Name: seeding and implantation of a biosynthetic tissue-engineered tracheal graft in a mouse model
Uploaded: 2019-04-01T14:30:00
Description: Watch this Scientific Journal Video about Seeding and Implantation of a Biosynthetic Tissue-engineered Tracheal Graft in a Mouse Model at JoVE.com

We would like to acknowledge Robert Strouse and the Research Information Solutions &#38; Innovations division at Nationwide Children&#39;s Hospital for their support in graphic design. This work was supported by a grant from the NIH (NHLBI K08HL138460).

All methods described here have been approved by the Institutional Animal Care and Use Committee (IACUC) at Nationwide Children&#39;s Hospital.
1. Scaffold Manufacturing
<ol>
	<li>Prepare a polymer nanofiber precursor solution by: 1) dissolving 8 wt% PET in 1,1,1,3,3,3-hexafluoroisopropanol and heating the solution to 60 &#176;C and by 2) dissolving 3 wt% PU in 1,1,1,3,3,3-hexafluoroisopropanol at room temperature.</li>
	<li>Once cooled, combine the solutions to create a final polymer mixtur...

<ol>
	<li>Macchiarini, P., 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=Clinical+transplantation+of+a+tissue-engineered+airway.">Clinical transplantation of a tissue-engineered airway.</a> The Lancet. 372 (9655), 2023-2030 (2008).</li><li>Jungebluth, P., 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=Tracheobronchial+transplantation+with+a+stem-cell-seeded+bioartificial+nanocomposite:+A+proof-of-concept+study.">Tracheobronchial transplantation with a stem-cell-seeded bioartificial nanocomposite: A proof-of-concept study.</a> The Lancet. 378 (9808), 1997-2004 (2011).</li><li>Elliott, M. 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=Stem-cell-based,+tissue+engineered+tracheal+replacement+in+a+child:+A+2-year+follow-up+study.">Stem-cell-based, tissue engineered tracheal replacement in a child: A 2-year follow-up study.</a> The Lancet. 380 (9846), 994-1000 (2012).</li><li>Chiang, T., Pepper, V., Best, C., Onwuka, E., Breuer, C. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+Translation+of+Tissue+Engineered+Trachea+Grafts.">Clinical Translation of Tissue Engineered Trachea Grafts.</a> Annals of Otology, Rhinology and Laryngology. 125 (11), 873-885 (2016).</li><li>Clark, E. 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=Effect+of+cell+seeding+on+neotissue+formation+in+a+tissue+engineered+trachea.">Effect of cell seeding on neotissue formation in a tissue engineered trachea.</a> Journal of Pediatric Surgery. 51 (1), 49-55 (2016).</li><li>Cole, B. B., Smith, R. W., Jenkins, K. M., Graham, B. B., Reynolds, P. R., Reynolds, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tracheal+basal+cells:+A+facultative+progenitor+cell+pool.">Tracheal basal cells: A facultative progenitor cell pool.</a> American Journal of Pathology. 177 (1), 362-376 (2010).</li><li>Onwuka, E., 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=The+role+of+myeloid+cell-derived+PDGF-B+in+neotissue+formation+in+a+tissue-engineered+vascular+graft.">The role of myeloid cell-derived PDGF-B in neotissue formation in a tissue-engineered vascular graft.</a> Regenerative Medicine. 12 (3), 249-261 (2017).</li><li>Grimmer, J. F., 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=Tracheal+reconstruction+using+tissue-engineered+cartilage.">Tracheal reconstruction using tissue-engineered cartilage.</a> Archives of Otolaryngology - Head and Neck Surgery. 130 (10), 1191-1196 (2004).</li><li>Wood, M. W., Murphy, S. V., Feng, X., Wright, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tracheal+reconstruction+in+a+canine+model.">Tracheal reconstruction in a canine model.</a> Otolaryngology - Head and Neck Surgery (United States). 150 (3), 428-433 (2014).</li><li>Haag, 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=Biomechanical+and+angiogenic+properties+of+tissue-engineered+rat+trachea+using+genipin+cross-linked+decellularized+tissue.">Biomechanical and angiogenic properties of tissue-engineered rat trachea using genipin cross-linked decellularized tissue.</a> Biomaterials. 33 (3), 780-789 (2012).</li><li>Best, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Designing+a+tissue-engineered+tracheal+scaffold+for+preclinical+evaluation.">Designing a tissue-engineered tracheal scaffold for preclinical evaluation.</a> International Journal of Pediatric Otorhinolaryngology. 104, 155-160 (2018).</li></ol>

Development of a mouse model for tissue engineered tracheas is essential in understanding the factors that have limited clinical translation of the TETGs; namely graft collapse, stenosis and delayed epithelialization4. A few factors that contribute to these limitations include selection of graft material, the manufacturing process, scaffold design and cell seeding protocols. This model allows for faster evaluation of these factors in order to understand the cellular and molecular mechanisms affect...

