This study was performed in the research program of the BioMedical Materials (BMM) institute. BMM is cofunded by the Dutch Ministry of Economic affairs, Agriculture and Innovation. The financial contribution of the Nederlandse Hartstichting is gratefully acknowledged.

1. Culture of Human Vena Saphena Cells
<ol>
	<li>Isolate cells from the vena saphena magna, acquired from a donor in accordance to guidelines for secondary use material, according to the protocol by Schnell et al.9 and store these in liquid nitrogen. From the part of the vena saphena magna from one donor cut pieces of 2 x 2 mm to culture in a six-well plate. Use 2 pieces per well. Generally enough cells can be obtained to fill about 3 vials with 0.25 x 106 cells in liquid nitrogen. HVSCs are characterized as myofibroblasts, by showing expression of vimentin, no expression of desmin and a subpopulation expressing &#945; smooth muscle actin10. Next start the protocol to thaw the cells from the liquid nitrogen to increase the number of cells.</li>
	<li>Place the cells from one&#160;vial into a T75 tissue culture flask and add growth medium (GM), consisting of Advanced DMEM, 50 ml fetal bovine serum (FBS), 5 ml penicillin/streptomycin and 5 ml L-glutamax. Change medium every 2-3 days.</li>
	<li>Cells grow confluent approximately after 14 days. Store 0.5 x 106 cells in one&#160;vial in liquid nitrogen, referred to as passage 1.</li>
</ol>
Note: Freezing of the cells is not necessary when harvesting HVSCs, but is solely used for storage.
<ol start="4">
	<li>Place the HVSCs from one&#160;vial into a T175 tissue culture flask and add GM. Change medium every 2-3 days. Cells grow confluent after approximately 7 days. Store 3 x 106 cells in one&#160;vial in liquid nitrogen, referred to as passage 2.</li>
	<li>Place the cells from one&#160;vial into a rollerbottle and add GM. Change medium every 2-3 days. Cells grow confluent approximately after 8 days. One rollerbottle contains approximately 20-30 x 106 cells. Culture cells up to passage 6. Do not use cells of a passage higher than passage 9, since cell phenotype may change.</li>
</ol>
2. Engineering of Fibrin-based Tissue Constructs
<ol>
	<li>Prepare silicone glue by mixing the elastomer with the curing agent (10:1). Cut 7 x 3 mm rectangular segments of Velcro. Glue the Velcro into a 6 well culture plate, with flexible membranes&#160;to form a cross, and to leave a squared space of 3 mm between the Velcro strips.</li>
</ol>
Notes: Only use the soft side of the Velcro and face this side upwards. When gluing the Velcro, only cover the Velcro with silicone glue, do not spread glue throughout the well. Since the culture plates have silicone membrane bottoms, use something underneath the well plate for reinforcing the flexible membranes, to ensure easy gluing in to the plate.
<ol start="2">
	<li>Dry the silicone glue overnight in an oven at 60 &#176;C to ensure hardening of the glue. Sterilize by adding 70% EtOH to the wells and incubate for 30 min. Rinse 3x with PBS and remove all PBS from the wells and the Velcro. Put under UV for 30 min and keep sterile until use.</li>
	<li>Prepare Tissue Engineering medium (TM), consisting of GM and 130 mg of L-ascorbic acid 2-phosphate.</li>
	<li>Add 1 mg/ml &#949;-Amino Caproic Acid (ACA) to the TM. ACA is used for the first 7 days of culture to prevent the fibrin from degrading11. Alternatively, aprotinin can be used.</li>
	<li>To prevent clump formation, allow fibrinogen to reach room temperature before opening. Without clumps fibrinogen will dissolve more easily. Dissolve fibrinogen to a concentration of 10 mg actual protein/ml TM7 supplemented with ACA. Sterile filter the fibrinogen solution, multiple filters might be needed. Store on ice until use.</li>
</ol>
Note: To dissolve fibrinogen mix gently to prevent too much foam formation.
<ol start="6">
	<li>Dissolve thrombin to a concentration of 10 IU/ml TM7 supplemented with ACA. Store on ice until use.</li>
</ol>
Note: Storage on ice is needed to prevent early gelation of thrombin and fibrinogen.
<ol start="7">
	<li>Trypsinize the cells, resuspend in GM and count.</li>
	<li>Use 15 x 106 cells/ml for seeding the fibrin-based tissue constructs (concentration based on methods for tissue engineering heart valves7). A single gel consists of 100 &#956;l gof el, and thus of 1.5 x 106 cells. Put 1.5 x 106 cells in one centrifuge tube, resulting in as many centrifuge tubes as the number of gels that will be made.</li>
