Despite significant progress in tissue engineering over the last decade, the development of real-time, non-destructive tools for monitoring the development of engineered tissues remains a great challenge. To date, the evaluation of cell proliferation and extracellular matrix production in response to various culture conditions depends upon traditional DNA, RNA and protein analysis which requires extraction of cell components from constructs resulting in loss of tissue morphology and integrity. In this study, we report how optical coherence tomography (OCT) can be exploited to monitor cell profiles in real-time and in a non-destructive manner. Scaffolds made from poly(lactic acid) (PLLA) with various porosities were scanned by OCT. A local porosity analysis method has been developed to quantify the porosity change. The hypothesis is whether the local porosity analysis can correlate with the tissue growth within the scaffold following seeding of the cells within it. Bone cells have been grown in the PLLA scaffolds under different culture conditions. The OCT images of these scaffolds have been collected. It has been found that the porosity of the cultured scaffold-cell constructs reduced under different culture conditions compared to blank scaffolds. A decrease in light penetration depth in OCT images has also been observed. There existed a good relationship between the local porosity and tissue growth. It has been demonstrated that the mean local porosity based on OCT images can become a unique method to correlate and monitor tissue growth.
Whole filed optical coherence microscopy system is used to image the cellular structures of highly scattering, as opposed to relatively transparent, biological tissues. The system used has imaging resolutions of 0.7 x 0.9 microns for axial x transversal directions, respectively, which represents arguably the highest resolution in the OCT filed reported so far, but with the compromise that imaging depth is less than that of the conventional OCT systems. Porcine tissues of articular cartilage and bronchus are used in the experimental demonstrations. Results demonstrate that whole filed OCT is capable of delineating faithfully the cells, nuclei and fiber bundles with an imaging depth up to 0.4 mm. It is envisaged that this technique would have an enormous applications in histopathology and other biological applications.
In the past decade, optical coherence tomography (OCT) has achieved a rapid development in clinical applications. Its capability of on-line measurement, non-destructive manner and high spatial resolution offers a great potential for tissue engineering in which the dynamic process of tissue growth need to be monitored on-line either for bulk constructs or at the cellular level. In this study, two OCT systems, time-domain Michelson interferometer based OCT (TD-OCT) and whole field OCT (WF-OCT) have been used to image poly(lactic acid) based scaffold and tissue engineered bone. It is demonstrated that TD-OCT is able to visualize the porous structure of the scaffold and its changes during culture at a macroscopic level, whilst the cells' distribution and morphology can be depicted clearly in WF-OCT. With the aid of an external contrast agent, magnetic beads, clearer cellular images have been obtained.
We present results of studies in embryology and ophthalmology performed using our ultrahigh-resolution full-field OCT system. We also discuss recent developments to our ultrashort acquisition time full-field optical coherence tomography system designed to allow in vivo biological imaging. Preliminary results of high-speed imaging in biological samples are presented. The core of the experimental setup is the Linnik interferometer, illuminated by a white light source. En face tomographic images are obtained in real-time without scanning by computing the difference of two phase-opposed interferometric images recorded by high-resolution CCD cameras. An isotropic spatial resolution of ~1 μm is achieved thanks to the short source coherence length and the use of high numerical aperture microscope objectives. A detection sensitivity of ~90 dB is obtained by means of image averaging and pixel binning. In ophthalmology, reconstructed xz images from rat ocular tissue are presented, where cellular-level structures in the retina are revealed, demonstrating the unprecedented resolution of our instrument. Three-dimensional reconstructions of the mouse embryo allowing the study of the establishment of the anterior-posterior axis are shown. Finally we present the first results of embryonic imaging using the new rapid acquisition full-field OCT system, which offers an acquisition time of 10 μs per frame.
We have developed a white-light interference microscope as an alternative technique to conventional optical coherence tomography (OCT). The experimental setup is based on a Linnik interferometer illuminated with a tungsten halogen lamp. En face tomographic images are obtained in real-time without scanning by computing the difference of two phase-opposed interferometric images recorded by a CCD camera. The short coherence length of the source yields an optical sectioning ability with 0.7 μm resolution (in water). Transverse resolution of 0.9 μm is achieved by using high numerical aperture microscope objectives. A shot-noise limited detection sensitivity of 90 dB can be reached with ~ 1 s acquisition time. High-resolution images of mouse and tadpole embryos are shown.