Temperature-sensitive polymers

Temperature-sensitive polymers, depending on polymer structure and polymer-polymer interactions, generally exhibit two behaviors, lower critical solution temperature (LCST) [31] and upper critical solution temperature (UCST). Phase diagrams for these behaviors are presented in Figure 9. 

Kim, S. W., Temperature Sensitive Polymers for Delivery of Macromolecular Drugs, in Advanced Biomaterials in Biomedical Engineering and Drug Delivery Systems (N. Ogata, et al., Eds.), pp. 125-133. Springer, Tokyo (1996). 

FIGURE 1.5. Schematic drawing showing the use of a temperature sensitive polymer to control access to the active sites of an enzyme. Access is denied when the polymer (dotted line) is in the crystalhne state (left), and allowed when the polymer is in the flexible state (right). 

In this study, we demonstrate new pH/temperature-sensitive polymers with transitions resulting from both polymer-polymer and polymer-water interactions and their applications as stimuli-responsive drug carriers [22-23], For this purpose, copolymers of (Ai,Ai-dimethylamino)ethyl methacrylate (DMAEMA) and ethylacrylamide (EAAm) [or acrylamide (AAm)] were prepared and characterized as polymeric drug delivery systems modulated for pulsatile and time release. 

New pH/temperature-sensitive polymer systems with transitions resulting from both polymer-polymer and polymer-water interactions have been demonstrated and their pH/temperature-induced phase transition has been investigated. Intra/intermolecular interactions via hydrogen bond play an important role in determining the phase transition. By manipulating the... 

Poly(A-isopropyl acrylamide) (PNIPAAm) is the most extensively studied temperature-sensitive polymer [10-20]. Crosslinked PNIPAAm exhibits drastic swelling transition at its lower critical solution temperature... 

In this work, we generated new PMAA/PNIPAAm IPN hydrogels with both pH and temperature sensitivities by the interpenetration of the pH-sensitive and temperature-sensitive polymer networks. 

Poly(N-isopropylacrylamide) (polyNIPAAM), formed by a free radical polymerization of N-isopropylacrylamide, is a water soluble, temperature sensitive polymer. In aqueous solution, it exhibits a lower critical solution temperature (LCST) in the range of 30-35 C depending on the concentration and the chain length of the polymer. Thus, as the solution temperature is raised above the LCST, the polymer undergoes a reversible phase transition characterized by the separation of a solid phase which redissolves when the solution temperature is lowered below the LCST. Its physicochemical properties have been investigated by several laboratories (1-3). 

Fig. 74. Phase change behavior of pH and temperature-sensitive polymers and hydrogels [452]...

In addition, the SEM can be used to study liquids or temperature sensitive polymers on a Cryostage. 

Affinity chromatography of streptavidin was performed on a PET chip. The microchannel was first filled with the dual-modified latex beads (as shown in Figure 6.3). The biotinylated beads were surface-modified with a temperature-sensitive polymer, poly(N-isopropylacrylamide (PNIPAAm, 11 kDa). When the temperature was raised above the lower critical solution temperature (LCST) of PNIPAAm, the beads aggregated and adhered to the channel wall, because of a hydrophilic-to-hydrophobic phase transition. Then streptavidin from a sample solution was captured by these adhered biotinylated beads. Thereafter, when the temperature was reduced below the LCST, the beads dissociated and eluted from the channel wall together with the captured streptavidin [203],... 

Large temperature rises due to viscous heating do indeed occur in melt capillary flow at moderate and high shear rates. These must be estimated and taken into account whenever temperature sensitive polymers are extruded and whenever the extrudate surface quality and extrudate properties are of critical importance. 

Figure 16.7 Sequence of insulin release from pH/temperature-sensitive polymer matrix. Both glucose oxidase and insulin are loaded inside the matrix. The decrease in pH by gluconic acid results in ionization of the polymer, which in turn increases the lower critical solution temperature. This makes the polymer water-soluble, and erosion of the polymer matrix at the surface releases the loaded insulin...

The approach of intramolecular cross-linking was further extended to temperature-sensitive polymers. PVME nanogels were obtained by irradiation of dilute PVME solutions by a pulsed electron beam [41], The Mw of these nanogels is independent of the radiation dose (above 2 kGy). The phase transition temperature Tc of PVME is slightly affected by the cross-linking reaction. With increasing radiation... 

The most popular way to synthesize microgel particles is via emulsion polymerization. Each micelle acts as a separate microreactor, preventing macrogelation during the reaction. Another way to obtain microgel particles is the irradiation of phase-separated polymer solutions (Fig. 5). Phase separation can be achieved by heating (for temperature-sensitive polymers) or mixing with non-solvents. 

Sershen, S. R., Westcott, S. L., Halas, N. J., and West, N. J. (2000), Temperature-sensitive polymer-nanoshell composites for photothermally modulated drug delivery, /. Biomed. Mater. Res., 51, 293-298. 

Mumick, P.S. Chiang, Y. Wang, J.H. Temperature-sensitive Polymers and Water-dispersible Products Containing the Polymers U.S. Patent No. 5,969,052, Oct 19, 1999. 

The resolution and the sharpness of the patterns were strongly influenced by the irradiation conditions. On example of the temperature-sensitive polymer hydroxypropylcellulose (HPC LOST in water of 41°C (Kley 1971)) and PNIPAAm, we investigated the influence of the acceleration voltage on the back-scattering and the proximity effect (Arndt et al. 2009). In closely packed patterns, the primary beam generates back-scattered electrons causing an over- or under-exposure in the resulting pattern. The so-called proximity effect is seen in the contour line in Fig. 19. It influences the spatial resolution of the structure. 

As a model to understand and to describe the processes during the response of a smart gel on changes of enviromnental properties, a two-step mechanism can be assumed (Fig. 8). In a first step, the stimulus which triggers the swelling/shrinking must permeate the gel. Heat transfer for temperature-sensitive polymers or mass transfer (ions, organic solvents) determine the rate of the first step. 

For the last 10 years the fundamentals of a MEMS technique based on temperature-sensitive polymers have been developed by our group at the Technische Universitat Dresden. In 2008 the first highly integrated hydrogel-based MEMS named artificial skin was presented (Richter and Paschew 2009). 

Kim YH, Bae YH, Kim SW. pH/temperature-sensitive polymers for macromolecular drug loading release. J Control... 

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