with higher melting point materials also permits the production of foams from higher melting point metals16. This may include other water-soluble materials, or insoluble ones including different types of sand. In this form the process becomes more like conventional sand casting as to remove the sand, high pressure water jets17, 18 or different forms of washing19 or agitating20 are required.
The essential process21 proceeds by taking grains of NaCl and placing them in a mold4, 22, 23. The basic method has been used to make aluminum and aluminum alloy foams24-26 for a wide range of foam behavior investigations. Additional steps have been introduced to further control the density and to increase the interconnectivity of the pores; these include the densification of the preform. To densify the preform, sintering has been employed27, 28 and has been used in different experiments since13, with the sintering behavior of NaCl based on temperature, granule size and density described by Goodall et al.29. Another method used for this purpose is cold isostatic pressing (CIP)5, 30; this is a faster technique that can achieve a larger spectrum of comparable densities. The procedure can also be performed in the solid state with metal powder and NaCl grains, and is then sometimes called the Sintering and Dissolution Process31.
A full survey of the use of the replication technique to date and comparison with other techniques is given in Goodall and Mortensen3.
In this work we report in detail equipment and experimental protocols that have been used for the processing of metal foams by the replication method, and which are relatively easy to implement in a research laboratory setting. It is important to acknowledge that other versions of the equipment, with different capabilities exist in other research groups, and that while the equipment presented here is suitable to process the material, it is not the only version or protocol that can be made to work. In any case, a thorough understanding of any particular method is essential for experimental success.
The precise protocols used are detailed below. The protocol variations (A, B, C and D) have small changes between them, principally intended to alter the density of the foams produced. The porosity has been calculated from measurements of the bulk weight of the samples, their volume and the density of aluminum (2.7 g/cm3). In developing the methods described for aluminum foam production by replication, attempts have been made to reduce the amount of advanced equipment to the smallest possible extent, such that the method is as easy to implement as possible. Other variations that may be used at different stages are discussed later.

