Name: assessing functional metrics of skeletal muscle health in human skeletal muscle microtissues
Uploaded: 2021-02-18T15:00:00
Description: Watch this Scientific Journal Video about Assessing Functional Metrics of Skeletal Muscle Health in Human Skeletal Muscle Microtissues at JoVE.com

We would like to thank Mohammad Afshar, Haben Abraha, Mohsen Afshar-Bakooshli, and Sadegh Davoudi for contributing to the invention of the MyoTACTIC culture platform and establishing the fabrication and analysis methods described herein. HL received funding from a Natural Sciences and Engineering Research Council (NSERC) Training Program in Organ-on-a-Chip Engineering and Entrepreneurship Scholarship and a University of Toronto Wildcat graduate scholarships. PMG is the Canada Research Chair in Endogenous Repair and received support for this study from the Ontario Institute for Regenerative Medicine, the Stem Cell Network, and from Medicine by Design, a Canada First Research Excellence Program. Schematic diagrams were created with BioRender.com.

1. PDMS MyoTACTIC plate fabrication
NOTE: PDMS MyoTACTIC plate fabrication requires a PU&#160;negative mold, which can be manufactured as previously described30. The computer-aided design (CAD) SolidWorks file for the MyoTACTIC plate design has been made available on GitHub (https://github.com/gilbertlabcode/MyoTACTIC-SolidWork-CAD-file).
<ol>
	<li>Prepare ~ 110 g of PDMS polymer solution in a disposable plastic cup at a 1:15 ratio of monomer to curing agent using the...

<ol>
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This manuscript describes methods to fabricate and analyze a 3D hMMT culture model that can be applied to studies of basic muscle biology, disease modeling, or for candidate molecule testing. The MyoTACTIC platform is cost-friendly, easy to manufacture, and requires a relatively small number of cells to produce skeletal muscle microtissues. hMMTs formed within the MyoTACTIC culture platform are comprised of aligned, multinucleated, and striated myotubes, and respond to electrical stimuli by initiating calcium transients ...

