Wrapping silicon microparticles by using well-dispersed single-walled carbon nanotubes for the preparation of high-performance lithium-ion battery anode.

Silicon microparticles (SiMPs) show considerable promise as an anode material in high-performance lithium-ion batteries (LIBs) because of their low-cost starting material and high capacity. The failure issues associated with the intrinsically low conductivity and significant volume expansion of Si have largely been resolved by designing silicon/carbon composites using carbon nanotubes (CNTs). The CNTs are important in terms of stress dissipation and the conductive network in Si/CNT composites. Here, we synthesized a SiMP/2D CNT sheet wrapping composite (SiMP/CNT wrapping) via a facile freeze-drying method with the use of highly dispersed single-walled CNTs. In this work, the well-dispersed CNTs are easily mixed with Si, resulting in effective CNT wrapping on the SiMP surface. During freeze-drying, the CNTs are self-assembled into a segregated 2D CNT sheet morphology via van der Waals interactions. The resulting CNT wrapping shows a unique wide range of conductive networks and mesh-like CNT sheets with void spaces. The SiMP/CNT wrapping 9 : 1 electrode exhibits good rate and cycle performance. The first charge/discharge capacity of SiMP/CNT wrapping 9 : 1 is 3160.7 mA h g-1/3469.1 mA h g-1 at 0.1 A g-1 with superior initial coulombic efficiency of 91.11%. After cycling, the SiMP/CNT wrapping electrode shows good structural integrity with preserved electrical conductivity. The superior electrochemical performance of the SiMP/CNT wrapping composite can be explained by an extensive conductive CNT network on the SiMPs and facile lithium-ion diffusion via mesh-like CNT wrapping.

3D Cell Printing of Functional Skeletal Muscle Constructs Using Skeletal Muscle-Derived Bioink.

Engineered skeletal muscle tissues that mimic the structure and function of native muscle have been considered as an alternative strategy for the treatment of various muscular diseases and injuries. Here, it is demonstrated that 3D cell-printing of decellularized skeletal muscle extracellular matrix (mdECM)-based bioink facilitates the fabrication of functional skeletal muscle constructs. The cellular alignment and the shape of the tissue constructs are controlled by 3D cell-printing technology. mdECM bioink provides the 3D cell-printed muscle constructs with a myogenic environment that supports high viability and contractility as well as myotube formation, differentiation, and maturation. More interestingly, the preservation of agrin is confirmed in the mdECM, and significant increases in the formation of acetylcholine receptor clusters are exhibited in the 3D cell-printed muscle constructs. In conclusion, mdECM bioink and 3D cell-printing technology facilitate the mimicking of both the structural and functional properties of native muscle and hold great promise for producing clinically relevant engineered muscle for the treatment of muscular injuries.

Tailoring mechanical properties of decellularized extracellular matrix bioink by vitamin B2-induced photo-crosslinking.

We have developed two-step process that uses sequential vitamin B2-induced UVA crosslinking and thermal gelation to solidify decellularized extracellular matrix (dECM) bioink; this process enables tailoring of mechanical properties of 3D-printed bioconstructs. This is the first evaluation of vitamin B2 for use in 3D bioprinting. The developed printing process offers easy control of the width of printed lines, and can therefore ensure that functional living tissue in printed with high fidelity. Using a dECM bioink combination that mimics a native microenvironment, a bioconstruct was designed to match the biomechanical properties of native cardiac tissue. The printed bioconstruct supported high cell viability and active proliferation of cardiac progenitor cells, and ultimately increased cardiomyogenic differentiation. This printing strategy is an additional tool for regulating biomechanical cues, and therefore provides new approaches to dECM-based cell printing. STATEMENT OF SIGNIFICANCE: 3D cell printing is an emerging strategy to create an engineered tissue construct by depositing biological components. The printable material used while printing cells is called "bioink"; to prevent cell damage during printing process. Recent development of printable tissue-specific dECM bioink has enabled 3D fabrication of tissues that are much more functionally matched than their predecessors. Demand for a method to tailor the mechanical properties of dECM bioink to improve both printability and tissue function has increased; thus, we here describe mechanical tailoring of dECM bioink by using vitamin B2 and UVA irradiation. By using this approach, we could fabricate a bioconstruct that has stiffness similar to that of the target tissue.

Engineered ECM-like microenvironment with fibrous particles for guiding 3D-encapsulated hMSC behaviours.