<table><tbody><tr><td>Salt</td><td>Hydrosoft</td><td>Granular Salt 25 kg 855754</td><td>http://www.travisperkins.co.uk/p/hydrosoft-granular-salt-25kg/855754/3893446</td></tr><tr><td>Aluminum</td><td>William Rowland</td><td>Aluminum Ingots 99.87% pure 25&amp;nbsp;kg drum</td><td>http://www.william-rowland.com/products/high-purity-metals#product-id-1</td></tr><tr><td>Crucible</td><td>Morgan Advance Materials</td><td>Syncarb Crucible</td><td>http://www.morganmms.com/crucibles-foundry-products/crucibles/syncarb/</td></tr><tr><td>Furnace</td><td>Elite Thermal Systems</td><td>TLCF10/27-3216CP &amp;amp; 2116 O/T</td><td>http://www.elitefurnaces.com/eng/products/furnaces/1200%20Top%20Loading%20Furnaces.php</td></tr><tr><td>Bar Mold</td><td>The University of Sheffield</td><td>Custom Made</td><td>Stainless Steel 304, 15&amp;nbsp;cm height, 5&amp;nbsp;cm inner diameter, 6&amp;nbsp;cm outer diameter</td></tr><tr><td>Band Saw</td><td>Clarke</td><td>CBS45MD (6&quot; x 4 1/2&quot;) 370W 060710025</td><td>http://www.machinemart.co.uk/shop/product/details/cbs45md-41-2in-x-6in-metal-cutting-ban</td></tr><tr><td>Sandpaper</td><td>Wickes</td><td>Specialist wet &amp;amp; dry sandpaper 501885</td><td>http://www.wickes.co.uk/Specialist-Wet+Dry-Sandpaper-PK4/p/501885</td></tr><tr><td>Sieves</td><td>Fisher Scientific</td><td>Fisherbrand test sieves 200 mm diamater</td><td>http://www.fisher.co.uk/product/brand_listing.php/F/Fisherbrand/Sieve</td></tr><tr><td>Balance</td><td>Precisa</td><td>XB 6200C</td><td>http://www.precisa.co.uk/precision_balances.php</td></tr><tr><td>Boron Nitride</td><td>Kennametal</td><td>500 ml spray can</td><td>http://www.kennametal.com/content/dam/kennametal/kennametal/common/Resources/Catalogs-Literature/Advanced%20Materials%20and%20Wear%20Components/B-13-03401_ceramic_powders&lt;br/&gt; _brochure_EN.pdf</td></tr><tr><td>Infiltration Mold, Base and Lid</td><td>The University of Sheffield</td><td>Custom Made</td><td>Stainless Steel 304, 15&amp;nbsp;cm height, 5.1&amp;nbsp;cm inner diameter, 6&amp;nbsp;cm outer diameter</td></tr><tr><td>Cylindrical Mold</td><td>The University of Sheffield</td><td>Custom Made</td><td>Low carbon steel 1020, 15 cm height, 5 cm inner diameter, 6 cm outer diameter</td></tr><tr><td>Graphite Gasket</td><td>Gee Graphite</td><td>Geegraf Stainless Steel Reinforced Graphite 1&amp;nbsp;mm thick</td><td>http://www.geegraphite.com/steel_reinforced.html</td></tr><tr><td>Mallet</td><td>Thor Hammer Co. Ltd.</td><td>Round Solid Super Plastic Mallet</td><td>http://www.thorhammer.com/Mallets/Round/</td></tr><tr><td>Wrench</td><td>Kennedy Professional</td><td>13 mm Ratchet Combination Wrench KEN5822166K</td><td>https://www.cromwell.co.uk/KEN5822166K</td></tr><tr><td>Nuts</td><td>Matlock</td><td>M8 Steel hex full nut galvanized</td><td>https://www.cromwell.co.uk/CTL6400068J</td></tr><tr><td>Washers</td><td>Matlock</td><td>M8 Form-A steel washer bzp</td><td>https://www.cromwell.co.uk/CTL6451208H</td></tr><tr><td>SS Nuts</td><td>Matlock</td><td>M8 A2 st/st hex full nut</td><td>https://www.cromwell.co.uk/CTL6423008F</td></tr><tr><td>SS Washers</td><td>Matlock</td><td>M8 A2 st/st Form-A washer</td><td>https://www.cromwell.co.uk/CTL6464008H</td></tr><tr><td>Stainless Steel Studding</td><td>Cromwell</td><td>M8 x 1 