William G. Pitt

Polymeric Biomaterials

Implanted medical devices in contact with living tissue usually elicit adverse responses from the body.  For example, blood contacting devices usually cause thrombus formation, and implants under the skin or in muscle cause a "foreign body" response in which the body encapsulates the implant with a collagenous "scar" tissue.  In tissue engineering, we desire to grow cells on solid substrates, and usually the cells don't grow well because they "recognize" the foreign surface.  We are currently working on a technology to fake out the cells by covalently attaching hyaluronic acid to the metal or polymeric surface.  Hyaluronic acid is a natural biopolymer made by the body as a "basement membrane" to which cells attach naturally in the body.  The cells grow well because they feel as if they are in their natural environment.  We have submitted one patent on attaching hyaluronic acid to polymers, and we are working on attaching them to orthopedic metals such as stainless steel and titanium alloys.

In another project involving polymer synthesis, we are polymerizing crosslinked hydrogels inside surfactant micelles.  These hydrogels have stealth character such that they are not recognized and cleared out by the body, so they circulate in the blood for long times.  The polymer inside the stealth micelles keeps the micelle from dissolving when they are diluted in the blood.  We have also discovered that we can selectively release the drugs from these carriers by the application of ultrasound.  We are actively studying this phenomenon, and are designing and synthesizing drug carriers and their stabilizing polymers.  Our goal is to be able to make a drug carrier that will release the drug in the body only when activated by ultrasound.