	<li>Centrifuge the cells at 350 x g for 7 min and discard the supernatant. Resuspend the cells in 50 &#956;l thrombin. Add 4 &#956;l of blue fluorescent polystyrene microspheres to this suspension. Put 50 &#956;l of fibrinogen in a vial. Use a pipette to take up the 50 &#956;l thrombin with cells. Increase the volume of the pipette to 100 &#956;l. Pipette the 50 &#956;l solution of thrombin with cells into the vial with fibrinogen to mix the thrombin and fibrinogen, and take up the 100 &#956;l mixture.</li>
</ol>
Note: The fluorescent polystyrene microspheres are used as internal reference markers for image analysis. When mixing thrombin and fibrinogen, prevent the formation of air bubbles by carefully pipetting the mixture. Air bubbles will result in holes in the fibrin gel.
<ol start="10">
	<li>Pipette the gel mixture into and in between the Velcro strips. The typical gelation time for the fibrin gels, once the components are mixed, is of the order of 20 sec.</li>
</ol>
Notes: Do this as quickly as possible to prevent gelation before the mixture is pipetted in the well plate. Practice before using cells and beads.
<ol start="11">
	<li>Incubate suspensions for 30 min at 37 &#176;C in a humidified 95% air/5%&#160;CO2 incubator to allow gelation before adding culture TM with ACA.</li>
	<li>Replace TM with ACA every 2-3 days for the first 7 days. Gels are stable enough after one week to be cultured without ACA. After the first week replace TM every 2-3 days. Add 6 ml of TM per well. On day 12 cells have produced enough collagen for visualization.</li>
</ol>
3. Applying Strain and Inducing Changes in Strain and Constraints
<ol>
	<li>Static strain is applied by the cells directly, due to cell traction and compaction12. To induce collagen reorganization, cut the tissue construct loose from two Velcro strips in one direction. This results in unidirectional constraints (Figure 1A). Perform this on day 12, since the construct is then stable enough and collagen has been deposited.</li>
	<li>Apply cyclic strain by applying a vacuum to the bottom of the culture plates with flexible membranes, with the use of the Flexcell FX4000T system. Place the plates on a baseplate, on top of loading posts (which are a part of the cyclic loading device). The pump applies a vacuum onto the membrane and thereby pulls the membrane over the rectangular post lying underneath. Due to the cross shaped attachments of the tissue constructs to the membrane (via the Velcro) and the rectangular post the applied cyclic strain is uniaxial (Figure 1B).</li>
	<li>Initially, use static culture for 5 days to achieve initial mechanical integrity, before application of cyclic strain starting on day 6. Program a cyclic stain protocol into the controller for the vacuum pump. For example use a previously established intermittent cyclic strain protocol, with uniaxial direction13. This consists of an intermittent strain of a sine wave with 1 Hz, straining from 0 to 5% strain, for periods of 3 hr, alternated with 3 hr resting periods. Perform this cyclic strain protocol for 7 days, inducing an aligned collagen organization.</li>
	<li>Typically after 12 days HVSCs have produced an aligned collagen organization. After an aligned collagen organization is reached, change the uniaxial cyclic strain direction, to be perpendicular to the original strain direction. Do this by turning the rectangular posts by 90&#176;.</li>
</ol>
4. Visualizing Cells and Collagen
<ol>
	<li>To visualize active, real-time collagen remodeling, label samples with probes that do not interfere with cell viability or collagen formation. Use probes to fluorescently stain the cell cytoplasm and collagen.</li>
	<li>Alternatively second harmonic generation using confocal laser scanning microscopy can be used to visualize collagen structures using autofluorescence14, with excitation at 780 nm and detection between 500-550 nm.</li>
	<li>Remove the culture plates from the setup and the incubator, for the cyclically strained samples during the 3 hr rest period, and transport them to a confocal laser scanning microscope to visualize cells and collagen.</li>
</ol>

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Eng. 39, 714-729 (2010).</li><li>van der Schaft, D. W., 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+Skeletal+Muscle+Tissues+from+Murine+Myoblast+Progenitor+Cells+and+Application+of+Electrical+Stimulation.">Engineering Skeletal Muscle Tissues from Murine Myoblast Progenitor Cells and Application of Electrical Stimulation.</a> J. Vis. Exp. (73), e4267 (2013).</li></ol>

The authors declare that they have no competing financial interests.

