A Parallelized Pumpless Artificial Placenta System Significantly Prolonged Survival Time in a Preterm Lamb Model

Echocardiographic assessment of cardiovascular physiology of preterm miniature piglets supported with a pumped artificial placenta system

OBJECTIVES

We evaluated fetal cardiovascular physiology and mode of cardiac failure in premature miniature piglets on a pumped artificial placenta (AP) circuit.

METHODS

Fetal pigs were cannulated via the umbilical vessels and transitioned to an AP circuit composed of a centrifugal pump and neonatal oxygenator and maintained in a fluid-filled biobag. Echocardiographic studies were conducted to measure ventricular function, umbilical blood flow, and fluid status. In utero scans were used as control data.

RESULTS

AP fetuses (n = 13; 102±4d gestational age [term 115d]; 616 ± 139 g [g]; survival 46.4 ± 46.8 h) were tachycardic and hypertensive with initially supraphysiologic circuit flows. Increased myocardial wall thickness was observed. Signs of fetal hydrops were present in all piglets. Global longitudinal strain (GLS) measurements increased in the left ventricle (LV) after transition to the circuit. Right ventricle (RV) and LV strain rate decreased early during AP support compared with in utero measurements but recovered toward the end of the experiment. Fetuses supported for >24 h had similar RV GLS to in utero controls and significantly higher GLS compared to piglets surviving only up to 24 h.

CONCLUSIONS

Fetuses on a pump-supported AP circuit experienced an increase in afterload, and redistribution of blood flow between the AP and systemic circulations, associated with elevated end-diastolic filling pressures. This resulted in heart failure and hydrops. These preterm fetuses were unable to tolerate the hemodynamic changes associated with connection to the current AP circuit. To better mimic the physiology of the native placenta and preserve normal fetal cardiovascular physiology, further optimization of the circuit will be required.

Transferring an extremely premature infant to an extra-uterine life support system: a prospective view on the obstetric procedure

To improve care for extremely premature infants, the development of an extrauterine environment for newborn development is being researched, known as Artificial Placenta and Artificial Womb (APAW) technology. APAW facilitates extended development in a liquid-filled incubator with oxygen and nutrient supply through an oxygenator connected to the umbilical vessels. This setup is intended to provide the optimal environment for further development, allowing further lung maturation by delaying gas exposure to oxygen. This innovative treatment necessitates interventions in obstetric procedures to transfer an infant from the native to an artificial womb, while preventing fetal-to-neonatal transition. In this narrative review we analyze relevant fetal physiology literature, provide an overview of insights from APAW studies, and identify considerations for the obstetric procedure from the native uterus to an APAW system. Lastly, this review provides suggestions to improve sterility, fetal and maternal well-being, and the prevention of neonatal transition.

Ethical challenges in first-in-human trials of the artificial placenta and artificial womb: not all technologies are created equally, ethically

Artificial placenta and artificial womb technologies to support extremely premature neonates are advancing toward clinical testing in humans. Currently, no recommendations exist comparing these approaches to guide study design and optimal enrollment eligibility adhering to principles of research ethics. In this paper, we will explore how scientific differences between the artificial placenta and artificial womb approaches create unique ethical challenges to designing first-in-human trials of safety and provide recommendations to guide ethical study design for initial human translation.

Artificial placenta technology: History, potential and perception

As presently conceptualised, the artificial placenta (AP) is an experimental life support platform for extremely preterm infants (i.e. 400-600 g; 21-23+6 weeks of gestation) born at the border of viability. It is based around the oxygenation of the periviable fetus using gas-exchangers connected to the fetal vasculature. In this system, the lung remains fluid-filled and the fetus remains in a quiescent state. The AP has been in development for some sixty years. Over this time, animal experimental models have evolved iteratively from employing external pump-driven systems used to support comparatively mature fetuses (generally goats or sheep) to platforms driven by the fetal heart and used successfully to maintain extremely premature fetuses weighing around 600 g. Simultaneously, sizable advances in neonatal and obstetric care mean that the nature of a potential candidate patient for this therapy, and thus the threshold success level for justifying its adoption, have both changed markedly since this approach was first conceived. Five landmark breakthroughs have occurred over the developmental history of the AP: i) the first human studies reported in the 1950's; ii) foundation animal studies reported in the 1960's; iii) the first extended use of AP technology combined with fetal pulmonary resuscitation reported in the 1990s; iv) the development of AP systems powered by the fetal heart reported in the 2000's; and v) the adaption of this technology to maintain extremely preterm fetuses (i.e. 500-600 g body weight) reported in the 2010's. Using this framework, the present paper will provide a review of the developmental history of this long-running experimental system and up-to-date assessment of the published field today. With the apparent acceleration of AP technology towards clinical application, there has been an increase in the attention paid to the field, along with some inaccurate commentary regarding its potential application and merits. Additionally, this paper will address several misrepresentations regarding the potential application of AP technology that serve to distract from the significant potential of this approach to greatly improve outcomes for extremely preterm infants born at or close to the present border of viability.

