Hierarchical Self‐Assembly of Poly‐Pseudorotaxanes into Artificial Microtubules

Hierarchical self‐assembly of building blocks over multiple length scales is ubiquitous in living organisms. Microtubules are one of the principal cellular components formed by hierarchical self‐assembly of nanometer‐sized tubulin heterodimers into protofilaments, which then associate to form micron‐length‐scale, multi‐stranded tubes. This peculiar biological process is now mimicked with a fully synthetic molecule, which forms a 1:1 host‐guest complex with cucurbit[7]uril as a globular building block, and then polymerizes into linear poly‐pseudorotaxanes that associate laterally with each other in a self‐shape‐complementary manner to form a tubular structure with a length over tens of micrometers. Molecular dynamic simulations suggest that the tubular assembly consists of eight poly‐pseudorotaxanes that wind together to form a 4.5 nm wide multi‐stranded tubule.     

Bilayer Cylindrical Conduit Consisting of Electrospun Polycaprolactone Nanofibers and DSC Cross‐Linked Sodium Alginate Hydrogel to Bridge Peripheral Nerve Gaps

Herein, a bilayer cylindrical conduit (P‐CA) is presented consisting of electrospun polycaprolactone (PCL) nanofibers and sodium alginate hydrogel covalently cross‐linked with N,N′‐disuccinimidyl carbonate (DSC). The bilayer P‐CA conduit is developed by combining the electrospinning and outer–inner layer methods. Using DSC, as a covalent crosslinker, increases the degradation time of the sodium alginate hydrogel up to 2 months. The swelling ratio of the hydrogel is also 503% during the first 8 h. The DSC cross‐linked sodium alginate in the inner layer of the conduit promotes the adhesion and proliferation of nerve cells, while the electrospun PCL nanofibers in the outer layer provide maximum tensile strength of the conduit during surgery. P‐CA conduit promotes the migration of Schwann cells along the axon in a rat model based on functional and histological evidences. In conclusion, P‐CA conduit will be a promising construct for repairing sciatic nerves in a rat model.     

A Multi‐Wall Sn/SnO2@Carbon Hollow Nanofiber Anode Material for High‐Rate and Long‐Life Lithium‐Ion Batteries

Multi‐wall Sn/SnO₂@carbon hollow nanofibers evolved from SnO₂ nanofibers are designed and programable synthesized by electrospinning, polypyrrole coating, and annealing reduction. The synthesized hollow nanofibers have a special wire‐in‐double‐wall‐tube structure with larger specific surface area and abundant inner spaces, which can provide effective contacting area of electrolyte with electrode materials and more active sites for redox reaction. It shows excellent cycling stability by virtue of effectively alleviating pulverization of tin‐based electrode materials caused by volume expansion. Even after 2000 cycles, the wire‐in‐double‐wall‐tube Sn/SnO₂@carbon nanofibers exhibit a high specific capacity of 986.3 mAh g^?1 (1 A g^?1) and still maintains 508.2 mAh g^?1 at high current density of 5 A g^?1. This outstanding electrochemical performance suggests the multi‐wall Sn/SnO₂@ carbon hollow nanofibers are great promising for high performance energy storage systems.     

Development of a Piezoelectric PVDF‐TrFE Fibrous Scaffold to Guide Cell Adhesion,Proliferation, and Alignment

Severe peripheral nervous system injuries currently hold limited therapeutic solutions. Existing clinical techniques such as autografts, allografts, and newer nerve guidance conduits have shown variable outcomes in functional recovery, adverse immune responses, and in some cases low or minimal availability. This can be attributed in part to the lack of chemical, physical, and electrical cues directing both nerve guidance and regeneration. To address this pressing clinical issue, electrospun nanofibers and microfibers composed of piezoelectric polyvinylidene flouride‐triflouroethylene (PVDF‐TrFE) have been introduced as an alternative template for tissue engineered biomaterials, specifically as it pertains to their relevance in soft tissue and nerve repair. Here, biocompatible scaffolds of PVDF‐TrFE are fabricated and their ability to generate an electrical response to mechanical deformations and produce a suitable regenerative microenvironment is examined. It is determined that 20% (w/v) PVDF‐TrFE in (6:4) dimethyl formamide (DMF):acetone solvent maintains a desirable piezoelectric coefficient and the proper physical and electrical characteristics for tissue regeneration. Further, it is concluded that scaffolds of varying thickness promoted the adhesion and alignment of Schwann cells and fibroblasts. This work offers a prelude to further advancements in nanofibrous technology and a promising outlook for alternative, autologous remedies to peripheral nerve damage.     

