Hydrophilic polymer shell

In all cases, the magnetic particles are surrounded by a hydrophilic polymer shell. 

Many kinds of nonbiodegradable vinyl-type hydrophilic polymers were also used in combination with aliphatic polyesters to prepare amphiphilic block copolymers. Two typical examples of the vinyl-polymers used are poly(/V-isopropylacrylamide) (PNIPAAm) [149-152] and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) [153]. PNIPAAm is well known as a temperature-responsive polymer and has been used in biomedicine to provide smart materials. Temperature-responsive nanoparticles or polymer micelles could be prepared using PNIPAAm-6-PLA block copolymers [149-152]. PMPC is also a well-known biocompatible polymer that suppresses protein adsorption and platelet adhesion, and has been used as the hydrophilic outer shell of polymer micelles consisting of a block copolymer of PMPC -co-PLA [153]. Many other vinyl-type polymers used for PLA-based amphiphilic block copolymers were also introduced in a recent review [16]. 

Polymer micelles are nanometer sized (usually several tens of nanometers) self-assembled particles having a hydrophobic core and hydrophilic outer shell composed of amphiphilic AB- or ABA-type block copolymers, and are utilized as drug delivery vehicles. The first polymer micelle-type drug delivery vehicle was made of PEG-b-poly(aspartic acid) (PEG-b-PAsp), immobilizing the hydro-phobic anticancer drugDXR [188-191]. After this achievement by Kataoka et al., a great amount of research on polymer micelles has been carried out, and there are several reviews available on the subject [192-194]. 

Recently, core-shell type microgels, which contain a hydrophobic core and a hydrophilic thermosensitive shell, have become attractive for scientists because such systems can combine the properties characteristic of both the core and the shell [53], We have prepared core-shell microgel particles consisting of a poly(styrene) core onto which a shell of polyCA-isopropylacrylamide) (PS-PNIPA) has been affixed in a seeded emulsion polymerization [54-56], In this case, the ends of the crosslinked PNIPA chains are fixed to a solid core, which defines a solid boundary of the network. In this respect, these core-shell latex particles present crosslinked polymer brushes on defined spherical surfaces. The solvent quality can be changed from good solvent conditions at room temperature to poor solvent conditions at a temperature... 

Finally, we attempt to propose a hydration model of the mucopolysaccharides, at least In the deeply cooled solutions. The model is shown In Figure 13. The data in Table HI clearly indicate that, similar to non-lonlzable hydrophilic polymers (8), the mucopolysaccharides chains are associated with a rather small number of water molecules, so that It may not be adequate to use the word "shell to show their sequence of association. Not only the Ionic but also hydroxyl groups strongly bind a few (approximately two) molecules of water (Wnf) per hydrophilic group and are further... 

Probe diffusion rates observed from parachutes or hollow polymer spheres may be indistinguishable since the probe could be bound in either a polymer bead or polymer shell with similar release characteristics. For example, only hydrophobic probes could be trapped in the polymerized vesicles synthesized by Nakache et al. Here, trapping refers to a decrease in the rate of probe release after vesicle polymerization. The trans-membrane diffusion rates of hydrophilic probes should decrease following polymerization if a polymer shell is successfully formed in the surfactant bilayer. Nakache et al. only observed a decrease in the trans-membrane diffusion rate of hydrophobic probes. This is important since the hydrophobic probe may be released from both hollow polymer spheres and polymer latices with similar release kinetics. Again, caution should be taken, as already shown by German et al. [20] in the case of the fluorescence... 

Besides the radical and anionic polymerization at the interface, polyaddition reactions can also be carried out at the droplet s interface. This technique can be realized in direct and inverse miniemulsion which enables the encapsulation of either hydrophobic or hydrophilic liquids. It is important to mention that the encapsulated liquids have to be a non-solvent for the generated polymer shell if capsules are the desired morphology. 

Polymersomes, self-assembled polymer shells composed of block copolymer amphiphiles. These synthetic amphiphiles with amphiphilicity similar to lipids constitute a new class of drug carriers. They are spontaneously formed in aqueous media, as unilamellar vesicles up to tens of microns in diameter. Amphiphilic block copolymers form a range of self-assembled aggregates including spherical, rod-like, tubular micelles, lamellae, or vesicles, depending on polymer architectnre and preparation conditions. Polymers having low hydrophobicity (less than 50%) favor the formation of micelles, however, intermediate level of hydrophobicity (50%-80%) favors the formation of vesicles. Polymeric vesicles, which have a liposome-like structure with a hydrophobic polymer membrane and hydrophilic inner cavity, are called polymersomes. 

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