Glycerol (G, a triol) and sebacic acid (S, an α,ω-dicarboxylic acid) were condensed in the bulk to obtain poly(glycerol sebacate) (PGS) cross-linked elastomers which were characterized in terms of their swelling, thermal, and mechanical properties. The soluble precursors to the elastomers were characterized in terms of their size, size distribution, and composition. In particular, G−S mixtures of five different compositions (molar G:S ratio = 2:1, 2:2, 2:3, 2:4, and 2:5) were copolymerized in the bulk at 120 °C in a three-step strategy (first step under inert gas atmosphere, followed by two steps in vacuo). When the G:S molar ratio was equal to (2:3) or close to (2:4), the stoichiometrically matched, network formation took place from the second condensation step, whereas three reaction steps were necessary for network formation far from stoichiometry, at G:S molar ratios equal to 2:2 and 2:5; at a G:S molar ratio of 2:1, no network formation was observed at all. Network composition also proved to be an important structural property, directly influencing the swelling and thermomechanical behavior of the elastomers. In particular, at the stoichiometrically matched G:S ratio of 2:3, corresponding to the cross-linking density maximum, the sol fraction extracted from the elastomers and the elastomer degree of swelling in aqueous media and in organic solvents presented a minimum, whereas the storage moduli of PGS elastomeric membranes in the dry state, measured within the temperature range between 35 and 140 °C, exhibited a maximum. The molecular weights of all soluble network precursors were found to be below 5000 g mol −1 (gel permeation chromatography), containing but traces of ring oligomers (electron-spray ionization mass spectrometry). 1 H NMR spectroscopy indicated that the precursor composition was close to that expected on the basis of the G:S feed ratio and that monomer-to-polymer conversion increased from the first to the second condensation step.

This study uses standard synthetic methodologies to produce tissue-mimicking materials that match the morphology and emulate the in vivo murine and human cardiac mechanical and imaging characteristics, with dynamic mechanical analysis, atomic force microscopy (AFM), scanning electron microscopy (SEM) and magnetic resonance imaging. In accordance with such aims, poly(glycerol sebacate) (PGS) elastomeric materials were synthesized (at two different glycerol (G)-sebacic (S) acid molar ratios; the first was synthesized using a G:S molar ratio of 2:2, while the second from a 2:5 G:S molar ratio, resulting in PGS2:2 and PGS2:5 elastomers, respectively). Unlike the synthesized PGS2:2 elastomers, the PGS2:5 materials were characterized by an overall mechanical instability in their loading behavior under the three successive loading conditions tested. An oscillatory response in the mechanical properties of the synthesized elastomers was observed throughout the loading cycles, with measured increased storage modulus values at the first loading cycle, stabilizing to lower values at subsequent cycles. These elastomers were characterized at 4 °C and were found to have storage modulus values of 850 and 1430 kPa at the third loading cycle, respectively, in agreement with previously reported values of the rat and human myocardium. SEM of surface topology indicated minor degradation of synthesized materials at 10 and 20 d post-immersion in the PBS buffer solution, with a noted cluster formation on the PGS2:5 elastomers. AFM nanoindentation experiments were also conducted for the measurement of the Young modulus of the sample surface (no bulk contribution). Correspondingly, the PGS2:2 elastomer indicated significantly decreased surface Young's modulus values 20 d post-PBS immersion, compared to dry conditions (Young's modulus = 1160 ± 290 kPa (dry) and 200 ± 120 kPa (20 d)). In addition to the two-dimensional (2D) elastomers, an integrative platform for accurate construction of three-dimensional tissue-mimicking models of cardiac anatomy from 2D MR images using rapid prototyping manufacturing processes was developed. For synthesized elastomers, doping strategies with two different concentrations of the MRI contrast agent Dotarem allowed independent and concurrent control of the imaging characteristics (contrast and relaxivity) during the synthetic process for increased contrast agent absorption, with tremendous potential for non-destructive in vivo use and applications to cardiovascular and cerebrovascular diseases.

Thickness measurements of thin films having thickness less than 1 µm are difficult to obtain by an interferometer. These difficulties arise from the overlap of the fringes from the upper and lower surfaces of the thin films. This paper presents a new methodology that mediates the consequences of this overlap and then implements it with thickness measurements of liquid crystal (LC) thin films. It takes into consideration the properties of light propagation within these films in order to rectify the images obtained from the interferometer. It assumes that the lower fringe pattern is much stronger that the upper one and hence the latter may be ignored. This occurs in situations where thin films are coated on substrates of significantly higher reflectivity, as happens when an LC thin film is coated on a polished iron substrate. The thickness and topography of LC thin films were experimentally measured with this methodology and were compared with measurements taken by an atomic force microscope.

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This study quantifies an error in the estimation of hemodynamic indices of global cardiac function from use of commercial catheters in mice. Male C57BL/6 mice (n=5, age=8–12wks, weight=25.5±3.3 g) were imaged on a 7T MRI scanner under 1.5% ISO in 100% O2; computational myocardial and catheter finite element models were constructed. A composite model of the catheter‐myocardium was imported in XFdtd for electric (E) field simulations. Comparison of end‐diastolic (ED) and end‐systolic (ES) volume estimates from such simulations show mean underestimation errors between −8.3±52.9 and −68.9±10.4%. Propagation of such errors in stroke volume, cardiac output, and ejection fraction estimation yields errors of 85.4±29.1, 182.3±117.4, 132.9±171.1%, respectively, given a catheter E‐field detection sensitivity of 5%. Modification of the commercial catheter design is shown to minimize underestimation errors of such indices, based on simulations. Elicited response improvements (peak amplitude and spatial extent) are quantified to be 405% and 52% (3.8 vs. 2.5 mm at 1% E‐field fall‐off) in ED, and 934 and 80% in ES, for the new catheter, compared to the commercially available design. Reductions in absolute hemodynamic error estimates were also computed (4.8–60.8%) for the new catheter in one mouse. Implementation of the newly proposed catheter design can lead to improved accuracy of indices of cardiac function.