**6. Conclusions**

410 Biomedical Science, Engineering and Technology

chemical precursors are a uniform and reproducible source of raw materials than can be made extremely pure through various synthetic means. Low processing temperatures, which result from microstructural control (e.g. high surface areas and small pore sizes), expand glass-forming regions by avoiding crystallization or phase separation, making new materials available to the technologist. The advantages of the sol-gel process (for preparing glass) are shown in Tab. 6 (Brinker & Scherer 1990). The disadvantages of sol-gel processing include the cost of the raw materials, shrinkage that accompanies drying and sintering, and

4. New noncrystalline solids outside the range of normal glass formation.

Table 6. Some advantages of the Sol-Gel Methods over Conventional Melting for Glass

There are books (Klein, 1988) and a number of review papers (Dislich, 1986; Johnson, 1985; Klein & Garvey, 1982; Mackenzie, 1988; Uhlmann et al., 1984; Ulrich, 1988a) which discuss this topic in detail and whose primary purpose is to provide a source of references to current technology, and at the same time to analyze critical issues associated with the various classes of applications that must be addressed in order to advance the sol-gel

1. Thin films and coatings, which can be applied to optical, electronic, protective, and porous thin films or coatings. That represents the earliest commercial application of sol-

2. Monoliths, i.e. applications for cast bulk shapes dried without cracking in such areas as optical components, transparent superinsulation, and ultralow-expansion glasses. 3. Powders, which can be used as ceramic precursors or abrasive grains and applications

4. Fibers, which are drawn directly from viscous sols and are used primarily for

processing time, as it is shown in Tab 7.

a. Saving energy;

1. Better homogeneity from raw materials. 2. Better purity from raw materials. 3.Low temperature of preparation:

d. No reactions with containers, thus purity;

5. New crystalline phases from new noncrystalline solids. 6. Better glass products from special properties of gel.

 b. Minimizing evaporation losses; c. Minimizing air pollution ;

e. Bypassing crystallization.

7. Special products such as film.

1. High cost of raw materials.

3. Residual fine pores. 4. Residual hydroxyl. 5. Residual carbon

7. Long process time

gel technology.

2. Large shrinkage during processing.

6. Health hazards of organic solution.

Table 7. Some disadvantages of the Sol-Gel Methods

technology; for example, a short outline can be as follows:

of dense or hollow ceramic or glass spheres.

reinforcement or fabrication of refractory textiles.

Sol-gel processing has attracted much attention, for the possibility that the method offers to new materials. We define sol-gel rather broadly as the preparation of glass, glass-ceramic and hybrid materials by a sol, its gelation and removal of the solvent. The sol-gel chemistry is based on the hydrolysis and polycondensation of molecular precursors such as metal alkoxides M(OR)x, where M = Si, Sn, Ti, Zr, Al, Mo, V, W, Ce and so forth.

There are many potential applications of sol-gel derived materials in the form of films, fibers, monoliths, powders, composites, and porous media. The most successful applications are those that utilize the potential advantages of sol-gel processing such as purity, homogeneity, and controlled porosity combined with the ability to form shaped objects at low temperatures, avoiding inherent disadvantages such as costs of raw materials, slow processing times, and high shrinkage.

The SiO2 + PCL (0, 6, 12 and 50 %wt) materials, prepared via sol-gel process, were found to be organic - inorganic hybrid materials. The polymer (PCL) can be incorporated into the network by hydrogen bonds between the carboxylic groups of organic polymer and the hydroxyl groups of inorganic matrix. The release kinetics demonstrates that the investigated materials supply high doses of the anti-inflammatory during the first hours when soaked in SBF and then a slower drug release allows a maintenance dose until the end of the experiment.
