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Zotzmann J.,Research Center Geesthacht GmbH | Zotzmann J.,Berlin Brandenburg Center for Regenerative Therapies | Behl M.,Research Center Geesthacht GmbH | Hofmann D.,Research Center Geesthacht GmbH | Lendlein A.,Research Center Geesthacht GmbH
Advanced Materials | Year: 2010

A reversible triple-shape effect is achieved for multi-phase polymer networks based on two different crystallizable segments. The reversibility of the two shape-changes is based on crystallization induced elongation (CIE) occurring during cooling and melting-Induced contraction (MIC) during heating under constant stress. (Figure Presented).

Scharnagl N.,Research Center Geesthacht GmbH | Lee S.,Research Center Geesthacht GmbH | Hiebl B.,Research Center Geesthacht GmbH | Sisson A.,Research Center Geesthacht GmbH | Lendlein A.,Research Center Geesthacht GmbH
Journal of Materials Chemistry | Year: 2010

The next generation of biomaterials for regenerative therapies requires the development of substances, which are able to influence and activate specific phenotype characteristics of cells and tissues. Research towards this aim has resulted in an increasing number of reports about material induced cellular functions and cell-cell interactions. In this context, polymeric materials, which are not intended to degrade can provide helpful in-vitro tools to gain more detailed knowledge about the cell-substrate crosstalk and the resulting cell specific effects. This review aims to consolidate current strategies to induce specific effects on adhesive cells which are related to defined characteristics of two-dimensional systems starting with the molecular dimension, following up with the nanostructure and ending with the surface microstructure. This includes approaches to induce direct or indirect biological responses towards cells by systematic changes in material properties such as hydrophilicity or elasticity. These properties are explained as a function of chemical composition such as the type and ratio of copolymers used for linear polymers, or the geometric arrangement of branching points for network polymer architectures. Surface topographical features are identified to strongly influence cell-substrate interactions and techniques are described to control the surface patterning of polymeric materials on the nano- or microscale. Finally we offer a strategy on how to develop complex and multifunctional materials, which might fulfill the requirements of cell and tissue adapted biomaterials for regenerative therapies. © 2010 The Royal Society of Chemistry.

Behl M.,Research Center Geesthacht GmbH | Lendlein A.,Research Center Geesthacht GmbH
Journal of Materials Chemistry | Year: 2010

Shape-memory polymers (SMPs) are an emerging class of active materials, which are able to change their shape in a predefined way upon appropriate stimulation. As SMPs can switch from a temporary to their permanent shape they are dual-shape materials. Recently, multiphase polymer networks were explored, which are able to switch from a first shape (A) to a second shape (B) and from there to a third shape (C). Here we highlight this triple-shape effect (TSE) as a thermally triggered effect. The generality of the concept will be explained by describing suitable polymer network architectures and appropriate triple-shape creation processes (TSCPs). TSCP is a thermomechanical treatment typically consisting of two consecutive deformation steps resulting in shapes B and A. The molecular architecture of triple-shape polymers (TSPs) also contains the essential elements for the dual-shape effect (DSE), which therefore was systematically investigated. The understanding of the underlying mechanisms recently led to the discovery of a system, where a thermomechanical treatment with only one single deformation step resulted in a TSE. TSPs enable complex, active deformations on demand, having a high potential as enabling technology for application fields including intelligent medical devices, textile and assembling systems. © The Royal Society of Chemistry 2010.

Wagermaier W.,Research Center Geesthacht GmbH | Kratz K.,Research Center Geesthacht GmbH | Heuchel M.,Research Center Geesthacht GmbH | Lendlein A.,Research Center Geesthacht GmbH
Advances in Polymer Science | Year: 2010

