Gel microparticle

Polymers, (II) and (III), containing hydrolytically susceptible segments at a physiological pH between 6.5 and 7.5 were previously prepared by the author [2] and used as viscoelastic liquids containing gel microparticles. 

The next paper we will comment on in this section is a letter by Nakatami et al. [147] in which they describe a microscale technique to study the dynamics of adsorption. This technique, the single-microparticle injection, is basically an optical method that uses Lambert-Beer law to follow the concentration of methylene blue on the surface of a silica gel microparticle. Their main conclusions are that equilibrium is attained within 20 min, Langmuir equation describes the experimental adsorption isotherm, methylene blue molecules penetrate into the pores and the whole process is controlled by adsorbate diffusion in water. 

We have shown elsewhere that sol-gel microparticle formation is one case in which soft matter is used to template the resulting porous material in a basic chemical strategy for making functional nanomaterials using lyotropic mesophases, foams and emulsion, that has been named by Ozin nanochemistry. "... 

Again, summarizing what has been extensively described elsewhere, the two main techniques to prepare sol-gel microparticles start either from W/0 or from oil-in-water (0/W) emulsions to entrap, respectively, hydrophilic or lipophilic ingredients inside the spherical shell of amorphous silica or organosilica. 

Delivery systems can be solid or liquid, depending on the food matrix where they are introduced. Some examples of solid systems are spray-dried and gel microparticles, whereas liquid systems include liposomal and emulsified systems. Each of these delivery systems has its own specific advantages and disadvantages for encapsulation, protection, and delivery of food ingredients. These aspects are briefly discussed in the following, together with a description of the basic principles of each technique, its physicochemical characteristics, and the current challenges for its application in foods. 

Gel microparticles are formed from the concept of gelation as an encapsulation technology. Gelation is based on the formation of a solution, dispersion, or the emulsification of the core material in an aqueous solution containing a hydrophilic polymer (hydrocolloid) capable of forming a gel under an external action, either physical or chemical. 

Encapsulation may be used to deliver traditional active ingredients, such as flavors, vitamins, minerals, sweeteners, and antioxidants, or relatively novel ones, such as probiotic microorganisms. SD and gel microparticles, liposome and emulsified systems, which are under focus in this chapter, have been used for some of these applications. Their functionality as delivery systems is discussed in Sections 32.4.1 through 32.4.5. 

Liu, K., Ding, H.J., Chen, Y, and Zhao, X.Z. 2006. Shape-controlled production of biodegradable calcium alginate gel microparticles using a novel microfluidic device. Langmuir 22 9453-9457. 

Figure 4.21. Variation in time of gel microparticle diameter with applied DC...

Infrared Analysis - The comparison of IR spectra of empty silica-gel microparticules and silica-gel microparticles loaded with TMPTA do not enable us to prove the encapsulation of the TMPTA. In effect, the two spectra present the same absorption bands because silica-gel shell contains a methacrylate compound - Figure 16. 

For that we have used silica-gel iiticrocapsules (empty microcapsules artd microcapsules loaded with TMPTA) with TEOS precursor alone (not methacrylate chain in this compound). The comparison between Infrared spectra of the empty silica-gel microparticles with TEOS precursor alone - Figure 17 (a) and silica-gel microparticles loaded with TMPTA - Figure 17 (c), shows the presence of new bands, in particular at 1721, 983 and 807 cm b These bands, characteristic of the TMPTA monomer, confirm the presence of TMPTA encapsulated in silica-gel microcapsules. 

An aqueous, polymer particle system, which behaves similarly to the Silica-nCis/ cyclohexane system, in the sense that the van der Waals forces may be tuned by varying temperature, has recently been described by Rasmusson et al. (2004). The particles were poly(N-isopropylacrylamide) (PNIPAM) gel microparticles, which carried surface —SO groups from the initiator residues. 

Figure 6.14 The variation in the fractal dimensions (df), as a function of temperature (beyond the CFT), for dispersions of PNIPAM gel microparticles in 1 M NaCI solution (Routh Vincent, 2002).

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