Perfluorocarbon emulsions as a promising technology: a review of tissue and vascular gas dynamics

Dodecafluoropentane improves neuro-behavioral outcomes and return of spontaneous circulation rate in a swine model of cardiac arrest

INTRODUCTION

Dodecafluoropentane emulsion (DDFPe) administration has previously demonstrated improved gas exchange in single-organ perfusion models. This could translate to prevention of brain injury in cardiac arrest.

METHODS

We induced cardiac arrest in 12 pigs, performing CPR after 5-minute downtime. Pigs were randomly assigned to DDFPe (n = 7) or saline placebo (n = 5) groups. Neurologic injury biomarkers were measured at baseline, after return of spontaneous circulation (ROSC), and every 24 hours in survivors. Blinded Neurological Alertness Score, Neurological Dysfunction Score, and Overall Performance Score was performed in addition to histopathological scoring of parietal and hippocampal sections.

RESULTS

One placebo and four DDFPe pigs survived the 96-hour observation period. The odds ratio for ROSC was 7.2 (p = 0.22). Survival odds ratio was 4.6 (p = 0.29). All surviving animals had impaired motor responses that recovered by 72 hours. DDFPe animals showed better neuro-behavioral scores than placebo.

CONCLUSION

The findings of this novel study provide a proof of concept and early signal toward efficacy of intravenous DDFPe in cardiac arrest. The trend toward improved ROSC and functional survival may reflect improved microcirculatory gas exchange in DDFPe animals. Improving gas exchange in brain microcirculation during resuscitation from cardiac arrest may provide a significant therapeutic benefit.

Fluorine materials scavenge excess carbon dioxide and promote Escherichia coli growth

Fluorinated solvents have been used as oxygen carriers in closed microbial cultures to sustain aerobic conditions. However, the growth-promoting effects of fluorinated solvents remain unclear. Therefore, this study aimed to elucidate the mechanism by which fluorinated solvents promote microbial growth and to explore alternative materials that can be easily isolated after culture. Escherichia coli and HFE-7200, a fluorinated solvent, were used to explore factors other than oxygen released by fluorinated solvents that promote microbial growth. E. coli growth was promoted in gas-permeable cultures, and HFE-7200 alleviated medium acidification. Gas chromatography confirmed that HFE-7200 functioned as a scavenger of carbon dioxide produced by E. coli metabolism. Because fluorinated solvents can dissolve various gases, they could scavenge metabolically produced toxic gases from microbial cultures. Furthermore, using polytetrafluoroethylene, a solid fluorine material, results in enhanced bacterial growth. Such solid materials can be easily isolated and reused for microbial culture, suggesting their potential as valuable technologies in food production and biotechnology.

A revision of the multiple-path particle dosimetry model focusing on tobacco product aerosol dynamics

To assess the health impact of inhaled aerosols, it is necessary to understand aerosol dynamics and the associated dosimetry in the human respiratory tract. Although several studies have measured or simulated the dosimetry of aerosol constituents, the respiratory tract focus areas have been limited. In particular, the aerosols generated from tobacco products are complex composites and simulating their dynamics in the respiratory tract is challenging. To assess the dosimetry of the aerosol constituents of tobacco products, we developed a revised version of the Multiple-Path Particle Dosimetry (MPPD) model, which employs (1) new geometry based on CT-scanned human respiratory tract data, (2) convective mixing in the oral cavity and deep lung, and (3) constituent partitioning between the tissue and air, and clearance. The sensitivity analysis was conducted using aerosols composed of four major constituents of electronic cigarette (EC) aerosols to investigate the parameters that have a significant impact on the results. In addition, the revised model was run with 4 and 10 constituents in ECs and conventional cigarettes (CCs), respectively. Sensitivity analysis revealed that the new modeling and the physicochemical properties of constituents had a considerable impact on the simulated aerosol concentration and dosimetry. The simulations could be carried out within 3 min even when 10 constituents of CC aerosols were analyzed simultaneously. The revised model based on MPPD is an efficient and easy-to-use tool for understanding the aerosol dynamics of CC and EC constituents and their effect on the human body.

Iatrogenic air embolism: pathoanatomy, thromboinflammation, endotheliopathy, and therapies

Iatrogenic vascular air embolism is a relatively infrequent event but is associated with significant morbidity and mortality. These emboli can arise in many clinical settings such as neurosurgery, cardiac surgery, and liver transplantation, but more recently, endoscopy, hemodialysis, thoracentesis, tissue biopsy, angiography, and central and peripheral venous access and removal have overtaken surgery and trauma as significant causes of vascular air embolism. The true incidence may be greater since many of these air emboli are asymptomatic and frequently go undiagnosed or unreported. Due to the rarity of vascular air embolism and because of the many manifestations, diagnoses can be difficult and require immediate therapeutic intervention. An iatrogenic air embolism can result in both venous and arterial emboli whose anatomic locations dictate the clinical course. Most clinically significant iatrogenic air emboli are caused by arterial obstruction of small vessels because the pulmonary gas exchange filters the more frequent, smaller volume bubbles that gain access to the venous circulation. However, there is a subset of patients with venous air emboli caused by larger volumes of air who present with more protean manifestations. There have been significant gains in the understanding of the interactions of fluid dynamics, hemostasis, and inflammation caused by air emboli due to in vitro and in vivo studies on flow dynamics of bubbles in small vessels. Intensive research regarding the thromboinflammatory changes at the level of the endothelium has been described recently. The obstruction of vessels by air emboli causes immediate pathoanatomic and immunologic and thromboinflammatory responses at the level of the endothelium. In this review, we describe those immunologic and thromboinflammatory responses at the level of the endothelium as well as evaluate traditional and novel forms of therapy for this rare and often unrecognized clinical condition.

Functional Imaging of Hypoxia: PET and MRI

Molecular and functional imaging have critical roles in cancer care. Existing evidence suggests that noninvasive detection of hypoxia within a particular type of cancer can provide new information regarding the relationship between hypoxia, cancer aggressiveness and altered therapeutic responses. Following the identification of hypoxia inducible factor (HIF), significant progress in understanding the regulation of hypoxia-induced genes has been made. These advances have provided the ability to therapeutically target HIF and tumor-associated hypoxia. Therefore, by utilizing the molecular basis of hypoxia, hypoxia-based theranostic strategies are in the process of being developed which will further personalize care for cancer patients. The aim of this review is to provide an overview of the significance of tumor hypoxia and its relevance in cancer management as well as to lay out the role of imaging in detecting hypoxia within the context of cancer.

