Sedimentary Environment Influences the Effect of an Infaunal Suspension Feeding Bivalve on Estuarine Ecosystem Function

The suspension feeding bivalve Austrovenus stutchburyi is a key species on intertidal sandflats in New Zealand, affecting the appearance and functioning of these systems, but is susceptible to several environmental stressors including sedimentation. Previous studies into the effect of this species on ecosystem function have been restricted in space and time, limiting our ability to infer the effect of habitat change on functioning. We examined the effect of Austrovenus on benthic primary production and nutrient dynamics at two sites, one sandy, the other composed of muddy-sand to determine whether sedimentary environment alters this key species' role. At each site we established large (16 m2) plots of two types, Austrovenus addition and removal. In winter and summer we deployed light and dark benthic chambers to quantify oxygen and nutrient fluxes and measured sediment denitrification enzyme activity to assess denitrification potential. Rates of gross primary production (GPP) and ammonium uptake were significantly increased when Austrovenus was added, relative to removed, at the sandy site (GPP, 1.5 times greater in winter and summer; ammonium uptake, 8 times greater in summer; 3-factor analysis of variance (ANOVA), p<0.05). Denitrification potential was also elevated in Austrovenus addition plots at the sandy site in summer (by 1.6 times, p<0.1). In contrast, there was no effect of Austrovenus treatment on any of these variables at the muddy-sand site, and overall rates tended to be lower at the muddy-sand site, relative to the sandy site (e.g. GPP was 2.1 to 3.4 times lower in winter and summer, respectively, p<0.001). Our results suggest that the positive effects of Austrovenus on system productivity and denitrification potential is limited at a muddy-sand site compared to a sandy site, and reveal the importance of considering sedimentary environment when examining the effect of key species on ecosystem function

Designing Bioactive Delivery Systems for Tissue Regeneration

The direct infusion of macromolecules into defect sites generally does not impart adequate physiological responses. Without the protection of delivery systems, inductive molecules may likely redistribute away from their desired locale and are vulnerable to degradation. In order to achieve efficacy, large doses supplied at interval time periods are necessary, often at great expense and ensuing detrimental side effects. The selection of a delivery system plays an important role in the rate of re-growth and functionality of regenerating tissue: not only do the release kinetics of inductive molecules and their consequent bioactivities need to be considered, but also how the delivery system interacts and integrates with its surrounding host environment. In the current review, we describe the means of release of macromolecules from hydrogels, polymeric microspheres, and porous scaffolds along with the selection and utilization of bioactive delivery systems in a variety of tissue-engineering strategies

Nerve guides manufactured from photocurable polymers to aid peripheral nerve repair

The peripheral nervous system has a limited innate capacity for self-repair following injury, and surgical intervention is often required. For injuries greater than a few millimeters autografting is standard practice although it is associated with donor site morbidity and is limited in its availability. Because of this, nerve guidance conduits (NGCs) can be viewed as an advantageous alternative, but currently have limited efficacy for short and large injury gaps in comparison to autograft. Current commercially available NGC designs rely on existing regulatory approved materials and traditional production methods, limiting improvement of their design. The aim of this study was to establish a novel method for NGC manufacture using a custom built laser-based microstereolithography (μSL) setup that incorporated a 405 nm laser source to produce 3D constructs with ∼50 μm resolution from a photocurable poly(ethylene glycol) resin. These were evaluated by SEM, in vitro neuronal, Schwann and dorsal root ganglion culture and in vivo using a thy-1-YFP-H mouse common fibular nerve injury model. NGCs with dimensions of 1 mm internal diameter × 5 mm length with a wall thickness of 250 μm were fabricated and capable of supporting re-innervation across a 3 mm injury gap after 21 days, with results close to that of an autograft control. The study provides a technology platform for the rapid microfabrication of biocompatible materials, a novel method for in vivo evaluation, and a benchmark for future development in more advanced NGC designs, biodegradable and larger device sizes, and longer-term implantation studies

Dynamic Seeding and in Vitro Culture of Hepatocytes in a Flow Perfusion System

Our laboratory has investigated hepatocyte transplantation using biodegradable polymer matrices as an alternative treatment to end-stage liver disease. One of the major limitations has been the insufficient survival of an adequate mass of transplanted cells. This study investigates a novel method of dynamic seeding and culture of hepatocytes in a flow perfusion system. In experiment I, hepatocytes were flow-seeded onto PGA scaffolds and cultured in a flow perfusion system for 24 h. Overall metabolic activity and distribution of cells were assessed by their ability to reduce MTT. DNA quantification was used to determine the number of cells attached. Culture medium was analyzed for albumin content. In Experiment II, hepatocyte/polymer constructs were cultured in a perfusion system for 2 and 7 days. The constructs were examined by SEM and histology. Culture medium was analyzed for albumin. In experiment I, an average of 4.4 X 106 cells attached to the scaffolds by DNA quantification. Cells maintained a high metabolic activity and secreted albumin at a rate of 13 pg/cell/day. In experiment II, SEM demonstrated successful attachment of hepatocytes on the scaffolds after 2 and 7 days. Cells appeared healthy on histology and maintained a high rate of albumin secretion through day 7. Hepatocytes can be dynamically seeded onto biodegradable polymers and survive with a high rate of albumin synthesis in the flow perfusion culture system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63347/1/107632700320874.pd

