Abstract. The effects of adhesive layer thickness and drug loading on estradiol crystallization were studied in a drug-in-adhesive patch. Patches containing different estradiol loadings (1.1% and 1.6% w/w) in different thicknesses (45, 60, and 90 μm) were prepared by coating of a homogenous mixture of adhesive solution and the drug on a siliconized release liner by a film applicator. After drying, the film was laminated on a Poly(ethylene terephthalate) backing layer and cut into appropriate size. Release tests were performed using thermostated Chien-type diffusion cells. Cross-section of the patches was observed by optical microscopy. Scanning electron microscopy was done for surface analysis of the patches after drug release test. Crystal formation was not expected in the adhesive layer based on the linear free-energy relationship formalisms however; crystalline regions were observed in different locations through the thickness of the patches. These regions were significantly more discontinuous in 45 μm samples which elucidated the effective role of adhesive layer thickness in drug crystallization. Extensive crystallization observed for thicker patches was attributed to the strong crosslinking capability of estradiol hemihydrate. Drug release study confirmed some of the crystallization results. No significant increase was observed in the burst release with increasing in thickness from 45 to 60 μm which can be attributed to the severe increase in the crystallization extent. Also, formation of a crystalline layer near the releasing surface and more discontinuous pattern of the crystals in some samples was confirmed by investigation of the drug release curves.
Formation of micellar morphologies in aqueous solutions of charged random copolymers has been reported in several studies. This paper reports on liquid crystallization of the cationic random acrylic terpolymer i.e., poly[(dimethylaminoethyl methacrylate)-co-(methyl methacrylate)-co-(butyl methacrylate)] containing no mesogenic groups. The viscometric behaviour of the terpolymer solutions deviated in several ways from ordinary behaviour of polyelectrolytes supporting the possibility of self-assembly of this cationic random terpolymer in a solvent mixture containing acetone, ethanol and 1-propanol or each of these solvents separately. The existence of nano-sized liquid-crystalline structures was demonstrated using small-angle X-ray scattering (SAXS) analysis of the terpolymer solutions. Morphology and sizes of the liquid-crystalline structures were determined according to the SAXS results and confirmed by dynamic light scattering and atomic force microscopy findings. Liquid crystallization was reasoned on the basis of the existence of a segregated chain microstructure as for polyelectrolytes containing folded parts connected to each other by monomer strings. In a random amphiphilic copolymer or the terpolymer under investigation, the folded parts and strings must be hydrophilic and hydrophobic, respectively. The role of alcohol aggregates should be considered in self-assembly of the terpolymer chains. The alcohol aggregates can act as physical crosslinkers leading to the formation of more compact liquid-crystalline structures. The deviations observed in the viscometric behaviour of the terpolymer solutions are suggested as the result of the ability of terpolymer chains to self-assemble.
Different amounts of two skin permeation enhancers, Oleic acid (OA) and Propylene glycol (PG), were mixed thoroughly with solution of a commercial acrylic pressure sensitive adhesive (Duro-Tak). Films with different adhesive layer thickness (30 and 60 m) were prepared by casting of formulations with a film applicator on a PET 80-m film and drying of solvents. Peel test was done on different formulations according to ASTM D3330. Surface study and thermal analysis were used for explaining the results. It was shown that the effect of interfacial work of adhesion on peel strength was too low to be considered. PG had no significant effect on peel strength, which was related to effect of hydrogen bonds between PG and copolymer chains acting as crosslinks. OA decreased peel strength significantly, which is due to important changes in copolymer structure. These changes can be found by relatively sharp drop in T g values. Adhesive-cohesive transition occurred in OA formulations as a result of OA crystals formation. OA migration to surface in concentrations of more than 10 (w/w %) was confirmed by results of DSC and surface study. In contrast with PG, doubling of thickness had no effect on peel strength.
Solutions of an acrylic copolymer pressure sensitive adhesive with different concentrations of propylene glycol (PG) and oleic acid (OA) were cast on a PET film. A rolling ball tack test was carried out on the adhesive coated tapes with different thicknesses. The results were explained on the basis of the surface (energy and roughness) and viscoelastic properties of the copolymer, which were related to the glass-transition temperature. The 60-m PG samples with an approximately equal glass-transition temperature and surface energy did not have a significantly different tack value. The tack value of the 30-m tapes decreased with PG concentrations above 15% (w/w), which was related to an increase in the surface roughness with a more prominent effect at the lower thickness. OA, which improved both the surface and viscoelastic properties, increased the tack value up to 15% (w/w). However, the tack value decreased above 15% (w/w). This was explained on the basis of OA large crystals, which can decrease viscoelastic energy dissipations and form a mechanically weak surface layer.
It has been proved that alcohol molecules exist as cyclic and chain aggregates of different sizes in pure or mixed solvent systems. Here, it will be shown that these aggregates can radically change the rheological properties of a concentrated polymer solution containing self-assembled chains. In a previous study by the same authors, the existence of self-assembled structures in dilute solution of poly(dimethylaminoethyl methacrylate-co-methyl methacrylate-co-butyl methacrylate) in an alcoholic solvent mixture was shown according to small angle X-ray scattering results, showing that these structure were much more compact than those in acetone. This finding is based on the role of alcohol aggregates as physical cross-linkers. Here, the existence of self-assembled structures in concentrated solutions of the same terpolymer was confirmed by atomic force microscopy and rheology results both in acetone (a good solvent) and in a solvent mixture composed of acetone, ethanol and 1-propanol. For the terpolymer solutions in the solvent mixture, very little decrease in complex viscosity and shear thickening were observed at high strains and frequencies, respectively. It can be concluded that the alcohol aggregates can cause the formation of strong self-assembled structures that can even resist high shear forces or strains.
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