Poloxamers

Poloxamers are a family of nonionic triblock copolymers consisting of a central hydrophobic poly(propylene oxide) block flanked by two hydrophilic poly(ethylene oxide) blocks, giving a PEO–PPO–PEO structure. They are amphiphilic and dissolve in water to form micelles and, at certain compositions and temperatures, thermoreversible gels. The polymers are marketed under various names, notably Pluronics or Lutrols, and are available in a wide range of molecular weights and block lengths.

In aqueous solution, poloxamers self-assemble into micelles with a PPO core and a PEO corona. They exhibit a critical micelle concentration and, for many compositions, a temperature-dependent transition that can lead to gel formation. Poloxamer 407, in particular, is known for forming gels at near-physiological temperatures when used at sufficient concentrations, enabling in situ gelling applications.

Applications span pharmaceutical, cosmetic, and biomedical fields. They are widely used as excipients: solubilizers for poorly water-soluble drugs, emulsifiers, stabilizers, and viscosity modifiers. In drug delivery, micellar solubilization can improve the solubility and bioavailability of hydrophobic compounds, and thermogelling formulations can provide controlled or sustained release for ocular, topical, or injectable routes. Their tunable hydrophilic–lipophilic balance, driven by the lengths of the PEO and PPO blocks, allows customization for specific formulations and release profiles.

Safety and regulation: poloxamers are commonly used and considered safe at approved concentrations, but toxicity and tolerability depend on molecular weight, block composition, concentration, and route of administration. Prolonged exposure or high concentrations may cause irritation or membrane interaction in some contexts.

Examples include poloxamer 188 (P188) and poloxamer 407 (P407; Pluronic F-127), with a spectrum of variants available for formulation design.