Long-segment tracheal defects can present as rare congenital conditions such as complete tracheal rings and tracheal agenesis, as well as trauma, malignancy, and infection. When exceeding 6 cm in adults or 30% of the tracheal length in children, these defects cannot be treated by surgical reconstruction. Attempts to replace the airway with autologous tissue, cadaveric transplants, and artificial constructs have been plagued by chronic infection, granulation, mechanical failure, and stenosis.
Tissue engineered tracheal grafts (TETGs) can potentially address these problems while avoiding the need for life-long immunosuppression. In the last decade, TETGs have been tested in animal models and utilized clinically in rare instances of compassionate use1,2,3. In both clinical and large animal studies, post-operative recovery from tissue engineered airway replacement required numerous interventions to combat stenosis (defined as &#62;50% luminal narrowing) and maintain airway patency. Additional TETG work has sought to reduce this stenosis through evaluating the role of cell seeding choice, vascularization and scaffold design. Cell seeding choices and scaffold design aimed at restoring native trachea structure/function have mainly been focused on respiratory epithelial cells and chondrocytes seeded on various resorbable, non-resorbable and decellularized scaffolds. As vascularization likely plays an major role in the development of stenosis, other groups have focused on optimizing in vitro or heterotopic models to expedite revascularization or neoangiogenesis4. Nonetheless, achieving successful vascularization while also maintaining a mechanically competent and functional TETG remains a challenge. Despite recent advances, minimizing stenosis remains a critical obstacle to clinical translation.
To investigate this histopathological response to TETG implantation in vivo, we developed an ovine model of tissue engineered tracheal replacement. The graft was composed of a mixed polyethylene terephthalate (PET) and polyurethane (PU) electrospun scaffold seeded with bone marrow-derived mononuclear cells (BM-MNCs). In this small cohort, we demonstrated that seeded autologous BM-MNCs accelerated re-epithelialization and delayed stenosis5. Although seeding with autologous BM-MNCs improved survival, the cellular mechanism by which BM-MNCs modulate the formation of functional neotissue remains unclear.
Investigation on the cellular level required development of a murine model of tissue engineered tracheal replacement. Similar to the ovine study, we utilized a PET:PU electrospun scaffold seeded with BM-MNCs. Consistent with the ovine model, TETG stenosis developed over the course of the first two weeks following implantation1,2,3,5. This suggested that the murine model recapitulated the pathology observed previously, enabling us to further interrogate the cellular mechanisms underlying airway stenosis.
In this report, we detail our protocol for tissue engineered tracheal replacement in the mouse model including scaffold manufacturing, BM-MNC isolation, graft seeding, and implantation (Figure 1, Figure 2).

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seeding and implantation of a biosynthetic tissue-engineered tracheal graft in a mouse model

Treatment options for congenital or secondary long segment tracheal defects have historically been limited due to an inability to replace functional tissue. Tissue engineering holds great promise as a potential solution with its ability to integrate cells and signaling molecules into a 3-dimensional scaffold. Recent work with tissue engineered tracheal grafts (TETGs) has seen some success but their translation has been limited by graft stenosis, graft collapse, and delayed epithelialization. In order to investigate the mechanisms driving these issues, we have developed a mouse model for tissue engineered tracheal graft implantation. TETGs were constructed using electrospun polymers polyethylene terephthalate (PET) and polyurethane (PU) in a mixture of PET and PU (20:80 percent weight). Scaffolds were then seeded using bone marrow mononuclear cells isolated from 6-8 week-old C57BL/6 mice by gradient centrifugation. Ten million cells per graft were seeded onto the lumen of the scaffold and allowed to incubate overnight before implantation between the third and seventh tracheal rings. These grafts were able to recapitulate the findings of stenosis and delayed epithelialization as demonstrated by histological analysis and lack of Keratin 5 and Keratin 14 basal epithelial cells on immunofluorescence. This model will serve as a tool for investigating cellular and molecular mechanisms involved in host remodeling.