The alginate hydrogel has been used as an attractive scaffold for tissue regeneration. In particular, its simple cross-linking, high water absorption, and biocompatibility have facilitated its utility in regulating the interaction with cells or organs. However, three-dimensional (3D) networks of the alginate hydrogel do not provide fibrous anchorage sites such as the collagen fibres in the natural extracellular matrix (ECM). This has partially limited the survival of anchorage-dependent cells in the 3D hydrogel environment. In this report, we established a hybrid hydrogel containing fibrous particles (FP) that closely mimics the ECM. The RGD peptide-coupled FP (R-FP) has a wide range of distribution and was homogeneously dispersed in the hydrogel. The encapsulated human mesenchymal stem cells in the hydrogel could bind to the R-FP presenting remarkable spreading morphology, augmented viability and differentiation. These findings may elicit the significance of a physical interaction in which the R-FP provides structural and biological cues to the cells. This strategy can be widely applicable to a variety of hydrogel systems.

Hydrogen-bonding-facilitated layer-by-layer growth of ultrathin organic semiconducting films.

We demonstrated that the layer-by-layer growth of thin film crystals of conjugated organic molecules is facilitated by their hydrogen-bonding capabilities. We synthesized bis(3-hydroxypropyl)-sexithiophene (bHP6T), which includes two hydroxyalkyl groups that promote interlayer and intermolecular molecular interactions during the crystal growth process. Under the optimal deposition conditions, the crystals grew in a nearly perfect layer-by-layer mode on the solid substrate surfaces, enabling the formation of uniform charge transporting films as thin as a few monolayers. A thin film transistor device prepared from a bHP6T film only 9 nm thick exhibited a charge carrier mobility well above 1 × 10(-2) cm(2)/(V s) and an on/off ratio exceeding 1 × 10(4). These properties are better than the properties of other sexithiophene-based devices yet reported. The devices exhibited enhanced stability under atmospheric conditions, and they functioned properly, even after storage for more than 2 months.

Catechol-functionalized chitosan/pluronic hydrogels for tissue adhesives and hemostatic materials.

Bioinspired from adhesion behaviors of mussels, injectable and thermosensitive chitosan/Pluronic composite hydrogels were synthesized for tissue adhesives and hemostatic materials. Chitosan conjugated with multiple catechol groups in the backbone was cross-linked with terminally thiolated Pluronic F-127 triblock copolymer to produce temperature-sensitive and adhesive sol-gel transition hydrogels. A blend mixture of the catechol-conjugated chitosan and the thiolated Pluronic F-127 was a viscous solution state at room temperature but became a cross-linked gel state with instantaneous solidification at the body temperature and physiological pH. The adhesive chitosan/Pluronic injectable hydrogels with remnant catechol groups showed strong adhesiveness to soft tissues and mucous layers and also demonstrated superior hemostatic properties. These chitosan/Pluronic hydrogels are expected to be usefully exploited for injectable drug delivery depots, tissue engineering hydrogels, tissue adhesives, and antibleeding materials.

Controlled gene-eluting metal stent fabricated by bio-inspired surface modification with hyaluronic acid and deposition of DNA/PEI polyplexes.

A metal stent that could elute plasmid DNA (pDNA) in a controlled manner for substrate-mediated gene transfection was fabricated by first coating with hyaluronic acid (HA) and subsequent deposition of pDNA. To create robust HA coating layer on stainless steel (SS316L) surface, HA was derivatized with dopamine which is a well-known adsorptive molecule involving mussel adhesion process. The HA-coated surface was verified by various analytical techniques and proved to be very hydrophilic and stable, also showing superior biocompatibility in terms of suppressed plasma protein adsorption. For surface loading of pDNA, cationic pDNA/polyethylenimine (PEI) polyplexes were prepared and ionically adsorbed onto the HA-coated SS316L surface. The adsorbed surface exhibited evenly distributed nano-granular topography while the polyplexes maintained the nano-particular morphology. The pDNA was released out in a controlled manner for a period of 10 days with maintaining structural integrity. The dual coated substrate with HA and pDNA/PEI polyplexes exhibited greatly enhanced gene transfection efficiency, when compared to both bare substrate adsorbed with the polyplexes and PEI/pDNA polyelectrolyte multilayers. Dually functionalized stent with HA and pDNA exhibited effective biocompatibility and gene transfection.

Surface-functionalized electrospun nanofibers for tissue engineering and drug delivery.

Electrospun nanofibers with a high surface area to volume ratio have received much attention because of their potential applications for biomedical devices, tissue engineering scaffolds, and drug delivery carriers. In order to develop electrospun nanofibers as useful nanobiomaterials, surfaces of electrospun nanofibers have been chemically functionalized for achieving sustained delivery through physical adsorption of diverse bioactive molecules. Surface modification of nanofibers includes plasma treatment, wet chemical method, surface graft polymerization, and co-electrospinning of surface active agents and polymers. A variety of bioactive molecules including anti-cancer drugs, enzymes, cytokines, and polysaccharides were entrapped within the interior or physically immobilized on the surface for controlled drug delivery. Surfaces of electrospun nanofibers were also chemically modified with immobilizing cell specific bioactive ligands to enhance cell adhesion, proliferation, and differentiation by mimicking morphology and biological functions of extracellular matrix. This review summarizes surface modification strategies of electrospun polymeric nanofibers for controlled drug delivery and tissue engineering.

