Name: environmental dynamic mechanical analysis to predict the softening behavior of neural implants
Uploaded: 2019-03-01T14:30:00
Description: Watch this Scientific Journal Video about Environmental Dynamic Mechanical Analysis to Predict the Softening Behavior of Neural Implants at JoVE.com

The authors want to thank Dr. Taylor Ware for allowing us to use his environmental DMA.
This work was supported by the Office of the Assistant Secretary of Defense for Health Affairs through the Peer Reviewed Medical Research Program [W81XWH-15-1-0607]. Opinions, interpretations, conclusions, and recommendations are those of the authors and not necessarily endorsed by the Department of Defense.

1. Preparation of polymer samples for testing
<ol>
	<li>Synthesize the softening thiol-ene polymer according to previous protocols inside a fume hood.1,2,4,18 Briefly, mix quantitative amounts of thiol to alkene monomers with a total of 0.1 wt% photo initiator.
	<ol>
		<li>Prepare a 20 mL glass vial for polymer mixing. Cover the vial in aluminum foil to prevent incident light from contacting ...

<ol>
	<li>Garcia-Sandoval, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chronic+softening+spinal+cord+stimulation+arrays.">Chronic softening spinal cord stimulation arrays.</a> Journal of Neural Engineering. 15 (4), 045002 (2018).</li><li>Ecker, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sterilization+of+Thiol-ene/Acrylate+Based+Shape+Memory+Polymers+for+Biomedical+Applications.">Sterilization of Thiol-ene/Acrylate Based Shape Memory Polymers for Biomedical Applications.</a> Macromolecular Materials and Engineering. 302 (2), 1600331 (2017).</li><li>Simon, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+demonstration+of+an+intracortical+probe+technology+with+tunable+modulus.">Design and demonstration of an intracortical probe technology with tunable modulus.</a> Journal of Biomedical Materials Research Part A. 105 (1), 159-168 (2017).</li><li>Do, D. -. H., Ecker, M., Voit, W. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+a+Thiol-Ene/Acrylate-Based+Polymer+for+Neuroprosthetic+Implants.">Characterization of a Thiol-Ene/Acrylate-Based Polymer for Neuroprosthetic Implants.</a> ACS Omega. 2 (8), 4604-4611 (2017).</li><li>Ware, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thiol-ene/acrylate+substrates+for+softening+intracortical+electrodes.">Thiol-ene/acrylate substrates for softening intracortical electrodes.</a> Journal of Biomedical Materials Research Part B-Applied Biomaterials. 102 (1), 1-11 (2014).</li><li>Ware, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thiol-Click+Chemistries+for+Responsive+Neural+Interfaces.">Thiol-Click Chemistries for Responsive Neural Interfaces.</a> Macromolecular Bioscience. 13 (12), 1640-1647 (2013).</li><li>Ware, T., Simon, D., Rennaker, R. L., Voit, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Smart+Polymers+for+Neural+Interfaces.">Smart Polymers for Neural Interfaces.</a> Polymer Reviews. 53 (1), 108-129 (2013).</li><li>Ware, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+Responsive,+Softening+Neural+Interfaces.">Fabrication of Responsive, Softening Neural Interfaces.</a> Advanced Functional Materials. 22 (16), 3470-3479 (2012).