Encapsulation PNIPAM

Encapsulation of PNIPAM inside non-temperature-sensitive (PSS/PAH) capsules templated on PS cores was achieved by the same ship in a bottle synthesis [37], providing temperature-responsive microcapsules. Encapsulated PNIPAM collapsed when the temperature of the system increased above 34 °C, forming discrete particles inside the capsule, without modification of the shell (Fig. 3.6). This prop-... 

Thus, the PEO segment actually becomes hydrophobic at higher temperatures. This temperature-dependent change converts the amphiphilic block copolymer to a water-insoluble hydrophobic polymer (Topp et al. 1997 Chung et al. 2000). The temperature at which the polymer exhibits this transition is called its lower critical solution temperature (LCST). In addition to PEO, substituted poly(A -isopropyl acrylamide) (PNIPAM Chart 2.1) exhibits temperature sensitivity, where the LCST can be tuned by varying the alkyl fimctionahty. The guest encapsulation combined with the temperature-sensitive precipitation of the polymers has been exploited to sequester and separate guest molecules from aqueous solutions (Fig. 2.4). 

Figure 11 shows the releasing and encapsulation of pyrene (an imitation of drugs/catalysts) by these PNIPAM-g-PEO copolymer chains in water in... 

Cationic PNIPAM-covered magnetic particles Hetero coagulation of iron oxide nanoparticles onto cationic particles. Encapsulation of preformed particles by polymerization of NIPAM, BAM and AEMH 300-1000 nm Superparamag-netic, bioreactive particles. Temperature, salinity and pH sensitive [10,18,19]... 

Qin et al. [229] produced a thermo-responsive PEO-fe-PNIPAM block copolymer that forms vesicles above the LCST of 32°C. The PEO-b-PNIPAm vesicles are shown to be stable at body temperature and to encapsulate both hydrophilic drugs (e.g., Doxorubicin) and hydrophobic molecules into their membranes (e.g., PKH 26). Temperature-controlled quick release of both types of compounds below 32°C was possible. 

Still using the same two-step procedure, monodisperse and thermoresponsive magnetic latex particles based on PNIPAM were prepared [157, 158], Anionic iron oxide nanoparticles were first adsorbed onto preformed cationic particles of various compositions [PS, poly(styrene-co-NIPAM) core-shell, or PNIPAM], The obtained heterocoagulates were then encapsulated with crosslinked PNIPAM through seeded precipitation polymaization (Fig. 24). The magnetic content varied from 6 to 23 wt%. These particles were successfiiUy used for the covalent immobilization of antibodies, and the resulting conjugates were tested as solid phases in immunoassays [159]. 

Moreover, it is interesting to note that for both Ag and Pd composite particles the catalytic activities of metal nanoparti-cles immobilized in SPEB are higher than that of a core-shell miaogel system. This can be explained by the diffusion speed of reactant molecules to metal nanopartides encapsulated in both carrier systems. For the microgels, the cross-linked PNIPAM shdl restricts diffusion and the reactant molecules need a longer time to reach the catalytic active center. The SPEBs have an open structure, and reactant molecules can diffuse through to reach the metal nanopartides more quickly. This demonstrates that SPB can work as stable carrier systems for metal nanopartides used in catalysis. 

DOX was encapsulated into the vesicle interior using an acid-gradient method. At temperatures below the LCST, the hydrophobic PNIPAM core of the vesicles became hydrophilic, causing rupture/disassembly. Therefore, more than 70% of the DOX was released within 2 h upon cooling to room temperature but no undetectable DOX was released for up to 7 h at 37... 

Physically crosslinked PNIPAM-based hydrogels were described for the first time by Han et al [51], who synthesized poly(N-isopropylacrylamide-co-acrylic acid) (p(NIPAM-co-AA)) to prepare thermosensitive matrices that were used in follow-up studies for biomedical purposes, particularly as synthetic matrices in refillable bio-artifidal pancreas. Encapsulated Langeran islets showed good viability, and the cellladen artificial matrices showed insulin release [52,53]. Similarly and more recently, p(NIPAM) networks were crosslinked using N, N -methylenebisacrylamide (BIS) and used for bovine serum albumin (BSA) release studies in vitro. The release of the protein... 

Zhang and co-workers reported the synthesis of size-controlled Au nanoparticles (2.6-6.3 nm) within a porous chelating hydrogel of poly(N-isopropylacrylamide)-co-poly[2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxypropyl ester] referred to as (PNIPAM-co-PMACHE]. The encapsulated Au nanoparticles were tested for aerobic alcohol oxidation (oxidation of 1-phenyethanol) in the presence of water and KOH. It was demonstrated that the catalytic activity depends on the Au particle size. The authors claimed that the Au-encapsulated nanoparticles in the hydrogel were highly efficient and reusable catalysts. 

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