Controlled release of paclitaxel from heparinized metal stent fabricated by layer-by-layer assembly of polylysine and hyaluronic acid-g-poly(lactic-co-glycolic acid) micelles encapsulating paclitaxel.

Drug-eluting stent (DES) has been widely used for effective treatment of obstructive coronary artery disease, preventing the occurrence of restenosis that is mainly caused by hyper-proliferation of smooth muscle cells. Here, we demonstrate the immobilization of heparin on the metal surface via a bioinspired manner and subsequent build-up of a therapeutic layer-by-layer multilayer composed of paclitaxel (PTX) encapsulated poly(lactic-co-glycolic acid) grafted hyaluronic acid (HA-g-PLGA) micelles, heparin, and poly-L-lysine (PLL). It was hypothesized that the heparinized metallic surface would create a nonthrombogenic environment, while controlled release of PTX from the surface could induce antiproliferation of smooth muscle cells. For the surface immobilization of heparin on the surface of cobalt-chromium alloy (L605), dopamine-derivatized heparin was synthesized and anchored on the surface by a mussel-inspired adhesion mechanism. An amphiphilic graft copolymer of HA-g-PLGA was synthesized and utilized for the formation of anionic PTX loaded micelles. A PTX eluting multilayer composed of anionic HA-g-PLGA micelles, heparin, and PLL was self-assembled on the metal surface by a layer-by-layer fashion. The loading amount of PTX on the metal surface could be readily controlled with concomitantly achieving sustained release profiles of PTX over an extended period. The proliferation of human coronary artery smooth muscle cells was successfully arrested by controlled released PTX from the therapeutic multilayer coated on the metallic substrate.

Macroporous and nanofibrous hyaluronic acid/collagen hybrid scaffold fabricated by concurrent electrospinning and deposition/leaching of salt particles.

A three-dimensional (3-D) macroporous and nanofibrous hyaluronic acid (HA) scaffold was fabricated by an electrospinning process combined with a salt leaching technique. HA and collagen were dissolved in a sodium hydroxide (NaOH)/N,N-dimethyl formamide (DMF) solvent mixture at a concentration of 10 wt.% and successfully electrospun into a nanofiber web with a soft, fluffy structure by the combined effects of numerous minijet evolutions and their subsequent vertical growth. To our knowledge, the formation of an extensive fluffy nanofiber morphology is the first time as a single route has been used to spontaneously generate a 3-D nanofibrous structure. By the simultaneous deposition of salt particulates as a porogen during electrospinning and subsequent chemical cross-linking and salt leaching, a water-swellable HA-based scaffold retaining a macroporous and nanofibrous geometry could be produced. Bovine chondrocytes were cultured on the HA/collagen scaffold to assessing the scaffold's cytocompatibility. The results revealed that cellular adhesion and proliferation were enhanced in proportion to the content of collagen, and the seeded chondrocytes maintained the roundness characteristic of a chondroblastic morphology.

Development of dual scale scaffolds via direct polymer melt deposition and electrospinning for applications in tissue regeneration.

The objective of this study was the fabrication of highly functionalized polymeric three-dimensional (3D) structures characterized by nano and microfibers for use as an extracellular matrix-like tissue engineering scaffold. A hybrid process utilizing direct polymer melt deposition (DPMD) and an electrospinning method were employed to obtain the structure. Each microfibrous layer of the scaffold was built using the DPMD process in accordance with computer-aided design modeling data considering some structural points such as pore size, pore interconnectivity and fiber diameter. Between the layers of the three-dimensional structure, polycaprolactone/collagen nanofiber matrices were deposited via an electrospinning process. To evaluate the fabricated scaffolds, chondrocytes were seeded and cultured within the developed scaffolds for 10 days, and the levels of cell adhesion and proliferation were monitored. The results showed that the polymeric scaffolds with nanofiber matrices fabricated using the proposed hybrid process provided favorable conditions for cell adhesion and proliferation. These conditions can be attributed to enhanced cytocompatibility of the scaffold due to surficial nanotopography in the scaffold, chemical composition by use of a functional biocomposite, and an enlarged inner surface of the structure for cell attachment and growth.

Highly open porous biodegradable microcarriers: in vitro cultivation of chondrocytes for injectable delivery.

