The authors want to thank Yabin Wu for culturing the tissues presented in Figure 2, the picture was taken by Bart van Overbeeke. The work was financially supported by SenterNovem, grant ISO 42022.

1. Culture of Murine Myoblast Progenitor Cells or C2C12 Cells
<ol>
	<li>Isolate cells according to the protocol initially published by Shefer and colleagues 10 and later adapted by Collins et al. 11 and Boonen et al. 12 and store these in liquid nitrogen. This requires mice, e.g. C57Bl/6. Alternative methods are used in other labs, e.g. a method published in Journal of Visualized Experiments by Li Y et al. 13. For the reagents and equipment you are referred to the table on page 7 and 8. From the muscle from one mouse you will generally obtain enough cells to cryopreserve about 20 vials in liquid nitrogen. Next, we start the protocol to thaw the cells from the liquid nitrogen storage.</li>
	<li>Place the cells from 1 vial into a 25 cm2 Matrigel (1 mg/ml) coated tissue culture flask and add growth medium (GM) consisting of (335 ml DMEM advanced, 100 ml fetal bovine serum (FBS), 50 ml HS, 5 ml penicillin/streptomycin, 5 ml L-glutamin, 5 ml chicken embryo extract (CEE)).</li>
</ol>
Note: coat for 2 hr at Room Temperature and remove the Matrigel by aspiration.
<ol start="3">
	<li>Subculture the cells approximately 1:3 every 3 days. 
	This means: on day 3: Passage cells from one 25 cm2 to a 75 cm2 flask, on day 6: passage cells from one 75 cm2 flask to two 150 cm2 flasks (with 30 min preplating in uncoated flasks). On day 9 transfer one 150 cm2 flask to 1 triple 150 cm2 flask, or if unavailable to three 150 cm2 flasks (if needed preplate again depending on the phenotype of the cells). On day 12 the cells are ready for seeding into a muscle construct.</li>
</ol>
Notes: - Per triple 150 cm2 the number of cells will be approximately 4.5 x 106 cells. 
- Use vials from different isolations to mix them to obtain a mixed population of cells at time of seeding.
Note: If you choose not to work with primary cells, C2C12 myoblasts are a good alternative.
2. Engineering Skeletal Muscle Tissues
<ol>
	<li>Prepare silicon glue by mixing the"elastomer" with the "curing agent" (10:1). Cut +/- 5 mm square segments of Velcro with one triangular side (house-like shape; Figure 1). Glue the Velcro into the wells of a 6-well culture plate at a space of approximately 12 mm between the squares.</li>
</ol>
Notes: - Only use the soft side of the Velcro and face this side upwards. 
- Make sure that the rooftops face each other. 
- Only cover the Velcro with silicon glue, do not spread glue throughout the well. 
- For later electrical stimulation it is relevant to align the constructs in vertical direction of the well plate (along the long axis).
<ol start="2">
	<li>Leave to dry overnight in vacuum oven, not heated, primarily to remove air bubbles. Sterilize by adding 70% EtOH to the wells and incubate for 15 min. Rinse 3x with PBS and put under UV for 15 min. Remove all PBS from the wells and the Velcro and place in incubator until use.</li>
	<li>Thaw Matrigel solution in the fridge and prepare the collagen solution to the desired concentration shortly before making the 3D constructs. Dilute the stock collagen with sterile 0.02% acetic acid (final concentration 3.2 mg/ml).</li>
</ol>
Note: leave everything on ice.
<ol start="4">
	<li>Trypsinize the cells, resuspend in GM and count. Leave cells in centrifuge tube in the incubator.</li>
	<li>Add the desired amount of Collagen stock solution for the numbers of constructs that you want to make to a tube (according to Table 1), add 0.5M NaOH to this collagen solution until a light pink color is indicating a pH of 7.5. Mix gently by pipetting up and down and avoid bubble formation. Then add the Matrigel and mix very gently but thoroughly. Finally, add the GM to the Collagen/Matrigel mixture (for the appropriate amounts see Table 1).</li>
</ol>
Notes: - Perform each step on ice! Matrigel and collagen will readily gel at increasing temperature. 
- Mind that the color indeed is pink! An increase in pH will also induce rapid gelation. 
- Final concentration of collagen: 1.6 mg/ml.
<ol start="6">
	<li>Centrifuge the desired amount of cells at 1,000 rpm for 5 min and remove the supernatant.</li>
</ol>
Note: - Depending on the activity of the cells the number of cells per construct needs to be adjusted. Typically, the number of cells lies between 750,000 and 1,250,000 cells per construct.
<ol start="7">
	<li>Use some of the gel mixture to resuspend the cell pellet and transfer the cells into the remaining mixture and mix thoroughly, but without introducing air bubbles.</li>
	<li>Take the preheated well plates out of the incubator and pipette 0.35 -0.4 ml of the cell-gel mixture into the Velcro first. Then, begin to pipette the mixture from the center between the attachment sites and extend to the Velcro. Finally, use the remainder of gel to fill up the gap between the two Velcro anchors and pipette around the Velcro pieces.</li>
	<li>Carefully check after 5-10 min if the gels are solid enough to be transferred, i.e. gently tap the dishes and inspect visually if the gel is rigid. If so, carefully place the dishes in an incubator. Usually, they can be picked up after ten minutes. Then, after 1-2 hr, gently overlay each gel with 4 ml of warm GM.</li>
</ol>
Note: -Do not make any vigorous movements when handling the plates.
<ol start="10">
	<li>Replace GM by differentiation medium (growth medium without chick embryo extract) after 24 hr, and replace with fresh medium every 2-3 days. On day 7 you should have obtained mature oriented muscle fibers, as can be evaluated with staining for cross striation development in the fused muscle fibers.</li>
</ol>
3. Electrical Stimulation
<ol>
	<li>Sterilize the electrodes from the ionoptix plate (see table of reagents and equipment) before use with 70% ethanol and subsequently dry under UV in a safety cabinet. Place the plate with electrodes onto the culture plate with the constructs and cover with the lid from the culture plate and transfer to an incubator. Connect the Ionoptix C-pacer with the appropriate cables.</li>
</ol>
Note: Electrodes are placed parallel alongside the muscle construct (Figure 2).
<ol start="2">
	<li>Apply the stimulation protocol as anticipated.</li>
</ol>
Note: We generally use 4 V/CM, 6ms pulses at a frequency of 2Hz. Change culture medium every 24 hr during stimulation.

