This paper was funded by the National Institutes of Health (R01AR074234, R21EB026824, R01 AR073822-01), the Brigham Research Institute Stepping Strong Innovator Award, and AHA Innovative Project Award (19IPLOI34660079).

This study was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. The protocol was approved by the institutional Animal Care and Use Committee (IACUC) of Brigham and Women&#39;s Hospital.
1. GelMA synthesis
<ol>
	<li>Dissolve 10 g of gelatin in 100 mL of Dulbecco&#39;s phosphate-buffered saline (DPBS) using a magnetic stirrer at 50 &#176;C.</li>
	<li>Add 8 mL of methacrylic anhydride slowly while stirring the gelatin prepolymer solution at 50 &#176;C for 2 h. Dilute the reacted gelatin solution with preheated DPBS at 50 &#176;C.</li>
	<li>Transfer the diluted solution into dialysis membranes (molecular weight cutoff = 12&#8211;14 kDa) and place them into deionized (DI) water. Perform dialysis at 40 &#176;C for about 1 week.</li>
	<li>Filter the dialyzed GelMA prepolymer solution using a sterile filter (pore size = 0.22 &#181;m) and transfer 25 or 30 mL of the solution into 50 mL tubes and store at -80 &#176;C for 2 days.</li>
	<li>Freeze-dry the frozen GelMA prepolymer solution using a freeze dryer for 5 days.</li>
</ol>
2. Preparation of poly(ethylene glycol) diacrylate (PEGDA) prepolymer solution
<ol>
	<li>Dissolve 200 mg (20% of total solution) of PEGDA (MW = 1,000) with 5 mg (0.5% of total solution) of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone (photo-initiator, PI) in 1 mL of DPBS.</li>
	<li>Incubate the prepolymer solution at 80 &#176;C for 5 min.</li>
</ol>
3. Preparation of GelMA-coated CNT dispersed stock solution
<ol>
	<li>Dissolve 80 mg of GelMA (used as a biosurfactant) in 4 mL of DPBS and then add 20 mg of COOH functionalized multiwalled carbon nanotubes (MWCNTs) into the GelMA prepolymer solution.</li>
	<li>Sonicate the MWCNT-laden GelMA prepolymer solution for 1 h (0.66Hz, 100 Watt). 
	NOTE: During the sonication process, the solution must be immersed in a water bath at ~15 &#176;C to prevent evaporation of solvent due to the rise in temperature.</li>
</ol>
4. Preparation of 1 mg/mL CNT containing 5% GelMA prepolymer solution
<ol>
	<li>Dissolve 50 mg of GelMA and 5 mg (0.5% of total solution) of PI in 0.8 mL of DPBS at 80 &#176;C for 10 min.</li>
	<li>Add 0.2 mL of the prepared CNT stock solution (step 3). Vortex and incubate the solution at 80 &#176;C for 10 min.</li>
</ol>
5. Preparation of a 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) coated glass slide
<ol>
	<li>Wash the glass slides (thickness = 1 mm, size = 5.08 cm x 7.62 cm) with pure ethanol.</li>
	<li>Stack the cleaned slides vertically in a 250 mL beaker and spread 3 mL of TMSPMA on top of them using a syringe. Cover the beaker with aluminum foil to prevent evaporation of TMSPMA.</li>
	<li>Incubate the slides in an 80 &#730;C oven for 1 day.</li>
	<li>Wash the coated glass slides by dipping them into pure ethanol, then dry.</li>
	<li>Store the coated glass slides wrapped in aluminum foil at room temperature (RT). 
	NOTE: Try to minimize touching the surfaces of the TMSPMA-coated glass slides.</li>
</ol>
6. Fabrication of the flexible Au microelectrodes
<ol>
	<li>Design a shadow mask using computer-aided design (Supplementary File 3).</li>
	<li>Fabricate and purchase a shadow mask.</li>
	<li>Wash the glass slide (thickness = 1 mm, size = 3 cm x 4 cm) with acetone and dry with a compressed air gun.</li>
	<li>Attach the shadow mask to the glass substrates using double sided tape, then put them in an E-beam evaporator and wait until the chamber pressure reaches at least 10-6 Torr. 
	NOTE: The two pieces of tape were placed manually on the support at a distance short enough to host the glass and large enough to fit the entire pattern. This step takes around 45&#8211;60 min.</li>
	<li>Deposit a 200 nm thick Au layer by E-beam evaporator (e.g., with Denton EE-4, vacuum = 10-6 Torr, power = 2.6%, rate = 2 &#197;/s) and cut the fabricated microelectrodes using a dicing saw machine (electrodes size = 7.38 mm x 8.9 mm x 200 nm).</li>
</ol>
7. Fabrication of an Au microelectrode-integrated micropatterned multilayered hydrogel scaffold
NOTE: The result of this procedure is a membrane where a micropatterned PEGDA hydrogel is in the bottom layer, a micropatterned CNT-GelMA hydrogel is on top, and the Au microelectrodes are between the two layers. This configuration ensures a better flexibility to the electrode and limits the risk of breaking.
<ol>
	<li>Design and fabricate two photomasks to create the micropatterned PEGDA (1st photomask) and the CNT-GelMA hydrogel (2nd photomask) layers. See Supplementary File 2&#8211;3. The design can be done by using CAD software. 
	NOTE: See Figure 2B, E.</li>
	<li>Place 50 &#956;m spacers made by stacking one layer of commercial invisible tape (Thickness: 50 &#956;m) on a TMSPMA coated glass. Pour 15 &#956;L of 20% PEGDA prepolymer solution on top of the TMSPMA coated glass, then cover with gold microelectrode. Place the 1st photomask for the glass slide (micropatterned PEGDA) on top of the gold microelectrode and expose the whole construct to UV light (200 W mercury vapor short arc lamp with 320&#8211;390 nm filter) at 800 mW of intensity and 8 cm distance for 110 s. 
	NOTE: See Figure 1A.</li>
	<li>Add DPBS to surround the glass slide and detach the micropatterned PEGDA hydrogel together with the Au microelectrodes from the uncoated glass substrate carefully after 5&#8211;10 min to obtain the glass slide that has the micropatterned PEGDA hydrogel with the Au microelectrodes. 
	NOTE: See Figure 1B. Due to the TMSPMA coating, the construct is transferred from the uncoated glass substrate to the TMSPMA-coated one. Detach carefully because the Au microelectrodes can break easily during this step (Figure 3).</li>
	<li>Place 100 &#956;m spacers made by stacking two layers of commercial transparent tape (thickness = 50 &#181;m) on the bottom of a Petri dish. Deposit a drop of 20 &#956;L CNT-GelMA prepolymer solution between the spacers and then flip the glass slide obtained in 7.3 and fix it onto the dish with adhesive tape.</li>
