Microfabrication & Manipulation

Micro-scale structure of natural biological creatures are made of membranes, which are relatively thin compared to their feature size. This fundamental characteristic of the architecture of biological microstructures, makes life a highly adaptable system from both chemical and physical perspectives. The small thickness of the membrane enhances transport of heat and substances between the body and its surroundings, and it provides softness to the body, enabling passive and active morphological changes for adapting to the environment. These characteristics of biological microstructures should greatly encourage us to develop new types of microdevices. We are investigating three-dimensional microfabrication technologies of soft membrane microdevices and its application in bio-medical fields.

One of the major application of the membrane-based microdevices is minimally invasive surgery tools. We have developed a pressure-driven micro active catheter and its fabrication process. The catheter was fabricated by using “membrane micro emboss following excimer laser ablation (MeME-X) process”. The catheter has a one-sided hollow bellows at the tip made of thin polymer membrane. The bellows is composed of a series of folded micro-chambers and microchannels connecting the micro-chambers. The folded-chambers expand on one side by increasing inner water pressure using a syringe, thus the whole bellows bends toward one direction within 0 to 180 degree. This micro active catheter should be useful for safe intravascular surgery in narrow and complicated blood vessels. Moreover, the nonelectrical actuation mechanism of this catheter can be widely applied to soft microrobots.

1. M. Ikeuchi and K. Ikuta, "Development of pressure-driven micro active catheter using membrane micro emboss following excimer laser ablation (MeME-X) process," 2009 IEEE International Conference on Robotics and Automation, 2009, pp. 4469-4472, doi: 10.1109/ROBOT.2009.5152869.

In electrospinning, the viscosity of the polymer solution affects the morphology of the product. By decreasing the viscosity of the polymer solution, the nanofibers are gradually particulated, and at sufficiently low viscosity, microparticles are formed – a process called electrospray. Here, we found another morphology “nano-meshed microcapsule” – intermediate state between the nanofiber and the microparticle, in the products of electrospray under high ambient humidity [1]. The nano-meshed microcapsule has the characteristic of both nanofiber and microparticle. That is, the surface of the microcapsule is composed of nanofibers, and at the same time, it can be treated as a particle. Here we introduce a new method using an electrostatic lens to focus the nano-meshed microcapsules. By moving the target electrode, the formation of microcapsules and patterning of arbitrary shape can be realized in a single step.

1. Ikeuchi, M., Tane, R. & Ikuta, K. Electrospray deposition and direct patterning of polylactic acid nanofibrous microcapsules for tissue engineering. Biomed Microdevices 14, 35–43 (2012). https://doi.org/10.1007/s10544-011-9583-x

We have developed a new method to fabricate microfluidic channels inside PDMS thin films by taking advantage of the moisture permeability of polydimethylsiloxane (PDMS). In this method, first, caramel prepared by heating sugar is applied directly to the PDMS film using a micro-nozzle. Next, microfluidic channels are fabricated by eluting the caramel sealed inside the PDMS with water vapor. Compared to soft lithography, which is an existing method, this method does not require special equipment, and the fabrication process is simple and quick. Furthermore, it can be applied to the fabrication of microfluidic channels with circular cross-sections. In addition, this method is biocompatible and can be applied to biotechnology and medical fields. The fabrication of circular cross-sectional straight channels with a minimum diameter of 1 µm, 2D-shaped channels with a minimum width of 8 µm, and stereo-crossing channels was achieved using this method.

1. Y. Koyata, M. Ikeuchi and K. Ikuta, "Sealless 3-D microfluidic channel fabrication by sacrificial caramel template direct-patterning," 2013 IEEE 26th International Conference on Micro Electro Mechanical Systems (MEMS), 2013, pp. 311-314, doi: 10.1109/MEMSYS.2013.6474240.