Elastic and Viscoelastic Characterization of Polydimethylsiloxane (PDMS) for Cell-Mechanics Applications
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1052-DD03-02
Elastic and Viscoelastic Characterization of Polydimethylsiloxane (PDMS) for CellMechanics Applications I-Kuan Lin1, Yen-Ming Liao2, Yan Liu1, Kuo-Shen Chen2, and Xin Zhang1 1 Manufacturing Engineering, Boston University, 15 Saint Marys St., Brookline, MA, 02446 2 Mechanical Engineering, National Cheng Kung University, No.1, Ta-Hsueh Road, Tainan, 701, Taiwan ABSTRACT The mechanical properties of polydimethylsiloxane (PDMS) were characterized by using uniaxial compression, dynamic mechanical analysis (DMA), and nanoindentation tests as well as finite element simulation methods. A five-parameter linear solid model was used to emulate the behavior of PDMS. The study results indicated that the effect of viscoelasticity affected the PDMS pillar arrays significantly. The traditional approach for calculating the cell force basing on the linear elastic mechanics could result in considerable errors. Keywords:
PDMS, Viscoelasticity, Stress relaxation, finite element methods
INTRODUCTION The mechanical interaction between cells and their neighboring extracellular matrix is believed to be of fundamental importance in various physiological processes such as division and it can be measured by soft material probes such as polydimethylsiloxane (PDMS) pillars [1]. Researches have constructed PDMS pillar arrays as extracellular matrices and the interaction forces can be characterized by converting the measured deflection of PDMS pillars, showing in Fig.1, using elastic mechanics of materials based on simple assumptions from mechanics of materials, where the elastic modulus of PDMS was assumed to be a constant [2]. However, PDMS is inherently a viscoelastic material and its elastic modulus changes with loading frequencies and elapsed time durations [3]. Neglecting the time- and frequency-dependent nature of PDMS could possibly result in significant errors in data interpretation and even on the mechanisms in cell responses. Unfortunately, to the best of our knowledge, no sophisticated constitutive models on PDMS have been reported. Therefore, it is important to perform a detail material characterization on PDMS materials for cell-mechanics applications. This paper presents a detail mechanical behavior characterization for PDMS materials. As shown in Fig. 2, the entire study includes PDMS specimen fabrication, material and mechanical characterization in both macro and micro scales, and the corresponding finite element analyses (FEA) and simulations.
PDMS Pillar
2µm
(a)
Cell
(b)
Fig. 1 A PDMS array for characterizing cell force Material Characterization Dynamic Mechanical Analysis (DMA)
Punch Test
Elastic modulus – Frequency Domain
Stress Relaxation
Finite Element Analysis (FEA) PDMS Film Indentation
Experiment
PDMS Pillar Bending
Fig. 2 The overall characterization flow
SPECIMEN FABRICATION AND EXPERIMENTS FOR PDMS VISCOELASTICITY BEHAVIOR PDMS specimens in form of bulk and film were fabricated for dynamic mechanical analysis (DMA) and nanoindentation characterization, respectively. On the other hand, PDM
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