Shape-memory polymers (SMPs) are able to fix a temporary deformed shape and recover their original permanent shape upon application of an external stimulus such as heat or light. A shape-memory functionalization can be realized for polymer based materials with an appropriate morphology by application of a specific shape-memory creation procedure (SMCP). Specific characterization methods have been tailored to explore the structure-function relations of SMPs in respective applications. This paper reviews characterization methods on different length scales from the molecular to the macroscopic level. On the molecular morphological level SMPs are comprised of netpoints determining the permanent shape and reversible crosslinks fixing the temporary shape. For polymers with covalent permanent netpoints the crosslinking density plays an important role, which can be quantified by means of swelling experiments or nuclear magnetic resonance (NMR) methods. In contrast, thermoplastic SMPs are typically phase-segregated polymers, where each domain is related to a different thermal transition, which can be explored by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Further suitable techniques for investigations of the SMP morphology on different levels of hierarchy are polarized light microscopy (POM), scanning or transmission electron microscopy (SEM, TEM) and atomic force microscopy (AFM) as well as wide and small X-ray scattering (WAXS, SAXS). On the macroscopic level the extent to which a temporary deformation can be fixed and the recovery of the permanent shape or the recovery stress are the most important characteristics of the shape-memory effect (SME), which can be quantified in cyclic, thermomechanical tensile tests or bending tests. Such cyclic tests consist of a SMCP module that can be performed either under stress or strain control followed by a recovery module under stress-free or constant strain conditions. The obtained shape-memory properties are strongly influenced by temperature dependent test parameters like deformation and fixation temperature or applied heating and cooling rate. In addition cyclic, photomechanical testing of light-induced dual-shape polymers, where the temporary shape is fixed by photoreversible chemical crosslinks and the testing of magnetically-induced shape-memory composites are described. In contrast multi-phase polymer networks, which exhibit a triple-shape effect, are explored in cyclic, thermomechanical experiments utilizing a specific two-step SMCP. Furthermore a selection of application-oriented tests for characterization of SME is presented. Finally, as part of a comprehensive characterization, modeling approaches for simulating the thermomechanical behavior of SMPs are presented. At the beginning linear viscoelastic models were applied consisting of coupled spring, dashpot and frictional elements. More recent approaches consider in detail the specific molecular transition underlying the SME, e.g. glass or melting transition. Currently models that incorporate the strain rate dependence and time dependent behavior are under development. © 2009 Springer-Verlag Berlin Heidelberg.

Behl M.,Research Center Geesthacht GmbH | Zotzmann J.,Research Center Geesthacht GmbH | Lendlein A.,Research Center Geesthacht GmbH
Advances in Polymer Science | Year: 2010

The ability of polymers to respond to external stimuli is of high scientific and technological significance. In the last few years, research activities have been intensified substantially, exploring whether stimuli-sensitive polymers can be designed that move actively. In this review actively-moving materials were classified according to the underlying mechanisms enabling the shape changes: shape-memory polymers and shape-changing polymers/shape-changing gels were identified. The application spectra of these materials as well as the current developments were elucidated and general molecular design principles presented. When applicable, a further distinction according to the applied stimulus was made. © 2009 Springer-Verlag Berlin Heidelberg.

Wischke C.,Research Center Geesthacht GmbH | Neffe A.T.,Research Center Geesthacht GmbH | Lendlein A.,Research Center Geesthacht GmbH
Advances in Polymer Science | Year: 2010

Biodegradable shape-memory polymers (SMPs) have attracted significant interest for biomedical applications. Modern concepts for biofunctional implants often comprise the controlled release of bioactive compounds to gain specific biofunctionalities. Therefore, a general strategy has been suggested for polymer systems combining degradability and shape-memory capability with controlled release of drugs. This chapter provides a detailed description of the molecular basis for such multifunctional SMPs including the selection of building blocks, the polymer morphology, and the three dimensional architecture. Moreover, drug loading and release, drug effects on thermomechanical properties of SMPs, and drug release patterns in a physiological environment are described and potential applications in minimally-invasive surgery are discussed. © 2009 Springer-Verlag Berlin Heidelberg.