Skeletal muscle is one of the most abundant tissues in the human body and supports key body functions such as locomotion, heat homeostasis and metabolism1. Historically, animal models and two-dimensional (2D) cell culture systems have been used to study biological processes and disease pathogenesis, as well as for testing pharmacological compounds in the treatment of skeletal muscle diseases2,3. While animal models have greatly improved our knowledge of skeletal muscle in health and in disease, their translational impact has been hampered by high costs, ethical considerations and interspecies differences2,4. In turning to human cell-based systems to study skeletal muscle, 2D cell culture systems are favorable due to their simplicity. However, there is a limitation. This format often fails to recapitulate the cell-cell and cell-extracellular matrix interactions that occur naturally within the body5,6. Over the last several years, three dimensional (3D) skeletal muscle models have emerged as a powerful alternative to whole animal models and conventional 2D culture systems by allowing the modeling of physiologically and pathologically relevant processes ex vivo7,8. Indeed, a plethora of studies have reported strategies to model human skeletal muscle in a bioartificial 3D culture format1. One limitation for many of these studies is that active force is quantified following the removal of the muscle tissues from the culture platforms and attachment to a force transducer, which is destructive and hence, limited to serving as an endpoint assay9,10,11,12,13,14,15,16,17,18,19,20,21. Others have designed culture systems that allow for non-invasive methods of measuring active force, but not all are amenable to high content molecule testing applications7,8,9,10,14,18,22,23,24,25,26,27,28,29.
This protocol describes a detailed method to fabricate human muscle microtissues (hMMTs) in the skeletal muscle (Myo) microTissue Array deviCe To Investigate forCe (MyoTACTIC) platform; a 96 well plate device that supports the bulk production of 3D skeletal muscle microtissues30. The MyoTACTIC plate fabrication method enables generation of a 96 well polydimethylsiloxane (PDMS) culture plate and all corresponding well features in a single casting step, whereby each well requires a relatively small number of cells for microtissue formation. Microtissues formed within MyoTACTIC contain aligned, striated, and multinucleated myotubes that are reproducible from well to well of the device, and upon maturation, can respond to chemical and electrical stimuli in situ30. Herein, the technique to manufacture a PDMS MyoTACTIC culture plate device from a polyurethane (PU) replica, an optimized method to implement immortalized human myogenic progenitor cells to fabricate hMMTs, and the functional assessment of engineered hMMT force generation and calcium handling properties are outlined and discussed.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
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		<tr>
			<td>0.9% Saline Solution, Sterile</td>
			<td>House Brand</td>
			<td>1010</td>
			<td>10 mL aliquots of the solution are made and stored at 4&#176;C</td>
		</tr>
		<tr>
			<td>25G Needle</td>
			<td>BD, Medstore, University of Toronto</td>
			<td>2548-CABD305127</td>
			<td></td>
		</tr>
		<tr>
			<td>6-Aminocaproic Acid, &#8805;99% (titration), Powder</td>
			<td>Sigma - Aldrich</td>
			<td>A2504-100G</td>
			<td>A 50 mg / mL stock solution is generated by dissolving 5 mg of 6-aminocaproic acid powder in 100 mL of autoclaved, distilled water. The solution is vaccum filtered and 10 mL aliquots are stored at 4&#176;C</td>
		</tr>
		<tr>
			<td>6.35 mm ID Tubing</td>
			<td>VWR</td>
			<td>60985-528</td>
			<td></td>
		</tr>
		<tr>
			<td>AB1167 Myoblast Cell Line</td>
			<td>Institut de Myologie (Paris, France)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Arbitrary Waveform Generator</td>
			<td>Rigol</td>
			<td>DG1022Z</td>
			<td></td>
		</tr>
		<tr>
			<td>Basement Membrane Extract (Geltrex)</td>
			<td>Thermo Fisher Scientific</td>
			<td>A14132-02</td>
			<td>Stored as aliquots of 50 &#181;L or 100 &#181;L at -80&#176;C</td>
		</tr>
		<tr>
			<td>Benchtop Vacuum Chamber</td>
			<td>Sigma - Aldrich</td>
			<td>D2672</td>
			<td></td>
		</tr>
		<tr>
			<td>BNC to Aligator Clip Cable</td>
			<td></td>
			<td></td>
			<td>Ordered from Amazon</td>
		</tr>
		<tr>
			<td>Culture Plastics</td>
			<td>Sarstedt</td>
			<td></td>
			<td>Includes culture plates, serological pipettes, etc</td>
		</tr>
		<tr>
			<td>Dimethyl Sulfoxide</td>
			<td>Sigma - Aldrich</td>