The described model system of cell-populated fibrin constructs has great potential for the study of cell and collagen (re)organization (de Jonge et al.15), e.g. to be used for tissue engineering purposes. By using fibrin as the initial cell carrier, after fibrin degradation, a tissue is created with cells and endogenous matrix only. In this way, cells are stimulated to react to strain, either static or cyclic in nature, by applying contractile forces16,17, sensing boundary stiffnes...

Cardiovascular tissues have a prominent load-bearing function. In particular content and organization of collagen fibers in the extracellular matrix contribute to the load-bearing properties and dominate overall tissue strength1. In tissue engineering mechanical conditioning of the construct is used - typically consisting of (cyclic) straining regimens - to enhance tissue organization and mechanical properties2,3. Full understanding of strain-induced collagen organization in complex tissue geometries to create tissues with predefined collagen architecture has not yet been achieved. This is mainly due to our limited knowledge of collagen remodeling in developing tissues. Existing models mainly give information about the final net outcome of collagen remodeling with use of static strain4-6. Here we provide a highly tunable model system that allows the study of collagen (re)organization in a real-time fashion, in 3D, under influence of static or cyclic strain. The tissue constructs are fibrin-based, ensuring that all collagen in the construct is endogenous. Cell and collagen organization in the constructs is visualized, and an internal reference system allows us to relocate cells and collagen structures for time-lapse analysis. In this protocol we will describe the use of the model system for Human Vena Saphena Cells (HVSCs), since these cells are known for their enhanced extra cellular matrix production and ability to remodel the matrix and our established use in engineered cardiovascular tissues7, based on the work of de Jonge et al.8

<table><tbody><tr><td>Culture plastic</td><td>Greiner</td><td></td><td>Includes culture flasks and pipettes</td></tr><tr><td>Advanced DMEM</td><td>Gibco</td><td>12491</td><td></td></tr><tr><td>Fetal bovine serum</td><td>Greiner</td><td>758075</td><td></td></tr><tr><td>Penicillin/streptomycin</td><td>Gibco</td><td>10378016</td><td></td></tr><tr><td>GlutaMax</td><td>Gibco</td><td>35050-079</td><td></td></tr><tr><td>Elastomer and curing agent</td><td>Dow Corning Corporation</td><td>3097358-1004</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>Bioflex culture plates</td><td>Flexcell Int</td><td>BF-3001U</td><td>Untreated</td></tr><tr><td>L-Ascorbic Acid 2-phosphatase</td><td>Sigma</td><td>A8960</td><td></td></tr><tr><td>&amp;epsilon;-Amino Caproic Acid</td><td>Sigma-Aldrich</td><td>D7754</td><td></td></tr><tr><td>Bovine thrombin</td><td>Sigma</td><td>T4648</td><td></td></tr><tr><td>Bovine fibrinogen</td><td>Sigma</td><td>F8630</td><td></td></tr><tr><td>0.45 syringe filter</td><td>Whatmann (Schleicher and Scheul)</td><td>10462100</td><td></td></tr><tr><td>Polystyrene microspheres</td><td>Invitrogen</td><td>F-8829</td><td>Blue fluorescent, 10 &amp;mu;m diameter</td></tr><tr><td>Flexcell FX-4000T</td><td>Flexcell Int</td><td></td><td>Includes rectangular loading posts</td></tr><tr><td>Cell Tracker Orange</td><td>Invitrogen Molecular Probes</td><td>C2927</td><td></td></tr><tr><td>CNA35-OG488</td><td></td><td></td><td>Cordially provided by the Laboratory for Macromolecular and Organic Chemistry, Department of Biomedical Engineering, Eindhoven University of Technology</td></tr><tr><td>Confocal laser scanning microscope</td><td>Carl Zeiss</td><td></td><td>LSM 510 Meta laser scanning microscope and Two-Photon-LSM mode</td></tr><tr><td>Amphotericin</td><td>Gibco</td><td>15290-018</td><td>Needed for cell isolation</td></tr></tbody></table>