	<li>Rotate the device upside down and place the 2nd photomask on top of the glass slide. Expose under UV light at 800 mW of intensity and 8 cm distance for 200 s. 
	NOTE: See Figure 1C. Alignment of the 2nd mask is important.</li>
	<li>Wash the obtained scaffold with DPBS and with cell culture medium that includes 10% fetal bovine serum (FBS).</li>
	<li>Leave them overnight in the 37 &#176;C incubator before seeding the cells.</li>
</ol>
8. Neonatal rat cardiomyocytes isolation and culture
<ol>
	<li>Isolate hearts from 2-day-old Sprague-Dawley rats following protocols approved by the Institute&#39;s Committee on Animal Care8.</li>
	<li>Put the heart pieces on the shaker overnight (around 16 h) in 0.05% trypsin without EDTA in HBSS in a cold room.</li>
	<li>Collect the heart pieces with a pipette gun and minimize the amount of trypsin, then put them in a 50 mL tube with 10 mL of warm cardiac media (10% FBS, 1% P/S, 1% L-glutamine).</li>
	<li>Swirl slowly (~60 rpm) in a 37 &#176;C water bath for 7 min. Remove the media carefully from the tube with a 10 mL pipette and leave the heart pieces in the tube.</li>
	<li>Add 7 mL of 0.1% collagenase type 2 in HBSS and swirl in a 37 &#176;C water bath for 10 min.</li>
	<li>Mix with a 10 mL pipette 10x gently to disrupt the heart pieces. Remove the media from the tube with a 1 mL pipette.</li>
	<li>Add 10 mL of 0.1% collagenase type 2 in HBSS and swirl quickly (~120&#8211;180 rpm) in a 37 &#176;C water bath for 10 min, then check if the heart pieces are dissolving.</li>
	<li>Mix with a 10 mL pipette, then repeat with a 1 mL pipette to break the last heart pieces.</li>
	<li>Once the solution looks homogeneous, place a 70 &#181;m cell strainer on a new 50 mL tube and pipette the solution 1 mL at a time on strainer.</li>
	<li>Centrifuge the heart cell solution at 180 x g for 5 min at 37 &#176;C. 
	NOTE: If there are still some heart pieces or mucus which did not dissolve, repeat steps 8.7&#8211;8.9 again.</li>
	<li>Carefully remove all the liquid above the cell pellet and resuspended the cells in 2 mL of cardiac media.</li>
	<li>Add 2 mL of cardiac media from the tube wall carefully to resuspend the cells and avoid breaking them.</li>
	<li>Add the suspended cells into a T175 flask with warm cardiac media drop by drop. Put the flask in a 37 &#176;C incubator for 1 h to allow cardiac fibroblasts to attach to the bottom. 
	NOTE: At this preplating step, the cardiac fibroblasts will attach to the flask while the cardiomyocytes will remain in the suspension medium.</li>
	<li>Collect the media from the flask that contains the cardiomyocytes and put it into a 50 mL tube.</li>
	<li>Count the cells, then centrifuge at 260 x g for 5 min at 37 &#176;C.</li>
	<li>Resuspend and seed the cells on top of the fabricated soft robot in step 7. Pour specific volume of cardiac media with the cardiomyocytes at a concentration of 1.95 &#215; 106 cell/mL drop by drop onto the entire surface of the device.</li>
	<li>Incubate the samples at 37 &#176;C and change the media with 5 mL cell culture media with 2% FBS and 1% L-glutamine on the first and the second days after seeding. Change the media every time the color of the media shifts.</li>
</ol>
9. Cell staining for alignment analysis
<ol>
	<li>Remove the media and wash with DPBS for 5 min at RT.</li>
	<li>Fix the cells using 4% paraformaldehyde (PFA) for 20 min at RT. Then wash with DPBS for 5 min at RT.</li>
	<li>Incubate the cells with 0.1% triton in DPBS at RT for 1 h. Wash 3x with PBS for 5 min at RT.</li>
	<li>Incubate the cells with 10% goat serum in DPBS at RT for 1 h.</li>
	<li>Incubate the cells with a primary antibody (sarcomeric &#945;-actinin and connexin-43) in 10% goat serum in DPBS at 4 &#176;C for ~14&#8211;16 h.</li>
	<li>Wash 3x with DPBS for 5 min at RT. Incubate the cells with the secondary antibody in 10% goat serum in DPBS at RT for 1 h.</li>
	<li>Wash 3x with DPBS for 5 min at RT, then counterstain cells with 4&#39;,6-diamidino-2-phenylindole (DAPI) in DI water (1:1,000) for 10 min at RT. Wash 3x with DPBS for 5 min at RT.</li>
	<li>Take fluorescence images using an inverted laser scanning confocal microscope.</li>
</ol>
10. Actuator testing and behavior evaluation
<ol>
	<li>Spontaneous beating of the cardiomyocytes on the soft robot
	<ol>
		<li>Incubate bioinspired actuators at 37 &#176;C for 5 days and refresh the media on day 1 and 2 and when necessary (i.e., when the media turns yellow). Use an inverted optical microscope to take images daily (5x and/or 10x). Record cell movements using video capture software on the microscope&#39;s live window for 30 s at 20 frames per second (5x and/or 10x) when the contractile activity starts (generally around day 3).</li>
		<li>At day 5, detach the membranes by gently lifting from the edge with a cover slide. 
		NOTE: If the cells show a strong beating behavior, the membranes will detach by themselves due to the mechanical action of the contractions.</li>
	</ol>
	</li>
	<li>Bulk electrical signal stimulation
	<ol>
		<li>Using a 3 cm spaced PDMS as a holder, affix two carbon rod electrodes with platinum (Pt) wire in a 6 cm Petri dish filled with cardiac media. Then carefully transfer the soft robot into the Petri dish.</li>
		<li>Apply a square waveform with 50 ms pulse width, DC offset value 0 V, and peak voltage amplitude between 0.5 and 6 V. The frequency varies between 0.5, 1.0, and 2.0 Hz with a duty cycle between 2.5%, 5%, and 10%, respectively. Record macroscale contractions using a commercially available camera.</li>
	</ol>
	</li>
	<li>Electrical stimulation with the Au microelectrodes
	<ol>
		<li>After fabrication of Au microelectrode-integrated multilayered hydrogel scaffold, attach two copper wires to the Au electrodes though an external square port using silver paste.</li>
		<li>Cover the silver paste with a thin layer of PDMS precured at 80 &#176;C for 5 min. Then put the samples on a hot plate at 45 &#176;C for 5 h to fully crosslink the PDMS.</li>
		<li>After seeding cardiomyocyte, apply a square wave electrical stimulus on the copper wires with DC offset value 1 V, peak voltage amplitude between 1.5 and 5 V, and frequencies of 0.5, 1.0, and 2.0 Hz respectively.</li>
	</ol>
	</li>
</ol>

