Variable phase dark-field contrast--a variant illumination technique for improved visualizations of transparent specimens

A bioartificial and vasculomorphic bone matrix-based organoid mimicking microanatomy of flat and short bones

We engineered an in vitro model of bioartificial 3D bone organoid consistent with an anatomical and vascular microenvironment common to mammalian flat and short bones. To achieve this, we chose the decellularized-decalcified matrix of the adult male rat scapula, implemented with the reconstruction of its intrinsic vessels, obtained through an original intravascular perfusion with polylevolactic (PLLA), followed by coating of the PLLA-fabricated vascularization with rat tail collagen. As a result, the 3D bone and vascular geometry of the native bone cortical and cancellous compartments was reproduced, and the rat tail collagen-PLLA biomaterial could in vitro act as a surrogate of the perivascular extracellular matrix (ECM) around the wall of the biomaterial-reconstituted cancellous vessels. As a proof-of-concept of cell compatibility and site-dependent osteoinductive properties of this bioartificial 3D construct, we show that it in vitro leads to a time-dependent microtopographic positioning of rat mesenchymal stromal cells (MSCs), initiating an osteogenic fate in relation to the bone compartment. In addition, coating of PLLA-reconstructed vessels with rat tail collagen favored perivascular attachment and survival of MSC-like cells (mouse embryonic fibroblasts), confirming its potentiality as a perivascular stroma for triggering competence of seeded MSCs. Finally, in vivo radiographic topography of bone lesions in the human jaw and foot tarsus of subjects with primary osteoporosis revealed selective bone cortical versus cancellous involvement, suggesting usefulness of a human 3D bone organoid engineered with the same principles of our rat organoid, to in vitro investigate compartment-dependent activities of human MSC in flat and short bones under experimental osteoporotic challenge. We conclude that our 3D bioartificial construct offers a reliable replica of flat and short bones microanatomy, and promises to help in building a compartment-dependent mechanistic perspective of bone remodeling, including the microtopographic dysregulation of osteoporosis.

Continuous live cell imaging using dark field microscopy

The optical observation of live cell behavior is critical for biological and biomedical studies. The development of techniques for long-term cell and tissue imaging is, however, hindered by phototoxicity induced by excited fluorophores. We, herein, propose a methodology to capture live cell behavior using dark field microscopy (DM). Since the light intensity of DM is merely ∼0.1% of bright-field microscopy (BM) and ∼0.5% of fluorescence microscopy (FM), it allows super long and frequent live cell imaging. Our results demonstrate that continuous exposure to DM light for 48 h brings about no observable effect on the growth rate of 3T3 fibroblasts and HepG2 hepatoma cells, indicating minimum photo-toxicity. Moreover, DM images show contrast comparable to FM, which does not depend on the probes and staining efficiency. We, therefore, conclude that the proposed approach is suitable for long-term live cell imaging with super-high temporal resolution.

Condenser-free contrast methods for transmitted-light microscopy

Phase contrast microscopy allows the study of highly transparent yet detail-rich specimens by producing intensity contrast from phase objects within the sample. Presented here is a generalized phase contrast illumination schema in which condenser optics are entirely abrogated, yielding a condenser-free yet highly effective method of obtaining phase contrast in transmitted-light microscopy. A ring of light emitting diodes (LEDs) is positioned within the light-path such that observation of the objective back focal plane places the illuminating ring in appropriate conjunction with the phase ring. It is demonstrated that true Zernike phase contrast is obtained, whose geometry can be flexibly manipulated to provide an arbitrary working distance between illuminator and sample. Condenser-free phase contrast is demonstrated across a range of magnifications (4–100×), numerical apertures (0.13–1.65NA) and conventional phase positions. Also demonstrated is condenser-free darkfield microscopy as well as combinatorial contrast including Rheinberg illumination and simultaneous, colour-contrasted, brightfield, darkfield and Zernike phase contrast. By providing enhanced and arbitrary working space above the preparation, a range of concurrent imaging and electrophysiological techniques will be technically facilitated. Condenser-free phase contrast is demonstrated in conjunction with scanning ion conductance microscopy (SICM), using a notched ring to admit the scanned probe. The compact, versatile LED illumination schema will further lend itself to novel next-generation transmitted-light microscopy designs. The condenser-free illumination method, using rings of independent or radially-scanned emitters, may be exploited in future in other electromagnetic wavebands, including X-rays or the infrared.

