Degradable polymers having a thermally induced shape memory can be fixed in a new, temporary shape after they have been processed into a permanent shape. They have great potential for biomedical applications, especially in the area of minimally invasive surgery. [1] One example is the insertion of a bulky medical device in a compressed temporary shape through a small surgical incision. When the implant is heated above a switching temperature (T trans ), it returns to its application-relevant permanent shape. After a given time the device degrades, and a second surgery for its removal is not necessary. [2,3] Shape-memory polymers generally consist of two components: cross-links determining the permanent shape and switching segments fixing the temporary shape at temperatures below T trans . Cross-linkage can be achieved either by physical interaction (e.g., in thermoplastic polymers) or by chemical bonds (e.g., in thermosets or photosets). In covalently cross-linked shape-memory polymer networks a maximum weight content of switching segments is possible. In constrast, thermoplastic materials must contain a sufficient amount of hard-segment-determining blocks so that a sufficient number of physical cross-links exist at temperatures above T trans . [4] The blocks that determine the switching segment may display T trans as either a melting temperature or a glass transition temperature. In biodegradable shape-memory polymers previously described as thermoplastic multiblockcopolymers [3] or photoset AB polymer networks [2,5] T trans is the melting point of crystallizable oligo(e-caprolactone) segments. Hydrogels with hydrophobic and crystallizable side chains as molecular switches also can show a thermoresponsive one-way shape-memory effect. [6] Based on noncrystallizable switching segments, completely amorphous shape-memory polymer networks having a glass transition temperature as T trans can be designed. These networks are transparent, and they should show a more

Biodegradable shape-memory polymers have attracted tremendous interest as potential implant materials for minimally invasive surgery. Here, the precise control of the material's functions, for example, the switching temperature T(sw), is a particular challenge. T(sw) should be either between room and body temperature for automatically inducing the shape change upon implantation or slightly above body temperature for on demand activation. We explored whether T(sw) of amorphous polymer networks from star-shaped rac-dilactide-based macrotetrols and a diisocyanate can be controlled systematically by incorporation of p-dioxanone, diglycolide, or epsilon-caprolactone as comonomer. Thermomechanical experiments resulted that T(sw) could be adjusted between 14 and 56 degrees C by selection of comonomer type and ratio without affecting the advantageous elastic properties of the polymer networks. Furthermore, the hydrolytic degradation rate could be varied in a wide range by the content of easily hydrolyzable ester bonds, the material's hydrophilicity, and its molecular mobility.

A. Alteheld Present Address: BASF Venture Capital GmbH, 4. Gartenweg -Z25, 67063 Ludwigshafen, Germany ---------Polyester urethane networks are versatile polymer systems as it is possible to tailor their mechanical properties and their hydrolytic degradation profile. For biomedical applications, the biodegradability as well as the thermomechanical properties of the polymer networks during the course of degradation is of importance. Therefore, we investigated the change of thermomechanical properties of networks based on star-shaped precursors of rac-dilactide and diglycolide, ε-caprolactone, or p-dioxanone, respectively, during hydrolytic degradation.Degradation rate and mechanical properties of the polymer networks were tailored by crosslink density, comonomers, and by changing the glass transition temperature. Most importantly, the degradation of the networks led to a controlled, step-by-step change of the mechanical properties of the networks. a Supporting information for this article is available at the bottom of the article's abstract page, which can be accessed from the journal's homepage at http://www.mrc-journal.de, or from the author. ((note: website is journal-specific)) b ATN and GT contributed equally to this work.-2 - IntroductionBiodegradable polymeric materials are the basis for implants needed for a certain time only and for which a second surgery for removal of the implant should be avoided, such as controlled drug release implants, [1] internal sutures, [2] and applications in tissue engineering and induced autoregeneration. [3,4] Principally, biodegradable materials are based on the cleavage of certain bonds under physiological conditions. The cleavage itself can happen through hydrolysis (e. g. of ester bonds), [5,6] by enzymatic cleavage, [7] or miscellaneous mechanisms such as reduction of disulfide bonds, [8] and can be in the main-or side chains, [9] depending on the monomers and architecture of the polymer. In biodegradable materials, cleavage of the bonds results in water soluble polymer fragments, which can be excreted from the body, e. g. through the kidney. [10] The degradation process of the polymer materials can be observed on different levels, including mass loss, change of molecular weight, change of thermomechanical properties, and the occurrence of degradation products. Additionally to degradation studies of bulk material, hydrolytic and enzymatic degradation can also be studied on polymer monolayers. [11] The degradation rate can generally be adjusted by the types of monomers, [12] the sequence structure and architecture of the polymer, [13][14][15][16] as well as by the morphology. One of the first and most-widely used classes of biodegradable polymers are the bulk degrading polyesters such as PLGA, however many other degradable materials are known such as poly(anhydrides), [17] poly(orthoesters), [18] poly(depsipeptides), [19] and poly(ether esters). [20] Semi-crystalline linear polyesters have been applied for sutures, for which mechanical stability is of high importance. O...

