As a practical and effective tool for quantitative in-plane deformation measurement of a planar object surface, two-dimensional digital image correlation (2D DIC) is now widely accepted and commonly used in the field of experimental mechanics. It directly provides full-field displacements to sub-pixel accuracy and full-field strains by comparing the digital images of a test object surface acquired before and after deformation. In this review, methodologies of the 2D DIC technique for displacement field measurement and strain field estimation are systematically reviewed and discussed. Detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided. Measures for achieving high accuracy deformation measurement using the 2D DIC technique are also recommended. Since microscale and nanoscale deformation measurement can easily be realized by combining the 2D DIC technique with high-spatial-resolution microscopes, the 2D DIC technique should find more applications in broad areas.

https://iopscience.iop.org/article/10.1088/0957-0233/20/6/062001/pdf

Two-dimensional digital image correlation for in-plane displacement and strain measurement: a review

Rationale:More than 25 million individuals have heart failure worldwide, with ≈4000 patients currently awaiting heart transplantation in the United States. Donor organ shortage and allograft rejection remain major limitations with only ≈2500 hearts transplanted each year. As a theoretical alternative to allotransplantation, patient-derived bioartificial myocardium could provide functional support and ultimately impact the treatment of heart failure. Objective:The objective of this study is to translate previous work to human scale and clinically relevant cells for the bioengineering of functional myocardial tissue based on the combination of human cardiac matrix and human induced pluripotent stem cell–derived cardiomyocytes. Methods and Results:To provide a clinically relevant tissue scaffold, we translated perfusion-decellularization to human scale and obtained biocompatible human acellular cardiac scaffolds with preserved extracellular matrix composition, architecture, and perfusable coronary vasculatur...

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Bioengineering Human Myocardium on Native Extracellular Matrix

Background— Extracellular matrix (ECM), a tissue-engineered scaffold, recently demonstrated cardiomyocyte population after myocardial implantation. Surgical restoration of myocardium frequently uses Dacron as a myocardial patch. We hypothesized that an ECM-derived myocardial patch would provide a mechanical benefit not seen with Dacron.

Methods and Results— Using a canine model, a full thickness defect in the right ventricle was repaired with either Dacron or ECM. A third group had no surgery and determined baseline RV function. Eight weeks later, global systolic function was assessed by the preload recruitable stroke work relationship. Regional systolic function was measured by systolic area contraction (SAC), calculated by high density mechanical mapping. Tau was used to assess global diastolic function. Recoil rate and diastolic shear were used as measures of regional diastolic function. After functional data acquisition, tissue was fixed for histological evaluation. Global systolic and diastolic functions were similar at baseline and after ECM and Dacron implantation. Regional systolic function was greater in the ECM group compared with the Dacron group (SAC: 4.1±0.9% versus −1.8±1.1, P <0.05). Regional diastolic function was also greater in the ECM group (recoil rate (° sec−1): −44±7 versus −17±2, ECM versus Dacron; P <0.05). Immunohistochemical analysis revealed cardiomyocytes in the ECM implant region, a finding not seen with Dacron.

Conclusion— At 8 weeks, an ECM-derived tissue-engineered myocardial patch provides regional mechanical function, likely related to cardiomyocyte population. These results are in sharp contrast to Dacron, a commonly used myocardial patch.

Tissue-engineered myocardial patch derived from extracellular matrix provides regional mechanical function.

The use of extracellular matrix as an inductive scaffold for the partial replacement of functional myocardium.

The need to regenerate tissue is paramount, especially for the heart that lacks the ability to regenerate after injury. The urinary bladder extracellular matrix (ECM), when used to repair a right ventricular defect, successfully regenerated some mechanical function. The objective of the current study was to determine whether the regenerative effect of ECM could be improved by seeding the patch with human mesenchymal stem cells (hMSCs) enhanced to differentiate down a cardiac linage. hMSCs were used to form three-dimensional spheroids. The expression of cardiac proteins was determined in cells exposed to the spheroid formation and compared with nonmanipulated hMSCs. To determine whether functional calcium channels were present, the cells were patch clamped. To evaluate the ability of these cells to regenerate mechanical function, the spheroids were seeded on ECM and then implanted into the canine heart to repair a full-thickness right ventricular defect. As a result, many of the cells spreading from the spheroids expressed cardiac-specific proteins, including sarcomeric α-actinin, cardiotin, and atrial natriuretic peptide, as well as the cell cycle markers cyclin D1 and proliferating cell nuclear antigen. A calcium current similar in amplitude to that of ventricular myocytes was present in 16% of the cells. The cardiogenic cell-seeded scaffolds increased the regional mechanical function in the canine heart compared with the unmanipulated hMSC-seeded scaffolds. In addition, the cells prelabeled with fluorescent markers demonstrated myocyte-specific actinin staining with sarcomere spacing similar to that of normal myocytes. In conclusion, the spheroid-derived cells express cardiac-specific proteins and demonstrate a calcium current similar to adult ventricular myocytes. When these cells are implanted into the canine heart, some of these cells appear striated and mechanical function is improved compared with the unmanipulated hMSCs. Further investigation will be required to determine whether the increased mechanical function is due to a differentiation of the cardiogenic cells to myocytes or to other effects.