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 allows for culturing myofibroblast-seeded fibrin gels. Figure 1A shows a tissue cultured first under static biaxial constraints. Tissue constraints are released by cutting the fibrin gel from two constraints, to create uniaxial static constraints, and tissue compacts and remodels afterwards (Figure 1A). For cyclic strain, the tissue is cultured under static biaxial constraints as well. After 5 days cyclic uniaxial strain can be applied (Figure 1B). To i...

Watch this Scientific Journal Video about Engineering Fibrin-based Tissue Constructs from Myofibroblasts and Application of Constraints and Strain to Induce Cell and Collagen Reorganization at JoVE.co

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

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 ...

engineering-fibrin-based-tissue-constructs-from-myofibroblasts

Universidad de Cartagena UDEC

Research

JoVE Journal

Bioengineering

10.8K Views.  Eindhoven University of Technology. 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.

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

Encapsulation of Cardiomyocytes in a Fibrin Hydrogel for Cardiac Tissue Engineering 

Culturing cells in a three dimensional hydrogel environment is an important technique for developing constructs for tissue engineering as well as studying cellular responses under various culture conditions in vitro. The three dimensional environment more closely mimics what the cells observe in vivo due to the application of mechanical and chemical stimuli in all dimensions 1. Three-dimensional hydrogels can either be made from synthetic polymers such as PEG-DA 2 and PLGA 3 or a number of naturally occurring proteins such as collagen 4, hyaluronic acid 5 or fibrin 6,7. Hydrogels created from fibrin, a naturally occurring blood clotting protein, can polymerize to form a mesh that is part of the body's natural wound healing processes 8. Fibrin is cell-degradable and potentially autologous 9, making it an ideal temporary scaffold for tissue engineering.
Here we describe in detail the isolation of neonatal cardiomyocytes from three day old rat pups and the preparation of the cells for encapsulation in fibrin hydrogel constructs for tissue engineering. Neonatal myocytes are a common cell source used for in vitro studies in cardiac tissue formation and engineering 4. Fibrin gel is created by mixing fibrinogen with the enzyme thrombin. Thrombin cleaves fibrinopeptides FpA and FpB from fibrinogen, revealing binding sites that interact with other monomers 10. These interactions cause the monomers to self-assemble into fibers that form the hydrogel mesh. Because the timing of this enzymatic reaction can be adjusted by altering the ratio of thrombin to fibrinogen, or the ratio of calcium to thrombin, one can injection mold constructs with a number of different geometries 11,12. Further we can generate alignment of the resulting tissue by how we constrain the gel during culture 13.
After culturing the engineered cardiac tissue constructs for two weeks under static conditions, the cardiac cells have begun to remodel the construct and can generate a contraction force under electrical pacing conditions 6. As part of this protocol, we also describe methods for analyzing the tissue engineered myocardium after the culture period including functional analysis of the active force generated by the cardiac muscle construct upon electrical stimulation, as well as methods for determining final cell viability (Live-Dead assay) and immunohistological staining to examine the expression and morphology of typical proteins important for contraction (Myosin Heavy Chain or MHC) and cellular coupling (Connexin 43 or Cx43) between myocytes.

Encapsulation of Cardiomyocytes in a Fibrin Hydrogel for Cardiac Tissue Engineering

We describe the isolation of neonatal cardiomyocytes and the preparation of the cells for encapsulation in fibrin hydrogel constructs for tissue engineering. We describe methods for analyzing the tissue engineered myocardium after the culture period including active force generated upon electrical stimulation and cell viability and immunohistological staining.

Culturing cells in a three dimensional hydrogel environment is an important technique for developing constructs for tissue engineering as well as studying ...

