Thermo-Responsive Block Co-Polymers As A Drug Carriers

Exogenous stimuli-responsive cell targeting:

By using the temperature, light, ultrasound pH, and magnetic field as an external stimuli, exogenous stimuli responsive cell targeting can be performed. In this scope only temperature change as a stimuli is discussed.

Temperature:

Temperature has been used as an effective external stimulitrigger for the design of responsive nano carriers due to its physiological significance. It is an important factor which has been found to be distributed oddly in the tumor cells as compared to normal tissues. Ideally, a temperature-responsive polymeric nano carrier should display thermal response in the biologically relevant important range of 10–40°C. In the past decades, a wide range of temperature-sensitive polymeric nano carriers have been investigated to specifically release their payloads during an induced narrow temperature range, after the delivery of a hyperthermic stimulus at the target tissue.

Thermoresponsive polymeric nano- carriers:

Thermo responsive DDS(Drug delivery systems) is one of the most investigated stimuli-responsive strategies used to specifically release their encapsulated or conjugated drug payloads during an induced narrow temperature range. This type of stimuli-responsive drug release can be facilitated since thermo responsive polymers can change their physical and chemical properties in response to heat.The ideal range in which a thermo responsive nano carrier should release its payload is between 37°C and 42°C, in order to minimize any toxic effects due to protein denaturation above the latter temperature.

Block copolymers that undergo conformational changes in response to temperature variation have been widely studied for the development of thermo responsive nano carriers since the initial report of the use of poly(N-isopropylacrylamide) (pNIPAM) by some scientists in the 1960s.

The most widely used thermo responsive polymers are hydrophilic below acertain temperature and become hydrophobic above a specific temperature. The temperature at which this phase transition occurs is referred to as lower critical solution temperature (LCST) Fig2 . In the diagram ,the minimum or the maximum point of solubility curves are the respective LCST and UCST points .Any other points along the respective curve is referred to as a cloud point, depending on the method (turbidimetric or calorimetric) used for detection.

Below LCST, polymers are soluble and above LCST, they are dehydrated and collapsed to an insoluble chain conformation. Stimuli-responsive polymers undergo a conformational change, a coil-to-globule transition, upon some external stimuli such as a change in temperature or light.

Conclusion

Blockcopolymer (thermoresponsive)-based smart nano carriers contain specific chains, ligands, or functional groups that are responsive to exogenous stimuli temperature which can be exploited for drug delivery applications, especially for the delivery of drugs(chemotherapeutic) for controlling the growth of tumor cells..