TY - GEN A1 - Jiang, Yi A1 - Mansfeld, Ulrich A1 - Fang, Liang A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Temperature-induced evolution of microstructures on poly[ethylene-co-(vinyl acetate)] substrates switches their underwater wettability T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Material surfaces with tailored aerophobicity are crucial for applications where gas bubble wettability has to be controlled, e.g., gas storage and transport, electrodes, bioreactors or medical devices. Here, we present switchable underwater aerophobicity of hydrophobic polymeric substrates, which respond to heat with multilevel micro- and nanotopographical changes. The cross-linked poly[ethylene-co-(vinyl acetate)] substrates possess arrays of microcylinders with a nanorough top surface. It is hypothesized that the specific micro-/nanotopography of the surface allows trapping of a water film at the micro interspace and in this way generates the aerophobic behavior. The structured substrates were programmed to a temporarily stable, nanoscale flat substrate showing aerophilic behavior. Upon heating, the topographical changes caused a switch in contact angle from aerophilic to aerophobic for approaching air bubbles. In this way, the initial adhesion of air bubbles to the programmed flat substrate could be turned into repellence for the recovered substrate surface. The temperature at which the repellence of air bubbles starts can be adjusted from 58 ± 3 °C to 73 ± 3 °C by varying the deformation temperature applied during the temperature-memory programming procedure. The presented actively switching polymeric substrates are attractive candidates for applications, where an on-demand gas bubble repellence is advantageous. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 639 KW - aerophobicity KW - temperature-memory effect KW - switchable wettability KW - air bubble repellence KW - thermo-responsive polymer Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-424601 SN - 1866-8372 IS - 639 ER - TY - JOUR A1 - Sauter, Tilman A1 - Kratz, Karl A1 - Heuchel, Matthias A1 - Lendlein, Andreas T1 - Fiber diameter as design parameter for tailoring the macroscopic shape-memory performance of electrospun meshes JF - Materials and design N2 - Fibrous shape-memory polymer (SMP) scaffolds were investigated considering the fiber as basic microstructural feature. By reduction of the fiber diameter in randomly oriented electrospun polyetherurethane (PEU) meshes from the micro-to the nano-scale, we observed changes in the molecular orientation within the fibers and its impact on the structural and shape-memory performance. It was assumed that a spatial restriction by reduction of the fiber diameter increases molecular orientation along the orientation of the fiber. The stress-strain relation of random PEU scaffolds is initially determined by the 3D arrangement of the fibers and thus is independent of the molecular orientation. Increasing the molecular orientation with decreasing single fiber diameter in scaffolds composed of randomly arranged fibers did not alter the initial stiffness and peak stress but strongly influenced the elongation at break and the stress increase above the Yield point. Reduction of the single fiber diameter also distinctly improved the shape-memory performance of the scaffolds. Fibers with nanoscale diameters (< 100 nm) possessed an almost complete shape recovery, high recovery stresses and fast relaxation kinetics, while the shape fixity was found to decrease with decreasing fiber diameter. Hence, the fiber diameter is a relevant design parameter for SMP. KW - Nanofiber KW - Shape-memory polymer KW - Electrospinning KW - Function by design KW - Molecular orientation Y1 - 2021 U6 - https://doi.org/10.1016/j.matdes.2021.109546 SN - 1873-4197 VL - 202 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Balk, Maria A1 - Behl, Marc A1 - Nöchel, Ulrich A1 - Lendlein, Andreas T1 - Enzymatically triggered Jack-in-the-box-like hydrogels JF - ACS applied materials & interfaces / American Chemical Society N2 - Enzymes can support the synthesis or degradation of biomacromolecules in natural processes. Here, we demonstrate that enzymes can induce a macroscopic-directed movement of