Artificial placenta support of extremely preterm ovine fetuses at the border of viability for up to 336 hours with maintenance of systemic circulation but reduced somatic and organ growth

Introduction: Artificial placenta therapy (APT) is an experimental life support system to improve outcomes for extremely preterm infants (EPI) less than 1,000 g by obviating the need for pulmonary gas exchange. There are presently no long-term survival data for EPI supported with APT. To address this, we aimed to maintain 95d-GA (GA; term-150d) sheep fetuses for up to 2 weeks using our APT system. Methods: Pregnant ewes (n = 6) carrying singleton fetuses underwent surgical delivery at 95d GA. Fetuses were adapted to APT and maintained for up to 2 weeks with constant monitoring of key physiological parameters and extensive time-course blood and urine sampling, and ultrasound assessments. Six age-matched in-utero fetuses served as controls. Data were tested for group differences with ANOVA. Results: Six APT Group fetuses (100%) were adapted to APT successfully. The mean BW at the initiation of APT was 656 ± 42 g. Mean survival was 250 ± 72 h (Max 336 h) with systemic circulation and key physiological parameters maintained mostly within normal ranges. APT fetuses had active movements and urine output constantly exceeded infusion volume over the experiment. At delivery, there were no differences in BW (with edema in three APT group animals), brain weight, or femur length between APT and in-utero Control animals. Organ weights and humerus lengths were significantly reduced in the APT group (p < 0.05). Albumin, IGF-1, and phosphorus were significantly decreased in the APT group (p < 0.05). No cases of positive blood culture were detected. Conclusion: We report the longest use of APT to maintain extremely preterm fetuses to date. Fetal systemic circulation was maintained without infection, but growth was abnormal. This achievement suggests a need to focus not only on cardiovascular stability and health but also on the optimization of fetal growth and organ development. This new challenge will need to be overcome prior to the clinical translation of this technology.

The new frontier in ECLS: Artificial placenta and artificial womb for premature infants

Outcomes for extremely low gestational age newborns (ELGANs), defined as <28 weeks estimated gestational age (EGA), remain disproportionately poor. A radical paradigm shift in the treatment of prematurity is to recreate the fetal environment with extracorporeal support and provide an environment for organ maturation using an extracorporeal VV-ECLS artificial placenta (AP) or an AV-ECLS artificial womb (AW). In this article, we will review clinical indications, current approaches in development, ongoing challenges, remaining milestones and ethical considerations prior to clinical translation.

Acute fetal cardiovascular adaptation to artificial placenta in sheep model

OBJECTIVE

To describe the acute cardiovascular adaptation of the fetus after connection to an artificial placenta (AP) in a sheep model, using ultrasound and invasive and non-invasive hemodynamic assessment.

METHODS

This was an experimental study of 12 fetal sheep that were transferred to an AP system, consisting of a pumpless circuit with umbilical cord connection, at 109-117 days' gestation. The study was designed to collect in-utero and postcannulation measurements in all the animals. The first six consecutive fetuses were fitted with intravascular catheters and perivascular probes to obtain invasive physiological data, including arterial and venous intravascular pressures and perivascular blood flows, with measurements taken in utero and at 5 and 30 min after cannulation. These experiments were designed with a survival goal of 1-3 h. The second set of six fetuses were not fitted with catheters, and experiments were aimed at 3-24 h of survival. Echocardiographic assessment of cardiac anatomy and function, as well as measurements of blood flow and pre- and postmembrane pressures recorded by circuit sensors in the AP system, were available for most of the fetuses. These data were acquired in utero and at 30 and 180 min after cannulation.