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The authors declare that they have no competing financial interests.

Using this method, we were able to successfully fabricate a batoid fish-like bioinspired soft robot with an integrated self-actuating cardiac tissue on a multilayer structured scaffold that is controlled by embedded Au microelectrodes. Due to two distinct micropatterned hydrogel layers made of PEGDA and CNT&#8211;GelMA hydrogels, the bioinspired scaffold showed good mechanical stability and ideal cell alignment and maturation. The PEGDA pattern layer, which serves as a cartilage joint of the skeletal architecture in a st...

Modern state-of-the-art soft robots can mimic the hierarchical structures and muscle dynamics of many living organisms, such as the jellyfish1,2, sting ray2, octopus3, bacteria4, and sperm5. Mimicking the dynamics and architecture of natural systems offers higher performances in terms of both energetic and structural efficiency6. This is intrinsically related to the soft nature of natural tissue (e.g., skin or muscle tissue with a Young&#39;s modulus between 104&#8722;109 Pa) which allows for higher degrees of freedom and superior deformation and adaptability when compared with standard engineered actuators (e.g., a Young's modulus usually between 109&#8722;1012 Pa)6. Cardiac muscle-based soft-actuators, especially, show superior energy efficiency due to their self-actuation as well as their potential for autorepair and regeneration when compared to a mechanically based robotic system7. However, the fabrication of soft robots is challenging due to the necessity of integrating different components with different physical, biological, and mechanical properties into the one system. For example, engineered synthetic systems need to be integrated with living biological systems, not only providing them with structural support but also influencing and modulating their actuation behavior. In addition, many microfabrication methods require harsh/cytotoxic processes and chemicals that decrease the viability and function of any living components. Therefore, new approaches are necessary to enhance the functionality of the soft robots and to control and modulate their behavior.
To successfully integrate living components with good viability, a hydrogel-based scaffold is an excellent material to create the body of a soft robot. A hydrogel's physical and mechanical properties can easily be tuned to create microenvironments for living components such as muscle tissues8,9. Also, it can easily adopt various microfabrication techniques, resulting in the creation of hierarchical structures with high fidelity1,2,10. Flexible electronic devices can be incorporated into the soft robot to control its behavior with electrical stimulation. For example, optogenetic techniques to engineer electrogenic cells (e.g., cardiomyocytes), which show a light-dependent electrophysiological activation, have been used to develop a polydimethylsiloxane (PDMS)-based soft robotic sting ray guided by light that was able to recreate the undulatory movement of the fish in vitro2. Although optogenetic techniques have shown excellent controllability, the work presented uses electrical stimulation, a conventional and traditional simulation method. This is because electrical stimulation via flexible microelectrodes is easy and simple compared to optogenetic techniques, which require extensive development processes11. The use of flexible electronic devices can allow for long-term stimulation and standard/simple fabrication processes as well as tunable biocompatibility and physical and mechanical properties12,13.
Here, we present an innovative method to fabricate a bioinspired soft robot, actuated by the beating of engineered cardiac muscle tissue and controlled by electrical stimulation through embedded flexible Au microelectrodes. The soft robot is designed to mimic the muscle and cartilage structure of the sting ray. The sting ray is an organism with a relatively easy to mimic structure and movement compared to other swimming species. The muscles are recreated in vitro by seeding cardiomyocytes on an electrically conductive hydrogel micropattern. As previously reported, incorporating electrically conductive nanoparticles such as CNT in the GelMA hydrogel not only improves the electrical coupling of the cardiac tissue, but also induces an excellent in vitro tissue architecture and arrangement8,9. The cartilage joints are then mimicked using a mechanically robust PEGDA hydrogel pattern that acts as the mechanically robust substrate of the whole system. Flexible Au microelectrodes with a serpentine pattern are embedded in the PEGDA pattern to locally and electrically stimulate the cardiac tissue.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>250 mL Beaker</td>
			<td>PYREX</td>
			<td>1000-250CNEa</td>
			<td></td>
		</tr>
		<tr>
			<td>2-Hydroxy-4&#39;-(2-hydroxyethoxy)-2-methylpropiophenone</td>
			<td>Sigma-Aldrich</td>
			<td>410896</td>
			<td></td>
		</tr>
		<tr>
			<td>3-(Trimethoxysilyl)propyl methacrylate</td>
