Background Investigating the mechanical properties of biological and biocompatible hydrogels is important in tissue engineering and biofabrication. Atomic force microscopy (AFM) and compression testing are routinely used to determine mechanical properties of tissue and tissue constructs. However, these techniques are slow and require mechanical contact with the sample, rendering in situ measurements difficult. Objective We therefore aim at a fast and contactless method for determining the mechanical properties of biological hydrogels and investigate if an optical method, like Laser-Doppler vibrometry (LDV), can accomplish this task. Methods LDV is a fast contactless method for mechanical analysis. Nonetheless, LDV setups operating in the visible range of the optical spectrum are difficult to use for transparent materials, such as biological hydrogels, because LDV relies on reflected or back-scattered light from the sample. We therefore use a near-infrared (NIR) scanning LDV to determine the vibration spectra of cylindrical gelatin discs of different gelatin concentration and compare the results to AFM data and unconfined compression testing. Results We show that the gelatin test structures can be analyzed, using a NIR LDV, and the Young’s moduli can be deduced from the resonance frequencies of the first normal (0,1) mode of these structures. As expected, the frequency of this mode increases with the square root of the Young’s modulus and the damping constant increases exponentially with gelatin concentration, which underpins the validity of our approach. Conclusions Our results demonstrate that NIR wavelengths are suitable for a fast, contactless vibrational analysis of transparent hydrogel structures.

中文翻译：

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使用激光多普勒测振法​​对透明水凝胶结构进行非接触式振动分析

背景研究生物和生物相容性水凝胶的机械性能在组织工程和生物制造中很重要。原子力显微镜 (AFM) 和压缩测试通常用于确定组织和组织结构的机械性能。然而，这些技术速度较慢，并且需要与样品进行机械接触，因此难以进行原位测量。目标因此，我们的目标是一种快速和非接触式方法来确定生物水凝胶的机械性能，并研究光学方法，如激光多普勒振动测量 (LDV)，是否可以完成这项任务。方法 LDV 是一种用于机械分析的快速非接触式方法。尽管如此，在可见光谱范围内运行的 LDV 设置很难用于透明材料，例如生物水凝胶，因为 LDV 依赖于来自样品的反射或背向散射光。因此，我们使用近红外 (NIR) 扫描 LDV 来确定不同明胶浓度的圆柱形明胶盘的振动光谱，并将结果与​​ AFM 数据和无侧限压缩测试进行比较。结果 我们表明可以使用 NIR LDV 分析明胶测试结构，并且可以从这些结构的第一正常 (0,1) 模式的共振频率推导出杨氏模量。正如预期的那样，这种模式的频率随着杨氏模量的平方根而增加，并且阻尼常数随着明胶浓度呈指数增加，这巩固了我们方法的有效性。结论 我们的结果表明 NIR 波长适用于快速、