RESULTS

Compared with in-utero conditions, the pulsatility index at 30 and 180 min after connection to the AP system was reduced in the umbilical artery (median, 1.36 (interquartile range (IQR), 1.06-1.50) vs 0.38 (IQR, 0.31-0.50) vs 0.36 (IQR, 0.29-0.41); P < 0.001 for extreme timepoints) and the ductus venosus (median, 0.50 (IQR, 0.41-0.67) vs 0.29 (IQR, 0.22-0.33) vs 0.36 (IQR, 0.22-0.41); P = 0.011 for extreme timepoints), whereas umbilical venous peak velocity increased (median, 20 cm/s (IQR, 18-22 cm/s) vs 39 cm/s (IQR, 31-43 cm/s) vs 43 cm/s (IQR, 34-54 cm/s); P < 0.001 for extreme timepoints) and flow became more pulsatile. Intravascular monitoring showed that arterial and venous pressures increased transiently after connection, with median values for mean arterial pressure at baseline, 5 min and 30 min of 43 mmHg (IQR, 35-54 mmHg), 72 mmHg (IQR, 61-77 mmHg) and 58 mmHg (IQR, 50-64 mmHg), respectively (P = 0.02 for baseline vs 5 min). Echocardiography showed a similar transient elevation of fetal heart rate at 30 and 180 min after connection compared with in utero (median, 145 bpm (IQR, 142-156 bpm) vs 188 bpm (IQR, 171-209 bpm) vs 175 bpm (IQR, 165-190 bpm); P = 0.001 for extreme timepoints). Fetal cardiac structure and function were mainly preserved; median values for right fractional area change were 36% (IQR, 34-41%) in utero, 38% (IQR, 30-40%) at 30 min and 37% (IQR, 33-40%) at 180 min (P = 0.807 for extreme timepoints).

CONCLUSIONS

Connection to an AP system resulted in a transient fetal hemodynamic response that tended to normalize over hours. In this short-term evaluation, cardiac structure and function were preserved. However, the system resulted in non-physiologically elevated venous pressure and pulsatile flow, which should be corrected to avoid later impairment of cardiac function. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

An Artificial Placenta Experimental System in Sheep: Critical Issues for Successful Transition and Survival up to One Week

Objective: To describe the development of an artificial placenta (AP) system in sheep with learning curve and main bottlenecks to allow survival up to one week. Methods: A total of 28 fetal sheep were transferred to an AP system at 110–115 days of gestation. The survival goal in the AP system was increased progressively in three consecutive study groups: 1–3 h (n = 8), 4–24 h (n = 10) and 48–168 h (n = 10). Duration of cannulation procedure, technical complications, pH, lactate, extracorporeal circulation (EC) circuit flows, fetal heart rate, and outcomes across experiments were compared. Results: There was a progressive reduction in cannulation complications (75%, 50% and 0%, p = 0.004), improvement in initial pH (7.20 ± 0.06, 7.31 ± 0.04 and 7.33 ± 0.02, p = 0.161), and increment in the rate of experiments reaching survival goal (25%, 70% and 80%, p = 0.045). In the first two groups, cannulation accidents, air bubbles in the extracorporeal circuit, and thrombotic complications were the most common cause of AP system failure. Conclusions: Achieving a reproducible experimental setting for an AP system is extremely challenging, time- and effort-consuming, and requires a highly multidisciplinary team. As a result of the learning curve, we achieved reproducible transition and survival up to 7 days. Extended survival requires improving instrumentation with custom-designed devices.

Design and In Vitro Evaluation of an Artificial Placenta Made From Hollow Fiber Membranes

For infants born at the border of viability, care practices and morbimortality rates vary widely between centers. Trends show significant improvement, however, with increasing gestational age and weight. For periviable infants, the goal of critical care is to bridge patients to improved outcomes. Current practice involves ventilator therapy, resulting in chronic lung injuries. Research has turned to artificial uterine environments, where infants are submerged in an artificial amniotic fluid bath and provided respiratory assistance via an artificial placenta. We have developed the Preemie-Ox, a hollow fiber membrane bundle that provides pumpless respiratory support via umbilical cord cannulation. Computational fluid dynamics was used to design an oxygenator that could achieve a carbon dioxide removal rate of 12.2 ml/min, an outlet hemoglobin saturation of 100%, and a resistance of less than 71 mmHg/L/min at a blood flow rate of 165 ml/min. A prototype was utilized to evaluate in-vitro gas exchange, resistance, and plasma-free hemoglobin generation. In-vitro gas exchange was 4% higher than predicted results and no quantifiable plasma-free hemoglobin was produced.

Updates in Neonatal Extracorporeal Membrane Oxygenation and the Artificial Placenta

Extracorporeal life support, initially performed in neonates, is now commonly used for both pediatric and adult patients requiring pulmonary and/or cardiac support. Data suggests the clinical feasibility of Extracorporeal Membrane Oxygenation for premature infants (29-33 weeks estimated gestational age [EGA]). For extremely premature infants less than 28 weeks EGA, an artificial placenta has been developed to recreate the fetal environment. This approach is investigational but clinical translation is promising. In this article, we discuss the current state and advances in neonatal and "preemie Extracorporeal Membrane Oxygenation" and the development of an artificial placenta and its potential use in extremely premature infants.