Mtr A2 Stainless Steel Studding QFT6397080K</td><td>https://www.cromwell.co.uk/QFT6397080K</td></tr><tr><td>Valves</td><td>Edwards</td><td>C33205000 SP16K, Nitrile Diaphragm</td><td>https://www.edwardsvacuum.com/Products/View.aspx?sku=C33205000</td></tr><tr><td>Fitting Cross</td><td>Edwards</td><td>C10512412 NW16 Cross Piece Aluminum</td><td>https://www.edwardsvacuum.com/Products/C10512412/View.aspx</td></tr><tr><td>Fitting T</td><td>Edwards</td><td>C10512411 NW16 T-Piece Aluminum</td><td>https://www.edwardsvacuum.com/Products/C10512411/View.aspx</td></tr><tr><td>Vacuum Pump</td><td>Edwards</td><td>A36310940 E2M18 200-230/380-415V, 3-ph, 50 Hz</td><td>http://www.edwardsvacuum.com/Products/View.aspx?sku=A36310940</td></tr><tr><td>Dial Gauge</td><td>Edwards</td><td>D35610000 CG16K, 0-1,040 mbar</td><td>http://www.edwardsvacuum.com/Products/View.aspx?sku=D35610000</td></tr><tr><td>Argon Gas</td><td>BOC</td><td>Pureshield Argon Gas</td><td>http://www.boconline.co.uk/en/products-and-supply/industrial-gases/inert-gases/pureshield-argon/pureshield-argon.html</td></tr><tr><td>Stainless Steel Hose</td><td>BOC</td><td>Stainless Steel Hose</td><td>http://www.boconline.co.uk/en/products-and-supply/speciality-equipment/hoses-and-pigtails/index.html</td></tr><tr><td>Regulator</td><td>BOC</td><td>HP 1500 Series Regulator</td><td>http://www.boconline.co.uk/en/products-and-supply/speciality-equipment/regulators/single-stage-regulators/hp1500-series/hp1500-series.html</td></tr><tr><td>Copper Block</td><td>William Rowland</td><td>Copper Ingot 25 kg</td><td>http://www.william-rowland.com/products/high-purity-metals#product-id-18</td></tr><tr><td>Vise</td><td>Record</td><td>T84-34 H/Duty Eng Vice 4 1/2&quot; Jaws REC5658326K</td><td>https://www.cromwell.co.uk/REC5658326K</td></tr><tr><td>Beaker</td><td>Fisher Scientific</td><td>11567402 - Beaker, squat form, with graduations and spout 800 ml</td><td>https://webshop.fishersci.com/insight2_uk/getProduct.do;jsessionid=16D5812&lt;br/&gt; D71B8CB37B475E94281E2BEA&lt;br/&gt; 5.ukhigjavappp11?productCode=11567402&amp;amp;resultSet&lt;br/&gt; Position=0</td></tr><tr><td>Stirring Hot Plate</td><td>Corning</td><td>Corning stirring hot plate Model 6798-420d</td><td>http://www.corning.com/lifesciences/us_canada/en/technical_resources/product_guid/shp/shp.aspx</td></tr><tr><td colspan="4">[header]</td></tr><tr><td>Stir Bar</td><td>Fisher Scientific</td><td>11848862 - PTFE Stir bar + Ring 25x6 mm</td><td>https://webshop.fishersci.com/insight2_uk/getProduct.do;jsessionid=16D5812&lt;br/&gt; D71B8CB37B475E94281E2BEA&lt;br/&gt; 5.ukhigjavappp11?productCode=11848862&amp;amp;resultSet&lt;br/&gt; Position=0</td></tr><tr><td>Air dryer</td><td>V05</td><td>V05 Max Air Turbo Dryer DR-120-GB</td><td>http://reviews.boots.com/2111-en_gb/1120627/v05-v05-max-air-turbo-hair-dryer-dr-120-gb-reviews/reviews.htm</td></tr><tr><td>Ceramic Sheet</td><td>Morgan Advance Materials</td><td>Kaowool Blanket 2 mm thick</td><td>http://www.morganthermalceramics.com/downloads/datasheets?f[0]=field_type%3A84</td></tr><tr><td>Vibrating Table</td><td>Peveril Machinery</td><td>Pevco Vibrating Table 1.25&amp;nbsp;m x 0.625&amp;nbsp;m x 0.6&amp;nbsp;m</td><td>https://peverilmachinery.co.uk/equipment/vibrating-tables</td></tr></tbody></table>