Perfluorocarbon nanodrug induced oxygen self-enriching sonodynamic therapy improves cancer immunotherapy after insufficient radiofrequency ablation

Residual lesions and undetectable metastasis after insufficient radiofrequency ablation (iRFA) are associated with earlier new metastases and poor survival in cancer patients, for induced aggressive tumor phenotype and immunosuppression. Programmed cell death protein 1(PD-1) blockade has been reported to enhance the radiofrequency ablation-elicited antitumor immunity, but its ability to eliminate incompletely ablated residual lesions has been questioned. Here, we report a combined treatment modality post iRFA based on integrating an oxygen self-enriching nanodrug PFH-Ce6 liposome@O2 nanodroplets (PCL@O2)-augmented noninvasive sonodynamic therapy (SDT) with PD-1 blockade. PCL@O2 containing Ce6 as the sonosensitizer and PFH as O2 reservoir, was synthesized as an augmented SDT nanoplatform and showed increased ROS generation to raise effective apoptosis of tumor cells, which also exposed more calreticulin to induce stronger immunogenic cell death (ICD). Combining with PD-1 blockade post iRFA, this optimized SDT induced a better anti-tumor response in MC38 tumor bearing mouse model, which not only arrested residual primary tumor progression, but also inhibited the growth of distant tumor, therefore prolonging the survival. Profiling of immune populations within the tumor draining lymph nodes and tumors further revealed that combination therapy effectively induced ICD, and promoted the maturation of dendritic cells, tumor infiltration of T cells, as well as activation of cytotoxic T lymphocytes. While iRFA alone could result in an increase of regulatory T cells (Tregs) in the residual tumors, SDT plus PD-1 blockade post iRFA reduced the number of Tregs in both primary and distant tumors. Moreover, the combined treatment could significantly initiate long-term immune memory, manifesting as elevated levels of CD8+ and CD4+ central memory cells. Therefore, this study establishes the preclinical proof of concept to apply oxygen self-enriching SDT to augment cancer immunotherapy after iRFA.

Nanodroplet-enhanced sonodynamic therapy potentiates immune checkpoint blockade for systemic suppression of triple-negative breast cancer

Immune checkpoint blockade (ICB) has shown great promise in treating various advanced malignancies including triple-negative breast cancer (TNBC). However, only limited number of patients could benefit from it due to the low immune response rate caused by insufficient matured dendritic cells (DCs) and inadequate tumor infiltration of cytotoxic T lymphocytes (CTLs). Here, we report a combination therapeutic strategy which integrates STING pathway activation, hypoxia relief and sonodynamic therapy (SDT) with anti-PD-L1 therapy to improve the therapeutic outcome. The synthesized nanodroplet consisted of a O₂-filled Perfluorohexane (PFH) core and a lipid membrane carrying sonosensitizer IR-780 and STING agonist Vadimezan (DMXAAs). It released O₂ inside the hypoxic tumor tissue, thereby enhancing SDT which relied on O₂ to generate cytotoxic reactive oxygen species (ROS). The co-delivered STING agonist DMXAAs promoted the maturation and tumor antigen cross-presenting of DCs for priming of CTLs. Moreover, SDT induced immunogenic cell death (ICD) of tumor to release abundant tumor-associated antigens, which increased tumor immunogenicity to promote tumor infiltration of CTLs. Consequently, not only a robust adaptive immune response was elicited but also the immunologically "cold" TNBC was turned "hot" to enable a potent anti-PD-L1 therapy. The nanodroplet demonstrated strong efficacy to systemically suppress TNBC growth and mimic distant tumor in vivo. STATEMENT OF SIGNIFICANCE: Only a limited number of triple-negative breast cancer (TNBC) patients can benefit from immune checkpoint blockade therapy due to its low immune response rate caused by insufficient matured DCs and inadequate tumor infiltration of cytotoxic T lymphocytes (CTLs). Interestingly, compelling evidence has shown that sonodynamic therapy (SDT) not only directly kills cancer cells but also elicits immunogenic cell death (ICD), which promotes tumor infiltration of cytotoxic T lymphocytes to transform an immunosuppressive "cold" tumor into a "hot" one. However, the hypoxic tumor microenvironment severely restricts the therapeutic efficiency of SDT, wherein, oxygen is indispensable in the process of ROS generation. Here, we report an O₂-filled nanodroplet-enhanced sonodynamic therapy that significantly potentiated immune checkpoint blockade for systemic suppression of TNBC.

Current perspectives of artificial oxygen carriers as red blood cell substitutes: a review of old to cutting-edge technologies using in vitro and in vivo assessments

Background

Several circumstances such as accidents, surgery, traumatic hemorrhagic shock, and other causalities cause major blood loss. Allogenic blood transfusion can be resuscitative for such conditions; however, it has numerous ambivalent effects, including supply shortage, needs for more time, cost for blood grouping, the possibility of spreading an infection, and short shelf-life. Hypoxia or ischemia causes heart failure, neurological problems, and organ damage in many patients. To address this emergent medical need for resuscitation and to treat hypoxic conditions as well as to enhance oxygen transportation, researchers aspire to achieve a robust technology aimed to develop safe and feasible red blood cell substitutes for effective oxygen transport.

Area covered

This review article provides an overview of the formulation, storage, shelf-life, clinical application, side effects, and current perspectives of artificial oxygen carriers (AOCs) as red blood cell substitutes. Moreover, the pre-clinical (in vitro and in vivo) assessments for the evaluation of the efficacy and safety of oxygen transport through AOCs are key considerations in this study. With the most significant technologies, hemoglobin- and perfluorocarbon-based oxygen carriers as well as other modern technologies, such as synthetically produced porphyrin-based AOCs and oxygen-carrying micro/nanobubbles, have also been elucidated.

Expert opinion

Both hemoglobin- and perfluorocarbon-based oxygen carriers are significant, despite having the latter acting as safeguards; they are cost-effective, facile formulations which penetrate small blood vessels and remove arterial blockages due to their nano-size. They also show better biocompatibility and longer half-life circulation than other similar technologies.

c-Met-Targeting 19F MRI Nanoparticles with Ultralong Tumor Retention for Precisely Detecting Small or Ill-Defined Colorectal Liver Metastases

Purpose

Precisely detecting colorectal liver metastases (CLMs), the leading cause of colorectal cancer-associated mortality, is extremely important. ¹H MRI with high soft tissue resolution plays a key role in the diagnosing liver lesions; however, precise detecting CLMs by ¹H MRI is a great challenge due to the limited sensitivity. Even though contrast agents may improve the sensitivity, due to their short half-life, repeated injections are required to monitor the changes of CLMs. Herein, we synthesized c-Met-targeting peptide-functionalized perfluoro-15-crown-5-ether nanoparticles (AH111972-PFCE NPs), for highly sensitive and early diagnosis of small CLMs.

Methods

The size, morphology and optimal properties of the AH111972-PFCE NPs were characterized. c-Met specificity of the AH111972-PFCE NPs was validated by in vitro experiment and in vivo ¹⁹F MRI study in the subcutaneous tumor murine model. The molecular imaging practicability and long tumor retention of the AH111972-PFCE NPs were evaluated in the liver metastases mouse model. The biocompatibility of the AH111972-PFCE NPs was assessed by toxicity study.