			<td>Milipore</td>
			<td>M6514</td>
			<td></td>
		</tr>
		<tr>
			<td>37&#176; Water bath</td>
			<td>VWR</td>
			<td>W6M</td>
			<td></td>
		</tr>
		<tr>
			<td>4&#39;,6-diamidino-2-phenylindole (DAPI)</td>
			<td>Sigma-Aldrich</td>
			<td>D9542</td>
			<td></td>
		</tr>
		<tr>
			<td>50mL Conical Centrifuge Tubes</td>
			<td>Falcon</td>
			<td>14-959-49A</td>
			<td></td>
		</tr>
		<tr>
			<td>70 &#181;m Cell Strainer</td>
			<td>Falcon</td>
			<td>352350</td>
			<td></td>
		</tr>
		<tr>
			<td>80&#176; incubator</td>
			<td>VWR</td>
			<td>1370GM</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 488 goat anti-mouse IgG (H+L)</td>
			<td>Invitrogen</td>
			<td>A11029</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 594 goat anti-rabbit IgG (H+L)</td>
			<td>Invitrogen</td>
			<td>A11037</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 488 Phalloidin</td>
			<td>Invitrogen</td>
			<td>A12379</td>
			<td></td>
		</tr>
		<tr>
			<td>Antibiotic/Antimycotic solution</td>
			<td>ThermoFisher Scientific</td>
			<td>15240062</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Connexin 43/GJAI antibody</td>
			<td>Abcam</td>
			<td>ab11370</td>
			<td>Rabbit polyclonal</td>
		</tr>
		<tr>
			<td>Anti-Sarcomeric &#945;-actinin</td>
			<td>Abcam</td>
			<td>ab9465</td>
			<td>Mouse monoclonal</td>
		</tr>
		<tr>
			<td>Benchtop Freeze Dryers</td>
			<td>Labconco</td>
			<td>77500-00 K</td>
			<td></td>
		</tr>
		<tr>
			<td>Biosafety cabinet</td>
			<td>Sterilgard</td>
			<td>A/B3</td>
			<td></td>
		</tr>
		<tr>
			<td>Carbon rod electrodes</td>
			<td>SGL Carbon Group</td>
			<td>6971105</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Eppendorf</td>
			<td>5804</td>
			<td></td>
		</tr>
		<tr>
			<td>CO2 incubator</td>
			<td>Forma Scientific</td>
			<td>3110</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase, Type II, Powder</td>
			<td>Gibco</td>
			<td>17-101-015</td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal Microscope</td>
			<td>Zeiss</td>
			<td>LSM 880</td>
			<td></td>
		</tr>
		<tr>
			<td>COOH Functionalized Carbon Nanotubes</td>
			<td>NanoLab</td>
			<td>PD30L5-20-COOH</td>
			<td></td>
		</tr>
		<tr>
			<td>Dicing saw machine</td>
			<td>Giorgio Technology</td>
			<td>DAD-321</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM, High Glucose</td>
			<td>Gibco</td>
			<td>11-965-118</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS without Calcium and Magnesium</td>
			<td>Gibco</td>
			<td>14-190-144</td>
			<td></td>
		</tr>
		<tr>
			<td>E-beam evaporator</td>
			<td>CHA</td>
			<td>57367</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Gibco</td>
			<td>10-437-028</td>
			<td></td>
		</tr>
		<tr>
			<td>Gelatin</td>
			<td>Sigma-Aldrich</td>
			<td>G9391</td>
			<td>Type B, 300 bloom from porcine skin</td>
		</tr>
		<tr>
			<td>Glass slide</td>
			<td>VWR</td>
			<td>48382-180</td>
			<td></td>
		</tr>
		<tr>
			<td>HBSS without Calcium, Magnesium or Phenol Red</td>
			<td>Gibco</td>
			<td>14-175-079</td>
			<td></td>
		</tr>
		<tr>
			<td>Inverted optical microscope</td>
			<td>Olympus</td>
			<td>CK40</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnetic hotplate</td>
			<td>Corning</td>
			<td>PC-420</td>
			<td></td>
		</tr>
		<tr>
			<td>methacrylic anhydride</td>
			<td>Sigma-Aldrich</td>
			<td>276695</td>
			<td>Contains 2,000ppm topanol A as inhibitor</td>
		</tr>
		<tr>
			<td>Nunc EasYFlask 175cm2</td>
			<td>ThermoFisher Scientific</td>
			<td>159910</td>
			<td></td>
		</tr>
		<tr>
			<td>Olicscope</td>
			<td>Siglent</td>
			<td>SDS1052DL+</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde Aqueous Solution -16%</td>
			<td>Electron Microscopy Sciences</td>
			<td>15710</td>
			<td></td>
		</tr>
		<tr>
			<td>PDMS SYLGARD 184</td>
			<td>Sigma-Aldrich</td>
			<td>761036</td>
			<td></td>
		</tr>
		<tr>
			<td>Photomask</td>
			<td>Mini micro stencil inc</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Platinum wire</td>
			<td>Alfa Aesar</td>
			<td>AA43014BU</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyethylene glycol dimethcrylate</td>
			<td>Polysciences Inc.</td>
			<td>15178-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Regenerated Cellulose Dialysis Tubing</td>
			<td>Fisherbrand</td>
			<td>21-152-14</td>
			<td></td>
		</tr>
		<tr>
			<td>Silver Epoxy Adhesive</td>
			<td>MG Chemicals</td>
			<td>8330S</td>
			<td></td>
		</tr>
		<tr>
			<td>Stericup Quick Release-GP Sterile Vacuum Filtration System</td>
			<td>Millipore</td>
			<td>S2GPU02RE</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra sonicator</td>
			<td>Qsonica</td>
			<td>Q500</td>
			<td></td>
		</tr>
		<tr>
			<td>UV Curing System</td>
			<td>OmniCure</td>
			<td>S2000</td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex mixer</td>
			<td>Scientific Industry</td>
			<td>SI-0246A</td>
			<td></td>
		</tr>
		<tr>
			<td>Waveform generator</td>
			<td>Agilent</td>
			<td>33500B</td>
			<td></td>
		</tr>
		<tr>
			<td>Wrap Aluminium foil</td>
			<td>Reynolds</td>
			<td>N/A</td>
			<td></td>
		</tr>
	</tbody>
</table>