<ol>
	<li>Langelaan, M. L. P., Boonen, K. J. M., Polak, R. B., 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=Meet+the+new+meat:+tissue+engineered+skeletal+muscle.">Meet the new meat: tissue engineered skeletal muscle.</a> Trends Food Sci. Tech. 21 (2), 59-66 (2010).</li><li>Shansky, J., Chromiak, J., Tatto, M., Vandenburgh, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simplified+method+for+tissue+engineering+skeletal+muscle+organoids+in+vitro.">A simplified method for tissue engineering skeletal muscle organoids in vitro.</a> In Vitro Cell Dev. Biol. Animal. 33 (9), 659-661 (1997).</li><li>Vandenburgh, H., Del Tatto, M., Shansky, 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=Tissue-engineered+skeletal+muscle+organoids+for+reversible+gene+therapy.">Tissue-engineered skeletal muscle organoids for reversible gene therapy.</a> Hum. Gene Ther. 7 (17), 2195-2200 (1996).</li><li>Yaffe, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retention+of+differentiation+potentialities+during+prolonged+cultivation+of+myogenic+cells.">Retention of differentiation potentialities during prolonged cultivation of myogenic cells.</a> Proc. Natl. Acad. Sci. U.S.A. 61 (2), 477-483 (1968).</li><li>Rando, T. A., Blau, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primary+mouse+myoblast+purification,+characterization,+and+transplantation+for+cell-mediated+gene+therapy.">Primary mouse myoblast purification, characterization, and transplantation for cell-mediated gene therapy.</a> J. Cell Biol. 125 (6), 1275-1287 (1994).</li><li>Koning, M., Werker, P. M. N., vander Schaft, D. W. J., Bank, R. A., Harmsen, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MicroRNA-1+and+MicroRNA-206+Improve+Differentiation+Potential+of+Human+Satellite+Cells:+A+Novel+Approach+for+Tissue+Engineering+of+Skeletal+Muscle.">MicroRNA-1 and MicroRNA-206 Improve Differentiation Potential of Human Satellite Cells: A Novel Approach for Tissue Engineering of Skeletal Muscle.</a> Tissue Eng. Part A. , (2011).</li><li>Darabi, R., Pan, W., Bosnakovski, D., 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=Functional+myogenic+engraftment+from+mouse+iPS+cells.">Functional myogenic engraftment from mouse iPS cells.</a> Stem Cell Rev. 7 (4), 948-957 (2011).</li><li>Langelaan, M. L. P., Boonen, K. J. M., Rosaria-Chak, K. Y., 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=Advanced+maturation+by+electrical+stimulation:+Differences+in+response+between+C2C12+and+primary+muscle+progenitor+cells.">Advanced maturation by electrical stimulation: Differences in response between C2C12 and primary muscle progenitor cells.</a> J. Tissue Eng. Regen. Med. 5 (7), 529-539 (2011).</li><li>van der Schaft, D., van Spreeuwel, A. C., van Assen, H. C., Baaijens, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanoregulation+of+vascularization+in+aligned+tissue+engineered+muscle;+a+role+for+VEGF.">Mechanoregulation of vascularization in aligned tissue engineered muscle; a role for VEGF.</a> Tissue Eng. Part A. , (2011).