Biomedical Engineering Reference
In-Depth Information
2.5.1
Elastomers for Biomedical Devices
h e use of elastomers for medical devices goes back to the time when the
rubber industry itself started: vulcanized natural rubber was used in medi-
cal devices soon at er the discovery of the rubber-vulcanization process.
h ere are three groups of elastomers used in biomedical applications:
(a) the commodity elastomers which happened to be used in the biomedi-
cal i eld; (b) medical grades of elastomers certii ed for short-term physio-
logical contact; and (c) a small group of elastomers suitable for longer-term
physiological contact or implantation. Biomedical elastomers require high
purity, desired physical, chemical and mechanical properties, easy fabrica-
bility and high stability and sterilizability. When applied in possible contact
with biological tissues and l uids [52-54], they must not cause thrombosis,
destroy cellular elements, alter plasma protein, destroy enzymes, deplete
electrolytes, cause immune response and cancer, or othersie generate toxic
o alrlergic reactions..
2.5.2
Shape-memory Polymer Systems Intended for
Biomedical Devices
Polymeric biomaterials are presently applied in implants, surgical instru-
ments, extracorporal devices, wound covers and controlled drug deliv-
ery systems. Each application requires a specii c combination of material
properties and functions. In many cases implants have to fuli ll certain
mechanical functions [55]. With respect to shape-memory polymers, bio-
medical applications require certain properties or functionalities, which
can be fuli lled by the appropriate choice of suitable shape-memory poly-
mer architectures. An example is a covalent shape-memory polymer
network in which the temporary shape is i xed only by one switching
domain. Another important point to be considered from an application
point of view is the processability of the dif erent shape-memory polymer
architectures [56, 57].
2.5.3
Metallic Materials for Biomedical Devices
Metallic biomaterials have the longest history among the various biomate-
rials. h ey are exploited due to their inertness and structural functions; they
do not possess biofunctionalities like blood compatibility, bone conductiv-
ity and bioactivity, hence, surface modii cations are required; improving
their bone conductivity has been done by coating with bioactive ceramics
like hydroxyapatite, or blood compatibility by coating with biopolymers.
