Members of the Society of Plastics Engineers got a glimpse inside the body - where polymers deliver timed-release drugs and help to grow new bones - during a biomaterials session May 2 at the Antec 2005 conference in Boston.
``My personal belief is that plastics and polymers have a huge future in medicine and medical devices,'' said keynote speaker Robert Langer.
Langer cited a ``real revolution in the way we take drugs'' over the past 25-30 years, and said, ``It's really largely due to plastics.''
Langer, a professor of chemical and biomedical engineering at Massachusetts Institute of Technology, is a leading expert in using polymers to deliver medicine. Current examples include the Norplant implant that delivers a contraceptive for five years and a one-day nitroglycerin patch for treating angina.
Polymers ``keep the drug level very steady, and also deliver it for a long time,'' Langer said.
The result has been a boom in sales of polymer-based drug-delivery systems, from zero in 1980 to $28 billion last year in the United States, and about $50 billion worldwide, he said.
Langer first got interested in the subject in the 1970s, working with a surgeon who pioneered the study of the growth of blood vessels. The goal was to deliver medicines, which were large molecules and hard to absorb, inside the body, while protecting it from harm over time. Conventional wisdom said that was impossible, he recalled.
After several years in the laboratory, Langer said they came up with polymer microspheres with a key pore structure that enabled a slow, controlled release of the molecules of medicine, Langer said.
``What we found is that there are many tight constrictions between the pores, and the pores are very winding and torturous. So it takes a very long time for the molecules to wind their way through. I sometimes explain this to people, it's like driving a car through Boston,'' Langer said, drawing chuckles.
Examples of microsphere delivery systems now on the market include treatments for prostate cancer and timed release of medicine for schizophrenia.
In his research, Langer discovered you could customize the timed-release function by ``dialing in the monomer ratio'' of the polymer. That avoided a sudden burst release of medicine, which in the case of harsh drugs like cancer medicines, can be harmful.
MIT research led to the practice of lining the brain cavity with small discs of polymers containing slow-release medicine, after brain surgery for cancer. The Food and Drug Administration approved the ``local chemotherapy'' treatment in 1997, he said.
Langer also took his audience far into the future of medical polymers. It might be possible to adopt the technology used to print tiny wires and wells onto computer chips to engineer a ``phamacy on a chip,'' he said.
The wells could be filled with several medicines, each carried by a polymer of a different molecular weight. The patient could carry a device that releases the medicines at different times.
Langer also speculated that doctors one day will use computer-aided design to grow cartilage tissue on a polymer scaffold - and custom-design a new nose for a patient.
The researcher also showed a video clip of a loosely tied, degradable plastic string that automatically tightens into a knot when it reaches body temperature. Given the interest today in minimally invasive surgery, a self-tying suture should get a lot of attention, he said.
Another speaker in the Antec biomedicals session, Thomas Barrows, is an authority on the tissue engineering of bones.
Barrows co-founded Bioamide Inc., which was sold in 2002 to Aderans Research Institute Inc. Today, he is director of product development at Aderans' facility in Atlanta.
The key is creating a scaffold structure on which to grow new bones, to repair a broken bone more quickly. Bone-growth cells, encapsulated inside polymers, are seeded onto the scaffold and the structure is implanted into the patient.
``The tissue-engineered construct will integrate with the damaged bone, and ultimately remodel to the fully functional bone,'' Barrow said.
The scaffold must be large and strong, but also very porous to accept the seeded bone cells, he said.
The scaffold degrades in 12-18 months, leaving the new bone.