Engineering a Bilayered Hydrogel to Control ASC Differentiation

Natural polymers over the years have gained more importance because of their host biocompatibility and ability to interact with cells in vitro and in vivo. An area of research that holds promise in regenerative medicine is the combinatorial use of novel biomaterials and stem cells. A fundamental strategy in the field of tissue engineering is the use of three-dimensional scaffold (e.g., decellularized extracellular matrix, hydrogels, micro/nano particles) for directing cell function. This technology has evolved from the discovery that cells need a substrate upon which they can adhere, proliferate, and express their differentiated cellular phenotype and function 2-3. More recently, it has also been determined that cells not only use these substrates for adherence, but also interact and take cues from the matrix substrate (e.g., extracellular matrix, ECM)4. Therefore, the cells and scaffolds have a reciprocal connection that serves to control tissue development, organization, and ultimate function. Adipose-derived stem cells (ASCs) are mesenchymal, non-hematopoetic stem cells present in adipose tissue that can exhibit multi-lineage differentiation and serve as a readily available source of cells (i.e. pre-vascular endothelia and pericytes). Our hypothesis is that adipose-derived stem cells can be directed toward differing phenotypes simultaneously by simply co-culturing them in bilayered matrices1. Our laboratory is focused on dermal wound healing. To this end, we created a single composite matrix from the natural biomaterials, fibrin, collagen, and chitosan that can mimic the characteristics and functions of a dermal-specific wound healing ECM environment.

This protocol focuses on utilizing the inherent ability of stem cells to take cue from their surrounding extracellular matrix and be induced to differentiate into multiple phenotypes. This methods manuscript extends our description and characterization of a model utilizing a bilayered hydrogel, composed of PEG-fibrin and collagen, to simultaneously co-differentiate adipose-derived stem cells1.

Natural polymers over the years have gained more importance because of their host biocompatibility and ability to interact with cells in vitro and in ...

Postproduction Processing of Electrospun Fibres for Tissue Engineering

Electrospinning is a commonly used and versatile method to produce scaffolds (often biodegradable) for 3D tissue engineering.1, 2, 3 Many tissues in vivo undergo biaxial distension to varying extents such as skin, bladder, pelvic floor and even the hard palate as children grow. In producing scaffolds for these purposes there is a need to develop scaffolds of appropriate biomechanical properties (whether achieved without or with cells) and which are sterile for clinical use. The focus of this paper is not how to establish basic electrospinning parameters (as there is extensive literature on electrospinning) but on how to modify spun scaffolds post production to make them fit for tissue engineering purposes - here thickness, mechanical properties and sterilisation (required for clinical use) are considered and we also describe how cells can be cultured on scaffolds and subjected to biaxial strain to condition them for specific applications.
Electrospinning tends to produce thin sheets; as the electrospinning collector becomes coated with insulating fibres it becomes a poor conductor such that fibres no longer deposit on it. Hence we describe approaches to produce thicker structures by heat or vapour annealing increasing the strength of scaffolds but not necessarily the elasticity. Sequential spinning of scaffolds of different polymers to achieve complex scaffolds is also described. Sterilisation methodologies can adversely affect strength and elasticity of scaffolds. We compare three methods for their effects on the biomechanical properties on electrospun scaffolds of poly lactic-co-glycolic acid (PLGA).
Imaging of cells on scaffolds and assessment of production of extracellular matrix (ECM) proteins by cells on scaffolds is described. Culturing cells on scaffolds in vitro can improve scaffold strength and elasticity but the tissue engineering literature shows that cells often fail to produce appropriate ECM when cultured under static conditions. There are few commercial systems available that allow one to culture cells on scaffolds under dynamic conditioning regimes - one example is the Bose Electroforce 3100 which can be used to exert a conditioning programme on cells in scaffolds held using mechanical grips within a media filled chamber.4 An approach to a budget cell culture bioreactor for controlled distortion in 2 dimensions is described. We show that cells can be induced to produce elastin under these conditions. Finally assessment of the biomechanical properties of processed scaffolds cultured with or without cells is described.

Electrospun scaffolds can be processed post production for tissue engineering applications. Here we describe methods for spinning complex scaffolds (by consecutive spinning), for making thicker scaffolds (by multi-layering using heat or vapour annealing), for achieving sterility (aseptic production or sterilisation post production) and for achieving appropriate biomechanical properties.

Electrospinning is a commonly used and versatile method to produce  scaffolds (often biodegradable) for 3D tissue engineering.1, 2, 3 Many tissues in vivo ...