casting protocols for the production of open cell aluminum foams by the replication technique and the effect on porosity

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many cases validated experimentally, for light weight or impact energy absorbing structures, as high surface area heat exchangers or electrodes, as implants to the body, and many more. Although great progress has been made in understanding their structure-properties relationships, the large number of different processing techniques, each producing material with different characteristics and structure, means that understanding of the individual effects of all aspects of structure is not complete. The replication process, where molten metal is infiltrated between grains of a removable preform material, allows a markedly high degree of control and has been used to good effect to elucidate some of these relationships. Nevertheless, the process has many steps that are dependent on individual &#8220;know-how&#8221;, and this paper aims to provide a detailed description of all stages of one embodiment of this processing method, using materials and equipment that would be relatively easy to set up in a research environment. The goal of this protocol and its variants is to produce metal foams in an effective and simple way, giving the possibility to tailor the outcome of the samples by modifying certain steps within the process. By following this, open cell aluminum foams with pore sizes of 1&#8211;2.36 mm diameter and 61% to 77% porosity can be obtained.

In Figure 4 the morphology of the NaCl grains can be seen (angular and spherical), for illustrative purposes. The foams obtained with Protocol A were made using angular shaped grains and the rest were made with the spherical grains. It was found that the use of different shape NaCl grains had no observed effect on the porosity obtained in the samples.
From the results we can determine that samples a, b, and c (made with Protocol A), are on average 63% porous (Figure 5<...

Watch this Scientific Journal Video about Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity at JoVE.com

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Replication is one of the processing techniques used for the production of porous metal sponges. In this paper one implementation of the method for the production of open celled porous aluminum is shown in detail.

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many ...

casting-protocols-for-production-open-cell-aluminum-foams-replication

Research

JoVE Journal

Engineering

14.5K Views.  The University of Sheffield. Replication is one of the processing techniques used for the production of porous metal sponges. In this paper one implementation of the method for the production of open celled porous aluminum is shown in detail.

Video: Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

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

Multi-Scale Modification of Metallic Implants With Pore Gradients, Polyelectrolytes and Their Indirect Monitoring In vivo

Metallic implants, especially titanium implants, are widely used in clinical applications. Tissue in-growth and integration to these implants in the tissues are important parameters for successful clinical outcomes. In order to improve tissue integration, porous metallic implants have being developed. Open porosity of metallic foams is very advantageous, since the pore areas can be functionalized without compromising the mechanical properties of the whole structure. Here we describe such modifications using porous titanium implants based on titanium microbeads. By using inherent physical properties such as hydrophobicity of titanium, it is possible to obtain hydrophobic pore gradients within microbead based metallic implants and at the same time to have a basement membrane mimic based on hydrophilic, natural polymers. 3D pore gradients are formed by synthetic polymers such as Poly-L-lactic acid (PLLA) by freeze-extraction method. 2D nanofibrillar surfaces are formed by using collagen/alginate followed by a crosslinking step with a natural crosslinker (genipin). This nanofibrillar film was built up by layer by layer (LbL) deposition method of the two oppositely charged molecules, collagen and alginate. Finally, an implant where different areas can accommodate different cell types, as this is necessary for many multicellular tissues, can be obtained. By, this way cellular movement in different directions by different cell types can be controlled. Such a system is described for the specific case of trachea regeneration, but it can be modified for other target organs. Analysis of cell migration and the possible methods for creating different pore gradients are elaborated. The next step in the analysis of such implants is their characterization after implantation. However, histological analysis of metallic implants is a long and cumbersome process, thus for monitoring host reaction to metallic implants in vivo an alternative method based on monitoring CGA and different blood proteins is also described. These methods can be used for developing in vitro custom-made migration and colonization tests and also be used for analysis of functionalized metallic implants in vivo without histology.

Multi-Scale Modification of Metallic Implants With Pore Gradients, Polyelectrolytes and Their Indirect Monitoring In vivo

In this video, we will demonstrate modification techniques for porous metallic implants to improve their functionality and to control cell migration. Techniques include development of pore gradients to control cell movement in 3D and production of basement membrane mimics to control cell movement in 2-D. Also, a HPLC-based method for monitoring implant integration in-vivo via analysis of blood proteins is described.

Metallic implants, especially titanium implants, are widely used in  clinical applications. Tissue in-growth and integration to these implants in  the ...

Bioengineering

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental ...

Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support substrates. Accomplishing this transfer in a highly controlled, mechanized, and reproducible manner can eliminate the creation of macroscale defect structures (e.g., tears, cracks, and wrinkles) within the thin film that compromise device performance and the usable area per sample. Here, we describe a general protocol for the highly controlled and mechanized transfer of a polymeric thin film onto an arbitrary porous support substrate for eventual use as a water filtration membrane device. Specifically, we fabricate a block copolymer (BCP) thin film on top of a sacrificial, water-soluble poly(acrylic acid) (PAA) layer and silicon wafer substrate. We then utilize a custom-designed, 3D-printed transfer tool and drain chamber system to deposit, lift-off, and transfer the BCP thin film onto the center of a porous anodized aluminum oxide (AAO) support disc. The transferred BCP thin film is shown to be consistently placed onto the center of the support surface due to the guidance of the meniscus formed between the water and the 3D-printed plastic drain chamber. We also compare our mechanized transfer-processed thin films to those that have been transferred by hand with the use of tweezers. Optical inspection and image analysis of the transferred thin films from the mechanized process confirm that little-to-no macroscale inhomogeneities or plastic deformations are produced, as compared to the multitude of tears and wrinkles produced from manual transfer by hand. Our results suggest that the proposed strategy for thin film transfer can reduce defects when compared to other methods across many systems and applications.

