Biomedical Engineering Reference
In-Depth Information
High and linearly increasing viscosity reduces the risk of leakage and gives a
predictable handling.
High cohesiveness optimizes the cement's filling pattern in the vertebra.
No toxic or smelling fumes
And after the procedure (Jarmar et al, 2008, Engqvist et al 2006)
Mechanical strength
Biocompatibility including integration
Long-term stability i.e. non-resorbable systems.
4.3 Drug carrier for drug delivery
General aspects of ceramics for use in drug delivery of drugs are presented by Ravaglioli et
al and by Lasserre and Bajpaj (Ravaglioli et al, 2000, Lasserre and Bajpaj, 1998). A short
description of carrier materials for drug delivery using chemically bonded ceramics,
especially Ca-aluminate and/or Ca-silicate systems are given below. The CBC carrier
material based on CA and CS structures exhibit some attractive features. The
manufacturing procedure at low temperatures, where no or limited degradation of the
medicaments occur, and the microstructure developed with open porosity as nano-sized
channels as described above, are the basic features that open up a possibility for controlled
release of medical agents. The precursor powder cures as a result of hydration reactions,
between a ceramic oxide powder, primarily Ca-silicates and/or Ca-aluminates, and water.
Through the hydration, new phases of hydrates are formed, which to a great part establish
the microstructures needed to control the release of drugs incorporated in the injectable
precursor material. An injectable material is formed into a paste by mixing it with a water-
based hydration liquid, which is then ready to be injected. Directly after the injection, the
paste starts to develop the final microstructure. The water-based liquid may also comprise
viscosity-controlling additives. These may be loaded with the drug before preparation of the
final injectable paste. A couple of unique reaction conditions related to the production of
materials yields materials with a variety of possible microstructures with porosities from the
nanoscale to the microscale. variety of possible microstructures with porosities from the
nanoscale to the microscale. 3) pore size and pore channel size, and 4) combination of
different porosity structures (Hermansson, 2010). Porosity generated during the hydration
of the Ca-aluminates and Ca-silicates is open porosity due to the reaction mechanism, and
can be in the interval of 5-60 vol.-%. The average pore channel size (i.e. the diameter of the
pores formed between the particles of the hydrated material) may be 1-10 nm. The crystal
size of the reacted hydrates is in the interval 10-50 nm. This was established by BET-
measurements, where the specific surface area of dried hydrated CA was determined to be
in the interval 400-500 m
2
, corresponding to a particle size of approximately 25 nm, and by
HRTEM [7], Fig. 1 below. When short hydration time and/or low amount of water, or
moisture at relative humidity > 70 %, are used, additional porosity is achieved with pore
sizes in the interval 0.1-1 micrometer due to incomplete reaction. The different pore sizes
obtained can be utilized for controlled release of drugs, when the Ca-aluminate implant
material also works as a carrier of medicaments.
Drug loading and controlled release of drugs
The following properties are of significance with regard to the carrier for controlling the
drug release; Type of ceramic precursor for producing the chemically bonded ceramic, grain
size distribution of the precursor powder particles and general microstructure of the