Observing and Quantifying Fibroblast-mediated Fibrin Gel Compaction

Cells embedded in collagen and fibrin gels attach and exert traction forces on the fibers of the gel. These forces can lead to local and global reorganization and realignment of the gel microstructure. This process proceeds in a complex manner that is dependent in part on the interplay between the location of the cells, the geometry of the gel, and the mechanical constraints on the gel. To better understand how these variables produce global fiber alignment patterns, we use time-lapse differential interference contrast (DIC) microscopy coupled with an environmentally controlled bioreactor to observe the compaction process between geometrically spaced explants (clusters of fibroblasts). The images are then analyzed with a custom image processing algorithm to obtain maps of the strain. The information obtained from this technique can be used to probe the mechanobiology of various cell-matrix interactions, which has important implications for understanding processes in wound healing, disease development, and tissue engineering applications.

Time-lapse microscopy and image processing techniques were used to observe and analyze fibroblast-mediated gel compaction and fibrin fiber realignment in an environmentally controlled bioreactor over a 48 hr&#160;period.

Cells embedded in collagen and fibrin gels attach and exert traction forces on the fibers of the gel. These forces can lead to local and global ...

Fabrication of Myogenic Engineered Tissue Constructs

Despite the fact that electronic pacemakers are life-saving medical devices, their long-term performance in pediatric patients can be problematic owing to the restrictions imposed by a child's small size and their inevitable growth. Consequently, there is a genuine need for innovative therapies designed specifically for pediatric patients with cardiac rhythm disorders. We propose that a conductive biological alternative consisting of a collagen-based matrix containing autologously-derived cells could better adapt to growth, reduce the need for recurrent surgeries, and greatly improve the quality of life for these patients. In the present study, we describe a procedure for incorporating primary skeletal myoblast cell cultures within a hydrogel matrix to fashion a surgically-implantable tissue construct that will serve as an electrical conduit between the upper and lower chambers of the heart. Ultimately, we anticipate using this type of engineered tissue to restore atrioventricular electrical conduction in children with complete heart block. In view of that, we isolate myoblasts from the skeletal muscles of neonatal Lewis rats and plate them onto laminin-coated tissue culture dishes using a modified version of established protocols[2, 3]. After one to two days, cultured cells are collected and mixed with antibiotics, type 1 collagen, Matrigel&trade;, and NaHCO3. The result is a viscous, uniform solution that can be cast into a mold of nearly any shape and size[1, 4, 5]. For our tissue constructs, we employ type 1 collagen isolated from fetal lamb skin using standard procedures[6]. Once the tissue has solidified at 37&deg;C, culture media is carefully added to the plate until the construct is submerged. The engineered tissue is then allowed to further condense through dehydration for 2 more days, at which point it is ready for in vitro assessment or surgical-implantation.

Here, we demonstrate fabrication of collagen-based, tissue constructs containing skeletal myoblasts. These 3-D engineered constructs may be used to replace or repair tissues in vivo. For our purposes, we have designed these as an atrioventricular electrical conduit for the repair of complete heart block[1].

Despite the fact that electronic pacemakers are life-saving medical devices, their long-term performance in pediatric patients can be problematic owing to ...

Biology

Engineering 3D Cellularized Collagen Gels for Vascular Tissue Regeneration

Synthetic materials are known to initiate clinical complications such as inflammation, stenosis, and infections when implanted as vascular substitutes. Collagen has been extensively used for a wide range of biomedical applications and is considered a valid alternative to synthetic materials due to its inherent biocompatibility (i.e., low antigenicity, inflammation, and cytotoxic responses). However, the limited mechanical properties and the related low hand-ability of collagen gels have hampered their use as scaffold materials for vascular tissue engineering. Therefore, the rationale behind this work was first to engineer cellularized collagen gels into a tubular-shaped geometry and second to enhance smooth muscle cells driven reorganization of collagen matrix to obtain tissues stiff enough to be handled.
The strategy described here is based on the direct assembling of collagen and smooth muscle cells (construct) in a 3D cylindrical geometry with the use of a molding technique. This process requires a maturation period, during which the constructs are cultured in a bioreactor under static conditions (without applied external dynamic mechanical constraints) for 1 or 2 weeks. The &#8220;static bioreactor&#8221; provides a monitored and controlled sterile environment (pH, temperature, gas exchange, nutrient supply and waste removal) to the constructs. During culture period, thickness measurements were performed to evaluate the cells-driven remodeling of the collagen matrix, and glucose consumption and lactate production rates were measured to monitor the cells metabolic activity. Finally, mechanical and viscoelastic properties were assessed for the resulting tubular constructs. To this end, specific protocols and a focused know-how (manipulation, gripping, working in hydrated environment, and so on) were developed to characterize the engineered tissues.

