@article{MachatschekSaretiaLendlein2021,
  author    = {Machatschek, Rainhard Gabriel and Saretia, Shivam and Lendlein, Andreas},
  title     = {Assessing the influence of temperature-memory creation on the degradation of copolyesterurethanes in ultrathin films},
  series = {Advanced materials interfaces},
  volume    = {8},
  journal   = {Advanced materials interfaces},
  number    = {6},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {2196-7350},
  doi       = {10.1002/admi.202001926},
  pages     = {8},
  year      = {2021},
  abstract  = {Copolyesterurethanes (PDLCLs) based on oligo(epsilon-caprolactone) (OCL) and oligo(omega-pentadecalactone) (OPDL) segments are biodegradable thermoplastic temperature-memory polymers. The temperature-memory capability in these polymers with crystallizable control units is implemented by a thermomechanical programming process causing alterations in the crystallite arrangement and chain organization. These morphological changes can potentially affect degradation. Initial observations on the macroscopic level inspire the hypothesis that switching of the controlling units causes an accelerated degradation of the material, resulting in programmable degradation by sequential coupling of functions. Hence, detailed degradation studies on Langmuir films of a PDLCL with 40 wt\% OPDL content are carried out under enzymatic catalysis. The temperature-memory creation procedure is mimicked by compression at different temperatures. The evolution of the chain organization and mechanical properties during the degradation process is investigated by means of polarization-modulated infrared reflection absorption spectroscopy, interfacial rheology and to some extend by X-ray reflectivity. The experiments on PDLCL Langmuir films imply that degradability is not enhanced by thermal switching, as the former depends on the temperature during cold programming. Nevertheless, the thin film experiments show that the leaching of OCL segments does not induce further crystallization of the OPDL segments, which is beneficial for a controlled and predictable degradation.},
  language  = {en}
}
@article{NeffeLoewenbergJulichGruneretal.2021,
  author    = {Neffe, Axel T. and L{\"o}wenberg, Candy and Julich-Gruner, Konstanze K. and Behl, Marc and Lendlein, Andreas},
  title     = {Thermally-induced shape-memory behavior of degradable gelatin-based networks},
  series = {International journal of molecular sciences},
  volume    = {22},
  journal   = {International journal of molecular sciences},
  number    = {11},
  publisher = {Molecular Diversity Preservation International},
  address   = {Basel},
  issn      = {1422-0067},
  doi       = {10.3390/ijms22115892},
  pages     = {15},
  year      = {2021},
  abstract  = {Shape-memory hydrogels (SMH) are multifunctional, actively-moving polymers of interest in biomedicine. In loosely crosslinked polymer networks, gelatin chains may form triple helices, which can act as temporary net points in SMH, depending on the presence of salts. Here, we show programming and initiation of the shape-memory effect of such networks based on a thermomechanical process compatible with the physiological environment. The SMH were synthesized by reaction of glycidylmethacrylated gelatin with oligo(ethylene glycol) (OEG) alpha,omega-dithiols of varying crosslinker length and amount. Triple helicalization of gelatin chains is shown directly by wide-angle X-ray scattering and indirectly via the mechanical behavior at different temperatures. The ability to form triple helices increased with the molar mass of the crosslinker. Hydrogels had storage moduli of 0.27-23 kPa and Young's moduli of 215-360 kPa at 4 degrees C. The hydrogels were hydrolytically degradable, with full degradation to water-soluble products within one week at 37 degrees C and pH = 7.4. A thermally-induced shape-memory effect is demonstrated in bending as well as in compression tests, in which shape recovery with excellent shape-recovery rates R-r close to 100\% were observed. In the future, the material presented here could be applied, e.g., as self-anchoring devices mechanically resembling the extracellular matrix.},
  language  = {en}
}