Results

AH111972-PFCE NPs with regular shape have particle size of 89.3 ± 17.8 nm. The AH111972-PFCE NPs exhibit high specificity, strong c-Met-targeting ability, and precise detection capability of CLMs, especially small or ill-defined fused metastases in ¹H MRI. Moreover, AH111972-PFCE NPs could be ultralong retained in metastatic liver tumors for at least 7 days, which is conductive to the implementation of continuous therapeutic efficacy monitoring. The NPs with minimal side effects and good biocompatibility are cleared mainly via the spleen and liver.

Conclusion

The c-Met targeting and ultralong tumor retention of AH111972-PFCE NPs will contribute to increasing therapeutic agent accumulation in metastatic sites, laying a foundation for CLMs diagnosis and further c-Met targeted treatment integration. This work provides a promising nanoplatform for the future clinical application to patients with CLMs.

Assessment of bubble activity generated by histotripsy combined with echogenic liposomes

Objective.Histotripsy is a form of focused ultrasound therapy that uses the mechanical activity of bubbles to ablate tissue. While histotripsy alone degrades the cellular content of tissue, recent studies have demonstrated it effectively disrupts the extracellular structure of pathologic conditions such as venous thrombosis when combined with a thrombolytic drug. Rather than relying on standard administration methods, associating thrombolytic drugs with an ultrasound-triggered echogenic liposome vesicle will enable targeted, systemic drug delivery. To date, histotripsy has primarily relied on nano-nuclei inherent to the medium for bubble cloud generation, and microbubbles associated with echogenic liposomes may alter the histotripsy bubble dynamics. The objective of this work was to investigate the interaction of histotripsy pulse with echogenic liposomes.Approach.Bubble clouds were generated using a focused source in anin vitromodel of venous flow. Acoustic emissions generated during the insonation were passively acquired to assess the mechanical activity of the bubble cloud. High frame rate, pulse inversion imaging was used to track the change in echogenicity of the liposomes following histotripsy exposure.Main results.For peak negative pressures less than 20 MPa, acoustic emissions indicative of stable and inertial bubble activity were observed. As the peak negative pressure of the histotripsy excitation increased, harmonics of the excitation were observed in OFP t-ELIP solutions and plasma alone. Additional observations with high frame rate imaging indicated a transition of bubble behavior as the pulse pressure transitioned to shock wave formation.Significance.These observations suggest that a complex interaction between histotripsy pulses and echogenic liposomes that may be exploited for combination treatment approaches.

Fluorinated Hyaluronic Acid Encapsulated Perfluorocarbon Nanoparticles as Tumor-Targeted Oxygen Carriers to Enhance Radiotherapy

The efficacy of radiotherapy is significantly constricted by tumor hypoxia. To overcome this obstacle, one promising approach is to use the perfluorocarbon-based O₂ carriers combined with hyperoxic respiration to relieve tumor hypoxia. However, this passively transported oxygen carrier during hyperoxic respiration is prone to cause systemic oxidative stress and toxicity, which further limits its clinical application. Herein, we fabricate O₂@PFC@FHA NPs for safe and specific oxygen delivery into tumors by using the fluorinated hyaluronic acid to encapsulate O₂-saturated perfluorocarbon. Due to the interaction between HA and CD44 receptors, more FHA@PFC NPs accumulated in the tumor and the O₂@PFC@FHA NPs significantly relieved tumor hypoxia. Notably, RT plus O₂@PFC@FHA NPs resulted in almost threefold therapeutic improvement compared with RT without obvious systemic toxicity. Therefore, the O₂@FHA@PFC NPs may have great potential to enhance the therapeutic efficacy of radiotherapy in the clinic.

Perfluorocarbon Nanodroplets for Dual Delivery with Ultrasound/GSH-Responsive Release of Model Drug and Passive Release of Nitric Oxide

Nitric oxide (NO) plays a critical role as an important signaling molecule for a variety of biological functions, particularly inhibiting cell proliferation or killing target pathogens. To deliver active radical NO gaseous molecule whose half-life is a few seconds in a stable state, the design and development of effective exogenous NO supply nanocarriers are essential. Additionally, the delivery of desired drugs with NO can produce synergistic effects. Herein, we report a new approach that allows for the fabrication of dual ultrasound (US)/glutathione (GSH)-responsive perfluorocarbon (PFC) nanodroplets for the controlled release of model drug and passive release of safely incorporated NO. The approach centers on the synthesis of a disulfide-labeled amphiphilic block copolymer and its use as a GSH-degradable macromolecular emulsifier for oil-in-water emulsification process of PFC. The fabricated PFC nanodroplets are colloidally stable and enable the encapsulation of both NO and model drugs. Encapsulated drug molecules are synergistically released when ultrasound and GSH are presented, while NO molecules are passively but rapidly released. Our preliminary results demonstrate that the approach is versatile and can be extended to not only GSH-responsive but also other stimuli-responsive block copolymers, thereby allowing for the fabrication of broad choices of stimuli-responsive (smart) PFC-nanodroplets in aqueous solution for dual delivery of drug and NO therapeutics.

Dose-dependent effects of perfluorocarbon-based blood substitute on cardiac function in myocardial ischemia-reperfusion injury

The main goal of this study was to investigate the cardioprotective properties in terms of effects on cardiodynamics of perfluorocarbon emulsion (PFE) in ex vivo-induced ischemia-reperfusion injury of an isolated rat heart. The first part of the study aimed to determine the dose of 10% perfluoroemulsion (PFE) that would show the best cardioprotective effect in rats on ex vivo-induced ischemia-reperfusion injury of an isolated rat heart. Depending on whether the animals received saline or PFE, the animals were divided into a control or experimental group. They were also grouped depending on the applied dose (8, 12, 16 ml/kg body weight) of saline or PFE. We observed the huge changes in almost all parameters in the PFE groups in comparison with IR group without any pre-treatment. Calculated in percent, dp/dt max was the most changed parameter in group treated with 8 mg/kg, while the dp/dt min, SLVP, DLVP, HR, and CF were the most changed in group treated with 16 mg/kg 10 h before ischemia. The effects of 10% PFE are more pronounced if there is a longer period of time from application to ischemia, i.e., immediate application of PFE before ischemia (1 h) gave the weakest effects on the change of cardiodynamics of isolated rat heart. Therefore, the future of PFE use is in new indications and application methods, and PFE can also be referred to as antihypoxic and antiischemic blood substitute with mild membranotropic effects.

