An integrated environmental perfusion chamber and heating system for long-term, high resolution imaging of living cells

Automated Multichamber Time-lapse Videography for Long-term In Vivo Observation of Migrating Cells

AIM

To observe and document the migration of living cells by time-lapse videography, we constructed a low-budget system based on a common inverted microscope.

MATERIALS AND METHODS

Long-term observation of six-well plates is enabled through maintenance of cell culture conditions (5% CO₂ in air at 37°C). Points of interest can be revisited in definable intervals with <1 μm repositioning error. Digital photographs from each programmed time point are paired with environmental data and combined into a record.

RESULTS

We used this new chamber to observe the migration of various cell lines. The design represents a good compromise between low cost and good precision. Detailed analyses verified that the environmental conditions were appropriately maintained, enabling long-term observation of viable cells. The stimulating influence of irradiation with photons (radiotherapy) on cellular motility of glioblastoma cells is presented.

CONCLUSION

This study demonstrates that useful videographic systems can be constructed at low cost.

Long-Term Live Cell Imaging of Cell Migration: Effects of Pathogenic Fungi on Human Epithelial Cell Migration

Long-term live cell imaging was used in this study to determine the responses of human epithelial cells to pathogenic biofilms formed by Candida albicans. Epithelial cells of the skin represent the front line of defense against invasive pathogens such as C. albicans but under certain circumstances, especially when the host's immune system is compromised, the skin barrier is breached. The mechanisms by which the fungal pathogen penetrates the skin and invade the deeper layers are not fully understood. In this study we used keratinocytes grown in culture as an in vitro model system to determine changes in host cell migration and the actin cytoskeleton in response to virulence factors produced by biofilms of pathogenic C. albicans. It is clear that changes in epithelial cell migration are part of the response to virulence factors secreted by biofilms of C. albicans and the actin cytoskeleton is the downstream effector that mediates cell migration. Our goal is to understand the mechanism by which virulence factors hijack the signaling pathways of the actin cytoskeleton to alter cell migration and thereby invade host tissues. To understand the dynamic changes of the actin cytoskeleton during infection, we used long-term live cell imaging to obtain spatial and temporal information of actin filament dynamics and to identify signal transduction pathways that regulate the actin cytoskeleton and its associated proteins. Long-term live cell imaging was achieved using a high resolution, multi-mode epifluorescence microscope equipped with specialized light sources, high-speed cameras with high sensitivity detectors, and specific biocompatible fluorescent markers. In addition to the multi-mode epifluorescence microscope, a spinning disk confocal long-term live cell imaging system (Olympus CV1000) equipped with a stage incubator to create a stable in vitro environment for long-term real-time and time-lapse microscopy was used. Detailed descriptions of these two long-term live cell imaging systems are provided.

A Scalable Perfusion Culture System with Miniature Peristaltic Pumps for Live-Cell Imaging Assays with Provision for Microfabricated Scaffolds

We present a perfusion culture system with miniature bioreactors and peristaltic pumps. The bioreactors are designed for perfusion, live-cell imaging studies, easy incorporation of microfabricated scaffolds, and convenience of operation in standard cell culture techniques. By combining with miniature peristaltic pumps—one for each bioreactor to avoid cross-contamination and to maintain desired flow rate in each—we have made a culture system that facilitates perfusion culture inside standard incubators. This scalable system can support multiple parallel perfusion experiments. The major components are fabricated by three-dimensional printing using VeroWhite, which we show to be amenable to ex vivo cell culture. Furthermore, the components of the system can be reused, thus making it economical. We validate the system and illustrate its versatility by culturing primary rat hepatocytes, live imaging the growth of mouse fibroblasts (NIH 3T3) on microfabricated ring-scaffolds inserted into the bioreactor, performing perfusion culture of breast cancer cells (MCF7), and high-magnification imaging of hepatocarcinoma cells (HuH7).

A microfluidic positioning chamber for long-term live-cell imaging

We report a microfluidic positioning chamber (MPC) that can rapidly and repeatedly relocate the same imaging area on a microscope stage. The "roof" of the microfluidic chamber was printed with serials of coordinate numbers that act as positioning marks for mammalian cells that grow attached to the "floor" of the microfluidic chamber. MPC cell culture chamber provided a simple solution for tracking the same cell or groups of cells over days or weeks. The positioning marks were used to register time-lapse images of the same imaging area to single-pixel accuracy. Using MPC cell culture chamber, we tracked the migration, division, and differentiation of individual PC12 cells for over a week using bright field and fluorescence imaging.

