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categories: ["bodies", "nanomedicine"]categories: ["bodies", "nanomedicine"]tags: ["transfusion", "oxygen carriers", "haemoglobin", "trauma", "cell culture", "clinical trials"]tags: ["transfusion", "oxygen carriers", "haemoglobin", "trauma", "cell culture", "clinical trials"]summary: "Engineered substitutes for the oxygen-carrying function of blood, including haemoglobin carriers, perfluorocarbon emulsions and cultured red cells, none in general clinical use."summary: "Engineered substitutes for the oxygen-carrying function of blood, including haemoglobin carriers, perfluorocarbon emulsions and cultured red cells, none in general clinical use."updated: "2026-07-27"updated: "2026-10-29"humanEvidence: "Trials of cell-free haemoglobin carriers in people showed excess mortality and myocardial infarction across sixteen studies; the human data on cultured red cells are small tagged-volume transfusions in volunteers."humanEvidence: "Trials of cell-free haemoglobin carriers in people showed excess mortality and myocardial infarction across sixteen studies; the human data on cultured red cells are small tagged-volume transfusions in volunteers."access: "No product is licensed in the United States for general transfusion; a polymerized bovine carrier is licensed in South Africa and available in the US only under expanded access, and cultured red cells exist only inside trials."access: "No product is licensed in the United States for general transfusion; a polymerized bovine carrier is licensed in South Africa and available in the US only under expanded access, and cultured red cells exist only inside trials."reversibility: "reversible"reversibility: "reversible"lines 30–36 → 30–3615 unchanged lines not shown
}}`````` **Artificial blood** refers to manufactured substitutes for the oxygen-carrying function of red cells. The term is misleading in a way worth stating at the outset: no product replaces blood. Blood carries oxygen and carbon dioxide, clots, transports immune cells, buffers pH, distributes hormones and regulates temperature. Every substitute developed so far addresses only oxygen transport, and is more accurately called an oxygen therapeutic. Four decades of development have produced one product approved and withdrawn in the United States, several approved in other jurisdictions or for veterinary use, a large trial record of harm, and a recent shift toward growing real red cells in culture instead.**Artificial blood** refers to manufactured substitutes for the oxygen-carrying function of red cells. The term is misleading, because no product replaces blood. Blood carries oxygen and carbon dioxide, clots, transports immune cells, buffers pH, distributes hormones and regulates temperature. Every substitute developed so far addresses only oxygen transport, and is more accurately called an oxygen therapeutic. Four decades of development have produced one product approved and withdrawn in the United States, several approved in other jurisdictions or for veterinary use, a large trial record of harm, and a recent shift toward growing real red cells in culture instead. ## What a substitute has to do## What a substitute has to do lines 38–44 → 38–441 unchanged line not shown
## Haemoglobin-based oxygen carriers## Haemoglobin-based oxygen carriers The obvious approach is to use haemoglobin without the cell around it. Cell-free haemoglobin binds oxygen, needs no blood typing, can be sterilized, and can be stored at room temperature for a year or more — the properties that make it attractive for trauma care, military medicine and settings without a cold chain.The obvious approach is to use haemoglobin without the cell around it. Cell-free haemoglobin binds oxygen, needs no blood typing, can be sterilized, and can be stored at room temperature for a year or more. Those properties make it attractive for trauma care, military medicine and settings without a cold chain. Raw haemoglobin outside a red cell behaves badly. The tetramer dissociates into dimers small enough to be filtered by the kidney, causing renal injury. It is not protected by the red cell's reducing enzymes, so it oxidizes to methaemoglobin and releases free haem and iron, which drive oxidative tissue damage. Its oxygen affinity is wrong without the 2,3-diphosphoglycerate that red cells supply. And, most consequentially, it moves freely into the space between endothelial cells and there scavenges nitric oxide, the signalling molecule that keeps arterioles dilated.Raw haemoglobin outside a red cell behaves badly. The tetramer dissociates into dimers small enough to be filtered by the kidney, causing renal injury. It is not protected by the red cell's reducing enzymes, so it oxidizes to methaemoglobin and releases free haem and iron, which drive oxidative tissue damage. Its oxygen affinity is wrong without the 2,3-diphosphoglycerate that red cells supply. And, most consequentially, it moves freely into the space between endothelial cells and there scavenges nitric oxide, the signalling molecule that keeps arterioles dilated. lines 51–57 → 51–576 unchanged lines not shown
The decisive analysis was a 2008 meta-analysis by Charles Natanson and colleagues covering sixteen trials of five different products across several clinical settings. It found an increase in mortality of roughly thirty percent and a near-tripling of myocardial infarction risk associated with these agents, and the effect was consistent across products, which pointed to a class mechanism rather than a manufacturing defect.[^natanson2008] The mechanism generally accepted is nitric oxide scavenging: an agent designed to deliver oxygen constricts the vessels that deliver it, raising blood pressure and reducing perfusion of the microcirculation, with the heart the most vulnerable organ.The decisive analysis was a 2008 meta-analysis by Charles Natanson and colleagues covering sixteen trials of five different products across several clinical settings. It found an increase in mortality of roughly thirty percent and a near-tripling of myocardial infarction risk associated with these agents, and the effect was consistent across products, which pointed to a class mechanism rather than a manufacturing defect.[^natanson2008] The mechanism generally accepted is nitric oxide scavenging: an agent designed to deliver oxygen constricts the vessels that deliver it, raising blood pressure and reducing perfusion of the microcirculation, with the heart the most vulnerable organ. > [!caution] A class effect, not a bad batch> [!caution] A class effect, not a bad batch> The consistency of the harm signal across chemically distinct products is what makes the haemoglobin approach hard to rescue. Any successor has to keep haemoglobin away from endothelial nitric oxide, which in practice means putting it back inside something — a vesicle, a polymer shell, a cell.> The consistency of the harm signal across chemically distinct products is what makes the haemoglobin approach hard to rescue. Any successor has to keep haemoglobin away from endothelial nitric oxide, which in practice means putting it back inside something: a vesicle, a polymer shell or a cell. ## Perfluorocarbons## Perfluorocarbons lines 65–75 → 65–757 unchanged lines not shown