Facile Fabrication of Ce/V‐Modified Multi‐Channel TiO2 Nanotubes and Their Enhanced Selective Catalytic Reduction Performance

To optimize one‐dimensional (1D) TiO₂ nanofibers, tailor‐made multi‐channel TiO₂ nanotubes have been successfully fabricated by electrospinning technology. After loading with Ce and V, the CeVTi‐tube catalyst exhibited a broad working temperature window and acceptable resistance to H₂O and SO₂ for elimination of NO_x. The corresponding analysis revealed that the multi‐channel structure provided more surface adsorbed oxygen species and that the wall of nanotubes anchored active components efficiently, which was beneficial to improve the stability as well as dispersion of the active components. Besides, a synergistic effect between Ce and V easily occurred at the CeVTi‐tube catalyst, and its reducibility was significantly improved since the electron transformation between Ce and V was dramatically enhanced. Consequently, the tailor‐made multi‐channel CeVTi‐tube catalyst exhibited satisfied de‐NO_x efficiency at the temperature range of 220–460 °C. It seemed that the multi‐channel TiO₂ nanotubes hold great potential as an excellent carrier for SCR catalysts.     

Micro‐Nanostructures of Cellulose‐Collagen for Critical Sized Bone Defect Healing

Bone tissue engineering strategies utilize biodegradable polymeric matrices alone or in combination with cells and factors to provide mechanical support to bone, while promoting cell proliferation, differentiation, and tissue ingrowth. The performance of mechanically competent, micro‐nanostructured polymeric matrices, in combination with bone marrow stromal cells (BMSCs), is evaluated in a critical sized bone defect. Cellulose acetate (CA) is used to fabricate a porous microstructured matrix. Type I collagen is then allowed to self‐assemble on these microstructures to create a natural polymer‐based, micro‐nanostructured matrix (CAc). Poly (lactic‐co‐glycolic acid) matrices with identical microstructures serve as controls. Significantly higher number of implanted host cells are distributed in the natural polymer based micro‐nanostructures with greater bone density and more uniform cell distribution. Additionally, a twofold increase in collagen content is observed with natural polymer based scaffolds. This study establishes the benefits of natural polymer derived micro‐nanostructures in combination with donor derived BMSCs to repair and regenerate critical sized bone defects. Natural polymer based materials with mechanically competent micro‐nanostructures may serve as an alternative material platform for bone regeneration.     

组织工程治疗大鼠失神经肌萎缩的实验研究

探讨用骨髓基质细胞构建组织工程神经修复坐骨神经损伤的方法使失神经骨骼肌重获神经再支配的可行性.用80只Wistar大鼠随机分为4组,每组20只.除对照组(A组)外,其他组切断右侧坐骨神经5mm建立腓肠肌失神经实验模型,硅胶管桥接神经两断端.B组将BMSCs ECM凝胶(约1×106/mL)植入硅胶管内;C组硅胶管内植入同样稀释后的ECM凝胶;D组硅胶管内注满生理盐水.术后观察功能恢复及肌肉萎缩情况.14周进行电生理检查、再生轴突染色及肌肉形态学的检查.检测失神经腓肠肌是否重新获得再生轴突的再支配.结果表明:骨髓基质细胞组术后14周可检测到新生轴突,其再生的轴突与靶肌肉已经建立神经突触连接.肌肉萎缩情况及电生理指标明显优于术后其他各组.组织工程人工神经修复坐骨神经断伤能够使远端失神经骨骼肌重新获得神经再支配.     

