The authors are grateful to Dr. Stephen Bartolucci and Dr. Joshua Maurer at the U.S. Army Benet Laboratories for the use of their scanning electron microscope. This work was supported by a Faculty Development Research Fund grant from the United States Military Academy, West Point.

&#8203;CAUTION: Consult all relevant safety data sheets (SDS) before use. Use appropriate safety practices when performing chemical reactions, to include the use of a fume hood and personal protective equipment (PPE). Rapid hydrogen gas evolution can cause high pressure in reaction tubes causing caps to pop and solutions to spray out. Ensure that reaction tubes remain open and pointed away from the experimenter as specified in the protocol.
1. Cellulose nanofiber hydrogel preparation
<ol>
	<li>Preparation of cellulose nanofiber solution: Prepare 3% (w/w) cellulose nanofiber solution by mixing 1.5 g of carboxymethyl cellulose nanofibers with 50 mL of deionized water. Shake the solution and vortex for 1 min. Sonicate the solution in a bath sonicator at ambient temperature for 24 h to ensure complete mixing.</li>
	<li>Preparation of cross-linking solution: First add 0.959 g of EDC and 0.195 g of 2-(N-morpholino)ethanesulfonic acid (MES) buffer to 2.833 mL of deionized water. Vortex. Add 0.167 mL of ethylenediamine. Vortex for 15 s. Adjust the final volume to 10 mL and pH to 4.5 by adding 1.0 M HCl and deionized water. 
	NOTE: Final crosslinking solution concentrations are 0.5 M EDC, 0.25 M ethylenediamine, and 0.1 M MES buffer.</li>
	<li>Centrifugation of cellulose nanofiber solution: Pipette 0.25 mL of the 3 % (w/w) cellulose nanofiber solution into each of 6 microfuge tubes (1.7 mL or 2.0 mL). Centrifuge the microfuge tubes for 20 min at 21,000 x g. Remove excess water above the compacted CNFs with a pipette avoiding contact with the top surface. 
	NOTE: After centrifuging, the cellulose nanofiber solutions present a distinct interface between the concentrated CNF&#39;s and the clear supernatant. Based on removal of the excess water, the final CNF concentration will be approximately 3.8 %.</li>
	<li>Cross-link the cellulose nanofiber hydrogels. Pipette 1.0 mL of the EDC and diamine crosslinking solution above the compacted cellulose nanofibers in each of the microfuge tubes. Wait at least 24 h for the crosslinking solution to diffuse through the gels and crosslink the CNFs.</li>
	<li>Gel rinsing: Remove the crosslinking solution supernatant in the microfuge tubes with a pipette. With the microfuge tube caps open, immerse the microfuge tubes containing the crosslinked CNF gels in 1 L of deionized water for at least 24 h to remove excess crosslinking solution from within the CNF hydrogels.</li>
	<li>Fourier-transform infrared (FTIR) spectroscopy: Place approximately 0.5 mL of 3% (w/w) CNF solution in deionized water on the sample stage and scan percent transmittance for 650 - 4000 cm-1. Use the same scan conditions and repeat for a CNF crosslinked hydrogel from Step 1.5.</li>
</ol>
2. Preparation of cellulose nanofiber - palladium composite hydrogels
<ol>
	<li>Prepare Pd(NH3)4Cl2 solution. Prepare 10 mL of 1.0 M Pd(NH3)Cl2 solution. Vortex the solution for 15 s. Dilute 1.0 M Pd(NH3)Cl2 solution to 1 mL volumes at 1, 10, 50, 100, 500, and 1000 mM. 
	NOTE: 1.0 M NaPdCl4 solution and respective dilutions may be used and results in similar final aerogel structures.</li>
	<li>Equilibrate cellulose nanofiber hydrogels in palladium solutions. Pipette 1 mL of the 1, 10, 50, 100, 500, and 1000 mM Pd(NH3)Cl2 solutions on the top of the cellulose nanofiber hydrogels in the microfuge tubes. Wait at least 24 h for the palladium solution to equilibrate within the hydrogels.</li>
	<li>Prepare NaBH4 reducing agent solution. Prepare 60 mL of 2 M NaBH4 solution. Aliquot 10 mL of NaBH4 solution into each of six 15 mL conical tubes. 
	NOTE: The 2 M NaBH4 solution is a highly concentrated reducing agent solution and should be handled within a chemical fume hood. Spontaneous decomposition and hydrogen gas evolution will be observed. Ensure that the tubes are pointed away from the experimenter and that proper PPE is worn.</li>
	<li>First reduction of palladium salts on cellulose nanofiber hydrogels: Invert the microfuge tubes with the palladium equilibrated CNF hydrogels and gently tap to remove the hydrogels. In a chemical fume hood, with flat tweezers, place each of the palladium equilibrated CNF hydrogels into each of the 15 mL conical tubes with 10 mL of NaBH4 solution. Allow the reduction to proceed for 24 h. 
	NOTE: Upon placing the palladium equilibrated CNF gels into the 2 M NaBH4 solution, violent hydrogen gas evolution will occur. Ensure that reaction tubes remain open and pointed away from the experimenter.</li>
	<li>Prepare second NaBH4 reducing agent solution. Prepare 60 mL of 0.5 M NaBH4 solution. Aliquot 10 mL of NaBH4 solution into each of six 15 mL conical tubes.</li>
	<li>Second reduction of palladium salts on cellulose nanofiber hydrogels: In a fume hood, using a pair of flat tweezers transfer each of hydrogels from the 2 M NaBH4 solutions into the 0.5 M NaBH4 solutions. Allow the reduction to proceed for 24 h. 
	NOTE: The initially reduced CNF gels in the 2 M NaBH4 solution will be mechanically stable during the transfer step. However, light pressure should be used with the flat tweezers during solution transfer steps to avoid gel compaction.</li>
	<li>Rinse the cellulose nanofiber-palladium composite gels. Using flat tweezers, transfer each of the reduced palladium-CNF gels into 50 mL deionized water in conical tubes. Exchange deionized water after 12 h and allow the gels to rinse for at least an additional 12 h.</li>
	<li>Perform ethanol solvent exchange in cellulose nanofiber-palladium gels. Use flat tweezers to transfer the rinsed CNF-palladium gels successively into 50 mL of 25%, 50%, 75%, and 100% ethanol solutions with at least 6 h in each solution.</li>
</ol>
3. Aerogel preparation
<ol>
	<li>After solvent exchange with ethanol, dry the CNF-palladium gels using CO2 in a supercritical dryer with a set point of 35 &#176;C and 1200 psi. After supercritical drying is complete, allow the chamber to equilibrate for at least 12 h prior to opening and removal of the aerogels. 
	NOTE: Occasionally, the 500 mM and 1000 mM samples have been observed to combust when removed from the supercritical dryer which is attributed to the presence of palladium hydride. The 12 h supercritical chamber equilibration is intended to allow for outgassing of hydrogen.</li>