			<td>D8418-250ML</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS, Powder, No Calcium, No Magnesium</td>
			<td>Thermo Fisher Scientific</td>
			<td>21600069</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle Medium (DMEM) (1X)</td>
			<td>Gibco</td>
			<td>11995-065</td>
			<td>This is a high glucose DMEM with L-glutamine and sodium pyruvate</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Fisher Scientific</td>
			<td>10437028</td>
			<td></td>
		</tr>
		<tr>
			<td>Fibrinogen from Bovine Plasma</td>
			<td>Sigma - Aldrich</td>
			<td>F8630-5G</td>
			<td>Aliquots ranging from 7 - 10 mg of fibrinogen powder are made and stored at -20&#176;C</td>
		</tr>
		<tr>
			<td>Filtropur Syringe Filter, 0.22um Pore Size</td>
			<td>Sarstedt</td>
			<td>83.1826.001</td>
			<td></td>
		</tr>
		<tr>
			<td>Horse Serum</td>
			<td>Gibco</td>
			<td>16050-122</td>
			<td></td>
		</tr>
		<tr>
			<td>Human Recombinant Insulin</td>
			<td>Sigma - Aldrich</td>
			<td>91077C</td>
			<td>Stock solution is 100X and made by dissolving 1 mg of human recombinant insulin in 1 mL of DMEM and 1 &#181;L of NaOH 10N. Solution is filtered and stored as 1 mL aliquots at 4&#176;C</td>
		</tr>
		<tr>
			<td>Image Acquisition Software</td>
			<td>Olympus</td>
			<td>cellSens Dimension</td>
			<td></td>
		</tr>
		<tr>
			<td>Image Processing Software</td>
			<td>National Institutes of Health</td>
			<td>ImageJ</td>
			<td></td>
		</tr>
		<tr>
			<td>Isotemp Oven</td>
			<td>Thermo Fisher Scientific</td>
			<td>201</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope</td>
			<td>Olympus</td>
			<td>IX83</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope - Camera Mount</td>
			<td>Labcam</td>
			<td>Labcam for iPhone</td>
			<td>Ordered from Amazon</td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin (10,000 U/mL)</td>
			<td>Gibco</td>
			<td>15140-122</td>
			<td></td>
		</tr>
		<tr>
			<td>Plastic Disposable Syringes, 1cc</td>
			<td>BD</td>
			<td>2606-309659</td>
			<td></td>
		</tr>
		<tr>
			<td>Plastic Disposable Syringes, 50cc</td>
			<td>BD</td>
			<td>2612-309653</td>
			<td></td>
		</tr>
		<tr>
			<td>Pluronic F-127, Powder, BioReagent</td>
			<td>Sigma - Aldrich</td>
			<td>P2443-250G</td>
			<td>A 5% stock solution of pluronic acid is made by dissolving 5 g of pluronic acid powder in 100 mL of chilled, autoclaved, distilled water. The solution is vaccum filtered and 10 mL aliquots are stored at 4&#176;C</td>
		</tr>
		<tr>
			<td>Polydimethylsiloxane (Sylgard 184 Silicone Elastomer Kit)</td>
			<td>Dow</td>
			<td>4019862</td>
			<td>Kits are also available at Thermo Fisher Scientific, Sigma - Aldrich, etc.</td>
		</tr>
		<tr>
			<td>Polyurethane Negative Mold</td>
			<td>In House</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Release Agent</td>
			<td>Mann Release Technologies</td>
			<td>200</td>
			<td></td>
		</tr>
		<tr>
			<td>Rotary Vane Vacuum Pump</td>
			<td>Edwards</td>
			<td>A65401906</td>
			<td></td>
		</tr>
		<tr>
			<td>Scalpel</td>
			<td>Almedic, Medstore, University of Toronto</td>
			<td>2586-M36-0100</td>
			<td></td>
		</tr>
		<tr>
			<td>Single Edge Razor Blade</td>
			<td>VWR</td>
			<td>55411-050</td>
			<td></td>
		</tr>
		<tr>
			<td>Skeletal Muscle Cell Basal Medium</td>
			<td>Promocell</td>
			<td>C-23260</td>
			<td>30 mL aliquotes are generated and at stored at 4&#176;C.</td>
		</tr>
		<tr>
			<td>Skeletal Muscle Cell Growth Medium (Ready-to-use)</td>
			<td>Promocell</td>
			<td>C-23060</td>
			<td>42 mL aliquots are generated and stored at 4&#176;C.</td>
		</tr>
		<tr>
			<td>Smartphone (iPhone)</td>
			<td>Apple</td>
			<td>SE</td>
			<td></td>
		</tr>
		<tr>
			<td>Standard Duty Dry Vacuum Pump</td>
			<td>Welch</td>
			<td>2546B-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterilization Bag</td>
			<td>Alliance</td>
			<td>211-SCM2</td>
			<td></td>
		</tr>
		<tr>
			<td>Thimble</td>
			<td>Igege</td>
			<td></td>
			<td>Ordered from Amazon</td>
		</tr>
		<tr>
			<td>Thrombin from human plasma</td>
			<td>Sigma - Aldrich</td>
			<td>T6884-250UN</td>
			<td>100 units of thrombin is dissolved in 1 mL of a 0.1% BSA solution. 10 &#181;L aliquots are prepared and stored at - 20&#176;C.</td>
		</tr>
		<tr>
			<td>Tin coated copper wire</td>
			<td>Arco</td>
			<td>B8871K48</td>
			<td>Ordered from Amazon</td>
		</tr>
		<tr>
			<td>Trypan Blue Solution, 0.4%</td>
			<td>Thermo Scientific</td>
			<td>15250061</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA, 0.25%</td>
			<td>Thermo FIsher Scientific</td>
			<td>25200072</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum Chamber 2</td>
			<td>SP Bel-Art</td>
			<td>F42027-0000</td>
			<td></td>
		</tr>
	</tbody>
</table>