Figure 1 illustrates a schematic of TETG seeding and implantation. Bone marrow was harvested from C57BL/6 mice and cultured in vitro. BM-MNCs were isolated by density centrifugation and seeded onto the TETG. Seeded TETGs were implanted into a syngeneic C57BL/6 recipient mouse.
Figure 2 is an overview of the PET:PU TETG scaffold manufacturing process. PET:PU sol...

Watch this Scientific Journal Video about Seeding and Implantation of a Biosynthetic Tissue-engineered Tracheal Graft in a Mouse Model at JoVE.com

Seeding and Implantation of a Biosynthetic Tissue-engineered Tracheal Graft in a Mouse Model

Graft stenosis poses a critical obstacle in tissue engineered airway replacement. To investigate cellular mechanisms underlying stenosis, we utilize a murine model of tissue engineered tracheal replacement with seeded bone marrow mononuclear cells (BM-MNC). Here, we detail our protocol, including scaffold manufacturing, BM-MNC isolation, graft seeding, and implantation.

Treatment options for congenital or secondary long segment tracheal defects have historically been limited due to an inability to replace functional ...

Clinical applications of tissue-engineered trachea have been limited due to graft stenosis and delayed epithelialization. A mouse model of orthotopic tracheal replacement permits the study of the cellular mechanisms driving regeneration. Long-segment defects of the airway can exceed what current therapies are able to cure.The tissue-engineered trachea offers the potential to create a replacement organ for these conditions. This model can be applied to animals with transgenic and lineage tracing properties. We can then modulate the host factors contributing to graft regeneration.One of the key challenges in producing the scaffolds will be measuring and determining that the electrospinning parameters are the same each time. So every time you produce a scaffold, you need to measure the tip-to-collector distance, the humidity, and the temperature to ensure the scaffolds are the same each time. Critical to the success of this model is refinement of the microsurgical techniques and maintenance of the correct plane of anesthesia to permit spontaneous ventilation throughout the procedure.Since the host trachea has an internal diameter of around one millimeter, graft and native tissue handling and suture placement are important and best demonstrated visually. Begin by dissolving eight weight percent polyethylene terephthalate, or PET, in hexafluoroisopropanol and heating the resulting solution to 60 degrees Celsius. While the solution is being warmed, dissolve three weight percent polyurethane, or PU, in hexafluoroisopropanol, combining the solutions once the PET solution has cooled.Load a 60-milliliter syringe equipped with a 20-gauge blunt-tip needle with the polymer mixture. Use the syringe and a high-voltage DC power supply set to positive 14 kilovolts on the needle, another high-voltage DC power supply set to minus three kilovolts, a five-milliliter-per-hour flow rate, and a 20-centimeter tip-to-substrate distance to electrospin the polymer onto a one-millimeter diameter stainless steel rod being turned at 350 rotations per minute. Continue electrospinning until a 300-micrometer scaffold wall thickness is achieved.Then, slide the scaffold off the rod, place the scaffold under vacuum overnight to remove any residual solvent, and sterilize the scaffold with an ultraviolet light dosage of 350 millijoules per centimeter squared for about 15 minutes. Under sterile conditions, remove the skin from the hind limbs of a six to eight-week-old, female, C57-Black/6 mouse with fine scissors and micro-Adson forceps, and use Dumont number five forceps and Dumont number 5/45 forceps to remove the fascia and the tendons. Separate the bones to allow each of them to be cut on both ends, and use a five-milliliter syringe equipped with a 25-gauge needle to flush the bone marrow into a Petri dish containing 30 milliliters of RPMI medium.When all of the bones have been flushed, filter the bone marrow through a 70-micrometer nylon cell strainer into a 50-milliliter conical tube, and transfer the tube to a biosafety cabinet. Gently add the filtered mononuclear cell solution down the side of a 15-milliliter tube containing five milliliters of polysucrose and sodium diatrizoate without mixing the layers, and separate the plasma from the white and red blood cells by density gradient separation. At the end of the centrifugation, collect the middle clear layer consisting of the bone marrow mononuclear cells, and wash the bone marrow mononuclear cells at a one-to-one ratio in PBS by centrifugation.Resuspend the pellet in five milliliters of PBS for a second wash, followed by resuspension in 10 milliliters of fresh RPMI medium for counting. Then, collect the cells with an additional centrifugation, and dilute the cells to a one times 10 to the seven cells per five microliters of fresh RPMI concentration. Before seeding the scaffold, cut the polymer to a five-millimeter length as necessary, and wet the scaffold with five microliters of RPMI medium for five minutes.At the end of the incubation, remove the excess medium, and load the scaffold lumen with five microliters of the bone marrow mononuclear cell solution for 10 minutes. Then, insert a 21-gauge needle through the lumen of the scaffold, and place the graft in one milliliter of RPMI medium overnight in a 37-degree Celsius incubator. After induction of general anesthesia, confirm a lack of response to toe pinch in the recipient animal, and apply ointment to the animal's eyes.Clip the hair on the surgical site from chin to clavicles, and place the animal on a surgical pad in a dorsal recumbent position. Using aseptic technique, disinfect the surgical site with a sequential povidone-iodine, 70%ethanol, povidone-iodine wipe series, and move the mouse under a dissecting microscope with the head at 12 o'clock. Use fine scissors and micro-Adson forceps to make a midline incision from the clavicles to the hyoid bone, and use Dumont number five and number seven fine forceps and a sterile cotton swab to clean the fascia before inserting a self-retaining Colibri retractor into the incision.Use the forceps to open the strap muscles to expose the thyroid cartilage, cricoid cartilage, and trachea, and bluntly separate the trachea from the recurrent laryngeal nerves running parallel on either side of the tissue, followed by circumferential separation of the trachea from the esophagus. Using a 20-gauge needle and surgical marker, stain the anterior portion of the trachea. Make an incision below the third tracheal cartilage ring using a pair of Vannas-Tubingen spring scissors and a pair of Dumont number seven fine forceps to resect a three-ring section of trachea.Holding the trachea with the fine curved forceps, use a sterile 9-0 nylon suture to secure the distal end of the trachea to the sternum to create a temporary tracheostomy, and use the 20-gauge needle and surgical marker to stain the anterior portion of the graft. To implant the graft, use a 9-0 sterile nylon suture, Dumont number seven fine forceps, and a needle holder to insert the proximal-posterior, proximal-lateral, and proximal-anterior stitches, and turn the animal 180 degrees. When the mouse is in position, release the temporary tracheostomy, and make a lateral incision five millimeters away from the anterior portion of the graft to facilitate the distal anastomosis.To complete the distal anastomosis, place the sutures in a similar fashion to the proximal anastomosis, and re-approximate the graft position and strap muscles. Then, close the incision with 9-0 sterile nylon sutures in a running pattern, and place the animal alone in a recovery cage placed on a heating pad with monitoring until full recovery. Two weeks after implantation, a few basal epithelial cells can be observed by basal cell keratin five and 14 staining in tissue-engineered tracheal graft tissue sections.Basal cells are also detected on the luminal surface of the graft at seven days after implantation. Upon explantation and histological analysis, graft stenosis has been identified as the main contributing factor in graft-implanted mice demonstrating signs of respiratory distress and stridor. Note that telescoping of the graft and native trachea is a common finding as a result of the surgical technique.Staining for F4/80 reveals host macrophages within the stenotic region of the graft in conjunction with the presence of the basal epithelial cells. Avoid manipulation of the recurrent laryngeal nerves, and ensure that the proximal and distal sutures are in place to allow an airtight seal at the anastomosis. As this protocol deals with bone marrow mononuclear cells derived from biosafety level one agent mice, it is important to wear appropriate personal protective equipment to avoid contamination.

