Multicompartment capsule

Besides the earlier described PG-based nanogels, other methods have also been applied to prepare multicompartment capsules and carrier systems based on dendrimers or hyperbranched polymers. 

Percec et al. [41,42] studied and reviewed various complex self-assembled structures in detail that can be obtained from dendritic molecules. Especially multicompartment capsules obtained by the self-assembly of a library of amphiphilic Janus-type dendrimers are impressive. The chemical linkage of two dissimilar dendritic building blocks results in Janus dendrimers and produces a break in the spherical symmetry characteristic to dendrimers. Consequently, these stmctures spontaneously promote the self-assembly upon injection of its ethanol solution to form stable unilamellar vesicular nanostructures and other complex architectures (Eig. 6.17). Dendriniersom.es... 

With regard to the preparation of multicompartment polymer capsules based on this SIP method, a successful approach was demonstrated by Kang et al. [17] who used a two-step distillation/precipitation polymerization of methacrylic acid (MAA) and A-isopropylacrylamide (NIPAM), respectively, onto silica nanoparticles as templates. More interestingly, due to the PMAA inner shell and PNIPAM outer shell, the hollow structure can respond independently to changes in pH and temperature. After loading DOX into the capsules, temperature- and pH-controlled release of anticancer drug behavior was demonstrated. 

For a further development of this method i.e., the preparation of multifunction-alized capsules, a series of multicompartment polymeric capsules were successfully constmcted. For example, Stadler et al. [19] synthesized multicon tartment polymeric capsules with embedded liposomes in the shell via the LbL technique by using poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) as the polyelectrolytes and 50nm zwitterionic l,2-dioleoyl-i n-glycero-3-phosphochohne (DOPC) liposomes as the cargo. The TEM images (Fig. 6.9) clearly show the encapsulated liposomes in the polymeric shell. 

FIGURE 6.9 Schematic illustration of the morphology of liposomes embedded in a multicompartment pol3meric capsule (left) and cryo-TEM image of a (PAH/PSS) /PAH/ liposomeSj gj/PSS/PAH/PSS multicompartment polymeric capsule embedded in ice (inset) and a close-up of the polyelectrol)ae shell, which contains intact liposomes (right). Source Stadler et al. [19]. Reproduced with permission of American Chemical Society. 

A slow and progressive release of the capsule content is usually aimed, whereas the capsules presented here were designed to open and release their content at once, triggered by a thermal stimulus. They are of three types, which may be used for different specific applications. The firsts are simple wax Si02 capsules [38], which were designed to encapsulate any type of hydrophobic adjuvant. Hence, their main drawback is the inability to encapsulate hydrophilic compounds. To overcome this issue, we developed two types of multicompart-mental capsules wax water Si02 [39] and water wax Si02 [40] capsules, which are able to encapsulate any compound. 

More sophisticated capsule systems, e.g., multicompartment hybrid assemblies, have recently been reported [43 7], which endow the systems with novel and advanced properties. Multicompartmentalized capsules can be constiucted via (i) assembly from preformed different subcompartments (ii) synthesis of particles on which capsules are assembled (iii) a combination of synthesis and assembly from preformed subcompartments [48]. The main advantages of these sophisticated stmctures are, for example, simultaneous delivery of different molecules using one entity with protection from the outside environment as weU as conduction of cascade reactions. MulticompartmentaUzation has been recently described as a suitable approach for theranostics because elements for diagnostics can be encapsulated in some subcompartments and drugs for therapy can be encapsulated in other subcompartments [49]. 

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