Consumers mediate the effects of experimental ocean acidification and warming on primary producers

It is well known that ocean acidification can have profound impacts on marine organisms. However, we know little about the direct and indirect effects of ocean acidification and also how these effects interact with other features of environmental change such as warming and declining consumer pressure. In this study, we tested whether the presence of consumers (invertebrate mesograzers) influenced the interactive effects of ocean acidification and warming on benthic microalgae in a seagrass community mesocosm experiment. Net effects of acidification and warming on benthic microalgal biomass and production, as assessed by analysis of variance, were relatively weak regardless of grazer presence. However, partitioning these net effects into direct and indirect effects using structural equation modeling revealed several strong relationships. In the absence of grazers, benthic microalgae were negatively and indirectly affected by sediment-associated microalgal grazers and macroalgal shading, but directly and positively affected by acidification and warming. Combining indirect and direct effects yielded no or weak net effects. In the presence of grazers, almost all direct and indirect climate effects were nonsignificant. Our analyses highlight that (i) indirect effects of climate change may be at least as strong as direct effects, (ii) grazers are crucial in mediating these effects, and (iii) effects of ocean acidification may be apparent only through indirect effects and in combination with other variables (e.g., warming). These findings highlight the importance of experimental designs and statistical analyses that allow us to separate and quantify the direct and indirect effects of multiple climate variables on natural communities

Proteome studies of carp and frog exposed to endocrine disrupting compounds

Vitellogenin (Vtg) is a well established plasma biomarker for endocrine disrupting compounds with estrogenic properties in fish. In the EU-project EASYRING carp were exposed to estrogens (17\uf061-ethynyl-estradiol, EE2), anti-estrogens (tamoxifen), androgens (17\uf061-methyldihydrotestosterone), and anti-androgens (flutamide), as well as to caging in polluted stretches of the Rivers Po and Lambro in Northern Italy. Monoclonal antibodies to carp Vtg were used for specific detection of Vtg in 1D- and 2D-western blotting, and in a quantitative sandwich ELISA and a qualitative lateral flow immunoassay (LFIA) dipstick, for measuring Vtg levels in plasma and mucus. Proteomic-based analysis using 2D-gel electrophoresis and mass spectrometry (MALDI-TOF, LC-MS/MS) identified Vtg as a prominent protein in liver, plasma, and mucus after EE2 exposure. At 64 ng EE2/l induction of multiple Vtg forms was observed in all tissues analyzed. In plasma a total of 30 EE2 inducible Vtg spots was identified, a response accompanied by alterations in the levels of other proteins identified as novel biomarker candidates. The induction and presence of numerous Vtg forms was confirmed by 1-D and 2-D western blot analysis. Quantitative Vtg ELISA showed a dose-dependent increase in plasma and mucus-Vtg, significantly different from control after 4 ng EE2/l in mucus, and 16 ng EE2/l in plasma. Regression analysis of plasma vs. mucus Vtg levels gave strong positive correlations for all groups, except for the fish from tamoxifen and field exposure. Analysis of river sediments using YES revealed a mixture of estrogens, and anti-androgens, suggesting that plasma vs. mucus Vtg profiles may be influenced by the nature of endocrine disrupting chemicals present in the environment

A biodegradable and biocompatible gecko-inspired tissue adhesive

There is a significant medical need for tough biodegradable polymer adhesives that can adapt to or recover from various mechanical deformations while remaining strongly attached to the underlying tissue. We approached this problem by using a polymer poly(glycerol-co-sebacate acrylate) and modifying the surface to mimic the nanotopography of gecko feet, which allows attachment to vertical surfaces. Translation of existing gecko-inspired adhesives for medical applications is complex, as multiple parameters must be optimized, including: biocompatibility, biodegradation, strong adhesive tissue bonding, as well as compliance and conformability to tissue surfaces. Ideally these adhesives would also have the ability to deliver drugs or growth factors to promote healing. As a first demonstration, we have created a gecko-inspired tissue adhesive from a biocompatible and biodegradable elastomer combined with a thin tissue-reactive biocompatible surface coating. Tissue adhesion was optimized by varying dimensions of the nanoscale pillars, including the ratio of tip diameter to pitch and the ratio of tip diameter to base diameter. Coating these nanomolded pillars of biodegradable elastomers with a thin layer of oxidized dextran significantly increased the interfacial adhesion strength on porcine intestine tissue in vitro and in the rat abdominal subfascial in vivo environment. This gecko-inspired medical adhesive may have potential applications for sealing wounds and for replacement or augmentation of sutures or staples