</ol>
4. Composite aerogel material characterization
<ol>
	<li>Scanning electron microscopy (SEM): Cut the CNF-palladium aerogel with a razor blade to obtain a thin film approximately 1 - 2 mm thick. Affix the thin film sample with carbon tape on a SEM sample stub. Initially use an accelerating voltage of 15 kV and beam current of 2.7 - 5.4 pA to perform imaging.</li>
	<li>X-ray diffractometry (XRD): Place the CNF-palladium aerogel in a sample holder and align the top of the aerogel with the top of holder. Alternatively, place a thin film sample section, as in Step 4.1, on a glass slide. Perform XRD scans for diffraction angles 2&#920; from 5 &#176; to 90 &#176; at 45 kV and 40 mA with Cu K&#945; radiation (1.54060 &#197;), a 2&#160;&#952; step size of 0.0130 &#176;, and 20 s per step.</li>
	<li>Thermal gravimetric analysis (TGA): Place the aerogel sample in the instrument crucible. Perform analysis by flowing nitrogen gas at 60 mL/min and heating at 10 &#176;/min from ambient temperature to 700 &#176;C.</li>
	<li>Nitrogen gas adsorption-desorption: Degas the samples for 24 h at room temperature. Use nitrogen at -196 &#176;C as the test gas with equilibration times for adsorption and desorption of 60 s and 120 s, respectively. 
	NOTE: Elevated degas temperatures are not recommended to avoid decomposition of the cellulose nanofibers.</li>
	<li>Electrochemical characterization.
	<ol>
		<li>Immerse the aerogel samples in 0.5 M H2SO4 electrolyte for 24 h.</li>
		<li>Use a 3-electrode cell with a Ag/AgCl (3 M NaCl) reference electrode, a 0.5 mm diameter Pt wire auxiliary/counter electrode, and a lacquer coated 0.5 mm diameter platinum working electrode. Place the lacquer coated wire with a 1 mm exposed tip in contact with the top surface of the aerogel at the bottom of the electrochemical vial12.</li>
		<li>Perform electrochemical impedance spectroscopy (EIS) from 1 MHz to 1 mHz with a 10 mV sine wave.</li>
		<li>Perform cyclic voltammetry (CV) using a voltage range of &#8722;0.2 to 1.2 V (vs. Ag/AgCl) with scan rates of 10, 25, 50, 75, and 100 mV/s.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The noble metal cellulose nanofiber biotemplated aerogel synthesis method presented here results in stable aerogel composites with tunable metal composition. The covalent crosslinking of the compacted cellulose nanofibers after centrifugation results in hydrogels that are mechanically durable during the subsequent synthesis steps of palladium ion equilibration, electrochemical reduction, rinsing, solvent exchange, and supercritical drying. The hydrogel stability is vital during the electrochemical reduction step given the high concentration (2 M NaBH4) of reducing agent solution and consequent violent hydrogen evolution. The commercially purchased TEMPO-oxidized cellulose nanofibrils used in this study had a nominal -COO-Na+&#160;molecular weight&#160;of 1.2 mmol/g with approximate length and width of the cellulose nanofibers of 300 and 10 nm, respectively, and the 3% (w/w) solutions had a pH of 5. Likely due to the short fiber length, crosslinking at concentrations 3% (w/w) and less did not result in stable hydrogels. Centrifuging the 3% (w/w) solutions to compact the fibers to an approximate concentration of 3.8 % (w/w) resulted&#160;in well crosslinked hydrogels that were stable during the electrochemical reduction of palladium step. The high NaBH4 concentration is necessary to drive the reducing agent diffusion into the hydrogel biotemplate. The preservation of the covalent hydrogel macroscopic shape and biotemplated mesoporous structure is a key advantage of this synthesis method. In the absence of covalent crosslinking using EDC in the presence of a diamine linker, compacted ionic CNF hydrogels disaggregate during the chemical reduction step. Further, no palladium nanoparticles were observed to diffuse away from the CNF-palladium aerogel composites during the reduction step suggesting that all of the reduced palladium is bound within the resulting aerogels.
Critical to synthesizing homogenous aerogel composites is to allow sufficient time for diffusion in each of the synthesis steps. Using shorter times than indicated in the protocol will result in unstable gels and incomplete metallization throughout the cross-section of the aerogels. This manifests in disaggregation during the reduction, rinsing, solvent exchange, and drying steps, and a ring-like metallization pattern in the aerogel cross-section with metallization near the outer surface and incomplete metallization, or bare cellulose toward the center of the monolith.
The presented synthesis method&#39;s primary benefit is the ability to control the aerogel monolith shape, control the composite aerogel metal content, and achieve a high surface area mesoporous structure. Material characterization with SEM, XRD, TGA, nitrogen gas adsorption, EIS, and CV indicate meaningful and reproducible results that correlate well with the nanostructures observed with SEM. Further, other noble metal salts such as HAuCl4&#8226;3H2O, K2PtCl4, Pt(NH3)4Cl2, and Na2PtCl6 may be employed to achieve similar noble metal composite aerogels11.
The protocol may be varied by changing the shape of the cellulose nanofiber covalent hydrogel template. Compacted CNFs may be shaped into flat films through spin coating, or conformally applied to arbitrary geometries and then crosslinked and processed in accordance with the presented method. The primary limitation of the method is the dependence of each synthesis step on the diffusion time of chemical species correlating with the thickness of the biotemplate hydrogel, and consequent diffusion path length. This poses a practical limit on the size and thickness of the resulting aerogels. Future work includes mass transfer modeling to determine the practical limits of the synthesis method based on diffusion, as well as convective flow approaches to overcome these limitations. Another potential issue with extended use of the CNF-palladium aerogel composite for catalytic applications is palladium leaching with detachment of palladium nanoparticles from the CNF template.
The synthesis method presented here offers an advancement in mechanically stable, shape-controlled, high surface area composite noble metal aerogels with tunable metal content. The covalent cellulose nanofiber hydrogels provide a material synthesis approach for a range of metal composites for energy, catalysis, and sensor applications.