Milestones for clinical translation of the artificial placenta

Despite significant advances in the treatment of prematurity, premature birth results in significant mortality and morbidity. In particular, extremely low gestational age newborns (ELGANs) defined as <28 weeks estimated gestational age (EGA) suffer from disproportionate mortality and morbidity. A radical paradigm shift in the treatment of prematurity is to recreate fetal physiology using an extracorporeal VV-ECLS artificial placenta (AP) or an AV-ECLS artificial womb (AW). Over the past 15 years, tremendous advances have been made in the laboratory confirming long-term support and organ protection and ongoing development. The major milestones to clinical application are miniaturization, anticoagulation, clinical risk stratification, specialized critical care protocols, a regulatory path and a strategy and platform to translate technology to the bedside. Currently, several groups are addressing the remaining milestones for clinical translation.

Impact of the Addition of a Centrifugal Pump in a Preterm Miniature Pig Model of the Artificial Placenta

The recent demonstration of normal development of preterm sheep in an artificial extrauterine environment has renewed interest in artificial placenta (AP) systems as a potential treatment strategy for extremely preterm human infants. However, the feasibility of translating this technology to the human preterm infant remains unknown. Here we report the support of 13 preterm fetal pigs delivered at 102 ± 4 days (d) gestation, weighing 616 ± 139 g with a circuit consisting of an oxygenator and a centrifugal pump, comparing these results with our previously reported pumpless circuit (n = 12; 98 ± 4 days; 743 ± 350 g). The umbilical vessels were cannulated, and fetuses were supported for 46.4 ± 46.8 h using the pumped AP versus 11 ± 13 h on the pumpless AP circuit. Upon initiation of AP support on the pumped system, we observed supraphysiologic circuit flows, tachycardia, and hypertension, while animals maintained on a pumpless AP circuit exhibited subphysiologic flows. On the pumped AP circuit, there was a progressive decline in umbilical vein (UV) flow and oxygen delivery. We conclude that the addition of a centrifugal pump to the AP circuit improves survival of preterm pigs by augmenting UV flow through the reduction of right ventricular afterload. However, we continued to observe the development of heart failure within a matter of days.

Ethical considerations in the use of artificial womb/placenta technology

Despite improvements in survival over the past few decades, pulmonary immaturity and the use of mechanical ventilation have stunted reduction in short- and long-term morbidities for infants at the borderline of viability (22-24 weeks of gestation). It has long been suspected that the use of an artificial womb or artificial placenta to preserve native fetal physiology and maintain fluid- rather than air-filled lungs would help to improve outcomes for these infants. As such, several institutions have ongoing efforts to develop this technology, bringing the field of neonatology within sight of clinical trials. Prior to use in humans, several important ethical issues should be considered and discussed, including the moral status of these patients and the term used to describe them, whether neonate, fetus, or another term entirely. These determinations will guide when it is appropriate to use the technology and when it is permissible to withdraw this support, as well as how to ascribe parental rights and the legal status of these patients.

Development of an artificial placenta for support of premature infants: narrative review of the history, recent milestones, and future innovation

Over 50 years ago, visionary researchers began work on an extracorporeal artificial placenta to support premature infants. Despite rudimentary technology and incomplete understanding of fetal physiology, these pioneering scientists laid the foundation for future work. The research was episodic, as medical advances improved outcomes of premature infants and extracorporeal life support (ECLS) was introduced for the treatment of term and near-term infants with respiratory or cardiac failure. Despite ongoing medical advances, extremely premature infants continue to suffer a disproportionate burden of mortality and morbidity due to organ immaturity and unintended iatrogenic consequences of medical treatment. With advancing technology and innovative approaches, there has been a resurgence of interest in developing an artificial placenta to further diminish the mortality and morbidity of prematurity. Two related but distinct platforms have emerged to support premature infants by recreating fetal physiology: a system based on arteriovenous (AV) ECLS and one based on veno-venous (VV) ECLS. The AV-ECLS approach utilizes only the umbilical vessels for cannulation. It requires immediate transition of the infant at the time of birth to a fluid-filled artificial womb to prevent umbilical vessel spasm and avoid gas ventilation. In contradistinction, the VV-ECLS approach utilizes the umbilical vein and the internal jugular vein. It would be applied after birth to infants failing maximal medical therapy or preemptively if risk stratified for high mortality and morbidity. Animal studies are promising, demonstrating prolonged support and ongoing organ development in both systems. The milestones for clinical translation are currently being evaluated.

