Switching Segments Research Articles

Synthesis and characterization of elastic star shape-memory polymers as self-expandable drug-eluting stents

Elastic shape-memory polymers as self-expendable polymeric drug-eluting stents are developed for the first time, with good mechanical properties, fast self-expansion, and sustained drug release. Novel star block co-polymer PCTOPDs containing hyperbranched poly(e-caprolactone) (PCL) switching segment and poly(2-oxepane-1,5-dione) (POPD) hard segment were synthesized in high yield and characterized by NMR, GPC, DSC, tensile test and cyclic thermomechanical tensile test. PCTOPD containing 15–27 wt% POPD (PCTOPD-15–27) are found to be non-cytotoxic thermoplastic elastomers (Tm of 39–40 and 120–129 °C, eb of 908–1060%, σm of 12–20 MPa, and E of 60–91 MPa) with good shape-memory properties at 40 °C (Rf of 95–97%, Rr of 97–99%, and shape recovery time of 35 s). The stent made from PCTOPD-27 gives nearly full self-expansion at 37 °C within 45 s. The collapse pressure at a compressive strain of 30% is 1.7 bar. A stent containing 3.0 wt% paclitaxel releases 42% drug linearly in the first 9 days and 67% drug in 30 days with a slower but nearly linear release for the period of 10–30 days. The developed SMP-based drug-eluting stents might be useful in biomedical application such as the treatment of coronary artery disease.

Triple-Shape Effect of Copolymer Networks Based on Poly(ω-pentadecalactone) and Poly(ε‑caprolactone) Segments Applying a Programming Procedure with an Adjusted Temperature Profile

ABSTRACTA triple-shape material based on the two crystallizable segments poly(ω‑pentadeca-lactone) and poly(ε-caprolactone) was synthesized by crosslinking star-shaped precursors. A newly developed programming procedure (TSCP2) was applied in order to achieve triple-shape behavior. The application of this modified triple-shape creation procedure enabled triple-shape capability by influencing the crystallization behavior of the two switching segments in these copolymer networks, which partly show no two distinct and separated melting points. The influence of molecular weight and content of the poly(ε-caprolactone) segment on the triple-shape effect programmed by application of TSCP2 was investigated.

Shape-memory properties of magnetically active triple-shape nanocomposites based on a grafted polymer network with two crystallizable switching segments

Thermo-sensitive shape-memory polymers (SMP), which are capable of memorizing two or more different shapes, have generated significant research and technological interest. A triple-shape effect (TSE) of SMP can be activated e.g. by increasing the environmental temperature (Tenv), whereby two switching temperatures (Tsw) have to be exceeded to enable the subsequent shape changes from shape (A) to shape (B) and finally the original shape (C). In this work, we explored the thermally and magnetically initiated shape-memory properties of triple-shape nanocompos- ites with various compositions and particle contents using different shape-memory creation procedures (SMCP). The nanocomposites were prepared by the incorporation of magnetite nanoparticles into a multiphase polymer network matrix with grafted polymer network architecture containing crystallizable poly(ethylene glycol) (PEG) side chains and poly(!- caprolactone) (PCL) crosslinks named CLEGC. Excellent triple-shape properties were achieved for nanocomposites with high PEG weight fraction when two-step pro- gramming procedures were applied. In contrast, single-step programming resulted in dual-shape properties for all investi- gated materials as here the temporary shape (A) was predominantly fixed by PCL crystallites.

The Influence of Programming Conditions on the Triple‐Shape Effect of Copolymer Networks with Poly(ω‐pentadecalactone) and Poly(ε‐caprolactone) as Switching Segments

AbstractA versatile triple‐shape material based on the two crystallizable segments poly(ω–pentadecalactone) and poly(ε‐caprolactone) was synthesized showing triple‐shape capability after application of the typical two‐step triple‐shape creation procedure at elevated temperatures (TSCP) as well as a one‐step programming procedure at high temperature or at room temperature by cold drawing. By applying TSCP and varying the sequence of programming temperatures, the influence of the programming procedure on the triple‐shape capability was investigated. The application of such a modified TSCP enabled to a certain extent the control of triple‐shape capability by influencing the crystallization behavior of the two switching segments in these copolymer networks.