Replica-moulded polydimethylsiloxane culture vessel lids attenuate osmotic drift in long-term cell cultures

An imbalance in medium osmolarity is a determinant that affects cell culture longevity. Even in humidified incubators, evaporation of water leads to a gradual increase in osmolarity over time. We present a simple replica-moulding strategy for producing self-sealing lids adaptable to standard, small-size cell-culture vessels. They are made of polydimethylsiloxane (PDMS), a flexible, transparent and biocompatible material, which is gas-permeable but largely impermeable to water. Keeping cell cultures in a humidified 5% CO2 incubator at 37 degrees C, medium osmolarity increased by +6.86 mosmol/kg/day in standard 35 mm Petri dishes, while PDMS lids attenuated its rise by a factor of four to changes of +1.72 mosmol/kg/ day. Depending on the lid membrane thickness,pH drifts at ambient CO2 levels were attenuated by a factor of 4 to 9. Comparative evaporation studies at temperatures below 60 degrees C yielded a 10-fold reduced water vapour flux of 1.75 g/day/ dm 2 through PDMS lids as compared with 18.69 g/day/dm 2 with conventional Petri dishes. Using such PDMS lids,about 2/3 of the cell cultures grew longer than 30 days in vitro. Among these,the average survival time was 69 days with the longest survival being 284 days under otherwise conventional cell culture conditions.

Encapsulated Petri dish system for single-cell drug delivery and long-term time lapse microscopy

We have developed a system that allows focal drug application for cell culture microscopy. Single-cell drug delivery is achieved through the insertion of a patch-clamp-like micropipette in a microenvironment-controlled chamber mounted on a standard 35-mm Petri dish. The system has precise control of temperature, CO(2) concentration, and humidity, while preventing contamination during experiments. The use of standard Petri dishes allows long-term experiments by alternating in situ microscopy with incubator growth. Modern biological long-term experiments such as the characterization of drug effects on cell movement, axonal guidance, mitosis, apoptosis, differentiation, or volume regulation can be performed. The chamber is compatible with any inverted microscope without significant modifications.

Design and construction of a new temperature-controlled chamber for light and confocal microscopy under monitored conditions: biological application for plant samples

A new light microscope-temperature-controlled chamber (LM-TCC) has been constructed. The special feature of the light microscope-temperature-controlled chamber is the Peltier-element temperature control of a specimen holder for biological samples, with a volume capacity of 1 mL. This system has marked advantages when compared to other approaches for temperature-controlled microscopy. It works in a temperature range of -10 degrees C to +95 degrees C with an accuracy of +/-0.1 degrees C in the stationary phase. The light microscope-temperature-controlled chamber allows rapid temperature shift rates. A maximum heating rate of 12.9 degrees C min(-1) and a maximum cooling rate of 6.0 degrees C min(-1) are achieved with minimized overshoots (<or=1.9 degrees C). This machinery operates at low cost and external coolants are not required. Especially with samples absorbing irradiation strongly, temperature control during microscopy is necessary to avoid overheating of samples. For example, leaf segments of Ficaria verna exposed to 4500 micromol photons m(-2) s(-1) in a standard microscopic preparation show a temperature increase (deltaT) of 18.0 degrees C, whereas in the light microscope-temperature-controlled chamber this is reduced to 4 degrees C. The kinetics of microscope-light induced deltaT are described and infrared thermography demonstrates the dissipation of the temperature. Chloroplasts of the cold adapted plant Ranunculus glacialis show the tendency to form stroma-filled protrusions in relation to the exposure temperature. The relative number of chloroplasts with protrusions is reduced at 5 degrees C when compared to 25 degrees C. This effect is reversible. The new light microscope-temperature-controlled chamber will be useful in a wide range of biological applications where a rapid change of temperature during microscopic observations is necessary or has to be avoided allowing a simulation of ecologically relevant temperature scenarios.

Cryoprotectant delivery and removal from murine insulinomas at vitrification-relevant concentrations

Development of optimal cryopreservation protocols requires delivery and removal of cryoprotective agents (CPAs) in such a way that negative osmotic and cytotoxic effects on cells are minimized. This is especially true for vitrification, where high CPA concentrations are employed. In this study, we report on the determination of cell membrane permeability parameters for water (L(p)) and solute (P(s)), and on the design and experimental verification of CPA addition and removal protocols at vitrification-relevant concentrations for a murine insulinoma cell line, betaTC-tet cells. Using membrane permeability values and osmotic tolerance limits, mathematical modeling and computer simulations were used to design CPA addition and removal protocols at high concentrations. The cytotoxic effects of CPAs were also evaluated. Cells were able to tolerate the addition and removal of 2.5M dimethyl sulfoxide (DMSO) and 2.5M 1,2 propanediol (PD) in single steps, but required multi-step addition and removal with 3.0M DMSO, 3.0M PD, and a vitrification-relevant concentration of 3.0M DMSO+3.0M PD. Cytotoxicity studies revealed that betaTC-tet cells were able to tolerate the presence of single component 6.0M DMSO and 6.0M PD and to a lesser extent 3.0M DMSO+3.0M PD. These results determine the time and concentration domain of CPA exposure that cells can tolerate and are essential for designing cryopreservation protocols for free cells as well as cells in engineered tissues.

