Abstract
Foams have frequently been used as systems for the delivery of cosmetic and therapeutic molecules; however, there is high variability in the foamability and long-term stability of synthetic foams. The development of pharmaceutical foams that exhibit desirable foaming properties, delivering appropriate amounts of the active pharmaceutical ingredient (API) and that have excellent biocompatibility is of great interest. The production of stable foams is rare in the natural world; however, certain species of frogs have adopted foam production as a means of providing a protective environment for their eggs and larvae from predators and parasites, to prevent desiccation, to control gaseous exchange, to buffer temperature extremes, and to reduce UV damage. These foams show great stability (up to 10 days in tropical environments) and are highly biocompatible due to the sensitive nature of amphibian skin. This work demonstrates for the first time that nests of the túngara frog (Engystomops pustulosus) are stable ex situ with useful physiochemical and biocompatible properties and are capable of encapsulating a range of compounds, including antibiotics. These protein foam mixtures share some properties with pharmaceutical foams and may find utility in a range of pharmaceutical applications such as topical drug delivery systems.
Highlights
Foams have been used as delivery systems or vehicles to deliver cosmetic and therapeutic molecules to normal and injured skin since the 1970s [1,2,3,4,5]
The protein composition of E. pustulosus foam fluid was analysed by sodium dodecyl sulfate poly-acrylamide gel electrophoresis (SDS-PAGE), confirming previous work that foam from this species contains six major proteins ranging between 10 and 40 kDa in size [18] and that the foam nests used in this study were of typical composition
We observed no variation between collection years or from nests collected at different locations in Trinidad and all foam collected was checked by SDS-PAGE and was of the composition previously detailed in [17,18,19] and electronic supplementary material, figure S1c
Summary
Foams have been used as delivery systems or vehicles to deliver cosmetic and therapeutic molecules to normal and injured skin since the 1970s [1,2,3,4,5]. The long-term stability of liquid aqueous foams has been a challenge, with some formulations offering useful foamability properties (e.g. foam expansion time), but poor stability [6]. There has been some progress made through the combination of various foam and surfactant components to create high foamability and long-term foam stability [6,7,8,9]. The development of biocompatible, liquid foams with high foamability and long-term stability remains a challenge in materials science [6]. One major difficulty can be the delivery of an adequate concentration of active pharmaceutical ingredients (APIs) for treatment over a sustained period, often necessitating repeated, regular applications. There is a need for the development of biomaterials that allow extended times between application combined with high stability and improved biocompatibility; natural foams can provide these benefits
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