Upscaling the synthesis of biodegradable multiblock copolymers capable of a shape-memory effect

Thermoplastic, phase-segregated multiblock copolymers (MBC) with shape-memory capability consisting of poly(ε-caprolactone) (PCL) switching segments and poly(p-dioxanone) (PDO) or poly(ω-pentadecalactone) (PPD) hard segments were prepared on a scale of several kilograms following a newly developed upscaling procedure. Dihydroxytelechelic poly(ether)esters were coupled by an aliphatic diisocyanate gaining products of sufficiently high molecular weights. The obtained biodegradable MBC exhibited good elastic properties and a shape-memory effect (SME) with a switching temperature (T (sw)) around body temperature. The yield of the synthesis could be improved and reaction time reduced, while mechanical and shape-memory properties were not affected. These multifunctional materials, which are now available in a larger scale have a high application potential as smart implant materials especially for minimally invasive surgery.

Processing and characterization of poly(ethylene oxide)/clay nanocomposites

Abstract In recent years, poly(ethylene oxide) (PEO) has gained two very important applications namely: 1) as solid polymer electrolytes for use in battery, supercapacitor and fuel cell, 2) as a crystallizable switching segment for shape memory polymer (SMP) systems. The common problem for all the applications is linked with the poor mechanical properties of PEO. Hence nanoreinforcement of PEO has been investigated to develop PEO based materials suitable for various applications. PEO/clay nanocomposites have been made by using a solution intercalation method or a melt mixing route. The nanocomposites were characterized by X-ray diffraction (XRD) and evaluated for their rheological and dynamic mechanical properties, Since PEO is sensitive to thermo-oxidative degradations, the effect of processing temperature on rheological properties was also investigated. The detailed processing and characterization of PEO/clay nanocomposites will be discussed in the present paper.

One-Way and Reversible Dual-Shape Effect of Polymer Networks Based on Polypentadecalactone Segments

A series of degradable polymer networks containing poly(ω-pentadecalactone) (PPD) switching segments showing a thermally-induced shape-memory effect were synthesized by co-condensation of PPD-macrotriols or -tetrols with an aliphatic diisocyanate. Thermal and mechanical properties at different temperatures were explored for polymer networks as a function of crosslink density by varying the polymer chain segment length or the netpoint functionality. All polymer networks exhibited excellent shape-memory properties with shape recovery rates Rr between 99% and 100% determined in the 5th cycle under stress-free conditions. Furthermore, the polymer networks were capable of a reversible dual-shape effect based on crystallization induced elongation (CIE) and melting-induced contraction (MIC) in cyclic, thermomechanical experiments under constant stress. In these tests, the polymer networks were capable of a shape-change of 130%. The associated temperatures at which CIE or MIC occurred (TCIE and TMIC) were shown to be a function of the applied stress. By an increase of stress of 1.6 MPa, TCIE could be increased by 10 K.

Polymers in Biomedicine and Electronics

The versatility of polymeric materials originates from the broad variety in their chemical structure and in their hierarchical organization as well as from the possibility to realize a wide spectrum of functions. Often such functions result from a combination ofamoleculararchitecture/morphology with a physical process and therefore require integration in a suitable system (e.g. medical device, electric circuit) or environment (e.g. physiological environment). Frequently, research in the area of functional polymers is motivated by applications. This special issue focuses on two application areas, in which polymer research as well as product development are progressing rapidly: Biomedicine and Electronics. Here (multi)functional polymers are an enabling technology and in this way create substantial and sustainable value. The significance of this topic is also highlighted at the conference ‘‘Polymers in Biomedicine and Electronics’’, which takes place from Oct 3 to 5, 2010 in Berlin combining the biannual meetings of the Gesellschaft Deutscher Chemiker (GDCh) Division ‘‘Macromolecular Chemistry’’ and of the Berlin-Brandenburgischer Verband fur Polymerforschung (BVP). Topics of the conference cover the design and the synthesis of functional polymers, physical principles underlying the function, the characterization of such functionswithin a system as well as product-oriented industrial research. Smart biomaterials, biocompatible coatings and their applications in controlled drug delivery systems or in regenerative therapies will be discussed in the biomedicine-oriented sessions of the conference. Photovoltaic, charge transport, light emission aswell as sensors andactuatorswill be subjects in the area of electronics.