Aerogels, first reported by Kistler, offer porous structures orders of magnitude less dense than their bulk material counterparts1,2,3. Noble metal aerogels have attracted scientific interest for their potential in power and energy, catalytic, and sensor applications. Noble metal aerogels have recently been synthesized via two basic strategies. One strategy is to induce the coalescence of pre-formed nanoparticles4,5,6,7. Sol-gel coalescence of nanoparticles can be driven by linker molecules, changes in solution ionic strength, or simple nanoparticle surface free energy minimization7,8,9. The other strategy is to form aerogels in a single reduction step from metal precursor solutions9,10,11,12,13. This approach has also been used to form bimetallic and alloy noble metal aerogels. The first strategy is generally slow and may require up to many weeks for nanoparticle coalescence14. The direct reduction approach, while generally more rapid, suffers from poor shape control over the macroscopic aerogel monolith.
One possible synthesis approach to address challenges with control of noble metal aerogel macroscopic shape and nanostructure is to employ biotemplating15. Biotemplating uses biological molecules ranging from collagen, gelatin, DNA, viruses, to cellulose to provide a shape-directing template for the synthesis of nanostructures, where the resulting metal-based nanostructures assume the geometry of the biological template molecule16,17. Cellulose nanofibers are appealing as a biotemplate given the high natural abundance of cellulosic materials, their high aspect ratio linear geometry, and ability to chemically functionalize their glucose monomers18,19,20,21,22,23. Cellulose nanofibers (CNF) have been used to synthesize three dimensional TiO2 nanowires for photoanodes24, silver nanowires for transparent paper electronics25, and palladium aerogel composites for catalysis26. Further, TEMPO-oxidized cellulose nanofibers have been used both as a biotemplate and reducing agent in the preparation of palladium decorated CNF aerogels27.
Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented26. Fragile aerogels with poor shape control occurs for a range noble metal aerogel synthesis methods. Carboxymethylated cellulose nanofibers (CNFs) used to form a covalent hydrogel allow for the reduction of metal ions such as palladium on the CNFs providing control over both nanostructure and macroscopic aerogel monolith shape after supercritical drying. Carboxymethylated cellulose nanofiber crosslinking is achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine as a linker molecule between CNFs. The CNF hydrogels maintain their shape throughout the synthesis steps including covalent crosslinking, equilibration with precursor ions, metal reduction with high concentration reducing agent, rinsing in water, ethanol solvent exchange, and CO2 supercritical drying. Precursor ion concentration variation allows for control over the final aerogel metal content through a direct ion reduction rather than relying on the relatively slow coalescence of pre-formed nanoparticles used in sol-gel methods. With diffusion as the basis to introduce and remove chemical species into and out of the hydrogel, this method is suitable for smaller bulk geometries and thin films. Characterization of the cellulose nanofiber-palladium composite aerogels with scanning electron microscopy, X-ray diffractometry, thermal gravimetric analysis, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry indicates a high surface area, metalized palladium porous structure.

