Enhancing Thermal Conductivity in Polymer Composites through Molding-Assisted Orientation of Boron Nitride.

Incrementing thermal conductivity in polymer composites through the incorporation of inorganic thermally conductive fillers is typically constrained by the requirement of high filler content. This necessity often complicates processing and adversely affects mechanical properties. This study presents the fabrication of a polystyrene (PS)/boron nitride (BN) composite exhibiting elevated thermal conductivity with a modest 10 wt% BN content, achieved through optimized compression molding. Adjustments to molding parameters, including molding-cycle numbers, temperature, and pressure, were explored. The molding process, conducted above the glass transition temperature of PS, facilitated orientational alignment of BN within the PS matrix predominantly in the in-plane direction. This orientation, achieved at low filler loading, resulted in a threefold enhancement of thermal conductivity following a single molding time. Furthermore, the in-plane alignment of BN within the PS matrix was found to intensify with increased molding time and pressure, markedly boosting the in-plane thermal conductivity of the PS/BN molded composites. Within the range of molding parameters examined, the highest thermal conductivity (1.6 W/m·K) was observed in PS/BN composites subjected to five molding cycles at 140 °C and 10 MPa, without compromising mechanical properties. This study suggests that compression molding, which allows low filler content and straightforward operation, offers a viable approach for the mass production of polymer composites with superior thermal conductivity.

Inorganic-Organic Hybrid Janus Fillers for Improving the Thermal Conductivity of Polymer Composites.

Janus fillers represent a combination of inorganic thermally conductive silver nanoparticles and organic polystyrene brushes on one entity but different sides. They are of practical importance for polymer composites with high thermal conductivity because of the improved dispersion and reduced interfacial heat resistance. Moreover, benefiting from the sheetlike structure and single-side deposition of inorganic particles, Janus fillers tend to align such that the heat pathway is constructed in the composite films, when fabricated by layer-by-layer doctor blading. As a result, the in-plane thermal conductivity of the polymer composite is as high as 4.57 W m-1 K-1, with only 10 vol % Janus filler loading.

Transition in Dynamics as Nanoparticles Jam at the Liquid/Liquid Interface.

Nanoparticles (NPs) segregated to the liquid/liquid interface form disordered or liquid-like assemblies that show diffusive motions in the plane of the interface. As the areal density of NPs at the interface increases, the available interfacial area decreases, and the interfacial dynamics of the NP assemblies change when the NPs jam. Dynamics associated with jamming was investigated by X-ray photon correlation spectroscopy. Water-in-toluene emulsions, formed by a self-emulsification at the liquid/liquid interface and stabilized by ligand-capped CdSe-ZnS NPs, provided a simple, yet powerful platform, to investigate NP dynamics. In contrast to a single planar interface, these emulsions increased the number of NPs in the incident beam and decreased the absorption of X-rays in comparison to the same path length in pure water. A transition from diffusive to confined dynamics was manifested by intermittent dynamics, indicating a transition from a liquid-like to a jammed state.

Construction of PRP-containing nanofibrous scaffolds for controlled release and their application to cartilage regeneration.

Platelet-rich plasma (PRP) has been widely used for decades in the clinic, since an abundance of growth factors can be released when it is activated. However, its clinical use is limited because the release of growth factors is temporal and PRP lacks mechanical strength. The aim of this study was to incorporate PRP-derived growth factors into PCL/gelatin nanofibers using the emulsion electrospinning method to determine how growth factors are released from the scaffolds and how the presence of these factors enhances the bioactivity of the scaffolds. Scaffolds with or without PRP were prepared and characterized. The release of proteins from scaffolds over time and rabbit BMSC chemotaxis, proliferation, and chondrogenic induction were quantified in vitro. The in vivo restoring effect of the scaffolds was also evaluated by transplanting the scaffolds into a cartilage defect in an animal model, and the outcomes were determined by histological assessment, micro-CT scanning, and IL-1 measurement. The results showed that the mechanical properties of the scaffolds were mildly compromised due to the addition of PRP, and that the sustained release of growth factors from PRP-containing scaffolds occurred up to ∼30 days in culture. The scaffold bioactivity was enhanced, as BMSCs demonstrated increased proliferation and notable chemotaxis in the presence of PRP. Chondrogenesis of BMSCs was also promoted when the cells were cultured on the PRP scaffolds. Furthermore, the PRP scaffolds showed better restorative effects on cartilage defects, as well as anti-inflammatory effects in the joint cavity (the IL-1 level was decreased). In conclusion, the results of the current study indicate the potential for using a PRP-containing electrospun nanofibrous scaffold as a bioactive scaffold, which is beneficial for optimizing the clinical application of PRP.

The effect of 3D nanofibrous scaffolds on the chondrogenesis of induced pluripotent stem cells and their application in restoration of cartilage defects.