</li><li>Shefer, G., Wleklinski-Lee, M., Yablonka-Reuveni, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skeletal+muscle+satellite+cells+can+spontaneously+enter+an+alternative+mesenchymal+pathway.">Skeletal muscle satellite cells can spontaneously enter an alternative mesenchymal pathway.</a> J. Cell. Sci. 117 (Pt. 22), 5393-5404 (2004).</li><li>Collins, C. A., Olsen, I., Zammit, P. S., 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=Stem+cell+function,+self-renewal,+and+behavioral+heterogeneity+of+cells+from+the+adult+muscle+satellite+cell+niche.">Stem cell function, self-renewal, and behavioral heterogeneity of cells from the adult muscle satellite cell niche.</a> Cell. 122 (2), 289-301 (2005).</li><li>Boonen, K. J. M., Rosaria-Chak, K. Y., Baaijens, F. P. T., van der Schaft, D. W. J., Post, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Essential+environmental+cues+from+the+satellite+cell+niche:+optimizing+proliferation+and+differentiation.">Essential environmental cues from the satellite cell niche: optimizing proliferation and differentiation.</a> Am. J. Physiol. Cell Physiol. 296 (6), C1338-C1345 (2009).</li><li>Li, Y., Pan, H., Huard, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolating+Stem+Cells+from+Soft+Musculoskeletal+Tissues.">Isolating Stem Cells from Soft Musculoskeletal Tissues.</a> J. Vis. Exp. (41), e2011 (2010).</li><li>Boonen, K. J. M., Langelaan, M. L. P., Polak, R. B., 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=Effects+of+a+combined+mechanical+stimulation+protocol:+Value+for+skeletal+muscle+tissue+engineering.">Effects of a combined mechanical stimulation protocol: Value for skeletal muscle tissue engineering.</a> J. Biomech. 43 (8), 1514-1521 (2010).</li><li>Gawlitta, D., Boonen, K. J. M., Oomens, C. W. J., Baaijens, F. P. T., Bouten, C. V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+serum-free+culture+conditions+on+skeletal+muscle+differentiation+in+a+tissue-engineered+model.">The influence of serum-free culture conditions on skeletal muscle differentiation in a tissue-engineered model.</a> Tissue Eng. Part A. 14 (1), 161-171 (2008).</li><li>Koning, M., van Luijn, M., van der Schaft, D. W. 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=Human+skeletal+muscle+formation+and+engraftment+In+vivo+is+independent+of+preconditioning+In+vitro+with+HUVEC.">Human skeletal muscle formation and engraftment In vivo is independent of preconditioning In vitro with HUVEC.</a> , (2013).</li><li>Levenberg, S., Rouwkema, J., Macdonald, 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=Engineering+vascularized+skeletal+muscle+tissue.">Engineering vascularized skeletal muscle tissue.</a> Nat. Biotechnol. 23 (7), 879-884 (2005).</li><li>Koffler, J., Kaufman-Francis, K., Yulia, S., 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=Improved+vascular+organization+enhances+functional+integration+of+engineered+skeletal+muscle+grafts.">Improved vascular organization enhances functional integration of engineered skeletal muscle grafts.</a> Proc. Natl. Acad. Sci. U.S.A. 108 (36), 14789-14794 (2011).</li></ol>