Stimuli‐Sensitive Polymers

Stimuli‐Sensitive Polymers

Modeling the morphology and mechanical behavior of shape memory polyurethanes based on solid-state NMR and synchrotron SAXS/WAXD

A combination of solid-state proton Wide-line Nuclear Magnetic Resonance (NMR) relaxometry and synchrotron Small-angle (SAXS) and Wide-angle (WAXD) X-ray scattering was used to elucidate the microphase morphology of shape memory thermoplastic multi-block polyurethanes based on poly(e-caprolactone), as switching segment and polyurethane based permanent or hard segments (HS). The polyurethanes are produced from the condensation of 1,4-butanediol (BDO) with hexamethylenediisocyanate (HDI). The morphology – induced by the hard-segment crystallization – converts from dispersed randomly placed hard-segment domains into progressively more periodic, but interconnected HS nanophases with increasing HS content. Irrespective of the actual morphology, the SAXS data could be described satisfactorily by using a clipped Gaussian random field (GRF) model. The NMR data demonstrate that the HS domain fraction corresponds to the chemical feed, pointing at a complete phase separation. The material mechanical behavior during repeated deformation cycles can be explained on morphological grounds and involves a spatially heterogeneous plastic deformation of the hard domains.

In vivo evaluation of the angiogenic effects of the multiblock copolymer PDC using the hen's egg chorioallantoic membrane test

Multiblock copolymers with shape-memory capability attracted tremendous interest as promising candidate materials for smart, degradable implants. In the present study the hen's egg-chorioallantoic membrane test (HET-CAM test) was used to investigate the angiogenic properties of a thermoplastic, biodegradable multiblock copolymer PDC composed of poly(p-dioxanone) hard segments (PPDO) and crystallizable poly(ε-caprolactone) switching segments (PCL), whereby PPDO and PCL homopolymers were investigated as controls. According to our HET-CAM test data, only PDC induced significant microvessel attraction and formation in the contact area of the test specimen after 48 hours of incubation showing newly formed blood vessels along the outer edge of the material. In contrast, no newly formed blood vessels were observed around the PPDO or PCL specimen after the same incubation period. These in vivo results indicate that the multiblock copolymer PDC possibly possesses an angiogenic effect and it can induce blood vessel formation in its direct vicinity when it is implanted in vivo.

Polymer Networks Combining Controlled Drug Release, Biodegradation, and Shape Memory Capability

A triple functional polymer network system that combines shape-memory capability, biodegradability, and drug release is developed. The choice of network structure and switching segment prevent that drug incorporation substantially changes the thermal and mechanical properties as well as the shape-memory functionality (see recovery curves). A diffusion-controlled release that is independent from biodegradation is enabled. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Novel synthetic strategy toward shape memory polyurethanes with a well-defined switching temperature

Shape memory polyurethanes (SMPUs) have been synthesised via a novel synthetic methodology, resulting in an improvement of the phase separation in the multi-block structure of the polyurethane and in its shape memory properties. ABA block copolymers based on semi-crystalline poly(ɛ-caprolactone) and amorphous poly(propylene oxide) (PPO) were used as precursor for the SMPUs. For their synthesis, poly(ɛ-caprolactone) diols have been converted into isocyanate end-capped prepolymers by using a mixture of 3(4) isocyanato-1-methyl-cyclohexylisocyanate isomers, after which a coupling with low-Tg poly(propylene oxide) oligomers is done. The shape memory polymers are obtained by reaction of the ABA block copolymers with hexamethylenediisocyanate and 1,4-butanediol as chain extender. Using this new strategy, a flexible segment (PPO) was introduced between the hard and the switching segments of the SMPU. For comparison, SMPUs without flexible segment have also been prepared with the conventional synthetic route. DSC, isostrain experiments and cyclic shape memory tests revealed narrower switching temperatures for the SMPUs including a flexible segment.