We present a procedure for highly controlled and wrinkle-free transfer of block copolymer thin films onto porous support substrates using a 3D-printed drain chamber. The drain chamber design is of general relevance to all procedures involving transfer of macromolecular films onto porous substrates, which is normally done by hand in an irreproducible fashion.

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support ...

A Facile and Eco-friendly Route to Fabricate Poly(Lactic Acid) Scaffolds with Graded Pore Size

Over the recent years, functionally graded scaffolds (FGS) gaineda crucial role for manufacturing of devices for tissue engineering. The importance of this new field of biomaterials research is due to the necessity to develop implants capable of mimicking the complex functionality of the various tissues, including a continuous change from one structure or composition to another. In this latter context, one topic of main interest concerns the design of appropriate scaffolds for bone-cartilage interface tissue. In this study, three-layered scaffolds with graded pore size were achieved by melt mixing poly(lactic acid) (PLA), sodium chloride (NaCl) and polyethylene glycol (PEG). Pore size distributions were controlled by NaCl granulometry and PEG solvation. Scaffolds were characterized from a morphological and mechanical point of view. A correlation between the preparation method, the pore architecture and compressive mechanical behavior was found. The interface adhesion strength was quantitatively evaluated by using a custom-designed interfacial strength test. Furthermore, in order to imitate the human physiology, mechanical tests were also performed in phosphate buffered saline (PBS) solution at 37 &#176;C. The method herein presented provides a high control of porosity, pore size distribution and mechanical performance, thus offering the possibility to fabricate three-layered scaffolds with tailored properties by following a simple and eco-friendly route.

A Facile and Eco-friendly Route to Fabricate PolyLactic Acid Scaffolds with Graded Pore Size

In this work, poly(lactic acid)/polyethylene glycol (PLA/PEG) scaffolds were prepared by using a combination of melt mixing and selective leaching. The method herein discussed permitted to develop three-layer scaffolds by highly controlling both porosity and pore size. The mechanical properties were also evaluated in a physiological environment.

Over the recent years, functionally graded scaffolds (FGS) gaineda crucial role for manufacturing of devices for tissue engineering. The importance of ...

Fabrication of Extracellular Matrix-derived Foams and Microcarriers as Tissue-specific Cell Culture and Delivery Platforms

Cell function is mediated by interactions with the extracellular matrix (ECM), which has complex tissue-specific composition and architecture. The focus of this article is on the methods for fabricating ECM-derived porous foams and microcarriers for use as biologically-relevant substrates in advanced 3D in vitro cell culture models or as pro-regenerative scaffolds and cell delivery systems for tissue engineering and regenerative medicine. Using decellularized tissues or purified insoluble collagen as a starting material, the techniques can be applied to synthesize a broad array of tissue-specific bioscaffolds with customizable geometries. The approach involves mechanical processing and mild enzymatic digestion to yield an ECM suspension that is used to fabricate the three-dimensional foams or microcarriers through controlled freezing and lyophilization procedures. These pure ECM-derived scaffolds are highly porous, yet stable without the need for chemical crosslinking agents or other additives that may negatively impact cell function. The scaffold properties can be tuned to some extent by varying factors such as the ECM suspension concentration, mechanical processing methods, or synthesis conditions. In general, the scaffolds are robust and easy to handle, and can be processed as tissues for most standard biological assays, providing a versatile and user-friendly 3D cell culture platform that mimics the native ECM composition. Overall, these straightforward methods for fabricating customized ECM-derived foams and microcarriers may be of interest to both biologists and biomedical engineers as tissue-specific cell-instructive platforms for in vitro and in vivo applications.