bioinspired soft robot with incorporated microelectrodes

Bioinspired soft robotic systems that mimic living organisms using engineered muscle tissue and biomaterials are revolutionizing the current biorobotics paradigm, especially in biomedical research. Recreating artificial life-like actuation dynamics is crucial for a soft-robotic system. However, the precise control and tuning of actuation behavior still represents one of the main challenges of modern soft robotic systems. This method describes a low-cost, highly scalable, and easy-to-use procedure to fabricate an electrically controllable soft robot with life-like movements that is activated and controlled by the contraction of cardiac muscle tissue on a micropatterned sting ray-like hydrogel scaffold. The use of soft photolithography methods makes it possible to successfully integrate multiple components in the soft robotic system, including micropatterned hydrogel-based scaffolds with carbon nanotubes (CNTs) embedded gelatin methacryloyl (CNT-GelMA), poly(ethylene glycol) diacrylate (PEGDA), flexible gold (Au) microelectrodes, and cardiac muscle tissue. In particular, the hydrogels alignment and micropattern are designed to mimic the muscle and cartilage structure of the sting ray. The electrically conductive CNT-GelMA hydrogel acts as a cell scaffold that improves the maturation and contraction behavior of cardiomyocytes, while the mechanically robust PEGDA hydrogel provides structural cartilage-like support to the whole soft robot. To overcome the hard and brittle nature of metal-based microelectrodes, we designed a serpentine pattern that has high flexibility and can avoid hampering the beating dynamics of cardiomyocytes. The incorporated flexible Au microelectrodes provide electrical stimulation across the soft robot, making it easier to control the contraction behavior of cardiac tissue.

Flow diagram of the steps for developing the Au microelectrode-incorporated bioinspired soft robot 
The aim of the soft robot design was to build a membrane capable of actuating a swimming movement with minimal complexity. The structure must be able to sustain strong flexions repeatedly over time (about 1 Hz) and be able to keep its shape while achieving a strong beating. By selectively photo crosslinking the polymer using photomasks, we fabricated a hierarchically structured scaffold comprised of a...

Watch this Scientific Journal Video about Bioinspired Soft Robot with Incorporated Microelectrodes at JoVE.com

Bioinspired Soft Robot with Incorporated Microelectrodes

A bioinspired scaffold is fabricated by a soft photolithography technique using mechanically robust and electrically conductive hydrogels. The micropatterned hydrogels provide directional cardiomyocyte cell alignment, resulting in a tailored direction of actuation. Flexible microelectrodes are also integrated into the scaffold to bring electrical controllability for a self-actuating cardiac tissue.

Bioinspired soft robotic systems that mimic living organisms using engineered muscle tissue and biomaterials are revolutionizing the current biorobotics ...

bioinspired-soft-robot-with-incorporated-microelectrodes

Research

JoVE Journal

Bioengineering

8.6K Views.  Harvard Medical School. A bioinspired scaffold is fabricated by a soft photolithography technique using mechanically robust and electrically conductive hydrogels. The micropatterned hydrogels provide directional cardiomyocyte cell alignment, resulting in a tailored direction of actuation. Flexible microelectrodes are also integrated into the scaffold to bring electrical controllability for a self-actuating cardiac tissue.

Video: Bioinspired Soft Robot with Incorporated Microelectrodes

Adaptation of a Haptic Robot in a 3T fMRI

Functional magnetic resonance imaging (fMRI) provides excellent functional brain imaging via the BOLD signal 1 with advantages including non-ionizing radiation, millimeter spatial accuracy of anatomical and functional data 2, and nearly real-time analyses 3. Haptic robots provide precise measurement and control of position and force of a cursor in a reasonably confined space. Here we combine these two technologies to allow precision experiments involving motor control with haptic/tactile environment interaction such as reaching or grasping. The basic idea is to attach an 8 foot end effecter supported in the center to the robot 4 allowing the subject to use the robot, but shielding it and keeping it out of the most extreme part of the magnetic field from the fMRI machine (Figure 1).
The Phantom Premium 3.0, 6DoF, high-force robot (SensAble Technologies, Inc.) is an excellent choice for providing force-feedback in virtual reality experiments 5, 6, but it is inherently non-MR safe, introduces significant noise to the sensitive fMRI equipment, and its electric motors may be affected by the fMRI's strongly varying magnetic field. We have constructed a table and shielding system that allows the robot to be safely introduced into the fMRI environment and limits both the degradation of the fMRI signal by the electrically noisy motors and the degradation of the electric motor performance by the strongly varying magnetic field of the fMRI. With the shield, the signal to noise ratio (SNR: mean signal/noise standard deviation) of the fMRI goes from a baseline of &tilde;380 to &tilde;330, and &tilde;250 without the shielding. The remaining noise appears to be uncorrelated and does not add artifacts to the fMRI of a test sphere (Figure 2). The long, stiff handle allows placement of the robot out of range of the most strongly varying parts of the magnetic field so there is no significant effect of the fMRI on the robot. The effect of the handle on the robot's kinematics is minimal since it is lightweight (&tilde;2.6 lbs) but extremely stiff 3/4" graphite and well balanced on the 3DoF joint in the middle. The end result is an fMRI compatible, haptic system with about 1 cubic foot of working space, and, when combined with virtual reality, it allows for a new set of experiments to be performed in the fMRI environment including naturalistic reaching, passive displacement of the limb and haptic perception, adaptation learning in varying force fields, or texture identification 5, 6.

