Hydrogel implants: fiber optic network for your body?

[rhoenix]

The biggest problem with wetware is the “ware” part. Enormous metal implants like those seen in The Matrix or Elysium look cool and all, but any real-world interface of metal and flesh is precarious; surface implants are often rejected by the body, leading to infection and even death. Technology has gotten smaller, more efficient, and able to better communicate wirelessly, but for all the nifty implants we can build, actually implanting them has proven difficult, and controlling them even more so. Now, researchers at Massachusetts General Hospital claim that a special hydrogel could change all that.

A hydrogel is an extremely absorbent type of gel, a network of simple polymers that can contain up to 99.9% water, by weight. While life has had little time to make friends with aluminum or sterile plastic, water-heavy polymer networks are its bread and butter, and this research found that mice have no trouble accepting implants made out of this flexible, non-toxic substance.

To understand why that matters, consider a fiber optic cable. Like the walls of this transparent hydrogel, the material lining the interior of an optical fiber is clear, but tuned to produce a phenomenon called total internal reflection. This means that light moving at certain angles from the cable’s core material to its lining will be entirely reflected, as though by a mirror. By tuning their hydrogel to create the same effect, they created a form of bio-compatible optical cable — the researchers call it a “light guiding hydrogel.”

Getting light into the body is important for a number of reasons. In the most basic sense, pulses of light are information, and having a hard-wired line of communication to implanted technology will be important for their development; wireless tech is still too unreliable for most people to bet their lives on, and it’s also notoriously hard on power consumption. This hydrogel implant stretched four centimeters into the mouse’s body, giving the scientists a hard-wire to both read and control the mouse’s internal states.

This study opted to test a more advanced possible use for the hydrogel, however: optogenetics. If that word seems foreign, it’s because the field is actually only a few years old. Cutting edge techniques in genetic manipulation let scientists create light-sensitive neurons that fire when exposed to blue light — so-called “on demand” neural control. Quickly enough the logic was reversed, so colonies of cells can now light up to signal the presence of some toxin or other chemical trigger. Light-sensitive proteins can now even turn specific cellular processes on and off at will.

And yet, just as we saw with mechanical implants, putting all this wonderful technology to use in the real world proves problematic. Light control was usually only skin deep, or required implants too invasive for use in humans. This hydrogel provides a literal path for such light signals to follow, ferrying light signals either from surface to cells or from cells to surface.

As their proof of concept, the researchers used their hydrogel implant as a scaffold for small colonies that produce the protein GLP-1 in response to blue light. GLP-1 is an important protein for glucose metabolism, helping to stimulate the secretion of insulin, so the researchers here have demonstrated a very broad possible mechanism for treating certain types of diabetes. Implanted, diabetic mice exposed to the blue light signal showed a markedly better response to glucose than implanted diabetic mice that received no light.

This is the first time anybody has been able to speak optically with cells deep inside the body, and the sheer number of possible applications is dizzying. Monitor cells could sit happily for years near a problem site until they light up in response to a worrying chemical symptom — imagine if your wristwatch could alert you to allergens in your system, prompting you to pop an antihistamine. Hunter-killer immune cells could flood the blood stream in response to a blue-light signal, a sort of endogenous antibiotic under your doctor’s control. Such uses are totally plausible, given a mechanism of communication between internal cells and the outside world.

The next step for the team is to improve its results; how can the hydrogel be refined or reshaped to provide better light propagation? How can we improve or specifically control the gel’s lifetime within the body? Could a light emitter in one part of the body speak directly to a receiver elsewhere, without ever interacting with the surface? Such questions in bio-networking are quickly becoming relevant.

Well now, this is vaguely disquieting and yet very interesting.