The tissue-specific extracellular matrix (ECM) is a key mediator of cell function. This article describes methods for synthesizing pure ECM-derived foams and microcarriers that are stable in culture without the need for chemical crosslinking for applications in advanced 3D in vitro cell culture models or as pro-regenerative bioscaffolds.

Cell function is mediated by interactions with the extracellular matrix (ECM), which has complex tissue-specific composition and architecture. The focus ...

Synthesis of Biocompatible Liquid Crystal Elastomer Foams as Cell Scaffolds for 3D Spatial Cell Cultures

Here, we present a step-by-step preparation of a 3D, biodegradable, foam-like cell scaffold. These scaffolds were prepared by cross-linking star block co-polymers featuring cholesterol units as side-chain pendant groups, resulting in smectic-A (SmA) liquid crystal elastomers (LCEs). Foam-like scaffolds, prepared using metal templates, feature interconnected microchannels, making them suitable as 3D cell culture scaffolds. The combined properties of the regular structure of the metal foam and of the elastomer result in a 3D cell scaffold that promotes not only higher cell proliferation compared to conventional porous templated films, but also better management of mass transport (i.e., nutrients, gases, waste, etc.). The nature of the metal template allows for the easy manipulation of foam shapes (i.e., rolls or films) and for the preparation of scaffolds of different pore sizes for different cell studies while preserving the interconnected porous nature of the template. The etching process does not affect the chemistry of the elastomers, preserving their biocompatible and biodegradable nature. We show that these smectic LCEs, when grown for extensive time periods, enable the study of clinically relevant and complex tissue constructs while promoting the growth and proliferation of cells.

This study presents a methodology to prepare 3D, biodegradable, foam-like cell scaffolds based on biocompatible side-chain liquid crystal elastomers (LCEs). Confocal microscopy experiments show that foam-like LCEs allow for cell attachment, proliferation, and the spontaneous alignment of C2C12s myoblasts.

Here, we present a step-by-step preparation of a 3D, biodegradable, foam-like cell scaffold. These scaffolds were prepared by cross-linking star block ...

Fabrication of Gradient Nanopattern by Thermal Nanoimprinting Technique and Screening of the Response of Human Endothelial Colony-forming Cells

Nanotopography can be found in various extracellular matrices (ECMs) around the body and is known to have important regulatory actions upon cellular reactions. However, it is difficult to determine the relation between the size of a nanostructure and the responses of cells owing to the lack of proper screening tools. Here, we show the development of reproducible and cost-effective gradient nanopattern plates for the manipulation of cellular responses. Using anodic aluminum oxide (AAO) as a master mold, gradient nanopattern plates with nanopillars of increasing diameter ranges [120-200&#8239;nm (GP 120/200), 200-280&#8239;nm (GP 200/280), and 280-360&#8239;nm (GP 280/360)] were fabricated by a thermal imprinting technique. These gradient nanopattern plates were designed to mimic the various sizes of nanotopography in the ECM and were used to screen the responses of human endothelial colony-forming cells (hECFCs). In this protocol, we describe the step-by-step procedure of fabricating gradient nanopattern plates for cell engineering, techniques of cultivating hECFCs from human peripheral blood, and culturing hECFCs on nanopattern plates.

Here, we present a protocol for the fabrication of gradient nanopattern plates via thermal nanoimprinting and the method of screening responses of human endothelial progenitor cells to the nanostructures. By using the described technology, it is possible to produce a scaffold that can manipulate cell behavior by physical stimuli.

Nanotopography can be found in various extracellular matrices (ECMs) around the body and is known to have important regulatory actions upon cellular ...

