The use of pH-responsive poly (methacrylic-g-ethylene glycol) hydrogels as oral delivery vehicles for insulin was evaluated. 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.

Niosomes

These are nonionic surfactant vesicles having a bilayer structure formed by the self-assembly of hydrated surfactant monomers. The bilayer is multilamellar or unilamellar and enclose aqueous solution of solutes and lipophilic components. Niosomes are formed by the hydration of nonionic surfactant dried film, resulting in imbibing or encapsulating the hydrating solution. The major component of niosomes is a nonionic surfactant. This gives an advantage of being more stable when compared to liposomes, thus overcoming problems such as susceptibility to oxidation, high cost, difficulty in procuring and high purity levels, which can influence the size, shape and stability of the vesicles. Niosomes can entrap both hydrophilic and lipophilic drugs in aqueous layer and vesicular membrane, respectively. Niosomes can serve as drug depots in the body, which release the drug in a controlled or sustained manner. They improve the oral bioavailability of poorly soluble drugs and also enhance the skin permeability of drugs when applied topically.

Microsponges

These can be defined as microscopic spheres capable of absorbing skin secretions. They contain particles of size 1025 microns in diameter and are capable of entrapping a wide range of ingredients in a single microsponges system and releasing them at desired rates. Drug release from microsponges is done by external stimuli such as pH, temperature and rubbing. It has several advantageous over the other topical preparations in being nonallergenic, nontoxic, nonirritant and nonmutagenic in nature. Microsponges can be used in sunscreens, creams, ointments and over-the-counter skin care preparations.

Liposomes

These are microscopic spheres with an aqueous core surrounded by one or more outer shells consisting of lipids arranged in a bilayer configuration. Liposomes can encapsulate hydrophilic and lipophilic drugs and protect them from degradation. They also have an affinity to keratinize horny layer of skin and can penetrate deeper into skin to give better absorption. Applied on the skin, liposomes may act as a solubilizing matrix for poorly soluble drugs, a penetration enhancer and a local drug depot. Topical liposome formulations could be more effective and less toxic than conventional formulations. The liposome gel formulations could act as prolonged and controlled release topical dosage forms, which may lead to improved efficiency and better patient compliance.