Homogenizer microparticles preparation

The process has been extensively explored by Barbe and coworkers in Australia (where the same scientists established the spin-off company Ceramisphere), and can be viewed as an emulsification of a sol-gel solution in which gelation takes place concomitantly. Depending on the order of addition of the different chemicals, furthermore, the porous microparticles prepared from interfacial hydrolysis and condensation of TEOS in W/0 emulsion will be full porous matrix particles or core-shell capsules. Normally, if the emulsification of the sol-gel solution takes place concomitantly with gelation, full microparticles are formed with the dopant molecules homogeneously distributed within the inner huge porosity of the particles (Figure 18.3). 

The pore size and distribution in the porous particles play essential roles in NPS synthesis. For example, only hollow capsules are obtained when MS spheres with only small mesopores (<3 nm) are used as the templates [69]. This suggests that the PE has difficulty infiltrating mesopores in this size range, and is primarily restricted to the surface of the spheres. The density and homogeneity of the pores in the sacrificial particles is also important to prepare intact NPSs. In a separate study, employing CaC03 microparticles with radial channel-like pore structures (surface area 8.8 m2 g 1) as sacrificial templates resulted in PE microcapsules that collapse when dried, which is in stark contrast to the free-standing NPSs described above [64]. 

Calvor and Muller used high-pressure homogenization and a novel method to prepare biodegradable microparticles of poly(D,L-lactide) (PLA) and poly (D,L-lactide-co-glycolide) (PLGA). They heated the... 

Microparticles can be produced by a simple technique that consists of spraying a polymer, e.g., PLLA, solution in dichloromethane (or dimethylsulfoxide), through a nozzle into a reactor filled with supercritical carbon dioxide (Reverchon et al, 2000). This process is known as supercritical antisolvent precipitation (SAS). The experimental parameters have a limited influence on the particle size (1-4 /im). A modified version of the process, known as the SAS-EM process, allows nanoparticles of a controlled size (30-50 nm) to be produced (Chattopadhay et al., 2002). In order to restrict the use of an organic solvent. Pack and co-workers fed the SAS reactor with a solution of PLLA prepared by homogeneous ring-opening polymerisation in supercritical HCFC-22 (Pack et al, 2003a). 

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