Responsive polymer materials can adapt to surrounding environments, regulate transport of ions and molecules, change wettability and adhesion of different species on external stimuli, or convert chemical and biochemical signals into optical, electrical, thermal and mechanical signals, and vice versa. These materials are playing an increasingly important part in a diverse range of applications, such as drug delivery, diagnostics, tissue engineering and 'smart' optical systems, as well as biosensors, microelectromechanical systems, coatings and textiles. We review recent advances and challenges in the developments towards applications of stimuli-responsive polymeric materials that are self-assembled from nanostructured building blocks. We also provide a critical outline of emerging developments.

Emerging applications of stimuli-responsive polymer materials

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

The fact that light carries both linear and angular momentum is well-known to physicists. One application of the linear momentum of light is for optical tweezers, in which the refraction of a laser beam through a particle provides a reaction force that draws the particle towards the centre of the beam. The angular momentum of light can also be transfered to particles, causing them to spin. In fact, the angular momentum of light has two components that act through different mechanisms on various types of particle. This Review covers the creation of such beams and how their unusual intensity, polarization and phase structure has been put to use in the field of optical manipulation.

Tweezers with a twist

Keywords: Fragmentation Chain-Transfer ; Self-Assembled Monolayers ; Walled Carbon Nanotubes ; Well-Defined Polymer ; Nitroxide-Mediated Polymerization ; Block-Copolymer Brushes ; Poly(Methyl Methacrylate) Brushes ; Transfer Raft Polymerization ; Quartz-Crystal Microbalance ; Poly(Acrylic Acid) Brushes Reference EPFL-REVIEW-148464doi:10.1021/cr900045aView record in Web of Science Record created on 2010-04-23, modified on 2017-05-10

Polymer Brushes via Surface-Initiated Controlled Radical Polymerization: Synthesis, Characterization, Properties, and Applications

Janus particles: synthesis, self-assembly, physical properties, and applications.

Overview of Adaptive Structures. A Review of Structural Dynamics. Linear Systems and Signals. Signal Processing and Digital Filters. Transduction Device Dynamics and the Physical System. Integration of Spatial and Temporal Signal Processing. Classical Control for Adaptive Structures. Active Control: System Architectures and Algorithms. Adaptive Structures: Dynamics and Control. Appendices. About the Disk. Index.

Adaptive Structures: Dynamics and Control

Fabrication of elastin-like polypeptide nanoparticles for drug delivery by electrospraying.

UVA generates pyrimidine dimers in DNA directly.

Controllable porous polymer particles generated by electrospraying

Stimulus-responsive macromolecules have attracted significant interest due to their potential applications in molecular motors, drug delivery, sensors, and actuation devices. Poly(N-isopropylacrylamide) (pNIPAAM) alone or as a copolymer is a stimulus-responsive polymer that undergoes an inverse phase transition triggered by changes in the solvent quality, such as temperature, ionic strength, pH, or co-solvent concentration. Associated with this phase transition is a significant conformational change. We show that micro-cantilevers, decorated on one side with a pNIPAAM brush or poly(N-isopropylacrylamide-co-N-vinylimidazole) (pNIPAAM-VI) (7:3) brush, can be used to detect and transduce this phase transition behavior. Changes in the conformational state of the brush, induced by the phase transition or changes in osmotic pressure, cause significant changes in the surface stress in the brush that leads to detectable changes in cantilever deflection. We show that the use of pNIPAAM and its copolymers is exciting for cantilever actuation and sensing because commonly available micro-fabricated cantilever springs offer a simple and non-intrusive way to detect changes in solvent type, temperature, and pH, promising great potential for sensing applications in micro-fluidic devices.

Robert L. Clark

Papers

Adaptive Structures: Dynamics and Control

Fabrication of elastin-like polypeptide nanoparticles for drug delivery by electrospraying.

UVA generates pyrimidine dimers in DNA directly.

Controllable porous polymer particles generated by electrospraying

Micro-cantilevers with end-grafted stimulus-responsive polymer brushes for actuation and sensing