Biomedical Engineering Reference
In-Depth Information
[48] of metal implants, as well as function as resorbable lattices,
providing temporary structures and frameworks those are dissolved
and/or replaced as the body rebuilds the damaged tissues [49-55].
Some types of bioceramics even feature a drug-delivery capability
[56, 57].
A progressive deterioration of all tissues with age is the major
contributor to the need for spare parts for the body. Bone is especially
vulnerable to fracture in older people due to a loss of density and
strength with age. This effect is especially severe in women due
to the hormonal changes associated with menopause. A graphical
representation of the effect of time on bone strength and density
from the age of 30 years onward is available in literature [Ref. 51, Fig.
1]. Bone density decreases because bone-growing cells (osteoblasts)
become progressively less productive in making new bone and
repairing micro-fractures. The lower density greatly deteriorates
the strength of bones and an unfortunate consequence is that many
old people fracture their hips or have collapsed vertebrae and spinal
problems [51].
Bioceramics are needed to alleviate pain and restore functions to
diseased or damaged calcified tissues (bones and teeth) of the body.
A great challenge facing its medical application is to replace old,
deteriorating bone with a material that can function the remaining
years of the patient's life and, ideally, be replaced by a new mature
bone without transient loss of mechanical support [2]. Surface
reactivity is one of the common characteristics of bioceramics. It
contributes to their bone bonding ability and their enhancing effect
on bone tissue formation. During implantation, various interactions
occur at the material/tissue interfaces that lead to time-dependent
changes in the surface characteristics of the implanted bioceramics
and the surrounding tissues [58]. Because the average life span
of humans is now 80+ years and the major need for spare parts
begins at about 60 years of age, the implanted non-resorbable
bioceramics need to last, at least, for 20+ years. This demanding
requirement of survivability is under conditions of use that are
especially harsh to implanted materials: corrosive saline solutions
at 37°C under variable, multiaxial and cyclical mechanical loads. The
excellent performance of the specially designed bioceramics that
have survived these clinical conditions represents one of the most
remarkable accomplishments of research, development, production
and quality assurance during the past century [51].
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