Injectable cell therapy would provide a patient-friendly procedure for treatment of degenerated or wounded tissue. Biodegradable injectable porous microspheres were fabricated to use as dual-purpose microcarriers for cell culture and injectable scaffold for tissue regeneration. Gas foaming in a water-in-oil-in-water double emulsion was performed for fabricating the well-interconnected porous microcarriers using poly(lactic-co-glycolic acid) (PLGA). The gas foaming conditions were finely tuned to control the structural and morphological characteristics. Porous microcarriers with a mean size of approximately 175 microm and an average pore diameter of approximately 29 microm were produced for cell cultivation and injectable delivery. To promote cell seeding, amine-functionalized porous microcarriers were prepared by blending amine-functionalized PLGA with unreacted PLGA. To assess the porous microcarriers for chondrocyte cultivation, bovine articular chondrocytes were seeded and cultured in vitro in spinner flasks for 4 weeks. Visualization and biochemical analyses of the microcarrier-cell constructs were performed to demonstrate cell proliferation and phenotypic expression. Quantification of deoxyribonucleic acid, glycosaminoglycan, and collagen content showed that much greater cell proliferation and expression of cartilage-specific phenotype were observed for cultures in the following order: amine-functionalized porous microcarriers, porous microcarriers, nonporous microcarriers, and monolayer culture.

Controlled protein release from electrospun biodegradable fiber mesh composed of poly(epsilon-caprolactone) and poly(ethylene oxide).

A blend mixture of poly(epsilon-caprolactone) (PCL) and poly(ethylene oxide) (PEO) was electrospun to produce fibrous meshes that could release a protein drug in a controlled manner. Various biodegradable polymers, such as poly(l-lactic acid) (PLLA), poly(epsilon-caprolactone) (PCL), and poly(d,l-lactic-co-glycolic acid) (PLGA) were dissolved, along with PEO and lysozyme, in a mixture of chloroform and dimethylsulfoxide (DMSO). The mixture was electrospun to produce lysozyme loaded fibrous meshes. Among the polymers, the PCL/PEO blend meshes showed good morphological stability upon incubation in the buffer solution, resulting in controlled release of lysozyme over an extended period with reduced initial bursts. With varying the PCL/PEO blending ratio, the release rate of lysozyme from the corresponding meshes could be readily modulated. The lysozyme release was facilitated by increasing the amount of PEO, indicating that entrapped lysozyme was mainly released out by controlled dissolution of PEO from the blend meshes. Lysozyme released from the electrospun fibers retained sufficient catalytic activity.

Surface functionalized electrospun biodegradable nanofibers for immobilization of bioactive molecules.

A blend mixture of biodegradable poly(epsilon-caprolactone) (PCL) and poly(d,l-lactic-co-glycolic acid)-poly(ethylene glycol)-NH(2) (PLGA-b-PEG-NH(2)) block copolymer was electrospun to produce surface functionalized nanofibers. The resulting nanofibrous mesh with primary amine groups on the surface was applied for immobilization of biologically active molecules using lysozyme as a model enzyme. Lysozyme was immobilized via covalent conjugation by using a homobifunctional coupling agent. The nanofibrous mesh could immobilize a far greater amount of lysozyme on the surface with concomitantly increased activity, primarily due to its larger surface area, compared to that of the solvent casting film. It was also found that the enzyme immobilization process slightly altered thermal and pH-dependent catalytic activity profiles compared to those of native lysozyme. The results demonstrated the surface functionalized electrospun nanofibrous mesh could be used as a promising material for immobilizing a wide range of bioactive molecules.

Biomimicking extracellular matrix: cell adhesive RGD peptide modified electrospun poly(D,L-lactic-co-glycolic acid) nanofiber mesh.

A cell adhesive peptide, Arg-Gly-Asp (RGD), was immobilized onto the surface of electrospun poly(D,L-lactic-co-glycolic acid) PLGA nanofiber mesh in an attempt to mimic an extracellular matrix structure. A blend mixture of PLGA and PLGA-b-PEG-NH(2) di-block copolymer dissolved in a 1:1 volume mixture of dimethylformamide and tetrahydrofuran was electrospun to produce a nanofiber mesh with functional primary amino groups on the surface. Various electrospinning parameters, such as polymer concentration and the blend ratio, were optimized to produce a nanofiber mesh with desirable morphology, surface characteristics, and fiber diameter. A cell adhesive peptide, GRGDY, was covalently grafted onto the aminated surface of the electrospun mesh under a hydrating condition. The amounts of surface primary amino groups and grafted RGD peptides were quantitatively determined. Cell attachment, spreading, and proliferation were greatly enhanced in the RGD modified electrospun PLGA nanofiber mesh compared with that of the unmodified one.