Compound-specific isotope analysis of individual amino acids (AA) is a rapidly growing tool in ecological studies to assess diet and trophic position (TP) in both modern and ancient foodwebs. We conducted the first controlled feeding study examining δ 15 N values in AAs in a marine mammal (harbor seal Phoca vitulina). The pattern of δ 15 N variation among AAs in seals was similar to that observed in other heterotrophs, although exceptions were found with proline and threonine. However, many δ 15 N changes with trophic transfer were very different than those reported for zooplankton and other lower TP marine consumers. In particular the measured trophic enrichment factor (TEF) now broadly used for TP estimation (TEF Glu-Phe) was much lower in harbor seals (~4.3 ‰) than the current commonly applied value (~7.5 ‰). Recently published data on wild marine birds (penguins) and elasmobranchs (stingrays) suggests that similar, low TEF values may also be characteristic of these taxa. Together, these data imply that marine mammals and other higher animals have different, but also diagnostic, changes in δ 15 N-AA with trophic transfer vs. organisms examined in previous feeding studies (e.g. zooplankton, bony fish and mollusks), possibly due to dietary protein content, trophic position, and/or form of nitrogen excretion (urea vs. ammonia). Therefore, we propose that for marine mammals, a multi-TEF calculation is required to account for variations of TEF between animals within a food web, and we demonstrate that this approach can predict accurate TP estimates for harbor seals. These results also have significant implication for the application of compound-specific isotope analysis of AAs on terrestrial ecology and trophic structure.

Fused deposition modeling (FDM), a low cost and easy-to-use additive manufacturing technique, was pushed to its typical resolution limit to produce poly(lactic acid) (PLA) gyroid scaffolds. A gyroid morphology was selected as scaffold structure due to its spring shape architecture, high porosity, leading to good nutrient and waste diffusion, and favorable mechanical properties, such as isotropic resistance to pressure. Printing parameters were optimized and the need of a support material to improve printing quality was evidenced. The gyroid structure was compared with the more common strut-based structure. Scaffold porosity was measured by micro-CT, and mechanical properties were determined by compressive mechanical tests. The effect of mesh geometry, printing resolution, and PLA crystallinity on resistance against compression was evaluated. Moreover, the impact of PLA scaffold geometry and crystallinity on its degradation was studied in vitro. Porosity of the gyroid structure was 71%, close to the 74% expected from the model used for printing. The compression tests showed that the gyroid scaffold has an isotropic behavior, in contrast with the typical strut-based scaffold, which exhibits an orientation-dependent deformation. Upon aging in physiological conditions, gyroid scaffolds retained their integrity during 64 weeks, while control scaffolds lost struts one after the other starting from week 33, in a way that depended on crystallinity and printing resolution. For both geometries, the remaining mass started to decrease at week 52. Based on these results, the gyroid design is proposed as a suitable mesh architecture for tissue engineering scaffolds that can be elaborated using FDM techniques, to produce low cost and personalized implants.

A standard method of protein immobilization is proposed, based on the use of protein-polyelectrolyte complexes (PPCs) as building blocks for layer-by-layer assembly. Thicker multilayers, with a higher polyelectrolyte fraction, are obtained with PPCs compared to single protein molecules. Biological activity is not only maintained, but specific activity is also higher, as demonstrated for lysozyme-poly(styrene sulfonate) complexes. This is attributed to the more hydrated state of the assemblies. This new method of protein immobilization opens up perspectives for biotechnology and biomedical applications.

Decellularized mammalian extracellular matrices (ECM) have been widely accepted as an ideal substrate for repair and remodelling of numerous tissues in clinical and pre-clinical studies. Recent studies have demonstrated the ability of ECM scaffolds derived from site-specific homologous tissues to direct cell differentiation. The present study investigated the suitability of hydrogels derived from different source tissues: bone, spinal cord and dentine, as suitable carriers to deliver human apical papilla derived mesenchymal stem cells (SCAP) for spinal cord regeneration. Bone, spinal cord, and dentine ECM hydrogels exhibited distinct structural, mechanical, and biological characteristics. All three hydrogels supported SCAP viability and proliferation. However, only spinal cord and bone derived hydrogels promoted the expression of neural lineage markers. The specific environment of ECM scaffolds significantly affected the differentiation of SCAP to a neural lineage, with stronger responses observed with spinal cord ECM hydrogels, suggesting that site-specific tissues are more likely to facilitate optimal stem cell behavior for constructive spinal cord regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 319-328, 2017.