The discovery of induced pluripotent stem cells (iPSCs) rendered the reprogramming of terminally differentiated cells to primary stem cells with pluripotency possible and provided potential for the regeneration and restoration of cartilage defect. Chondrogenic differentiation of iPSCs is crucial for their application in cartilage tissue engineering. In this study we investigated the effect of 3D nanofibrous scaffolds on the chondrogenesis of iPSCs and articular cartilage defect restoration. Super-hydrophilic and durable mechanic polycaprolactone (PCL)/gelatin scaffolds were fabricated using two separate electrospinning processes. The morphological structure and mechanical properties of the scaffolds were characterized. The chondrogenesis of the iPSCs in vitro and the restoration of the cartilage defect was investigated using scanning electron microscopy (SEM), the Cell Counting Kit-8 (CCK-8), histological observation, RT-qPCR, and western blot analysis. iPSCs on the scaffolds expressed higher levels of chondrogenic markers than the control group. In an animal model, cartilage defects implanted with the scaffold-cell complex exhibited an enhanced gross appearance and histological improvements, higher cartilage-specific gene expression and protein levels, as well as subchondral bone regeneration. Therefore, we showed scaffolds with a 3D nanofibrous structure enhanced the chondrogenesis of iPSCs and that iPSC-containing scaffolds improved the restoration of cartilage defects to a greater degree than did scaffolds alone in vivo.

Human urine-derived stem cells in combination with polycaprolactone/gelatin nanofibrous membranes enhance wound healing by promoting angiogenesis.

BACKGROUND: Despite advancements in wound healing techniques and devices, new treatments are needed to improve therapeutic outcomes. This study aimed to evaluate the potential use of a new biomaterial engineered from human urine-derived stem cells (USCs) and polycaprolactone/gelatin (PCL/GT) for wound healing. METHODS: USCs were isolated from healthy individuals. To fabricate PCL/GT composite meshes, twin-nozzle electrospinning were used to spin the PCL and gelatin solutions in normal organic solvents. The morphologies and hydrophilicity properties of PCL/GT membranes were investigated. After USCs were seeded onto a PCL/GT, cell adhesion, morphology, proliferation, and cytotoxicity were examined. Then, USCs were seeded on a PCL/GT blend nanofibrous membrane and transplanted into rabbit full-thickness skin defects for wound repair. Finally, the effect of USCs condition medium on proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) were performed in vitro. RESULTS: USCs were successfully isolated from urine samples and expressed specific mesenchymal stem cells markers and could differentiate into osteoblasts, adipocytes, and chondrocytes. PCL/GT membrane has suitable mechanical properties similar with skin tissue and has good biocompatibility. USCs-PCL/GT significantly enhanced the healing of full-thickness skin wounds in rabbits compared to wounds treated with PCL/GT membrane alone or untreated wounds. USCs-PCL/GT-treated wounds closed much faster, with increased re-epithelialization, collagen formation, and angiogenesis. Moreover, USCs could secrete VEGF and TGF-ß1, and USC-conditioned medium enhanced the migration, proliferation, and tube formation of endothelial cells. CONCLUSION: USCs in combination with PCL/GT significantly prompted the healing of full-thickness skin wounds in rabbits. USCs based therapy provides a novel strategy for accelerating wound closure and promoting angiogenesis.

Improved cathode for high efficient microbial-catalyzed reduction in microbial electrosynthesis cells.

Microbial electrosynthesis cells (MECs) are devices wherein microorganisms can electrochemically interact with electrodes, directly donating or accepting electrons from electrode surfaces. Here, we developed a novel cathode by using nickel nanowires anchored to graphite for the improvement of microbial-catalyzed reduction in MEC cathode chamber. This porous nickel-nanowire-network-coated graphite electrode increased the interfacial area and interfacial interactions between the cathode surface and the microbial biofilm. A 2.3 fold increase in bio-reduction rate over the untreated graphite was observed. Around 282 mM day(-1) m(-2) of acetate resulting from the bio-reduction of carbon dioxide by Sporomusa was produced with 82 ± 14% of the electrons consumed being recovered in acetate.

A route to rapid carbon nanotube growth.

CNTs were synthesized in 15-20 seconds by a single carbon fiber initiating the pyrolysis of ferrocene under microwave field without any other chemicals. The growth of CNTs can also be triggered by other carbonaceous materials and influenced by their configurations.

Effects of chain conformation and entanglement on the electrospinning of pure alginate.

As a natural biopolymer, sodium alginate (SA) has been widely used in the biomedical field in the form of powder, liquid, gel, and compact solid, but not in the form of nanofiber. Electrospinning is an effective method to fabricate nanofibers. However, electrospinning of SA from its aqueous solution is still a challenge. In this study, an effort has been made to solve this problem and find the key reasons that hinder the electrospinning of alginate aqueous solution. Through this research, it was found that pure SA nanofibers could be fabricated successfully by introducing a strong polar cosolvent, glycerol, into the SA aqueous solutions. The study on the properties of the modified SA solution showed that increasing glycerol content increased the viscosity of the SA solution greatly and, meanwhile, decreased the surface tension and the conductivity of the SA solution. The rheological results indicated that the increase in glycerol content could result in the enhanced entanglements of SA chains. Two schematic molecular models were proposed to depict the change of SA chain conformation in aqueous solution with and without glycerol. The main contribution of glycerol to the electrospinning process is to improve the flexibility and entanglement of SA chains by disrupting the strong inter- and intramolecular hydrogen bondings among SA chains, then forming new hydrogen bondings with SA chains.