seeding-implantation-biosynthetic-tissue-engineered-tracheal-graft

Research

JoVE Journal

Bioengineering

Creating Two-Dimensional Patterned Substrates for Protein and Cell Confinement

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1 While microcontact printing can be employed to directly print a large number of molecules, including proteins,2 DNA,3 and silanes,4 the formation of self-assembled monolayers (SAMs) from long chain alkane thiols on gold provides a simple way to confine proteins and cells to specific patterns containing adhesive and resistant regions. This confinement can be used to control cell morphology and is useful for examining a variety of questions in protein and cell biology. Here, we describe a general method for the creation of well-defined protein patterns for cellular studies.5 This process involves three steps: the production of a patterned master using photolithography, the creation of a PDMS stamp, and microcontact printing of a gold-coated substrate. Once patterned, these cell culture substrates are capable of confining proteins and/or cells (primary cells or cell lines) to the pattern.
The use of self-assembled monolayer chemistry allows for precise control over the patterned protein/cell adhesive regions and non-adhesive regions; this cannot be achieved using direct protein stamping. Hexadecanethiol, the long chain alkane thiol used in the microcontact printing step, produces a hydrophobic surface that readily adsorbs protein from solution. The glycol-terminated thiol, used for backfilling the non-printed regions of the substrate, creates a monolayer that is resistant to protein adsorption and therefore cell growth.6 These thiol monomers produce highly structured monolayers that precisely define regions of the substrate that can support protein adsorption and cell growth. As a result, these substrates are useful for a wide variety of applications from the study of intercellular behavior7 to the creation of microelectronics.8
While other types of monolayer chemistry have been used for cell culture studies, including work from our group using trichlorosilanes to create patterns directly on glass substrates,9 patterned monolayers formed from alkane thiols on gold are straight-forward to prepare. Moreover, the monomers used for monolayer preparation are commercially available, stable, and do not require storage or handling under inert atmosphere. Patterned substrates prepared from alkane thiols can also be recycled and reused several times, maintaining cell confinement.10