Methylcobalamin‐Loaded PLCL Conduits Facilitate the Peripheral Nerve Regeneration

The feasible fabrication of nerve guidance conduits (NGCs) with good biological performance is important for translation in clinics. In this study, poly(d ,l ‐lactide‐co‐caprolactone) (PLCL) films loaded with various amounts (wt; 5%, 15%, 25%) of methylcobalamin (MeCbl) are prepared, and are further rolled and sutured to obtain MeCbl‐loaded NGCs. The MeCbl can be released in a sustainable manner up to 21 days. The proliferation and elongation of Schwann cells, and the proliferation of Neuro2a cells are enhanced on these MeCbl‐loaded films. The MeCbl‐loaded NGCs are implanted into rats to induce the regeneration of 10 mm amputated sciatic nerve defects, showing the ability to facilitate the recovery of motor and sensory function, and to promote myelination in peripheral nerve regeneration. In particular, the 15% MeCbl‐loaded PLCL conduit exhibits the most satisfactory recovery of sciatic nerves in rats with the largest diameter and thickest myelinated fibers.     

A Self‐Growing Strategy for Large‐Scale Crystal Assembly Tubes

Assembled tubular materials have attracted widespread attention due to their potential applications in catalysis, bionics, and optic‐electronics. Many versatile methods, including template assistance and self‐assembly, have been developed for fabrication of tubular materials. Here we demonstrate a self‐growing strategy to prepare large‐scale crystal assembly tubes. Addition of the template and the need for the sophisticated equipment are avoided with this method. The sidewall of the tubes is composed of a layer of polyhedral crystals that are connected together through grain coalescence. We demonstrate that the assembled tubular structure is obtained by the synergetic effect of the passivation layer and the dissolution‐recrystallization process. This facile one‐step strategy and the formation mechanism will offer guidance for fabrication of new superstructures.     

Electrochemical Properties of Fiber‐in‐Tube‐ and Filled‐Structured TiO2 Nanofiber Anode Materials for Lithium‐Ion Batteries

Phase‐pure anatase TiO₂ nanofibers with a fiber‐in‐tube structure were prepared by the electrospinning process. The burning of titanium‐oxide‐carbon composite nanofibers with a filled structure formed as an intermediate product under an oxygen atmosphere produced carbon‐free TiO₂ nanofibers with a fiber‐in‐tube structure. The sizes of the nanofiber core and hollow nanotube were 140 and 500 nm, respectively. The heat treatment of the electrospun nanofibers at 450 and 500 °C under an air atmosphere produced grey and white filled‐structured TiO₂ nanofibers, respectively. The initial discharge capacities of the TiO₂ nanofibers with the fiber‐in‐tube and filled structures and the commercial TiO₂ nanopowders were 231, 134, and 223 mA h g^?1, respectively, and their corresponding charge capacities were 170, 100, and 169 mA h g^?1, respectively. The 1000th discharge capacities of the TiO₂ nanofibers with the fiber‐in‐tube and filled structures and the commercial TiO₂ nanopowders were 177, 64, and 101 mA h g^?1, respectively, and their capacity retentions measured from the second cycle were 89, 82, and 52 %, respectively. The TiO₂ nanofibers with the fiber‐in‐tube structure exhibited low charge transfer resistance and structural stability during cycling and better cycling and rate performances than the TiO₂ nanofibers with filled structures and the commercial TiO₂ nanopowders.     

Nanoparticle‐enhanced bamboo‐like tubular nanofibers for active capture of particulate matter

We proposed a thought of active capture of particles by improving the interaction force between fibers and particles. Nanoparticle‐enhanced tubular nanofibers (Ag‐SPNTs) were prepared by template‐free cationic polymerization followed by surface modification. Ag‐SPNTs have coarse surface and bamboo‐like tubular structure with a diameter of approximately 80‐150 nm. Ag nanoparticles were embedded on the nanofibers surface, and the content of Ag nanoparticles in the nanofibers could be tuned by changing the concentration of [Ag(NH₃)₂]⁺ in the preparation process. f‐d curve measured by AFM showed that increasing the content of Ag nanoparticles in the nanofibers resulted in the enhanced interaction force between the nanofiber surface and particles. Particle matter capture test showed that the number of captured microscaled/naonoscaled particles on the fiber surface increased obviously for the nanoparticle‐enhanced tubular nanofibers (Ag‐SPNTs) compared to the nanofibers without nanoparticle (SPNTs), probably due to the increased interaction force and adhesion energy between fiber surface and particles. Filtration property test showed that the Ag‐SPNTs fiber films had a better filtration performance with a higher filter efficiency and QF value than that of SPNTs. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019     

