Quantitative evaluation of cardiomyocyte contractility in a 3D microenvironment.

Three-dimensional cultures in a microfabricated environment provide in vivo-like conditions for cells, and have been used in a variety of applications in basic and clinical studies. In this study, the contractility of cardiomyocytes in a 3D environment using complex 3D hybrid biopolymer microcantilevers was quantified and compared with that observed in a 2D environment. By measuring the deflections of the microcantilevers with different surfaces and carrying out finite element modeling (FEM) of the focal pressures of the microcantilevers, it was found that the contractile force of high-density cardiomyocytes on 3D grooved surfaces was 65-85% higher than that of cardiomyocytes on flat surfaces. These results were supported by immunostaining, which showed alignment of the cytoskeleton and elongation of the nuclei, as well as by quantitative RT-PCR, which revealed that cells on the grooved surface had experienced sustained stimuli and tighter cell-to-cell interactions.

Establishment of a fabrication method for a long-term actuated hybrid cell robot.

We developed a novel method to fabricate a crab-like microrobot that can actuate for a long period in a physiological condition. The microrobot backbone was built with a biocompatible and elastic material-polydimethylsiloxane (PDMS)-by using a specially designed 3D molding aligner, and consisted of three strips of PDMS "legs" connected across a "body." Cardiomyocytes were then plated on the grooved top surface of the backbone, resulting in a high concentration of pulsating cells. These key techniques enabled the microrobot to walk continuously for over ten days. The performance of our crab-like microrobot was measured at an average velocity of 100 microm s(-1), and the estimated total distance it travelled was 50 m over a one-week period. Thus, we have demonstrated for the first time a walking robot that exhibited reliable and long-term actuation performances.

Cantilever arrayed blood pressure sensor for arterial applanation tonometry.

The authors developed a cantilever-arrayed blood pressure sensor array fabricated by (111) silicon bulk-micromachining for the non-invasive and continuous measurement of blood pressure. The blood pressure sensor measures the blood pressure based on the change in the resistance of the piezoresistor on a 5-microm-thick-arrayed perforated membrane and 20-microm-thick metal pads. The length and the width of the unit membrane are 210 and 310 microm, respectively. The width of the insensible zone between the adjacent units is only 10 microm. The resistance change over contact force was measured to verify the performance. The good linearity of the result confirmed that the polydimethylsiloxane package transfers the forces appropriately. The measured sensitivity was about 4.5%/N. The maximum measurement range and the resolution of the fabricated blood pressure sensor were greater than 900 mmHg (= 120 kPa) and less than 1 mmHg (= 133.3 Pa), respectively.

A self-aligned single carbon nanotube field emission source fabricated by UV lithography.

We suggest a novel process for fabricating a carbon nanotube field emission source having one carbon nanotube per gate aperture. The fabrication is based on UV lithography, instead of electron beam lithography. We used only one patterning step to define the gate, insulator, and cathode. We applied a DC voltage to the anode and a pulse signal to the gate. We then investigated the I-V characteristics of the structure, changing the frequency and the duty-cycle of the pulse signal applied to the gate. We found that the optimum frequency and duty-cycle were 250 kHz and 22%, respectively. The structure had a turn-on voltage of 1.1 V under these conditions. The anode voltage did not have much effect. Finally, we checked the stability of the source for 40 h. We obtained an average emission current of 1.093 µA with a standard deviation of 1.019 × 10(-2) µA.

Realistic computational modeling for hybrid biopolymer microcantilevers.

Three dimensional cultures in a microfabricated environment provide in vivo-like conditions to cells, and have used in a variety of applications in basic and clinical studies. Also, the analysis of the contractility of cardiomyocytes is important for understanding the mechanism of heart failure as well as the molecular alterations in diseased heart cells. This paper presents a realistic computational model, which considers the three dimensional fluid-structural interactions (FSI), to quantify the contractile force of cardiomyocytes on hybrid biopolymer microcantilevers. Prior to this study, only static modeling of the microscale cellular force has been reported. This study modeled the dynamics of cardiomyocytes on microcantilevers in a medium using the FSI. This realistic model was compared with static FEM analysis and the experimental results. Using harmonic response analysis in FSI modeling, the motion of a hybrid biopolymer microcantilever in the medium was identified as a second-order system and the influence of the dynamics of cardiomyocytes could be evaluated quantitatively.

Potential of Poly-(N-Isopropylacrylamide) hydrogel as a clamper of the microrobot in gastrointestinal tract.

We successfully demonstrate that a thermally actuated reversible hydrogel, the poly N-Isopropylacrylamide (PNIPAAm), based clampers holds the intestines of a pig during the inchworm motion of microrobot. Although there are no direct relationship between hydro affinity and friction force, we found the significant friction force difference according to the surface condition change of PNIPAAm hydrogel. On the small intestine of a pig, a clamping mechanism was realized based on simple switching hydrophobic/hydrophilic surface conditions of PNIPAAm due to heating/cooling. In order to estimate response time of the clamper, the characteristic transition time of PNIPAAm film from hydrophilic to hydrophobic condition was investigated. Water contact angle (WCA) was monitored to normalize the transition time characteristics of PNIPAAm film in the course of time. From these results, we calculated the minimum heating time of the various thickness of PNIPAAm film to the clamping after its change to the hydrophobic condition. The minimum heating time was 15 seconds until 1 mm thickness of PNIPAAm film had enough friction force.