Thermo-Responsive
Block Co-Polymers As A Drug Carriers

Dr. Subhas C Shit
Ex-Principal Director CIPET
(Ministry of Chemicals and Fertilisers, Govt.of
India) |
Abstract
In recent years the polymers are being extensively
used with stimuli triggers for delivery of drugs
to the human tissues by exogenous triggers. Ths
type of delivery of drugs phenomenon by a polymer
in a particular location and time helps in
exploiting its potential for various drug delivery
in clinical practices. In this study out of many
stimuli- responsive polymers only benefits of
thermo responsive block copolymers are presented
with the support of literature data.
Introduction
Polymers are being recently
being utilised for delivery of drugs to the
various tumors in the human body. Initially it was
thought that it could be due to preferential |
accumulation of certain macromolecular
drugs to tumors .This preferential distribution of
macrmolecular drugs to the tumors was ascribed to the
defective tumor vasculature with disorganised
endothelium at the tumor sight and poor lymphatic
drainage system .The combination of these two
phenomena was termed as the enhanced permeation and
retention( EPR) effect. But at later date with the
advancement of personalised medicine, this idea has
become outdated. And recently stimuli responsive
polymers as drug carrier has come into limelight.
Stimuli –triggers used for the targeted drug drug
delivery an be classified into two types :endogenous
and exo-genoustriggers. Endogenous triggers (PH ,redox
state and enzymic triggers)exploit the un ique
characteristics of the diseased tissue and the micro
environment which is completely different from normal
tissue physiology.
There are a number of other parameters
beyond the inner body which are termed as external
stimuli(temperature, light, ultrasound, magnetic
fields, etc.). Compared with the internal stimuli that
make use of characteristics within a diseased tissue
micro environments, the external stimuli -responsive
system s could introduce contrast agents to visualise
the accumulation of nano carriers in the target
tissues, cells, organelles and then activate the nano
carriers out of the body by exogenous triggers at the
assured time.
In this text examples of such drug
delivery which is spatiotemporal, by exogenous
triggers are discussed for potential clinical
applications.
Mechanism of release of drugs by
polymers:
Exogenous stimuli-responsive polymeric
nanocarriers can be engineered to release their
therapeutic cargo in a programmed manner according to
a specific extracellular stimuli-trigger via chemical,
biochemical, or physical means .(Fig1) Evidently,
exogenous triggers can be used to enhance the nano
carrier activity as well as the triggered drug release
to achieve diagnosis and/or therapeutic effect at
disease sites.
Functionalized nanoparticles that can
be triggered to enhance their activity by triggers as
temperature, light, magnetic field, and US have been
developed. For instance, if the drug is encapsulated
within a polymeric carrier, the release can be
triggered by causing structural changes such as
polymer degradation, disassembly of surface layers,
and charge switching. On the other hand, drugs which
are covalently conjugated to the polymer backbone can
be released by breaking of the polymer drug bonds. In
this chapter, DDS(drug delivery systems) are discussed
in order to take the advantages of externally applied
stimuli temperature changes.

Fig.1 Exogenously triggered drug release by stimuli
such as heat, ultrasound, magneticenergy, and light. |