Mirani, B. | bioRxiv Science

bioRxiv2023

Characterization of pediatric porcine pulmonary valves as a model for tissue engineered heart valves

Heart valve tissue engineering holds the potential to transform the surgical management of congenital heart defects affecting the pediatric pulmonary valve (PV) by offering a viable valve replacement with the compositional, architectural and mechanical properties required to function in situ. While aiming to recapitulate the native valve, the minimum requirement for tissue engineered heart valves (TEHVs) has historically been adequate mechanical function at implantation. However, long-term in situ functionality of TEHVs remains elusive, suggesting that a closer approximation of the native valve is required. The realization of biomimetic engineered pediatric PV is impeded by insufficient characterization of healthy pediatric tissue. In this study, we comprehensively characterized the planar biaxial tensile behaviour, extracellular matrix (ECM) composition and organization, and valvular interstitial cell (VIC) phenotypes of PVs from piglets to provide benchmarks for TEHVs. The piglet PV possessed an anisotropic and non-linear tension-strain profile from which material constants for a predictive constitutive model were derived. Further, the ECM of the pediatric PV possessed a trilayer organization populated by collagen, glycosaminoglycans, and elastin. Biochemical quantification of ECM proteins normalized to wet weight and DNA content of PV tissue revealed homogenous distribution of proteins across sampled regions of the leaflet. Finally, the predominant phenotype of VICs in the piglet PV was quiescent vimentin-expressing fibroblasts, with a small proportion of activated -smooth muscle actin-expressing myofibroblasts residing primarily at the base of the leaflet. Overall, the properties characterized in this study can be used to inform TEHV design parameters towards generation of biomimetic pediatric PVs. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/553926v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@bff7d2org.highwire.dtl.DTLVardef@1272b90org.highwire.dtl.DTLVardef@9d1b54org.highwire.dtl.DTLVardef@6d3a93_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2022

High-frequency quantitative ultrasound to assess the acoustic properties of engineeredtissues in vitro

Acoustic properties of biomaterials and engineered tissues reflect their structure and cellularity. High-frequency ultrasound (US) can non-invasively characterize and monitor these properties with sub-millimetre resolution. We present an approach to estimate the acoustic properties of cell-laden hydrogels that accounts for frequency-dependent effects of attenuation in coupling media, hydrogel thickness, and interfacial transmission/reflection coefficients of US waves, all of which can bias attenuation estimates. Cell-seeded fibrin hydrogel disks were raster-scanned using a 40 MHz US transducer. Thickness, speed of sound, acoustic impedance, and acoustic attenuation coefficients were determined from the difference in the time-of-flight and ratios of the magnitudes of US signals, interfacial transmission/reflection coefficients, and acoustic properties of the coupling media. With this approach, hydrogel thickness was accurately measured by US, with excellent agreement to confocal microscopy (r2 = 0.97). Accurate thickness measurement enabled acoustic property measurements that were independent of hydrogel thickness, despite up to 60% reduction in thickness due to cell-mediated contraction. Notably, acoustic attenuation coefficients increased with increasing cell concentration (p<0.001), reflecting hydrogel cellularity independent of contracted hydrogel thickness. This approach enables accurate measurement of the intrinsic acoustic properties of biomaterials and engineered tissues to provide new insights into their structure and cellularity.

bioengineering↗