TY  - JOUR
A1  - Deng, Zijun
A1  - Wang, Weiwei
A1  - Xua, Xun
A1  - Gould, Oliver E. C.
A1  - Kratz, Karl
A1  - Ma, Nan
A1  - Lendlein, Andreas
T1  - Polymeric sheet actuators with programmable bioinstructivity
JF  - PNAS
N2  - Stem cells are capable of sensing and processing environmental inputs, converting this information to output a specific cell lineage through signaling cascades. Despite the combinatorial nature of mechanical, thermal, and biochemical signals, these stimuli have typically been decoupled and applied independently, requiring continuous regulation by controlling units. We employ a programmable polymer actuator sheet to autonomously synchronize thermal and mechanical signals applied to mesenchymal stem cells (MSC5). Using a grid on its underside, the shape change of polymer sheet, as well as cell morphology, calcium (Ca2+) influx, and focal adhesion assembly, could be visualized and quantified. This paper gives compelling evidence that the temperature sensing and mechanosensing of MSC5 are interconnected via intracellular Ca2+. Up-regulated Ca2+ levels lead to a remarkable alteration of histone H3K9 acetylation and activation of osteogenic related genes. The interplay of physical, thermal, and biochemical signaling was utilized to accelerate the cell differentiation toward osteogenic lineage. The approach of programmable bioinstructivity provides a fundamental principle for functional biomaterials exhibiting multifaceted stimuli on differentiation programs. Technological impact is expected in the tissue engineering of periosteum for treating bone defects.
KW  - reversible shape-memory actuator
KW  - mesenchymal stem cells
KW  - calcium influx
KW  - HDAC1
KW  - RUNX2
Y1  - 2020
U6  - https://doi.org/10.1073/pnas.1910668117
SN  - 1091-6490
VL  - 117
IS  - 4
SP  - 1895
EP  - 1901
PB  - National Academy of Sciences
CY  - Washington, DC
ER  - 
TY  - JOUR
A1  - Fang, Liang
A1  - Gould, Oliver E. C.
A1  - Lysyakova, Liudmila
A1  - Jiang, Yi
A1  - Sauter, Tilman
A1  - Frank, Oliver
A1  - Becker, Tino
A1  - Schossig, Michael
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Implementing and quantifying the shape-memory effect of single polymeric micro/nanowires with an atomic force microscope
JF  - ChemPhysChem : a European journal of chemical physics and physical chemistry
N2  - The implementation of shape-memory effects (SME) in polymeric micro- or nano-objects currently relies on the application of indirect macroscopic manipulation techniques, for example, stretchable molds or phantoms, to ensembles of small objects. Here, we introduce a method capable of the controlled manipulation and SME quantification of individual micro- and nano-objects in analogy to macroscopic thermomechanical test procedures. An atomic force microscope was utilized to address individual electro-spun poly(ether urethane) (PEU) micro- or nanowires freely suspended between two micropillars on a micro-structured silicon substrate. In this way, programming strains of 10 +/- 1% or 21 +/- 1% were realized, which could be successfully fixed. An almost complete restoration of the original free-suspended shape during heating confirmed the excellent shape-memory performance of the PEU wires. Apparent recovery stresses of sigma(max,app)=1.2 +/- 0.1 and 33.3 +/- 0.1MPa were obtained for a single microwire and nanowire, respectively. The universal AFM test platform described here enables the implementation and quantification of a thermomechanically induced function for individual polymeric micro- and nanosystems.
KW  - cyclic thermomechanical testing
KW  - atomic force microscopy
KW  - soft matter micro- and nanowires
KW  - shape-memory effect
KW  - materials science
Y1  - 2018
U6  - https://doi.org/10.1002/cphc.201701362
SN  - 1439-4235
SN  - 1439-7641
VL  - 19
IS  - 16
SP  - 2078
EP  - 2084
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Izraylit, Victor
A1  - Gould, Oliver E. C.