Perfluorocarbon Emulsion Contrast Agents: A Mini Review

Perfluorocarbon emulsions offer a variety of applications in medical imaging. The substances can be useful for most radiological imaging modalities; including, magnetic resonance imaging, ultrasonography, computed tomography, and positron emission tomography. Recently, the substance has gained much interest for theranostics, with both imaging and therapeutic potential. As MRI sequences improve and more widespread access to ¹⁹F-MRI coils become available, perfluorocarbon emulsions have great potential for new commercial imaging agents, due to high fluorine content and previous regulatory approval as antihypoxants and blood substitutes. This mini review aims to discuss the chemistry and physics of these contrast agents, in addition to highlighting some of the past, recent, and potential applications.

Oxygenation therapies for improved wound healing: Current trends and technologies

Degree of oxygenation is one of the important parameters governing various processes, including cell proliferation, angiogenesis, extracellular matrix production, and even combating the microbial burden at the wound site, all...

Recent advances in in situ oxygen-generating and oxygen-replenishing strategies for hypoxic-enhanced photodynamic therapy

Cancer is a leading cause of death worldwide, accounting for an estimated 10 million deaths by 2020. Over the decades, various strategies for tumor therapy have been developed and evaluated. Photodynamic therapy (PDT) has attracted increasing attention due to its unique characteristics, including low systemic toxicity and minimally invasive nature. Despite the excellent clinical promise of PDT, hypoxia is still the Achilles' heel associated with its oxygen-dependent nature related to increased tumor proliferation, angiogenesis, and distant metastases. Moreover, PDT-mediated oxygen consumption further exacerbates the hypoxia condition, which will eventually lead to the poor effect of drug treatment and resistance and irreversible tumor metastasis, even limiting its effective application in the treatment of hypoxic tumors. Hypoxia, with increased oxygen consumption, may occur in acute and chronic hypoxia conditions in developing tumors. Tumor cells farther away from the capillaries have much lower oxygen levels than cells in adjacent areas. However, it is difficult to change the tumor's deep hypoxia state through different ways to reduce the tumor tissue's oxygen consumption. Therefore, it will become more difficult to cure malignant tumors completely. In recent years, numerous investigations have focused on improving PDT therapy's efficacy by providing molecular oxygen directly or indirectly to tumor tissues. In this review, different molecular oxygen supplementation methods are summarized to alleviate tumor hypoxia from the innovative perspective of using supplemental oxygen. Besides, the existing problems, future prospects and potential challenges of this strategy are also discussed.

Injectable oxygenation therapeutics: evaluating the oxygen delivery efficacy of artificial oxygen carriers and kosmotropes in vitro

The aim of this paper was to utilise an existing in vitro setup to quantify the oxygen offloading capabilities of two different subsets of injectable oxygenation therapeutics: (1) artificial oxygen carriers (AOCs), which bind or dissolve oxygen and act as transport vectors, and (2) kosmotropes, which increase water hydrogen bonding and thereby decrease the resistance to oxygen movement caused by the blood plasma. Dodecafluoropentane emulsion (DDFPe) was chosen to represent the AOC subset while trans sodium crocetinate (TSC) was selected to represent the kosmotrope subset. PEG-Telomer-B (PTB), the surfactant utilised to encapsulate DDFP in emulsion form, was also tested to determine whether it affected the oxygen transport ability of DDFPe. The in vitro set-up was used to simulate a semi closed-loop circulatory system, in which oxygen could be delivered from the lungs to hypoxic tissues. Results of this study showed that (1) 0.5 ml of a PFC outperformed 6.25 ml of a kosmotrope in a controlled, in vitro setting and (2) that PTB and sucrose do not contribute to the overall oxygen transportation efficacy of DDFPe. These results could be therapeutically beneficial to ongoing and future pre-clinical and clinical studies involving various oxygenation agents.

Oxygen-Releasing Composites: A Promising Approach in the Management of Diabetic Foot Ulcers

In diabetes, lower extremity amputation (LEA) is an irreversible diabetic-related complication that easily occurs in patients with diabetic foot ulcers (DFUs). Because DFUs are a clinical outcome of different causes including peripheral hypoxia and diabetic foot infection (DFI), conventional wound dressing materials are often insufficient for supporting the normal wound healing potential in the ulcers. Advanced wound dressing development has recently focused on natural or biocompatible scaffolds or incorporating bioactive molecules. This review directs attention to the potential of oxygenation of diabetic wounds and highlights current fabrication techniques for oxygen-releasing composites and their medical applications. Based on different oxygen-releasable compounds such as liquid peroxides and solid peroxides, for example, a variety of oxygen-releasing composites have been fabricated and evaluated for medical applications. This review provides the challenges and limitations of utilizing current oxygen releasable compounds and provides perspectives on advancing oxygen releasing composites for diabetic-related wounds associated with DFUs.

Asymmetrically coating Pt nanoparticles on magnetic silica nanospheres for target cell capture and therapy

A Janus cargo has been developed via the combination of magnetic mesoporous silica (MMS) with asymmetric decoration of Pt nanoparticles (PtNPs). Mesoporous morphology of MMS provides plenty of space for loading photosensitizers and targeting agents; the magnetic feature endows the as-formed nanospheres with satisfactory isolation function in removal of low abundant target cells. The excellent catalytic ability of PtNPs can effectively alleviate the hypoxia condition of tumor microenvironment via the decomposition of hydrogen peroxide (H2O2), as well as an O2-drived nanomotor for highly efficient drug release. Using CCRF-CEM as the model target cell, the Janus cargo is demonstrated to possess significantly improved performance in cell capture and photodynamic therapy. Specially, owing to the patchy Pt decoration, the loaded photosensitizers exhibit a more efficient release behavior. More importantly, asymmetric O2-emission from one side of the nanocargo acts as a driving force, which could effectively accelerate the motion ability of cargo in cell media, thus leading to an enhanced therapeutic effect compared with the traditionally symmetric nanocargo. This Janus cargo would offer a new paradigm to design highly efficient drug carrier for gaining an improved photodynamic therapy in hypoxic cancer cells.

Multifunctional biomaterials that modulate oxygen levels in the tumor microenvironment

A characteristic feature of solid tumors is their low oxygen tension, which confers resistance to radiotherapy, photodynamic therapy, and chemotherapy. Therefore, to improve treatment outcomes, it is critical to develop biomaterials capable of targeted modulation of oxygen levels in tumors. In this review, we summarize four types of oxygen-modulating biomaterials, namely, oxygen-carrying biomaterials to deliver oxygen into tumors (e.g., perfluorocarbon and hemoglobin), oxygen-generating biomaterials to promote in situ oxygen generation (e.g., MnO2, catalase, and CuO), oxygen-consuming biomaterials to starve tumors (e.g., photosensitizer, glucose oxidase, and magnesium silicide), and oxygen-circulating biomaterials capable of both providing and consuming oxygen (e.g., ENBS-B). The current literature suggests that these biomaterials are useful for anticancer therapeutics. We present the key molecular mechanisms involved in modulating oxygen levels and the potential applications of these biomaterials in the context of hypoxic tumor treatment.

