Microencapsulation is the process of packaging solids, liquids, or gaseous materials as active compound with continuous films as coating to forms microparticles of micrometer to milimeter size(1). Microparticles can be distinguished into microsphere or microcapsule according to their internal structure (Figure 1). Microspheres based on a matrix system whereas mi-croparticles are reservoir system are a common method of immobilization, protection and stabilization of active compounds. Microencapsulation widely used in the development and production of drug delivery systems within the pharmaceutical field. The benefits are reduction of side effect, masking of taste and odor of certain drug, enhancement of the stability of a drug and the control of the drug release(2). In the Food field, protection of active compounds to environmental stress and improving the physicochemical functionalities of compound. In the cosmetic sector, microencapsulation can be used to stabilize essential oil for example.
The microencapsulation technology was first presented by Greenand Schleicher in 1950s with a patent registration for the preparation of capsules containing dyes, which were developed to be incorporated into paper for copying purposes(3). Since then, varieties of techniques have been proposed and can be classified in three groups: physical methods (spray drying, spray coating…), physico-chemical method (coacervation, ion gelation…) and chemical method (interfacial polymerization , transacylation reaction …) . In our laboratory, the preparation method of microparticle is an emulsion by transacylation (Figure 2). This method is based on the formation of amide bound (covalent bonds) in alkaline medium between the amine groups of the protein (Human Serum Albumin (HSA) ) and the acid groups of the polymer (Propylene Glycol Alginate (PGA)) forming thus a solid and thermostable membrane consisting of a protein directly linked to polysaccharide. During the transacylation reaction, glycol propylene is released. Advantages of this method are that it uses natural and non-aggressive reactive and form biodegradable, stable, biocompatible and non-toxic microparticles.
The first aim of this work consists to determine the critical Hydrophilic-Lipophilic- Balance (HLB) value of the isopropyl myristate in order to get this value, emulsion were prepared with an aqueous phase (containing water and HSA) and an organic phase (containing isopropyl myristate and surfactants mixture). Emulsion were prepared with HLB ranging from 1,8 to 8,6. Once the critical HLB was found, the goal was to determine the best surfactant percentage for the formulation. Surfactant is added to the emul-sion to stabilize it, allowing the formation of a stable continuous and dis-persed phase, with the latter presenting a droplet shape.
According to the result of previous experiment and in order to go further, we considered changing isopropyl myristate for paraffin oil and modifying some factors (critical HLB value, best surfactants percentage and agitation speed).
The transacylation reaction starts by alkalization of the emulsion. NaOH (alkaline reagent) can be also consumed by saponification of isopropyl myristate and surfactants (Span85 and Span20) (4). In the final section, the effects of variation of the NaOH volume has been studied with the aim of determine if the kinetic of the saponification of isopropyl myristate was faster than kinetic of transacylation reaction.