</li><li>Stiller, A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chronic+Intracortical+Recording+and+Electrochemical+Stability+of+Thiol-ene/Acrylate+Shape+Memory+Polymer+Electrode+Arrays.">Chronic Intracortical Recording and Electrochemical Stability of Thiol-ene/Acrylate Shape Memory Polymer Electrode Arrays.</a> Micromachines. 9 (10), 500 (2018).</li><li>Biran, R., Martin, D. C., Tresco, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuronal+cell+loss+accompanies+the+brain+tissue+response+to+chronically+implanted+silicon+microelectrode+arrays.">Neuronal cell loss accompanies the brain tissue response to chronically implanted silicon microelectrode arrays.</a> Experimental Neurology. 195 (1), 115-126 (2005).</li><li>Polikov, V. S., Tresco, P. A., Reichert, W. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Response+of+brain+tissue+to+chronically+implanted+neural+electrodes.">Response of brain tissue to chronically implanted neural electrodes.</a> Journal of Neuroscience Methods. 148 (1), 1-18 (2005).</li><li>Lacour, S. P., Courtine, G., Guck, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Materials+and+technologies+for+soft+implantable+neuroprostheses.">Materials and technologies for soft implantable neuroprostheses.</a> Nature Reviews Materials. 1 (10), 16063 (2016).</li><li>Stiller, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Meta-Analysis+of+Intracortical+Device+Stiffness+and+Its+Correlation+with+Histological+Outcomes.">A Meta-Analysis of Intracortical Device Stiffness and Its Correlation with Histological Outcomes.</a> Micromachines. 9 (9), 443 (2018).</li><li>Lecomte, A., Descamps, E., Bergaud, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+on+mechanical+considerations+for+chronically-implanted+neural+probes.">A review on mechanical considerations for chronically-implanted neural probes.</a> Journal of Neural Engineering. 15 (3), 031001 (2018).</li><li>Nguyen, J. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanically-compliant+intracortical+implants+reduce+the+neuroinflammatory+response.">Mechanically-compliant intracortical implants reduce the neuroinflammatory response.</a> Journal of Neural Engineering. 11 (5), 056014 (2014).</li><li>Ecker, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+Softening+Polymers+to+Multi-Material+Based+Bioelectronic+Devices.">From Softening Polymers to Multi-Material Based Bioelectronic Devices.</a> Multifunctional Materials. , (2018).</li><li>Hess, A. E., Potter, K. A., Tyler, D. J., Zorman, C. A., Capadona, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Environmentally-controlled+Microtensile+Testing+of+Mechanically-adaptive+Polymer+Nanocomposites+for+ex+vivo+Characterization.">Environmentally-controlled Microtensile Testing of Mechanically-adaptive Polymer Nanocomposites for ex vivo Characterization.</a> Journal of Visualized Experiments. (78), e50078 (2013).</li><li>Black, B. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+compatibility+testing+of+thiol-ene/acrylate-based+shape+memory+polymers+for+use+in+implantable+neural+interfaces.">In vitro compatibility testing of thiol-ene/acrylate-based shape memory polymers for use in implantable neural interfaces.</a> Journal of Biomedical Materials Research Part A. 106 (11), 2891-2898 (2018).</li><li>Hassler, C., Boretius, T., Stieglitz, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymers+for+neural+implants.">Polymers for neural implants.</a> Journal of Polymer Science Part B: Polymer Physics. 49 (1), 18-33 (2011).</li></ol>