<table><tbody><tr><td>0.5 mm platinum wire electrode</td><td>BASi</td><td>MW-4130</td><td>Used for auxillery electrode and separately for lacquer coating and use as a working electrode</td></tr><tr><td>1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)</td><td>Sigma-Aldrich</td><td>&amp;nbsp;1892-57-5</td><td></td></tr><tr><td>2-(N-morpholino)ethanesulfonic acid (MES)</td><td>Sigma-Aldrich</td><td>117961-21-4&amp;nbsp;</td><td></td></tr><tr><td>Ag/AgCl (3M NaCl) Reference Electrode</td><td>BASi</td><td>MF-2052</td><td></td></tr><tr><td>Carboxymethyl cellulose, TEMPO Cellulose Nanofibrils, Dry Powder</td><td>University of Maine Process Development Center</td><td>No 8</td><td></td></tr><tr><td>Ethanol, 200 proof</td><td>PHARMCO-AAPER</td><td>241000200</td><td></td></tr><tr><td>Ethylenediamine</td><td>Sigma-Aldrich</td><td>&amp;nbsp;107-15-3</td><td></td></tr><tr><td>Fourier-Transform Infrared (FTIR) Spectrometer, Frontier</td><td>Perkin Elmer</td><td>L1280044</td><td></td></tr><tr><td>Hydrochloric Acid</td><td>CORCO</td><td>7647-01-0</td><td></td></tr><tr><td>Na&lt;sub&gt;2&lt;/sub&gt;PdCl&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>13820-40-1</td><td></td></tr><tr><td>NaBH&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>16940-66-2</td><td></td></tr><tr><td>Pd(NH&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;4&lt;/sub&gt;Cl&lt;sub&gt;2&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>13933-31-8</td><td></td></tr><tr><td>Potentiostat</td><td>Biologic-USA</td><td>VMP-3</td><td>Electrochemical analysis-EIS, CV</td></tr><tr><td>Scanning Electron Mciroscope (SEM) Helios 600 Nanolab</td><td>ThermoFisher Scientific</td><td></td><td></td></tr><tr><td>Supercritical Dryer</td><td>Leica</td><td>EM CPD300</td><td>Aerogel supercritical drying with CO&lt;sub&gt;2&lt;/sub&gt;</td></tr><tr><td>Surface and Pore Analyzer</td><td>Quantachrome</td><td>NOVA 4000e</td><td>Nitrogen gas adsorption</td></tr><tr><td>Thermal Gravimetric Analysis</td><td>TA instruments</td><td>TGA Q500</td><td></td></tr><tr><td>Ultrasonic Cleaner</td><td>MTI</td><td>EQ-VGT-1860QTD</td><td></td></tr><tr><td>XRD</td><td>PanAlytical</td><td>Empyrean</td><td>X-ray diffractometry</td></tr></tbody></table>

synthesis method for cellulose nanofiber biotemplated palladium composite aerogels

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often result in fragile aerogels with poor shape control. The use of carboxymethylated cellulose nanofibers (CNFs) to form a covalently bonded hydrogel allows for the reduction of metal ions such as palladium on the CNFs with control over both nanostructure and macroscopic aerogel monolith shape after supercritical drying. Crosslinking the carboxymethylated cellulose nanofibers is achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine. The CNF hydrogels maintain their shape throughout synthesis steps including covalent crosslinking, equilibration with precursor ions, metal reduction with high concentration reducing agent, rinsing in water, ethanol solvent exchange, and CO2 supercritical drying. Varying the precursor palladium ion concentration allows for control over the metal content in the final aerogel composite through a direct ion chemical reduction rather than relying on the relatively slow coalescence of pre-formed nanoparticles used in other sol-gel techniques. With diffusion as the basis to introduce and remove chemical species into and out of the hydrogel, this method is suitable for smaller bulk geometries and thin films. Characterization of the cellulose nanofiber-palladium composite aerogels with scanning electron microscopy, X-ray diffractometry, thermal gravimetric analysis, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry indicates a high surface area, metallized palladium porous structure.