Biomaterials for human space exploration: A review of their untapped potential

As biomaterial advances make headway into lightweight radiation protection, wound healing dressings, and microbe resistant surfaces, a relevance to human space exploration manifests itself. To address the needs of the human in space, a knowledge of the space environment becomes necessary. Both an understanding of the environment itself and an understanding of the physiological adaptations to that environment must inform design parameters. The space environment permits the fabrication of novel biomaterials that cannot be produced on Earth, but benefit Earth. Similarly, designing a biomaterial to address a space-based challenge may lead to novel biomaterials that will ultimately benefit Earth. This review describes several persistent challenges to human space exploration, a variety of biomaterials that might mitigate those challenges, and considers a special category of space biomaterial. STATEMENT OF SIGNIFICANCE: This work is a review of the major human and environmental challenges facing human spaceflight, and where biomaterials may mitigate some of those challenges. The work is significant because a broad range of biomaterials are applicable to the human space program, but the overlap is not widely known amongst biomaterials researchers who are unfamiliar with the challenges to human spaceflight. Additionaly, there are adaptations to microgravity that mimic the pathology of certain disease states ("terrestrial analogs") where treatments that help the overwhelmingly healthy astronauts can be applied to help those with the desease. Advances in space technology have furthered the technology in that field on Earth. By outlining ways that biomaterials can promote human space exploration, space-driven advances in biomaterials will further biomaterials technology.

Platelet and White Cell Reactivity to Top-Load Intravenous Perfluorocarbon Infusion in Healthy Sheep

BACKGROUND

Perfluorocarbon emulsions (PFCs) are intravenous artificial oxygen carriers with enhanced gas solubility. As lipid micelle nanoparticle emulsions, PFCs may have a class effect that causes degrees of thrombocytopenia. Understanding the extent of the platelet effects, including mechanism and potential inflammation after PFC infusion, is important for safe human trials.

METHODS

Normal sheep (Dorper) were infused with 5 mL/kg of Oxygent (w/v 60% PFC) or Perftoran (w/v 20% PFC). Controls received 6% Hetastarch or were naive. Blood samples were analyzed from baseline, time 0 (the end of infusion), 3 and 24 hours, and 4 and 7 days. Platelet count, plateletcrit, mean platelet volume, platelet distribution width, and CD-62p (a platelet activation-dependent membrane protein) were measured. Neutrophils, monocytes, and total white blood cell counts were analyzed.

RESULTS

In these inflammatory cell lines, there were no consistent changes or cellular activation after PFC infusion. A decrease (<10% from baseline and naive controls) in platelet count was seen on day 4 after Oxygent infusion (3 g/kg), which recovered by day 7. No platelet effect was seen in Perftoran (1 g/kg). Plateletcrit, mean platelet volume, and platelet distribution width did not change significantly at any time point among the groups. CD-62p, ADP, and collagen aggregometry showed no significant change in platelet function.

CONCLUSION

There was no evidence of overall reduction in platelet number, or any correlation with the change in platelet activation or inhibition. Therefore, the risk of increased thrombosis/bleeding after PFC intravenous infusion is low in this non-trauma sheep model.

Advances in removing mass transport limitations for more physiologically relevant in vitro 3D cell constructs

Spheroids and organoids are promising models for biomedical applications ranging from human disease modeling to drug discovery. A main goal of these 3D cell-based platforms is to recapitulate important physiological parameters of their in vivo organ counterparts. One way to achieve improved biomimetic architectures and functions is to culture cells at higher density and larger total numbers. However, poor nutrient and waste transport lead to low stability, survival, and functionality over extended periods of time, presenting outstanding challenges in this field. Fortunately, important improvements in culture strategies have enhanced the survival and function of cells within engineered microtissues/organs. Here, we first discuss the challenges of growing large spheroids/organoids with a focus on mass transport limitations, then highlight recent tools and methodologies that are available for producing and sustaining functional 3D in vitro models. This information points toward the fact that there is a critical need for the continued development of novel cell culture strategies that address mass transport in a physiologically relevant human setting to generate long-lasting and large-sized spheroids/organoids.

Stratified 3D Microtumors as Organotypic Testing Platforms for Screening Pancreatic Cancer Therapies

Cancer-associated pancreatic stellate cells installed in periacinar/periductal regions are master players in generating the characteristic biophysical shield found in pancreatic ductal adenocarcinoma (PDAC). Recreating this unique PDAC stromal architecture and its desmoplastic microenvironment in vitro is key to discover innovative treatments. However, this still remains highly challenging to realize. Herein, organotypic 3D microtumors that recapitulate PDAC-stroma spatial bioarchitecture, as well as its biomolecular, metabolic, and desmoplastic signatures, are bioengineered. Such newly engineered platforms, termed stratified microenvironment spheroid models - STAMS - mimic the spatial stratification of cancer-stromal cells, exhibit a reproducible morphology and sub-millimeter size. In culture, 3D STAMS secrete the key molecular biomarkers found in human pancreatic cancer, namely TGF-β, FGF-2, IL-1β, and MMP-9, among others. This is accompanied by an extensive desmoplastic reaction where collagen and glycosaminoglycans (GAGs) de novo deposition is observed. These stratified models also recapitulate the resistance to various chemotherapeutics when compared to standard cancer-stroma random 3D models. Therapeutics resistance is further evidenced upon STAMS inclusion in a tumor extracellular matrix (ECM)-mimetic hydrogel matrix, reinforcing the importance of mimicking PDAC-stroma bioarchitectural features in vitro. The 3D STAMS technology represents a next generation of biomimetic testing platforms with improved potential for advancing high-throughput screening and preclinical validation of innovative pancreatic cancer therapies.

Hypoxia-modulatory nanomaterials to relieve tumor hypoxic microenvironment and enhance immunotherapy: Where do we stand?

The past several years have witnessed the blooming of emerging immunotherapy, as well as their therapeutic potential in remodeling the immune system. Nevertheless, with the development of biological mechanisms in oncology, it has been demonstrated that hypoxic tumor microenvironment (TME) seriously impairs the therapeutic outcomes of immunotherapy. Hypoxia, caused by Warburg effect and insufficient oxygen delivery, has been considered as a primary construction element of TME and drawn tremendous attention in cancer therapy. Multiple hypoxia-modulatory theranostic agents have been facing many obstacles and challenges while offering initial therapeutic effect. Inspired by versatile nanomaterials, great efforts have been devoted to design hypoxia-based nanoplatforms to preserve drug activity, reduce systemic toxicity, provide adequate oxygenation, and eventually ameliorate hypoxic-tumor management. Besides these, recently, some curative and innovative hypoxia-related nanoplatforms have been applied in synergistic immunotherapy, especially in combination with immune checkpoint blockade (ICB), immunomodulatory therapeutics, cancer vaccine therapy and immunogenic cell death (ICD) effect. Herein, the paramount impact of hypoxia on tumor immune escape was initially described and discussed, followed by a comprehensive overview on the design tactics of multimodal nanoplatforms based on hypoxia-enabled theranostic agents. A variety of nanocarriers for relieving tumor hypoxic microenvironment were also summarized. On this basis, we presented the latest progress in the use of hypoxia-modulatory nanomaterials for synergistic immunotherapy and highlighted current challenges and plausible promises in this area in the near future. STATEMENT OF SIGNIFICANCE: Cancer immunotherapy, emerging as a novel treatment to eradicate malignant tumors, has achieved a measure of success in clinical popularity and transition. However, over the last decades, hypoxia-induced tumor immune escape has attracted enormous attention in cancer treatment. Limitations of free targeting agents have paved the path for the development of multiple nanomaterials with the hope of boosting immunotherapy. In this review, the innovative design tactics and multifunctional nanocarriers for hypoxia alleviation are summarized, and the smart nanomaterial-assisted hypoxia-modulatory therapeutics for synergistic immunotherapy and versatile biomedical applications are especially highlighted. In addition, the challenges and prospects of clinical transformation are further discussed.

