**4.1 Poloxamer**

A thermoresponsive polymer called poloxamer begins as a liquid between 4 and 5°C and in a concentration range of 20 to 30% wt/wt before changing to a gel when the temperature of the medium increases. When used alone, higher concentrations of Poloxamer are necessary in a formulation; nevertheless, such amounts have been shown to irritate the eyes. In order to reduce the overall amount of Poloxamer utilised, enhance the gelling and mechanical properties of Poloxamer, and lower the risk of eye irritation, Poloxamer was combined with other polymers such methyl cellulose, chitosan, and others [43]. Poloxamers, also known as Pluronics, are tri-block copolymers made up of poly (ethylene oxide), poly (propylene oxide), and poly (ethylene oxide) (PEO-PPO-PEO). Kolliphor P188 (also known as Poloxamer 188 or Pluronic F-68) has roughly 27 PPO groups on one side and 80 PEO groups on the other. Kolliphor P188 has a molecular weight of about 8400 g mol1, which is higher than that of normal emulsifying surfactants [44]. Below 50°C, it exists as single molecules (unimers) and at higher temperatures polymolecular micelles starts to form. These can be used in a wide range of occular drug delivery applications due to the variety of microemulsion types created [45].
