Knowledge on the availability of dissolved oxygen inside microfluidic cell culture systems is vital for recreating physiological-relevant microenvironments and for providing reliable and reproducible measurement conditions. It is important to highlight that in vivo cells experience a diverse range of oxygen tensions depending on the resident tissue type, which can also be recreated in vitro using specialized cell culture instruments that regulate external oxygen concentrations. While cell-culture conditions can be readily adjusted using state-of-the-art incubators, the control of physiological-relevant microenvironments within the microfluidic chip, however, requires the integration of oxygen sensors. Although several sensing approaches have been reported to monitor oxygen levels in the presence of cell monolayers, oxygen demands of microfluidic three-dimensional (3D)-cell cultures and spatio-temporal variations of oxygen concentrations inside two-dimensional (2D) and 3D cell culture systems are still largely unknown. To gain a better understanding on available oxygen levels inside organ-on-a-chip systems, we have therefore developed two different microfluidic devices containing embedded sensor arrays to monitor local oxygen levels to investigate (i) oxygen consumption rates of 2D and 3D hydrogel-based cell cultures, (ii) the establishment of oxygen gradients within cell culture chambers, and (iii) influence of microfluidic material (e.g., gas tight vs. gas permeable), surface coatings, cell densities, and medium flow rate on the respiratory activities of four different cell types. We demonstrate how dynamic control of cyclic normoxic-hypoxic cell microenvironments can be readily accomplished using programmable flow profiles employing both gas-impermeable and gas-permeable microfluidic biochips.

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Physiological‐relevant in vitro tissue models with their promise of better predictability have the potential to improve drug screening outcomes in preclinical studies. Despite the advances of spheroid models in pharmaceutical screening applications, variations in spheroid size and consequential altered cell responses often lead to nonreproducible and unpredictable results. Here, a microfluidic multisize spheroid array is established and characterized using liver, lung, colon, and skin cells as well as a triple‐culture model of the blood‐brain barrier (BBB) to assess the effects of spheroid size on (a) anticancer drug toxicity and (b) compound penetration across an advanced BBB model. The reproducible on‐chip generation of 360 spheroids of five dimensions on a well‐plate format using an integrated microlens technology is demonstrated. While spheroid size‐related IC50 values vary up to 160% using the anticancer drugs cisplatin (CIS) or doxorubicin (DOX), reduced CIS:DOX drug dose combinations eliminate all lung microtumors independent of their sizes. A further application includes optimizing cell seeding ratios and size‐dependent compound uptake studies in a perfused BBB model. Generally, smaller BBB‐spheroids reveal an 80% higher compound penetration than larger spheroids while verifying the BBB opening effect of mannitol and a spheroid size‐related modulation on paracellular transport properties.

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Reengineering functional vascular networks remains an integral part in tissue engineering, since the incorporation of non-perfused tissues results in restricted nutrient supply and limited waste removal. Microfluidic devices are routinely used to mimic both physiological and pathological vascular microenvironments. Current procedures either involve the investigation of growth factor gradients and interstitial flow on endothelial cell sprouting alone or on the heterotypic cell-cell interactions between endothelial and mural cells. However, limited research has been conducted on the influence of flow on co-cultures of these cells. Here, we exploited the ability of microfluidics to create and monitor spatiotemporal gradients to investigate the influence of growth factor supply and elution on vascularization using static as well as indirect and direct flow setups. Co-cultures of human adipose-derived stem/stromal cells and human umbilical vein endothelial cells embedded in fibrin hydrogels were found to be severely affected by diffusion limited growth factor gradients as well as by elution of reciprocal signaling molecules during both static and flow conditions. Static cultures formed pre-vascular networks up to a depth of 4 mm into the construct with subsequent decline due to diffusion limitation. In contrast, indirect flow conditions enhanced endothelial cell sprouting but failed to form vascular networks. Additionally, complete inhibition of pre-vascular network formation was observable for direct application of flow through the hydrogel with decline of endothelial cell viability after seven days. Using finite volume CFD simulations of different sized molecules vital for pre-vascular network formation into and out of the hydrogel constructs, we found that interstitial flow enhances growth factor supply to the cells in the bulk of the chamber but elutes cellular secretome, resulting in truncated, premature vascularization.

