We present a combined experimental and theoretical study of the trajectory of a large solid cylindrical disc suspended within a fluid-filled rotating cylindrical vessel. The experimental set-up is relevant to tissue-engineering applications where a disc-shaped porous scaffold is seeded with cells to be cultured, placed within a bioreactor filled with nutrient-rich culture medium, which is then rotated in a vertical plane to keep the growing tissue construct suspended in a state of "free fall." The experimental results are compared with theoretical predictions based on the model of Cummings and Waters (2007), who showed that the suspended disc executes a periodic motion. For anticlockwise vessel rotation three regimes were identified: (i) disc remains suspended at a fixed position on the right-hand side of the bioreactor; (ii) disc executes a periodic oscillatory motion on the right-hand side of the bioreactor; and (iii) disc orbits the bioreactor. All three regimes are captured experimentally, and good agreement between theory and experiment is obtained. For the tissue engineering application, computation of the fluid dynamics allows the nutrient concentration field surrounding a tissue construct (a property that cannot be measured experimentally) to be determined (Cummings and Waters, 2007). The implications for experimental cell-culture protocols are discussed.

Bioreactor systems that maintain cells and tissues in suspension are increasingly popular for culturing 3D constructs to avoid the loss of in vivo cell function associated with traditional 2D culture methods. There is a need for the online monitoring of such systems to provide better understanding and control of the processes involved and to prevent the disruption of these processes caused by offline sampling and endpoint analysis. We describe a system for the imaging and analysis of cell aggregation, over long periods, within a high aspect rotating vessel (HARV). The system exploits side illumination, using an adjustable beam pattern, to restrict the detected light to that scattered by the cell aggregates, thus eliminating the need for the fluorescent labeling of the cells. The in situ aggregation of mammalian cells (MCF-7 breast carcinoma cells) was monitored over an 8 h period and image sequences showing the growth and motion of the aggregates within the bioreactor were obtained. Detailed size and population data have been derived characterizing the development of the aggregates during this time. We show how the number of resolvable aggregates increases to reach a peak and then declines as these aggregates merge. Once formed, remaining aggregates are found to consolidate to form more tightly packed bodies, typically reducing in cross-sectional area by one third. These results provide the basis for the development of an automated feedback system to control the growth of 3D cell cultures for repeatable, reliable, and quality controlled experimentation.

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We describe a wide field phase sensitive confocal microscope based on correlation between speckles. In this system, parallel optical phase stepping provides for the simultaneous capture of four interferograms using a single camera, giving the system the potential to operate at high speed. The interferograms are mapped to a common frame of reference, removing any relative distortion in the process, so that phase, amplitude, and interference efficiency images can be obtained. We use a new phase stepping algorithm that accounts for the unequal phase steps and unbalanced beam amplitudes that are a consequence of the optical arrangement. Experimental results to show that the system operates as a wide field amplitude and phase confocal system are presented.

A new scanning common-path interferometric profiler capable of absolute-phase measurement is described. The key element is a computer-generated hologram, which acts as the beam-splitting element. Unlike most absolute phase systems, it can be made entirely common path with respect to piston microphonics and is thus exceptionally stable. In addition to operating in scanning mode, the optical configuration permits simultaneous operation as a single-shot phase measuring interferometer and is thus capable of simultaneous form and texture measurements. The operation and stability of the scanning profiler are demonstrated experimentally.