| Sažetak (engleski) | PEO-PPO-PEO copolymers are symmetric nonionic amphiphilic triblock copolymers
with poly (ethylene oxyde), PEO, as the hydrophilic end blocks and poly (propylene
oxyde), PPO, as the hydrophobic middle block: PEO-PPO-PEO copolymers
are commercially available in a range of molecular weights (PEO and PPO block length)
and copolymer composition (PPO/PEO ratio). As a result, PEO-PPO-PEO copolymers
have different physicochemical properties and find widespread industrial applications.
The aim of this work was to focus on specialized pharmaceutical applications.
PEO-PPO-PEO copolymers are found to be an efficient drug delivery system with
multiple effects. The single molecular chain of copolymer, unimers, inhibit drug efflux
transporters in both the blood-brain barrier and in the small intestine, which provides
for the enhanced transport of select drugs to the brain and increases oral bioavailability.
Furthermore, the interactions of the unimers with multidrug-resistant cancer cells
results in sensitization of these cells with respect to various anticancer agent. Due to
the amphiphilic nature of PEO-PPO-PEO copolymers they are able to self-aggregate
to form variety of associated structures such as micelles and liquid crystalline phases.
The micelles formed in aqueous solutions consist of a hydrophobic core of PPO and
hydrophilic corona of PEO. The interesting feature of the block copolymer micelles is
that they remain stable for longer time, even when the concentration is reduced below
the critical micelle concentration (crne). Another characteristic property of PEOPPO-
PEO block copolymer systems is the thermoreversible gelation displayed by some
concentrated block copolymers at temperatures close to room temperature. Both
the micellisation and gelation are affected by range of factors such as temperature, copolymer
composition, molecular weight, concentration, and presence of cosolutes
(surfactants, electrolytes, and hydrophobic substances). The incorporation of drugs
into the micelles or gels can improve solubility, reduce hydrolytic/metabolic degradation,
achieve sustained release, and result in imporoved bioavailability. The toxicity of
PEO-PPO-PEO copolymers bave been investigated for different pharmaceutical applications
and found to be quite low. However, the toxicity of these copolymers is a
complex issue and therefore; the toxicological aspects have to be considered from
each formulation perspective. |