microstructured hydrogels following a mechanism that we call a "Jack-in-the-box" effect. The material's design is based on the formation of internal stresses induced by a deformation load on an architectured microscale, which are kinetically frozen by the generation of polyester locking domains, similar to a Jack-in-thebox toy (i.e., a compressed spring stabilized by a closed box lid). To induce the controlled macroscopic movement, the locking domains are equipped with enzyme-specific cleavable bonds (i.e., a box with a lock and key system). As a result of enzymatic reaction, a transformed shape is achieved by the release of internal stresses. There is an increase in entropy in combination with a swelling-supported stretching of polymer chains within the microarchitectured hydrogel (i.e., the encased clown pops-up with a pre-stressed movement when the box is unlocked). This utilization of an enzyme as a physiological stimulus may offer new approaches to create interactive and enzyme-specific materials for different applications such as an optical indicator of the enzyme's presence or actuators and sensors in biotechnology and in fermentation processes. KW - enzyme KW - hydrogels KW - stimuli-sensitive materials KW - shape change KW - poly(e-caprolactone) KW - switch KW - microporous Y1 - 2021 U6 - https://doi.org/10.1021/acsami.1c00466 SN - 1944-8244 SN - 1944-8252 VL - 13 IS - 7 SP - 8095 EP - 8101 PB - American Chemical Society CY - Washington, DC ER - TY - JOUR A1 - Folikumah, Makafui Yao A1 - Neffe, Axel T. A1 - Behl, Marc A1 - Lendlein, Andreas T1 - Thiol Michael-Type reactions of optically active mercapto-acids in aqueous medium JF - MRS advances : a journal of the Materials Research Society N2 - Defined chemical reactions in a physiological environment are a prerequisite for the in situ synthesis of implant materials potentially serving as matrix for drug delivery systems, tissue fillers or surgical glues. ‘Click’ reactions like thiol Michael-type reactions have been successfully employed as bioorthogonal reaction. However, due to the individual stereo-electronic and physical properties of specific substrates, an exact understanding their chemical reactivity is required if they are to be used for in-situ biomaterial synthesis. The chiral (S)-2-mercapto-carboxylic acid analogues of L-phenylalanine (SH-Phe) and L-leucine (SH-Leu) which are subunits of certain collagenase sensitive synthetic peptides, were explored for their potential for in-situ biomaterial formation via the thiol Michael-type reaction. In model reactions were investigated the kinetics, the specificity and influence of stereochemistry of this reaction. We could show that only reactions involving SH-Leu yielded the expected thiol-Michael product. The inability of SH-Phe to react was attributed to the steric hindrance of the bulky phenyl group. In aqueous media, successful reaction using SH-Leu is thought to proceed via the sodium salt formed in-situ by the addition of NaOH solution, which was intented to aid the solubility of the mercapto-acid in water. Fast reaction rates and complete acrylate/maleimide conversion were only realized at pH 7.2 or higher suggesting the possible use of SH-Leu under physiological conditions for thiol Michael-type reactions. This method of in-situ formed alkali salts could be used as a fast approach to screen mercapto-acids for thio Michael-type reactions without the synthesis of their corresponding esters. KW - biomaterial KW - biomedical KW - biomimetic (chemical reaction) KW - chemical synthesis Y1 - 2019 U6 - https://doi.org/10.1557/adv.2019.308 SN - 2059-8521 VL - 4 IS - 46-47 SP - 2515 EP - 2525 PB - Springer Nature Switzerland AG CY - Cham ER - TY - JOUR A1 - Machatschek, Rainhard Gabriel A1 - Saretia, Shivam A1 - Lendlein, Andreas T1 - Assessing the influence of temperature-memory creation on the degradation of copolyesterurethanes in ultrathin films JF - Advanced materials interfaces N2 - 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. KW - block copolymers KW - degradation KW - Langmuir monolayers KW - rheology KW - temperature-memory polymers Y1 - 2021 U6 - https://doi.org/10.1002/admi.202001926 SN - 2196-7350 VL - 8 IS - 6 PB - Wiley-VCH CY - Weinheim ER -