The authors have nothing to disclose.

The engineering of muscle tissues has great potential for the use as a disease model, for drug screening, in regenerative medicine and for meat production. However, the requirements for these applications vary. We chose to work with a combination of collagen and matrigel, because collagen allows for cell alignment and because the myoblast progenitor cells require the presence of basement membrane derived proteins as determined in previous 2D studies 12. Moreover, fibrin gels have been tested in our labo...

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments (optional)</td>
 </tr>
 <tr>
 <td>Matrigel-growth factor reduced</td>
 <td>Beckton and Dickinson</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>DMEM (high glucose)*</td>
 <td>Gibco</td>
 <td>42430</td>
 <td></td>
 </tr>
 <tr>
 <td>Advanced DMEM</td>
 <td>Gibco</td>
 <td>12491</td>
 <td></td>
 </tr>
 <tr>
 <td>Horse serum</td>
 <td>Gibco</td>
 <td>65050-122</td>
 <td></td>
 </tr>
 <tr>
 <td>Fetal bovine serum</td>
 <td>Greiner</td>
 <td>758075</td>
 <td></td>
 </tr>
 <tr>
 <td>0.45 and 0.22 &mu;m syringe filter*</td>
 <td>Whatmann (Schleicher and Scheull)</td>
 <td>10462100</td>
 <td></td>
 </tr>
 <tr>
 <td>L-glutamine</td>
 <td>Gibco</td>
 <td>25030024 </td>
 <td></td>
 </tr>
 <tr>
 <td>Penicillin/streptomycin</td>
 <td>Gibco</td>
 <td>10378016 </td>
 <td></td>
 </tr>
 <tr>
 <td>Amphotericin</td>
 <td>Gibco</td>
 <td>15290-018 </td>
 <td></td>
 </tr>
 <tr>
 <td>Culture plastic</td>
 <td>Greiner</td>
 <td></td>
 <td>Includes culture flasks and pipettes</td>
 </tr>
 <tr>
 <td>Chick embryo extract</td>
 <td>United States Biological</td>
 <td>C3999</td>
 <td></td>
 </tr>
 <tr>
 <td>Pasteur pipette*</td>
 <td>Hilgenberg</td>
 <td></td>
 <td>Pasteur pipettes, with constriction, with cotton, open tip L: 230 mm with tip diameter of 0,9 - 1,1 mm </td>
 </tr>
 <tr>
 <td>Pasteur pipette*</td>
 <td>Hilgenberg</td>
 <td></td>
 <td>Pasteur pipettes, with constriction, with cotton, open tip L: 230 mm with tip diameter of 1,4 - 1,6 mm </td>
 </tr>
 <tr>
 <td>Pasteur pipette</td>
 <td>VWR</td>
 <td>612-1702</td>
 <td></td>
 </tr>
 <tr>
 <td>Collagenase type I*</td>
 <td>Sigma</td>
 <td>C0130-16</td>
 <td></td>
 </tr>
 <tr>
 <td>40 &mu;m cell strainer*</td>
 <td>BD Falcon</td>
 <td>352340</td>
 <td></td>
 </tr>
 <tr>
 <td>19G needle</td>
 <td></td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Elastomer</td>
 <td>Dow Corning corporation</td>
 <td>3097358-1004</td>
 <td>Silastic MDX 4-4210#</td>
 </tr>
 <tr>
 <td>Curing agent</td>
 <td>Dow Corning corporation</td>
 <td></td>
 <td>Silastic MDX 4-4210#</td>
 </tr>
 <tr>
 <td>Velcro</td>
 <td>Regular store</td>
 <td></td>
 <td>You can buy this at a regular store, only use the soft side</td>
 </tr>
 <tr>
 <td>Collagen type I, rat tail</td>
 <td>BD Biosciences</td>
 <td>3544236</td>
 <td></td>
 </tr>
 <tr>
 <td>C-Pace EP Culture Pacer </td>
 <td>Ionoptix</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>6-well culture dishes for electrical stimulation </td>
 <td>Beckton Dickinson-Falcon</td>
 <td>BD Falcon #353846 </td>
 <td></td>
 </tr>
 <tr>
 <td>C-Dish culture dish electrodes</td>
 <td>Ionoptix</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>* Needed for the isolation of cells (point 1.1) 
# Together in one kit</td>
 </tr>
 </tbody>
</table>

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.