Fluorosurfactants for medical nanoemulsions, their surface-active and biological properties

Nano- and microemulsions have found various applications in pharmaceutical and medical areas both in research field as well as in applied solutions for drug delivery or diagnostic agents. However, production of stable and bio- / hemocompatible nanoemulsions are still challenging. New group of ionic surfactants have been synthesized with perfluorohexyl- or perfluorooctyl-groups as hydrophobic tail. The CMC and the parametres of the O/W emulsion (the particle size distribution and the zeta-potential) were determined. The influence of the surfactants on in vitro proliferation of human endothelial cell lines HMEC-1, murine fibroblasts L929 and hemolysis were investigated as characteristic for biocompatibility. Three candidates of surfactants were selected for pre-clinical tests on a small animal model (adult Sprague Dawley rats) on the basis of preliminary studies. This allowed to obtain nanoemulsions with narrow droplets size (average droplet diameter 141-147 nm with PDI index 0.059 - 0.065) and showed better stability over time in comparison to the commercially available surfactants. Neither cytotoxic nor hemolytic potential were observed during incubation of obtained fluorosurfactans with model cell lines L929 and HMEC-1 (average cell viability above 85 % after incubation with 1% solutions) and erythrocytes (hemolysis rate below 3.1 % for all 0.5 % solutions). During acute toxicity test on rat model, it was found that all three tested surfactant solutions showed no significant differences in controlled parameters and survival rate with control group (p > 0.05). Presented surfactants are dedicated but not limited to emulsification of organic fluorocompounds.

Oxygen releasing materials: Towards addressing the hypoxia-related issues in tissue engineering

Manufacturing macroscale cell-laden architectures is one of the biggest challenges faced nowadays in the domain of tissue engineering. Such living constructs, in fact, pose strict requirements for nutrients and oxygen supply that can hardly be addressed through simple diffusion in vitro or without a functional vasculature in vivo. In this context, in the last two decades, a substantial amount of work has been carried out to develop smart materials that could actively provide oxygen-release to contrast local hypoxia in large-size constructs. This review provides an overview of the currently available oxygen-releasing materials and their synthesis and mechanism of action, highlighting their capacities under in vitro tissue cultures and in vivo contexts. Additionally, we also showcase an emerging concept, herein termed as "living materials as releasing systems", which relies on the combination of biomaterials with photosynthetic microorganisms, namely algae, in an "unconventional" attempt to supply the damaged or re-growing tissue with the necessary supply of oxygen. We envision that future advances focusing on tissue microenvironment regulated oxygen-supplying materials would unlock an untapped potential for generating a repertoire of anatomic scale, living constructs with improved cell survival, guided differentiation, and tissue-specific biofunctionality.

Perfluorocarbon-based oxygen carriers: from physics to physiology

Developing biocompatible, synthetic oxygen carriers is a consistently challenging task that researchers have been pursuing for decades. Perfluorocarbons (PFC) are fascinating compounds with a huge capacity to dissolve gases, where the respiratory gases are of special interest for current investigations. Although largely chemically and biologically inert, pure PFCs are not suitable for injection into the vascular system. Extensive research created stable PFC nano-emulsions that avoid (i) fast clearance from the blood and (ii) long organ retention time, which leads to undesired transient side effects. PFC-based oxygen carriers (PFOCs) show a variety of application fields, which are worthwhile to investigate. To understand the difficulties that challenge researchers in creating formulations for clinical applications, this review provides the physical background of PFCs’ properties and then illuminates the reasons for instabilities of PFC emulsions. By linking the unique properties of PFCs and PFOCs to physiology, it elaborates on the response, processing and dysregulation, which the body experiences through intravascular PFOCs. Thereby the reader will receive a scientific and easily comprehensible overview why PFOCs are precious tools for so many diverse application areas from cancer therapeutics to blood substitutes up to organ preservation and diving disease.

Künstliche Sauerstofftransporter können mehr als Sauerstoff liefern

Zum gegenwärtigen Zeitpunkt ist in der EU und den USA kein artifizieller Sauerstofftransporter zugelassen. Hämoglobin-basierte Sauerstoff-Carrier (HBOC) sind bereits seit Jahrzehnten Gegenstand wissenschaftlicher Untersuchungen. Ein wesentliches Hindernis bei der Zulassung war bisher der Anspruch der Entwickler, einen universell einsetzbaren Blutersatz zu produzieren. Die Beschränkung auf eine Indikation scheint erfolgversprechender zu sein. Der Ansatz, nicht nur Sauerstoff von der Lunge zum Gewebe, sondern auch der Abtransport von Kohlendioxid vom Gewebe zur Lunge zu transportieren, der effektiver als mit Erythrozyten durchgeführt werden kann, erscheint besonders attraktiv. Aufgrund vielversprechender präklinischer sowie klinischer Untersuchungen besteht die Hoffnung, dass in absehbarer Zeit auch in der EU künstliche Sauerstofftransporter für therapeutische Zwecke zur Verfügung stehen werden.

A 3D Cell Culture Organ-on-a-Chip Platform With a Breathable Hemoglobin Analogue Augments and Extends Primary Human Hepatocyte Functions in vitro

Remarkable advances in three-dimensional (3D) cell cultures and organ-on-a-chip technologies have opened the door to recapitulate complex aspects of human physiology, pathology, and drug responses in vitro. The challenges regarding oxygen delivery, throughput, assay multiplexing, and experimental complexity are addressed to ensure that perfused 3D cell culture organ-on-a-chip models become a routine research tool adopted by academic and industrial stakeholders. To move the field forward, we present a throughput-scalable organ-on-a-chip insert system that requires a single tube to operate 48 statistically independent 3D cell culture organ models. Then, we introduce in-well perfusion to circumvent the loss of cell signaling and drug metabolites in otherwise one-way flow of perfusate. Further, to augment the relevancy of 3D cell culture models in vitro, we tackle the problem of oxygen transport by blood using, for the first time, a breathable hemoglobin analog to improve delivery of respiratory gases to cells, because in vivo approximately 98% of oxygen delivery to cells takes place via reversible binding to hemoglobin. Next, we show that improved oxygenation shifts cellular metabolic pathways toward oxidative phosphorylation that contributes to the maintenance of differentiated liver phenotypes in vitro. Lastly, we demonstrate that the activity of cytochrome P450 family of drug metabolizing enzymes is increased and prolonged in primary human hepatocytes cultured in 3D compared to two-dimensional (2D) cell culture gold standard with important ramifications for drug metabolism, drug-drug interactions and pharmacokinetic studies in vitro.