The use of environmental DMA allows the study of the behavior of various polymers used as substrates for neural implants19 or other biomedical devices in solution and to mimic in vivo conditions. This includes, but is not limited to, polyimide, parylene-C, PDMS, and SU-8. Hydrogels and extracellular matrix (ECM) materials can also be investigated using this method. The differences of overall softening of the polymer as well as its softening kinetics can be easily compared between differen...

A new generation of materials used as substrates for neural implants comprises softening shape memory polymers1,2,3,4,5,6,7,8,9. These materials are stiff enough during implantation to overcome critical buckling forces, but they become up to three orders of magnitude softer after implantation in a body environment. It is predicted that these materials show a better device-tissue interaction due to the reduced mismatch in modulus as compared to traditional materials used in neural implants, such as tungsten or silicon. Traditional, stiff devices show inflammatory response after implantation, followed by tissue encapsulation and astroglial scarring which often results in device failure10,11. It is a common assumption that less stiff devices minimize the foreign body response12,13,14. The stiffness of a device is dictated by its cross-sectional area and modulus. Therefore, it is important to reduce both factors to improve the device compliance and, ultimately, the device tissue interaction.
The work on softening polymers was inspired by the work of Nguyen et al.15, who demonstrated that mechanically-compliant intracortical implants reduce the neuroinflammatory response. They have previously used mechanically-adaptive poly(vinyl acetate)/tunicate cellulose nanocrystal (tCNC) nanocomposites (NC), which become compliant after implantation.
The Voit lab, on the other hand, uses the highly tunable system of thiol-ene and thiol-ene/acrylate polymers. These materials are advantageous in that the degree of softening after exposure to in vivo conditions can easily be tuned by the polymer design. By choosing the right polymer composition and crosslink density, the glass transition temperature and Young&#39;s modulus of the polymer can be modified2,4,5,6,8. The underlying effect of the softening is the plasticization of the polymer in an aqueous environment. By having a polymer with a glass transition temperature (Tg) above body temperature when dry (the state during implantation), but below body temperature after being immersed in water or PBS, the resulting stiffness/modulus of the polymer can shift from glassy (stiff) when dry to rubbery (soft) when implanted16.
However, exact and reliable measurements of the softening due to plasticization and the shift of Tg from the dry to wet states have not been able to be measured in the past. Traditional dynamic mechanical analysis is performed in air or inert gases and does not allow for measuring of the thermomechanical properties of polymers inside a solution. In previous studies, the polymers have been immersed in PBS for various amounts of time. Swollen samples were then used to perform dynamic mechanical analysis (DMA)6,7,8. However, since the procedure involves a temperature ramp, samples start to dry during the measurement and do not yield representative data. This is especially true if the sample size becomes smaller. In order to predict the softening of neural probes, it would be necessary to test 5 to 50 &#181;m-thin polymer films, which is not possible with traditional DMA due to the abovementioned drying of the samples during the measurement.
Hess et al.17 have designed a custom-built microtensile testing machine to assess the mechanical properties of mechanically adaptive materials using an environmentally controlled method. They have previously used an airbrush system to spray water on samples during the measurement to prevent them from drying out.
The use of environmental DMA (Figure 1), however, allows for measurement of polymer films in solutions, such as water and PBS, at various temperatures. This allows not only measurement of the polymer&#39;s thermomechanical properties in the soaked/softened state but also measurement of its softening kinetics. Even tensile tests and swelling measurements are possible inside the immersion bath of this machine. This allows for exact studies of the plasticization-induced softening of polymer substrates to predict in vivo behaviors.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1,3,5-Triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO)</td>
			<td>Sigma-Aldrich</td>
			<td>114235-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>2,2-Dimethoxy-2-phenylacetophenone (DMPA)</td>
			<td>Sigma-Aldrich</td>
			<td>196118-50G</td>
			<td></td>
		</tr>
		<tr>
			<td>CO2 laser Gravograph LS100</td>
			<td>Gravotech, Inc.</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Corning Large Glass Microscope Slides, 75 x 50mm</td>
			<td>Ted Pella</td>
			<td>26005</td>
			<td></td>
		</tr>
		<tr>
			<td>Environmental DMA: RSA-G2 Solids Analyzer</td>
			<td>TA Instruments</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ESD Safe Plastic Tweezer, Tips; Flat, Duckbill, 11.5 cm</td>
			<td>Cole Palmer</td>
			<td>EW-07387-17</td>
			<td></td>
		</tr>
		<tr>
			<td>Laurell WS-650-8B spin coater</td>
			<td>Laurell Technologies Corporation</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>liquid nitrogen</td>
			<td>Air gas</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PBS, 1X Solution, Fisher BioReagents</td>
			<td>Fisher Scientific</td>
			<td>BP243820</td>
			<td></td>
		</tr>
		<tr>
			<td>SHEL LAB vacuum oven</td>
			<td>VWR International</td>
			<td>89409-484</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon wafer</td>
			<td>University Wafer</td>
			<td></td>
			<td>Mechanical grade</td>
		</tr>
		<tr>
			<td>The RSA-G2 Immersion System</td>
			<td>TA Instruments</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Trimethylolpropane tris(3-mercaptopropionate) (TMTMP)</td>
			<td>Sigma-Aldrich</td>
			<td>381489-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>UVP CL-1000 crosslinking chamber with 365 nm bulbs</td>
			<td>VWR International</td>
			<td>21474-598</td>
			<td></td>
		</tr>
	</tbody>
</table>

environmental dynamic mechanical analysis to predict the softening behavior of neural implants