assessing functional metrics of skeletal muscle health in human skeletal muscle microtissues

Three-dimensional (3D) in vitro models of skeletal muscle are a valuable advancement in biomedical research as they afford the opportunity to study skeletal muscle reformation and function in a scalable format that is amenable to experimental manipulations. 3D muscle culture systems are desirable as they enable scientists to study skeletal muscle ex vivo in the context of human cells. 3D in vitro&#160;models closely mimic aspects of the native tissue structure of adult skeletal muscle. However, their universal application is limited by the availability of platforms that are simple to fabricate, cost and user-friendly, and yield relatively high quantities of human skeletal muscle tissues. Additionally, since skeletal muscle plays an important functional role that is impaired over time in many disease states, an experimental platform for microtissue studies is most practical when minimally invasive calcium transient and contractile force measurements can be conducted directly within the platform itself. In this protocol, the fabrication of a 96-well platform known as &#39;MyoTACTIC&#39;, and en masse production of 3D human skeletal muscle microtissues (hMMTs) is described. In addition, the methods for a minimally invasive application of electrical stimulation that enables repeated measurements of skeletal muscle force and calcium handling of each microtissue over time are reported.

Described herein are methods to cast a 96-well PDMS-based MyoTACTIC culture platform from a PU mold, to fabricate arrays of hMMT replica tissues, and to analyze two aspects of hMMT function within the culture device-force generation and calcium handling. Figure 1 offers a schematic overview of the preparation of MyoTACTIC culture wells before hMMT seeding. PDMS is a widely used silicone-based polymer, that can be easily molded to create complex devices32. A PDMS-based...

Watch this Scientific Journal Video about Assessing Functional Metrics of Skeletal Muscle Health in Human Skeletal Muscle Microtissues at JoVE.com

Assessing Functional Metrics of Skeletal Muscle Health in Human Skeletal Muscle Microtissues

This manuscript describes a detailed protocol to produce arrays of 3D human skeletal muscle microtissues and minimally invasive downstream in situ assays of function, including contractile force and calcium handling analyses.

Three-dimensional (3D) in vitro models of skeletal muscle are a valuable advancement in biomedical research as they afford the opportunity to study ...

