The current clinical successes of tissue engineering are limited primarily to low-metabolism, acellular, pre-vascularized or thin tissues. Mass transport has been identified as the primary culprit, limiting the delivery of nutrients (such as oxygen and glucose) and removal of wastes, from tissues deep within a cellular scaffold. While strategies to develop sufficient vasculature to overcome hypoxia in vitro are promising, inconsistencies between the in vitro and the in vivo environments may still negate the effectiveness of large-volume tissue-engineered scaffolds. While a common theme in tissue engineering is to maximize oxygen supply, studies suggest that moderate oxygenation of cellular scaffolds during in vitro conditioning is preferable to high oxygen levels. Aiming for moderate oxygen values to prevent hypoxia while still promoting angiogenesis may be obtained by tailoring in vitro culture conditions to the oxygen environment the scaffold will experience upon implantation. This review discusses the causes and effects of tissue-engineering hypoxia and the optimization of oxygenation for the minimization of in vivo hypoxia.

A consensus is lacking whether monochromatic rather than broad-spectrum illumination is more efficient for photosynthetic microbe production platforms. Light wavelength and intensity were tuned to pigment composition for growth of the Cyanobacterium Synechocystis PCC 6803. Phycocyanin (PC)-targeting LEDs (620nm) provided more than 6times the peak efficiency of white LEDs, with peak efficiency growth rates of 0.063h(-1) at 81μEm(-2)s(-1) and 0.039h(-1) at 126μEm(-2)s(-1) for red and white LEDs, respectively. Chlorophyll a (Chl a)-targeting LEDs (680- and 440-nm) performed poorly. Indeed, 10 times greater mass abundance was observed for PC than Chl a. PC levels did not change while Chl a levels decreased when Synechocystis transitioned from white light at 50μEm(-2)s(-1) to 250μEm(-2)s(-1) with 620nm, 680nm, or white LEDs. This work demonstrates that light wavelengths and intensity need to be optimized for each strain.

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