The scheme to covalently crosslink cellulose nanofibers with EDC in the presence of ethylenediamine is depicted in Figure 1. EDC crosslinking results in an amide bond between a carboxyl and primary amine functional group. Given that the carboxymethyl cellulose nanofibers possess only carboxyl groups for crosslinking, the presence of a diamine linker molecule such as ethylenediamine is essential to covalently link two adjacent CNFs via two amide bonds. To confirm crosslinking,&#160;Figure 2 shows FTIR spectra for 3% (w/w) CNF solutions compared to CNF hydrogels after crosslinking with&#160;1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)&#160;in the presence of ethylenediamine. Both CNF and crosslinked CNF hydrogels were equilibrated in deionized water prior to FTIR analysis. The 3% (w/w) CNF solution presents a broad peak between approximately 3200 to 3600 cm-1 and is attributed to O-H stretching28. The prominent peak at 1595 cm-1 is likely attributed to the vibration of the -COO-Na+ groups on the carboxymethyl cellulose nanofibers29. After crosslinking the carboxymethyl cellulose nanofibers with EDC in the presence of ethylenediamine, three bonding possibilities result. The first is an effective crosslink between two CNF&#39;s with ethylenediamine forming two amide bonds with carboxylates on the CNF&#39;s. The second is ethylenediamine forming a single amide bond with a CNF carboxylate with a primary amine at the other end of the diamine molecule. The third possibility is EDC forming an unstable o-acylisourea intermediate that hydrolyzes to reform the initial carboxyl group30.
After crosslinking, the broad O-H absorption band between 3200 to 3600 cm-1 decreases, with the emergence of prominent peaks at 3284 and 3335 cm-1, attributed to primary amines and amide bonds resulting from both amides of crosslinked CNFs, and single amide bonds between CNFs and ethylenediamine resulting in a primary amine at the terminal end of the ethylenediamine molecule28,31. The peak at 2903 cm-1 associated with C-H stretching becomes more prominent after crosslinking and is attributed to the increased presence of -NH3+ from the terminal primary amines. The decrease in the carbonyl stretch at a wavenumber of 1595 cm-1 is attributed to the decreased number of -COO-Na+ groups due to crosslinking with ethylenediamine. The formation of amide bonds due to crosslinking is seen in the amide peaks at 1693 and 1668 cm-1, as well as at 1540 cm-1, and a small peak at 1236 cm-1&#160;28,29,31.
Figure 3&#160;depicts photographs of each of the synthesis steps to include: the covalently crosslinked CNF hydrogels (Figure 3a); CNFs equilibrated across a concentration range of 1, 10, 50, 100, 500, and 1000 mM Pd(NH3)4Cl2 (Figure 3b), or Na2PdCl4 (Figure 3c) solution; reduced CNF-palladium gels (Figure 3d); and supercritically dried aerogel composites (Figure 3e). The photographs demonstrate the shape control offered by this synthesis method.
The SEM images in Figure 4a-f depict composite CNF-palladium aerogels synthesized from 1, 10, 50, 100, 500, and 1000 mM Pd(NH3)4Cl2 solutions, respectively. In general, the aerogels present interconnected fibrillary ligaments with increasing nanoparticle size correlating with increasing palladium solution concentration. The average nanoparticle diameters and pore sizes for lower concentration samples are: 1 mM) 12.6 &#177; 2.2 nm and 32.4 &#177; 13.3 nm; and 10 mM) 12.4 &#177; 2.0 nm and 32.2 &#177; 10.4 nm. Aerogels synthesized with 50 mM and higher palladium concentrations present more distinctly interconnected nanoparticles. The average nanoparticle diameters resulting from 50, 100, 500, and 1000 mM palladium synthesis concentrations are 19.5 &#177; 5.0 nm, 41.9 &#177; 10.0 nm, 45.6 &#177; 14.6 nm, and 59.0 &#177; 16.4 nm, respectively.
XRD spectra for 2&#160;&#952; angles from 15 &#8211; 70&#160;&#176; in Figure 5 indicate peaks for palladium and palladium hydride indexed to Joint Committee on Powder Diffraction Standards (JCPDS) reference numbers 01-087-0643 and 00-018-0951, respectively. The palladium hydride and palladium peaks become more convoluted with increasing palladium synthesis concentration, where they are not distinguishable at 1000 mM. The decrease in peak broadening correlates with the increase in nanoparticle diameters observed in Figure 4.
The thermogravimetric spectra shown in Figure 6 indicate increasing metal content in the CNF-palladium composite aerogels with increasing synthesis palladium solution concentration. The weight% versus palladium synthesis concentration shown in Figure 6c demonstrates control of metal content in the aerogel composite between 0 - 75.5%.
Nitrogen adsorption-desorption isotherms, and corresponding cumulative pore volumes with differential pore volume are shown for aerogel composites synthesized from 1, 100, and 1000 mM palladium solutions in Figure 7a-b, Figure 7c-d, and Figure 7e-f, respectively. The physisorption data indicates type IV adsorption-desorption isotherms indicating mesoporous and macroporous structure. The Brunauer-Emmett-Teller (BET) specific surface areas were 582, 456, and 171 m2/g for the 1, 100, and 1000 mM palladium samples, respectively, indicating decreasing specific surface area with increasing metal content32. Barrett-Joyner-Halenda (BJH) pore size analysis also indicates that as the aerogel palladium content increases, there is a decreasing frequency of mesopores33. Using BJH analysis of the desorption curves, the cumulative pore volumes (Vpore) for the 1, 100 and 1000 mM samples were 7.37 cm3/g, 6.10 cm3/g, and 2.40 cm3/g. Average sample specific volumes (Vsample) were determined by measuring the volume and dividing by the sample mass. Aerogel porosities were 97.3%, 95.0%, and 90.4% for the 1, 100, and 1000 mM, respectively using Equation (1),
