Although the technological and scientific importance of functional polymers has been well established over the last few decades, the most recent focus that has attracted much attention has been on stimuli-responsive polymers. This group of materials is of particular interest due to its ability to respond to internal and/or external chemico-physical stimuli, which is often manifested as large macroscopic responses. Aside from scientific challenges of designing stimuli-responsive polymers, the main technological interest lies in their numerous applications ranging from catalysis through microsystem technology and chemomechanical actuators to sensors that have been extensively explored. Since the phase transition phenomenon of hydrogels is theoretically well understood advanced materials based on the predictions can be prepared. Since the volume phase transition of hydrogels is a diffusion-limited process the size of the synthesized hydrogels is an important factor. Consistent downscaling of the gel size will result in fast smart gels with sufficient response times. In order to apply smart gels in microsystems and sensors, new preparation techniques for hydrogels have to be developed. For the up-coming nanotechnology, nano-sized gels as actuating materials would be of great interest.
Aliphatic
poly(carbonate)s (APCs) with rapid and controlled degradation
upon specific stimulation have great advantages for a variety of biomedical
and pharmaceutical applications. In the present work, we reported
a new poly(trimethylene carbonate) (PTMC)-based copolymer containing
multiple 4,5-dimethoxy-2-nitrobenzyl photo cleavable groups as pendent
chains. The six-membered light-responsive cyclic carbonate monomer
(LrM) was first prepared from 2-(hydroxymethyl)-2-methylpropane-1,3-diol
and 4,5-dimethoxy-2-nitrobenzyl alcohol and then copolymerized with
trimethylene carbonate (TMC) by 1,8-diazabicyclo(5.4.0)undec-7-ene
(DBU) catalyzed ring-opening polymerization (ROP) to afford the light-responsive
polycarbonate (LrPC). The light-triggered decomposition
of LrM and LrPC was studied by NMR, UV/vis
spectroscopy, and size exclusion chromatography (SEC), as well as
ESI-ToF mass spectrometry. Stable monodisperse nanoparticles with
hydrodynamic diameter of 100 nm could be formulated from 25% LrPC and 75% poly(lactide-co-glycolide) (PLGA)
and applied for the encapsulation of temoporfin. Upon irradiation
with UV light these particles displayed a significant decrease of
the particle countrate and increased the release rate of temoporfin
in comparison to standard PLGA nanoparticles. This work demonstrated
that a combination of encapsulation of photosensitizer and light degradation
using light-responsive polymers is suitable to enhance photodynamic
therapy (PDT).
First lab-on-chip devices based on active transport by biomolecular motors have been demonstrated for basic detection and sorting applications. However, to fully employ the advantages of such hybrid nanotechnology, versatile spatial and temporal control mechanisms are required. Using a thermo-responsive polymer, we demonstrate the selective starting and stopping of modified microtubules gliding on a kinesin-1-coated surface. This approach allows the self-organized separation of multiple microtubule populations and their respective cargoes.
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