Oxygen therapeutic agents to target hypoxia in cancer treatment

Solid tumors have abnormal microcirculation that limits oxygen delivery and leads to a hypoxic tumor microenvironment. Tumor hypoxia stabilizes the transcription factor HIF-1α that can trigger immunosuppression through A2A adenosine receptors which prevents immune attack on tumors. In addition, success of chemotherapy and radiation therapy appears to be dependent on oxygen levels. Two main pharmaceutical classes of agents (hemoglobin based and perfluorocarbon man-made carbon oils) have been tested in tumor models as enhanced oxygen therapeutics. This article will review how these agents function as well as examine work to date with both drug classes.

Perfluorocarbons-Based 19F Magnetic Resonance Imaging in Biomedicine

Fluorine-19 (¹⁹F) magnetic resonance (MR) molecular imaging is a promising noninvasive and quantitative molecular imaging approach with intensive research due to the high sensitivity and low endogenous background signal of the ¹⁹F atom in vivo. Perfluorocarbons (PFCs) have been used as blood substitutes since 1970s. More recently, a variety of PFC nanoparticles have been designed for the detection and imaging of physiological and pathological changes. These molecular imaging probes have been developed to label cells, target specific epitopes in tumors, monitor the prognosis and therapy efficacy and quantitate characterization of tumors and changes in tumor microenvironment noninvasively, therefore, significantly improving the prognosis and therapy efficacy. Herein, we discuss the recent development and applications of ¹⁹F MR techniques with PFC nanoparticles in biomedicine, with particular emphasis on ligand-targeted and quantitative ¹⁹F MR imaging approaches for tumor detection, oxygenation measurement, smart stimulus response and therapy efficacy monitoring, et al.

Mini-review: Perfluorocarbons, Oxygen Transport, and Microcirculation in Low Flow States: in Vivo and in Vitro Studies

The in vivo study of microvascular oxygen transport requires accurate and challenging measurements of several mass transfer parameters. Although recommended, blood flow and oxygenation are typically not measured in many studies where treatments for ischemia are tested. Therefore, the aim of this communication is to briefly review cardinal aspects of oxygen transport, and the effects of perfluorocarbon (PFC) treatment on blood flow and oxygenation based mostly on studies performed in our laboratory. As physiologically relevant events in oxygen transport take place at the microvascular level, we implemented the phosphorescence quenching technique coupled with noninvasive intravital videomicroscopy for quantitative evaluation of these events in vivo. Rodent experimental models and various approaches have been used to induce ischemia, including hemorrhage, micro- and macroembolism, and microvessel occlusion. Measurements show decrease in microvascular blood flow as well as intravascular and tissue oxygen partial pressure (PO2) after these procedures. To minimize or reverse the effects of ischemia and hypoxia, artificial oxygen carriers such as different PFCs were tested. Well-defined endpoints such as blood flow and tissue PO2 were measured because they have significant effect on tissue survival and outcome. In several cases, enhancement of flow and oxygenation could be demonstrated. Similar results were found in vitro: PFC emulsion mixed with blood (from healthy donors and sickle cell disease patients) enhanced oxygen transport. In summary, PFCs may provide beneficial effects in these models by mechanisms at the microvascular level including facilitated diffusion and bubble reabsorption leading to improved blood flow and oxygenation.

Advances in nanomaterials for treatment of hypoxic tumor

The hypoxic tumor microenvironment is characterized by disordered vasculature and rapid proliferation of tumors, resulting from tumor invasion, progression and metastasis. The hypoxic conditions restrict efficiency of tumor therapies, such as chemotherapy, radiotherapy, phototherapy and immunotherapy, leading to serious results of tumor recurrence and high mortality. Recently, research has concentrated on developing functional nanomaterials to treat hypoxic tumors. In this review, we categorize such nanomaterials into (i) nanomaterials that elevate oxygen levels in tumors for enhanced oxygen-dependent tumor therapy and (ii) nanomaterials with diminished oxygen dependence for hypoxic tumor therapy. To elevate oxygen levels in tumors, oxygen-carrying nanomaterials, oxygen-generating nanomaterials and oxygen-economizing nanomaterials can be used. To diminish oxygen dependence of nanomaterials for hypoxic tumor therapy, therapeutic gas-generating nanomaterials and radical-generating nanomaterials can be used. The biocompatibility and therapeutic efficacy of these nanomaterials are discussed.

Nanomedicine-Enabled Modulation of Tumor Hypoxic Microenvironment for Enhanced Cancer Therapy

Hypoxia is a common condition of solid tumors that is mainly caused by enhanced tumor proliferative activity and dysfunctional vasculature. In the treatment of hypoxic human solid tumors, many conventional therapeutic approaches (e.g., oxygen-dependent photodynamic therapy, anticancer drug-based chemotherapy or X-ray induced radiotherapy) become considerably less effective or ineffective. In recent years, various strategies have been explored to deliver or generate oxygen inside solid tumors to overcome tumorous hypoxia and show promising evidence to improve the antitumor efficiency. In this review, the extrinsic regulation of tumor hypoxia via nanomaterial delivery is discussed followed by a summary of the mechanisms through which the modulated tumor hypoxic microenvironment improves therapeutic efficacy. The review concludes with future perspectives, to specifically address the translation of nanomaterial-based therapeutic strategies for clinical applications.

Perfluorocarbons for the treatment of decompression illness: how to bridge the gap between theory and practice

Decompression illness (DCI) is a complex clinical syndrome caused by supersaturation of respiratory gases in blood and tissues after abrupt reduction in ambient pressure. The resulting formation of gas bubbles combined with pulmonary barotrauma leads to venous and arterial gas embolism. Severity of DCI depends on the degree of direct tissue damage caused by growing bubbles or indirect cell injury by impaired oxygen transport, coagulopathy, endothelial dysfunction, and subsequent inflammatory processes. The standard therapy of DCI requires expensive and not ubiquitously accessible hyperbaric chambers, so there is an ongoing search for alternatives. In theory, perfluorocarbons (PFC) are ideal non-recompressive therapeutics, characterized by high solubility of gases. A dual mechanism allows capturing of excess nitrogen and delivery of additional oxygen. Since the 1980s, numerous animal studies have proven significant benefits concerning survival and reduction in DCI symptoms by intravenous application of emulsion-based PFC preparations. However, limited shelf-life, extended organ retention and severe side effects have prevented approval for human usage by regulatory authorities. These negative characteristics are mainly due to emulsifiers, which provide compatibility of PFC to the aqueous medium blood. The encapsulation of PFC with amphiphilic biopolymers, such as albumin, offers a new option to achieve the required biocompatibility avoiding toxic emulsifiers. Recent studies with PFC nanocapsules, which can also be used as artificial oxygen carriers, show promising results. This review summarizes the current state of research concerning DCI pathology and the therapeutic use of PFC including the new generation of non-emulsified formulations based on nanocapsules.

