The ultimate goal of tissue engineering is to replace damaged tissues by applying engineering technology and the principles of life sciences. To successfully engineer a desirable tissue, three main elements of cells, scaffolds and growth factors need to be harmonized. Biomaterial-based scaffolds serve as a critical platform both to support cell adhesion and to deliver growth factors. Various methods of fabricating scaffolds have been investigated. One recently developed method that is growing in popularity is called electrospinning. Electrospinning is known for its capacity to make fibrous and porous structures that are similar to natural extracellular matrix (ECM). Other advantages to electrospinning include its ability to create relatively large surface to volume ratios, its ability to control fiber size from micro- to nano-scales and its versatility in material choice. Although early work with electrospun fibers has shown promise in the regeneration of certain types of tissues, further modification of their chemical, biological and mechanical properties would permit future advancements. In this paper, current approaches to the development of modular electrospun fibers as scaffolds for tissue engineering are discussed. Their chemical and physical characteristics can be tuned for the regeneration of specific target tissues by co-spinning of multiple materials and by post-modification of the surface of electrospun fibers. In addition, topology or structure can also be controlled to elicit specific responses from cells and tissues. The selection of proper polymers, suitable surface modification techniques and the control of the dimension and arrangement of the fibrous structure of electrospun fibers can offer versatility and tissue specificity, and therefore provide a blueprint for specific tissue engineering applications.

No abstract

BackgroundEnteric Escherichia coli survives the highly acidic environment of the stomach through multiple acid resistance (AR) mechanisms. The most effective system, AR2, decarboxylates externally-derived glutamate to remove cytoplasmic protons and excrete GABA. The first described system, AR1, does not require an external amino acid. Its mechanism has not been determined. The regulation of the multiple AR systems and their coordination with broader cellular metabolism has not been fully explored.ResultsWe utilized a combination of ChIP-Seq and gene expression analysis to experimentally map the regulatory interactions of four TFs: nac, ntrC, ompR, and csiR. Our data identified all previously in vivo confirmed direct interactions and revealed several others previously inferred from gene expression data. Our data demonstrate that nac and csiR directly modulate AR, and leads to a regulatory network model in which all four TFs participate in coordinating acid resistance, glutamate metabolism, and nitrogen metabolism. This model predicts a novel mechanism for AR1 by which the decarboxylation enzymes of AR2 are used with internally derived glutamate. This hypothesis makes several testable predictions that we confirmed experimentally.ConclusionsOur data suggest that the regulatory network underlying AR is complex and deeply interconnected with the regulation of GABA and glutamate metabolism, nitrogen metabolism. These connections underlie and experimentally validated model of AR1 in which the decarboxylation enzymes of AR2 are used with internally derived glutamate.Electronic supplementary materialThe online version of this article (doi:10.1186/s12918-016-0376-y) contains supplementary material, which is available to authorized users.

Tissue engineering has become an alternative method to traditional surgical treatments for the repair of bone defects, and an appropriate scaffold supporting bone formation is a key element in this approach. In the present study, nanofibrous organic and inorganic composite scaffolds containing nano-sized demineralized bone powders (DBPs) with biodegradable poly(L-lactide) (PLA) were developed using an electrospinning process for engineering bone. To assess their biocompatibility, in vitro osteogenic differentiation of human mandible-derived mesenchymal stem cells (hMSCs) cultured on PLA or PLA/DBP composite nanofiber scaffolds were examined. The mineralization of hMSCs cultured with osteogenic supplements on the PLA/DBP nanofiber scaffolds was remarkably greater than on the PLA nanofiber scaffold during the first 14 days of culture but reached the same level after 21 days. The in vivo osteoconductive effect of PLA/DBP nanofibrous scaffolds was further investigated using rats with critical-sized skull defects. Micro-computerized tomography revealed that a greater amount of newly formed bone extended across the defect area in PLA/DBP scaffolds than in the nonimplant and PLA scaffolds 12 weeks after implantation and that the defect size was almost 90% smaller. Therefore, PLA/DBP composite nanofiber scaffolds may serve as a favorable matrix for the regeneration of bone tissue.

We fabricated composite fibrous scaffolds from blends of poly(lactide-co-glycolide) (PLGA) and nano-sized hydroxyapatite (HA) via electrospinning. SEM-EDX and AFM analysis demonstrated that HA was homogeneously dispersed in the nanofibers, and the roughness increased along with the amount of incorporated HA. When hMSCs were cultured on these PLGA/HA composite nanofibers, we found that incorporation of HA on the nanofibers did not affect cell viability whereas increased ALP activity and expression of osteogenic genes as well as the calcium mineralization of hMSCs. Our results indicate that the composite nanofibers can be offered as a potential bone regenerative biomaterial for stem cell based therapies.