Polymer multilayer particles with radial variation in refractive index can possess a photonic band gap and therefore can be used as spherical dielectric resonators (SDRs). We synthesized multilayer microspheres with morphology "predesigned" by modeling their scattering cross section. The particles had a polystyrene core and four 150 ( 20 nm thick alternating layers of polystyrene and poly(trifluoroethyl methacrylate) which were used as a high and a low refractive index counterpart, respectively. We confirmed the morphology of microspheres by transmission electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy. We undertook a further step in increasing refractive index contrast between the layers by copolymerizing styrene with vinylcarbazole.

We report synthesis of polymer particles comprising layers with alternating high and low refractive index. We used poly(heptafluorobutyl methacrylate) as the low refractive index component and polystyrene as the high refractive index counterpart. We employed a copolymerization approach, the addition of a phase transfer catalyst (cyclodextrin), and a mixed initiator approach to produce spherical particles with a well-defined morphology. The composition and morphology of these particles were proven by DSC, XPS, NMR, and SEM. The refractive index contrast between these alternating high and low refractive index layers was ca. 0.20 ± 0.018. This work shows a route toward synthesis of polymeric spherical dielectric resonators.

Completely amorphous copoly(ether)ester networks based on oligo(propylene glycol) and oligo[(rac-dilactide)-co-glycolide] segments were synthesized by crosslinking star-shaped hydroxyl-telechelic cooligomers using an aliphatic low-molecular weight diisocyanate. Two different network architectures were applied exhibiting differences in the phase-separation behavior. For networks from oligo(propylene glycol)-block-oligo[(rac-lactide)-co-glycolide] triols (G(3)OPG-bl-OLG) only one glass transition was obtained. However, networks from a mixture of oligo(propylene glycol) triols (G(3)OPG) and oligo[(rac-lactide)-co-glycolide] tetrols (P(4)OLG) with a ratio of components in a certain range show two glass transition temperatures (T (g)) being attributed to two segregated amorphous phases. In this way a wide spectrum of mechanical properties can be realized and adjusted to the requirements of a specific application.

Abbaubare Polymere mit einem thermisch induzierten Formgedächtniseffekt können nach Herstellung einer permanenten Form in einer neuen, temporären Form fixiert werden. Diese Materialien haben ein großes Potenzial für biomedizinische Anwendungen, besonders im Bereich der minimalinvasiven Chirurgie.[1] Ein Beispiel ist das Einführen eines sperrigen Medizinprodukts in einer komprimierten, temporären Form durch eine kleine Öffnung in den Körper. Durch Erwärmen des Implantates über die Schalttemperatur T trans nimmt es die für die Anwendung relevante Form ein. Nach einer bestimmten Zeit baut sich das Implantat ab, sodass eine zweite Operation zu dessen Entfernung entfällt. [2,3] Formgedächtnispolymere bestehen im Allgemeinen aus zwei Komponenten: aus Netzpunkten, die die permanente Form festlegen, und aus Schaltsegmenten, die bei Temperaturen unterhalb von T trans die temporäre Form fixieren. Die Vernetzung kann entweder über chemische Bindungen (z. B. Thermosets oder Photosets) oder durch physikalische Wechselwirkungen (z. B. thermoplastische Elastomere) erfolgen. Bei kovalent vernetzten Formgedächtnispolymernetzwerken ist der Einbau des maximal möglichen Gewichtsanteils an Schaltsegmentketten möglich, thermoplastische Materialien dagegen benötigen einen genügend hohen Gewichtsanteil an den das Hartsegment bestimmenden Blöcken, um eine ausreichende Zahl von physikalischen Netzpunkten oberhalb von T trans zu gewährleisten. [4] Die das Schaltsegment bestimmenden Blöcke können ein T trans in Form einer Schmelztemperatur oder einer Glasüber-gangstemperatur aufweisen. In kürzlich beschriebenen, bioabbaubaren Formgedächtnispolymeren wie thermoplastischen Multiblockcopolymeren [3] oder Photoset-AB-Polymernetzwerken [2,5] ist T trans der Schmelzpunkt von kristallisierbaren Oligo(e-caprolacton)segmenten. Hydrogele mit hydrophoben und kristallisierbaren Seitenketten als molekularen

The need of intelligent implant materials for applications in the area of minimally invasive surgery leads to tremendous attention for polymers which combine degradability and shape-memory capability. Application of heat, and thereby exceeding a certain switching temperature Tsw, causes the device to changes its shape. The precise control of Tsw is particularly challenging. It was investigated in how far Tg, that can be used as Tsw, of amorphous polymer networks from star-shaped polyester macrotetrols crosslinked with a low-weight linker can be controlled systematically by incorporation of different comonomers into poly(rac-lactide) prepolymers. The molecular mass of the prepolymers as well as type and content of the comonomers was varied. The Tg could be adjusted by selection of comonomer type and ratio without affecting the advantageous elastic properties of the polymer networks.