Development of acrylic-based copolymers for oral insulin delivery.

We developed nanospheres of crosslinked networks of methacrylic acid grafted with poly(ethylene glycol), and acrylic acid grafted with poly(ethylene glycol) nanospheres for use as oral insulin delivery devices. The copolymer nanospheres were synthesized via free-radical precipitation/dispersion. The average particle diameter of the copolymer gel nanospheres at various physiologically relevant pH values was characterized using photon correlation spectroscopy. Their size increased dramatically as the surrounding pH rose above the pK(a) of the network. The nanospheres ranged in diameters from 200 nm at pH of 2.0 to 2 microm at pH around 6.0. Insulin was loaded into the copolymers at levels of 9.33 and 9.54 mg per 140 mg solid sample, by partitioning from concentrated insulin solutions. In vitro studies were performed to study the passage of the insulin-loaded copolymer samples in the gastrointestinal tract. Insulin was entrapped at low pH (pH=3.0) but released at more neutral pH (pH=7.0). Animal studies were performed to investigate the abilities of insulin-loaded copolymer samples to influence the serum glucose levels of rats. In studies with diabetic rats, the serum glucose level was lower than control values for the animals that received the insulin-loaded copolymers and lasted for at least 6 h. The insulin loaded copolymer nanospheres caused a significant reduction of serum glucose with respect to that of a control animal.