The adaptation and use of a haptic robot in a 3T fMRI is described.

Functional magnetic resonance imaging (fMRI) provides excellent functional brain imaging via the BOLD signal 1 with advantages including non-ionizing ...

Engineering Skeletal Muscle Tissues from Murine Myoblast Progenitor Cells and Application of Electrical Stimulation

Engineered muscle tissues can be used for several different purposes, which include the production of tissues for use as a disease model in vitro, e.g. to study pressure ulcers, for regenerative medicine and as a meat alternative 1. The first reported 3D muscle constructs have been made many years ago and pioneers in the field are Vandenburgh and colleagues 2,3. Advances made in muscle tissue engineering are not only the result from the vast gain in knowledge of biochemical factors, stem cells and progenitor cells, but are in particular based on insights gained by researchers that physical factors play essential roles in the control of cell behavior and tissue development. State-of-the-art engineered muscle constructs currently consist of cell-populated hydrogel constructs. In our lab these generally consist of murine myoblast progenitor cells, isolated from murine hind limb muscles or a murine myoblast cell line C2C12, mixed with a mixture of collagen/Matrigel and plated between two anchoring points, mimicking the muscle ligaments. Other cells may be considered as well, e.g. alternative cell lines such as L6 rat myoblasts 4, neonatal muscle derived progenitor cells 5, cells derived from adult muscle tissues from other species such as human 6 or even induced pluripotent stem cells (iPS cells) 7. Cell contractility causes alignment of the cells along the long axis of the construct 8,9 and differentiation of the muscle progenitor cells after approximately one week of culture. Moreover, the application of electrical stimulation can enhance the process of differentiation to some extent 8. Because of its limited size (8 x 2 x 0.5 mm) the complete tissue can be analyzed using confocal microscopy to monitor e.g. viability, differentiation and cell alignment. Depending on the specific application the requirements for the engineered muscle tissue will vary; e.g. use for regenerative medicine requires the up scaling of tissue size and vascularization, while to serve as a meat alternative translation to other species is necessary.

Engineered muscle tissue has great potential in regenerative medicine, as disease model and also as an alternative source for meat. Here we describe the engineering of a muscle construct, in this case from mouse myoblast progenitor cells, and the stimulation by electrical pulses.

Engineered muscle tissues can be used for several different purposes, which include the production of tissues for use as a disease model in vitro, e.g. to ...

Designing a Bio-responsive Robot from DNA Origami

Nucleic acids are astonishingly versatile. In addition to their natural role as storage medium for biological information1, they can be utilized in parallel computing2,3 , recognize and bind molecular or cellular targets4,5 , catalyze chemical reactions6,7 , and generate calculated responses in a biological system8,9. Importantly, nucleic acids can be programmed to self-assemble into 2D and 3D structures10-12, enabling the integration of all these remarkable features in a single robot linking the sensing of biological cues to a preset response in order to exert a desired effect.
Creating shapes from nucleic acids was first proposed by Seeman13, and several variations on this theme have since been realized using various techniques11,12,14,15 . However, the most significant is perhaps the one proposed by Rothemund, termed scaffolded DNA origami16. In this technique, the folding of a long (&gt;7,000 bases) single-stranded DNA 'scaffold' is directed to a desired shape by hundreds of short complementary strands termed 'staples'. Folding is carried out by temperature annealing ramp. This technique was successfully demonstrated in the creation of a diverse array of 2D shapes with remarkable precision and robustness. DNA origami was later extended to 3D as well17,18 .
 
The current paper will focus on the caDNAno 2.0 software19 developed by Douglas and colleagues. caDNAno is a robust, user-friendly CAD tool enabling the design of 2D and 3D DNA origami shapes with versatile features. The design process relies on a systematic and accurate abstraction scheme for DNA structures, making it relatively straightforward and efficient.
In this paper we demonstrate the design of a DNA origami nanorobot that has been recently described20. This robot is 'robotic' in the sense that it links sensing to actuation, in order to perform a task. We explain how various sensing schemes can be integrated into the structure, and how this can be relayed to a desired effect. Finally we use Cando21 to simulate the mechanical properties of the designed shape. The concept we discuss can be adapted to multiple tasks and settings.

DNA origami is a powerful method for fabricating precise nanoscale objects by programming the self-assembly of DNA molecules. Here, we describe how DNA origami can be utilized to design a robotic robot capable of sensing biological cues and responding by shape shifting, subsequently relayed to a desired effect.

Nucleic acids are astonishingly versatile. In addition to their natural role as storage medium for biological information1, they can be utilized in ...

