The goal of oral insulin delivery devices is to protect the sensitive drug from proteolytic degradation in the stomach and upper portion of the small intestine. In this work, we investigate the use of pH-responsive, poly(methacrylic-g-ethylene glycol) hydrogels as oral delivery vehicles for insulin. Insulin was loaded into polymeric microspheres and administered orally to healthy and diabetic Wistar rats. In the acidic environment of the stomach, the gels were unswollen due to the formation of intermolecular polymer complexes. The insulin remained in the gel and was protected from proteolytic degradation. In the basic and neutral environments of the intestine, the complexes dissociated which resulted in rapid gel swelling and insulin release. Within 2 h of administration of the insulin-containing polymers, strong dose-dependent hypoglycemic effects were observed in both healthy and diabetic rats. These effects lasted for up to 8 h following administration.

The purpose of this study was to assess the relative advantages and drawbacks of the nanoprecipitation-solvent displacement method for a range of drugs with respect to the particle size and drug encapsulation in polylactic-co-glycolic acid (PLGA) nanoparticles. The particle size analysis indicated a unimodal particle size distribution in all systems, with a mean diameter of 160-170 nm, except for insulin nanoparticles, which showed a smaller particle size. The results of the encapsulation efficiency analysis demonstrated that more lipophilic drugs, such as cyclosporin and indomethacin, do not suffer from the problems of drug leakage to the external medium, resulting in improved drug content in the nanoparticles. In spite of the fact that valproic acid is a liquid that is very sparingly soluble in water, very low encapsulation efficiency was obtained. Ketoprofen, a drug sparingly soluble in water, demonstrated intermediate values of encapsulation that were well correlated with its intermediate lipophilicity. More hydrophilic drugs, such as vancomycin and phenobarbital, were poorly encapsulated in PLGA nanoparticles. Insulin was preferentially surface bound on the PLGA nanoparticles. However, a strong hypoglycemic effect of the insulin was observed after administration of the suspension of PLGA nanoparticles with surface-bound insulin to the ileum loop of male Wistar rats.

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