@phdthesis{Dunlop2015,
  author    = {Dunlop, John William Chapman},
  title     = {The physics of shape changes in biology},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-96554},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vii, 202},
  year      = {2015},
  abstract  = {Biological materials, in addition to having remarkable physical properties, can also change shape and volume. These shape and volume changes allow organisms to form new tissue during growth and morphogenesis, as well as to repair and remodel old tissues. In addition shape or volume changes in an existing tissue can lead to useful motion or force generation (actuation) that may even still function in the dead organism, such as in the well known example of the hygroscopic opening or closing behaviour of the pine cone. Both growth and actuation of tissues are mediated, in addition to biochemical factors, by the physical constraints of the surrounding environment and the architecture of the underlying tissue. This habilitation thesis describes biophysical studies carried out over the past years on growth and swelling mediated shape changes in biological systems. These studies use a combination of theoretical and experimental tools to attempt to elucidate the physical mechanisms governing geometry controlled tissue growth and geometry constrained tissue swelling. It is hoped that in addition to helping understand fundamental processes of growth and morphogenesis, ideas stemming from such studies can also be used to design new materials for medicine and robotics.},
  language  = {en}
}
@article{LiuGouldRudolphetal.2020,
  author    = {Liu, Yue and Gould, Oliver E. C. and Rudolph, Tobias and Fang, Liang and Kratz, Karl and Lendlein, Andreas},
  title     = {Polymeric microcuboids programmable for temperature-memory},
  series = {Macromolecular materials and engineering},
  volume    = {305},
  journal   = {Macromolecular materials and engineering},
  number    = {10},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1438-7492},
  doi       = {10.1002/mame.202000333},
  pages     = {7},
  year      = {2020},
  abstract  = {Microobjects with programmable mechanical functionality are highly desirable for the creation of flexible electronics, sensors, and microfluidic systems, where fabrication/programming and quantification methods are required to fully control and implement dynamic physical behavior. Here, programmable microcuboids with defined geometries are prepared by a template-based method from crosslinked poly[ethylene-co-(vinyl acetate)] elastomers. These microobjects could be programmed to exhibit a temperature-memory effect or a shape-memory polymer actuation capability. Switching temperaturesT(sw)during shape recovery of 55 +/- 2, 68 +/- 2, 80 +/- 2, and 86 +/- 2 degrees C are achieved by tuning programming temperatures to 55, 70, 85, and 100 degrees C, respectively. Actuation is achieved with a reversible strain of 2.9 +/- 0.2\% to 6.7 +/- 0.1\%, whereby greater compression ratios and higher separation temperatures induce a more pronounced actuation. Micro-geometry change is quantified using optical microscopy and atomic force microscopy. The realization and quantification of microparticles, capable of a tunable temperature responsive shape-change or reversible actuation, represent a key development in the creation of soft microscale devices for drug delivery or microrobotics.},
  language  = {en}
}
@article{SchueringsNevskyiEliaschetal.2016,
  author    = {Sch{\"u}rings, Marco-Philipp and Nevskyi, Oleksii and Eliasch, Kamill and Michel, Ann-Katrin and Liu, Bing and Pich, Andrij and B{\"o}ker, Alexander and von Plessen, Gero and W{\"o}ll, Dominik},
  title     = {Diffusive Motion of Linear Microgel Assemblies in Solution},
  series = {Polymers},
  volume    = {8},
  journal   = {Polymers},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2073-4360},
  doi       = {10.3390/polym8120413},
  pages     = {14},
  year      = {2016},
  abstract  = {Due to the ability of microgels to rapidly contract and expand in response to external stimuli, assemblies of interconnected microgels are promising for actuation applications, e.g., as contracting fibers for artificial muscles. Among the properties determining the suitability of microgel assemblies for actuation are mechanical parameters such as bending stiffness and mobility. Here, we study the properties of linear, one-dimensional chains of poly(N-vinylcaprolactam) microgels dispersed in water. They were fabricated by utilizing wrinkled surfaces as templates and UV-cross-linking the microgels. We image the shapes of the chains on surfaces and in solution using atomic force microscopy (AFM) and fluorescence microscopy, respectively. In solution, the chains are observed to execute translational and rotational diffusive motions. Evaluation of the motions yields translational and rotational diffusion coefficients and, from the translational diffusion coefficient, the chain mobility. The microgel chains show no perceptible bending, which yields a lower limit on their bending stiffness.},
  language  = {en}
}
@article{BalkBehlLendlein2020,
  author    = {Balk, Maria and Behl, Marc and Lendlein, Andreas},
  title     = {Actuators based on oligo[(epsilon-caprolactone)-co-glycolide] with accelerated hydrolytic degradation},
  series = {MRS advances : a journal of the Materials Research Society (MRS)},
  volume    = {5},
  journal   = {MRS advances : a journal of the Materials Research Society (MRS)},
  number    = {12-13},
  publisher = {Cambridge University Press},
  address   = {New York, NY},
  issn      = {2059-8521},
  doi       = {10.1557/adv.2019.447},
  pages     = {655 -- 666},
  year      = {2020},
  abstract  = {Polyester-based shape-memory polymer actuators are multifunctional materials providing reversible macroscopic shape shifts as well as hydrolytic degradability. Here, the function-function interdependencies (between shape shifts and degradation behaviour) will determine actuation performance and its life time. In this work, glycolide units were incorporated in poly(epsilon-caprolactone) based actuator materials in order to achieve an accelerated hydrolytic degradation and to explore the function-function relationship. Three different oligo[(epsilon-caprolactone)-co-glycolide] copolymers (OCGs) with similar molecular weights (10.5 +/- 0.5 kg center dot mol(-1)) including a glycolide content of 8, 16, and 26 mol\% (ratio 1:1:1 wt\%) terminated with methacrylated moieties were crosslinked. The obtained actuators provided a broad melting transition in the range from 27 to 44 degrees C. The hydrolytic degradation of programmed OCG actuators (200\% of elongation) resulted in a reduction of sample mass to 51 wt\% within 21 days at pH = 7.4 and 40 degrees C. Degradation results in a decrease of T-m associated to the actuating units and increasing T-m associated to the skeleton forming units. The actuation capability decreased almost linear as function of time. After 11 days of hydrolytic degradation the shape-memory functionality was lost. Accordingly, a fast degradation behaviour as required, e.g., for actuator materials intended as implant material can be realized.},
  language  = {en}
}