Stability evaluation of emulsion-based topical preparations: a valuable potential of dynamic- mechanical thermoanalysis (DMTA) test as a rapid rheological alternative to conventional freeze- thaw test

Abstract

The assessment of stability in emulsion-based topical preparations can be approached through real-time monitoring and/or accelerated methods, drawing predictions from pertinent stability-related physicochemical parameters. Ensuring the robustness and durability of topical products during storage, transport, and application necessitates thorough stability testing. However, due to the diversity of emulsion types and their intended use, there is no universal standard test, placing the liability on formulators/manufacturer to tailor appropriate assessments. Notably, topical emulsions, particularly cosmetic variants, often exhibit impressive stability with extended shelf lives. Nonetheless, evaluating their stability and decision-making remain challenging and time-consuming in industrial contexts. This underscores the demand for alternative testing protocols that expedite stability assessments and predict emulsion-based product stability accurately. This article comprehensively surveys literature, enriched with practical insights, exploring core mechanisms behind emulsion stability and prevention of instability. The discussion encompasses diverse approaches to stability assessment, revealing methodologies and parameters under examination during testing. Particular focus is placed on the dynamic-mechanical thermoanalysis (DMTA) method explored as a rapid, rheologically-based alternative to the conventional freeze-thaw test, emphasizing its usefulness for expediting the stability evaluation of emulsion-based topical preparations.

Procena stabilnosti emulzionih preparata za topikalnu primenu može se sprovesti praćenjem promena u realnom vremenu i/ili primenom ubrzanih metoda, te predviđanjem stabilnosti i roka trajanja proizvoda na osnovu merenja relevantnih fizičkohemijskih parametara tokom ispitivanja. Kako bi se obezbedila robusnost i dugoročnost emulzionih proizvoda za kožu tokom čuvanja, transporta i primene, neophodno je sprovesti pažljivo isplanirano, opsežno ispitivanje stabilnosti. Međutim, imajući u vidu različite tipove emulzija i njihovu namenu, ne postoji univerzalni standardni protokol za ispitivanje stabilnosti, što formulatore/proizvođača čini odgovornim kada je u pitanju izbor odgovarajućeg testa i metodologije. Evidentno je da emulzije za topikalnu primenu, a posebno kozmetičke emulzije, često pokazuju visoku stabilnost sa dugim rokovima upotrebe. S druge strane, procena stabilnosti ovakvih emulzija i donošenje odgovarajućih odluka i dalje ostaje izazov u industrijskom okruženju i zahteva dosta vremena, što nameće potrebu za alternativnim protokolima koji omogućavaju ubrzano ispitivanje, ali i uspešno predviđanje stabilnosti emulzionih proizvoda. Prikazani rad daje sveobuhvatni pregled literature prožet praktičnim pogledima na ključne fenomene odgovorne za stabilnost emulzija, zatim daje uvid u različite pristupe za procenu njihove stabilnosti, uključujući metodologije koje se koriste i parametre koji se prate tokom ispitivanja. Rad u poseban fokus stavlja dinamičko-mehanički termoanalitički (DMTA) metod kao brzu reološku alternativu konvencionalnom testu smrzavanje-odmrzavanje, posebno ističući primenljivost metoda za ubrzano ispitivanje stabilnosti emulzionih preparata za topikalnu primenu.