Advances in extracorporeal membrane oxygenator design for artificial placenta technology

Extreme prematurity, defined as a gestational age of fewer than 28 weeks, is a significant health problem worldwide. It carries a high burden of mortality and morbidity, in large part due to the immaturity of the lungs at this stage of development. The standard of care for these patients includes support with mechanical ventilation, which exacerbates lung pathology. Extracorporeal life support (ECLS), also called artificial placenta technology when applied to extremely preterm (EPT) infants, offers an intriguing solution. ECLS involves providing gas exchange via an extracorporeal device, thereby doing the work of the lungs and allowing them to develop without being subjected to injurious mechanical ventilation. While ECLS has been successfully used in respiratory failure in full-term neonates, children, and adults, it has not been applied effectively to the EPT patient population. In this review, we discuss the unique aspects of EPT infants and the challenges of applying ECLS to these patients. In addition, we review recent progress in artificial placenta technology development. We then offer analysis on design considerations for successful engineering of a membrane oxygenator for an artificial placenta circuit. Finally, we examine next-generation oxygenators that might advance the development of artificial placenta devices.

Achieving sustained extrauterine life: Challenges of an artificial placenta in fetal pigs as a model of the preterm human fetus

Artificial placenta (AP) technology aims to maintain fetal circulation, while promoting the physiologic development of organs. Recent reports of experiments performed in sheep indicate the intrauterine environment can be recreated through the cannulation of umbilical vessels, replacement of the placenta with a low-resistance membrane oxygenator, and incubation of the fetus in fluid. However, it remains to be seen whether animal fetuses similar in size to the extremely preterm human infant that have been proposed as a potential target for this technology can be supported in this way. Preterm Yucatan miniature piglets are similar in size to extremely preterm human infants and share similar umbilical cord anatomy, raising the possibility to serve as a good model to investigate the AP. To characterize fetal cardiovascular physiology, the carotid artery (n = 24) was cannulated in utero and umbilical vein (UV) and umbilical artery were sampled. Fetal UV flow was measured by MRI (n = 16). Piglets were delivered at 98 ± 4 days gestation (term = 115 days), cannulated, and supported on the AP (n = 12) for 684 ± 228 min (range 195-3077 min). UV flow was subphysiologic (p = .002), while heart rate was elevated on the AP compared with in utero controls (p = .0007). We observed an inverse relationship between heart rate and UV flow (r2  = .4527; p < .001) with progressive right ventricular enlargement that was associated with reduced contractility and ultimately hydrops and circulatory collapse. We attribute this to excessive afterload imposed by supraphysiologic circuit resistance and augmented sympathetic activity. We conclude that short-term support of the preterm piglet on the AP is feasible, although we have not been able to attain normal fetal physiology. In the future, we propose to investigate the feasibility of an AP circuit that incorporates a centrifugal pump in our miniature pig model.

Diagnostic Specificity of Cerebral Magnetic Resonance Imaging for Punctate White Matter Lesion Assessment in a Preterm Sheep Fetus Model

Recent studies, using magnetic resonance imaging (MRI) to assess white matter injury in preterm brains, increasingly recognize punctate white matter lesions (PWML) as the primary lesion type. There are some papers showing the relationship between the size and number of PWML and the prognosis of infants. However, the histopathological features are still unknown. In this study, we experimentally induced periventricular leukomalacia (PVL) in a sheep fetus model, aiming to find whether MRI can visualize necrotic foci (small incipient lesions of PVL) as PWML. Three antenatal insults were employed to induce PVL in preterm fetuses at gestational day 101-117: (i) hypoxia under intrauterine inflammation, (ii) restriction of artificial placental blood flow, and (iii) restriction of artificial placental blood flow after exposure to intrauterine inflammation. MRI was performed 3-5 days after the insults, and standard histological studies of the PVL validated its findings. Of the 89 necrotic foci detected in histological samples from nine fetuses with PVL, 78 were visualized as PWML. Four of the lesions detected as abnormal findings on MRI could not be histologically detected as corresponding abnormal findings. The diagnostic sensitivity and positive predictive values of histologic focal necrosis visualized as PWML were 0.92 and 0.95, respectively. The four lesions were excluded from these analyses. These data suggest that MRI can visualize PVL necrotic foci as PWML 3-5 days after the injury induction. PWML can spontaneously become obscure with time after birth, so their accurate diagnosis in the acute phase can prevent overlooking mild PVL.

Artificial lungs--Where are we going with the lung replacement therapy?

Lung transplantation may be a final destination therapy in lung failure, but limited donor organ availability creates a need for alternative management, including artificial lung technology. This invited review discusses ongoing developments and future research pathways for respiratory assist devices and tissue engineering to treat advanced and refractory lung disease. An overview is also given on the aftermath of the coronavirus disease 2019 pandemic and lessons learned as the world comes out of this situation. The first order of business in the future of lung support is solving the problems with existing mechanical devices. Interestingly, challenges identified during the early days of development persist today. These challenges include device-related infection, bleeding, thrombosis, cost, and patient quality of life. The main approaches of the future directions are to repair, restore, replace, or regenerate the lungs. Engineering improvements to hollow fiber membrane gas exchangers are enabling longer term wearable systems and can be used to bridge lung failure patients to transplantation. Progress in the development of microchannel-based devices has provided the concept of biomimetic devices that may even enable intracorporeal implantation. Tissue engineering and cell-based technologies have provided the concept of bioartificial lungs with properties similar to the native organ. Recent progress in artificial lung technologies includes continued advances in both engineering and biology. The final goal is to achieve a truly implantable and durable artificial lung that is applicable to destination therapy.

