**5. Conclusion**

70 Biomaterials – Physics and Chemistry

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 waterbased 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 BETmeasurements, where the specific surface area of dried hydrated CA was determined to be in the interval 400-500 m2, 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

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

High and linearly increasing viscosity reduces the risk of leakage and gives a

High cohesiveness optimizes the cement's filling pattern in the vertebra.

And after the procedure (Jarmar et al, 2008, Engqvist et al 2006)

predictable handling.

Mechanical strength

No toxic or smelling fumes

**4.3 Drug carrier for drug delivery** 

Biocompatibility including integration

Long-term stability i.e. non-resorbable systems.

material also works as a carrier of medicaments. **Drug loading and controlled release of drugs** 

The Ca-aluminate technology provides a platform upon which Ca-aluminate based materials may work as a general biomaterial and as a complement to other chemically bonded ceramics based on phosphates, silicates or sulphates. Identified areas are in the first place within the dental and orthopedic areas, where injectable stable biomaterials are required. These include also properties as bioactivity related to apatite formation, antibacterial properties as well as nanostructural features useful for carriers for controlled drug delivery. The studies presented in this paper can be summarised as follows;


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