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Abstract

The aging of bone tissue, bone defects that form during the removal of cysts,
tumours, genetic defects and other bone‐tissue‐related diseases, together with
demands for a better quality of life, mean a requirement for materials, artificial or
autogenous, that will have a long functionality and survivability under the body’s
environmental conditions.
For hard‐tissue replacement, the most widely used materials are titanium alloys.
They are commonly used for bone substitutes, joints and dental implants, with the
aim of permanently supporting or replacing injured or disease‐damaged bone.
Titanium itself is considered to be a biocompatible material that satisfies the need
for mechanical support relatively well due to its high flexural strength and tolerable
elastic modulus. However, when an implant is in direct contact with bone tissue in
a complex dynamic system, it is typically not only exposed to mechanical loads, but it
is also affected by extracellular liquid and proteins. This exposure results in a slow,
but continuous, release of ions; for example, in the case of the Ti6Al4V alloy,
titanium is released, as well as harmful alloying elements like aluminium and
vanadium that are important constituents of the alloy.
Titanium, although it is biocompatible, is also bioinert, and as such it cannot form
strong, interfacial, chemical bonding with bone, and in comparison with bioactive
materials, its osseointegration rate is slow. Therefore, to avoid the dissolution of
the alloying elements and their diffusion into the body, it is necessary to improve
the quality of the native oxide layer and to increase its thickness. Furthermore,
a surface modification is necessary to improve the osseointegration.
In this study, a naturally formed, amorphous TiO2 layer was transformed into
a crystalline one by a hydrothermal treatment in the presence of titanium ions.
Morphology advantageous for bioactivity was achieved by using the appropriate
dopants and surface‐active agents during the processing. Different morphologies,
sizes of crystals and thicknesses of the coatings were achieved by changing the
hydrothermal conditions, such as temperature, time, pH and additives. Firmly
attached anatase coatings were prepared. These coatings were tested both in vitro
and in vivo, whereas the cell adhesion and proliferation tests revealed that the
morphology of anatase crystals is important for cell attachment and growth.
Similarly, the formation of hydroxyapatite when soaked in simulated body‐fluid
solution was influenced by the different anatase planes.
This investigation showed titania to be bioactive, but the rate of hydroxyapatite
formation is still slow compared to other bioactive materials such as hydroxyapatite
or other calcium phosphate ceramics and bioactive glasses. Bioactive glass is
a bioresorbable material with an excellent bioactivity that is osteoconductive and
osteoproductive and can form a strong bond with soft and hard tissues. However,
due to its poor mechanical properties, bioactive glass is not suitable for use in
load‐bearing applications and its use is therefore mainly limited to coatings.
It was proposed that a combination of a porous titanium surface layer coated with
BAG would significantly improve the osseointegration. However, to prepare BAG
coating within the porous titanium structure, fine bioactive glass particles are
needed. As melt‐derived BAG does not meet the requirements, a particulate sol‐gel
method was developed in this study to prepare nanosized spherical particles that
were then applied to the alloy substrate from the suspension by vacuum infiltration.
Different bioactive glass compositions were prepared and characterized in terms of
sintering, crystallization, antibacterial properties, and bioactivity, as well as in vivo
tests on the BAG coatings.
Both coatings combined were applied and examined. Titania and bioactive glass
were applied on the Ti‐alloy to achieve good bioactivity provided by bioactive glass
and to assure protection from the metal ions released by the titania coating even
long after the bioactive glass is resorbed.