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Nutrient and oxygen supply of cells are crucial to tissue engineering in general. If a sufficient supply cannot be maintained, the development of the tissue will slow down or even fail completely. Previous studies on oxygen supply have focused on measurement of oxygen partial pressures (pO(2)) in culture media or described the use of invasive techniques with spatially limited resolution. The experimental setup described here allows for continuous, noninvasive, high-resolution pO(2) measurements over the cross-section of cultivated tissues. Applying a recently developed technique for time-resolved pO(2) sensing using optical sensor foils, containing luminescent O(2)-sensitive indicator dyes, we were able to monitor and analyze gradients in the oxygen supply in a tissue over a 3-week culture period. Cylindrical tissue samples were immobilized on top of the sensors. By measuring the luminescence decay time, two-dimensional pO(2) distributions across the tissue section in contact with the foil surface were determined. We applied this technique to cartilage explants and to tissue-engineered cartilage. For both tissue types, changes were detected in monotonously decreasing gradients of pO(2) from the surface with high pO(2) to minimum pO(2) values in the center of the samples. Nearly anoxic conditions were observed in tissue constructs ( approximately 0 Torr) but not in excised cartilage discs ( approximately 20 Torr) after 1 day. Furthermore, the oxygen supply seemed to strongly depend on cell density and cell function. Additionally, histological analysis revealed a maximum depth of approximately 1.3 mm of regular cartilage development in constructs grown under the applied culture conditions. Correlating analytical and histological analysis with the oxygen distributions, we found that pO(2) values below 11 Torr might impair proper tissue development in the center. The results illustrate that the method developed is an ideal one to precisely assess the oxygen demand of cartilage cultures., (Copyright 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 73-83, 2002.)

Background: Oxygen-dependent quenching of luminescence using transparent planar sensor foils was shown to overcome the limitations of the polarographic electrode technique in an animal model. This method was then transferred to a clinical setting to measure the transcutaneous pO2 (ptcO2). Methods: In six healthy subjects, a cuff on the upper arm was occluded up to 20 mmHg above systolic pressure and released after 8 min. PtcO2 was measured at the lower arm every 30 s before, during, and up to 20 min after cuff occlusion (40 °C applied skin temperature) using luminescence lifetime imaging (LLI) of platinum(II)-octaethyl-porphyrin immobilized in a polystyrene matrix. For validation, the polarographic Clark electrode technique was applied in close proximity, and measurements were conducted simultaneously. Results: PtcO2 measurements before (70.8±19.1 vs. 66.2±7.7 mmHg) and at the end of ischemic (2.7±1.2 vs. 3.6±1.7 mmHg) and reperfusion phases (72.2±3.6 vs. 68.4±8.9 mmHg) did not differ significantly using the Clark electrode vs. LLI. At both the initial ischemic and the reperfusion phases, the Clark electrode measured a faster decrease or increase, respectively, in ptcO2 because of the oxygen consumption occurring in this method. Conclusion: The presented method provides accurate and reproducible ptcO2 values under changing microcirculatory conditions. The lack of oxygen consumption during measurement allows both a more realistic estimation of ptcO2 than compared with the gold standard and permanent use in regions with critical oxygen supply. [ABSTRACT FROM AUTHOR]

Objective: Oxygen-dependent quenching of luminescence of metal porphyrin complexes has been used to image the p O 2 distribution over tumor and normal tissue. Methods: An experimental setup is described using a platinum(II)–octaethyl–porphyrin immobilized in a polystyrene matrix as transparent planar sensor. Results: Sensitivity over a broad range is high at low p O 2 values (± 0.2 mm Hg at 0 mm Hg; ± 1.5 mm Hg at 160 mm Hg p O 2 ). Due to intrinsically referencing via lifetime encoding there was no modification of the sensor response in vivo in the dorsal skinfold chamber model with amelanotic melanoma (A-MEL-3) in awake hamsters when compared to the in vitro calibration. p O 2 measurements over normal tissue (25.8 ± 5.1 mm Hg) and tumor tissue (9.2 ± 5.1 mm Hg) were in excellent agreement with previous results obtained in this model using a surface multiwire electrode. Conclusions: Using the presented method the surface p O 2 distribution can be mapped with a high temporal resolution of approximately 100 ms and a spatial resolution of at least 25 μ m. Moreover, the transparent sensor allows the simultaneous visualization of the underlying microvasculature. [ABSTRACT FROM AUTHOR]