Synthesis and Characterization of Three-Arm Poly(ε-caprolactone)-Based Poly(ester−urethanes) with Shape-Memory Effect at Body Temperature

Novel biodegradable star poly(ester−urethanes) containing three-arm poly(ε-caprolactone) (PCL) as switching segment were prepared as shape-memory polymers (SMPs) with switching temperature (Ts) around body temperature. PCL-triols with molecular weight (Mn) of 2700−4200 g/mol and Tm of 45−47 °C were synthesized in 55−67% yield by Novozym 435-catalyzed ring-opening polymerization of ε-caprolactone with glycerol as initiator, and their three-arm structures were confirmed by 1H and 13C NMR analysis. Reaction of the PCL-triols with methylene diphenyl 4,4′-diisocyanate isocynate and 1,6-hexanediol gave three-arm PCL-based poly(ester−urethane)s (tPCL-PUs) in 83−92% yield, with 65−75% soft segment. The structure of tPCL-PUs was confirmed by 1H NMR analysis, and the thermal properties were analyzed by DSC with Ts of 36−39 °C. tPCL-PUs showed excellent shape-memory effects at 38 °C during cyclic thermomechanical tensile tests: shape recovery within 10 s, shape fixity rate of 92%, and shape recovery rate of 99%. The novel biodegradable star SMPs are potentially useful in biomedical applications.

Investigation of parameters to achieve temperatures required to initiate the shape-memoryeffect of magnetic nanocomposites by inductive heating

The activation of the shape-memory effect of nanocomposites (NC) byalternating magnetic fields requires exceeding the switching temperatureTs. Different factors, which can influence this process, have been investigated. The intrinsicproperties of magnetic nanoparticles (MNP), their content and distribution in the polymermatrix as well as the heat transport conditions, which are essentially determinedby the surface to volume ratio (S/V) of the specimens and their surroundings,influence the achievable temperature in an alternating magnetic field. We usedMNP having an iron (II, III) oxide core embedded in amorphous silica, whichwas homogeneously distributed in a polymer matrix by extrusion moulding. Thethermoplastic polymer matrix consists either of an aliphatic polyetherurethane(TFX) for demonstration of the basic correlations between magnetic field and thesample, or of a biodegradable multiblock copolymer (PDC), which is prepared fromhard segment forming poly(p-dioxanone)diol (PPDO), switching segment formingpoly(ε-caprolactone)diol (PCL) and 2,2(4),4-trimethylhexanediisocyanate (TMDI) as a junctionunit. We could demonstrate that a nanoparticle content up to 10 wt% does not decisivelychange the shape-memory properties or mechanical properties of PDC-basedmaterials.

Competition and cooperation between brands in a segment: an analysis based on a semi-Markov model

Because the market position of a product brand is influenced by consumers' buying behaviour, it is important to identify the potential for competition and cooperation between different brands in a product category by using consumer behaviour analysis. To help marketing managers discover the market positions of their brands and to make decisions about competitive or cooperative strategies, we propose an integrated semi-Markov model for consumer behaviour, which combines brand choice, purchase quantity and purchase timing. Based on the model, we mathematically formulate some measures for consumer behaviour and describe a brand's market structure in a new way using semi-Markov processes. The brand's market in the presented structure is classified into one transient segment and several recurrent segments, which can be further classified into loyal segments and switching segments. With the help of this brand's market structure, we analyse the coexistence of competition and cooperation among different brands. To validate the model, we conducted an experiment using the data from a consumer panel of college students.

