We developed a new approach to fabricate pressure sensitive adhesive (PSA) hydrogel films for dermatological applications. These hydrogel films were fabricated using polyvinylpyrrolidone (PVP), poly(ethylene glycol) diacrylate (PEGDA) and polyethylene glycol (PEG) with/without propylene glycol (PG) via photo-polymerization. Hydrogel films with a thickness ranging from 130 to 1190 mm were obtained. The surface morphology and drug distribution within the films were found to be uniform.The effects of different factors (polymeric composition, i.e., PEG/PG presence and film thickness) on the functional properties (i.e., rheological and mechanical properties, adhesion performance and drug distribution) of the films were investigated. The addition of plasticizers, namely PEG and PG, resulted in a simultaneous increase in elasticity and adhesiveness of these hydrogels, via the formation of hydrogen bonds, which has a direct correlation with their adhesion properties. The new approach is potentially useful for industrial applications, due to the simple procedure, precise control over film thickness, minimal usage of solvents and adjustable mechanical, rheological and adhesive properties.engineering. 4,13 The requirements of medical PSAs are challenging as they must be able to exhibit appropriate gel strength and sufficient adhesiveness against varying skin types and at the same time, 14 they should be easily removable from the skin surface without excessive irritation to the skin and leaving no residues on the skin. Hydrogel polymers have been used to produce medical PSAs. 4 The major chemical systems used for medical PSAs are acrylate based hydrogels, due to their suitable adhesive properties and a low level of skin irritation. Other polymer types, used as PSAs, include silicone-based adhesives, polyvinyl ether-based adhesives and polyvinylpyrrolidone-based adhesives. 4,15 In general, conventional hydrogels used as adhesives for medical applications are developed by chemical or physical crosslinkings.Solvent-free pressure sensitive adhesives, i.e., hot-melt PSAs (HMPSAs) and radiation curable PSAs, are a relatively new group of self-adhesive medical products and are of increasing importance due to environmental pressure on solvent-borne PSAs and the performance shortcomings of aqueous systems. 4,15 Both HMPSAs and radiation curable PSAs have grown lately due to reduced solvent consumption and waste emissions. These environmentally friendly adhesives are made from reactive compounds that contain almost no solvents (or negligible amount) or other volatile substances. In addition, photo-polymerization enables rapid conversion of monomer or macromer precursor solutions into a gel or solid under physiological conditions potentially useful for medical applications. 16 Photopolymerization is simply initiated by irradiation with light, such

Technological advances in drug discovery have resulted in increasing number of molecules including proteins and peptides as drug candidates. However, how to deliver drugs with satisfactory therapeutic effect, minimal side effects and increased patient compliance is a question posted before researchers, especially for those drugs with poor solubility, large molecular weight or instability. Microfabrication technology, polymer science and bioconjugate chemistry combine to address these problems and generate a number of novel engineered drug delivery systems. Injection routes usually have poor patient compliance due to their invasive nature and potential safety concerns over needle reuse. The alternative non-invasive routes, such as oral, mucosal (pulmonary, nasal, ocular, buccal, rectal, vaginal), and transdermal drug delivery have thus attracted many attentions. Here, we review the applications of the novel engineered systems for oral, mucosal and transdermal drug delivery.

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