% Porosity = (Vpore / Vsample) x 100 % (1)
With the same starting CNF covalent hydrogel and pore size distribution, sample porosities decrease with increasing metal content as the reduced metal fills the pore space.
Figure 8a shows the EIS spectra conducted in 0.5 M H2SO4 using a 10 mA amplitude sine wave across a frequency range of 140 kHz to 15 mHz. The incomplete semicircle in the high frequency region shown in Figure 8b indicates low charge transfer resistance and double layer capacitance for the CNF-palladium composite aerogel. CV scans performed in 0.5 M H2SO4 from -0.2 V to 1.2 V (vs Ag/AgCl) at scan rates of 10, 25, 50, and 75 mV/s are shown in Figure 8c, with the 10 mV/s scan shown separately in Figure 8d. The CV scans indicate hydrogen adsorption and desorption at potentials less than 0 V, as well as characteristic oxidation and reduction peaks for palladium greater than 0.5 V.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59176/59176fig1.jpg" />
Figure 1. Aerogel synthesis scheme. (a) Cross linking carboxymethyl cellulose nanofibers (CNF) with EDC and ethylenediamine as a linker molecule. (b, c) Cross-linked carboxymethyl cellulose nanofibers. (d) CNF hydrogel equilibrated with palladium salt solution. (e) CNF biotemplated palladium composite aerogel after reduction with NaBH4, rinsing, solvent exchange with ethanol, and CO2 supercritical drying. Reproduced from reference 26 with permission. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59176/59176fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/59176/59176fig2.jpg" /> 
Figure 2. FTIR spectra for 3 % (w/w) carboxymethyl cellulose nanofiber (CNF) solution in deionized water and CNF hydrogels crosslinked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine and subsequently equilibrated in deionized water. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59176/59176fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/59176/59176fig3.jpg" /> 
Figure 3. Aerogel synthesis process photos. (a) Cross-linked carboxymethyl cellulose nanofiber hydrogels with EDC and ethylenediamine as a linker molecule. CNF hydrogels equilibrated with palladium salt solutions of 1, 10, 50, 100, 500, and 1000 mM for (b) Pd(NH3)4Cl2, and (c) Na2PdCl4. (d) CNF biotemplated palladium aerogel after reduction with NaBH4. (e) CNF-Pd composite aerogels after rinsing, solvent exchange with ethanol, and CO2 supercritical drying. Reproduced from reference 26 with permission.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59176/59176fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/59176/59176fig4.jpg" /> 
Figure 4. Scanning electron microscopy images of CNF-Pd composite aerogels prepared from Pd(NH3)4Cl2 concentrations of (a) 1 mM; (b) 10 mM; (c) 50 mM; (d) 100 mM; (e) 500 mM; and (f) 1000 mM.&#160;Reproduced from reference 26 with permission. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59176/59176fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/59176/59176fig5.jpg" /> 
Figure 5. X-ray diffraction spectra for CNF-Pd composite aerogels synthesized from Pd(NH3)4Cl2 salt solution concentrations of 1 mM, 10 mM, 50 mM, 100 mM, 500 mM, and 1000 mM. JCPDS reference 00-018-0951 palladium hydride peak positions are indicated with a light blue dashed line, and dashed gray lines for 01-087-0643 palladium peak positions. Reproduced from reference 26 with permission. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59176/59176fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/59176/59176fig6.jpg" /> 
Figure 6. Thermogravimetric analysis (TGA). (a) TGA of aerogels synthesized with Pd(NH3)4Cl2 salt solutions. (b) TGA of 50 mM Pd(NH3)4Cl2 sample from (a) with differential thermal analysis (DTA). (c) Palladium sample mass at 600 &#176;C from (a) for the varying palladium concentrations. Reproduced from reference 26 with permission. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59176/59176fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/59176/59176fig7.jpg" /> 
Figure 7. Brunauer-Emmett-Teller analysis. Nitrogen adsorption-desorption isotherms, and pore size distribution with cumulative pore volume for aerogels synthesized with Pd(NH3)4Cl2 salt solutions of (a,b) 0 mM, (c,d) 100 mM and (e,f) 1000 mM. Reproduced from reference 26 with permission. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59176/59176fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/59176/59176fig8.jpg" /> 
Figure 8. Electrochemical characterization in 0.5 M H2SO4 of CNF-Pd aerogels prepared from 1000 mM Pd(NH3)4Cl2. (a) Electrochemical impedance spectroscopy with a 10 mV sine wave was used across frequencies from 140 kHz to 15 mHz. (b) High frequency spectra from 140 kHz to 1.3 kHz from (a). (c) Cyclic voltammetry (CV) at scan rates of 10, 25, 50, and 75 mV/s. (d) CV scan at 10 mV/s from (c). Reproduced from reference 26 with permission.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/59176/59176fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels at JoVE.com

Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

A synthesis method for cellulose nanofiber biotemplated palladium composite aerogels is presented.The resulting composite aerogel materials offer potential for catalysis, sensing, and hydrogen gas storage applications.

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often ...

synthesis-method-for-cellulose-nanofiber-biotemplated-palladium

Nanyang Technological University

Research

JoVE Journal

Chemistry

8.0K Views.  United States Military Academy. Deze methode met behulp van cellulose nanofiber biopolymeer covalente hydrogels om een palladium metalen aerogel composiet te bereiken kan generalizable zijn voor een breed scala van biopolymeer sjablonen en metalen. Deze samengestelde aerogel synthese methode maakt gebruik van cellulose nanovezels als een biotemplaat om controle te krijgen over zowel pallium metalen nanostructuur en macroscopische aerogel monolith vorm. De vormregeling en de mechanische integriteit van biotemplated metaal ae...

Video: Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

Towards Biomimicking Wood: Fabricated Free-standing Films of Nanocellulose, Lignin, and a Synthetic Polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

The objective of this research was to form synthetic plant cell wall tissue using layer-by-layer assembly of nanocellulose fibrils and isolated lignin assembled from dilute aqueous suspensions.&#160; Surface measurement techniques of quartz crystal microbalance and atomic force microscopy were used to monitor the formation of the polymer-polymer nanocomposite material.

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and ...

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

Engineering

Preparation of Biopolymer Aerogels Using Green Solvents

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers (gelatin, agar, cellulose), only recently have biomasses been recognized as an abundant source of chemically diverse macromolecules for functional aerogel materials. Biopolymer aerogels (pectin, alginate, chitosan, cellulose, etc.) exhibit both specific inheritable functions of starting biopolymers and distinctive features of aerogels (80-99% porosity and specific surface up to 800 m2/g). This synergy of properties makes biopolymer aerogels promising candidates for a wide gamut of applications such as thermal insulation, tissue engineering and regenerative medicine, drug delivery systems, functional foods, catalysts, adsorbents and sensors. This work demonstrates the use of pressurized carbon dioxide (5 MPa) for the ionic cross linking of amidated pectin into hydrogels. Initially a biopolymer/salt dispersion is prepared in water. Under pressurized CO2 conditions, the pH of the biopolymer solution is lowered to 3 which releases the crosslinking cations from the salt to bind with the biopolymer yielding hydrogels. Solvent exchange to ethanol and further supercritical CO2 drying (10 - 12 MPa) yield aerogels. Obtained aerogels are ultra-porous with low density (as low as 0.02 g/cm3), high specific surface area (350 - 500 m2/g) and pore volume (3 - 7 cm3/g for pore sizes less than 150 nm).

A new way for the production of biopolymer-based aerogels by carbon dioxide (CO2) induced gelation is shown. The technique utilizes pressurized carbon dioxide (5 MPa) for the production of biopolymer hydrogels and supercritical CO2 (12 MPa) to convert gels into aerogels. The only solvents needed besides CO2 are water and ethanol.

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers ...

Highly Stable, Functional Hairy Nanoparticles and Biopolymers from Wood Fibers: Towards Sustainable Nanotechnology

Nanoparticles, as one of the key materials in nanotechnology and nanomedicine, have gained significant importance during the past decade. While metal-based nanoparticles are associated with synthetic and environmental hassles, cellulose introduces a green, sustainable alternative for nanoparticle synthesis. Here, we present the chemical synthesis and separation procedures to produce new classes of hairy nanoparticles (bearing both amorphous and crystalline regions) and biopolymers based on wood fibers. Through periodate oxidation of soft wood pulp, the glucose ring of cellulose is opened at the C2-C3 bond to form 2,3-dialdehyde groups. Further heating of the partially oxidized fibers (e.g., T = 80 &#176;C) results in three products, namely fibrous oxidized cellulose, sterically stabilized nanocrystalline cellulose (SNCC), and dissolved dialdehyde modified cellulose (DAMC), which are well separated by intermittent centrifugation and co-solvent addition. The partially oxidized fibers (without heating) were used as a highly reactive intermediate to react with chlorite for converting almost all aldehyde to carboxyl groups. Co-solvent precipitation and centrifugation resulted in electrosterically stabilized nanocrystalline cellulose (ENCC) and dicarboxylated cellulose (DCC). The aldehyde content of SNCC and consequently surface charge of ENCC (carboxyl content) were precisely controlled by controlling the periodate oxidation reaction time, resulting in highly stable nanoparticles bearing more than 7 mmol functional groups per gram of nanoparticles (e.g., as compared to conventional NCC bearing &#60;&#60; 1 mmol functional group/g). Atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) attested to the rod-like morphology. Conductometric titration, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), dynamic light scattering (DLS), electrokinetic-sonic-amplitude (ESA) and acoustic attenuation spectroscopy shed light on the superior properties of these nanomaterials.

