Osteogenic differentiation of MC3T3-E1 cells on poly(L-lactide)/Fe3O4 nanofibers with static magnetic field exposure.

Proliferation and differentiation of bone-related cells are modulated by many factors such as scaffold design, growth factor, dynamic culture system, and physical simulation. Nanofibrous structure and moderate-intensity (1 mT-1 T) static magnetic field (SMF) have been identified as capable of stimulating proliferation and differentiation of osteoblasts. Herein, magnetic nanofibers were prepared by electrospinning mixture solutions of poly(L-lactide) (PLLA) and ferromagnetic Fe3O4 nanoparticles (NPs). The PLLA/Fe3O4 composite nanofibers demonstrated homogeneous dispersion of Fe3O4 NPs, and their magnetism depended on the contents of Fe3O4 NPs. SMF of 100 mT was applied in the culture of MC3T3-E1 osteoblasts on pure PLLA and PLLA/Fe3O4 composite nanofibers for the purpose of studying the effect of SMF on osteogenic differentiation of osteoblastic cells on magnetic nanofibrous scaffolds. On non-magnetic PLLA nanofibers, the application of external SMF could enhance the proliferation and osteogenic differentiation of MC3T3-E1 cells. In comparison with pure PLLA nanofibers, the incorporation of Fe3O4 NPs could also promote the proliferation and osteogenic differentiation of MC3T3-E1 cells in the absence or presence of external SMF. The marriage of magnetic nanofibers and external SMF was found most effective in accelerating every aspect of biological behaviors of MC3T3-E1 osteoblasts. The findings demonstrated that the magnetic feature of substrate and microenvironment were applicable ways in regulating osteogenesis in bone tissue engineering.

Enhanced osteogenic differentiation of mesenchymal stem cells on poly(L-lactide) nanofibrous scaffolds containing carbon nanomaterials.

Carbon nanomaterials (CNMs), such as carbon nanotube (CNT) and graphene, are highlighted in bone regeneration because of their osteoinductive properties. Their combinations with nanofibrous polymeric scaffolds, which mimic the morphology of natural extracellular matrix of bone, arouse keen interest in bone tissue engineering. To this end, CNM were incorporated into nanofibrous poly(L-lactic acid) scaffolds by thermal-induced phase separation. The CNM-containing composite nanofibrous scaffolds were biologically evaluated by both in vitro co-culture of bone mesenchymal stem cells (BMSCs) and in vivo implantation. The nanofibrous structure itself demonstrated significant enhancement in cell adhesion, proliferation and oseogenic differentiation of BMSCs, and with the incorporation of CNM, the composite nanofibrous scaffolds further promoted osteogenic differentiation of BMSCs significantly. Between the two CNMs, graphene showed stronger effect in promoting osteogenic differentiation of BMSCs than CNT. The results of in vivo experiments revealed that the composite nanofibrous scaffolds had both good biocompatibility and strong ability in inducing osteogenesis. CNMs could remarkably enhance the expression of osteogenesis-related proteins as well as the formation of type I collagen. Similarly, the graphene-containing composite nanofibrous scaffolds demonstrated the strongest effect on inducing osteogenesis in vivo. These findings demonstrated that CNM-containing composite nanofibrous scaffolds were obviously more efficient in promoting osteogenesis than pure polymeric scaffolds.

Electrospun biodegradable polyorganophosphazene fibrous matrix with poly(dopamine) coating for bone regeneration.

Biodegradable polyphosphazenes were categorized as osteoinductive materials because of their phosphorus-containing feature; however, they were less supportive in cell attachment and proliferation at earlier points in comparison with biodegradable aliphatic polyesters. Therefore, mussel-inspired surface modification of poly(alanine ethyl ester-co-glycine ethyl ester)phosphazene (PAGP) was studied, intending to circumvent the above-mentioned disadvantage of polyphosphazene. To this end, PAGP and poly(L-lactide) (PLLA) were electrospun into nanofibrous substrates and surface treated with dopamine aqueous solution. With the analysis of scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscope, and Fourier transform infrared spectroscope, the successful poly(dopamine) coating was identified on both PAGP and PLLA nanofibers. MC3T3-E1 osteoblasts were found attaching and proliferating much well on poly(dopamine)-modified nanofibrous substrates in comparison with the pristine ones. In addition, the poly(dopamine) coating demonstrated high activity in promoting osteogenous differentiation. Because the phosphorus content on nanofiber surface was decreased with the poly(dopamine) coating, the poly(dopamine)-coated PAGP nanofibrous substrate was slightly inferior to pure PAGP nanofibrous substrate in osteogenous differentiation. In a summary, the results confirmed that poly(dopamine)-modified polyphosphazenes were promising scaffold materials with both high cell affinity and high osteocompatibility for bone regeneration.

Thermo-sensitive graphene oxide-polymer nanoparticle hybrids: synthesis, characterization, biocompatibility and drug delivery.