The end product will be muscle constructs as indicated in Figure 3. The size of the tissue will be approximately 8 mm long, 2 mm wide and 0.5 mm thick. Electrical stimulation during differentiation will change the expression of myosin heavy chain isoforms, but does not greatly enhance the differentiation process as induced by the differentiation medium 8, but electrical stimulation can also be applied at the end of the process to check for functionality of the muscle, because a muscle with fully d...

Watch this Scientific Journal Video about Engineering Skeletal Muscle Tissues from Murine Myoblast Progenitor Cells and Application of Electrical Stimulation at JoVE.com

 Eindhoven University of Technology, The Netherlands.  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.

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

20.8K Views.  Eindhoven University of Technology, The Netherlands. 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.

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

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 ...

engineering-skeletal-muscle-tissues-from-murine-myoblast-progenitor

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JoVE Journal

Bioengineering

Fabrication of Micro-tissues using Modules of Collagen Gel Containing Cells

This protocol describes the fabrication of a type of micro-tissues called modules.  The module approach generates uniform, scalable and vascularized tissues.  The modules can be made of collagen as well as other gelable or crosslinkable materials.  They are approximately 2 mm in length and 0.7 mm in diameter upon fabrication but shrink in size with embedded cells or when the modules are coated with endothelial cells.  The modules individually are small enough that the embedded cells are within the diffusion limit of oxygen and other nutrients but modules can be packed together to form larger tissues that are perfusable.  These tissues are modular in construction because different cell types can be embedded in or coated on the modules before they are packed together to form complex tissues.  There are three main steps to making the modules: (1) neutralizing the collagen and embedding cells in it, (2) gelling the collagen in the tube and cutting the modules and (3) coating the modules with endothelial cells.

Creation of micro-tissues using cylindrical collagen gels, called modules, that contain embedded cells and which surface is coated with endothelial cells.

This protocol describes the fabrication of a type of micro-tissues called modules.  The module approach generates uniform, scalable and vascularized ...

Engineering Fibrin-based Tissue Constructs from Myofibroblasts and Application of Constraints and Strain to Induce Cell and Collagen Reorganization

Collagen content and organization in developing collagenous tissues can be influenced by local tissue strains and tissue constraint. Tissue engineers aim to use these principles to create tissues with predefined collagen architectures. A full understanding of the exact underlying processes of collagen remodeling to control the final tissue architecture, however, is lacking. In particular, little is known about the (re)orientation of collagen fibers in response to changes in tissue mechanical loading conditions. We developed an in&#160;vitro model system, consisting of biaxially-constrained myofibroblast-seeded fibrin constructs, to further elucidate collagen (re)orientation in response to i) reverting biaxial to uniaxial static loading conditions and ii) cyclic uniaxial loading of the biaxially-constrained constructs before and after a change in loading direction, with use of the Flexcell FX4000T loading device. Time-lapse confocal imaging is used to visualize collagen (re)orientation in a nondestructive manner.
Cell and collagen organization in the constructs can be visualized in real-time, and an internal reference system allows us to relocate cells and collagen structures for time-lapse analysis. Various aspects of the model system can be adjusted, like cell source or use of healthy and diseased cells. Additives can be used to further elucidate mechanisms underlying collagen remodeling, by for example adding MMPs or blocking integrins. Shape and size of the construct can be easily adapted to specific needs, resulting in a highly tunable model system to study cell and collagen (re)organization.

This model system starts from a myofibroblast-populated fibrin gel that can be used to study endogenous collagen (re)organization real-time in a nondestructive manner. The model system is very tunable, as it can be used with different cell sources, medium additives, and can be adapted easily to specific needs.

Collagen content and organization in developing collagenous tissues can be influenced by local tissue strains and tissue constraint. Tissue engineers aim ...