Our protocol describes detailed methods to fabricate and analyze a 3D human skeletal muscle microtissue culture. Muscle microtissues can be applied to studies of basic muscle biology, disease modeling, or for candidate molecule testing. The main advantage of this technique is that it permits in-situ assessment of contractile force and calcium transients.Because of this, you can conduct longitudinal studies of muscle tissue function. Demonstrating the procedure will be Brennen Musgrave and Heta Lad, graduate students from my laboratory. Two to three hours before cell seeding, place a six well mild tactic plate portion into a 10 centimeter cell culture dish.Prepare each individual myotactic culture well by adding 100 microliters of a 5%pluronic F-127 solution. Use the lid to cover the wells, and apply a paraffin film to seal the dish. Centrifuge the dish at 1, 550 times G for one minute in a centrifuge outfitted with a plate spinner adapter.Store the culture dish at four degrees Celsius until the cells are ready for seeding. Then slowly thaw 150 microliter aliquot of basement membrane extract, and 110 microliter aliquot of thrombin on ice in the culture hood. Working in the cell culture hood, add 700 microliters of 0.9%saline solution to a 1.5 milliliter micro centrifuge tube containing seven milligrams of powdered fibrinogen.Place the tube in a 37 degrees Celsius cell culture incubator for three to five minutes without vortexing. Remove and flick the tube gently, then pulse spin the dissolved solution in a micro centrifuge before returning it to the culture hood. Filter the fibrinogen solution using a one milliliter syringe outfitted with a 0.22 micrometer syringe filter.Then transfer the dissolved fibrinogen solution to ice alongside the basement membrane extract and thrombin aliquots. Prepare and pre-warm the tissue growth media at 37 degrees Celsius, which will be introduced to the culture wells after seeding the tissues. Remove the cell culture plates from the incubator and aspirate the culture media.Then wash the cells once by adding five milliliters of DPBS into each culture plate. Aspirate the DPBS and detach the cells by adding one milliliter of 0.25%trypsin EDTA into each culture dish. Place the plate in the cell culture incubator for three minutes, hold the trypsin by adding three milliliters of wash medium to the culture dish, then transfer the cells to an appropriately sized conical tube.Pellet the cells by centrifuging at 400 times G for 10 minutes. Aspirate the media carefully without damaging the cell pellet, then re-suspend the cells in one milliliter of the wash medium. Count the cells using a hemocytometer and trypan blue dye under bright field microscopy.To seed six tissues, prepare enough cells and extracellular matrix for eight tissues, thus accounting for losses and bubble formation. Transfer 1.2 million cells to a new conical tube, then increase the volume to 10 millimeters with wash medium. Pellet the cells by centrifuging at 400 times G for 10 minutes.Prepare 150 microliters of ECM mixture in a 1.5 milliliter micro centrifuge tube, and store the mixture on ice until use. Aspirate the media from the conical tube containing the cells, taking care to avoid the cell pellet. Vigorously flick the end of the tube with a gloved finger until the pellet appears as a cell slurry.Transfer 120 microliters of the ECM solution to the tube containing the cell slurry, and carefully pipette up and down to completely re-suspend the cells within the ECM to generate a single cell suspension. Avoid creating bubbles, then place the cell ECM suspension on ice until use. Place the refrigerated 10 centimeter dish containing the myotactic wells on top of an ice pack inside of the cell culture hood, and aspirate the pluronic F-127 solution from each well.Allow residual pluronic F-127 solution to release from the porous PDMS, and settle to the bottom of the well by letting the wells sit for five minutes on ice, then aspirate again. Pipette the cell ECM suspension carefully to re-suspend the cells, then transfer 105 microliters of the suspension into a fresh, pre-chilled 1.5 milliliter tube by grasping it close to the top. Add 0.84 microliters of 100 units per milliliter thrombin stock solution to the 105 microliters of cell ECM suspension.Pipette rapidly and thoroughly to mix, avoiding the introduction of bubbles. Add 15 microliters of the cell ECM mixture to each well without pressing the pipette into the bottom of the well. With two light motions, spread the cell suspension behind each post in the well.Place the lid on the 10 centimeter culture plate and transfer it to a 37 degrees Celsius tissue culture incubator for approximately five minutes. Add 200 microliters of pre-warmed tissue growth media to each myotactic well after the cell ECM mixture has polymerized. Replace the lid on the 10 centimeter dish and keep it in the incubator until the differentiation.During a 14 day culture period, myoblasts displayed the aspects of native tissue by self-organizing in the mild tactic well to form a 3D microtissue with multi-nucleated striated myotubes. Myotubes have sarcomere striations, which were visualized by immunostaining for sarcomeric alpha actinin. To achieve well-aligned myotubes, technical errors such as bubble formation while pipetting, or damaging pluronic coating during aspiration, should be avoided.A representative displacement of the myotactic well plate post in response to low and high frequency electrical stimulation, is shown here, indicating that myotubes responds to varying electrical stimuli and contract accordingly. Quantification of the post displacement allows for conversion to absolute contractile force of the HMMTs. Calcium transience on HMMTs made from GCaMP6-transduced myoblasts were also analyzed in response to low and high frequency stimulation.Quantification of fluorescent intensity can be used as measurement for the calcium handling properties of HMMTs. Most people who perform this tissue seeding for the first time, struggle with adding the cell extracellular matrix to the wells, and with bubble formation. We recommend practicing the technique on some spare microtissue culture wells with a very simple viscous solution before the first attempt with cells.