Ganesan R.,Research Center Geesthacht GmbH | Kratz K.,Research Center Geesthacht GmbH | Lendlein A.,Research Center Geesthacht GmbH
Journal of Materials Chemistry | Year: 2010

Micro- and nano-scale protein patterns have gained significant technological interest. While certain techniques for single-component protein patterning are well-established, multicomponent protein patterning approaches are a current topic of intensive research, which might enable complex biosensor systems and expand the knowledge in protein-protein and protein-cell or cell-cell interactions. Only a few patterning methods are suitable for the realization of three dimensional patterns, which are essential for many applications e.g. in the design of scaffolds for regenerative therapies. In this feature article representative approaches for creating multicomponent protein patterning are presented and their potential for tailoring microenvironments for cells on biomaterials surfaces is discussed. © 2010 The Royal Society of Chemistry.

Wischke C.,University of Michigan | Wischke C.,Research Center Geesthacht GmbH | Zhang Y.,University of Michigan | Mittal S.,Merck And Co. | Schwendeman S.P.,University of Michigan
Pharmaceutical Research | Year: 2010

Purpose: Although efficient in vitro, fenretinide has not been successful clinically for either of the targeted indications-cancer prevention and dry age-related macular degeneration-because of various issues, such as low oral bioavailability. Therefore, controlled release carriers for parenteral delivery of fenretinide were developed. Methods: After examining the solubility profile of fenretinide, the drug was encapsulated in poly(lactic-co-glycolic acid) (PLGA) microparticles at 20% drug loading by an s/o/w methodology as well as into in situ-forming PLGA implants. The carrier morphology and drug release kinetics in an elevated polysorbate 80-containing release medium were studied. Results: Preformulation studies revealed increased fenretinide solubility in various PLGA solvents including N-methylpyrrolidone (NMP) and 1:9 v/v methanol:methylene chloride. Co-solvent emulsion methods resulted in low encapsulation efficiency. With a s/o/w method, fenretinide release rates from injectable microparticles were adjusted by the o-phase concentration of end-capped PLGA, the drug particle size, and the particle porosity. In situ implants from non-capped PLGA in NMP exhibited a continuous release of ~70% drug over 1 month. Conclusions: Injectable carriers for fenretinide were successfully prepared, exhibiting excellent drug stability. Based on the in vitro release properties of the different carriers, the preferred injection sites and in vivo release rates will be determined in future preclinical studies. © 2010 Springer Science+Business Media, LLC.

Da Conceicao T.F.,Helmholtz Center Geesthacht | Scharnagl N.,Research Center Geesthacht Gmbh | Dietzel W.,Helmholtz Center Geesthacht | Kainer K.U.,Helmholtz Center Geesthacht
Corrosion Science | Year: 2011

In this study, investigations on the protectiveness of poly(ether imide) coatings against corrosion of magnesium AZ31 alloy sheets are performed. The coatings were prepared in different pre-treated substrates by the dip coating method using N'N'-dimethyl acetamide (DMAc) and N'-methyl pyrrolidone solutions. The optimal performance was obtained for hydrofluoric acid treated substrates coated using DMAc solution (coating thickness 13μm) which showed impedances in the order of 10 7Ωcm 2 even after more than 3300h of exposure to a 3.5wt.% NaCl solution. This high performance is associated to an acid-base interaction at the interface as observed by X-ray photoelectron spectroscopy. © 2010 Elsevier Ltd.

Lendlein A.,Research Center Geesthacht GmbH | Behl M.,Research Center Geesthacht GmbH | Hiebl B.,Research Center Geesthacht GmbH | Wischke C.,Research Center Geesthacht GmbH
Expert Review of Medical Devices | Year: 2010

Polymeric materials are clinically required for medical devices, as well as controlled drug delivery systems. Depending on the application, the polymer has to provide suitable functionalities, for example, mechanical functions or the capability to actively move, so that an implant can be inserted in a compact shape through key-hole incisions and unfold to its functional shape in the body. Shape-memory polymers, as described herein regarding their general principle, compositions and architectures, have developed to a technology platform that allows the tailored design of such multifunctionality. In this way, defined movements of implants triggered either directly or indirectly, tailored mechanical properties, capability for sterilization, biodegradability, biocompatibility and controlled drug release can be realized. This comprehensive review of the scientific and patent literature illustrates that this technology enables the development of novel medical devices that will be clinically evaluated in the near future. © 2010 Expert Reviews Ltd.

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