A Protocol for Bioinspired Design: A Ground Sampler Based on Sea Urchin Jaws

Bioinspired design is an emerging field that takes inspiration from nature to develop high-performance materials and devices. The sea urchin mouthpiece, known as the Aristotle's lantern, is a compelling source of bioinspiration with an intricate network of musculature and calcareous teeth that can scrape, cut, chew food and bore holes into rocky substrates. We describe the bioinspiration process as including animal observation, specimen characterization, device fabrication and mechanism bioexploration. The last step of bioexploration allows for a deeper understanding of the initial biology. The design architecture of the Aristotle's lantern is analyzed with micro-computed tomography and individual teeth are examined with scanning electron microscopy to identify the microstructure. Bioinspired designs are fabricated with a 3D printer, assembled and tested to determine the most efficient lantern opening and closing mechanism. Teeth from the bioinspired lantern design are bioexplored via finite element analysis to explain from a mechanical perspective why keeled tooth structures evolved in the modern sea urchins we observed. This circular approach allows for new conclusions to be drawn from biology and nature.

A protocol for bioinspired design is described for a sampling device based on the jaws of a sea urchin. The bioinspiration process includes observing the sea urchins, characterizing the mouthpiece, 3D printing of the teeth and their assembly, and bioexploring the tooth structure.

Bioinspired design is an emerging field that takes inspiration from nature to develop high-performance materials and devices. The sea urchin mouthpiece, ...

Medical-grade Sterilizable Target for Fluid-immersed Fetoscope Optical Distortion Calibration

We have developed a calibration target for use with fluid-immersed endoscopes within the context of the GIFT-Surg (Guided Instrumentation for Fetal Therapy and Surgery) project. One of the aims of this project is to engineer novel, real-time image processing methods for intra-operative use in the treatment of congenital birth defects, such as spina bifida and the twin-to-twin transfusion syndrome. The developed target allows for the sterility-preserving optical distortion calibration of endoscopes within a few minutes. Good optical distortion calibration and compensation are important for mitigating undesirable effects like radial distortions, which not only hamper accurate imaging using existing endoscopic technology during fetal surgery, but also make acquired images less suitable for potentially very useful image computing applications, like real-time mosaicing. In this paper proposes a novel fabrication method to create an affordable, sterilizable calibration target suitable for use in a clinical setup. This method involves etching a calibration pattern by laser cutting a sandblasted stainless steel sheet. This target was validated using the camera calibration module provided by OpenCV, a state-of-the-art software library popular in the computer vision community.

This article describes the design and development of a sterilizable custom camera optical distortion calibration target for the peri-operative, fluid-immersed calibration of endoscopes during endoscopic interventions.

We have developed a calibration target for use with fluid-immersed endoscopes within the context of the GIFT-Surg (Guided Instrumentation for Fetal ...

Rapid Mix Preparation of Bioinspired Nanoscale Hydroxyapatite for Biomedical Applications

Hydroxyapatite (HA) has been widely used as a medical ceramic due to its good biocompatibility and osteoconductivity. Recently there has been interest regarding the use of bioinspired nanoscale hydroxyapatite (nHA). However, biological apatite is known to be calcium-deficient and carbonate-substituted with a nanoscale platelet-like morphology. Bioinspired nHA has the potential to stimulate optimal bone tissue regeneration due to its similarity to bone and tooth enamel mineral. Many of the methods currently used to fabricate nHA both in the laboratory and commercially, involve lengthy processes and complex equipment. Therefore, the aim of this study was to develop a rapid and reliable method to prepare high quality bioinspired nHA. The rapid mixing method developed was based upon an acid-base reaction involving calcium hydroxide and phosphoric acid. Briefly, a phosphoric acid solution was poured into a calcium hydroxide solution followed by stirring, washing and drying stages. Part of the batch was sintered at 1,000 &#176;C for 2 h in order to investigate the products&#39; high temperature stability. X-ray diffraction analysis showed the successful formation of HA, which showed thermal decomposition to &#946;-tricalcium phosphate after high temperature processing, which is typical for calcium-deficient HA. Fourier transform infrared spectroscopy showed the presence of carbonate groups in the precipitated product. The nHA particles had a low aspect ratio with approximate dimensions of 50 x 30 nm, close to the dimensions of biological apatite. The material was also calcium deficient with a Ca:P molar ratio of 1.63, which like biological apatite is lower than the stoichiometric HA ratio of 1.67. This new method is therefore a reliable and far more convenient process for the manufacture of bioinspired nHA, overcoming the need for lengthy titrations and complex equipment. The resulting bioinspired HA product is suitable for use in a wide variety of medical and consumer health applications.

This paper describes a novel method for the rapid manufacture of high quality bioinspired nanoscale hydroxyapatite. This biomaterial is of great significance in the manufacture of a wide range of innovative medical devices for clinical applications in orthopedics, craniofacial surgery and dentistry.

Hydroxyapatite (HA) has been widely used as a medical ceramic due to its good biocompatibility and osteoconductivity. Recently there has been interest ...

Soft Lithographic Procedure for Producing Plastic Microfluidic Devices with View-ports Transparent to Visible and Infrared Light

Infrared (IR) spectro-microscopy of living biological samples is hampered by the absorption of water in the mid-IR range and by the lack of suitable microfluidic devices. Here, a protocol for the fabrication of plastic microfluidic devices is demonstrated, where soft lithographic techniques are used to embed transparent Calcium Fluoride (CaF2) view-ports in connection with observation chamber(s). The method is based on a replica casting approach, where a polydimethylsiloxane (PDMS) mold is produced through standard lithographic procedures and then used as the template to produce a plastic device. The plastic device features ultraviolet/visible/infrared (UV/Vis/IR) -transparent windows made of CaF2 to allow for direct observation with visible and IR light. The advantages of the proposed method include: a reduced need for accessing a clean room micro-fabrication facility, multiple view-ports, an easy and versatile connection to an external pumping system through the plastic body, flexibility of the design, e.g., open/closed channels configuration, and the possibility to add sophisticated features such as nanoporous membranes.