assessing-functional-metrics-skeletal-muscle-health-human-skeletal

Research

JoVE Journal

Bioengineering

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 ...

Transplantation of Induced Pluripotent Stem Cell-derived Mesoangioblast-like Myogenic Progenitors in Mouse Models of Muscle Regeneration

Patient-derived iPSCs could be an invaluable source of cells for future autologous cell therapy protocols. iPSC-derived myogenic stem/progenitor cells similar to pericyte-derived mesoangioblasts (iPSC-derived mesoangioblast-like stem/progenitor cells: IDEMs) can be established from iPSCs generated from patients affected by different forms of muscular dystrophy. Patient-specific IDEMs can be genetically corrected with different strategies (e.g. lentiviral vectors, human artificial chromosomes) and enhanced in their myogenic differentiation potential upon overexpression of the myogenesis regulator MyoD. This myogenic potential is then assessed in vitro with specific differentiation assays and analyzed by immunofluorescence. The regenerative potential of IDEMs is further evaluated in vivo, upon intramuscular and intra-arterial transplantation in two representative mouse models displaying acute and chronic muscle regeneration. The contribution of IDEMs to the host skeletal muscle is then confirmed by different functional tests in transplanted mice. In particular, the amelioration of the motor capacity of the animals is studied with treadmill tests. Cell engraftment and differentiation are then assessed by a number of histological and immunofluorescence assays on transplanted muscles. Overall, this paper describes the assays and tools currently utilized to evaluate the differentiation capacity of IDEMs, focusing on the transplantation methods and subsequent outcome measures to analyze the efficacy of cell transplantation.

Induced pluripotent stem cell (iPSC)-derived myogenic progenitors are promising candidates for cell therapy strategies to treat muscular dystrophies. This protocol describes transplantation and functional measurements required to evaluate the engraftment and differentiation of iPSC-derived mesoangioblasts (a type of muscle progenitors) in mouse models of acute and chronic muscle regeneration.

Patient-derived iPSCs could be an invaluable source of cells for future autologous cell therapy protocols. iPSC-derived myogenic stem/progenitor cells ...

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 ...

Engineered Vascularized Muscle Flap

One of the main factors limiting the thickness of a tissue construct and its consequential viability and applicability in vivo, is the control of oxygen supply to the cell microenvironment, as passive diffusion is limited to a very thin layer. Although various materials have been described to restore the integrity of full-thickness defects of the abdominal wall, no material has yet proved to be optimal, due to low graft vascularization, tissue rejection, infection, or inadequate mechanical properties. This protocol describes a means of engineering a fully vascularized flap, with a thickness relevant for muscle tissue reconstruction. Cell-embedded poly L-lactic acid/poly lactic-co-glycolic acid constructs are implanted around the mouse femoral artery and vein and maintained in vivo for a period of one or two weeks. The vascularized graft is then transferred as a flap towards a full thickness defect made in the abdomen. This technique replaces the need for autologous tissue sacrifications and may enable the use of in vitro engineered vascularized flaps in many surgical applications.