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Investigating the phase-morphology of PLLA-PCL multiblock copolymer/PDLA blends cross-linked using stereocomplexation
JF  - MRS advances
N2  - The macroscale function of multicomponent polymeric materials is dependent on their phase-morphology. Here, we investigate the morphological structure of a multiblock copolymer consisting of poly(L-lactide) and poly(epsilon-caprolactone) segments (PLLA-PCL), physically cross-linked by stereocomplexation with a low molecular weight poly(D-lactide) oligomer (PDLA). The effects of blend composition and PLLA-PCL molecular structure on the morphology are elucidated by AFM, TEM and SAXS. We identify the formation of a lattice pattern, composed of PLA domains within a PCL matrix, with an average domain spacing d0 = 12 - 19 nm. The size of the PLA domains were found to be proportional to the block length of the PCL segment of the copolymer and inversely proportional to the PDLA content of the blend. Changing the PLLA-PCL / PDLA ratio caused a shift in the melt transition Tm attributed to the PLA stereocomplex crystallites, indicating partial amorphous phase dilution of the PLA and PCL components within the semicrystalline material. By elucidating the phase structure and thermal character of multifunctional PLLA-PCL / PDLA blends, we illustrate how composition affects the internal structure and thermal properties of multicomponent polymeric materials. This study should facilitate the more effective incorporation of a variety of polymeric structural units capable of stimuli responsive phase transitions, where an understanding the phase-morphology of each component will enable the production of multifunctional soft-actuators with enhanced performance.
KW  - polymer
KW  - blend
KW  - nanostructure
KW  - morphology
Y1  - 2020
U6  - https://doi.org/10.1557/adv.2019.465
SN  - 2059-8521
VL  - 5
IS  - 14-15
SP  - 699
EP  - 707
PB  - Cambridge Univ. Press
CY  - New York
ER  - 
TY  - JOUR
A1  - Izraylit, Victor
A1  - Hommes-Schattmann, Paul J.
A1  - Neffe, Axel T.
A1  - Gould, Oliver E. C.
A1  - Lendlein, Andreas
T1  - Polyester urethane functionalizable through maleimide side-chains and cross-linkable by polylactide stereocomplexes
JF  - European polymer journal
N2  - Sustainable multifunctional alternatives to fossil-derived materials, which can be functionalized and are degradable, can be envisioned by combining naturally derived starting materials with an established polymer design concept. Modularity and chemical flexibility of polyester urethanes (PEU) enable the combination of segments bearing functionalizable moieties and the tailoring of the mechanical and thermal properties. In this work, a PEU multiblock structure was synthesized from naturally derived L-lysine diisocyanate ethyl ester (LDI), poly(L-lactide) diol (PLLA) and N-(2,3-dihydroxypropyl)-maleimide (MID) in a one-step reaction. A maleimide side-chain (MID) provided a reactive site for the catalyst-free coupling of thiols shown for L-cysteine with a yield of 94%. Physical cross-links were generated by blending the PEU with poly(D-lactide) (PDLA), upon which the PLLA segments of the PEU and the PDLA formed stereocomplexes. Stereocomplexation occurred spontaneously during solution casting and was investigated with WAXS and DSC. Stereocomplex crystallites were observed in the blends, while isotactic PLA crystallization was not observed. The presented material platform with tailorable mechanical properties by blending is of specific interest for engineering biointerfaces of implants or carrier systems for bioactive molecules.
KW  - Functionalization
KW  - Polylactide stereocomplex
KW  - Biomolecules coupling
Y1  - 2020
U6  - https://doi.org/10.1016/j.eurpolymj.2020.109916
SN  - 0014-3057
SN  - 1873-1945
VL  - 137
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Izraylit, Victor
A1  - Hommes-Schattmann, Paul Jacob
A1  - Neffe, Axel T.
A1  - Gould, Oliver E. C.