Electrospun Fibrous Scaffolds of Poly(glycerol-dodecanedioate) for Engineering Neural Tissues From Mouse Embryonic Stem Cells

For tissue engineering applications, the preparation of biodegradable and biocompatible scaffolds is the most desirable but challenging task. &#160;Among the various fabrication methods, electrospinning is the most attractive one due to its simplicity and versatility. Additionally, electrospun nanofibers mimic the size of natural extracellular matrix ensuring additional support for cell survival and growth. This study showed the viability of the fabrication of long fibers spanning a larger deposit area for a novel biodegradable and biocompatible polymer named&#160;poly(glycerol-dodecanoate) (PGD)1 by using a newly designed collector for electrospinning. PGD exhibits unique elastic properties with similar mechanical properties to nerve tissues, thus it is suitable for neural tissue engineering applications. The synthesis and fabrication set-up for making fibrous scaffolding materials was simple, highly reproducible, and inexpensive. In biocompatibility testing, cells derived from mouse embryonic stem cells could adhere to and grow on the electrospun PGD fibers. In summary, this protocol provided a versatile fabrication method for making PGD electrospun fibers to support the growth of mouse embryonic stem cell derived neural lineage cells.

Electrospun Fibrous Scaffolds of Polyglycerol-dodecanedioate for Engineering Neural Tissues From Mouse Embryonic Stem Cells

Synthesis and fabrication of electrospun long fibers spanning a larger deposit area via a newly designed collector from a novel biodegradable polymer named poly(glycerol-dodecanoate) (PGD) was reported. The fibers were able to support the growth of cells derived from mouse pluripotent stem cells.

For tissue engineering applications, the preparation of biodegradable and biocompatible scaffolds is the most desirable but challenging task. &#160;Among ...

Measurement of Maximum Isometric Force Generated by Permeabilized Skeletal Muscle Fibers

Analysis of the contractile properties of chemically skinned, or permeabilized, skeletal muscle fibers offers a powerful means by which to assess muscle function at the level of the single muscle cell. Single muscle fiber studies are useful in both basic science and clinical studies. For basic studies, single muscle fiber contractility measurements allow investigation of fundamental mechanisms of force production, and analysis of muscle function in the context of genetic manipulations. Clinically, single muscle fiber studies provide useful insight into the impact of injury and disease on muscle function, and may be used to guide the understanding of muscular pathologies. In this video article we outline the steps required to prepare and isolate an individual skeletal muscle fiber segment, attach it to force-measuring apparatus, activate it to produce maximum isometric force, and estimate its cross-sectional area for the purpose of normalizing the force produced.

Analysis of the contractile properties of chemically skinned, or permeabilized, skeletal muscle fibers offers a powerful means by which to assess muscle function at the level of the single muscle cell. In this article we outline a valid and reliable technique to prepare and test permeabilized skeletal muscle fibers in vitro.

Analysis of the contractile properties of chemically skinned, or permeabilized, skeletal muscle fibers offers a powerful means by which to assess muscle ...

Engineering Three-dimensional Epithelial Tissues Embedded within Extracellular Matrix

The architecture of branched organs such as the lungs, kidneys, and mammary glands arises through the developmental process of branching morphogenesis, which is regulated by a variety of soluble and physical signals in the microenvironment. Described here is a method created to study the process of branching morphogenesis by forming engineered three-dimensional (3D) epithelial tissues of defined shape and size that are completely embedded within an extracellular matrix (ECM). This method enables the formation of arrays of identical tissues and enables the control of a variety of environmental factors, including tissue geometry, spacing, and ECM composition. This method can also be combined with widely used techniques such as traction force microscopy (TFM) to gain more information about the interactions between cells and their surrounding ECM. The protocol can be used to investigate a variety of cell and tissue processes beyond branching morphogenesis, including cancer invasion.

This manuscript describes a soft lithography-based technique to engineer uniform arrays of three-dimensional (3D) epithelial tissues of defined geometry surrounded by extracellular matrix. This method is amenable to a wide variety of cell types and experimental contexts and allows for high-throughput screening of identical replicates.

The architecture of branched organs such as the lungs, kidneys, and mammary glands arises through the developmental process of branching morphogenesis, ...