Neurologic outcomes of the premature lamb in an extrauterine environment for neonatal development

BACKGROUND/PURPOSE

Neurologic injury remains the most important morbidity of prematurity. Those born at the earliest gestational ages can face a lifetime of major disability. Perinatal insults result in developmental delay, cerebral palsy, and other profound permanent neurologic impairments. The EXTracorporeal Environment for Neonatal Development (EXTEND) aims to transition premature neonates through this sensitive period, but it's impact on neurologic development requires analysis.

METHODS

Fetal sheep were maintained in a fluid-filled environment for up to 28 days. Physiologic parameters were measured continuously; tissues were subsequently fixed and preserved for myelin quantification, glial cell staining, and structural assessment via magnetic resonance. Surviving animals were functionally assessed.

RESULTS

No evidence of fetal brain ischemia or white matter tract injury associated with the EXTEND system was detected, and the degree of myelination was regionally appropriate and consistent with age matched controls. No evidence of neurologic injury or immaturity was visible on magnetic resonance; animals that transitioned from the system had no persistent neurologic deficits.

CONCLUSIONS

No evidence of major neurologic morbidity was found in animals supported on the EXTEND system, though more work needs to be done in order to verify its safety during critical periods of neurologic development.

Feasibility of Non-invasive Pulse Pressure Measurement Using the Phased-Tracking Method

Phased tracking (PT) is a high-precision ultrasonic technology that enables measurements of pulse pressure (PP). The aim of this study was to verify the accuracy of estimated PP using PT. Estimated PPs were compared with measured PPs in three sheep fetuses that were connected to an artificial placenta system. Similarly, estimated and measured PPs of 30 human neonates were compared. PP was calculated using the Water-Hammer equation (PP = ρ × PWV (pulse wave velocity) × ΔU). PWV was estimated by measuring the transit times of pulse waves at two sites along the aorta using the PT method, and ΔU was obtained by subtracting end-diastolic velocity from peak systolic velocity. The correlation between the estimated and measured PPs of the sheep fetuses was strong (r = 0.95, p ˂ 0.01), as was the case with the human neonates (r = 0.88, p ˂ 0.05). It can be concluded from the results of this study that PT may be a non-invasive alternative method used to predict PP.

Artificial placenta and womb technology: Past, current, and future challenges towards clinical translation

Extreme prematurity remains a major cause of neonatal mortality and severe long-term morbidity. Current neonatal care is associated with significant morbidity due to iatrogenic injury and developmental immaturity of extreme premature infants. A more physiologic approach, replacing placental function and providing a womb-like environment, is the foundational principle of artificial placenta (AP) and womb (AW) technology. The concept has been studied during the past 60 years with limited success. However, recent technological advancements and a greater emphasis on mimicking utero-placental physiology have improved the success of experimental models, bringing the technology closer to clinical translation. Here, we review the rationale for and history of AP and AW technology, discuss the challenges that needed to be overcome, and compare recent successful models. We conclude by outlining some remaining challenges to be addressed on the path towards clinical translation and opportunities for future research.

Successful use of an artificial placenta to support extremely preterm ovine fetuses at the border of viability

BACKGROUND

Ex vivo uterine environment therapy is an experimental life support platform designed to reduce the risk of morbidity and mortality for extremely preterm infants born at the border of viability (21-24 weeks' gestation). To spare the functionally immature lung, this platform performs gas exchange via a membranous oxygenator connected to the umbilical vessels, and the fetus is submerged in a protective bath of artificial amniotic fluid. We and others have demonstrated the feasibility of extended survival with ex vivo uterine environment therapy therapy in late preterm fetuses; however, there is presently no evidence to show that the use of such a platform can support extremely preterm fetuses, the eventual translational target for therapy of this nature.

OBJECTIVE

The objective of the study was to use our ex vivo uterine environment therapy platform to support the healthy maintenance of 600-700 g/95 days gestational age (equivalent to 24 weeks of human gestation) sheep fetuses. Primary outcome measures were as follows: (1) maintenance of key physiological variables; (2) absence of infection; (3) absence of brain injury; and (4) growth and cardiovascular function patterns matching that of noninstrumented, age-matched in utero controls.

