INTRODUCTION TO PROCESSING OF BIOMATERIALS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 245

properties at high precision. Moreover, the recent fabrication techniques allow
for synthesis of metal alloys which combines the desirable properties of constitu-
ent metals, thereby fostering potential for new horizons in the fi eld. Along with
these developments, novel surface modifi cation techniques have also been devel-
oped to improve the surface property and functionality of an implant to improve
biointegration. Hence, the modern techniques for metal fabrication hold promise
for the future and will hopefully continue to improve the development of metal-
based devices for biomedical applications.
8.3.2 Ceramics
8.3.2.1 Introduction. Basic composition of hard tissue includes natural
polymers — such as collagen — and ceramics — such as hydroxyapatite — which im-
part strength to the tissue. Ceramics are inorganic, non-metallic biomaterials with
a wide range of properties such as inertness, bioactivity, high strength, wear resis-
tance and durability. These properties have led to their use in a wide range of bio-
medical applications such as orthopedic implants, neurostimulaters, pacemakers,
artifi cial heart valves and cochlear implants. The most commonly used ceramic
biomaterials are alumina, zirconia, pyrolytic carbon, bioglass, hydroxyapatite, and
triclacium phosphate.
There are a number of techniques available for the processing of ceramics
and the choice of an appropriate technique is largely driven by the properties
desired from the ceramic. Although the basic steps of fabrication of ceramics can
be similar, post-fabrication modifi cations can differ depending on the ultimate
use of the biomaterial device [34].
8.3.2.2 Processing. Ceramics are currently used as biomaterials in a num-
ber of forms and compositions. Processing of ceramics is critical because this gen-
erally controls the fi nal properties and functions of the fi nished ceramic product.
Hence, it is important to understand the basic mechanism occurring in each step
of processing to obtain the fi nal product with desirable properties (microstruc-
ture and architecture) in a reproducible manner.
Broadly, ceramic processing techniques involve, preparation of powders,
shaping and sintering of ceramic components and surface treatment of product.
8.3.2.2.1 PREPARATION OF POWDERS. This fi rst step involves processing of
raw ceramic materials to obtain uniform size of power, which can be further pro-
cessed for shaping and sintering. The conventional methods of powder prepara-
tion include crushing, grinding, milling and screening, spray drying, freeze dry-
ing, and solution-precipitation (Figure 8.3) [35]. These processing techniques
appropriately control purity, particle size and particle size distribution, which in
turn enable homogeneous microstructure and high-sintered density. The method
of preparation of powders can also infl uence the structure over many length
scales, ranging from particle size to macroscopic dimensions of the material,
which in turn can infl uence biomaterial host tissue interactions. Hence, powder