Biomedical Engineering Reference
In-Depth Information
engineered materials impact most product sectors, their development for
biomedical applications in particular has been rapidly expanding. h is is
partly a result of the convergence of nanoscale science and biological sci-
ence over the past decade. Nanoscience, as applied to materials, addresses
the same size scales of physical phenomena that are critical in living tis-
sues. Consequently,
Nanostructured Materials
are now being engineered at
a scale that matches the size range of attributes and physiological processes
associated with human cells. New nanostructured sot and hard materials
are being introduced every year. As of May 2013, 1,164 patents have been
issued worldwide that reference nanomaterials.
Sot material structures, such as polymers and polymer-based compos-
ites, are the most prominent class of biomedical materials. h is is partly
because they are similar to sot tissues that predominate in human physi-
ology. h ey are readily tailored to physiological applications since their
nano/micro/macro-scale internal structures and surfaces can be function-
alized for specii c biomedical environments. h ey can be made biodurable
for long-time use through surgical implantation, or biodegradable for tem-
porary functions such as aiding drug delivery.
Aside from wood and other nature-made substances, metal is the old-
est class of engineered biomaterial. Gold was used by the Greeks for frac-
tures around 200 B.C. and iron and bronzes were used in sutures as early as
the 17
th
century [1]. Silver, gold, and platinum were used as pins and wires
for fractures in the 19
th
century. Steel was introduced for use in bone plates
and screws at the beginning of the early 20
th
century, and in an ever grow-
ing number of orthopedic devices in the latter half of the 20
th
century [1].
h e metals that are most prominently used in biomedical applications today
are stainless steel, titanium, and cobalt-chromium (Co-Cr) alloys. Stainless
steel, invented and produced i rst between 1908 and 1919, was used in bone
plates by 1926. Co-Cr i rst appeared in bone plates 10 years later. Tantalum,
a refractory metal, appeared in prostheses by 1939 and has since been used
as radiographic markers, vascular clips, stents, and in repair of cranial defects
[2]. Titanium and its alloys appeared in bone plates and hip joints by 1947.
h e well-known NiTi alloy Nitinol, discovered in 1958 found its way into
orthodontic applications in the 1970s and cardiovascular stents in 1991 [1, 3].
Biomedical applications have traditionally required only small volumes
of metal relative to the high tonnage production volumes that are most com-
mon in the metals manufacturing industry. Consequently, the alloys used
in medical applications have typically been selected from those available for
high volume non-medical applications, such as aerospace. However, dur-
ing the past 20 years the attention to biomedical applications of metals has
continued to grow, driven in part by increasing attention to quality of life,
