Sebastian Joseph A, Strohm Eric M, Chérin Emmanuel, Mirani Bahram, Démoré Christine E M, Kolios Michael C, Simmons Craig A
Institute of Biomedical Engineering, University of Toronto, Toronto, Canada; Translational Biology and Engineering Program, Ted Rogers Center for Heart Research, Toronto, Canada.
Department of Physics, Toronto Metropolitan University, Toronto, Canada; Institute of Biomedical Engineering, Science and Technology (iBEST), A Partnership Between Toronto Metropolitan University and St. Michael's Hospital, Toronto, Canada; Keenan Research Centre for Biomedical Science, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Canada.
Acta Biomater. 2023 Feb;157:288-296. doi: 10.1016/j.actbio.2022.12.014. Epub 2022 Dec 12.
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 speed of sound, acoustic impedance, and acoustic attenuation 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 agreement to confocal microscopy (r = 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. STATEMENT OF SIGNIFICANCE: High-frequency ultrasound can measure the acoustic properties of engineered tissues non-invasively and non-destructively with µm-scale resolution. Acoustic properties, including acoustic attenuation, are related to intrinsic material properties, such as scatterer density. We developed an analytical approach to estimate the acoustic properties of cell-laden hydrogels that accounts for the frequency-dependent effects of attenuation in coupling media, the reflection/transmission of ultrasound waves at the coupling interfaces, and the dependency of measurements on hydrogel thickness. Despite up to 60% reduction in hydrogel thickness due to cell-mediated contraction, our approach enabled measurements of acoustic properties that were substantially independent of thickness. Acoustic attenuation increased significantly with increasing cell concentration (p < 0.001), demonstrating the ability of acoustic attenuation to reflect intrinsic physical properties of engineered tissues.
生物材料和工程组织的声学特性反映了它们的结构和细胞组成。高频超声（US）能够以亚毫米级分辨率对这些特性进行非侵入性表征和监测。我们提出了一种方法来估计载有细胞的水凝胶的声速、声阻抗和声衰减，该方法考虑了耦合介质中衰减的频率依赖性效应、水凝胶厚度以及超声波的界面传输/反射系数，所有这些都会使衰减估计产生偏差。使用40 MHz超声换能器对接种细胞的纤维蛋白水凝胶圆盘进行光栅扫描。根据飞行时间的差异以及超声信号幅度的比值、界面传输/反射系数和耦合介质的声学特性，确定厚度、声速、声阻抗和声衰减系数。通过这种方法，超声能够准确测量水凝胶厚度，与共聚焦显微镜测量结果一致（r = 0.97）。尽管由于细胞介导的收缩导致厚度减少了60%，但准确的厚度测量使得能够进行与水凝胶厚度无关的声学特性测量。值得注意的是，声衰减系数随着细胞浓度的增加而增加（p < 0.001），这反映了水凝胶的细胞组成，而与收缩后的水凝胶厚度无关。这种方法能够准确测量生物材料和工程组织的固有声学特性，从而为它们的结构和细胞组成提供新的见解。重要性声明：高频超声能够以微米级分辨率对工程组织的声学特性进行非侵入性和无损测量。包括声衰减在内的声学特性与诸如散射体密度等固有材料特性相关。我们开发了一种分析方法来估计载有细胞的水凝胶的声学特性，该方法考虑了耦合介质中衰减的频率依赖性效应、超声波在耦合界面的反射/传输以及测量对水凝胶厚度的依赖性。尽管由于细胞介导的收缩导致水凝胶厚度减少了60%，但我们的方法能够进行基本上与厚度无关的声学特性测量。声衰减随着细胞浓度的增加而显著增加（p < 0.001），这表明声衰减能够反映工程组织的固有物理特性。