STUDY DESIGN

Singleton fetuses from 8 ewes underwent surgical delivery at 95 days' gestation (term, 150 days). Fetuses were adapted to ex vivo uterine environment therapy and maintained for 120 hours with real-time monitoring of key physiological variables. Umbilical artery blood samples were regularly collected to assess blood gas data, differential counts, inflammation, and microbial load to exclude infection. Brain injury was evaluated by gross anatomical and histopathological approaches after euthanasia. Nine pregnant control animals were euthanized at 100 days' gestation to allow comparative postmortem analyses. Data were tested for mean differences with an analysis of variance.

RESULTS

Seven of 8 ex vivo uterine environment group fetuses (87.5%) completed 120 hours of therapy with key parameters maintained in a normal physiological range. There were no significant intergroup differences (P > .05) in final weight, crown-rump length, and body weight-normalized lung and brain weights at euthanasia compared with controls. There were no biologically significant differences in hematological parameters (total or differential leucocyte counts and plasma concentration of tumor necrosis factor-α and monocyte chemoattractant protein 1) (P > .05). Daily blood cultures were negative for aerobic and anaerobic growth in all ex vivo uterine environment animals. There was no difference in airspace consolidation between control and ex vivo uterine environment animals, and there was no increase in the number of lung cells staining positive for the T-cell marker CD3. There were no increases in interleukin-1, interleukin-6, interleukin-8, tumor necrosis factor-α, and monocyte chemoattractant protein 1 mRNA expression in lung tissues compared with the control group. No cases of intraventricular hemorrhage were observed, and white matter injury was identified in only 1 ex vivo uterine environment fetus.

CONCLUSION

For several decades, there has been little improvement in outcomes of extremely preterm infants born at the border of viability. In the present study, we report the use of artificial placenta technology to support, for the first time, extremely preterm ovine fetuses (equivalent to 24 weeks of human gestation) in a stable, growth-normal state for 120 hours. With additional refinement, the data generated by this study may inform a treatment option to improve outcomes for extremely preterm infants.

An EXTrauterine environment for neonatal development: EXTENDING fetal physiology beyond the womb

Extreme prematurity is a major cause of neonatal mortality and morbidity, and remains an unsolved clinical challenge. The development of an artificial womb, an extrauterine system recreating the intrauterine environment, would support ongoing growth and organ maturation of the extreme preterm fetus and would have the potential to substantially improve survival and reduce morbidity. Previous efforts toward the development of such a system have demonstrated the ability to maintain the isolated fetus for short periods of support, but have failed to achieve the long-term stability required for clinical application. Here we describe our initial experiments demonstrating the stable support of fetal lambs developmentally equivalent to the extreme premature infant for up to four weeks with stable hemodynamics, growth, and development. The achievement of long-term physiologic support of the fetus in an extrauterine system has the potential to fundamentally change the management and clinical outcome of the extreme premature infant.

Attenuation of ductus arteriosus intimal thickening in preterm sheep twins compared with singletons

Preterm twins have a higher morbidity rate of patent ductus arteriosus (PDA) than do singletons. However, the effect of multiple births on maturation of the ductus arteriosus (DA) has not been reported. Because intimal thickening (IT) is required for DA anatomical closure, we examined IT development in the DA of preterm twins and singletons. Sheep DA tissues obtained from preterm fetuses were subjected to elastica van Gieson staining to evaluate IT. The total IT score in each DA was the sum of the IT scores obtained from six evenly divided parts of the DA, which was positively correlated with gestational ages in singletons. Total IT scores were smaller in preterm twins than in singletons, although no difference in gestational age, birth weight, or gender ratio was observed. These data suggest that IT development of the DA is attenuated in sheep preterm twins, which may affect the higher morbidity of PDA.

Successful maintenance of key physiological parameters in preterm lambs treated with ex vivo uterine environment therapy for a period of 1 week

BACKGROUND

Extremely preterm infants born at the border of viability (22-24 weeks' gestation) have high rates of death and lasting disability. Ex vivo uterine environment therapy is an experimental neonatal intensive care strategy that provides gas exchange using parallel membranous oxygenators connected to the umbilical vessels, sparing the extremely preterm cardiopulmonary system from ventilation-derived injury.

OBJECTIVE

In this study, we aimed to refine our ex vivo uterine environment therapy platform to eliminate fetal infection and inflammation, while simultaneously extending the duration of hemodynamically stable ex vivo uterine environment therapy to 1 week.

STUDY DESIGN

Merino-cross ewes with timed, singleton pregnancies were surgically delivered at 112-115 days of gestation (term is ∼150 days) and adapted to ex vivo uterine environment therapy (treatment group; n = 6). Physiological variables were continuously monitored; humerus and femur length, ductus arteriosus directional flow, and patency were estimated with ultrasound; serial blood samples were collected for hematology and microbiology studies; weight was recorded at the end of the experiment. Control group animals (n = 7) were euthanized at 122 days of gestation and analyzed accordingly. Bacteremia was defined by positive blood culture. Infection and fetal inflammation was assessed with white blood cell counts (including differential leukocyte counts), plasma and lung proinflammatory cytokine measurements, and lung histopathology.