In this work, we present a technique for the rapid fabrication of living vascular tissues by direct culturing of collagen, smooth muscle cells and endothelial cells. In addition, a new protocol for the mechanical characterization of engineered vascular tissues is described.

Synthetic materials are known to initiate clinical complications such as inflammation, stenosis, and infections when implanted as vascular substitutes. ...

A Multi-Cue Bioreactor to Evaluate the Inflammatory and Regenerative Capacity of Biomaterials under Flow and Stretch

The use of resorbable biomaterials to induce regeneration directly in the body is an attractive strategy from a translational perspective. Such materials induce an inflammatory response upon implantation, which is the driver of subsequent resorption of the material and the regeneration of new tissue. This strategy, also known as in situ tissue engineering, is pursued to obtain cardiovascular replacements such as tissue-engineered vascular grafts. Both the inflammatory and the regenerative processes are determined by the local biomechanical cues on the scaffold (i.e., stretch and shear stress). Here, we describe in detail the use of a custom-developed bioreactor that uniquely enables the decoupling of stretch and shear stress on a tubular scaffold. This allows for the systematic and standardized evaluation of the inflammatory and regenerative capacity of tubular scaffolds under the influence of well-controlled mechanical loads, which we demonstrate on the basis of a dynamic co-culture experiment using human macrophages and myofibroblasts. The key practical steps in this approach&#8212;the construction and setting up of the bioreactor, preparation of the scaffolds and cell seeding, application and maintenance of stretch and shear flow, and sample harvesting for analysis&#8212;are discussed in detail.

The goal of this protocol is to execute a dynamic co-culture of human macrophages and myofibroblasts in tubular electrospun scaffolds to investigate material-driven tissue regeneration, using a bioreactor which enables the decoupling of shear stress and cyclic stretch.

The use of resorbable biomaterials to induce regeneration directly in the body is an attractive strategy from a translational perspective. Such materials ...

Engineering

Treatment of Ligament Constructs with Exercise-conditioned Serum: A Translational Tissue Engineering Model

In vitro experiments are essential to understand biological mechanisms; however, the gap between monolayer tissue culture and human physiology is large, and translation of findings is often poor. Thus, there is ample opportunity for alternative experimental approaches. Here we present an approach in which human cells are isolated from human anterior cruciate ligament tissue remnants, expanded in culture, and used to form engineered ligaments. Exercise alters the biochemical milieu in the blood such that the function of many tissues, organs and bodily processes are improved. In this experiment, ligament construct culture media was supplemented with experimental human serum that has been &#39;conditioned&#39; by exercise. Thus the intervention is more biologically relevant since an experimental tissue is exposed to the full endogenous biochemical milieu, including binding proteins and adjunct compounds that may be altered in tandem with the activity of an unknown agent of interest. After treatment, engineered ligaments can be analyzed for mechanical function, collagen content, morphology, and cellular biochemistry. Overall, there are four major advantages versus traditional monolayer culture and animal models, of the physiological model of ligament tissue that is presented here. First, ligament constructs are three-dimensional, allowing for mechanical properties (i.e., function) such as ultimate tensile stress, maximal tensile load, and modulus, to be quantified. Second, the enthesis, the interface between boney and sinew elements, can be examined in detail and within functional context. Third, preparing media with post-exercise serum allows for the effects of the exercise-induced biochemical milieu, which is responsible for the wide range of health benefits of exercise, to be investigated in an unbiased manner. Finally, this experimental model advances scientific research in a humane and ethical manner by replacing the use of animals, a core mandate of the National Institutes of Health, the Center for Disease Control, and the Food and Drug Administration.

