The objective of this study was to characterize and evaluate the physicochemical properties and drug release profiles of hydrogels composed of silk protein (SP) polymers. SPs with a low MW (SPL, ca. 18 kDa) and a high MW (SPH, ca. 76 kDa) were used for preparing hydrogels. Both the random coil form and beta-sheet conformation simultaneously existed in the hydrogels according to Fourier-transformed IR determination. Morphologically, the hydrogels showed a sponge-like cross-linked structure produced by physical entanglement as well as chemical hydrogen and covalent bindings. The in vitro buprenorphine delivery from SPH hydrogels showed a slow-release effect, and a zero-order rate was obtained for all preparations. Drug release could be controlled by varying the SPH concentrations or incorporation of SPL into the systems. SP hydrogels showed a stronger barrier property for hydrophilic solutes than for hydrophobic solutes. The incorporation of SPH into Pluronic F-127 (PF-127) hydrogels changed the gel structure from amorphous micelles to a regularly interconnected texture with pores. Furthermore, SPH as an adjuvant polymer in PF-127 and chitosan hydrogels lowered and controlled the amount of drug released from those systems.

Sodium nonivamide acetate (SNA; C 19 H 28 NO 5 Na) is a non-pungent derivative of capsaicin which is synthesized by alkylation of the phenolic hydroxyl group of nonivamide with bromoacetic acid.1) The antinociceptive potency of SNA is 1.75 and 27.5 times than that of capsaicin and indomethacin, respectively.2) Transdermal drug delivery is preferable for SNA to avoid the short half-life (16.80 min) with intravenous administration.3) Methods for transdermal enhancement by iontophoresis (electric current density application) have been utilized to overcome the poor permeability of SNA. [4][5][6] A common aim of the development of transdermal devices is the controlled delivery of drugs, so that the rate of drug input into the bloodstream is predictable and reproducible. When drugs applied to skin in vivo, the semisolid forms or the solution forms incorporated with a membrane (patches) were practically preferable to restrict the applied site in a certain area. Transdermal therapeutic systems, which utilize rate-controlling membranes, provide more-reproducible delivery compared to the skin alone, and produce smaller interand intra-subject variations.7) Solupor ® is a microporous polymeric membrane composed of a unique combination of randomly oriented thick and thin fibrils of ultra high molecular weight (MW) polyethylene of 5-7ϫ10 6 Da. Solupor can be used as a substrate through which a liquid or gas can be released in a controlled manner. It has good chemical resistance, high tortuosity, and favorable biocompatibility. 8)Hence Solupor may be suitable as a membrane for transdermal drug delivery systems.The aim of this study was to investigate the influence of Solupor membranes on the transdermal iontophoretic delivery of SNA. SNA permeation across various types of skin or artificial membranes was elucidated to explain the possible mechanisms. Electroporation is also an electrically-assisted technique which involves the application of short, high-voltage electric field pulses to create transient elevation of the permeation of lipid bilayer membranes. SNA permeation by electroporation application was performed to compare with data from iontophoresis. Sodium nonivamide propionate (SNP; C 20 H 30 NO 5 Na) is another derivative of capsaicin. The difference in the structures between SNA and SNP is that the ether-linked group of the phenol is acetate and propionate, respectively. Another purpose of this present study was to investigate the influence of different molecular sizes on the iontophoretic permeation of drugs. MATERIALS AND METHODS MaterialsThe synthesis procedures for SNA and SNP were performed in our laboratory and were reported earlier. 1)A series of Solupor ® membranes was kindly provided by Teijin Solfill Ltd. (Tokyo, Japan), which is authorized by DSM N.V. (Heerlen, the Netherlands). The CelluSep ® cellulose membrane (with a MW cutoff of 6000-8000) was obtained from Membrane Filtration Products (Seguin, TX, U.S.A.). All other chemicals and solvents were of analytical grade.In Vitro Permeation Procedures The in ...

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