To date, thick tissue defects are typically reconstructed by applying autologous tissue flaps or engineered tissues. In this protocol, we present a new method for engineering vascularized tissue flap bearing an autologous pedicle, to serve as a substitute to autologous flaps.

One of the main factors limiting the thickness of a tissue construct and its consequential viability and applicability in vivo, is the control of oxygen ...

Computed Tomography and Optical Imaging of Osteogenesis-angiogenesis Coupling to Assess Integration of Cranial Bone Autografts and Allografts

A major parameter determining the success of a bone-grafting procedure is vascularization of the area surrounding the graft. We hypothesized that implantation of a bone autograft would induce greater bone regeneration by abundant blood vessel formation. To investigate the effect of the graft on neovascularization at the defect site, we developed a micro&#8211;computed tomography (&#181;CT) approach to characterize newly forming blood vessels, which involves systemic perfusion of the animal with a polymerizing contrast agent. This method enables detailed vascular analysis of an organ in its entirety. Additionally, blood perfusion was assessed using fluorescence imaging (FLI) of a blood-borne fluorescent agent. Bone formation was quantified by FLI using a hydroxyapatite-targeted probe and &#181;CT analysis. Stem cell recruitment was monitored by bioluminescence imaging (BLI) of transgenic mice that express luciferase under the control of the osteocalcin promoter. Here we describe and demonstrate preparation of the allograft, calvarial defect surgery, &#181;CT scanning protocols for the neovascularization study and bone formation analysis (including the in vivo perfusion of contrast agent), and the protocol for data analysis.
The 3D high-resolution analysis of vasculature demonstrated significantly greater angiogenesis in animals with implanted autografts, especially with respect to arteriole formation. Accordingly, blood perfusion was significantly higher in the autograft group by the 7th day after surgery. We observed superior bone mineralization and measured greater bone formation in animals that received autografts. Autograft implantation induced resident stem cell recruitment to the graft-host bone suture, where the cells differentiated into bone-forming cells between the 7th and 10th postoperative day. This finding means that enhanced bone formation may be attributed to the augmented vascular feeding that characterizes autograft implantation. The methods depicted may serve as an optimal tool to study bone regeneration in terms of tightly bounded bone formation and neovascularization.

Implantation of autologous and allogeneic bone grafts constitute accepted approaches to treat major craniofacial bone loss. Yet the effect of graft composition on the interplay among neovascularization, cell differentiation and bone formation is unclear. We present a multimodal imaging protocol aimed to elucidate the angiogenesis-osteogenesis interdependence at the graft proximity.

A major parameter determining the success of a bone-grafting procedure is vascularization of the area surrounding the graft. We hypothesized that ...

Applications of In Vivo Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair

Despite the regenerative capacity of skeletal muscle, permanent functional and/or cosmetic deficits (e.g., volumetric muscle loss (VML) resulting from traumatic injury, disease and various congenital, genetic and acquired conditions are quite common. Tissue engineering and regenerative medicine technologies have enormous potential to provide a therapeutic solution. However, utilization of biologically relevant animal models in combination with longitudinal assessments of pertinent functional measures are critical to the development of improved regenerative therapeutics for treatment of VML-like injuries. In that regard, a commercial muscle lever system can be used to measure length, tension, force and velocity parameters in skeletal muscle. We used this system, in conjunction with a high power, bi-phase stimulator, to measure in vivo force production in response to activation of the anterior crural compartment of the rat hindlimb. We have previously used this equipment to assess the functional impact of VML injury on the tibialis anterior (TA) muscle, as well as the extent of functional recovery following treatment of the injured TA muscle with our tissue engineered muscle repair (TEMR) technology. For such studies, the left foot of an anaesthetized rat is securely anchored to a footplate linked to a servomotor, and the common peroneal nerve is stimulated by two percutaneous needle electrodes to elicit muscle contraction and dorsiflexion of the foot. The peroneal nerve stimulation-induced muscle contraction is measured over a range of stimulation frequencies (1-200 Hz), to ensure an eventual plateau in force production that allows for an accurate determination of peak tetanic force. In addition to evaluation of the extent of VML injury as well as the degree of functional recovery following treatment, this methodology can be easily applied to study diverse aspects of muscle physiology and pathophysiology. Such an approach should assist with the more rational development of improved therapeutics for muscle repair and regeneration.

