Traumatic brain injury (TBI) is often accompanied by hemorrhage, and treatment of hemorrhagic shock (HS) after TBI is particularly challenging because the two therapeutic treatment strategies for TBI and HS often conflict. Ischemia/reperfusion injury from HS resuscitation can be exaggerated by TBI-induced loss of autoregulation. In HS resuscitation, the goal is to restore lost blood volume, while in the treatment of TBI the priority is focused on maintenance of adequate cerebral perfusion pressure and avoidance of secondary bleeding. In this study, we investigate the responses to resuscitation from severe HS after TBI in rats, using fresh blood, polymerized human hemoglobin (PolyhHb), and lactated Ringer’s (LR). Rats were subjected to TBI by pneumatic controlled cortical impact. Shortly after TBI, HS was induced by blood withdrawal to reduce mean arterial pressure (MAP) to 35–40 mmHg for 90 min before resuscitation. Resuscitation fluids were delivered to restore MAP to ~ 65 mmHg and animals were monitored for 120 min. Increased systolic blood pressure variability (SBPV) confirmed TBI-induced loss of autoregulation. MAP after resuscitation was significantly higher in the blood and PolyhHb groups compared to the LR group. Furthermore, blood and PolyhHb restored diastolic pressure, while this remained depressed for the LR group, indicating a loss of vascular tone. Lactate increased in all groups during HS, and only returned to baseline level in the blood reperfused group. The PolyhHb group possessed lower SBPV compared to LR and blood groups. Finally, sympathetic nervous system (SNS) modulation was higher for the LR group and lower for the PolyhHb group compared to the blood group after reperfusion. In conclusion, our results suggest that PolyhHb could be an alternative to blood for resuscitation from HS after TBI when blood is not available, assuming additional testing demonstrate similar favorable results. PolyhHb restored hemodynamics and oxygen delivery, without the logistical constraints of refrigerated blood.

To understand how the microvasculature grows and remodels, researchers require reproducible systems that emulate the function of living tissue. Innovative contributions toward fulfilling this important need have been made by engineered microvessels assembled in vitro using microfabrication techniques. Microfabricated vessels, commonly referred to as "vessels on a chip," are from a class of cell culture technologies that uniquely integrate microscale flow phenomena, tissue-level biomolecular transport, cell-cell interactions, and proper 3-D extracellular matrix environments under well-defined culture conditions. Here, we discuss the enabling attributes of microfabricated vessels that make these models more physiological compared to established cell culture techniques, and the potential of these models for advancing microvascular research. This review highlights the key features of microvascular transport and physiology, critically discusses the strengths and limitations of different microfabrication strategies for studying the microvasculature, and provides a perspective on current challenges and future opportunities for vessel on a chip models.

Hepatic hollow fiber (HF) bioreactors can be used to provide temporary support to patients experiencing liver failure. Before being connected to the patient's circulation, cells in the bioreactor must be exposed to a range of physiological O 2 concentrations as observed in the liver sinusoid to ensure proper performance. This zonation in cellular oxygenation promotes differences in hepatocyte phenotype and may better approximate the performance of a real liver within the bioreactor. Polymerized human hemoglobin (PolyhHb) locked in the tense quaternary state (T-state) has the potential to both supply and regulate O 2 transport to cultured hepatocytes in the bioreactor due to its low O 2 affinity. In this study, T-state PolyhHb production and purification processes were optimized to minimize the concentration of low-molecularweight PolyhHb species in solution. Deconvolution of size-exclusion chromatography spectra was performed to calculate the distribution of polymeric Hb species in the final product. Fluid flow and mass transport within a single fiber of a hepatic HF bioreactor was computationally modeled with finite element methods to simulate the effects of employing T-state PolyhHb to facilitate O 2 transport in a hepatic bioreactor system. Optimal bioreactor performance was defined as having a combined hypoxic and hyperoxic volume fraction in the extracapillary space of less than 0.05 where multiple zones were observed. The Damköhler number and Sherwood number had strong inverse relationships at each cell density and fiber thickness combination. These results suggest that targeting a specific Damköhler number may be beneficial for optimal hepatic HF bioreactor operation. K E Y W O R D S fluid flow modeling, hemoglobin-based oxygen carrier, hollow fiber bioreactor, polymerized human hemoglobin, red blood cell substitute