A1  - Lendlein, Andreas
T1  - Alkynyl-functionalized chain-extended PCL for coupling to biological molecules
JF  - European polymer journal
N2  - Chemical functionalization of poly(epsilon-caprolactone) (PCL) enables a molecular integration of additional function. Here, we report an approach to incorporate reactive alkynyl side-groups by synthesizing a chain-extended PCL, where the reactive site is introduced through the covalently functionalizable chain extender 3 (prop-2-yn-1-yloxy)propane-1,2-diol (YPD). Chain-extended PCL with M-w of 101 to 385 kg.mol(-1) were successfully synthesized in a one-pot reaction from PCL-diols with various molar masses, L-lysine ethyl ester diisocyanate (LDI) or trimethyl(hexamethylene)diisocyanate (TMDI), and YPD, in which the density of functionalizable groups and spacing between them can be controlled by the composition of the polymer. The employed diisocyanate compounds and YPD possess an asymmetric structure and form a non-crystallizable segment leaving the PCL crystallites to dominate the material's mechanical properties. The mixed glass transition temperature T-g = - 60 to - 46 degrees C of the PCL/polyurethane amorphous phase maintains the synthesized materials in a highly elastic state at ambient and physiological conditions. Reaction conditions for covalent attachment in copper(I)-catalyzed azide-alkyne-cycloaddition reactions (CuAAC) in solution were optimized in a series of model reactions between the alkyne moieties of the chain-extended PCL and benzyl azide, reaching conversions over 95% of the alkyne moieties and with yields of up to 94% for the purified functionalized PCL. This methodology was applied for reaction with the azide-functionalized cell adhesion peptide GRGDS. The required modification of the peptide provides selectivity in the coupling reactions. The obtained results suggest that YPD could potentially be employed as versatile molecular unit for the creation of a variety of functionalizable polyesters as well as polyurethanes and polycarbonates offering efficient and selective click-reactions.
KW  - copper-catalyzed alkyne-azide cycloaddition
KW  - chain-extended
KW  - polycaprolactone
KW  - RGD-peptide
KW  - side-chains functionalization
Y1  - 2020
U6  - https://doi.org/10.1016/j.eurpolymj.2020.109908
SN  - 0014-3057
SN  - 1873-1945
VL  - 136
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Lendlein, Andreas
A1  - Balk, Maria
A1  - Tarazona, Natalia A.
A1  - Gould, Oliver E. C.
T1  - Bioperspectives for Shape-Memory Polymers as Shape Programmable, Active Materials
JF  - Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences
N2  - Within the natural world, organisms use information stored in their material structure to generate a physical response to a wide variety of environmental changes. The ability to program synthetic materials to intrinsically respond to environmental changes in a similar manner has the potential to revolutionize material science. By designing polymeric devices capable of responsively changing shape or behavior based on information encoded into their structure, we can create functional physical behavior, including a shape memory and an actuation capability. Here we highlight the stimuli-responsiveness and shape-changing ability of biological materials and biopolymer-based materials, plus their potential biomedical application, providing a bioperspective on shape-memory materials. We address strategies to incorporate a shape memory (actuation) function in polymeric materials, conceptualized in terms of its relationship with inputs (environmental stimuli) and outputs (shape change). Challenges and opportunities associated with the integration of several functions in a single material body to achieve multifunctionality are discussed. Finally, we describe how elements that sense, convert, and transmit stimuli have been used to create multisensitive materials.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.biomac.9b01074
SN  - 1525-7797
SN  - 1526-4602
VL  - 20
IS  - 10
SP  - 3627
EP  - 3640
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Lendlein, Andreas
A1  - Gould, Oliver E. C.
T1  - Reprogrammable recovery and actuation behaviour of shape-memory polymers
JF  - Nature reviews. Materials
N2  - Shape memory is the capability of a material to be deformed and fixed into a temporary shape. Recovery of the original shape can then be triggered only by an external stimulus. Shape-memory polymers are highly deformable materials that can be programmed to recover a memorized shape in response to a variety of environmental and spatially localized stimuli as a one-way effect. The shape-memory function can also be generated as a reversible effect enabling actuation behaviour through macroscale deformation and processing, specifically by dictating the macromolecular orientation of actuation units and of the skeleton structure of geometry-determining units in the polymers. Shape-memory polymers can be programmed and reprogrammed into arbitrary shapes. Both recovery and actuation behaviour are reprogrammable. In this Review, we outline the common basis and key differences between the two shape-memory behaviours of polymers in terms of mechanism, fabrication schemes and characterization methods. We discuss which combination of macromolecular architecture and macroscale processing is necessary for coordinated, decentralized and responsive physical behaviour. The extraction of relevant thermomechanical information is described, and design criteria are shown for microscale and macroscale morphologies to gain high levels of recovered or actuation strains as well as on-demand 2D-to-3D shape transformations. Finally, real-world applications and key future challenges are highlighted.
