Impact of exposure of crude oil and dispersant (Corexit) on aggregation of extracellular polymeric substances.

Spilled oil treated with Corexit dispersant can cause unintended impacts on marine environment systems including altering marine organic matter dynamics; however, impacts on microgels and marine oil snow (MOS) formation are still debated and remain to be fully understood. Extracellular polymeric substances (EPS) are a major source of marine organic carbon for MOS and microgel formation. EPS initial aggregation plays key roles in the oil degrading process and various biogeochemical reactions. Here we used four types of EPS with water accommodated fraction (WAF), chemically-enhanced WAF (CEWAF) and Corexit, to represent potential situations during oil spills and post-application of Corexit. We found that Corexit alone can inhibit EPS aggregation and disperse pre-existing microgels. CEWAF can enhance EPS aggregation with efficiency by up to 80%-100% and more aggregates accumulated within the air-water interface. Additionally, more hydrophobic EPS aggregates showed high resistance to Corexit dispersion while hydrophilic EPS were more sensitive. Effects of oil spills on marine gel particle formation are primarily determined by chemical characteristics (hydrophobicity and protein content) of the constituent EPS. This study offers unique insights for organic particle dynamics and identifies controlling factors for MOS or gel particles associated with oil spills and Corexit dispersant used.

The impact of nanoplastics on marine dissolved organic matter assembly.

The environmental impact of nanoplastics (NPs) released into natural aquatic surroundings is an increasing concern. NPs are widely generated from our daily waste disposal and eventually reach the ocean, wherein consequent influences on aquatic environments remain unclear. In this regard, there are few studies investigating NP-related ecological impacts. Comprising one of Earth's major carbon pools, marine dissolved organic matter (DOM) serves an essential role in global carbon dynamics. The spontaneous assembly of DOM into particulate organic matter (POM) plays important roles in the marine carbon cycle, and is involved in hemostasis of various ecological communities. Here, we report that 10 ppb NPs (polystyrene/polymethyl methacrylate, 25 nm) appeared in a water column accelerate the kinetic assembly rate of DOM-POM transition. NPs with various characteristics show similar influences on DOM assembly, and seawater samples collected from disparate sites were used to further confirm this unanticipated phenomenon. In this study, we demonstrated that hydrophobic interactions contribute to the facilitation of NP-DOM aggregations. Our results illustrate that NPs alter DOM-POM assembly, which may potentiate unanticipated perturbation to the largest marine carbon pool. Such effects would warrant increased vigilance on current practices of plastic usage and disposal.

Microgrooved Surface Modulates Neuron Differentiation in Human Embryonic Stem Cells.

Stem cell-based therapies have drawn intensive attention in the neuronal regenerative fields. Several studies have revealed that stem cells can serve as an inexhaustible source for neurons for transplantation therapies. However, generation of neurons and directionality has not yet been fully investigated. Herein, we investigate the mechanical ramifications of surface topography on human embryonic cell differentiation. Microgrooved surfaces with various pitches were applied to modulate the neuron differentiation. Our protocol showed that neuron differentiation increased as grove pitch decreased. The results indicated that 2 µm microgrooves can improve neuron growth by ~1.7-fold. Our results indicate the importance of mechanotransduction on neuronal differentiation and highlight the feasibility of manipulating the neuronal differentiation with surface topography, providing new perspectives for accommodating clinical transplantation.