May 4, 2012

Gastric fluid interactions with plastics

Green apple timeline.jpg

The environment of the upper gastrointestinal tract, including the stomach, can challenge materials placed into this environment. The pH environment can range from 1.5-2.0 prior to eating, but can spike up to pH~7 during and immediately after meals, requiring an hour or more to fall back to normal levels. Contrary to commonly held beliefs, the stomach does not continuously contain fluid, but only partially fills in anticipation of eating or drinking. The peristaltic action of the stomach grinds food against the stomach walls and itself, and enzymes act to help degrade food, along with the hydrochloric acid present in stomach acid.

Polymers sometimes find their way into the stomach environment, in the form of sutures, drug-release components, satiety treatments (e.g. balloons), and other temporary or permanent implants. Knowledge of how these materials will respond to the stomach environment will help to predict their performance. In some cases, the polymers are designed to respond to the stomach environment itself, swelling or deswelling in response to pH, salinity, temperature, or fluid content. In other cases, the polymer may degrade in response to these conditions.

Researchers at Cambridge Polymer Group have designed custom systems to simulate the stomach's environment. Using test methods with reference to ASTM D523, polymers systems are tested before and after model gastric fluid exposure to demonstrate the change in mechanical, chemical, and morphological properties.