In vivo degradation behavior of PDC multiblock copolymers containing poly(para-dioxanone) hard segments and crystallizable poly(epsilon-caprolactone) switching segments

AbstractThe degradation behavior of biodegradable multiblock copolymers (PDC) containing poly(p-dioxanone) hard segments (PPDO) and crystallizable poly(epsilon-caprolactone) switching segments (PCL) synthesized via co-condensation of two oligomeric macrodiols with an aliphatic diisocyanate as junction unit was explored in in vivo and in vitro experiments. The in vitro experiments for enzymatic degradation resulted that the poly(epsilon-caprolactone) segments are degraded faster, than the poly(p-dioxanone) segments. During degradation the outer layer of the test specimen becomes porous. Finally non-soluble degradation products in form of particles were found at the surface. This observation is in good agreement with the in vivo studies, where the non-soluble degradation products in the periimplantary tissues showed a diameter of 1 – 3 micron.

Shape-memory capability of binary multiblock copolymer blends with hard and switching domains provided by different components

The structural concept of shape-memory polymers (SMP) is based on two key components: covalent or physical crosslinks (hard domains) determining the permanent shape and switching domains fixing the temporary shape as well as determining the switching temperature Tsw. In conventional thermoplastic SMP hard and switching domains determining segments are combined in one macromolecule. In this paper we report on binary polymer blends from two different multiblock copolymers, whereby the first one provides the segments forming hard domains and the second one the segments forming the switching domains. A poly(alkylene adipate) mediator segment is incorporated in both multiblock copolymers to promote their miscibility as the hard segment poly(p-dioxanone) (PPDO) and the switching segment poly(e-caprolactone) (PCL) are non-miscible. All polymer blends investigated showed excellent shape-memory properties. The melting point associated to the PCL switching domains Tm,PCL is almost independent of the weight ratio of the two blend components. At the same time the mechanical properties can be varied systematically. In this way complex synthesis of new materials can be avoided. Its biodegradability, the variability of mechanical properties and a Tsw around body temperature are making this binary blend system an economically efficient, suitable candidate for diverse biomedical applications.

Technical Note—Price Promotions in Asymmetric Duopolies with Heterogeneous Consumers

In this note I investigate the outcome of a static price competition between a strong firm (a firm with an established loyal consumer base) and a weak firm (a firm without loyal consumers). The consumers are divided into the strong firm's loyal segment and the switching segment, members of which have heterogeneous tastes for the firms' products. In the presence of loyal consumers, for a large set of the parameters of the demand function, the firms use mixed strategies over a finite number of prices. These strategies can be interpreted as occurrences of sales. The most common case is that of the strong firm's using two prices and the weak firm's using one price. However, when both firms use sales, the weak firm promotes more often than the strong firm.

Synthesis, Characterization, Curing and Shape Memory Properties of Epoxy‐Polyether System

Epoxy resins were cured by an amine telechelic poly(tetramethylene oxide) (PTMO). The telechelic amine was synthesized from hydroxy telechelic PTMO and was characterized. The kinetics of curing of epoxy monomer by the polyether amine was studied in detail by differential scanning calorimetry (DSC) and rheology to optimize the cure conditions. The cured epoxy system exhibited shape memory properties where PTMO served as the switching segment. Molar ratios of the epoxy monomer and the amine were varied to get polymers with different compositions. The developed polymers were analyzed by DSC, X‐ray diffraction, and Dynamic Mechanical Thermal (DMTA) analyses. Shape memory property was evaluated by bending tests. As the concentration of epoxy resin increased, the transition temperature (Ttrans) increased. The tensile strength and % elongation also increased with epoxy resin‐content. The extent of shape recovery increased with PTMO‐content with a minor penalty in recovery time. The polymer with the maximum PTMO‐content exhibited 99% shape recovery with a recovering time of 12 s.