A protocol for the fabrication of plastic microfluidic devices with transparent view-ports for visible and infrared light imaging is described.

Infrared (IR) spectro-microscopy of living biological samples is hampered by the absorption of water in the mid-IR range and by the lack of suitable ...

Isokinetic Robotic Device to Improve Test-Retest and Inter-Rater Reliability for Stretch Reflex Measurements in Stroke Patients with Spasticity

Measuring spasticity is important in treatment planning and determining efficacy after treatment. However, the current tool used in clinical settings has been shown to be limited in inter-rater reliability. One factor in this poor inter-rater reliability is the variability of passive motion while measuring the angle of catch (AoC) measurements. Therefore, an isokinetic device has been proposed to standardize the manual joint motion; however, the benefits of isokinetic motion for AoC measurements has not been tested in a standardized manner. This protocol investigates whether isokinetic motion itself can improve inter-rater reliability for AoC measurements. For this purpose, a robotic isokinetic device was developed that is combined with surface electromyography (EMG). Two conditions, manual and isokinetic motions, are compared with the standardized method to measure the angle and subjective feeling of catch. It is shown that in 17 stroke patients with mild elbow flexor spasticity, isokinetic motion improved the intraclass correlation coefficient (ICC) for inter-rater reliability of AoC measurements to 0.890 [95% confidence interval (CI): 0.685&#8211;0.961] by the EMG criteria, and 0.931 (95% CI: 0.791&#8211;0.978) by the torque criteria, from 0.788 (95% CI: 0.493&#8211;0.920) by manual motion. In conclusion, isokinetic motion itself can improve inter-rater reliability of AoC measurements in stroke patients with mild spasticity. Given that this system may provide greater standardized angle measurements and catch of feeling, it may be a good option for the evaluation of spasticity in a clinical setting.

Using a robotic isokinetic device with electromyography (EMG) measurements, this protocol illustrates that isokinetic motion itself can improve inter-rater reliability for the angle of catch measurements in stroke patients with mild elbow flexor spasticity.

Measuring spasticity is important in treatment planning and determining efficacy after treatment. However, the current tool used in clinical settings has ...

Focused Ion Beam Lithography to Etch Nano-architectures into Microelectrodes

With advances in electronics and fabrication technology, intracortical microelectrodes have undergone substantial improvements enabling the production of sophisticated microelectrodes with greater resolution and expanded capabilities. The progress in fabrication technology has supported the development of biomimetic electrodes, which aim to seamlessly integrate into the brain parenchyma, reduce the neuroinflammatory response observed after electrode insertion and improve the quality and longevity of electrophysiological recordings. Here we describe a protocol to employ a biomimetic approach recently classified as nano-architecture. The use of focused ion beam lithography (FIB) was utilized in this protocol to etch specific nano-architecture features into the surface of non-functional and functional single shank intracortical microelectrodes. Etching nano-architectures into the electrode surface indicated possible improvements of biocompatibility and functionality of the implanted device. One of the benefits of using FIB is the ability to etch on manufactured devices, as opposed to during the fabrication of the device, facilitating boundless possibilities to modify numerous medical devices post-manufacturing. The protocol presented herein can be optimized for various material types, nano-architecture features, and types of devices. Augmenting the surface of implanted medical devices can improve the device performance and integration into the tissue.

We have shown that the etching of nano-architecture into intracortical microelectrode devices may reduce the inflammatory response and has the potential to improve electrophysiological recordings. The methods described herein outline an approach to etch nano-architectures into the surface of non-functional and functional single shank silicon intracortical microelectrodes.

With advances in electronics and fabrication technology, intracortical microelectrodes have undergone substantial improvements enabling the production of ...

Experimental and Data Analysis Workflow for Soft Matter Nanoindentation

Nanoindentation refers to a class of experimental techniques where a micrometric force probe is used to quantify the local mechanical properties of soft biomaterials and cells. This approach has gained a central role in the fields of mechanobiology, biomaterials design&#160;and tissue engineering, to obtain a proper mechanical characterization of soft materials with a resolution comparable to the size of single cells (&#956;m). The most popular strategy to acquire such experimental data is to employ an atomic force microscope (AFM); while this instrument offers an unprecedented resolution in force (down to pN) and space (sub-nm), its usability is often limited by its complexity that prevents routine measurements of integral indicators of mechanical properties, such as Young&#39;s Modulus (E). A new generation of nanoindenters, such as those based on optical fiber sensing technology, has recently gained popularity for its ease of integration while allowing to apply sub-nN forces with &#181;m spatial resolution, therefore being suitable to probe local mechanical properties of hydrogels and cells.
In this protocol, a step-by-step guide detailing the experimental procedure to acquire nanoindentation data on hydrogels and cells using a commercially available ferrule-top optical fiber sensing nanoindenter is presented. Whereas some steps are specific to the instrument used herein, the proposed protocol can be taken as a guide for other nanoindentation devices, granted some steps are adapted according to the manufacturer&#39;s guidelines. Further, a new open-source Python software equipped with a user-friendly graphical user interface for the analysis of nanoindentation data is presented, which allows for screening of incorrectly acquired curves, data filtering, computation of the contact point through different numerical procedures, the conventional computation of E, as well as a more advanced analysis particularly suited for single-cell nanoindentation data.

The protocol presents a complete workflow for soft material nanoindentation experiments, including hydrogels and cells. First, the experimental steps to acquire force spectroscopy data are detailed; then, the analysis of such data is detailed through a newly developed open-source Python software, which is free to download from GitHub.

Nanoindentation refers to a class of experimental techniques where a micrometric force probe is used to quantify the local mechanical properties of soft ...