Self-assembled monolayers (SAMs) formed from long chain alkane thiols on gold provide well-defined substrates for the formation of protein patterns and cell confinement. Microcontact printing of hexadecanethiol using a polydimethylsiloxane (PDMS) stamp followed by backfilling with a glycol-terminated alkane thiol monomer produces a pattern where protein and cells adsorb only to the stamped hexadecanethiol region.

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1  While microcontact printing ...

Autologous Endothelial Progenitor Cell-Seeding Technology and Biocompatibility Testing For Cardiovascular Devices in Large Animal Model

Implantable cardiovascular devices are manufactured from artificial materials (e.g. titanium (Ti), expanded polytetrafluoroethylene), which pose the risk of thromboemboli formation1,2,3. We have developed a method to line the inside surface of Ti tubes with autologous blood-derived human or porcine endothelial progenitor cells (EPCs)4. By implanting Ti tubes containing a confluent layer of porcine EPCs in the inferior vena cava (IVC) of pigs, we tested the improved biocompatibility of the cell-seeded surface in the prothrombotic environment of a large animal model and compared it to unmodified bare metal surfaces5,6,7 (Figure 1). This method can be used to endothelialize devices within minutes of implantation and test their antithrombotic function in vivo. 
Peripheral blood was obtained from 50 kg Yorkshire swine and its mononuclear cell fraction cultured to isolate EPCs4,8. Ti tubes (9.4 mm ID) were pre-cut into three 4.5 cm longitudinal sections and reassembled with heat-shrink tubing. A seeding device was built, which allows for slow rotation of the Ti tubes. 
We performed a laparotomy on the pigs and externalized the intestine and urinary bladder. Sharp and blunt dissection was used to skeletonize the IVC from its bifurcation distal to the right renal artery proximal. The Ti tubes were then filled with fluorescently-labeled autologous EPC suspension and rotated at 10 RPH x 30 min to achieve uniform cell-coating9. After administration of 100 USP/ kg heparin, both ends of the IVC and a lumbar vein were clamped. A 4 cm veinotomy was performed and the device inserted and filled with phosphate-buffered saline. As the veinotomy was closed with a 4-0 Prolene running suture, one clamp was removed to de-air the IVC. At the end of the procedure, the fascia was approximated with 0-PDS (polydioxanone suture), the subcutaneous space closed with 2-0 Vicryl and the skin stapled closed. 
After 3 - 21 days, pigs were euthanized, the device explanted en-block and fixed. The Ti tubes were disassembled and the inner surfaces imaged with a fluorescent microscope.
We found that the bare metal Ti tubes fully occluded whereas the EPC-seeded tubes remained patent. Further, we were able to demonstrate a confluent layer of EPCs on the inside blood-contacting surface.
Concluding, our technology can be used to endothelialize Ti tubes within minutes of implantation with autologous EPCs to prevent thrombosis of the device. Our surgical method allows for testing the improved biocompatibility of such modified devices with minimal blood loss and EPC-seeded surface disruption.

A method for seeding titanium blood-contacting biomaterials with autologous cells and testing biocompatibility is described. This method uses endothelial progenitor cells and titanium tubes, seeded within minutes of surgical implantation into porcine venae cavae. This technique is adaptable to many other implantable biomedical devices.

Implantable cardiovascular devices are manufactured from artificial materials (e.g. titanium (Ti), expanded polytetrafluoroethylene), which pose the risk ...

Protocol for Relative Hydrodynamic Assessment of Tri-leaflet Polymer Valves

Limitations of currently available prosthetic valves, xenografts, and homografts have prompted a recent resurgence of developments in the area of tri-leaflet polymer valve prostheses. However, identification of a protocol for initial assessment of polymer valve hydrodynamic functionality is paramount during the early stages of the design process. Traditional in vitro pulse duplicator systems are not configured to accommodate flexible tri-leaflet materials; in addition, assessment of polymer valve functionality needs to be made in a relative context to native and prosthetic heart valves under identical test conditions so that variability in measurements from different instruments can be avoided. Accordingly, we conducted hydrodynamic assessment of i) native (n = 4, mean diameter, D = 20 mm), ii) bi-leaflet mechanical (n= 2, D = 23 mm) and iii) polymer valves (n = 5, D = 22 mm) via the use of a commercially available pulse duplicator system (ViVitro Labs Inc, Victoria, BC) that was modified to accommodate tri-leaflet valve geometries. Tri-leaflet silicone valves developed at the University of Florida comprised the polymer valve group. A mixture in the ratio of 35:65 glycerin to water was used to mimic blood physical properties. Instantaneous flow rate was measured at the interface of the left ventricle and aortic units while pressure was recorded at the ventricular and aortic positions. Bi-leaflet and native valve data from the literature was used to validate flow and pressure readings. The following hydrodynamic metrics were reported: forward flow pressure drop, aortic root mean square forward flow rate, aortic closing, leakage&#160;and regurgitant volume, transaortic closing, leakage, and total energy losses. Representative results indicated that hydrodynamic metrics from the three valve groups could be successfully obtained by incorporating a custom-built assembly into a commercially available pulse duplicator system and subsequently, objectively compared to provide insights on functional aspects of polymer valve design.

There has been renewed interest in developing polymer valves. Here, the objectives are to demonstrate the feasibility of modifying a commercial pulse duplicator to accommodate tri-leaflet geometries and to define a protocol to present polymer valve hydrodynamic data in comparison to native and prosthetic valve data collected under near-identical conditions.

Limitations of currently available prosthetic valves, xenografts, and homografts have prompted a recent resurgence of developments in the area of ...

Surgical Technique for the Implantation of Tissue Engineered Vascular Grafts and Subsequent In Vivo Monitoring

The development of Tissue Engineered Vessels (TEVs) is advanced by the ability to routinely and effectively implant TEVs (4-5 mm in diameter) into a large animal model. A step by-step protocol for inter-positional placement of the TEV and real-time digital assessment of the TEV and native carotid arteries is described here. In vivo monitoring is made possible by the implantation of flow probes, catheters and ultrasonic crystals (capable of recording dynamic diameter changes of implanted TEVs and native carotid arteries) at the time of surgery. Once implanted, researchers can calculate arterial blood flow patterns, invasive blood pressure and artery diameter yielding parameters such as pulse wave velocity, augmentation index, pulse pressures and compliance. Data acquisition is accomplished using a single computer program for analysis throughout the duration of the experiment. Such invaluable data provides insight into TEV matrix remodeling, its resemblance to native/sham controls and overall TEV performance in vivo.

Surgical Technique for the Implantation of Tissue Engineered Vascular Grafts and Subsequent In Vivo Monitoring

A step-by-step protocol for the inter-positional placement of Tissue Engineered Vessels (TEVs) into the carotid artery of a sheep using end-to-end anastomosis and real-time digital assessment in vivo until animal sacrifice.

The development of Tissue Engineered Vessels (TEVs) is advanced by the ability to routinely and effectively implant TEVs (4-5 mm in diameter) into a large ...

Generation and Grafting of Tissue-engineered Vessels in a Mouse Model

The construction of vascular conduits is a fundamental strategy for surgical repair of damaged and injured vessels resulting from cardiovascular diseases. The current protocol presents an efficient and reproducible strategy in which functional tissue engineered vessel grafts can be generated using partially induced pluripotent stem cell (PiPSC) from human fibroblasts. We designed a decellularized vessel scaffold bioreactor, which closely mimics the matrix protein structure and blood flow that exists within a native vessel, for seeding of PiPSC-endothelial cells or smooth muscle cells prior to grafting into mice. This approach was demonstrated to be advantageous because immune-deficient mice engrafted with the PiPSC-derived grafts presented with markedly increased survival rate 3 weeks after surgery. This protocol represents a valuable tool for regenerative medicine, tissue engineering and potentially patient-specific cell-therapy in the near future.

Here, we present a protocol to generate tissue engineered vessel grafts that are functional for grafting into mice by double seeding partially induced pluripotent stem cell (PiPSC) - derived smooth muscle cells and PiPSC - derived endothelial cells on a decellularized vessel scaffold bioreactor.

The construction of vascular conduits is a fundamental strategy for surgical repair of damaged and injured vessels resulting from cardiovascular diseases. ...

Production, Characterization and Potential Uses of a 3D Tissue-engineered Human Esophageal Mucosal Model

The incidence of both esophageal adenocarcinoma and its precursor, Barrett&#8217;s Metaplasia, are rising rapidly in the western world. Furthermore esophageal adenocarcinoma generally has a poor prognosis, with little improvement in survival rates in recent years. These are difficult conditions to study and there has been a lack of suitable experimental platforms to investigate disorders of the esophageal mucosa.
A model of the human esophageal mucosa has been developed in the MacNeil laboratory which, unlike conventional 2D cell culture systems, recapitulates the cell-cell and cell-matrix interactions present in vivo and produces a mature, stratified epithelium similar to that of the normal human esophagus. Briefly, the model utilizes non-transformed normal primary human esophageal fibroblasts and epithelial cells grown within a porcine-derived acellular esophageal scaffold. Immunohistochemical characterization of this model by CK4, CK14, Ki67 and involucrin staining demonstrates appropriate recapitulation of the histology of the normal human esophageal mucosa.
This model provides a robust, biologically relevant experimental model of the human esophageal mucosa. It can easily be manipulated to investigate a number of research questions including the effectiveness of pharmacological agents and the impact of exposure to environmental factors such as alcohol, toxins, high temperature or gastro-esophageal refluxate components. The model also facilitates extended culture periods not achievable with conventional 2D cell culture, enabling, inter alia, the study of the impact of repeated exposure of a mature epithelium to the agent of interest for up to 20 days. Furthermore, a variety of cell lines, such as those derived from esophageal tumors or Barrett&#8217;s Metaplasia, can be incorporated into the model to investigate processes such as tumor invasion and drug responsiveness in a more biologically relevant environment.

This manuscript describes the production, characterization and potential uses of a tissue engineered 3D esophageal construct prepared from normal primary human esophageal fibroblast and squamous epithelial cells seeded within a de-cellularized porcine scaffold. The results demonstrate the formation of a mature stratified epithelium similar to the normal human esophagus.

The incidence of both esophageal adenocarcinoma and its precursor, Barrett&#8217;s Metaplasia, are rising rapidly in the western world. Furthermore ...

A Combined 3D Tissue Engineered In Vitro/In Silico Lung Tumor Model for Predicting Drug Effectiveness in Specific Mutational Backgrounds

In the present study, we combined an in vitro 3D lung tumor model with an in silico model to optimize predictions of drug response based on a specific mutational background. The model is generated on a decellularized porcine scaffold that reproduces tissue-specific characteristics regarding extracellular matrix composition and architecture including the basement membrane. We standardized a protocol that allows artificial tumor tissue generation within 14 days including three days of drug treatment. Our article provides several detailed descriptions of 3D read-out screening techniques like the determination of the proliferation index Ki67 staining&#39;s, apoptosis from supernatants by M30-ELISA and assessment of epithelial to mesenchymal transition (EMT), which are helpful tools for evaluating the effectiveness of therapeutic compounds. We could show compared to 2D culture a reduction of proliferation in our 3D tumor model that is related to the clinical situation. Despite of this lower proliferation, the model predicted EGFR-targeted drug responses correctly according to the biomarker status as shown by comparison of the lung carcinoma cell lines HCC827 (EGFR -mutated, KRAS wild-type) and A549 (EGFR wild-type, KRAS-mutated) treated with the tyrosine-kinase inhibitor (TKI) gefitinib. To investigate drug responses of more advanced tumor cells, we induced EMT by long-term treatment with TGF-beta-1 as assessed by vimentin/pan-cytokeratin immunofluorescence staining. A flow-bioreactor was employed to adjust culture to physiological conditions, which improved tissue generation. Furthermore, we show the integration of drug responses upon gefitinib treatment or TGF-beta-1 stimulation - apoptosis, proliferation index and EMT - into a Boolean in silico model. Additionally, we explain how drug responses of tumor cells with a specific mutational background and counterstrategies against resistance can be predicted. We are confident that our 3D in vitro approach especially with its in silico expansion provides an additional value for preclinical drug testing in more realistic conditions than in 2D cell culture.

A Combined 3D Tissue Engineered In Vitro/In Silico Lung Tumor Model for Predicting Drug Effectiveness in Specific Mutational Backgrounds

We present a three-dimensional (3D) lung cancer model based on a biological collagen scaffold to study sensitivity towards non-small-cell-lung-cancer-(NSCLC)-targeted therapies. We demonstrate different read-out techniques to determine the proliferation index, apoptosis and epithelial-mesenchymal transition (EMT) status. Collected data are integrated into an in silico model for prediction of drug sensitivity.