We report the covalent interaction mediated assembly of thermo-sensitive polymer nanoparticles (PNPs) on functionalized graphene oxide (GO) nanosheets to create novel GO-PNP hybrids for drug delivery. To this end, thermo-sensitive PNPs with an average diameter of about 50 ± 12 nm were first synthesized with the free radical polymerization reaction, and GO nanosheets were noncovalently modified with a bifunctional linker to provide reactive sites for the binding of PNPs. Finally, GO-PNP hybrids were successfully synthesized by the covalent interaction mediated assembly of PNPs on GO nanosheets. Multi-characterization techniques were utilized to identify the formation of PNPs, the modification of GO nanosheets, and the formation of GO-PNP hybrids. Cell culture experiment with the mouse osteoblast-like MC3T3-E1 cells indicates that the synthesized GO-PNP hybrids have satisfactory biocompatibility. The loading efficiency of drug molecules (Adriamycin, ADR) with GO-PNP (∼87%) is close to that with GO (∼91%), but significantly higher than that with PNPs (∼46%). The release efficiency of GO-PNP hybrids with the highest surface coverage of PNPs (∼85 PNPs per µm2) is about 22%, which is very close to that of PNPs (∼25%) and significantly higher than that of GO (∼11%). Our study indicates that this thermo-sensitive GO-PNP hybrid, when considering the drug loading and release comprehensively, has better performance than both PNPs and GO and thus can be used as a novel nanocarrier for temperature-controllable drug release. The GO-PNP hybrids with and without ADR were applied to kill cancer cells in vitro and the result shows that the GO-PNP hybrid with ADR has an obvious effect on killing cancer cells, and its performance is obviously better than both GO and PNPs. It is expected that this new hybrid material based on GO and PNPs will have great potential for in vivo applications such as to kill target cancer cells by modifying with specific antibodies.

Electrospun magnetic poly(L-lactide) (PLLA) nanofibers by incorporating PLLA-stabilized Fe3O4 nanoparticles.

Magnetic poly(L-lactide) (PLLA)/Fe3O4 composite nanofibers were prepared with the purpose to develop a substrate for bone regeneration. To increase the dispersibility of Fe3O4 nanoparticles (NPs) in the PLLA matrix, a modified chemical co-precipitation method was applied to synthesize Fe3O4 NPs in the presence of PLLA. Trifluoroethanol (TFE) was used as the co-solvent for all the reagents, including Fe(II) and Fe(III) salts, sodium hydroxide, and PLLA. The co-precipitated Fe3O4 NPs were surface-coated with PLLA and demonstrated good dispersibility in a PLLA/TFE solution. The composite nanofiber electrospun from the solution displayed a homogeneous distribution of Fe3O4 NPs along the fibers using various contents of Fe3O4 NPs. X-ray diffractometer (XRD) and vibration sample magnetization (VSM) analysis confirmed that the co-precipitation process had minor adverse effects on the crystal structure and saturation magnetization (Ms) of Fe3O4 NPs. The resulting PLLA/Fe3O4 composite nanofibers showed paramagnetic properties with Ms directly related to the Fe3O4 NP concentration. The cytotoxicity of the magnetic composite nanofibers was determined using in vitro culture of osteoblasts (MC3T3-E1) in extracts and co-culture on nanofibrous matrixes. The PLLA/Fe3O4 composite nanofibers did not show significant cytotoxicity in comparison with pure PLLA nanofibers. On the contrary, they demonstrated enhanced effects on cell attachment and proliferation with Fe3O4 NP incorporation. The results suggested that this modified chemical co-precipitation method might be a universal way to produce magnetic biodegradable polyester substrates containing well-dispersed Fe3O4 NPs. This new strategy opens an opportunity to fabricate various kinds of magnetic polymeric substrates for bone tissue regeneration.

Paranodal myelin damage after acute stretch in Guinea pig spinal cord.

Mechanical injury causes myelin disruption and subsequent axonal conduction failure in the mammalian spinal cord. However, the underlying mechanism is not well understood. In mammalian myelinated axons, proper paranodal myelin structure is crucial for the generation and propagation of action potentials. The exposure of potassium channels at the juxtaparanodal region due to myelin disruption is thought to induce outward potassium currents and inhibit the genesis of the action potential, leading to conduction failure. Using multimodal imaging techniques, we provided anatomical evidence demonstrating paranodal myelin disruption and consequent exposure and redistribution of potassium channels following mechanical insult in the guinea pig spinal cord. Decompaction of paranodal myelin was also observed. It was shown that paranodal demyelination can result from both an initial physical impact and secondary biochemical reactions that are calcium dependent. 4-Aminopyridine (4-AP), a known potassium channel blocker, can partially restore axonal conduction, which further implicates the role of potassium channels in conduction failure. We provide important evidence of paranodal myelin damage, the role of potassium channels in conduction loss, and the therapeutic value of potassium blockade as an effective intervention to restore function following spinal cord trauma.