We present a model of ligament tissue in which three-dimensional constructs are treated with the human exercise-conditioned serum and analyzed for collagen content, function, and cellular biochemistry.

In vitro experiments are essential to understand biological mechanisms; however, the gap between monolayer tissue culture and human physiology is large, ...

Finite Element Modelling of a Cellular Electric Microenvironment

Clinical studies show electrical stimulation (ES) to be a potential therapy for the healing and regeneration of various tissues. Understanding the mechanisms of cell response when exposed to electrical fields can therefore guide the optimization of clinical applications. In vitro experiments aim to help uncover those, offering the advantage of wider input and output ranges that can be ethically and effectively assessed. However, the advancements in in vitro experiments are difficult to reproduce directly in clinical settings. Mainly, that is because the ES devices used in vitro differ significantly from the ones suitable for patient use, and the path from the electrodes to the targeted cells is different. Translating the in vitro results into in vivo procedures is therefore not straightforward. We emphasize that the cellular microenvironment's structure and physical properties play a determining role in the actual experimental testing conditions and suggest that measures of charge distribution can be used to bridge the gap between in vitro and in vivo. Considering this, we show how in silico finite element modelling (FEM) can be used to describe the cellular microenvironment and the changes generated by electric field (EF) exposure. We highlight how the EF couples with geometric structure to determine charge distribution. We then show the impact of time dependent inputs on charge movement. Finally, we demonstrate the relevance of our new in silico model methodology using two case studies: (i) in vitro fibrous Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT-PSS) scaffolds and (ii) in vivo collagen in extracellular matrix (ECM).

This paper presents a strategy for building finite element models of fibrous conductive materials exposed to an electric field (EF). The models can be used to estimate the electrical input that cells seeded in such materials receive and assess the impact of changing the scaffold's constituent material properties, structure or orientation.

Clinical studies show electrical stimulation (ES) to be a potential therapy for the healing and regeneration of various tissues. Understanding the ...

Fibroblast Derived Human Engineered Connective Tissue for Screening Applications

Fibroblasts are phenotypically highly dynamic cells, which quickly transdifferentiate into myofibroblasts in response to biochemical and biomechanical stimuli. The current understanding of fibrotic processes, including cardiac fibrosis, remains poor, which hampers the development of new anti-fibrotic therapies. Controllable and reliable human model systems are crucial for a better understanding of fibrosis pathology. This is a highly reproducible and scalable protocol to generate engineered connective tissues (ECT) in a 48-well casting plate to facilitate studies of fibroblasts and the pathophysiology of fibrotic tissue in a 3-dimensional (3D) environment. ECT are generated around the poles with tunable stiffness, allowing for studies under a defined biomechanical load. Under the defined loading conditions, phenotypic adaptations controlled by cell-matrix interactions can be studied. Parallel testing is feasible in the 48-well format with the opportunity for the time-course analysis of multiple parameters, such as tissue compaction and contraction against the load. From these parameters, biomechanical properties such as tissue stiffness and elasticity can be studied.

Presented here is a protocol to generate engineered connective tissues for a parallel culture of 48 tissues in a multi-well plate with double poles, suitable for mechanistic studies, disease modeling, and screening applications. The protocol is compatible with fibroblasts from different organs and species and is exemplified here with human primary cardiac fibroblasts.

Fibroblasts are phenotypically highly dynamic cells, which quickly transdifferentiate into myofibroblasts in response to biochemical and biomechanical ...

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

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Encapsulation of Cardiomyocytes in a Fibrin Hydrogel for Cardiac Tissue Engineering

Engineering a Bilayered Hydrogel to Control ASC Differentiation

Postproduction Processing of Electrospun Fibres for Tissue Engineering

Observing and Quantifying Fibroblast-mediated Fibrin Gel Compaction

Fabrication of Myogenic Engineered Tissue Constructs

Engineering 3D Cellularized Collagen Gels for Vascular Tissue Regeneration

A Multi-Cue Bioreactor to Evaluate the Inflammatory and Regenerative Capacity of Biomaterials under Flow and Stretch

Treatment of Ligament Constructs with Exercise-conditioned Serum: A Translational Tissue Engineering Model

Finite Element Modelling of a Cellular Electric Microenvironment

Fibroblast Derived Human Engineered Connective Tissue for Screening Applications