The in vitro study aimed at the determination of the bacterial reduction in root canals used pulsed Nd:YAG laser radiation without a photosensitizing dye. In addition the temperature change in the root canals was determined during laser irradiation. The study sample was 114 root canals of extracted single-rooted human teeth that have been enlarged mechanically, sterilized, and randomly assigned to two experimental units. The source of radiation was a Nd:YAG laser device emitting pulsed infrared radiation at a wavelength of 1.064 microm, a pulse duration of 100 micros, and a pulse repetition rate of 20 pps. Samples of each experimental unit were inoculated with Escherichia coli (ATCC 25922) or Staphylococcus aureus (ATCC 25923), respectively, and divided into subgroups of 13 teeth each for irradiation for 20 s at 100 mJ or 200 mJ. One subgroup was left untreated as positive control and one subgroup was rinsed with 0.5 ml of sodium hypochloride. After laser treatment or rinsing with sodium hypochloride the number of bacteria in each root canal was determined using the surface spread plate technique. Statistical analysis of the results was performed with ANOVA and Scheffé test at a level of significance of 5% (p < 0.05). In case of E. coli the number of bacteria was reduced from 8.67 x 10(6) (+/-4.11 x 10(5)) colony-forming units (CFU)/ml to 4.39 x 10(4) (+/-1.72 x 10(4)) CFU/ml after laser radiation at 200 mJ. Regarding S. aureus the number of bacteria decreased from 1.44 x 10(6) (+/-1.59 x 10(5)) CFU/ml to 3.8 x 10(4) (+/-1.06 x 10(4)) CFU/ml at a radiation energy of 200 mJ. Rinsing with sodium hypochloride reduced the number of bacteria to 1.03 x 10(3) (+/-4.02 x 10(2)) CFU/ml regarding E. coli and to 1.84 x 10(3) (+/-7.4 x 10(2)) CFU/ml in case of S. aureus. The temperature increase at 100 mJ was 24.3 degrees C (+/-3.9) and that at 200 mJ was 61.8 degrees C (+/-4.2). The Nd:YAG laser radiation has antimicrobial effects in root canals even in the absence of photosensitizing dyes but also causes considerable temperature increase.

Each year, combustion at municipal solid waste incineration (MSWI) plants produces millions of tons of fly ash globally. This ash is characterized as a hazardous material and is mostly placed in landfills after a stabilization process or stored in hazardous waste sites. Thus, disposal of fly ash leaves a considerable social and environmental footprint and leads to high waste management costs. Thermochemical energy storage (TCES) systems are considered to be outstanding because of their high-energy density and near-zero energy loss over long periods of time. Calcium oxide (CaO), a main MSWI fly ash component, is a promising candidate for TCES. In this study, we investigate the potential of fly ash as a TCES material. To do so, we analyzed representative samples from different MSWIs using simultaneous thermal analysis (STA) under N2, CO2, and CO2/H2O atmospheres. These analyses were supported by additional techniques such as X-ray fluorescence (XRF) spectroscopy, inductively coupled plasma-optical emission spectroscopy (ICP-OES), and scanning electron microscopy (SEM). The STA results illustrate fly ash reactivity under different atmospheres. All samples could store heat through endothermic reactions and one sample was able to release stored heat under selected operating conditions. XRF analysis verified an average fly ash composition of 27% CaO, ICP-OES analysis demonstrated the presence of different heavy metals, and SEM analysis revealed the sintering and agglomeration of fly ash particles at high temperatures (1150 °C). This study shows that the use of fly ash as a TCES material is promising and that further investigation in the field is needed to corroborate this application.