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Respirocytes are hypothetical, microscopic, artificial red blood cells that are intended to emulate the function of their organic counterparts, so as to supplement or replace the function of much of the human body's normal respiratory system. Respirocytes were proposed by Robert A. Freitas Jr in his 1998 paper "A Mechanical Artificial Red Blood Cell: Exploratory Design in Medical Nanotechnology".[1]
Respirocytes are an example of molecular nanotechnology, a field of technology still in the very earliest, purely hypothetical phase of development. Current technology is not sufficient to build a respirocyte due to considerations of power, atomic-scale manipulation, immune reaction or toxicity, computation and communication.

DNA origami nanorobot takes drug direct to cancer cell
By Jessica Hamzelou
How is this for a clever robot? Tiny probes built from DNA can seek and destroy cancer cells, leaving healthy cells untouched. These clam-like bots, which release their drug payload only when they reach and identify their target, could improve many treatments for disease.
Shawn Douglas and his colleagues at Harvard University’s Wyss Institute have used “DNA origami” to build the nanorobot.
The team designed the device with DNA modelling software that understands how DNA base pairs bind together, as well as the helical structure that results. When they enter a shape of their choosing into the program, it returns a list of DNA strands that can be mixed together to create the desired shape.
The shape that Douglas and his colleagues had in mind was clam-like, so that the nanorobot could hold a drug dose inside until it was time to deliver it.
To ensure that the clam only opened when it found its target, the team fitted the nanorobot with two locks. Each lock is a strand of DNA called an aptamer that can be designed to recognise a specific molecule. When the aptamer and target molecule meet, the DNA strand unzips, unlocking the clam and releasing the payload.
Collateral damage
To test its therapeutic potential, Douglas’s team created a nanorobot with locks that unzipped in response to molecules expressed on the surface of leukaemia cells. The team then loaded it with a single molecule known to kill cells by interfering with their growth cycle. Finally, they released millions of copies into a mixture of healthy and cancerous human blood cells.
Three days later, around half of the leukaemia cells had been destroyed, but no healthy cells had been harmed.
Douglas reckons that by adding additional payloads to cripple more of the cells’ normal functioning, his team could target every last one of the leukaemia cells. What’s more, by altering the lock, the nanorobots could be designed to target any type of cell.
Having two locks means that a nanorobot is better able to distinguish diseased and healthy cells, says Douglas. “It would require that two different signals have to be present to open it, increasing its specificity,” he says. He hopes the cancer-targeting nanorobots can leave untouched other types of rapidly dividing cells, such as those in the gut and at hair follicles, that often suffer collateral damage during chemotherapy.
Exquisitely targeted
Jørgen Kjems at Aarhus University in Denmark agrees. “The group provide proof of principle that DNA origami has the capacity to create highly intelligent drugs that activate only on encountering diseased cells,” he says. “This will inevitably lower the toxicity and side effects of the drugs carried within the device.”
Paul Rothemund at the California Institute of Technology in Pasadena is also hopeful. “Smart drugs which can be exquisitely targeted to specific cell types are a major goal of biomedical research,” he says. “The ability to [match] the binding of the clam shell to the targeted cell type and use this as a trigger for delivery is a major step beyond the smart drugs of today.”
“The next step will be to ensure the DNA nanorobot can withstand the destructive environment of living organisms,” says Kjems. “Once this has been accomplished, there’s promise that scientists can create new and more effective medicines for animals and humans.”

A microbivore is a speculative future device, a micromachine with numerous internal nanomachines, which would function as an artificial white blood cell, or phagocyte. Although a detailed design for a microbivore has been outlined by its inventor, Robert Freitas, we currently lack the means to fabricate it.
Including moving parts with dimensions as small as 150 nanometers, fabrication of a microbivore would likely require atom-by-atom manufacturing based on mechanosynthesis. “Mechanosynthesis” refers to chemical reactions orchestrated by the specific programmed motions of nanoscale robotic arms. Such a manufacturing technology has been referred to as molecular nanotechnology by its primary conceiver, Dr. Eric Drexler. Some futurists anticipate the development of molecular nanotechnology in the 2020-2030 time range.
The medical necessity for a microbivore is obvious – there are numerous pathologies involving the presence of foreign organisms in the bloodstream. Collectively, these are called sepsis, with ~1.5 million annual cases and ~0.5 million annual deaths worldwide. Foreign infections in the bloodstream are especially dangerous to immunocompromised individuals, such as those suffering from AIDS. Many of the current therapies are crude and merely arrest the growth of foreign organisms in the bloodstream rather than wipe them out entirely. Many physicians would welcome a synthetic device capable of performing search-and-destroy missions on such microbes.

关键性问题是能够自我复制或者批量制造么？

将生命还给自然，可控制他人健康的科技监管不利得有多可怕。