Applications of In Vivo Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair

We describe an in vivo protocol to measure dorsiflexion of the foot following stimulation of the peroneal nerve and contraction of the anterior crural compartment of the rat hindlimb. Such measurements are an indispensable translational tool for evaluating skeletal muscle pathology and tissue engineering approaches to muscle repair and regeneration.

Despite the regenerative capacity of skeletal muscle, permanent functional and/or cosmetic deficits (e.g., volumetric muscle loss (VML) resulting from ...

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. ...

Semiautomated Longitudinal Microcomputed Tomography-based Quantitative Structural Analysis of a Nude Rat Osteoporosis-related Vertebral Fracture Model

Osteoporosis-related vertebral compression fractures (OVCFs) are a common and clinically unmet need with increasing prevalence as the world population ages. Animal OVCF models are essential to the preclinical development of translational tissue engineering strategies. While a number of models currently exist, this protocol describes an optimized method for inducing multiple highly reproducible vertebral defects in a single nude rat. A novel longitudinal semiautomated microcomputed tomography (&#181;CT)-based quantitative structural analysis of the vertebral defects is also detailed. Briefly, rats were imaged at multiple time points post-op. The day 1 scan was reoriented to a standard position, and a standard volume of interest was defined. Subsequent &#181;CT scans of each rat were automatically registered to the day 1 scan so the same volume of interest was then analyzed to assess for new bone formation. This versatile approach can be adapted to a variety of other models where longitudinal imaging-based analysis could benefit from precise 3D semiautomated alignment. Taken together, this protocol describes a readily quantifiable and easily reproducible system for osteoporosis and bone research. The suggested protocol takes 4 months to induce osteoporosis in nude ovariectomized rats and between 2.7 and 4 h to generate, image, and analyze two vertebral defects, depending on tissue size and equipment.

The goal of this protocol is to generate a nude rat osteoporosis-related vertebral compression fracture model that can be longitudinally evaluated in vivo using a semiautomated microcomputed tomography-based quantitative structural analysis.

Osteoporosis-related vertebral compression fractures (OVCFs) are a common and clinically unmet need with increasing prevalence as the world population ...

Melt Electrospinning Writing of Three-dimensional Poly(&#949;-caprolactone) Scaffolds with Controllable Morphologies for Tissue Engineering Applications

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology with great potential for biomedical applications. The technique facilitates the direct deposition of biocompatible polymer fibers to fabricate well-ordered scaffolds in the sub-micron to micro scale range. The establishment of a stable, viscoelastic, polymer jet between a spinneret and a collector is achieved using an applied voltage and can be direct-written. A significant benefit of a typical porous scaffold is a high surface-to-volume ratio which provides increased effective adhesion sites for cell attachment and growth. Controlling the printing process by fine-tuning the system parameters enables high reproducibility in the quality of the printed scaffolds. It also provides a flexible manufacturing platform for users to tailor the morphological structures of the scaffolds to their specific requirements. For this purpose, we present a protocol to obtain different fiber diameters using melt electrospinning writing (MEW) with a guided amendment of the parameters, including flow rate, voltage and collection speed. Furthermore, we demonstrate how to optimize the jet, discuss often experienced technical challenges, explain troubleshooting techniques and showcase a wide range of printable scaffold architectures.

This protocol serves as a comprehensive guideline to fabricate scaffolds via electrospinning with polymer melts in a direct writing mode. We systematically outline the process and define the appropriate parameter settings for achieving targeted scaffold architectures.

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology ...