Name: nondestructive monitoring of degradable scaffold-based tissue-engineered blood vessel development using optical coherence tomography
Uploaded: 2018-10-03T14:00:00
Description: Watch this Scientific Journal Video about Nondestructive Monitoring of Degradable Scaffold-Based Tissue-Engineered Blood Vessel Development Using Optical Coherence Tomography at JoVE.com

We would like to acknowledge the Science and Technology Planning Project of the Guangdong Province of China (2016B070701007) for supporting this work.

1. Degradable PGA Scaffold based Tissue-engineered Vessels Culture
<ol>
	<li>PGA Scaffold Fabrication
	<ol>
		<li>Sew PGA mesh (19 mm diameter and 1 mm thick) around silicone tubing sterilized by ethylene oxide (17 cm length, 5.0 mm diameter, and 0.3 mm thick) using 5-0 suture.</li>
		<li>Sew polytetrafluoroethylene (ePTFE, 1cm length) with 4-0 suture onto each end of PGA mesh and overlapped by 2 mm.</li>
		<li>Dip PGA scaffolds with the hand in 1 mol/L NaOH for 1 min to adjust the spatial structure of the mesh and soa...

<ol>
	<li>Chan-Park, M. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomimetic+control+of+vascular+smooth+muscle+cell+morphology+and+phenotype+for+functional+tissue-engineered+small-diameter+blood+vessels.">Biomimetic control of vascular smooth muscle cell morphology and phenotype for functional tissue-engineered small-diameter blood vessels.</a> Journal of Biomedical Materials Research Part A. 88, 1104-1121 (2009).</li><li>Ballyns, J. J., Bonassar, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Image-guided+tissue+engineering.">Image-guided tissue engineering.</a> Journal of Cellular &amp; Molecular Medicine. 13, 1428-1436 (2009).</li><li>Smith, L. 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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=Imaging+and+characterization+of+bioengineered+blood+vessels+within+a+bioreactor+using+free-space+and+catheter-based+OCT.">Imaging and characterization of bioengineered blood vessels within a bioreactor using free-space and catheter-based OCT.</a> Lasers in Surgery and Medicine. 45, 391-400 (2013).</li><li>Chen, 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=In+vitro+remodeling+and+structural+characterization+of+degradable+polymer+scaffold-based+tissue-engineered+vascular+grafts+using+optical+coherence+tomography.">In vitro remodeling and structural characterization of degradable polymer scaffold-based tissue-engineered vascular grafts using optical coherence tomography.</a> Cell &amp; Tissue Research. 370, 417-426 (2017).</li><li>Naito, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+the+natural+history+of+extracellular+matrix+production+in+tissue-engineered+vascular+grafts+during+neovessel+formation.">Characterization of the natural history of extracellular matrix production in tissue-engineered vascular grafts during neovessel formation.</a> Cells Tissues Organs. 195, 60-72 (2012).</li><li>Ye, C., 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+design+conception+and+realization+of+pulsatile+ventricular+assist+devices-from+Spiral-Vortex+pump+to+Luo-Ye+pump.">The design conception and realization of pulsatile ventricular assist devices-from Spiral-Vortex pump to Luo-Ye pump.</a> Chinese Journal of Thoracic and Cardiovascular Surgery. 9, 35-40 (2002).</li><li>Chen, 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=Application+of+optical+coherence+tomography+in+tissue+engineered+blood+vessel+culture+based+on+Luo-Ye+pump.">Application of optical coherence tomography in tissue engineered blood vessel culture based on Luo-Ye pump.</a> Chinese Journal of Thoracic and Cardiovascular Surgery. 31, 687-690 (2015).</li><li>Pickering, J. G., Boughner, D. R., 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=Quantitative+assessment+of+the+age+of+fibrotic+lesions+using+polarized+light+microscopy+and+digital+image+analysis.">Quantitative assessment of the age of fibrotic lesions using polarized light microscopy and digital image analysis.</a> American Journal of Pathology. 138, 1225-1231 (1991).</li><li>Martinho, J. 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=Dependence+of+optical+attenuation+coefficient+and+mechanical+tension+of+irradiated+human+cartilage+measured+by+optical+coherence+tomography.">Dependence of optical attenuation coefficient and mechanical tension of irradiated human cartilage measured by optical coherence tomography.</a> Cell Tissue Bank. 16, 47-53 (2015).</li><li>Poirierquinot, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-resolution+1.5-Tesla+magnetic+resonance+imaging+for+tissue-engineered+constructs:+a+noninvasive+tool+to+assess+three-dimensional+scaffold+architecture+and+cell+seeding.">High-resolution 1.5-Tesla magnetic resonance imaging for tissue-engineered constructs: a noninvasive tool to assess three-dimensional scaffold architecture and cell seeding.</a> Tissue Engineering Part C Methods. 16, 185-200 (2010).</li><li>Naito, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beyond+burst+pressure:+initial+evaluation+of+the+natural+history+of+the+biaxial+mechanical+properties+of+tissue-engineered+vascular+grafts+in+the+venous+circulation+using+a+murine+model.">Beyond burst pressure: initial evaluation of the natural history of the biaxial mechanical properties of tissue-engineered vascular grafts in the venous circulation using a murine model.</a> Tissue Engineering Part A. 20, 346-355 (2014).</li><li>Smart, N., Dube, K. N., Riley, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coronary+vessel+development+and+insight+towards+neovascular+therapy.">Coronary vessel development and insight towards neovascular therapy.</a> International Journal of Clinical and Experimental Pathology. 90, 262-283 (2009).</li></ol>

To generate engineered vessels with structural and mechanical properties similar to those of native blood vessels can lead to shorten the time for clinical use and is the ultimate goal of vascular engineering. Optical imaging techniques permit the visualization of tissue engineered vascular specific components, which cannot monitor individual constructs throughout culture and exposure grafts to a culture environment without compromising sterility7. In this article, the culture chamber is separated...

Tissue-engineered blood vessels (TEBVs) is of the most promising material as an ideal vascular graft1. In order to develop grafts to be clinically useful with similar structural and functional properties as native vessels, multiple techniques have been designed to maintain vascular function2,3. Although there have been engineered vessels with acceptable patency rates during implantation and in Phase III clinical study4, long-term culture and high cost also show the necessity of monitoring the development of TEBVs. Understanding of extracellular matrix(ECM) growth, remodeling, and adaptation processes in TEBVs in the biomimetic chemo-mechanical environment can provide crucial information for the development of vascular tissue engineering.
The ideal strategy to track the development of small-diameter engineered vessels5 should be nondestructive, sterile, longitudinal, three-dimensional and quantitative. TEBVs under different culture conditions could be assessed by this imaging modality, even including changes before and after vascular transplantation. Strategies to describe features of living engineered vessels are needed. Optical imaging techniques allow visualization and quantification of tissue deposition and biomaterials. Other advantages are the possibility to enable deep-tissue and label-free imaging with high resolution6,7. However, image-specific molecules and less easily accessible optical equipment for real-time monitoring is a significant practical obstacle, which has limited the extensive application of nonlinear optical microscopy. Optical coherence tomography (OCT) is an optical approach with intravascular imaging modality as a widely-used clinical tool to guide cardiac interventional therapy8. In the literature the method of OCT was reported as a way to assess the wall thickness of TEBVs9,10, coupled with affirmative imaging modalities for vascular tissue engineering research. Whereas, the dynamics of engineered vascular growth and remodeling was not observed.
In this manuscript, we detail the preparation of biodegradable polymeric scaffold-based TEBVs for four weeks culture. Human umbilical arteries vascular smooth muscle cells (HUASMCs) are expanded and seeded into a porous degradable polyglycolic acid (PGA) scaffolds in the bioreactor. Biodegradable polymers play the role in a temporary substrate for tissue engineering and have a certain degradation rate11. In order to ensure an appropriate match between scaffold degradation and neo-tissue formation, ECM and PGA scaffolds are crucial factors for effective vascular remodeling. The perfusion system simulates the biomechanical microenvironment of native vessels and maintains a consistent deformation under pressure stimulation. 
The aim of the presented protocol is to describe a relatively simple and nondestructive strategy for TEBVs imaging and long-term monitoring of culture. This protocol can be utilized for visualization of morphological changes and thickness measurements of engineered vessels under different culture conditions. Additionally, the analyses of polymer-based materials degradation in the tissue engineering scaffolds can be performed for the identification. By combining methods of scanning electron microscopic(SEM) and polarized microscope used in this protocol, correlation and quantification of extracellular matrix distribution and PGA degradation can be made, which can facilitate assessing scaffold degradation combined with OCT imaging.

<table border="0" cellpadding="0" cellspacing="0" style="width:797px;" width="797">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PGA mesh</td>
			<td style="width:265px;">Synthecon</td>
			<td style="width:149px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">silicone tube</td>
			<td style="width:265px;">Cole Parmer</td>
			<td style="width:149px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">connector</td>
			<td style="width:265px;">Cole Parmer</td>
			<td style="width:149px;"></td>
			<td></td>
		</tr>
		<tr height="46">
			<td height="46" style="height:47px;width:216px;">intravascular OCT system</td>
			<td style="width:265px;">St. Jude Medical, Inc</td>
			<td style="width:149px;">ILUMIEN&#8482; OPTIS&#8482; SYSTEM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">scanning electron microscopic</td>
			<td style="width:265px;">Philips&#160;</td>
			<td style="width:149px;">FEI Philips XL-30</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">polarized microscope</td>
			<td style="width:265px;">Olympus</td>
			<td style="width:149px;">Olympus BX51</td>
			<td></td>
		</tr>
		<tr height="30">
			<td height="30" style="height:31px;width:216px;">sutures</td>
			<td style="width:265px;">Johnson &#38; Johnson</td>
			<td style="width:149px;"></td>
			<td></td>
		</tr>
		<tr height="30">
			<td height="30" style="height:30px;width:216px;">pulsatile pump</td>
			<td style="width:265px;">Guangdong Cardiovascular Institute</td>
			<td style="width:149px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">LightLab Imaging software</td>
			<td style="width:265px;">St. Jude Medical, Inc</td>
			<td style="width:149px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

nondestructive monitoring of degradable scaffold-based tissue-engineered blood vessel development using optical coherence tomography

Engineered vascular grafts with structural and mechanical properties similar to natural blood vessels are expected to meet the growing demand for arterial bypass. Characterization of the growth dynamics and remodeling process of degradable polymer scaffold-based tissue-engineered blood vessels (TEBVs) with pulsatile stimulation is crucial for vascular tissue engineering. Optical imaging techniques stand out as powerful tools for monitoring vascularization of engineered tissue enabling high-resolution imaging in real-time culture. This paper demonstrates a nondestructive and fast real-time imaging strategy to monitor the growth and remodeling of TEBVs in long-term culture by using optical coherence tomography (OCT). Geometric morphology is evaluated, including vascular remodeling process, wall thickness, and comparison of TEBV thickness in different culture time points and presence of pulsatile stimulation. Finally, OCT provides practical possibilities for real-time observation of the degradation of polymer in the reconstructing tissues under pulsatile stimulation or not and in each vessel segment, by compared with the assessment of polymer degradation using scanning electron microscopic(SEM) and polarized microscope.

The three-dimensional culture system consisted of a culture chamber in the bioreactor and the perfusion system with a closed fluid cycle10,13 (Figure 1). The OCT imaging catheter was inserted into the distal end of the Y-junction and pulled back in the silicone tube for imaging. OCT imaging was first used to delineate the structural characterization of biodegradable polymeric scaffold-based TEBVs duri...

Watch this Scientific Journal Video about Nondestructive Monitoring of Degradable Scaffold-Based Tissue-Engineered Blood Vessel Development Using Optical Coherence Tomography at JoVE.com

Nondestructive Monitoring of Degradable Scaffold-Based Tissue-Engineered Blood Vessel Development Using Optical Coherence Tomography

A step by step protocol for nondestructive and long-period monitoring the process of vascular remodeling and scaffold degradation in real-time culture of biodegradable polymeric scaffold-based tissue-engineered blood vessels with pulsatile stimulation using optical coherence tomography is described here.

Engineered vascular grafts with structural and mechanical properties similar to natural blood vessels are expected to meet the growing demand for arterial ...

This method can help answer key questions in the vascular tissue-engineering field such as monitoring the dynamics of engineer vascular growth and remodeling during long-term culture. The main advantage of using optical coherence tomography, or OCT, is that it is a readily available, realtime and nondestructive imaging strategy to characterize the structural features and remodeling process of engineered vessels. Demonstrating the procedure will also be Shangmin Liu, and Wentao Ma, technicians from my laboratory.To begin this procedure, fabricate the PGA scaffold as described in the text protocol Dip PGA scaffolds in one mol-per-liter sodium hydroxide for one minute, to adjust the spacial structure of the mesh. Then, soak the scaffolds in tissue-culture-grade water three times for two minutes each. Each time, gently pat dry the scaffold with a tissue paper.Then, dry up the scaffolds in a hood with a blower for one hour. To assemble the bioreactor and the y-junction for OCT imaging, first, soak the self-developed glass cylindrical bioreactor, PGA scaffolds, silicone tube, bio-compatible tubes, connectors, stir bar, and equipment for assembly in a 95 percent ethanol tank for two hours. Pull the PGA scaffold through the side arms of the bioreactor connected to one side with a connector, as well as to another side with the y-junction used to deliver the OCT guide wire.Assemble another PGA scaffold in the bioreactor in the same way. Fit the polytetrafluoroethylene to the bioreactor lips by tightening it with 4-0 sutures. Put the bioreactor in the ethanol tank again for one hour before drying it overnight in a hood with the blower on.Now, isolate human umbilical artery smooth muscle cells from human umbilical arteries by standard explant techniques In the cause of saving the cells into PGA scaffolds, avoid any dripping of cell suspension on the bottom of bioreactor. Also, cover the bioreactor with silicone-stopper lid as soon as possible after cell seating to prevent contamination. Expand and maintain the cells in smooth muscle growth medium.Seed the human umbilical artery smooth muscle cells at a concentration of 5 million cells-per-milliliter in the above culture medium onto the PGA scaffolds. After placing a sir bar in the bioreactor, cover it the silicone stopper lid that has one feeding tube and three short tubing segments inserted for gas exchange. Attach PTFE 0.22 micron filters to each air change tube, and attach one heparin cap to the feeding tube.Adjust the stir bar with a stirring speed of 13 rounds-per-minute. Then, assemble the glass bioreactor, silicone stopper lid, and PGA scaffold into the culture system. Allow the cells to adhere for 45 minutes by leaning the bioreactor every 15 minutes with a stand to the left and to the right.Now, connect the LOO-OH-YEE pump, phosphate-buffered saline bag, and driver with the biocompatible tubes in order to create the profusion system. Open the driver to fill the tubes with PBS. Place the overall bioreactor in a humidified incubator with 5 percent CO2 at 37 degrees Celsius.Fill the culture chamber with 450 milliliters of the culture medium. Grow the seeded scaffolds under static culture for one week, changing the culture medium every three to four days by aspirating half of the old medium through the feeding tube and refilling the reactor with an equivalent amount of fresh culture medium. To prepare the profusion system for OCT imaging, pump fluids in the PBS bag to circulate them through the biocompatible tubes and back to the bag.Open the power of the driver and regulate the pump setting with a frequency of 60 beats-per-minute and an output systolic pressure of 120 millimeters of mercury. Adjust the mechanical parameters according to the needs of the tissue-engineering vascular culture. Click the run button to make the profusion system work.Provide the fix pulsatile simulation to the vessels for three weeks by iteratively pressurizing the biocompatible tubes after one week of static culture. Use a light source to ensure the axial resolution of ten to twenty microns and the image depth of one to two millimeters to identify the structure of the tissue-engineered blood vessels, or TEVBs, based on the frequency domain OCT intravascular imaging system. Turn on the power switch and open the image capture software Connect the fiber-optic imaging catheter to the drive motor and optical controller, with the catheter automatic retreat function.Set the parameters of the image acquisition rate to ten frames-per-second, with an automatic pullback speed of ten millimeters-per-second. Now, attach the imaging catheter to the y-junction via the heparin cap with an 18-gauge needle. Place the catheter into the silicone tube and identify the structure tightness of the PGA mesh before loading the PGA scaffold onto the bioreactor.Now, place the catheter tip over the region of interest. Adjust the pullback device and check for the image quality. Acquire images at one, four, seven, ten, 14, 17, 21, and 28 days in culture for each individual TEBV.Save these images sequentially with a realtime observation of the TEBV microstructure including surface morphology, internal structure, and composition. Repeat the measurement three times to get a reliable measurement of the engineered vessels each time. Capture a series of images throughout the testing using the image capture software.To use image analysis software to measure the tissue-engineered blood vessel wall thickness, first select the image to be analyzed. Then, click the tracking tool to automatically identify the inner side of the tissue-engineered blood vessel with the software and manually sketch the outer side. A diagram of thickness will appear on the screen.Repeat the measurement for five times to get a reliable measurement of the constructs. Consider using two independent investigators obligated to the obtain information. Open the silicone stopper lid placed over the bioreactor when the culture is finished, and discard the culture medium.Loosen the polytetrafluoroethylene from the bioreactor lips and cut the silicone tubes from the outer side of the polytetrafluoroethylene with scissors. Harvest the TEBVs from the bioreactor, and cut them into sections for a scanning-electron microscopy examination. Pull out the supporting silicone tube, and fix the sections with 4 percent power formaldehyde.Perform routine histological staining with masson's trichrome and sirious red to examine the morphology of collagen and PGA. To assess the PGA content and collagen component, observe histologic samples with sirious red staining through a polarized microscope. OCT images are compared with histopathological finds of TEBVs after four weeks of culture.The OCT image shows compact microstructure and specific components compared with histological assessment. The culture medium, the silicone tube, the TEBV, and the PGA fragment are visible. Masson's trichrome staining demonstrates collagen fibers distributed in a certain direction, along with PGA remnants in the media layer of the engineered vessels.Sirius red staining reveals PGA remnants and a collagen component by using a polarized microscope. Scanning-electron micrographs of engineered vessels demonstrate a compact microstructure. Meanwhile, this intraluminal imaging modality adopts nondestructive and easy monitoring of TEBVs, including the remodeling process and visual morphology in-situ in long-running culture.As shown here, the remodeling occurs earlier and the morphological changes manifest more obviously in the dynamic group through comparison of TEBV thickness. This technique paves the way for researchers in the field of vascular tissue engineering to explore structure features and the long-term remodeling process of engineered vessels. Clear display of polymeric remnants by polarized microscopy combined with OCT imaging might be useful for assessing scaffold degradation.

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Research

JoVE Journal

Bioengineering

Magnetic Resonance Elastography Methodology for the Evaluation of Tissue Engineered Construct Growth

Traditional mechanical testing often results in the destruction of the sample, and in the case of long term tissue engineered construct studies, the use of destructive assessment is not acceptable. A proposed alternative is the use of an imaging process called magnetic resonance elastography. Elastography is a nondestructive method for determining the engineered outcome by measuring local mechanical property values (i.e., complex shear modulus), which are essential markers for identifying the structure and functionality of a tissue. As a noninvasive means for evaluation, the monitoring of engineered constructs with imaging modalities such as magnetic resonance imaging (MRI) has seen increasing interest in the past decade1. For example, the magnetic resonance (MR) techniques of diffusion and relaxometry have been able to characterize the changes in chemical and physical properties during engineered tissue development2. The method proposed in the following protocol uses microscopic magnetic resonance elastography (&mu;MRE) as a noninvasive MR based technique for measuring the mechanical properties of small soft tissues3. MRE is achieved by coupling a sonic mechanical actuator with the tissue of interest and recording the shear wave propagation with an MR scanner4. Recently, &mu;MRE has been applied in tissue engineering to acquire essential growth information that is traditionally measured using destructive mechanical macroscopic techniques5. In the following procedure, elastography is achieved through the imaging of engineered constructs with a modified Hahn spin-echo sequence coupled with a mechanical actuator. As shown in Figure 1, the modified sequence synchronizes image acquisition with the transmission of external shear waves; subsequently, the motion is sensitized through the use of oscillating bipolar pairs. Following collection of images with positive and negative motion sensitization, complex division of the data produce a shear wave image. Then, the image is assessed using an inversion algorithm to generate a shear stiffness map6. The resulting measurements at each voxel have been shown to strongly correlate (R2&gt;0.9914) with data collected using dynamic mechanical analysis7. In this study, elastography is integrated into the tissue development process for monitoring human mesenchymal stem cell (hMSC) differentiation into adipogenic and osteogenic constructs as shown in Figure 2.

The procedure demonstrates the methodology of magnetic resonance elastography for monitoring the engineered outcome of adipose and osteogenic tissue engineered constructs through noninvasive local assessment of the mechanical properties using microscopic magnetic resonance elastography (&mu;MRE).

Traditional mechanical testing often results in the destruction of the sample, and in the case of long term tissue engineered construct studies, the use ...

Monitoring the Wall Mechanics During Stent Deployment in a Vessel

Clinical trials have reported different restenosis rates for various stent designs1. It is speculated that stent-induced strain concentrations on the arterial wall lead to tissue injury, which initiates restenosis2-7. This hypothesis needs further investigations including better quantifications of non-uniform strain distribution on the artery following stent implantation. A non-contact surface strain measurement method for the stented artery is presented in this work. ARAMIS stereo optical surface strain measurement system uses two optical high speed cameras to capture the motion of each reference point, and resolve three dimensional strains over the deforming surface8,9. As a mesh stent is deployed into a latex vessel with a random contrasting pattern sprayed or drawn on its outer surface, the surface strain is recorded at every instant of the deformation. The calculated strain distributions can then be used to understand the local lesion response, validate the computational models, and formulate hypotheses for further in vivo study.

Stent-induced arterial strain distributions are characterized using an optical surface strain measurement system. This visualization technique is used to gain insights into the impact of stent implantation on the host vessel.

Clinical trials have reported different restenosis rates for various stent designs1. It is speculated that stent-induced strain concentrations on the ...

Integrated Photoacoustic Ophthalmoscopy and Spectral-domain Optical Coherence Tomography

Both the clinical diagnosis and fundamental investigation of major ocular diseases greatly benefit from various non-invasive ophthalmic imaging technologies. Existing retinal imaging modalities, such as fundus photography1, confocal scanning laser ophthalmoscopy (cSLO)2, and optical coherence tomography (OCT)3, have significant contributions in monitoring disease onsets and progressions, and developing new therapeutic strategies. However, they predominantly rely on the back-reflected photons from the retina. As a consequence, the optical absorption properties of the retina, which are usually strongly associated with retinal pathophysiology status, are inaccessible by the traditional imaging technologies.
Photoacoustic ophthalmoscopy (PAOM) is an emerging retinal imaging modality that permits the detection of the optical absorption contrasts in the eye with a high sensitivity4-7 . In PAOM nanosecond laser pulses are delivered through the pupil and scanned across the posterior eye to induce photoacoustic (PA) signals, which are detected by an unfocused ultrasonic transducer attached to the eyelid. Because of the strong optical absorption of hemoglobin and melanin, PAOM is capable of non-invasively imaging the retinal and choroidal vasculatures, and the retinal pigment epithelium (RPE) melanin at high contrasts 6,7. More importantly, based on the well-developed spectroscopic photoacoustic imaging5,8 , PAOM has the potential to map the hemoglobin oxygen saturation in retinal vessels, which can be critical in studying the physiology and pathology of several blinding diseases 9 such as diabetic retinopathy and neovascular age-related macular degeneration.
Moreover, being the only existing optical-absorption-based ophthalmic imaging modality, PAOM can be integrated with well-established clinical ophthalmic imaging techniques to achieve more comprehensive anatomic and functional evaluations of the eye based on multiple optical contrasts6,10 . In this work, we integrate PAOM and spectral-domain OCT (SD-OCT) for simultaneously in vivo retinal imaging of rat, where both optical absorption and scattering properties of the retina are revealed. The system configuration, system alignment and imaging acquisition are presented.

Photoacoustic ophthalmology (PAOM), an optical-absorption-based imaging modality, provides the complementary evaluation of the retina to the currently available ophthalmic imaging technologies. We report the using of PAOM integrated with spectral-domain optical coherence tomography (SD-OCT) for simultaneous multimodal retinal imaging in rats.

Both the clinical diagnosis and fundamental investigation of major ocular diseases greatly benefit from various non-invasive ophthalmic imaging ...

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. ...

Multimodal Volumetric Retinal Imaging by Oblique Scanning Laser Ophthalmoscopy (oSLO) and Optical Coherence Tomography (OCT)

While fluorescence imaging is widely used in ophthalmology, a large field of view (FOV) three-dimensional (3D) fluorescence retinal image is still a big challenge with the state-of-the-art retinal imaging modalities because they would require z-stacking to compile a volumetric dataset. Newer optical coherence tomography (OCT) and OCT angiography (OCTA) systems overcome these restrictions to provide three-dimensional (3D) anatomical and vascular images, but the dye-free nature of OCT cannot visualize leakage indicative of vascular dysfunction. This protocol describes a novel oblique scanning laser ophthalmoscopy (oSLO) technique that provides 3D volumetric fluorescence retinal imaging. The setup of the imaging system generates the oblique scanning by a dove tail slider and aligns the final imaging system at an angle to detect fluorescent cross-sectional images. The system uses the laser scanning method, and therefore, allows an easy incorporation of OCT as a complementary volumetric structural imaging modality. In vivo imaging on rat retina is demonstrated here. Fluorescein solution is intravenously injected to produce volumetric fluorescein angiography (vFA).

Multimodal Volumetric Retinal Imaging by Oblique Scanning Laser Ophthalmoscopy oSLO and Optical Coherence Tomography OCT

Here, we present a protocol to get a large field of view (FOV) three-dimensional (3D) fluorescence and OCT retinal image by using a novel imaging multimodal platform. We will introduce the system setup, the method of alignment, and the operational protocols. In vivo imaging will be demonstrated, and representative results will be provided.

While fluorescence imaging is widely used in ophthalmology, a large field of view (FOV) three-dimensional (3D) fluorescence retinal image is still a big ...

Intra-cardiac Side-Firing Light Catheter for Monitoring Cellular Metabolism using Transmural Absorbance Spectroscopy of Perfused Mammalian Hearts

Absorbance spectroscopy of cardiac muscle provides non-destructive assessment of cytosolic and mitochondrial oxygenation via myoglobin and cytochrome absorbance respectively. In addition, numerous aspects of the mitochondrial metabolic status such as membrane potential and substrate entry can also be estimated. To perform cardiac wall transmission optical spectroscopy, a commercially available side-firing optical fiber catheter is placed in the left ventricle of the isolated perfused heart as a light source. Light passing through the heart wall is collected with an external optical fiber to perform optical spectroscopy of the heart in near real- time. The transmission approach avoids numerous surface scattering interference occurring in widely used reflection approaches. Changes in transmural absorbance spectra were deconvolved using a library of chromophore reference spectra, providing quantitative measures of all the known cardiac chromophores simultaneously. This spectral deconvolution approach eliminated intrinsic errors that may result from using common dual wavelength methods applied to overlapping absorbance spectra, as well as provided a quantitative evaluation of the goodness of fit. A custom program was designed for data acquisition and analysis, which permitted the investigator to monitor the metabolic state of the preparation during the experiment. These relatively simple additions to the standard heart perfusion system provide a unique insight into the metabolic state of the heart wall in addition to conventional measures of contraction, perfusion, and substrate/oxygen extraction.

Here we introduce a method for using an intra-ventricle optical catheter in perfused hearts to perform absorbance spectroscopy across the heart wall. The data obtained provides robust information on tissue oxygen tension as well as substrate utilization and membrane potential simultaneously with cardiac performance measures in this ubiquitous preparation.

Absorbance spectroscopy of cardiac muscle provides non-destructive assessment of cytosolic and mitochondrial oxygenation via myoglobin and cytochrome ...

Tissue-Engineered Graft for Circumferential Esophageal Reconstruction in Rats

The use of biocompatible materials for circumferential esophageal reconstruction is a technically challenging task in rats and requires an optimal implant technique with nutritional support. Recently, there have been many attempts at esophageal tissue engineering, but the success rate has been limited due to difficulty in early epithelization in the special environment of peristalsis. Here, we developed an artificial esophagus that can improve the regeneration of the esophageal mucosa and muscle layers through a two-layered tubular scaffold, a mesenchymal stem cell-based bioreactor system, and a bypass feeding technique with modified gastrostomy. The scaffold is made of polyurethane (PU) nanofibers in a cylindrical shape with a three-dimensional (3D) printed polycaprolactone strand wrapped around the outer wall. Prior to transplantation, human-derived mesenchymal stem cells were seeded into the lumen of the scaffold, and bioreactor cultivation was performed to enhance cellular reactivity. We improved the graft survival rate by applying surgical anastomosis and covering the implanted prosthesis with a thyroid gland flap, followed by temporary nonoral gastrostomy feeding. These grafts were able to recapitulate the findings of initial epithelialization and muscle regeneration around the implanted sites, as demonstrated by histological analysis. In addition, increased elastin fibers and neovascularization were observed in the periphery of the graft. Therefore, this model presents a potential new technique for circumferential esophageal reconstruction.

Esophageal reconstruction is a challenging procedure, and development of a tissue-engineered esophagus that enables regeneration of esophageal mucosa and muscle and that can be implanted as an artificial graft is necessary. Here, we present our protocol to generate an artificial esophagus, including scaffold manufacturing, bioreactor cultivation, and various surgical techniques.

The use of biocompatible materials for circumferential esophageal reconstruction is a technically challenging task in rats and requires an optimal implant ...

Cerebral Blood Flow-Based Resting State Functional Connectivity of the Human Brain using Optical Diffuse Correlation Spectroscopy

To obtain a comprehensive understanding of the human brain, utilization of cerebral blood flow (CBF) as a source of contrast is desired because it is a key hemodynamic parameter related to cerebral oxygen supply. Resting state low frequency fluctuations based on oxygenation contrast have been shown to provide correlations between functionally connected regions. The presented protocol uses optical diffuse correlation spectroscopy (DCS) to assess blood flow-based resting state functional connectivity (RSFC) in the human brain. Results of CBF-based RSFC in human frontal cortex indicate that intra-regional RSFC is significantly higher in the left and right cortices compared to inter-regional RSFC in both cortices. This protocol should be of interest to researchers who employ multi-modal imaging techniques to study human brain function, especially in the pediatric population.

This protocol demonstrates how to measure resting state functional connectivity in the human prefrontal cortex using a custom-made diffuse correlation spectroscopy instrument. The report also discuss practical aspects of the experiment as well as detailed steps for analyzing the data.

To obtain a comprehensive understanding of the human brain, utilization of cerebral blood flow (CBF) as a source of contrast is desired because it is a ...