Mechanical Properties of Soft Materials

Soft materials have gained attention in many research and industrial fields. For example, kinds of hydrogels have been developed to provide the mechanical environments favorable for culturing cells. Wearable or foldable electronic devices require conducting materials with an excellent flexibility. We characterize the mechanical properties of soft materials in terms of elasticity, plasticity, and viscosity using various techniques such as rheometry, AFM (Atomic Force Microscopy), nano-indentation, magnetic tweezers, and optical tweezers. Not only the properties of themselves but also interaction between soft materials are characterized in our group. Followings are soft materials of our interest.

- Cytoskeletal filaments and networks
- Hydrogels and biopolymers
- Flexible electronic materials

research1_11 Figure – 3D matrix of actin bundles
polymerized with alpha-actinin

research1_12Figure – High resolution CCD image
of actin bundles polymerized
with alpha-actinin

F-actin networks reconstituted in vitro using purified actin and actin binding proteinsFigure – F-actin networks reconstituted in vitro using
purified actin and actin binding proteins


Tissue, Cellular, and Molecular Engineering

Single molecule engineering - Protein mechanics (unfolding and unbinding)
- Effect of mechanical forces on protein binding
- Filament polymerization and network formation
Cellular Engineering - Dynamics behaviors of single cell
- Interaction between cells, and cell and extracellular matrix
- Effect of shape on cellular function
Tissue Engineering - Artificial muscle fabrication
- Fabrication of cell
- Elastomer hybrid system
- Bio-inspired sensors/robots

research2_1Figure – SEM image of hydrogel

research2_2Figure – Schematic of single molecular assay developed
using optical tweezers to probe the binding interaction
between actin filaments (green) and filamin (small red)
shown in the confocal image

Measurement Techniques for Biological Applications

We develop various measurement techniques to probe forces in biological specimens properly. Optical tweezers are used to generate a force in the order of pN which is relevant to force produced in single molecular events such as antibody-antigen binding and protein unfolding. Traction Force Microscopy (TFM) combined with the patterning technique is advantageous in studying the force generation for shaped-controlled cells. We are able to characterize mechanical properties of tissues using Atomic Force Microscopy (AFM) and rheometry.

Line of microbeads aligned using standing surface acoustic waveFigure – Line of microbeads aligned using standing surface acoustic wave

research3_2Figure – Traction force microscopy and thin film assay
to measure forces for single cells and tissues


Inspired by nature, we mimic structures and systems of living species at the multiscales.  Highly ordered structures of cell are reconstituted in vitro by polymerizing cytoskeletal filaments at the environments where the mechanical, chemical or electrical conditions are similar to those in vivo. Tissue organization is replicated by culturing cells with specific patterns on a soft substrate with the physiologically-relevant stiffness. The principles learned from the biomimicry are applied to design engineering devices. Applications include an in vitro platform to test efficacy/toxicity of drugs, bio-inspired robots, and biosensors.

research4Figure – Shape-controlled single cells and tissue structures
of cardiac myocytes using the patterning technique


Cells are able to produce, sense, and response to mechanical cues. Mechanotransduction refers to the mechanisms by which mechanical cues are converted into biochemical activities. We are specially interested in how mechanotransduction is altered in the state of diseases where the mechanical environments such as stiffness, boundary, and shape change significantly. Results of the studies are applied in understanding causes of diseases, developing new treatments, and constructing biomimetic tissue platform for drug tests.

research5Figure – Aβ1-42 fibril aggregated at room temperature