Solid emulsion gel as a novel construct for topical applications: synthesis, morphology and mechanical properties Kirill I. Shingel Æ Christophe Roberge Æ Oleg Zabeida Æ Marielle Robert Æ Jolanta E. Klemberg-Sapieha Received: 11 July 2008 / Accepted: 2 October 2008 / Published online: 24 October 2008 Ó Springer Science+Business Media, LLC 2008 Abstract A series of the solid emulsion gels with the oil volume fraction in the range of 0–50% were synthesized through a polycondensation reaction between activated p- nitrophenyl carbonate poly(ethylene glycol) and protein- stabilized oil-in-water emulsions. The resultant structures were investigated in terms of swelling behavior, compo- sition, morphology, mechanical and skin hydration properties. Solid emulsions gels share the properties of both hydrogel and emulsion. Similar to the classical hydrogel, the SEG swells in water up to equilibrium swelling degree, which decreases as the oil volume fraction increases, and comprises immobilized drops of protein- stabilized oil. The impregnation of the oil phase is found to reduce tensile stiffness of the material, but improves material’s extensibility. The mechanical properties of the constructs (Young moduli in the range of 9–15 kPa and the elongation at break of 120–220%) are interpreted accord- ing to the ‘‘rule of elasticity mixture’’ that considers the elasticity of the composite material to be a sum of the contributions from individual components, i.e. hydrogel and dispersed oil drops. An idealized model that takes into account the history of the material preparation has been proposed to explain the improved extensibility of the constructs. The results of the mechanical tests, equilibrium swelling, and the skin hydration effect of the solid emulsion gels in vivo are discussed from the perspective of the biomedical applications of the solid emulsion gels, in particular, for the transdermal delivery of hydrophilic and lipophilic drugs. 1 Introduction Recent years have witnessed development of many attractive approaches for overcoming the problems of poor drug solubility and bioavailability of liposoluble compounds, among which oil-in-water nano- and microemulsions are perhaps the most prominent drug delivery solutions [1–3]. The advantages of using oil-in-water emulsions as a drug delivery system are the reduction of drug toxicity, the protection of the active compounds from hydrolysis or oxi- dation, and the relative ease of the formulation preparation. As a consequence of the broad exploitation of the emulsion drug encapsulation technology for pharmaceuti- cal use, emulsion-containing hydrogels have recently emerged as a new class of biomaterials [4–7]. These polymer assemblies are designed to integrate dispersed oil drops within an abundant water-rich hydrogel phase and have been shown to present interesting release profiles of lipophilic drugs. Additionally, such emulsion-containing hydrogels may offer the advantage of improved mechanical resistance for easier handling and the opportunity for hydrophilic drug delivery from a hydrogel compartment [5, 7]. Surfactant molecules in these systems are not bound to the matrix and, as noted by some authors, can eventually diffuse from the material along with a drug [5]. This can be considered a drawback of the emulsion-containing hydro- gels, since poor biocompatibility, possible toxicity and low clearance rates of the oil-stabilizing components after K. I. Shingel (&)  C. Roberge  M. Robert Bioartificial Gel Technologies (BAGTECH) Inc., 400 De Maisonneuve Ouest, Suite 1156, Montreal , QC, Canada H3A 1L4 e-mail: kirill.shingel@bagtech.com O. Zabeida  J. E. Klemberg-Sapieha Department of Engineering Physics, Ecole Polytechnique, Box 6079, Station ‘‘Centre ville’’, Montreal, QC, Canada H3C 3A7 123 J Mater Sci: Mater Med (2009) 20:681–689 DOI 10.1007/s10856-008-3613-0