In the present study, we combined an in vitro 3D lung tumor model with an in silico model to optimize predictions of drug response based on a specific ...

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 ...

Three-dimensional Tissue Engineered Aligned Astrocyte Networks to Recapitulate Developmental Mechanisms and Facilitate Nervous System Regeneration

Neurotrauma and neurodegenerative disease often result in lasting neurological deficits due to the limited capacity of the central nervous system (CNS) to replace lost neurons and regenerate axonal pathways. However, during nervous system development, neuronal migration and axonal extension often occur along pathways formed by other cells, referred to as &#34;living scaffolds&#34;. Seeking to emulate these mechanisms and to design a strategy that circumvents the inhibitory environment of the CNS, this manuscript presents a protocol to fabricate tissue engineered astrocyte-based &#34;living scaffolds&#34;. To create these constructs, we employed a novel biomaterial encasement scheme to induce astrocytes to self-assemble into dense three-dimensional bundles of bipolar longitudinally-aligned somata and processes. First, hollow hydrogel micro-columns were assembled, and the inner lumen was coated with collagen extracellular-matrix. Dissociated cerebral cortical astrocytes were then delivered into the lumen of the cylindrical micro-column and, at a critical inner diameter of &#60;350 &#181;m, spontaneously self-aligned and contracted to produce long fiber-like cables consisting of dense bundles of astrocyte processes and collagen fibrils measuring &#60;150 &#181;m in diameter yet extending several cm in length. These engineered living scaffolds exhibited &#62;97% cell viability and were virtually exclusively comprised of astrocytes expressing a combination of the intermediate filament proteins glial-fibrillary acidic protein (GFAP), vimentin, and nestin. These aligned astrocyte networks were found to provide a permissive substrate for neuronal attachment and aligned neurite extension. Moreover, these constructs maintain integrity and alignment when extracted from the hydrogel encasement, making them suitable for CNS implantation. These preformed constructs structurally emulate key cytoarchitectural elements of naturally occurring glial-based &#34;living scaffolds&#34; in vivo. As such, these engineered living scaffolds may serve as test-beds to study neurodevelopmental mechanisms in vitro or facilitate neuroregeneration by directing neuronal migration and/or axonal pathfinding following CNS degeneration in vivo.

We showcase the development of self-assembled, three-dimensional bundles of longitudinally aligned astrocytic somata and processes within a novel biomaterial encasement. These engineered &#34;living scaffolds&#34;, exhibiting micron-scale diameter yet extending centimeters in length, may serve as test-beds to study neurodevelopmental mechanisms or facilitate neuroregeneration by directing neuronal migration and/or axonal pathfinding.

Neurotrauma and neurodegenerative disease often result in lasting neurological deficits due to the limited capacity of the central nervous system (CNS) to ...

Fabrication of Custom Agarose Wells for Cell Seeding and Tissue Ring Self-assembly Using 3D-Printed Molds

Engineered tissues are being used clinically for tissue repair and replacement, and are being developed as tools for drug screening and human disease modeling. Self-assembled tissues offer advantages over scaffold-based tissue engineering, such as enhanced matrix deposition, strength, and function. However, there are few available methods for fabricating 3D tissues without seeding cells on or within a supporting scaffold. Previously, we developed a system for fabricating self-assembled tissue rings by seeding cells into non-adhesive agarose wells. A polydimethylsiloxane (PDMS) negative was first cast in a machined polycarbonate mold, and then agarose was gelled in the PDMS negative to create ring-shaped cell seeding wells. However, the versatility of this approach was limited by the resolution of the tools available for machining the polycarbonate mold. Here, we demonstrate that 3D-printed plastic can be used as an alternative to machined polycarbonate for fabricating PDMS negatives. The 3D-printed mold and revised mold design is simpler to use, inexpensive to produce, and requires significantly less agarose and PDMS per cell seeding well. We have demonstrated that the resulting agarose wells can be used to create self-assembled tissue rings with customized diameters from a variety of different cell types. Rings can then be used for mechanical, functional, and histological analysis, or for fabricating larger and more complex tubular tissues.

This protocol describes a platform for fabricating self-assembled tissue rings in variable sizes using a customized 3D-printed plastic mold. PDMS negatives are cured in the 3D-printed mold; then agarose is cast in the cured PDMS negatives. Cells are seeded into the resulting agarose wells where they aggregate into tissue rings.

Engineered tissues are being used clinically for tissue repair and replacement, and are being developed as tools for drug screening and human disease ...