Biomedical Engineering Reference
In-Depth Information
of bone. Another important property related to Ca-aluminate materials is the possibility to
control the dimensional change during hardening. In contrast to the shrinkage behaviour of
many polymer-based biomaterials, the Ca-aluminates exhibit a small expansion, 0.1-0.3
linear-% (Kraft 2002).
3.1 Biocompatibility including bioactivity
Definitions used
The terms biocompatibility and bioactivity are used in different ways by different categories
of scientists. Below are presented the definitions used in this paper, mainly agreeing with
the definitions discussed in (Williams, 1987) Biocompatibility: “The ability of a material to
perform with an appropriate host response in a specific application”.
Bioactivity (bioactive material): “A material which has been designed to induce specific
biological activity”. Another definition according to (Cao and Hench,1996) “A bioactive
material is one that elicits a specific response at the interface of the material which results in
the formation of a bond between the tissues and the material”.
Thus a material cannot in itself be classified as biocompatible without being related to the
specific application, for which it is intended. Bioactivity from a materials viewpoint is
frequently divided into
in vitro
and
in vivo
bioactivity. The
in vitro
bioactivity of a material is
however only an indication that it might be bioactive in a specific
in vivo
application.
Another aspect of bioactivity is that this term can be adequate only when the biomaterial is
in contact with a cellular tissue. However, often a material is claimed to be bioactive if it also
reacts with body liquids forming an apatite-phase.
In vitro
bioactivity is tested in phosphate
buffer systems similar to that of saliva or body liquid, and apatite formation is the claimed
sign of bioactivity. A further aspect of bioactivity and also biocompatibility deals with the
different curing times and temperatures at which the observation (testing) is performed.
This is important to issues such as initial pH-development, cohesiveness and initial strength.
Finally the biocompatibility and bioactivity can only be confirmed in clinical situations, with
the actual implant/biomaterial in the designed amount or content and shape. This is
especially important for injectable biomaterials which are formed (hydrated) and cured
in
vivo
, and for implants where movements, even micro-movement, can influence the outcome.
Standards and methods
Relating to the definition aspects above, the acceptance of a biomaterial is a crucial issue,
and to some extent the question has been solved by relating to the following toxicological
endpoints indicating biocompatibility as referred in the harmonized standard ISO
10993:2003, which comprises the following sections:
Cytotoxicity (ISO10993-5), Sensitization (ISO10993-10), Irritation/Intracutaneous reactivity
(ISO10993-10), Systemic toxicity (ISO10993-11), Sub-acute, sub-chronic and chronic toxicity
(ISO10993-11), Genotoxicity (ISO10993-3), Implantation (ISO10993-6), Carcinogenicity
(ISO10993-3) and Hemocompatibility (ISO10993-4).
This will be the main guideline when presenting the status of the biocompatibility of the
CASPH-system, but was complemented by corrosion testing, elementary analysis, pH-
change and additional cytotoxicity testing.
The corrosion resistance test - using a water jet impinging technique - was conducted
according to EN 29917:1994/ISO 9917:1991,where removal of material is expressed as a
height reduction using 0.1 M lactic acid as solution, pH 2.7 . The duration time of the test is
