Macro- and Micro-Scale Probing of the Mechanical Properties of DNA-Crosslinked Gels Using Embedded Inclusions
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0897-J02-02.1
Macro- and Micro-Scale Probing of the Mechanical Properties of DNA-Crosslinked Gels Using Embedded Inclusions David C. Lin1, Bernard Yurke2, David I. Shreiber3, Uday Chippada1, Xue Jiang3, George P. Watson2, and Noshir A. Langrana1,3 1 Department of Mechanical and Aerospace Engineering, Rutgers University, Piscataway, NJ 08854, U.S.A. 2 Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ 07974, U.S.A. 3 Department of Biomedical Engineering, Rutgers University, Piscataway, NJ 08854, U.S.A. ABSTRACT Mechanical properties of a class of self-assembling hydrogels based on DNA hybridization were studied using rigid, embedded inclusions. Because inclusions can be deflected without direct contact with a manipulator (e.g., magnet) once they are embedded within the subject material, the measurement technique is well suited for monitoring instantaneous and time-varying changes in the mechanical properties of active materials as they respond to external stimuli. In gels crosslinked with complementary strands of oligonucleotides, hybridization chemistry and strand displacement mechanisms allow reversible assembly, shape change, and large changes in compliance through the application of particular strands of DNA. In earlier work using large (diameter ~0.8 mm) magnetic beads, the scaling behavior of the global elastic modulus with crosslink density was determined. More recently, it was shown that a threefold increase in stiffness was possible by generating prestress in the DNA-crosslinked gel network. Currently, the gels are functionalized to support cell attachment and embedded with microfabricated nickel bars. Through the measurement of local elastic and shear moduli as well as Poisson’s ratios, cell-substrate interactions can be used as a means of evaluating the potential of DNA-crosslinked gels as active cellular engineering substrates and tissue engineering scaffolds.
INTRODUCTION Investigators have used polyacrylamide gels covalently crosslinked with bis-acrylamide in the cellular engineering of different cell types, including fibroblasts [1,2], macrophages [3], epithelial cells [1], smooth muscle cells [4,5], hepatocytes [6], and spinal cord neurons [7]. These studies demonstrate the relative cyto-compatibility of polyacrylamide and its versatility as a substrate with easily controllable compliance (i.e., stiffness at equilibrium is changed by adjusting monomer and crosslinker concentrations). However, the dependence on covalent crosslinking permits the creation of only single compliances or permanent compliance gradients. Cellular response is thus limited by the lack of an avenue to dynamically tune substrate properties. Measurements of global and local mechanical properties of these substrates can be performed using a number of established methods such as direct compression [4,8], macroscopic indentation [1,2,4], and microscopic indentation via microneedles and atomic force microscopy [1,9].
0897-J02-02.2
The use of short DNA strands to crosslink poly(N,N-dimethylacrylamide-co-N
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