When using dynamically softening substrates for neural implants, it is important to have a reliable in vitro method to characterize the softening behavior of these materials. In the past, it has not been possible to satisfactorily measure the softening of thin films under conditions mimicking body environment without substantial effort. This publication presents a new and simple method that allows dynamic mechanical analysis (DMA) of polymers in solutions, such as phosphate buffered saline (PBS), at relevant temperatures. The use of environmental DMA allows measurement of the softening effects of polymers due to plasticization in various media and temperatures, which therefore allows a prediction of the materials behavior under in vivo conditions.

The use of environmental DMA allows the analysis of softening kinetics and overall softening capabilities of polymers. By using the temperature-time measuring mode of the protocol, the softening profiles of different polymer formulations can be compared to each other (Figure 6). This method can also be used to quantify softening and swelling rates of polymers. It can be seen in Figure 4 that different polymer formulations may und...

Watch this Scientific Journal Video about Environmental Dynamic Mechanical Analysis to Predict the Softening Behavior of Neural Implants at JoVE.com

Environmental Dynamic Mechanical Analysis to Predict the Softening Behavior of Neural Implants

To allow reliable predictions of the softening of polymeric substrates for neural implants in an in vivo environment, it is important to have a reliable in vitro method. Here, the use of dynamic mechanical analysis in phosphate buffered saline at body temperature is presented.

When using dynamically softening substrates for neural implants, it is important to have a reliable in vitro method to characterize the softening behavior ...

Research

JoVE Journal

Bioengineering

Microfabricated Platforms for Mechanically Dynamic Cell Culture

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

Fabrication of Micropatterned Hydrogels for Neural Culture Systems using Dynamic Mask Projection Photolithography

Increasingly, patterned cell culture environments are becoming a relevant technique to study cellular characteristics, and many researchers believe in the ...

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic ...

Graphene Coatings for Biomedical Implants

Atomically smooth graphene as a surface coating has potential to improve implant properties. This demonstrates a method for coating nitinol alloys with ...

Correlative Microscopy for 3D Structural Analysis of Dynamic Interactions

Cryo-electron tomography (cryoET) allows 3D visualization of cellular structures at molecular resolution in a close-to-physiological state1. However, ...

Controlled Microfluidic Environment for Dynamic Investigation of Red Blood Cell Aggregation

Blood, as a non-Newtonian biofluid, represents the focus of numerous studies in the hemorheology field. Blood constituents include red blood cells, white ...

In Situ Mapping of the Mechanical Properties of Biofilms by Particle-tracking Microrheology

In Situ Mapping of the Mechanical Properties of Biofilms by Particle-tracking Microrheology

Bacterial cells are able to form surface-attached biofilm communities known as biofilms by encasing themselves in extracellular polymeric substances ...

Microbiologically Induced Calcite Precipitation Mediated by Sporosarcina pasteurii

Microbiologically Induced Calcite Precipitation Mediated by Sporosarcina pasteurii

The particular bacterium under investigation here (S. pasteurii) is unique in its ability, under the right conditions, to induce the hydrolysis of urea ...

Modeling Ovarian Cancer Multicellular Spheroid Behavior in a Dynamic 3D Peritoneal Microdevice

Ovarian cancer is characterized by extensive peritoneal metastasis, with tumor spheres commonly found in the malignant ascites. This is associated with ...

Biaxial Mechanical Characterizations of Atrioventricular Heart Valves

Extensive biaxial mechanical testing of the atrioventricular heart valve leaflets can be utilized to derive&#160;optimal parameters used in constitutive ...