Cardiac Muscle-cell Based Actuator and Self-stabilizing Biorobot - PART 1

Biological machines often referred to as biorobots, are living cell- or tissue-based devices that are powered solely by the contractile activity of living components. Due to their inherent advantages, biorobots are gaining interest as alternatives to traditional fully artificial robots. Various studies have focused on harnessing the power of biological actuators, but only recently studies have quantitatively characterized the performance of biorobots and studied their geometry to enhance functionality and efficiency. Here, we demonstrate the development of a self-stabilizing swimming biorobot that can maintain its pitch, depth, and roll without external intervention. The design and fabrication of the PDMS scaffold for the biological actuator and biorobot followed by the functionalization with fibronectin is described in this first part. In the second part of this two-part article, we detail the incorporation of cardiomyocytes and characterize the biological actuator and biorobot function. Both incorporate a base and tail (cantilever) which produce fin-based propulsion. The tail is constructed with soft lithography techniques using PDMS and laser engraving. After incorporating the tail with the device base, it is functionalized with a cell adhesive protein and seeded confluently with cardiomyocytes. The base of the biological actuator consists of a solid PDMS block with a central glass bead (acts as a weight). The base of the biorobot consists of two composite PDMS materials, Ni-PDMS and microballoon-PDMS (MB-PDMS). The nickel powder (in Ni-PDMS) allows magnetic control of the biorobot during cells seeding and stability during locomotion. Microballoons (in MB-PDMS) decrease the density of MB-PDMS, and enable the biorobot to float and swim steadily. The use of these two materials with different mass densities, enabled precise control over the weight distribution to ensure a positive restoration force at any angle of the biorobot. This technique produces a magnetically controlled self-stabilizing swimming biorobot.

In this two-part study, a biological actuator was developed using highly flexible polydimethylsiloxane (PDMS) cantilevers and living muscle cells (cardiomyocytes), and characterized. The biological actuator was incorporated with a base made of modified PDMS materials to build a self-stabilizing, swimming biorobot.

Biological machines often referred to as biorobots, are living cell- or tissue-based devices that are powered solely by the contractile activity of living ...

Cardiac Muscle Cell-based Actuator and Self-stabilizing Biorobot - Part 2

In recent years, hybrid devices that consist of a living cell or tissue component integrated with a synthetic mechanical backbone have been developed. These devices, called biorobots, are powered solely by the force generated from the contractile activity of the living component and, due to their many inherent advantages, could be an alternative to conventional fully artificial robots. Here, we describe the methods to seed and characterize a biological actuator and a biorobot that was designed, fabricated, and functionalized in the first part of this two-part article. Fabricated biological actuator and biorobot devices composed of a polydimethylsiloxane (PDMS) base and a thin film cantilever were functionalized for cell attachment with fibronectin. Following functionalization, neonatal rat cardiomyocytes were seeded onto the PDMS cantilever arm at a high density, resulting in a confluent cell sheet. The devices were imaged every day and the movement of the cantilever arms was analyzed. On the second day after seeding, we observed the bending of the cantilever arms due to the forces exerted by the cells during spontaneous contractions. Upon quantitative analysis of the cantilever bending, a gradual increase in the surface stress exerted by the cells as they matured over time was observed. Likewise, we observed movement of the biorobot due to the actuation of the PDMS cantilever arm, which acted as a fin. Upon quantification of the swimming profiles of the devices, various propulsion modes were observed, which were influenced by the resting angle of the fin. The direction of motion and the beating frequency were also determined by the resting angle of the fin, and a maximum swim velocity of 142 &#181;m/s was observed. In this manuscript, we describe the procedure for populating the fabricated devices with cardiomyocytes, as well as for the assessment of the biological actuator and biorobot activity.

In this study, a biological actuator and a self-stabilizing, swimming biorobot with functionalized elastomeric cantilever arms are seeded with cardiomyocytes, cultured, and characterized for their biochemical and biomechanical properties over time.

In recent years, hybrid devices that consist of a living cell or tissue component integrated with a synthetic mechanical backbone have been developed. ...