RESULTS

Five of 6 fetuses in the treatment group completed the 1-week study period with key physiological parameters, blood counts remaining within normal ranges, and no bacteremia detected. There were no significant differences (P > .05) in arterial blood oxygen content or lactate levels between ex vivo uterine environment therapy and control groups at delivery. There was no significant difference (P > .05) in birthweight between control and ex vivo uterine environment groups. In the ex vivo uterine environment group, we observed growth of fetal humerus (P < .05) and femur (P < .001) over the course of the 7-day experimental period. There was no difference in airway or airspace morphology or consolidation between control and ex vivo uterine environment animals, and there was no increase in the number of lung cells staining positive for T-cell marker CD3⁺.

CONCLUSION

Five preterm lambs were maintained in a physiologically stable condition for 1 week with significant growth and without clinically significant bacteremia or systemic inflammation. Although substantial further refinement is required, a life support platform based around ex vivo uterine environment therapy may provide an avenue to improve outcomes for extremely preterm infants.

An extra-uterine system to physiologically support the extreme premature lamb

In the developed world, extreme prematurity is the leading cause of neonatal mortality and morbidity due to a combination of organ immaturity and iatrogenic injury. Until now, efforts to extend gestation using extracorporeal systems have achieved limited success. Here we report the development of a system that incorporates a pumpless oxygenator circuit connected to the fetus of a lamb via an umbilical cord interface that is maintained within a closed 'amniotic fluid' circuit that closely reproduces the environment of the womb. We show that fetal lambs that are developmentally equivalent to the extreme premature human infant can be physiologically supported in this extra-uterine device for up to 4 weeks. Lambs on support maintain stable haemodynamics, have normal blood gas and oxygenation parameters and maintain patency of the fetal circulation. With appropriate nutritional support, lambs on the system demonstrate normal somatic growth, lung maturation and brain growth and myelination.

Artificial Organs 2016: A Year in Review

In this Editor's Review, articles published in 2016 are organized by category and briefly summarized. We aim to provide a brief reflection of the currently available worldwide knowledge that is intended to advance and better human life while providing insight for continued application of technologies and methods of organ Replacement, Recovery, and Regeneration. As the official journal of The International Federation for Artificial Organs, The International Faculty for Artificial Organs, the International Society for Mechanical Circulatory Support, the International Society for Pediatric Mechanical Cardiopulmonary Support, and the Vienna International Workshop on Functional Electrical Stimulation, Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level." Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ Replacement, Recovery, and Regeneration from all over the world. We were pleased to publish our second Virtual Issue in April 2016 on "Tissue Engineering in Bone" by Professor Tsuyoshi Takato. Our first was published in 2011 titled "Intra-Aortic Balloon Pumping" by Dr. Ashraf Khir. Other peer-reviewed Special Issues this year included contributions from the 11th International Conference on Pediatric Mechanical Circulatory Support Systems and Pediatric Cardiopulmonary Perfusion edited by Dr. Akif Ündar and selections from the 23rd Congress of the International Society for Rotary Blood Pumps edited by Dr. Bojan Biocina. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide meaningful suggestions to the author's work whether eventually accepted or rejected. Without these excellent and dedicated reviewers the quality expected from such a journal could not be possible. We also express our special thanks to our Publisher, John Wiley & Sons for their expert attention and support in the production and marketing of Artificial Organs. We look forward to reporting further advances in the coming years.

Artificial placenta: Analysis of recent progress

The artificial placenta (AP) has for many decades captured the imagination of scientists and authors with popular fiction including The Matrix and Aldous Huxley's "Brave New World", depicting a human surviving ex-utero in an artificial uterine environment (AUE). For scientists this has fascinated as a way forward for extremely preterm infants (EPIs) born less than 28 weeks of gestation. Early successes with mechanical ventilation (MV) for infants born above 28 weeks of gestation meant that AP research lost momentum. More recently, the gestational age limit for survival now borders on 23 weeks and corresponds to the biological milestone of lung development marked by the early canalicular stage of lung morphogenesis. The so called greyzone of 23-25 weeks represents a steep increase in mortality with decreasing gestational age and current options in neonatal care are on the fringes of efficacy for this population. A shift in thinking recognizes the vitality of EPIs as a fetus rather than a 37-40 week neonate and this has reinvigorated the concept of the AP. This review will discuss the scale of extreme preterm birth with special reference to previable infants born in the greyzone. Recent AP studies using sheep models are compared, technical obstacles discussed and future research themes identified.