The current field splits along the line the meta-analysis drew.The current field splits along the line the meta-analysis drew. One branch puts haemoglobin back inside a container. Liposome-encapsulated haemoglobin vesicles, developed principally in Japan using haemoglobin purified from expired donor blood, are in early-phase human testing; the encapsulation is intended to prevent extravasation and nitric oxide scavenging while retaining long shelf life. Polymer-nanoparticle carriers with pH-sensitive oxygen release are in preclinical development under military funding, on the argument that the decisive use case is prehospital haemorrhage where no blood bank exists. These belong to the same family of engineered carriers described in [[targeted-drug-delivery]] and [[lipid-nanoparticles]]. They are also the closest existing objects to the artificial red cell proposed in [[respirocytes]], and the comparison is instructive: the proposed device assumes pressurised diamondoid vessels and onboard control systems of a kind that [[medical-nanorobots]] as a field has not built, while the real vesicles are liposomes filled with purified human protein and perform a fraction of the imagined function.One branch puts haemoglobin back inside a container. Liposome-encapsulated haemoglobin vesicles, developed principally in Japan using haemoglobin purified from expired donor blood, are in early-phase human testing; the encapsulation is intended to prevent extravasation and nitric oxide scavenging while retaining long shelf life. Polymer-nanoparticle carriers with pH-sensitive oxygen release are in preclinical development under military funding, on the argument that the decisive use case is prehospital haemorrhage where no blood bank exists. These belong to the same family of engineered carriers described in [[targeted-drug-delivery]] and [[lipid-nanoparticles]]. They are also the closest existing objects to the artificial red cell proposed in [[respirocytes]]. That proposed device assumes pressurised diamondoid vessels and onboard control systems of a kind that [[medical-nanorobots]] as a field has not built, while the real vesicles are liposomes filled with purified human protein and perform a fraction of the imagined function. The other branch grows real red cells. Human haematopoietic stem cells from donated blood, or immortalized erythroid progenitor lines of the kind established at Bristol, can be differentiated in culture into enucleated red cells.[^trakarnsanga2017] The RESTORE trial in the United Kingdom, run by NHS Blood and Transplant with university partners, performed the first in-human transfusion of laboratory-grown red cells in 2022, giving volunteers small volumes of tagged cultured cells alongside standard donor cells to compare survival in circulation. Cultured cells are all newly made, whereas a donated unit contains cells of every age, so a cultured transfusion may last longer and require less frequent transfusion — the trial's actual hypothesis, and one that matters most for patients with thalassaemia or sickle cell disease who are transfused for life and accumulate alloantibodies. See [[casgevy]] for the curative alternative in those diseases.The other branch grows real red cells. Human haematopoietic stem cells from donated blood, or immortalized erythroid progenitor lines of the kind established at Bristol, can be differentiated in culture into enucleated red cells.[^trakarnsanga2017] The RESTORE trial in the United Kingdom, run by NHS Blood and Transplant with university partners, performed the first in-human transfusion of laboratory-grown red cells in 2022, giving volunteers small volumes of tagged cultured cells alongside standard donor cells to compare survival in circulation. Cultured cells are all newly made, whereas a donated unit contains cells of every age, so a cultured transfusion may last longer and require less frequent transfusion. That is the trial's actual hypothesis, and it matters most for patients with thalassaemia or sickle cell disease who are transfused for life and accumulate alloantibodies. See [[casgevy]] for the curative alternative in those diseases. The obstacle is arithmetic. A single unit of blood contains about two trillion red cells. Culturing that many, reproducibly, at a cost within reach of a health service, is a manufacturing problem several orders of magnitude beyond current bioreactor capacity, and cultured units are presently many times more expensive than donated ones. It is the same scale-up wall that constrains [[tissue-engineering]] generally, without the additional requirement of building a structure. Deriving red cells from [[induced-pluripotent-stem-cells]] would remove the dependence on donor progenitors entirely, and has been demonstrated at laboratory scale with poor enucleation efficiency. The near-term application is therefore not general transfusion but small volumes of rare blood groups that are difficult to source from donors.The obstacle is arithmetic. A single unit of blood contains about two trillion red cells. Culturing that many, reproducibly, at a cost within reach of a health service, is a manufacturing problem several orders of magnitude beyond current bioreactor capacity, and cultured units are presently many times more expensive than donated ones. It is the same scale-up wall that constrains [[tissue-engineering]] generally, without the additional requirement of building a structure. Deriving red cells from [[induced-pluripotent-stem-cells]] would remove the dependence on donor progenitors entirely, and has been demonstrated at laboratory scale with poor enucleation efficiency. The near-term application is therefore small volumes of rare blood groups that are difficult to source from donors, rather than general transfusion. A parallel line of work attacks supply rather than substitution, using enzymes discovered in gut bacteria to strip the A and B antigens from donor red cells and convert them to universal group O.[^rahfeld2019] Efficiency has improved and the approach would ease matching rather than replace donation.A parallel line of work attacks supply rather than substitution, using enzymes discovered in gut bacteria to strip the A and B antigens from donor red cells and convert them to universal group O.[^rahfeld2019] Efficiency has improved and the approach would ease matching rather than replace donation. removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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