Dual-responsive polymer

Stimuli-responsive polymers and blends thereof for ophthalmic drug delivery systems are reviewed. These include polyaci ylic acid, temperature sensitive polymers, which are convertible into gels at body temperature, dual responsive polymers, ion-sensitive polymers, such as alginates, and enzyme-sensitive polymers, such as xanthan gum. 26 refs. 

V. Sundaresan, J.U. Menon, M. Rahimi, K.T. Nguyen, and A.S. Wadajkar, Dual-responsive polymer-coated iron oxide nanoparticles for drug delivery and imaging applications. Inter. J. Pharm., 466 (1-2), 1-7,2014. 

Dual-responsive polymer-based drug delivery vehicles offer even more versatility. Both temperature and enzyme-responsive micelles were formed from block polymers. While the thermoresponsive properties of the material allow it to be injected and subsequently form a reservoir in the body from where micelles enter the blood stream, the enzyme-responsive component allows triggered degradation of the micelles and release of the drug at the location of the diseased tissue (Garripelli et fl/.,2011). A doubly enzyme-responsive system can be obtained, for example, by designing polymer capsules with a shell that contains two layers. The two layers are degraded by different enzymes thus, proteins entrapped in the outer layer itself can be released upon exposure to the first enzyme, whereas the second enzyme destroys the capsule completely and liberates the proteins entrapped in the cavity of the vehicle (Itoh et al, 2008). 

Dual-responsive polymer-based systems have been also proposed. The design and synthesis of polymers containing cholic acid pendant groups has been reported. Random copolymers derived from 2-(metha-ctyloylo gr)ethyl cholate (MAECA) with polyethylene glycol methyl ether... 

Two routes toward positive-type proofs were discovered. R. D. Kempf of Towanda R D showed that the dual response system, in which a visible exposure gave rise to an inhibitor, followed by a flooding UV exposure yielded masters, which could be toned with our conventional liquid toning system, and gave positive-working proofs. This was an illustration of applying the photo-polymer technology of HABI chemistry for yet another application. 

Due to the relative ease of control, temperature is one of the most widely used external stimuli for the synthesis of stimulus-responsive bmshes. In this case, thermoresponsive polymer bmshes from poly(N-isopropylacrylamide) (PNIPAM) are the most intensively studied responsive bmshes that display a lower critical solution temperature (LOST) in a suitable solvent. Below the critical point, the polymer chains interact preferentially with the solvent and adopt a swollen, extended conformation. Above the critical point, the polymer chains collapse as they become more solvophobic. Jayachandran et reported the synthesis of PNIPAM homopolymer and block copolymer brushes on the surface of latex particles by aqueous ATRP. Urey demonstrated that PNIPAM brushes were sensitive to temperature and salt concentration. Zhu et synthesized Au-NPs stabilized with thiol-terminated PNIPAM via the grafting to approach. These thermosensitive Au-NPs exhibit a sharp, reversible, dear opaque transition in solution between 25 and 30 °C. Shan et al. prepared PNIPAM-coated Au-NPs using both grafting to and graft from approaches. Lv et al. prepared dual-sensitive polymer by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide from trithiocarbonate groups linked to dextran and sucdnoylation of dextran after polymerization. Such dextran-based dual-sensitive polymer is employed to endow Au-NPs with stability and pH and temperature sensitivity. 

Kutnyanszky, E., Hempenius, M. A., Vancso, G. J. (2014). Polymer bottlebrushes with a redox responsive backbone feel the heat synthesis and characterization of dual responsive poly(ferrocenylsilane)s with PNIPAM side chains. Polymer Chemistry. 

Sui, X., Feng, X., Di Luca, A., Van Blitterswijk, C. A., Moroni, L., Hempenius, M. A., et al. (2013). Poly(N-isopropylacrylamide)-poly(ferrocenylsilane) dual-responsive hydrogels synthesis, characterization and antimicrobial applications. Polymer Chemistry, 4,337—342. 

Mu, B. and Liu, P. (2012). Temperature and pH dual responsive crosslinked polymeric nanocapsules via surface-initiated atom transfer radical polymerization. Reactive and Functional Polymers, 72,983-989. 

Hu, X., Xiong, L., Wang, T., Lin, Z., Liu, X., Tong, Z., 2009. S5mthesis and dual response of ionic nanocomposite hydrogels with ultrahigh tensibiUty and transparence. Polymer 50, 1933-1938. 

In a previous study, our group synthesized a new temperature and pH-sensitive poly(2-(dimethylamino) ethylmethacrylate-fe-vinylcaprolactam-fc-(2-(dimethylamino) ethyl methacrylate)), PDMAEMA- i-PVCL-fc-PDMAEMA, triblock copolymer by RAFT polymerization. PDMAEMA is dual sensitive (pH and temperature) and its LCST was around 50 °C, while PVCL is a thermo-responsive polymer and its LCST was around 32 °C. By modifying the structure and adjusting the composition of these polymers it is possible reduce the LSCT and pK values in order to ensure compatibility with physiological temperature and pH (see Table 9.1, Triblock 1). The results showed that these polymers can self-assemble into micelles in different environments [60]. 

Fei Li, Hong Wu, Fan Li, Hui Zhang, et al. Study of Dual Responsive Dex-MA-graft-PNIPAAm hydrogel nanoparticles preparation, characterization and biological evaluation. Polymer International. Early View. 

---