Biomedical Engineering Reference
In-Depth Information
to fill only small bone defects. However, their strength increases
gradually when bones ingrow into the porous network of calcium
orthophosphate implants [495-498]. For example, Martin et al.
reported bending strengths of 40-60 MPa for a porous HA implant
filled with 50-60% of cortical bone [495], while in another study
an ingrown bone increased strength of porous HA bioceramics by a
factor of 3-4 [497].
To conclude this topic, one should mention that filters for
microbial filtration might be manufactured from porous HA [499].
4.5
Biomedical Applications
Since Levitt et al. described a method of preparing a FA bioceramics
and suggested its possible use in medical applications in 1969
[500], calcium orthophosphate bioceramics have been widely
tested for clinical applications. Namely, calcium orthophosphates
in a number of forms and compositions (Table 4.2) currently are
either in use or under a consideration in many areas of dentistry
and orthopedics, with even more in development. For example, bulk
materials, available in dense and porous forms, are used for alveolar
ridge augmentation, immediate tooth replacement and maxillofacial
reconstruction [64, 377]. Other examples include burr-hole buttons
[505], orbital implants (Bio-Eye
®
) [506-509], other ophthalmic
applications [510, 511], increment of the hearing ossicles, spine
fusion and repair of bone defects [512, 513]. In order to permit
growth of new bone into defects, a suitable bioresorbable material
should fill these defects. Otherwise, ingrowth of fibrous tissue might
prevent bone formation within the defects.
In spite of the aforementioned serious mechanical limitations,
bioceramics of calcium orthophosphates is available in various
physical forms: powders, particles, granules (or granulates [12]),
dense blocks, porous scaffolds, self-setting formulations (Chapter 5),
implant coatings and composite component (Chapter 6) of different
origin (natural, biological or synthetic) often with the specific
shapes, such as implants, prostheses or prosthetic devices (Table
4.3) [2, 95]. Furthermore, bone grafts are also proposed as non-
hardening pastes (= “putty”). Generally, the latter materials consist
of a mixture of calcium orthophosphate powders or granules and a
“glue,” typically a highly viscous hydrogel (see section 6.4.6 Injectable
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