Perfusion flow bioreactor for 3D in situ imaging: Investigating cell/biomaterials interactions

The capability to image real time cell/material interactions in a three-dimensional (3D) culture environment will aid in the advancement of tissue engineering. This paper describes a perfusion flow bioreactor designed to hold tissue engineering scaffolds and allow for in situ imaging using an upright microscope. The bioreactor can hold a scaffold of desirable thickness for implantation (>2 mm). Coupling 3D culture and perfusion flow leads to the creation of a more biomimetic environment. We examined the ability of the bioreactor to maintain cell viability outside of an incubator environment (temperature and pH stability), investigated the flow features of the system (flow induced shear stress), and determined the image quality in order to perform time-lapsed imaging of two-dimensional (2D) and 3D cell culture. In situ imaging was performed on 2D and 3D, culture samples and cell viability was measured under perfusion flow (2.5 mL/min, 0.016 Pa). The visualization of cell response to their environment, in real time, will help to further elucidate the influences of biomaterial surface features, scaffold architectures, and the influence of flow induced shear on cell response and growth of new tissue.

Chondrocyte intracellular calcium, cytoskeletal organization, and gene expression responses to dynamic osmotic loading

While chondrocytes in articular cartilage experience dynamic stimuli from joint loading activities, few studies have examined the effects of dynamic osmotic loading on their signaling and biosynthetic activities. We hypothesize that dynamic osmotic loading modulates chondrocyte signaling and gene expression differently than static osmotic loading. With the use of a novel microfluidic device developed in our laboratory, dynamic hypotonic loading (−200 mosM) was applied up to 0.1 Hz and chondrocyte calcium signaling, cytoskeleton organization, and gene expression responses were examined. Chondrocytes exhibited decreasing volume and calcium responses with increasing loading frequency. Phalloidin staining showed osmotic loading-induced changes to the actin cytoskeleton in chondrocytes. Real-time PCR analysis revealed a stimulatory effect of dynamic osmotic loading compared with static osmotic loading. These studies illustrate the utility of the microfluidic device in cell signaling investigations, and their potential role in helping to elucidate mechanisms that mediate chondrocyte mechanotransduction to dynamic stimuli.

A biocompatible micro cell culture chamber (microCCC) for the culturing and on-line monitoring of eukaryote cells

We have previously shown that a polymeric (PMMA) chip with medium perfusion and integrated heat regulation provides sufficiently precise heat regulation, pH-control and medium exchange to support cell growth for weeks. However, it was unclear how closely the cells cultured in the chip resembled cells cultured in the culture flask. In the current study, gene expression profiles of cells cultured in the chip were compared with gene expression profiles of cells cultured in culture flasks. The results showed that there were only two genes that were differently expressed in cells grown in the cell culture chip compared to cell culture flasks. The cell culture chip could without further modification support cell growth of two other cell lines. Light coming from the microscope lamp during optical recordings of the cells was the only external factor identified, that could have a negative effect on cell survival. Low grade light exposure was however compatible with optical recordings as well as cell viability. These results strongly indicate that a cell culture chip could be constructed that allowed for on-line optical recording of cellular events without affecting the cell culturing condition compared to cell cultured in culture flasks incubated in a dark and CO2 conditioned incubator.

The influence of the pericellular microenvironment on the chondrocyte response to osmotic challenge

OBJECTIVE

To examine whether differences in the pericellular microenvironment of different chondron preparations influence the chondrocyte volume regulatory response to experimental osmotic challenge.

DESIGN

Mechanically extracted chondrons (MC), enzymatically extracted chondrons (EC) and isolated chondrocytes (IC) were seeded into agarose and sampled at 1, 3 and 7 days. Samples mounted in a perfusion chamber were subjected to osmotic challenge. The cross-sectional areas of the chondrocyte and pericellular microenvironment were measured under isotonic, hypertonic and hypotonic conditions, and percentage change calculated. Separate samples were immunolabeled for type VI collagen and keratan sulfate.

RESULTS

Initially, the microenvironment of MC represented 60% of the chondron area and was occupied by type VI collagen and keratan sulfate. In EC, the microenvironment comprised 18% of the chondron area with narrow bands of type VI collagen and keratan sulfate. IC had no visible microenvironment, with small amounts of type VI collagen and keratan sulfate present. All preparations sequestered additional pericellular macromolecules during culture. Under isotonic conditions, the EC and IC chondrocytes were larger than those of MC. All chondrocytes shrank under hypertonic conditions and swelled under hypotonic conditions. MC were the least responsive, displaying the most efficient volume regulation. IC showed the largest response initially but this decreased with time. EC exhibited intermediate responses that decreased as the microenvironment increased in size.

CONCLUSIONS

The composition and structural integrity of the pericellular microenvironment do influence the cellular response to experimental osmotic challenge. This suggests that the microenvironment functions in situ to mediate the chondrocyte response to physicochemical changes associated with joint loading.