Biomedical Engineering Reference
In-Depth Information
have had limited implant success lifetimes and often require secondary, revision surgery
to either correct or replace them.
Within the past 10 years, tissue engineering has driven biomaterials development toward
the understanding and subsequent precise control of the implant material/host-tissue
interface, resulting in improved cellular attachment, proliferation, and eventual ingrowth.
All these factors are required to prolong implant lifetimes.
Tissue engineered devices consist of an implantable biomaterial scaffold that is resorbed
at the implant site and replaced with regenerated, healthy tissue. Often the scaffold is seeded
with cells appropriate for biological interaction with the host tissue implant site. This
approach requires biomaterials to act as temporary mechanical structures mimicking the
host tissue extracellular matrix and eventually being replaced with new, regenerated tis-
sue. It is hoped that this biodriven development focus will result in controlled protein
absorption and release, cellular attachment, proliferation, and differentiation resulting in
significantly improving implant lifetimes (see Figure 9.2). Recently, much research effort
has concentrated on the use of nanotechnology (via morphological and physiochemical
approaches) to further mimic extracellular matrix behavior, thus promoting faster rates of
tissue ingrowth into the implant surface, prolonged tissue/implant attachment, and sub-
sequent improved implant lifetime.
BioceramicsandGlasses
Ceramics are composed of inorganic and nonmetallic components usually fabricated using
traditional pottery processing techniques such as [41]:
1. Ceramic particles suspended in a lubricant or binder solution for shaping and
iring
2. Raw materials (e.g., silicates, aluminum silicates, nonsilicates such as alumina)
melted to form a liquid and shaped during cooling and solidification
Their mechanical properties (see Table 9.1) coupled with inertness in aqueous environments
make them desirable implant material candidates for orthopedic load-bearing applications
(see Table 9.2).
Since ceramics have low strength in tension, their application has been limited to com-
pressive loading conditions (see Table 9.2). Readers wanting to know more about bioceramics
not classified as either bioactive glass or glass-ceramics should refer to the seminal works
by Hench and Wilson [9] and recently by Kokubo [10]. Here, I will refer to them as first-
generation bioceramics: they are bioinert and cannot be resorbed or replaced with regener-
ated host tissue. First-generation ceramics include alumina (Al
2
O
3
) and zirconia (ZrO
2
).
In the late 1960s, Hench discovered and developed the first bioceramics that elicited a spe-
cific biological response at the implant/tissue interface, resulting in direct biological bond-
ing into the material and subsequent fixation. Here I will refer to them as second-generation
bioceramics. They are commonly termed bioactive ceramics. Although included in many
texts as a ceramic, Hench's material was not actually a ceramic but a glass whose compo-
sition was based on the Na
2
O-P
2
O
5
-CaO-SiO
2
system (45S5 composition). Traded under
the name Bioglass, bioceramics research focus shifted from bioinert materials toward a
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