Three-dimensional (3D) bioprinting of hydrogel-based constructs at adequate consistency and reproducibility can be obtained through a compromise between the hydrogel's inherent instability and printing fidelity.There is an increasing demand to develop bioprinting modalities that enable high-fidelity fabrication of 3D hydrogel structures that closely correspond to the envisioned design. In this work, we performed a systematic, in-depth characterization and optimization of embedded 3D bioprinting to create 3D gelatin-methacryloyl (gelMA) structures with highly controlled fidelity using Carbopol as suspension bath. The role of various embedded printing process parameters in bioprinting fidelity was investigated using a combination of experimental and theoretical approaches. We examined the effect of rheological properties of gelMA and Carbopol at varying concentrations, as well as printing conditions on the volumetric flow rate of gelMA bioink. Printing speed was examined and optimized to successfully print gelMA into the support bath at varying Carbopol concentrations. Printing fidelity was characterized in terms of printed strand diameter, uniformity, angle, and area. The optimal Carbopol solution that retained filament shape at highest fidelity was determined. The efficacy of developed bioprinting approach was then demonstrated by fabricating 3D hydrogel constructs with varying geometries and visualized using an advanced synchrotron-based imaging technique. We also investigated the influence of the Carbopol medium on cross-linking and the resulting stiffness of gelMA constructs. Finally, in vitro cytotoxicity of the developed bioprinting approach was assessed by printing human umbilical vein endothelial cells encapsulated in the gelMA bioink. These results demonstrate the significance of the close interplay between bioink−support bath rheology and printing parameters and help to establish an optimized workflow for creating 3D hydrogel structures with high fidelity and cytocompatibility via embedded bioprinting techniques. This robust platform could further expand the application of bioprinted soft tissue constructs in a wide variety of biomedical applications.

Using an approach that emphasizes early complete unifocalization and repair with incorporation of all pulmonary vascular supply, we have achieved excellent results in patients with both native and previously operated tetralogy of Fallot and major aortopulmonary collateral arteries.

Bauser-Heaton HD, Bohlen HG. Cerebral microvascular dilation during hypotension and decreased oxygen tension: a role for nNOS. Am J Physiol Heart Circ Physiol 293: H2193-H2201, 2007. First published July 13, 2007; doi:10.1152/ajpheart.00190.2007 and neuronal nitric oxide synthase (nNOS) are implicated as important contributors to cerebral vascular regulation through nitric oxide (NO). However, direct in vivo measurements of NO in the brain have not been used to dissect their relative roles, particularly as related to oxygenation of brain tissue. We found that, in vivo, rat cerebral arterioles had increased NO concentration ([NO]) and diameter at reduced periarteriolar oxygen tension (PO 2) when either bath oxygen tension or arterial pressure was decreased. Using these protocols with highly selective blockade of nNOS, we tested the hypothesis that brain tissue nNOS could donate NO to the arterioles at rest and during periods of reduced perivascular oxygen tension, such as during hypotension or reduced local availability of oxygen. The decline in periarteriolar PO 2 by bath manipulation increased [NO] and vessel diameter comparable with responses at similarly decreased PO 2 during hypotension. To determine whether the nNOS provided much of the vascular wall NO, nNOS was locally suppressed with the highly selective inhibitor N-(4S)- (4-amino-5-[aminoethyl]aminopentyl)-NЈ-nitroguanidine. After blockade, resting [NO], PO 2, and diameters decreased, and the increase in [NO] during reduced PO 2 or hypotension was completely absent. However, flow-mediated dilation during occlusion of a collateral arteriole did remain intact after nNOS blockade and the vessel wall [NO] increased to ϳ80% of normal. Therefore, nNOS predominantly increased NO during decreased periarteriolar oxygen tension, such as that during hypotension, but eNOS was the dominant source of NO for flow shear mechanisms. nitric oxide; brain; arterioles; in vivo; microelectrode; neuronal nitric oxide synthase SUPPRESSION OF NITRIC OXIDE (NO) formation by an intravascular arginine analog decreases cerebral blood flow by 10 -40% (17,18,40,42). This indicates that a source of NO actively influences cerebral resistance vessels at rest. Furthermore, Jones et al. (25) and Kajita et al. (26) found that, during hypotension, the lower limit of brain blood flow autoregulation was increased to ϳ90 mmHg in the presence of nitroarginine compared with ϳ65 mmHg in the natural state. The observations of reduced resting blood flow and impaired flow autoregulation indicate that NO regulation has important roles in both maintaining brain resting blood flow and dilatory responses to hypotension. These various observations would predict that, when the various NO synthase (NOS) isoforms are inhibited, even a mild reduction in arterial blood pressure would compromise brain blood flow and tissue oxygenation.Exactly how NO mechanisms are involved in brain blood flow regulation are difficult to predict but may involve feedback processes linked to oxygen. In studies of the small int...

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