Stimuli-responsive “smart temperature

A novel approach to immobilization of enzymes via covalent attachment is the use of stimulus-responsive smart polymers, which undergo dramatic conformational changes in response to small alterations in the environment, such as temperature, pH, and ionic strength [401 03], The most prominent example is a thermo-responsive and biocompatible polymer (poly-iV-isopropyl-acrylamide), which exhibits a critical solution temperature around 32°C, below which it readily dissolves in water, while it precipitates at elevated temperatures due to the expulsion of water molecules from its polymeric matrix. Hence, the biolransformation is performed under conditions, where the enzyme is soluble. Raising the temperature leads to precipitation of the immobilized protein, which allows its recovery and reuse. In addition, runaway reactions are avoided because in case the reaction temperature exceeds the critical solution temperature, the catalyst precipitates and the reaction shuts down. 

The era of biomimetic peptide- and sugar-based polymer vesicles has just begun and seems very promising. Bioinspired vesicles are mainly applied for drug deliv-ery/release and the fabrication of composite materials, but could readily be used for biomimetic materials science, biomineralization, and so on. Especially interesting are smart vesicles changing properties in response to an external stimulus (temperature, pH, ions). 

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. 

In the last two decades, the development of poljoners which change their structures and properties in response to environmental stimuli such as pH, temperature, and light has attracted a great deal of attention (1-3). Such polymers have been called smart polymers, intelligent polymers, stimulus-sensitive pol3uners, or responsive polymers. They have been used in many applications, ranging from bioactive agent delivery to separation (4,5). Various delivery systems based on the smart polymers have been proposed because of their... 

In most cases, the as-obtained nanocarriers can release the loaded biomolecules in response to only one kind of external stimulus, such as light, pH, or temperature, and realize a monoresponsive nanochannel. However, the sensitivity of these nanocarriers is not very efficient. Even for NIR-triggered phototherapy, the effective penetration depth of NIR light is still limited to no more than 1 cm and its sensitivity and accuracy to treat tumors located deep inside the body is thus limited. Therefore, delivery systems triggered by at least two different inputs have recently been considered by researchers. Generally, in order to get dual-responsive nanocarriers, two kinds of smart materials or one material with two functional groups must be included in the same NP. For example, two kinds of responsive materials, such as PAA and PNIPAm, can be simultaneously employed in the a pH- and... 

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