Evaluation of pliable bioresorbable, elastomeric aortic valve prostheses in sheep during 12 months post implantation

Pliable microfibrous, bioresorbable elastomeric heart valve prostheses are investigated in search of sustainable heart valve replacement. These cell-free implants recruit cells and trigger tissue formation on the valves in situ. Our aim is to investigate the behaviour of these heart valve prostheses when exposed to the high-pressure circulation. We conducted a 12-month follow-up study in sheep to evaluate the in vivo functionality and neo-tissue formation of these valves in the aortic position. All valves remained free from endocarditis, thrombotic complications and macroscopic calcifications. Cell colonisation in the leaflets was mainly restricted to the hinge area, while resorption of synthetic fibers was limited. Most valves were pliable and structurally intact (10/15), however, other valves (5/15) showed cusp thickening, retraction or holes in the leaflets. Further research is needed to assess whether in-situ heart valve tissue engineering in the aortic position is possible or whether non-resorbable synthetic pliable prostheses are preferred.</p

Time-dependent failure in load-bearing polymers. A potential hazard in structural applications of polylactides

Polylactides are commonly praised for their excellent mechanical properties (e.g. a high modulus and yield strength). In combination with their bioresorbability and biocompatibility, they are considered prime candidates for application in load-bearing biomedical implants. Unfortunately, however, their long-term performance under static load is far from impressive. In a previous in vivo study on degradable polylactide spinal cages in a goat model it was observed that, although short-term mechanical and real-time degradation experiments predicted otherwise, the implants failed prematurely under the specified loads. In this chapter we demonstrate that this premature failure is attributed to the time-dependent character of the material used. The phenomenon is common to all polymers, and finds its origin in stress-activated segmental molecular mobility leading to a steady rate of plastic flow. The main conclusion is that knowledge of the instantaneous strength of a polymeric material is insufficient to predict its long-term performance

Rotational Isomerism of an Amide Substituted Squaraine Dye: A Combined Spectroscopic and Computational Study

The conformational analysis of a 2,4-bis(4-dialkylamino-2-amido)phenyl squaraine dye revealed the presence of two rotational isomers at room temperature. Combination of spectroscopic and computational techniques showed that the rotational barrier is influenced by hydrogen bonds between the amido substituents and the oxygen atoms at the quadratic core. Even small amounts of trifluoroacetic acid interfered with the intramolecular hydrogen bond formation and accelerated the interconversion of the conformers

Liquid crystalline properties of poly(propylene imine) dendrimers functionalized with cyanobiphenyl mesogens at the periphery

Three generations poly(propylene imine) dendrimers with 4, 16, and 64 terminal amine groups have been functionalized with pentyloxycyanobiphenyl and decyloxycyanobiphenyl mesogens. The liq.-cryst. properties of these dendrimers have been studied in detail by differential scanning calorimetry, optical polarization microscopy, and X-ray diffraction. All the mesogenic dendrimers orient into a smectic A mesophase. Thermal properties are influenced to a large extent by the spacer length, showing g -&gt; SA -&gt; I transitions for the dendritic mesogens with the pentyloxy spacers and K -&gt; SA -&gt; I transitions for the ones with a decyloxy spacer. In the latter, the temp. range of the mesophase increases with dendrimer generation. Mesophase formation in the case of the pentyloxy series is more difficult compared with the corresponding decyloxy analogs, when the transition enthalpies and the kinetics of obtaining microscopic textures are considered. The effect of generation on mesophase formation cannot be clearly distinguished, although in the case of the fifth-generation dendrimer with a decyloxy spacer, microscopic textures could be obtained more easily, compared with the lower generations. X-ray diffraction measurements of oriented samples indicate that the cyanobiphenyl endgroups of both series orient into an antiparallel-overlapping interdigitated structure. The obsd. SA-layer spacings are independent of the dendrimer generation for both spacer lengths, indicating that the dendritic backbone has to adopt a completely distorted conformation, even for the higher generation

Magnetic Resonance Monitoring of Opaque Temperature-Sensitive Polymeric Scaffolds

The monitoring of location and degradation rates of injectable biomaterials is an area of particular interest in the design and implementation of therapeutic scaffolds and carriers for tissue repair and replacement. We describe here the fabrication and characterization of gadolinium (Gd)-labeled temperature-responsive hydrogels that can be detected noninvasively using T1-weight magnetic resonance. Two acrylamide-functionalized GdIIIDOTA-monoamide complexes with either a short n-butylene spacer (GdIII-C4-AA) or a long hydrophilic spacer (GdIII-PEG-AA) were synthesized and incorporated into the hydrogels. At temperatures above the lower critical solution temperature (LCST), 37 °C, these hydrogels have the capacity to enhance relaxivity (r1) due to the hydrophobic interactions of the polyamide chains around the gadolinium chelates. This effect is further accentuated by the presence of the polyethylene glycol groups of the Gd complex GdIII-PEG-AA

Self-healing supramolecular polymers in action

Sophisticated polymeric materials with "responsive" properties, such as self-healing, are beginning to reach the market. Supramolecular polymers, i.e., polymers that owe their mechanical properties primarily to the reversible, non-covalent interactions, such as hydrogen bonding interactions, between the macromolecules, have frequently been employed as self-healing materials. The quadruple hydrogen bonding ureidopyrimidinone (UPy) unit is a particularly effective and versatile design motif, since it forms very strong but reversible linkages, and can be incorporated into virtually any type of polymer backbone, leading to materials with increased mechanical properties. Supramolecular polymers are presented, with an emphasis on those based on the UPy-unit, and their use in self-healing applications is highlighted and discussed. Supramolecular polymers are eminently useful in self-healing applications. The reversible nature of supramolecular polymers allows for self-healing processes to take place, using a contact pressure trigger or a heat trigger. Several materials are presented with an emphasis on ureidopyrimidinone (UPy) comprising supramolecular polymer

Self-healing supramolecular polymers in action

\u3cp\u3eSophisticated polymeric materials with responsive properties, such as self-healing, are beginning to reach the market. Supramolecular polymers, i.e., polymers that owe their mechanical properties primarily to the reversible, non-covalent interactions, such as hydrogen bonding interactions, between the macromolecules, have frequently been employed as self-healing materials. The quadruple hydrogen bonding ureidopyrimidinone (UPy) unit is a particularly effective and versatile design motif, since it forms very strong but reversible linkages, and can be incorporated into virtually any type of polymer backbone, leading to materials with increased mechanical properties. Supramolecular polymers are presented, with an emphasis on those based on the UPy-unit, and their use in self-healing applications is highlighted and discussed. Supramolecular polymers are eminently useful in self-healing applications. The reversible nature of supramolecular polymers allows for self-healing processes to take place, using a contact pressure trigger or a heat trigger. Several materials are presented with an emphasis on ureidopyrimidinone (UPy) comprising supramolecular polymer.\u3c/p\u3