Search

Mesenchymal stem cells (MSCs) have great therapeutic potential for tissue engineering and regenerative medicine due to their multipotency and paracrine functions. However, shortly after in vivo implantation, MSCs tend to migrate to the lungs and undergo apoptosis, which impairs their clinical efficacy. In addition, the ex vivo two-dimensional expansion of MSCs results in changes in their immunophenotype and functional activities compared to those in vivo. The use of biomaterials to culture and deliver MSCs has the potential to overcome these limitations. MSC-biomaterial constructs retain MSCs in situ and prolong their survival, while the MSCs ameliorate the foreign body reaction and fibrosis caused by the biomaterial. Biomaterial scaffolds can both preserve the tissue architecture and provide a three-dimensional biomimetic milieu for embedded MSCs, which enhance their paracrine functions, including their immunomodulatory potential. The dimensionality, physical characteristics, topographical cues, biochemistry, and microstructure can enhance the immunomodulatory potential of MSCs. Here, we review the link between the properties of biomaterial and the immunomodulatory potential of MSCs. Impact Statement Regeneration of cells, tissues, and whole organs is challenging. Mesenchymal stem cells (MSCs) have therapeutic potential in tissue engineering and regenerative medicine due to their paracrine functions, including immunomodulatory activity. The dimensionality, physical characteristics, topographical cues, biochemistry, and microstructure of biomaterial can be harnessed to enhance the immunomodulatory potential of MSCs for tissue engineering, which will increase their clinical efficacy, particularly for immune-related diseases.

Ultralow-dielectric-constant (k) porous SiCOH films have been prepared using 1,2-bis(triethoxysilyl)ethane, triethoxymethylsilane, and a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer template by means of spin-coating. The resulting films were characterized by cross-section scanning electron microscopy, small-angle x-ray diffraction, atomic force microscopy, Fourier-transform infrared spectroscopy, nanomechanical testing, and electrical measurements. Thermal treatment at 350°C for 2 h resulted in the formation of ultralow-k films with k of ∼2.0, leakage current density of 3 × 10−8 A/cm2 at 1 MV/cm, reduced modulus (E r) of ∼4.05 GPa, and hardness (H) of ∼0.32 GPa. After annealing between 400°C and 500°C for 30 min, the resulting films showed fluctuant k values of 1.85 to 2.22 and leakage current densities of 3.7 × 10−7 A/cm2 to 3 × 10−8 A/cm2 at 0.8 MV/cm, likely due to the change of the film microstructure. Compared with 350°C annealing, higher-temperature annealing can improve the mechanical strength of the ultralow-k film, i.e., E r ≈ 5 GPa and H ≈ 0.56 GPa after 500°C annealing.

2,2′-Position aryl-substituted tetracarboxylic dianhydrides including 2,2′-bis(biphenyl)-4,4′,5,5′-biphenyl tetracarboxylic dianhydride and 2,2′-bis[4-(naphthalen-1-yl)phenyl)]-4,4′,5,5′-biphenyl tetracarboxylic dianhydride were synthesized. A new series of aromatic polyimides (PIs) were synthesized via a two-step procedure from 3,3′,4,4′-biphenyl tetracarboxylic dianhydride and the newly synthesized tetracarboxylic dianhydrides monomers reacting with 2,2′-bis[4′-(3″,4″,5″-trifluorophenyl)phenyl]-4,4′-biphenyl diamine. The resulting polymers exhibited excellent organosolubility and thermal properties associated with Tg at 264 °C and high initial thermal decomposition temperatures (T5%) exceeding 500 °C in argon. Moreover, the fabricated sandwich structured memory devices of Al/PI-a/ITO was determined to present a flash-type memory behaviour, while Al/PI-b/ITO and Al/PI-c/ITO exhibited write-once read-many-times memory capability with different threshold voltages. In addition, Al/polymer/ITO devices showed high stability under a constant stress or continuous read pulse voltage of − 1.0 V. Copyright © 2011 Society of Chemical Industry

Two novel 3′,4′,5′-trifluorobiphenyl-based aromatic polyimide monomers, 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′-biphenyl diamine (BTFBPD) and 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′,5,5′-biphenyltetracarboxylic dianhydride (BTFBPDA) were synthesized. Two fluorinated polyimides (PIs), PI(BTFBPD-DPBPDA) and PI(BTFBPD-BTFBPDA) were prepared via a two-step procedure using BTFBPD reacting with 2,2′-diphenyl-4,4′,5,5′-biphenyltetracarboxylic dianhydride (DPBPDA) and BTFBPDA, respectively. BTFBPD was characterized with single crystal X-ray diffraction analysis and the geometric parameters showed the noncoplanar twisted character. PIs exhibited highly organo-solubility and thermal stability. The PI films sandwiched between an indium-tin oxide(ITO) bottom electrode and Al top electrode exhibited two accessible conductivity states and can be switched from the low-conductivity to the high-conductivity. The memory devices with the configuration of Al/PI(BTFBPD-DPBPDA)/ITO exhibited a flash type memory capability, whereas the Al/PI(BTFBPD-BTFBPDA)/ITO presented a write once read many times (WORM) memory capability. The fabricated devices showed low turn-on threshold voltages of −1.3 V (PI(BTFBPD-DPBPDA)) and −1.7 V (PI(BTFBPD-BTFBPDA)) and both ON/OFF current ratios on the order of 103 to 104.

F-doped SiOCN films with low dielectric constant have been prepared using SiH 4 , C 2 F 6 and N 2 O as reactants by PECVD, and characterized by X-ray photoelectron spectroscopy (XPS), capacitance -voltage (C-V) and current-voltage (I–V) measurements, and nano-indenter. With an increment of the flow rate of C 2 F 6 , the concentrations of fluorine and carbon incorporated in the films increase, and the concentration of nitrogen decreases. This leads to a decrease in the dielectric constant of the film. When the flow rate of C 2 F 6 is 750 sccm, the percentages of C and F elements amount to 5.2% and 9.9%, respectively. Meanwhile, the resulting dielectric constant is reduced to 2.6, and the leakage current density is lower than 3×10−8 A/cm2 at 1MV/cm. The hardness and Young's modulus of the films are higher than 3 GPa and 84 GPa, respectively. It is thus believed that the introduction of carbon and fluorine can lower the dielectric constant of the films, and the presence of N can improve the mechanical properties of film.

Porous organosilica thin films using 1,2-bis (triethoxysily) ethane, triethoxymethylsilane and a poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) triblock copolymer template have been prepared by spin-on technique. The films were characterized by cross-sectional scanning electron microscopy, x-ray diffraction and Fourier-transform infrared spectroscopy. After thermal treatment at 350 °C in N 2 for two hours, the films show well ordered porous structure as well as uniform and crack-free surface. The dielectric constant (k) as low as 2.0 was obtained at 100k Hz, and kept good thermal stability up to 500 °C. Meanwhile, the resulting low-k porous films also exhibit low leakage current densities, e.g., 3.0×10−8 A/cm2 at 1 MV/cm, and good mechanical properties with elastic modulus of 4.7 GPa and hardness of 0.56 GPa in the case of 500 °C annealing.