Non‐Covalent Interactions Enable the Length‐Controlled Generation of Discrete Tubes Capable of Guest Exchange

Supramolecular chemistry in confined spaces constructed from macrocyclic molecules has attracted much attention because it can utilize the specific binding properties of macrocyclic cavities. Herein we report the preparation of length‐controlled discrete tubular structures by homo‐/co‐assembly of rim‐differentiated and peralkylamino‐substituted pillar[5]arenes via hydrogen bonds and salt bridges. By dimerization and trimerization, the expanded tubes show a fivefold helical structure and stepwise binding, respectively. We found that the exchange speed of guest molecules in the tubes could be controlled by varying the tube length.     

Biodegradable glutaraldehyde-crosslinked casein conduit promotes regeneration after peripheral nerve injury in adult rats

In this study, GCC protein was used for the first time to construct a biodegradable conduit for peripheral nerve repair. The GCC was highly stable with a sufficiently high level of mechanical properties and it was non-toxic and non-apoptotic which could maintain the survival and outgrowth of Schwann cells. Noninvasive bioluminescence imaging accompanied with histochemical assessment showed the GCC was highly biocompatible after subcutaneous implantation in transgenic mice. Electrophysiology, labeling of calcitonin gene-related peptide in the lumbar spinal cord and histology analysis also showed a rapid morphological and functional recovery for disrupted rat sciatic nerves repaired with the GCC conduits. Therefore, we conclude that the GCC can offer great nerve regeneration characteristics and can be a promising material for the successful repair of peripheral nerve defects.     

Hollow Nanotubes of N‐Doped Carbon on CoS

Low‐cost, single‐step synthesis of hollow nanotubes of N‐doped carbon deposited on CoS is enabled by the simultaneous use of three functionalities of polyacrylonitrite (PAN) nanofibers: 1) a substrate for loading active materials, 2) a sacrificial template for creating hollow tubular structures, and 3) a precursor for in situ nitrogen doping. The N‐doped carbon in hollow tubes of CoS provides a high‐capacity anode of long cycle life for a rechargeable Li‐ion or Na‐ion battery cell that undergoes the conversion reaction 2 A⁺+2 e^?+CoS →Co+A₂S with A=Li or Na.     

Tubular Morphology of Mesoporous Silica MCM‐41

We investigated detailed conditions for synthesizing the tubular form of MCM‐41 mesoporous aluminosilicate. The method is the delayed neutralization method in which the rate of neutralization is one of the controlling factors. Rapid neutralization results in the particulate form while gradual neutralization leads to tubules. It is found that the tubule morphology has several sub‐categories. There are thick‐walled, think‐walled hollow tubular MCM‐41 and solid core tubules. There are void structures in the channel framework that makes the nanochannels to be effectively interconnected.     

Self‐Rolled Porous Hollow Tubes Made up of Biodegradable Polymers

A tubular highly porous scaffold of polylactide (PLA) and poly‐ε‐caprolactone (PCL) is fabricated by self‐rolling of a 2D fibrous bilayer of PLA and PCL in water without use of any classical thermo‐/pH‐responsive polymers. The self‐rolling and diameter of the tube are dependent upon the bilayer thickness and temperature. A 75 µm thick 2D bilayer (PLA = 25 µm; PCL = 50 µm) rolls to a hollow tube of diameter around 0.41 mm with multilayered wall at 40 °C within 5 min. The tubes keep their form and size in water at all temperatures once they are formed. The interesting properties of the hollow tubes, that is, permeation of gases through the walls and flow of water without leakage under tested conditions in combination with good mechanical stability, use of only biodegradable polymers, and easy and reproducible fabrication method, allow them to be promising candidates for future studies as scaffolds for tissue engineering.

