Hohne Danial N, Younger John G, Solomon Michael J
Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
Langmuir. 2009 Jul 7;25(13):7743-51. doi: 10.1021/la803413x.
We introduce a flexible microfluidic device to characterize the mechanical properties of soft viscoelastic solids such as bacterial biofilms. In the device, stress is imposed on a test specimen by the application of a fixed pressure to a thin, flexible poly(dimethyl siloxane) (PDMS) membrane that is in contact with the specimen. The stress is applied by pressurizing a microfabricated air channel located above the test area. The strain resulting from the applied stress is quantified by measuring the membrane deflection with a confocal laser scanning microscope. The deflection is governed by the viscoelastic properties of the PDMS membrane and of the test specimen. The relative contributions of the membrane and test material to the measured deformation are quantified by comparing a finite element analysis with an independent (control) measurement of the PDMS membrane mechanical properties. The flexible microfluidic rheometer was used to characterize both the steady-state elastic modulus and the transient strain recoil of two soft materials: gellan gums and bacterial biofilms. The measured linear elastic moduli and viscoelastic relaxation times of gellan gum solutions were in good agreement with the results of conventional mechanical rheometry. The linear Young's moduli of biofilms of Staphylococcus epidermidis and Klebsiella pneumoniae, which could not be measured using conventional methods, were found to be 3.2 and 1.1 kPa, respectively, and the relaxation time of the S. epidermidis biofilm was 13.8 s. Additionally, strain hardening was observed in all the biofilms studied. Finally, design parameters and detection limits of the method show that the device is capable of characterizing soft viscoelastic solids with elastic moduli in the range of 102-105 Pa. The flexible microfluidic rheometer addresses the need for mechanical property characterization of soft viscoelastic solids common in fields such as biomaterials, food, and consumer products. It requires only 200 pL of the test specimen.
我们介绍了一种灵活的微流控装置，用于表征诸如细菌生物膜等软粘弹性固体的机械性能。在该装置中，通过对与试样接触的薄柔性聚二甲基硅氧烷（PDMS）膜施加固定压力，对测试试样施加应力。通过对位于测试区域上方的微加工空气通道加压来施加应力。通过使用共聚焦激光扫描显微镜测量膜的挠度来量化由施加应力产生的应变。挠度由PDMS膜和测试试样的粘弹性特性决定。通过将有限元分析与PDMS膜机械性能的独立（对照）测量进行比较，量化膜和测试材料对测量变形的相对贡献。使用柔性微流控流变仪表征了两种软材料（结冷胶和细菌生物膜）的稳态弹性模量和瞬态应变回弹。测得的结冷胶溶液的线性弹性模量和粘弹性弛豫时间与传统机械流变学的结果吻合良好。表皮葡萄球菌和肺炎克雷伯菌生物膜的线性杨氏模量分别为3.2 kPa和1.1 kPa，这是使用传统方法无法测量的，表皮葡萄球菌生物膜的弛豫时间为13.8 s。此外，在所研究的所有生物膜中均观察到应变硬化。最后，该方法的设计参数和检测限表明，该装置能够表征弹性模量在10² - 10⁵ Pa范围内的软粘弹性固体。柔性微流控流变仪满足了生物材料、食品和消费品等领域中常见的软粘弹性固体机械性能表征的需求。它仅需要200 pL的测试试样。
