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Gold nanorods emit strong photoluminescence under two photon excitation; the efficient two photon lumininescence (TPL) arises from the local field enhancement assisted by surface plasmons. The surface plasmon effects on the TPL efficiency and spectrum are investigated by measuring the TPL of gold nanorods with various aspect ratios. A large TPL efficiency is found when incident light wavelength coincides with the longitudinal surface plasmon mode of the gold nanorods. However, the emission spectra of nanorods with various aspect ratios look similar and exhibit modest surface plasmon features, which implies a major non-radiative decay of excited surface plasmons.

Electrospinning is a simple and efficient method of fabricating a non-woven polymeric nanofiber matrix. However, using fluorinated alcohols as a solvent for the electrospinning of proteins often results in protein denaturation. TEM and circular dichroism analysis indicated a massive loss of triple-helical collagen from an electrospun collagen (EC) matrix, and the random coils were similar to those found in gelatin. Nevertheless, from mechanical testing we found the Young's modulus and ultimate tensile stresses of EC matrices were significantly higher than electrospun gelatin (EG) matrices because matrix stiffness can affect many cell behaviors such as cell adhesion, proliferation and differentiation. We hypothesize that the difference of matrix stiffness between EC and EG will affect intracellular signaling through the mechano-transducers Rho kinase (ROCK) and focal adhesion kinase (FAK) and subsequently regulates the osteogenic phenotype of MG63 osteoblast-like cells. From the results, we found there was no significant difference between the EC and EG matrices with respect to either cell attachment or proliferation rate. However, the gene expression levels of OPN, type I collagen, ALP, and OCN were significantly higher in MG63 osteoblast-like cells grown on the EC than in those grown on the EG. In addition, the phosphorylation levels of Y397-FAK, ERK1/2, BSP, and OPN proteins, as well as ALP activity, were also higher on the EC than on the EG. We further inhibited ROCK activation with Y27632 during differentiation to investigate its effects on matrix-mediated osteogenic differentiation. Results showed the extent of mineralization was decreased with inhibition after induction. Moreover, there is no significant difference between EC and EG. From the results of the protein levels of phosphorylated Y397-FAK, ERK1/2, BSP and OPN, ALP activity and mineral deposition, we speculate that the mechanism that influences the osteogenic differentiation of MG63 osteoblast-like cells on EC and EG is matrix stiffness and via ROCK-FAK-ERK1/2.

A polycaprolactone (PCL) nanofibrous composite matrix having mesoporous bioactive glass nanoparticles (MBG) was fabricated using the electrospinning method, and the microstructural, physical and biological properties of the composite matrix were characterized. The fiber diameters of PCL, 5 % MBG/PCL (5 M-PCL) and 10 % MBG/PCL (10 M-PCL) were 575 ± 162 nm, 312 ± 134 nm and 321 ± 144 nm, respectively. The bioactivity of the composite matrix was evaluated by soaking the matrix in 1.5× simulated body fluid; the MBG/PCL matrix showed a better biomineralization capability than did the PCL matrix. The biological performance of the PCL and the MBG/PCL were evaluated using an in vitro culture of MG63 osteoblast-like cells. We found that the cell attachment and proliferation rates were significantly higher on the 10 M-PCL than on the PCL. Moreover, the expression of several genes, including ANX-V, type I collagen and OCN, ALP activity, the deposition of calcium, and the BSP protein, were also significantly higher on 10 M-PCL than PCL. These results indicated that MBG/PCL has the ability to support cell attachment, growth, and differentiation and can also yield high bioactivity. Therefore, MBG/PCL could be potentially applied in bone implants.

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