     

Controllable Fabrication of TiO2 1D‐Nano/Micro Structures: Solid,Hollow, and Tube‐in‐Tube Fibers by Electrospinning and the Photocatalytic Performance

The solid, hollow, and tube‐in‐tube porous nanofiber structures of TiO₂ are synthesized successfully by a simple non‐coaxial electrospinning method without using a complicated coaxial jet head, combined with adjusting the concentration of the TiO₂ precursor and the pinhole diameter of the jet head and by final calcination. The formation mechanisms of different structured TiO₂ fibers are discussed in detail. This method is facile and effective, and easy to scale up. Furthermore, it is a versatile method for constructing tube‐in‐tube fibers of other metal oxides such as ZrO₂, SiO₂, SnO₂, and In₂O₃. The photocatalytic activity of tubular TiO₂ nanofibers for the degradation of 2‐chlorophenol and 2,4‐dichlorophenol under UV or visible‐light irradiation is better than the one of commercial available TiO₂ powder, rutile, and anatase TiO₂ fibers.     

Continuous Reversible Addition‐Fragmentation Chain Transfer Polymerization in Miniemulsion Utilizing a Multi‐Tube Reaction System

Summary: A unique, multi‐tube, continuous reactor has been successfully designed and implemented for the study of reversible addition‐fragmentation chain transfer (RAFT) in miniemulsions. Data collection is greatly enhanced by the ability to simultaneously collect samples at five different residence times. The results of a styrene homopolymerization show that kinetically, the reactor exhibits similar behavior to a batch reaction. Number‐average molecular weights increased linearly with conversion, typical of living polymerizations.

The number‐average molecular weight of the polymers produced in the tubular reactor increased linearly with conversion, indicative of a controlled polymerization.     

Point‐to‐Plane Nonhomogeneous Electric‐Field‐Induced Simultaneous Formation of Giant Unilamellar Vesicles (GUVs) and Lipid Tubes

It is well‐known that homogeneous electric fields can be used to generate giant unilamellar vesicles (GUVs). Herein we report an interesting phenomenon of formation of GUVs and lipid tubes simultaneously using a nonhomogeneous electric field generated by point‐to‐plane electrodes. The underlying mechanism was analyzed using finite element analysis. The two forces play main roles, that is, the pulling force (F) to drag GUVs into lipid tubes induced by fluid flow, and the critical force (Fc) to prevent GUVs from deforming into lipid tubes induced by electric fields. In the center area underneath the needle electrode, the GUVs were found because F is less than Fc in that region, whereas in the edge area the lipid tubes were obtained because F is larger than Fc. The diffusion coefficient of lipid in the tubes was found to be 4.45 μm² s^?1 using a fluorescence recovery after photobleaching (FRAP) technique. The method demonstrated here is superior to conventional GUV or lipid tube fabrication methods, and has great potential in cell mimic or hollow material fabrication using GUVs and tubes as templates.     

Self‐Assembled Peptide‐Based Hydrogels as Scaffolds for Proliferation and Multi‐Differentiation of Mesenchymal Stem Cells

Fluorenyl‐9‐methoxycarbonyl (Fmoc)‐diphenylalanine (Fmoc‐FF) and Fmoc‐arginine‐glycine‐­aspartate (Fmoc‐RGD) peptides self‐assemble to form a 3D network of supramolecular hydrogel (Fmoc‐FF/Fmoc‐RGD), which provides a nanofibrous network that uniquely presents bioactive ligands at the fiber surface for cell attachment. In the present study, mesenchymal stem cells (MSCs) in Fmoc‐FF/Fmoc‐RGD hydrogel increase in proliferation and survival compared to those in Fmoc‐FF/Fmoc‐RGE hydrogel. Moreover, MSCs encapsulated in Fmoc‐FF/Fmoc‐RGD hydrogel and induced in each defined induction medium undergo in vitro osteogenic, adipogenic, and chondrogenic differentiation. For in vivo differentiation, MSCs encapsulated in hydrogel are induced in each defined medium for one week, followed by injection into gelatin sponges and transplantation into immunodeficient mice for four weeks. MSCs in Fmoc‐FF/Fmoc‐RGD hydrogel increase in differentiation into osteogenic, adipogenic, and chondrogenic differentiation, compared to those in Fmoc‐FF/Fmoc‐RGE hydrogel. This study concludes that nanofibers formed by the self‐assembly of Fmoc‐FF and Fmoc‐RGD are suitable for the attachment, proliferation, and multi‐differentiation of MSCs, and can be applied in musculoskeletal tissue engineering.