ObjectiveThe focus of this communication was to study phospholipid-structured emulsions whose phase behaviour is modified with monoalkyl fatty amphiphiles. Ideally, these systems would mimic key physical and structural attributes observed in human stratum corneum (SC) so that they better alleviate xerotic skin conditions. MethodsPhosphatidylcholine-structured emulsions were prepared, and their phase behaviour modified with monoalkyl fatty amphiphiles. The effect of molecular volume, acyl chain length and head-group interactions was studied using a combination of physical methods. Water vapour transmission rate (WVTR) was used as a primary test to assess occlusive character. Changes in the vibrational modes observed in Fourier transform infrared (FTIR) spectroscopy and bilayer spacing measured by X-ray diffraction (XRD) were then applied to elucidate the lateral and lamellar microstructural characteristics in the systems. ResultsWater vapour transmission rate demonstrated that as the phosphatidylcholine acyl chain length increased from C14, to C18, to C22, there was a corresponding increase in occlusive character. The addition of monoalkyl fatty amphiphiles such as behenic acid, behenyl alcohol or cetostearyl alcohol to a base formulation incorporating dipalmitoyl and distearoylphosphatidylcholine (C18) was seen to further increase barrier characteristics of the emulsions. FTIR methods used to probe lipid-chain conformational ordering demonstrated that as phosphatidylcholine acyl chain lengths increased, there was a corresponding improvement in acyl chain ordering, with an increase in thermal transition temperatures. The addition of a monoalkyl fatty amphiphile resulted in conformational order and thermal transition temperature improvements trending towards those observed in stratum corneum. FTIR also demonstrated that systems containing behenic acid or behenyl alcohol exhibited features associated with orthorhombic character. X-ray diffraction data showed that addition of monoalkyl fatty amphiphile also resulted in thicker lamellar structures than when those agents are not present. ConclusionThe generalized approach described herein is shown to mechanistically describe the occlusive character of phospholipid-structured formulations in the presence of long-chain fatty acids or alcohols and that they exhibit characteristics mimicking those found in human SC lipids. Resume ObjectifL'objectif de cette communication est l'etude des emulsions structurees aux phospholipides - dont le comportement de phase est modifie par des amphiphiles gras monoalkyles. Idealement, ces systemes pourraient imiter les attributs physiques et structurels cles observes dans le stratum corneum humain (SC) afin qu'ils puissent mieux alleger les conditions xerotiques de la peau. MethodesDes emulsions structurees a la phosphatidylcholine ont ete preparees et leur comportement de phase modifies avec des amphiphiles gras monoalkyle. Les effets du volume moleculaire, de la longueur de chaine acyle et des interactions des tetes ont ete etudies en utilisant une combinaison de methodes physiques. Le taux de transmission de la vapeur d'eau (WVTR) a ete utilise comme critere principal pour evaluer le caractere occlusif. Les changements dans les modes vibratoires observes dans la transformee de Fourier infra-rouge (FTIR) et l'espacement des bicouches mesure par diffraction des rayons X (XRD) ont ensuite ete utilises pour elucider les micro-structures caracteristiques laterales et lamellaires dans le systems. ResultatsLa WVTR a demontre que, lorsque la longueur de la chaine acyle de la phosphatidylcholine est passee de C14 a C18 puis a C22 il y avait une augmentation correspondante du caractere occlusif. L'addition d'amphiphiles gras monoalkyle tels que l'acide behenique, l'alcool behenique ou l'alcool cetostearylique a une formulation de base incorporant la distearylphosphatidylcholine (C18) augmente encore les caracteristiques de barriere des emulsions. Les etudes FTIR utilisees pour sonder la conformation de l'agencement des chaines lipidiques ont montre que des lors que les longueurs de chaine acyle de la phosphatidylcholine augmentent, il y avait une amelioration correspondante de l'arrangement des chaines d'acyle; conjointement avec une augmentation des temperatures de transition thermique. L'addition d'un agent amphiphile gras monoalkyle a donne lieu al' amelioration de l'ordre conformationnel et des temperatures de transition thermique qui tendent vers ceux observes dans la couche cornee. FTIR a egalement demontre que les systemes contenant de l'alcool ou de l'acide behenique montraient des motifs associes a un caractere orthorhombique. Les donnees de la diffraction au rayons X ont montre que l'addition de l' amphiphile gras monoalkyl a egalement abouti a des structures lamellaires plus epaisses que lorsque ces agents ne sont pas presents. ConclusionL'approche generale decrite ici illustre le caractere occlusif mecanistique des preparations de phospholipides structurees en presence d'acides gras ou des alcools a longue chaine et qu'ils presentent des caracteristiques qui imitent ceux trouvees dans les lipides de la couche cornee humaine.