Microfluidic Bioprinting for Engineering Vascularized Tissues and Organoids

Engineering vascularized tissue constructs and organoids has been historically challenging. Here we describe a novel method based on microfluidic bioprinting to generate a scaffold with multilayer interlacing hydrogel microfibers. To achieve smooth bioprinting, a core-sheath microfluidic printhead containing a composite bioink formulation extruded from the core flow and the crosslinking solution carried by the sheath flow, was designed and fitted onto the bioprinter. By blending gelatin methacryloyl (GelMA) with alginate, a polysaccharide that undergoes instantaneous ionic crosslinking in the presence of select divalent ions, followed by a secondary photocrosslinking of the GelMA component to achieve permanent stabilization, a microfibrous scaffold could be obtained using this bioprinting strategy. Importantly, the endothelial cells encapsulated inside the bioprinted microfibers can form the lumen-like structures resembling the vasculature over the course of culture for 16 days. The endothelialized microfibrous scaffold may be further used as a vascular bed to construct a vascularized tissue through subsequent seeding of the secondary cell type into the interstitial space of the microfibers. Microfluidic bioprinting provides a generalized strategy in convenient engineering of vascularized tissues at high fidelity.

We provide a generalized protocol based on a microfluidic bioprinting strategy for engineering a microfibrous vascular bed, where a secondary cell type could be further seeded into the interstitial space of this microfibrous structure to generate vascularized tissues and organoids.

Engineering vascularized tissue constructs and organoids has been historically challenging. Here we describe a novel method based on microfluidic ...

Two Methods for Decellularization of Plant Tissues for Tissue Engineering Applications

The autologous, synthetic, and animal-derived grafts currently used as scaffolds for tissue replacement have limitations due to low availability, poor biocompatibility, and cost. Plant tissues have favorable characteristics that make them uniquely suited for use as scaffolds, such as high surface area, excellent water transport and retention, interconnected porosity, preexisting vascular networks, and a wide range of mechanical properties. Two successful methods of plant decellularization for tissue engineering applications are described here. The first method is based on detergent baths to remove cellular matter, which is similar to previously established methods used to clear mammalian tissues. The second is a detergent-free method adapted from a protocol that isolates leaf vasculature and involves the use of a heated bleach and salt bath to clear the leaves and stems. Both methods yield scaffolds with comparable mechanical properties and low cellular metabolic impact, thus allowing the user to select the protocol which better suits their intended application.

Here we present, and contrast two protocols used to decellularize plant tissues: a detergent-based approach and a detergent-free approach. Both methods leave behind the extracellular matrix of the plant tissues used, which can then be utilized as scaffolds for tissue engineering applications.

The autologous, synthetic, and animal-derived grafts currently used as scaffolds for tissue replacement have limitations due to low availability, poor ...

Simultaneous Electrical and Mechanical Stimulation to Enhance Cells' Cardiomyogenic Potential

Cardiovascular diseases are the leading cause of death in developed countries. Consequently, the demand for effective cardiac cell therapies has motivated researchers in the stem cell and bioengineering fields to develop in vitro high-fidelity human myocardium for both basic research and clinical applications. However, the immature phenotype of cardiac cells is a limitation on obtaining tissues that functionally mimic the adult myocardium, which is mainly characterized by mechanical and electrical signals. Thus, the purpose of this protocol is to prepare and mature the target cell population through electromechanical stimulation, recapitulating physiological parameters. Cardiac tissue engineering is evolving toward more biological approaches, and strategies based on biophysical stimuli, thus, are gaining momentum. The device developed for this purpose is unique and allows individual or simultaneous electrical and mechanical stimulation, carefully characterized and validated. In addition, although the methodology has been optimized for this stimulator and a specific cell population, it can easily be adapted to other devices and cell lines. The results here offer evidence of the increased cardiac commitment of the cell population after electromechanical stimulation. Electromechanically stimulated cells show an increased expression of main cardiac markers, including early, structural, and calcium-regulating genes. This cell conditioning could be useful for further regenerative cell therapy, disease modeling, and high-throughput drug screening.

Simultaneous Electrical and Mechanical Stimulation to Enhance Cells&#039; Cardiomyogenic Potential

Here we present a protocol for training a cell population using electrical and mechanical stimuli emulating cardiac physiology. This electromechanical stimulation enhances the cardiomyogenic potential of the treated cells and is a promising strategy for further cell therapy, disease modeling, and drug screening.

Cardiovascular diseases are the leading cause of death in developed countries. Consequently, the demand for effective cardiac cell therapies has motivated ...