Hemorrhagic Shock (HS) after Traumatic Brain Injury (TBI) is common and lethal among military and civilians. Blood transfusion has been the resuscitation gold standard procedure for many years. However, only 3% of age‐eligible individuals donate blood, which limits blood availability and cannot meet current blood demands. This study was compared the efficacy to resuscitate from HS after TBI via infusion of Lactated Ringer’s solution (LR, electrolyte solution used to restore the loss of blood volume), fresh blood (Blood, autologous blood drawn during the hemorrhage), or Polymerized Hemoglobin [PolyHb, a Hemoglobin Based Oxygen Carrier (HBOC) that shows promise in increasing oxygenation]. Fifteen Wistar rats (350–400g) were instrumented with catheters in the femoral artery and vein and subjected to TBI through a pneumatic controlled cortical impact (CCI) (Leica Biosystems, Vista, CA). To induce TBI, a 5mm craniotomy over the right cerebral cortex was performed, and the scalp was impacted at a velocity of 5m/s and dwell time of 200ms. The scalp was subsequently closed and animals were given 10 min to stabilize before performing HS. HS was induced by blood withdrawal from the femoral artery catheter to achieve a mean arterial pressure (MAP) between 35–40mmHg, and the hypotensive state was maintained for 90 min before resuscitation. Animals were separated into 3 groups based on the resuscitation solution: Blood, LR, or PolyHb. Animals were monitored for an additional 120 min before euthanasia. Measurements were taken at baseline (BL), 90 min into HS (HS), and 30 min (R1) and 2 hours (R2) after resuscitation. The MAP, systolic blood pressure (SBP), and diastolic blood pressure (DBP) were decreased equally in all groups during HS. Blood and PolyHb groups increased MAP compared to the LR group at R1. The MAP was not different between Blood and PolyHb at R2. The SBP was increased only for the Blood group as compared to the LR group at R1. Moreover, DBP was increased for both Blood and PolyHb compared to the LR group at R1 and R2. As expected, hematocrit decreased in all groups after HS, with only the Blood group recovering hematocrit after resuscitation. Total hemoglobin (tHb) decreased after HS, and increased after resuscitation for the Blood and PolyHb groups but not in the LR group. Oxygen saturation was decreased for the Blood and PolyHb groups compared to the LR group at R1 and R2. The oxygen saturation was increased on the Blood group compared to PolyHb group at R2. After HS all groups increased lactate, after R1 just Blood and LR group recovered lactate to BL levels, and PolyHb did not decreased lactate concentration at R2 compared to the blood group. In conclusion, our results show that PolyHb was effective to resuscitation from HS after TBI, restoring blood pressure similarly to Blood group and could be a good alternative to transfusion for field resuscitation from HS after TBI. Support or Funding Information This work was supported by the NIH Heart Lung and Blood Institute under Grant, R01‐HL126945, and the DOD ...

The need for alternatives to allogeneic red blood cells (RBCs) for transfusion medicine has been recognized for more than a century. Large molecular size polymerized human hemoglobin (Hb) (PolyhHb) is a Hb based oxygen (O2) carrier (HBOC) recently evaluated with promising results in efficient O2 delivery and minimal toxicity. Despite significant commercial development, late stage clinical results of HBOC solutions hampered development. To evaluate the safety of PolyhHb as an O2 therapeutic agent in a vulnerable population, the present study was performed in a guinea pigs subjected to a high fat and high sucrose diet (HDHS). This model mimics human dyslipidemia and potentially induces endothelial dysfunction (ED). The objective of this study was to evaluate the impact of large molecular size PolyhHb on cardiovascular function in guinea pigs with dyslipidemia. Animals weighing between 150–200 g were fed a HDHS for 12 weeks. The metabolic characterization of the model included glucose tolerance testing (GTT) and measurement of the lipid profile. After metabolic characterization, the carotid artery and jugular vein were catheterized and catheters were exteriorized dorsally. Then, PolyhHb (n = 5) was subjected to a 20% blood volume (BV) exchange‐transfusion (BV estimated as 7.5% of body weight) with PolyhHb at 10 g/dL. Sham (n = 5) was subjected to the same procedure, but no exchange transfusion was performed. Post exchange, the animals were allowed to recover for 24 hours, after which blood pressure (BP) and heart rate (HR) were recorded, and BP and HR variability (HRV) were evaluated by spectral analysis. Animals were subjected to a sequence of vasoactive drugs to evaluate their baroreflex (phenylephrine, sodium nitroprusside, 1 and 2 ug), endothelial function (acethocoline (ACH), 2 and 4 ug), and nitric oxide response (Nitro‐L‐arginine methyl ester (L‐NAME), 12 mg/kg). Animals presented glucose intolerance and dyslipidemia. PolyhHb induced an 18% increase in MAP 24 hours after exchange‐transfusion. PolyhHb showed a decreased response to L‐NAME, suggesting a deficiency in nitric oxide (NO) dependent regulation of vascular tone, a known consequence of acellular Hb NO scavenging. There were no differences in baroreflex between groups nor significant endothelial dysfunction for the PolyhHb group compared to the Sham group. An increase in HRV and in sympathetic nervous system (SNS) modulation of the heart (low frequency band, LF) was observed in the PolyhHb group compared to Sham. On the other hand, parasympathetic modulation of the heart (high frequency band, HF) was decreased for the PolyhHb group compared to Sham, culminating in a 2‐fold increase in sympathetic vagal balance. Moreover, BP variability as well as blood vessel SNS modulation was increased for PolyhHb compared to Sham. In conclusion, PolyhHb transfusion impaired the autonomic nervous system in guinea pigs with dyslipidemia. Our results suggest that dyslipidemic patients might be more vulnerable to PolyhHb transfusion side effects. Support or Funding Info...