Synthesis schemes to prepare highly stable wood fiber-based hairy nanoparticles and functional cellulose-based biopolymers have been detailed.

Nanoparticles, as one of the key materials in nanotechnology and nanomedicine, have gained significant importance during the past decade. While ...

Manufacturing Of Robust Natural Fiber Preforms Utilizing Bacterial Cellulose as Binder

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose and short sisal fibers are dispersed into a water suspension containing bacterial cellulose. The fiber and nanocellulose suspension is then filtered (using vacuum or gravity) and the wet filter cake pressed to squeeze out any excess water, followed by a drying step. This will result in the hornification of the bacterial cellulose network, holding the loose natural fibers together.
Our method is specially suited for the manufacturing of rigid and robust preforms of hydrophilic fibers. The porous and hydrophilic nature of such fibers results in significant water uptake, drawing in the bacterial cellulose dispersed in the suspension. The bacterial cellulose will then be filtered against the surface of these fibers, forming a bacterial cellulose coating. When the loose fiber-bacterial cellulose suspension is filtered and dried, the adjacent bacterial cellulose forms a network and hornified to hold the otherwise loose fibers together.
The introduction of bacterial cellulose into the preform resulted in a significant increase of the mechanical properties of the fiber preforms. This can be attributed to the high stiffness and strength of the bacterial cellulose network. With this preform, renewable high performance hierarchical composites can also be manufactured by using conventional composite production methods, such as resin film infusion (RFI) or resin transfer molding (RTM). Here, we also describe the manufacturing of renewable hierarchical composites using double bag vacuum assisted resin infusion.

We present a novel method of manufacturing rigid and robust short natural fiber preforms using a papermaking process. Bacterial cellulose acts simultaneously as the binder for the loose fibers and provides rigidity to the fiber preforms. These preforms can be infused with a resin to produce truly green hierarchical composites.

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose ...

Bioengineering

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

A Salt-Templated Synthesis Method for Porous Platinum-based Macrobeams and Macrotubes

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed by rinsing and supercritical drying steps, often resulting in mechanically fragile materials. Here, a method to synthesize nanostructured porous platinum-based macrotubes and macrobeams with a square cross section from insoluble salt needle templates is presented. The combination of oppositely charged platinum, palladium, and copper square planar ions results in the rapid formation of insoluble salt needles. Depending on the stoichiometric ratio of metal ions present in the salt-template and the choice of chemical reducing agent, either macrotubes or macrobeams form with a porous nanostructure comprised of either fused nanoparticles or nanofibrils. Elemental composition of the macrotubes and macrobeams, determined with x-ray diffractometry and x-ray photoelectron spectroscopy, is controlled by the stoichiometric ratio of metal ions present in the salt-template. Macrotubes and macrobeams may be pressed into free standing films, and the electrochemically active surface area is determined with electrochemical impedance spectroscopy and cyclic voltammetry. This synthesis method demonstrates a simple, relatively fast approach to achieve high-surface area platinum-based macrotubes and macrobeams with tunable nanostructure and elemental composition that may be pressed into free-standing films with no required binding materials.

A synthesis method to obtain porous platinum-based macrotubes and macrobeams with a square cross section through chemical reduction of insoluble salt-needle templates is presented.

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed ...

Microhoneycomb Monoliths Prepared by the Unidirectional Freeze-drying of Cellulose Nanofiber Based Sols: Method and Extensions

Monolithic honeycomb structures have been attractive to multidisciplinary fields due to their high strength-to-weight ratio. Particularly, microhoneycomb monoliths (MHMs) with micrometer-scale channels are expected as efficient platforms for reactions and separations because of their large surface areas. Up to now, MHMs have been prepared by a unidirectional freeze-drying (UDF) method only from very limited precursors. Herein, we report a protocol from which a series of MHMs consisting of different components can be obtained. Recently, we found that cellulose nanofibers function as a distinct structure-directing agent towards the formation of MHMs through the UDF process. By mixing the cellulose nanofibers with water soluble substances which do not yield MHMs, a variety of composite MHMs can be prepared. This significantly enriches the chemical constitution of MHMs towards versatile applications.

Here, we present a general protocol to prepare a variety of microhoneycomb monoliths (MHMs) in which fluid can pass through with an extremely low pressure drop. MHMs obtained are expected to be used as filters, catalyst supports, flow-type electrodes, sensors and scaffolds for biomaterials.

Monolithic honeycomb structures have been attractive to multidisciplinary fields due to their high strength-to-weight ratio. Particularly, microhoneycomb ...

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 ...

Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

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