Y1  - 2019
U6  - https://doi.org/10.1038/s41578-018-0078-8
SN  - 2058-8437
VL  - 4
IS  - 2
SP  - 116
EP  - 133
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Liu, Yue
A1  - Gould, Oliver E. C.
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Shape-memory actuation of individual micro-/nanofibers
JF  - MRS Advances
N2  - Advances in the fabrication and characterization of polymeric nanomaterials has greatly advanced the miniaturization of soft actuators, creating materials capable of replicating the functional physical behavior previously limited to the macroscale. Here, we demonstrate how a reversible shape-memory polymer actuation can be generated in a single micro/nano object, where the shape change during actuation of an individual fiber can be dictated by programming using an AFM-based method. Electrospinning was used to prepare poly(epsilon-caprolactone) micro-/nanofibers, which were fixed and crosslinked on a structured silicon wafer. The programming as well as the observation of recovery and reversible displacement of the fiber were performed by vertical three point bending, using an AFM testing platform introduced here. A plateau tip was utilized to improve the stability of the fiber contact and working distance, enabling larger deformations and greater rbSMPA performance. Values for the reversible elongation of epsilon(rev)= 3.4 +/- 0.1% and 10.5 +/- 0.1% were obtained for a single micro (d = 1.0 +/- 0.2 mu m) and nanofiber (d = 300 +/- 100 nm) in cyclic testing between the temperatures 10 and 60 degrees C. The reversible actuation of the nanofiber was successfully characterized for 10 cycles. The demonstration and characterization of individual shape-memory nano and microfiber actuators represents an important step in the creation of miniaturized robotic devices capable of performing complex physical functions at the length scale of cells and structural component of the extracellular matrix.
Y1  - 2020
U6  - https://doi.org/10.1557/adv.2020.276
SN  - 2059-8521
VL  - 5
IS  - 46-47
SP  - 2391
EP  - 2399
PB  - Cambridge Univ. Press
CY  - New York
ER  - 
TY  - JOUR
A1  - Liu, Yue
A1  - Gould, Oliver E. C.
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - On demand sequential release of (sub)micron particles controlled by size and temperature
JF  - Small : nano micro
N2  - Polymeric devices capable of releasing submicron particles (subMP) on demand are highly desirable for controlled release systems, sensors, and smart surfaces. Here, a temperature-memory polymer sheet with a programmable smooth surface served as matrix to embed and release polystyrene subMP controlled by particle size and temperature. subMPs embedding at 80 degrees C can be released sequentially according to their size (diameter D of 200 nm, 500 nm, 1 mu m) when heated. The differences in their embedding extent are determined by the various subMPs sizes and result in their distinct release temperatures. Microparticles of the same size (D approximate to 1 mu m) incorporated in films at different programming temperatures T-p (50, 65, and 80 degrees C) lead to a sequential release based on the temperature-memory effect. The change of apparent height over the film surface is quantified using atomic force microscopy and the realization of sequential release is proven by confocal laser scanning microscopy. The demonstration and quantification of on demand subMP release are of technological impact for assembly, particle sorting, and release technologies in microtechnology, catalysis, and controlled release.
KW  - on demand particle release
KW  - temperature-memory effect
KW  - thermosensitive
KW  - polymer surface
Y1  - 2022
U6  - https://doi.org/10.1002/smll.202104621
SN  - 1613-6810
SN  - 1613-6829
VL  - 18
IS  - 5
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Liu, Yue
A1  - Gould, Oliver E. C.
A1  - Rudolph, Tobias
A1  - Fang, Liang
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Polymeric microcuboids programmable for temperature-memory
JF  - Macromolecular materials and engineering
N2  - 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.
KW  - actuation
KW  - atomic force microscopy
KW  - biomaterials
KW  - microparticles
KW  - shape-memory polymers
Y1  - 2020
U6  - https://doi.org/10.1002/mame.202000333
SN  - 1438-7492
SN  - 1439-2054
VL  - 305
IS  - 10
PB  - Wiley-VCH
CY  - Weinheim
ER  -