Microfluidic laminate-based phantom for diffusion tensor-magnetic resonance imaging (DT-MRI).

This paper reports fabrication of a magnetic resonance imaging (MRI) phantom created by stacking of multiple thin polydimethylsiloxane (PDMS) layers. PDMS is spin coated on SU-8 molds to obtain the desired layer thickness and imprints of the microchannel patterns that define the phantom geometry. This paper also identifies the unique challenges related to the fabrication and assembly of multiple thin layers and reports for the first time assembly of a large number of thin laminates of this nature. Use of photolithography techniques allows us to create a wide range of phantom geometries. The target dimensions of the phantoms reported here are (i) a stack of 30 thin PDMS layers of 10 µm thickness (ii) curved 5 µm × 5 µm microchannels with 8.7 µm spacing, and (iii) straight 5 µm × 5 µm microchannels with 3.6 µm spacing. SEM scans of the assembled phantoms show open microchannels and a monolithic cross-section with no visible interface between PDMS layers. Based on the results of diffusion tensor magnetic resonance imaging (DT-MRI) scan, the anisotropic diffusion of water molecules due to the physical restriction of the microchannels was detected, which means that the phantom can be used to calibrate and optimize MRI instrumentation.

Maximizing Fibroblast Adhesion on Protein-Coated Surfaces Using Microfluidic Cell Printing.

translation of in vitro cell based assays to in vivo cellular response is imprecise at best. The advent of three-dimensional cell cultures in addition to bioreactor type microfluidics has improved the situation. However, these technical advances cannot be easily combined due to practical limitations. Development of a vertical microfluidic cell printer overcomes this obstacle, providing the ability to more closely recapitulate complex cellular environments and responses. As a proof of concept, we investigated the adhesion of fibroblasts under flow on protein-coated surfaces using a novel vertical microfluidic print head to isolate and manipulate both mechanical and biological factors as a model of fibroblast behavior during the foreign body response following implant insertion. A low flow rate with larger microfluidic channels onto a serum-coated surface has been determined to allow the highest density of viable fibroblasts to attach to the surface. While these insights into fibroblast surface attachment may lead to better material designs, the methods developed herein will certainly be useful as a biomaterials testing platform.

A micromachined electrical field-flow fractionation (mu-EFFF) system.

In this work, micromachining technologies are employed to develop a miniaturized electrical field-flow fractionation (EFFF) separation system. EFFF systems are used to separate colloidal particles such as cells, liposomes, proteins, or other particulates, and to characterize emulsions and other mixtures according to particle charge density. Macromachining techniques have been used to develop existing EFFF technologies. At the present time, the limiting factor in the development of higher precision EFFF separation systems has been the manufacturing approach. In this paper, the theory behind the operation and resolution of a micron-sized EFFF (mu-EFFF) system is described and the advantages to be gained from application of micromachining technologies are given, thus motivating the need for further miniaturization. A completely fabricated mu-EFFF system is developed, separations are performed, and the mu-EFFF system is compared to the theoretically predicted results as well as the results from current macro EFFF systems.

Geometric scaling effects in electrical field flow fractionation. 1. Theoretical analysis.

This work outlines the fundamental scaling laws associated with electrical field flow fractionation channels. Although general FFF theory indicates few advantages from miniaturization, EFFF theory indicates clear advantages to miniaturization of the EFFF channel. Retention, plate heights, resolution, equilibration times, and time constants are examined. The outlined theory predicts scaling advantages in each of these areas after miniaturization. Potential applications, such as the use of these systems for sample preparation in microscale total analysis systems, and improvements associated with these theoretical predictions are also discussed.