A sintering schedule to allow the reliable formation of inorganic or
ceramic materials, exemplified using porous calcium polyphosphate samples
to be used for forming novel implants for bone interfacing applications.
The key to the successful definition of the process was the determination
of the factors affecting the crystallization temperature of the powders
that are gravity sintered to form porous samples of desired density and
with a pore size range suitable for the particular application. The
method involves applying a sintering procedure to a packed amorphous
inorganic powder which gives control over densification and includes
choosing sintering temperatures and times sequentially that correspond to
the inorganic material being amorphous but having a viscosity to develop
significant sinter necks between adjacent powder particles by a viscous
flow sintering mechanism while maintaining a desired open-pored
structure, followed by a second temperature at which crystallization of
the packed amorphous inorganic powder occurs and during which slower
diffusion-related mechanisms control sinter neck growth and densification
to give a substantially crystalline porous, inorganic structure. In
addition, interpenetrating phase composites of biodegradable organic
polymers throughout the porous calcium polyphosphate samples were formed
and resulted in the development of novel composites with attractive
strength and toughness. These materials hold promise for formation of
biodegradable fracture fixation implants and degradable anchoring systems
for temporary stabilization of bone-interfacing implants designed for
fixation by bone ingrowth.