Variable multimodal light microscopy with interference contrast and phase contrast; dark or bright field

Using the optical methods described, specimens can be observed with modified multimodal light microscopes based on interference contrast combined with phase contrast, dark- or bright-field illumination. Thus, the particular visual information associated with interference and phase contrast, dark- and bright-field illumination is joined in real-time composite images appearing in enhanced clarity and purified from typical artefacts, which are apparent in standard phase contrast and dark-field illumination. In particular, haloing and shade-off are absent or significantly reduced as well as marginal blooming and scattering. The background brightness and thus the range of contrast can be continuously modulated and variable transitions can be achieved between interference contrast and complementary illumination techniques. The methods reported should be of general interest for all disciplines using phase and interference contrast microscopy, especially in biology and medicine, and also in material sciences when implemented in vertical illuminators.

Phase contrast without phase plates and phase rings--optical solutions for improved imaging of phase structures

Using the optical methods described, phase specimens can be observed with a modified light microscope in enhanced clarity, purified from typical artifacts which are apparent in standard phase contrast illumination. In particular, haloing and shade-off are absent, lateral and vertical resolution are maximized and the image quality remains constant even in problematic preparations which cannot be well examined in normal phase contrast, such as specimens beyond a critical thickness or covered by obliquely situated cover slips. The background brightness and thus the range of contrast can be continuously modulated and specimens can be illuminated in concentric-peripheral, axial or paraxial light. Additional contrast effects can be achieved by spectral color separation. Normal glass or mirror lenses can be used; they do not need to be fitted with a phase plate or a phase ring. The methods described should be of general interest for all disciplines using phase microscopy.

Variable phase bright-field contrast--an alternative illumination technique for improved imaging in transparent specimens

In variable phase bright-field contrast, a bright-field image based on axial or concentric-peripheral light is optically superimposed with a phase-contrast image, so that typical details that are imminent in one or the other technique contribute to the resulting composite image. In particular, complex structured specimens consisting of high-density light absorbing details and additional low-density phase shifting components can be observed with improved clarity. As both partial images interfere with each other, fine details within thin specimens can be highlighted further by additional contrast effects based on interference. Haloing and shade-off are significantly reduced when compared with phase contrast carried out stand-alone. Our method is characterized by several technical means that are relevant for the high image quality that can be achieved: both illuminating light components associated with bright field and phase contrast are filtered at different colors and separated from each other so that they meet the specimen at different angles of incidence. The intensities of the phase-contrast- and bright-field-producing light can be selectively regulated so that the final image can be dominated by phase contrast or bright field, or be equalized. The condenser aperture diaphragm can be used for modulations of the image's appearance.

Composite imaging method for histological image analysis

A composite imaging method has been developed that enables the user to directly capture a composite image by one-image capturing. It was experimentally verified that the composite images of bright-field, dark-field, and phase-contrast images can be captured with an arbitrary composition ratio. The difference in pixel values between the captured composite image and the computer composite image was small. This imaging method is realized only by placing below the condenser a masking plate, which can easily be made using Neutral Density filters. Therefore, little additional time and cost are needed. The composite imaging method was applied for extracting Helicobacter pylori in microscopic images of HE-stained gastric histological sections. H. pylori is difficult to extract because the colors in H. pylori are similar to those in other areas. It is experimentally shown that a composite image of phase-contrast and dark-field images captured using the proposed method improves the accuracy for extracting H. pylori.

The Micro-Indentation Detection of Multilayer Structured Transparent Film Based on Dark Field Illumination

It is difficult to keep the precise conveyance in film discontinuous winding system, while there are no etch or print marks on the transparent film. Based on dark field illumination theory, a micro-indentation detection method is proposed for multilayer structured transparent film roll-to-roll processing. Two parallel strip lights are involved in the vision system to illuminate the indentation at a low angle, which ensures that the distinct image of the cutting indentation can be obtained in reflection and diffuse homogeneous lights. The measurement of micro-indentations can be used to evaluate the film conveying positioning accuracy and calculate the compensation of film feeding position control. An experiment platform was established to show the efficiency and feasibility of proposed scheme. Experimental results showed that the micro-indentation detection method, based on dark field illumination, is successful to increase the feeding precision of multilayer structured transparent film discontinuous winding system.