Oxygenated UW Solution Decreases ATP Decay and Improves Survival After Transplantation of DCD Liver Grafts

BACKGROUND

Donation after circulatory death (DCD) liver grafts are known to be predisposed to primary nonfunction and ischemic cholangiopathy. Many DCD grafts are discarded because of older donor age or long warm ischemia times. Thus, it is critical to improve the quality of DCD liver grafts. Here, we have tested whether an enriched oxygen carrier added to the preservation solution can prolong graft survival and reduce biliary damage.

METHODS

We assessed the adenosine triphosphate (ATP) content decay of mouse liver grafts after cold ischemia, warm ischemia, and combined warm+cold ischemia. In addition, we used a rat model of liver transplantation to compare survival of DCD grafts preserved in high-oxygen solution (preoxygenated perfluorocarbon [PFC] + University of Wisconsin [UW] solution) versus lower oxygen solution (preoxygenated UW solution).

RESULTS

Adenosine triphosphate levels under UW preservation fall to less than 10% after 30 minutes of warm ischemia. Preoxygenated UW solution with PFC reached a significantly higher PaO2. After 45 minutes of warm ischemia in oxygenated UW + PFC solution, grafts showed 63% higher levels of ATP (P = 0.011). In addition, this was associated with better preservation of morphology when compared to grafts stored in standard UW solution. Animals that received DCD grafts preserved in higher oxygenation solution showed improved survival: 4 out of 6 animals survived long-term whereas all control group animals died within 24 hours.

CONCLUSIONS

The additional oxygen provided by PFC during static cold preservation of DCD livers can better sustain ATP levels, and thereby reduce the severity of ischemic tissue damage. PFC-based preservation solution extends the tolerance to warm ischemia, and may reduce the rate of ischemic cholangiopathy.

Multinuclear MRI at Ultrahigh Fields

In this article, an overview of the current developments and research applications for non-proton magnetic resonance imaging (MRI) at ultrahigh magnetic fields (UHFs) is given. Due to technical and methodical advances, efficient MRI of physiologically relevant nuclei, such as Na, Cl, Cl, K, O, or P has become feasible and is of interest to obtain spatially and temporally resolved information that can be used for biomedical and diagnostic applications. Sodium (Na) MRI is the most widespread multinuclear imaging method with applications ranging over all regions of the human body. Na MRI yields the second largest in vivo NMR signal after the clinically used proton signal (H). However, other nuclei such as O and P (energy metabolism) or Cl and K (cell viability) are used in an increasing number of MRI studies at UHF. One major advancement has been the increased availability of whole-body MR scanners with UHFs (B0 ≥7T) expanding the range of detectable nuclei. Nevertheless, efforts in terms of pulse sequence and post-processing developments as well as hardware designs must be made to obtain valuable information in clinically feasible measurement times. This review summarizes the available methods in the field of non-proton UHF MRI, especially for Na MRI, as well as introduces potential applications in clinical research.

Artificial Oxygen Carriers-Past, Present, and Future-a Review of the Most Innovative and Clinically Relevant Concepts

Blood transfusions are a daily practice in hospitals. Since these products are limited in availability and have various, harmful side effects, researchers have pursued the goal to develop artificial blood components for about 40 years. Development of oxygen therapeutics and stem cells are more recent goals. Medline (https://www.ncbi.nlm.nih.gov/pubmed/?holding=ideudelib), ClinicalTrials.gov (https://clinicaltrials.gov), EU Clinical Trials Register (https://www.clinicaltrialsregister.eu), and Australian New Zealand Clinical Trials Registry (http://www.anzctr.org.au) were searched up to July 2018 using search terms related to artificial blood products in order to identify new and ongoing research over the last 5 years. However, for products that are already well known and important to or relevant in gaining a better understanding of this field of research, the reader is punctually referred to some important articles published over 5 years ago. This review includes not only clinically relevant substances such as heme-oxygenating carriers, perfluorocarbon-based oxygen carriers, stem cells, and organ conservation, but also includes interesting preclinically advanced compounds depicting the pipeline of potential new products. In- depth insights into specific benefits and limitations of each substance, including the biochemical and physiologic background are included. "Fancy" ideas such as iron-based substances, O₂ microbubbles, cyclodextranes, or lugworms are also elucidated. To conclude, this systematic up-to-date review includes all actual achievements and ongoing clinical trials in the field of artificial blood products to pursue the dream of artificial oxygen carrier supply. Research is on the right track, but the task is demanding and challenging.

Air Embolism During TEVAR: Liquid Perfluorocarbon Absorbs Carbon Dioxide in a Combined Flushing Technique and Decreases the Amount of Gas Released From Thoracic Stent-Grafts During Deployment in an Experimental Setting

Purpose:To investigate the influence of flushing thoracic stent-grafts with carbon dioxide and perfluorocarbon on the amount of gas released during stent-graft deployment in thoracic endovascular aortic repair (TEVAR). Materials and Methods: Ten TX2 ProForm thoracic stent-grafts were deployed into a water-filled container with a curved plastic pipe and flushed sequentially with carbon dioxide, 20 mL of liquid perfluorocarbon (PFC), and 60 mL of saline. Released gas was measured using a calibrated setup. The volume of released gas was compared with the results of an earlier published reference group, in which identical stent-grafts were flushed with 60 mL saline alone as recommended in the instructions for use. Results: The average amount of gas released in the test group was 0.076 mL, significantly lower (p<0.001) than the mean 0.79 mL of gas released in the reference group. Big bubbles appearing at the tip of the sheath when deployment was started were seen in all grafts of the reference group but in only 2 of the test group stent-grafts. Small bubbles were less frequent in the test group. Conclusion: The amount of gas released from thoracic stent-grafts during deployment can be influenced by different flushing techniques. The use of PFC in addition to the carbon dioxide flushing technique reduces the volume of gas released during deployment of tubular thoracic stent-grafts to a few microliters. This significant effect is presumably based on the high solubility of carbon dioxide in perfluorocarbon and could be a potential future approach to lower the risk of cerebral injury and stroke from air embolism during TEVAR.