https://www.physiology.org/doi/pdf/10.1152/ajpheart.00219.2008

Enhanced recovery of mechanical function in the canine heart by seeding an extracellular matrix patch with mesenchymal stem cells committed to a cardiac lineage

An investigation of the inhomogeneous and anisotropic properties of myocardium necessitates a whole field measurement technique with high spatial resolution Computer aided speckle interferometry (CASI) may be applied to measuring deformation on the epicardial surface of the heart Silicone carbide particles (approximately 40 μm in diameter) were sprinkled randomly onto the epicardial surface of isolated rabbit hearts When illuminated with white light, speckles may be observed with a charge coupled device (CCD) camera A balloon was placed in the left ventricle to control the intracavitary load on the arrested heart To compare CASI to the “gold” standard technique of sonomicrometry, two ultrasonic transducers were implanted into the wall of the myocardium Three hearts were exposed to various loading conditions, and at each condition speckle images were recorded CASI was used to determine the distribution of displacement vectors (both direction and magnitude) in the region imaged by the CCD camera Strain along the axis of the implanted transducers was determined with CASI and compared to that obtained with sonomicrometry Strain determined from CASI and sonomicrometry produced equivalent results Unlike sonomicrometry, whereby the displacement between two points with a relatively large gauge length is obtained, CASI is able to determine displacement vectors for hundreds of “points” within the same region In conclusion, CASI produced equivalent results to those obtained from sonomicrometry (although not with the same temporal resolution), but it is a whole field deformation mapping technique that has a spatial resolution three orders of magnitude higher than that of sonomicrometry © 2001 Biomedical Engineering Society

Computer aided speckle interferometry: a technique for measuring deformation of the surface of the heart.

BACKGROUND Surgically induced ischemia in the arrested heart can result in changes in the mechanical properties of the myocardium. Regions of ischemia may be characterized based on the amount of epicardial deformation for a given load. Computer aided speckle interferometry (CASI), which tracks the movement of clusters of particles, is developed as a technique for measuring epicardial deformation, thereby determining the perfusion status of the passive heart. MATERIALS AND METHODS Silicone carbide particles and retroreflective beads were dispersed randomly onto the epicardial surface of 11 isolated rabbit hearts to form speckle images. The hearts were arrested with hyperkalemic Krebs-Henseleit buffered solution. Each heart was then exposed to a series of intracavitary pressures, and at each pressure speckle images were acquired with a charge-coupled device (CCD) camera. Nine hearts were exposed to global ischemia, and two hearts were exposed to regional ischemia by occluding the second diagonal branch of the left anterior descending artery (LAD). The hearts were again loaded and the speckle images were acquired. CASI was used to determine the distribution of deformation field. RESULTS CASI was able to determine displacements with a spatial resolution of about 50 microns. Global ischemia resulted in a significant increase in the maximum principle strain and the first invariant of the 2-D strain tensor. In the regionally ischemic heart, a large difference in deformation between the ischemic and perfused regions was clearly observed. CONCLUSION Based on epicardial deformation, CASI is able to distinguish between perfused and ischemic myocardium, with a spatial resolution of 50 microns.

Effects of ischemia on epicardial deformation in the passive rabbit heart.

Commonly used techniques for analysis of regional heart function include sonomicrometry, implanted markers, and surface markers. However, these techniques cannot offer the high spatial resolution needed to define regional abnormalities in the heart. We have recently applied a computer aided speckle interferometry technique (CASI) with high spatial resolution to measuring the deformation of heart muscle. We applied silicon carbide particles to the surface of the isolated heart and loaded the heart by increasing the intracavitary pressure. The movement of the speckle pattern was tracked with a CCD camera. This technique produces equivalent results to that of the gold standard in heart mechanics, sonomicrometry, but with three orders of mapitude higher spatial resolution. We have used this technique to determine changes in myocardial deformation of perfused, ischemic and reperfused rabbit hearts.

Joseph Todaro

Papers

Computer aided speckle interferometry: a technique for measuring deformation of the surface of the heart.

Effects of ischemia on epicardial deformation in the passive rabbit heart.

The Application of Speckle Metrology to Heart Mechanics