Bioinert materials: do not
interact with biological
bone screws and plates, knee
prostheses and tooth
Bioactive materials are
durable materials that can
bind chemically with the
surrounding bones and in
some cases even with soft
degrade on implantation to
the body. Desirable is that the
material degrades at the
same rate at which the host
• Carbon, Yttria Stabilized Zirconia
• Articulating surfaces in joint replacements
• high surface finish and its excellent wear resistance, alumina
is often used for wear surfaces in joint replacement
prostheses. Such applications include femoral heads for hip
replacements and wear plates in knee replacements.
• Bone Spacers
• Porous alumina may also be used to replace large sections of
bone that have been removed for reasons such as cancer.
These may take the shape of rings that are concentric around a
metallic pin, inserted up the centre of the remaining bone
itself. The porous nature of these implants will allow new bone
to grow into the pores, effectively using the alumina as a
scaffold for new bone formation.
• Dental Applications
• Bioactive glass, Glass Ceramics, Hydroxy Apatite
• Hydroxy apatite, calcium phosphates
• The method of fixation has suffered from limitations,
both theoretical and real.
– Bone cement can fragment and the formation of particles at the
– bone interface can result in osteolysis and loosening.
– Osteolytic reactions have also been related to wear debris
– Differing metabolic activities
– The bioactive properties of ceramics such as
hydroxyapatite, some calcium phosphates and various
types of bioactive glass, are well known.
– When placed in bone tissue, these materials promote
bone formation, and bond to bone at various rates.
– plasma-sprayed hydroxyapatite coatings.
Calcium phosphate ceramics
• Include several materials which differ not only in their chemical
composition, but also in their specific surface area, crystal structure
and macro- and microporosity.
• There are differences due to variations in the calcium to phosphate
ratio; tricalcium phosphate, hydroxyapatite and tetracalcium
phosphate have Ca/P ratios of 1.5, 1.67 and 2 respectively, and
there are other materials with ratios in between these
• Plasma spraying can have a profound effect on the chemical and
physical characteristics of the deposited coating and few
commercial coatings are alike.
– Fortunately, the compositional and structural changes which result
from the spraying usually enhance the bone-forming properties of
hydroxyapatite, but at the price of increasing the rate of progressive
resorption of the coating with time. This would not necessarily be
detrimental if the function of the coating was simply to stimulate bone
How do Bioactive and Resorbable Bioceramics help bone
• The bioceramic provides the right environment for the new bone to
• They also have a special chemical composition that allows a type
of cell called osteoblasts - responsible for bone production - to
attach to the ceramic’s surface, and start generating new bone.
The interconnected tiny holes within the bioceramic structure
facilitate the proliferation of the cell network, and the growth of
the bone, within the synthetic scaffold.
• The calcium content of the bioceramic provides the inorganic
component that new bone requires to develop its mineral-like
• The complex processes underlying bone’s astonishing capability to
regenerate are only partially understood.
• Each new finding in our research throws ten new questions that
need an answer, and so on. This is proving to be the major
impediment to the further development of bioceramics. At the
moment, they are improving only slowly, by trial and error: the
researchers slightly change the properties of the material, and then
study the biological response to the synthetic material.
• Calcium Phosphate Bioceramics
• There are several calcium phosphate ceramics that are considered biocompatible.
Of these, most are resorbable and will dissolve when exposed to physiological
environments. Some of these materials include, in order of solubility:
• Tetracalcium Phosphate (Ca4P2O9) > Amorphous calcium Phosphate > alpha-
Tricalcium Phosphate (Ca3(PO4)2) > beta-Tricalcium Phosphate (Ca3(PO4) 2) >>
• Unlike the other calcium phosphates, hydroxyapatite does not break down under
physiological conditions. In fact, it is thermodynamically stable at physiological pH
and actively takes part in bone bonding, forming strong chemical bonds with
surrounding bone. This property has been exploited for rapid bone repair after
major trauma or surgery.
• While its mechanical properties have been found to be unsuitable for load-bearing
applications such as orthopaedics, it is used as a coating on materials such as
titanium and titanium alloys, where it can contribute its 'bioactive' properties,
while the metallic component bears the load. Such coatings are applied by plasma
spraying. However, careful control of processing parameters is necessary to
prevent thermal decomposition of hydroxyapatite into other soluble calcium
phosphates due to the high processing temperatures.