Smart polymers other mechanisms

Physically dependent stimuli include a wide range of variables such as temperature and mechanical deformation, amongst others. However, thermo-responsive polymers are the most relevant class of smart polymers studied because of their enormous variety and their great potential for different biomedical applications. Usually these polymers have both hydrophilic and hydrophobic phases, and undergo abrupt changes in their electrostatic and hydrophobic interactions in an aqueous medium at a critical solution temperature. 

The preparation of polymer-protein conjugates is possible by two mechanisms random and site-specific conjugation. In the case of random conjugation, the polymer is usually linked to lysine groups of the proteins. Site-specific conjugation, on the other hand, is based on the insertion of cysteine residues with exposed thiol groups which react preferentially with vinyl or vinyl sulfon groups of the smart polymers (Hoffman and Stayton, 2007). 

Smart materials and in particular smart polymers represent a class of materials increasingly used for advanced applications, hi particular, biomedical and biotechnological approaches specifically take advantage of metamorphic polymers to develop advanced tissue engineering, drug-delivery systems, and specific therapies. Some of these approaches are based on biomimetic approaches, some others rely on the specificity of the variations of temperature, pH, mechanical or electrical signals within the livmg body. 

Of the various stimuli-response mechanisms used in smart polymers, the lower critical solution temperature (LOST) transition of PNIPAAm is most widely investigated. Other response mechanisms include changes induced by pH, photoresponsive polymers, and changes in polarity and hydrophilicity through isomerization or ionization. Photodimerization has also been used to induce changes in hydrogels to make them responsive. 

Other possible applications of smart elastomers are in the area of polymer engine which can produce maximum power density (4 W/g) and output both in terms of electrical and mechanical power without any noise. These features are superior compared to conventional electrical generator, fuel cell, and conventional IC engine. Many DoD applications (e.g., robotics, MAV) require both mechanical and electrical (hybrid) power, and polymer engine can eliminate entire transducer steps and can also save engine parts, weight, and is more efficient. 

Beyond the usual mechanical and electrical performances, this review also points out the emergence of other original properties, like the remarkable capability of some nanotube/PVA composites to absorb mechanical energy and shape memory phenomena that differ from traditional behaviors of other polymers. These features are opening new investigation fields, in which several fundamental questions will have to be solved. But they also offer new opportunities for a variety of applications like smart or protective clothing, helmets, bullet proof vests, or active composites. 

Further exploration of these triggering mechanisms in association with the chemistry of the polymers concerned not only would expand the appUcation potentials of such materials, but combination and design versatility of these SMPs with specified trigger mechanisms could provide an array of smart functionaUties with highly sophisticated task duties in implants, drug delivery, tissue engineering, wound dressings, and many other technical applications in everyday consumable and industrial products. 

The chief advantages of polymer-based batteries are that they do not contain liquids that can leak, that they are mechanically relatively strong and that they can be easily shaped for various applications. Some other uses of polymer electrolytes are in displays, optical modulators and smart windows whose reflectance or transmission can be electrically controlled. 

Van den Ber et al. [166] has prepared nanocomposites of semi conducting polymers reinforced with tunicate cellulose whiskers with a typical diameter or around 20 nm. The results showed that the nanocomposites synergistically combine the electronic characteristic of the conjugated polymers with the improved mechanical properties of the cellulose scaffold. Other studies suggest that cellulose whisker can be used for electrical applications such as the creation of circuitry in a special kind of smart paper [167]. 

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