Endoscopic cellular microscopy for in vivo biomechanical assessment of tendon function

Abstract

This study explores a novel method to quantify in vivo soft tissue biomechanics from endoscopic confocal fluorescence microscope images of externally loaded biological tissues. A custom algorithm based on normalized cross-correlation is used to track fluorescently labeled cells within soft tissue structures as they deform. Cellular displacements are subsequently reduced to tissue strains by deriving the spatial gradient of the spline smoothed cellular displacement field. The relative performance of the tracking method is verified using a synthetic dataset with known underlying deformation. In biological application of the method, tissue strains are measured in the Achilles tendon of an anesthetized mouse. Over repeated trials, structural strain in the tendon (i.e., the relative change in distance between cells located at view field extremes) is 20.3+/-3.1%, thus establishing the reproducibility of the loading protocol. Analysis of local tendon tissue strains reveal primary engineering strains in the tissue to range from 5 to 55%, signifying a highly inhomogeneous strain state, with complex relative motions of neighboring tendon substructures. In summary, the current work establishes a baseline for a promising experimental method, and demonstrates its technical feasibility.

Vector correlation technique for pixel-wise detection of collagen fiber realignment during injurious tensile loading

“…Also, using this approach, a vector correlation map can be created between any two alignment maps in which the tissue is in the same position, regardless of the time history or map sequence. Although a QPLI system provides the microstructural data in this study, this vector correlation technique could be adapted to other imaging modalities, such as secondharmonic-generation microscopy or optical coherence tomography 12,14,36 capable of measuring fiber alignment in an in vivo setting. Ultimately, an assessment of anomalous fiber realignment during tissue loading in vivo could provide unique insight into the relationship between microstructural injury and potential physiologic consequences of such injuries.…”

“…Polarized light imaging, 10,11 optical coherence tomography, 12 confocal microscopy, 13,14 and small-angle light scattering 15 techniques have all been used to quantify microstructural changes in soft tissue during mechanical loading. However, of these, quantitative polarized light imaging ͑QPLI͒ has been used to infer collagen fiber kinematics through the thickness of soft tissues in all regions during continuous loading because of its ability to acquire data with high temporal resolution and adjustable spatial resolution.…”

Tendon injury and repair – A perspective on the basic mechanisms of tendon disease and future clinical therapy

“…the deltoid; the gastrocnemius). Here a large degree of lateral sliding between collagen fascicles enables such joint motions [43][44][45][46][47][48][49].…”

A novel method for assessing adherent single-cell stiffness in tension: design and testing of a substrate-based live cell functional imaging device

“…The routine integrated an ImageJ plug-in (bUnwarpJ) that performed a simultaneous registration of the two images (reference and deformed) (Arganda-Carreras et al 2006), producing a spline interpolated displacement field. We then calculated the two principal strains (equal to radial and circumferential strains in a 2D equibiaxial strain state) deriving the spatial gradient of the spline smoothed displacement field (Snedeker et al 2006). Maximum principal strain was considered as an effective measure to account for both dilatational strains (stretching along the axes of the imaging plane) and distortional (shear) strains.…”