3D Printed Porous Cellulose Nanocomposite Hydrogel Scaffolds

This work demonstrates the use of three-dimensional (3D) printing to produce porous cubic scaffolds using cellulose nanocomposite hydrogel ink, with controlled pore structure and mechanical properties. Cellulose nanocrystals (CNCs, 69.62 wt%) based hydrogel ink with matrix (sodium alginate and gelatin) was developed and 3D printed into scaffolds with uniform and gradient pore structure (110-1,100 &#181;m). The scaffolds showed compression modulus in the range of 0.20-0.45 MPa when tested in simulated in vivo conditions (in distilled water at 37 &#176;C). The pore sizes and the compression modulus of the 3D scaffolds matched with the requirements needed for cartilage regeneration applications. This work demonstrates that the consistency of the ink can be controlled by the concentration of the precursors and porosity can be controlled by the 3D printing process and both of these factors in return defines the mechanical properties of the 3D printed porous hydrogel scaffold. This process method can therefore be used to fabricate structurally and compositionally customized scaffolds according to the specific needs of patients.&#160;

The three critical steps of this protocol are i) developing the right composition and consistency of the cellulose hydrogel ink, ii) 3D printing of scaffolds into various pore structures with good shape fidelity and dimensions and iii) demonstration of the mechanical properties in simulated body conditions for cartilage regeneration.

This work demonstrates the use of three-dimensional (3D) printing to produce porous cubic scaffolds using cellulose nanocomposite hydrogel ink, with ...

Fabricating Highly Open Porous Microspheres (HOPMs) via Microfluidic Technology

Compared to bulk scaffolds and direct injection of cells alone, the injectable modular units have garnered enormous interest in repairing malfunctioned tissues due to convenience in the packaging of cells, improved cell retention, and minimal invasiveness. Moreover, the porous conformation of these microscale carriers could enhance the medium exchange and improve the level of nutrients and oxygen supplies. The present study illustrates the convenient fabrication of poly(lactic-co-glycolic acid)-based highly open porous microspheres (PLGA-HOPMs) by the facile microfluidic technology for cell delivery applications. The resultant monodispersed PLGA-HOPMs possessed particle sizes of ~400 &#181;m and open pores of ~50 &#181;m with interconnecting windows. Briefly, the emulsified oil droplets (PLGA solution in dichloromethane, DCM), wrapped with the 7.5% (w/v) gelatin aqueous phase, were introduced into the 1% (w/v) continuous flowing poly(vinyl alcohol) (PVA) aqueous solution through the coaxial nozzle in the customized microfluidic setup. Subsequently, the microspheres were subjected to solvent extraction and lyophilization procedures, resulting in the production of HOPMs. Notably, various formulations (concentrations of PLGA and porogen) and processing parameters (emulsifying power, needle gauge, and flow rate of dispersed phase) play crucial roles in the qualities and characteristics of the resulting PLGA HOPMs. Moreover, these architectures might potentially encapsulate various other biochemical cues, such as growth factors, for extended drug discovery and tissue regeneration applications.

Fabricating Highly Open Porous Microspheres HOPMs via Microfluidic Technology

The present protocol describes the fabrication of poly(lactic-co-glycolic acid)-based highly open porous microspheres (HOPMs) via the single-emulsion formulation based facile microfluidic technology. These microspheres have potential applications in tissue engineering and drug screening.

Compared to bulk scaffolds and direct injection of cells alone, the injectable modular units have garnered enormous interest in repairing malfunctioned ...

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

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

Multi-Scale Modification of Metallic Implants With Pore Gradients, Polyelectrolytes and Their Indirect Monitoring In vivo

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

A Facile and Eco-friendly Route to Fabricate Poly(Lactic Acid) Scaffolds with Graded Pore Size

Fabrication of Extracellular Matrix-derived Foams and Microcarriers as Tissue-specific Cell Culture and Delivery Platforms

Synthesis of Biocompatible Liquid Crystal Elastomer Foams as Cell Scaffolds for 3D Spatial Cell Cultures

Fabrication of Gradient Nanopattern by Thermal Nanoimprinting Technique and Screening of the Response of Human Endothelial Colony-forming Cells

3D Printed Porous Cellulose Nanocomposite Hydrogel Scaffolds

Fabricating Highly Open Porous Microspheres (HOPMs) via Microfluidic Technology