the size of a human rbc. they are made from purified human hemoglobin proteins that have been coated with a synthetic polymer. thanks to the special materials of the artificial rbc, they can capture oxygen when blood ph is high, and release oxygen when blood ph is low. the polymer coating also keeps the hemoglobin from reacting with nitric oxide in the bloodstream, thus preventing dangerous constriction of the blood vessels. allan doctor, md, stated that the artificial rbc can be used by anyone, with any blood type because the coating is immune silent. testes men whom have sustained testicular abnormalities through birth defects or injury have been able to replace the damaged testicle with a testicular prosthesis. although the prosthetic does not restore biological reproductive function, the device has been shown to improve mental health for these patients. thymus an implantable machine that performs the function of a thymus does not exist. however, researchers have been able to grow a thymus from reprogrammed fibroblasts. they expressed hope that the approach could one day replace or supplement neonatal thymus transplantation. as of 2017, researchers at ucla developed an artificial thymus that, although not yet implantable, is capable of performing all functions of a true thymus. the artificial thymus would play an important role in the immune system, it would use blood stem cells to produce more t cells, which would help the body fight infections, it would also grant the body the ability to eliminate cancer cells. since when people become old, their thymus don't work well, an artificial thymus would be a good choice to replace an old, not-functioning-well thymus. the idea of using t cells to fight against infections has been around for a time, but until recently, the idea of using a t cell source, an artificial thymus is proposed. "we know that the key to creating a consistent and safe supply of cancer-fighting t cells would be to control the process in a way that deactivates all t cell receptors in the transplanted cells, except for the cancer-fighting receptors," said dr. gay crooks of ucla. the scientist also found that the t cells produced by the artificial thymus carried a diverse range of t cell receptors and worked similarly to the t cells produced by a normal thymus. since they can work like human thymus, artificial thymus can supply a consistent amount of t cells to the body for the patients who are in need of treatments. trachea the field of artificial tracheas went through a period of high interest and excitement with the work of paolo macchiarini at the karolinska institute and elsewhere from 2008 to around 2014, with front-page coverage in newspapers and on television. concerns were raised about his work in 2014 and by 2016 he had been fired and high level management at karolinska had been dismissed, including people involved in the nobel prize. as of 2017 engineering a trachea—a hollow tube lined with cells—had proved more challenging than originally thought; challenges include the difficult clinical situation of people who present as clinical candidates, who generally have been through multiple procedures already; creating an implant that can become fully developed and integrate with host while withstanding respiratory forces, as well as the rotational and longitudinal movement the trachea undergoes. enhancement it is also possible to construct and install an artificial organ to give its possessor abilities that are not naturally occurring. research is proceeding in areas of vision, memory, and information processing. some current research focuses on restoring short-term memory in accident victims and long-term memory in dementia patients. one area of success was achieved when kevin warwick carried out a series of experiments extending his nervous system over the internet to control a robotic hand and the first direct electronic communication between the nervous systems of two humans. this might also include the existing practice of implanting subcutaneous chips for identification and location purposes (ex. rfid tags). microchips organ chips are devices containing hollow microvessels filled with cells simulating tissue and/or organs as a microfluidic system that can provide key chemical and electrical signal information. this is distinct from an alternative use of the term microchip, which refers to small, electronic chips that are commonly used as an identifier and can also contain a transponder. this information can create various applications such as creating "human in vitro models" for both healthy and diseased organs, drug advancements in toxicity screening as well as replacing animal testing. using 3d cell culture techniques enables scientists to recreate the complex extracellular matrix, ecm, found in in vivo to mimic human response to drugs and human diseases. organs on chips are used to reduce the failure rate in new drug development; microengineering these allows for a microenvironment to be modeled as an organ.