Biomedical Engineering Reference
In-Depth Information
2.6
Stimuli-responsive Polymers Used in
Medical Devices
A biomaterial may be dei ned as any type of material (natural or synthetic)
that supports or replaces a natural function. Many types of materials are
used in the fabrication of biomaterials, such as polymers, ceramics, glasses,
metals and alloys and composites, in devices whose purpose is, for example,
to substitute heart valves, joints, tubing, or intra-ocular lenses. Biomaterials
can be divided into 4 categories: a) apparatuses developed for in vitro diag-
nosis, b) hybrid organs c) implants and prostheses, and d) medical devices.
Depending on the duration of the contact and on the nature of the interac-
tions between the material and the living medium, three dif erent biocom-
patibility levels are classii ed. h e highest classii cation corresponds to the
longest contact duration, which can be several weeks or longer.
Polymers are widely used in the fabrication of biomaterials because
of their low production cost and easy manufacturing and handling. h e
requirements for the biomaterials are compatibility with living tissues,
good mechanical properties (elasticity, deformation, wear resistance, yield
stress, ductility, toughness, hardness, etc.) and ease of production, at rea-
sonable cost, including sterilization. Besides, the route selected for drug
delivery has a signii cant ef ect on the drug's therapeutic ei cacy, safety,
and bioavailability [67]. h e ideal aim of administration should be to
deliver the drug at a required concentration within the therapeutic win-
dow at the right time to a specii c target, in a safe and reproducible manner.
However, in certain cases such as hormone delivery, diabetic treatment,
and others, the preferred method of drug delivery is in the form of pulses at
variable time intervals [68]. h ere are also instances such as the treatment
of malaria, cancer, and others, wherein combination therapies involving
multiple drugs to exploit the synergistic and additive potential of individ-
ual drugs are required [69]. All these requirements were initially achieved
by employing stimuli-responsive polymers as drug carrying matrices,
wherein their dif usive, degradability, and responsive properties to exter-
nal stimuli controlled the sustained release of the drug [70-73].
For that reason nowadays, research is being conducted to improve
design, synthesis and fabrication of medical devices based on stimuli-
responsive [74]. Stimuli-responsive polymers mimic the behavior of bio-
logical molecules where external stimuli or changes in local environment
can trigger a change in property: conformation, solubility, shape, charge,
and size. Drug release can be regulated not only spatially via targeting,
but also temporally in the presence of externally-applied stimuli [75]. One
