Philip Sargent
January 05, 1999
Medical implants which deliver drugs and metabolic supplements will grow in sophistication and capability; driven not so much by technology as by human need.
Initial implants give staged delivery of drugs stored in a reservoir which must be periodically refilled. Some implants extend this to handling several drugs and to responding to internal or external stimuli, e.g. blood sugar level or the presence of an external magnetic field.
There is a distinct limit to how far this can go since dozens of drugs and and annual refillings become unpleasant and costly. At some point, it becomes sensible for implants to synthesize the drug from a few standard reagents - which leads directly to the conclusion that the drugs could be proteins and the raw materials the amino acids. A simpler alternative would be where the drugs are RNA fragments themselves with no protein synthesis step. RNA fragments do not have anything like the range of shape and catalytic action that enzymes have; but they do have useful activity. In either case, the implant technology can then create drugs which were unthought of at the time the implant was inserted into the patient; but still use the same raw materials. Some of this chip technology has been developed already.
This is an immense advantage but it can only be useful if the implant can be reprogrammed in place. It has a strong commercial driving force in that programmable drugs mean that only one implant design is required and they can be manufactured in millions.
RNA or amino acids are in principle derivable from the blood, and getting rid of the need to recharge raw materials by injection would be greatly appreciated. However some materials are perhaps more easily extracted: sugars. Polysaccharides are constructed from a smaller range of raw materials than proteins, but can have shapes and catalytic actions almost as complex. There is no simple code for translating RNA to polysaccharides (as there is for RNA to protein) as sugars can be attached to each other at several positions; unlike amino acids which (mostly) have a single amino group and a single acid group and so string together like beads in a row. However, polysaccharide drugs may be an appropriate engineering solution for medicine-delivering implants.
An implant industry would create a situation where eventually a great part of the value of the market would be in the software which created slightly improved drugs, probably specific to each individual.