Colonization Characteristics of Bacterial Communities on Plastic Debris Influenced by Environmental Factors and Polymer Types in the Haihe Estuary of Bohai Bay, China.

The colonization characteristics of bacterial communities on microplastics or plastic debris (PD) have generated great concern in recent years. However, the influence of environmental factors and polymer types on the formation of bacterial communities on PD in estuarine areas is less studied. To gain additional insights, five types of PD (polyvinyl chloride, polypropylene, polyethylene, polystyrene, and polyurethane) were exposed for three-time periods (two weeks, four weeks, and six weeks) in the Haihe Estuary. 16S rRNA gene sequencing was used to identify the bacterial communities on PD, in seawater, and in sediment samples. The results indicate that the average growth rate of a biofilm is affected by nutrients (total nitrogen and total phosphorus) and salinity. Furthermore, salinity is the primary factor affecting bacterial diversity of the colonies on PD. In addition, genera of bacteria show selectivity toward the PD polymer type and tend to colonize their preferred substrate. Compared with seawater and sediment, PD could be carriers for enrichment of Vibrio in the estuarine environment with salinity ≥26 (± 2‰), which might increase the ecological risk of PD in marine environments.

Colonization characteristics of bacterial communities on microplastics compared with ambient environments (water and sediment) in Haihe Estuary.

The bacterial communities on microplastics in marine and freshwater environments have been described by many studies. However, the migration and transportation processes of bacterial communities on microplastics in estuarine areas remain unclear. In this study, the bacterial communities on three substrates (microplastics, surface water and sediment) in estuarine areas (the Haihe Estuary (HHE) in Bohai Bay, China) were investigated based on 16S rRNA sequencing. The mean OTUs of the three substrates - water, microplastics and sediments - were 1091, 2213 and 3419, respectively. The partitioning of the OTUs among the three substrates indicated that the microplastics could be messengers facilitating the bacterial transportation between water and sediment. According to nMDS and relative abundance analyses, it was found that the microplastics enriched the particular bacteria (e.g., Halobacteriaceae and Pseudoalteromonadaceae) and weakened the influence of environmental variation. In addition, taxonomic and metabolic-pathway analyses indicated that the abundance of potentially pathogenic bacteria (e.g., Pseudomonas and Bacillus) on microplastics was significantly higher than that in the ambient environment. Meanwhile, the microplastic polymer types had little effect on the abundance and structure of the bacterial communities. Compared with surface water and sediments, microplastics could be a good habitat for bacterial communities and could lead to potential ecological risks because of the high stability, pathogenicity and stress tolerance of the bacterial communities on microplastics.

Silk-Hydroxyapatite Nanoscale Scaffolds with Programmable Growth Factor Delivery for Bone Repair.

Osteoinductive biomaterials are attractive for repairing a variety of bone defects, and biomimetic strategies are useful toward developing bone scaffolds with such capacity. Here, a multiple biomimetic design was developed to improve the osteogenesis capacity of composite scaffolds consisting of hydroxyapatite nanoparticles (HA) and silk fibroin (SF). SF nanofibers and water-dispersible HA nanoparticles were blended to prepare the nanoscaled composite scaffolds with a uniform distribution of HA with a high HA content (40%), imitating the extracellular matrix (ECM) of bone. Bone morphogenetic protein-2 (BMP-2) was loaded in the SF scaffolds and HA to tune BMP-2 release. In vitro studies showed the preservation of BMP-2 bioactivity in the composite scaffolds, and programmable sustained release was achieved through adjusting the ratio of BMP-2 loaded on SF and HA. In vitro and in vivo osteogenesis studies demonstrated that the composite scaffolds showed improved osteogenesis capacity under suitable BMP-2 release conditions, significantly better than that of BMP-2 loaded SF-HA composite scaffolds reported previously. Therefore, these biomimetic SF-HA nanoscaled scaffolds with tunable BMP-2 delivery provide preferable microenvironments for bone regeneration.

Silk scaffolds with tunable mechanical capability for cell differentiation.

Bombyx mori silk fibroin is a promising biomaterial for tissue regeneration and is usually considered an "inert" material with respect to actively regulating cell differentiation due to few specific cell signaling peptide domains in the primary sequence and the generally stiffer mechanical properties due to crystalline content formed in processing. In the present study, silk fibroin porous 3D scaffolds with nanostructures and tunable stiffness were generated via a silk fibroin nanofiber-assisted lyophilization process. The silk fibroin nanofibers with high ß-sheet content were added into the silk fibroin solutions to modulate the self-assembly, and to directly induce water-insoluble scaffold formation after lyophilization. Unlike previously reported silk fibroin scaffold formation processes, these new scaffolds had lower overall ß-sheet content and softer mechanical properties for improved cell compatibility. The scaffold stiffness could be further tuned to match soft tissue mechanical properties, which resulted in different differentiation outcomes with rat bone marrow-derived mesenchymal stem cells toward myogenic and endothelial cells, respectively. Therefore, these silk fibroin scaffolds regulate cell differentiation outcomes due to their mechanical features.